A deep dive into lithium ion battery power loss. 

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LFP and NMC are both lithium-ion chemistries. Learn the real differences in safety, lifespan, energy density, cost, and best-fit applications.

LFP vs. NMC Batteries: Lithium-ion Chemistry Compared

<h1>LFP vs. NMC: Clearing Up the “Lithium-ion vs. Lithium-ion” Confusion</h1><h2>Introduction: Why the Framing Is Wrong</h2>If you Google “lithium-ion versus LiFePO₄” right now, you’ll often see an AI-generated overview that says LiFePO₄ (lithium iron phosphate) and lithium-ion batteries are both rechargeable but differ in safety, lifespan, energy density, and cost. The problem starts right there: LiFePO₄ is a subset of lithium-ion.The “L” in LiFePO₄ stands for lithium, and the “Fe” stands for iron. What people usually mean by “lithium-ion versus LFP” is NMC (nickel-manganese-cobalt) lithium-ion versus LFP lithium-ion. In other words: NMC vs. LFP—two chemistries under the same lithium-ion umbrella. This distinction isn’t pedantic; it’s foundational for making good technical and purchasing decisions. A clear taxonomy keeps comparisons fair and context-appropriate.<h2>The Misconception in Search Results</h2>What’s supposed to be a high-quality answer from a trusted provider at the top of a results page can wind up nonsensical without this context. The very first thing that response should say is that LiFePO₄ batteries are a type of lithium-ion battery. When people say “lithium-ion versus LFP,” or “LFP versus lithium-ion,” they usually mean NMC vs. LFP—lithium-ion vs. lithium-ion with different cathode chemistries.Saying “LFP vs. lithium-ion” is like asking, “What’s better, a Ford or a truck?” A truck is a category of vehicle. Ford makes models of trucks you might like. Using precise terms avoids apples-to-oranges answers and helps consumers evaluate trade-offs realistically.<h2>Examples of How the Confusion Spreads</h2>Scroll past the AI blurb and Reddit and you might see brand articles titled along the lines of “LiFePO₄ vs. Lithium-ion: What’s the Best Choice?” The title is understandable for SEO, but the article should explicitly say that LFP is a subset of lithium-ion. Too often, it doesn’t. &nbsp;One piece opens with, “The LFP battery type has come down in price in recent years and its efficiency has dramatically improved.It’s surpassing lithium-ion as the battery of choice for many applications, including off-grid and solar power and even electric vehicles.” It continues, “LiFePO₄ batteries are similar to ion but have significant advantages that make them the ideal option for consumer-grade backup power solutions.” This kind of language glosses over the fact that LFP is lithium-ion, and it treats “lithium-ion” as if it meant only NMC. This gives in to the misconception instead of correcting it, which misleads readers and muddies technical understanding.<h2>Getting It Right: The Simple Definition</h2>The information is out there and easy to state clearly. For example, a correct first sentence would be: “The lithium iron phosphate (LiFePO₄, or LFP) battery is a type of lithium-ion battery that uses lithium iron phosphate as the cathode material.” That’s it. Once this foundation is set, meaningful comparisons can follow.Clear definitions make the rest of the discussion straightforward: you’re comparing two lithium-ion chemistries, not lithium-ion vs. something else. From here, we can fairly evaluate LFP vs. NMC on the metrics that matter.<h2>Energy Density: Size and Weight Trade-offs</h2>LFP: About 90–160 Wh/kg. You’ll need a larger, heavier pack for the same kWh. NMC: About 150–250 Wh/kg. More energy per kilogram yields more range or smaller packs for the same capacity.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:287,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXePUwsjUfgVVvjDn8u3kXfE9gIKIHxx8PXPejxRiFHEnIM9P4q86WesC0QFgtWQ4Z6FBYQKeLzFhqyDH6ZV6g0Gfv5h8AdRRCU3S5W6826pU96_tObEDa7Tvv-DM-f3mJJys1NO?key=abUGaQ4cW8m9d8-lC_PBGw&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXePUwsjUfgVVvjDn8u3kXfE9gIKIHxx8PXPejxRiFHEnIM9P4q86WesC0QFgtWQ4Z6FBYQKeLzFhqyDH6ZV6g0Gfv5h8AdRRCU3S5W6826pU96_tObEDa7Tvv-DM-f3mJJys1NO?key=abUGaQ4cW8m9d8-lC_PBGw" width="624" height="287"><figcaption class="attachment__caption"></figcaption></figure> These numbers explain why space-constrained, range-sensitive applications often land on NMC. Conversely, if volume and mass are less critical, LFP’s lower energy density may be perfectly acceptable. <figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:580,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXf_YdgpJ17RnqF2psjy7CkJaK6t9AFzZK8BdAZnoW426e1AGdd_kKoue-x5rmQfBK0THrSmb5S7IrY4eLMovfeukM1BS2PTrNbgFqw2DGwplV38FRKqdzPi1oiJsd2_wDtUenlm?key=abUGaQ4cW8m9d8-lC_PBGw&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXf_YdgpJ17RnqF2psjy7CkJaK6t9AFzZK8BdAZnoW426e1AGdd_kKoue-x5rmQfBK0THrSmb5S7IrY4eLMovfeukM1BS2PTrNbgFqw2DGwplV38FRKqdzPi1oiJsd2_wDtUenlm?key=abUGaQ4cW8m9d8-lC_PBGw" width="624" height="580"><figcaption class="attachment__caption"></figcaption></figure> <h2>Cycle Life: Longevity Wins for LFP</h2>LFP: “1,500 to 3,000 cycles before there is 80% capacity loss.” (Clarification: commonly understood as reaching ~80% of original capacity, i.e., ~20% capacity loss.) That’s tremendous cycle life in practical use.NMC: Roughly 500 to 1,000 cycles under gentle use. Longer cycle life can dominate total cost of ownership for stationary storage and daily-cycle use cases. This is why LFP is so attractive for home batteries and off-grid systems.<h2>Thermal Stability and Safety</h2>LFP: Excellent thermal stability with a much lower risk of thermal runaway. More tolerant to heat and abuse.NMC: Relatively stable for its power density, but significantly more sensitive to abuse and heat. A BMS (Battery Management System) is absolutely required. Safety isn’t only about catastrophic failure; it’s also about predictable behavior under stress. LFP’s chemistry provides a wider safety margin, especially in less controlled environments.<h2>Cost and Materials</h2>LFP: Cells are cheaper to build. Cathodes use abundant iron and phosphate—no nickel or cobalt—so material costs and supply risks are lower. NMC: Pricier and exposed to volatile nickel and cobalt markets. Material choice influences not just price but also supply chain resilience and ethical sourcing considerations, which many buyers now factor into procurement.<h2>Cold-Weather Performance</h2>LFP: The loser here. Charging below 0 °C requires preheating the pack and limiting charge current (via the charge controller or BMS) to avoid damage. NMC: Better low-temperature performance than LFP, though still requires care—just at higher temperatures. If you operate in harsh winters without reliable preconditioning, chemistry matters. Cold derates are real and can define the user experience.<h2>Charge Rate and Fast Charging</h2>LFP: Typically can’t charge as fast as NMC. NMC: Can charge extremely fast, but careful thermal management is critical to prevent overheating. Infrastructure, duty cycle, and thermal design dictate whether fast charging is a must-have or a nice-to-have. Pick the chemistry that aligns with your charging reality.<h2>Calendar Aging and State of Charge</h2>LFP: More resilient to calendar aging and can sit at a high state of charge with less degradation. NMC: Less tolerant of sustained high voltage/SoC; storing at high SoC accelerates aging. If your asset spends long periods parked or idling at high charge, LFP’s calendar-life traits can translate into years of extra useful life.<h2>Best-Fit Applications</h2>LFP excels when size is not paramount: grid storage, home batteries, buses, short-range EVs, and systems where safety, cycle life, and $/kWh dominate. NMC shines where space and power density rule: long-range EVs, high-performance vehicles, and tightly packaged applications. Application fit is about constraints: volume, mass, thermal budget, duty cycle, climate, and charging profile. Map those constraints to the chemistry’s strengths.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:324,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXdnTkN2-ZdPwG1VkNrCANl5ylsOJFxRV9FTOVp7j_-JENljZn6-3_nK2sStVSZI5i_m-y7pKXIS_CK-82pxBVgFWtslRA9qRVh_GJ6_qwyQGWhrO689hc2mApQbN19a_2ynzuW5?key=abUGaQ4cW8m9d8-lC_PBGw&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXdnTkN2-ZdPwG1VkNrCANl5ylsOJFxRV9FTOVp7j_-JENljZn6-3_nK2sStVSZI5i_m-y7pKXIS_CK-82pxBVgFWtslRA9qRVh_GJ6_qwyQGWhrO689hc2mApQbN19a_2ynzuW5?key=abUGaQ4cW8m9d8-lC_PBGw" width="624" height="324"><figcaption class="attachment__caption"></figcaption></figure><h2>Practical Guidance and Decision Points</h2><ul><li>Max range / smallest pack: Choose NMC. </li><li>Longest overall life, highest safety margin, lowest $/kWh (cell level): Choose LFP, accepting a larger pack. </li><li>Extremely cold climates with limited preconditioning: NMC is often the better choice. </li><li>Daily fast charging and frequent high SoC storage with longevity goals: LFP is the safer bet. Framing the choice this way—NMC lithium-ion vs. LFP lithium-ion—keeps the conversation technically honest. It prevents the “Ford vs. truck” problem and leads to better-informed decisions. </li></ul><h2>Conclusion</h2>The core mistake in many “LFP vs. lithium-ion” pieces is category confusion. LFP is lithium-ion. The real comparison most people want is NMC vs. LFP. Once that’s clear, the trade-offs line up: NMC for energy and power density; LFP for safety, longevity, and cost stability. Precise language isn’t nitpicking—it’s how we avoid misleading readers and how we choose the right battery for the job.

LFP vs. NMC: The Real “Lithium-ion vs. Lithium-ion” Battery Comparison

Learn how lithium-ion battery fires start, why they’re rare but dangerous, how to prevent them, and what to do if one occurs. Covers charging, storage, shipping, and EV safety tips.

Lithium-Ion Battery Fire Safety: Risks, Prevention Tips, and Emergency Actions

Lithium-ion batteries power phones, laptops, e-bikes, power tools, and even cars. They’re remarkably reliable overall, yet when something goes wrong the consequences can be severe. This article organizes the key points into clear sections, corrects spelling and punctuation, and adds brief clarifications where helpful.<h1>How Common Are Lithium-Ion Battery Fires?</h1>They’re actually extremely uncommon relative to how many batteries are out there in use. But the consequences can be severe. There are billions and billions of lithium-ion cells in the wild, and only a tiny fraction ever have any problems. The risk rises with large batteries for e-bikes, scooters, and electric vehicles and with abuse—either abuse in the manufacturing process by using cheap or low-grade cells, or abuse in use by charging too fast, running a pack at currents it’s not rated for, bypassing safety measures, or letting it overheat in storage.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:405,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXdh_8wWZ3pOByof0AIvi8XVRpOyZqM6_0GT3Ha6jiBssQyS__e6jKRcp4ICx8KMtV0B8Ck85yxaxgxDtsDoTCLxsdukDL5aVtsUIUnmR9WxhXIvrLDDpVUPYDXw3OS8n9iyal1uyQ?key=D0LXWogGqr5TmhbcNcYkKQ&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXdh_8wWZ3pOByof0AIvi8XVRpOyZqM6_0GT3Ha6jiBssQyS__e6jKRcp4ICx8KMtV0B8Ck85yxaxgxDtsDoTCLxsdukDL5aVtsUIUnmR9WxhXIvrLDDpVUPYDXw3OS8n9iyal1uyQ?key=D0LXWogGqr5TmhbcNcYkKQ" width="624" height="405"><figcaption class="attachment__caption"></figcaption></figure> Think of risk like seatbelts: most drives are uneventful, but the belt matters in the rare crash; likewise, good cells and good habits drastically lower already-low odds.<h1>Where and When Do Lithium-Ion Battery Fires Typically Occur?</h1><figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:353,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXdhtI2TYuz-U_tTCt-K1eQ48zO6r07PL7HrapNl6Rv19shqaCYoX-hSIX8Y7bA0cTGnSKSrDBdnxcdTgHAqocjuRPITeL9GpiqNempDO7vGUiwPqZ96J3tl2f5jFnebn52uBZip?key=D0LXWogGqr5TmhbcNcYkKQ&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXdhtI2TYuz-U_tTCt-K1eQ48zO6r07PL7HrapNl6Rv19shqaCYoX-hSIX8Y7bA0cTGnSKSrDBdnxcdTgHAqocjuRPITeL9GpiqNempDO7vGUiwPqZ96J3tl2f5jFnebn52uBZip?key=D0LXWogGqr5TmhbcNcYkKQ" width="624" height="353"><figcaption class="attachment__caption"></figcaption></figure>Lithium-ion battery fires are extremely rare when compared to how many lithium-ion batteries are in use, but when fires occur, they generally occur in five situations: while they’re charging, while they’re stored in workshops and garages, while they are being shipped, while they’re in waste facilities, and in electric vehicles. Incidents cluster where batteries are concentrated (charging areas, repair benches, warehouses), so organizing these spaces pays off.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:399,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXdp-bQ8pgVfWN9E6CmSC8CPjjWyLvc7BCPkivbWdQU3jQG16H_qRR5-hg8wsF0y7yqg3RXHKiJN0EQNZj5CFScFTAEQfaldYcrsir0z3NbpvHWTuEz2byIQL9yFF8OmjRP0BkoMGA?key=D0LXWogGqr5TmhbcNcYkKQ&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXdp-bQ8pgVfWN9E6CmSC8CPjjWyLvc7BCPkivbWdQU3jQG16H_qRR5-hg8wsF0y7yqg3RXHKiJN0EQNZj5CFScFTAEQfaldYcrsir0z3NbpvHWTuEz2byIQL9yFF8OmjRP0BkoMGA?key=D0LXWogGqr5TmhbcNcYkKQ" width="624" height="399"><figcaption class="attachment__caption"></figcaption></figure><h1>Why Charging Is a Common Trigger</h1>When they’re being charged and catch on fire, that’s because they’re being charged with too much current or they have the discharge bypassed on the BMS and they just depleted the battery pack at extreme current levels and did not let it rest before charging it. Another way they can catch on fire when they’re being charged is if they are over-volted. This can happen when you charge the battery through the discharge port of the BMS. The BMS can only cut off charging on the charge port.So if it’s a separate-port BMS and you’re charging it through the discharge port, the charging process will work just fine, but it won’t be able to cut off charging when the cell voltages get to a certain point. It will just balance out naturally with Ohm’s law, and that means you could easily overcharge a cell to 4.5 or even 5 volts or more, which can cause a fire. Label your charge leads/ports and use chargers matched to the pack’s chemistry and voltage to avoid mix-ups.<h1>Storage, Shipping, and Workshop Risks</h1>When a lithium-ion battery catches fire in a workshop or garage, it’s because they’re not being properly stored, they’re being overheated, or they are easy to tamper with—with exposed terminals in the presence of animals, small children, and things like that. If a lithium-ion battery is sitting on a shelf properly stored, it will never have any kind of problem. It’s not going to catch on fire or suddenly burst into flames. It’s a similar situation when they’re being shipped.They’re totally safe when packed properly, but when they’re not packed properly and the side of the box is dented or something, if it was some glassware it would just be a bad day. If it was some computer, again, it would just be an inconvenience. But if it’s a battery and it gets dented and totally compromised and the cell gets shorted internally, it’s going to be a really bad day for that person or that truck or, worse, that flight. Insulate terminals, protect against crushing, and keep cells away from conductive items (like tools or loose hardware).<h1>Electric Vehicles and Collision Scenarios</h1>In electric vehicles, collisions are always going to be some percentage of all traffic. Electric vehicles are getting more and more common. This is going to happen more and more often. As a battery gets impacted, there’s really nothing you can do to stop that chain reaction.That would take either a new battery chemistry that is totally safe when being absolutely ruptured and punctured or some very high-tech, very elaborate armor or cage or otherwise protective structure for the batteries, which is pretty much what they’re doing now. These things do happen. They’re definitely not random, and they are rare. After any significant impact, treat the pack as compromised even if there’s no smoke—keep distance and follow manufacturer/first-responder guidance.<h1>What to Do If a Lithium-Ion Battery Fails or Catches Fire</h1>If you see or hear any swelling, hissing, or popping; have a strong smell; or definitely if you see smoke or there is enough heat to melt plastics or the wrap of the battery, then you need to unplug and immediately power down—if you can do so safely—whatever device is running the battery. Immediately move it outside to a clear area on top of a non-combustible surface like concrete or pavement. If at all possible, try to wrap it in something non-flammable as you pick it up and carry it out. But in the heat of the moment (no pun intended), that might not be viable and might take too much time.So you may have to carry the battery pack from the safest possible position furthest from the heat or while holding the hot part of the battery away from you as you walk through the house. Once it’s outside somewhere that it can’t burn anything down or hurt anybody, the best thing you can do is just let it run its course. If you try to put water on it or suffocate it in some way with the incorrect tools, you may cause more of a problem than you already have. So if you don’t have the proper equipment to deal with a lithium-ion battery fire, then the best thing you can do is just let it burn out. You don’t have to overreact and immediately call the fire department or anything.&nbsp;You only need to do that if the situation is out of your control. If fire is spreading or can spread to other parts of the property and you have no way of containing it, then that’s when you need to call emergency services. But if you have a battery that’s on fire on a concrete slab or in your driveway and there’s at least 20 or 30 feet of clearance all the way around, then the worst thing that can happen is a flaming cell could fly a few dozen yards away from the battery and you would want to run over and put that out. It’s a terrible situation to be in, but all in all, it’s pretty containable as long as you can get the battery outside and onto a safe surface. If in doubt, prioritize life safety: clear people and pets, ventilate if smoke is inside, and consider calling emergency services early for guidance.<h2>How to Prevent Lithium-Ion Battery Fires</h2>The first thing is to just buy good stuff. Don’t buy cheap junk. Cheap stuff will always get hotter than nice, high-quality stuff under the same currents in terms of charge or discharge. The second thing is to charge safely. Don’t overcharge it. Charge it with the right voltage and make sure you’re charging it through the charge port if it has a common-port BMS. Keep the battery temperatures between a reasonable level, say somewhere between 0 and 35 °C.&nbsp;<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:417,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXe-s7tXe7fPRhZLg_R3fjJuBJkUSTdM_J4Pk-zvM381KmdtMLGq1Xyb7bOQJLI_-iCHDb2uzaoInC6K0Ou7Baa8XlJvSj-so225FyfTYGcuFJ-XKL4X3JzoGyi2mKRS185kIvmfmw?key=D0LXWogGqr5TmhbcNcYkKQ&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXe-s7tXe7fPRhZLg_R3fjJuBJkUSTdM_J4Pk-zvM381KmdtMLGq1Xyb7bOQJLI_-iCHDb2uzaoInC6K0Ou7Baa8XlJvSj-so225FyfTYGcuFJ-XKL4X3JzoGyi2mKRS185kIvmfmw?key=D0LXWogGqr5TmhbcNcYkKQ" width="624" height="417"><figcaption class="attachment__caption"></figcaption></figure>Just because they can run hotter than that doesn’t mean that it’s a good idea for you to do so. As previously stated, it’s important to keep the pack physically safe. So use lots of padding or plastic casing or something like that to keep the battery pack secure from external impacts.&nbsp;Store them in the proper ways. Don’t store them in a hot garage—they can get up to 120 °F in the middle of the summer—or in some shed in the same or worse conditions. Don’t leave lithium-ion batteries in a car really any time of the year, especially in the summer. And finally, dispose of them correctly. Take them to battery drop-off centers or go down to the landfill and pay the fee that you have to pay for them to take them. Don’t just throw them away. A simple metal tray or concrete paver under your charging area adds a cheap extra layer of protection.<h2>Characteristic of a Lithium-Ion Battery Fire</h2>Thermal runaway is the number one characteristic of a lithium-ion battery fire. A failing cell, as it overheats, triggers its neighbors to overheat, which can cause the temperature to climb rapidly. The signs are hissing or popping; whitish-grayish smoke; a chemical and, believe it or not, somewhat sweet odor; swelling; or rapid heating. And here’s a really good sign that you’re facing a lithium-ion battery fire: jet-like flames. When you see the jet-like flame, you pretty much know for sure what you’re dealing with is a lithium battery fire.Flammable vapors, gases, and particulates come out of the battery, and with some chemistries oxygen is even released from the cathode. So that means these things will burn underwater. That makes re-ignition likely if you try to put these out with water and you don’t really know what kind of lithium-ion battery you’re dealing with. Treat any off-gassing as hazardous—avoid breathing the plume and increase distance fast.<h2>Likelihood and Contributing Factors</h2>For a quality consumer device that’s used as directed, the chance is very low over the entire lifetime of that device. The likelihood increases as the number of cells in the battery pack increases or as the battery packs become very old or physically damaged or exposed to water. Also, if they’re stored in hot devices—think of iPads and things that are left in cars or in hot trunks during August’s blazing heat—or using incompatible or cheap chargers that don’t provide the right voltage levels or charge them faster than they’re intended to be charged.Overall, light electric vehicles like e-scooters and bikes are dominating recent incident totals in many cities because of the recent popularity of these devices and the recent influx of battery builders on the open market. All in all, you can pretty much be guaranteed to not deal with a lithium battery fire. If it does happen, that will be the exception, not the rule. As packs age, reduce stress: slower charging and gentler storage conditions help.<h2>What Causes Lithium-Ion Batteries to Catch Fire?</h2>A simple list of what causes batteries to catch on fire would be internal defects, physical damage, electrical abuse, thermal stress, and water intrusion. Most failures trace back to one of these buckets, even if the exact trigger isn’t obvious in the moment.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:409,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXfSfvuonojzWCsX51A1mq-gA_D7QC-P6zD0cth6Z1R9r_l6SNV645j4T4TVdXzUH-XjUZRC64dcXVEKCXSG11ue9X7hRESPr6cCno9CAmNAQX3u5HRQQgvDfXh2uj1JXWsRjFlu?key=D0LXWogGqr5TmhbcNcYkKQ&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfSfvuonojzWCsX51A1mq-gA_D7QC-P6zD0cth6Z1R9r_l6SNV645j4T4TVdXzUH-XjUZRC64dcXVEKCXSG11ue9X7hRESPr6cCno9CAmNAQX3u5HRQQgvDfXh2uj1JXWsRjFlu?key=D0LXWogGqr5TmhbcNcYkKQ" width="624" height="409"><figcaption class="attachment__caption"></figcaption></figure><h2>Will a CO₂ Extinguisher Put Out a Lithium-Ion Battery Fire?</h2>The answer is usually no. CO₂ displaces oxygen but doesn’t cool the cells, so the fire often reignites. So basically the only advantage you get from using a CO₂ fire extinguisher isn’t its fire-extinguishing capabilities, but it’s just blowing on it with air that’s not oxygenated. If it’s all you have, you can use it to briefly knock down the flames. But you probably still need a lot of water to cool the pack, but you don’t know what kind of chemistry it is and adding water might really hurt the situation.So really you want to suffocate it. If it’s inside and you cannot get it outside—it’s either too heavy, it’s burned into something, or it’s just too hot—it’s probably past the point of being able to carry it at all or touch it. Well, then you have to suffocate it with something non-flammable and non-porous, and then wet the surface of that after many layers to reduce the temperature and enhance evaporation, but don’t just pour water onto it. Keep a Class ABC extinguisher handy for spot fires around the device (curtains, carpet) even if it won’t stop the battery itself.<h2>Final Thoughts</h2>These events are definitely not random, and they are rare. Buy quality gear, charge and store it sensibly, protect packs from damage, and dispose of them properly. If a failure happens, move fast, create space, and prioritize safety. A little planning—a clear outdoor spot, labeled chargers, and a tidy charging area—turns a bad day into a manageable one.

Lithium-Ion Battery Fires: Causes, Prevention, and What to Do if One Happens

Learn what lithium-ion C-rate means, how it affects charging, discharging, heat buildup, and why internal resistance matters more than you think.

Lithium-Ion C-Rate: Charge/Discharge Limits & Heat Effects

What is a lithium-ion C-rating? A C-rating tells you how fast the lithium-ion battery can be charged or discharged relative to its capacity.Short note: Think of C-rate as “current relative to size.” The same C-rate means “equally hard use” only when you’re talking about very similar cells.<h2>Quick C-Rate Examples</h2>So if a battery has a 1 C charge rate and it is a 2.5 amp-hour battery, then you can charge that battery at 2.5 amps. If it has a half C charge rate, then you can charge that battery at 1.25 amps. If you have a 3 amp-hour cell and you discharge it at half a C, then you are discharging that cell at 1.5 amps of current. Or if you have a 2,200 milliamp-hour battery, which is 2.2 amp-hours, and you discharge it at 25 C, that would be 55 amps. And the 50 C burst would be 110 amps for a few seconds.Short note: Manufacturers often publish separate continuous and burst C-ratings. Use the continuous rating for anything sustained; treat burst ratings as brief ceiling numbers.<h2>Why C-Rate Is Used</h2>But there are definitely some important things that you need to know. C-rate is used in an attempt to normalize stresses across different sizes. It essentially normalizes how hard you're pushing the cell. Here's the logic behind it. Capacity is amp-hours, so that's how much charge the cell can hold. Current is amps, which is how fast you can pull or push that charge. If you divide those, you get the C-rate. The reason this can be physically meaningful is for cells of similar designs in chemistry, the allowable current scales with capacity. So because you have more active material and more electrode area. So 2 C is roughly the same stress on a 500 milliamp-hour cell as it is on a 5 amp-hour cell, even though 2 C for the 500 milliamp-hour cell is 1 amp and 2 C for the 5 amp-hour cell is 10 amps. But this is only true if the cells are otherwise identical. So the same exact chemistry, the same proportions in the same package and format just scale differently. That's the only time you can use the C-rate to compare batteries like that.Short note: C-rate is a handy shorthand inside a family of like-for-like cells. Once you change chemistry, construction, or format, the shorthand stops being reliable.<h2>Thermals and Scaling</h2>For similar cells, the thermals actually scale nicely. The internal heat is current squared times resistance, and resistance tends to drop as the cells get bigger. So it works out to be inverse with capacity. But that's only if they're the same exact design cell in the same kind of chemistry. In reality, cells have different designs and are going to have different resistances. So you can have two identical capacity cells; they're both 2,000 milliamp-hours, and you do 2 C on one of them and 2 C on the other, and one of them can get very hot and the other one could only get lukewarm. The one with the higher resistance is going to be the one that gets hotter.Short note: In packs, contact resistance, wiring, and airflow can shift temperatures a lot, even if the cells themselves match on paper.<h2>What C-Rate Ignores</h2>While C-rate is a convenient normalization, it hides two big variables. It totally ignores internal resistance. Internal resistance causes heat loss inside of a cell with the formula of I squared times R. So if one cell is 30 milliamp and the other is 15 milliamp, they are going to be stressed different amounts for the same current. It also ignores the thermal pathway. So better can design, better tab design, and better cooling features will lower the temperature delta for the same amount of current.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:372,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXdupT2wVzdZXJaxc-TOE7HWYkj1LK8voho65WQNoRrzEGj2sU_dfd97xFQ4Q65jK2aPD7Nu83j_mfqlB2yLxIrxIzZP6U88OvbY6QqcrnMHLvYfIAsoF7EtkoN3oTmZSgQulcj43g?key=3FmTTjcS_5mQzHqrFYcMoA&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXdupT2wVzdZXJaxc-TOE7HWYkj1LK8voho65WQNoRrzEGj2sU_dfd97xFQ4Q65jK2aPD7Nu83j_mfqlB2yLxIrxIzZP6U88OvbY6QqcrnMHLvYfIAsoF7EtkoN3oTmZSgQulcj43g?key=3FmTTjcS_5mQzHqrFYcMoA" width="624" height="372"><figcaption class="attachment__caption"></figcaption></figure>Short note: Datasheets usually list internal resistance (often in milliohms) and sometimes thermal characteristics; those numbers are crucial for predicting heat rise.<h2>Why C-Rate Is Still Used (and Where It Breaks)</h2>So why is C-rate still used? Because it's easy, and it's a simple way to look at it, and it works good enough most of the time. For similar chemistries and constructions, resistance tends to scale down as the cells get bigger. So the same C often means similar stresses per watt-hour. But across different designs, high power versus high energy, or pouch versus 18650, different porosities and binders, there's so many variables that goes into this, that scaling will totally break.Short note: Treat stated C-ratings as a convenient starting point, then verify with measurements in your actual use case.<h2>When to Use C-Rating</h2>So when is it the best time to use C rating? You can just treat C rating as a general starting point, not as a guarantee. You should really only use it when you're comparing the same exact type of batteries. The best thing to do is to measure the internal resistance or at least look it up in the data sheet. If they're brand-new cells, you can rely on that. And then you will know the performance of the cell and how many watts of heat it will dissipate at any current.Short note: Remember that temperature, state of charge, and aging all increase effective resistance, which lowers the safe continuous C-rate over time.<h2>Power Loss Example</h2>You can see in this power loss chart here, comparing a 15 milliohm cell and a 30 milliohm cell from 0 to 50 amps. At 10 amps, we have just 1.5 watts of power loss with the 15 milliohm cell, but the 30 milliohm cell has 3 watts of power loss. That's double. And then at 20 amps, we have 6 watts of power loss for the 15 milliohm cell. And what do you know? Double that, 12 watts of power loss in the 30 milliohm cell. And you can see it scales all the way up. For each amp of flowing current, you are going to have double the amount of heat.&nbsp;<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:408,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXdC-0vC0j0kBrWVWMvUrKMTzPcvOxH_nYIrnCEc4WIzEXN2y1yJVSQ6PRKgjt-wUqPl-zTplnhDxmwCMjJVshN9bAQ0wntoPM4YsZKJT6sbLnMPmar5qsNTwbbCFyDChTWdG0ZE?key=3FmTTjcS_5mQzHqrFYcMoA&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXdC-0vC0j0kBrWVWMvUrKMTzPcvOxH_nYIrnCEc4WIzEXN2y1yJVSQ6PRKgjt-wUqPl-zTplnhDxmwCMjJVshN9bAQ0wntoPM4YsZKJT6sbLnMPmar5qsNTwbbCFyDChTWdG0ZE?key=3FmTTjcS_5mQzHqrFYcMoA" width="624" height="408"><figcaption class="attachment__caption"></figcaption></figure>So you can see the power loss scales linearly. At 40 amps, the 15 milliohm cell dissipates 24 watts, and the 30 milliohm cell dissipates 48 watts. It's exactly double going one way and exactly half going the other. But look at the current scale. Look left to right instead of top to bottom. For the 15 milliohm cell, we have 1.5 watts at 10 amps and then 6 watts at 20 amps. So it's adding 4.5 watts for every 10 amps. So it seems, but if you go up another 10 amps to 30 amps, you'll see that much more than 4.5 watts was added.And then go up another 10 amps, and you can see how it increases more and more. So with a fixed resistance, as you increase the current, the heat output increases exponentially. But with a fixed current, as you increase resistance, the heat output increases linearly.Short note: Small increases in current can drive disproportionately higher heat, so leave generous thermal margin and validate with real measurements.

Lithium-Ion Battery C-Rate Explained: Charge & Discharge Limits, Heat, and Safety

Learn what lithium-ion batteries are used for, how safe they are, the difference between lithium and lithium-ion, and practical steps to prevent fires and accidents.

Lithium-Ion Battery Safety: Uses, Hazards, and How to Prevent Fires

<h2>What Is Lithium Ion Used For?</h2>Lithium ion batteries are pretty much used for everything portable these days. Anything that needs a rechargeable battery, like phones, laptops, tablets, cameras, headphones, wearables, handheld game consoles, power tools, e-bikes and scooters, drones, backup power banks, and even electric cars and home battery packs, these days. Lithium ion has an extremely high energy density chemistry, and it has the ability to be recharged hundreds, two thousands of times depending on which chemistry you're using, and that's why it shows up absolutely everywhere.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:416,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXfxOFxiNdvBHSy-TtcuaW0-B-gMFZeUrbXYwGMFJUdHs7iFY3sFGsBwVHPUtnFcrxsK7l84fmZjv8jY6IArBo6QDQnoSY9mbmAk0jP74Mj7rJC6mRubHXO3vAODPbULK24Pz1vY-g?key=yTNog27QJ83RWJ3UM0Ev2A&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfxOFxiNdvBHSy-TtcuaW0-B-gMFZeUrbXYwGMFJUdHs7iFY3sFGsBwVHPUtnFcrxsK7l84fmZjv8jY6IArBo6QDQnoSY9mbmAk0jP74Mj7rJC6mRubHXO3vAODPbULK24Pz1vY-g?key=yTNog27QJ83RWJ3UM0Ev2A" width="624" height="416"><figcaption class="attachment__caption"></figcaption></figure>Beyond consumer electronics, lithium ion shows up in cordless home appliances, medical devices, stationary energy storage for solar and grid backup, and even aerospace and marine applications. Its popularity comes from the balance of energy density, power capability, low self-discharge, and flexible shapes (pouch, prismatic, cylindrical), which let designers fit more battery into thinner, lighter products.<h2>Are Lithium Ions Safe?</h2>The short answer is yes. When they are used, charged, and stored as intended, completely properly, they are totally safe. The risk comes from abuse or defects. If a cell is crushed, punctured, overheated, over-currented, used with the wrong charger without a BMS, or the BMS is bypassed on discharge and they're over-currented, they can trigger things like thermal runaway, which is an overheating that feeds on itself, and it could cause the battery pack to catch on fire.Most reputable packs and devices go through safety standards and shipping tests (like UN transportation testing and product safety listings) and include protection circuits that reduce risk in normal use. Practical habits help too: keep batteries out of hot cars, don’t cover devices while charging, avoid visibly damaged or swollen packs, and stick to compatible, certified chargers and cables.<h2>What Does Lithium Ion do to Your Body?</h2>The answer is nothing if you're using them in anything close to a normal manner. The cells are safe and totally sealed. If a battery vents, leaks, or burns, then the electrolyte and smoke can be a totally different story. That can irritate your eyes, your skin, and, even worse, your lungs. The smoke from a burning pack is really nasty.If you’re ever exposed to vented electrolyte or smoke, move to fresh air immediately. Avoid touching residues; if it gets on skin or in eyes, rinse with plenty of water for at least 15 minutes and seek medical advice. If symptoms like coughing, shortness of breath, or eye irritation persist, contact emergency services or poison control.<h2>What's the Difference Between Lithium and Lithium Ion?</h2>Lithium is an element, which is a soft, highly reactive metal. In the context of lithium ion batteries, instead of metallic lithium, it's lithium ions that shuttle between a carbon anode and a metal oxide or phosphate cathode. Variants like lithium polymer and lithium ion phosphate are still lithium ion, but none of those things contain metallic lithium.A useful way to think about it: “lithium” (metal) often refers to primary, non-rechargeable coin cells you might find in watches or remotes, while “lithium ion” refers to rechargeable chemistries used in most modern gadgets. Never attempt to recharge a primary lithium metal cell, and don’t expose metallic lithium to water—it reacts vigorously.<h2>Do Cell Phones Have Lithium Batteries?</h2>Absolutely. All modern cell phones are powered by lithium ion batteries that have built-in protection circuits. Lithium ion gives the best combination of thinness, capacity, and rechargeability compared to any other battery technology on the planet. It's pretty much the only batteries that can be used in smartphones, and smartphones basically wouldn't exist without lithium ion batteries.Because phone batteries are tightly integrated with the device’s charging system and thermal design, replacements should be high-quality and properly matched. Signs of trouble include swelling, sudden shutdowns, or excessive heat while charging; if you see those, stop using the device and get the battery professionally evaluated or replaced.<h2>How Can You Prevent Lithium Battery Fires?</h2>The first step is to buy a quality battery, or, if you're building a battery, do quality testing on the cells and build the battery in a quality manner with quality connections. Avoid the absolute cheapest stuff. That's the easiest way to do it. If you're looking at a battery and it's the absolute cheapest one that you can find, don't buy that one. Just buy the next most expensive one, and that will probably save you most of the trouble in this phase.The general rule of thumb is don't buy any lithium ion battery that is an entire battery pack and is sold in the thousands of milliamp hours, unless it's an RC battery pack. Only RC battery packs are going to be real battery packs that advertise the thousands of milliamp hours, like 6,000 milliamp hours, 10,000 milliamp hours. Generally, if you see something that says 100,000 milliamp hours and they're claiming 100 amp hours, it's absolutely not the case. E-bike batteries that are sold in the milliamp hours are almost always scam fake counterfeit batteries.Regardless of whether you buy or build, there are definitely some other things that you can do.&nbsp;<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:397,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXfDCZDX5EZBcdzwwZSnRkCZ0LFlrv9OCVxH10ws4iqaGs1bNdMfM7L1AwAmdV7G6rTB9rWzeiRwSB9-e6DaWVZ7jmiEuyW5YMZfb0t1lTOBA6Z35PFCzQOBJJlHW1PQ7-cRuxw6_A?key=yTNog27QJ83RWJ3UM0Ev2A&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfDCZDX5EZBcdzwwZSnRkCZ0LFlrv9OCVxH10ws4iqaGs1bNdMfM7L1AwAmdV7G6rTB9rWzeiRwSB9-e6DaWVZ7jmiEuyW5YMZfb0t1lTOBA6Z35PFCzQOBJJlHW1PQ7-cRuxw6_A?key=yTNog27QJ83RWJ3UM0Ev2A" width="624" height="397"><figcaption class="attachment__caption"></figcaption></figure> Make sure that the charger voltage is no higher than the max safe voltage of the battery. If you have a 36 volt lithium ion battery, the max charge voltage for that is 42 volts. With the charger unplugged from the battery, take a multimeter and test the voltage of the charger. It should read no higher than 42 volts. If it's any higher, then it will overcharge the battery without the BMS's intervention. Sure, the BMS can prevent overcharging by disconnecting the charging when any one cell group reaches a maximum threshold, but that means you're depending on a 10- to 50-dollar BMS as your very last line of defense. And that's highly disavowed. Don't charge the battery faster than it should be charged. Look at the ratings on the battery. If it says that it can take a 5 amp charge, well, feel the side of the battery or the cells if you have access to them and see how hot it's getting at 5 amps. If it's lukewarm after charging for an hour straight at 5 amps, you can probably turn the charge current up a little bit. If it's burning hot, then, regardless of what the label says, you probably need to turn the charge current down.&nbsp;<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:339,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXdvfTYeZM0acT5DngA6slic046WSpIrs1EeBuj9DwWyK-lRciNa8bmtimquWRxGoNomwq83DQrpg5gXLfRMHTNQQzYZEoV0ai_PJnXao1VTXoSAbjftYjowL83yJj_DK3rn59gD?key=yTNog27QJ83RWJ3UM0Ev2A&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXdvfTYeZM0acT5DngA6slic046WSpIrs1EeBuj9DwWyK-lRciNa8bmtimquWRxGoNomwq83DQrpg5gXLfRMHTNQQzYZEoV0ai_PJnXao1VTXoSAbjftYjowL83yJj_DK3rn59gD?key=yTNog27QJ83RWJ3UM0Ev2A" width="624" height="339"><figcaption class="attachment__caption"></figcaption></figure>If you just go by how hot the cells feel under an hour of charge and verifying the max charge voltage of a charger, you can cut out almost all battery fires that would start as a result of overcharging a battery. Don't bypass the discharge port of a BMS to get more power out of a battery.&nbsp; That's one of the leading ways battery fires are caused. And even if you don't bypass the BMS, you could still possibly draw too much current from your battery because the BMS is just one line of defense. The cells themselves actually have their own internal limits. So if you have a hundred amp BMS but your cell groups can only support 40 amps, well, you don't have to bypass your BMS to put yourself at fire risk. So feel the battery under intense discharge. Like run it from full charge all the way down and feel the battery. If it's burning hot and too hot to touch or just very, very hot and uncomfortably hot, you know, then you're drawing too much power for the battery. So you either need a bigger battery or turn the power down on your controller or use a smaller motor or something. And if you go by that, then you'll almost definitely never have a battery fire as a result of discharging too much current for your battery. It will tell you from how hot it's getting if it's having a hard time.Take your e-bike battery and draw one amp from it for an hour. See what happens. It's probably going to be undetectably warmer, maybe just barely across the threshold of detectable, because that's just one amp across maybe four or six, eight P, depending on how big your battery is. Then go up from there. You'll see it gets hotter. So if you don't stress out the battery, it can't burst into flames from being stressed out. Dispose of lithium ion batteries properly For everyday safety, store packs in a cool, dry place away from flammables, avoid charging unattended or on soft surfaces, and use enclosures/holders that protect against crushing and short circuits. For long storage, a partial state of charge is kinder to the cells. Recycle at approved collection points (many home-improvement and electronics stores accept them). If a pack is damaged, swelling, or has been submerged, isolate it in a non-flammable area and consult a professional; if a fire starts, prioritize getting people clear and call emergency services.If you throw away even a half charged e-bike battery and then the garbage truck comes and gets it and throws it in the back, and a couple streets later compresses it down, it's literally going to burst into flames, and they'll probably trace it back to the house that it came from, and you'll be responsible for that. So you should probably consider that.What if the garbage man is in just the wrong position and the battery explodes and sends a piece of shrapnell directly into his eye which causes him to be rushed to the hospital where he is initially stabilized but later dies of an infection. Then what are you gonna do? Spend the rest of your life in prison, that's what you’re gonna do, and those kids are gonna grow up without a father. So you should probably consider that.<h2>Conclusion</h2>Lithium-ion powers almost everything portable—from phones and laptops to e-bikes, power tools, EVs, and home storage—because it’s light and energy-dense. It’s safe when used as intended, but abuse, defects, or excess heat can cause problems, so rely on protection circuits, sane charging, and keep an eye on temps. Normal use doesn’t expose you to chemicals; if a pack vents, get fresh air and rinse—irritation is possible. Remember: lithium metal (non-rechargeable) ≠ lithium-ion (rechargeable), phones all use lithium-ion, and to prevent fires match charger voltage/current, don’t bypass the BMS, and recycle batteries properly instead of tossing them in the trash. Well, that about wraps it up for these common lithium ion related questions. Thanks for reading!

Lithium-Ion Batteries: Uses, Safety, and Fire Prevention Guide

Learn why lithium-ion batteries have a negative temperature coefficient (NTC) — meaning resistance drops as they heat up — and how this affects performance, voltage sag, and safety.

Lithium-Ion Battery NTC Effect: Why They Perform Better When Warm

As most things increase in temperature, they also increase in resistance. And if current is flowing through a conductor, its resistance directly governs how much voltage is going to drop across that conductor. The amount of voltage drop across the conductor governs how many watts of power are lost within the conductor as waste heat. That heat, in turn, causes the conductor's resistance to increase more, at which point it has more voltage drop, at which point it produces more watts of heat loss, and so on. The death cycle continues.Most things work that way. That is called having a negative temperature coefficient. But there are some things that do not do that. In fact, there are some things that do the exact opposite of that. And you know what that is called? You guessed it. That is called having a negative temperature coefficient.<h2>PTC vs NTC at a Glance</h2>Metals are usually PTC. Semiconductors, electrolytes, and many ionic conductors are NTC. NTC, or negative temperature coefficient, materials generally behave like this: as temperature rises, the carrier mobility and availability rise and resistance falls. <figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:387,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXelF3bkIlOYV7zCtynpdV4O9MtpDpTLSToAF0gcMhNbSqVuu_izd6vvW3UQcR-olLP0k2ViCq8fhgbVvjIU3W7PjTHnJPXvbhsgDCphGfKy7d6h2QV4uXK6U-LQ2eUa74WovMKr?key=q4yW2WSDBwQPkW6GBWNrsA&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXelF3bkIlOYV7zCtynpdV4O9MtpDpTLSToAF0gcMhNbSqVuu_izd6vvW3UQcR-olLP0k2ViCq8fhgbVvjIU3W7PjTHnJPXvbhsgDCphGfKy7d6h2QV4uXK6U-LQ2eUa74WovMKr?key=q4yW2WSDBwQPkW6GBWNrsA" width="624" height="387"><figcaption class="attachment__caption"></figcaption></figure>A practical example is an NTC thermistor, which is used to control many devices. It is because the hotter parts will essentially self throttle their waste heat, because power is current squared times resistance, and it drops as R drops.<h2>The Funny Thing About Lithium Ion Batteries</h2>This article today is about how lithium ion battery cells actually have a negative temperature coefficient. There is this funny thing about lithium ion batteries: their resistance actually decreases as they get hotter. It is one of the weird, rare things that actually does that.<h2>Why Lithium Ion Cells Show NTC Behavior</h2>Inside of a cell, there is a dominant resistance under load that is ionic and electrochemical. It is not metallic. As the electrolyte gets warmer, it has a lower viscosity, which results in higher ion mobility. This results in faster charge transfer kinetics at the electrodes, which results in a lower interfacial impedance. The net result of this situation is that, in the normal operating band of a lithium ion battery, which covers its entire operational temperature range, as it gets hotter, its internal resistance decreases. <h2>What This Means Under Load</h2>For any given current, the lower the resistance, you will get a lower voltage drop, which gives you lower power losses and less self heating from conduction. Voltage sag improves at higher temperatures, so performance looks better warm than cold. That is why batteries work better after they warm up. This also produces a naturally stabilizing effect against thermal runaway by suppressing the I squared R heating.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:372,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXfZkco2oikCWR0THfzSqrw2UxFT-JLP3RdHJmfu0OZ-e0UhOeCXhIEM8hWM9zGMJwfEfeZypkTcekE-Jz7uTult3q4thyIPAtMatKBRx-p2OPKnVpXF11k-E7H3I_jA3-0O6GM02A?key=q4yW2WSDBwQPkW6GBWNrsA&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfZkco2oikCWR0THfzSqrw2UxFT-JLP3RdHJmfu0OZ-e0UhOeCXhIEM8hWM9zGMJwfEfeZypkTcekE-Jz7uTult3q4thyIPAtMatKBRx-p2OPKnVpXF11k-E7H3I_jA3-0O6GM02A?key=q4yW2WSDBwQPkW6GBWNrsA" width="624" height="372"><figcaption class="attachment__caption"></figcaption></figure><h2>Limitations and Caveats</h2>But there are some limitations and caveats. The NTC situation does not completely cancel out the chemistry. At high temperatures, there are parasitic reactions that accelerate. Gas is generated, and there is plating that can happen on the SCI conductors, causing SCI growth and venting. Thermal runaway is something that is driven by exothermic reactions, not all the losses. Once certain temperatures are achieved, and those thresholds are crossed, there is no turning back. This, of course, all depends on the state of charge and the health of the battery.<figure data-trix-attachment="{&quot;contentType&quot;:&quot;image&quot;,&quot;height&quot;:387,&quot;url&quot;:&quot;https://lh7-rt.googleusercontent.com/docsz/AD_4nXfJ5tTX6SMJ0raAM3AtHwTFeHgPMVo7ixc3IvijT2Tcb_bzmJoKTuWd68bbyM-9ldAEVdrkQXuOXshjc7EbMm4eVpzd0fq_Pg9qc-XvjRuPFezq4KexsF4qZQGCWeaBEiTmOnLN?key=q4yW2WSDBwQPkW6GBWNrsA&quot;,&quot;width&quot;:624}" data-trix-content-type="image" class="attachment attachment--preview"><img src="https://lh7-rt.googleusercontent.com/docsz/AD_4nXfJ5tTX6SMJ0raAM3AtHwTFeHgPMVo7ixc3IvijT2Tcb_bzmJoKTuWd68bbyM-9ldAEVdrkQXuOXshjc7EbMm4eVpzd0fq_Pg9qc-XvjRuPFezq4KexsF4qZQGCWeaBEiTmOnLN?key=q4yW2WSDBwQPkW6GBWNrsA" width="624" height="387"><figcaption class="attachment__caption"></figcaption></figure><h2>Low State of Charge Behavior</h2>As voltage drops toward the end of state of charge, the resistance increases dramatically, which will increase voltage drop, which will cause more heat loss, which will cause a runaway chain reaction.<h2>Key Ideas Without Symbols</h2><ul><li>Ohms Law stated in words: voltage equals current times resistance. </li><li>Conductive heating stated in words: power loss equals current squared times resistance. </li><li>Lower resistance at higher temperature means lower voltage drop for a given current and lower self heating. </li></ul><h2>Practical Implications</h2><ul><li>Cold packs show more voltage sag and feel weak until they warm up. </li><li>Warm (but within safe limits) packs have less internal resistance and deliver better performance. </li><li>Cell health and state of charge still dominate safety and longevity. </li></ul><h2>Design and Use Notes</h2><ul><li>Battery management systems account for temperature to predict voltage sag and power limits. </li><li>Packs should be kept within their recommended operating temperature range for both performance and life. </li><li>Do not rely on NTC behavior to prevent thermal runaway. Chemical side reactions can still take over at high temperatures. </li></ul><h2>Bottom Line</h2>While it is not good for the long term health of the cells, and over a long period of time will cause the cell to actually have a higher resistance and produce more heat, while a healthy cell is hot it will have a lower voltage drop, a lower resistance, a lower power loss to heat, and perform better when it is hot.

Why Lithium-Ion Batteries Have a Negative Temperature Coefficient

Understand lithium-ion charging: cell structure, CC/CV phases, SEI layer, and proper practices for performance and safety.

Lithium-Ion Battery Charging Explained – Phases & SEI

This article explains how the lithium-ion battery charging process actually works. We’ll start with the internal structure of a lithium-ion cell, then cover the charging phases, the electrochemical reactions, formation of the SEI layer, how energy is transferred from the charger to the cell, and proper charging practices.<h2>Internal Structure of a Lithium-Ion Cell</h2>Inside a lithium-ion cell you have a cathode, which contains a lithium metal oxide, and during charge lithium is extracted from here. You also have an anode; it's usually made of graphite, and during charge lithium is inserted here, which is also called intercalated. There's an electrolyte between the cathode and the anode. It's an ionic conductor between both of these electrodes and it allows lithium ions to move, but electrons cannot pass through it. There's also a separator that physically separates the cathode and anode while permitting ion flow. Electrons flow through the external circuit from the charger into the anode. Lithium ions then move internally through the electrolyte from the cathode to the anode to maintain the charge balance.<h2>Charging Phases</h2>Charging is typically done in two stages: constant current and constant voltage. (I say typically because you don't always have to do the constant voltage stage. In fact, many devices completely skip that stage.)<h3>Constant Current Stage</h3>The first constant current stage is a fixed current—so whatever you set, say 3 amps or 5 amps, it will maintain that current during this phase, and it will allow the cell voltage to rise. It does this by automatically changing the voltage to whatever it needs to be above the cell voltage to maintain the amount of current that you set. The cell voltage rises as lithium accumulates in the anode. This is the charging stage that delivers the most capacity the fastest.<h3>Constant Voltage Stage</h3>After that is the constant voltage stage. Once the cell reaches its upper limit—for lithium-ion NMC chemistry that would be 4.2 per cell—the charger switches to constant voltage mode, where it holds the voltage solid but lets the current slowly fall. The current will decrease or taper down as the battery approaches its full charge voltage.<h3>Charge Termination</h3>Charging is generally terminated when the current falls below a set cutoff value, say 10 milliamps for some chargers or 100 milliamps for others. If you're charging with a bench power supply or something like that, it will never cut off charging. It will just equalize and stabilize, and as long as you don't have any self-discharge or a BMS that draws a lot of current, no current will appear to be flowing on the meter. But some tiny, tiny bit will still flow because all cells have some amount of internal self-discharge, and the BMS—even simple ones—have components that have to be powered. The current will fall so low that on just about any power supply or meter it will say zero.<h2>Electrochemical Reactions During Charge</h2>The cathode undergoes deintercalation and the anode goes under intercalation. The electrons are supplied externally—that’s from the wire, connector, power supply, etc. The stuff outside that you're using to charge the battery is pumping electrons through a system. That's where they stop there at the lithium-ion battery, because, as you know, electrons are negatively charged; lithium ions are made of ions which are positively charged because ions are atoms without their electrons, right? Everybody understands that the flow of electrons is primarily responsible for electricity. When you store energy inside of a battery, you're definitely not using electrons; you're using ions. These externally supplied electrons cause lithium ions to migrate through the electrolyte to the anode.<h2>Solid Electrolyte Interface (SEI) Formation and Abuse</h2>On the first few charge cycles—especially on the first charge cycle—there is an SEI, or solid electrolyte interface, layer that forms on the graphite anode. That SEI formation consumes a small amount of lithium, which is irreversible, but it stabilizes and forms a skin and prevents further parasitic reactions. If you abuse a cell—like overcurrent it, run it too low, or expose it to high temperatures—you'll cause that SEI layer to grow much more than it normally would and make it much less stable.<h2>Energy Transfer from Charger to Cell</h2>How exactly does the charging process work? How is energy transferred from the charger to the cell? Yes, we understand the different charging phases—the constant current, the constant voltage, etc.—but how exactly is the energy transferred?Well, that all comes down to a voltage difference. If you connect two things together, energy is going to flow from the high voltage to the low voltage as things try to stabilize. If I hook a 12-volt battery up to a 0-volt light—because the light has no power of its own—then the amount of current that flows is a function of the difference in the voltage (so that would just be the voltage itself, right? Because the destination, the load, has zero volts). So the volts of the power supply and the resistance of not only the power supply but also the load and the connection between them—the entire series circuit resistance—along with the voltage difference is what determines how much current flows.This goes in both directions: if the load has a higher voltage than the power supply, then power will flow from the load to the power supply. Now obviously, in normal circumstances that's not going to happen because a light, a speaker, a fan—they have no voltage; you have to give them voltage. They're already at zero volts. But if you hook a 24-volt battery up to a 20-volt power supply, there's a 4-volt difference in that direction, and lithium-ion batteries and power supplies generally have very, very low resistances, so a lot of current is going to flow from the battery to the power supply unless there is a diode on the output of the power supply that prevents reverse current flow.So the same phenomenon is taking place when you charge a battery, whether you're properly charging it or improperly charging it, whether you're overcharging it or using too much current. One way or the other, you're connecting that battery to something that has a higher voltage than that battery. The only way to properly charge a lithium-ion battery is to set the voltage to whatever voltage it needs to be to produce the current you want to flow and then slowly increase the voltage over time to maintain that amount of current flow. A constant current power supply or official lithium-ion battery charger does that automatically.<h2>Proper Charging Practices</h2>Proper charging involves controlling both the current and the voltage so that the battery is driven toward full charge without undue stress. Skipping stages, using excessive current, or exposing the cell to abusive conditions can degrade the SEI, cause irreversible capacity loss, or introduce safety risks. Monitoring the tapering current during the constant voltage stage and terminating charge at an appropriate cutoff helps ensure longevity and stability.<h2>Conclusion</h2>That pretty much covers how the lithium-ion battery charging process works. Energy is transferred via voltage difference, lithium ions shuttle between electrodes while electrons flow externally, and careful control of current and voltage—along with respect for the SEI and operating limits—keeps the system stable and effective. We hope this article helped you gain insight on these things. Thank you for reading.

How Lithium-Ion Battery Charging Really Works: Inside the Cell, Charging Phases, and SEI Formation

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