What are the reasons why Tesla uses Panasonic 18650 lithium batteries?

The Panasonic 18650 lithium battery used by Tesla uses NCA as the positive electrode and has designed a complex battery management system to ensure and improve the efficiency and safety of battery work as much as possible. As for whether it is absolutely safe or not, I cannot answer this question. If you want to talk about spontaneous combustion, I would also like to say that gasoline cars also ignite spontaneously in summer. Regarding pure electric vehicles (regardless of plug-in hybrid and pure hybrid, people can rely on gasoline to open and hang), what is the most tangled thing about us? The mileage anxiety means that you can’t drive far because the energy density of the battery is too low. The energy density of the car battery is usually 100~150Wh/kg after being assembled. The value of gasoline is about 10000, so even if you are like a tortoise The same car battery does not necessarily deal with the problem. Everyone complains about what to do if the electric car is not charged and runs out of power every day, because the energy density is too low. The biggest shortcoming of current battery technology is that the energy density is too low, which is infinitely far behind Moore's law. Don’t talk about those lithium-air or something, even if their energy density is not high enough, the key is that they are far from practical and why not use iron phosphate. Lithium batteries, I want to say, the main reason should be capacity (Capacity unit is Ah), and energy (Energy, that is, the Ah of the capacity multiplied by the voltage to get Wh) is low (the capacity of lithium iron phosphate is a little lower than the three yuan, the voltage It is still low, only 3.4V, so the multiplied energy is even lower). The actual car battery packs are combined in series and parallel, and the voltage must be increased in series. At this time, the voltage of a single cell and the consistency of the capacity between different batteries are very important. It is not rigorous to say that the capacity is low. of. My job is to research and develop an upgraded product of lithium iron phosphate in a domestic research, and I also look at some other materials, lithium batteries and electric vehicles, so I will answer here. (Currently starting to develop Smidak in a beautiful and semi-academic way) Power, Life, Cost, Safety, and Energy. The comparative materials are NMC/NCA ternary materials/NCA, LCO lithium cobalt oxide, LFP lithium iron phosphate, LMO lithium manganate. NCA and NCM are relatively similar and can be regarded as close relatives in the material, so they are grouped together here. LCOu003dLiCoO2,layered,NMCu003dLiNixMnyCozO2,layered,NCAu003dLiNi1-y-zCoyAlzO2,layered,LMOu003dLiMn2O4spinel,LFPu003dLiFePO4olivine From this figure, we can see: • LFP material has the lowest energy (tragedy, low capacity) On the one hand, the low voltage of 3.4V is the problem. The negative example is lithium nickel manganate spinel, voltage 4.7V). Due to space limitations, the charge and discharge curves are not here. Power is not low at all (the pilot-level lithium iron phosphate made by the Institute of Technology, 5C can achieve 130mAh/g drop (of course, PHOSTECH can also...). Coated carbon + nano material rate performance It is still very powerful! Life and safety are the best, which is mainly due to the combined use of the polyanion PO43- in the material, which makes the oxygen binding better and has low reactivity with the electrolyte, unlike ternary materials In that way, oxygen bubbling is more likely to occur. In terms of life, it is generally considered that it can be more than 4000 cycles. Cost cost, lithium iron phosphate is not bad, and the cost is second only to LMO lithium manganate material (this thing, air burning, manganese The source is cheap), and the second is competitive. The raw materials of lithium iron phosphate, lithium iron phosphate are relatively cheap, but it takes some costs to make nano powders, and the thermal solution must be carried out in an inert atmosphere. Various process requirements lead to the material The cost (about 10W/t domestically produced) is not as low as LMO (6~7W/t), but compared to NMC (13W/t), LCO (more expensive) is still cheaper. Reason: Cobalt is more expensive than nickel ( Is there any cobalt-poor in our country? Nickel is more expensive than ferromanganese. What raw materials are used and what are the costs. • Then compare and decompose the following NCM/NCA materials that have the most energy advantages (electric vehicles want to run farther, this is the most important) In addition, with the development and launch of high-nickel NCM materials, the energy density of this material can be further improved and the power can be further improved (in fact, it is enough. For pure electric vehicles, energy is more important than power characteristics. For Toyota Prius, this For hybrid vehicles, the power characteristics are more important, but the premise is that the energy cannot be too frustrated.) The life span is also good. Previously, the ternary material may have a life span of about 1,000 cycles, but with the progress of research and development in recent years, the material’s The life expectancy can reach 2000 weeks (as if the standard is still 80% or how much, I can’t remember), this is already impressive, for example, your electric car, one charge a day, 365 times a year, 2000 times is enough for you 6 Years, many people are planning to change cars at this time. The cost is a bit high (admit this first). After all, some nickel-cobalt metal is used. The high cost is normal, but this material is at least cheaper than LCO lithium cobalt oxide, so in the future In the field of daily consumer electronics, it is relatively promising to replace LCO materials. The safety is poor, especially for lithium iron phosphate. NCM/NCA materials will emit oxygen when charging, and the possibility of accidents during use is also higher than that of LFP materials. There have always been some problems with the safety of ternary material batteries. But at this point, not only the positive electrode material in the battery, we can also adjust the electrolyte composition, optimize the diaphragm (ceramic diaphragm) and optimize the battery control system (cooling, safety protection) ) To alleviate this problem. Although the safety of NCM/NCA materials has always been a problem, there is still room for improvement and ways to deal with it. I think those who can completely deal with safety problems are playing rogues. The battery control system, It is to increase the degree of safety as much as possible, and it is impossible to guarantee 100% safety. Disclaimer: Some pictures and content of the articles published on this site are from the Internet. If there is any infringement, please contact to delete.