How to solve the safety problem of large-capacity lithium iron phosphate battery pack?
Li-ion battery pack needs to solve the safety problem from the fundamental principle of technology. In the past, most of us considered improving the safety of the battery from the process, such as the design of safety valves, avoid short circuit, control the manufacturing process, etc., but these efforts can only be said to minimize safety accidents, it is impossible to completely avoid accidents. Can be optimized through the construction and design of lithium iron phosphate batteries to improve safety. Such as the use of high thermal stability of the cathode material, flame-resistant electrolyte, lithium does not precipitate anode material and high-performance diaphragm.
Choose a safe cathode material, the current cathode has lithium cobaltate and lithium manganate two mass production of material products. Lithium cobaltate is a very mature system in terms of small electric cells, due to the characteristics of lithium cobaltate in terms of molecular structure (LiCo): after fully charged, there are still a large number of lithium ions left in the cathode, and when overcharged, the lithium ions remaining in the cathode will surge to the cathode, and the formation of dendrites on the cathode is an inevitable result when the battery with lithium cobaltate material is overcharged, and even in the normal charging and discharging process, there may be excess Lithium ions may be free to the negative electrode to form dendrites.
The choice of lithium manganate material, in terms of molecular structure, ensures that in the fully charged state, the lithium ions of the positive electrode are completely embedded in the carbon pores of the negative electrode, which fundamentally avoids the generation of dendrites. At the same time, the solid structure of lithium manganate makes its oxidation performance much lower than that of lithium cobaltate, and the decomposition temperature exceeds 100 degrees Celsius. Even if internal short circuit (pinprick) or external short circuit occurs due to external force, the danger of combustion and explosion caused by precipitated lithium metal can be completely avoided when overcharging.
Comparison of the safety of lithium batteries
Lithium Nickel Cobalt Manganate Ternary Battery
In the actual available theoretical specific energy has greatly improved, compared with lithium cobalt-acid batteries, can better play a high-capacity role, but from a material point of view, ternary batteries using lithium nickel cobalt manganate and organic electrolyte, not yet fundamentally solve the safety problem, if the battery short-circuit speaks of excessive current, thus causing safety hazards.
Lithium iron phosphate battery
Theoretical capacity is 170mAh/g, made of materials with an actual capacity of 160mAh/g. In terms of safety, lithium iron phosphate has high thermal stability and low oxidation capacity of electrolyte, thus high safety; however, the defect is low conductivity, excessive volume, high electrolyte usage, and poor battery consistency due to high capacity.
Lithium cobaltate battery
In the preparation of * is characterized by a large number of lithium ions remain in the positive electrode after a full charge, that is, the negative electrode can not accommodate more lithium ions attached to the positive electrode, but in the state of overcharge, the excess lithium ions on the positive electrode will still swim to the negative electrode, because it can not be fully accommodated back to the negative electrode to form lithium metal, because the lithium metal is a dendritic crystal, and therefore is called dendrite, once the dendrite is formed, it will give Once the dendrite is formed, it will give the opportunity to pierce the diaphragm, and the diaphragm piercing will form an internal short circuit. Since the main component of electrolyte is carbonate, the flash point and boiling point is low, and it will burn or even explode at higher temperature. Controlling the formation of lithium dendrites is easier in small-capacity lithium batteries, so lithium cobalt acid batteries are currently limited to small-capacity batteries such as portable electronic devices, and cannot be used for power batteries.
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