Comparison of safety of lithium batteries with different structures

From the mainstream technology of lithium ion batteries currently used, there are mainly several types of lithium cobaltate, lithium manganate, lithium iron phosphate and polymers, and their different materials and structural characteristics may affect the battery preparation technology and use, thereby the security comes with it.

1. Lithium cobaltate battery: The biggest feature in preparation is that after fully charged, a large amount of lithium ions remain in the positive electrode. That is to say, the negative electrode does not accommodate more lithium ions attached to the positive electrode, but in the overcharged state, excess lithium ions on the positive electrode still swim toward the negative electrode, and metal can be formed on the negative electrode because it cannot be completely accommodated. Lithium, because this metal lithium is a dendritic crystal, is called dendrites and once formed dendrites provide an opportunity to pierce the membrane. Diaphragm piercing will create an internal short circuit. Since the main component of the electrolyte is carbonate, the lightning and boiling point are low, so that it will burn or even explode at higher temperatures. Controlling the formation of lithium dendrites is relatively easy on small-capacity lithium batteries. Therefore, lithium cobalt oxide batteries are currently limited to small-capacity batteries such as portable electronic devices, and cannot be used for power batteries.

2. The polymer lithium battery: in the actual available theoretical specific energy is greatly improved, compared to the lithium cobalt oxide battery, can play a higher capacity, but in terms of materials, the polymer battery also uses cobalt acid Lithium and organic electrolytes do not fundamentally address safety issues. From the point of view of use, if the battery is short-circuited, it will generate excessive current. The electrolyte of the polymer lithium battery is colloidal and is not easy to leak, which eliminates the possibility of liquid leakage, but will cause more intense combustion. Therefore, spontaneous combustion is the biggest hidden danger of polymer lithium batteries.

3. Lithium Manganate Battery: The material of lithium manganate battery has certain advantages. It can ensure that the lithium ion of the positive electrode can be completely embedded in the carbon hole of the negative electrode under full charge, instead of being like the lithium cobaltate. There is a certain residue, which fundamentally avoids the generation of dendrites. This is theoretically understood. In fact, if the lithium manganate battery encounters a strong external force or cuts the workmanship during the preparation process, it may cause the lithium ions to rapidly move during the charge and discharge cycle. Dendrites are formed in the case where the negative electrode does not have complete lithium ion reception. Avoiding this consequence is guaranteed by testing the battery at the factory. In short, a qualified lithium manganese oxide battery generally does not cause a safety accident. Because the stable structure of lithium manganate makes its oxidation performance much lower than that of lithium cobaltate, even if it is externally short-circuited (not internal short-circuit), it can basically prevent the precipitation of metal lithium to cause combustion and explosion.

Fourth, lithium iron phosphate battery: This is an ideal power battery, can be used for power tools and power cars, the theoretical capacity of lithium iron phosphate is 170mAh / g, the actual capacity of the material made of 160mAh / g. In terms of safety, lithium iron phosphate is thermally stable and high, and the electrolyte has low oxidation ability, so the safety is high; but the defect is that the conductivity is low, and the modification technology is required to be improved. As a result, the volume is too large, and the electrolyte is used in a large amount. Moreover, due to the large capacity and poor battery consistency, lithium iron phosphate technology is still in progress.

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