Lithium cobalt oxide batteries are structurally stable, have high specific capacity, and outstanding overall performance; however, they suffer from poor safety and very high cost, and are mainly used in small to medium-sized cells with a nominal voltage of 3.7V. Regarding the safety performance analysis of lithium cobalt oxide batteries, we will explain in detail through a safety comparison of four types of batteries: lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium cobalt oxide, and lithium manganese oxide.
1. Lithium nickel cobalt manganese oxide (ternary) battery
The theoretical specific energy is greatly improved in practical use, and it can better play the role of high capacity compared with lithium cobalt oxide batteries. However, from the perspective of materials, ternary batteries use lithium nickel cobalt manganese oxide and organic electrolytes, which has not yet fundamentally solved the safety problem. If the battery short circuits, it will generate excessive current, thereby causing safety hazards.
2. Lithium iron phosphate battery
The theoretical capacity is 170 mAh/g, while the actual achievable capacity of the material is 160 mAh/g. In terms of safety, lithium iron phosphate has high thermal stability and low electrolyte oxidation capacity, thus ensuring high safety; however, its drawbacks include low conductivity, large size, high electrolyte consumption, and poor battery consistency due to its large capacity.
3. Lithium cobalt oxide battery
The most significant characteristic in its manufacturing process is that even after full charging, a large number of lithium ions remain at the positive electrode. This means the negative electrode cannot accommodate more lithium ions attached to the positive electrode. However, under overcharge conditions, excess lithium ions on the positive electrode will still migrate towards the negative electrode. Since they cannot be fully accommodated, they revert to forming metallic lithium on the negative electrode. Because metallic lithium is a dendritic crystal, it is called dendrites. Once dendrites form, they provide an opportunity to puncture the separator, leading to an internal short circuit. Since the main component of the electrolyte is carbonate, which has a low flash point and boiling point, it can burn or even explode at high temperatures. Controlling lithium dendrite formation is relatively easy in small-capacity lithium batteries; therefore, lithium cobalt oxide batteries are currently limited to small-capacity batteries for portable electronic devices and cannot be used in power batteries.
4. Lithium manganese oxide battery
Lithium manganese oxide batteries have certain advantages in their materials. They ensure that, when fully charged, lithium ions at the positive electrode can be completely embedded into the carbon pores of the negative electrode, unlike lithium cobalt oxide batteries where some residue remains at the positive electrode. This fundamentally avoids dendrite formation. However, in reality, if a lithium manganese oxide battery is subjected to strong external forces or if substandard materials are used during manufacturing, rapid lithium ion movement can occur during charge-discharge cycles. If the negative electrode cannot fully absorb the lithium ions in time, dendrites can form. Preventing this consequence requires rigorous testing during battery manufacturing.
In summary, qualified lithium manganese oxide batteries generally do not cause safety accidents. The stable structure of lithium manganese oxide makes its oxidation performance much lower than that of lithium cobalt oxide. Even if there is an external short circuit, it can basically avoid combustion and explosion caused by the precipitation of metallic lithium.
