Methods to improve the overcharge safety of various internal components of lithium-ion batteries.
1. Electrode
For the positive and negative electrodes of lithium-ion batteries, developing overcharge-resistant electrodes is an important aspect of improving safety. Qiu Weihua et al. synthesized a series of LiCoxNi using a solid-state method and found that when the Ni/Co ratio was 8:2, it exhibited good overcharge resistance. Wan Xinhua et al. assembled AA-type lithium-ion batteries with lithium cobalt oxide embedded in them and found that their overcharge resistance was far superior to that of lithium cobalt oxide.
Another method for overcharge protection of electrodes is to coat a PTC layer between the current collector and the active material. When the internal temperature of the battery is too high, the PTC layer dissociates due to heat, and the active material detaches from the electrode, thereby preventing further overcharging of the battery.
2. Overcharge protection mechanism of electroactive polymer membrane
Electroactive polymer overcharge protection mechanisms utilize the significant changes in conductivity during the redoping and dedoping processes of certain polymers. It can provide overcharge protection for a battery in an overcharged state without affecting the normal operation of other batteries; and when the overall system is operating normally, the protected battery can resume normal operation. Research by Karen E. Thomas-Alyea shows that electroactive polymer films made of butylthiophene (poly(3-butylthiophene)P3BT) can provide reversible overcharge protection of approximately 4.2V for lithium-ion batteries without affecting battery performance.
3. Overcharge protection for electrolyte
Adding appropriate amounts of additives to lithium-ion battery electrolysis can provide overcharge protection. Current research focuses primarily on redox couple additives and electropolymer additives. Ferrocene and its derivatives, dihydrophenazine derivatives, sodium imidazole, and dimethylbromobenzene all belong to redox couples. Biphenyl, cyclohexylbenzene, thiophene, furan, dichloroanisole, and trifluoromethoxybenzene can all polymerize under certain voltages, providing protection for lithium-ion batteries.
