Lithium-ion batteries are widely used in electronic devices due to their high energy density and long cycle life. However, the improper sealing of these batteries can cause corrosion and degradation of the components, leading to a reduction in the battery’s performance and potentially even causing safety hazards. One of the main culprits of this degradation is the formation of hydrofluoric acid (HF), from reaction between moisture and lithium hexafluorophosphate (LiPF6), a typical lithium salt electrolyte.
When HF comes in contact with lithium-ion battery components, it can react and cause damage through several mechanisms. Here are some examples:
1. Etching of silicon anodes: Si + 4HF → SiF 4 + 2H 2 O
Silicon is a common material used in anodes of lithium-ion batteries due to its high theoretical capacity. However, it is susceptible to etching by HF, which can damage the anode and reduce battery performance. The water generated from this reaction will react with the electrolyte to form additional HF and further accelerates all detrimental reactions.
2. Corrosion of aluminium current collectors: 2Al + 6HF → 2AlF 3 + 3H 2
Aluminium is often used as a current collector in lithium-ion batteries. The corrosion by HF can cause lead to loss of active material and a loss of electrical contact between the electrode material and the current collector, leading to a decrease in the battery’s performance.
3. Formation of lithium fluoride on cathode surfaces: LiCoO 2 + 2HF → LiF + CoF 2 + H 2 O
Lithium fluoride can form on the surface of cathodes, such as lithium cobalt oxide, when exposed to HF. This can increase the resistance of the cathode and reduce the overall performance of the battery.
4. Degradation of polymer electrolytes: (CH2CH2O) n + nHF → (CH2CH2F) n + nH2O
Polymer electrolytes are used in some types of lithium-ion batteries, but they can be degraded by HF, leading to reduced battery performance. If carbonate electrolytes are used, gases such CO 2 may form and cause swelling.
In conclusion, the formation of HF due to the degradation of electrolyte can lead to corrosion and degradation of the components in lithium-ion batteries. Proper sealing of the battery can help to prevent the formation of HF and ensure optimal performance of the battery. As the use of lithium- ion batteries continues to grow, it is important to be aware of these potential issues and take steps to mitigate them.