Nonaqueous Electrolyte Cell SEI Film Composition

The patent applies preliminary action by adding LiBOB as a film forming agent that decomposes first during initial charging to form a stable SEI film on the negative electrode surface. This pre-formed SEI film prevents subsequent continuous decomposition of the electrolytic solution, thereby stabilizing the negative electrode while minimizing capacity loss. The SEI film acts as a protective barrier that is formed in advance before operational degradation occurs.

The patent applies parameter changes by precisely controlling the amount of lithium phosphate added to the electrolytic solution. By optimizing the concentration of lithium phosphate within specific ranges, the patent achieves effective heat suppression during overcharge while minimizing the negative impact on charge/discharge performance. This quantitative optimization balances thermal management requirements with electrochemical performance.

The patent applies the blessing in disguise principle by utilizing the controlled decomposition of LiBOB during initial charging. Although this decomposition is an irreversible reaction that consumes some electrolytic solution and reduces cell capacity, it produces a stable SEI film that prevents much larger amounts of electrolytic solution from decomposing during subsequent charging and discharging cycles. The initial harmful decomposition is converted into a beneficial protective layer that preserves overall cell performance and extends battery life.