Lithium-ion Battery Electrolyte Additives for Silicon Anode Stability

The patent changes the chemical composition parameters of the electrolyte by introducing a specific multi-component additive system (cyclic fluoro carbonate, cyclic phosphazene, cyclic sulfate, and lithium fluoro oxalate borate) with controlled ratios. This compositional parameter change enables the formation of a stable SEI film that maintains low interface impedance while providing long-term cycle stability, resolving the contradiction between cycle life extension and impedance control.

The patent employs a composite additive system combining four different types of additives (cyclic fluoro carbonate, cyclic phosphazene, cyclic sulfate, and lithium fluoro oxalate borate) that work synergistically. Each component contributes specific functions: cyclic fluoro carbonate provides fluorinated SEI formation, cyclic phosphazene enhances stability, cyclic sulfate improves interface protection, and lithium fluoro oxalate borate optimizes ion transport. This composite approach achieves both extended cycle life and maintained rate capability.

The patent applies preliminary action by having the cyclic fluoro carbonate and other additives form a pre-stabilized SEI film on the silicon anode surface before normal battery operation begins. This preliminary SEI film formation creates a protective barrier that accommodates silicon's volume expansion during cycling, preventing subsequent SEI breakdown and continuous solvent consumption, thus enabling high energy density with maintained stability.

The patent changes the chemical composition of the electrolyte by incorporating fluorinated cyclic carbonate and lithium fluoro oxalate borate, which promote the formation of a fluorinated SEI film with different physical-chemical properties compared to conventional SEI. This parameter change in electrolyte composition leads to an SEI film with enhanced mechanical strength and flexibility, capable of withstanding silicon's volume expansion while maintaining stability.

The patent converts the potential harm of additive decomposition into a benefit by designing a fluoride-containing additive system that preferentially forms a fluorinated SEI film. This fluorinated film is highly stable and resistant to acid gas generation during redox processes. The fluorinated SEI acts as a protective barrier that prevents acid gas formation and protects the passivation films, thus extending cycle life while eliminating safety threats.

The patent changes the chemical composition parameters by introducing fluorinated compounds (cyclic fluoro carbonate and lithium fluoro oxalate borate) into the electrolyte system. This parameter change fundamentally alters the decomposition behavior of the additives, shifting from acid gas-generating reactions to stable fluorinated SEI formation. The resulting fluorinated SEI film exhibits superior chemical stability and suppresses harmful acid gas generation during battery cycling.