The electrolyte is one of the key components of LiFePO4 batteries, which has a significant impact on the performance, safety and longevity of the battery.
The electrolyte has the functions of ion conduction, chemical stability and interface protection: during the charging and discharging process, the Li⁺ in the electrolyte migrates between the positive electrode (LiFePO₄) and the negative electrode to complete the charge transfer. The operating voltage range of the battery (about 2.5-3.8V in LiFePO₄) is stable to avoid decomposition, and a stable SEI film and CEI film (positive electrolyte interface) are formed, reducing side reactions.
LiFePO₄ batteries typically use an organic liquid electrolyte, which is mainly composed of the following three parts:
1. Lithium salt: It is a carrier that provides lithium ions (Li⁺). Commonly used lithium salts are: lithium hexafluorophosphate (LiPF₆), lithium tetrafluoroborate (LiBF₄), lithium perchlorate (LiClO₄), etc. Due to its good balance between conductivity, stability and cost, LiPF₆ is the most commonly used.
2. Organic solvent: its role is to dissolve lithium salts and act as a medium for ion transport. Commonly used solvents: carbonate mixed solvents,
Include:
Cyclic carbonates: ethylene carbonate (EC), propylene carbonate (PC) (high dielectric constant, aids in lithium salt dissociation). Chain carbonates: dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC) (low viscosity, improved flowability).
Mixing ratio: typically EC DMC or EC EMC to balance the permittivity and viscosity.
3. Additives (small amounts): improve specific properties.
Film-forming additives, such as vinylene carbonate (VC), fluorocarbonate (FEC), form a stable SEI film (solid electrolyte interface) on the surface of the anode.
Anti-overcharge additives: such as biphenyl (BP), which prevents the electrolyte from decomposing when the battery is overcharged.
Flame retardant additives, such as phosphate esters, for added safety.
The electrolyte of LiFePO₄ battery is an organic liquid system with LiPF₆ as lithium salt and carbonate mixture as solvent, supplemented by functional additives. It needs to be designed with ionic conductivity, chemical stability, and interfacial compatibility in mind. In the future, solid electrolytes and high-safety formulations will be the main development directions.
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