lithium difluorophosphate is a powerful electrolyte additive which improves battery performance. It can build a robust solid electrolyte interphase (SEI) on the electrode and enhance the rate performance of high-voltage cathodes and Li metal anodes at extreme temperatures.
LiDFP is a versatile additive that can be applied in various battery systems, i.e., lithium-ion batteries, nickel-metal hydride batteries and sodium-ion batteries. It is able to suppress dendrite growth, construct SEI layer and improve cycling and rate performance by enhancing Li ion diffusion into and out of the cell.
Several types of LiDFP-based additives have been developed to increase the capacity retention and cyclability of high-voltage lithium-ion batteries. However, the mechanism of how they operate remains unclear.
The most promising electrolyte additives are based on the fluorine substitution reaction between anions and carbonate solvents. Amongst these anions, lithium difluorophosphate (LiPO2F2) is particularly interesting for its ability to mitigate the electrolyte degradation by reducing the oxidation of carbonate solvents on the surface of the cathode material and by enriching the SEI layer.
A series of difluorophosphate salts, including NaFO and MAFO, have been prepared in-house to assess their efficacies as additives for a wider range of battery chemistry. Compared with the widely-used LFO additive, they have been found to exhibit different behaviours on the cell.
To evaluate the effect of difluorophosphate salts on the cell, a long-term cycling test was performed at C/3 rate and 40 degC in order to measure the performance of each additive over a range of cycle times. Despite the differences between additives, there was no significant difference in the cell impedance and charge transfer resistance.