Improving the performances of low concentration electrolytes via dual interfacial modification of the fluoroethylene carbonate solvent and lithium difluoro(oxalato)borate additive

Abstract

The high price of lithium salts hinders the sustainable development of high concentration electrolytes, while the poor electrochemical performance limits the large-scale application of low concentration electrolytes. Herein, the electrochemical performance of a low concentration electrolyte is improved via dual interfacial modification of the fluoroethylene carbonate (FEC) solvent and the lithium difluoro(oxalato)borate (LiODFB) additive. LiODFB is preferentially oxidized via a ring-opening path to generate a lithium fluoride (LiF)-rich inner layer on the surface of a ferrous lithium phosphate cathode, and then a large amount of C–F polycarbonate oligomers is generated in the outer layer via a reaction between LiODFB and FEC. LiF has a large bandgap and a low lithium ion (Li⁺) diffusion barrier, and the electronegative C–F groups provide the lithiophilic sites to reduce the interaction between Li⁺ and solvents, resulting in a repulsive force towards the CO dipole of the carbonate ester solvent to improve the oxidation stability of the electrolyte. The clever design of the multi-layer cathode electrolyte interphase suppresses the excessive decomposition of the electrolyte, improves the diffusion of Li⁺, and enables much-improved cycling stability of the cathodes. This work gives a fruitful insight into the key role of cathode electrolyte interphase components in Li⁺ diffusion and improves the performance of low-concentration electrolytes.