Stabilizing zinc deposition through solvation sheath regulation and preferential adsorption by electrolyte additive of lithium difluoro(oxalato)borate

Aqueous zinc ion batteries have become one of the most promising energy storage technologies due to intrinsic safety, low price, and high capacity. However, zinc metal anode suffers from severe dendrites and harmful side reactions in aqueous electrolytes, resulting in low coulombic efficiency and short life span. Although organic electrolyte additives have proven to be very effective in improving zinc plating/stripping reversibility, they would not only reduce the ionic conductivity of electrolytes but also bring about toxic and flammable issues. Herein, an inorganic lithium salt, i.e., lithium difluoro(oxalate)borate (LiODFB), is utilized and the following benefits can be realized. Firstly, ODFB− ions can be preferentially adsorbed at the surface of Zn metal to restraint "tip-effect", resist corrosion, and mitigate side reactions. Secondly, the water activity can be significantly weakened through intense interaction between ODFB− and H2O. Thirdly, the desolvation process can be promoted. Hence, the LiODFB additive with a very low concentration of 30 mM endows Zn//Zn cell with long lifespan (1000 h at 4 mAh cm−2) and enables Zn//Cu cell to deliver very high coulombic efficiency (average value of 99.74 % during 1500 cycles). Moreover, the rate and cycling performances of Zn//MnO2 and Zn//V2O5 full batteries can be dramatically improved by the LiODFB additive. This work extends our knowledge of interfacial engineering for aqueous batteries.