Dilute dual-salt electrolyte for successful passivation of in-situ deposited Li anode and permit effective cycling of high voltage anode free batteries

Abstract

An investigation of the cycling stability of anode-free batteries (AFBs) using dilute dual-salt electrolytes is conducted in a mixture of ether and carbonate solvents. Using the AFB configuration, various compositions of the dual-salt electrolyte were optimized and it was found that 0.9M-LiTFSI+0.3M-LiDFOB in FEC/TTE (2:3, v/v) is the best. An in-depth investigation of the electrochemical performance of AFB was conducted in this optimized dual-salt composition in comparison to 1.2 M LiTFSI in the same solvent ratio. Accordingly, the performance of Cu||NMC cell in the dual-salt electrolyte surpassed that of the single-salt. The relative better performance of the AFB in the dual-salt electrolyte is attributed to the co-existence of dual-ion (TFSI−&DFOB−) in the electrolyte, which enhanced conductivity and introduces entirely new interphases via preferential decomposition mechanisms. The newly formed interface is stable, ionically conductive, and able to intercept parasitic side reactions between the electrolyte solvent and the deposited Li by blocking electron and solvent flow towards the deposit. As a result of the unique interfacial chemistry brought by this dual-salt system, this electrolyte supports a unique CE (98.6%) and capacity retention (63%) in 4.5V Cu||NMC cell and exhibited >27% improvement over the single salt electrolyte after 50 cycles.