Rational design of electrolyte solvation structure for stable cycling and fast charging lithium metal batteries

Developing dimethyl ether (DME)-based localized high-concentration electrolytes (LHCEs) is regarded as a promising approach to the application of lithium metal batteries (LMBs). However, LHCEs with DME: Li+ ratio ∼1.5: 1 still present many challenges including oxidation decomposition at high voltage and poor charging capability owing to low conductivity. Herein, we design an electrolyte consisting of lithium bis(fluorosulfonyl)imide (LiFSI, 1.1 M) in DME-hydrofluoroether (TTE) (DME: Li+ = 4: 1) with potassium trifluoro(trifluoromethyl)borate (PTB) as additive. PTB is found to strengthen the interaction between Li+ and DME/FSI− anions, which stabilizes the DME solvent against reduction/oxidation and facilitates the reduction reactivity of FSI− anions for stabilizing the interface of Li metal anode. Besides, the CF3BF3− anions of PTB involve in stabilizing LiNi0.9Mn0.05Co0.05O2 (NMC90) cathode by forming a LiF-rich interfacial layer. Notably, the Li||NMC90 (8 mAh cm−2 Li, ∼4.0 mAh cm−2 NMC90, ∼6 g electrolyte per Ah) battery can demonstrate a much-enhanced capacity retention of 84.1% after 170 cycles at charging current density of 4.0 mA cm−2 with a charge cut-off voltage of 4.5 V. This work offers a fundamental guidance in rational design solvation structures of electrolyte to improve the stability of electrode/electrolyte interface and kinetics for LMBs.