1,3,5-Trifluorobenzene and fluorobenzene co-assisted electrolyte with thermodynamic and interfacial stabilities for high-voltage lithium metal battery

High-voltage lithium metal battery (LMB) with LiCoO2 (>4.5 V) as the cathode shows great prospect in achieving high energy density, yet its performance is far below expectation. Diluted high-concentration electrolytes (DHCE) are proven effective to improve the performance, however the inherently thermodynamic instability of highly fluorinated diluents and the constitutionally interfacial instability of monofluorinated diluents hinders the stable operation under high voltage. Herein, a unique additive, 1,3,5-trifluorobenzene (3FB) is rationally incorporated with fluorobenzene (FB)-based DHCE to boost thermodynamic and interfacial stabilities of the electrolyte compared with hydrofluoroethers-based DHCE and FB-DHCE, respectively. Particularly, the FB possesses high energy barrier to defluorination, leading to superior thermodynamic stability of developed DHCE. Furthermore, 3FB can be preferentially reduced into a LiF-rich solid electrolyte interphase (SEI) and partial low-fluorated aromatic hydrocarbons, while these 3FB derivatives are likely to be oxidized on cathode, forming robust cathode electrolyte interphase (CEI) and significantly mitigating side reactions under high-voltage conditions. As a result, the Li-Cu cell using optimized electrolyte is endowed with ultrahigh Coulombic efficiency (CE: 99.2%) and long-term cycle life (>300 cycles) even at 3 mA cm−2. A 4.5V Li-LCO cell exhibits outstanding cycling stability (600 cycles, 80 % capacity retention) and the Li-LCO pouch cell deliver high specific energy of more than 370 Wh kg−1 under the practical condition. This work provide direction for further development of advanced electrolytes for high-voltage LMBs.