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.

_{含 LiCoO 2}的高压锂金属电池 (LMB)（>4.5 V）作为正极在实现高能量密度方面显示出巨大的前景，但其性能远低于预期。稀释的高浓度电解质 (DHCE) 已被证明可有效提高性能，但高度氟化稀释剂固有的热力学不稳定性和单氟化稀释剂的结构界面不稳定性阻碍了在高压下的稳定运行。在此，与基于氢氟醚的 DHCE 和 FB-DHCE 相比，将独特的添加剂 1,3,5-三氟苯 (3FB) 与基于氟苯 (FB) 的 DHCE 合理结合，以提高电解质的热力学和界面稳定性。特别是，FB 对脱氟具有高能垒，导致开发的 DHCE 具有优异的热力学稳定性。此外，3FB 可以优先还原为富含 LiF 的固体电解质界面 (SEI) 和部分低氟芳烃，而这些 3FB 衍生物很可能在正极上被氧化，形成坚固的正极电解质界面 (CEI) 并显着减轻在高压条件。因此，使用优化电解质的 Li-Cu 电池即使在 3 mA cm 下也具有超高的库仑效率（CE：99.2%）和长期循环寿命（>300 次循环）^-2。4.5V Li-LCO 电池表现出出色的循环稳定性（600 次循环，80% 容量保持率），Li-LCO 软包电池在实际条件下可提供超过 370 Wh kg ^{-1的高比能量。}这项工作为进一步开发用于高压LMB的先进电解质提供了方向。