Low Resistance and High Stable Solid–Liquid Electrolyte Interphases Enable High‐Voltage Solid‐State Lithium Metal Batteries

Abstract Solid‐state batteries (SSBs) with addition of liquid electrolytes are considered to possibly replace the current lithium‐ion batteries (LIBs) because they combine the advantages of benign interfacial contact and strong barriers for unwanted redox shuttles. However, solid electrolyte and liquid electrolyte are generally (electro)‐chemically incompatible and the resistance of the newly formed solid–liquid electrolyte interphase (SLEI) appears as an additional contribution to the overall battery resistance. Herein, a boron, fluorine‐donating liquid electrolyte (B, F‐LE) is introduced into the interface between the high‐voltage cathode and ultrathin composite solid electrolyte (CSE), which is fabricated by adhering a high content of nanosized Li 6.4 La 3 Zr 1.4 Ta 0.6 O 12 (LLZTO) with poly(vinylidene fluoride‐ co ‐hexafluoropropylene) (PVDF‐HFP), to generate a low resistance and high stable SLEI in situ, giving a stable high‐voltage output with a reinforced cathode|CSE interface. B, F‐LE, consisting of a highly fluorinated electrolyte with a lithium bis(oxalato)borate additive, exhibits good chemical compatibility with CSE and enables rapid and uniform transportation of Li + , with its electrochemically and chemically stable interface for high‐voltage cathode. Eventually, the B, F‐LE assisted LiNi 0.6 Co 0.2 Mn 0.2 O 2 |Li battery displays the enhanced rate capability and high voltage cycling stability. The findings provide an interfacial engineering strategy to turn SLEI from a “real culprit” into the “savior” that may pave a brand‐new way to manipulate SLEI chemistry in hybrid solid–liquid devices.