An additive-enabled ether-based electrolyte to realize stable cycling of high-voltage anode-free lithium metal batteries

Abstract

To achieve stable cycling of high-energy-density and high-voltage anode-free lithium metal batteries, the interfacial stability of both lithium metal anode and high-voltage cathode is demanded. Electrolytes based on ether solvents tend to have excellent compatibility with the lithium metal anode, but due to their low oxidation potential (generally less than 4.0 V vs. Li+/Li), they render high-voltage LiNi0.8Co0.1Mn0.1O2 (NCM811) cathodes unsatisfactory electrochemical performance. Here, an average Coulombic efficiency of 99.4% is realized for lithium metal plating-striping by using an ether-based local high-concentration electrolyte. By further introducing a minute amount of lithium difluoro(oxalate)borate (LiDFOB) additive (0.02 M) into this baseline electrolyte, its oxidation stability is increased to 4.3 V without compromising its high Coulombic efficiency towards reversible lithium plating-striping. Consequently, this additive-supported electrolyte enables the high-loading (3.0 mAh cm−2) Cu||NCM811 anode-free cells to achieve high-capacity retention at both room temperature (∼95% capacity retention after 50 cycles) and -20 ˚C (∼79% capacity retention after 30 cycles). A combination of microscopic and spectroscopic investigations aided by theoretical calculations demonstrate that the LiDFOB additive helps generate a Li3N- and LiF-rich solid electrolyte interphase on the lithium metal anode side, enabling dense and uniform lithium deposition, meanwhile, it also leads to a uniform and compact cathode electrolyte interphase on the high-voltage NCM811 cathode side, mitigating the transition metals dissolution. This work provides a simple and promising strategy for the electrolyte design of high-voltage anode-free batteries.