No abstract

Approaches for regulating electrochemical stability of liquid electrolytes in contact with solid-state electrodes are a requirement for efficient and reversible electrical energy storage in batteries. Such methods are particularly needed in electrochemical cells in which the working potentials of the electrodes lie outside the thermodynamic stability limits of the liquid electrolyte. Here we study electrochemical stability of liquids at electrolyte/ electrode interfaces protected by nanometer thick, high electrical bandgap ceramic phases. We report that welldesigned ceramic interphases extend the oxidative stability limits for both protic and aprotic liquid electrolytes, in some cases by as much as 1.5 V. It is shown further that such interphases facilitate stable electrodeposition of reactive metals such as lithium at high Coulombic efficiency and in electrochemical cells subject to extended galvanostatic cycling at a current density of 3 mA cm −2 and at capacities as high as 3 mAh cm −2 . High-resolution cryo-FIB-SEM characterization reveals that solid/compact Li electrodeposits anchored by the ceramic interphase are the source of the enhanced Li deposition stability. The results enable a proof-of-concept "anode-free" Li metal rechargeable battery in which Li initially provided in the cathode is the only source of lithium in the cell.

New electrolyte designs are necessary for overcoming multiple challenges posed by emerging lithiummetal battery chemistries. Task-specific viscoelastic electrolytes are specifically required that are capable of simultaneously sustaining reversible electrochemistry at the Li metal anode, maintaining high oxidative stability at the battery cathode and achieving high room-temperature ionic conductivity in the electrolyte bulk. Here, we synthesize and study a series of polymeric electrolytes composed of poly-1,3dioxolane (poly-DOL) networks formed by ring-opening polymerization of 1,3-dioxolane/ethylene carbonate (EC) mixtures by a commonly used LiPF 6 electrolyte salt. The complex kinetics of the DOL polymerization reaction in EC results in nonlinear phase behavior, including the appearance of a critical transition to an entangled, solid-like electrolyte state at 40% DOL. The transition is mediated by a range of physicochemical regimesfrom liquid-like solutions to highly viscous conducting gels. We show that poly-DOL/EC electrolytes with a high concentration of the DOL precursor exhibit improved electrochemical stability compared to conventional DOL-based electrolytes, while maintaining good room temperature ionic conductivity. We show further that the EC component imparts oxidative stability, enabling their use in rechargeable, roomtemperature Li||LiNi 0.6 Co 0.2 Mn 0.2 O 2 electrochemical cells.