Dual‐Functional Lithium Nitrate Mediator Eliminating Water Hazard for Practical Lithium Metal Batteries

Abstract Water, an unwelcome guest in current battery industry, has been strictly prohibited in almost all the battery production procedures. In particular, the requirement for an extremely low water content (below 20 ppm) in electrolyte has necessitated the use of water‐free raw materials and ultradry conditions, which resulting in significantly higher material cost, energy consumption, and production complexity. Here, it is shown that lithium nitrate (LiNO 3 ) can efficiently restore water‐containing electrolyte for Li metal full batteries through a simple and scalable approach. The dual‐functional NO 3 − anion not only exhibits strong interaction with water molecules which suppresses the hydrolysis of hexafluorophosphate anion, but also contributes to a robust solid‐electrolyte interphase (SEI) that improves the electrochemical reversibility of Li metal plating and stripping process. These enable the first practical Li metal/LiNi 0.8 Co 0.1 Mn 0.1 O 2 full cell with a negative/positive electrode capacity (N/P) ratio of 3.8 using a water‐containing electrolyte, which delivers a high energy density of 511 Wh kg −1 and impressive cycling stability of 240 cycles. Remarkably, the introduction of LiNO 3 can tolerate moist raw materials for electrolyte preparation, and revitalize moist electrolytes after 5‐day storage, which provides a new paradigm to overcome the water hazard in the current battery industry.