HIGH-SAFETY ELECTROLYTES DESIGN FOR HIGH ENERGY DENSITY BATTERY DEVICES

Recently, the market share of lithium-ion batteries (LIBs) increase rapidly in the global energy market, while accidents related to fires and explosions of LIBs reported worldwide in the past several years, thus battery safety is a vital prerequisite for battery application in our daily life. The flammable organic solvent in the electrolyte of the battery is the main source that leads to fires and explosions of batteries. Designing intrinsically safe electrolytes is the key to enhancing the safety properties of batteries. Fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes are attractive due to their inherent non- or less-combustibles. However, the energy density, cycle stability, and battery cycle life of the LIBs using the above electrolyte systems are far from commercial batteries due to poor solid electrolyte interphase (SEI) and cathode electrolyte interphase (CEI). In this dissertation, we designed SEI/CEI on anode/cathode surfaces in fluorinated organic electrolytes, polymer electrolytes, and aqueous electrolytes to enhance battery performance. Specifically, 1. By building a highly stable CEI on a high-voltage LiCoO2 cathode, we improved the energy density of fluorinated organic electrolyte batteries. 2. By introducing UV-curable polymer into the organic electrolytes, we lowered the flammability of the sodium batteries and enhanced the energy density of the sodium battery system with stable CEI on sodium cathode. 3. By limiting the water activity in the bulk electrolyte and constructing an effective SEI layer on anode surface, we expanded the electrochemical stability window of the aqueous electrolytes. We seek to understand the working mechanism of SEI/CEI in different high-safety electrolyte systems. The corresponding electrochemistry, thermodynamics, kinetics, and reaction reversibility are studied in this work