Engineering A Boron-Rich Interphase with Nonflammable Electrolyte toward Stable Li||NCM811 Cells Under Elevated Temperature

Despite the high energy of LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode, it still suffers serious decay due to the continuous solvents decomposition and unstable cathode electrolyte interphase (CEI) layers, especially under high temperatures. The intense exothermic reaction between delithiated NCM811 and flammable electrolyte, on the other hand, pushes the batteries to their safety limit. Herein, these two issues are tackled via engineering the electrolytes, that is, utilizing salts with higher HOMO levels and nonflammable solvents with lower HOMO levels, to reduce the massive decomposition of solvents and improve battery safety under elevated temperatures. Consequently, a thin and boron-rich CEI is generated, which effectively inhibited the side reactions, thus improving the cycling stability and safety. Deviated from the highly concentrated electrolytes which heavily relies on the usage of massive salts, the electrolyte recipe can introduce a robust inorganic-rich CEI but use much less salt (i.e., dilute electrolyte), and thus, offer an encouraging alternative toward practical applications. As such, the NCM811 cathode exhibits a high-capacity retention of 81.2% after 950 cycles at 25 degrees C and 75% after 300 cycles at 55 degrees C. This work provides a universal electrolyte design strategy for designing stable and safe high-temperature electrolytes for the NCM811 cathode. The generation of boron-rich CEI is proposed by selecting salts and solvents with reasonable HOMO levels, which can stabilize the NCM811 at both RT and high temperature by suppressing the degradation of particles and decreasing the consumption of electrolytes. Besides, it improves the flame-retardancy to decrease the safety risk of NCM811||Li battery.image