Formation of a stable interfacial layer for developing high-performance LiNi0.8Mn0.1Co0.1O2–Li4Ti5O12 aqueous batteries based on molecular crowding electrolytes

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Aqueous electrolytes with wide electrochemical stability windows are crucial for developing high-energy and safe lithium-ion batteries, and molecular crowding electrolytes, which use polyethylene glycol as a molecular crowding agent to inhibit water decomposition by forming strong hydrogen bonds, are promising candidates. However, the polymer increases the viscosity of the electrolyte and decreases the ionic conductivity. In addition, the electrode–electrolyte interfacial layer is ineffective to protect the electrodes from water decomposition at a low salt concentration. Here, a molecular crowding electrolyte is prepared by dissolving lithium bis(trifluoromethanesulfonyl)imide in a mixture of a small-molecular crowding agent (tetraethylene glycol) and H2O. Succinonitrile (SN) is introduced to widen the electrochemical stability window of the aqueous electrolyte up to 4.3 V and improve the ionic conductivity. SN also promotes the formation of a stable and uniform electrode/electrolyte interfacial layer on LiNi0.8Mn0.1Co0.1O2 (NMC811), which can then be used as a cathode material. The fabricated NMC811/Li4Ti5O12 full cell delivers a maximum energy density of 148 W h/kg, a Coulombic efficiency of 99.2%, and retains 72% of its initial capacity after 150 cycles at 0.2C with a positive/negative capacity ratio of 1.11. This paper introduces a viable strategy for developing high-energy-density aqueous batteries.