Ionic liquid additive stabilized cathode/electrolyte interface in LiCoO2 based solid-state lithium metal batteries

Abstract Poly(ethylene oxide) (PEO)-based solid state batteries is one of the most attractive candidates for next-generation high performance energy storage devices, especially when it matches the LiCoO2 cathode of high volumetric energy density. However, cathode/electrolyte interface reactions will be triggered at high voltage, leading to high interfacial resistance and fast capacity decay. In this work, a selected ionic liquid, 1-methyl-1-propylpiperidinium tetrafluoroborate (PP13BF4), is prepared and applied in LiCoO2 electrode operating at high work voltages of 3.0–4.3 V to regulate the interface. Electrochemical impedance spectroscopy and holding test indicate that facilitated by the PP13BF4, the cathode/electrolyte interfacial reaction is effectively suppressed and the resistance is reduced. When an optimal content, 2  wt%, PP13BF4 is added into the LiCoO2 electrode, the solid-state lithium metal cell delivers an initial discharge capacity of 125.1 mAh g−1 under the current density of 0.05 C at 55 °C, which is almost twice that of bare electrode. Meantime, it retains 76.3% of its capacity in 100 cycles under 0.2 C rate. Further characterizations illustrate that PP13BF4 participates in the formation of a protective CEI, which effectively suppresses parasitic reactions between electrolyte and electrode. This work provides a facile and practical idea for the development of 4 V class solid state lithium metal batteries.