Vanadium pentoxide interfacial layer enables high performance all-solid-state thin film batteries

Lithium cobalt oxide (LiCoO₂) is considered as one of the promising building blocks that can be used to fabricate all-solid-state thin film batteries (TFBs) because of its easy accessibility, high working voltage, and high energy density. However, the slow interfacial dynamics between LiCoO₂ and LiPON in these TFBs results in undesirable side reactions and severe degradation of cycling and rate performance. Herein, amorphous vanadium pentoxide (V₂O₅) film was employed as the interfacial layer of a cathode-electrolyte solid-solid interface to fabricate all-solid-state TFBs using a magnetron sputtering method. The V₂O₅ thin film layer assisted in the construction of an ion transport network at the cathode/electrolyte interface, thus reducing the electrochemical redox polarization potential. The V₂O₅ interfacial layer also effectively suppressed the side reactions between LiCoO₂ and LiPON. In addition, the interfacial resistance of TFBs was significantly decreased by optimizing the thickness of the interfacial modification layer. Compared to TFBs without the V₂O₅ layer, TFBs based on LiCoO₂/V₂O₅/LiPON/Li with a 5 nm thin V₂O₅ interface modification layer exhibited a much smaller charge transfer impedance (R_ct) value, significantly improved discharge specific capacity, and superior cycling and rate performance. The discharge capacity remained at 75.6% of its initial value after 1000 cycles at a current density of 100 μA cm^-2. This was mainly attributed to the enhanced lithium ion transport kinetics and the suppression of severe side reactions at the cathode-electrolyte interface in TFBs based on LiCoO₂/V₂O₅/LiPON/Li with a 5 nm V₂O₅ thin layer.