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

Lithium cobalt oxide (LiCoO) 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 LiCoO and LiPON in these TFBs results in undesirable side reactions and severe degradation of cycling and rate performance. Herein, amorphous vanadium pentoxide (VO) 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 VO 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 VO interfacial layer also effectively suppressed the side reactions between LiCoO 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 VO layer, TFBs based on LiCoO/VO/LiPON/Li with a 5 nm thin VO interface modification layer exhibited a much smaller charge transfer impedance () 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. 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 LiCoO/VO/LiPON/Li with a 5 nm VO thin layer.