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 (Rct) 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.
Because of their high reversible capacity and wide operation voltage window, P2-type layered transition metal oxides are considered as one type of potential cathode candidate for sodium-ion batteries. However, they still suffer from low kinetics, phase degeneration, and ambiguous mechanism of Na+ diffusion. Here, we synthesized a P2-type Na0.6Li0.07Mn0.66Co0.17Ni0.17O2 with a high Na+ diffusion performance by sintering a nanoplate-structural precursor with alkali metal salt and proposed a possible mechanism for improving Na+ diffusion. The as-prepared P2-type layered oxide presents a quasi-hexagon shape and demonstrates a discharge capacity of 87 mAh g-1 at a current density of 875 mA g-1 (5 C rate), twice that of the sample synthesized from a non-nanoplate particle precursor. Rietveld refinement and results of X-ray photoelectron spectroscopy reveal the probable mechanism that the expanded interplanar spacing along the c-axis orientation would facilitate Na+ diffusion during Na+ intercalation/deintercalation processes, and the expanded interplanar spacing may arise from a high oxidation state of transition metal ions.
