Improved high-voltage and high-temperature electrochemical performances of LiCoO2 cathode by electrode sputter-coating with Li3PO4

• Electron-insulating/ion-conducting Li3PO4 (LPO) is used to coat LiCoO2 electrodes.
• Amorphous LPO layer is coated by a facial magnetron sputtering approach.
• High-voltage (4.5 V) and high-temperature (50 °C) cell performances are studied.
• LPO-coated LiCoO2 electrodes exhibit improved cycling and rate performances.
• High-temperature performance improvements are more dominant after LPO coating.

Surface coating has long been an important strategy to improve the electrochemical performances of electrode materials for Li-ion batteries. In this work, an amorphous Li3PO4 (LPO) layer, which is a poor electronic conductor but good ionic conductor, is coated directly on LiCoO2 composite electrodes by magnetron sputtering. The battery performances of the electrodes are studied at both room temperature (RT) and 50 °C. The LPO sputter-coating allows significant improvement of the electrode's cycling stability at both temperatures. With an optimum coating thickness of ∼60 nm, the electrode's capacity after 100 cycles at 1 C can reach 146 mAh g−1 (79.3% retention) and 140 mAh g−1 (78.2% retention) at RT and 50 °C, which are improved by 30% and 200%, respectively, compared to those of the bare LCO electrode. More impressively, the rate capability is also greatly enhanced by LPO-coating, and the observed high-temperature rate capability is even superior to the room-temperature one. The remarkable improvement of the LPO-coated electrodes is mainly attributed to the high chemical stability and temperature-enhanced electrochemical activity of the LPO coating layer, which synergistically serves as a physiochemical protection layer and an efficient pathway for Li+ transport.