High nickel layered oxide LiNi0.8Mn0.1Co0.1O2 (NMC811) was coated with a nanometer layer coating of a lithium ion conducting solid electrolyte, lithium phosphorus oxynitride (LiPON) by using RF-magnetron sputtering. The cells with LiPON coated NMC811 exhibit much improved cycling performance compared to the cells with pristine NMC811 with 64.1% and 42.6% capacity retention respectively over 100 cycles in an all solid-state battery. The LiPON layer provides interfacial stability at high voltages, suppresses the growth of impedance with cycling and improves the rate capability. Thicker coatings show a negative impact on the performance owing to the increase in electronic resistance with increasing thickness of the LiPON layer. The dQ/dV analysis, electrochemical impedance spectroscopy (EIS), and the overpotential study during galvanostatic cycling were conducted to elucidate the improvement of the cycling stability and enhancement of Li+ transport through LiPON layers surrounding NMC811.

Ni rich LiNi0.8Mn0.1Co0.1O2 (NMC811) is one of the most promising cathode materials for high energy all solid-state batteries. However, its poor ionic and electronic conductivity along with high interfacial instability with thiophosphate-based solid electrolytes result in severe capacity loss with cycling. In this paper, a polyacrylonitrile (PAN) coating is applied on the surface of NMC811 followed by a simple heat treatment in air. The PAN coating layer not only helps to improve the electronic conductivity of the cathode composite but also prevents the direct contact of NMC811 active material with the solid electrolyte, reducing the decomposition of the electrolyte and formation of passivating layers with low ionic conductivity. Compared to pristine NMC811, the electrochemical properties of PAN-NMC composites are significantly improved. When cycled at 0.1C rate, the PAN-NMC composite shows an initial capacity of 192.16 mAh g-1 and capacity retention of 68.5% over 100 cycles compared to the lower capacity of 173.06 mAh g-1 and retention 58.68% for the pristine NMC811. These results indicate that the PAN coating greatly improves the conductivity and cycling performance of NMC811.