An ultrathin LiF film coated on NCM electrode surface via magnetron sputtering for optimized structure stability and cycling performance

Abstract

Nickel-riched layered oxide cathode is one of the most promising cathode materials for high energy density lithium-ion batteries, but the capacity decay and poor cycling stability due to the occurrence of side reactions at the electrode-electrolyte interface are huge obstacles preventing its performance. Surface coating is an effective method to solve this problem. In this paper, nanoscale LiF films were deposited on the surface of Ni0.83Co0.11Mn0.06O2 (NCM811) by magnetron sputtering, which effectively improved the electrochemical performance of NCM811 in half-cells. Scanning electron microscopy (SEM), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) showed that LiF was uniformly deposited onto the electrode surface and was not embedded in the cathode particles. After 100 cycles at 0.5C, the discharge specific capacity of the coated modified NCM was 181.82 mAh/g with a retention rate of 93.95%, which was much higher than that of the original NCM811 at 160.84 mAh/g with a capacity retention rate of 83.11%, while the capacity remained basically unchanged. In addition, the modified rate capability was also significantly improved, with the discharge specific capacity of the modified sample at 5C being 167.26 mAh/g, which was 12.45% higher than that of the uncoated sample at 148.73 mAh/g. The deposited LiF film can protect the electrode interface, inhibit the decomposition of electrolyte and thus protect the positive electrode, and stabilize the structure of the particles.