Preparation of Li2S–FePS3 composite positive electrode materials and their electrochemical properties

Abstract For an attempt to incorporate phosphorous ions into the Fe-containing Li 2 S, we have prepared Li 2 S–FePS 3 composite positive electrode materials using the combination process of the thermal heating and the mechanical milling. The XRD results showed that the Li 2 S–FePS 3 composite samples consisted of low-crystalline Li 2 S and small amounts of FeP as impurity. The electrochemical tests demonstrated that the Li 2 S-rich composite sample cells (Li 2 S:FePS 3  = 4:1 mol) showed relatively high initial discharge capacity (ca. 780 mAh·g − 1 ) without any pre-cycling treatments. This makes a clear contrast to the Fe-containing Li 2 S (Li 2 S–FeS x composite) sample cells, which showed the initial discharge capacity of ca. 330 mAh·g − 1 and it was enlarged to ca. 730 mAh·g − 1 after the stepwise pre-cycling treatment. Ex-situ XRD and XAFS measurements showed the reversible changes of the peaks ascribed to Li 2 S and the local structures around S atoms during cycling. The incorporation of phosphorous ions into the Fe-containing Li 2 S was effective for improving the structural reversibility against Li extraction/insertion reactions, resulting in the improved electrochemical performance of the cells.