High Volumetric Energy Density of LiFePO 4 /KB Cathode Materials Based on Ketjen Black Additive

High tap density and superior electronic conductivity of LiFePO 4 /KB was synthesized by a combination of wet ball‐milling, spray drying, and carbothermal reduction with Ketjen black (KB) as a carbon additive. KB is a conductive carbon black with the special chain‐like structure. When KB is used to coat on the surface of primary particles of LiFePO 4 , the chain‐like structure can form a developed 3D network structure between the primary particles of LiFePO 4 . This special structure can not only provide conductive channels for electrons but also cause the primary particles of LiFePO 4 to aggregate tightly. Comparing to the conventional carbon coating materials (only glucose as the carbon source) with a low volumetric energy density of 452.5 Wh L −1 at 1 C rate, we simultaneously increased the electrical conductivity (7.8×10 −2  S cm −1 ) and tap density (1.6 g cm −3 ) by adding KB, resulting in a higher volumetric energy density of 829.9 Wh L −1 at 1 C rate. When KB is added at 5 % of glucose mass, the LiFePO 4 /KB composite shows an excellent discharge capacity of 161.6 mAh g −1 at 0.2 C and the 97.7 % retention rate after 500 cycles at 5 C.