Commercial LIBs use graphite, which has a moderate theoretical capacity of 372 mAh/g and can promote the growth of lithium dendrites leading to a short circuit [1]. Thus, the search for anode materials alternative to graphite is an actual task. Among the potential promising anode materials, a number of transition metal oxides are considered [2, 3], which have a high theoretical capacity. In particular, a promising anode material for lithium-ion batteries is mixed cobalt oxide Co3O4 with a high theoretical capacity (890 mAh/g), which is 2.39 times higher than the theoretical capacity of graphite. Additional interest is caused by the possibility of using Co3O4 in sodium-ion batteries due to the linear dimensions of Co3O4 particles into which Na+ can intercalate. However, the practical use of anodes based on Co3O4 is difficult due to a significant drop in capacitance during long-term cycling of the electrodes and low performance at high currents. There are various ways to solve these problems, including varying the morphology of the material [3] and selecting a binder [4].
In this work, electrode materials based on Co3O4 with different morphologies were studied, obtained by three different synthesis methods (hydrothermal, precipitation and decomposition) using various binder compositions (PVDF, PEDOT:PSS/CMC 1:1, PAA/CMC 1:1). The best results were shown by cobalt oxide obtained by the hydrothermal method at a temperature of 260°C using NH3•H2O as hydroxide ions in combination with a PVDF binder. Co3O4 particles formed under these conditions are obtained in the form nanoprisms with an average size of 72 nm are distinguished by high crystallinity and low specific surface area relative to particles obtained under other conditions. Electrodes based on them in the first cycles give capacity of 1060 mAh/g at current of 0.2 C in potential range 0.01 – 2 V, and the capacity decreases to 910 mAh/g at current of 2 C. For 100 charge-discharge cycles at current of 0.5 C, 43% of the capacity is retained. With an aqueous binder for this sample, relatively low capacities and a noticeable deterioration in stability are observed. The precipitation method makes it possible to obtain large highly porous particles with a diameter of 20 µm, which give high and even growing capacities of the order of 1000 mAh/g at any currents, including 2 C, with an aqueous PEDOT:PSS/CMC binder. However, in this case, no improvement in stability was achieved. At a current of 0.5 C, already in the first 50 cycles, the capacity drops by 78%.