Tailoring microstructural features to achieve high C-rate batteries
ABSTRACT :
Lithium ion batteries (LIB) are the power sources for all the portable electronics. In order to use these batteries for electric vehicle applications, high energy density and fast charging/discharging characteristics are essential. However, lower capacity of electrodes and severe capacity loss at higher current rates limits its application. The main reason for the decrease in the capacity at high current rates is the slow diffusion of lithium ions in the electrode materials. Understanding lithium diffusion is therefore very important for enhancing the performance of the battery. The structure, size and morphology play important role in controlling the diffusion coefficient. In oxide cathodes, lithium diffusion can happen in 1D or 2D or 3D pathways. In LiFePO4, where Li diffuses along [010] 1D channels, fast charging/discharging can be achieved by using nanowire morphology [1] or (010) facet nanosheets [2]. Therefore, controlling the size and shape will improve the Li diffusion coefficient. While LiFePO4 is a desirable cathode due to its higher capacity, it exhibit lower operating voltage compared to LiMnPO4. In this presentation, I will discuss how the Li diffusion gets altered in Li(Fe, Mn)PO4 nanowires. We have prepared LiFe1-xMnxPO4 (x = 0, 0.2 and 0.5) nanowires and analyzed the capacity loss at various current rates over large number of charging/discharging cycles to understand the influence of Mn on the lithium diffusion and rate capability of the system. The rapid loss of capacity at high current rates arises from the sluggish lithium ion diffusion in presence of Mn. In another study lithium diffusion characteristics in 2D layered structure (nanosheets of MoS2) is explored. MoS2 is desirable anode material because of its high capacity ~ 670 mA h g-1 (compared to commercial anode, graphite ~ 370 mA h g-1). The syntheses of MoS2 nanosheets and electrochemical investigation in view of understanding the Li diffusion is being pursued.