Nanostructured-microfibrillar polypyrrole coated NiTi current collectors for high power and shape memory LiFePO4 cathodes for Li-ion batteries

Powering the shape-memory alloy-based actuators and wearables needs flexible and compatible energy sources. Lithium iron phosphates are also attractive for their unique properties for safe operation. This study used NiTi thin film as the shape memory current collector coated with one-dimensional (1D) polypyrrole microfibrils for flexible and high-power lithium-ion batteries. The PPy microfibrils facilitated the electron pathway and improved the rate capability of the LiFePO4 cathode significantly. While the pure LiFePO4 showed a 108 mAh/g capacity at 0.1 C, the nanocomposite with microfibril PPy had 136 mAh/g. Discharging at 10 C was associated with a significant loss of capacity for pure cathode (15 mAh/g), whereas 75 mAh/g for nanocomposite with PPy. The rate capability of the LiFePO4 cathode was also improved significantly using PPy microfibrils. For a single-layer pouch battery, the capacity of the flat cell was retained at about 20 mAh. In contrast, the capacity of the nanocomposite decreased to about 18 mAh after curving the cell and recovered to about 19 mAh once relieving at 1 C.