Shape controlled and structurally stabilized Co-doped olivine lithium phosphate cathodes for high voltage conventional, thin and flexible Li-ion batteries

A novel approach of Co-doping at the 4c site of Ni enhances the electrical conductivity of LiNi0.5Co0.5PO4 (LNCP). A facile and sustainable protocol for the synthesis of three different shaped nanoparticles of LNCP/C by supercritical fluid hydrothermal method. High-resolution transmission electron microscopy analysis reveals that the Co doping improves Li-ion diffusion, elimination of anti-site defects, well crystalline nature and average particle size of LNCP/C nanospheres (SP2) is 18 nm. Thicknesses of LNCP/C nanosheet (SH2) and nanoplates (PL2) are 39 and 37 nm, respectively. First-principle calculations proved that the single electron of Co-3dyz orbital provides the energy states across the Fermi level and enhance the electrical conductivity. Conventional Li-ion batteries deliver the discharge capacities in the range of 145–159 mA h g−1, their gravimetrical energy, and power densities within the range of 645–697 W h Kg−1 and 2277–2601 W Kg−1, respectively. Thin flexible batteries exhibit the discharge capacities in the range of 130–134 mA h g−1, the volumetric energy, and power densities are in the range of 0.46–0.49 W h cm−3 and 3.3–3.4 W cm−3, respectively. The microfiber flexible batteries show the discharge capacities within the range of 131–133 mA h g−1.