Nanoparticle shapes of LiMnPO4, Li+ diffusion orientation and diffusion coefficients for high volumetric energy Li+ ion cathodes

Nanoparticles of LiMnPO₄ were fabricated in rod, elongated as well as cubic shapes. The 1D Li⁺ preferred diffusion direction for each shape was determined via electron diffraction spot patterns. The shape of nano-LiMnPO₄ varied the diffusion coefficient of Li⁺ because the Li⁺ diffusion direction and the path length were different. The particles with the shortest dimension along the b-axis provided the highest diffusion coefficient, resulting in the highest gravimetric capacity of 135, 100 and 60 mAh g⁻¹ at 0.05C, 1C and 10C, respectively. Using ball-milling, a higher loading of nano-LiMnPO₄ in the electrode was achieved, increasing the volumetric capacity to 263 mAh cm⁻³, which is ca. 3.5 times higher than the one obtained by hand-mixing of electrode materials. Thus, the electrochemical performance is governed by both the diffusion coefficient of Li⁺, which is dependent on the shape of LiMnPO₄ nanoparticles and the secondary composite structure