Surface Modification Driven Initial Coulombic Efficiency and Rate Performance Enhancement of Li1.2 Mn0.54 Ni0.13 Co0.13 O2 Cathode

Due to its high energy density and low cost, Li-rich Mn-based layered oxides are considered potential cathode materials for next generation Li-ion batteries. However, they still suffer from the serious obstacle of low initial Coulombic efficiency, which is detrimental to their practical application. Here, an efficient surface modification method via NH4 H2 PO4 assisted pyrolysis is performed to improve the Coulombic efficiency of Li1.2 Mn0.54 Ni0.13 Co0.13 O2 , where appropriate oxygen vacancies, Li3 PO4 and spinel phase are synchronously generated in the surface layer of LMR microspheres. Under the synergistic effect of the oxygen vacancies and spinel phase, the unavoidable oxygen release in the cycling process was effectively suppressed. Moreover, the induced Li3 PO4 nanolayer could boost the lithium-ion diffusion and mitigate the dissolution of transition metal ions, especially manganese ions, in the material. The optimally modified sample yielded an impressive initial Coulombic efficiency and outstanding rate performance.

Hollow porous carbon spheres for high initial coulombic efficiency and low-potential sodium ion storage

It is critical to develop carbon material anodes with high initial Coulombic efficiency and energy density for sodium ion batteries. Herein, a novel mushroom spore with chitin as carbon precursor is first reported for energy storage, and its special porous spherical structure, fine structure and oxygen functional groups can be accurately controlled by carbonization temperature. The hollow porous carbon spheres obtained from mushroom spore at 1400 °C have appropriate porous structure, d₀₀₂ spacing (0.364 nm), 7.12% oxygen content and ultra-low specific surface area of 5.5 m² g^-1. It could obtain 81.2% initial Coulombic efficiency and has reversible discharge capacity of 411.1 mA h g^-1, wherein about 75% (308 mA h g^-1) of its total capacity is derived from low-potential plateau (below 0.1 V Na⁺/Na), and the capacity is 384.5 mA h g^-1 after 50 cycles. Furthermore, Density functional theory calculation showed that the residual oxygen functional groups (CO) in carbon materials are beneficial to sodium into graphite-like layers, and graphite-like layers spacing is smaller than the reported unadulterated carbon with 0.37 nm. Therefore, the excellent electrochemical performance and low-cost of natural mushroom spore derived hollow porous carbon spheres provide advantages for sodium ion batteries in large-scale storage devices.