Heat-Treatment-Assisted Molten-Salt Strategy to Enhance Electrochemical Performances of Li-Rich Assembled Microspheres by Tailoring Their Surface Features.

Constructing Li-rich Mn-based layered oxide (LMRO) assembled microspheres with fast kinetics and a stable surface will significantly improve discharge capacity and cyclic stability. In this work, a heat-treatment-assisted (HA) molten-salt (MS) strategy has been designed to prepare LMRO assembled microspheres HA-MS-LMRO (LMRO with heat-treatment-assisted molten-salt process). Electrochemical measurements demonstrate that HA-MS-LMRO possesses superior performance as a cathode for lithium-ion batteries. It delivers an initial discharge capacity of 181 mA h g-1 at 200 mA g-1 , which is much higher than that of the LMRO (145 mA h g-1 ). After 100 cycles, the capacity retention ratio for HA-MS-LMRO is 74.69 %, which is far larger than that of LMRO (23.06 %). Detailed analysis of the structure, valence state, and electrochemical impedance spectra shows that the heat-treatment-assisted molten-salt process plays an important role in the excellent performance of HA-MS-LMRO. The HA process enables the transition-metal ions in the synthesized samples to have stable surface valence states, which is conducive to maintaining structural stability and improving cycling performance. The following MS process facilitates the movement of lithium salt into the interior of the assembled microsphere precursors to prohibit the formation of lithium-containing amorphous compounds on the surface during the lithiation process, thus enhancing the Li-ion kinetics and increasing the initial discharge capacity. The current work provides guidance to promote the electrochemical performances of assembled microsphere cathode materials.