Hierarchical waxberry-like LiNi0.5Mn1.5O4 as an advanced cathode material for lithium-ion batteries with a superior rate capability and long-term cyclability

Abstract

A hierarchical porous micro/nano structure composed of agminated single-crystalline nanoparticles is crucial for engineering high performance LiNi_0.5Mn_1.5O₄ cathode materials, because it can not only shorten the transport route for electrons and lithium ions, but also withstand the structural strain during reduplicative Li⁺ ion insertion/extraction processes. In this paper, we report an efficient solvothermal method for fabricating hierarchically porous waxberry-shaped LiNi_0.5Mn_1.5O₄ assembled from interconnected single-crystalline nanoparticles. Experimental results indicate that the solvent ethylene glycol and the precipitant hexamethylenetetramine in the solvothermal process could make the reagents blend uniformly and nucleate slowly, thus leading to a homogeneous distribution and a lower impurity content in the final products, which are beneficial to the rate capability and cycling performance. Besides, the porous structure resulting from the decomposition of the carbonate precursor could favourably attenuate the volume change during the high-rate charge/discharge process. As expected, the resultant waxberry-like LiNi_0.5Mn_1.5O₄ presents an excellent rate capability and ultralong cycling stability. Even at a high discharge rate of 30C, a capacity retention of about 84% after 1200 cycles can still be attained. The superior performance can be ascribed to the intrinsic hierarchical porous micro/nano structure, which could not only facilitate the diffusion of lithium ions but also furnish pore spaces to relieve the volume deformation during repeated Li⁺ insertion/extraction processes.