A homogeneous intergrown material of LiMn2O4 and LiNi0.5Mn1.5O4 as a cathode material for lithium-ion batteries

Abstract

Micro-/nano-structured spherical intergrown LiMn₂O₄–LiNi_0.5Mn_1.5O₄ (LMO–LNMO I, LiNi_0.25Mn_1.75O₄) particles as a cathode material have been synthesized by an impregnation method with highly reactive chestnut-like MnO₂ nano-spheres as a manganese source and structural template. The LMO–LNMO I consisted of aggregates of nano-sized particles with a well-defined cubic spinel structure. The electrochemical performance and thermostability of LMO–LNMO I are better than those of a simple mechanical mixture of LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ (LMO–LNMO M), and much better than those of individual LiMn₂O₄ and LiNi_0.5Mn_1.5O₄ monomers. Within this special structure, LNMO acts as a skeleton to stabilize the structure of LMO and enables more lithium ions in LMO to participate in the charge–discharge process along with those in LNMO, leading to high specific discharge capacities. In addition, this material exhibits excellent cycle stabilities at room temperature (25 °C) as well as at elevated temperature. It presented a discharge capacity of 130 mA h g⁻¹, with 96.2% capacity retention after 100 cycles at 25 °C at 1 C. When the temperature and rate are increased to 55 °C and 5 C, it still delivers a discharge capacity of 131 mA h g⁻¹, with a capacity retention of 95% after 100 cycles. Being synthesized by a special impregnation method, LMO–LNMO I shows a more homogeneous ion mixing of Ni and Mn in the structure at the atomic level with a more enhanced thermostability due to its high Mn content compared to LNMO. The structural stability and high electrical conductivity of LMO–LNMO I are responsible for the excellent electrochemical performance and outstanding thermal stability.