Synthesis of Honeycomb-Shaped LiNi0.5Mn0.5O2 Using a Sol-Gel Method with Polymethylmethacrylate (PMMA) and Organic Surfactant

Abstract

Layered-structural LiNi0.5Mn0.5O2 has high discharge capacity, abundant availability, enhanced chemical stability, convenient environmental benignancy, and low cost. However, LiNi0.5Mn0.5O2 suffers from poor intrinsic rate capability due to its poor ionic conductivity (2.54 × 10-7 S/cm) and poor cycle stability owing to the volume change of the cathode materials during cycling. To address this issue, honeycomb-shaped LiNi0.5Mn0.5O2 was developed for lithium-ion batteries using a sol-gel method with spherical polymethylmethacrylate (PMMA) particles. PMMA particles provide spherical voids in LiNi0.5Mn0.5O2 cathode materials due to their relatively low decomposition temperature (< 350 °C). Honeycomb-shaped LiNi0.5Mn0.5O2 has a higher surface area (2.63 m2/g) than the LiNi0.5Mn0.5O2 (2.00 m2/g) produced by conventional sol-gel method. The initial discharge capacities of conventional nano LiNi0.5Mn0.5O2 and honeycomb-shaped LiNi0.5Mn0.5O2 are 151.9 mAh g-1 and 200.4 mAh g-1, respectively at 0.1 C. After 50 cycles at 1 C, honeycomb-shaped LiNi0.5Mn0.5O2 has a larger capacity retention than conventional nano LiNi0.5Mn0.5O2, measuring 67.9% and 58.8%, respectively. The superior electrochemical performance of honeycomb-shaped LiNi0.5Mn0.5O2 increases the effective surface area for Li-ion diffusion, leading to better rate capability, and buffers the volume change during Li+ion insertion/extraction, improving the cycling stability.