Synthesis of Single Crystalline Spinel LiMn₂O₄ Nanowires for a Lithium Ion Battery with High Power Density

How to improve the specific power density of the rechargeable lithium ion battery has recently become one of the most attractive topics of both scientific and industrial interests. The spinel LiMn₂O₄ is the most promising candidate as a cathode material because of its low cost and nontoxicity compared with commercial LiCoO₂. Moreover, nanostructured electrodes have been widely investigated to satisfy such industrial needs. However, the high-temperature sintering process, which is necessary for high-performance cathode materials based on high-quality crystals, leads the large grain size and aggregation of the nanoparticles which gives poor lithium ion battery performance. So there is still a challenge to synthesize a high-quality single-crystal nanostructured electrode. Among all of the nanostructures, a single crystalline nanowire is the most attractive morphology because the nonwoven fabric morphology constructed by the single crystalline nanowire suppresses the aggregation and grain growth at high temperature, and the potential barrier among the nanosize grains can be ignored. However, the reported single crystalline nanowire is almost the metal oxide with an anisotropic crystal structure because the cubic crystal structure such as LiMn₂O₄ cannot easily grow in the one-dimentional direction. Here we synthesized high-quality single crystalline cubic spinel LiMn₂O₄ nanowires based on a novel reaction method using Na_0.44MnO₂ nanowires as a self-template. These single crystalline spinel LiMn₂O₄ nanowires show high thermal stability because the nanowire structure is maintained after heating to 800 °C for 12 h and excellent performance at high rate charge−discharge, such as 20 A/g, with both a relative flat charge−discharge plateau and excellent cycle stability.