The enhancement of rate and cycle performance of LiMn 2O 4 at elevated temperatures by the synergistic roles of porous structure and dual-cation doping

摘要

Spinel LiMn~(2)O~(4)-based cathode material has been successfully commercialized for power lithium ion batteries for large-scale applications in pure electric vehicles. However, pure LiMn~(2)O~(4)suffers from poor rate performance and fast capacity fading especially at elevated temperatures derived from Mn dissolution and structural distortion. Herein, a study on the rate and cycle performance of single/double-cation doped porous LiMn~(2)O~(4)microspheres, which was prepared by an easy method using porous MnCO~(3)microspheres as a self-supporting template, was performed. The as-synthesized porous Li~(1.02)Co~(0.05)Mn~(1.90)Li~(0.05)O~(4)(LMO-S4) microspheres constructed with nanometer-sized primary particles show an obvious enhancement of cyclability over other LiMn~(2)O~(4)-based materials such as Li~(1.02)Mn~(2)O~(4)(LMO-S1), Li~(1.02)Mn~(1.95)Li~(0.05)O~(4)(LMO-S2) and Li~(1.02)Co~(0.05)Mn~(1.95)O~(4)(LMO-S3), especially at an elevated temperature (55?°C). The obtained LMO-S4/lithium half cells deliver capacities of 113.1 and 109.0 mAh?g_(?1)at 1.0 and 5?C, respectively, with the corresponding capacity retentions of 88.9 and 90.2% for up to 1000 cycles. Meanwhile, it can deliver an initial capacity of 114.0 mAh?g_(?1)at 5?C with a capacity retention of 80.1% after 1000 cycles at 55?°C. Furthermore, it displays superior rate performance and cycle performance at 0?°C with a specific capacity of 106 mAh?g_(?1), and the capacity retention is 79.6% after 1000 cycles at 5?C. These results reveal that a dual-doping strategy and porous structure design play synergistic roles in the preparation of high performance LiMn~(2)O~(4)-based spinel cathode material. The cation co-doped strategy can maintain the crystal structural stability and provide interfacial stability while preserving fast Li_(+)diffusion during the long-time cycling at elevated temperatures. Furthermore, the porous structure favors fast Li_(+)intercalation/deintercalation kinetics by allowing electrolyte