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

Abstract: 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 insertion through the nanoparticles during the reversible electrochemical process. Graphical Abstract: Lithium and cobalt co-doped LiMn ₂ O ₄ with a nominal composition of Li _1.02 Co _0.05 Mn _1.90 Li _0.05 O ₄ exhibits an obviously improved cycle performance at high temperature than that of single-doped LiMn ₂ O ₄ . [Figure not available: see fulltext.].