Encouraging Voltage Stability upon Long Cycling of Li-Rich Mn-Based Cathode Materials by Ta–Mo Dual Doping

摘要

The Li-rich and Mn-based material x Li_(2)MnO_(3)·(1–x )LiMO_(2) (M = Ni, Co, and Mn) is regarded as one of the new generations of cathode materials for Li-ion batteries due to its high energy density, low cost, and less toxicity. However, there still exist some drawbacks such as its high initial irreversible capacity, capacity/voltage fading, poor rate capability, and so forth, which seriously limit its large-scale commercial applications. In this paper, the Ta–Mo codoped Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_(2) with high energy density is prepared via a coprecipitation method, followed by a solid–state reaction. The synthetic mechanism and technology, the effect of charge–discharge methods, the bulk doping and the surface structure design on the structure, morphology, and electrochemical performances of the Li_(1.2)Ni_(0.13)Co_(0.13)Mn_(0.54)O_(2) cathode are systematically investigated. The results show that Ta~(5+) and Mo~(6+) mainly occupy the Li site and transition-metal site, respectively. Both the appropriate Ta and Ta–Mo doping are conductive to increase the Mn~(3+) concentration and suppress the generation of Li/Ni mixing and the oxygen defects. The Ta–Mo codoped cathode sample can deliver 243.2 mA h·g~(–1) at 1 C under 2.0–4.8 V, retaining 80% capacity retention after 240 cycles, and decay 1.584 mV per cycle in 250 cycles. The capacity retention can be still maintained to 80% after 410 cycles over 2.0–4.4 V, and the average voltage fading rate is 0.714 mV per cycle in 500 cycles. Compared with the pristine, the capacity and voltage fading of Ta–Mo codoped materials are effectively suppressed, which are mainly ascribed to the fact that the highly valence Ta~(5+) and Mo~(6+) that entered into the crystal lattice are favorable for maintaining the charge balance, and the strong bond energies of Ta–O and Mo–O can help to maintain the crystal structure and relieve the corrosion from the electrolyte during the charging/discharging process.