Dual-site lattice modification regulated cationic ordering for Ni-rich cathode towards boosted structural integrity and cycle stability

摘要

The cationic ordering of Ni-rich cathode materials at original state and in lithiation/delithiation process is the key factor in obtaining high discharge capacity and excellent cycle performance. However, it is still one of the greatest challenges to synthesize Ni-rich cathodes with low cationic disordering and maintain the well-ordered layered structure with no phase degradation during cycling. Herein, cationic ordering tuned Ni-rich cathodes with well-ordered layered structure at as-prepared state and suppressed cationic mixing during cycling are synthesized by synchronous dual-site doping of Zn2+ at transition metal (TM) and lithium sites. The proper amount of Zn2+ ions doped at TM sites reduce the content of Ni2+, thus promoting the ordering of layered structure in as-prepared state and ensuring high capacity. Meanwhile, a part of Zn2+ ions substituted for Li+ ions act as pillaring ions, inhibiting the migration of TM ions from TM slabs to Li slabs and maintaining the integrity of crystal structure during lithiation, especially at highly delithiated state. The first principle calculations demonstrate that the dual-site doping of Zn2+ in Ni-rich cathode is thermodynamically favorable and the modified cathodes have excellent structure and phase stability during electrochemical reaction. With the tuned cationic ordering, Zn modified cathode shows high capacity and stable cyclability, with significantly improved capacity retention of 86% at 5C over 200 cycles and excellent high-temperature performance.