The Decay Mechanism Related to Structural and Morphological Evolution in Lithium-Rich Cathode Materials for...

Li-rich oxides have garnered intense interest recently for their excellent capacity in rechargeable lithium-ion batteries (LIBs). However, poor cycling stability and capacity degradation during the cycling process impede their practical application. Herein, two ball-shaped cobalt-free oxide materials, Li_1.1 Mg_0.05 Ni_0.3 Mn_0.55 O₂ and Li_1.1 Zn_0.05 Ni_0.3 Mn_0.55 O₂ , which exhibit excellent cycling performance at a high current between 2 V and 4.8 V, are demonstrated. The two Li-rich materials are prepared from hydrothermally synthesized carbonated precursors. Both oxides exhibit high reversible capacities of 237 and 231 mAh g^-1 at 20 mA g^-1 , respectively, originating from the redox of Ni²⁺ /Ni⁴⁺ and O^2- /(O₂ )^n- . Li_1.1 Mg_0.05 Ni_0.3 Mn_0.55 O₂ presents excellent cycling stability after 200 cycles with 90 % capacity retention. Studies of the structural evolution upon electrochemical cycling implies the cathodes undergo a volume expansion, which results in continuous expanding, cracking, and crushing of the spherical particles, which further induces capacity fading in the cathodes.