Enhancement on inter-layer stability on Na-doped LiNi0.6Co0.2Mn0.2O2 cathode material

A review on nickel-rich nickel-cobalt-manganese ternary cathode materials LiNi0.6Co0.2Mn0.2O2 for lithium-ion batteries: performance enhancement by modification

The new energy era has put forward higher requirements for lithium-ion batteries, and the cathode material plays a major role in the determination of electrochemical performance. Due to the advantages of low cost, environmental friendliness, and reversible capacity, high-nickel ternary materials are considered to be one of ideal candidates for power batteries now and in the future. At present, the main design idea of ternary materials is to fully consider the structural stability and safety performance of batteries while maintaining high energy density. Ternary materials currently face problems such as low lithium-ion diffusion rate and irreversible collapse of the structure, although the battery performance can be improved utilizing coating, ion doping, etc., the actual demand requires a more effective modification method based on the intrinsic properties of the material. Based on the summary of the current research status of the ternary material LiNi0.6Co0.2Mn0.2O2 (NCM622), a comparative study of the modification paths of the material was conducted from the level of molecular action mechanism. Finally, the major problems of ternary cathode materials and the future development direction are pointed out to stimulate more innovative insights and facilitate their practical applications.

A Synergistic Effect of Na+ and Al3+ Dual Doping on Electrochemical Performance and Structural Stability of LiNi0.88Co0.08Mn0.04O2 Cathodes for Li-Ion Batteries

The synergistic effect of Na⁺/Al³⁺ dual doping is investigated to improve the structural stability and electrochemical performance of LiNi_0.88Co_0.08Mn_0.04O₂ cathodes for Li-ion batteries. Rietveld refinement and density functional theory calculations confirm that Na⁺/Al³⁺ dual doping changes the lattice parameters of LiNi_0.88Co_0.08Mn_0.04O₂. The changes in the lattice parameters and degree of cation mixing can be alleviated by maintaining the thickness of the LiO₆ slab because the energy of Al-O bonds is higher than that of transition metal (TM)-O bonds. Moreover, Na is an abundant and inexpensive metal, and unlike Al³⁺, Na⁺ can be doped into the Li slab. The ionic radius of Na⁺ (1.02 Å) is larger than that of Li⁺ (0.76 Å); therefore, when Na⁺ is inserted into Li sites, the Li slab expands, indicating that Na⁺ serves as a pillar ion for the Li diffusion pathway. Upon dual doping of the Li and TM sites of Ni-rich Ni_0.88Co_0.08Mn_0.04O₂ (NCM) with Na⁺ and Al³⁺, respectively, the lattice structure of the obtained NNCMA is more ideal than those of bare NCM and Li⁺- and Na⁺-doped NCM (NNCM and NCMA, respectively). This suggests that NNCMA with an ideal lattice structure presents several advantages, namely, excellent structural stability, a low degree of cation mixing, and favorable Li-ion diffusion. Consequently, the rate capability of NNCMA (83.67%, 3 C/0.2 C), which presents favorable Li-ion diffusion because of the expanded Li sites, is higher than those of bare NCM (78.68%), NNCM (81.15%), and NCMA (83.18%). The Rietveld refinement, differential capacity analysis, and galvanostatic intermittent titration technique results indicate that NNCMA exhibits low polarization, favorable Li-ion diffusion, and a low degree of cation mixing; moreover, its phase transition is hindered. Consequently, NNCMA demonstrates a higher capacity retention (84%) than bare NCM (79%), NNCM (82%), and NCMA (82%) after 50 cycles at 1 C. This study provides insight into the fabrication of Ni-rich NCMs with excellent electrochemical performance.