Improving the electrochemical performances of Li-rich Li1.2Ni0.13Co0.13Mn0.54O2 through cooperative doping of Na+ and Mg2+

Enhancing the electrochemical performance of lithium-rich manganese-based layered oxides through the phosphorus-vanadium coating of single-crystalline particles

Lithium-rich manganese-based cathode materials are considered next-generation cathode materials for high-energy-density lithium-ion batteries. However, their practical application is limited by continuous voltage decay, poor cycle stability, and inferior rate performance. In this study, single-crystalline Li1.2Ni0.13Co0.13Mn0.54O2 (LNCMO) with different coating levels of Li3V2(PO4)3 was synthesized using the sol-gel method, moreover, a spinel phase and oxygen vacancies were induced between the bulk material and coating layer during the coating process. This modification strategy can effectively suppress voltage decay, improve the rate performance, and reduce side reactions between the active materials and electrolytes during cycling. These results showed that the Li+ ion diffusion coefficient of the LNCMO electrode modified with 3 wt% phosphorus-vanadium is 52 times that of the original sample. The 3 wt% phosphorus-vanadium modified LNCMO delivers a capacity of 201.4 mA h g-1 at 1C rate and retains 176.4 mA h g-1 (87.7% retention) after 100 cycles at 1C, while the pristine material only displayed 72.2% retention under identical conditions. Furthermore, the average discharge midpoint voltage decay of pristine LNCMO (2.4 mV per cycle) decreased to 1.9 mV per cycle. These results provide insights into the future application of lithium-rich manganese-based materials.

Ni/Mg Dual Concentration-Gradient Surface Modification to Enhance Structural Stability and Electrochemical Performance of Li-Rich Layered Oxides

Li-rich layered oxides (LRLOs), with the advantages of high specific capacity and low cost, are considered as candidates for the next-generation cathode of lithium-ion batteries (LIBs). Unfortunately, sluggish kinetics and interfacial degradation lead to capacity loss and voltage decay of the material during cycling. To address these issues, we propose a Ni/Mg dual concentration-gradient modification strategy for LRLOs. From the center to the surface of the modified materials, the contents of Ni and Mg are gradually increased while the content of Mn is decreased. The high Ni content on the surface increases the proportion of cationic redox, elevating the operating voltage and accelerating reaction kinetics. Moreover, the doped Mg on the surface of the material acting as a stabilizing pillar suppresses the migration of transition metals, stabilizing the layered structure. Therefore, the material with the Ni/Mg dual concentration-gradients delivers a superior electrochemical performance, exhibiting a suppressed voltage decay of 2.8 mV per cycle during 200 cycles (1 C, 2-4.8 V) and an excellent rate capability of 94.84 mAh/g at 7C. This study demonstrates a synergic design to construct high-performance LRLO cathode materials for LIBs.

Anion-Cation Dual-Ion Multisite Doping Stabilizes the Crystal Structure of Li-Rich Layered Oxides

Li-rich layered oxide (LLOs) cathode materials are gaining increasing attention as lithium-ion batteries (LIBs) pursue greater energy density. However, LLOs still suffer from severe capacity fading and voltage decay due to their unstable crystal structure. Hence, the anion-cation dual-ion multisite doping strategy based on Mg and S atoms is used to stabilize the crystal structures of LLOs. Mg substitutes Li atoms in the Li and transition-metal (TM) layers, while S atoms occupy tetrahedral interstitial sites and lattice O sites, all of which contribute to the crystal structure stability of LLOs. Theoretical calculations show that Mg/S dual-ion multisite doping successfully reduces the energy levels of the TM 3d-O 2p and isolated O 2p orbitals, which effectively stabilizes the lattice oxygen. Therefore, multisite-doped samples exhibit promising electrochemical performance. This strategy provides a new approach to enhance the crystal structure stability of LLOs for the design of high-energy-density Li-ion batteries.