LiVOPO 4 ‐Modified Lithium‐Rich Layered Composite Cathodes for High‐Performance Lithium‐Ion Batteries

Lithium Antievaporation-Loss Engineering via Sodium/Potassium Doping Enables Superior Electrochemical Performance of High-Nickel Li-Rich Layered Oxide Cathodes

Low-cost Mn- and Li-rich layered oxides suffer from rapid voltage decay, which can be improved by increasing the nickel content to derive high nickel Li-rich layered oxides (HNLO) but is normally accompanied by reduced capacity and inferior cycling stability. Herein, Na or K ions are successfully doped into the lattice of high nickel Li-rich Li_1.2-xM_xNi_0.32Mn_0.48O₂ (M = Na, K) layered oxides via a facile expanded graphite template-sacrificed approach. Both Na- and K-doped samples exhibit excellent rate capability and cycling stability compared with the un-doped one. The Na-doped sample shows a capacity retention of 93% after 200 cycles at 1C, which is quite outstanding for HNLO. The greatly improved electrochemical performances are attributed to the increased effective Li content in the lattice via Li antievaporation-loss engineering, the expanded Li slab, the pillaring effect, the increased C2/m component, and the improved electronic conductivity. Different performances by the introduction of sodium and potassium ions may be ascribed to their different ionic radii, which give rise to their different doping behaviors and threshold doping amounts. This work provides a new idea of enhancing electrochemical performance of HNLO by doping proper alien elements to increase the lattice lithium content effectively.

Surface LiMn1.4Ni0.5Mo0.1O4 Coating and Bulk Mo Doping of Li-Rich Mn-Based Li1.2Mn0.54Ni0.13Co0.13O2 Cathode with Enhanced Electrochemical Performance for Lithium-Ion Batteries

To improve the initial Coulombic efficiency, cycling stability, and rate performance of the Li-rich Mn-based Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ cathode, the combination of LiMn_1.4Ni_0.5Mo_0.1O₄ coating with Mo doping has been successfully carried out by the sol-gel method and subsequent dip-dry process. This strategy buffers the electrodes from the corrosion of electrolyte and enhances the lattice parameter, which could inhibit the oxygen release and maintain the structural stability, thus improving the cycle stability and rate capability. After LiMn_1.4Ni_0.5Mo_0.1O₄ modification, the initial discharge capacity reaches 272.4 mAh g^-1 with a corresponding initial Coulombic efficiency (ICE) of 84.2% at 0.1C (1C = 250 mAh g^-1), far higher than those (221.5 mAh g^-1 and 68.9%) of the pristine sample. Besides, the capacity retention of the coated sample is enhanced by up to 66.8% after 200 cycles at 0.1C. Especially, the rate capability of the coated sample is 95.2 mAh g^-1 at 5C. XRD, SEM, TEM, XPS, and Raman spectroscopy are adopted to characterize the morphologies and structures of the samples. This coating strategy has been demonstrated to be an effective approach to construct high-performance energy storage devices.