Metal–Ligand\nSpin-Lock Strategy for Inhibiting\nAnion Dimerization in Li-Rich Cathode Materials

Anion dimerization poses a significant challenge for\nthe application\nof Li-rich cathode materials (LCMs) in high-energy-density Li-ion\nbatteries because of its deleterious effects, including rapid capacity\nand voltage decay, sluggish reaction kinetics, and large voltage hysteresis.\nHerein, we propose a metal–ligand spin-lock strategy to inhibit\nanion dimerization, which involves introducing an Fe–Ni couple\nhaving antiferromagnetic superexchange interaction into the LCM to\nlock the spin orientations of the unpaired electrons in the anions\nin the same direction. As proof of concept, we applied this strategy\nto intralayer disordered Li<sub>2</sub>TiS<sub>3</sub> (ID-LTS) to\ninhibit S–S dimerization. Electrochemical characterization\nusing the galvanostatic charge/discharge and intermittent titration\ntechnique demonstrated the considerably enhanced anionic redox activity,\nreduced voltage hysteresis, and improved kinetics of the Fe–Ni-couple-incorporated\nID-LTS. Fe L<sub>2,3</sub>-edge X-ray absorption spectroscopy and\nmagnetic susceptibility measurements revealed that the metal–ligand\nspin-lock effect and consequent suppression of anion dimerization\ninvolve ligand-to-metal charge transfer between S and Fe. Further\nelectrochemical tests on a Fe–Ni-couple-incorporated Li-rich\nlayered oxide (Li<sub>0.7</sub>Li<sub>0.1</sub>Fe<sub>0.2</sub>Ni<sub>0.1</sub>Mn<sub>0.6</sub>O<sub>2</sub>) indicated the importance\nof the π backbond in enhancing ligand-to-metal charge transfer\nfrom S to Fe. These findings demonstrate the potential application\nof our metal–ligand spin-lock strategy in the development of\nhigh-performance LCMs.