Dual Modification\nfor Low-Strain Ni-Rich Cathodes\nToward Superior Cyclability in Pouch Full Cells

Rapid capacity fading, interfacial instability, and thermal\nrunaway\ndue to oxygen loss are critical obstacles hindering the practical\napplication and commercialization of Ni-rich cathodes (LiNi<sub>0.8</sub>Co<sub>0.1</sub>Mn<sub>0.1</sub>O<sub>2</sub>, NCM811). Herein, a\nSn<sup>4+</sup>/F<sup>–</sup> codoping and LiF-coated Ni-rich\ncathode, denoted as NCM811-SF, is structurally fabricated that demonstrates\nvery high cyclic and thermal stabilities. The introduction of Sn<sup>4+</sup> regulates the local electronic structure and facilitates\nthe conversion of the layered structure into a spinel phase; F<sup>–</sup> captures lithium impurities to form LiF coatings and\nforms TM–F bonds to reduce Ni/Li disordering. The compositionally\ncomplex codoping strategy reduces the internal structure strain, inhibits\nthe Li<sup>+</sup>/Ni<sup>2+</sup> intermixing during cycling and\ndegradation of the nanoscale structure, and further improves the thermal\nstability and the crystal structure. The cathodic electrode showed\na little volume shift at 2.8–4.5 V, which significantly decreased\nlattice flaws and fractures generated by local strain, based on detailed\nanalyses performed using COMSOL simulations, X-ray diffraction, and\nscanning transmission electron microscopy. Benefiting from this, after\n300 cycles, our as-prepared NCM811-SF cathode maintains 85.4% of its\ninitial capacity at 4.5 V and has an excellent reversible capacity\nequal to 169 mAh·g<sup>–1</sup> at 1 C. In addition, the\nNCM811-SF/graphite cell in a pouch-type complete cell retained 94.8%\nof its starting capacity following 500 cycles. These findings underscore\nthe effectiveness of introducing the Sn–O and TM–F bonds\nin improving the durability and electrochemical efficiency of the\ncathode material, which makes it a good choice for high-efficiency\nLi-ion batteries.