Dual Modification for Low-Strain Ni-Rich Cathodes Toward Superior Cyclability in Pouch Full Cells.

Abstract

Rapid capacity fading, interfacial instability, and thermal runaway due to oxygen loss are critical obstacles hindering the practical application and commercialization of Ni-rich cathodes (LiNi0.8Co0.1Mn0.1O2, NCM811). Herein, a Sn4+/F- codoping and LiF-coated Ni-rich cathode, denoted as NCM811-SF, is structurally fabricated that demonstrates very high cyclic and thermal stabilities. The introduction of Sn4+ regulates the local electronic structure and facilitates the conversion of the layered structure into a spinel phase; F- captures lithium impurities to form LiF coatings and forms TM-F bonds to reduce Ni/Li disordering. The compositionally complex codoping strategy reduces the internal structure strain, inhibits the Li+/Ni2+ intermixing during cycling and degradation of the nanoscale structure, and further improves the thermal stability and the crystal structure. The cathodic electrode showed a little volume shift at 2.8-4.5 V, which significantly decreased lattice flaws and fractures generated by local strain, based on detailed analyses performed using COMSOL simulations, X-ray diffraction, and scanning transmission electron microscopy. Benefiting from this, after 300 cycles, our as-prepared NCM811-SF cathode maintains 85.4% of its initial capacity at 4.5 V and has an excellent reversible capacity equal to 169 mAh·g-1 at 1 C. In addition, the NCM811-SF/graphite cell in a pouch-type complete cell retained 94.8% of its starting capacity following 500 cycles. These findings underscore the effectiveness of introducing the Sn-O and TM-F bonds in improving the durability and electrochemical efficiency of the cathode material, which makes it a good choice for high-efficiency Li-ion batteries.