The effect of lithium-excess on Ni-rich LiNi0.6Co0.2Mn0.2O2 cathode materials prepared by a Taylor flow reactor

Two birds with one stone: One-pot concurrent Ta-doping and -coating on Ni-rich LiNi0.92Co0.04Mn0.04O2 cathode materials with fiber-type microstructure and Li+-conducting layer formation

A novel scalable Taylor-Couette reactor (TCR) synthesis method was employed to prepare Ta-modified LiNi0.92Co0.04Mn0.04O2 (T-NCM92) with different Ta contents. Through experiments and density functional theory (DFT) calculations, the phase and microstructure of Ta-modified NCM92 were analyzed, showing that Ta provides a bifunctional (doping and coating at one time) effect on LiNi0.92Co0.04Mn0.04O2 cathode material through a one-step synthesis process via a controlling suitable amount of Ta and Li-salt. Ta doping allows the tailoring of the microstructure, orientation, and morphology of the primary NCM92 particles, resulting in a needle-like shape with fine structures that considerably enhance Li+ ion diffusion and electrochemical charge/discharge stability. The Ta-based surface-coating layer effectively prevented microcrack formation and inhibited electrolyte decomposition and surface-side reactions during cycling, thereby significantly improving the electrochemical performance and long-term cycling stability of NCM92 cathodes. Our as-prepared NCM92 modified with 0.2 mol% Ta (i.e., T2-NCM92) exhibits outstanding cyclability, retaining 84.5 % capacity at 4.3 V, 78.3 % at 4.5 V, and 67.6 % at 45 ℃ after 200 cycles at 1C. Even under high-rate conditions (10C), T2-NCM92 demonstrated a remarkable capacity retention of 66.9 % after 100 cycles, with an initial discharge capacity of 157.6 mAh g-1. Thus, the Ta modification of Ni-rich NCM92 materials is a promising option for optimizing NCM cathode materials and enabling their use in real-world electric vehicle (EV) applications.

Cobalt-free composite-structured cathodes with lithium-stoichiometry control for sustainable lithium-ion batteries

Lithium-ion batteries play a crucial role in decarbonizing transportation and power grids, but their reliance on high-cost, earth-scarce cobalt in the commonly employed high-energy layered Li(NiMnCo)O2 cathodes raises supply-chain and sustainability concerns. Despite numerous attempts to address this challenge, eliminating Co from Li(NiMnCo)O2 remains elusive, as doing so detrimentally affects its layering and cycling stability. Here, we report on the rational stoichiometry control in synthesizing Li-deficient composite-structured LiNi0.95Mn0.05O2, comprising intergrown layered and rocksalt phases, which outperforms traditional layered counterparts. Through multiscale-correlated experimental characterization and computational modeling on the calcination process, we unveil the role of Li-deficiency in suppressing the rocksalt-to-layered phase transformation and crystal growth, leading to small-sized composites with the desired low anisotropic lattice expansion/contraction during charging and discharging. As a consequence, Li-deficient LiNi0.95Mn0.05O2 delivers 90% first-cycle Coulombic efficiency, 90% capacity retention, and close-to-zero voltage fade for 100 deep cycles, showing its potential as a Co-free cathode for sustainable Li-ion batteries.