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.

In Situ Insights into Cathode Calcination for Predictive Synthesis: Kinetic Crystallization of LiNiO2 from Hydroxides.

Calcination is a solid-state synthesis process widely deployed in battery cathode manufacturing. However, its inherent complexity associated with elusive intermediates hinders the predictive synthesis of high-performance cathode materials. Here, correlative in situ X-ray absorption/scattering spectroscopy is used to investigate the calcination of nickel-based cathodes, focusing specifically on the archetypal LiNiO2 from Ni(OH)2. Combining in situ observation with data-driven analysis reveals concurrent lithiation and dehydration of Ni(OH)2 and consequently, the low-temperature crystallization of layered LiNiO2 alongside lithiated rocksalts. Following early nucleation, LiNiO2 undergoes sluggish crystallization and structural ordering while depleting rocksalts; ultimately, it turns into a structurally-ordered layered phase upon full lithiation but remains small in size. Subsequent high-temperature sintering induces rapid crystal growth, accompanied by undesired delithiation and structural degradation. These observations are further corroborated by mesoscale modeling, emphasizing that, even though calcination is thermally driven and favors transformation towards thermodynamically equilibrium phases, the actual phase propagation and crystallization can be kinetically tuned via lithiation, providing freedom for structural and morphological control during cathode calcination.