Morphology Engineering in Cobalt-Free Li-Rich Oxides for High-Capacity and Strain-Tolerant Cathodes

Morphology engineering plays a critical role in enhancing ionic diffusion kinetics and activating oxygen redox activity in cobalt-free lithium-rich layered oxides (LROs), addressing their intrinsic limitations for high-energy-density batteries. Herein, a morphology-engineering strategy is proposed to synthesize cobalt-free LRO cathodes with radially arranged primary grains (LRO-RA) and short rod-like grains (LRO-SR). The radial architecture of LRO-RA establishes fast Li⁺ diffusion pathways, as evidenced by its near-identical Li⁺ diffusion coefficient to LRO-SR despite dominating oxygen redox contributions. This accelerated ion transport facilitates reversible anionic redox, yielding a 79 mAh g^-1 higher initial discharge capacity (0.1C) and a 50.6 mV lower O oxidation potential compared to LRO-SR. Advanced spectroscopic and diffraction analyses confirm that the radial morphology stabilizes anionic redox, minimizes MnO₆ distortion, and mitigates strain accumulation. Consequently, LRO-RA achieves a 94.8% capacity retention after 400 cycles (1C), far exceeding LRO-SR (75.6%), with mitigated voltage decay. Post-cycling analysis confirms that the dense radial grains resist electrolyte infiltration and phase transformation, preserving structural integrity. This work elucidates how morphology-driven ion transport optimization amplifies oxygen redox reversibility, offering a universal design principle for high-capacity Li-rich cathodes.