Structural Unpredictability of a Cobalt‐Free Layered Cathode and Its Mitigation for Producing Reliable, Sustainable Batteries

Abstract To advance the sustainable development of Li‐ion batteries, reducing the Co content in Li[Ni_xCo_y(Mn or Al)_(1–x–y)]O₂ has become essential, prompting the exploration of Co‐free Li[Ni_xMn_(1–x)]O₂ alternatives. Among the promising solutions are Co‐free layered cathodes with compositional concentration gradients, which offer significant potential. However, their unique microstructure and compositional partitioning, key to their performance, are highly sensitive to synthesis temperatures. Over‐sintering can lead to the structural unpredictability of Co‐free cathode materials and detrimental effects on electrochemical properties. In this study, a highly stable Co‐free layered oxide cathode is developed by doping a concentration gradient Li[Ni_0.9Mn_0.1]O₂, with high‐valence ions. This innovative strategy significantly reduces sensitivity to calcination temperatures, minimizing nano‐ and microstructural changes across a broad temperature range (750–810 °C). The particle‐level compositional gradation and grain‐level heteroelement encapsulation contribute to the cathode material's exceptional electrochemical performance. Mo doping, in trace amounts, plays a pivotal role in maintaining the stability of Co‐free cathodes, enabling the development of high‐potential (4.3 V vs graphite) Co‐free cathodes suitable for practical and sustainable Li‐ion battery applications.