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.