Optimization of Ni-rich Li[Ni0.92−xCo0.04Mn0.04Alx]O2 cathodes for high energy density lithium-ion batteries

Abstract

A high-performance Ni-rich Li[Ni1−x−y−zCoxMnyAlz]O2 (NCMA) is developed by comparing the electrochemical performance of Li[Ni0.92−xCo0.04Mn0.04Alx]O2 cathodes (x = 0, 0.01, 0.03, and 0.05). The introduction of excess Al results in the accumulation of Al on secondary particle surfaces and at grain boundaries, resulting in a refined cathode microstructure. The degree of refinement (primary particle elongation and radial alignment) increases with increasing Al content. The refined microstructure effectively dissipates strain resulting from the abrupt contraction of unit cells during second hexagonal phase → third hexagonal phase transition near charge end, thus suppressing the formation of internal cracks. An Al content of 3 mol% affords optimal overall electrochemical performance; a full cell featuring the optimized Li[Ni0.894Co0.041Mn0.034Al0.031]O2 cathode demonstrates excellent long-term cycling stability, retaining >90% of its initial capacity after 500 cycles and an energy density of 740 Wh Kg−1. In contrast, a Li[Ni0.91Co0.04Mn0.04Al0.01]O2 cathode, currently considered a next-generation cathode, in which Li and Ni cation mixing is suppressed, loses 38.3% of its initial capacity after 500 cycles. This research demonstrates that an NCMA cathode, a hybrid of conventional layered cathodes, with optimal Al content can outperform existing layered cathodes and represents a new class of Ni-rich layered cathodes suitable for high-performance electric vehicles.