Optimization of Sr-Doping Boosting the Structural Stability for Single Crystalline Lini0.8co0.1mn0.1o2 Cathode to Enhance its Electrochemical Performance at Elevated Voltage and Temperature

Abstract

Single crystalline (SC) Ni-rich cathode materials have been considered the potential cathodes for the next generation lithium-ion batteries because of their high discharge capacity, excellent thermal stability and environmental friendly. Unfortunately, some inevitable defects, such as severe irreversible phase transition, microcracks formation and transition metal dissolution at high voltage, hinder its commercial applications. Herein, a high stable modified single crystalline LiNi0.8Co0.1Mn0.1O2 cathode is prepared by using Sr doping strategy, which is helpful to tackle the above challenges simultaneously. The introduction of Sr atoms can occupy the transition metal sites of the material, resulting in the increase of Li/Ni exchange energy and the improvement of oxygen layer stability. Meanwhile, the Sr doping is beneficial to promote the growth of primary particles and reduce the agglomeration of single crystal particles.  The electrochemical performance of the doped sample exhibits pronounced improvements in pouch-type full cell at high temperature (45oC). The pouch-type full cell for the doped sample delivers a remarkable capacity retention of 86.6% after 1200 cycles at 1C between 2.8-4.35V, while the pristine sample only shows a capacity retention of 80.8% after 798 cycles. The significant enhanced electrochemical properties of the doped sample should be attributed to the effectively bulk doping that could prevent the irreversible phase transition, reduce the oxygen loss, improve the thermal stability and suppress the formation of microcracks as verified by the transmission electron microscopy, differential scanning calorimetry and density functional theory calculation. This work provides a facile strategy to regulate the bulk structure of Ni-rich single crystal materials, which is suitable for the current industrialized system of Ni-rich materials and may promote the development of high energy density lithium-ion batteries.

Keywords: Single crystalline Ni-rich cathode materials, Irreversible phase transition, electrochemical performance, Density functional theory, Lithium-ion batteries