A modification strategy for synthesizing single-crystal LiNi0.6Co0.2Mn0.2O2 with superior electrochemical performance

Abstract

Monocrystalline Ni-rich layered oxide is a promising cathode material with excellent cyclic stability attributed to the absence of grain boundaries. However, the majority of single-crystal LiNi_xCo_yMn_1-x-yO₂ (NCM) cathodes are prepared by the traditional high-temperature solid-phase method displays "quasi single crystals" formed through particle aggregation, and then the true single crystals can be obtained through subsequent ball milling or air crushing, leading to irregular and uneven morphology. Herein, we synthesize microsized single-crystal LiNi_0.6Co_0.2Mn_0.2O₂ (SC 622) materials utilize a modified molten-salt method, which using LiOH·H₂O and Li₂SO₄ as molten agent. Furthermore, the influence of the ratio of LiOH·H₂O and Li₂SO₄ on the morphology and electrochemical properties of LiNi_0.6Co_0.2Mn_0.2O₂ cathode is studied firstly in detail. Multiple characterization results manifested that the SC 622 material when prepared by using the molar ratio of Li₂SO₄ to LiOH·H₂O is 1:12 (SC 622–12) exhibits superior electrochemical performance. The SC 622–12 displays a specific capacity of 185.1 mAh g⁻¹ at 0.1 C and 123.4 mAh g⁻¹ at 5 C rate under the voltage range of 2.7–4.3 V. The capacity retention rates were 93.2 % and 91.7 % after 200 cycles at 1 C and 5 C, respectively. This work confirmed that the single-crystal NCM can be prepared by an effective molten-assisted strategy and can guide the synthesis of other cathode materials.