Advanced electrochemical and mechanical performance of a LiNi0.91Co0.06Mn0.03O2 cathode via use of a NaCl flux agent

Abstract

The high energy density and operating voltage required for lithium-ion batteries used in various fields have made high-Ni Li(Ni_1−x−yCo_xMn_y)O₂ (NCM, x + y + z = 1, x + y ≤ 0.2) cathodes attractive. However, there are still a significant number of points that need to be addressed, including issues such as rapid performance degradation and stability. In particular, micro-cracks and particle collapse during cycling are considered a major degradation factor in polycrystalline high-Ni NCM, resulting in excessive penetration of the electrolyte into the cathode active materials. This phenomenon ultimately leads to a deterioration in the electrochemical behavior of the high-Ni NCM cathode due to an increase in unwanted side reactions. To suppress such degradation factors, single crystalline high-Ni LiNi_0.91Co_0.06Mn_0.03O₂ was successfully synthesized using the molten salt flux method. The reduction of grain boundaries and specific surface area through single crystallization caused a decrease in unwanted side reactions, resulting in superior electrochemical behavior compared to polycrystalline high-Ni LiNi_0.91Co_0.06Mn_0.03O₂. In particular, single crystalline high-Ni LiNi_0.91Co_0.06Mn_0.03O₂ showed a higher resistance to capacity degradation, retaining 88.3% of its capacity after 100 cycles, compared to the polycrystalline high-Ni NCM which retained 73.1% of its capacity after the same number of cycles. Therefore, this single crystallization method can be considered as an efficient and forward-looking approach for the production of high-Ni NCM, which deserves attention in the future.