Single-crystal structure helps enhance the thermal performance of Ni-rich layered cathode materials for lithium-ion batteries

Single-crystal (SC) LiNixCoyMn1-x-yO2 (NCM) materials have come into people's field of view recently. The poor thermal stability of polycrystalline (PC) high-nickel NCM materials has always been an obvious shortcoming, and the thermal performance of SC materials is also an important factor which cannot be ignored. Therefore, it is necessary to investigate the safety difference between SC and PC NCM materials. In this research, LiNi0.8-Co0.1Mn0.1O2 (NCM811) and LiNi0.6Co0.2Mn0.2O2 (NCM622) materials with single-crystal and polycrystalline structure are used to study the thermal performance, and the SC materials show obviously better thermal stability than PC materials. Due to the existence of internal crystal gaps, the PC materials have higher lithium-ion transport impedance and lower ion diffusion coefficient, which leads to more heat generation in the cycle process. At the same time, crystal gaps will increase the inhomogeneity of PC materials during charging and discharging, along with the rise of delithiation degree in some parts of the materials, making the structural damage more serious, which would reduce the binding of oxygen and become the initiating factor of oxygen release in advance. In conclusion, the single-crystal structure can improve the thermal properties of high nickel NCM materials during the cycle and under high temperature conditions.