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

The polycrystalline NCM materials have lower ion diffusion coefficient and higher lithium ion transmission resistance, resulting in more heat generation during the cycle than single crystal NCM materials. In addition, obvious inhomogeneities in polycrystalline materials during cycle bring more delithiation in some particles, which becomes the initiating factor for the charged materials to release oxygen in advance. • Reveal the better thermal properties of single crystal NCM materials than polycrystalline materials. • Demonstrate the heterogeneity of polycrystalline NCM materials in the process of lithium deintercalation. • Prove the higher lithium ion transfer coefficient and smaller impedance of single crystal NCM materials. • Verify another important advantage of single crystal NCM materials, which is conducive to its large-scale production. Single-crystal (SC) LiNi x Co y Mn 1−x−y O 2 (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, LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) and LiNi 0.6 Co 0.2 Mn 0.2 O 2 (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.