Revealing Phase Transition in Ni-Rich Cathodes via a Nondestructive Entropymetry Method

With the expanding requirements of recent energy regulations and economic interest in high-performance batteries, the need to improve battery energy density and safety has gained prominence. High-energy-density lithium batteries, employed in next-generation energy storage devices, rely on nickel-rich cathode materials. Since they have extremely high charge/discharge capacity, high operating voltage, prolonged cycle life, and lower cost, nickel-rich cathode materials such as Ni-rich NCM (LiNi_{x > 0.8}Co_yMn_zO₂) and Ni-rich NCA (LiNi_{x > 0.8}Co_yAl_zO₂) are of particular interest to researchers. Several in situ characterization methodologies are currently used to understand lithium-ion battery electrode response and deterioration better. Nevertheless, in many contexts, these measurement methodologies must be combined with specially designed cells and electrode materials with distinct forms, which is sometimes inconvenient. As an alternative, thermo-voltammetric dynamic characterization may be utilized to describe the thermal internal characteristics of various electrode materials, such as the structural changes and electrode reactions that occur during charging and discharging. In this paper, a nondestructive entropy measurement method demonstrates that phase change occurs for NCM (LiNi_0.83Co_0.12Mn_0.05O₂) and NCA (LiNi_0.88Co_0.09Al_0.03O₂) at 40-30% of state of charge (SOC) and 90-80% of SOC, respectively. This is confirmed by ex situ X-ray diffraction (XRD) measurements for these highly popular cathodes.