Lattice Spacing, Morphology, Properties, and Quasi—In Situ Impedance of Ternary Lithium-Ion Batteries at a Low Temperature

The study about the low-temperature performance of lithium-ion batteries (LIB) is of great significance at extreme temperatures, such as polar scientific research, space exploration, deep-sea exploration, military fields, and so on. In this study, normal devices and symmetrical devices were fabricated by ternary Li(Ni 0.5 Mn 0.3 Co 0.2 )O 2 as cathode and graphite as anode at 25 and −20 °C. The results show that the specific discharge capacity of normal device is up to 120 mAh g −1 at 1 C and 25 °C. The specific capacity and energy density at 0.2 C and −20 °C are 106.05 mAh g −1 and 376.53 mWh g −1 , respectively, which can reach 92.82% of that at 1 C and 25 °C. The value of activation energy E a of the interface reaction of the LIB is calculated to be 63.72 kJ/mol by the Arrhenius equation. When the temperature dropped from 25 to −20 °C, the lattice spacing of Li 1−x (Ni 0.5 Mn 0.3 Co 0.2 )O 2 hardly changed, while the lattice spacing (002) of graphite reduces 0.00248 Å. In addition, some cracks were observed on the charged cathode at −20 °C. We carried out quasi-in situ electrochemical impedance spectroscopy (EIS) when the voltages of normal device discharged to 3.8, 3.6, 3.4, 3.2, and 3.0 V. Unlike the relationship of voltage–resistance at 25 °C, the values of the series resistance (R s ), charge transfer resistance (R ct ), and ion transfer resistance (R it ) gradually decrease as the voltage decreases at −20 °C. Compared with the resistance of the symmetrical device based on the anode at 25 °C, the values of R s and R it at −20 °C both obviously increase. The main reason of performance degradation for normal device at −20 °C is large ion transfer resistance and the decrease of lattice spacing of the graphite (002).