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(Ni0.5Mn0.3Co0.2)O-2 as cathode and graphite as anode at 25 and -20 degrees C. The results show that the specific discharge capacity of normal device is up to 120 mAh g(-1) at 1 C and 25 degrees C. The specific capacity and energy density at 0.2 C and -20 degrees 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 degrees 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 degrees C, the lattice spacing of Li1-x(Ni0.5Mn0.3Co0.2)O-2 hardly changed, while the lattice spacing (002) of graphite reduces 0.00248 angstrom. In addition, some cracks were observed on the charged cathode at -20 degrees 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 degrees 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 degrees C. Compared with the resistance of the symmetrical device based on the anode at 25 degrees C, the values of R-s and R-it at -20 degrees C both obviously increase. The main reason of performance degradation for normal device at -20 degrees C is large ion transfer resistance and the decrease of lattice spacing of the graphite (002).