LiNi0.8Mn0.1Co0.1O2||SiOx@graphite (NCM811||SiOx@G)-based lithium-ion batteries (LIBs) exhibit high energy density and have found wide applications in various fields, including electric vehicles. Nonetheless, its low-temperature performance remains a challenge. One of the most efficacious strategies to enhance the low-temperature functionality of battery is the development of appropriate electrolytes with low-temperature suitability. Herein, p-tolyl isocyanate (PTI) and 4-fluorophenyl isocyanate (4-FI) are used as additive substances to integrate into the electrolytes to improve the low-temperature performance of the battery. Theoretical calculations and experimental results indicate that PTI and 4-FI can both preferentially generate a stable SEI on the electrode surface, which is beneficial to reduce the interfacial impedance. As a result, the additive, i.e. 4-FI, is superior to PTI in improving the low-temperature performance of the battery due to the optimization of F in the SEI membrane components. At room temperature, the cyclic stability of the NCM811/SiOx@G pouch cell increases from 92.5% (without additive) to 94.2% (with 1% 4-FI) after 200 cycles at 0.5 C. Under the operating temperature of -20 °C, the cyclic stability of the NCM811/SiOx@G pouch cell increases from 83.2% (without additive) to 88.6% (with 1% 4-FI) after 100 cycles at 0.33 C. Therefore, a rational interphase design involving the modification of the additive structure is a cost-effective way to improve the performance of LIBs.
Keywords: anode interphase; electrolyte additive; isocyanate; lithium-ion battery; low-temperature.