Electropolymerizable isocyanate-based electrolytic additive to mitigate diffusion-controlled self-discharge for highly stable and capacitive activated carbon supercapacitors

Isocyanate Additives Improve the Low-Temperature Performance of LiNi0.8Mn0.1Co0.1O2||SiOx@Graphite Lithium-Ion Batteries

LiNi_0.8Mn_0.1Co_0.1O₂||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.

Effects of Fe Impurities on Self-Discharge Performance of Carbon-Based Supercapacitors

Activated carbon is widely used as an electrode material in supercapacitors due to its superior electrochemical stability, excellent electrical conductivity, and environmental friendliness. In this study, the self-discharge mechanisms of activated carbon electrodes loaded with different contents of Fe impurities (Fe and Fe₃O₄) were analyzed by multi-stage fitting to explore the tunability of self-discharge. It is was found that a small quantity of Fe impurities on carbon materials improves the self-discharge performance dominated by redox reaction, by adjusting the surface state and pore structure of carbon materials. As the content of Fe impurities increases, the voltage loss of activated carbon with the Fe impurity concentrations of 1.12 wt.% (AF-1.12) decreases by 37.9% of the original, which is attributable to the reduce of ohmic leakage and diffusion, and the increase in Faradic redox at the electrode/electrolyte interface. In summary, self-discharge performance of carbon-based supercapacitors can be adjusted via the surface state and pour structure, which provides insights for the future design of energy storage.