Electrolyte Improves Discharge Rate Performance Of Fluorinated Carbon Cathodes

With the continuous development of electric vehicles and portable electronic products,significantly efforts have been devoted to developing lithium-ion batteries with high energy density and high power density.The fluorinated carbons（CF_x）are widely studied because they have the highest energy density as a cathode material for lithium primary batteries.In order to improve the energy density and power density of Li/CF_xbatteries,quite a few efforts have been made,such as adjusting the carbon source,surface modification,controlling fluorine stoichiometry,reducing particle size,introducing conductive coatings,etc.,and have achieved certain results.In this work,the discharge mechanism of Li/CF_x batteries is further studied,and the characteristics of the solvent participating in the discharge reaction of carbon fluoride are used to improve the energy density and power density of the battery by adjusting the electrolyte components composition.In this work,the influences of electrolyte in aspects of Li-ion concentration,anion species,and solvent species on the performances of Li/CF_x batteries are systematically explored.The results showed that Li/CF_x batteries exhibited higher discharge voltages in electrolytes with lower lithium salt concentrations,and in electrolytes with different solvents,Li/CF_x batteries exhibited voltage differences of 190 m V.The Nernst equation is used to calculate the effect of lithium salt concentration and solvent molecules on the potential displacement of the lithium anode and the CF_x cathode.I came to the following conclusions:（1）Electrolyte has influences on voltage for Li/CF_x.（2）A higher Li-salt concentration offers a lower operational voltage.（3）A solvent solvating Li⁺with more molecular numbers provides a higher operational voltage.（4）Li-free electrolyte（0 M）offers a specific discharging capacity of 738 m Ah g^-1.In order to further increase the discharge capacity of the CF_x cathode material,extend the discharge voltage window to 1.0 V.By regulating the electrolyte components,the battery appeared a second discharge platform at about 1.7 V,and by analyzing the Raman spectrum of the electrolyte,it was concluded that the new discharge platform was mainly due to the fact that the solvated lithium ion structure of Li⁺（DMSO）（DOL）₃ can be co-embedded in the carbon layer generated after the fluorine-graphene discharge.By optimizing the electrolyte,the fluorine-graphene CF_1.12 cathode achieves excellent performance of 1483 m Ah g^-1 and 3011 Wh kg^-1 at 0.1C in a 1.5 M Li BF₄ DMSO/DOL（1:9 by vol.）electrolyte.