Study On Application Of Bi-functional Electrolyte Additive In Lithium-CO₂ Batteries

Lithium carbon dioxide(Li-CO2)battery with high specific energy density is a new type of energy storage and conversion system,which possesses great potential in capturing and fixing CO2 and is considered as the most promising next-generation battery system.Although considerable progress has been made in rapidly emerging battery field,there are still many thorny problems to be solved before Li-CO2 battery can be applied on a large scale,such as CO2 reduction,decomposition of discharge products and cycle life.These problems are mainly caused by slower reaction kinetics owing to thermally inert discharge products.In addition,the contact area between solid-state discharge products and cathode is limited,and it is difficult to be oxidized and decomposed,thus discharge products gradually are accumulating on the cathode surface,which leads to higher energy requirements and increases the overpotential in the subsequent charge process.The commonly used heterogeneous catalysts can effectively reduce the overpotential of battery,but their limited catalytic reaction sites make that the conductivity between heterogeneous catalysts,discharge products and electrodes is relatively low.Therefore,the catalysts are difficult to fully reflect their own advantages to improve reaction kinetics of battery.In contrast,soluble catalysts seem to have more advantages.They can not only catalyze the decomposition of discharge products through homogeneous catalytic reaction mechanism in electrolyte,but also provide more reactive sites for discharge/charge process through solid-liquid contact.Therefore,soluble catalyst can replace heterogeneous catalyst to catalyze the discharge/charge reaction of the Li-CO2 battery about overall performance.This paper mainly explores the application of soluble electrolyte additive in Li-CO2 battery.The reaction mechanism and electrochemical performance of soluble electrolyte additives in Li-CO2 battery system were investigated through reasonable design experiments.The main research contents and innovations of this paper are as follows:1.The organic molecule o-phenylenediamine can be directly used as the electrolyte additive in Li-CO2 battery.Due to the enhanced activity of CO2 reduction and evolution reactions catalyzed by OPD,Li-CO2 battery obtained excellent electrochemical performance.At the current density of 200 mA g-1 and cut-off capacity of 1000 mAh g-1,the battery can maintain 127 cycles and possess an extremely low overpotential(0.39 V).Under the condition of 200 mA g-1 current density,the free discharge capacity of battery can reach 20314 mAh g-1.In discharge process of Li-CO2 battery,the addition of OPD can form stable OPD:CO2-adduct in electrolyte,which not only accelerates the activation of CO2 and facilitates the migration of discharge intermediates,but also promotes the growth of discharge products through the solution phase path to improve the capacity of battery.In addition,OPD can effectively decompose discharge products by its own feature which is OPD can disperse uniformly on the surface of solid discharge products in solid-liquid contact mode with the help of electrolyte.The above two advantages greatly promote the oxidation decomposition efficiency of discharge products and improve the coulomb efficiency of Li-CO2 batteryi.2.SPCP-M-x/y(M=Mn,Fe,Co,Ni,Cu;x/y=3/1,2/2,0/4)materials was synthesized by mechanochemical reaction strategy,and then the solubility test confirmed that SPCP-M-3/1 materials can be used as soluble electrolyte additive into Li-CO2 battery.Thanks to the good catalytic activity of SPCP-M-3/1,the kinetics of CO2 reduction reaction and discharge capacity are improved.According to Gaussian calculation,the materials are preferentially oxidized in electrolyte,then they possess the properties of high-valence transition metal to effectively decompose discharge products with the advantages of solid-liquid contact.In particular,when SPCP-Co3/1 electrolyte additives are applied to Li-CO2 battery,the discharge specific capacity can reach 8788.2 mAh g-1 at current density of 200 mA g-1.Under the cut-off capacity of 1000 mAh g-1,the battery has a low overpotential and can maintain a high discharge voltage platform stable for 104 cycles(1040 h).