Study On The Influence Of Sulfonate Additives And Solid Electrolytes On The Performance Of Lithium Batteries

Nowadays,the demand for energy density of lithium batteries is increasing.Li Ni_xCo_yMn_1–x–yO₂（NCM）is a typical cathode material.The key to further improving performance and promoting commercial applications of NCM/graphite batteries is to choose a suitable electrolyte.During the cycle,the continuous contact between organic solvent molecules and NCM is likely to cause side reactions in the electrolyte,so how to improve the safety of lithium batteries is extremely important problem.Compared with other methods to solve this problem,the application of film-forming electrolyte additives is a more cost-effective method.Compared with the base electrolyte,these additives usually show the ability of preferential reduction potential,which is conducive to the construction of passive film to protect the active electrode.However,most electrolyte additives is not able to ameliorate the performance of lithium-ion batteries at different temperature at the same time.This means that new-type electrolyte additives that should configurate a stable interface film between the cathode and anode surfaces can be developed to need the demands of lithium-ion batteries using in a wide temperature range.Considering the characteristics of high electronegativity,low polarity and intrinsic elements,some sulfonate molecules may become appropriate electrolyte additives to ameliorate the capability of lithium batteries with high nickel content NCM cathode.In the solid state electrolyte,garnet type Li₇La₃Zr₂O₂（LLZO）with inorganic oxide has high conductivity,so garnet type all solid state lithium ion battery has high application value.However,the preparation process of LLZO reported at present has many defects,for example,the wide range of sintering temperature and the poor stability of the final product,which are not conducive to the mass preparation of electrolyte,so this article has done some preliminary explorations.Based on the above situation,this article has completed the following work（1）Li Ni_0.8Co_0.1Mn_0.1O₂/graphite soft pack battery was prepared by adding fluorosulfonyloxy benzene（FSOB）into the electrolyte as film forming additives,the effects of different contents of FSOB on the battery were explored,and the SEI film formed on graphite was studied.The electrochemical method is used to test whether FSOB can achieve the effect of early reduction.Then,through the charge discharge test,it is discussed whether the addition of different content of FSOB improves the cycle performance of soft pack battery at different temperatures.Finally,the SEM and TEM are used to prove whether SEI film is effectively formed.（2）The sulfanate additives,phenyl methanesulfonate（PMS）and hydroquinone difluoro sulfuric acid（HBFS）,were selected to make Li Ni_0.5Co_0.2Mn_0.3O₂/graphite soft pack battery,and its performance at different temperatures was studied.The results show that PMS and HBFS additives can form a stable interfacial film on the surface of graphite,and study all the electrochemical properties at 60℃storage,-20℃discharge,high temperature cycle and room temperature cycle.In addition,the composition and morphology of the electrode surface were studied to reveal the reaction mechanism.（3）New oxide solid electrolytes Li Ga₅O₈and Li Ga O₂ were synthesized,which are similar to garnet electrolytes.The effects of lithium salt compensation,ball milling process,sintering temperature and sintering time on electrolyte were studied.The results show that when 10%excess lithium carbonate（Li₂CO₃）is used as raw material,a more stable cubic phase can be formed at 800℃for the first sintering and1250℃for the second sintering.The ionic conductivity of Li Ga₅O₈-6h can reach 4.7×10^-5S/cm at 25℃.When the lithium symmetrical battery is assembled,it can be stable at 0.06 V（small overpotential）for 100 hours at the current density of 0.375 m A/cm~2 and at the end of the charging/discharging process.This study systematically analyzes the influence of the preparation process on the electrolyte,which can provide a useful reference for the macro stable preparation of solid electrolytes such as LiGa₅O₈and LiGaO₂.