Construction And Performance Study Of Electrode-electrolyte Interface For High Voltage Lithium Ion Batteries

The energy density of lithium-ion batteries has been placed higher demands as the rapid development of electric vehicles since the 21st century.At present,the discharge capacity of lithium-ion batteries are still difficult to meet the national strategic requirements(mass specific capacity of 300Wh kg^-1)on the basis of existing materials,most critical of which is the positive electrode material.Researching and developing higher specific capacity cathode materials is an urgent demand.The cathode materials that receiving widespread attention are LiNi_0.5Mn_1.5O₄,Li₂MnO₃·LiMO₂?M=Ni,Co,Mn?,etc.,but these are high voltage materials?the maximum voltage is above 4.5 V?,only when it is charged above 4.5 V its specific capacity and specific energy can be fully utilized.However,the commercial electrolytes undergo severe oxidative decomposition at high voltages,resulting in poor cycle performance.Although scientists have conducted extensive research and tried various methods to solve this problem,the result is still not satisfactory.Therefore,finding an oxidation-resistant electrolyte to match high-voltage cathode materials is still one of the research hotspots.In this paper,we select film-forming additives to resolve the problem.The added film-forming additive will form an inert protective film on the electrodes prior to oxidation?positive electrode?or reduction?negative electrode?of the electrolyte in the process of battery formation,which effectively controls the impedance and improves the cycling performance of the battery by isolating the electrolyte and the electrode.1)In-situ construct the organic inorganic hybrid interface for high voltage batteries.At first,the effect of Ti-containing compound tetrakis?trimethylsilyl?titanate as electrolyte film-forming additive on the cycle performance of Li_1.17Ni_0.25Mn_0.58O₂/Gr high-voltage lithium battery was studied.The SEI film was characterized with SEM,TEM,TOF-SIMS and so on.It was found that TT can produce an organic-inorganic hybrid interface film on both electrode,which effectively promotes the cycle stability of the battery.2)Regulating the electrolyte-electrode interfaces of 5 V degree lithium metal batteries with boron containing compound.Then,the cycle performance of LiNi_0.5Mn_1.5O₄/Li battery was studied by using tris?pentafluorophenyl?boron as electrolyte additive.The interface between the positive and negative electrodes was characterized by electrochemical and physical characterization.The experiment confirmed that the compound can simultaneously build interface film on the both surface of the positive and negative electrodes.In addition,the problems of lithium dendrites and coulombic efficiency are effectively solved,and the cycle stability of the battery system is significantly improved.3)Study on the stability of additive containing electrolytes.At last,Commonly used electrolyte film-forming additives are generally oxidation or moisture sensitive,and decomposition of the additive will produce other products,which will also have an impact on the performance of the batteries.1,1,1,3,3,3-hexafluoroisopropanol phosphate is a commonly used electrolyte additive,but its stability is poor and easy to decompose.Experiments have confirmed that this compound is almost completely decomposed after being formulated into an electrolyte for one week.After the cycle test,the promotion of the cycle performance of the battery is still remarkable,indicating that the valid group is part of the additives.