Study On Electrochemical Performance Of High Voltage Electrolyte Additives For Lithium Ion Batteries

In order to meet the urgent requirements of higher mileage,the growing electric vehicle?EV?market urgently requires the use of higher energy density lithium-ion batteries.Increasing the operating voltage of lithium-ion batteries is one of the ways,but the first thing to be solved is electrolytic.The problem of liquid decomposition at high voltage.At present,the conventional electrolytes used in business are mainly composed of LiPF₆ and carbonate solvents.The inherent instability at a voltage higher than 4.3V will lead to serious decomposition of the electrolyte solvent and continuous growth of the surface layer,resulting in low Coulomb efficiency and fast capacity decay.Therefore,the development and research of high-voltage-resistant electrolytes can promote the development of new energy industries.In view of the above problems,this paper uses LiNi_0.8Co_0.15Al_0.05O₂ and LiNi_0.5Mn_1.5O₂ cathode materials to study the effects of two high-voltage electrolytes on their electrochemical performance.Through a comprehensive comparison of cycle performance tests,2%adiponitrile was added to 0.5 mol L^-1LiPF₆-EC/EMC+0.5molL^-1LiBF₄-GBL,and the ternary cathode material LiNi_0.8Co_0.15Al_0.05O₂ was used.Investigate its electrochemical performance.Compared with ordinary commercial electrolytes and systems without ADN,the discharge specific capacity can reach 196.2 mAh/g and 207.2 mAh/g respectively at room temperature 4.5 V,and the cycle capacity retention rate after 200 cycles is 60%and 36%.The additive system has a specific discharge capacity of 212 mAh/g,a retention rate of73%for 200 cycles,and a retention rate of 82%for 100 cycles even at-20?.According to XPS and TEM analysis,the advantages of adiponitrile's high oxidation stability make LiNi_0.8Co_0.15Al_0.05O₂ form a dense and uniform electronic insulator during high voltage cycling,but it is a good conductor SEI film of Li⁺,preventing the electrolyte continuous decomposition,thereby improving the electrochemical performance of the battery.After that,based on the high anti-oxidation stability adiponitrile as the main solvent,this article is formulated with 2%fluoroethylene carbonate?FEC?as a good film-forming effect as an additive.The effect of 2 mol L^-1LiBF₄-GBL/ADN+2%FEC on the electrochemical performance of lithium LiNi_0.5Mn_1.5O₄ cathode material was studied.The system with FEC additives can improve the cycle stability of the battery.At 1C rate,the capacity retention rate of 100 cycles can reach 83%,while the capacity retention rates of FEC-free systems and ordinary commercial electrolyte systems are only 77%and68%.The rate performance also shows excellent performance,but the advantage of large rate performance is not obvious enough.By using Li₄Ti₅O₁₂ as a negative electrode in a full cell,the high-voltage electrolyte has good compatibility with lithium cells and the reversibility of deintercalated lithium under the synergistic effect of adiponitrile and fluoroethylene carbonate.