Study On Reaction And Mechanism Of Cyclic Sulfonate Ester As Electrolyte Additives In Lithium-ion Battery

The challenges faced by electrolyte becomes more and more serious as the energy density of lithium-ion battery?LIB?increases.Using electrolyte additive is an effective method to improve the performance of LIB.However,the research of additive is still at the primary stage of trial and error.Establishing a relationship between structure and performance for additive is a key factor to promote the development of LIB.The effects of cyclic sulfonate ester on the performance of LIB are systematically investigated by X-ray photoelectron spectroscopy?XPS?,liquid chromatography-mass spectrometry?LC-MS?,transmission electron microscopy?TEM?and other methods.The reactions between electrolytes and electrodes are also studied.The structure of additive has an impressive impact on the electrochemical performance and the working mechanism of additive is also studied.Meanwhile,the working mechanism of additive lays a theoretical foundation for the development of high-performance electrolyte additives and its application in high energy density lithium ion batteries.It is found that cyclic sulfonate ester can promote the formation of a better solid electrolyte interphase?SEI?and cathode electrolyte interphase?CEI?,which can improve the cycle performance and high temperature?60oC?storage of LIB.The specific conclusions are as follows:?1?Sulfur-containing electrolyte additives 1,3-propane sultone?PS?and 1,4-butane sultone?BS?are employed as additives to study the influence of cyclic sulfonate ester electrolyte additives?1wt.%?on the electrochemical performance of 1Ah Li Ni_0.6Co_0.2Mn_0.2O₂?NCM622?/artificial graphite?AG?pouch cell,and the working mechanism of electrolyte and electrode is also studied.It is found that the addition of additives changes the composition and structure of anode and cathode interfaces.Meanwhile,it promotes the stability of CEI&SEI membranes and electrochemical performance of pouch cell.PS gets higher capacity retention and lower impedance growth after 200 cycles at 45oC and current of 500m A.The gas production of the battery can be more effectively inhibited in high temperature storage by using PS.Theoretical calculation is engaged to calculate highest occupied molecular?HOMO?and lowest unoccupied molecular?LUMO?.The results show that PS gets a higher HOMO and lower LUMO than PS.Which means PS is more reactive with electrode materials and can form stronger and more uniform CEI&SEI films.SEI&CEI inhibits the reaction between electrolyte and electrode and improves the battery's high-temperature storage and long-term cycle performance.?2?The combination of 1wt.%vinylene carbonate?VC?and 1wt.%PS is used to improve the electrochemical performance of NCM622/AG pouch cell as the same with the combination of VC and BS.The results show that PS,BS and VC had good electrochemical compatibility in the pouch cell.However,PS/VC system gets better high-temperature performance and high-temperature storage performance.The capacity retention of PS/VC system and BS/VC system is 97.66%and 95.60%after 200 cycles at 45oC and current 500 m A,respectively.Meanwhile,LC-MS results show VC can inhibit the decomposition of electrolyte on the anode surface.TEM images show PS and BS can form a stable CEI on the cathode.In conclusion,VC/PS and VC/BS have synergistic effect and PS/VC get a better performance.?3?As a positive electrode material with higher energy density,Li Ni_0.8Co_0.1Mn_0.1O₂?NCM811?is more prone to electrochemical reaction with the electrolyte,which makes the cycle performance of the battery worse.In order to improve its cycle performance,the additives VC,PS and BS are studied in detail based on NCM811/AG pouch cell.The effects of PS and BS on high voltage cathode material Li Ni_0.5Mn_1.5O₄?LNMO?are also investigated.1wt.%PS+1wt.%VC system gets the best high temperature performance for NCM811/AG pouch cell.The results show that the addition of 1wt.%VC+1wt.%PS and 1wt.%VC+1wt.%BS can effectively change the composition and structure of CEI&SEI and improve the high temperature cycling performance of the battery.Among them,1wt.%VC+1wt.%PS electrolyte has better cycling performance.For LNMO/Li coin cell,PS and BS can also improve the cycle performance very well.However,1wt.%BS has the best improvement on the cycle performance of the battery.At the same time,it is found that PS could not be detected in the electrolyte after100 cycles under high pressure.However,a small amount of BS still exists in the electrolyte after 100 cycles at 25oC and 0.5C rate.The work in this paper has guiding significance for the researches on the mechanism of electrolyte additives in lithium-ion battery.And it also provides theoretical guidance for the development of high performance lithium-ion battery electrolyte.