Research On Construction And Performance Of Stable Interface Between Anode And Electrolytes In Lithium Secondary Batteries

Due to the rapid development of various portable electronic devices and the increasing number of electric vehicles,the safety of lithium-ion battery with highly flammable organic electrolytes has gradually attracted worldwide attention.Therefore,the design of novel safe non-flammable electrolytes is essential to improve the safety of lithium-ion batteries.Aqueous electrolytes and inorganic solid electrolytes are ideal choices due to their inherent incombustibility.However,the energy density,cycle stability and cycle life of batteries based on these two systems inferior to the existing commercial lithium-ion batteries.Many studies has indicated that the effects of electrode|electrolyte interface on the cell performance should not be ignored in addition to the properties of the electrodes and electrolytes.Here,stable interphase was constructed between anodes and aqueous/solid electrolytes by taking advantages of the relevant interfacial reactions,to improve the compatibility between the anodes and the electrolytes while maintaining their safety characteristics,which was expected to increase the current energy density and prolong the cycle life.The interface design between Li anode and Li_6.85La_2.9Ca_0.1Zr_1.75Nb_0.25O₁₂（LLCNZO）electrolyte was studied.Inferior contact and large interface impedance caused by poor wettability between Li metal and LLCNZO would induce the growth of lithium dendrites at the interface,thus limiting the long-term stable cycle of all-solid lithium metal battery.Different types of interfacial buffer layers were constructed between LLCNZO and Li metal,and the effects on interface performance were comprehensively investigated.It was found that buffer layers（e.g Si-Ti）,showing both ion and electronic conductivity after reacting with Li metal,could improve the affinity beween electrolyte and Li metal,increase the contact area,achieve uniform electric field across the interface and stabilize the interface structure during cycling.Thus,the interface impedance of Li|LLCNZO|Li symmetric cell was reduced,the growth of lithium dendrites in the electrolyte was relieved,and the cycle life was improved as well.The construction of interface phase between Li metal（or alloy anode）and Li₃PS₄（LPS）sulfide electrolyte was also studied.Detrimental reactions with Li metal or electrochemical decomposition during cycling under low potential are prone to occur due to its narrow electrochemical stable window,which lead to the formation of high impedance interphase and lithium dendrites,resulting in invalidation of electrolyte or short-circuit failure of battery.Here,on the one hand,by referring to the succucess usage of 2 M Li PF₆-mix THF organic electrolyte on alloy anodes and lithium-free anodes,the Li F-riched interphase was obtained with in-situ decomposition of 2 M Li PF₆-mix THF after introduction between Li metal and LPS,which effectively alleviated the decomposition of LPS and formation of Li dendrites,leading to increased cycle life of Li|LPS|Li cell to more than 350 h.On the other hand,the Li₃PO₄ interphase between Bi anode and LPS was constructed by electrochemical decomposition of Bi PO₄,alleviating the electrochemical decomposition of LPS at low potential.Thus,the stability of Bi electrode|LPS interface was improved,and the stable cycle of Bi anode was realized.At 25 m A/g under room temperature,Bi@Li₃PO₄ composite can be cycled more than 150 times,with an average coulombic efficiency of 99.3%and a capacity retention of 86%.Based on the previous research results and experiences of SEI on Li metal or alloy anode surface,the interface design on Li₄Ti₅O₁₂（LTO）in aqueous electrolyte was explored.In the traditional dilute aqueous solution,due to the lack of stable interfacial phase on LTO surface and the narrow electrochemical stability window of the electrolyte itself,the continuous decomposition of water occurs on the electrode surface during the charging and discharging process,which will greatly affect the cycling performance of aqueous lithium-ion batteries.Here,TMP as co-solvent was introduced into the high-concentration aqueous electrolyte（21 m Wi SE）for preparing Li TFSI-TMP/H₂O electrolyte,and an effective and stable interface phase SEI layer was constructed on the LTO surface by the preferential decomposition of TFSI^-and TMP at the interface.The composition of the interphase was analyzed using XPS.The results indicated compatibility between the LTO electrode and the aqueous electrolytes was improved attributed to the SEI layer by suppressing the occurrence of H₂O decomposition,leading to high cycling efficiency of approximate 100%of the LTO electrode,and achieving a stable cycling performance of capacity-matched LTO||LMO full cell with 2.9 V output in the aqueous electrolytes.