Study On Preparation And Performance Of Electrolyte For High Voltage Resistant Dual-Ion Batteries

Despite the wide application of lithium-ion batteries?LIBs?in portable electronic devices and electric vehicles,the demand for new battery systems with the merits of high voltage,environmental friendliness,safety,and cost efficiency is still quite urgent.Therefore,more and more researches have been focusing on the novel battery systems that can replace the conventional LIBs.A new battery system called Dual-ion batteries?DIBs?and Dual-graphite batteries?DGBs?has attracted much attention from scientists.It can afford all the long cycle life,high energy density and low cost requirements of EVs and smart grids.The working principle of DIBs and DGBs is that both cations and anions participate in the battery reaction during charging and discharging.The intercalation/deintercalation of anions on the graphitic cathode enables a high cut-off voltage up to 5.2 V vs.Li⁺/Li,which is favorable for relatively high energy density.Nevertheless,DIBs and DGBs suffer from severe structural collapse of cathode and significant electrolyte decomposition,which result in a low Coulombic efficiency and poor cycleability during repeated charge/discharge,which is difficult to meet the practical application.In order to solve these problems,we present DIBs and DGBs using themethyl ethyl carbonate?EMC?and sulfolane?SL?mixture as solvents in combination with hexafluorophosphate?LiPF₆?electrolyte,and the electrochemical performances of the DIBs and DGBs with optimized electrolyte are characterized.The main conclusionsare as follows:?1?Herein,a HCE of 2.0 M LiPF₆-EMC/SL with high oxidative stability and reduction stability is developed and introduced to comprehensively enhance the electrochemical performance of DGB.The DGB exhibits a high charging cut-off voltage of 5.3 V,which is of great important to enhance its energy density.Furthermore,an ultra-long cycle life with 94.7%capacity retention after 1000 cycles at 5 C rate.At the same time,the discharge specific capacities of DGB using HCE at1?2?5?10?15 and 20 C multiples are 96.7?97.4?97.0?94.8?93.6 and 91.3 mAh g^-1,respectively.Importantly,the DGB delivers an impressive energy density of 115.6Wh kg^-11 even at a power density of 2600.4 W kg^-11 based on the total mass both of the cathode and anode.The possible mechanisms of HCE for improving electrochemical performance of DGBs are proposed by analyzing the variation of the crystalline structure of graphite cathodes,the interfacial chemistry composition on graphite anodes and ion environment in varied concentration electrolytes.Our work would significantly boost the further enhancement of low cost DGBs with high energy density,superior rate property and excellent cycleability.?2?Herein,a self-supported gel polymer electrolyte?GPE?based on polyvinylidenefluoride/poly?vintlacetate?matrix and 1M LiPF₆-EMC)/SL?1:4 vol:vol?is reported to optimize the cycleability of graphite cathode.It is found that the abundant electron-withdrawing functional group?–C–F?and strong intermolecular interactions in this GPE can greatly restrain the parasitic electrolyte oxidation which lead to the CO₂ release,CEI generation as well as the structural collapse of graphite cathode.As a result,an outstanding cycle performance with 92%capacity retention after 2000 cycles is achieved even the cell potential reach 5.35 V vs.Li⁺/Li.At the same time,the discharge specific capacities of the DIBs using the GPE at 0.5,1,2,5,and 10 C were 94.5,92.5,91.4,88.1,and 84.2 mAh g^-1,respectively.More importantly,a satisfying cycle life with 79%capacity retention after 350 cycles at50?is obtained.To our best knowledge,this is the highest cell potential and best cycle performance in current GPE based DIBs.It should be emphasized that this GPE-reinforcement strategy will boost the energy density of DIBs with outstanding cycle life and low-cost.