The Performance Of Phosphate-based Gel Polymer Electrolytes For Lithium/sodium Ion Batteries With High Safety

Lithium/sodium ion batteries have been widely used due to their high energy density,high output power,high working voltage,good cycle performance and portability.The electrolyte provides the possibility of ion transport,has an important influence on the electrochemical performance of the battery,and is also one of the important factors that determine the safety problem of the battery.At present,most of the commercial electrolytes are liquid electrolytes,with characteristics of volatility,low lightning,and leakage,which easily cause fire or explosion.In order to improve the safety of the battery,a series of spirocyclic pentaerythritol diphosphate crosslinkers with different chain lengths and a dibutyl phosphate comonomer were designed and synthesized which combine with the strong flame retardancy of phosphate esters,the excellent polymerization ability of acrylate esters,the easily adjustable flexibility of ethylenedioxy,Three kinds of phosphate esters were selected and copolymerized with acrylate monomers respectively to obtain three kinds of phosphate-based gel polymer electrolytes,which were applied to the field of lithium/sodium ion batteries respectively,and tested their thermal stability and a series of electrochemical properties to prove their potential application value.The specific content is as follows:A series of spirocyclic pentaerythritol diphosphate cross-linkers with different chain lengths were prepared by the nucleophilic substitution reaction of spirocyclic pentaerythritol diphosphoryl dichloride and acryl hydroxyethyl compounds.The structure was characterized by NMR,FT-IR and HR-MS to verify the validity of the structure and purity of the compounds.Two representative cross-linkers were selected and copolymerized with ethyl acrylate and trifluoroethyl methacrylate to prepare two kinds of spirocyclic pentaerythritol bisphosphate-based gel polymer electrolytes.The study found that the two polymer matrices have an amorphous structure which is conducive to ion transport,good thermal stability?no decomposition under 260°C?and obviously flame retardance.Meanwhile,the two gel polymer electrolytes have good compatibility with glass fiber separator and high ionic conductivity(3.256×10^-3 S cm^-1and 2.893×10^-3 S cm^-1,respectively),a wide electrochemical stability window?no decomposition in 5.0 V vs.Na/Na⁺?,a stable interface can be formed in a short time,and a long life?still working smoothly at 750 h?.On this basis,in order to further verify the ion transport effect and interface stability,one of the gel polymer electrolytes was selected for relevant performance characterization.The gel polymer electrolyte has a high ion migration number?0.604?and good interfacial stability.The above tests indicate that the prepared spirocyclic pentaerythritol diphosphate gel polymer electrolytes satisfiy the basic conditions of a better electrolyte.Two spirocyclic pentaerythritol diphosphate gel polymer electrolytes and electrode material of Na₃V₂?PO₄?₃ were assembled into a sodium ion battery,and the relevant performance characterization at room temperature showed that both gel polymer electrolyte batteries have better cycle performance(cycle to 1600 weeks,the specific capacity of the liquid battery is reduced to 58.0 m Ah g^-1,and the specific capacity of the two gel polymer electrolyte batteries is reduced to 71.9 m Ah g^-1 and81.5 m Ah g^-1,respectively)and slightly better rate performance than liquid batteries.On this basis,in order to further explore the high-temperature performance of Na₃V₂?PO₄?₃ batteries,one of the batteries was selected to perform relevant performance characterization at 60°C.The results showed that the specific capacity of gel polymer electrolyte battery(93.4 m Ah g^-1)is much higher than that of the liquid battery(62.5 m Ah g^-1)under the constant current density of 270 m A g^-1.In order to further explore the wide applicability of the electrolyte,one of the gel polymer electrolyte and organic electrode material of 3,4,9,10-perylene-bis?dicarboximide?was selected to assemble a sodium ion battery.The results show that the gel polymer electrolyte battery has slightly better electrochemical performance than the liquid battery,which proves that the phosphate based gel polymer electrolytes are not only suitable for inorganic electrode materials,but also suitable for organic electrode materials.?2-Methacryloyloxyethyl?dibutyl phosphate monomer was synthesized by a nucleophilic substitution reaction of dibutyl chlorophosphate and hydroxyethyl methacrylate,which copolymerized with triethylene glycol dimethacrylate and methyl methacrylate to prepare dibutyl phosphate-based gel polymer electrolyte.Thermogravimetric analysis of the polymer matrix showed excellent thermal stability with the initial decomposition temperature above 225°C.The linear scan of gel polymer electrolyte showed that it has a wide electrochemical stability window?without decomposition within 4.5 V vs.Li/Li⁺?.The gel polymer electrolyte and the electrode material Li Fe PO₄ were used to assemble a lithium ion battery.The results showed that the initial specific capacity was 137.9 m Ah g^-1,and the capacity retention rate was 81.8%after 50 cycles.The initial coulombic efficiency was 94.5%,and the subsequent coulombic efficiency was above 95%,which exhibits better cycle performance and higher coulombic efficiency.These two works expand the system of gel polymer electrolyte with flame retardant properties,and a series of electrochemical tests show that the three phosphates-based gel polymer electrolytes have good electrochemical performance,which has great significance to study high-safety ion batteries.