Preparation Of Quasi-dissociated LiPF₆ At Room Temperature And Its Application In Solid-state Cell

Electrolyte is an indispensable part of the electrochemical energy storage systems,and the high energy and security solid-state battery that people pursue mainly depends on the breakthrough of the solid-state electrolyte.Combined with the development history and current status of solid-state electrolyte,this thesis proposes a "two-step"idea for the preparation of a new hybrid solid-state electrolyte:first,a quasi-dissociated lithium salt at ambient temperature is prepared,and then a hybrid solid-state electrolyte was obtained by mixing the quasi-dissociated lithium salt with PEO to apply in solid cell.The main results obtained are as follows:1.A quasi-dissociated LiPF6 composites based on ZIF-8 at room temperature was constructed and its ionic conductivity was 7.20 × l0-6 S cm-1 at ambient temperature.2.Combined with calculations,the mechanism of LiPF6 dissociation was discussed.The imidazole ring of ZIF-8 can interact with lithium ions to drive the lithium salt LiPF6 to a certain degree of dissociation,making it "fluffy",and solid EC as a stabilizer to achieve a quasi-dissociated lithium salts at ambient temperature.3.Based on the solid quasi-dissociated LiPF6 composites,a hybrid solid-state electrolyte(HSE)with excellent performance was prepared.A flexible hybrid solidstate electrolyte was obtained by hybridizing the solid quasi-dissociated LiPF6 composites with PEO.And the HSE exhibits a high Li-ion conductivity of 1.07×10-3 S cm-1 at room temperature,good mechanical strength,flexibility and good compatibility with electrode4.A LiFePO4(LFP)| HSE | Li cell configuration was constructed.At room temperature,the solid cell exhibits excellent electrochemical performance with an initial discharge specific capacity 142.2 mAh g-1 at 0.5 C.And there is almost no decrease of the specific capacity after 200 cycles.5.The COF-TpBD material was synthesized by the condensation reaction of benzidine with 1,3,5-trimethylresorcinol.The quasi-dissociated LiPF6 composites based on COF-TpBD material was prepared in a similar mechanism to ZIF-8 to promote the dissociation of lithium salts and it shows a ionic conductivity of 1.05 ×10-6 S cm-1.Then by mixing the composites with PEO,the hybrid solid-state electrolyte has been obtained and displays an ionic conductivity 3.28 ×10-4 S cm-1 at room temperature.When applied to LFP solid cell,it is provided with an initial discharge specific capacity of 140.9 mAh g-1 at 0.2C.And,it shows excellent cycling stability with a retain capacity of 138.9 mAh g-1 after 200 cycles.