Rapid Self-healing Polymer Electrolytes Based On Reversible Covalent Bonds At Room Temperature

The theoretical specific capacity of lithium metal cathodes(3860 m Ah g^-1)is ten times higher than that of graphite cathodes.Using lithium metal as anode can effectively improve the energy density of lithium-ion batteries.However,lithium-metal batteries assembled with liquid electrolytes suffer from electrolyte leakage,growth of lithium dendrites,low coulombic efficiency and continuous corrosion of lithium metal,which seriously affects the safety performance of the batteries.Polymer electrolytes possess excellent flexibility,low density and high safety,and can be combined with lithium metal cathodes to produce lithium metal batteries with higher energy density and better safety.Self-healing polymer electrolytes can automatically repair structural damage,improve the security and reliability of batteries,which has a good application prospect in solid-state lithium batteries.However,self-healing polymer electrolytes suffer from low ionic conductivity,slow self-healing speed and low mechanical strength.To address the above issues,in this thesis,reversible covalent bonds were introduced into the polymer electrolyte to achieve rapid self-healing of polymer electrolyte at room temperature,and high ionic conductivity plasticizer was introduced to achieve regulation of chain segment motion ability,which effectively improved the ionic conductivity and self-healing speed of the self-healing polymer electrolyte.The key studies are described below:（1）Rapid self-healing polymer electrolyte based on reversible imine bonding at room temperature:A self-healing polymer electrolyte（PBPE）with dynamic imine bond crosslinking was prepared by Schiff base reaction of polyethylene glycol diamine and paraphenyltriformaldehyde.The reversible breakage and reorganisation of the imine bonds allows PBPE to have good self-healing properties and can be self-healed within 1 hour at room temperature.The plasticised PBPE achieves an ionic conductivity of 4.79×10^-3 S cm^-1at 30°C and exhibits good flexibility and flame retardancy.The Li Fe PO₄ battery assembled with PBPE exhibited excellent rate performance and excellent cycling performance,with a specific capacity of 118.2 m Ah g^-1 at 5 C rate and a capacity retention rate of 97.8%after 125cycles of charge and discharge.The self-healing PBPE was able to maintain the same cycling performance of the original PBPE in Li Fe PO₄ battery.（2）Self-healing polymer electrolytes based on synergistic reversible imine and B-O bonds:A self-healing polymer electrolyte（IBsh PE）cross-linked by synergistic reversible imine and B-O bond dynamic was fabricated by the reaction of 2-formylbenzoylboric acid with polyethylene glycol diamine.The nitrogen atom of IBsh PE amidine bond can coordinate with the boron atom of B-O bond,reduce the acidity of phenylboric acid,promote the formation of B-O bond,and accelerate the balance between B-O bond and boric acid.IBsh PE has a 97%self-healing efficiency after 4 hours of self-healing at room temperature.The ionic conductivity of plasticized IBsh PE exhibits 5.08×10^-3 S cm^-1 at 30°C.The Li Fe PO₄ battery assembled with IBsh PE has a capacity retention rate of 98.6%after 80 cycles.After cutting and self-healing,IBsh PE can still restore the same cycle performance.（3）Rapid self-healing polymer electrolytes based on reversible borate bonds at room temperature:A self-healing polymer electrolyte BDB-PEG was prepared from a multifunctional monomer（BDB）containing two dynamic borate bonds,pentaerythritol tetra（3-mercaptopropionic acid）and polyethylene glycol diacrylate via thiol-ene click reaction.The dynamic reversible borate bond endows BDB-PEG with excellent self-healing properties,and BDB₆-PEG₄ can self-heal within 1 hour at room temperature.The Lewis acid-base interaction between boron atoms and anions of BDB₆-PEG₄ contributes to ultrahigh lithium-ion transference number（0.71）,BDB₄-PEG₆ possesses high ionic conductivity of8.67×10^-4 S cm^-1.The Li Fe PO₄ battery assembled with BDB₆-PEG₄ exhibits a discharge specific capacity of 120.3 m Ah g^-1 after 200 cycles at 1 C rate.