Preparation And Electrochemical Properties Of PEO-based Composite Solid Electrolyte Based On Intermolecular Force

Solid polymer electrolyte（SPE）has the advantages of good contact with electrode materials,low density and easy processing.It is considered to be one of the ideal electrolytes for manufacturing the next generation of high energy density energy storage devices.Polyethene oxide（PEO）electrolytes have become the leading research object among many polymer electrolytes because of their excellent solubility to lithium salt and soft transport chain segment.However,the low room temperature ionic conductivity and narrow electrochemical window of PEO electrolytes hinder their practical application.Therefore,the researchers added inorganic nano-particles to improve the room temperature conductivity and antioxidant reduction ability of PEO electrolytes.The results show that the PEO/filler interface is a fast transport channel of lithium ions.However,it is often difficult to modify the surface of stable inorganic materials,resulting in poor interfacial compatibility between PEO and filler.Due to the high density of inorganic materials,many particles need to be added to build a continuous transmission channel,which is not conducive to the improvement of energy density.Based on this,this paper uses an ultra-light skeleton and highly designable porous polyaminal as filler.It explores the effects of different functional groups on the properties of PEO composite solid electrolytes by changing the functional groups of polyaminal.The specific research contents are as follows:1.Based on van der Waals forces,the interaction of electron-withdrawing and donating groups on the polymer matrix/filler interface on the transport of lithium ions was investigated,as well as the effect of different groups on the formation of solid electrolyte layers（SEI）on the surface of lithium metal.The experimental results show that:（1）Compared with methyl modified polyaminal（PAN-MP）,the addition of fluoromethyl modified polyaminal（PAN-FMP）improves the movement ability of chain segments and and promotes the dissociation of more lithium salts through ions-dipoles interactions.（2）Compared with the-CH₃group,the interaction between ether oxygen and-CF₃group in the PEO chain makes the formation of loose ion pairs between ether oxygen and Li⁺,which significantly improves the ionic conductivity,so that Li Fe PO₄（LFP）/SPE/Li battery has a reversible capacity of 124 m Ah g^-1at 1C,and can still have a retention rate of 83%after 1000 charge-discharge cycles.（3）Unlike-CH₃,-CF₃can promote TFSI defluorination and form a rich-Li F-SEI layer.The stable and dense Li F-SEI layer prevents the emergence of lithium dendrites and prolongs the battery’s cycle life.（2）Based on the multiple hydrogen bond interaction,strong hydrogen bond interactions such as N-H···F、C-H···F or N-H···O are formed in the electrolyte,and then the effect of the hydrogen bond on the electrochemical performance of the electrolyte is explored.It is found that:（1）The addition of hydrogen bonds hinders the rearrangement and crystallization of PEO segments and limits the migration of anions,which effectively improves the electrochemical properties such as ionic conductivity and lithium transference number.（2）The anchoring of anions hinders the formation of the space charge layer,reduces the transmission barrier and polarization of lithium ions,and makes the solid-state battery maintain stable cycle performance at high current density.LFP/3-IC/Li cell can have a discharge capacity of 120.4 m Ah g^-1at 2C current density and still have 80.7%capacity after 1500 cycles.（3）The existence of hydrogen bonds effectively regulates the structure of lithium-ion solvent sheath.It promotes the formation of a high-quality rich-Li F-SEI layer so that lithium can be deposited evenly,and the assembled whole battery can still maintain a stable cycle at a high current density.