Fabrication And Electrochemical Property Of Flexible Solid Electrolyte For Lithium Battery

At present,commercial Li-ion batteries contain flammable organic liquid electrolytes,which are easy to cause safety problems such as fire and explosion.It is an effective way to solve the safety problem of lithium battery via replacing flammable organic liquid electrolyte with solid electrolyte.Among various types of solid electrolytes,composite solid electrolytes（CSEs）have become a kind of electrolyte with great development potential.The specific contents in this dissertation are as follows:1.Al₄B₂O₉nanofibers（Al₄B₂O₉NFs）were successfully prepared by electrospinning technology,and the prepared Al₄B₂O₉NFs were filled into PEO polymer matrix to obtain composite solid electrolyte Al₄B₂O₉NFs-PEO-Li TFSI（abbreviated as ABP）.Al₄B₂O₉NFs can fix the PEO chain and promote the dissociation of lithium salt through Lewis acid-base interaction.Then,on the basis of ABP electrolyte film,short-chain polymer polyethylene glycol（PEG）was added to prepare Al₄B₂O₉NFs-PEO-PEG-Li TFSI（marked as ABPP）CSE.The added plasticizer PEG can further fix the PEO chain by hydrogen bonding,thereby promote the transmission of Li-ions.The assembled Li-LFP batteries with lithium iron phosphate（Li Fe PO₄,marked as LFP）as cathode and Li metal as anode manifest excellent cycle and rate performance.2.A novel Janus-structured CSE was designed and constructed,viz.I₂-PEO-Li TFSI（IP）/Li_6.4La₃Zr₂Al_0.2O₁₂（LLZAO）-PEO-Li TFSI（LLP）（abbreviated as IP/LLP）.The double-layer CSE has a flexible IP layer facing Li anode,which can closely contact with Li anode and generate a stable rich-Li SEI film.The SEI film can effectively inhibit lithium dendrites,even if lithium dendrites accidentally insert into the electrolyte,they will also be swallowed by I₂loaded in the IP layer.Hence,such“double insurance”mechanism for inhibiting lithium dendrites is successfully realized.Therefore,the assembled Li-Li symmetrical cell ensures stable plating/stripping Li for more than 2000 h at a current density of 0.2 m A cm^-2.Meanwhile,the assembled Li||IP/LLP||LFP cell still has a discharge specific capacity of 146.20 m Ah g^-1after 500 cycles with a capacity decay rate of only0.024%per cycle at 0.2 C under 55?C,demonstrating superior long cycling stability.3.A laminated asymmetric Se-PEO-Li TFSI（SP）/LLZAO-PEO-Li TFSI（LLP）（abbreviated as SP/LLP）CSE was constructed.The flexible SP layer faced Li anode realizes close contact with Li and reduces the interface resistance,and thus effectively passivates the Li metal to stabilize the interface between Li anode and the electrolyte.The assembled Li||SP/LLP/SP||Li cell shows excellent stability for Li even at a high current density of 1 m A cm^-2.Moreover,the assembled Li||SP/LLP||LFP cell still has a discharge specific capacity of 115.48 m Ah g^-1after 400 cycles at 0.2 C under 55?C,and the average decay rate per cycle is only 0.048%,displaying excellent cycle and rate performance.4.A 3D chitosan aerogel（CA）reinforced LLP CSE（labeled as 3D-CA@LLP）was designed and constructed.The-OH functional group in the structure of chitosan can form hydrogen bond with PEO chain,which reduces the crystallinity of PEO.Meanwhile,a flexible LLP buffer layer is formed on the surface of the 3D-CA@LLP electrolyte via reduplicative pouring,which is conducive to the interface contact between the electrolyte and the electrode.Moreover,ionic-conductor LLZAO uniformly distributed in PEO matrix can further promote the transmission of Li⁺.Based on these advantages,the assembled Li/3D-CA@LLP/LFP cell displays good cycle and rate performance.In this thesis,four CSEs are creatively constructed by combining electrospinning technology and solution coating/pouring technology to improve the electrochemical properties of ASSLBs.For CSEs,the fillers are explored from 1D fiber to 3D skeleton,and the performances of the electrolyte are constructed and studied film from mono-layer film to Janus-structured film.This advanced CSEs design concept is of great significance to the development of high-performance ASSLBs.