| Lithium metal batteries have attracted much attention due to their low redox potential,light weight density and high theoretical specific capacity.At present,the electrolyte commonly used in lithium metal battery is organic liquid electrolyte,which has the advantages of high conductivity and good contact with the electrode.However,its flammability,high volatility and leakage in the process of packaging have inpeded its practical application.In addition,during the lithium ion deposition/stripping process in organic electrolyte,the"tip effect"leads to the uneven distribution of lithium ions on the surface of lithium metal,and induces the spontaneous formation of dendritic lithium dendrites.The phenomenon would result in low coulombic efficiency and short circuit of batteries,which could give rise to security risks.All solid state batteries constructed with all solid state electrolytes are expected to solve the above problems.Moreover,they can further simplify the assemblage technology and inhibit the growth of lithium dendrites mechanically.Compared with organic electrolyte,solid electrolyte has the advantages of high mechanical strength,wide electrochemical window and stable chemical properties.In addition,the solid electrolyte with high Li+transference plays an important role in the uniform distribution of lithium ions.However,the development of solid electrolyte still faces many problems,such as high interface resistance,low room temperature ionic conductivity and poor processability.In order to solve these problems,polymer,ionic liquid and inorganic solid electrolyte were compounded to prepare the solid electrolyte film of lithium metal battery with high ionic conductivity,good safety performance and long cycle life,which provided an effective way to realize the high performance all solid state lithium battery at room temperature.The specific research work is as follows:?1?Polyvinylidene fluoride?PVDF?polymer was used as the framework,and Pyr1?201?TFSI and Li1.3Al0.3Ge1.7?PO4?3?LAGP?were used as fillers,respectively.The composite all solid electrolyte membrane was prepared by solution casting.The membrane combines the soft property of PVDF matrix and the high shear modulus of LAGP.The addition of LAGP can not only enhance the shear modulus of solid electrolyte membrane,but also mechanically inhibit the growth of lithium dendrites under high current density,promoting the release of fluorine-containing anions in IL.The anions in IL oxidize and decompose on the surface of lithium anode to form Li F-rich SEI membrane.By cooperating with the high mechanical modulus,the assembled Li|Li symmetrical cell can cycle for more than 2700 h under the current density of 0.1 m A cm-2,and the polarization voltage is kept at about 50 m V.The Li Fe PO4 solid-state battery constructed with the solid electrolyte membrane can provide improved cycle stability at room temperature?25??,with the discharge capacity maintaining128.2 m Ah g-1 after 100 cycles at 1 C.?2?The solid electrolyte prepared with PVDF-HFP as polymer matrix,combined with IL and LAGP,showed good electrochemical performance and safety.The copolymerized-HFP reduced the crystallinity and glass transition temperature of the main chain of PVDF.That is the reason why the prepared membrane exhabit a lower glass transition temperature than that of the electrolyte membrane of PVDF,but still higher than that of the commercial PP membrane.The swelling property of polymer matrix was improved to absorb more plasticizers?IL?,so that the ionic conductivity was 5.43×10-4 S cm-1 and the lithium ion migration number was 0.53.At room temperature at the current density of 0.1 m A cm-1,the Li symmetric cell can maintain a stable cycle of 500 h?250 cycles?with a small over potential.At the end of the cycle,the surface of the lithium sheet is smooth,forming a layer of Li F-rich SEI.It shows that the separator plays an important role in inhibiting the growth of lithium dendrite and improving the safety of the battery. |
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