Effect Of Small Molecule DMF On Electrochemical Performance Of PEO Polymer-Ceramic Composite Electrolyte

Compared with liquid electrolytes,solid electrolytes can match well metal lithium anode.Organic-inorganic composite electrolytes have becoming a research hotspot in the field of solid electrolytes due to its high ionic conductivity and good mechanical properties.In organic-inorganic composite electrolytes,the different properties of organic-inorganic lead to large interfacial resistance between the two phases,which hinders the transport of lithium ion in organic-inorganic composite electrolytes.In this paper,N,N-dimethylformamide（DMF）was introduced into Polyethylene oxide（PEO）-based composite electrolytes to improve the lithium ion transport at the interface of polymer and inorganic ceramic particles by combining DMF molecules with inorganic ceramic particles,further enhancing ionic conductivity of the organic-inorganic composite electrolytes.At the same time,the effect of the content of DMF on the electrochemical properties of PEO polymer-ceramic composite electrolytes was explored.The research indicates that the PEO polymer-ceramic composite electrolytes have higher ionic conductivity and are more stable with metallic lithium when the DMF content is controlled below 3wt%.The main contents are as follows:1.PEO polymer-ceramic composite electrolytes were prepared by using Li_6.75La₃Zr_1.75Ta_0.25O₁₂,Li_0.34La_0.56Ti O₃ and Li_1.3Al_0.3Ti_1.7（PO₄）₃ inorganic ceramic particles respectively and DMF was added to reduce the organic-inorganic two-phase interface resistance.It can be seen that when PEO polymer-ceramic composite electrolyte contains trace DMF,2.49wt%and9.65wt%,the ionic conductivity increases by 2.3 times,4 times and 6.4 times,respectively,compared with that without DMF.2.The effect of DMF content on the stability of PEO polymer-ceramic composite electrolytes and metal lithium was investigated.Li-Li symmetrical cell exhibits good cycle stability when trace of DMF is coordinated on PEO polymer-ceramic composite electrolytes.When PEO polymer-ceramic composite electrolytes contain 2.49wt%DMF,DMF reacts with Li,resulting in the rise of overpotential of Li-Li symmetrical cell.When DMF is consumed,Li-Li symmetrical cell returns to stability.When PEO polymer-ceramic composite electrolytes contain 9.65wt%DMF,the corresponding overpotential of the Li-Li symmetric battery continues to increase.The application of PEO-DMF composite electrolyte in all solid state battery was evaluated.The assembled Li-Li Fe PO₄ battery has good cycle stability and rate performance.It is cycled 100 times at 0.2 C rate,the capacity retention rate is higher than98%and the capacity at 1 C rate is 137.4 m Ah g^-1.