Study On Superionic Transport Properties Of LiBH₄-based Solid Electrolyte

All-solid-state batteries have the advantages of high energy density,small size,flexibility,and low potential safety hazards.However,the poor low-temperature ion transport performance of the currently developed solid electrolytes is a key problem that hinders their practical application.This article reviews the development of solid electrolytes at home and abroad,focusing on the research and development of key materials for all-solid-state lithium-ion batteries based on metal hydride electrolytes,especially the current status and existing problems of Li BH₄ solid electrolytes.On this basis,three groups of composite solid electrolytes(Li BH₄/Si O₂,Li BH₄/B₁₀H₁₄,and Li BH₄/B₁₀H₁₄/SBA-15)are designed and prepared,using X-ray diffraction analysis（XRD）,Rietveld full spectrum fitting method,scanning electron microscope（SEM）,energy dispersive spectrometer（EDS）,cyclic voltammetry,and electrochemistry characterization such as AC impedance,constant current charging and discharging,and limiting current density to systematically study the changes in the phase structure,ion transport characteristics and electrochemical properties of the composite solid electrolytes and their internal correlations.The relevant research content and conclusions are as follows:（1）A series of LiBH₄/SM（SiO₂ micron particles）,Li BH₄/MSN（porous Si O₂）,and Li BH₄/SBA-15（mesoporous Si O₂）composite solid electrolytes with different ratios and different Si O₂ carriers are prepared by melt impregnation.The study finds that the Li BH₄/SBA-15（47%）composite material has the best ionic transport characteristics as a solid electrolyte,which is attributed to the fact that the SBA-15 carrier provides a channel for the conduction of lithium ions in Li BH₄.At 35℃,the ionic conductivity of Li BH₄/SBA-15（47%）is 2.9×10^-2 m S cm^-1,and the activation energy is 0.59 e V.The electrochemical stability window of the electrolyte is 0～5 V,and it has good chemical stability and cycle performance to Li metal.（2）A series of LiBH₄/B₁₀H₁₄ composite solid electrolytes in different ratios are prepared by one-step heat treatment,and the ratio of Li BH₄ and B₁₀H₁₄ is adjusted to control the generation content of different kinds of polyanionic substances in the composite solid electrolyte.Studies have find that the Li BH₄/B₁₀H₁₄（40%）composite material has the best ionic transport characteristics as a solid electrolyte,which is attributed to the higher ionic conductivity of Li₂B₁₀H₁₀ generated in the composite solid electrolyte.At 35℃,the ionic conductivity of Li BH₄/B₁₀H₁₄（40%）is 3.0×10^-2 m S cm^-1,and the activation energy is 0.43e V.The electrochemical stability window of the electrolyte is 0～5 V and it has good compatibility with Li metal.However,its cycle performance needs to be further improved.（3）LiBH₄/SBA-15/B₁₀H₁₄ composite solid electrolytes in different proportions are prepared by eutectic method and in-situ generation method.Experiments have confirmed that the composite solid electrolyte produced by the in-situ method has better ion transport characteristics,and the ratio of raw materials also has an effect on ion transport.The LS/B₁₀H₁₄（60%）composite material has the best ionic transport characteristics as a solid electrolyte which is attributable to the synergistic effect of nano-confinement and polyanions.At 35℃,the ionic conductivity of LS/B₁₀H₁₄（60%）is 4×10^-2 m S cm^-1,and the activation energy is 0.35 e V.The electrochemical stability window of the electrolyte is 0～5 V,and it has good stability to Li metal and cycle performance.