| Lithium ion batteries have become an irreplaceable and excellent energy storage device in modern society because of their high energy density,high output power,high voltage,and low self-discharge,making lithium ion batteries widely applied in our life.However,lithium dendrites are easily formed due to the uneven deposition of the lithium on the anode in traditional liquild electrolyte based lithium ion batteries,which may pierce the separator and cause internal short circuit of the battery.This leads to serious safety probloms and inhibites the development of lithium ion batteries.Replacing liquild eelectrolyte by solid electrolyte can fundamentally solve the safety problem.All-solid-state battery exhibits simple assembly process,high energy dfensity,long cycle life and large operating temperature range.An all-solid-state battery consists of cathode,anode and solid electrolyte.Among them,solid electrolyte is the key component.There are many kinds of solid electrolytes,including inorganic solid electrolyte?oxide,sulfide?,polymer and polymer/inorganic composite solid electrolyte.Among them,inorganic solid electrolyte materials have been widely used due to their advantages of nonflammability and nonvolatility,high mechanical strength and high temperature resistance.Lithium borohydride?LiBH4?has been extensively studied for its high lithium ion conductivity of up to 2×10-3 S cm-1 at 120°C due to the phase transformlation to P63mc phase.The ionic conductivity at room temperature is generally improved by doping LiBH4 or loading it into an electronically insulated nanopore for space confinement.However,the conductivity performance of the modified LiBH4 by a single method is still difficult to meet the requirements at room temperature,and further modification is highly needed.Based on the review of previous research work and related literatures,this paper takes Li BH4 material as the starting material,and through the method of synergistic treatment of doping and space confinement,a series of solid electrolytyes with high ionic conductivity and electrochemical window are prepared.In addition,the systematic study on the structural properties and electrochemical properties of the materials is also performed.The main work is listed as follows:?1?Doping modification and performance study of LiBH4-based solid electrolyte:combined with the inherent advantages of Li BH4 solid electrolyte material,different lithium salts were used to dope and modify LiBH4,and the mechanism of material preparation was studied by a preliminary structural characterization.The doping materials are Li NH2,LiI and lithium salts containing large anion groups such as Li BF4,LiPF6,LiAlH4,Li3PO4.Different types of doping modification of LiBH4 materials are achieved by high temperature calcination under high hydrogen pressure.By introducing different ions into LiBH4,the structure of LiBH4 is changed,and the ionic conductivity of LiBH4is promoted.The LiBH4-based solid electrolyte material with high lithium ion conductivity can also be prepared by adjusting the ratio of Li BH4 and lithium salt to optimize the conductivity performance.Compared with the pure LiBH4,the conductivity of the doped material can be improved by two orders of magnitude.At room temperature,the conductivity of the material can reach more than 5×10-5 S cm-1.?2?N-doping-space confinement and performance of LiBH4-based solid electrolytes:Based on the previous work,the following two strategies were adopted to achieve N-doping of LiBH4 to improve the ionic conductivity and other electrochemical propeties of Li BH4 at room temperature.?1?Selecting a certain stoichiometric ratio of LiBH4 and LiNH2 for ball milling,calcinate to achieve N-doping of Li BH4,and then loading N-doped LiBH4 into the SBA-15 channel by melt impregnation.Achieve the combined effect of N doping and space confinement processing of LiBH4.?2?A certain proportion of LiBH4 is loaded into SBA-15 to form a solid Li BH4@SBA-15 material,and then a gas molecule NH3 is selected to react with the material.Li BH4 and NH3 react to form Li BH4·NH3.Therefore,LiBH4 in the tunnel is N-doped.The electrical conductivity of the prepared material is excellent,which can reach more than 10-4 S cm-1 at room temperature.The selected mesoporous material SBA-15 has the advantages of low electron conductivity,controllable mesoporous pore size and high porosity,which is an ideal matrix for space confinement of materials.?3?LiI doping-space confinement and properties of LiBH4-based solid electrolytes:Li4?BH4?3I formed by Li BH4 after LiI doping can maintain the P63mc phase with higher conductivity at room temperature.Li4?BH4?3I was loaded into the pores of SBA-15,and the LiBH4-based solid electrolyte with high lithium ion conductivity at room temperature was prepared by adjusting the loading method and loading amount loaded into SBA-15material.The conductivity performance can reach 2.5×10-4 S cm-1.The electrolyte has a very good lithium anode stability,and Li-S and Li-LiCoO2 solid-state batteries assembled based on this electrolyte material show good cycle stability.In summary,in this paper,LiBH4 was doped with different types of lithium salts to screen out suitable lithium salts that are conducive to improving ionic conductivity.Then,based on the strategy of space confine,the synergistic optimization of LiBH4 doped composite and nanometer restriction was realized.Solid electrolyte materials with high ionic conductivity,wide electrochemical window and wide application range were prepared and applied to all solid state batteries.This work has important guiding significance for the research of complex hydride based electrolyte materials and provides a new idea for the design and development of solid electrolyte materials and solid state batteries. |
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