Preparation And Investigation Of Sulfide Electrolytes For All-solid-state Lithium Batteries

The application of the all-solid-state lithium batteries is limited by the immature preparation methods of solid electrolytes,low ionic conductivities,poor inteface contact between cathodes and electrolyte,low interface stabilitys of all-solid-state batteries.In our research,we design and fabricate the high-performance sulfide all-solid-state batteries by optimizing preparation conditions,modifying the composition of electrolytes,modifying the interfaces between electroldes and electrolytes and decreasing the thickness of solid electrolytes.We further investigate the mechanisms of lithium transport in solid electrolytes and charge/discharge processes of all-solid-state batteries by XRD,Raman,SEM,TEM and XPS analysis.Our research can provide theoretical basis and technical support for sulfide all-solid-state battereis.The main works can be summarized as follows:(1)Li7P3S11 sulfide solid electrolytes are fabricated by dissolution-evaporation approach using tetrahydrofuran(THF),acetonitrile(ACN)and mixed solvent of tetrahydrofuran and acetonitrile(THF&ACN).The solvent effect on the electrochemical performance of Li7P3S11 is investigated by electrochemical impedance spectroscopy and chronoamperometry tests.The Li7P3S11 electrolyte prepared by ACN has a high ionic conductivity of 0.97 mS cm-1 at 298 K and a low activation of 31.2 KJ mol-1,much better than other counterparts synthesized by THF and THF&ACN.Impressively,a wide and stable electrochemical window up to 5.0 V vs Li/Li+is demonstrated between the solid electrolyte prepared by ACN and lithium electrode.In addition,we analyze the mechanism of the influence of different solvents for the properties of sulifde electroltytes.(2)Taking Li7P3S11 sulfide solid electrolyte as the research object,we synthesize a nove high-quality MoS2-doped Li2S-P2S5(Li7P2.9S10.85Mo0.01)prepared by a facile method of high-energy ball milling plus annealing.Impressively,the obtained Li7P2.9S10.85Mo0.01 exhibits a high ionic conductivity of 4.8 mS cm-1 at room temperature,and a stable wide electrochemical window up to 5.0 V vs.Li/Li+.The MoS2-doped electrolyte is demonstrated to have more stablility on the lithium metal as compared to the Li7P3SI11 counterpart.In addition,all-solid-state Li-S cells are assembled based on Li7P2.9S10.85Mo0.01 electrolyte and show a high discharge capacity of 1020 mAh g-1.We also synthesize a lithium superionic conductor of Li7P2.9Mn0.1S10.71I0.3 as a solid electrolyte via high-energy milling.The Li7P2.9Mn0.1S210.7I0.3 glass-ceramic possesses a high ionic conductivity of 4.8 mS cm-1 at room terperature and a wide voltage stability up to 5.0 V vs.Li/Li+.All-sold-state Li-S batteries based on L17P2.9Mn0.1S10.7I0.3 electrolytes show a large capacity of 796 mAh g-1 and maintain a capacity around 800 mAh g-1 after 60 cycles.Furthermore,we compare the the mechanisms between all-solid-state and liquid Li-S batteries and clarify the advantages of all-solid-state Li-S batteries.(3)Sulfur/reduced graphene oxide(rGO)and Li9.54Si1.74P1.44S11.7Cl0.3 are synthesized to modify the cathode/electrolyte interface.In the composite cathode,the Li9.54Si1.74P1.44S11.7Cl0.3 powder is homogeneously mixed with the S/rGO composite to enhance the ionic conductivity.Coupled with a metallic Li anode and solid electrolyte,the designed Li9.54Si1.74P1.44S11.7Cl0.3-S/rGO composite cathode exhibits a high specific capacity and good cycling stability.A high initial discharge capacity of 969 mAh g-1 is achieved at a current density of 80 mA g-1 at room temperature and the cell retains a reversible capacity of over 827 mAh g-1.In addition,a uniform coating of Li7P3S11 solid electrolyte on MoS2 enlarges the contact area between the electrolyte and cathode and offers more active sites for Li+ insertion and extraction,leading to a high utilization of the active materials and excellent electrochemical performance.The all-solid-state batteries based on the MoS2/Li7P3S11 composite electrode exhibits a high initial discharge capacity of 868.4 mAh g-1 at 0.1 C with a high Coulombic efficiency and a high reversible capacity of 547.1 mAh g-1 is retained after 60 cycles.Due to the homogeneous coating,the obtained all-solid-state battery possesses excellent rate performance and cycling stability.(4)A LiF(or LiI)layer at the interface between Li and sulfide electrolyte and HFE(or I solution)penetrated inside in sulfide electrolyte are used to suppress the Li dendrite growth.Due to the high interface energy of LiF(or LiI),the interlayer shows high capability in suppressing Li dendrite and enhancing the electrochemical performance.Even if the Li dendrite breaks through LiF(or LiI)interlayer,the Li dendrite will be consumed by coated/penetrated HFE(or I)forming LiF(or LiI)thus preventing Li dendrite growth.The Li-Li symmetrical cell using LiF coated Li and HFE infiltrated sulfide electrolyte can be stably charge/dischrged for 200 cycles without Li dendrite formation in the room temperature at a current of 0.5 mA cm-2.Coupled with the LiNbO3@LiCoO2(LNO@LCO)cathode,the all-solid-state Li@LiF/Li7P3S11/LNO@LCO full cell exhibits a high initial reversible capcaity of 118.9 mAh g-1 at 0.1 mA cm-2 and retains 96.8 mAh g-1 after 100 cycles.Furthermore,the density functional theory(DFT)is used to calcalated the interface energy at Li/Li7P3S11,Li/LiF and Li/Lil to understand the interface stability and Li dendrite suppression capability.(5)A novel reinforced concrete methode for synthesizing thin sulfide solid electrolyte film is used to overcome the mechnical breakages during preparation by dropping Li3PS4 suspension into a Kevlab Fiber,which provides a support to electrolytes and enables the fabrication of all-solid-state with high energy densities.In addition,3D stainless-steel mesh is introduced into the cathode to improve the Li2S loading.A Li-Li2S solid cell employing Li3PS4-Kevlab fiber as thin electrolyte and Li2S@LiI composites as cathode reaches a high reversible discharge capacity of 949.9 mAh g-1 at 0.05 C with a Li2S loading of 2.54 mg cm-2 and shows a high rate performance at room temperature.Benefiting from the thin solid electrolyte film,the fabricated all-solid-state cell with 7.64 mg cm-2 Li2S loading exceeds the cell-based energy density of 370 Wh kg-1 for the first time in the reported solid cells with sulfide electrolytes.