Sulfide Solid Electrolytes Based All-solid-state Lithium Batteries

Lithium ion batteries have been widely applied in portable electronic devices such as mobile phones and lap tops,and further extended their application in electronic vehicles and large-scale energy storage devices.However,commercial lithium ion battery employing organic liquid electrolyte has nearly reached its energy density limit and possesses potential safety hazard.By utilizing nonflammable inorganic instead of organic liquid electrolyte,the safety performance of all-solid-state lithium battery can be greatly improved,and the application pf metallic lithium anode could be realized,which could further improve energy density,service life and storage time.Due to high safety performance,high energy density and wide operation temperature range,all-solid-state lithium battery is considered as one of the ultimate solutions to address the safety issues of lithium battery such as thermal runaway and electrolyte leakage.As one of the crucial technologies in the high-energy battery research field,the all-solid-state battery has received much attention for both academic and industrial communities.Lithium superionic conductor（LISICON）solid electrolytes are key components for high safety all-solid-state lithium battery.The lithium ionic/electronic conductivities,electrochemical window,and chemical/electrochemical stability are vital parameters and major evaluation indicators of the solid electrolytes.Compared with other solid electrolytes,sulfide electrolyte possesses superior conductivity,better mechanical ductility and good electrode/electrolyte interfacial compatibility,making it most promising solid electrolyte for all-solid-state lithium batteries.However,in order to realize high energy density all-solid-state lithium battery with good safety,the ionic conductivity of the sulfide electrolyte should be further improved.In addition,the chemical/electrochemical stability of the sulfide electrolyte should be enhanced to mitigate the side reactions between sulfide electrolyte and electrode materials.Moreover,the solid electrolyte layer in present all-solid-state lithium battery is thick and heavy,which hinders the improvement of energy density of all-solid-state lithium battery.As a result,this dissertation concentrates on improving the ionic conductivity and chemical/electrochemical stability of the sulfide electrolyte and reducing the thickness of the sulfide electrolyte layer in the all-solid-state lithium battery,so as to realize high energy density all-solid-state lithium battery.The main contents are listed as following.1.The enhancement of ionic conductivity of sulfide electrolyteFirstly,we focused on Li₃PS₄ sulfide electrolyte.On the basis of computational analysis of high throughput material genome engineering,Zn O is selected as dopant to perform dual doping on Li₃PS₄ for the first time.Through high energy ball-milling,a new sulfide electrolyte of Li_3+3xP_1-xZn_xS_4-xO_x（x=0.01～0.06）were successfully synthesized.Via doping,partial P⁵⁺is substituted by Zn²⁺,and a part of S^2-is replaced by O^2-.The substitution of larger ions enlarges the Li⁺migration channel and introduces more Li⁺into the crystal structure,resulting in highly conductive Li_3+3xP_1-xZn_xS_4-xO_x（x=0.02）solid electrolyte.The Li_3.06P_0.98Zn_0.02S_3.98O_0.02 electrolyte material exhibits good stability against lithium and air.Through first-principles density functional theory（DFT）calculation and bond valence（BV）analysis,the crystal structure and ion migration barrier have been analyzed to gain deep understanding of the influence of Zn O dual doping on Li₃PS₄ electrolyte and the mechanism of the performance improvement of the electrolyte.The Li Co O₂/Li₁₀Ge₂PS₁₂/Li_3.06P_0.98Zn_0.02S_3.98O_0.02/Li all-solid-state lithium battery was assembled and cycled for 100 cycles at 0.1 C,showing a reversible capability of 112.7 m Ah g^-1.To further improve the ionic conductivity of sulfide electrolyte,argyrodite sulfide electrolyte Li₆PS₅Cl with higher conductivity is investigated.By analyzing the crystal structure and Li⁺migration mechanism of Li₆PS₅Cl,Br doping is employed to enhance its ionic conductivity.Through high energy ball-milling method followed by multiple-sintering,Li₆PS₅Cl_xBr_1-x（x=0.1,0.3,0.5,0.7,0.9）was synthesized.The Li₆PS₅Cl_0.5Br_0.5electrolyte shows the highest ionic conductivity of 10.01 m S cm^-1 with the lowest activation energy of 0.26 e V.In addition,Li₆PS₅Cl_0.5Br_0.5 exhibits small and uniform electrolyte particle size and outstanding stability against lithium.The SPAN/Li₆PS₅Cl_0.5Br_0.5/Li all-solid-state lithium battery shows reversible capacities of839.7 m Ah g^-1 for 200 cycles at 0.1 C and 468.5 m Ah g^-1 for 1000 cycles at 0.5 C.2.The interfacial modification for high voltage application at the electrode/electrolyte interfaceLi₆PS₅Cl possessing high conductivity and good compatibility with Li Ni_0.5Mn_1.5O₄（LNMO）is chosen as electrolyte material to assemble 5V all-solid-state battery.To effectively passivate and stabilize the cathode/electrolyte interface and inhibit the side reactions,pristine LNMO particles with cubic spinel structure were rationally designed to be coated by Li Nb O₃,Li₃PO₄ and Li₄Ti₅O₁₂ with various amounts through a facile,cost-effective and scalable wet-chemistry approach.Electrochemical characterization reveals that the Li Nb O₃ and Li₃PO₄-coated LNMO cathodes in combination with argyrodite Li₆PS₅Cl solid electrolyte can enable the operation of 5V-class all-solid-state batteries,while Li₄Ti₅O₁₂-coated LNMO cathode cannot be cycled.More specifically,8 wt.%Li Nb O₃-coated LNMO demonstrated the best electrochemical performance with an initial discharge capacity of 115 m Ah g^-1,which gradually decreased to～80 m Ah g^-1 at the 20th cycle.In order to further improve the cycling stability of all-solid-state battery,dense Li₆PS₅Cl electrolyte pellet with smooth surface is obtained.The Li₆PS₅Cl electrolyte pellet shows high ionic conductivity of 6.11 m S cm^-1 at 25 ^oC and good dendrite-suppressing capability.The critical current densities of pellet-sintered Li₆PS₅Cl annealed for 4h reach 1.05 m A cm^-2 and 2.45 m A cm^-2 at 25 ^oC and 100 ^oC,respectively.The Li/pellet-sintered Li₆PS₅Cl/Li cell exhibits outstanding cycling stability for 3000 h at 0.5 m A cm^-2 at 25 ^oC.Furthermore,the Li Co O₂/pellet-sintered Li₆PS₅Cl/Li battery possesses superior electrochemical performances in terms of excellent rate capability as well as high cycling stability,showing 92.6 m Ah g^-1 with capacity retention of 80.3%after 100 cycles at 0.35 m A cm^-2 and 25 ^oC.This work provides an effective strategy to improve dendrite suppression capability of Li₆PS₅Cl solid electrolyte and paves the way for the application of lithium metal in all-solid-state lithium batteries.3.The preparation of sulfide electrolyte thin film and the enhancement of energy density of the all-solid-state lithium batteryTo avoid the undesired reaction between sulfide electrolyte and water,a novel polydopamine coating strategy using organic alkali solution is utilized for the surface modification of Li₆PS₅Cl particles to obtain adhesive surface.Upon surface modification,a 5 nm-thick continuous and homogeneous polydopamine layer is coated on the Li₆PS₅Cl particle,and a compact free-standing polydopamine-coated Li₆PS₅Cl thin film with a thickness of 35μm could be easily prepared with cold pressing,which was further employed in the ASSLBs.The Co₃S₄/polydopamine-coated Li₆PS₅Cl/Li ASSLB exhibits a reversible capacity of 485.1 m Ah g^-1 after 100 cycles at 0.1 C and a good rate capability of 662.6,552.8,355.6,and 226.4 m Ah g^-1 at 0.1,0.2,0.4,and 0.5C,respectively.With elevated cathode loading to 6.37 mg cm^-2,the full-cell level energy density could reach 284.4 Wh kg^-1.More importantly,this strategy could be further applied in the preparation of different thin film electrolyte and provides a new route for development of high energy density all-solid-state batteries.