Preparation And Electrochemical Performances Of Inorganic Solid Electrolytes For Solid-State Batteries

The rapid development of portable electronic devices,new energy vehicles and large-scale energy storage devices put forward higher demands for current secondary battery systems.Due to the use of flammable organic liquid electrolyte and intrinsic restriction of the intercalation chemistry mechanism,traditional Li/Na-ion batteries show potential safety hazards and limited energy density.Through replacing organic liquid electrolyte with non-flammable inorganic solid electrolyte,the resultant inorganic solid electrolyte based solid-state batteries exhibit significantly enhanced safety performances,meanwhile,the application of low-potential and high-capacity metal anode and high-voltage cathode could be achieved owing to excellent mechanical strength and wide electrochemical window of inorganic solid electrolyte,which can further improve energy densities.However,further improvement of the ionic conductivity of the electrolyte and prominent electrolyte/electrode interfacial issues are still huge challenges for inorganic solid electrolyte mainly including oxide and sulfide electrolyte.Thus,it is of great theoretical and practical value to optimize the ionic conductivity of inorganic solid electrolyte and the inorganic solid electrolyte/electrode interface for achieving superior performance solid-state batteries,and the corresponding research contents are as follows:1.High ionic conductivity and dendrite-resistant NASICON solid electrolyteFirstly,focusing on the NASICON oxide solid electrolyte with high air stability and excellent stability against sodium metal,the optimized Na_3.4Mg_0.1Zr_1.9Si_2.2P_0.8O₁₂electrolyte is obtained by simultaneously substituting the Zr⁴⁺and P⁵⁺in Na₃Zr₂Si₂PO₁₂ electrolyte with Mg²⁺and Si⁴⁺through solid-state reaction.The Na_3.4Mg_0.1Zr_1.9Si_2.2P_0.8O₁₂electrolyte has superior room temperature ionic conductivity of 3.6×10^-3S cm^-1,which is 17 times higher than that of pristine Na₃Zr₂Si₂PO₁₂.No short circuit of the Na/Na_3.4Mg_0.1Zr_1.9Si_2.2P_0.8O₁₂/Na symmetric battery is observed up to 2.0 m A cm^-2,and the symmetric battery displays stable sodium plating/stripping cycles for over 2000 h at 0.1 m A cm^-2 and 300 h at 1.0 m A cm^-2,showing outstanding dendrites suppression capability.The resultant Na_3.4Mg_0.1Zr_1.9Si_2.2P_0.8O₁₂ electrolyte is further employed in two-type all-solid-state batteries.The Na₃V₂（PO₄）₃/Na_3.4Mg_0.1Zr_1.9Si_2.2P_0.8O₁₂/Na all-solid-state battery maintains a discharge capacity of 93.3 m Ah g^-1 at 0.1C after 50 cycles and the Fe S₂/Na_3.4Mg_0.1Zr_1.9Si_2.2P_0.8O₁₂/Na all-solid-state battery delivers a discharge capacity of 173.1 m Ah g^-1 at 0.1C after 20 cycles under 60^oC,which show significantly improved reversible discharge capacities compared with those based on pristine Na₃Zr₂Si₂PO₁₂.2.High-performance flexible NASICON based solid electrolyte with 80 wt%inorganic contentDue to the solid-solid physical contact at the NASICON oxide electrolyte/cathode interface,the NASICON based solid-state batteries are hard to operate at room temperature.To alleviate the relatively low interfacial transport kinetics caused by point-to-point contact between NASICON electrolyte and cathode active particles,a flexible NASICON based solid electrolyte with 80 wt%Na_3.4Zn_0.1Zr_1.9Si_2.2P_0.8O₁₂ispreparedthroughcompounding Na_3.4Zn_0.1Zr_1.9Si_2.2P_0.8O₁₂particles with appropriate amount of polyethylene oxide and highly stable ionic liquid.The optimized flexible NASICON based solid electrolyte delivers high ionic conductivity of 1.48×10^-4 S cm^-1at 25^oC,outstanding thermal stability and good interfacial stability against sodium metal.The assembled NASICON based Na₃V₂（PO₄）₃//Na solid-state batteries show low charge-discharge polarization voltage,as well as demonstrate excellent rate performances and cycling stability with a capacity retention of 90.0%after 150 cycles at 0.5 C under 60^oC.At the same time,stable operation of NASICON based Na₃V₂（PO₄）₃//Na solid-state battery is successfully realized at room temperature,exhibiting an initial discharge capacity of 109.4 m Ah g^-1 with a capacity retention of 85.4%after 150 cycles at0.2C.Moreover,the NASICON based Na₃V₂（PO₄）₃//Na pouch battery exhibits impressive flexibility and safety.3.Long-cycling stable Li₁₀GeP₂S₁₂ based all-solid-state batteriesCompared with NASICON oxide solid electrolyte,Li₁₀GeP₂S₁₂ sulfide solid electrolyte as another representative inorganic electrolyte has intrinsic advantages in ionic conductivity and electrolyte-cathode contact,which is expected to further improve the long-cycling stability of solid-state batteries at room temperature.However,Li₁₀GeP₂S₁₂ is thermodynamically unstable with lithium metal,leading to continued Li₁₀GeP₂S₁₂ reduction at Li₁₀GeP₂S₁₂/Li interface.In order to stabilize the Li₁₀GeP₂S₁₂/Li interface,Li F-rich multifunctional protective layer,consisting of three functional components of Li F,carbon particles and C-F bond thin-layer,are in-situ constructed on the Li metal surface（Li@Li F）by spontaneous reaction between Li metal and poly（tetrafluoroethylene）at room temperature.Li F,as the main component,significantly suppresses the interfacial reaction due to low electronic conductivity and promote smooth lithium plating on the Li metal surface arising from high interface energy against Li.Meanwhile,carbon particles with excellent Li⁺affinity and strong polar C-F bond thin-layer enable homogeneous Li⁺flux as well as fast Li⁺migration across the Li F-rich interface,respectively.Consequently,in-situ constructed Li F-rich multifunctional protective layer enables significantly prolonged cycling stability and increased critical current density of 1.9 m A cm^-2 for Li₁₀GeP₂S₁₂ based symmetric lithium cell.The assembled Li@Li F/Li₁₀GeP₂S₁₂/Li Co O₂ all-solid-state batteries exhibit excellent rate capability and cycling stability at 25^oC,achieving reversible discharge capacity of 100.2 m Ah g^-1 with a high capacity retention of 80.9%after 300 cycles at 0.1 C.