Positive And Negative Interface Modification And Performance Regulation Of Lithium Lanthanum Zirconium Oxide Solid-state Batteries

The solid-state battery（SSB）is considered as the best alternative to liquid lithium battery,which has high safety and high energy density.However,in SSBs,the interfaces between solid-state electrolytes（SSEs）and electrodes have severe challenges.For example,it is difficult to form a compact and continuous conductive interface between the SSEs and the electrodes,bringing a large resistance to the electrode/electrolyte interface.In addition,the granet-type Li_6.4La₃Zr_1.4Ta_0.6O₁₂（LLZTO）SSE can spontaneously react with the humid air to form the surface lithium carbonate impurities,which leads to the non-wettability against molten lithium.In view of the above challenges faced by LLZTO SSE,we have worked on the interfacial modification at LLZTO/electrodes and the surface treatment of LLZTO SSE.The relevant results are shown below:（1）By introducing trace ionic liquid into the interface between the LLZTO SSE and the LiNi_0.6Co_0.2Mn_0.2O₂（NCM622）cathode,a stable and conductive interface between the LLZTO and the NCM622 is achieved.Based on this interfacial modification strategy,the interface polarization is dramatically reduced.At the rates of 0.2,0.5,and 1.0 C,the NCM622 full batteries deliver the initial discharge capacities of 163.5,148.8,and 131.2mAh g^-1,respectively.In addition,the high capacity retention rate of 87.6%after 100 cycles is obtained.（2）To improve the interfacial contact and boost the Li⁺transfer between the LLZTO SSE and the Li anode,the trace ether electrolyte with high ionic conductivity and superior wettability is introduced into the LLZTO/Li interface.Based on this interface modification strategy,the close solid-solid conductive contact and low interface impedance are realized.In addition,the Li symmetric batteries can be stably cycled with the small overpotential at different current densities(0.2,0.5,and 1.0 mA cm^-2).More importantly,the critical current density of LLZTO SSE is enhanced to 2.1 mA cm^-2.（3）The lithium carbonate impurities on the LLZTO surface are removed by polishing,phosphoric acid,and hydrochloric acid treatment.The specific time of erasing the surface contaminations by acid treatment is determined by XRD,Raman,and XPS techniques.Based on the detailed results,the polishing treatment can not completely remove the impurity layer on the LLZTO surface,while hydrochloric acid treatment for 5 s or phosphoric acid treatment for 30 s can completely remove the lithium carbonate impurities.After the acid treatment,the LLZTO electrolyte shows the small contact angle against the molten Li and the stable charging/discharging cycles.