Optimization Of Anode Interface Buffer Layers For Inorganic Solid State Lithium Metal Batteries

Inorganic solid-state batteries(ISSBs)based on inorganic solid electrolytes(ISEs)have qualities in safety,energy density and designability,which is one of the most promising candidates for the next generation battery systems.The key of ISSBs is the ISEs.Li1.5Al0.5Ge1.5(PO4)3(LAGP)solid-state electrolytes and Li6.4La3Zr1.4Ta0.6O12(LLZTO)solid-state electrolytes possess good environmental stability,high Li-ion conductivity and are easy for preparation or preservation,which are potential to be applied in the ISSBs.However,poor physical contact,badly chemical stability and huge interfacial impedance at the ISEs/Li interface obstruct the application of ISSBs.To solve the problems of LAGP/Li interface and LLZO/Li interface,we constructed and further optimized the anode interface buffer layers.The main works are as follows:To solve the intrinsic thermodynamic instability of LAGP to Li anode and the high impedance at LAGP/Li interface,Bi buffer layer was constructed on the surface of LAGP to optimize the LAGP/Li interface(Bi@LAGP).As a result,Bi buffer layer not only enhanced the contact between LAGP and Li anode,but also inhibited the reduction of Ge4+by Li metal,and maintained the stability of the LAGP/Li interface.Therefore,the internal resistance of Li|Bi@LAGP|Li symmetric cell was reduced,the Cycle performances were improved,thus LFP|Bi@LAGP|Li full cell can exhibited a better battery performance in comparison to LFP|LAGP|Li full cell.However,obvious interfacial reaction was observed at the Bi@LAGP/Li interface after 300 h cycling,indicated that the LAGP/Li interface needed further optimization.The alloying reaction between Bi buffer layer and Li metal not only lead to the stress concentration at the interface,but also caused the diffusion of buffer layer element,thus the optimization effect from the buffer layer became lower as the electrochemical cycling.Cu metal has lower reactivity with Li metal,so that the Cu buffer layer could maintain the anode interface.Therefore,a Cu buffer layer was introduced on the surface of LAGP solid electrolyte(Cu@LAGP)to enhance the battery performances of both symmetric cells and full cells.In addition,the Cu buffer layer effectively optimize LLZTO/Li interface and realized a good cycle performance of Li|Cu@LLZTO|Li symmetric cell.To further promote the critical current density(CCD)of the Li|Cu@LLZTO|Li symmetric cell,the ability of Cu buffer layer in conducting Li+should be strengthened.Based on Cu buffer layer modified LLZTO/Li interface,a Cu-Al2O3/Al2Cu buffer layer was deposited on the surface of LLZTO by dual-target magnetron sputtering to enhance the Li+conductivity of the anode interface.The introduction of Cu-Al2O3/Al2Cu buffer layer uniformed the current density,avoid the growth of Li dendrites caused by excessive local current density,and finally improved the performances as well as CCD of the symmetric cells.The stability of the anode interface between ISSEs and Li anode would be further promoted if the rigid contact at the interface can be improved by the buffer layer.Therefore,DME liquid electrolyte dissolved with LiNO3 and CuF2 was added to the ISSEs/Li interface to remit the contact failure arose from the rigid contact.The in-situ reaction between CuF2 additive and Li anode constructed the LiF/Cu buffer layer,which restrain the interface reaction and the dendrites growth at LAGP/Li interface.Battery performance and CCD of the symmetric cells improved a lot according to electrochemical test results.In this study,we have optimized the anode interface buffer layer to promote the stability of the ISSEs/Li interface,so that the electrochemical performances of ISSBs was improved.However,the capacity and stability of the existing ISSBs are far away from the practical application requirements.Therefore,the performance of ISSBs needs to be further improved.