Interface modification in solid-state lithium batteries based on garnet-type electrolytes with high ionic conductivity

The garnet-structure lithium-stuffed solid electrolyte Li7La3Zr2O12 is a promising candidate as lithiumion conductors for next-generation lithium batteries. We present a comprehensive investigation on the effect of alkaline-earth-metal elements (Ca, Sr, Ba) doping on the structure, mechanical and electrochemical properties in the garnet-type solution Li6.6La3Zr1.6Sb0.4O12. The crystal structure, micromorphology, bending strength, fracture toughness and ionic conductivity of Li(6.65)La(2.95)A(0.05)Zr(1.6)Sb(0.4)O(12) (A = Ca, Sr, Ba) samples are analyzed systematically by X-ray diffraction (XRD), scanning electron microscopy (SEM), three-point bending method, single edge notch beam and impedance analysis. The results show that alkaline-earth-metal ion substitution may increase the total Li-ion conductivity by promoting ceramic densification in combination with enhancing Li-ion concentration. Among the investigated compounds, Li6.65La2.95Ba0.05Zr1.6Sb0.4O12 samples show excellent performances with a relative density of 96.6%, bending strength of 148.2 +/- 2.1 MPa, fracture toughness of 0.94 +/- 0.055 MPa.m(1/2), Li-ion conductivity of 1.14 x 10(-3) S.cm(-1) as well as activation energy of 0.361 eV. Additionally, Li/garnet interfacial problems in the solid-state lithium batteries need to be addressed because the poor contact between the garnet electrolyte and Li electrode will cause large interfacial impedance and uneven Li-ion flux during cycling. A methodology is proposed to negate the Li/garnet interfacial impedance by screen-printing the Ag layer on the garnet. A decrease in the interfacial resistance from 986 to 136.7 Omega.cm(2) and a stable lithium stripping/platting profile at different current densities are observed, indicating a homogeneous Li-ion flux and appreciable electrochemical performance at Li/garnet interface. The fabricated full batteries with LiFePO4 cathode, modified garnet electrolyte and lithium metal anode show excellent cycling performances under high current density at room temperature. (C) 2021 Published by Elsevier Ltd.

Automated summary

The study thoroughly investigated the doping of alkaline-earth-metal elements in the garnet-structure lithium-stuffed solid electrolyte Li7La3Zr2O12, with Ba-doped samples showing the best performance. The results indicated that alkaline-earth-metal ion substitution can enhance the total Li-ion conductivity, promoting ceramic densification and increasing Li-ion concentration.