Solid-state batteries could greatly boost current Li-ion technologies; they are expected to endure tens of thousands recharges, pack 2-3 times more energy as well as being safe from combustion and non-toxic. However, a widespread application of solid-state batteries is still far from being achieved owing mainly to limitations of the solid electrolyte component. Key challenges are achieving high ionic conductivity-in the range of 1 mS/cm-, good interfacial contact with the electrodes and easy/cost efficient processing. Among ceramic electrolytes, the garnet family Li₇La₃Zr₂O₁₂ (LLZO) is one of the most promising because of its high lattice conductivity for Li ion and its wide electrochemical stability [1],[2]. Unfortunately, these garnet-type materials often show highly resistive grain boundaries and have proven difficult to process into dense ceramic bodies.

In this presentation I will show our research on developing high-performance LLZO solid electrolytes. By using a wide variety of techniques, such as solid-state NMR, XRD, SEM and EIS, as well as DFT simulations, we investigate the role of crystal chemistry, doping and processing to the total conductivity and sintering properties of the ceramic electrolyte. I will particularly focus on the fundamental understanding and enhancement of ionic conductivity via substitutional doping of Li⁺ by Ga³⁺, which led to values as high as 1.3 mS/cm for Li_6.55Ga_0.15La₃Zr₂O₁₂ at room temperature[3]. Alternative substitutions on the Zr⁴⁺ site can lead to a wider range of compositional possibilities and even higher conductivity values. The implementation of these LLZO garnet electrolytes into full cell devices, with LFP or LCO as cathode and Li metal as anode, will be also presented.

Finally I will report on a novel solid electrolyte concept based on the combination of doped LLZO garnets and polymeric Li-ion conductors, such as polyethylene oxide (PEO). These ceramic-polymeric composites show great promise as solid electrolyte membranes given the superior mechanical and interfacial properties compared to pure ceramics.