Correlating the Microstructure and Current Density of the Li/Garnet Interface

Abstract

Solid-state lithium batteries hold great promise for next-generation energy storage systems. However, the formation of lithium filaments within the solid electrolyte remains a critical challenge. In this study, we investigate the crucial role of morphology in determining the resistance of garnet-type electrolytes to lithium filaments. By proposing a new test method, namely, cyclic linear sweep voltammetry, we can effectively evaluate the electrolyte resistance against lithium filaments. Our findings reveal a strong correlation between the microscopic morphology of the solid electrolyte and its resistance to lithium filaments. Samples with reduced pores and multiple grain boundaries demonstrate remarkable performance, achieving a critical current density of up to 3.2 mA cm–2 and excellent long-term cycling stability. Kelvin probe force microscopy and finite element method simulation results shed light on the impact of grain boundaries and electrolyte pores on lithium-ion transport and filament propagation. To inhibit lithium penetration, minimizing pores and achieving a uniform morphology with small grains and plenty of grain boundaries are essential.

Lithium Dendrite Propagation in Ta-Doped Li7La3Zr2O12 (LLZTO): Comparison of Reactively Sintered Pyrochlore-to-Garnet vs LLZTO by Solid-State Reaction and Conventional Sintering

“…The SSR pellets also shorted at a “critical voltage” of ∼0.3–0.5 V, similar to the findings by others, , where LSV on LLZTO prepared by SSR displayed shorting at ∼0.4 V. In contrast, the critical voltage for the P2G pellets was more than doubled. P1, which had the highest relative density and ionic conductivity, showed a critical voltage of ∼1 V and a CCD of 1.11 mA/cm 2 .…”

“…This is similar to the results and explanation reported by Cheng et al , where fine-grained LLZTO was prepared by attrition milling of SSR powders and displayed improved cycling performance compared to large-grained samples . Ouyang et al arrived at a similar conclusion and further highlighted the benefit of using small-grained LLZO with minimal pores to achieve higher CCD compared to that achieved using large-grained LLZO . Su et al also showed that fine-grained Ga-doped LLZO prepared using two-step sintering displayed better resistance to cracking after exposure to Li compared to samples with larger grains, some of which displayed abnormal grain growth .…”

“…However, since LSV is unidirectional, the interface where plating takes place should be void free. This is believed to be the reason for the higher CCDs seen in LSV measurements compared to the galvanostatic measurements. , …”

“…13 Ouyang et al arrived at a similar conclusion and further highlighted the benefit of using small-grained LLZO with minimal pores to achieve higher CCD compared to that achieved using large-grained LLZO. 56 Su et al also showed that fine-grained Ga-doped LLZO prepared using two-step sintering displayed better resistance to cracking after exposure to Li compared to samples with larger grains, some of which displayed abnormal grain growth. 63 The authors proposed that LLZO pellets with more homogeneous grain size can endure higher stresses, since such cracks could form from lattice volume changes when Li enters the LLZO structure.…”