Solid Electrolytes and Dendrite Dynamics in Solid-State Lithium–Sulfur Batteries

As the demand for safer lithium batteries grows, the quality of solid electrolytes, a critical component for solid-state lithium batteries (SSLBs) construction, has become increasingly important. SSLBs typically underperform compared to conventional batteries with liquid electrolytes. In this study, two ceramic-based composite solid electrolytes (CSEs) with differing dispersion qualities were prepared, consisting of dispersion-treated and as-received Li6.4La3Zr1.4Ta0.6O12 (LLZTO) particles within a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) matrix. These two CSEs were assembled with a sulfur cathode into solid-state lithium–sulfur batteries (SSLSBs) and assessed using electrochemical impedance spectroscopy and distribution of relaxation times to investigate factors affecting battery performance. To clarify the individual contributions of the cathode and anode, a three-electrode configuration was employed, allowing a more detailed understanding of the internal processes of SSLSBs. Additional techniques, including critical current density testing, in situ optical microscopy for lithium dendrite observation, and finite element simulations, were utilized to evaluate the impact of LLZTO and PVDF-HFP dispersion uniformity on electrolyte and cell performances. Results reveal that low-quality CSEs led to uneven charge transport and increased lithium dendrite formation during cycling, significantly reducing battery lifespan. Importantly, while CSEs can mitigate the shuttle effect, uncontrolled lithium dendrite growth emerged as a primary cause of capacity decline and cell failure for solid-state batteries.