Here, we investigate the doping effects on the lithium ion transport behavior in garnet Li₇La₃Zr₂O₁₂ (LLZO) from the combined experimental and theoretical approach. The concentration of Li ion vacancy generated by the inclusion of aliovalent dopants such as Al³⁺ plays a key role in stabilizing the cubic LLZO. However, it is found that the site preference of Al in 24d position hinders the three dimensionally connected Li ion movement when heavily doped according to the structural refinement and the DFT calculations. In this report, we demonstrate that the multi-doping using additional Ta dopants into the Al-doped LLZO shifts the most energetically favorable sites of Al in the crystal structure from 24d to 96 h Li site, thereby providing more open space for Li ion transport. As a result of these synergistic effects, the multi-doped LLZO shows about three times higher ionic conductivity of 6.14 × 10⁻⁴ S cm⁻¹ than that of the singly-doped LLZO with a much less efforts in stabilizing cubic phases in the synthetic condition.

Despite significant advancements in all‐solid‐state batteries (ASSBs), the reliance on thick solid electrolyte (SE) membranes hinders their commercial viability. Although the dry process using polytetrafluoroethylene (PTFE) binder is proposed for thin SE membranes, a comprehensive understanding of the correlation between PTFE fibrillation and SE membrane quality remains lacking. Here an important guidance is provided for producing durable SE membranes that can be reduced to sub‐20‐µm thickness by regulating the entanglement networks of PTFE. While establishing fabrication parameters; shear time and shear temperature, a dominant effect of the number‐average molecular weight (M _n ) on PTFE fibrillation is revealed for the first time. Moreover, the degree of PTFE fibrillation is quantified using systematic X‐ray diffraction (XRD) analysis. The SE membrane utilizing the high‐M _n PTFE binder that achieves a maximum fibrillation degree (≈98%) and thus forms highly entangled fibrous PTFE network interweaving SE particles, exhibited superior toughness. Consequently, the 18 µm thick SE membrane with 0.5 wt% high‐M _n PTFE shows a considerably higher areal conductance. The ASSB using this durable, ultrathin SE membrane outperforms its counterparts that used flimsy SE membranes or pure SE pellets. Finally, uniquely thin ASSBs demonstrate significantly improved cell‐level energy densities, showcasing the promising potential for practical ASSB fabrication.

Developing all solid-state batteries (ASSBs) employing inorganic solid electrolytes is currently attracting much attention due to their possibility of improved safety in a wide operating temperature range and increased energy density compared to those from traditional lithium ion batteries. Among various kinds of solid electrolytes (SEs), sulfide SEs are widely recognized as one of the most promising candidates as they exhibit high lithium ion conductivity comparable to that of liquid electrolytes. However, it is well realized that sulfide SEs have a limited electrochemical potential window, which is closely linked to unfavorable side reactions with other components (e.g., active materials, conductive carbon, and binders) during battery operation. Herein, for the first time, we reveal a parasitic reaction of nitrile butadiene rubber (NBR), mainly used in the fabrication of wet-process electrodes for ASSBs, and also systematically investigate the chemical decomposition of nitrile substitutions in NBR, resulting in a huge interfacial resistance in the sulfide-composite electrode. To address this challenge, we propose modifying the chemical stability of nitrile groups by introducing Li ions. This modification helps suppress side reactions during the initial charge–discharge process and ultimately enhances battery performance.

Here, we investigate the nonlinear relationship between the content of solid electrolytes in composite electrodes and the irreversible capacity via the degree of nanoscale uniformity of the surface morphology and chemical composition of the solid electrolyte interphase (SEI) layer. Using electrochemical strain microscopy (ESM) and X-ray photoelectron spectroscopy (XPS), changes of the chemical composition and morphology (Li and F distribution) in SEI layers on the electrodes as a function of solid electrolyte contents are analyzed. As a result, we find that the solid electrolyte content affects the variation of the SEI layer thickness and chemical distributions of Li and F ions in the SEI layer, which, in turn, influence the Coulombic efficiency. This correlation determines the composition of the composite electrode surface that can maximize the physical and chemical uniformity of the solid electrolyte on the electrode, which is a key parameter to increase electrochemical performance in solid-state batteries.