Kota Motohashi

Aluminum (Al) is a promising alloy-type anode material for all-solid-state rechargeable lithium (Li) batteries (SSBs) owing to its high theoretical specific capacity, abundance, low cost, and recyclability. However, mechanical degradation during lithiation/delithiation and limited Li diffusion kinetics remain critical challenges in the application of Li–Al alloy (LixAl: 0 < x < 1 at room temperature) in SSBs. This study explores the use of nanoporous aluminum (NPAl) sheets as a potential approach to mitigate these challenges. NPAl sheets were fabricated via a galvanic replacement reaction method, resulting in bundles of Al filaments with an interfilament spacing of ∼200 nm. Compressed NPAl sheets (∼13 μm in thickness and with 17% porosity) were used as anodes and assembled into SSBs utilizing a Li6PS5Cl (LPSCl) solid electrolyte and a Li–In alloy counter electrode. Scanning electron microscopy observations confirmed that the nanoporous structure accommodated volume expansion during initial lithiation and suppressed crack formation upon delithiation. Backscattered electron images suggested that fast surface diffusion promoted long-range Li diffusion within NPAl anodes. Also, the NPAl anode reduced part of the interfacial resistance compared with the dense Al foil anode. Notably, the NPAl anode exhibited a capacity of 618 mAh g–1 (1.97 mAh cm–2) at 0.1 C after 50 cycles at 25 °C. The results suggest that nanoporous architecture leads to distinct mechanical and Li transport behaviors, offering an alternative design strategy for Li–Al alloy anodes for SSBs.

All-solid-state potassium batteries have attracted considerable attention as energy storage devices. The development of suitable ionic conductors has received significant attention for the commercialization of the batteries. Here, we report the potassium-ion conductors KTaCl6 prepared using the mechanochemical method and then heat treatment. The mechanochemically prepared sample comprises the monoclinic crystalline phase embedded within the amorphous component, as revealed by X-ray diffraction and transmission electron microscopy. The mechanochemically prepared sample exhibits an ionic conductivity of 1.8 × 10−5 S cm−1 at 30 °C. Upon heat treatment, the sample undergoes crystallization, leading to a decrease in ionic conductivity. It is suggested that the amorphous phase plays a key role in the ion conduction of the KTaCl6 chlorides.

The development of solid electrolytes with a high ionic conductivity is crucial for realizing all-solid-state sodium batteries. Chloride solid electrolytes, particularly NaTaCl6, have garnered significant attention because of their high conductivity, favorable formability, and good electrochemical stability at high potentials. Mechanochemically synthesized NaTaCl6 consists of both amorphous and crystalline phases, with the former being closely associated with its high ionic conductivity. In this study, xZrO2·NaTaCl6 (x = 0–2) samples were prepared by the mechanochemical method, in which the addition of ZrO2 is intended to facilitate the amorphization of the NaTaCl6 crystalline phase. This approach yielded NaTaCl6 with nanocrystalline ZrO2 particles dispersed in the amorphous phase. The 1.1ZrO2·NaTaCl6 sample exhibited an ionic conductivity of 1.3 × 10–3 S cm–1 at 25 °C and an electrochemical stability window of approximately 1.4–4.1 V versus Na+/Na. The amorphization of NaTaCl6, induced by the addition of ZrO2, contributed to its high ionic conductivity and improved electrochemical stability. This study demonstrates that the amorphization of NaTaCl6-based solid electrolytes leads to enhanced ionic conductivity.

Sodium-ion-conducting chlorides, particularly NaTaCl6, have attracted attention for their high ionic conductivity and oxidation stability. Here, NaTaCl6−xFx (x = 0–6) was synthesized by mechanochemical treatment to improve electrochemical stability. F doping decreased ionic conductivity, whereas NaTaCl5.75F0.25 exhibited an electrochemical potential window of 1.5–4.1 V vs. Na+/Na and stable cycling for 50 cycles at 60 °C in an all-solid-state cell. These results suggest that F doping effectively tunes the electrochemical stability of NaTaCl6-based solid electrolytes.

Li6PS5Cl argyrodite sulfide electrolytes exhibit high ionic conductivity, making them promising candidate electrolyte materials for all-solid-state batteries. Although water is an environmentally friendly and attractive solvent, its use in the synthesis of Li6PS5Cl has been limited due to the low moisture stability of Li6PS5Cl. In this study, Li6PS5Cl argyrodite sulfide electrolytes were synthesized via liquid-phase synthesis using water as the main solvent through optimization of both the synthesis conditions and the composition of the Li3PS4·Li2S·LiCl precursor. In this process, the precursor is formed via the aqueous phase, followed by heat treatment that drives the crystallization of Li6PS5Cl and improves its crystallinity. A series of electrolyte samples derived from precursors with varying Li3PS4 contents, xLi3PS4·Li2S·LiCl (x = 1.0–1.4), were systematically prepared and characterized, revealing their structural and electrochemical properties. The electrolyte derived from the optimal precursor composition (x = 1.2) exhibited a high ionic conductivity of 1.2 × 10–3 S cm–1 at 25 °C in a green compact, and the all-solid-state cells assembled using this electrolyte demonstrated reversible charge–discharge behavior over 100 cycles at room temperature. These results demonstrate that water can be successfully used as the main solvent to synthesize argyrodite-type sulfide electrolytes and provide a versatile strategy for sustainable production of high-performance sulfide solid electrolytes suitable for practical use.

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The development of a mass production process for sulfide electrolytes is crucial for the advancement of all-solid-state batteries. In this context, liquid-phase synthesis has gained attention as a practical and scalable approach for the synthesis of these materials. However, conventional liquid-phase synthesis typically employs organic solvents, which pose both environmental and safety concerns. In this study, a novel liquid-phase synthetic strategy is presented for the preparation of sulfide electrolytes using an aqueous solution, which eliminates the requirement for organic solvents. Consequently, a Li₁₀GeP₂S₁₂ electrolyte was successfully synthesized, and was demonstrated to exhibit an ionic conductivity of 1.6 × 10^-3 S cm^-1 at 25 °C in a powder compact. Additionally, an all-solid-state Li-In/LiNi_1/3Co_1/3Mn_1/3O₂ cell incorporating the developed electrolyte demonstrated stable and reversible cycle performances over 500 cycles. Overall, this work demonstrates the feasibility of using water as an environmentally friendly solvent for synthesizing high-performance sulfide electrolytes.

Li-rich layered oxides offer high capacities for solid-state batteries. However, they suffer from sluggish ion transport, interfacial side reactions, and structural instability. Herein, we address these limitations using an amorphous-based LiNiO₂-Li₂MnO₃-Li₂SO₄ positive electrode that couples an S-enriched amorphous matrix with Ni-enriched nanocrystalline domains. A two-step process, in which LiNiO₂ and Li₂MnO₃ react prior to the addition of Li₂SO₄, suppresses Ni/Mn segregation and eliminates highly oxidized Li-Ni-O domains formed during charge-discharge reactions. In situ scanning transmission electron microscopy with electron energy-loss spectroscopy directly visualizes the evolution of the Li distribution and electronic states of O and Ni during cycling, confirming that both the nanoparticles and the amorphous matrix are electrochemically active, whereas localized deep charging is absent. The ductile amorphous-crystalline framework accommodates reversible volume changes without cracking and interfacial delamination. Consequently, sulfide-based solid-state cells obtained using the two-step synthesis route delivered 173 mAh/g initially and retained 79% capacity after 300 cycles at an aggressive 4.6 V vs Li cutoff voltage without any positive electrode coating. These findings demonstrate that cation homogeneity, nanoscale particle-size control, and flexibility provided by the amorphous matrix act synergistically to enhance the potential of Li-rich positive electrodes in solid-state batteries. The synthesis strategy and mechanistic insights presented herein provide a clear roadmap for the design of robust, high-capacity amorphous-based positive electrodes with extended lifetimes.

The elastic moduli of approximately 40 sodium-ion conductors were calculated. Sulfide-, chloride-, and hydride-based materials generally exhibit low elastic moduli and high B / G , whereas oxide materials exhibit high elastic moduli and low B / G .