Yukio Cho

Lithiophilic and conductive TiN-coated copper current collectors facilitate the formation of faceted crystalline lithium seeds at moderate current densities.

Sodium–sulfur (Na–S) batteries are hindered by sluggish sulfur conversion kinetics and polysulfides dissolution. Although catalysts are widely introduced to improve kinetics, the crucial question persists in how catalytic sites can be effectively accessible to polysulfides especially when pursuing a highly confined sulfur redox pathway. Here we bring catalyst accessibility into focus and demonstrate that a synthetic strategy based on in situ embedded catalytic sites maximizes catalytic accessibility and efficiency. Through a bottom‐up, precursor‐integrated host synthesis route, we in situ embedded Nb ₂ O ₅ catalyst into carbon nanotubes in parallel with formation of extensive nanoporosity. Subsequent sulfur impregnation yields a cathode structure (I‐Nb ₂ O ₅ @C–S) featuring abundant catalyst–pore–sulfur triple‐phase interfaces. As a result, I‐Nb ₂ O ₅ @C−S delivers among the most promising sulfur utilization in literature, achieving 1540 mAh g ⁻¹ at 0.1 C, and 1044 mAh g ⁻¹ at 3 C with a low‐capacity decay of 0.027% per cycle over 1500 cycles. In contrast, a counterpart with spatially isolated Nb ₂ O ₅ and sulfur exhibits deficient catalytic accessibility and negligible improvement in sulfur redox kinetics. Kinetic diagnostics, combined with niobium K‐edge and operando sulfur K‐edge x‐ray absorption spectroscopy, reveal that direct accessibility of catalytic sites to sulfur is essential for synergizing polysulfide confinement and kinetic improvement.

Interfacial polymerization (IP) offers a rapid and inexpensive method for fabricating thin polymer films. In this work, a one-step IP reaction between a triacyl chloride monomer and sulfonated diamine monomer is employed to add a dense, charge-selective sulfonated thin-film coating onto a commercial separator to improve selective transport in lithium-sulfur batteries. The coating effectively suppresses polysulfide shuttling, enhancing capacity retention, although at the expense of compromised rate performance due to hindered lithium conduction through the dense film. Fractional substitution of the trifunctionalized acyl chloride monomer for a difunctionalized analogue reduces the film cross-link density, which improves rate performance but decreases uniformity in film coverage. Uniform film coverage is achieved upon addition of a small fraction (0.25 wt %) of higher reactivity, nonsulfonated diamine in the IP reaction. This optimized thin film coating breaks the rate-capacity retention trade-off, enabling a capacity of 711.6 mAh g^-1 after 200 cycles at 0.5C while still reaching over 800 mAh g^-1 during rate testing at 2C.

The solid–electrolyte interphase (SEI) on lithium metal forms through electrolyte reduction at a dynamically evolving metal surface, yet how its chemistry and spatial organization develop during lithium plating and stripping remains poorly understood. Here, using a 1,2-dimethoxyethane (DME)/1 M lithium bis(fluorosulfonyl)imide (LiFSI) electrolyte system, we show that three-dimensional lithium growth drives spatiochemical segregation of interphase products into chemically heterogeneous domains that are mechanically reorganized during stripping into a porous electrolyte-retaining framework. Correlative X-ray photoelectron spectroscopy, scanning electron microscopy, nanoscale secondary ion mass spectrometry (NanoSIMS), and synchrotron X-ray absorption spectroscopy reveal that FSI^–-derived inorganic species, dominated by LiF, become enriched in regions spatially decoupled from oxygen-containing phases near the lithium surface. Stripping-induced contraction compacts these chemically distinct domains into confined intergranular volumes, where supersaturation promotes precipitation and consolidation, yielding a porous SEI that retains electrolyte-derived species within a buried pore network beyond the reach of surface-sensitive probes. Spatiochemical segregation thus couples interfacial reaction pathways to lithium chemo-mechanics, dictating interphase composition, architecture, and permeability. These findings establish a chemo-mechanical framework for SEI evolution and suggest strategies to mitigate electrolyte retention and interphase instability in lithium–metal batteries.

Interfacial polymerization (IP) offers a rapid and inexpensive method to fabricate thin polymer films. In this work, a one-step, scalable IP reaction between a tri-acyl chloride monomer and sulfonated diamine monomer is employed to add a dense, charge-selective sulfonated thin-film coating onto a commercial separator to improve selective transport in lithium-sulfur batteries. The coating effectively suppresses polysulfide shuttling, enhancing capacity retention, though at the expense of compromised rate performance due to hindered lithium conduction through the dense film. Fractional substitution of the tri- functionalized acyl chloride monomer for a di-functionalized analog reduces the film crosslink density, which improves rate performance but decreases uniformity in film coverage. Uniform film coverage is achieved upon addition of a small fraction (0.25 wt%) of higher reactivity, non-sulfonated diamine in the IP reaction. This optimized thin film coating breaks the rate-capacity retention tradeoff, enabling a capacity of 885.5 mAh g-1 after 100 cycles at 0.2 C while still reaching over 800 mAh g-1 during rate testing at 2 C.

Solid-state batteries (SSBs) hold notable promise for advancing energy storage technologies. However, their commercial viability is limited by the poor cycle stability and complex degradation mechanism. This study underscores the pivotal role of electro-chemo-mechanical interactions in driving the failure of SSBs. Leveraging advanced x-ray imaging and spectroscopy techniques, we analyzed LiNi _0.8 Mn _0.1 Co _0.1 O ₂ (NMC811) cathodes from cycled Li _x In||Li ₆ PS ₅ Cl (LPSC)||NMC811 SSBs, uncovering the interplay between microstructure, chemical heterogeneity, mechanical characteristics, and electrochemical performance. Our results show that revealing electro-chemo-mechanical interactions is essential to develop strategies to suppress the degradation of SSBs. Particularly, we revisit a LiNbO ₃ (LNO) coating layer to mitigate electrochemical degradation. The LNO@NMC811 cathode retains 116 milliampere-hours per gram after 200 cycles, showing excellent stability, while the uncoated NMC811 cathode keeps degrading over time, with suppressed chemical heterogeneity and mechanical failure. This work highlights the importance of synergizing advanced material design with coating techniques, ensuring uniform lithium flux and improving mechanical properties to achieve stable, high-performance SSBs.

Solution‐phase heterogeneous catalysts benefit from nanoscale dimensions, which maximize specific surface area and enhance catalytic activity. However, the ease of recovering such nanocatalysts depends on the design of the support materials, which are often particle‐like. Rigid 1D nanomaterials are proposed as supports that can enhance separability while offering high volumetric specific surface area for greater catalyst loading and activity. Here, aramid amphiphiles (AAs) are designed to spontaneously self‐assemble in water into high‐aspect‐ratio supramolecular nanotubes with tunable surface chemistry. These AA nanotubes exhibit high persistence lengths ( P = 750 ± 340 µm) and mechanical stiffnesses (3 N/m). Incorporating surface thiol groups enables immobilization of catalytic gold nanoparticles. The resulting AA nanotube‐gold nanoparticle complexes exhibit high catalytic activity, efficient recoverability via simple microfiltration, and sustained reusability over ten reaction cycles. This study demonstrates the utility of molecular self‐assembled 1D nanomaterials as versatile scaffolds for the reuse and recovery of nanoscale catalysts.

Performance often overshadows recyclability in contemporary battery designs, leading to sustainability challenges. Preemptive strategies integrating recyclable chemistry from the outset are thus increasingly critical for addressing the complexities in conventional recycling. Here we harness bio-inspired molecular self-assembly to create inherently recyclable battery materials. We use aramid amphiphiles that self-assemble in water through strong, collective hydrogen bonding and π–π stacking, forming air-stable, high-aspect-ratio nanoribbons with gigapascal-level stiffness. When processed into bulk solid-state electrolytes, these nanoribbons retain their ordered molecular arrangement and exhibit total conductivities of 1.6 × 10⁻⁴ S cm⁻¹ at 50 °C, Young’s moduli of 70 MPa and toughness values of 1 MJ m⁻³, despite being stabilized solely by reversible non-covalent bonds. We further demonstrate clean separation of battery components by exposing used cells to an organic solvent, which disrupts the non-covalent cohesion and reverts all battery components to their original forms. This study underscores the potential of molecular self-assembly for specialized recyclable designs in energy storage applications.

Area‐selective atomic layer deposition (AS‐ALD) is of increasing importance in nanostructure fabrication, and precursor selection is critical to realizing a successful process. This work explores the role of the precursor in achieving AS‐ALD of Al ₂ O ₃ on a dielectric (SiO ₂ ) in the presence of a metal (Cu/CuO _x ). Four different precursors—dimethylaluminum isopropoxide (DMAI), trimethylaluminum (TMA), triethylaluminum (TEA), and triisobutylaluminum (TIBA)—are tested against a benzenethiol (BT) inhibitor. BT forms monolayers on Cu, whereas on CuO _x it forms a thick crystalline multilayer composed of 1D‐coordination polymers of Cu‐thiolate (CuBT). This work observes that DMAI provides exceptional selectivity: 22 nm of Al ₂ O ₃ can be deposited on patterned substrates with 99.9% selectivity, and in the case of thick CuBT can achieve excellent pattern transfer on nanoscale patterns with well‐defined material interfaces. In contrast, none of the alkylaluminum precursors show significant selectivity, a result attributed to their miscibility in the CuBT multilayer leading to its degradation. This work proposes that the miscibility of the alkylaluminum precursors depends on ligand length and structure. The results show that the ligand‐dependent miscibility and subsequent degradation of CuBT impact the location of Al ₂ O ₃ nucleation. This study highlights new considerations for AS‐ALD process design to achieve high selectivity.

The use of atomic layer deposition (ALD) and molecular layer deposition (MLD) in energy sectors such as catalysis, batteries, and membranes has emerged as a growing approach to fine-tune surface and interfacial properties at the nanoscale, thereby enhancing performance. However, compared to the microelectronics field where ALD is well established on conventional substrates such as silicon wafers, employing ALD and MLD in energy applications often requires depositing films on unconventional substrates such as nanoparticles, secondary particles, composite electrodes, membranes with a wide pore size distribution, and two-dimensional materials. This review examines the challenges and perspectives associated with implementing ALD and MLD on these unconventional substrates. We discuss how the complex surface chemistries and intricate morphologies of these substrates can lead to non-ideal growth behaviors, resulting in inconsistent film properties compared to those grown on standard wafers, even within the same deposition process. Additionally, the review outlines the strengths and limitations of several characterization techniques when employed for ALD or MLD films grown on unconventional substrates, and it highlights a few example studies in which these growth methods have been applied for energy applications with a focus on energy storage. With ALD and MLD continuing to gain attention, this review aims to deepen the understanding of how to achieve controllable, predictable, and scalable deposition with atomic-scale precision, ultimately advancing the development of more efficient and durable energy devices.