Extremely Superhydrophobic Surfaces with Micro- and Nanostructures Fabricated by Copper Catalytic Etching

We demonstrate a simple method for the fabrication of rough silicon surfaces with micro- and nanostructures, which exhibited superhydrophobic behaviors. Hierarchically rough silicon surfaces were prepared by copper (Cu)-assisted chemical etching process where Cu nanoparticles having particle size of 10−30 nm were deposited on silicon surface, depending on the period of time of electroless Cu plating. Surface roughness was controlled by both the size of Cu nanoparticles and etching conditions. As-synthesized rough silicon surfaces showed water contact angles ranging from 93° to 149°. Moreover, the hierarchically rough silicon surfaces were chemically modified by spin-coating of a thin layer of Teflon precursor with low surface energy. And thus it exhibited nonsticky and enhanced hydrophobic properties with extremely high contact angle of nearly 180°

Cost-Effective Scalable Synthesis of Mesoporous Germanium Particles <i>via</i> a Redox-Transmetalation Reaction for High-Performance Energy Storage Devices

Nanostructured germanium is a promising material for high-performance energy storage devices. However, synthesizing it in a cost-effective and simple manner on a large scale remains a significant challenge. Herein, we report a redox-transmetalation reaction-based route for the large-scale synthesis of mesoporous germanium particles from germanium oxide at temperatures of 420–600 °C. We could confirm that a unique redox-transmetalation reaction occurs between Zn⁰ and Ge⁴⁺ at approximately 420 °C using temperature-dependent <i>in situ</i> X-ray absorption fine structure analysis. This reaction has several advantages, which include (i) the successful synthesis of germanium particles at a low temperature (∼450 °C), (ii) the accommodation of large volume changes, owing to the mesoporous structure of the germanium particles, and (iii) the ability to synthesize the particles in a cost-effective and scalable manner, as inexpensive metal oxides are used as the starting materials. The optimized mesoporous germanium anode exhibits a reversible capacity of ∼1400 mA h g^–1 after 300 cycles at a rate of 0.5 C (corresponding to the capacity retention of 99.5%), as well as stable cycling in a full cell containing a LiCoO₂ cathode with a high energy density (charge capacity = 286.62 mA h cm^–3)

Effect of the Li₂O–B₂O₃–Li₂SO₄ Amorphous Boundary Layer on the Ionic Conductivity and Humidity Stability of the LiTa₂PO₈ Solid Electrolyte

Recently, a Li-ion solid electrolyte material LiTa2PO8 (LTPO) which exhibits a high bulk ionic conductivity of 1.6 × 10–3 S/cm and a total ionic conductivity of 2.5 × 10–4 S/cm was developed. In a previous study, we sintered the LTPO pellet, which has a high relative density of 82% and a total ionic conductivity of 1.05 × 10–5 S/cm at room temperature via a cold sintering process (CSP). In this study, to achieve the ionic conductivity comparable to LTPO ceramic electrolytes obtained via high-temperature sintering, a Li2O–B2O3–Li2SO4 amorphous layer was formed at the interface between LTPO particles via the CSP, and the microstructure and electrochemical properties of LTPO with the Li2O–B2O3–Li2SO4 amorphous layer were investigated. Moreover, humidity acceleration tests were conducted to confirm the chemical stability of the pellet under ambient humidity conditions. It was found that pellets of LTPO prepared via the CSP exhibited a relative density of 85–87%, which is comparable to the density of high-temperature sintered pellets, and high adhesion between LTPO particles was observed due to the Li2O–B2O3–Li2SO4 amorphous layer forming a particle interface. LTPO pellets with the Li2O–B2O3–Li2SO4 amorphous boundary layer exhibited a high grain boundary ionic conductivity of 7.47 × 10–5 S/cm, a total ionic conductivity of 1.07 × 10–4 S/cm, and an extremely low activation energy of 0.215 eV. After humidity acceleration testing, the pellets showed good chemical stability against humidity, and the grain boundary and total ionic conductivities were increased by approximately 1.3 times to 9.21 × 10–4 and 1.38 × 10–4 S/cm, respectively. These results provide evidence that introducing an amorphous layer at the particle interface is a solution to the issues associated with low grain boundary ionic conductivity in ceramic-based solid electrolytes

Interplay of Cathode–Halide Solid Electrolyte in Enhancing Thermal Stability of Charged Cathode Material in All-Solid-State Batteries

All-solid-state batteries (ASSBs) are expected to address the thermal instability of conventional rechargeable batteries, given nonflammable inorganic solid electrolytes (SEs). However, the interaction between sulfide SEs and electrode materials can cause an exothermic reaction accompanied by the formation of explosive decomposition products. Herein, we demonstrate the enhanced thermal stability of a charged cathode material (Li1–xNi0.6Co0.2Mn0.2O2, x ≈ 0.5) with a Li3InCl6 halide SE compared to sulfide SEs. Li3InCl6 and the cathode composite not only delay the decomposition of NCM622 but also mitigate oxygen evolution from the cathode via oxidation decomposition of the halide SE. Furthermore, the halide SE suppresses combustible oxygen-gas evolution by capturing oxygen species through a mitigated exothermic reaction accompanying an endothermic phase transition from oxychloride to oxide. Oxygen capture was also observed in other halide SEs (Li3YCl6 and Li2ZrCl6). These findings emphasize the pivotal role of the cathode–SE interfacial interplay in governing the thermal stability of ASSBs and suggest SE design criteria for thermally safe battery systems

Flexible High-Energy Li-Ion Batteries with Fast-Charging Capability

With the development of flexible mobile devices, flexible Li-ion batteries have naturally received much attention. Previously, all reported flexible components have had shortcomings related to power and energy performance. In this research, in order to overcome these problems while maintaining the flexibility, honeycomb-patterned Cu and Al materials were used as current collectors to achieve maximum adhesion in the electrodes. In addition, to increase the energy and power multishelled LiNi_0.75Co_0.11Mn_0.14O₂ particles consisting of nanoscale V₂O₅ and Li_<i>x</i>V₂O₅ coating layers and a Li_δNi_{0.75–<i>z</i>}Co_0.11Mn_0.14V_<i>z</i>O₂ doping layer were used as the cathode–anode composite (denoted as PNG-AES) consisting of amorphous Si nanoparticles (<20 nm) loaded on expanded graphite (10 wt %) and natural graphite (85 wt %). Li-ion cells with these three elements (cathode, anode, and current collector) exhibited excellent power and energy performance along with stable cycling stability up to 200 cycles in an in situ bending test