Myung-Hyun Ryou

We demonstrate that dispersion stability and excellent coating quality are achieved in polyethylene (PE) separators by premixing heterogeneous ceramics such as silica (SiO₂) and alumina (Al₂O₃) in an aqueous solution, without the need for functional additives such as dispersing agents and surfactants. Due to the opposite polarities of the zeta potentials of SiO₂ and Al₂O₃, SiO₂ forms a sheath around the Al₂O₃ surface. Electrostatic repulsion occurs between the Al₂O₃ particles encapsulated in SiO₂ to improve the dispersion stability of the slurry. The CCSs fabricated using a dual ceramic (SiO₂ and Al₂O₃)-containing aqueous coating slurry, denoted as DC-CCSs, exhibit improved physical properties, such as a wetting property, electrolyte uptake, and ionic conductivity, compared to bare PE separators and CCSs coated with a single ceramic of Al₂O₃ (SC-CCSs). Consequently, DC-CCSs exhibit an improved electrochemical performance, in terms of rate capability and cycle performance. The half cells consisting of DC-CCSs retain 93.8% (97.12 mAh g⁻¹) of the initial discharge capacity after 80 cycles, while the bare PE and SC-CCSs exhibit 22.5% and 26.6% capacity retention, respectively. The full cells consisting of DC-CCSs retain 90.9% (102.9 mAh g⁻¹) of the initial discharge capacity after 400 cycles, while the bare PE and SC-CCS exhibit 64.7% and 73.4% capacity retention, respectively.

Developing uniform ceramic-coated separators in high-energy Li secondary batteries has been a challenging task because aqueous ceramic coating slurries have poor dispersion stability and coating quality on the hydrophobic surfaces of polyolefin separators. In this study, we develop a simple but effective strategy for improving the dispersion stability of aqueous ceramic coating slurries by changing the mixing order of the ceramic slurry components. The aqueous ceramic coating slurry comprises ceramics (Al₂O₃), polymeric binders (sodium carboxymethyl cellulose, CMC), surfactants (disodium laureth sulfosuccinate, DLSS), and water. The interaction between the ceramic slurry components is studied by changing the mixing order of the ceramic slurry components and quantitatively evaluating the dispersion stability of the ceramic coating slurry using a Lumisizer. In the optimized mixing sequence, Al₂O₃ and DLSS premixed in aqueous Al₂O₃-DLSS micelles through strong surface interactions, and they repel each other due to steric repulsion. The addition of CMC in this state does not compromise the dispersion stability of aqueous ceramic coating slurries and enables uniform ceramic coating on polyethylene (PE) separators. The prepared Al₂O₃ ceramic-coated separators (Al₂O₃–CCSs) exhibit improved physical properties, such as high wettability electrolyte uptake and ionic conductivity, compared to the bare PE separators. Furthermore, Al₂O₃–CCSs exhibit improved electrochemical performance, such as rate capability and cycling performance. The half cells (LiMn₂O₄/Li metal) comprising Al₂O₃–CCSs retain 90.4% (88.4 mAh g⁻¹) of initial discharge capacity after 150 cycles, while 27.6% (26.4 mAh g⁻¹) for bare PE. Furthermore, the full cells (LiMn₂O₄/graphite) consisting of Al₂O₃–CCSs exhibit 69.8% (72.2 mAh g⁻¹) of the initial discharge capacity and 24.9% (25.0 mAh g⁻¹) for bare PE after 1150 cycles.

The microblade cutting method, so-called SAICAS, is widely used to quantify the adhesion of battery composite electrodes at different depths. However, as the electrode thickness or loading increases, the reliability of adhesion values measured by the conventional method is being called into question more frequently. Thus, herein, a few underestimated parameters, such as friction, deformation energy, side-area effect, and actual peeing area, are carefully revisited with ultrathick composite electrodes of 135 μm (6 mAh cm−2). Among them, the existence of side areas and the change in actual peeling area are found to have a significant influence on measured horizontal forces. Thus, especially for ultrahigh electrodes, we can devise a new SAICAS measurement standard: 1) the side-area should be precut and 2) the same actual peeling area must be secured for obtaining reliable adhesion at different depths. This guideline will practically help design more robust composite electrodes for high-energy-density batteries.

Silicon is an attractive anode material for lithium-ion batteries (LIBs) because of its natural abundance and excellent theoretical energy density. However, Si-based electrodes are difficult to commercialize because of their significant volume changes during lithiation that can result in mechanical damage. To overcome this limitation, we synthesized an eco-friendly water-soluble polyimide (W-PI) precursor, poly(amic acid) salt (W-PAmAS), as a binder for Si anodes via a simple one-step process using water as a solvent. Using the W-PAmAS binder, a composite Si electrode was achieved by low-temperature processing at 150 °C. The adhesion between the electrode components was further enhanced by introducing 3,5-diaminobenzoic acid, which contains free carboxylic acid (–COOH) groups in the W-PAmAS backbone. The –COOH of the W-PI binder chemically interacts with the surface of Si nanoparticles (SiNPs) by forming ester bonds, which efficiently bond the SiNPs, even during severe volume changes. The Si anode with W-PI binder showed improved electrochemical performance with a high capacity of 2061 mAh g⁻¹ and excellent cyclability of 1883 mAh g⁻¹ after 200 cycles at 1200 mA g⁻¹. Therefore, W-PI can be used as a highly effective polymeric binder in Si-based high-capacity LIBs.

Li metal thickness has been considered a key factor in determining the electrochemical performance of Li metal anodes. The use of thin Li metal anodes is a prerequisite for increasing the energy density of Li secondary batteries intended for emerging large-scale electrical applications, such as electric vehicles and energy storage systems. To utilize thin (20 μm thick) Li metal anodes in Li metal secondary batteries, we investigated the synergistic effect of a functional additive (Li nitrate, LiNO₃) and a dual-salt electrolyte (DSE) system composed of Li bis(fluorosulfonyl)imide (LiTFSI) and Li bis(oxalate)borate (LiBOB). By controlling the amount of LiNO₃ in DSE, we found that DSE containing 0.05 M LiNO₃ (DSE–0.05 M LiNO₃) significantly improved the electrochemical performance of Li metal anodes. DSE–0.05 M LiNO₃ increased the cycling performance by 146.3% [under the conditions of a 1C rate (2.0 mA cm^–2), DSE alone maintained 80% of the initial discharge capacity up to the 205th cycle, whereas DSE–0.05 M LiNO₃ maintained 80% up to the 300th cycle] and increased the rate capability by 128.2% compared with DSE alone [the rate capability of DSE–0.05 M LiNO₃ = 50.4 mAh g^–1, and DSE = 39.3 mAh g^–1 under 7C rate conditions (14.0 mA cm^–2)]. After analyzing the Li metal surface using scanning electron microscopy and X-ray photoelectron spectroscopy, we were able to infer that the stabilized solid electrolyte interphase layer formed by the combination of LiNO₃ and the dual salt resulted in a uniform Li deposition during repeated Li plating/stripping processes.

Making Li metal batteries (LMBs) with thinner Li is necessary to improve the cell energy density in practice. Li metal powders (LMPs) are beneficial for the facile manufacturing of thin Li, flexible cell design, and the 3D control of Li plating/stripping. However, the inhomogeneous surfaces of commercial LMPs limit their practical use in LMBs. Herein, a 20 µm‐thick, LiNO₃ preplanted LMP (LN‐LMP) composite electrode, rationally designed for LMP surface stabilization, is presented. The addition of LiNO₃ into the slurry uniformly modified the LMP surface by N‐rich solid‐electrolyte interphase (SEI). Preplanted LiNO₃ further acts as a reservoir for the sustainable release into the electrolyte, thereby repairing the SEI upon cycling. The LMBs with LN‐LMP exhibited excellent cycling performances (450 cycles at 87.3% retention) compared to the control cells, and even outperformed the cells with LiNO₃‐containing electrolytes. Further verification with high loading of a LiNi_xMn_yCo_1–x–yO₂ (NMC) cathode demonstrated the feasibility of the practical cells and the versatility of the thin, LN‐LMP anode combined with advanced electrolytes.

A method of microalgae-templated spray drying to develop hierarchical porous Fe₃O₄/C composite microspheres as anode materials for Li-ion batteries was developed. During the spray-drying process, individual microalgae serve as building blocks of raspberry-like hollow microspheres via self-assembly. In the present study, microalgae-derived carbon matrices, naturally doped heteroatoms, and hierarchical porous structural features synergistically contributed to the high electrochemical performance of the Fe₃O₄/C composite microspheres, enabling a discharge capacity of 1375 mA·h·g⁻¹ after 700 cycles at a current density of 1 A/g. Notably, the microalgal frameworks of the Fe₃O₄/C composite microspheres were maintained over the course of charge/discharge cycling, thus demonstrating the structural stability of the composite microspheres against pulverization. In contrast, the sample fabricated without microalgal templating showed significant capacity drops (up to ~40% of initial capacity) during the early cycles. Clearly, templating of microalgae endows anode materials with superior cycling stability.