Facile Construction of Nanofilms from a Dip-Coating Process to Enable High-Performance Solid-State Batteries

The use of solid-state electrolytes (SSEs) instead of those liquid ones has found promising potential to achieve both high energy density and high safety for their applications in the next-generation energy storage devices. Unfortunately, SSEs also bring forth challenges related to solid-to-solid contact, making the stability of the electrode/electrolyte interface a formidable concern. Herein, using a garnet-type Li_6.5La₃Zr_1.5Ta_0.5O₁₂ (LLZT) electrolyte as an example, we demonstrated a facile treatment based on the dip-coating technique, which is highly efficient in modifying the LLZT/Li interface by forming a MgO interlayer. Using polyvinyl pyrrolidone (PVP) as a coordination polymer, uniform and crack-free nanofilms are fabricated on the LLZT pellet with good control of the morphological parameters. We found that the MgO interlayer was highly effective to reduce the interfacial resistance to 6 Ω cm² as compared to 1652 Ω cm² of the unmodified interface. The assembled Li symmetrical cell was able to achieve a high critical current density of 1.2 mA cm^-2 at room temperature, and it has a long cycling capability for over 4000 h. Using the commercialized materials of LiFePO₄ and LiNi_0.83Co_0.07Mn_0.1O₂ as the cathode materials, the full cells based on the LLZT@MgO electrolyte showed excellent cyclability and high rate performance at 25 °C. Our study shows the feasibility of precise and controllable surface modification based on a simple liquid phase method and highlights the essential importance of interface control for the future application of high-performance solid-state batteries.

Aqueous synthesis of tin- and indium-doped WO3 films via evaporation-driven deposition and their electrochromic properties

M-doped WO3 (M = Sn or In) films were prepared from aqueous coating solutions via evaporation-driven deposition during low-speed dip coating. Sn- and In-doping were easily achieved by controlling the chemical composition of simple coating solutions containing only metal salts and water. The crystallinity of the WO3, Sn-doped WO3, and In-doped WO3 films varied with heating temperature, where amorphous and crystalline films were obtained by heating at 200 and 500 °C, respectively. All the amorphous and crystalline films showed an electrochromic response, but good photoelectrochemical stability was observed only for the crystalline samples heated at 500 °C. The crystalline In-WO3 films exhibited a faster electrochromic color change than the WO3 or Sn-WO3 films, and good cycle stability for the electrochromic response in the visible wavelength region.

Evaporation-Driven Deposition of ITO Thin Films from Aqueous Solutions with Low-Speed Dip-Coating Technique

We suggest a novel wet coating process for preparing indium tin oxide (ITO) films from simple solutions containing only metal salts and water via evaporation-driven film deposition during low-speed dip coating. Homogeneous ITO precursor films were deposited on silica glass substrates from the aqueous solutions containing In(NO₃)₃·3H₂O and SnCl₄·5H₂O by dip coating at substrate withdrawal speeds of 0.20-0.50 cm min^-1 and then crystallized by the heat treatment at 500-800 °C for 10-60 min under N₂ gas flow of 0.5 L min^-1. The ITO films heated at 600 °C for 30 min had a high optical transparency in the visible range and a good electrical conductivity. Multiple-coating ITO films obtained with five-times dip coating exhibited the lowest sheet (ρ_S) and volume (ρ_V) resistivities of 188 Ω sq^-1 and 4.23 × 10^-3 Ω cm, respectively.

Evaporation-Driven Deposition of WO₃ Thin Films from Organic-Additive-Free Aqueous Solutions by Low-Speed Dip Coating and Their Photoelectrochemical Properties

We prepared tungsten trioxide (WO3) photoelectrode films from organic-additive-free aqueous solutions by a low-speed dip-coating technique. The evaporation-driven deposition of the solutes occurred at the meniscus during low-speed dip coating, resulting in the formation of coating layer on the substrate. Homogeneous WO3 precursor films were obtained from (NH4)10W12O41·5H2O aqueous solutions and found to be crystallized to monoclinic WO3 films by the heat treatment at 400-700 °C. All the films showed a photoanodic response irrespective of the heat treatment temperature, where a good photoelectrochemical stability was observed for those heated over 500 °C. The highest photoanodic performance was observed for the WO3 film heated at 700 °C, where the IPCE (incident photon-to-current efficiency) was 36.2% and 4.6% at 300 and 400 nm, respectively.