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 manufacturing of flexible electronics requires flexible batteries. However, the development of high-performance flexible batteries has been rather slow. A majority of the available techniques are impractical and too expensive for industrial applications because of the type of equipment needed for preparing these flexible electrodes. Therefore, in this study, we developed a simple approach for fabricating free-standing flexible cathodic electrodes. The process involves the slurry casting of a well-dispersed electrode mixture comprising the active material, carbon fibers, polymer, plasticizer, and lithium salts. By adjusting the weight ratios, we realized the best trade-off between flexibility and specific capacity. The prepared free-standing flexible cathodic electrodes of lithium manganese oxide exhibited remarkably long cycling performance over 5000 cycles at 10 C versus Li metal anode with a coulombic efficiency (C.E.) > 99% The pouch cell also had excellent cycling performance of over 500 cycles at 5 C with a C.E. > 99%. This method is simple and uses current battery production line equipment without the need for new specialized equipment. This could be cost-effective and efficient for manufacturing free-standing electrodes.

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.