Advancements in battery technology have dramatically increased demand for improvements in liquid solid separation design, as the separator plays a critical role in ensuring the safety and electrochemical performance of the cells. Current separators, either in commercial usage or under investigation, have yet to meet the high stability and lifespan performance standards necessary to prevent deterioration in the efficiency and reliability of the battery technologies. Recently, considerable effort has been devoted to developing functionalized separators, ranging from designing a variety of new materials and modification methods, and increasingly, to optimizing advanced preparation processes. In order to understand how the mechanisms of vibrating separator performance are affected by different properties, we will first summarize recent research progress and then have in-depth discussions regarding the separator’s significant contribution to enhancing the safety and performance of the cell. We then provide our design strategy for future separators, which not only meets the requirements of different type of batteries, but also aims for multifunctionality. We hope such a perspective could provide new inspiration in the development of liquid solid separator research for future battery technologies.
Filter paper usually removes particles based on five physical effects: gravity, collision, screening, diffusion, and static electricity.6 The removal efficiency of filter paper is closely related to the relative size of the particle diameter and the paper pore size. Smaller pore sizes of the paper correspond to smaller sizes of the particles that it can intercept under the same filtration efficiency.7,8 Adjusting the structure of the filter paper to improve the air flow resistance can increase the residence time of the pollutant particles in the filter paper, resulting in a higher removal efficiency.9,10 However, the filter filtration resistance directly affects the energy consumption of the pressure leaf filter, such that extremely high filtration resistances are not recommended.11 The filtration efficiency has exhibited dependence on the fiber coarseness. Specifically, finer fibers have exhibited higher filtration efficiencies at a constant pressure drop.12 However, air filter paper must maintain a certain porosity to allow air flow. Nanofibers can increase the specific surface area of the filter paper to generate filter papers with small pore sizes, high filtration efficiencies, and high porosities.
2.2 Preparation of the PF–MWCNT–CF air vertical pressure leaf filter paper
In this study, phenol-formaldehyde (PF) resin was used to impregnate the MWCNT–CF air filter paper to improve the physical strength of the paper. PF resin (solid content 58%) was purchased from Shanghai Kain Chemical, China. The CF filter paper loaded with 0.5% MWCNTs was impregnated for the second time with PF (dissolved in 99.5% anhydrous methanol). The experiments followed an impregnation time of 30 s, a drying temperature of 105 °C, and a drying time of 15 min. By heating the PF, the gelatinous resin formed a polymer chain resin,17 which gradually hardened from a viscous flow state and appropriately improved the strength of the paper. After the CF filter paper was impregnated with an MWCNT dispersion, MWCNTs adhered to the surface of the vibrating filter paper, thus reducing the pore size and resulting in a higher filter paper surface content compared with that inside the paper. When the load of MWCNTs was greater than 4.56%, the pores readily became blocked, which was not conducive to filtration. At a loading rate of 3.68%, the resistance increased by 26.56% and the dust-holding capacity only increased by 8.33%. At this time, the filtration efficiency was 99.69% (2000 Pa), and the paper strength was also enhance