Liquid Filtration Solutions in Battery Manufacturing

With the rapid growth of the power battery industry, production increasingly demands high purity and cleanliness in liquids. Tiny metal particles, dust, or moisture can affect battery performance and safety. Liquid filtration, essential for process stability, product yield, and safety, is thus becoming more important. This article explores liquid filtration in power battery manufacturing and recycling, covering solutions for cell material preparation, separator coating, and electrolyte purification and recycling.

1. Liquid Filtration in the Pretreatment Process of Battery Structural Components

In power battery module and case manufacturing, structural components like aluminum and stainless steel shells and trays undergo pretreatment—degreasing, washing, surface conditioning, phosphating/passivation, and electrophoretic coating - to remove oil and ensure coating adhesion. Liquid filtration systems circulate and purify chemicals and wash solutions, removing metal debris, insoluble particles, and corrosion products from pipelines. This prevents clogging or damage to equipment such as spray systems and heaters, extending their service life and ensuring effective treatment.

Commonly used equipment includes SS Bag and Cartridge Filter Housings, typically filtering 5-50 μm. The housing material affects equipment stability and lifespan. 316/316L stainless steel, the industry standard, provides excellent corrosion and pressure resistance. Precision casting and polishing ensure reliable sealing and stable pressure, allowing efficient and continuous tank liquid purification.

The filtering performance mainly depends on the material selection of the pleated filter cartridge; a high dirt-holding capacity is essential to extend filter life and reduce operating costs. PP Pleated Filter Cartridge: Handles most room-temperature acids and alkalis; cost-effective. PTFE Membrane Pleated Filter Cartridge: Resistant to strong acids, alkalis, and organic solvents; ideal for highly corrosive environments. PVDF Membrane Pleated Filter Cartridge: Highly heat- and chemical-resistant; suitable for harsh conditions. Some systems also use automatic backwash filters to purify circulating water or cleaning fluids, ensuring continuous production and reducing maintenance.

In summary, liquid filtration in pretreatment processes relies not only on a robust stainless steel housing but also on the optimal selection of filter media. Only the right materials can ensure effective filtration, stabilize the production process, and improve the quality of the electrophoretic paint film.

2. Liquid Filtration in Coating and Wastewater Treatment

During battery module spray coating, liquid paint produces wastewater containing paint mist particles. It is usually pre-treated in a water curtain cabinet, then deeply purified using bag filters in multi-stage filtration systems - an essential step for environmental compliance. Liquid Filter Bags, made from polyester (PET), nylon, or polypropylene (PP), provide corrosion resistance, high strength, and 1–10 μm filtration accuracy. Multi-stage filtration lowers total suspended solids (TSS), enhances biochemical and MBR membrane efficiency, reduces maintenance, and enables wastewater reuse, supporting energy conservation, environmental protection, and clean production.

3. Liquid Filtration in Battery Material Preparation

1) Positive and Negative Electrode Slurry Filtration

Positive and negative electrode slurries consist of active materials, conductive agents, binders, and solvents (such as water or NMP). They have high viscosity and a high solids content. They must be rigorously filtered before coating to remove undispersed conductive agent/binder aggregates, environmental foreign matter, and gel particles. This ensures uniform electrode coating and prevents large particles from piercing the separator during winding or lamination, potentially causing internal short circuits.

A. Coarse Filtration: 50–100 μm, can use multi- bag filter housing. Purpose: Removes large particle aggregates and gels, protects the fine filter element, and ensures stable slurry flow.Advantages: High flow rate, high dirt holding capacity, chemical resistance, and reduced replacement and downtime costs.

B. Fine Filtration: 5–15 μm, large-size, can use high-flow pleated filter housing. Purpose: Retains fine particles, ensuring uniform electrode coating, reducing coating defects, and improving battery cell consistency and safety. Advantages: High precision, high dirt holding capacity, multi-layer pleated design, chemical resistance and high pressure differential, and reliable sealing. Two-stage filtration purifies slurry from coarse to fine, enhancing coating quality, battery safety, and production efficiency. 

2) Electrolyte Filtration

The electrolyte, the core electrochemical medium of power batteries (e.g., LiPF? dissolved in carbonate), is highly sensitive to moisture and particles (especially metal ions). Its purity directly impacts battery cycle life, self-discharge rate, and safety. Filter fineness is 0.1-0.45 μm (or even lower) or the common filter materials: PTFE, PVDF, and PES pleated filter elements (membrane surface filtration). System requirements: The entire filtration and transfer process must be performed in a dry, sealed environment (e.g., argon-filled). Filter housings and filter elements should utilize low-extractables and low-metal ion designs (e.g., passivated 316L stainless steel) to prevent secondary contamination.Unlike traditional needle-punched felt filter bags, high-precision pleated membrane filter elements provide absolute filtration ratings and are the leading choice for electrolyte purification, ensuring electrolyte purity and stable battery performance.

3) Diaphragm Coating Fluid Filtration

Ceramic or PVDF coatings applied to the diaphragm surface can significantly improve battery thermal stability and safety. The coating fluid must be filtered with extremely high precision to remove all gel particles and impurities, ensuring a uniform, defect-free coating. Filtration accuracy is  0.1-1 μm; common filter materials are high-precision, high-purity polymer pleated filters (such as nylon, PES, PVDF) or ultra-clean ceramic membrane filters. And the metal sintered filters are rarely used in this process due to the potential for ion release. Precise filtration is critical to ensuring diaphragm coating quality and battery safety.

4. Liquid Filtration in Power Battery Recycling

In wet recycling of used power batteries, filtration is crucial for solid-liquid separation and solution purification, directly affecting metal recovery and product purity.

1) Leaching Residue Separation

Crushed battery materials are leached with acid or alkaline solutions, forming a slurry with undissolved impurities. Plate-and-frame filter presses and belt filters are commonly used for large-scale, high-efficiency solid-liquid separation, producing a solution rich in metal ions like cobalt, nickel, and lithium.

2) Solution Purification

During extraction, precipitation, and crystallization, bag or cartridge filters provide pre-filtration to protect precision equipment. For high-purity lithium salts (e.g., lithium carbonate and lithium hydroxide), ceramic microfiltration (MF) or ultrafiltration (UF) membranes remove submicron colloids and organic matter, enhancing product quality, recycling value, and environmental protection.

Conclusion

Liquid filtration is essential across power battery production and recycling—from component pretreatment to electrode slurry, electrolyte, and separator coating fluids, and finally to resource recovery. Proper filtration design and high-quality equipment ensure battery performance, safety, and consistency, while reducing costs and enhancing environmental benefits.