The application of high-temperature Mini Pleat HEPA filters in the electrode drying ovens of lithium-ion battery manufacturing workshops is a crucial technology that directly affects the safety, consistency, and lifespan of battery products. This application is a standard configuration for high-end lithium battery production.
I. Application Stage and Core Functions
1. Application Stage: The manufacturing process of lithium-ion battery electrodes (both positive and negative electrodes).
- Specific Process: After the slurry (active material, conductive agent, binder, etc.) is evenly coated on the metal foil current collector (aluminum foil for the positive electrode, copper foil for the negative electrode), it needs to enter a long drying oven (also known as a drying chamber or drying box) to evaporate the solvent in the slurry (usually NMP or water).
- Application Position: Installed at the end of the air supply system of the electrode drying oven, which is the last checkpoint before the clean hot air enters the drying oven chamber.
2. Core Functions: To provide extremely clean, high-temperature hot air for the electrode drying process.
- Eliminate Dust Contamination: Prevent metal dust, fibers, and common dust particles in the ambient air from settling on the wet electrode coating before it dries.
- Ensure Battery Safety: This is the most fundamental purpose. Any residual conductive dust (especially metal particles such as iron, copper, and zinc) may pierce the separator inside the battery, causing micro-short circuits during charging and discharging, leading to excessive self-discharge, heating, swelling, and even thermal runaway and fire or explosion of the battery.
II. Why High-Temperature and High-Efficiency Filters Are Essential in This Stage?
1. High-Temperature Resistance (Typically 180°C - 220°C or higher):
- Process Requirements: The drying of electrode coating is a precise process carried out in segments, with different temperature zones having different temperatures. However, the highest temperature zone usually needs to reach above 180°C to ensure the complete evaporation of the solvent and the stability of the coating structure. Ordinary filters cannot work long-term at this temperature.
- Material Stability: High-temperature filters use stainless steel frames, high-temperature resistant sealants, and glass fiber filter paper, ensuring no decomposition, no release of pollutants, and no deformation under long-term high-temperature conditions, maintaining filtration efficiency and structural integrity.
2. High-Efficiency Filtration (Must Reach H13 Level or Higher):
- Target Particles: The goal is to capture micrometer and sub-micrometer particles that are most harmful to batteries, especially conductive metal dust with a particle size of ≥0.3μm. An H13 level efficiency (≥99.97% filtration efficiency for 0.3μm particles) or H14 level (≥99.997%) is a basic requirement.
- Advantages of Mini Pleat Design:
- High Dust Holding Capacity: The electrode drying oven operates continuously and requires a filter with a longer service life. The Mini Pleat design increases the effective filtration area, resulting in a higher dust holding capacity and longer replacement cycle.
- Structural Safety: It avoids the risk of metal shavings from traditional partitioned filters due to vibration or corrosion, fundamentally eliminating the possibility of introducing metal contamination.
- Lightweight: Reducing the burden on the structure of the oven's air supply system.
III. Specific Technical Requirements and Industry Characteristics
1. Extremely High Cleanliness Standards:
- Lithium Battery Manufacturing Workshop: The electrode manufacturing area of the lithium battery workshop is usually a Class 10,000 or even Class 1,000 cleanroom. As a core device, the drying oven has higher cleanliness requirements for its internal environment than the surrounding environment, which must be ensured by high-efficiency filters.
- Stringent Control of Magnetic Foreign Matter: There are extremely strict concentration control requirements for magnetic foreign matter (such as iron, nickel) (in units of mg/m² or particles/m²), and high-efficiency filters are the core means to achieve this control.
2. Strict Material Control:
- All Materials of the Filter: All materials of the filter (frame, filter medium, sealant) must be low-magnetic or non-magnetic materials. For example, the frame should prioritize the use of 304 or 316 stainless steel and ensure that it contains little or no ferromagnetic substances.
- Prevent the Filter from Becoming a Contamination Source.
3. Performance Verification**: After installation, a PAO/DOP smoke test should be conducted to scan for leaks, ensuring that there are no gaps between the filter and the installation frame, guaranteeing "zero leakage".
IV. Summary of the Value and Importance of the Application
1. Foundation of Safety: It is the first and one of the most critical technical defenses against thermal runaway in batteries due to internal short circuits.
2. Enhancing Cell Consistency: Reducing impurity contamination can significantly lower the self-discharge rate of batteries, improve the consistency of voltage and internal resistance, which is crucial for the performance and lifespan of battery packs.
3. Reducing Defect Rate: Avoiding the scrapping of electrode sheets due to dust contamination directly increases production yield and saves costs.
4. Meeting High-End Customer Requirements: Leading companies producing power batteries (for electric vehicles) and energy storage batteries have mandatory technical and standard requirements for this.
Conclusion: In the electrode drying ovens of lithium-ion batteries, high-temperature Mini Pleat HEPA filters are no longer ordinary ventilation components but core process quality control and safety assurance devices. The selection, installation, and maintenance quality of these filters directly reflect the technical level and quality control capabilities of a battery manufacturing company. They are indispensable key elements for producing high-safety, high-performance lithium batteries.