In the production of cylindrical lithium-ion batteries suitable for power tools, environmental humidity control is crucial for ensuring the stability of electrode material performance and preventing moisture absorption and deterioration. Electrode materials are extremely sensitive to moisture, especially lithium compounds in the positive electrode and graphite in the negative electrode. Excessive moisture absorption can trigger a series of irreversible chemical reactions, leading to battery capacity decay, increased internal resistance, and even safety hazards. Therefore, a multi-dimensional humidity control system must be constructed, encompassing production environment design, humidity monitoring and control, and process optimization, to ensure that electrode materials remain dry throughout their entire lifecycle.
Humidity control in the production environment requires consideration of spatial layout and equipment selection. Electrode production areas (such as coating and rolling processes) must maintain extremely low relative humidity. This is typically achieved through a combination of rotary dehumidifiers and air conditioning systems, using absorbent materials like silica gel to remove moisture from the air, coupled with a high-efficiency filtration system to ensure air cleanliness. For critical processes such as cell assembly and electrolyte injection, an extremely dry environment with a dew point temperature ≤-40℃ is required in a closed space to prevent moisture from seeping into the electrolyte during injection, which could lead to hydrofluoric acid formation or battery bulging. In addition, the workshop must maintain a positive pressure environment. An air supply volume greater than the exhaust volume design prevents the infiltration of humid external air. Simultaneously, a well-planned air duct system ensures even distribution of dry air, preventing localized humidity spikes.
Humidity monitoring and real-time control are crucial for humidity management. High-precision temperature and humidity sensors must be deployed throughout the workshop, covering all process nodes including batching, coating, drying, and assembly, collecting data in real time and transmitting it to the central control system. When humidity approaches a safe threshold, the system automatically activates dehumidification equipment or triggers an audible and visual alarm, prompting manual intervention. For ultra-dry environments such as the injection room, glove boxes or drying rooms are required, further isolating external moisture through airtight doors and windows and sealing any openings. Dew point meters or moisture analyzers are also necessary to accurately reflect humidity fluctuations and provide a basis for process adjustments.
Process optimization is a direct means of reducing the risk of electrode moisture absorption. In the raw material storage stage, sealed packaging and desiccants are required in moisture-proof warehouses to prevent raw materials from absorbing moisture during storage. During electrode fabrication, coated electrodes must be immediately placed in a vacuum drying oven to rapidly remove solvents and moisture in a low-temperature vacuum environment. This prevents graphite and other negative electrode materials from absorbing moisture and altering their surface properties, which could affect lithium-ion insertion/extraction efficiency. If the dried electrodes are not used immediately, they must be stored under vacuum in a low-humidity environment or protected with nitrogen to prevent contact with air. During cell assembly, stacking and winding operations must be completed in a drying chamber, minimizing exposure time and reducing the chance of moisture adsorption.
Material selection and formulation improvements can fundamentally reduce the tendency of electrodes to absorb moisture. For positive electrode materials, lithium iron phosphate, with its higher thermal stability, can replace ternary materials, or its moisture resistance can be improved through doping, coating, and other modification techniques. For negative electrode materials, the binder formulation can be optimized to reduce the use of highly hygroscopic components such as CMC, thereby reducing the moisture absorption rate of graphite. The electrolyte system needs to incorporate flame-retardant additives and overcharge protection additives to suppress moisture-induced side reactions. Simultaneously, optimizing the solvent ratio improves the wettability of the electrolyte to the electrodes, preventing localized electrolyte drying and the formation of dead zones for lithium deposition. Personnel management and operational procedures are implicit safeguards for humidity control. Operators must wear anti-static cleanroom suits, gloves, and masks to prevent moisture from being introduced through sweat and respiration. Before entering low-humidity areas, they must pass through an air shower for dust removal and an airlock for transition, reducing the amount of moisture they carry. Production equipment requires regular maintenance, such as cleaning conveyor tracks, calibrating temperature sensors, and replacing worn nozzles, to prevent parameter drift due to equipment aging, which could affect humidity control effectiveness. Furthermore, a strict material flow system must be established to ensure the rapid transfer of raw materials and semi-finished products in a dry environment, minimizing their residence time in humid areas.
Humidity control in the production of cylindrical lithium-ion batteries suitable for power tools needs to be integrated throughout the entire process. Through multi-dimensional collaboration involving environmental design, monitoring and control, process optimization, material improvement, and personnel management, a humidity control system covering raw materials, production equipment, and operational procedures can be built. This system not only effectively prevents electrode deterioration due to moisture absorption, improving battery capacity, cycle life, and safety, but also reduces the defect rate, saving production costs for enterprises and enhancing market competitiveness. As battery technology develops towards higher energy density and longer lifespan, the refinement and intelligence of humidity control will become a key direction for industry upgrading.
