Detailed Explanation of the Application and Precautions for Sealants in Batteries

　　Epoxy resin sealants specially designed for batteries are primarily used for bonding the cell cover to the battery case and sealing the terminal posts in maintenance‑free lead‑acid batteries, and they are divided into mid‑cover adhesive and terminal post adhesive. Mid‑cover adhesive, also known as cell cover adhesive, sealant, or cover sealing adhesive, is employed to bond and seal the gap between the battery cell cover and the battery case; terminal post adhesive, also referred to as red–black adhesive, red–blue adhesive, terminal adhesive, marking adhesive, or identification adhesive, is used to seal and mark the positive and negative terminals of the battery. The sealing between the battery case and cover is critical to the overall battery seal, primarily because the contact area between the case and cover is large and the geometry is complex. The adhesive layer is directly exposed to acidic gases and electrolyte, while also frequently subjected to external impacts. As a result, air and liquid leakage can easily occur at the interface between the case and cover. To ensure that the cell cover remains firmly bonded to the battery case throughout the battery’s service life, mid‑cover adhesive must exhibit excellent adhesion and acid resistance.
　　Improving the adhesive and sealing performance of batteries is inseparable from the proper use of battery sealant. Therefore, during application, it is essential to follow the sealant’s instructions precisely. In the actual operation, whether the condition of the battery’s bonding surfaces, the mixing ratio of the epoxy resin adhesive, the curing temperature, and the potting process are handled correctly all have a direct impact on the final adhesive performance of the sealant.
　　1. Contact Surface Treatment
　　The surfaces of battery cell covers, casings, and terminal posts are often prone to contamination by sweat, oil, dust, and other substances. In addition, ABS, PP, or recycled plastic surfaces may still have mold release agents. During the application of sealing compounds, organic solvents (such as acetone) are used to directly clean and dry the ABS casing before proceeding with sealing.
　　2. Proportional Mixing
　　The mixing ratio for two‑component epoxy resin AB adhesive is determined based on the reaction mechanism. If the mixing ratio deviates too much, one component may become excessively abundant, leading to incomplete curing or a significant reduction in the adhesive strength that it should possess. The correct mixing method involves thoroughly stirring the components until they are evenly distributed, using the weight ratio rather than the volume ratio of the two components—and ensuring that the error does not exceed 3%. When A adhesive is used in environments with lower temperatures, it may exhibit high viscosity and be difficult to stir evenly; simply preheating it to around 30°C will reduce its viscosity, making it easier to mix with B adhesive. At this point, thorough and uniform mixing becomes even more critical. Even when the mixing ratio is accurate, insufficient stirring often results in localized areas that fail to cure properly or remain sticky to the touch. As a result, both the adhesive performance and the acid resistance will fall far short of the required standards. To address this, we recommend using mechanical mixing during application, and periodically scraping down any adhesive adhering to the inner walls of the mixing container with a spatula before stirring again—this ensures that all adhesive is fully and uniformly mixed.
　　3. Curing Temperature
　　The epoxy resin adhesives used in the manufacturing process of storage batteries belong to room‑temperature curing systems. However, the curing speed and effectiveness are directly influenced by ambient temperature: the higher the temperature, the faster the curing; the lower the temperature, the slower the curing. Yet when the ambient temperature falls below 15°C during curing, the required curing time increases significantly, the crosslink density of the adhesive layer is low, and the curing reaction remains incomplete. Moreover, extending the curing time or raising the curing temperature within a certain range does not yield equivalent results—when the curing temperature is too low, simply prolonging the curing time is often insufficient to compensate. This is because the complete chemical bonding between the adhesive interior and the surface of the adherend requires sufficiently high temperatures to proceed. Therefore, heat curing is the optimal choice for low‑temperature environments. Heating also softens the adhesive layer, enhancing its wettability on the substrate surface and facilitating molecular movement, enabling molecules at the bonding interface to form complementary interactions that maximize intermolecular forces. Consequently, heating is beneficial for improving adhesive strength. However, if the curing temperature is too high, it can easily lead to adhesive loss or cause the adhesive layer to become brittle, resulting in a decline in bond strength. Heating methods include oven or tunnel drying, as well as chamber heating. The heating process should involve gradual temperature increases, with the heating temperature typically controlled around 40–60°C. For ease of operation, we recommend using a direct heating method via a tunnel dryer: after sealing the battery with adhesive, it should remain in the heated tunnel for an appropriate duration (approximately 1 hour) before being removed from the production line.
　　4. Control of Adhesive Application Volume
　　The amount of adhesive dispensed is a critical factor affecting curing performance. In theory, a larger adhesive volume and thicker adhesive layer result in higher shear strength at the bonding interface. However, in practical applications, if the adhesive layer is too thick—especially during hot summer months—the heat generated by the polymerization reaction cannot dissipate in a timely manner. Excessive adhesive temperature can cause air bubbles within the adhesive to expand, while volatile components in the adhesive may vaporize and form bubbles throughout the adhesive layer. This leads to inadequate adhesion between the adhesive and the housing, resulting in weak interfacial bonding and ultimately reducing the product’s bonding performance. Therefore, during the adhesive dispensing process for battery terminal posts, it is recommended to adopt a layered dispensing method: control the bottom-layer adhesive to around 5–10 mm, and the top-layer adhesive to 10–15 mm.
　　5. Acid Migration Along the Terminal Post
　　The terminals of lead-acid batteries are typically made of lead or lead alloys, while the battery casing is generally constructed from materials such as ABS or PP. This necessitates that the epoxy resin adhesive itself possess excellent physical properties, including high strength, high toughness, acid resistance, and fatigue resistance, while also exhibiting strong adhesion to both metallic and organic substrates. Moreover, the negative terminal of a battery is more prone to acid creep than the positive terminal—this is because the positive terminal is in an oxidized state, where a passive layer readily forms on its surface, inhibiting the reaction between the terminal and sulfuric acid and thus preventing corrosion and acid creep. In contrast, the negative terminal is constantly in a reduced state, with a highly active surface that easily reacts with acid mist; furthermore, during charging and discharging, the two terminals undergo mutual conversion, gradually leading to corrosion over time. Currently, anti‑acid‑creep terminals are available on the market, with a key feature being that the terminal body incorporates at least one thread, effectively delaying acid creep and significantly extending the service life of the terminal.
　　In summary, when using epoxy resin adhesive to seal the cell cover and terminal posts of maintenance‑free lead‑acid batteries, in addition to ensuring that the epoxy sealing compound possesses excellent adhesion, acid resistance, impact resistance, and a low acid absorption rate, the following measures can be adopted during use to optimize the curing performance of the adhesive and thereby enhance the battery’s sealing integrity: