The main safety hazard points in the production process of polymer batteries

In recent years, polymer lithium batteries have been widely used in mobile phones, tablets, smart wearables, drones, and new energy 

fields due to their advantages such as lightness, thinness, high energy density, and customizability. Their flexible shell design is more 

adaptable than traditional metal shell lithium batteries, but it also brings more safety challenges in the manufacturing process. The 

internal components of polymer batteries, such as highly reactive lithium metal oxide cathodes, graphite anodes, and electrolytes, 

are flammable and reactive substances. Coupled with the complex production process, there are numerous safety hazards throughout 

the entire production process. If not properly managed, it can easily lead to short circuits, leaks, explosions, fires, and other accidents, 

endangering equipment, personnel, and even the entire production system.

The production of polymer batteries generally involves the following processes: raw material preparation, coating and drying of 

electrode sheets, rolling, slitting, stacking or winding, electrode welding, liquid injection, packaging, formation, aging, capacity sorting 

and testing, etc. Each step may potentially lead to safety incidents and must be identified and strictly controlled from the source.

During the raw material preparation stage, the cathode materials involved (such as lithium cobalt oxide and ternary materials) are 

fine powders that are highly prone to dust generation. In a confined space, there is a risk of dust explosion. The conductive agents 

(such as carbon black and carbon nanotubes) themselves are highly flammable. Once static electricity accumulates or sparks are 

generated due to operational friction, they may ignite the dust particles in the air. Additionally, the solvents used for the anode slurry, 

such as NMP, not only have strong volatility and toxicity but are also low flash point flammable substances. They are prone to causing 

fires or poisoning incidents when exposed to open flames or high temperatures. Therefore, in this stage, it is essential to strictly control 

the humidity and ventilation in the workshop, install explosion-proof exhaust systems, and require operators to wear protective masks 

and gloves to prevent inhalation poisoning and skin corrosion.

The coating process is one of the most crucial steps in the production of polymer batteries and is also a high-risk procedure. The slurry 

used in coating usually needs to be dried through a heating oven. If the temperature setting or control is incorrect, it can easily lead to 

overheating, material self-ignition or electrical fires. At the same time, the high-speed operation of the coating machine also brings 

mechanical injury risks, such as clothing entanglement and finger entanglement. Since most solvent recovery systems use condensation 

and ventilation methods, if maintenance is not in place or there is a leak, it is easy to cause local high concentration gas accumulation, 

and in some special environments, it may even reach the lower explosive limit. Therefore, a complete temperature control system, 

solvent detector and automatic fire extinguishing equipment must be configured.

Entering the roller pressing and slitting processes, although the overall risk is lower than that of chemical-related processes, the 

equipment still operates under high pressure and high speed. If the thickness of the electrode sheets is uneven during roller pressing,

 it is easy to cause equipment jamming and overload, which may result in operators being pinched or crushed. In addition, the slitting 

blades are extremely sharp, and if the metal powder and burrs from the slitting process are not cleaned up in time, they may pierce 

the separator during the subsequent stacking process, causing a risk of micro-short circuits. Therefore, equipment maintenance and 

cleaning management must strictly follow institutionalized and standardized procedures, and it is strictly prohibited to operate the 

equipment when it is faulty.

During the lamination or winding process, as polymer cells are mostly pouch-type structures, higher precision is required for the size 

and position of the electrode sheets. Misalignment of the electrode sheets or the mixture of dust will directly increase the risk of internal 

short circuits in the finished battery. Some manufacturers use automated equipment to increase production capacity. If a good sensing 

and recognition system is not set up during this process, it is easy to cause equipment misoperation, resulting in structural defects or 

even direct accidents. In addition, burrs on the edges of the electrode sheets can easily pierce the separator or aluminum-plastic film, 

thus laying the hidden danger of thermal runaway of the cell.

The safety hazards in the electrode welding process mainly focus on the use of laser equipment and the control of welding quality. 

The packaging material of polymer batteries is aluminum-plastic film, which has weak resistance to high temperatures. If the welding 

temperature is too high or not properly controlled, it is very likely to burn through the shell, causing leakage of the electrolyte. Poor 

welding or short circuits will also directly affect the safety and stability of the battery during subsequent charging processes. Therefore, 

during the operation, the energy output must be strictly controlled, and the appearance and electrical performance of the welding must 

be strengthened for inspection.

Liquid injection, as one of the key processes in polymer battery manufacturing, is one of the most risky stages in the entire process. 

The electrolyte itself is a flammable, volatile and highly irritating chemical. Even the slightest mistake during operation can lead to 

leakage, burns or poisoning of personnel. If the environment during the liquid injection process is sealed, the temperature rises or 

ventilation is poor, the concentration of flammable gas may increase to the explosive limit, greatly increasing the risk of fire. Operators 

must wear compliant chemical protective equipment, and the liquid injection room must be equipped with explosion-proof lighting, 

anti-static flooring and gas concentration alarm systems to ensure timely intervention and handling before an accident occurs.

During the heat sealing or vacuum packaging stage, polymer cells are in the form of aluminum-plastic film soft packs and need to be 

heat-sealed or vacuumed at high temperatures. If the temperature setting is unreasonable, the equipment gets stuck or the sealing 

pressure is insufficient, it may cause leakage at the edge of the seal, allowing the electrolyte to seep out. In addition, poor packaging 

can also lead to moisture in the cell or abnormal internal reactions, laying the groundwork for subsequent hazards such as swelling, 

leakage, or even fire during the formation process.

Formation and capacity sorting are the battery activation processes. During this stage, the battery cells are charged and discharged 

for the first time, which is one of the most concentrated periods of thermal runaway risks. If the battery cells have manufacturing 

defects, such as dust on the electrode sheets, short circuits, or abnormal welding, they are highly likely to generate abnormal heat 

during formation, causing cell swelling, rupture, fire, or even explosion. Therefore, testing equipment with multiple monitoring capabilities

 for temperature, voltage, and current must be used, and automatic power-off and fire-extinguishing mechanisms should be in place. 

The formation workshop should implement strict zonal control to prevent a single point failure from escalating into a group accident.

The final aging and testing stage is equally important and cannot be overlooked. Although the battery has completed the main chemical 

reactions, it still remains in a high-voltage state internally. If the aging room has poor heat dissipation, temperature and humidity are 

out of control, or the battery cells are improperly stacked, there are still potential safety hazards such as fire and thermal runaway. 

Additionally, if unqualified cells that fail the capacity sorting are not promptly sorted and isolated and mistakenly enter subsequent 

processes, they may cause quality complaints or even safety accidents when used by customers.

In summary, polymer batteries face a superimposition of various risk factors during the production process, including chemical management, 

electrical safety, mechanical injury from equipment, high-temperature thermal control, clean environment, and human operational errors. 

The overall safety management requirements are extremely high. Enterprises must establish a complete safety production management 

system, starting from multiple dimensions such as design origin, process optimization, equipment selection, personnel training, and 

emergency plans, to build an intrinsic safety guarantee mechanism throughout the entire process. Only by aiming for "zero accidents" and 

continuously promoting safety technology and management innovation can the high-quality and sustainable development of the polymer 

battery industry be truly achieved.