Column rechargeable battery

Safety, detection and solutions of Column rechargeable battery packs, please keep it!

Please keep it, the composition, safety detection and solutions of Column rechargeable battery packs. In recent years, accidents caused by safety problems of Column rechargeable battery packs are everywhere, and the consequences of many problems are shocking, which once again sounded the alarm for the safety of lithium batteries. In this article, the editor of Cunneng Electric will share with you the dry goods-the safety, detection and solutions of Column rechargeable battery packs, please keep it!

1. Composition and working principle of Column rechargeable battery packs

Column rechargeable battery packs are mainly composed of positive electrodes, negative electrodes, electrolytes, diaphragms, and external connections and packaging components. Among them, the positive and negative electrodes contain active electrode materials, conductive agents, adhesives, etc., which are evenly coated on copper foil and aluminum foil current collectors.

During the charging process, inside the battery, lithium is released from the positive electrode in the form of ions, transmitted through the diaphragm by the electrolyte, and embedded in the negative electrode; outside the battery, electrons migrate from the external circuit to the negative electrode. During the discharge process: lithium ions inside the battery escape from the negative electrode, pass through the diaphragm, and are embedded in the positive electrode; outside the battery, electrons migrate from the external circuit to the positive electrode. As the battery is charged and discharged, it is "lithium ions" that migrate between the batteries, not the single substance "lithium", so the battery is called a "lithium-ion battery".

2. Safety hazards of lithium batteries

Generally speaking, safety problems with Column rechargeable battery packs are manifested as combustion or even explosion. The root cause of these problems is thermal runaway inside the battery. In addition, some external factors, such as overcharging, fire sources, extrusion, puncture, short circuits, etc., can also cause safety problems.

1. Safety hazards of positive electrode materials

When Column rechargeable battery packs are used improperly, the temperature inside the battery rises, causing the positive electrode material to decompose the active material and oxidize the electrolyte. At the same time, these two reactions can generate a lot of heat, causing the battery temperature to rise further. Different delithiation states have very different effects on the lattice transformation of active materials, decomposition temperature and thermal stability of batteries.

2. Safety hazards of negative electrode materials

The negative electrode material used in the early days was metallic lithium. The assembled battery was prone to lithium dendrites after multiple charge and discharge, which then punctured the diaphragm, causing battery short circuit, leakage and even explosion. Lithium-intercalated compounds can effectively avoid the generation of lithium dendrites and greatly improve the safety of lithium-ion batteries. As the temperature rises, the carbon negative electrode in the lithium-intercalated state first reacts with the electrolyte to release heat. Under the same charge and discharge conditions, the heat release rate of the electrolyte reaction with lithium-intercalated artificial graphite is much greater than the heat release rate of the reaction with lithium-intercalated intermediate carbon microspheres, carbon fibers, coke, etc.

3. Safety hazards of diaphragms and electrolytes

The electrolyte of lithium batteries is a mixed solution of lithium salts and organic solvents. The commercial lithium salt is lithium hexafluorophosphate. This material is prone to thermal decomposition at high temperatures and undergoes thermochemical reactions with trace amounts of water and organic solvents, reducing the thermal stability of the electrolyte. The organic solvent of the electrolyte is a carbonate ester. This type of solvent has a low boiling point and flash point. It is easy to react with lithium salts to release PF5 at high temperatures and is easily oxidized.

4. Safety hazards in the manufacturing process

During the manufacturing process of lithium batteries, processes such as electrode manufacturing and battery assembly will affect the safety of the battery. For example, the quality control of the positive and negative electrode mixing, coating, rolling, cutting or punching, assembly, electrolyte filling, sealing, formation and other processes all affect the performance and safety of the battery. The uniformity of the slurry determines the uniformity of the distribution of the active material on the electrode, which affects the safety of the battery. If the slurry fineness is too large, the expansion and contraction of the negative electrode material will change greatly during the battery charging and discharging, and the precipitation of metallic lithium may occur; if the slurry fineness is too small, the internal resistance of the battery will be too large. If the coating heating temperature is too low or the drying time is insufficient, the solvent will remain, the binder will partially dissolve, and some active materials will be easily peeled off; if the temperature is too high, the binder may be carbonized, and the active material may fall off, causing an internal short circuit in the battery.

5. Safety hazards during battery use

Column rechargeable battery packs should be used to reduce overcharging or overdischarging as much as possible during use, especially for batteries with high monomer capacity, because thermal disturbances may trigger a series of exothermic side reactions, leading to safety problems.

3. Safety test indicators of lithium-ion batteries

After lithium-ion batteries are produced, they need to undergo a series of tests before they reach consumers to ensure the safety of the batteries as much as possible and reduce safety hazards.

1. Extrusion test:

Put a fully charged battery on a plane, apply an extrusion force of 13±1KN by a hydraulic cylinder, and squeeze the battery with a steel bar with a diameter of 32mm. Once the extrusion pressure reaches the maximum, stop squeezing. The Column rechargeable battery does not catch fire or explode.

2. Impact test:

After the Column rechargeable battery is fully charged, place it on a plane, place a steel column with a diameter of 15.8mm vertically in the center of the battery, and let a weight of 9.1kg fall freely from a height of 610mm onto the steel column above the battery. The battery does not catch fire or explode.

3. Overcharge test:

Fully charge the battery with 1C, and perform an overcharge test according to 3C overcharge 10V. When the battery is overcharged, the voltage rises to a certain voltage and stabilizes for a period of time. When it approaches a certain time, the battery voltage rises rapidly. When it rises to a certain limit, the battery cap is pulled off, and the voltage drops to 0V. The battery does not catch fire or explode.

4. Short circuit test:

After the battery is fully charged, use a wire with a resistance of no more than 50mΩ to short-circuit the positive and negative poles of the battery, and test the surface temperature change of the battery. The highest surface temperature of the battery is 140℃. The battery cap is pulled open, and the Column rechargeable battery does not catch fire or explode.

5. Needle puncture test:

Put the fully charged battery on a plane and pierce the battery radially with a steel needle with a diameter of 3mm. Test that the battery does not catch fire or explode.

6. Temperature cycle test:

The temperature cycle test of lithium-ion batteries is used to simulate the safety of lithium-ion batteries repeatedly exposed to low and high temperature environments during transportation or storage. The test is carried out using rapid and extreme temperature changes. After the test, the sample should not catch fire, explode or leak.

4. Column rechargeable battery pack safety solution

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How to improve the parts that are prone to safety problems in the process of materials, manufacturing and use of lithium-ion batteries is a problem that lithium-ion battery manufacturers need to solve.

1. Improve the safety of electrolyte

The safety hazards of Column rechargeable battery pack electrolyte can be effectively solved by adding functional additives, using new lithium salts and using new solvents.

According to the different functions of additives, they can be mainly divided into the following types: safety protection additives, film-forming additives, positive electrode protection additives, stable lithium salt additives, lithium precipitation additives, current collector anticorrosive additives, wettability enhancement additives, etc.

For solvents, many researchers have proposed a series of new organic solvents, such as carboxylic acid esters and organic ether organic solvents. In addition, ionic liquids also have a class of highly safe electrolytes, but compared with the commonly used carbonate electrolytes, the viscosity of ionic liquids is several orders of magnitude higher, and the conductivity and ion self-diffusion coefficient are lower, and there is still a lot of work to be done before practical application.

2. Improve the safety of electrode materials

Lithium iron phosphate battery packs and ternary composite materials are considered to be low-cost and "safe" positive electrode materials, which may be widely used in the electric vehicle industry. For positive electrode materials, a common method to improve their safety is coating modification, such as coating the surface of positive electrode materials with metal oxides, which can prevent direct contact between positive electrode materials and electrolytes, inhibit phase change of positive electrode materials, improve their structural stability, reduce the disorder of cations in the lattice, and reduce heat generation by side reactions.

For negative electrode materials, since their surface is often the part of lithium batteries that is most prone to thermochemical decomposition and heat release, improving the thermal stability of SEI film is a key method to improve the safety of negative electrode materials. The thermal stability of negative electrode materials can be improved by weak oxidation, metal and metal oxide deposition, polymer or carbon coating.

3. Improve the safety protection design of batteries

In addition to improving the safety of battery materials, such as setting battery safety valves, hot melt fuses, connecting components with positive temperature coefficients in series, using heat-sealed diaphragms, loading dedicated protection circuits, dedicated battery management systems, etc., are also means to enhance safety.

As the safety of Column rechargeable battery packs has attracted more and more attention, many companies have conducted research and development specifically targeting the safety hazards in lithium-ion batteries and proposed effective battery safety solutions.

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