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Cause analysis of leakage of soft pack lithium battery
225 2023-11-15
Regarding the corrosion leakage problem in the packaging of soft pack batteries, the important process of the sealing effect of the battery is the packaging process, and the packaging quality directly determines the performance of the battery. In general, the causes of aluminum-plastic film corrosion leakage can be divided into three categories:
1. Chemical corrosion
For lithium-ion batteries, because water will react with the electrolyte and attack HF, hydrofluoric acid is a particularly corrosive acid, which will attack serious damage to the aluminum plastic film, the collection liquid, and the positive data, the reaction is as follows: when the film corrodes, the battery is broken.
2. Electrochemical corrosion
Because the electrochemical reaction corrosion leakage of soft pack lithium batteries is difficult to find, generally with the extension of the use of time, the corrosion leakage of the battery will be found to be gradually serious. Due to the long latency time of this failure form, once it occurs, it is also easy to constitute a crisis of trust for customers. Electrochemical corrosion generally has two cases:
Ion short circuit. The aluminum layer of the aluminum film forms an ion short-circuit channel with the anode.
Electronic short circuit. Aluminum film The aluminum layer and the anode form an electronic short-circuit channel.
In this way, the aluminum layer of the aluminum-plastic film that encapsulates the battery forms a short circuit with the anode. The anode is the cathode of the battery, in the low-potential part. Once exposed to aluminum, an electrochemical reaction occurs through a highly conductive electrolyte, resulting in continuous consumption of the aluminum layer. These two conditions are necessary for the battery to be attacked and corroded when short-circuited, and neither is necessary.
The simple structure of the ion channel is that the PP layer of the sealed part is broken during the heat sealing process, or the PP layer is broken during the folding process, thus forming an ion channel between the aluminum layer and the negative electrode.
The simple composition of the electronic short-circuit channel is: the packaging position of the polar ear is destroyed, and the negative ear contacts with the aluminum layer to form the electronic channel. If the cathode is extended too long, it is also easy to form direct contact with the aluminum layer during heat sealing, constituting an electronic short circuit.
In addition to the electronic channels inside the battery, the external contact between the negative ear and the aluminum layer is also one of the reasons for the corrosion leakage of flexible packaging, which happens a little faster. When ion channels and electronic channels are formed, aluminum layer aluminum-plastic film is gradually embedded into lithium ions to form aluminum lithium alloy, and the water after corrosion of aluminum layer can be brazenly immersed in the battery, attacking more serious damage, resulting in the emergence of soft-pack battery leakage failure.
3. Physical reasons
Due to improper use of the battery, accidental bump, resulting in the battery itself flatulence and packaging failure, will also lead to battery leakage. Battery misuse, including battery overcharge, overdischarge, high temperature use, etc., can constitute battery gas, swelling and increase packaging failure. Whether the battery is used at normal temperature cycle, high temperature cycle, and high temperature, it will have different degrees of inflation and gas production. According to the present results, the substance of cell fouling is caused by the bursting and differentiation of the electrolyte. Electrolyte differentiation has two conditions, electrolyte impurities, such as water and metal impurities gas electrolyte differentiation, the other is the low electrolyte electrochemical window, which constitutes the differentiation in the process of charging,EC electrolyte, December, such as the solvent after getting electrons, free radicals will attack, directly resulting in the free radical reaction of low boiling point hydrocarbons, esters, ethers and carbon dioxide. If there is too much water in the battery, it will also constitute more gas, form the battery drum, and form the weak place of the package to break.