What is the structure design of lithium ion aa battery
In terms of design requirements, because the battery case is selected as AA type (Φ14mm 50mm), the battery structure design mainly refers to the battery cover, the tightness of the battery assembly, the size of the electrode sheet, the size of the upper air chamber of the battery, and the size of the two-pole material. Matching and other design. Whether their design is reasonable will directly affect the internal resistance, internal pressure, capacity and safety of the battery.
(1) The design of the battery cover
According to the performance of lithium-ion batteries, at the end of battery charging, the anode voltage is as high as 4.2V or more. Such a high voltage can easily cause stainless steel or nickel-plated stainless steel to be anodicized and corroded. Therefore, the stainless steel or nickel-plated stainless steel cover used in traditional AA-type Cd/Ni and MH/Ni batteries cannot be used for AA-type lithium-ion batteries. Considering that the anode current collector of the lithium ion battery can use aluminum foil without oxidation and corrosion, so based on the AA type Cd/Ni battery cover, the design can be modified.
First, without changing the double-layer structure and appearance of the AA-type Cd/Ni battery cover, replace the nickel-plated stainless steel bottom layer of the battery cover with metal aluminum, and then wrap the aluminum sheet and the nickel-plated stainless steel upper layer by crimping to make It becomes a whole, and an ethylene-propylene rubber vent valve with a pressure resistance of 1.0~1.5MPa is placed between them. Experiments have confirmed that the modified battery cover not only has good airtightness and safety, but is also corrosion-resistant and easy to weld with the aluminum positive electrode tabs.
(2) Determination of assembly tightness
The size of the assembly tightness is mainly determined by the different battery series, the size of the electrode and the diaphragm and the degree of expansion.
For the design of lithium ion aa battery, the expansion of the electrode is mainly caused by the additives of acetylene black and polyvinylidene fluoride in the positive and negative materials. Due to the small amount of addition, the expansion of the electrode after liquid absorption will not be too large. ; During the charge and discharge process, the electrode expansion caused by the insertion/detachment of Lit in the cathode material, such as LiCoO2 and the electrolyte is also very small; the thickness of the battery diaphragm is only 25m, and its composition is Celgard2300PP/PE/PP three-layer film , The swelling degree is also smaller after liquid absorption.
Taking the above factors into consideration, lithium-ion batteries should adopt a tightly assembled structural design. Through the battery winding, casing and battery injection experiments, combined with the results of whether the pole powder falls off or adheres to the diaphragm after the battery is dissected, it can be determined that the tightness of the assembly of the lithium ion aa battery is η=86%~92 %.