What's the structure of  lithium polymer battery?

What's the structure of lithium polymer battery?

Published by Kevan XiaoEdith at2021-04-23

What's the structure of  lithium polymer battery?

Part 1:Internal structure of polymer lithium battery

The structure of polymer lithium battery is divided into:

  • Positive pole piece
  • Negative pole piece
  • Battery electrolyte
  • Battery diaphragm
  • aluminum plastic film
  • Packaging aluminum plastic film
  • Positive pole ear
  • Negative pole ear

Part 2: The working principle of each part of the lithium battery

1. Positive pole piece: Coating the positive electrode material on the aluminum foil, and then stamping and forming.

2. Negative pole piece: The negative electrode material is coated on the copper foil, and then stamped and formed.

3. Welding electrode ears for lithium batteries: The main function of the lug is to transfer the electrical energy of the internal positive and negative poles to the external circuit. The tabs of the polymer battery are made of aluminum tape for the positive pole and nickel tape for the negative pole. Considering the sealing with the aluminum-plastic packaging film, there is a layer of tab glue on the tabs of the seal. At the same time, since the anode aluminum strip is easy to break, special attention should be paid to protection during processing, transportation, storage, and use.

Structure diagram of polymer lithium battery cell

In order to ensure the sealing effect, the material of the tab glue is basically the same as that of the inner layer of the packaging film, mainly PE substances.

4. Separator: It is placed between the positive pole piece and the negative pole piece. The function of the separator is to separate the positive and negative poles of the battery to prevent the two poles from being directly short-circuited. The diaphragm itself does not conduct electricity, but electrolyte ions can pass through.

5.battery solution : The electrolyte acts as a carrier of energy transfer in the battery. The voltage of lithium-ion batteries is as high as 3~4.2V. Therefore, only organic solvents can be used as electrolytes, and aqueous electrolytes cannot be used (the decomposition voltage of water is 1.23V).

Commonly used lithium salts for lithium ion batteries are LiPF6, LiBF4, LiCl04, and organic solvents include PC (propylene carbonate), EC (ethylene carbonate), BC (butene carbonate), DMC (dimethyl carbonate), DEC ( Diethyl carbonate), MEC (methyl ethylene carbonate), etc.

The electrolyte used in lithium ion batteries should have the following characteristics: high conductivity, high chemical and electrochemical stability, wide usable temperature range, good safety, and low cost.

6. Packaging film: The polymer battery is packaged with aluminum-plastic composite film, which is divided into at least three layers: the middle layer is an aluminum layer, which isolates moisture; the outer layer is a glue layer, which protects the aluminum from being oxidized by the external environment; The layer is a glue layer, which plays a role of sealing and preventing the electrolyte from corroding the aluminum layer. The aluminum-plastic film is stamped and formed into the required shell shape. The pressure resistance of aluminum-plastic film packaging is much worse than that of metal shell batteries. The internal short circuit of the battery can easily cause swelling, and the sealing part will crack in severe cases. Because of this, the safety performance of batteries packaged with aluminum-plastic film is better than that of metal-shell batteries.

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