November 21, 2018

Analysis of common leakage and rust of 18650 batteries

In this page, the following terms mean:

  • A, PP and steel shell wall
  • B, PP and cap assembly
  • C, D, F, steel shell and cap assembly
  • E, cap internal components.

First, summary of leakage type:

  • 1. black substance
  • 2, yellow rust
  • 3, white crystal
  • 4, green rust

EDS analysis: The black substance is mainly composed of carbon and oxygen, and the electrolyte, iron and nickel are mixed.

Yellow rust contains iron and a small amount of electrolyte.

The main components of white crystals are: electrolyte, aluminum and trace iron.

The specific formation process:

Yellow substance: The electrolyte leaks out of the corrosion surface pad and causes the battery to short circuit.

Yellow rust: The shell leakage causes the steel shell to rust.

White crystal: poor sealing causes the electrolyte to leak from the inside of the cap.

Analysis of the cause of leakage:

1. Black substance: the residual electrolyte of the steel shell and the cap PP gap A is changed due to the external environment or internal temperature. After the electrolyte leaks along the C channel, the infiltrating surface pad shorts the positive and negative electrodes. A black substance is produced behind the mat.

2, yellow rust: the sealing is not strict or the inside of the cell changes (temperature rise, internal pressure is too large), causing the internal electrolyte of the cell to leak outward along the channel F through B, leaking to D to make the battery positive and negative A micro-short circuit occurs, causing corrosion of the steel shell and the top cover.

3, white crystal: the battery core is not tight or the internal changes (temperature rise, excessive internal pressure) cause the internal electrolyte to leak along the channel F through B, leaking from E to the upper surface of CID, in CID The surface is crystallized to produce white crystals.

4. Green rust: The sealing is not strict, causing the internal electrolyte of the battery to leak outward along the channel F through B. Leakage to D causes micro-short circuit between the positive and negative poles of the battery, or just due to electrolyte leakage, the steel shell and The nickel plating on the top cover surface is rusted, resulting in green rust.