Do you Know the Expansion Process of Graphite Electrodes?

Jan. 29, 2021

As a Graphite Electrodes Exporter, share it with you.

Gas generated inside the battery is an important cause of battery swelling. Whether the battery is stored at room temperature, high temperature cycle, or high temperature, it will produce different degrees of swelling and gas production. According to the current research results, the essence of the cell bloating is caused by the decomposition of the electrolyte. There are two cases of electrolyte decomposition. One is that there are impurities in the electrolyte, such as moisture and metal impurities, which cause the electrolyte to decompose and produce gas. The other is that the electrochemical window of the electrolyte is too low, which causes decomposition during the charging process. Solvents such as EC, DEC, etc. will generate free radicals after getting electrons. The direct consequence of free radical reactions is the production of low-boiling hydrocarbons, esters, ethers and CO2.

HP Graphite Electrodes

HP Graphite Electrodes

The thickness changes of the battery pole pieces have the following situations:

(1) After the pole piece is rolled, the thickness of the pole piece rebounds when it is placed. The greater the compaction density, the greater the rebound; under the same stress, the greater the elastic modulus of the adhesive, the smaller the pole piece rebounds when placed, and drying will also cause The pole piece rebounds.

(2) The pole piece absorbs the electrolyte and swells, and the thickness of the pole piece increases.

(3) During charging and discharging, the insertion of lithium leads to electrode expansion caused by changes in lattice parameters.

In the process of lithiation of the graphite button half-cell and the expansion of the pole piece, during the first discharge lithiation, as the lithium ions intercalate between the graphite layers, the electrode potential gradually decreases and the pole piece thickness expansion rate gradually increases. The whole process can be divided into multiple stages a~e. As the amount of lithium intercalated between graphite layers increases (x gradually increases), LixC6 has several different phases. The characteristics of these phases are listed. x represents the compound LixC6 The molar content of lithium in the middle, d is the lattice parameter graphite layer spacing. As the amount of lithium insertion increases, the graphite changes sequentially from 2H phase. When the SOC is 50%, it changes to LiC12 and becomes LiC6 after complete lithiation. The theoretical capacity is 372mAh/ g. During this transition, the layer spacing d gradually increases, which leads to an increase in the thickness of the pole piece.

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