18650 rechargeable battery lithium 3.7v 3500mah.Introduction and analysis of lithium-ion battery principles and process flow

　　Introduction and analysis of lithium-ion battery principles and process flow

　　Lithium-ion battery principle and process flow 1.

　　Principle

　　1.0 positive electrode structure LiCoO2 (lithium cobalt oxide) + conductive agent (acetylene black) + binder (pVDF) + current collector (aluminum foil) positive electrode

　　2.0 negative electrode structure graphite + conductive agent (acetylene black) + thickener (CMC) + binder (SBR) + current collector (copper foil) negative electrode

　　3.0 working principle

　　3.1 Charging process The power supply charges the battery. At this time, the electrons e on the positive electrode run to the negative electrode through the external circuit. The positive lithium ions Li+ "jump" into the electrolyte from the positive electrode and "crawl" through the small winding holes in the diaphragm. , "swim" to reach the negative electrode, and combine with the electrons that have run over long ago. The reaction that occurs on the positive electrode is LiCoO2 = charging = Li1-xCoO2 + Xli++Xe (electrons) and the reaction that occurs on the negative electrode is 6C + Resistance discharge and constant current discharge actually add a variable resistor in the external circuit that can change with the voltage change. The essence of constant resistance discharge is to add a resistor to the positive and negative terminals of the battery to allow electrons to pass. It can be seen that as long as the electrons on the negative electrode cannot run from the negative electrode to the positive electrode, the battery will not discharge. Both electrons and Li+ move at the same time, in the same direction but in different paths. During discharge, the electrons run from the negative electrode through the electronic conductor to the positive electrode. The lithium ions Li+ "jump" into the electrolyte from the negative electrode and "crawl" across the separator. small hole, "swim" to reach the positive electrode, and combine with the electrons that have run over long ago.

　　2. Process flow

　　3. Battery defective items and causes:

　　1. Reasons for low capacity:

　　a. The amount of attachments is too small;

　　b. The amount of material attached to both sides of the pole piece is quite different;

　　c. The pole piece is broken;

　　d. Less electrolyte;

　　e. The conductivity of the electrolyte is low;

　　f. The positive and negative electrodes are not matched properly;

　　g. The porosity of the separator is small;

　　h. Aging of adhesive → attachment material falling off;

　　i. The roll core is extremely thick (not dried or the electrolyte has not penetrated)

　　j. Not fully charged when dividing the capacity;

　　k. The positive and negative electrode materials have small specific capacities.

　　2. Causes of high internal resistance:

　　a. The negative electrode piece and the tab are welded;

　　b. The positive electrode piece and the tab are weakly welded;

　　c. The positive electrode lug and the cap are weakly welded;

　　d. The negative electrode lug and the shell are weakly welded;

　　e. The internal resistance of the contact between the rivet and the pressure plate is large;

　　f. No conductive agent is added to the positive electrode;

　　g. The electrolyte does not contain lithium salt;

　　h. The battery has been short-circuited;

　　i. The separator paper has small porosity.

　　3. Causes of low voltage:

　　a. Side reactions (electrolyte decomposition; impurities in the positive electrode; water);

　　b. Not well formed (the SEI film is not formed safely);

　　c. The customer’s circuit board leaks electricity (referring to the cells sent back after processing by the customer);

　　d. The customer failed to spot weld as required (cells processed by the customer);

　　e. Burr;

　　f.Micro short circuit;

　　g. The negative electrode produces dendrites.

　　4. Over-thickness The reasons for over-thickness are as follows:

　　a. Weld leakage;

　　b. Decomposition of electrolyte;

　　c. Undried moisture;

　　d. The cap has poor sealing performance;

　　e. The shell wall is too thick;

　　f.The shell is too thick;

　　g. The core is too thick (too many attachments; the pole piece is not compacted; the diaphragm is too thick).

　　5. The causes are as follows:

　　a. Not well formed (the SEI film is incomplete and dense);

　　b. The baking temperature is too high → the adhesive ages → the material is removed;

　　c. The specific capacity of the negative electrode is low;

　　d. The positive electrode has more materials and the negative electrode has less materials;

　　e. The cap is leaking and the weld is leaking;

　　f. The electrolyte decomposes and the conductivity decreases.

　　6. Explosion

　　a. The sub-capacity cabinet is faulty (causing overcharging);

　　b. Poor diaphragm closing effect;

　　c. Internal short circuit 7. Short circuit

　　a. Material dust; b. Broken during shelling;

　　c. Scrape with a ruler (the small diaphragm paper is too small or not padded properly);

　　d. Uneven winding;

　　e. Not wrapped well;

　　f. There is a hole in the diaphragm;

　　g. Burr

　　8.Break circuit

　　a) The tabs and rivets are not welded properly, or the effective solder joint area is small;

　　b) The connecting piece is broken (the connecting piece is too short or is welded too far down when spot welding with the pole piece)

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