Analysis on safety problems of lithium battery

　　Look at the real cause of the accident. Some are due to battery problems, and some are not. Is the battery safe and reliable? Why does the battery explode when using a mobile phone? The most commonly used mobile phones in our lives are equipped with lithium ion batteries. There are six main reasons for lithium ion battery explosion:

　　(1) It is an internal short circuit. Improper operation or misuse may cause internal short circuit. Due to internal short circuit, the discharge current of the battery is large, which will heat the battery. High temperature will shrink or completely damage the diaphragm in the battery, leading to external short circuit and explosion. Possible position of internal short circuit: the electrified core is not aligned, resulting in positive and negative pole contact; The electric core ignites during the overturning process;

　　(2) The positive and negative poles are short circuited when users use it; The protection circuit board has failed. Internal short circuitAs a result of external short circuit, large current discharge of the battery will generate a lot of heat and burn the diaphragm, leading to greater short circuit. In this way, the battery will generate high temperature and decompose the electrolyte into gas, resulting in high external pressure. When the battery case cannot withstand this pressure, the battery will explode. External short circuit station: 2 positive and negative burrs; The positive and negative pole pieces fall off; Negative riveting is not flattened, with burrs; Uneven winding; Incorrect gluing position; Wrap the negative terminal lug with high-temperature tape; The adhesive primer cannot completely cover the bottom surface; 2. The diaphragm paper has sand holes; If the temperature is too high during baking, the diaphragm will be damaged; 2. Excessive pressure during flattening; 2. The assembled short circuit battery is not detected; Assemble miniature short circuit battery upstream; Short circuit unit of laser welding is not detected;

　　(3) When the overcharge cell is overcharged, the excessive release of positive lithium will change the structure of the positive electrode. The excessive release of lithium is easy to be unable to insert into the negative electrode, and it is easy to cause lithium precipitation on the negative electrode surface. In addition, when the voltage exceeds 4.5V, the electrolyte will decompose and generate a large amount of gas. All of the above conditions may lead to explosion. Possible overcharging station: the current is set too high during pre charging; The current at each point of the pre charging cabinet is too large; Current setting is too large during detection; Insufficient battery capacity; The voltage at individual points is too high during detection; When the user uses the charger, the charger voltage is too high.

　　(4) Excessive discharge. If the water content is too high, the water will react with the electrolyte in the battery to produce gas. During the charging process, it will react with the generated lithium to generate lithium oxide, which will lead to the loss of battery capacity and easy to overcharge the battery and generate gas. The decomposition voltage of water is low, so it is easy to decompose and generate gas when charging. When the gas generated in this series will increase the external pressure of the battery, the battery will explode when the battery shell cannot bear it.

　　(5) Insufficient capacity of the negative pole When the capacity of the negative pole next to the positive pole is insufficient or there is no capacity at all, part or all of the lithium produced during the charging process cannot be inserted into the interlayer structure of the negative pole graphite, and will precipitate on the surface of the negative pole to form a convex "dendrite", which is more likely to cause lithium precipitation during the next charging. After tens to hundreds of charging and discharging cycles, the "dendrite" will grow up and eventually pierce the diaphragm paper, Causes external short circuit. Sites with insufficient negative capacity:

　　(6) High positive incoming line capacity; The positive and negative poles are mixed unevenly; Excessive amount of positive dressing; Anode coating is uneven; Stacking of positive terminal and positive tail; Low capacity of negative incoming line; Anode coating is uneven; Negative dark mark; Negative pole scratch; Negative concave point; Negative exposed foil; Negative electrode particles; Die when pressing negative electrode; Positive and negative pole matching error; The negative pole cannot wrap the positive pole;

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