lithium ion batteries discharge process

　　Points to note when discharging lithium ion batteries:

　　First, the discharge current should not be too large. Excessive current will cause heat inside the battery, which may cause permanent damage. On the mobile phone, this is not a problem, so you can ignore it.

　　Lithium ion batteries charging process

　　The positive electrode of the battery is generated by lithium ions. The generated lithium ions “jump” into the electrolyte from the positive electrode, and then “climb” through the small tortuous holes in the diaphragm through the electrolyte, move to the negative electrode, and ran through the external circuit. The electrons of the negative electrode bind together. ●The reaction on the positive electrode is: LiCoO2==charging==Li1-xCoO2+Xli++Xe (electron) ●The reaction on the negative electrode is: 6C+XLi++Xe=====LixC6 during charging Li+ is extracted from the positive electrode LiCoO2, enters the electrolyte, moves to the negative electrode under the action of the external electric field added by the charger, and sequentially enters the negative electrode composed of graphite or coke C, forming LiC compound on the negative electrode. 2. Discharge process of lithium ion batteries

　　When discharging, both electrons and Li+ act at the same time, with the same direction but different paths. The electrons run from the negative electrode to the positive electrode through the external circuit; the lithium ion Li+ "jumps" from the negative electrode into the electrolyte and "climbs" over the diaphragm. The small hole, "swimming" to the positive pole, combines with the electrons that have ran over. What we usually call battery capacity refers to discharge capacity.

　　Second, it must not be over-discharged! Lithium ion batteries are most afraid of over-discharge. Once the discharge voltage is lower than 2.7V, the battery may be scrapped. Fortunately, a protection circuit has been installed inside the battery of the mobile phone, and the voltage is not low enough to damage the battery, the protection circuit will work and stop discharging. It can be seen from the figure that the larger the battery discharge current, the smaller the discharge capacity and the faster the voltage drop.

　　An electrode that obtains electrons from an external circuit when the battery is discharged. At this time, the electrode undergoes a reduction reaction. It is usually an electrode with a high potential. Lithium cobalt oxide and lithium manganate electrodes in lithium ion batteries.

　　The battery protection board is mainly an integrated circuit board that protects rechargeable batteries (generally referred to as lithium ion batteries). Lithium ion batteries (rechargeable) need to be protected because the material of lithium ion batteries determines that they cannot be overcharged, overdischarged, overcurrent, short circuited, and ultra-high temperature charging and discharging, so lithium ion batteries are always protected The board and a piece of current fuse appear. The following figure shows the battery board protection circuit. PTC: Positive temperature coefficient thermistor; NTC: Negative temperature coefficient thermistor. When the ambient temperature rises, its resistance decreases. The electrical equipment or charging equipment can respond in time, control internal interruptions and stop charging and discharging; U1 is Circuit protection chip, U2 is two reversed MOSFET switches. In the normal state, the CO and DO of the battery board U1 output high voltage, and both MOSFETs are in the on state, and the battery can be charged and discharged freely.

　　Overcharge protection: When U1 detects that the battery voltage reaches the overcharge protection threshold, the CO pin outputs a low level, the MOS tube switch 2 turns from on to off, the charging circuit is turned off, and the charger can no longer charge the battery. Overcharge protection.

　　Over-discharge protection: During battery discharge, when U1 detects that the battery voltage is lower than the over-discharge protection threshold, the DO pin changes from high to low, and MOS switch 1 is turned off, making the battery unable to discharge; over-discharge In the protection state, the battery voltage can no longer be reduced, and the current of the protection circuit is required to be extremely small, and the control circuit enters low power consumption. Over-current protection: Under normal circumstances, the battery discharges the load, and the current passes through two series-connected MOS transistor switches. The VM pin detects that the voltage drop of the two MOS transistors is U. If the load causes U to be abnormal due to some reason, the loop current increases. When U is greater than a certain value, the DO pin changes from high voltage to low voltage, and MOS tube switch 1 is turned off, so that the current in the discharge loop becomes zero and reaches over Current protection.

　　Negative electrode: active material (graphite, MCMB, CMS), binder, solvent, matrix.

　　The electrode that transports electrons to the circuit when the battery is discharged, and the electrode undergoes an oxidation reaction. Usually the electrode with low potential, graphite electrode in lithium ion battery.

　　Diaphragm

　　The separator is placed between the two poles as a device to isolate the electrodes, so as to avoid direct contact between the active materials on the two poles and cause short circuits inside the battery. But the diaphragm still needs to allow charged ions to pass through to form a path.

　　Diaphragm requirements:

　　1. Large ion permeability

　　2. Appropriate mechanical strength

　　3. It is an insulator

　　4. Does not react with electrolyte and electrodes

　　Material: single-layer PE (polyethylene) or three-layer composite PP (polypropylene) +PE+PP

　　Thickness: single layer is generally 0.016～0.020mm, three layer is generally 0.020～0.025mm

　　Electrolyte

　　Shell hardware (steel shell, aluminum shell, cover plate, lugs, insulating sheet, insulating tape)