stw14@stwpower.com 
Lithium batteries are divided into lithium metal batteries and lithium ion batteries.
1. Lithium metal battery
Lithium metal batteries generally use manganese dioxide as the positive electrode material, metal lithium or its alloy metal as the negative electrode material, and use a non-aqueous electrolyte solution. The principle of discharge reaction is: Li+MnO2=LiMnO2
2. Lithium-ion battery
Lithium-ion batteries generally use lithium alloy metal oxides as positive electrode materials, graphite as negative electrode materials, and use non-aqueous electrolytes. The reaction on the charging positive electrode is: LiCoO2==Li(1-x)CoO2+XLi++Xe- (electron); the reaction on the charging negative electrode is: 6C+XLi++Xe- = LixC6; the total reaction of the rechargeable battery : LiCoO2+6C = Li(1-x)CoO2+LixC6
Lithium battery principle
The positive electrode material of lithium ion battery is usually composed of lithium active compounds, and the negative electrode is carbon with special molecular structure. The main component of the common cathode material is LiCoO2. When charging, the potential applied to the two poles of the battery forces the compound of the cathode to release lithium ions, which are embedded in the carbon whose molecules of the anode are arranged in a lamellar structure. During discharge, lithium ions are precipitated from the carbon in the lamellar structure and recombine with the compound of the positive electrode. The movement of lithium ions creates an electric current.
Although the chemical reaction principle is very simple, in actual industrial production, there are many practical problems that need to be considered: the positive electrode material needs additives to maintain the activity of multiple charges and discharges, and the negative electrode material needs to be designed at the molecular structure level. To accommodate more lithium ions; the electrolyte filled between the positive and negative electrodes, in addition to maintaining stability, also needs to have good conductivity and reduce the internal resistance of the battery.
Although lithium-ion batteries rarely have the memory effect of nickel-cadmium batteries, the principle of memory effect is crystallization, which hardly occurs in lithium batteries. However, the capacity of lithium-ion batteries will still decrease after multiple charging and discharging, and the reasons are complex and diverse. It is mainly the change of the positive and negative materials themselves. From the molecular level, the hole structure that accommodates lithium ions on the positive and negative electrodes will gradually collapse and block; from a chemical point of view, it is the active passivation of the positive and negative materials, resulting in stable side reactions. other compounds. Physically, the positive electrode material will gradually peel off, which ultimately reduces the number of lithium ions in the battery that can move freely during the charging and discharging process.
Overcharging and overdischarging will cause permanent damage to the positive and negative electrodes of lithium-ion batteries. From the molecular level, it can be intuitively understood that overdischarging will cause the negative electrode carbon to excessively release lithium ions and cause its lamellar structure to collapse. Overcharging will force so many lithium ions into the negative carbon structure that some of them can no longer be released. This is also the reason why lithium-ion batteries are usually equipped with control circuits for charging and discharging.
Unsuitable temperature will trigger other chemical reactions inside the lithium-ion battery to generate compounds that we do not want to see, so many lithium-ion batteries are provided with protective temperature-controlled separators or electrolyte additives between the positive and negative electrodes. When the temperature of the battery reaches a certain level, the pores of the composite membrane are closed or the electrolyte is denatured, the internal resistance of the battery increases until the circuit is disconnected, and the battery does not heat up any more to ensure that the battery charging temperature is normal.
And can deep charge and discharge increase the actual capacity of lithium-ion batteries? Experts tell me unequivocally that it doesn't make sense. They even said that the so-called "activation" using the first three full charges and discharges is also unnecessary. However, why do many people change the capacity indicated in the Battery Information after deep charging and discharging? It will be mentioned later.
Lithium-ion batteries generally have a management chip and a charge control chip. Among them, there are a series of registers in the management chip, which store the values of capacity, temperature, ID, charging state, and discharge times. These values will gradually change during use. I personally think that the main function of the method of "full charge and discharge once a month or so" in the instruction manual should be to correct the improper values in these registers, so that the charging control and the nominal capacity of the battery match the actual situation of the battery.
The charging control chip mainly controls the charging process of the battery. The charging process of the lithium-ion battery is divided into two stages, the constant current fast charging stage (when the battery indicator light turns yellow) and the constant voltage current decreasing stage (the battery indicator light flashes green. In the constant current fast charging stage, the battery voltage gradually increases The standard voltage of the battery is reached, and then it is transferred to the constant voltage stage under the control chip, the voltage will not increase to ensure that it will not be overcharged, and the current will gradually weaken to 0 with the increase of the battery power, and finally complete the charging.
The power statistics chip can sample and calculate the power of the battery by recording the discharge curve (voltage, current, time), which is the wh. value we read in the Battery Information. The discharge curve of a lithium-ion battery will change after multiple uses. If the chip has no chance to read out a complete discharge curve again, the calculated power will be inaccurate. So we need deep charge and discharge to calibrate the battery chip.