The lithium ion battery is generally a battery using lithium alloy metal oxide as a positive electrode material, graphite as a negative electrode material, and a non-aqueous electrolyte. The mobile phones we usually use are almost all lithium batteries. At present, the power supplies of the more popular electric vehicles on the market are mostly lithium iron phosphate batteries. How do lithium batteries charge and discharge?

First of all, let's understand the structure of lithium batteries. Lithium batteries are generally composed of positive electrodes, negative electrodes, electrolyte and separators. In daily life, our common mobile phone lithium batteries are square, and the batteries in electric vehicle battery packs are generally round. There are other shapes. Laminated and wound type. The four contacts on the common mobile phone battery, in addition to the positive and negative poles, the remaining contacts are simply to detect (or monitor) various information of the mobile phone battery.

The positive electrode of lithium battery is generally lithium manganate or lithium cobalt oxide, nickel cobalt lithium manganate material, and electric bicycles generally use nickel cobalt lithium manganate (commonly known as ternary) or a small amount of ternary lithium manganate;The negative electrode is generally graphite as an active material, or carbon with an approximate graphite structure. The separator between the positive electrode and the negative electrode is a specially formed polymer film. The pore size meets good ion passability and has electronic insulation. Lithium ions can pass freely, but electrons cannot pass through.The electrolyte plays the role of transporting charge between the positive and negative electrodes, and is generally a carbonate solvent in which lithium hexafluorophosphate is dissolved, and a gel electrolyte is used for polymers.

When the lithium battery is charged, the positive electrode releases lithium ions, and the lithium ions pass through the separator through the electrolyte, move to the negative electrode, and combine with the electrons of the abdominal muscle. At this time, the chemical reaction at the positive electrode is LiCoO2 = Li(1-x)CoO2 xLi xe-(electron), and the chemical reaction at the negative electrode is 6C xLi xe- = LixC6. When the lithium battery is discharged, the lithium ion movement is just the opposite. The lithium ion enters the electrolyte from the negative electrode, passes through the diaphragm and finally reaches the positive electrode, while the electron is from the negative electrode to the positive electrode by the external circuit (the direction of electron movement is opposite to the direction of current), and the lithium ion of the positive electrode is combined. This process can make the lithium battery output electric energy.

The charging process of lithium batteries is generally divided into three stages: trickle charging, constant current charging and constant voltage charging. Taking a mobile phone battery as an example, when charging starts, an internal charging management chip first detects the voltage of the battery to be charged. If the voltage is lower than 3V, pre-charging is performed first. The charging current is 1/10 of the set current. After the voltage rises to 3V, the standard charging process is entered. The standard charging process is: constant current charging with a set current. When the battery voltage rises to 4.20V, it is changed to constant voltage charging to keep the charging voltage at 4.20V. At this time, the charging current gradually decreases, and when the current decreases to 1/10 of the set charging current, the charging ends. Generally, the output voltage of the mobile phone charger is 5V, and the charging management chip inside the mobile phone is responsible for reducing the voltage to 3.7V suitable for the mobile phone battery.

Lithium battery energy is relatively high. It has a high storage energy density, which has reached 460-600Wh/kg, which is about 6-7 times that of lead-acid batteries; it has a long service life, generally up to more than six years; it has high power endurance; and it has the characteristics of low self-discharge rate. The application in daily life is getting wider and wider.

Source: Book Grocery Store