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Introduction to Positive and Negative Electrode Materials of Lithium-Ion Batteries

Lithium-ion batteries have the advantages of being lightweight, high-capacity, and having no memory effect, so they have been widely used - many digital devices now use lithium-ion batteries as power sources, despite being relatively expensive. The high energy density of lithium-ion batteries means that they have a capacity 1.5-2 times that of nickel-hydrogen batteries of the same weight, and they also have a very low self-discharge rate. In addition, the lack of "memory effect" and absence of toxic substances in lithium-ion batteries are also important reasons for their widespread use.

Working principle of lithium-ion batteries

Lithium-ion batteries are divided into lithium batteries and lithium-ion batteries. Currently, lithium-ion batteries are used in mobile phones and laptops, and they are commonly referred to as lithium batteries. Currently, mobile phones and other devices use lithium-ion batteries, while true lithium batteries, which have a greater risk, are not used in everyday electronic products.

Positive and negative electrode materials of lithium-ion batteries

The negative electrode material of lithium-ion batteries is carbon material, and the positive electrode material of lithium-ion batteries is a compound containing lithium, with no metallic lithium present, only lithium ions. This is what is meant by lithium-ion batteries. Lithium-ion batteries refer to a general term for batteries in which lithium ions are embedded in compounds as positive electrode materials. The charge and discharge process of lithium-ion batteries involves the insertion and extraction of lithium ions. This process also involves the insertion and extraction of equivalent electrons with lithium ions. During the charge and discharge process, lithium ions move back and forth between the positive and negative electrodes, which is figuratively called a "rocking chair battery".

Lithium-ion batteries have a high energy density and a high average output voltage. They have low self-discharge, less than 10% per month. They do not have a memory effect and have a wide operating temperature range of -20°C to 60°C. They have superior cycle performance, can be rapidly charged and discharged, with a charging efficiency of up to 100%, and have a large output power. They have a long service life and are environmentally friendly, earning the title of "green batteries".

Charging is an important step in the repeated use of batteries. The charging process of lithium-ion batteries consists of two stages: constant current fast charging stage (indicated by a red or yellow LED) and constant voltage current decrease stage (indicated by a green LED). During the constant current fast charging stage, the battery voltage gradually increases to the standard voltage of the battery, and then it enters the constant voltage stage under the control of the chip to ensure that overcharging does not occur. The current gradually decreases to 0 as the battery level rises, and the charging is finally completed. The battery capacity is calculated by sampling the discharge curve using a power estimation chip. After multiple uses, the discharge curve of lithium-ion batteries may change. Although lithium-ion batteries do not have a memory effect, improper charging can seriously affect battery performance.

Excessive charging and discharging of lithium-ion batteries can cause permanent damage to the positive and negative electrodes. Excessive discharge causes the collapse of the carbon layer structure of the negative electrode, which prevents the insertion of lithium ions during the charging process. Excessive charging causes excessive insertion of lithium ions into the negative electrode carbon structure, making it difficult for some of the lithium ions to be released. The charging capacity is equal to the charging current multiplied by the charging time. Under the condition of a certain charging control voltage, the larger the charging current (the faster the charging speed), the smaller the charging capacity. Charging the battery too quickly and improper termination voltage control can also result in insufficient battery capacity, where some of the active electrode substances in the battery have not undergone sufficient reactions before charging is stopped. This phenomenon of insufficient charging becomes more pronounced with increasing cycle count.

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