The working principle of lithium ion battery and positive and negative materials

A lithium-ion battery is a rechargeable battery that relies on lithium ions to move between the positive and negative electrodes to work. During charge and discharge, Li+ is intercalated and deintercalated between the two electrodes: when charging the battery, Li+ is deintercalated from the positive electrode, and the electrolyte is embedded in the negative electrode, and the negative electrode is in a lithium-rich state. The following article is about details of the principle and maintenance of the lithium battery.

A lithium-ion battery is a rechargeable battery that relies on lithium ions to move between the positive and negative electrodes to work. During charge and discharge, Li+ is intercalated and deintercalated between the two electrodes: when charging the battery, Li+ is deintercalated from the positive electrode, and the electrolyte is embedded in the negative electrode, and the negative electrode is in a lithium-rich state, containing a lithium element as electrode is generally used. It is representative of modern high performance batteries.

Lithium-ion battery - introduction

Lithium-ion battery Lithium-ion battery Lithium-ion battery (Li-ion, Lithium IonBattery): Lithium-ion battery has the advantages of light weight, large capacity, no memory effect, etc., and thus has been widely used - many of today's digital devices use lithium ion battery as a power source, although its price is relatively expensive. Lithium-ion batteries have a high energy density, and their capacity is 1.5 to 2 times that of nickel-hydrogen batteries of the same weight, and has a very low self-discharge rate. In addition, the lithium-ion battery has almost no "memory effect" and does not contain toxic substances, which is also an important reason for its wide application.

How lithium-ion batteries work

Lithium-ion battery Lithium-ion battery principle structure Lithium-based battery is divided into lithium battery and lithium-ion battery. At present, mobile phones and laptops use lithium-ion batteries, which are commonly referred to as lithium batteries. Currently, lithium-ion batteries used in mobile phones and the like, and true lithium batteries are not used in everyday electronic products because of their high risk.

Lithium ion battery positive and negative materials

The anode material of the lithium ion battery is a carbon material, and the cathode material of the lithium ion battery is a lithium-containing compound. There is no metal lithium, only lithium ions, which is a lithium ion battery. A lithium ion battery is a general term for a battery in which a lithium ion intercalation compound is used as a positive electrode material. The charging and discharging process of a lithium ion battery is a process of intercalating and deintercalating lithium ions. In the process of intercalation and deintercalation of lithium ions, concomitant insertion and deintercalation of equivalent electrons with lithium ions (commonly referred to as embedding or deintercalation of the positive electrode and insertion or deintercalation of the negative electrode). During charge and discharge, lithium ions are intercalated/deintercalated and inserted/deintercalated between the positive and negative electrodes, and are aptly referred to as "rocking chair batteries".

Lithium-ion batteries have high energy density and high average output voltage. Self-discharge is small, less than 10% per month. There is no memory effect. The operating temperature range is -20 ° C ~ 60 ° C. Excellent cycle performance, fast charge and discharge, charging efficiency up to 100%, and high output power long lasting. Without environmental pollution, it is called a green battery.

Charging is an important step in the repeated use of the battery. The charging process of the lithium-ion battery is divided into two phases: a constant current fast charging phase (the indicator light is red or yellow) and a constant voltage current decreasing phase (the indicator light is green). During the constant current fast charge phase, the battery voltage is gradually increased to the standard voltage of the battery, and then transferred to the constant voltage stage under the control chip, the voltage is no longer raised to ensure that it does not overcharge, and the current is gradually weakened as the battery power rises. Go to 0 and finish charging. The power statistic chip can calculate the battery power by recording the discharge curve. Lithium-ion batteries will change their discharge curve after repeated use. 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. Over-discharge leads to collapse of the negative carbon sheet structure, and collapse causes lithium ions to be inserted during charging; excessive charging causes excessive lithium ions to be inserted into the negative carbon structure, and some of the lithium ions are no longer released.

The amount of charge is equal to the charging current multiplied by the charging time. When the charging control voltage is constant, the charging current is larger (the charging speed is faster), and the charging amount is smaller. If the battery charging speed is too fast and the termination voltage control point is improper, the battery capacity will also be insufficient. Actually, some of the electrode active materials of the battery are not fully reacted and the charging is stopped. This phenomenon of insufficient charging is aggravated as the number of cycles increases.

Steel shell / aluminum shell series:

(1) Battery upper and lower cover

(2) Positive electrode - the active material is generally lithium cobalt oxide

(3) Separator - a special composite membrane

(4) Negative electrode - the active material is carbon

(5) Organic electrolyte

(6) Battery case (divided into steel case and aluminum case)

Flexible packaging series

(1) Positive electrode - the active material is generally lithium cobalt oxide

(2) Separator - PP or PE composite film

(3) Negative electrode - the active material is carbon

(4) Organic electrolyte

(5) Battery case - aluminum-plastic composite film

How lithium-ion batteries work

Lithium ion battery schematic

When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the generated lithium ions move to the negative electrode through the electrolyte. The carbon as the negative electrode has a layered structure, and it has many micropores. The lithium ions reaching the negative electrode are embedded in the micropores of the carbon layer, and the more lithium ions are embedded, the higher the charging capacity. Similarly, when the battery is discharged (ie, the process we use the battery), the lithium ions embedded in the carbon layer of the negative electrode come out and move back to the positive electrode. The more lithium ions return to the positive electrode, the higher the discharge capacity.

Generally, the charging current of the lithium battery is set between 0.2C and 1C. The larger the current is, the faster the charging and the greater the heat of the battery. Moreover, excessive current charging, the capacity is not full, because the electrochemical reaction inside the battery takes time. Just like pouring beer, if it is too fast, it will produce bubbles, but it will not be full. For batteries, normal use is the process of discharging.

Need to pay attention to the discharge of lithium battery:

First, the discharge current should not be too large. Excessive current causes heat inside the battery, which may cause permanent damage. On the mobile phone, this is no problem, you can not consider it.

Second, you must never over discharge. Lithium batteries are most afraid of over-discharge. Once the discharge voltage is lower than 2.7V, the battery may be scrapped. Fortunately, the inside of the mobile phone battery has been installed with a protection circuit, the voltage is not low enough to damage the battery, the protection circuit will work, stop discharging. The larger the discharge current of the battery, the smaller the discharge capacity and the faster the voltage drop.

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