The working principle of lithium-ion batteries

The lithium ion battery uses a carbon material as a negative electrode and a lithium-containing compound as a positive electrode, and no lithium metal exists, and only lithium ions. 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. No memory effects. The operating temperature range is -20 °C to 60 °C. High cycle performance, fast charging and discharging, charging efficiency up to 100 %, and output power. Long service life. There is no environmental pollution and it is called a green battery.

Mechanism of action

The lithium ion battery uses a carbon material as a negative electrode and a lithium-containing compound as a positive electrode, and no lithium metal exists, and only lithium ions. 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".

When the battery is charged, lithium ions are generated on the positive electrode of the battery, and the resulting lithium ions move through the electrolyte to the negative electrode. The carbon as a negative electrode has a layered structure. It has many micropores. Lithium ions that reach the negative electrode are embedded in the micropores of the carbon layer. The more lithium ions embedded, the higher the charging capacity. Similarly, when the battery is discharged (that is, when we use the battery), the lithium ions embedded in the negative carbon layer are removed and moved back to the positive pole. The more lithium ions that return to the positive pole, the higher the discharge capacity.

In general, the charging current of a lithium battery is set between 0.2 C and 1C. The greater the current, the faster the charge, and the greater the battery heat. Moreover, excessive current charging is not full enough because the electrochemical reaction inside the battery takes time. Just like pouring beer, if you pour too fast, you will produce foam, but you are dissatisfied.

Use(discharge) precautions

For batteries, normal use is the process of discharge. Lithium battery discharge needs to pay attention to several points:

First, the discharge current must not be too large. Excessive current causes heat inside the battery and may cause permanent damage. On the phone, there's nothing wrong with that.

From the figure on the right, it can be seen that the larger the discharge current of the battery, the smaller the discharge capacity and the faster the voltage drop.

Second, absolutely not over discharge! The internal storage of electrical energy in a lithium battery is achieved by a reversible chemical change in electrochemistry. Excessive discharge will lead to an irreversible reaction of this chemical change. Therefore, the lithium battery is most afraid of over discharge. Once the discharge voltage is lower than 2.7 V, it may cause the battery to scrap. Fortunately, the protective circuit has been installed inside the cell phone battery. The voltage is not yet low enough to damage the battery. The protective circuit will work and stop the discharge.

"Lithium battery" is a type of battery that uses lithium metal or lithium alloy as a negative electrode material and uses a non-aqueous electrolyte solution. In 1912, the lithium metal battery was first proposed and studied by GilbertN. Lewis. In the 1970s, M.S. Whittingham proposed and began to study lithium ion batteries. Due to the very lively chemical properties of lithium metals, the processing, preservation, and use of lithium metals require very high environmental requirements. Therefore, lithium batteries have not been used for a long time. With the development of science and technology, lithium batteries have now become the mainstream.

Lithium batteries can be roughly divided into two categories: lithium metal batteries and lithium ion batteries. Lithium-ion batteries do not contain metallic lithium and can be charged. The fifth-generation lithium metal battery of rechargeable batteries was born in 1996, and its safety, specific capacity, self-discharge rate and performance price are better than those of lithium-ion batteries. Due to its own high-tech requirements, companies in only a few countries are now producing this lithium metal battery.

Lithium metal battery:

Lithium metal batteries generally use manganese dioxide as a positive electrode material, lithium metal or its alloy metal as a negative electrode material, and batteries using non-aqueous electrolyte solutions.

Basic Principles of Lithium Battery

Basic Principles of Lithium Battery

Discharge reaction: Li + MnO2 = LiMnO2

Lithium-ion batteries:

Lithium-ion batteries generally use lithium alloy metal oxides as positive electrode materials, graphite as negative electrode materials, and batteries using non-aqueous electrolytes.

The reaction that occurs on the charging positive pole is

LiCoO2 = Li(1-x) CoO2 + XLi + Xe-(electron)

The reaction that occurs on the charge negative pole is

6C + XLi + Xe-= LixC 6

Total rechargeable battery reaction: LiCoO2 +6 C = Li(1-x) CoO2 + LixC6

positive electrode

Positive materials: There are many optional positive materials, and mainstream products are mostly lithium iron phosphate. Different positive material comparisons:

LiCoO2

3.7 V

140mAh/g

Li2Mn2O4

4.0 V

100 mAh/g

LiFePO4

3.3 V

100 mAh/g

Li2FePO4F

3.6 V

115 mAh/g

Positive electrode reaction: Lithium ions are embedded during discharge, and lithium ions are deintercalated during charging. When charging: LiFePO4→Li1-xFePO4+xLi++xe-discharge: Li1-xFePO4+xLi++xe-→LiFePO4.

Negative electrode

Negative materials: More graphite. New research has found that titanate may be a better material.

Negative electrode reaction: Lithium ions are deintercalated during discharge, and lithium ions are embedded during charging.

When charging: xLi + + XE-+6C → LixC6

Discharge: LixC6 → xLi + XE-+6C

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