Lithium battery working principle and assembly process

The working principle of lithium-ion battery refers to its charging and discharging principle. 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.

By the same token, 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. What we usually call battery capacity refers to the discharge capacity.

It is not difficult to see that during the charging and discharging process of the lithium ion battery, the lithium ion is in a state of motion from the positive electrode to the negative electrode to the positive electrode. If we compare the lithium-ion battery to a rocking chair, the two ends of the rocking chair are the two poles of the battery, and the lithium ion is like an excellent sportsman, running back and forth at both ends of the rocking chair. Therefore, the experts gave the lithium-ion battery a cute name rocking chair battery.

Assembly:

According to the positive electrode sheet, the separator-negative electrode sheet, the separator is placed in the order from top to bottom, and the battery core core is wound up, and then the electrolyte is injected, the sealing process is completed, that is, the assembly process of the battery is completed, and the finished product is finished. battery.

Charge and discharge test the finished battery with a dedicated battery charge and discharge device, test each battery, and filter out qualified finished batteries to be shipped.

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. There is no memory effect. The operating temperature range is -20 ° C ~ 60 ° C wide. 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.

Mechanism of action

Lithium-ion batteries use a carbon material as the negative electrode and a lithium-containing compound as the positive electrode. There is no metal lithium, only lithium ions. This 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".

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 a lithium battery is set between 0.2 degrees Celsius and 1 c. The higher the current, 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.

Use (discharge) precautions

For batteries, normal use is the process of discharging. Need to pay attention to the discharge of lithium battery:

First, a 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. The larger the battery discharge current, the smaller the discharge capacity and the faster the voltage drop.

Second, it must not be over-discharged! The internal storage of electrical energy in a lithium battery is achieved by a reversible chemical change in electrochemistry. Excessive discharge can cause irreversible reactions of this chemical change, so lithium batteries are most afraid of over-discharge. A discharge voltage below 2.7 v may cause the battery to 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.

"Lithium battery" is a kind of battery that uses lithium metal or lithium alloy as negative electrode material and uses non-aqueous electrolyte solution. The lithium metal battery in 1912 was first proposed and studied by Gilbert N. Lewis. In the 1970s, MSWhittingham proposed and Started research on lithium-ion batteries. Due to the very active chemical properties of lithium metal, lithium metal processing, storage, use, and environmental requirements are very high, so lithium batteries have not been used for a long time. With the development of science and technology, lithium batteries have 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 are rechargeable. The fifth-generation lithium-metal battery for rechargeable batteries was born in 1996. Its safety, specific capacity, self-discharge rate and performance-price ratio are superior to those of lithium-ion batteries. Due to its own high technical requirements, only a few companies in the country are producing such lithium metal batteries.

In the 1970s, M.S. Whittingham of Exxon used titanium sulfide as the positive electrode material and lithium metal as the negative electrode material to make the first lithium battery.

In 1980, J. Goodenough discovered that lithium cobaltate can be used as a positive electrode material for lithium ion batteries.

In 1982, R.R. Agarwal and J.R. Selman of the Illinois Institute of Technology discovered that lithium ions have the property of being embedded in graphite, which is fast and reversible. At the same time, the lithium battery made of lithium metal has attracted much attention, so people tried to make a rechargeable battery by utilizing the characteristics of lithium ion embedded graphite. The first available lithium ion graphite electrode was successfully produced by Bell Labs.

In 1983, M. Thackeray, J. Goodenough et al. found that manganese spinel is an excellent positive electrode material with low price, stability and excellent electrical conductivity and lithium-conducting properties. The decomposition temperature is high, and the oxidation is much lower than that of lithium cobaltate. Even if a short circuit occurs, overcharged electricity can avoid the danger of burning and explosion.

In 1989, A. Manthiram and J. Goodenough discovered that a positive electrode with a polymeric anion would produce a higher voltage.

In 1991, Sony released the first commercial lithium-ion battery. Subsequently, lithium-ion batteries revolutionized the face of consumer electronics.

In 1996, Padhi and the foreword found that phosphates with olivine structure, such as lithium iron phosphate (lithium iron phosphate), are superior to traditional positive electrode materials, and thus have become the mainstream cathode materials.

With the widespread use of digital products such as mobile phones, notebook computers, etc., lithium-ion batteries have been widely used in such products with excellent performance, and are gradually being developed into other product applications. In 1998, Tianjin Power Research Institute began commercial Production of lithium-ion batteries. Habitually, people also call lithium-ion batteries lithium batteries, but these two batteries are not the same. Lithium-ion batteries have become mainstream.

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