How lithium-ion batteries work

Lithium battery" is a kind of battery with lithium metal or lithium alloy as negative electrode material and non-aqueous electrolyte solution. In 1912, lithium metal batteries were first proposed and studied by gilbertn.lewis. In the 1970s, m.s. willingham proposed and began to study lithium-ion batteries. Due to the chemical characteristics of lithium metal is very lively, making the processing, preservation, use of lithium metal, the environment is very high requirements. So lithium batteries have not been used for a long time. With the development of science and technology, lithium battery has 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 of rechargeable lithium metal battery was born in 1996. Its safety, specific capacity, self-discharge rate and performance-to-price ratio are all better than lithium ion battery. Because of its own high technology requirements, only a few companies in a few countries now in the production of the lithium metal battery.

Lithium batteries were first used in pacemakers. Lithium battery self-discharge rate is very low, the discharge voltage is gentle, so that the implanted pacemaker can operate for a long time without recharging. Lithium batteries generally have a nominal voltage higher than 3.0 volts, more suitable for integrated circuit power supply. Manganese dioxide batteries are widely used in calculators, digital cameras and watches.

In order to develop better varieties of performance, various materials have been studied to produce unprecedented products.

In 1992, Sony successfully developed lithium ion battery. Its practical, so that people's mobile phones, laptops, calculators and other portable electronic equipment weight and volume greatly reduced.

1. 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.

2. In 1980, j.godenough found that lithium cobalt oxide could be used as the anode material of lithium ion battery.

3, 1982, university of Illinois institute of technology (the Illinois Institute of Technology) R.R.A garwal and J.R.S elman found embedded lithium ion has the properties of the graphite, the process is quick, and reversible. At the same time, lithium batteries made of lithium metal have attracted much attention because of their potential safety hazards. Therefore, people try to make rechargeable batteries with lithium ion embedded in graphite. The first available lithium - ion graphite electrode was successfully manufactured by bell laboratories.

4. In 1983, m.hackeray, j.groodenough et al. found that manganese spinel was an excellent cathode material with low price, stability and excellent performance of conducting electricity and lithium. Its decomposition temperature is high, and the oxidation is far lower than the lithium cobalt oxide, even if there is a short circuit, overcharge, also can avoid the risk of combustion, explosion.

5. In 1989, a.m. thiram and j.groodenough found that the adoption of positive poles of polymerized anions would generate higher voltages.

6. In 1991, SONY released the first commercial lithium ion battery. Then lithium-ion batteries revolutionized consumer electronics.

7. In 1996, Padhi and Goodenough found that peridotite-structured phosphates, such as lithium iron phosphate (LiFePO4), are superior to traditional anode materials and have become the mainstream anode materials.

With the wide use of digital products such as mobile phones, laptops and other products, lithium ion batteries have been widely used in such products with excellent performance, and gradually to other products in the application field. In 1998, tianjin power research institute began to produce lithium ion battery commercially. Lithium ion batteries are also known as lithium batteries, but they are not the same. Lithium-ion batteries have gone mainstream.

Lithium ion battery with carbon material as the negative pole, with lithium compounds as the positive pole, there is no metal lithium, only lithium ions. Lithium ion battery is the general term of battery with lithium ion embedded compound as positive electrode material. The charging and discharging process of lithium ion battery is the embedding and de-embedding process of lithium ion. In the process of lithium ion embedding and delocking, it is accompanied by the embedding and delocking of equivalent electrons with lithium ion (the positive pole is conventionally denoted by embedding or delocking, while the negative pole is denoted by insertion or delocking). In the process of charging and discharging, lithium ions are inserted/removed and inserted/removed between the positive and negative poles, which is vividly called "rocking chair battery".

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. Wide working temperature range for - 20 ℃ ~ 60 ℃. Excellent cycle performance, fast charging and discharging, charging efficiency up to 100%, and large output power. Long service life. There is no environmental pollution and it is called green battery.

Mechanism of action

The lithium ion battery takes the carbon material as the negative pole, takes the lithium compound as the positive pole, does not have the metal lithium existence, only has the lithium ion, this is the lithium ion battery. Lithium ion battery is the general term of battery with lithium ion embedded compound as positive electrode material. The charging and discharging process of lithium ion battery is the embedding and de-embedding process of lithium ion. In the process of lithium ion embedding and delocking, it is accompanied by the embedding and delocking of equivalent electrons with lithium ion (the positive pole is conventionally denoted by embedding or delocking, while the negative pole is denoted by insertion or delocking). In the process of charging and discharging, lithium ions are inserted/removed and inserted/removed between the positive and negative poles, which is vividly called "rocking chair battery".

When the battery is charged, lithium ions are formed on the positive electrode of the battery, and the lithium ions generated move to the negative electrode through the electrolyte. As a negative carbon, it has a lamellar structure, and it has many micro pores. Lithium ions that reach the negative electrode are embedded into the micro pores of the carbon layer. The more lithium ions embedded, the higher the charging capacity. Similarly, when the battery is discharged (the process by which we use the battery), lithium ions embedded in the negative carbon layer escape and move back to the positive electrode. The more positively charged lithium ions, the higher the discharge capacity.

Generally, the charging current of lithium battery is set between 0.2c and 1C. The higher the current is, the faster the charging will be, and the higher the battery heat will be. In addition, too much current charging, the capacity is not full, because the battery internal electrochemical reaction needs time. Like pouring beer, pouring too fast will produce foam, but dissatisfaction.

Precautions for use (discharge)

For batteries, normal use is the discharge process. Lithium battery discharge need to pay attention to:

First, the discharge current should not be too large. Excessive current will cause heat inside the battery, which may cause permanent damage. Mobile phone, this is no problem, can not consider.

As can be seen from the figure on the right, the larger the discharge current, the smaller the discharge capacity and the faster the voltage drop.

Second, never over discharge! The internal storage of electric energy in lithium battery relies on electrochemistry, which is a reversible chemical change. Excessive discharge will lead to irreversible reaction of this chemical change. Therefore, lithium battery is most afraid of over-discharge. Fortunately, the battery inside the phone has been installed with a protective circuit, the voltage is not low enough to damage the battery, the protective circuit will work, stop discharging.

Lithium ion battery: it is a secondary battery (rechargeable battery), which mainly relies on lithium ions to move between the positive and negative poles to work. During charging and discharging, Li+ is embedded and delinked back and forth between the two electrodes. During charging, Li+ is delinked from the positive pole and embedded into the negative pole through the electrolyte. Discharge is the opposite.

Lithium batteries are divided into lithium batteries and lithium ion batteries. Cell phones and laptops use lithium-ion batteries, commonly known as lithium-ion batteries. Batteries generally use materials containing lithium as electrodes, which is the representative of modern high performance batteries. True lithium batteries are rarely used in everyday electronics because they are dangerous.

Lithium-ion batteries were first developed in 1990 by SONY of Japan. Lithium ions are embedded in carbon (petroleum coke and graphite) to form a negative electrode. Anode materials such as LixCoO2, LixNiO2, and LixMnO4 are commonly used, and electrolytes such as LiPF6+ diethylene carbonate (EC) + dimethyl carbonate (DMC).

Petroleum coke and graphite as negative electrode materials are non-toxic and the resources are sufficient. Lithium ion embedded in carbon overcomes the high activity of lithium and solves the safety problems existing in traditional lithium batteries. The positive electrode LixCoO2 can reach a higher level in charge and discharge performance and service life, which reduces the cost. Lithium ion batteries are expected to have a large market in the 21st century.

During charging and discharging of lithium ion secondary batteries, the equation is LiCoO2+C= li1-xcoo2 +LixC[1].

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