Development and Structure of Lithium Batteries

Lithium battery is a new type of high-energy battery successfully developed in the 20th century. With the proposal of "carbon neutrality" and "carbon peak", lithium battery has become the focus of attention from all walks of life. Today, CHNL will lead you to understand the development and structure of lithium battery.

Introduction to Lithium Batteries

Lithium batteries can be understood as batteries containing lithium elements (including metal lithium, lithium alloys, lithium ions, lithium polymers), and can be divided into lithium metal batteries (very rarely produced and used) and lithium batteries (a large number of use today). Because of its high specific energy, high battery voltage, wide operating temperature range, and long storage life, it has been widely used in military and civilian small electrical appliances, such as mobile phones, portable computers, video cameras, cameras, etc., partially replacing traditional batteries. .

The origin and development of lithium batteries

In the 1970s, M.S. Whittingham of Exxon used titanium sulfide as the positive electrode material and metallic lithium as the negative electrode material to make the first lithium battery.
In 1980, J. Goodenough discovered that lithium cobalt oxide could be used as a cathode material for lithium batteries.

In 1982, R.R.Agarwal and J.R.Selman of the Illinois Institute of Technology (Illinois Institute of Technology) discovered that lithium ions have the characteristics of intercalating graphite, and this process is fast and reversible. At the same time, the safety hazards of lithium batteries made of metal lithium have attracted much attention. Therefore, people have tried to use the characteristics of lithium ions embedded in graphite to make rechargeable batteries. The first usable lithium-ion graphite electrode was successfully trial-produced at Bell Laboratories.

In 1983, M. Thackeray, J. Goodenough and others found that manganese spinel is an excellent cathode material, with low price, stability and excellent conductivity and lithium conductivity. Its decomposition temperature is high, and its oxidizing property is much lower than that of lithium cobalt oxide. Even if there is a short circuit or overcharge, it can avoid the danger of burning and explosion.
In 1991, Sony released the first commercial lithium battery. Subsequently, lithium batteries revolutionized the face of consumer electronics.

In 1996, Padhi and Goodenough found that phosphates with an olivine structure, such as lithium iron phosphate (LiFePO4), are more superior than traditional cathode materials, so they have become the current mainstream cathode materials.
Lithium batteries (Li-ion Batteries) are developed from lithium batteries. So before introducing Li-ion, let's first introduce lithium batteries. For example, a button cell battery is a lithium battery. The positive electrode material of lithium battery is manganese dioxide or thionyl chloride, and the negative electrode is lithium. After the battery is assembled, the battery has voltage and does not need to be charged. This kind of battery can also be charged, but the cycle performance is not good. During the charging and discharging cycle, it is easy to form lithium dendrites, resulting in an internal short circuit of the battery, so in general, this kind of battery is forbidden to be charged.

Later, Sony Corporation of Japan invented a lithium battery with carbon material as the negative electrode and a lithium-containing compound as the positive electrode. During the charging and discharging process, there is no metal lithium, only lithium ions. This is a lithium battery.
In the early 1990s, Japan's Sony Energy Development Corporation and Canada's Moli Energy Corporation successfully developed new lithium-ion batteries, which not only perform well, but also do not pollute the environment. With the rapid development of information technology, hand-held machinery and electric vehicles, the demand for high-efficiency power sources has grown rapidly, and lithium batteries have become one of the fastest growing fields.

The structure of lithium battery

The main components of lithium batteries:
(1) Positive electrode - active materials mainly refer to lithium cobalt oxide, lithium manganate, lithium iron phosphate, lithium nickelate, lithium nickel cobalt manganate, etc. The conductive current collector generally uses aluminum foil with a thickness of 10--20 microns;
(2) Diaphragm - a special plastic film that allows lithium ions to pass through, but is an electronic insulator. Currently, there are mainly PE and PP and their combinations. There is also a type of inorganic solid diaphragm, such as alumina diaphragm coating is a kind of inorganic solid diaphragm;

(3) Negative electrode - the active material mainly refers to graphite, lithium titanate, or carbon material with a similar graphite structure, and the conductive current collector generally uses copper foil with a thickness of 7-15 microns;
(4) Electrolyte - generally an organic system, such as a carbonate solvent dissolved with lithium hexafluorophosphate, and some polymer batteries use a gel electrolyte;
(5) Battery case - mainly divided into two types: hard case (steel case, aluminum case, nickel-plated iron case, etc.) and soft case (aluminum-plastic film).

When the battery is charged, lithium ions are deintercalated from the positive electrode and intercalated in the negative electrode, and vice versa when discharging. This requires an electrode to be in a lithium intercalation state before assembly. Generally, a lithium intercalation transition metal oxide with a potential greater than 3V relative to lithium and stable in air is selected as the positive electrode, such as LiCoO2, LiNiO2, LiMn2O4.
As the material of the negative electrode, an intercalable lithium compound with a potential as close as possible to the lithium potential is selected, such as various carbon materials including natural graphite, synthetic graphite, carbon fiber, mesophase spherical carbon, etc. and metal oxides, including SnO, SnO2, Tin composite oxide SnBxPyOz (x=0.4～0.6, y=0.6～0.4, z=(2+3x+5y)/2) etc.
The electrolyte adopts a mixed solvent system of LiPF6 ethylene carbonate (EC), propylene carbonate (PC) and low-viscosity diethyl carbonate (DEC) and other alkyl carbonates.

The diaphragm adopts polyolefin microporous film such as PE, PP or their composite film, especially the PP/PE/PP three-layer diaphragm not only has a low melting point, but also has a high puncture resistance, which plays a role in thermal insurance.
The shell is made of steel or aluminum, and the cover assembly has the function of explosion-proof and power-off.
Well, the above is all about lithium batteries today. Since the birth of lithium batteries in 1970, they have developed rapidly. Lithium batteries have penetrated into all aspects of our lives, and there are still huge development prospects in the future.
I hope the above content is helpful to you, more information will be continuously updated, see you in the next issue.