Lithium battery knowledge, an article to help you understand lithium batteries

With the development and popularization of technology, lithium batteries have become one of the most important energy storage and conversion devices nmp solvent. Lithium-ion batteries have improved the design of portable electronics with their advantages of small size, light weight, high energy density, and fast charging and discharging, and have promoted the rapid development of electric vehicles and renewable energy storage systems.

History of lithium battery development

Lithium battery technology has experienced nearly half a century of development and has been making rapid progress nmp. Its key technologies and important historical events mainly include:

In the 1970s, the Whittingham Research Working Group of Exxon Corporation proposed for the first time to use different titanium sulfide negative electrodes and cobalt oxide positive electrodes to develop reversible charge-discharge lithium-ion power batteries, and established a basic realization of intercalation and extraction of lithium ions based on layered structure materials. Principle, which marks the birth of lithium secondary use battery management technology.

In the early 1980s, Goodenough et al 1 methyl 2 pyrrolidone. found that layered lithium cobalt is a better cathode material for lithium ion batteries, which was achieved by lithium cobalt oxide batteries using graphite negative electrodes

How Lithium Batteries Work

Lithium batteries are secondary batteries, and their basic working principle is that under the action of an external electric field, the working fluid in the battery undergoes a reversible redox reaction, accompanied by the reversible intercalation and extraction of lithium ions between the positive and negative electrodes and electrons in the external circuit. flow, so as to realize the function of charging and discharging energy.

Specifically, a typical lithium-ion battery consists of four main components: positive electrode, negative electrode, separator, and electrolyte. The active materials of the two electrodes are physically or chemically embedded in a light metal foil substrate such as aluminum or copper, and a separator is placed between the electrodes to separate the electrodes while allowing ion exchange, and the electrolyte is The smooth migration of lithium ions between the electrodes provides a lithium-containing medium. The electrolytes used in modern lithium-ion batteries are mainly organic liquid or gel electrolytes.

Positive pole

During charging, the anode undergoes an oxidation reaction, loses electrons and releases an equal amount of lithium ions into the electrolyte; when discharging, a reduction reaction occurs to obtain electrons and absorb lithium ions. Currently, cathode materials commonly used in commercial lithium-ion batteries include:

Lithium cobalt oxide (LiCoO2), which is our initial commercialized lithium-ion power battery as the positive electrode, has the advantages of stable structure development and good charge and discharge performance. At present, it is mainly used in portable mobile electronic technology equipment in my country;

Nickel-cobalt-molybdenum oxides, such as nickel-cobalt-manganese (nCM) and nickel-cobalt-aluminum (nCA), are the most common lithium-ion batteries due to their price variations, offering higher theoretical capacity and lower cost than lithium-cobalt

Lithium iron phosphate has long service life, good thermal stability, non-toxic, but slightly lower energy density, and is mainly used in electric tools.

The sulfur multi-electron reaction in lithium-sulfur batteries can theoretically achieve the highest energy density, but the charge-discharge stability is poor, and it is mainly used for large-scale energy storage applications.

Negative pole

During discharge, the negative electrode undergoes an oxidation reaction, losing electrons and lithium ions; during charging, a reduction reaction occurs, gaining electrons and intercalating lithium ions. At present, the commonly used anode materials for commercial lithium-ion batteries mainly include:

Graphite, which uses the gap between the development of graphite layered structure to reversibly intercalate and extract a large number of lithium ions, is currently the most widely used negative electrode material;

Hard carbon is more disordered than graphite structure, which can achieve higher charge and discharge rates;

Lithium titanate, bulky, poor conductivity;

As a new generation of high-capacity anode material, silicon is currently in the development stage, and its theoretical capacity is more than 10 times that of graphite.

diaphragm

The function of the separator is to electrically isolate the positive and negative electrodes, and at the same time have a certain porosity, allowing lithium ions to migrate quickly and smoothly between the two electrodes. The selection of the separator needs to comprehensively consider many factors such as mechanical strength, stability, ionic conductivity, and cost. Porous membrane materials such as polyethylene (PE) and polypropylene (PP) are commonly used in commercial lithium-ion batteries.

electrolyte

The electrolyte solution enables lithium ions to reversibly migrate between the two electrodes, and can complete the transport of a charge in the process of learning migration research, which is the key working medium for battery technology to realize system charge and discharge. Excellent electrolytes need to continuously meet multiple development requirements such as high solubility, wide voltage window stability, high concurrent conductivity, and low toxicity. At present, the commonly used electrolyte in my country is a mixture of organic carbonate solvents (such as ethylene carbonate EC, dimethyl carbonate DMC, etc.) and lithium salts (such as lithium hexafluorophosphate LiPF6), and the liquid is used as the electrolyte index system. This kind of student organic liquid electrolyte can dissolve lithium salt so that it can achieve its own sufficient conductivity, and it also has a wider voltage stability time window.

Under the action of the external circuit, the positive electrode oxidizes and releases lithium ions into the electrolyte, while the negative electrode reduces and absorbs lithium ions in the electrolyte, electrons flow from the positive electrode to the negative electrode through the external circuit, on the contrary, the positive electrode is reducing Lithium ions are absorbed during the reaction, the negative electrode is oxidized and lithium ions are released into the electrolyte, electrons flow from the negative electrode to the positive electrode, and the battery realizes the discharge process. The whole reaction process is a reversible oxidation-reduction process of different active substances under the action of electrochemical potential energy difference, and no permanent chemical reaction occurs. Therefore, the battery can be repeatedly charged and discharged by reverse current to realize the function of a secondary battery.

Compared with disposable primary batteries, secondary lithium batteries can be repeatedly charged and discharged, which is more economical and environmentally friendly. At present, the average working voltage of the positive electrode material of commercial lithium-ion batteries is about 3.6-3.7V, and the working voltage of the negative electrode is about 0.1V, so the working voltage of the whole battery is about 3.5-3.8V, far exceeding that of lead-acid batteries. High operating voltage is one of the important reasons for the high energy density of lithium batteries.

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