Materials Science —— Energy Materials

Research progress of lithium ion battery

The electrochemical reaction principle, general characteristics and research progress of cathode materials, anode materials and electrolyte materials for lithium ion batteries are introduced, as well as the existing problems and development prospects.

Keywords lithium ion battery, research progress, prospect

Development of R& lithium ion secondary battery

Sun wenchun

(Department of Applied Chemistry, Tianjin University, 300072)

In this paper, the basic principle and general characteristics of electrochemical reaction of lithium ion battery and the research progress of anode, cathode and electrolyte materials are introduced. At the same time, it also summarizes its existing problems and development prospects.

Keywords lithium ion battery, research progress, prospect

Since gaston Plante put forward the concept of lead-acid battery in 1859, the chemical power industry has been developing new secondary batteries with high specific energy and long cycle life. 1990, Sony Corporation of Japan took the lead in developing a lithium-ion battery [1]. It embeds lithium ions into carbon to form a negative electrode, replacing the metal lithium or lithium alloy of traditional lithium batteries as a negative electrode. The negative electrode material is carbon material, such as graphite and coke. At present, LiCoO2 is the main cathode material, followed by LiNiO2 and LiMn2O4. Electrolytes are LiAsF6+PC (propylene carbonate), LiAsF6+PC+EC (vinyl carbonate) and LiPF6+EC+DMC (dimethyl carbonate). The diaphragm is PP microporous membrane, PE microporous membrane or both. Lithium-ion battery not only maintains the main advantages of high voltage and high capacity of lithium battery, but also has the remarkable characteristics of long cycle life and good safety performance. It has shown good application prospects and potential economic benefits in portable electronic equipment, electric vehicles, space technology, national defense industry and other fields, and has become a research hotspot that has attracted extensive attention in recent years.

Electrochemical reaction principle and characteristics of 1 lithium ion battery

The anode and cathode of this battery adopt active materials that can be freely intercalated and deintercalated by lithium ions (Li+). When charging, Li+ escapes from the positive electrode and embeds in the negative electrode. During the discharge, Li+ precipitates from the negative electrode and embeds in the positive electrode. This charging and discharging process is like a rocking chair. Therefore, this kind of battery is also called rocking chair battery. Lithium-ion battery with LiCoO2 as cathode material and graphite as cathode material has the following charge-discharge reaction formula.

General characteristics of lithium-ion batteries [2];

(1) high volume and mass energy density; (2) The output voltage of single battery is high, 4.2v；; ; (3) Low self-discharge rate; (4) It can also be used at a high temperature of about 60℃; (5) No toxic substances, etc.

Research progress of lithium ion battery

The key technology to study lithium-ion batteries is to use anode and cathode materials that can intercalate and deintercalate lithium ions during charging and discharging, and to select appropriate electrolyte materials.

2. 1 cathode material

Lithium intercalation compounds as cathode materials are lithium ion storage. In order to obtain higher battery voltage, lithium intercalation compounds with high potential should be selected. Generally speaking, the cathode material should meet the requirements of [3 ~ 7]: (1) and have electrochemical compatibility with the electrolyte solution within the required charging and discharging potential range; (2) mild electrode process dynamics; (3) High reversibility; (4) In the state of complete lithium, it has good stability in air. At present, the research mainly focuses on the compounds with layered Li2O3 and spinel Li2O3 structures (transition metal ions such as M=Co, Ni, Mn, V).

LiCoO2, LiNiO2 and LiMn2O4 can be used as cathode active materials. The cathode LiCoO2, which was first used in commercial lithium ion batteries, belongs to α-FeO _ 2 structure. Its synthesis method is to mix Li2CO3 and CoCO3 according to the molar ratio of Li/co = 1: 1, and then calcine at 700℃ in the air. Its reversibility, discharge capacity, charge-discharge efficiency and voltage stability are very good. So at present, the main cathode material is LiCoO2, or lithium cobaltate with al, in and other elements added. However, due to the high cost and lack of resources of cobalt materials, it is necessary to develop materials that use little or no cobalt or are cheap and easy to obtain, such as replacing cobalt with nickel or manganese, which greatly reduces the unit price of batteries.

LiNiO2 is a layered compound that has been studied more after LiCoO2. Generally, it is prepared by solid-state reaction of lithium salt and nickel salt at 700 ~ 850℃. Nickel and cobalt have similar properties and are cheaper than cobalt. At present, the maximum capacity of LiNiO2 _ 2 is 150 mAh/g, and the working voltage range is 2.5 ~ 4. 1 V, and there is no limitation of overcharge and overdischarge. Ohzuku [9] thinks it is one of the most promising cathode materials in lithium ion batteries. However, due to many problems in the preparation of LiNiO2, the practical application of LiNiO2 is still limited. For example, when cubic LiNiO2 is prepared, it is easy to produce cubic LiNiO2, especially when the heat treatment temperature is higher than 900℃, it will all exist in cubic form, but in non-aqueous electrolyte solution, cubic LiNiO2 has no electrochemical activity.

M2O4 skeleton in spinel Li2O3 (m = Mn, Co, V, etc. ) is a three-dimensional network of tetrahedron and octahedron, which is beneficial to the diffusion of Li+ ions. Its typical representative is LiMn2O4. The preparation of high-capacity LiMn2O4 is complicated, because oxygen is easily lost during heating, which leads to poor electrochemical performance of anoxic compounds. At present, the commonly used synthesis methods include multi-step heating solid-state synthesis, solution-gel method, precipitation method and so on. How to overcome the problem of capacity decline in the circulation process is the focus of LiMn2O4 research at present. Therefore, the preparation of spinel LiMn2O4, especially doped LiMn2O4, and the relationship between structure and properties are still the research direction of electrode materials for lithium ion batteries in the future.

2.2 anode materials

As a new type of high-energy battery, lithium-ion battery still has a lot of room to improve its performance, and the improvement of carbon material performance is the main key. The anode carbon material should have large capacity, good charge-discharge characteristics, highly reversible intercalation reaction, thermodynamic stability and electrolyte stability.

1973 proposed to use carbon as lithium intercalation material, but it was not until 1990 that Sony used petroleum coke as the negative electrode that the research of lithium-ion battery entered the practical stage, thus setting off a worldwide research upsurge. Carbon materials used for lithium-ion batteries mainly include the following types, as shown in the following table.

At present, the main carbon anode materials studied are graphite, metallurgical coke and petroleum coke. Among them, graphite has a layered structure, so it is possible to embed atoms or atomic groups between layers to form carbon interlayer compounds. Graphite is used as the negative electrode of lithium ion battery. Lithium ions can be intercalated between carbon layers by charging and deintercalated by discharging. When lithium-embedded graphite is used as negative electrode, the main research focuses are: the mechanism and inhibition method of irreversible capacity loss, the relationship between graphite structure and electrochemical performance, etc.

The crystallinity, microstructure and stacking form of graphite will all affect its lithium intercalation capacity. It is found that the existence of partial disordered arrangement is the reason why the lithium intercalation capacity of graphite is less than the theoretical capacity, and controlling the accumulation form of graphite by adjusting the heat treatment temperature is an effective means to obtain high capacity. Honda R&D Company of Japan solved the problem of low specific capacity of lithium-ion battery through special treatment. Specifically, lithium (molecule) is placed between ordered graphite plates, and the material is heat-treated with polystyrene (PPP), and then highly oriented graphite is pyrolyzed under high pressure (5 000~6 000 MPa). The graphite obtained by this method is used as a negative electrode, so that the negative electrode can reach a high specific capacity of116 mah/g [10].

199 1 year, when the graphite electrode was evaporated by vacuum arc in Iijima, NEC, Japan, nano-scale carbon multilayer tubes-carbon nanotubes were discovered. Since then, it has aroused people's extensive interest and in-depth research. Carbon nanotubes (CNTs) have the characteristics of small size, high mechanical strength, large specific surface area, high conductivity and strong interface effect, and their top opening filling has been used as efficient catalytic carriers and microwave absorbing materials. In recent years, carbon nanotubes have been used as anode materials for lithium ion batteries, and they have been found to have excellent electrode properties, such as high reversible capacity. At present, the research on carbon electrode materials is very active, and it will still be the focus of lithium ion battery research in the future.

2.3 electrolyte materials

The material is mainly composed of lithium salt and mixed organic solvents, such as LiClO4/PC (propylene carbonate) +DME (dimethyl glycol), PC+DME, PC+DME+EC (vinyl carbonate), EC+DEC (diethyl carbonate), LiAsF6/EC+THF (tetrahydrofuran) and so on. Some experts think that LiClO4 _ 4 is a strong oxidant, so it is unsafe to use. PC is highly reactive in storage battery and easy to enter the carbon interlayer, so it is not advisable to use it in lithium-ion battery. LiPF6 is a suitable salt, and 1 ~ 2 mol/l lipf6/EC+DMC is an ideal electrolyte [1 1]. The stability of electrolyte is also the key technology in the research of lithium ion batteries.

In addition, improving the capacity, electrode cycle life, battery safety, reducing self-discharge and realizing fast charging of lithium-ion batteries are still key technologies in the future.

3 outlook

In recent years, as a new type of high-energy battery, lithium-ion battery has made great progress in its research and development. However, because lithium-ion battery is an interdisciplinary field involving chemistry, physics, materials, energy and electronics, there are still many problems in its development. Using traditional electrochemical research methods combined with in-situ and off-site spectral methods to evaluate and optimize the design of lithium-ion battery system will strongly promote the research and application of lithium-ion battery. Lithium-ion battery will be the second battery with the best market prospect and the fastest development in the next century for a long time after nickel-cadmium battery and nickel-hydrogen battery.

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