Research on negative electrode materials for button battery 2032

　　With the increasing depletion of non-renewable energy sources such as coal, oil, and natural gas, and the environmental pollution problems caused by their combustion, energy and environment have become two major problems affecting the sustainable development of the world today. In order to solve these two problems, it is urgent to develop new renewable green energy to replace traditional fossil fuels. As a new generation of energy storage devices, button battery 2032 have the advantages of high energy density, high operating voltage, long cycle life, low environmental pollution, and no memory effect. They are currently one of the most promising energy storage devices. As the core component of button battery 2032, electrode materials determine the performance of button battery 2032, and anode materials play a vital role in button battery 2032. Therefore, research on anode materials has become a hot topic in recent years.

　　1. Lithium-ion battery research direction

　　With the rapid development of the economy, science and technology are changing with each passing day, and the popularity of electronic products has reached the highest level in history. The development of electric vehicles, one of the important application fields, has led to the improvement of battery performance and also put forward higher requirements for batteries, including the improvement of energy density and the extension of cycle life. Current research on anode materials focuses on new carbon materials, silicon-based materials, tin-based materials and their oxide anode materials.

　　2. New carbon materials

　　New carbon materials are compared to traditional carbon materials. Graphite, a traditional carbon material, is currently commonly used commercially as anode material for button battery 2032. However, its theoretical capacity is low and it is increasingly unable to meet the development needs of button battery 2032. New carbon materials, such as carbon nanotubes and graphene, have great potential in lithium-ion battery applications due to their special one- and two-dimensional flexible structures and excellent thermal and electrical conductivity.

　　2.1 Carbon nanomaterials

　　Carbon nanomaterials mainly include carbon nanotubes and nano-doping of carbon materials.

　　Carbon nanotubes have attracted widespread attention since their discovery in 1991. They have high hardness, strength, toughness and conductivity. Although carbon nanotubes have a high lithium storage capacity, it is difficult to directly use carbon nanotubes as anode materials for button battery 2032. When carbon nanotubes are used as electrode materials, they will have lower efficiency, no discharge platform, and poor cycle performance. , voltage lag and other defects. The relationship between the structure of carbon nanotubes and the lithium insertion mechanism still needs further study, and its application as anode material still has a long way to go.

　　Doping carbon materials into nanoscale electrode materials can also effectively improve battery performance. For example, when nano-state silicon atoms are doped into carbon materials, the theoretical capacity of Li4.4Si formed when silicon is embedded in lithium is as high as 4200mA·h/g.

　　2.2 Graphene

　　Graphite is currently the most commonly used negative electrode material for button battery 2032. Due to the stacked layered structure of graphite, lithium ions can only interact with sp2 hybridized carbon six-membered rings to form LiC6. From this, the theoretical specific capacity of graphite is calculated to be 372mA·h. /g. For graphene, both sides of the sheet can store lithium ions at the same time, so the theoretical capacity can reach 740mA·h/g. Research shows that lithium may be embedded in disordered carbon materials in the form of Li2 covalent molecules to form LiC2. The theoretical specific capacity of graphene calculated using this lithium storage mechanism is 1116mA·h/g. In summary, graphene's lithium ion storage capacity is much higher than that of graphite, so it has great development potential as an anode material for lithium ion batteries.

　　However, graphene as an anode also has shortcomings such as voltage hysteresis and low Coulomb efficiency similar to carbon nanotubes, and it is also difficult to directly use it as an anode material. Therefore, the current research on graphene in anode materials is mainly in composite form. Graphene-based lithium-ion battery anode materials can be divided into the following categories: (1) graphene or heteroatom-doped graphene; (2) Composite materials of graphene and other carbon materials; (3) Composite materials of graphene and other inorganic substances. Graphene has good electrochemical properties and application prospects. The focus of research in the future will be how to reduce its preparation cost and composite it with other materials.

　　3.Silicon-based materials

　　Compared with other lithium battery anode materials, silicon-based anode materials have very high specific capacities. However, the high expansion rate of silicon during charge and discharge limits its application in negative electrode materials. Negative electrode materials prepared by composites of silicon and other materials can overcome this defect to a certain extent.

　　3.1 Multi-element mixing

　　Silicon cannot be used alone when used in button battery 2032. After repeated research, compounding with multiple elements can enhance its performance. The most prominent of these is compounding with carbon materials. During the charge and discharge process, the volume of carbon materials changes relatively little, but its electrical conductivity is outstanding, such as graphite. Previous relevant research has proven that during the conductive process of graphite, the volume will only increase by 10 About %, which is a superior performance that most simple substances do not have. The chemical properties of carbon and silicon are similar. The structure of the carbon material itself and a large number of lithium ion channels increase the embedding position of lithium ions, which can greatly improve the problem of rapid increase in volume during the working process of silicon. This is also the reason for the silicon-based negative electrode. The main ways in which materials are currently used.

　　3.2 Nanotechnology of silicon

　　The problem of volume expansion is the main problem limiting the use of silicon materials. The volume expansion rate of pure silicon anode materials can reach 200% or even more than 300% when working in button battery 2032. Nanotechnology treatment of silicon materials can effectively improve this problem. The research direction is mainly to carry out two-dimensional nanometerization, one-dimensional nanometerization and zero-dimensional nanometerization of silicon. Taking zero-dimensional nanotechnology as an example, that is, preparing nano-silica powder with a size of less than 100 nm, so that the noble material with refined particles can weaken the adverse effects of absolute volume changes. It can also control the direct contact between silicon and active materials and electrolytes, and improve Coulomb resistance. efficiency. However, the production cost of this nanoscale silicon material is high and it needs to be prepared by laser, so it is difficult to promote it.

　　3.3 Multi-component silicon-based alloy

　　Multi-component silicon-based alloys combine different elements with silicon to improve its performance in all aspects, weaken the problem of volume increase, and control electrochemical sintering. Research has found that binary Si-M anode materials can effectively control volume expansion. If a small amount of inert substances are added, the volume change can be controlled at about 10%. However, the negative effect is that electrochemical agglomeration may occur when active particles circulate in the Si-M system. , resulting in a reduction in the electrochemical contact performance of the matrix. Based on the above point of view, the transition metal Fe is added to change the performance of the Si-Ti-Ni alloy negative electrode. As a result, the initial capacity of the material was reduced by 6%-12%, but the overall capacity of the negative electrode material remained basically stable. Moreover, the Coulombic efficiency of the improved anode material has been significantly improved.

　　4. Tin-based materials and their oxides

　　Metal tin and lithium can undergo alloying reactions to form a variety of intermetallic compounds LixSn (x=0.4, 1.0, 2.33, 2.5, 2.6, 3.5, 4.4), which is an anode material with great application prospects.

　　4.1 Tin-based materials

　　Elemental tin, as the negative electrode material of button battery 2032, has many problems that are difficult to solve. The alloying process of tin and lithium is accompanied by severe volume expansion, with an expansion rate as high as 300%, which can easily lead to tin fragmentation and powdering, and a significant decrease in capacity. So the simple tin circulation performance is very poor.

　　4.2 Tin oxide

　　In 1997, it was discovered that tin oxide can be used as an anode material for button battery 2032 and has a high theoretical capacity. Tin oxide materials can reversibly deintercalate lithium in lithium-ion battery systems to achieve lithium storage. The capacity can reach 782mA·h/g, while the capacity of nano-tin oxide materials is expected to reach 1494mA·h/g. However, there are many problems when tin oxide is used as anode material. For example, the first lithium insertion will produce a large irreversible capacity, and it will also produce a large volume effect during cycle charge and discharge.

　　The key to improving the electrochemical performance of metallic tin is to alleviate the material's volume effect. The structural components of the material can be adjusted, and the structural stability of the material can be improved by introducing inert or non-inert elements to form alloys or intermetallic compounds or introducing other substances to form conforming materials. Inert elements commonly used for tin alloying include Cu, Ni, Co, etc., and non-inert elements include Sb, Ge, Zn, etc.

　　In order to improve the structural stability of the material and thereby improve its electrochemical performance, the preparation of electrodes with high specific surface area structures has become the first choice. Among them, the structures that attract more attention are zero-dimensional nanoparticles and three-dimensional porous materials.

　　Tin-based materials are often combined with various carbon materials and other materials to form composite materials. The purpose of preparing composite materials is to learn from each other's strengths and weaknesses. It can not only use carbon materials to alleviate the volume effect of tin-based materials and the agglomeration of nanoparticles, but also help tin-based materials express their high capacity characteristics. Therefore, it has become an important research direction. Tin-based materials can be compounded with a variety of carbon materials (such as amorphous carbon, graphitic carbon, carbon nanotubes, graphene, etc.) by doping, coating, embedding, etc.

　　summary

　　The future development direction of button battery 2032 should be towards high energy density, good safety performance, long cycle life, green environmental protection and low cost. Most of the existing button battery 2032 do not have the advantages of high specific capacity, high charging efficiency, and long cycle life. The actual capacity is far from the theoretical capacity. Therefore, technological innovation is very urgent, and new types of batteries with excellent performance are developed. Lithium-ion battery electrode materials are currently the focus of researchers' efforts.

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