1. Definition: The negative electrode material is the carrier of lithium ions and electrons in the battery charging process, and plays the role of energy storage and release. In the cost of the battery, the negative electrode material accounts for about 5%-15%, and it is one of the important raw materials for lithium-ion batteries.

2. As a carrier for lithium ion insertion, the anode material must meet the following requirements:

The insertion redox potential of lithium ions in the negative electrode matrix is ​​as low as possible, close to the potential of metal lithium, so that the input voltage of the battery is high;

``A large amount of lithium in the matrix can be reversibly inserted and deintercalated to obtain high capacity;

During the insertion/de-embedding process, the main structure of the negative electrode has little or no change;

The redox potential changes with the insertion and removal of Li should be as little as possible, so that the voltage of the battery will not change significantly, and stable charging and discharging can be maintained;

The insertion compound should have good electronic conductivity and ionic conductivity, so that polarization can be reduced and high current charge and discharge can be carried out;

The host material has a good surface structure and can form a good SEI with the liquid electrolyte;

The intercalation compound has good chemical stability in the entire voltage range, and does not react with electrolytes etc. after the formation of SEI;

Lithium ions have a large diffusion coefficient in the main material, which is convenient for rapid charging and discharging;

From a practical point of view, the material should be economical and environmentally friendly.

Three, carbon-based anode:

Fourth, silicon-based anode materials are mainly divided into two categories:

1, crystalline silicon material; advantage: high capacity, (4200mAh/g(Li4.4Si)),

Disadvantages: The volume expansion can reach 300%, which will not only cause the particles of the Si anode to break, but also damage the conductive network and binder network of the electrode, resulting in the loss of active materials, which will seriously affect the cycle performance of the silicon anode material.

There are three main ideas for solving the problem of large volume expansion of Si materials:

1) Nanometerization: Nanoparticles can reduce the damage of the material particles and electrodes caused by volume expansion, but they are larger than the table and affect the first effect; and the method has a high cost, a complicated process, and a difficult preparation.

2) Si crystal materials with special shapes, such as honeycomb materials and dendritic Si materials, use the deformation of the Si material itself to absorb the volume change during charging and discharging and improve the cycle performance of the Si material; but the compaction density is small, and the process The process is complicated and the preparation is difficult.

3) Si/C composite material, through the combination of Si and graphite material, the graphite material is used to buffer the volume change of the Si material during the cycle, so as to improve the cycle performance of the Si material. Although the expansion space is reserved and the cycle performance is improved, the compaction density is small and the industrialization is difficult. At present, scholars at Central South University have prepared a composite Si anode material of silicon, graphite, carbon nanotubes and pitch by spray drying.

2, silicon oxide material

Silicon oxide: The volume expansion is small, but the first effect is too low. The volume expansion of SiOx material is much smaller than that of crystalline silicon material, but its expansion level is still much higher than that of graphite materials. Therefore, the development of SiOx material still needs to focus on the volume expansion problem to reduce the material particle crushing and pulverization during the cycle. , Improve the cycle life of the material. Therefore, nanoization is also a common method for SiOx materials; there is also the use of high-energy ball milling to treat SiOx materials, reducing the particle size of SiOx materials, thereby improving the cycle and rate performance of the material, but the first efficiency of the material is only 63%. In order to substantially improve the efficiency of SiOx materials for the first time, KAIST developed a Si-SiOx-C composite structure silicon anode material. Nano Si particles are dispersed in SiOx particles, and the surface of the particles is covered with a layer of porous Carbon material. Electrochemical tests show that the material has excellent electrochemical performance, with a reversible capacity of 1561.9mAh/g at 0.06C, a first efficiency of 80.2%, 100 cycles of 1C, and a capacity retention rate of 87.9%.

5. Lithium metal anode material

Metal lithium is one of the metals with the lowest density. The standard electrode potential is -3.04V and the theoretical specific capacity is 3860mAh/g. From this data, it is second only to 4200mAh/g of silicon. Application areas: Lithium-sulfur battery (2600wh/kg), lithium-air battery (11680wh/kg), etc.

Lithium metal batteries have high capacity performance, but in use, due to the presence of lithium dendrites, negative electrode precipitation, negative negative side reactions, which seriously affect the safety of the battery, it is in the conceptual stage at this stage.

Lithium-sulfur battery. Sulfur is also a very widespread element in nature. The higher energy density (2600wh/kg) of lithium-sulfur batteries may be the focus of the next generation of lithium battery research and development.

Lithium-air battery. Lithium-air battery has a very high energy density (11680wh/kg), which is close to the energy density of fuel, and is environmentally friendly. The reaction product is water.

VI. Lithium titanate anode material

Lithium titanate, spinel structure, potential platform 1.5V, three-dimensional ion diffusion channel, stable crystal lattice, theoretical capacity 176mAh/g. The material has the characteristics of high safety, high magnification, and long life. Compared with graphite, it has higher ion diffusivity, high safety, and long life, but its conductivity is poor, and it needs carbon coating and doping modification; it has high potential and can only form 2.4-2.6V with high-potential cathode materials. Voltage, it is necessary to lower the potential of lithium titanate (the metal replaces part of Ti); the theoretical capacity is relatively low, 176mAh/g compared to 372mAh/g of graphite, there is no advantage in capacity.

七 contrast

Lithium-ion battery anode materials will develop towards high capacity, high energy density, high rate performance, and high cycle performance in the future.

At this stage, lithium-ion power battery anode materials are basically graphite-based carbon anode materials. The surface coating modification of graphite-based carbon anode materials increases compatibility with electrolytes, reduces irreversible capacity, and increases rate performance. An important point.

The anode material is lithium titanate, which is doped to improve the electronic and ion conductivity is an important improvement direction at this stage.

Although hard carbon, soft carbon, alloy and other negative electrode materials have higher capacity, the problem of cycle stability is still plagued us, and the modification research is still in the process of exploring and improving. Accelerated demand may urge the development and application of such materials.

Although the lithium metal negative electrode has a high energy density, there is no effective solution to its inherent safety problems such as lithium dendrites, and its large-scale practical application will take time.