The negative electrode of lithium-ion batteries is composed of negative active substances

Lithium-ion battery refers to a secondary battery system in which two different lithium-in-the-top compounds that can be reversibly embedded and removed from lithium ions are used as the positive and negative electrodes of the battery, respectively. When charging, lithium ions are de-intercalated from the positive electrode, embedded into the negative electrode through the electrolyte and separator; In discharge, on the contrary, lithium ions are de-intercalated from the negative electrode and embedded into the positive electrode through the electrolyte and separator.

The negative electrode of lithium-ion batteries is made of a mixture of negative active substances, binders and additives to make a paste adhesive evenly applied on both sides of the copper foil, dried and rolled.

Advantages of graphite as an anode material

Graphite is an allotrope of carbon, and the two are closely related. Graphite is the most stable form of carbon. (Diamond is a metastable allotrope of carbon, and although its hardness is much higher than graphite, it is the hardest substance in nature, but its stability is lower than graphite.) )

Lithium-ion battery refers to a secondary battery system in which two different lithium-in-the-top compounds that can be reversibly embedded and removed from lithium ions are used as the positive and negative electrodes of the battery, respectively. When charging, lithium ions are de-intercalated from the positive electrode, embedded into the negative electrode through the electrolyte and separator; In discharge, on the contrary, lithium ions are de-intercalated from the negative electrode and embedded into the positive electrode through the electrolyte and separator.

The negative electrode of lithium-ion batteries is made of a mixture of negative active substances, binders and additives to make a paste adhesive evenly applied on both sides of the copper foil, dried and rolled.

Advantages of graphite as an anode material

Graphite is an allotrope of carbon, and the two are closely related. Graphite is the most stable form of carbon. (Diamond is a metastable allotrope of carbon, and although its hardness is much higher than graphite, it is the hardest substance in nature, but its stability is lower than graphite.) )

Low temperature lithium iron phosphate battery 3.2V 20A Low temperature lithium iron phosphate battery 3.2V 20A-20

°C charging, -40 °C 3C discharge capacity≥70%
Charging temperature: -20~45 °C - Discharge temperature: -40~+55 °C-40 °C Support maximum discharge rate: 3C-40
°C

3C discharge capacity retention rate≥ 70%

Click on details

The term 'graphite' comes from the Greek word 'graphein'. This material is resistant to high temperatures, corrosion, good conductivity, thermal conductivity, and stable chemical properties, while being lighter than aluminum. In addition to being used as anode material for lithium ion batteries, high-quality graphite can also be used in fuel cells, solar cells, semiconductors, light-emitting diodes, nuclear reactors and other fields.

Overall, graphite has the advantages of high electronic conductivity, small volume change in layered structure before and after lithium insertion, high lithium insertion capacity, and low lithium insertion potential, and has become the mainstream commercial negative electrode material for lithium-ion batteries.

How to obtain graphite

There are two ways to obtain graphite: natural ore and synthesis of Coal tar. The graphite material used in lithium-ion batteries is generally prepared by blending 55% synthetic graphite with 45% low purity natural graphite.

Manufacturers once favored synthetic graphite because its uniformity and purity were superior to natural graphite. Now, it's different. The application of modern chemical purification methods enables natural graphite with a purity of 99.9% to be obtained after heat treatment. In contrast, the purity of synthetic graphite is 99%, making the former more popular.

Compared with synthetic graphite, purified natural flake graphite has higher crystallinity and exhibits better conductivity and thermal conductivity. In addition, natural graphite is expected to reduce the production cost of lithium-ion batteries, while also achieving equivalent or even better battery performance.

It can be expected that synthetic graphite will eventually be replaced, and the future belongs to cheaper and more environmentally friendly natural graphite, and graphene synthesized from natural graphite will show its talents.

Lithium intercalation mechanism of graphite

Graphite has good conductivity, high degree of crystallinization, good layered structure, is very suitable for repeated intercalation-de-intercalation of lithium ions, and is currently the most widely used and most mature anode material. After the lithium ions are embedded between the graphite layers, the lithium intercalation LixC6 (0≤x≤1) is formed, the theoretical capacity can reach 372mAh/g (x=1), and the reaction formula is: xLi++6C+xe-→LixC6

Lithium-ion embedding changes the stacking mode between graphite layers from ABAB to AAAA, as shown in the figure below.

Modification of graphite

Since the graphite layer spacing (d≤0.34nm) is smaller than the crystal surface spacing of graphite lithium intercalation compound LixC6 (0.37nm), the graphite layer spacing changes during the charging and discharging process, which is easy to cause the graphite layer to peel off and pulverize, and lithium ions and organic solvent molecules are co-embedded in the graphite layer and organic solvent decomposition, which affects the battery cycle performance.

Through graphite modification, such as oxidation on the surface of graphite and coating with polymer pyrolysis carbon, the formation of composite graphite with core-shell structure can improve the charge-discharge performance of graphite and increase the specific capacity.

Other anode materials

At present, graphite is the mainstream commercial lithium battery anode material, its theoretical gram capacity is 372mAh/g, the graphite anode material with better performance on the market has reached 360mAh/g, and the gram capacity gradually tends to the limit value. Although graphite as a negative electrode material has the disadvantages of low gram capacity and cyclic deviation, in view of the high cost performance of graphite anode materials, it will not be immediately replaced by new materials, for the following reasons:

The technology of new anode materials is not mature, and it will take a long time to improve performance;

The price of new anode materials is higher, and the price advantage of graphite anodes is obvious;

The negative electrode material needs to be used with the positive electrode material, electrolyte, etc., and the specific capacity of the current positive electrode material is generally low.

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