陰極材料の分類と生産プロセス

陰極材料 は主に二つのカテゴリーに分かれる：炭素材料と非炭素材料。炭素は炭素ベースのシステムを指し、主にメソカーボンマイクロスフェア、人工グラファイト、天然グラファイト、およびハードカーボンを含む。現在、最も広く使用されている炭素材料はグラファイト陰極材料であり、その中でも人工グラファイトと天然グラファイトは大規模な産業用途を持つ。非炭素材料は主にシリコンベースの材料、スズベースの材料、リチウムチタン酸塩などを含む。その中で、シリコンベースの陰極材料は現在の主要な陰極材料メーカーの研究対象であり、将来的に大規模に適用される可能性が最も高い新たな陰極材料の一つである。

天然グラファイトの加工

天然グラファイト陰極材料は天然フレークグラファイトを原材料とし、粉砕、分類、球状化、精製、表面処理などのプロセスを経て陽極材料から準備される。

人工グラファイト陰極材料の準備プロセス

Artificial graphite manufacturing process can be divided into four steps, more than ten small procedures, granulation and graphitization is the key. 

人工グラファイト陰極材料の生産プロセスは四つのステップに分かれる：

1) 前処理

2) 顆粒化

3) グラファイト化

4) ボールミリングおよびふるい分け。

 Among the four steps, crushing and screening are relatively simple, and granulation and graphitization are the two links that reflect the technical threshold and production level of the anode industry.

Specific to the production process, firstly, one or more of the coke and conductive particles, carbon nanotubes, carbon black, acetylene black are premixed, and then the mixed material and carbon are sintered and coated once, and the prepared particles are graphitized. Graphitized materials and resin materials for secondary coating; Surface treatment with solvent, centrifugation, precipitation and other methods to separate solid particles from the solvent, and then carbonization, 5-20um particles, to obtain a high rate of carbon anode material. In this method, by mixing and fabricating particles, the particles are coated twice to fill the inner shell of the material, so that the internal structure of the material is stable, so that the carbon anode material has the advantages of high rate performance, high pressure compaction, high specific capacity and so on.

(1) 前処理

Graphite raw material (needle coke or petroleum coke) is mixed with binder for air milling (crushing).According to the different products, the graphite raw materials and adhesive (graphitization) according to different proportions, the mixing ratio is 100 :(5~20), the material through the vacuum feeding machine into the hopper, and then the hopper into the air flow mill for air 粉砕, 粉砕 5~10mm diameter of the raw and auxiliary materials to 5-10 microns. After air 粉砕, cyclone dust collector is used to collect the required particle size materials, the dust collection rate is about 80%, the tail gas is filtered by the filter core filter and discharged, the dust removal efficiency is more than 99%. The material of the filter element is the filter cloth with pores less than 0.2 micron, which can intercept all the dust above 0.2 micron. The fan control system is in negative pressure state.

違い： pretreatment mill is divided into mechanical mill and jet mill, now the mainstream is jet mill. There are more kinds of adhesives, such as petroleum asphalt, coal asphalt, phenolic resin or epoxy resin.

(2) 顆粒化/二次顆粒化

顆粒化 is a key step in artificial graphite processing. 顆粒化 is divided into pyrolysis process and ball milling process.

熱分解プロセス： the intermediate material 1 is put into the reaction reactor and electrically heated according to a certain temperature curve in inert gas atmosphere and under a certain pressure. It is stirred at 200-300 ℃ for 1-3h and then heated to 400-500℃ to obtain the material with a particle size of 10-20mm. The material is cooled and discharged, namely the intermediate material

2. Ball mill and sieve division of labor: vacuum feeding, conveying intermediate material 2 to the ball mill for mechanical ball 粉砕, 粉砕 10~20mm material into 6~10 micron particle size material, and screening to get intermediate material

3. The material on the screen is transported back to the ball mill by vacuum pipe for ball 粉砕.

The size, distribution and morphology of graphite particles affect many properties of anode materials. In general, the smaller the particle size, the better the rate performance and cycle life, but the first efficiency and compaction density (affecting the volume energy density and specific capacity) are worse, and vice versa. Reasonable particle size distribution (mixing large particles with small particles, later process) can improve the specific capacity of the negative electrode. The particle morphology also has a great influence on the rate and low temperature performance.

二次造粒: small particles have large specific surface area, more channels and shorter paths for lithium ion migration, good rate performance, and large particles have high compaction density and large capacity. How to take into account the advantages of large and small particles, and achieve high capacity and high rate at the same time? The answer is to take secondary granulation. Using the base material such as small grain petroleum coke and needle coke, by adding coating materials and additives, under the condition of high temperature agitation, by controlling the material proportion, temperature rise curve and agitation speed, the small grain base material can be granulated twice, and the product with larger grain size can be obtained. Compared with the product of the same particle size, the secondary granulation can effectively improve the liquid retention performance of the material and reduce the expansion coefficient of the material (there are concave holes between small particles and small particles), shorten the diffusion path of lithium ions, improve the rate performance, but also improve the high and low temperature performance and cycling performance of the material.

違い: The secondary granulation process has high barriers, many types of coating materials and additives, and is prone to problems such as uneven coating or coating shedding, or poor coating effect, etc. It is an important process for high-end artificial graphite.

(3) グラファイト化

グラファイト化 is the orderly transformation of thermodynamically unstable carbon atoms from chaotic layer structure to graphite crystal structure by thermal activation. Therefore, high temperature heat treatment (HTT) is used in the graphitization process to provide energy for atomic rearrangement and structural transformation. In order to improve the graphitization degree of refractory carbon materials, catalysts can also be added.

より良いグラファイト化効果を得るためには、三つの側面を行う必要があります:

1. 抵抗材料と材料を炉にロードする方法（水平ロード、垂直ロード、変位および混合ロードなど）を習得し、抵抗材料の異なる性能に応じて材料間の距離を調整できること;

2. according to the different capacity and product specifications of the graphitization furnace, different power curve is used to control the rate of rise and fall in the process of graphitization;

3, in specific circumstances, in the ingredients to add catalyst, improve the degree of graphitization, that is, “catalytic graphitization”.

違い: Different qualities of artificial graphite have different heating and cooling rates, holding time, catalysts, etc. It is expected that the types of graphitization furnaces used are different, resulting in relatively large differences in performance and cost. グラファイト化 separated from the front-end and back-end processes, especially the heating and cooling process, is basically programmed, but the graphitization time is long and the equipment investment is large, so more outsourced processing is required, and there is no risk of technology leakage.

(4) コーティング炭化

コーティング炭化: コーティング炭化 uses a graphite-like carbon material as a “core”, and coats a layer of uniform amorphous carbon material on its surface to form particles similar to a “core-shell” structure. The precursors of commonly used amorphous carbon materials include low-temperature pyrolysis carbon materials such as phenolic resin, pitch, and citric acid. The interlayer spacing of amorphous carbon materials is larger than that of graphite, which can improve the diffusion performance of lithium ions in it. SEI film, improve the first effect, cycle life, etc.

違い: Different manufacturers choose different precursors and different heating procedures, so that the thickness and uniformity of the coating layer are also different, so the product cost and performance will also be different.

(5) スクリーニング/ドーピング

グラファイト化された材料は真空でボールミルに運ばれ、物理的混合とボールミル処理を行います。270メッシュの分子ふるいでふるい分けを行い、ふるい下の材料を検査、測定、包装、保管します。ふるいの上の材料はさらなるボールミル処理を行い、粒度要件を満たしてからふるい分けます。

ドーピング修飾:ドーピング修飾法は、柔軟性があり、ドーピング元素も多様です。現在、研究者たちはこの方法の研究を積極的に進めています。グラファイトに非炭素元素をドーピングすることで、グラファイトの電子状態を変え、電子を取得しやすくし、リチウムイオンの挿入をさらに増加させます。例えば、リンやホウ素原子をグラファイト表面に成功裏にドーピングし、化学結合を形成することは、高密度のSEI膜を形成するのに役立ち、グラファイトのサイクル寿命とレート性能を効果的に改善しました。グラファイト材料に異なる元素をドーピングすることは、その電気化学性能に対して異なる最適化効果を持ちます。その中でも、リチウムを蓄える能力を持つ元素（Si、Sn）の追加は、グラファイト負極材料の比容量を大幅に改善することができます。