An article reading graphene in its entirety

Whenever there is a breakthrough news about graphene, it always causes a frenzy in the industry, especially in the battery field. At this point, we should calm down and know what graphene is, what it can do, and the biggest problem it currently faces.

Graphene is a two-dimensional crystal composed of tightly packed carbon atoms. Professor André Heim and Professor Konstantin Novoselov of the University of Manchester took the lead in 2004 through a simple method. A single layer of graphene was obtained by stripping off the graphite. Among the two-dimensional materials currently obtained, graphene has the thinnest thickness and large specific surface area, and is the material with the highest strength, the best toughness, the lightest weight, the highest transmittance and the best conductivity. It is because of these excellent physical properties and great application prospects that the founders of graphene won the Nobel Prize in Physics in 2010.

Due to the special structure of graphene, it also exhibits special properties that many other materials do not have.

1. Excellent conductivity: The carrier electrons and holes in graphene are continuous, and the mobility can reach 1 &; TImes; 105cm2 / Vs, electrons transmit at a speed of 1/300 of the speed of light, which greatly exceeds the conduction speed in general metal conductors and semiconductors, and thus has excellent conductivity.

2. Ultra-high light permeability: Monolayer graphene has a light absorption of only 2.3 % in a very wide wavelength range, that is, monolayer graphene has a light permeability of 97.7 %, which is much higher than 85 % of the international standard for transparent conductive films.

3. Ultra-high strength: Graphene was found to be the material with the highest elastic modulus and strength after carbon nanotubes. Its strength is 100 times that of the best steel in the world. Its hardness is higher than that of the hardest material diamond in nature. At the same time, it has excellent flexibility and can bend at will.

4. Ultra-high thermal conductivity: Similar to graphite, diamond, and carbon nanotubes, graphene also has a very high thermal conductivity. The free-state single-layer graphene has a thermal conductivity of 5000W/mK at room temperature, which is currently known. The material with the highest thermal conductivity.

5. Oversized specific surface area: Since graphene is only one carbon atom thick, single-layer graphene has an oversized specific surface area that can reach 2630m2 / g, which is much larger than the specific surface area of ordinary activated carbon.

If you look at these properties alone, graphene is perfect. The only thing that is not perfect is how to prepare it in large quantities.

Graphene preparation technology

The emergence of graphene has caused a huge wave in the scientific community. Since 2006, research papers have increased dramatically. As a new potential material for the "post-silicon age" to form nanometer size transistors and circuits, the research and development of graphene is also applied. There has been a sharp increase in the world. The United States, South Korea, China, Japan and other countries are particularly active in research.

At present, many major international manufacturers such as Dow Chemical, Samsung, IBM, Huawei, and Apple are actively promoting the industrialization of graphene. Since 2004, international patent applications for graphene have reached several thousand. It is mainly used in the preparation of graphene, applications in the field of energy, applications in display technology, graphene nano materials, and graphene composites. However, there is no precedent for mass production on a global scale. This is mainly due to the fact that a method and method suitable for mass production has not yet been found. This is also the reason why the cost of graphene has remained high.

At present, there are five main manufacturing methods for graphene: mechanical stripping, vapor deposition(CVD), SiC thermal decomposition, and Redox. Among them, the closest to actual production is the vapor deposition method.

Potential applications of graphene in the automotive industry

Graphene is a kind of two-dimensional carbon material with very high technical content and wide application potential. It has extensive and even subversive application prospects in many industries. The automotive industry is an integrated industry based on many industries, so graphene also has important application value and prospects for the automotive industry.

1. Applied to lithium-ion batteries, greatly shorten the charging time and increase battery capacity

At present, the power batteries used by global automobile manufacturers mainly use lithium batteries, lithium nickel cobalt aluminate batteries represented by Tesla, lithium iron phosphate batteries represented by BYD, and lithium manganates represented by Japanese automobiles..

These three types of batteries have the highest energy density of lithium cobalt acid batteries, but it is also the most unstable at high temperatures; lithium iron phosphate batteries are the most stable, but the energy density is the lowest. Lithium-ion battery technology has been silent for 20 years without major technological innovations. The biggest obstacle is that lithium-ion batteries have limited power density and their large amount of energy can not be quickly received or released(that is, they can not achieve rapid charge and release).

Graphene is applied to lithium ion batteries because of its oversized carrier mobility, which can significantly reduce charging time; And because of its stability, the battery cycle stability can be improved. In addition, the extra surface area can also increase battery capacity.

The Tesla upgraded version of the Model S uses improved lithium cells. The newly improved 18650 lithium cell capacity has been greatly increased. The number of batteries in 6831 has not increased, but the total battery capacity has increased from 53kWh to 70kWh. Tesla did not confirm whether graphene was added, but its performance has improved so much that only graphene can do it.

The traditional manufacturing countries of lithium batteries are Japan and South Korea, and they are also taking the lead in technology on graphene batteries. South Korean scientists announced in November 2014 that the newly invented graphene super mobile phone battery can store the same amount of power as a conventional battery, but the charging time is only 16 seconds. Researchers at Rensselaer Polytechnic Institute in the United States also expect graphene anode materials to charge or discharge 10 times faster than graphite anodes used in today's lithium-ion batteries.

At the beginning of December 2014, Western media reported that the graphene battery developed by the Spanish company Graphenano and the University of Corvado in Spain, can only travel for 1000 minutes in just 8 minutes. If this result is true, then there is no doubt that electric vehicles will completely subvert the traditional gasoline car and become the main force of the car.

2. Surface protection materials

Graphene has a stable structure, corrosion resistance, oxidation resistance, high strength, and easy to grow on various metal surfaces. It can be widely used for surface protection of metal materials. At the same time, due to its conductivity and high thermal conductivity, it can also be widely used in the protection and anti-static of organic materials. Imagine if you coated the surface of the car panel with graphene, no longer have to worry about the car being scratched!

3. Replace Silicon for integrated circuits to help driverless

Silicon has brought us into the electronic age. Polycrystalline Silicon has become the basic raw material for the semiconductor industry and has been used as a substrate for integrated circuits. With the improvement of process technology, the operating speed of silicon-based chips has reached the GHz level. However, with the continuous advancement of technology, the requirements for computer speed are getting higher and higher.

However, silicon-based chips are limited by the material's own performance, and it is difficult to increase the processing speed after reaching 4-5 GHz, and it has gradually failed to meet people's requirements for speed. Among the many alternatives, graphene is most noticeable for its super strength, ultra-high thermal conductivity, and Super conductivity.

Processors produced using graphene as a matrix can reach THz(That is 1000GHz). IBM has developed an ultra-fast graphene transistor in 2010. Its maximum frequency can reach 230 GHz, far exceeding the current silicon-based transistor. Run speed. IBM announced in July 2014 that it will invest another 3 billion U.S. dollars in the development of carbon chip technology including graphene. Graphene is likely to replace silicon in the future as the basic material for the semiconductor industry.

Unmanned technology is in the ascendant. It requires Super and ultra-fast computing power. Data storage and processing systems require very high requirements for integrated circuits. Existing silicon-based chips are difficult to fully meet their needs. The development and application of graphene carbon chips will solve this technical bottleneck and provide strong computing support.

4. Apply to Super capacitors, perfect acceleration

Super-capacitors are a new type of energy storage device. Compared with rechargeable batteries, they can carry out unlimited current charging, so the charging and discharging rate is very fast. They can complete the charging and discharging process within a few seconds, and they have high power and long service life. Features. The combination of Super capacitor and lithium-ion battery can effectively solve the problem of slow acceleration of electric vehicles.

Due to the large surface area of graphene, the super-capacitor with graphene as the electrode has an ultra-high capacity, which can reach hundreds of F/g, which is much higher than the super-capacitor with other materials as the electrode, and is more suitable as a power cell. Power source.

5. Preparation of ultra-efficient solar cells and folding displays instead of ITO

On July 2 this year, Hanergy announced four concept cars using solar energy as a power source. If one idea can be promoted in the automotive field one day, it is conceivable that the demand for solar cells in the automotive industry will increase significantly. At present, the transparent conductive material used in solar cells, displays and touch screens is mainly indium tin oxide (ITO). However, due to the fact that the transmittance of ITO to infrared light is actually relatively low, the utilization efficiency of solar cells for solar energy is still relatively low. In addition, the toughness of ITO materials is poor, which may affect the display effect when folded or stretched.

Graphene has a very high conductivity due to its special structure. At the same time, it is almost transparent. The light transmission rate is extremely high for all bands. It is an ultra-excellent transparent conductive material, so it is widely regarded as replacing ITO.

In the solar cell field, Japan's Fuji Electric is in the lead in development. The resulting graphene sheet has a conductivity of several times that of ITO and can ensure that 90 % of the optical transmission has reached a level that can fully meet the performance targets. In the field of displays and touch screens, graphene has higher strength and better toughness than the current mainstream ITO materials. As a transparent conductive material, it can be made into a flexible display device.

6. Graphene aerogel for exhaust air purification, catalytic carrier

The purification of indoor and exhaust air has always been an important issue in the field of automotive environmental protection. In 2013, Professor Gao Chao of the Polymer Science Department of Zhejiang University produced the world's lightest material, graphene ultra-light aerogel, with a material density of only 0.16 mg/cm3. This material has a simple preparation process and excellent performance. It has high elasticity and can be restored to its original state after being compressed by 80%. At the same time, it has ultra-fast and ultra-high adsorption capacity, and it is the material with the strongest oil absorption capacity so far. It can be widely used in air purification, catalytic carrier and other fields, and is of great significance for indoor air purification and catalytic reduction of exhaust gas.

Summary: The long way ahead, looking forward to the future in the hustle and bustle

The graphene obtained by removing the mechanical stripping method from other processes can not achieve consistent quality, and the mechanical stripping method is extremely inefficient. Therefore, the existing synthetic technologies can not adapt to industrial applications. It is also the limitations of the preparation process that lead to graphene prices being still relatively expensive. All applications for graphene are still laboratory research stages. For graphene applications, until the preparation process is mature, its cost can be reduced to a level that can be commercialized, and its practical application and industrialization can be described as a long road.

In view of the excellent performance and huge application prospects of graphene, governments and companies have invested a lot of manpower, material resources, and financial resources to conduct research on graphene. Perhaps in order to attract constant attention and investment, companies often claim that they have made very powerful graphene products, which in the author's view is just a real hustle and bustle.

However, it is also under this turmoil and huge investment that graphene research has indeed achieved a lot of good results. The price of graphene has slowly decreased, and larger, higher-quality graphene has gradually been developed. Downstream industrial chains are also gradually trying to use graphene.

In terms of technical maturity and demand urgency, its application to lithium-ion batteries to improve battery charging and discharge efficiency, battery capacity and battery stability obviously plays a decisive role in the development of automobiles, especially electric vehicles. For electric cars to become mainstream, graphene is crucial. If driverless and solar-powered cars are taken into account, graphene will undoubtedly have a wider application space in the automotive industry.

Of course, the prospects are vast, but the reality is cold-blooded. Due to the immature preparation process and the incomplete opening of the downstream industrial chain, graphene still has no large-scale application, and it may take some time to change this status quo. It is believed that with the deepening of research, the singularity of graphene will surely come one day, when many industries will undergo earth-shaking changes and even subversion.

The page contains the contents of the machine translation.