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The most professional article to date reveals the true face of graphene!

Issuing time:2018-12-21 Popularity:848

Graphene was first isolated in 2004. It was well known to the graphene discoverers in 2010 after winning the Nobel Prize. It is only a short time in more than a decade. Although the global graphene industry is still in the early stage, due to the public's enthusiasm for new graphene materials, the graphene industry is over-expanded, showing the falsehood of “sudden springs and springs, thousands of trees and pears blossoming” Prosperous scene.

Especially in some areas with relatively abundant graphite ore resources, graphite ore is mixed with graphene, and the development of graphene industry is regarded as a “magic bullet” for local economic transformation and upgrading, and plans for the construction of graphene industrial parks are planned.
Undoubtedly, graphene, as the forerunner of the new material industry, is driving the transformation and upgrading of traditional manufacturing industries, cultivating the growth points of emerging industries, and promoting the role of mass entrepreneurship and innovation. Under the guidance of national policies, graphene was laid out everywhere. At present, China's graphene full industrial chain is in its infancy, covering all aspects from raw materials, preparation, product development to downstream applications. The Yangtze River Delta, Pearl River Delta and Beijing-Tianjin-Hebei regions have been formed as a gathering area. The development of the graphene industry pattern. In 2016, the overall scale of China's graphene market exceeded 4 billion yuan, and it has formed six major market segments in the application of new energy fields, applications in the field of large health, applications in composite materials, applications in energy conservation and environmental protection, graphene raw materials and graphene equipment.
However, behind the bustle is chaos, and the temporary prosperity brings only permanent pain. It cannot be said that China's graphene industry still faces some deep-seated problems, its basic research capabilities are weak, lack of leading enterprises, the upstream and downstream enterprises are out of line, the industrial chain is immature, the capital market is over-extension of graphene concept, and the industry standard is lacking. Etc., all seriously restrict the healthy and sustainable development of China's graphene industry.
According to statistics, there are more than 40 graphene industrial parks, graphene innovation centers and graphene research institutes that have been built or under construction in China, and more than 2,000 companies are engaged in the research and development of graphene raw materials and products, and this number is still Gradually increase. At present, the domestically vigorous "Leader Movement" of the Great Leap Forward is not advisable. The future graphene industry will be based on the application of the killer grade of graphene materials, rather than as a balm-type additive.
At present, some products in the domestic market, including apparel, coatings, composite materials, adsorption lubrication products, and graphene lithium batteries, graphene mobile phone touch screens, etc., represent the current mainstream products of graphene in China, which should be said to be internationally First party team. However, compared with foreign countries, we still lag behind. The EU Graphene Flagship Program launched 17 new graphene research projects in October last year. They are concerned with graphene super cars, IoT sensors, wearable devices and health. Frontier areas such as management, data communications, energy technology, and composite materials.
Graphene lithium battery?
What is graphene? Let's take a look at the definition of Wikipedia: "Graphene is a planar film composed of carbon atoms with a sp2 hybrid orbital of hexagonal honeycomb crystal lattice, a two-dimensional material with only one carbon atom thickness. Graphene is currently It is the thinnest but hardest nanomaterial in the world. It is almost completely transparent and absorbs only 2.3% of light. Its thermal conductivity is as high as 5300 W/m·K, higher than that of carbon nanotubes and diamonds. Its electron mobility at normal temperature. More than 15000 cm2/V·s, which is higher than carbon nanotubes or silicon crystals, and the resistivity is only about 10-8 俜m, which is lower than copper or silver, and is the material with the lowest resistivity in the world."
The current term "graphene battery" is very hot. In fact, there is no such thing as a "graphene battery" in the international lithium battery academia and industry. The author searched Wikipedia and found no explanation for the terms "graphene battery" or "graphene Li-ion battery".
According to the relatively authoritative graphene website of Graphene-info, the "graphene battery" is defined as a battery with a graphene material added to the electrode material. This explanation is obviously misleading. According to the classical electrochemical nomenclature, the lithium-ion battery used in general smartphones should be named "lithium cobaltate-graphite battery". The reason why it is called "lithium-ion battery" is because SONY put the lithium-ion battery on the market in 1991. Considering that the classic nomenclature is too complicated, people can't remember it, and the charging and discharging process is realized by the migration of lithium ions. The system does not contain metallic lithium, so it is called "Lithium ion battery". The name "Li-ion battery" is widely accepted worldwide, which also reflects SONY's special contribution in the field of lithium.

At present, almost all commercial lithium-ion batteries use graphite-based anode materials. In the case of similar anode performance, the performance of lithium-ion batteries depends largely on the cathode material, so now lithium-ion batteries have the habit of referring to the positive electrode. . For example, lithium iron phosphate battery (BYD called "iron battery" is not in the discussion of the author), lithium cobalt oxide battery, lithium manganese oxide battery, ternary battery, etc., are all for the positive electrode.
Then, if the negative electrode of the battery is made of silicon, will it be called a silicon battery? Maybe it is possible. But no matter what, whoever plays the main role will be named. According to this calculation, if the graphene battery is to be a battery whose graphene plays a major role in electrochemistry. Just like a lithium cobalt oxide battery with carbon black added, can't it be called a carbon black battery? To further clarify the concept of "graphene cells", we first summarize the application areas where graphene may be (only possible) in lithium-ion batteries.
·Negative electrode: 1. Graphene is used alone in the anode material; 2. It forms a composite material with other new anode materials, such as silicon-based and tin-based materials and transition metal compounds; 3. Negative electrode conductive additive.

Positive electrode: It is mainly used as a conductive agent to be added to the lithium iron phosphate positive electrode to improve the rate and low temperature performance. It is also added to the lithium manganese phosphate and lithium vanadium phosphate to improve the cycle performance. Graphene functional coated aluminum foil, its actual performance and ordinary carbon coated aluminum foil (A123 combined with Henkel development) did not increase much, but the cost and process complexity increased a lot, the possibility of commercialization of this technology is very low. It can be clearly seen from the above analysis that there are only two fields in which graphene may play a role in lithium ion batteries: directly for negative electrode materials and for conductive additives.
The prospect of industrialization of lithium anodes is still difficult.
Let us first discuss the possibility of using graphene alone as a lithium anode material. The charge and discharge curves of pure graphene are very similar to those of high specific surface area hard carbon and activated carbon materials. They all have the disadvantages of very low first cycle coulombic efficiency, high charge and discharge platform, severe potential hysteresis and poor cycle stability. It is the basic electrochemical characteristic of high specific surface disordered carbon materials.
High-quality graphene has very low tapping and compaction densities and is extremely expensive. There is no possibility of replacing graphite materials directly as negative electrodes for lithium-ion batteries. Since graphene alone is not feasible as a negative electrode, what about graphene composite anode materials?
Graphene and other new anode materials, such as silicon-based and tin-based materials and transition metal compounds form a composite material, is currently the most popular research field of "nano-lithium", published thousands of papers in the past few years. The principle of recombination, on the one hand, is to use the flexibility of graphene sheets to buffer the volume expansion of these high-capacity electrode materials during the cycle. On the other hand, the excellent electrical conductivity of graphene can improve the electrical contact between the particles to reduce polarization. These factors can improve the electrochemical performance of the composite.

However, it is not that only graphene can achieve improvement results. Practical experience shows that similar conventional carbon material composite technologies and processes can achieve similar or even better electrochemical performance. For example, Si/C composite anode material, composite graphene does not significantly improve the electrochemical properties of the material compared to the conventional dry composite process, but increases the complexity of the process due to the dispersion and compatibility of graphene. It affects batch stability.
If the material cost, production process, processability and electrochemical performance are comprehensively considered, the possibility that the graphene or graphene composite material is actually used for the lithium battery negative electrode is small, and the industrialization prospect is difficult.
There is no obvious advantage as a conductive agent.
Let us talk about the additional problem of graphene used for conductive agents. Currently, the conductive agents commonly used in lithium batteries are conductive carbon black, acetylene black, Ketjen black, Super P, etc. Now, battery manufacturers are beginning to use carbon fiber (VGCF) on power batteries. And carbon nanotubes (CNT) as a conductive agent.
The principle of using graphene as a conductive agent is its excellent electron transport capability due to its special structure of two-dimensional high specific surface area. From the current accumulated test data, VGCF, CNT and graphene have higher rate performance than Super P, but the difference in electrochemical performance between the three is small, and graphene does not. Shows a clear advantage.
So, is it possible to add graphene to make the electrode material performance break out? The answer is very embarrassing. Taking the iPhone battery as an example, the increase in battery capacity is mainly due to the increase in LCO operating voltage, which increases the upper limit charging voltage from 4.2V to 4.35V on the current i-Phone 6, making the LCO capacity from 145 mAh/g. Gradually increase to 160-170 mAh / g (high-pressure LCO must be modified by bulk phase coating and surface coating), these improvements are independent of graphene. In other words, if you use high-pressure lithium cobalt oxide with a cut-off voltage of 4.35V and a capacity of 170mAh/g, how much graphene you add will not increase the capacity of lithium cobaltate to 180mAh/g, let alone increase it several times. The so-called "graphene battery" of capacity. Is it possible to add graphene to increase battery cycle life? This is also awkward. Graphene has a larger specific surface area than CNT, and only a large amount of SEI is formed in the negative electrode to consume lithium ions, so CNTs and graphene can generally be added only to the positive electrode for improving the rate and low temperature performance.
So what about the cost? At present, the production cost of high-quality graphene is still expensive, and the so-called cheap "graphene" products on the market are basically graphite nanosheets (the proportion of layers in the powder exceeds ten layers). If you compare graphene and CNT, we will find that the two have striking similarities, and they all have almost the same "peculiar performance". These "magic properties" of CNTs are now completely applied to graphite. On the body. CNTs began to heat up internationally at the end of the last century, reaching a climax between 2000 and 2005. CNTs are said to have many functions, and there are many "unique features" in the field of lithium batteries.
But after more than 20 years, I have not seen any real-time scale application of these "peculiar performance" of CNT. In terms of lithium battery, CNT is only used as a positive electrode conductive agent. In the past two years, a small-scale trial was started in the LFP power battery (the price/performance ratio is still not as good as VGCF), and the LFP power battery is destined to become the mainstream technical route for electric vehicles. Compared with CNT, graphene has very similar electrochemical properties. There is no special cost. The production cost is higher, the environmental pollution is more serious in the production process, and the actual operation and processing performance are more difficult. The current so-called "graphene battery" is a lot of pure speculation, and there are not many R&Ds that are really quiet. Most of them take the "fast food economy" route. Comparing CNTs and graphene, "history is always similar!"
What is the real application prospect of graphene? The future application of graphene on lithium ion batteries is difficult. Compared to lithium-ion batteries, the application prospects of graphene in supercapacitors, especially micro-supercapacitors, seem to be a little bit more reliable, but we still have to be vigilant about some academic hype.
In fact, after reading a lot of these so-called "academic breakthroughs", you will find that many professors have intentionally or unintentionally confused some basic concepts in their paper. Commercially available activated carbon supercapacitors typically have an energy density of 7-8 Wh/kg, which refers to the device energy density of the entire supercapacitor containing all components. The breakthroughs mentioned by the professors generally refer to the energy density of the materials, so the actual graphene super-electricity is far from being as good as mentioned in the paper.
Relatively speaking, the cost of micro-supercapacitors is not as strict as that of ordinary capacitors. Graphene composites are used as electrochemically active materials, and a suitable ionic liquid electrolyte is selected. It is possible to achieve both conventional capacitors and lithium-ion batteries. Superior energy storage devices may have a certain application value in a niche area such as microelectromechanical systems (MEMS).
Is there any real news on graphene battery news?
There are many news about graphene batteries, such as the graphene battery used in the first graphene mobile phone in China. The author first found out that according to Tesla founder and CEO Elon Musk in 2014, Tesla is preparing to upgrade the performance of the Model S, the upcoming Model X crossover and the affordable electric model 3 .
"Our car's cruising range will probably exceed 500 miles. In fact, our development progress is very fast, but the car price may increase. In the near future, the driving range of Tesla electric vehicles is expected to increase again." He said in an interview with the British car weekly "Auto Express."
Musk did not disclose the details of the plan, but according to numerous media reports, the "super battery" made of graphene may be the key to Tesla's realization of the plan. The author has searched several foreign related reports, and all of them said that the news originated from Chinese media reports. It is clear that Musk has not said to use graphene or graphene batteries. Chinese media people have written a report on Tesla's use of "graphene batteries" as the next generation of electric vehicle batteries.
The other is the graphene battery in Spain. The Spaniard claims that a lithium battery (which is based on the most advanced) has a specific energy value of 180 Wh/kg, while a graphene battery has a specific energy of more than 600 Wh/kg. In other words, it has three times the amount of electricity stored on the market. The battery also has a long life, and its service life is four times that of a conventional NiMH battery, which is twice that of a lithium-ion battery. Electric vehicles that use it to provide electricity can travel up to 1000 kilometers. It takes less than eight minutes to fully charge it.
However, no one has actually seen the company's products, even related basic parameters such as charge and discharge curves, median voltage, etc. can not be found. According to my own years of lithium battery knowledge, this battery performance is impossible to achieve, if the battery still uses the embedded reaction principle of ordinary lithium-ion batteries. In addition, if this is a secondary air battery using graphene, it is obviously not called a "graphene battery". As for the Spanish graphene battery, it is true or false, that is, "the benevolent sees the wise and sees the wisdom".
Also put two news:
The first news: Hong Kong 120 people trapped in graphene investment scam, involving 67 million! Hong Kong police released a message that two men were arrested for allegedly defrauding 120 people for HK$67 million. They claimed to invest in a high-tech mobile phone charger (mobile power) made of a magical material called graphene. . According to the Hong Kong Commercial Crime Bureau, fraudsters claim that graphene is a revolutionary material that will ignite the next technological revolution as a bait to attract victims.
The second news: "Charging 5 seconds of conversation for 2 hours! Zhejiang University has developed a new aluminum-graphene super battery" - on December 24th, this news caused an explosive hot debate on the Internet. However, in response to this statement, the team of the Department of Polymer Science and Engineering of Zhejiang University, in an interview with the Legal Evening News and opinion reporters on the 25th, said that “charging for 5 seconds of talking for 2 hours” is actually only the prospect of the study. "If you really make a product in the future, there is still hope for it, but it is not realized at present."
At present, many graphenes produced by many manufacturers on the market have different numbers of graphite sheets. There are a lot of defects and functional groups on the surface. Whether it is conductivity, thermal conductivity or mechanical properties, it is different from the Nobel Prize-winning graphene. In addition, some manufacturers add a large amount of surfactants in the production process, and some surfactants have a great influence on the conductivity of the powder. At present, many "graphene" actually have the conductivity of the upstream raw material---the graphite is not as good as! In addition, the large amount of surfactant contained in the powder allows downstream manufacturers to fully consider the effects of these additives during use. We often say that below ten layers is graphene, but for graphene powder producers, it should be reported in the report below the proportion of ten layers. If manufacturers of graphene powders are unable to produce high-quality graphene, what about application breakthroughs? The establishment of the graphene standard as soon as possible will enable the industry to develop in a benign direction.
Since 2007, the project has systematically carried out chemical vapor deposition (CVD) and chemical oxidation stripping methods to prepare high-quality graphene materials and their basic research in the field of energy storage, optoelectronics and composite materials. Sexual results: A template-oriented CVD method using porous metal as a growth substrate was proposed to prepare a highly conductive and flexible graphene three-dimensional network structure material, and a high-performance elastic conductor based on the material and a lightweight and efficient flexible electromagnetic shielding were developed. Materials expand the physical properties and applications of graphene. The boundary-dependent growth kinetics of graphene is revealed. The first-order high-quality single crystal graphene is prepared. The universal electrochemical gas bubble lossless transfer method is invented, which lays a foundation for the application of graphene in optical/electronic devices. basis. Combining the structural characteristics of graphene and high-capacity metal oxides, the idea of combining the two is proposed to prepare high-performance graphene anchor metal oxide nanoparticle composite electrode materials for lithium ion batteries and supercapacitors. Synergistic energy storage between people. A hydrogen arc rapid heating expansion cleavage and reduction method and a high-efficiency and non-destructive hydriodic acid reduction method were proposed, which significantly improved the electrical conductivity of the reduced graphene oxide material, which laid a foundation for the scale preparation and application of graphene.
From the perspective of scientific research and innovation, it is a long-term journey of a step, a difficult marathon run. As far as the graphene industry is concerned, it has just started. It is necessary to show the unique use performance of graphene. It also requires a lot of scientific research work and a lot of work to be done. There is no real technological innovation, difficult exploration and long-term research. China's The graphene industry cannot quickly reach the kind of prosperity we expect.
Any new thing can't be smooth sailing, and it can't be done overnight. Graphene has only been in existence for more than 10 years, and it is still in the developing "juvenile era". The road of "growth" and "development" in the future is still very long. It needs all aspects of down-to-earth, no Forget the initial heart and make unremitting efforts. As a graphene producer, you should seek a technological breakthrough to produce reliable graphene powder. As a downstream application, it should be based on the upstream manufacturer to truly reflect the role of graphene in the product.

Keywords in this article:Graphene, graphene precursor, expanded graphite wo
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