What are the prospects for graphene?

Graphene is a hexagonal planar film with a honeycomb lattice composed of carbon atoms. It is currently the thinnest and hardest nano-materials in the world. Its thermal conductivity is higher than that of carbon nano-tubes and diamonds. At room temperature, its electron mobility is higher than that of carbon nano-tubes or Silicon crystals, and its resistivity is lower than that of copper or silver.

Graphene is the thinnest, hardest, hottest, and most conductive material in the world.

It is said that it was "Tear" by Andrei Heim and Konstantin Novoselov in 2004 with tape tearing graphite. Both were physicists at the University of Manchester in the UK because of "two-dimensional graphene. The groundbreaking experiment of materials won the 2010 Nobel Prize in Physics.

Later, graphene was widely known as a magical material. In the past two years, graphene has also been fired in the country. Statistics show that in 2016, the overall size of the graphene market in China exceeded 4 billion yuan, and the sales of graphene related products reached about 3 billion yuan. China's graphene market will expand rapidly in 2017 and is expected to exceed 10 billion yuan, making it the world's largest consumer of graphene, according to the strategic alliance for technological innovation in the graphene industry.

Graphene instantly received favor from all walks of life. Especially in electric cars, where graphene batteries are popularly known as "charging for five minutes and running a thousand kilometers", my mother no longer has to worry about my endurance.

So what the hell is a graphene battery?

Graphene batteries have an energy density of up to 600 Wh / kg, while a lithium battery(based on the most advanced) has a specific energy value of 180 Wh / kg.

In other words, if an electric car wants to achieve the total energy of a power cell battery, the weight of a graphene cell is only one-eighth of that of a normal power cell(graphene cell itself is only half the weight of a conventional battery). In theory, its service life is also four times that of conventional hydrogenated batteries and twice that of lithium batteries.

However, pure graphene batteries are not currently defined by Wikipedia. Even the famous graphene battery that was co-operated by Graphenano and Cordoba in Spain, we gave him twice as much time before we found a piece of hair for mass production after bragabout was about to go into production in 2015.

At present, most of the so-called graphene batteries on the market are technically added to some graphene in batteries such as lithium batteries, and they are more often used as supporting materials.

Let's look at the possible(but only possible) applications of graphene in lithium-ion batteries.

As a negative pole:

1, graphene alone for negative material;

2, with other new negative polar materials, such as silicon and tin based materials and transition metal compounds to form composite materials;

3, negative electrode conductive additives.

Could graphene be used as a lithium electrode material alone?

Used as the industrialization prospect of lithium battery anode

The charging and discharging curve of pure graphene is very similar to that of hard carbon and activated carbon materials with a high specific surface area. Both have the disadvantages of extremely low efficiency of the first cycle Coulomb, high charging and discharging platform, serious potential lag, and poor cycle stability. These problems are actually the basic electrochemical characteristics of high-specific surface disordered carbon materials.

Graphene's compaction and compaction density are very low, and the cost is extremely expensive. There is no possibility of replacing graphite materials directly as negative electrodes for lithium ion batteries. Since it is not feasible to use graphene as a negative pole alone, what about graphene composite negative electrode materials?

Graphene and other new negative polar materials, such as silicon and tin-based materials and transition metal compound formation composites, are currently the most popular research areas for "nanometer lithium electricity" and have published thousands of papers in the past few years. The principle of compounding is to use graphene layer flexibility to buffer the volume expansion of these high-capacity electrode materials during the cycle. On the other hand, graphene's excellent electrical conductivity can improve the electrical contact between material particles to reduce polarization. All these factors can improve the electrochemical properties of composites.

However, it is not that only graphene can achieve improved results. Using conventional carbon material composite technologies and processes, similar or even better electrochemical properties can be achieved. For example, Si/C composite negative electrode materials, compared to ordinary dry method composite processes, composite graphene does not significantly improve the electrochemical performance of the material, but due to the dispersion of graphene and compatibility issues, the complexity of the process is increased. And affect batch stability.

If the material cost, production process, process-ability, and electrochemical properties are considered, the possibility that graphene or graphene composite materials are actually used for lithium electro-negativity is very small.

As a positive pole:

It is mainly used as a conductive agent to be added to the positive electrode of iron phosphate to improve the multiplier and low temperature performance; There are also studies on the improvement of cycling properties added to lithium manganese phosphate and lithium vanadium phosphate.

There is no obvious advantage in being used as a conductive agent

Let's go on to talk about the possibility of graphene being used as a conductive agent. Nowadays, the conductive agents commonly used in lithium electricity include conductive carbon black, acetylene black, coriander black, Super-P, etc.. Battery manufacturers have also begun to use carbon fiber(VGCF) and carbon nano-tubes(CNT) as conductive agents on power batteries.

The principle that graphene is used as a conductive agent is the excellent electronic transmission capability brought about by its special structure of two-dimensional high-specific surface area. According to the accumulated test data, VGCF, CNT, and graphene all have a certain improvement in magnification performance compared to Super-P, but the difference in electrochemical performance between the three is small, and graphene does not show obvious advantages..

So is it possible to add graphene to allow the electrode material to explode? The answer is no. Take the iPhone battery as an example. The increase in battery capacity is mainly due to the increase in the operating voltage of LCO, increasing the upper charging voltage from 4.2 V to 4.35 V on the current i-Phone6. This gradually increases the capacity of LCO from 145 mAh/g to 160-170 mAh/g(high pressure LCO must go through body phase doping and surface coating and other modification measures), and these improvements have nothing to do with graphene.

That is, if you use lithium cobalt oxide with a cut-off voltage of 4.35 V and a capacity of 170 mAh/g, it is impossible to increase the capacity of lithium cobalt to 180 mAh/g by how much graphene you add. Not to mention the so-called "graphene batteries" that tend to increase capacity by several times. Could adding graphene increase battery cycle life? This is also impossible. Graphene has a larger surface area than CNT, and the addition of negative poles can only form more SEIs and consume lithium ions, so CNT and graphene can generally only be added to positive poles to improve Magnification and low temperature performance.

However, the rich functional groups on the surface of graphene are small wounds on the surface of graphene. Adding too much will not only reduce the battery energy density, but also increase the amount of electrolytic fluid absorption. On the other hand, it will also increase the side reaction with the electrolyte and affect circulation. Sex may even bring about safety problems. What about costs? At present, graphene production is extremely expensive, and the so-called cheap "graphene" products on the market are basically graphene oxides.

Even graphene oxide costs more than CNT, and CNT costs more than VGCF. And in terms of fragmentation and process-ability, VGCF is easier to operate than CNT and graphene, which is the main reason why Showa Electric's VGCF is gradually entering the power cell market. It can be seen that graphene is used as a conductive additive and currently has no advantages with CNT and VGCF in terms of price performance.

What are the real applications of graphene?

The future application of graphene in lithium-ion batteries has little prospect. Compared to lithium-ion batteries, graphene's application prospects for super-capacitors, especially miniature super-capacitors, seem to be slightly more reliable, but we still have to be vigilant about some academic hype.

In fact, looking at many of these so-called "academic breakthroughs", you will find that many professors have intentionally or unintentionally confused some basic concepts in their paper. At present, commercial activated carbon super-capacitors have an energy density of 7-8Wh / kg, which refers to the device energy density of the entire super-capacitor containing all components. The breakthroughs mentioned by the professors generally refer to the energy density of the material, so the actual graphene superpower supply is not as good as mentioned in the paper.

In contrast, the cost requirements of micro-super-capacitors are not as strict as ordinary capacitors. Graphene composites are used as electrochemical active materials and suitable Ionic liquid electrolytes are selected. It is possible to achieve the dual advantages of both conventional capacitors and lithium ion batteries. Energy storage devices, In niche areas such as micro-electromechanical systems(MEMS), there may(only possible) be some application value.

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