How important is graphene in lithium battery field?

Graphene's performance, no doubt, but whether it can be used for the lithium ion batteries?" Graphene claims on market at present, battery is a concept of inaccurate, accurate speak are basically add a bit of graphene in materials, in order to improve lithium battery part of the performance, can be called graphene lithium ion batteries. Do not rule out lab in graphene as anode materials lithium battery or the super capacitor, but demand is high. In conclusion, the spice of graphene can be used as a lithium-ion battery, but as an advocate material is not suitable.

1. The structure and properties of graphene

Physical structure: graphene, is by the thin film of single atomic layer of carbon atoms, the thickness of only 0.34 nm, single layer thickness is equivalent to one over one hundred and fifty thousand of the diameter of a human hair. Is known in the world the most thin, the hardest nanomaterials, pervious to light and can fold.Because only a layer of atom, the electron motion is limited in one plane, graphene has a new electrical properties. Graphene specific surface area is about 2630 m2 / g, the thermal conductivity of 5000 w/m;K.

Electrical properties: graphene has unique features and present massless Dirac fermion properties. The electron mobility can be up to 2 x 105 cm2 / Vt.S, which is about 140 times that of the electron mobility in silicon, gallium arsenide 20 times, high temperature stability, electrical conductivity of up to 108 Ω/m, the surface resistance is about 31 Ω/sq (310 Ω/m2), lower than that of copper or silver, is the best material conductivity at room temperature.

In addition, the carrier and the electrons in graphene hole carrier of half integer quantum hall effect can be observed by electric fields change the chemical potential, and under the condition of room temperature was observed such as Novoselov graphene the quantum hall effect.

2. The role of graphene in lithium-ion batteries

It is because of graphene with nanometer size effect of the above, has a great specific surface area, good electrical conductivity and excellent mechanical properties, such as graphene widely research by scientists all over the world, and created the concept of "graphene lithium battery",

1) anode materials

Graphene due to its unique two-dimensional structure, excellent electron transmission capacity and the advantages of the large specific surface area extremely has the potential to replace graphite as a new generation of lithium ion battery anode materials.Graphene lithium storage mechanism similar to other carbon materials, rechargeable lithium ion from the positive out after electrolyte embedded carbon material layer is formed between the formation of Li2C6, discharging lithium ion out back to the anode. Because of the special two-dimensional graphene structure, when the lamella spacing greater than 0.7 nm, graphene can be stored on the both sides of the lithium ion, at the same time because of the fold graphene exist can also save lithium, so in theory the capacity may be twice that of graphite is higher than 744 mah/g.

In addition, graphene for micro/Nano size, graphite is far less than the body, make Li ion diffusion path shorter, graphene layer spacing is usually far greater than graphite, also provides the lithium ion transport more channels.So compared with graphite, graphene as cathode is more advantageous to improve the battery performance.Since put forward the concept of graphene batteries, a lot of academic research results showed that graphene lithium battery reversible capacity can reach more than 500 mah/g, and have excellent performance ratio.Preparation of li-ion battery cathode laboratory conditions with CVD method and hydrazine hydrate reduction, vacuum suction filter and freeze drying, etc. The preparation of graphene, flake or for hollow spheres, each are not identical.

2) graphene as conductive agent

Primary role is to improve the electrical conductivity of the conductive agent, is due to the electrolyte ion conductive, and there is no conduction electrons, so the conductive agent is to promote electronic arrived quickly through the living materials. In addition, the conductive agent can also improve the pole piece workability, promote the electrolyte infiltration of pole piece, lower resistivity, so as to improve the service life of lithium-ion batteries.

At present commonly used have SP, acetylene black conductive agent, etc., traditional carbon black as the ball, with the live material mixed easier mixing each other, but the contact form as little contact, and limit the conductive role play, increase the conductive agent content.But graphene is lamellar structure, for point of contact with the active substances - surface contact, can maximize play a role of conductive agent, reducing the amount of conductive agent, and can use more active substances, improve lithium battery capacity.Of sheets of graphene is also its drawback, sheet of graphene in solvents harder to disperse, are more likely to reunite together, but need to increase the amount of graphene.At the same time, the lamellar structure for lithium ion diffusion, cause cell internal resistance increases, the battery failure.

Theoretically, super-fast conductivity of graphene can improve the rate performance of the battery, but the fact is that the monolithic layer of graphene hindered the diffusion of lithium ions as a result, especially in large ratio when charging and discharging inside the battery polarization aggravating, the discharge capacity of the battery. Related studies have shown that under the condition of low discharge, using graphene partly replace conductive carbon black to a certain extent, reduce the conductive agent, improve battery energy density, too much of a good thing.

3. The industrialization of graphene lithium battery?

Laboratory and anode materials research and development under the condition of the preparation of graphene and graphene successful example for the industrial production of conductive agent in graphene lithium-ion battery production provides a strong scientific research base, so what is the reality of graphene lithium battery case?

First product is a product of east lumena electric launched in 2016 "ene king".On July 8, 2016, the east lumena electricity in diaoyutai held graphene lithium ion battery product launch, launched the world's first graphene base - "king ene" lithium ion battery products.

The second product is huawei launched in December 2016, the industry's first high temperature and long life of graphene power lithium batteries.Graphene addition, high temperature lithium ion battery technology breakthrough comes mainly from three aspects: adding special additives in the electrolyte, removal of trace water, avoid the high temperature of the electrolyte decomposition;Battery anode with modified large single crystal ternary material, improve the thermal stability of materials;At the same time, using new material graphene, which can realize the lithium ion battery between the environment and efficient heat dissipation.

Mentioned in the third product is the media of east lumena electricity and best "domestic graphene battery", is the fact that graphene in the diaphragm...

Continuously on the market, of course, all kinds of graphene lithium battery patent is came out, but also only stay in the patent stage.Including Samsung, Panasonic, LG, and so on have graphene related patent applications.There is currently no enterprises on the market for graphene lithium-ion batteries for mass production.

4. To summarize

Graphene's performance, no doubt, but whether it can be used for the lithium ion battery?With small make up imho, graphene is not suitable for lithium ion batteries, consider the following:

1. The cost problem

Use of graphene as conductive agent costs much higher than the average carbon black, the cost of lithium-ion batteries are the key controlling factors, does not reduce the cost of raw materials, even if the graphene electrical performance is good, the cost of consumption of a ton of hundreds of thousands of battery manufacturer also can't afford to use.

2. Process problems

Process of the problems of graphene sheet structure is mainly the preparation of electrode paste.Electrode paste has good liquidity, dispersion and suitable viscosity.Sheet of graphene in electrode paste dispersion is a very thorny problem, especially the electrode paste could not add dispersant to help spread.Graphene surface area is large, for the sedimentation stability of the slurry has a great influence, and there is no guarantee that each batch consistency, affect battery performance.

3. The other factors

Graphene sheet structure of lithium ion diffusion, easy to cause the battery polarization serious, which reduces the battery capacity. Graphene is abundant functional groups on the surface of the graphene surface small wound, adding too much will not only reduce the battery energy density, and can increase the amount of liquid electrolyte, on the other hand also increases and the side reaction of the electrolyte and affect sexual cycles, may even bring security problems.

Claim on market at present "graphene battery" is a concept of inaccurate, accurate speak are basically add a bit of graphene in materials, in order to improve the part of the performance of lithium-ion batteries, can call to graphene for lithium ion batteries. Do not rule out lab in graphene as an anode material for lithium battery or super capacitor, but the demand is higher. In conclusion, the spice of graphene can be used as a lithium-ion battery, but as an advocate material is not suitable.

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