talk about itGraphene for batteryRole in lithium batteries

Because the battery-specific graphene has the above-mentioned nano-scale effect, good conductivity and excellent mechanical properties, it has been widely studied by scientists all over the world, and the concept of "graphene lithium battery" has emerged. What role does graphene play in lithium batteries?

1. Anode materials

Due to its unique two-dimensional structure, excellent electron transport capacity and large specific surface area, graphene has great potential to replace graphite as a new generation of lithium-ion battery anode material. The lithium storage mechanism of graphene is similar to that of other carbon materials. When charging, lithium ions are separated from the positive electrode and inserted into the carbon material layer to form Li2C6. When discharged, lithium ions are separated and returned to the positive electrode. Due to the special two-dimensional structure of graphene, when the lamellar spacing is greater than 0.7nm, both sides of graphene can store lithium ions. At the same time, due to the existence of wrinkles, graphene can also store lithium, so theoretically its capacity may be twice that of graphite, higher than 744 mAh/g.

In addition, graphene is mostly in micro-nano size, which is much smaller than bulk graphite, which makes the diffusion path of lithium ions shorter, and the layer spacing of graphene is usually much larger than that of graphite, which also provides more channels for lithium ion transmission. Therefore, compared with graphite, using graphene as a negative electrode is more conducive to improving battery performance. Since the concept of graphene battery was proposed, many academic research results have shown that, the reversible capacity of graphene lithium battery can reach more than 500 mAh/g, and has excellent rate performance. The cathode of lithium battery prepared in the laboratory is mostly prepared by CVD method, hydrazine hydrate reduction method, vacuum filtration method and freeze-drying method. Graphene is either flake or hollow sphere, which is different.

2, battery-specific graphene as a conductive agent.

The main function of the conductive agent is to improve the conductivity of electrons, because the electrolyte is ionic conductive, but the electrons cannot conduct electricity. The conductive agent is to promote the electrons to quickly pass through the living material to the current collector. In addition, the conductive agent can also improve the processing performance of the pole piece, promote the electrolyte to penetrate into the pole piece, reduce the resistivity, and extend the service life of the lithium battery.

At present, commonly used conductive agents include SP, acetylene black, etc. Traditional carbon black is spherical and easier to mix evenly with living substances. However, its contact form is point-to-point contact, which limits the effect of conductive agent and increases the addition amount of conductive agent. However, graphene has a sheet structure and the contact with active substances is point-to-surface contact, which can maximize the effect of conductive agent and reduce the amount of conductive agent, the active material is used more and the capacity of the lithium battery is improved. However, the flake graphene is also its disadvantage. The flake graphene is more difficult to disperse in the solvent and is easier to agglomerate together, but the amount of graphene needs to be increased. At the same time, its flake structure is not conducive to the diffusion of lithium ions, which increases the internal resistance of the battery and accelerates the failure of the battery.

In theory, the ultra-fast conductivity of graphene for batteries can improve the rate performance of batteries, but the fact is that single-layer graphene hinders the diffusion of lithium ions, especially when charging and discharging at high rates, the internal polarization of the battery is intensified and the discharge capacity of the battery is reduced. Related studies have shown that under the condition of low-rate discharge, partial replacement of conductive carbon black with graphene can reduce the amount of conductive agent and improve the energy density of the battery to a certain extent.

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