1. Anode material

Due to its unique two-dimensional structure, excellent electronic transmission capacity and large specific surface area, Graphene for batteries has great potential to replace graphite as a new generation of negative electrode material for lithium ion batteries. The lithium storage mechanism of Graphene is similar to other carbon materials. When charging, lithium ions are separated from the positive electrode and embedded in the carbon material layer, forming Li2C6. When discharging, 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 0.7 nm, both sides of Graphene can store lithium ions. At the same time, due to the existence of wrinkles, Graphene can also store lithium. In theory, its capacity may be twice that of graphite, higher than 744 mAh/g.

In addition, Graphene is mostly micro nano sized, much smaller than bulk graphite, which makes the diffusion path of lithium ions shorter. 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 500mAh/g, and it has excellent rate performance. The positive electrode of lithium battery prepared in the laboratory mostly adopts CVD method, hydrazine hydrate reduction method, vacuum filtration method, and freeze drying method to prepare Graphene. Graphene is either flake or hollow sphere, which is different from each other.

2. Special Graphene for battery as conductive agent

The main function of conductive agents is to improve the conductivity of electrons, as the electrolyte is ion conductive, but electrons cannot conduct electricity. Conductive agents promote the rapid passage of electrons through living materials to the collector. In addition, conductive agents can improve the processing performance of the electrode, promote electrolyte infiltration into the electrode, reduce resistivity, and extend the service life of lithium batteries.

At present, the commonly used conductive agents are SP, acetylene black, etc. The traditional carbon black is spherical, which is easier to mix evenly with living substances, but its contact form is point-to-point contact, which limits the role of conductive agent and increases the amount of conductive agent. Graphene has a sheet structure, and its contact with active substances is point to surface contact, which can maximize the role of conductive agent and reduce the amount of conductive agent, It makes more use of active substances and improves the capacity of lithium batteries. However, flaky Graphene is also its disadvantage. Flaky Graphene is more difficult to disperse in solvent and easier to agglomerate, but it needs to increase the amount of Graphene. At the same time, its flaky structure is not conducive to lithium ion diffusion, leading to increased internal resistance of the battery and accelerated battery failure.

Theoretically, the ultrafast conductivity of Graphene for battery can improve the rate performance of the battery, but the fact is that the monolayer Graphene blocks the diffusion of lithium ions, especially in the case of high rate charge and discharge, the internal polarization of the battery will increase, and the discharge capacity of the battery will decrease. Relevant research shows that under the condition of low rate discharge, the amount of conductive agent can be reduced by partially replacing conductive carbon black with Graphene, To some extent, increase the energy density of the battery.