Interpretation of the Origin and Present Situation of Graphene Lithium Battery Conductor

With the increasingly prominent energy and environmental problems, the development of new energy sources and the promotion of electric vehicles have become the general trend. As the most important energy storage devices, lithium-ion batteries have received close attention from researchers and industry. Various new key materials for lithium-ion batteries have been developed. The rapid development of lithium-ion batteries has been promoted. The currently widely used lithium-ion battery positive materials include lithium cobalt acid(LiCoO2, LCO), lithium manganate (LiMn2O4, LMO), lithium iron phosphate(LiFePO4, LFP) and ternary materials(LiNix CoyMn1xyO2, NCM), etc.. Due to the low conductivity of the above-mentioned positive electrode materials, it is necessary to add conductive agents to the material particles to build electronic conductive networks to provide rapid access for electronic transmission. And ...

Electrochemical reactions in lithium-ion batteries require electrons and lithium-ions to reach the surface of the active material at the same time, so electrons can participate in the electrochemical reaction in time to achieve good performance of the positive polar active material. If the conductive agent is not used, the ohmic polarization inside the battery increases, The battery capacity will be significantly reduced. Therefore, The conductive agent is also a key material in lithium-ion batteries, which can ensure the full development of the active material capacity and plays an important role in improving the performance of lithium-ion batteries.

On the other hand, since the conductive agent itself does not provide capacity during the charging and discharging process, it is often hoped that the use of conductive agents will be minimized while ensuring that the active substance capacity is used to increase the proportion of active substances in the positive electrode. Thus, the mass energy density of the battery is improved. The conductive agents currently used are usually carbon materials such as conductive carbon black, conductive graphite, and carbon nanoparticles. Since these carbon materials have a low density relative to the active material, reducing the use of conductive agents can significantly increase the battery's volume energy density.

Graphene is a new type of Nano carbon material with unique geometric structure characteristics and physical properties. Since 2010, it has been the first to be used as a conductive agent in commercialized lithium ion batteries. The group carried out systematic research on graphene conductive agents. graphene as a conductive agent has the characteristics of "softness to thinness to density" and has the following four advantages:

(1) The electron conductivity is high, and the use of a very small amount of graphene can effectively reduce the ohmic polarization inside the battery;

(2) Two-dimensional film layer structure. Compared with zero-dimensional carbon black particles and one-dimensional carbon nanotubes, graphene can achieve "face-point" contact with active substances with lower conductivity thresholds. And it is possible to build a conductive network in the electrode from a larger spatial span to achieve a "long-range electrical conductivity" on the entire electrode(the size of graphene materials obtained by different preparation methods is different; The size of the graphene sheet layer obtained by thermal reduction of stone oxide was about 2um).

(3) Ultrathin properties, graphene is a typical superficial solid, compared to carbon black with a multi-sp2 carbon layer, conductive graphite and multi-walled carbon nanotubes, all carbon atoms on graphene can be exposed for electron transfer, atomic efficiency, Therefore, it can form a complete conductive network with the least amount of usage, and improve the energy density of the battery;

(4) High flexibility, can be in good contact with the active material, buffer the volume expansion and contraction of the active material material during the charge and discharge process, inhibit the rebound effect of the electrode, and ensure the battery's good recycling performance.

Due to the above advantages, lithium-ion batteries based on graphene conductors can achieve dense construction. graphene conductors with the characteristics of "softness to thinness to density" show a good prospect for application. Compared with the idea of making graphene and cathode materials into composite electrode materials, Direct use as a conductor of lithium-ion batteries would be the first industrial application of graphene materials.

Although graphene has a very obvious advantage over other conductive agents in terms of electron conductivity, there are still many bottleneck in the actual application process. On the one hand, within the electrode, its planar structure will transmit ions. The steric hindrance effect, This effect is more obvious especially at a large current multiplier.

The page contains the contents of the machine translation.