Graphene for Lithium Batteries

The evolution stage of lithium-ion battery conductive agents ranges from zero-dimensional conductive agent carbon black materials to one-dimensional fiber-like carbon nanotube materials, and then to two-dimensional graphene materials with lamellar structure.

Conductive agent materials are an important part of lithium-ion batteries and play an important role in the electrochemical performance of lithium-ion batteries. After an appropriate amount of conductive agent is added to the electrode, the electron transfer rate inside the electrode can be effectively improved.

Graphene has the advantages of excellent mechanics, optical properties, high thermal conductivity, small resistivity and strong stability. As a new type of lithium battery conductive agent, due to its unique sheet structure (two-dimensional structure), the contact with the active material is a point-surface contact form, which can maximize the role of the conductive agent and reduce the amount of conductive agent, so that more active materials can be used and the capacity of the lithium battery can be improved.

Conductive mechanism 

(1) The electronic conductivity is high, and the use of a small amount of graphene can effectively reduce the ohmic polarization inside the battery; (2) The two-dimensional sheet structure, graphene can achieve "surface-point" contact with the active material, and can build a conductive network in the pole piece from a larger spatial span. Realize "long-range conductivity" on the entire electrode ;(3) Ultra-thin characteristics, all carbon atoms on graphene can be exposed for electron transport, high atom utilization efficiency, so it can form a complete conductive network with minimal usage. 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 during charge and discharge, inhibit the rebound effect of the pole piece, and ensure the good cycle performance of the battery. 

The effect as a conductive agent is closely related to the amount of it added. In the case of small addition, graphene is much better than conductive carbon black because it can better form a conductive network. However, graphene with a thicker layer will hinder the diffusion of lithium ions and reduce the ionic conductivity of the electrode (6-9 layers are generally considered to be the most suitable). However, due to its high cost, difficulty in dispersion and hindering lithium ion transmission, it has not been fully industrialized.

Production process 

Graphene production process methods mainly include mechanical peeling method, chemical liquid phase stripping method, redox method, chemical vapor deposition method, etc., liquid phase stripping method and redox method have low cost and low purity, suitable for batteries, supercapacitors, conductive coatings and conductive inks.

In the latest research progress, the conductive agent selected for some lithium batteries is a binary or ternary conductive paste mixed between CNT, graphene and conductive carbon black. The composite of conductive agents into conductive slurry is the demand of industrial applications, and it is also the result of synergy and excitation between conductive agents.

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