What are the problems faced by graphene as a negative electrode material for lithium batteries?

Jul 12, 2019   Pageview:11

In recent years, graphene, a prize-winning material, has been widely concerned by the society, and is also filled with news of various "graphene batteries" in related media.


The masses may be curious at this time: How much is the use of graphene in this material, can it rely on it to solve a series of technical bottlenecks encountered in materials, batteries, etc., helping electric vehicles, energy storage and other industries to leap? Coating online combined with the actual gives the correct answer!


Cost problem


Traditional conductive carbon black and graphite are sold in tons (one ton of tens of thousands). On the basis of the graphene sold by gram, can it be reduced to this price? Even if the graphene is reduced to 3 yuan/g according to some media reports, It is also required to be converted into tons of 3 million yuan / ton. We must know that all kinds of materials used in lithium batteries are tens of thousands of tons of things, and they are under pressure from all walks of life to reduce prices. It is totally unrealistic to replace them with graphene.


If it can be cheaper, some companies claim that their graphene can approach the price of ordinary carbon black and graphite. In fact, the material used at this time is graphite microchip (may have dozens of layers), not single or several layers at all. Graphene. At this time, the problem that manufacturers have is the concept of false propaganda and hype, which violates the integrity of the government and the taxpayers.


2. Process characteristics are not compatible


That is, the specific surface area of graphene is too large, which brings a lot of process problems to the process of dispersing and homogenizing the existing lithium ion battery. If the battery factory adjustment process is exhausted, and there is no sufficient profit margin driven by breakthrough performance indicators, who is willing to apply this technology? Graphene surface characteristics are greatly affected by chemical state, batch stability, cycle life, etc. There are a lot of problems, and at present it cannot meet the detailed requirements of lithium battery production.


Regarding the influence of graphene on the actual process of slurrying, the results of the disclosures of Oak Ridge NaTIonal Laboratory and Vorbeck (known as the graphene industry), they found that graphene has a negative impact on the performance of the slurry process.


Even if the above problems are solved, the following problems exist.


3. Low efficiency


If graphene is used as a negative electrode: theoretically it is at most twice the capacity of a graphite negative electrode, the first efficiency is low, and the performance is greatly affected by the surface state.


4. Graphene is expensive as a conductive agent


Graphene can be used as a conductive agent to promote fast charge and discharge. In theory, the rate performance can be improved. However, if the dispersion process is not inconsistent, all things are in the air. In addition, the carbon family has many inexpensive materials and does not exist. The reason for using expensive graphene is not to be used; and graphene is a 2D material, and if it is unfolded in combination with an electrode active material, it blocks the passage of lithium ion diffusion. Therefore, if it is really practical, it will be beneficial or harmful. In fact, it is not very good to say.


Coating online, let's talk a little bit: Graphene is only a kind of nano-materials. In the past ten years, the nano-materials research community has often been too inclined to make hoes and "watering", and the reproducibility of work is often very poor. The disconnection between the technology and the practical goal is very serious. This phenomenon has been widely recognized by some people in the scientific research community and the industry.


For example, Lithium Power Goodenough, Mauger, and Julien have questioned MIT's Battery Materials for ultrafast ging and disging, and published an article Unsupported claims of ultrafast ging of LiFePO4 Li-ion batteries. Charge, the corresponding time is a few minutes charge and discharge), think that these results are at most conceptually feasible.


The excellent performance of many nanomaterials is only reflected in the laboratory level of gram or even microgram capacity. Many of the prospects for scale-up production have inherent defects, and many technologies based on micron-scale materials in the existing industry, fundamentally incompatible.


Moreover, nanomaterials are often only present or used in the form of low-dimensional materials and cannot be truly applied in practical macroscopic three-dimensional applications. The author suggests that the government should promote the development of technologies with industrialization prospects from the policy orientation, increase the support for pilot projects, and achieve the purpose of selecting talents and abilities, so that scientific research can better promote the advancement of industrial technology.


5. Graphene functional coated aluminum foil is costly


As for the graphene functional coated aluminum foil: its actual performance is not much improved compared with the ordinary carbon coated aluminum foil (A123 combined with Henkel), but the cost and process complexity are increased a lot, and the possibility of commercialization of the technology is very low.


In short, graphene is used as a negative electrode material for lithium ion batteries, which has no obvious performance advantages over traditional carbon-based materials, and the application of nano-materials is difficult, the cost is high, and the development prospect is worrisome.


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