At present, graphite is the most widely used carbon-based lithium-ion battery anode material. The actual specific capacity of graphite is low, and the cycle stability and safety are difficult to effectively improve. The anode material is a hot spot in current research to replace the current commercial anode material and improve the overall performance of the battery.
Anode materials are widely used in many fields, such as energy storage and catalysis. Because porous carbon has a high specific surface area, controllable micromorphology, rich pore structure, good electrical conductivity, good stability, and a lower synthesis cost. How big is its potential in lifepo4 batteries. Let's take a look together.
1. Porous carbon for lithium battery advantages
Lithium-ion batteries use li+ as the energy transfer medium, and the electrodes have embedded electrochemical lithium storage mechanisms. When charging, lithium ions are generated on the battery cathode, and the generated lithium ions are deintercalated from the cathode and moved to the anode by the electrolyte.
The carbon material that is the anode has a layered structure and many micropores. Lithium ions reaching the anode are embedded in the carbon material's micropores, and the more lithium ions embedded, the higher the charging capacity.
At this time, the anode is in a lithium-rich state and the cathode is in a lithium-poor state. At the same time, the compensation charge of electrons will be supplied to the carbon anode from the external circuit, thus ensuring the charge balance of the anode.
On the other hand, the opposite is true. Lithium ions are deintercalated from the anode and embedded in the cathode through the electrolyte. When used as an anode for lithium-ion batteries, a high specific surface area allows it to bind more lithium ions and provide high battery capacity.
At the same time, the complex multi-dimensional pore structure of ingredients of anode provides an effective diffusion channel and a short diffusion distance for lithium ions.
Defects such as voids and heteroatom doping can be used as lithium storage points. In the process of lithium deintercalation, the mechanical stress of volume expansion and contraction is small, and the cycle stability is good. As a result, this kind of materials often exhibits better electrochemical performance than conventional graphite carbon.
2. What size anode ingredient is best suited for
Porous carbon can be divided into three types according to the pore size: microporous (pore size less than 2nm), medium porous (pore size between 2 and 50 nm), and macroporous (pore size greater than 50nm).
① Microporous material
Advantages: Microporous carbon has a high specific surface area and a high specific capacity as an electrode material.
Disadvantages: Microporous material with a high specific surface area that has a large irreversible capacity (2547 mAh/g) as a lithium-ion battery anode.
This is due to the high specific surface area of microporous, which leads to an increase in the SEI, while the high specific surface area provides more binding sites for functional groups containing oxygen and hydrogen.
These functional groups irreversibly react with lithium ions, resulting in a high irreversible capacity of microporous ingredients as an anode electrode material. And significant capacity decay can be observed in the first few cycles. Therefore, a single structure stuff cannot be used as an ideal lithium ion anode material.
② Mesoporous material
The mesoporous of the carbon can also be used as anode material for lithium-ion batteries. By using ordered silica as a template, ordered CMK-3 with high reversible specific capacity and good charge-discharge cycle characteristics can be synthesized.
After the first cycle, the charge-discharge capacity remains largely unchanged due to the ordered porous structure that minimizes ion transport resistance, resulting in excellent cycling stability.
③ Macroporous material
Ordered macroporous stuff can also be used as an anode material for lithium-ion batteries. Using inverted-phase silica opal as a template, ordered the macroporous of the carbon with three-dimensional (3D) interconnecting pore structure and a graphitized pore wall can be prepared by chemical vapor deposition (CVD) of benzene.
3. Graded material
However, the graded carbon material with a single hole is more or less defective, so in order to improve the performance of graded carbon, with pore size structures of different sizes, pore structures connected to each other and combined in the form of grading has become a research hotspot.
The combined advantages are as follows:
- Micropores provide the material with a high specific surface area to enhance charge storage capacity, thus increasing the capacity of lithium-ion batteries.
- Mesopores provide a fast channel for the transport of electrolyte ions and improve electrolyte permeation.
- Macropores provide a short diffusion distance for electrolyte ions, promote ion diffusion, and have a high capacity retention rate for large currents.
By simply heating lithium carbonate and lithium hydride, spongy graded carbon with an ultra-high specific surface area is synthesized environmentally and efficiently. When used as an anode for lithium-ion batteries, porous carbon has an ultra-high reversible capacity, ultra-long cycle life, and superior rate performance.
Graded carbon can also replace some carbon atoms in the structure of it with other heteroatoms, and adjust the charge distribution and defect generation inside it by taking advantage of the difference in the electronegativity of atoms, thereby improving its physicochemical properties.
4. Potential applications of anode ingredient
The top 10 lithium ion battery anode material companies believe that porous carbon has the potential for widespread use in self-supporting electrodes and current collectors.
This is because the development of the next generation of lithium-ion batteries will develop in the direction of higher capacity, longer service life, more environmental protection, which will require more stable electrochemical performance of current collectors, better conductivity, lighter and cheaper devices.
And future wearable devices will also require current collectors with flexible structures. A anode porous film was studied to obtain a high specific surface area. This porous carbon film can be used directly as an active material and current collector.
Moreover, the large pores in it can withstand large volume changes during charge and discharge. Asymmetric membranes can provide high-speed electron transport pathways and facilitate the diffusion of electrolytes and lithium ions.
As an important part of lithium-ion batteries, the performance of anode materials directly affects the performance of lithium batteries. Although porous carbon as a current collector may not be as good as materials such as carbon nanotubes and graphene, porous carbon is ideal for high electrode mass loads.
Subsequent porous carbon may be combined with nano-carbon materials such as graphene and carbon nanotubes to prepare a more excellent flexible lithium-ion battery current collector to meet the general trend of future wearable device development.