Application Note:

Carbon nanofibers can be used to add conductive structural integrity that extends the cycle life of electrodes.

Detailed Explanation:

There are several unique characteristics of graphitized vapor grown carbon fibers that enhance their usefulness as constituents in electrodes of lithium-ion batteries, including:

  1. The small diameter of the fiber makes it possible to distribute the fibers homogeneously in a thin electrode material and to introduce a large surface area to react with the electrolyte.
  2. The improved electrical conductivity of the electrode is related to the high electrical conductivity of the fiber itself, and the network formation of the fibers with the graphite particles in the anode to form a fiber-mat type configuration.
  3. Compared to conventional whiskers, the relatively high intercalation ability of the submicron VGCFs does not lower the capacity of anode materials upon cycling.
  4. A high flexibility of the electrode is achieved due to the network formation of the submicron VGCFs in the fiber-mat structure.
  5. The high endurance of the electrode can be attributed to the ability of the VGCFs to absorb the stress caused by intercalation of Li ions
  6. Improved penetration of the electrolyte due to the homogeneous distribution of fibers surrounding the anode material.
  7. Compared to carbon black, the cyclic efficiency of the Li-ion battery was improved for a relatively long cycle time.

Source Data:

Top table: Basic properties for submicron vapor grown carbon fibers.

Bottom left graph: Charge-discharge curve of graphitized submicron vapor grown carbon fiber batteries during the first cycle. After contact is made, the potential decreases immediately to 0.8 V and the curve shows a shoulder around 0.7 V only during the first discharge process, as is also observed in other carbon materials. The discharge capacity is 283 mAh/g, and the cycle efficiency is about 77%.

Bottom right graph: Good cyclic efficiency was observed up to above 200 cycles, possibly because of its superior bulk properties, such as higher resiliency and lower volume resistivity.

The process of graphitization involves the motion and rearrangement of carbon-layer planes. As heat-treatment temperature increase, the surface layers tend to straighten out. This process indicates that atomic rearrangement of carbon atoms is taking place within the carbon fibers.



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