A new category of CNT-Carbon hybrid materials for energy storage applications

R. Prada Silvy
CHASM Advanced Materials,
United States

Keywords: battery materials, nanotechnology, carbon nanotubes, CNTs, energy storage, battery performance

Summary:

A large number of industrial applications are driven by the need to improve the performance and durability of rechargeable batteries. For example, electric vehicles require lighter batteries that take up less space, that show a faster charging capacity and higher energy density to give them a range of autonomy equivalent to fossil fueled vehicles. Portable electronic and computing devices need higher energy density to power brighter displays and higher performance processing architectures. The market demands an increase in the functionality and/or performance of devices which requires the same of its power source, consisting mainly of batteries based on lithium-ion technology in a limited set of formulations and configurations. The devices must be safe under a wide variety of operating conditions. These needs require innovation in engineering and battery design and in particular, in the development of new materials for their manufacture at lower cost. The integration of carbon nanotubes (CNTs) into standard materials employed for lithium-ion battery electrodes fabrication (graphite, graphene, conductive carbon) enables an increase in their reversible energy capacity and the number of charge and discharge cycles without experiencing any power capacity loss. The technological challenge, however, has been the cost-effective integration of this material, which can be expensive, in a traditionally cheap set of materials. CHASM Advanced Materials has developed a new category of hybrid carbon materials that uses a new way of incorporating CNTs directly onto the surface of other battery material electrodes, based on natural or synthetic graphite and conductive carbon. These hybrid carbon nanomaterials, called NTeCTM, which stands for carbon nanotube enhanced carbons, is fabricated by chemical vapor deposition method (CCVD) in a catalytic reactor where active transition metals are employed to initiate the carbon nanotube growth on the carbon substrate. The catalyst reacts with a carbon source in gas phase at temperatures generally comprising between 600 and 800 C. A dense carpet of carbon nanotubes is formed on the graphite particles whose length, diameter, density and CNT/graphite composition ratio can be tailored according to the specific application. An important property of these materials is the increase in specific surface area and pore volume that is essential for improving lithium holding capacity in the battery anode. For example, the surface area and pore volume in a sample increased from 18 m2/g to about 122 m2/g and from 0.058 cc/g to about 0.253 cc/g, respectively. It was demonstrated that a carpet of CNTs directly attached to the graphite surface is much more effective than blending CNTs and graphite particles for improving electrical conductivity and mechanical reinforcement of batteries electrodes. NTeCTM-G has demonstrated significant improvement in energy capacity, fast charging and longer cycle life, even when operating at very low temperatures (- 30 C). CHASM NTeCTM technology is a scalable and safer process and its production cost is significantly lower than commercial carbon nanotubes.