With the rapid evolution of autonomous vehicles, electric vehicles are anticipated to continue to grow rapidly. The electric vehicles offer many benefits such as zero emissions, less noise and vibrations, and are operated by simple electric motors with energy conversion in the range of 80-90%. Electric vehicles also have superior energy resilience since they can be charged using a number of energy sources such as renewable energy, conventional power-plant energy, and regenerative braking energy.
Unfortunately, the electric vehicles suffer some limitations such as cost, safety, mileage, limited lifespan, long charging time, and lack of grid for charging. These problems have led to the development of power systems with Lithium-ion batteries. In a bid to fix cost and mileage issues, the energy density of lithium-ion batteries must be increased, and the only way to improve the energy density would be to come up with new active materials with high theoretical capacity for anodes and cathodes.
Although high capacity materials can be applied to the Li-ion batteries, Li-ion batteries would still take long time to charge owing to their low power densities. Unfortunately, even the recently developed fast chargers with pulse power cannot overcome energy-density fading in the course of high-current charge/discharge reference to the limitation in the energy-conversion reaction of Li-ion batteries.
Researchers led by Professor Youn Sang Kim at Seoul National University, Republic of Korea, proposed a novel all-nanowire electrode structure for fast-charging-discharging Li-ion batteries implementing copper nanowires and multi-walled carbon nanotubes without binders or even conductive agents. Theoretically, the multi-walled carbon nanotubes as the representative one-dimensional carbon-based nanostructure provided fast channels for the effective transport of both electrons as well as ions for Li-ion batteries owing to their unique features that had high aspect ratio as well as large surface area. However, the large voltage range between charging and discharging is normally limited the multi-walled carbon nanotubes to be used for active materials in full cells, due to their morphology and resistivity. The authors firstly overcame this limitation of multi-walled carbon nanotubes, and their work is published in peer-reviewed journal, Nano Research.
The authors fabricated a lightweight 3-dimensional composite anode for a fast charging-discharging Li-ion battery implementing two of 1-dimensional nanomaterials, which were copper nanowires and multi-walled carbon nanotubes. Reference to superior electrical conductivity, large surface areas, and high aspect ratio of these materials, the copper nanowire-multi walled carbon nanotubes composite with 3-dimensional structure provided several advantages concerning transport channels of ions and electrons.
The copper nanowires applied as the current collector and multi-walled carbon nanotubes applied as the active materials provided a number of benefits for enhancing the Li-ion battery performances. These included efficient ion diffusion, thick electrode formation, fast electron transport, and flexible cell design. As an advanced binder-free anode, the proposed composite film with tunable thickness indicated a significant low sheet resistance and internal cell resistance. The copper nanowires network with 3-dimensional structure functioned as a rigid framework connected to the multi-walled carbon nanotubes. They prevented the shrinkage and expansion of the multi-walled carbon nanotubes owing to swelling and aggregation, and minimized the effects of volume change of the carbon nanotubes during the charging-discharging process.
Both the full and half-cells of the Li-ion batteries with 3D-composite film anode indicated high specific capacities and Coulombic efficiencies even at high currents. The authors were able to overcome, for the first time, the limitations of carbon nanotubes as anode materials for fast charging and discharging Li-ion batteries by implementing copper nanowires, and the proposed anode can be used in flexible Li-ion batteries. This new development could result in the development of ultrafast chargeable Li-ion batteries for electric vehicles.
Zhenxing Yin, Sanghun Cho, Duck-Jae You, Yong-keon Ahn, Jeeyoung Yoo, and Youn Sang Kim. Copper nanowire/multi-walled carbon nanotube composites as all-nanowire flexible electrode for fast-charging/discharging lithium-ion battery. Nano Res. 2017, DOI: 10.1007/s12274-017-1686-0.Go To Nano Research