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China LI Battery 033116 56efc495569e8

Recently, researchers at Tsinghua University, China have proposed a graphene-based nanostructured lithium metal anode for lithium metal batteries to inhibit dendrite growth and improve electrochemistry performance. They report their findings in Advanced Materials, published on March 16, 2016.

“Widely used lithium-ion batteries cannot satisfy the increasing requirement of energy storage systems in portable electronics and electric vehicles. New anode batteries, like Li-S and Li-air batteries, are highly sought. Lithium metal provides an extremely high theoretical specific capacity, which is almost 10 times more energy than graphite,” said Prof. Qiang Zhang, at the Department of Chemical Engineering, Tsinghua University. “However, the practical applications of lithium metals are strongly hindered by lithium dendrite growth in continuous cycles. This induces safety concerns. The lithium dendrites may cause internal short circuits resulting in fire. Furthermore, the formation of lithium dendrites induces very low cycling efficiency.” The dendrite growth and unstable solid electrolyte interphase consume large amount of lithium and electrolyte, and therefore leading to irreversible battery capacity losses. Consequently, inhibiting the dendrites growth is highly expected.

Many approaches have been proposed to retard the growth of dendrites through electrolyte modification, artificial solid electrolyte interphase layers, electrode construction, and others. “We noticed that by decreasing the local current density heavily, lithium dendrite growth could be efficiently inhibited. Based on this concept, we employed unstacked graphene with an ultrahigh specific surface area to build a nanostructured anode. And it turned out to be a very efficient idea,” said Rui Zhang, a Ph.D. student and the first author. “Additionally, we have employed the dual-salt electrolyte to acquire more stable and more flexible solid electrolyte interphase, which can protect the lithium metal from further reactions with electrolyte.”

This graphene-based anode offered great improvement, including (1) ultralow local current density on the surface of graphene anode (a ten-thousandth of that on routine Cu foil-based anodes) induced by the large specific surface area of 1666 m2 g-1, which inhibited and brought uniform lithium deposition morphology; (2) high stable cycling capacity of 4.0 mAh mg-1 induced by the high pore volume (1.65 cm3 g-1) of unstacked graphene, over 10 times of the graphite anode in lithium-ion batteries (0.372 mAh mg-1); (3) high electrical conductivity (435 S cm-1), leading to low interface impedance, stable charging/discharging performance, and high cycling efficiencies.

“We hope that our research can point out a new strategy to deal with the dendrite challenge in lithium metal anodes. The ultralow local current density induced by conductive nanostructured anodes with high specific surface area can help improve the stability and electrochemistry performance of lithium metal anodes,” said Xin-Bing Cheng, a co-author of the work. Future investigation is required to design preferable anode structures and to produce more protective solid electrolyte interphase layers. The researchers also call for additional study of the diffusion behavior of Li ions and electrons in the process of lithium depositing and stripping to advance the commercial applications of lithium metal anodes.

Explore further: Nanostructure enlightening dendrite-free metal anode

More information: R. Zhang, X.-B. Cheng, C.-Z. Zhao, H.-J. Peng, J.-L. Shi, J.-Q. Huang, J. Wang, F. Wei, Q. Zhang. Conductive Nanostructured Scaffolds Render Low Local Current Density to Inhibit Lithium Dendrite Growth. Adv. Mater. 2016, 28, 2155-2162. DOI: 10.1002/adma.201504117.

McMaster Cellulose 151006132027_1_540x360

McMaster University: Summary: New work demonstrates an improved three-dimensional energy storage device constructed by trapping functional nanoparticles within the walls of a foam-like structure made of nanocellulose. The foam is made in one step and can be used to produce more sustainable capacitor devices with higher power density and faster charging abilities compared to rechargeable batteries. This development paves the way towards the production of lightweight, flexible, and high-power electronics for application in wearable devices, portable power sources and hybrid vehicles.

McMaster Engineering researchers Emily Cranston and Igor Zhitomirsky are turning trees into energy storage devices capable of powering everything from a smart watch to a hybrid car.

The scientists are using cellulose, an organic compound found in plants, bacteria, algae and trees, to build more efficient and longer-lasting energy storage devices or supercapacitors. This development paves the way toward the production of lightweight, flexible, and high-power electronics, such as wearable devices, portable power supplies and hybrid and electric vehicles.

“Ultimately the goal of this research is to find ways to power current and future technology with efficiency and in a sustainable way,” says Cranston, whose joint research was recently published in Advanced Materials. “This means anticipating future technology needs and relying on materials that are more environmentally friendly and not based on depleting resources.

Cellulose offers the advantages of high strength and flexibility for many advanced applications; of particular interest are nanocellulose-based materials. The work by Cranston, an assistant chemical engineering professor, and Zhitomirsky, a materials science and engineering professor, demonstrates an improved three-dimensional energy storage device constructed by trapping functional nanoparticles within the walls of a nanocellulose foam.

The foam is made in a simplified and fast one-step process. The type of nanocellulose used is called cellulose nanocrystals and looks like uncooked long-grain rice but with nanometer-dimensions. In these new devices, the ‘rice grains’ have been glued together at random points forming a mesh-like structure with lots of open space, hence the extremely lightweight nature of the material. This can be used to produce more sustainable capacitor devices with higher power density and faster charging abilities compared to rechargeable batteries.

Lightweight and high-power density capacitors are of particular interest for the development of hybrid and electric vehicles. The fast-charging devices allow for significant energy saving, because they can accumulate energy during braking and release it during acceleration.

“I believe that the best results can be obtained when researchers combine their expertise,” Zhitomirsky says. “Emily is an amazing research partner. I have been deeply impressed by her enthusiasm, remarkable ability to organize team work and generate new ideas.”

Story Source:

The above post is reprinted from materials provided by McMaster University. Note: Materials may be edited for content and length.

Journal Reference:

  1. Xuan Yang, Kaiyuan Shi, Igor Zhitomirsky, Emily D. Cranston. Cellulose Nanocrystal Aerogels as Universal 3D Lightweight Substrates for Supercapacitor Materials. Advanced Materials, 2015; DOI: 10.1002/adma.201502284

Rice Nanoporus Battery 102315 untitledPhoto: Jeff Fitlow

Researchers at Rice University in Houston, Texas, have developed a nanoporous material that has the energy density (the amount of energy stored per unit mass) of an electrochemical battery and the power density (the maximum amount of power that can be supplied per unit mass) of a supercapacitor. It’s important to note that the energy storage device enabled by the material is not claimed to be either of these types of energy storage devices.

The research community has wearied of claims that some new nanomaterial enables a “supercapacitor,” when in fact the energy storage device is not a supercapacitor at all, but a battery. However, in this case, the Rice University researchers, led by James Tour, who is known for having increased the storage capacity of lithium-ion (Li-ion) batteries with graphene, don’t make any claims that the device they created is a supercapacitor. Instead it is described as an electrochemical capacitor with nanoporous nickel-fluoride electrodes layered around a solid electrolyte that is flexible and relatively easy to scale up for manufacturing.Rice logo_rice3

The issue of appropriate nomenclature aside, the reported performance figures for this energy storage material are very attractive. In the Journal of the American Chemical Society (“Flexible Three-Dimensional Nanoporous Metal-Based Energy Devices“),  the researchers report energy density of 384 watt-hours per kilogram (Wh/kg), and power density of 112 kilowatts per kilogram (kW/kg).

To give some context to these numbers, a typical energy density for a Li-ion battery is 200Wh/kg, whereas commercially available supercapacitors store around 5- to 25 Wh/kg and research prototype supercapacitors have made claims of anywhere from 85 to 164 Wh/kg. In terms of power density, the numbers for the new nanoporous material is in line with those of supercapacitors, which range from 10 to 100 kW/kg—far higher than the 0.005 to 0.4kW/kg that batteries can deliver.

“The numbers are exceedingly high in the power that it can deliver, and it’s a very simple method to make high-powered systems,” Tour said in a press release. “We’re already talking with companies interested in commercializing this.”

To make the battery-supercapacitor hybrid, the Rice team deposited a nickel layer on a backing material. They then etched the nickel layer to create pores five nanometers in diameter. The result is high surface area for storing ions. After removing the backing, the nickel-based electrode material is wrapped around a solid electrolyte of potassium hyrodroxide in polyvinyl alcohol. In testing, the researchers found that there was no degradation of the pore structure after 10 000 charge-discharge cycles, or any significant degradation of the electrode-electrolyte interface.

“Compared with a lithium-ion device, the structure is quite simple and safe,” said Yang Yang, lead author of the paper, in the press release. “It behaves like a battery but the structure is that of a supercapacitor. If we use it as a supercapacitor, we can charge quickly at a high current rate and discharge it in a very short time. But for other applications, we find we can set it up to charge more slowly and to discharge slowly like a battery.”

With the device’s flexibility and high charge-up rate, it’s possible to imagine this storage device powering flexible mobile devices. However, charging rates for the battery/supercapacitor will be limited by the typical 200-amp 240V single-phase residential service, which is only capable of providing (absent any other load) only 48 kW.

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