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Expanding the Use of Silicon in Batteries, By Preventing Electrodes From Expanding

Posted By Graphene Council, The Graphene Council, Tuesday, March 26, 2019
The latest lithium-ion batteries on the market are likely to extend the charge-to-charge life of phones and electric cars by as much as 40 percent. This leap forward, which comes after more than a decade of incremental improvements, is happening because developers replaced the battery’s graphite anode with one made from silicon. Research from Drexel University and Trinity College in Ireland now suggests that an even greater improvement could be in line if the silicon is fortified with a special type of material called MXene.

This adjustment could extend the life of Li-ion batteries as much as five times, the group recently reported in Nature Communications. It’s possible because of the two-dimensional MXene material’s ability to prevent the silicon anode from expanding to its breaking point during charging — a problem that’s prevented its use for some time.

Silicon anodes are projected to replace graphite anodes in Li-ion batteries with a huge impact on the amount of energy stored,” said Yury Gogotsi, PhD, Distinguished University and Bach Professor in Drexel’s College of Engineering and director of the A.J. Drexel Nanomaterials Institute in the Department of Materials Science and Engineering, who was a co-author of the research. “We’ve discovered adding MXene materials to the silicon anodes can stabilize them enough to actually be used in batteries.”

In batteries, charge is held in electrodes — the cathode and anode — and delivered to our devices as ions travel from anode to cathode. The ions return to the anode when the battery is recharged. Battery life has steadily been increased by finding ways to improve the electrodes’ ability to send and receive more ions. Substituting silicon for graphite as the primary material in the Li-ion anode would improve its capacity for taking in ions because each silicon atom can accept up to four lithium ions, while in graphite anodes, six carbon atoms take in just one lithium. But as it charges, silicon also expands — as much as 300 percent — which can cause it to break and the battery to malfunction.

Most solutions to this problem have involved adding carbon materials and polymer binders to create a framework to contain the silicon. The process for doing it, according to Gogotsi, is complex and carbon contributes little to charge storage by the battery.

By contrast, the Drexel and Trinity group’s method mixes silicon powder into a MXene solution to create a hybrid silicon-MXene anode. MXene nanosheets distribute randomly and form a continuous network while wrapping around the silicon particles, thus acting as conductive additive and binder at the same time. It’s the MXene framework that also imposes order on ions as they arrive and prevents the anode from expanding.

“MXenes are the key to helping silicon reach its potential in batteries,” Gogotsi said. “Because MXenes are two-dimensional materials, there is more room for the ions in the anode and they can move more quickly into it — thus improving both capacity and conductivity of the electrode. They also have excellent mechanical strength, so silicon-MXene anodes are also quite durable up to 450 microns thickness.”

MXenes, which were first discovered at Drexel in 2011, are made by chemically etching a layered ceramic material called a MAX phase, to remove a set of chemically-related layers, leaving a stack of two-dimensional flakes. Researchers have produced more than 30 types of MXene to date, each with a slightly different set of properties. The group selected two of them to make the silicon-MXene anodes tested for the paper: titanium carbide and titanium carbonitride. They also tested battery anodes made from graphene-wrapped silicon nanoparticles.

All three anode samples showed higher lithium-ion capacity than current graphite or silicon-carbon anodes used in Li-ion batteries and superior conductivity — on the order of 100 to 1,000 times higher than conventional silicon anodes, when MXene is added.

“The continuous network of MXene nanosheets not only provides sufficient electrical conductivity and free space for accommodating the volume change but also well resolves the mechanical instability of Si,” they write.  “Therefore, the combination of viscous MXene ink and high-capacity Si demonstrated here offers a powerful technique to construct advanced nanostructures with exceptional performance.”

Chuanfang Zhang, PhD, a post-doctoral researcher at Trinity and lead author of the study, also notes that the production of the MXene anodes, by slurry-casting, is easily scalable for mass production of anodes of any size, which means they could make their way into batteries that power just about any of our devices.

“Considering that more than 30 MXenes are already reported, with more predicted to exist, there is certainly much room for further improving the electrochemical performance of battery electrodes by utilizing other materials from the large MXene family,” he said.

Tags:  Batteries  Battery  Chuanfang Zhang  Drexel University  Graphene  Li-ion batteries  Trinity College in Ireland  Yury Gogotsi 

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Graphene-alumina heterostructures show their strength

Posted By Graphene Council, The Graphene Council, Monday, March 4, 2019
Updated: Monday, March 4, 2019

Heterostructures of graphene and other 2D or ultrathin materials have potential applications in sensing, electronics, and battery technology. For example, graphene transistors encapsulated with alumina (Al2O3) are of interest for flexible electronics, and graphene/metal oxide heterostructures are widely used in lithium ion batteries.

The mechanical strength, properties and stability of these structures is important for applications that make use of flexibility, or for applications that put to test the mechanical robustness of the materials, such as in high-performance electrochemical cells. Nevertheless, the mechanical properties of graphene heterostructures have not been widely and carefully investigated.



Now, an international team from the US, Germany and Spain have performed careful tests of graphene/alumina heterostructures for varying thickness of the alumina layer. The research revealed that graphene enhances the stiffness (Young’s modulus) compared to bare alumina, and that the alumina film strengthens the resistance of graphene to fracture under load. These findings indicate that such heterostructures have good mechanical strength and can thus be utilized in many devices. The measured values of stiffness and breaking strength add to the expanding body of knowledge of mechanical properties of graphene-related materials.

The method presented in the paper, published in the journal Nanotechnology, blends state-of-the-art fabrication, characterization, and calculation. The basis of the heterostructures is graphene on TEM grids, a single atomic layer of graphene deposited on a grid of circular holes. The monolayer graphene is thus suspended over the holes, making membranes with a diameter of two micrometers.

Alumina is deposited on top of the graphene with atomic layer deposition (ALD), with thickness ranging from 1.5nm to 4.5nm. The mechanical properties are tested with atomic force microscopy, by landing an extremely sharp tip on top of the membrane, pushing on the membrane and studying the deflection. In strength tests, the membrane is pushed until it ruptures under load. The resulting force-distance curves are compared to results of finite element numerical calculations, yielding a quantitative measure of the mechanical properties.

The calculations further revealed a nonintuitive shear stress distribution which indicates a maximum shear away from the line of symmetry and closer to the point of contact of diamond tip and the film, which is a key finding for reliable mechanical performance of the composite devices.

Additionally, these findings illustrate the versatility of ALD techniques for use in heterostructure fabrication, and ease of implementation of graphene into thin-film hybrid structures in order to take advantage of its superior mechanical properties.

Tags:  Battery  Graphene  Li-ion batteries  Sensors 

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First Graphene and Swinburne University Developing New battery Technology Using Graphene

Posted By Terrance Barkan, Wednesday, February 21, 2018

Advanced materials company, First Graphene Limited (“FGR” ) has announced an update on its work with the Swinburne University of Technology (SUT) on the development of a new energy storage technology using graphene, referring to their new product as the "BEST™ Battery".

 

While it is generally accepted that lithium-ion batteries are the state-of-the-art energy storage device available for consumer products today, they are not without their issues. In particular, there are examples where they have been the cause of fires in some instances. There is a vast number of companies and research institutions working to provide safer, more reliable and longer life batteries which utilise materials other than lithium-ion. Some of these involve the use of graphene. 

 

First Graphene, through its research and licencing agreements with Swinburne University of Technology, is pursuing a significantly different path to the development of the next generation of energy storage devices. Rather than trying to improve existing chemical battery technology, it is pioneering the field of advanced supercapacitors which have the potential to change the future for energy storage forever, particularly in handheld and consumer products.

 

Using the advanced qualities of graphene, First Graphene is developing the BEST™ Battery. This energy storage device promises to be chargeable in a fraction of the time and it will be fit for purpose for at least 10 times the life of existing batteries. It will be significantly safer and more environmentally friendly. All these improvements are made possible because the science relies on physics rather than chemical reactions, and on the remarkable properties of graphene materials. 

 

The table below provides an interesting comparison of key operating parameters of the BEST™ Battery alongside existing lithium-ion batteries and existing supercapacitors available in the market. What is particularly noteworthy is the 10x increase in the energy density expected for the BEST™ Battery, when compared with supercapacitors currently on sale in the market place, and the much lower cost per Wh. These features will provide great commercial advantages.

 

Table 1: Comparison between BEST™ Target development and existing Li Ion AA Batteries and an existing commercial Supercapacitor.

 

While the exact details of the design and construction of the BEST™ Battery must remain confidential for reasons of commercial security, First Graphene have disclosed the process of manufacturing the battery involves the use of lasers to create nanopores in graphene-based materials which achieve energy densities more than 10x as great as the pre-existing technology. Practical matters being addressed include the scaling up to the size of the battery from simple laboratory demonstrations of the effectiveness of the science, to devices which will be effective substitutes for batteries used in a wide range of hand held consumer products.

 

Recent Progress 

 

The first few months of the BEST™ Battery development project entailed the recruitment of additional, highly qualified research scientists and the acquisition of specialised equipment needed to prepare and manufacture the components of the BEST™ Battery.

 

Work has commenced on the improvement of many design aspects in order to optimise the configuration of the battery, with the ultimate objective being to develop a product suitable for mass scale production. At the same time, the methodology of making the battery is being subjected to continuous experimentation to improve the effectiveness and efficiency of the materials and processes used in the device. In addition, the pilot production line for building the BEST™ Battery prototype has been set up, which enables the manufacturing of the BEST™ Battery to meet industrial standards. 

 

Swinburne recently reported that a single layer of the BEST™ Battery prototype that made by the pilot production line was able to sustain an LED globe for a period of 15-20 minutes with only a few seconds of initial charge. This is a very significant outcome, auguring well for the ultimate product which is intended to comprise much more than 100 stacked layers of graphene sheets. 

 

The Ragone plot below tracks the continuing improvements in the performance of the BEST™ Battery.

 


 

Figure 1: Ragone Plot demonstrating the progress of the BEST™ Battery development toward its goal

 

Graphene-Based Flexible Smart Watch 

 

The research being undertaken also involves the development of flexible batteries for smart watches which can be incorporated into the watchband itself. These will be light-weight and flexible, they will be able to be recharged in 1-2 minutes, and they will be fit for purpose for many tens of thousands of cycles. Information will be displayed not only on the watch face, but also on the band itself.

Figure 2: Graphene Watch – Flexible Smart Watch concept

 

Target Markets 

 

While it is intended that the BEST™ Battery development program will eventually provide suitable substitutes for many devices which currently used flat pack and cylindrical batteries, it will also provide batteries for new, innovative purposes. The thin profile of the Battery, and its flexibility, will make it suitable for use in clothing. It could also be integrated into smart watch bands, as an example, rather than having a solid block configuration. It is already showing excellent ability to convert kinetic energy into stored energy due to the speed at which it can charge i.e. simple movement of shaking can recharge the Battery. 

 

Commenting on these progress, FGR’s Managing Director Craig McGuckin said:

 

“The demonstration of full scale commerciality of the BEST™ Battery will take time, but so far the results have been very encouraging. The science has been proved at laboratory scale and now we are advancing many aspects of materials used and design processes leading to the development and optimisation of production methodology. We are very pleased that Swinburne University of Technology has advised us that the pilot production line is a world first. We are confident that the advantages offered by our technology will bring revolutionary changes to how we use batteries in the future, with added safety, efficiencies and flexibilities. The BEST™ Battery will be a serious game changer”.

 

 

Tags:  Battery  First Graphene  Li-ion  Supercapacitor  Swinburne University 

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