PhD student at the University of Cambridge, working on advanced battery materials
Fabrication of advanced structures that create longer lasting and faster charging batteries
In today’s society we are consistently looking for improved battery lifetime and very fast charging in our many portable devices. Also for the move towards electric vehicles those two factors are crucial. However, when we are looking at the current Lithium ion batteries, it will be very hard to improve the lifetime (energy density) and the charging speed (power density) significantly, keeping the same material and film structure. Increasing the thickness of the film at the electrodes would lead to longer lasting batteries as there will be more material to store the Lithium ions in. However, thicker films make it harder for the Lithium ions to move through the film and reach the material on the bottom (diffusion limited process). Hence, this is not an ideal way to improve the battery lifetime.
In order to address those issues and enable a huge step forward towards electric vehicles, we have created a structure out of Carbon nanotubes that is mechanically robust with pores that enable improved Lithium-ion transport, even with thick structures with lots of active material. In addition to that, we are using an active materials that stores up to 3x more Lithium ions per gram compared to the currently used standard for battery anodes (graphite). The material is directly synthesized onto the conductive structure and thus decreases losses in energy transport.
Future of energy storage with electric vehicles - here we come. :)
We believe that this new approach to create hierarchical structures will find applications in energy storage as well as catalysis, scaffolds for cell growth, and several other emerging Carbon nanotube applications.
Abstract: An advanced battery architecture composed of 3D carbon nanotube (CNT) current collectors is used to mitigate stresses in flexible batteries. On Page 6705, C. George, M. De Volder, and co-workers describe the fabrication process and characteristics of this new generation of ultraflexible batteries, which show high rate and cyclablility. These batteries may find applications in the powering of flexible displays and logics.
Pub.: 12 Aug '16, Pinned: 01 Jul '17
Abstract: Li-ion batteries are used in many applications in everyday life: cell phones, laser pointers, laptops, cordless drillers or saws, bikes and even cars. Yet, there is room for improvement in order to make the batteries smaller and last longer. The Fromm group contributes to this research focusing mainly on nanoscale lithium ion cathode materials. This contribution gives an overview over our current activities in the field of batteries. After an introduction on the nano-materials of LiCoO(2) and LiMnPO(4), the studies of our cathode composition and preparation will be presented.
Pub.: 05 Feb '16, Pinned: 01 Jul '17
Abstract: The skins of many plants and animals have intricate microscale surface features that give rise to properties such as directed water repellency and adhesion, camouflage, and resistance to fouling. However, engineered mimicry of these designs has been restrained by the limited capabilities of top-down fabrication processes. Here we demonstrate a new technique for scalable manufacturing of freeform microstructures via strain-engineered growth of aligned carbon nanotubes (CNTs). Offset patterning of the CNT growth catalyst is used to locally modulate the CNT growth rate. This causes the CNTs to collectively bend during growth, with exceptional uniformity over large areas. The final shape of the curved CNT microstructures can be designed via finite element modeling, and compound catalyst shapes produce microstructures with multidirectional curvature and unusual self-organized patterns. Conformal coating of the CNTs enables tuning of the mechanical properties independently from the microstructure geometry, representing a versatile principle for design and manufacturing of complex microstructured surfaces.
Pub.: 30 Jul '14, Pinned: 01 Jul '17
Abstract: Vertically aligned carbon nanotube (CNT) arrays are grown on a moving substrate, demonstrating continuous growth of nanoscale materials with long-range order. A cold-wall chamber with an oscillating moving platform is used to locally heat a silicon growth substrate coated with an Fe/Al2O3 catalyst film for CNT growth via chemical vapor deposition. The reactant gases are introduced over the substrate through a directed nozzle to attain high-yield CNT growth. Aligned multi-wall carbon nanotube arrays (or 'forests') with heights of approximately 1 mm are achieved at substrate speeds up to 2.4 mm s(-1). Arrays grown on moving substrates at different velocities are studied in order to identify potential physical limitations of repeatable and fast growth on a continuous basis. No significant differences are noted between static and moving growth as characterized by scanning electron microscopy and Raman spectroscopy, although overall growth height is marginally reduced at the highest substrate velocity. CNT arrays produced on moving substrates are also found to be comparable to those produced through well-characterized batch processes consistent with a base-growth mechanism. Growth parameters required for the moving furnace are found to differ only slightly from those used in a comparable batch process; thermal uniformity appears to be the critical parameter for achieving large-area uniform array growth. If the continuous-growth technology is combined with a reaction zone isolation scheme common in other types of processing (e.g., in the manufacture of carbon fibers), large-scale dense and aligned CNT arrays may be efficiently grown and harvested for numerous applications including providing interlayers for advanced composite reinforcement and improved electrical and thermal transport.
Pub.: 16 Sep '09, Pinned: 01 Jul '17
Abstract: Nanostructuring silicon (Si) and combining Si with carbon shells have been studied in recent Li-ion battery electrodes, yet it remains a grand challenge to overcome the low electrical conductivity and associated volume change of Si. Here, by first coating a mesoporous SiO2 (meso-SiO2) onto carbon nanotube (CNT) networks and then converting it into a meso-Si layer covered by carbon, we obtained a freestanding, highly porous composite sponge electrode consisting of three-dimensionally interconnected sandwiched carbon-Si-CNT skeletons. In this hierarchical structure, the macropores among the sponge connect to mesopores in the meso-Si layer so that Li(+) diffusion is facilitated, whereas the underlying CNT networks serve as conductive paths for electrons transport. Meanwhile, the outer carbon coating on meso-Si could buffer the volume expansion and prevent material shedding. As a result, our sandwiched carbon-Si-CNT electrodes exhibit large specific capacity, high rate capability and long cycle life. The combination of carbon-wrapped meso-Si and CNT sponges might be a potential strategy for developing efficient electrodes in various energy storage systems.
Pub.: 01 Jul '17, Pinned: 01 Jul '17
Abstract: Transition metal oxides (TMOs) have attracted significant attention for energy storage applications such as supercapacitors due to their good electrical conductivity, high electrochemical response (by providing Faradaic reactions), low manufacturing costs, and easy processability. Despite exhibiting these attractive characteristics, the practical applications of TMOs for supercapacitors are still relatively limited. This is largely due to their continuous Faradaic reactions, which can lead to major changes or destruction of their structure as well phase changes (in some cases) during cycling, leading to the degradation in their capacitive performance over time. Hence, there is an immediate need to develop new synthesis methods, which will readily provide stable porous architectures, controlled phase, as well as useful control over dimensions (1-D, 2-D, and 3-D) of the metal oxides for improving their performance in supercapacitor applications. Since its discovery in late 1990s, metal–organic frameworks (MOFs) have influenced many fields of material science. In recent years, they have gained significant attention as precursors or templates for the derivation of porous metal oxide nanostructures and nanocomposites for next-generation supercapacitor applications. Even though these materials have widespread applications and have been widely studied in terms of their structural features and synthesis, it is still not clear how these materials will play an important role in the development of the supercapacitor field. In this review, we will summarize the recent developments in the field of MOF-derived porous metal oxide nanostructures and nanocomposites for supercapacitor applications. Furthermore, the current challenges along with the future trends and prospects in the application of these materials for supercapacitors will also be discussed.
Pub.: 14 Jun '17, Pinned: 29 Jun '17
Abstract: Metal oxide nanosheets have attracted great attention in various fields, such as energy storage, catalysis, and sensors. Current synthesis methods of metal oxide nanosheets are laborious and not scalable. Herein, a facile and scalable method for the synthesis of metal oxide nanosheets is presented, which requires neither hydro-/solvothermal conditions nor postsynthesis template removal. The synthesis is versatile, as evidenced by the wide variety of metal oxide nanosheets derived. Nanosheet properties such as crystallinity, crystallite size, and carbon content can be controlled by tuning the synthesis conditions. The metal oxide nanosheets demonstrate promising performance as Li-ion battery anodes.
Pub.: 24 Jun '17, Pinned: 29 Jun '17
Abstract: The design and development of materials for electrochemical energy storage and conversion devices requires fundamental understanding of chemical interactions at electrode/electrolyte interfaces. For Li–S batteries that hold the promise for outperforming the current generation of Li ion batteries, the interactions of lithium polysulfide (LPS) intermediates with the electrode surface strongly influence the efficiency and cycle life of the sulfur cathode. While metal oxides have been demonstrated to be useful in trapping LPS, the actual binding modes of LPS on 3d transition metal oxides and their dependence on the metal element identity across the periodic table remain poorly understood. Here, we investigate the chemical interactions between LPS and oxides of Mn, Fe, Co, and Cu by combining X-ray photoelectron spectroscopy and density functional theory calculations. We find that Li–O interactions dominate LPS binding to the oxides (Mn3O4, Fe2O3, and Co3O4), with increasing strength from Mn to Fe to Co. For Co3O4, LPS binding also involves metal–sulfur interactions. We also find that the metal oxides exhibit different binding preferences for different LPS, with Co3O4 binding shorter-chain LPS more strongly than Mn3O4. In contrast to the other oxides, CuO undergoes intense reduction and dissolution reactions upon interaction with LPS. The reported findings are thus particularly relevant to the design of LPS/oxide interfaces for high-performance Li–S batteries.
Pub.: 15 Jun '17, Pinned: 29 Jun '17