Carbon Nanotubes

Cylindrical carbon nanoparticles with novel electronic, thermal, and mechanical properties.

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After huge hype and disillusionment, CNTs have gained market traction as a high-price, high-performance conductive additive for composites and batteries, but without advancements in manufacturing and integration, their disruptive potential is limited.

What's New

Lux Research analysts and the Lux Intelligence Engine have added the following recent carbon nanotubes developments.

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The wave is here: Opportunities for materials in mmWave electronics for 5G networks: 5G networks – which promise widely available high-speed connectivity – are one of the hottest technology areas in 2018. In our 18 for 2018 report, we called out that patenting and publication activity in 5G is in the top 1% of more than 2,000 technologies assessed, and in our report on Material Innovations Driving Digital Transformation, we identified communication hardware as critical. Despite this hype, or perhaps because of it, there is still confusion and uncertainty around what constitutes 5G – for a full breakdown and analysis of opportunities and threats in 5G, see this insight. Here, we will focus on the one key enabling technology and the resulting opportunity for materials: millimeter wave (mmWave) connectivity for mobile broadband.mmWave refers to a spectrum of electromagnetic radiation at frequencies between 24 GHz and 300 GHz. This is a higher frequency than typical mobile broadband, which operates at less than 6 GHz. mmWave is promising because it can transfer data at much faster rates than current mobile broadband frequencies; for this reason, electronics and telecom players like IBM, Samsung, and Qualcomm have made major commitments to mmWave. Despite the promise of mmWave, there are still major challenges to overcome before mmWave can go mainstream. From a materials perspective, this primarily means advances in printed antennas. Antennas consist of a few main materials: the substrate on which the antenna is printed (typically fire-retardant glass fiber reinforced epoxy, or FR4), additives to the substrate material that alter its properties, and the electrically conductive printed ink. The main materials-specific challenges are in the substrates – common silver nanoparticle-based inks are largely adequate for mmWave applications. The material challenges are:mmWave antennas require very low dielectric constant (dk) and dissipation factor (df, or loss tangent) substrates. Reducing the dk is necessary to lower the energy needed to transmit a signal at a given frequency. Df, on the other hand, measures how much energy is wasted during operation. At high frequencies, more energy is dissipated by the antenna during operation, which weakens the signal, reduces the sensitivity of the antenna, and generates heat. mmWave antennas also require substrates with very stable properties across different temperatures. Due to their high frequencies, small differences in dielectric constant can substantially change the emitted frequency. Because mobile broadband antennas are exposed to hot and cold temperatures outdoors and generate heat when operating, they are particularly vulnerable to these issues. Moisture can also create variations in properties, adding an additional challenge in many regions.These challenges mean that mmWave antennas will need substrates that are cheap and easy to manufacture to allow widespread rollout in both phones and base stations, but also have superior properties. Basic FR4 epoxy/glass printed circuit board materials are likely not sufficient for mmWave, and currently viable materials are too expensive or not available at sufficient scale, creating opportunities for new resin systems, resin additives, and manufacturing for mmWave. Lux surveyed the innovation occurring in these spaces:Substrates: Current manufacturers of high-performance mmWave substrates materials use high-temperature thermoset polymers, most notably polyimide (PI), polytetrafluorethylene (PTFE), and liquid crystal polymers (LCPs). These materials offer the dielectric properties needed for mmWave but are substantially more expensive than epoxy. There are emerging approaches: For example, Isola has patented epoxy resins mixed with a styrene maleic anhydride (SMA) copolymer; the SMA copolymer helps enhance the thermal and electrical properties of the epoxy. Competitor Park Electrochemical has patented thermoset resins based on polyphenylene ether resins, which it claims offers similar electrical properties to PTFE but better temperature stability. While academic work has been concentrated on more common materials for mmWave, such as LCPs, academics have proposed many material classes, including polydimethylsiloxane and benzocyclobutene. Additives: Overall, the novel additives space for mmWave appears to be underserved. While existing players for 5G substrates certainly highlight their use of additives in new designs, there is not much apparent momentum for new materials. Corporations like Park Electrochemical and Isola that have introduced new resin types appear to be working exclusively with silica-based additives. Rodgers Corporation's recent work is far more focused on development of novel laminates and combinations of materials, rather than additives themselves. The academic space is similarly unfocused – while there are certainly explorations on the effect that additives like carbon nanotubes and graphene has on polymers, there have been none that specifically targeted these materials for applications within mmWave, though both graphene and CNTs have been proposed as inks or coating films for mmWave antennas. Manufacturing: mmWave antennas require increasingly small and precisely designed antennas and packaging. Both commercial and academic groups have begun to explore the use of 3D printing for mmWave, as it allows relatively cheap production of complex structures that can help address both the loss and directionality issues. An example company in this space is Nuvotronics, which has developed a copper printing technology for mmWave assemblies. This company promises higher efficiency and lower manufacturing costs, but appears to have only supplied into high-value defense applications. The use of 3D printing to make mmWave antennas has recently become a hot topic among academics – while the total volume of publications is still small, there is strong momentum in publication growth. Academic work on this topic is broader – covering high-precision metal printing as well as the use of inkjet printing and FDM to create novel antenna designs.Our review of the opportunities for materials for mmWave broadband shows a space with a lot of uncertainty. Existing materials systems for antennas – such as liquid crystal polymers – are acceptable from a performance standpoint but are painfully expensive compared to FR4. This creates an opportunity for new materials, but there are no obvious emerging low-cost alternatives. Clients approaching this space have a few options:Work on methods to bring down cost of existing materials solutions. This is the most obvious play in the near term but presents risks of being displaced in the longer term and is likely only viable for those companies that are already entrenched in the electronics supply chain. Attempt to match existing materials from other applications to mmWave needs. The near-term roll-out of mmWave (starting in 2019 and 2020) means that a full R&D effort to create a new polymer or additive will likely not be commercially ready in time for initial adoption of mmWave. Clients who want to ride this wave will need to work with already commercially mature materials. Target R&D efforts at truly disruptive options: The long timelines of most material R&D efforts mean that any truly novel material will likely enter the market once mmWave is mature and have to displace an established incumbent. Clients who know that they cannot leverage their existing material portfolio will be best served by targeting their R&D efforts at material systems that offer the potential to both improve performance and reduce cost in order to maximize chances of adoption.

MOFs promising performance in labs is unlikely to make a commercial impact for batteries: Years ago, when carbon nanotubes (CNTs) were first discovered, they were lauded for their high tensile strength and low electrical resistance, with obvious, albeit ambitious applications in structural cables, electrical wires, and integrated circuits. However, these expectations never came to fruition, as we simply didn’t have the capability to manufacture them consistently, accurately, or in large enough quantities to make them cost-effective. Today, CNTs have been put to some use, but mostly by being mixed in with more common materials for marginal gains.A new material, metal organic frameworks (MOFs), have appeared as the next CNTs: MOFs are a type of material with cage-like lattices that can contain other guest molecules. Although MOFs have not hit the same level of hype compared to CNTs, they have extraordinary material properties that garner interest in the scientific field: one gram of certain types of MOFs has a surface area equal that of a football field. This makes them attractive for areas that need high surface area, including carbon capture, gas storage, catalyst support, and even supercapacitors. Their ability to store gas has allowed one company to commercialize the material, but only in the very niche area of fruit preservation. MOFs’ lattices also make it attractive for battery anodes, since they could potentially hold far more lithium ions than normal graphite anodes. Research interest in MOFs for batteries is strong, as a recent review paper details. Some of the experiments deliver remarkable results (including one ZnO/ZnFe2O4/C (ZZFC) MOF cathode in an Li-O2 battery - a technology which itself is 20 years to relevancy - delivered a first discharge capacity exceeding 11,000 mAh/g). Unfortunately, it seems the materials research community has no clear direction on a specific chemistry or application for MOFs, and unlike CNTs, they have a large amount of material combinations available which complicates attempts at commercialization. Additionally, many of these complex combinations are difficult to manufacture.While some researchers are branching out, using more complex molecular combinations for their MOFs, others are simplifying by using MOF-like structures made entirely out of a single material, called clathrates. Silicon-based clathrates have been particularly attractive for battery scientists (overviewed in this paper) since their latticed cage structure made specifically for lithium molecules could theoretically  employ silicon’s specific capacity of 4,200 mAh/g without the degradation or size change that comes from repeated cycling. Unfortunately, labs have been unable to consistently reproduce this; in some experiments, repeated insertion and removal of lithium ions caused degradation to the structure, dramatically reducing capacity over use. Additionally, even in simulations with ideal conditions, the maximum theoretical specific capacity of pure silicon clathrates was calculated to be 123 mAh/g - three times lower than graphite.MOFs and clathrates seem to be following the same story we’ve seen in the past with CNTs. However, while CNTs have mainly a manufacturing problem, MOFs have too many material combination possibilities and clathrates are too unstable. It looks like the development of MOFs are where carbon nanotubes (CNTs) were 10 years ago. The Lux Tech Signal shows that CNT commercialization required a decade of high level research activity, and MOFs are only now reaching this level.There may be a day when we build our elevator cables out of CNTs and MOFs provide untold battery life and performance, but the research and manufacturing field for these materials will have to mature considerably before that happens. But there is hope: while not the wonder material it was claimed to be, one of the main applications of CNTs today is in batteries. Clients looking for long-term breakthroughs in materials for energy storage are encouraged to consider MOFs as one potential research path, but given commercialization is likely more than a decade away, focus on partnerships with universities and research consortiums. For more near-term opportunities for battery materials, clients should consider solid electrolytes, lower-cost cathodes which reduce or eliminate cobalt content, or conductive additives which allow for faster charging.

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