,

Exploring the Capabilities of Electrospinning

Nature is full of fibrous structures, such as wool, silk, and spider webs from the animal world and cotton, linen, and bamboo from the plant world. These fibrous materials perform special functions not available from bulk materials. If the diameter of the fibers is in the tens or hundreds of nanometers, we enter the world of nanofibers. Nanofibers, whether natural or synthetic, belong to nanomaterials and possess new material properties and functions due to the unique shape and size of the fibers and the myriad of ways these fibers are assembled. Some advantages of nanofibers are a high surface area (1 – 100 m2/g), high porosity (ca 90%), small diameter (10 nm – 1 mm), and a small, interconnected pore size. These unique features make nanofibers useful in numerous diverse application areas, such as filtration, catalyst, sensor, tissue engineering, and energy storage. Several methods are used to make nanofibers: template, self-assemble, phase-separation, melt-blowing, and electrospinning. Among these, electrospinning is deemed the most promising due to its ability to produce continuous nanofibers on a large scale and adjustable fiber structures from a variety of electrospinnable polymers. Read more

/by
,

Solid Electrolytes: Are we there yet?

Solid Electrolytes for Lithium-ion and Lithium-Sulfur Batteries: A Safer Solution

Lithium-ion batteries have provided a lightweight energy-storage solution that has enabled many of today’s high-tech devices – from smartphones to electric cars. Although these batteries are generally safe, fire and explosion concerns have caused the industry to seek solutions. The importance of safety has been highlighted by several rare, yet highly publicized battery hazards such as the explosion in a Japan Airlines 787 Dreamliner’s cargo hold in 2013 and Samsung’s Galaxy Note 7 catching fire, which resulted in the recall of more than 1 million smartphones in 2016. The combustion is mainly due to leakage of the liquid electrolyte, or short-circuit of the electrodes caused by the failure of the polymer gel separator, which also contains liquid.[1] For this reason, it is desirable to replace liquid components used in existing lithium-ion batteries with all solid materials.[2] This would not only solve the safety issue, but would also provide several other significant advantages, such as greater energy storage ability (pound for pound at the battery pack level), no dendrite formation (tiny, fingerlike metallic projections called dendrites that can grow through the electrolyte layer and lead to short-circuits), chemical and electrochemical stability over a wide voltage window (0 – 6V), and exceptionally long cycle life (>50,000 cycles)[3].

Solid state electrolytes can be broadly classified into three categories: (1) inorganic electrolytes, (2) solid polymer electrolytes (SPE), and (3) composite electrolytes. As the performance of batteries depends on the diffusion of lithium ions within the electrolyte, solid electrolytes need to have high ionic conductivity and negligible electronic conductivity. A summary is given here of the three classes of solid electrolyte materials. The data presented here is based on materials produced and measurements performed at NEI Corporation as part of NEI’s R&D program.

Inorganic Electrolytes

Inorganic solid state electrolytes present high lithium ionic conductivity at temperatures below their melting point. The highest room temperature conductivity reported for any inorganic solid electrolyte is 2.5 × 10−2 S/cm for Li9.54Si1.74P1.44S11.7Cl0.3,[4] which is comparable to the conductivity of a liquid electrolyte. Besides having impressive conductivity values, inorganic electrolytes are single ion conductors, allowing the lithium transference number to approach unity. These characteristics, and the absence of leakage and pollution, make the inorganic electrolyte a highly appealing electrolyte material for lithium-ion and lithium-sulfur batteries. Inorganic electrolytes can be either crystalline or amorphous (glass), or have mixed phases (glass-ceramic).

Sulfur Based Solid Electrolytes (Thio-LiSICONS)

One of the early crystalline lithium ion conductors was based on an oxide compound of lithium zinc germanium, Li14ZnGe4O16, which was reported by Hong.[5] This type of crystalline ion conductor is referred to as LISICON (lithium superconductor). Although the ionic conductivity of Li14ZnGe4O16 reaches 0.125 S/cm at 300°C, it is only 10-7 S/cm at room temperature. Efforts to improve the ionic conductivity of LISICON-type ion conductors have resulted in the replacement of oxygen by sulfur in the framework. Since the radius of S2- is greater than O2-, and S2- has better polarization capability than O2-, the substitution weakens the interaction between the crystal lattice and Li+ ions, thus fostering Li+ ion transport. The incorporation of sulfides in the form of partial sulfide substitution (e.g., oxy-sulfide[6]  compounds) or full sulfide substitution[7] can raise the room temperature conductivity of the electrolyte to about ~10-3 S/cm. An example of the highly conductive sulfur substituted LISICON ion conductor is , Lithium Germanium Phosphorous Sulfide (LGPS). Li10GeP2S12 is a superionic conducting solid that conducts lithium ions at room temperature with conductivity in the range of 10-4 S/cm to 10-2 S/cm, depending on material form (powder, pellet, or sintered pellet) and measurement conditions.

Since germanium is an expensive rare earth element, a similar material was synthesized replacing germanium with much less expensive tin, yielding a crystalline LISICON type ion conductor, Li10SnP2S12, Lithium Tin Phosphorous Sulfide (LSPS), which has conductivity slightly lower than that of LGPS, but is much more affordable. Basic characteristics of the Lithium Tin Phosphorous Sulfide powder produced at NEI Corporation are listed here. The solid electrolyte is phase pure and has Li-ion conductivity in the range of 10-4 to 10-2 S/cm (approaching that of liquid electrolytes) depending upon material/pellet processing conditions, and electrochemically stable up to 6V.

[ezcol_1half]

[/ezcol_1half] [ezcol_1half_end]

[/ezcol_1half_end][ezcol_1half]

[/ezcol_1half] [ezcol_1half_end]

[/ezcol_1half_end]

More recently, Li9.54Si1.74P1.44S11.7Cl0.3 and Li9.6P3S12 have been reported. Exceptional room temperature conductivity (2.5 x 10-2 S/cm for Li9.54Si1.74P1.44S11.7Cl0.3) as well as high stability (∼0 V versus Li metal for Li9.6P3S12) were achieved1. NEI has successfully produced the following sulfur based solid electrolytes: (LSPS – Li10SnP2S12, LGPS – Li10GeP2S12, β-LPS – Li3PS4, LPSCl – Li6PS5Cl, LSPSCl – Li9.54Si1.74P1.44S11.7Cl0.3, and LPS – Li9.6P3S12) in bulk quantities (gram to kilogram scale).

Oxide Based Garnet-Type Solid Electrolytes

Garnet-type lithium solid electrolytes have a general formula of Li5La3M2O12 where M can be Ta or Nb. These were first reported in 2005[8] and have been intensively studied in recent years. The most attractive property of this class of crystalline solid electrolyte is its excellent chemical stability against lithium metal and also against moisture, in addition to its high ionic conductivity. These materials can be handled in a dry room. An example of the Garnet-type solid electrolyte is Li6BaLa2Ta2O12, which displays a room temperature conductivity of 4 x 10-5 S/cm and a low grain boundary resistance.[9] When the Garnet-type solid electrolyte Li5La3M2O12 was partially substituted at the M site by Y or In, conductivity was further improved. For example, the composition Li5.5La3Nb1.75In0.25O12 showed an enhanced conductivity of 1.8 x 10-4 S/cm at 50 °C with a low activation energy of 49.2 kJ/mol.[10] Another composition, Li6.5La3Nb1.25Y0.75O12, showed a high conductivity of 2.7 x 10-4 S/cm at 25 °C.[11]

Most recently, a Garnet-type Lithium Lanthanum Zirconate (LLZO – Li7La3Zr2O12) has quickly become a promising solid electrolyte for all solid-state lithium and lithium ion batteries because of its high conductivity (> 10−4 S/cm) at room temperature, excellent thermal performance, and stability versus Li metal and oxygen. The material shows great potential to offer high energy density and minimize battery safety concerns to meet many applications in large energy storage systems such as electric vehicles and aerospace. LLZO exists in tetragonal and cubic crystal structures, with the cubic phase displaying about two orders of magnitude higher ionic conductivity than that of tetragonal phase. The cubic phase is stabilized by doping with Al or Ga.

Al or Ga-doped LLZO (Li6.24La3Zr2Al0.24O11.98 and Li6.24La3Zr2Ga0.24O11.98) have been synthesized at NEI Corporation in various batch sizes. Both the materials are fairly phase pure, crystallized in cubic phase (see PXRD pattern) and have room temperature conductivity in the order of 10-4 – 10-5 S/cm, depending upon the pellet processing and annealing condition (see the impedance plot below). Negligible electronic conductivity, large band gap (~6 eV) and wide electrochemical stability window (0 – 6V), are attractive properties for this material.[12]

[ezcol_1half]

[/ezcol_1half] [ezcol_1half_end]

[/ezcol_1half_end]

Oxide Based Perovskite-Type Solid Electrolytes

Lithium Lanthanum Titanate (LLTO), Li0.5La0.5TiO3, with Perovskite structure has been considered to be a promising solid electrolyte material for lithium-ion and lithium-oxygen batteries due to numerous outstanding advantages, such as: (i) high lithium conductivity at room temperature, (ii) high lithium diffusion coefficient, (iii) low electronic conductivity, and (iv) electrochemical stability window larger than 4 V. NEI has prepared LLTO and various metal doped LLTO (e.g., Al-doped LLTO), and analyzed the crystal structure, particle size, and conductivity.

 

 

 

 

There are two challenges that LLTO electrolyte faces: grain boundary resistance and instability against lithium metal. Although the bulk conductivity of LLTO can reach 10-3 S/cm at room temperature, the grain boundary conductivity is relatively low (10-5 S/cm).[13]

Phosphate Based LISICON-Type Solid Electrolytes

Lithium Aluminum Titanium Phosphate (LATP) is a phosphate based LISICON (Lithium Super Ionic Conductor) with the general molecular formula Li1+xAlxTi2-x(PO4)3, which shows high ionic conductivity of ~10-3 S/cm for x = 0.3 composition. It is electrochemically stable above 1.8 V and thermally stable up to 1000 °C. Phosphate based LISICON type materials have applications in batteries, fuel cells, gas sensors, catalysis, and low thermal expansion ceramics. NEI has synthesized LATP compositions and its sodium analogs (NaSICON) and studied the conductivity.[14]

[ezcol_1half]

[/ezcol_1half] [ezcol_1half_end]

[/ezcol_1half_end]

Sulfide Based Glassy and Glass-Ceramic Solid Electrolytes

Sulfur based glassy and glass-ceramic solid electrolytes, such as Li2S–SiS2[15] and Li2S–P2S5,[16] can achieve ionic conductivity of 10-5 S/cm to 10-3 S/cm due to the high polarizability of sulfur ions. A general composition of the Li2S–P2S5 system can be represented by x Li2S + (1-x) P2S5, where x is the molar fraction. The Li2S–P2S5 system varies widely in crystal form, crystal content, and the resulting ionic conductivity, depending on the composition and processing method. Usually, the grain-boundaries around crystal domains in Li2S–P2S5 glass–ceramics are surrounded by amorphous phases. Therefore, these glass-ceramic solid electrolytes often have lower grain boundary resistance than in polycrystalline systems, which results in improvement in the observed total conductivity.

The composition of x Li2S + (1-x) P2S5 when x = 0.75, or Li3PS4, represents the most stable chemical in the Li2S−P2S5 system. The crystal domains of Li3PS4 exist in either γ or b phase – among these b phase is the more ionically conductive material. β-Li3PS4 (β-LPS) is a “superionic” solid that conducts lithium ions at room temperature. β-LPS synthesized at NEI is phase pure and has a Li-ion conductivity of 10-4 – 10-5 S/cm, depending upon material/pellet processing conditions. The material is electrochemically stable versus lithium over a wide voltage window (0 – 5V).

[ezcol_1half]

[/ezcol_1half] [ezcol_1half_end]

[/ezcol_1half_end]

Although the best of the inorganic solid electrolytes have demonstrated high ionic conductivity comparable to liquid electrolytes, several limitations have to be overcome before they can be widely used as solid electrolyte. First, bulk conductivity is usually higher than grain boundary conductivity, which makes the total conductivity smaller than the intrinsic bulk conductivity, unless the material is sintered at high temperature and pressure. A related and often asked question is that if sintering is not an economically viable method, what processing alternatives are available to utilize these highly ionic conducting powders? Second, a critical issue for the development of high power, solid-state lithium batteries is the high resistance at the electrode/solid electrolyte interface. Inorganic solid electrolytes are generally not flexible enough to handle the stress developed as a result of volumetric expansion/contraction of the electrodes. Therefore, how to create and maintain a favorable interface between the electrode and solid electrolyte is a challenge. Polymer electrolytes when used alone, or in combination with inorganic electrolytes, have the potential to address both of these issues pertaining to inorganic solid electrolytes.

Solid Polymer Electrolytes (SPE)

The most common solid polymer electrolytes (SPE) for rechargeable solid-state lithium batteries are composed of low lattice energy lithium salts (e.g., LiClO4, LiN(CF3SO2)2, LiCF3SO3, or LiBC4O8) dissolved in polyether-containing polymers such as poly(ethylene oxide), poly(propylene oxide), or poly(ethylene glycol). Other polymers have also been studied, such as polyphosphazenes, which have oligoethyleneoxy side chains to facilitate lithium ion conduction and reduce glass transition temperature (Tg). Since solid polymer electrolytes are flexible and can be easily made into free standing membranes, they have been predominantly used as solid electrolytes in a variety of electrochemical devices. A traditional dry, PEO-based electrolyte has a severe drawback in that its conductivity only becomes sufficient at elevated temperatures (above 60 °C). PEO is a semi-crystalline material where PEO crystalline and amorphous domains co-exist. It has been widely accepted that ion transport occurs in the amorphous region. PEO crystals melt above 60 °C and a jump of conductivity is observed above the melting point. To overcome this limitation, polymer gel electrolytes were developed. These are crosslinked polymer networks with liquid electrolyte imbibed to boost the room temperature ionic conductivity, which generally exceeds 1×10-3 S/cm. However, the liquid electrolyte in gel polymer electrolytes still poses safety issues, and the polymer gel has inferior mechanical properties. For these reasons, there is renewed interest in developing truly dry polymer electrolyte systems and some systems have room temperature conductivity values approaching 10-4 S/cm. We discuss only the 100% solid polymer electrolyte here.

One of the polymers developed at NEI Corporation using the copolymer strategy is H-polymer. As a 100% solid material, H-polymer combines the benefits of high room temperature lithium-ion conductivity (5 x 10-5 S/cm) with good mechanical properties of a solid polymer. H-polymer is a PEO-based copolymer with PEO segments in the polymer backbone that has four orders of magnitude higher room temperature conductivity than that of pure PEO. The significant improvement of room temperature conductivity is due to the amorphous nature of PEO segments in the copolymer. H-polymer can be used as a separator, or as a conductive binder for active cathode and anode materials.

Another series of copolymers that shows good room temperature conductivity has been reported in the literature.[17] These are POEA-g-PDMS or POEM-g-PDMS copolymers, which are graft copolymers made of grafted PEO chains and grafted PDMS (poly(dimethylsiloxane)) chains. The oligomeric nature of PEO segments prevents it from crystallizing and the low Tg PDMS segments make the polymer a rubbery flexible ionic conductor, where the conductivity reaches in the range of 10-5 S/cm to 10-4 S/cm at room temperature.

Composite Electrolytes

Composite electrolytes are SPEs with sub-micron or nano- sized inorganic particles dispersed in the polymer matrix. Adding inorganic particles induces a favorable interaction between the ceramic surface states and the anions of both the lithium salt and PEO segments, thereby promoting lithium-ion transport and inhibiting polymer crystallite formation. This results in enhanced ionic conductivity, promoting interfacial stability at Li/Li+ interface, suppressing the growth of dendrites, improving mechanical properties, and increasing Li+ transference number. It has been found that particle size is important and nanoparticles are more effective than larger particles. One to two orders of magnitude enhancement in room temperature ionic conductivity can be realized with the addition of ceramic nanoparticles in an SPE host, compared to the undispersed system, along with improvements in the physical, mechanical and electrochemical properties. A few of the ceramic nanoparticles that have been investigated that demonstrated a significant improvement in conductivity are Al2O3, SiO2, TiO2, ZrO2, and BaTiO3.

Most of the systems studied involve inert ceramic particles and PEO with lithium salt. NEI Corporation has explored producing composite electrolytes using active ionic conductive inorganic particles in a conductive polymer host. For example, by incorporating LLZO in H-polymer, we were able to fabricate mechanically sturdy electrolyte membranes/separators with conductivity approaching 10-4 S/cm.

Opportunity for New Materials Development

Market-driven interest in developing practical solid electrolyte materials for use in Lithium-ion and Lithium-sulfur batteries has created opportunities for producing materials with new compositions, chemistry and morphology. Being able to process the material in a usable form is the key to enabling commercial utilization of the solid electrolyte materials. Combining the attributes of inorganic and organic solid electrolyte materials offers a path to high ionic conductivity materials wherein the high ionic conductivity of inorganic electrolytes is combined with the processing advantages and superior mechanical properties of solid polymer electrolytes.

About NEI Corporation

NEI Corporation is an applications-driven company that develops and produces advanced materials. NEI Corporation offers specialty cathode and anode materials (both powders and coated electrodes), and solid state electrolytes for use in lithium-ion and lithium-sulfur batteries. NEI produces battery materials through a scalable and economical synthesis process, which is adaptable to different materials compositions and particle morphologies. The company also offers battery materials development and cell-level testing services.

Contact Us »

 

References:

[1] http://www.nydailynews.com/news/scientists-solve-mystery-flaming-laptops-article-1.445634

[2] https://chargedevs.com/newswire/japanese-researchers-use-superionic-conductors-as-electrolytes-for-solid-state-batteries/

[3] https://www.excellatron.com/advantage.htm

[4] Y. Kato, S. Hori, T. Saito, K. Suzuki, M. Hirayama, A. Mitsui, M. Yonemura, H. Iba, and R. Kanno, Nature Energy, 2016, 3, 438-446, and references therein

[5] H. Y.-P. Hong, Mater. Res. Bull., 1978, 13, 117.

[6] S. Kondo, K. Takada, and Y. Yamaura, Solid State Ionics, 1992, 53-56, 1183.

[7] J. H. Kennedy and Y. Yang, J. Solid State Chem., 1987, 69, 252.

[8] V. Thangadurai, and W. J. Weppner, J. Am. Ceram. Soc., 2005, 88, 411–418.

[9] V. Thangadurai, and W. J. Weppner, Adv. Funct. Mater., 2005, 15, 107–112.

[10] V. Thangadurai, and W. J. Weppner, J. Solid State Chem., 2006, 179, 974–984.

[11] S. Narayanan, F. Ramezanipour, and V. Thangadurai, J. Phys. Chem.C 2012, 116, 20154.

[12] T. Thompson et al, Energy Letters, 2017, 2, 462-468.

[13] C. W. Ban, and G. M. Choi, Solid State Ionics, 2001, 140, 285–292.

[14] N. Anantharamulu et al, J. Mater. Sci. 2011, 46, 2821.

[15] N. Machida, and T. Shigematsu, Chem. Lett. 2004, 33, 376–377.

[16] M. Tatsumisago, Solid State Ionics, 2004, 175, 13–18.

[17] Q. Hu, A. Caputo, D. R. Sadoway, J. Vis. Exp., 2013, 78, 50067.

/by
,

A New Perspective on Coatings and Surface Treatments

NEI Corporation’s Patented Technologies Provide a New Perspective on Coatings and Surface Treatment

Patents1Gains in productivity and efficiency are possible when a coating or surface treatment provides functionalities beyond the usual protective and aesthetic properties. This realization has sparked great interest in functional coatings in recent years for applications that traditionally have not used paints or coatings. A good example is the use of anti-ice coatings on power transmission lines. Mitigating ice accumulation will help prevent power outages, which has a tangible and beneficial economic impact. Another example is the use of a surface treatment to increase the efficiency of power generation turbines.

Examples of functionalities of interest for both industrial and consumer applications include:

  • Self-Healing: the coating or surface treatment autonomously repairs damage
  • Hydrophobicity: coated surfaces vigorously repel water droplets
  • Oleophobicity: prevents “oil” molecules from sticking to the surfacePatents2
  • Self-Cleaning / Easy-To-Clean: minimizes or eliminates the need for chemicals during washing

While great strides have been made in academic circles to understand the different surface phenomena of these so called ‘smart coatings’, commercial products to date have met with limited success because they are not engineered to meet all of the functional performance requirements that an application may need. For example, commercially available superhydrophobic coatings repel water droplets, but do not prevent the diffusion of water vapor – minimizing moisture ingress is a critical functionality for most protective coatings.

Patents3More often than not, many of the functionalities mentioned above need to be integrated into a single coating or surface treatment. For example, a transparent coating that resists finger printing also needs to be scratch resistant and durable. A coating that prevents fogging in eyewear and other transparent surfaces must also be durable and resistant to chemicals. Further, in order to meet the cost criteria, application of the coating must be compatible with conventional coating methods such as spray, dip, brush or flow. Over the past few years, NEI Corporation’s concerted efforts to develop and implement practical, multi-functional coatings are now coming to fruition.

Patents4Backed by a bevy of issued and pending patents, NEI has introduced an array of coating products under the registered trade name NANOMYTE®. For example, NANOMYTE® MEND is based on US Patent 8,987,352, where a thermally induced, physical self-healing phenomenon leads to gap closing and crack sealing. The self-healing coating involves a unique phase-separated morphology that facilitates the delivery of the self-healing agent to the damage site (such as a scratch or crack) thereby restoring the coating appearance & function. Utilizing commonly available polymer materials and nanoparticles arranged in a unique morphology to achieve self-healing, MEND offers a practical self-healing solution to common polymer coating systems. In response to the need for waterborne, self-healing coatings for non-metallic substrates, NEI developed a waterborne, polyurethane-based, self-healing coating. NANOMYTE® MEND for wood (US Patent 8,664,298) specifically targets the wood cabinet market. A more recent patent-pending version of MEND, referred to as MEND-RT, allows self-healing at near ambient temperature. It is used as the inter-layer of a coating stack and has been shown to enhance the corrosion resistance of traditional coating systems. The MEND coating platform is based on polyurethane, but the principle can be applied to other coating systems as well.

Patents5Self-healing principles can also be applied to surface treatments of metals, whereby the pretreatments can mimic the performance of chromate conversion coatings. To this end, NEI has developed a series of pretreatments for different metals where a chemical self-healing mechanism imparts corrosion resistance. For example, NANOMYTE® PT-60 is a patent-pending conversion coating for use on magnesium alloys. The nanoscale structure of the surface allows ions to diffuse to the damage site, forming a barrier that prevents further corrosion. In addition, PT-60 has been engineered to act as a tie layer that bonds the overlying primer with the metal, thereby leading to excellent performance in the field. Similarly, NEI’s NANOMYTE® PT-10M provides self-healing protection for aluminum, while patent-pending PT-20 is designed for use on steel, and PT-30 (US Patent 8,741,074) is used on copper alloys.

As previously mentioned, combining multiple functionalities in a coating, such as self-healing and superhydrophobicity, presents new opportunities not available until now. For example, NEI has been issued a patent (US Patent 8,968,459) for a superhydrophobic coating composition that also has a self-healing function similar to that of plant leaves. This self-healing, superhydrophobic coating mimics lotus leaves, which maintain their superhydrophobicity by repairing the damaged surface layer with a continuously-secreting hydrophobic epicuticular wax. Equipped with the ability to repair or renew itself, the novel NEI coating overcomes the durability problem of traditional superhydrophobic coatings.

Patents6Durable hydrophobic coatings are highly desirable for numerous applications as they usually impart easy-to-clean and stain-resisting properties to surfaces. For aesthetic reasons, there is also a need for a thin, transparent, easy-to-clean coating that does not add excess weight and does not change the appearance of the substrate to be coated. Further desirable properties of such coatings include a high degree of scratch/abrasion resistance, excellent adhesion, and chemical resistance, all of which are critical in maintaining a durable coating. In addressing these needs, NEI’s recently developed NANOMYTE® SuperCN and SR-100EC products are patent-pending transparent coatings with a unique combination of properties, including easy-to-clean and stain-resisting properties, excellent abrasion/scratch resistance, as well as good adhesion with a variety of substrates – including polymers, metals, and ceramics.

Patents7Scratch resistance is a sought-after property for coatings in a variety of applications, such as ophthalmic and sports-wear lenses, automobile and airplane windows. Plastic substrates, such as polycarbonate and acrylic, can scratch easily and lose transparency quickly during daily use and maintenance. Hard and optically transparent coatings for plastic substrates possess a significant market potential. NEI offers a patented (US Patent 9,006,370) transparent, scratch-resistant coating called NANOMYTE® SR-100, which exhibits significantly better abrasion resistance than commercially available, scratch-resistant coating products. A matte version of SR-100 has also been developed and is now commercially available.

Download Coatings Technology Brief (pdf) »

 

About NEI Corporation:

NEI is an application driven company that manufactures and sells Advanced Materials products, provides materials development services, and performs contract-based R&D for public and private entities. NEI’s products, which are sold under the registered trademark NANOMYTE®, are backed by a suite of issued and pending patents. NEI has built a strong manufacturing and R&D infrastructure that enables rapid transition of concepts to products. The company has a 10,000 square foot, state-of-the-art materials manufacturing and testing facility in Somerset, New Jersey, which includes high temperature furnaces with controlled atmospheres, mixing, blending and drying equipment, coaters, particle characterization instruments, corrosion testing equipment, polymer films & coatings characterization, and a Li-ion battery testing laboratory. Since its inception, NEI has partnered with small companies, large multinational corporations, U.S. Defense Laboratories, U.S. National Laboratories, and Universities. The relationships take on different forms, ranging from a strategic partnership to joint development efforts targeted at specific applications.

Contact Us »

 

/by
,

Recent Advances in Self-Healing Fiber-Reinforced Composites (updated)

A New Nanotechnology Approach for Micro-crack Prevention and Impact Resistance in Self-healing Fiber-Reinforced Composites

Composites are rapidly becoming the material of choice for various applications. The more familiar carbon fiber composites are used where a lightweight structural material is required. Airplanes, such as the Boeing Dreamliner, utilize fiber composites for their high strength to weight ratio, which ultimately decreases fuel consumption. This also translates to the automotive industry; the lighter the car is, the more energy efficient it can be. Another example is sporting goods, such as lightweight bicycle frames, as they offer a competitive advantage in speed and transport. One can also find composites in newer materials for home decking, where longevity and durability to the outside elements allows these composites to last longer without the maintenance required for wooden decks.

While a composite might provide a major benefit over conventional materials, often they have a deficiency in different materials properties. For example, although fiber composites meet the requirements for strength as a structural material, they are susceptible to microcracking and impact damage due to the brittleness of the epoxy matrix. New material developments can overcome these challenges. For example, an introduction of nanoscale additives to the epoxy resin can provide self-healing and/or damage mitigation through toughening.

Making a Better Composite

Nanomaterials can be incorporated into composite materials in different ways. The nature of nanomaterials allows them to interact in ways not otherwise possible. This is due to the very small size of the nanomaterial, where such properties as strength and electrical/thermal conductivities can be improved in the resulting nanocomposite. We at NEI Corporation, an Advanced Materials Company, have utilized our expertise to design nanomaterials for making better composites.

Fiber Composites:

Improving the reliability, reparability, and reusability of fiber reinforced composites (FRCs) is a key aspect to advancing the current state of the art. The major problem with composites is the inherent brittleness of the epoxy matrix, which is prone to microcrack formation. If not prevented, the microcracks can lead to potentially catastrophic structural damage. NEI has taken on this challenge by developing several technologies to both mitigate damage, as well as repair any damage that may have occurred. These technologies, based on nanoscale materials and nanoscale structures, can be combined into one composite system to create a toughened composite material with self-healing capabilities (examples shown in Figure 1).

FRC_Fig.1

Figure 1: (Left) – Self-healing FRC composite fabricated as a panel; (Right) – Composite Overwrapped Pressure Vessel (COPV).

The self-healing technology enables the composite to heal microcracks through the use of a novel self-healing agent, which is combined with the epoxy matrix to form a microcrack prevention technology. The two technologies have been demonstrated for proof of concept in FRC structures consisting of flat panel carbon FRCs, as well as in carbon fiber composite overwrapped pressure vessels (COPVs). In the self-healing technology, a brief heat treatment is used to initiate the healing process. Self-healing can be repeated multiple times. When introducing new functions to the composite, the intent is to ensure that the original material’s properties are not compromised.

In one resin system containing a surface-modified nanoadditive, a significant increase in burst performance was observed after the COPV was cryo-impact-damaged and then self-healed. Initial cross-sectional analysis via microscopy showed good resin infiltration of the carbon fibers and no voids. Steps were taken to improve the mechanical properties of the COPVs by using a low-viscosity resin system that contained a different curing agent. This lower viscosity improved the processing of the COPVs, and results show that the burst pressure of these new vessels was 20 to 25% higher than the original.

Recently, we have developed a self-healing system that does not require thermal initiation. The system is a multi-scale, hybrid fiber system that incorporates multiple functionalities, including self-healing and increased strength and is compatible with FRC manufacturing. As such, it can be tailored to give specific properties of interest to the end-use applications of the customer. This approach utilizes core-sheath fibers, which comprise of a straw-like morphology in which a self-healing fluid is entrapped within a polymer straw (see Figure 2). When a crack forms and cuts through the sheath, the core fluid flows out and begins to fill the crack before finally curing.

FRC_Fig.2

Figure 2: (Left) – Schematic of a core-sheath fiber showing the straw-like morphology; (Right) – FRC coupon containing self-healing, core-sheath fibers.

Unlike single-target approaches, where one material property is often improved at the expense of another, robustness can be introduced to a COPV by a combination of a modified resin and nanoparticle additives. Unique nanoparticles are surface-functionalized to be compatible with the resin. Both organic and inorganic components toughen the matrix and result in a more impact-resistant COPV.

We took this a step further by developing an epoxy composite possessing a uniquely engineered morphology using a completely different self-healing agent, one which has inherent toughening AND self-healing characteristics combined. The novel resin technology is capable of toughening the matrix as well as healing microcracks through the use of a uniquely engineered composite morphology. An FRC containing the newly developed resin was resistant to micro-cracks and was able to repair physical damage. In particular, this resulted in both a reduction in micro-cracks within the bulk resin, as well as evidence of repairable damage due to cryogenic cycling, as witnessed in the recovery of impact and flexural properties of bulk and FRC test coupons, respectively. Mechanical property testing was performed on resin test bars, and strength was recovered after cryo-cycling and self-healing using impact testing (Figure 3). Fiber reinforced composites (FRCs) were fabricated using the novel resin and were likewise able to demonstrate recovery of mechanical properties in the FRC after cryo-cycling followed by self-healing via flexural testing.

FRC_FIG3

Figure 3: Impact resistance of epoxy test bars containing toughening and self-healing characteristics.

The developed micro-crack prevention and repair resin capability will be a drop-in technology, thus decreasing the overall cost of implementation and manufacturability. The resin can be used for filament winding, layup, or be prepregged. Additionally, as the FRC structures are more reliable, their expected usage life will be extended which is an additional cost-saving advantage.

Nanocomposites:

Self-healing is one technology that can be imparted through the use of nanocomposites; however, nanocomposites can also be used to improve the bulk mechanical properties of different neat materials by incorporating nanoparticles into the matrix. For instance, NEI has developed nanoadditives for elastomer seals. These nanoscale particles act as “network modifiers” that have chain characteristics and thus are reactive, bonding to the elastomer network. The altered network structure has unique properties that are not possible with simple nanoscale fillers. For example, the nanocomposite elastomer has improved stiffness while preserving the flexibility and stretchability of a rubber (see Figure 4). Improvements in modulus and hardness, without decreasing the elongation at break, have been obtained in these novel nanocomposite materials. As the network structure largely determines the mechanical properties of an elastomer, traditional fillers (e.g. clay and silica particles) – even if they are at the nanoscale – do not alter the network structure of the elastomer. Therefore, these particles bring unbalanced changes to the properties of the elastomer. That is, they invariably increase the modulus but decrease the elongation at break of the elastomer. NEI’s nanoparticle strategy is fundamentally different from that of conventional approaches. The nanoparticles have been designed to become part of the elastomer network and alter the network structure.

FRC_Fig.3

Figure 4: Nanocomposite elastomer seals (left) show an improvement in mechanical properties with increasing nanoadditive concentration (right).

The examples above present the platform for new technologies that introduce nanoscale additives as a means to create bulk, composite, or coating materials with unique morphologies and improved physical and chemical properties. NEI has the capabilities to develop novel nanocomposites materials that can be tailored to a specific application. These capabilities include nanoscale particle synthesis including electrospinning for nanofibers, surface functionalization of nanoparticles, and prototyping of bulk nanocomposites materials and fiber reinforced composites. We also have experience in the scale-up of processes through numerous commercial endeavors.

Download Whitepaper (pdf) »

 

About NEI Corporation

NEI is an application driven company that manufactures and sells Advanced Materials products, provides materials development services, and performs contract-based R&D for public and private entities. NEI’s products, which are sold under the registered trademark NANOMYTE®, are backed by a suite of issued and pending patents. NEI has built a strong manufacturing and R&D infrastructure that enables rapid transition of concepts to products. The company has a 10,000 square foot, state-of-the-art materials manufacturing and testing facility in Somerset, New Jersey, which includes high temperature furnaces with controlled atmospheres, mixing, blending and drying equipment, coaters, particle characterization instruments, corrosion testing equipment, polymer films & coatings characterization, and a Li-ion battery testing laboratory. Since its inception, NEI has partnered with small companies, large multinational corporations, U.S. Defense Laboratories, U.S. National Laboratories, and Universities. The relationships take on different forms, ranging from a strategic partnership to joint development efforts targeted at specific applications.

Contact Us »

/by
,

A New Approach To Using Self-healing Coatings

Utilizing a Self-Healing Coating to Impart Enhanced Corrosion Protection to Metals

A traditional protective coating system on a metal substrate generally consists of a pretreatment, primer, and a topcoat. The base metal is pretreated and primed for enhanced adhesion and corrosion resistance. A topcoat is then applied on the primer. Many of the coatings in use today to inhibit corrosion are “passive” in nature, in that they provide only barrier protection and/or promote adhesion between the metal and overlaying paint. While these are important attributes, passive solutions do not offer the same level of protection as coatings that provide “active” corrosion protection. To date, coatings that repair themselves when damaged are limited to either unconventional chemistries or uncommonly used polymers, which require forming a complex molecular network and are too soft to satisfy the mechanical robustness required in a protective topcoat.

An “active” corrosion protection coating, or self-healing coating, can be categorized into two classes according to their self-healing mechanisms: chemical or physical. The traditional chromate-based corrosion protection coating uses hexavalent chromium either in the pretreatment or the primer, or both, to achieve chemical self-healing. In contrast, NEI’s self-healing coating involves physical gap closing and crack sealing, which has the potential to impart performance that matches that of a chromate-based system. Figure 1 illustrates the coating architecture containing NANOMYTE® MEND-RT, a self-healing intermediate layer between the topcoat and the primer. When the coating is physically damaged, the self-healing intermediate layer physically repairs the damage autonomously, closing and sealing the gap and providing an active physical barrier.

Self-Healing Coating System Architecture – (a) A defect occurs in the coating system; (b) The self-healing coating, MEND-RT, closes the defect and prevents further crack propagation.

Self-Healing Coating System Architecture – (a) A defect occurs in the coating system; (b) The self-healing coating, MEND-RT, closes the defect and prevents further crack propagation.

An obvious advantage with the use of a self-healing intermediate layer as shown in Figure 1 is that the topcoat is a standard topcoat, which satisfies all industrial standards. The main function of NANOMYTE® MEND-RT, the intermediate self-healing layer, is to self-repair damages. By separating the topcoat functions and the self-healing function into two distinct layers, a self-healing capability is added to the conventional coating system. The composition of MEND-RT is such that the adhesion between the primer and the topcoat is preserved. The MEND-RT layer can be introduced in any coating system, without deteriorating the original properties of the coating stack. MEND-RT can be used with any coating system applied on ferrous or non-ferrous metals, such as magnesium, aluminum, copper, zinc and alloys thereof, and steel.

The efficacy of the self-healing intermediate layer, MEND-RT, was verified using the standard accelerated test method. A chromate-free, self-healing coating system was applied on aluminum 2024 and 7075 alloys. Aluminum was selected for this evaluation as it is extensively used with chromate coatings in the aerospace and aircraft industry due to its high strength and light weight. Two sets of coating systems were applied and compared for corrosion resistance. The first coating stack consisted of a chromate-free corrosion resistant pretreatment, a chromate-free epoxy primer, and a standard polyurethane topcoat. The second stack was identical to the first one, but had MEND-RT inserted between the primer and topcoat. Corrosion resistance was evaluated using the Salt Spray Test (SST) ASTM B-117 method. Artificial defects (“X” shaped scribes) were made on the coated panels before exposing them to salt spray. The photographs in Figure 2 show the progression of corrosion on Al 2024 and 7075 coupons after 1,250 hours of SST.

MEND-RT_Fig.2

Photographs showing trends in corrosion resistance for Al 2024 and 7075 4” x 6” panels after 1,250 hours in salt spray test – (a) Commercial non-chromate coating system; (b) Commercial non-Chromate coating system with NANOMYTE® MEND-RT.

The first set of panels, i.e. without the self-healing interlayer, exhibited early signs of corrosion with white corrosion buildup in the scribed region. The samples with MEND-RT showed enhanced protection with no signs of corrosion. Examination under the microscope revealed that the defects in the coating were physically sealed by the MEND-RT coating. In addition, the gap closing occurred at near ambient temperature, without any external heat or other stimuli. This is direct evidence that the introduction of MEND-RT enhances the corrosion resistance of a coating system, leading to a longer lifetime of the coating.

Download White Paper (pdf) »

 

About NEI Corporation

NEI is an application driven company that manufactures and sells Advanced Materials products, provides materials development services, and performs contract-based R&D for public and private entities. NEI’s products, which are sold under the registered trademark NANOMYTE®, are backed by a suite of issued and pending patents. NEI has built a strong manufacturing and R&D infrastructure that enables rapid transition of concepts to products. The company has a 10,000 square foot, state-of-the-art materials manufacturing and testing facility in Somerset, New Jersey, which includes high temperature furnaces with controlled atmospheres, mixing, blending and drying equipment, coaters, particle characterization instruments, corrosion testing equipment, polymer films & coatings characterization, and a Li-ion battery testing laboratory. Since its inception, NEI has partnered with small companies, large multinational corporations, U.S. Defense Laboratories, U.S. National Laboratories, and Universities. The relationships take on different forms, ranging from a strategic partnership to joint development efforts targeted at specific applications.

Contact Us »

 

/by
,

NEI White Paper: Recent Advances in Self-Healing Fiber-Reinforced Composites

A New Nanotechnology Approach for Micro-crack Prevention and Impact Resistance in Self-healing Fiber-Reinforced Composites

Composites are rapidly becoming the material of choice for various applications. The more familiar carbon fiber composites are used where a lightweight structural material is required. Airplanes, such as the Boeing Dreamliner, utilize fiber composites for their high strength to weight ratio, which ultimately decreases fuel consumption. This also translates to the automotive industry; the lighter the car is, the more energy efficient it can be. Another example is sporting goods, such as lightweight bicycle frames, as they offer a competitive advantage in speed and transport. One can also find composites in newer materials for home decking, where longevity and durability to the outside elements allows these composites to last longer without the maintenance required for wooden decks.

While a composite might provide a major benefit over conventional materials, often they have a deficiency in different materials properties. For example, although fiber composites meet the requirements for strength as a structural material, they are susceptible to microcracking and impact damage due to the brittleness of the epoxy matrix. New material developments can overcome these challenges. For example, an introduction of nanoscale additives to the epoxy resin can provide self-healing and/or damage mitigation through toughening.

Making a Better Composite

Nanomaterials can be incorporated into composite materials in different ways. The nature of nanomaterials allows them to interact in ways not otherwise possible. This is due to the very small size of the nanomaterial, where such properties as strength and electrical/thermal conductivities can be improved in the resulting nanocomposite. We at NEI Corporation, an Advanced Materials Company, have utilized our expertise to design nanomaterials for making better composites.

Fiber Composites:

Improving the reliability, reparability, and reusability of fiber reinforced composites (FRCs) is a key aspect to advancing the current state of the art. The major problem with composites is the inherent brittleness of the epoxy matrix, which is prone to microcrack formation. If not prevented, the microcracks can lead to potentially catastrophic structural damage. NEI has taken on this challenge by developing several technologies to both mitigate damage, as well as repair any damage that may have occurred. These technologies, based on nanoscale materials and nanoscale structures, can be combined into one composite system to create a toughened composite material with self-healing capabilities (examples shown in Figure 1).

FRC_Fig.1

Figure 1: (Left) – Self-healing FRC composite fabricated as a panel; (Right) – Compression overwrapped pressure vessel (COPV).

The self-healing technology enables the composite to heal microcracks through the use of a novel self-healing agent, which is combined with the epoxy matrix to form a microcrack prevention technology. The two technologies have been demonstrated for proof of concept in FRC structures consisting of flat panel carbon FRCs, as well as in carbon fiber composite overwrapped pressure vessels (COPVs). In the self-healing technology, a brief heat treatment is used to initiate the healing process. Self-healing can be repeated multiple times. When introducing new functions to the composite, the intent is to ensure that the original material’s properties are not compromised.

In one resin system containing a surface-modified nanoadditive, a significant increase in burst performance was observed after the COPV was cryo-impact-damaged and then self-healed. Initial cross-sectional analysis via microscopy showed good resin infiltration of the carbon fibers and no voids. Steps were taken to improve the mechanical properties of the COPVs by using a low-viscosity resin system that contained a different curing agent. This lower viscosity improved the processing of the COPVs, and results show that the burst pressure of these new vessels was 20 to 25% higher than the original.

Recently, we have developed a self-healing system that does not require thermal initiation. The system is a multi-scale, hybrid fiber system that incorporates multiple functionalities, including self-healing and increased strength and is compatible with FRC manufacturing. As such, it can be tailored to give specific properties of interest to the end-use applications of the customer. This approach utilizes core-sheath fibers, which comprise of a straw-like morphology in which a self-healing fluid is entrapped within a polymer straw (see Figure 2). When a crack forms and cuts through the sheath, the core fluid flows out and begins to fill the crack before finally curing.

FRC_Fig.2

Figure 2: (Left) – Schematic of a core-sheath fiber showing the straw-like morphology; (Right) – FRC mat containing self-healing, core-sheath fibers.

Unlike single-target approaches, where one material property is often improved at the expense of another, robustness can be introduced to a COPV by a combination of a modified resin and nanoparticle additives. Unique nanoparticles are surface-functionalized to be compatible with the resin. Both organic and inorganic components toughen the matrix and result in a more impact-resistant COPV.

Nanocomposites:

Self-healing is one technology that can be imparted through the use of nanocomposites; however, nanocomposites can also be used to improve the bulk mechanical properties of different neat materials by incorporating nanoparticles into the matrix. For instance, NEI has developed nanoadditives for elastomer seals. These nanoscale particles act as “network modifiers” that have chain characteristics and thus are reactive, bonding to the elastomer network. The altered network structure has unique properties that are not possible with simple nanoscale fillers. For example, the nanocomposite elastomer has improved stiffness while preserving the flexibility and stretchability of a rubber (see Figure 3). Improvements in modulus and hardness, without decreasing the elongation at break, have been obtained in these novel nanocomposite materials. As the network structure largely determines the mechanical properties of an elastomer, traditional fillers (e.g. clay and silica particles) – even if they are at the nanoscale – do not alter the network structure of the elastomer. Therefore, these particles bring unbalanced changes to the properties of the elastomer. That is, they invariably increase the modulus but decrease the elongation at break of the elastomer. NEI’s nanoparticle strategy is fundamentally different from that of conventional approaches. The nanoparticles have been designed to become part of the elastomer network and alter the network structure.

FRC_Fig.3

Figure 3: Nanocomposite elastomer seals (left) show an improvement in mechanical properties with increasing nanoadditive concentration (right).

The examples above present the platform for new technologies that introduce nanoscale additives as a means to create bulk, composite, or coating materials with unique morphologies and improved physical and chemical properties. NEI has the capabilities to develop novel nanocomposites materials that can be tailored to a specific application. These capabilities include nanoscale particle synthesis including electrospinning for nanofibers, surface functionalization of nanoparticles, and prototyping of bulk nanocomposites materials and fiber reinforced composites. We also have experience in the scale-up of processes through numerous commercial endeavors.

Download White Paper (pdf) »

About NEI Corporation

Founded in 1997, NEI Corporation develops, manufactures, and sells nanoscale materials for a broad range of industrial customers around the world. NEI’s products incorporate proprietary nanotechnology and advanced materials science to create significant performance improvements in manufactured goods. NEI’s products include advanced protective coatings, high performance battery electrode materials, and specialty nanoscale materials for diverse applications. NEI has created a strong foundation in the emerging field of nanotechnology that has enabled the company to become a world leader in selected markets.

Contact Us »

/by
,

Case Studies in Designing New Nanoscale Materials

Core-Shell Particles

Core-shell

Example of core-shell nanoparticles produced at NEI Corporation

Core-Shell nanoparticles are composite particles where a core material is coated with a material of a different composition (shell), imparting unique functionalities that are otherwise unattainable for the individual materials. Such nanostructured particles have diverse applications. NEI Corporation has recently developed a patent pending, scalable process to produce core-shell nanoparticles. The process can be used to manufacture metallic and ceramic core-shell nanoparticles, such as metal / metal oxide and metal / metal boride core-shell nanoparticles. The versatility of the process allows core-shell nanoparticles to be synthesized in a wide range of compositions.

Applications:

  • Biomedical – in-vitro and deep tissue imaging
  • Solid propellants – launch vehicles, satellites, and missiles
  • Energetic materials – airbags, drug injection, and micro-valves
  • LEDs, lasers, and phosphors
  • Catalysis

 

Sulfide Nanomaterials

Lithium Tin Phosphorus Sulfide (LSPS) »

Lithium Tin Phosphorus Sulfide (LSPS) is a “superionic” solid that conducts lithium ions at room temperature. The patent pending solid electrolyte is designed to eliminate flammability issues associated with currently used liquid electrolytes, while providing high ion conductivity. At room temperature, the electrolyte has high lithium-ion conductivity (~10-3 S/cm) and can potentially be used in lithium-ion and lithium-sulfur rechargeable batteries. The processing methodology, which has been scaled to the kilogram level, can be adapted to other multi-element sulfide compositions.

Processes to produce tin (IV) sulfide (SnS2) nanoparticles (~100 nm), and micro-nano hybrid zinc sulfide (ZnS) particles, have also been developed at NEI.

Oxide Nanomaterials

Magnesium Oxide (MgO)

Magnesium oxide is commonly used as a grain growth inhibitor, desiccant, cement additive and an industrial cable insulator. Additional applications include visible and IR transparent windows, deacidification of at-risk paper items, protective coatings in plasma displays, and medicinal applications. We produce high surface area (specific surface area 10-15 m2/g, primary particle size ~150 nm) magnesium oxide nanoparticles.

We also produce and supply nanoparticles of yttrium oxide (cubic Y2O3), yttrium aluminum oxide (garnet, Y3Al3O12), and magnesium aluminum oxide (spinel MgAl2O4).

High Surface Area Hollow Silica Fibers

HSF_Fig1 HSF_Fig2

NANOMYTE® SuperSurf-C and SuperSurf-W are exceptionally high surface area, fibrous silica-based materials. Their nominal specific surface area (BET) is > 1000 m2/g. These materials are supplied in two forms: woven cloth (SuperSurf-C) and wool (SuperSurf-W). The fibers of these materials are hollow, which allows them to be infiltrated with other materials to achieve a desired functionality. The exceptionally high surface area of the fibers is due to the presence of nanoscale roughness and pores.

Applications:

  • Base for filters to remove hazardous materials from water & air
  • Antimicrobial textiles
  • Thermal insulators
  • Desiccants and sorbents

 

Download White Paper (pdf) »

 

About NEI Corporation

Founded in 1997, NEI Corporation develops, manufactures, and sells nanoscale materials for a broad range of industrial customers around the world. NEI’s products incorporate proprietary nanotechnology and advanced materials science to create significant performance improvements in manufactured goods. NEI’s products include advanced protective coatings, high performance battery electrode materials, and specialty nanoscale materials for diverse applications. NEI has created a strong foundation in the emerging field of nanotechnology that has enabled the company to become a world leader in selected markets.

Contact Us »

/by