The patent's assignee is
News editors obtained the following quote from the background information supplied by the inventors: "The various embodiments relate generally to polymer binders for porous composites used in energy storage devices, such as electrodes in primary and secondary batteries, double-layer capacitors, electrochemical capacitors, supercapacitors, electrochemical capacitor-battery hybrid devices, as well as dense (non-porous) composite dielectric layers in dielectric capacitors, and polymer separators for use in primary and secondary batteries, electrochemical capacitors, supercapacitors, double-layer capacitors, and electrochemical capacitor-battery hybrid devices.
"Growing efficient materials, components, and structures from plants are of the highest interest for the sustainable future, due to the preservation of the environment during the plant growing processes and a plant's ability to efficiently capture carbon dioxide. Particularly attractive are marine plants, such as algae, that can be grown on non-agricultural land, such as salt water or waste water, and need only a fraction of the area required by conventional crops.
"Due to rapidly increasing renewable energy demands, energy harvesting by ocean plants has drawn interest in recent years. Equally important is the development of high-performance, eco-efficient components for energy storage devices, such as batteries. Several breakthroughs have recently been achieved in the formation of organic cathodes and anodes for lithium-ion batteries. These bio-derived active materials show great promise, however they offer limited stability and capacity properties.
"A typical procedure for the preparation of Li-ion battery electrodes includes mixing electro-active powder with conductive carbon additives and a polymeric binder dissolved in a solvent. The produced slurry is then casted on metal foil current collectors and dried. Traditionally, most research has been focused on synthesis of active powders with improved properties and less attention was devoted to the advancement of the electrically inactive components of battery electrodes, such as binders. Yet, recent studies have shown that many important battery characteristics, including stability and irreversible capacity losses, are critically dependent on the binder's properties. High capacity electrochemically active particles that exhibit significant volume changes during insertion and extraction of Li require improved binder characteristics to ensure electrode integrity during use. Si, in particular, exhibits the largest volume changes during Li-ion battery operation. The interest in Si-based anodes stems from the abundance of Si in nature, its low cost, and its high theoretical capacity, which is an order of magnitude higher than that of the conventionally used graphite.
"Recent studies have shown that synthetic and bio-derived polymers which contain carboxy groups, such as polyacrylic acid (PAA) and carboxymethyl cellulose (CMC), demonstrate promising characteristics as binders for Si-based anodes. Low binder extensibility did not demonstrate a negative effect on the battery performance. Reasonably stable anode performance, however, could only be achieved when Si volume changes were minimized by incomplete Li insertion in the tests or accommodated by using extra-large binder content, which lowers the resulting anode capacity. The polar hydrogen bonds between the carboxy groups of the binder and the SiO.sub.2 on the Si surface were proposed to exhibit a self-healing effect and reform if locally broken. An alternative explanation for the observed stability of the rigid binders with lower extensibility could be that Si nanoparticles deform plastically during electrochemical alloying with Li, expanding towards the existing pores between the particles."
As a supplement to the background information on this patent application, VerticalNews correspondents also obtained the inventors' summary information for this patent application: "Various embodiments of the present invention provide an energy storage device, comprising at least one electrode, wherein the at least one electrode comprises an alginate-containing composition. In exemplary embodiments, the alginate-containing composition is a binder. The alginate-containing composition can form a porous film that binds to at least a portion of a surface of the at least one electrode.
"The alginate-containing composition can be alginate, alginic acid, or a salt of an alginic acid. Further, the salt of the alginic acid can be Na, Li, K, Ca, NH.sub.4, Mg, or Al salt of alginic acid. The alginate-containing composition can have a molecular weight of about 10,000 to about 600,000. In exemplary embodiments, the alginate containing composition has a molecular weight of about 200,000. The alginate-containing composition can be chemically or physically cross-linked. Further, the alginate-containing composition can comprise another polymer grafted with, cross-linked with, or blended with alginate. The polymer can be a water soluble polymer, organic soluble polymer, insoluble polymer, or combinations thereof.
"In some embodiments, the alginate-containing composition can be about 0.5 weight percent to about 60 weight percent of the at least one electrode. In other embodiments, the alginate-containing composition can be about 2 weight percent to about 25 weight percent of the at least one electrode. In exemplary embodiments where the alginate-composition forms the porous film, the porous film can have a thickness of about 1 micron to about 40 microns.
"In other exemplary embodiments, the alginate-containing composition can be a separator. The alginate-containing separator can be formed as a coating on the electrode or formed as a stand-alone separator.
"The energy storage device of the various embodiments can be an electric double layer capacitor, a supercapacitor, an electrochemical capacitor, a primary battery, a secondary battery, a battery-electrochemical capacitor hybrid device, or an electrochemical energy storage device.
"Other exemplary embodiments of the present invention provide a dielectric capacitor, comprising at least one dielectric layer, wherein the at least one dielectric layer comprises an alginate-containing composition. The alginate-containing composition can be a binder for particles having a dielectric constant in the range of about 3 to about 60,000. The thickness of the at least one dielectric layer can be about 0.05 microns to about 50 microns. In exemplary embodiments, the alginate-containing composition can be about 0.8 weight percent to about 80 weight percent of the at least one dielectric layer. In other exemplary embodiments, the alginate containing composition has a molecular weight of about 500 to about 800,000.
BRIEF DESCRIPTION OF THE DRAWINGS
"Advantages of the present invention will become apparent to those skilled in the art with the benefit of the following detailed description of embodiments and upon reference to the accompanying drawings in which:
"FIGS. 1A-C graphically compare viscosities of sodium alginate (Na alginate) and sodium carboxymethyl cellulose (Na CMC) binders as a function of weight percent (wt. %) in water, as a function of the shear rate, and as a function of temperature;
"FIGS. 2A-B graphically illustrate electrochemical performance characteristics of a silicon anode including an alginate-containing binder;
"FIG. 3 provides a scanning electron microscopy (SEM) image of silicon nanopowder;
"FIGS. 4A-B provide SEM images of silicon nanopowder;
"FIG. 5 provides .sup.1H nuclear magnetic resonance (NMR) data of a Na alginate sample;
"FIGS. 6-9 provide atomic microscopy (AFM) data comparing Young's modulus of Na alginate and PVDF binders in both dry and wet states;
"FIG. 10 provides SEM images of silicon nanoparticles;
"FIG. 11 provides energy dispersive spectroscopy (EDS) and X-ray diffraction data (XRD) of silicon nanoparticles;
"FIG. 12 provides N.sub.2 sorption isotherm data collected on silicon nanopowder at 77 K;
"FIG. 13 provides an SEM image of silicon nanopowder bonded with a Na alginate binder and forming an electrode;
"FIGS. 14 and 15 provide X-ray photoelectron spectroscopy (XPS) data of the initially used silicon powder, Na alginate, silicon-Na (Si--Na) alginate, and silicon obtained from the silicon-Na alginate electrode after dissolution and multiple washing steps;
"FIG. 16 provides Fourier transform infrared (FTIR) spectroscopy data of Na-alginate, the Si--Na alginate electrode, and the Si powder (used for the electrode formulation);
"FIG. 17 graphically illustrates reversible deintercalation specific capacity of a silicon anode comprising 15 wt. % Na alginate, 64 wt. % Si nanoparticles, and 21 wt. % C particles (C conductive additives) normalized by the weight of Si and C combined;
"FIGS. 18A-C provide XPS data of electrodes before and after cycling in Li half cells within the potential range from 0.01 to 1 V vs. Li/Li.sup.+;
"FIG. 19 graphically illustrate differential capacity curves for lithium insertion into and lithium extraction from the Si, C, and alginate-containing composite electrode;
"FIGS. 20 and 21 graphically illustrate the shape of the galvanostatic lithium insertion and extraction profiles of the Si, C, and alginate-containing composite electrode;
"FIG. 22 graphically compares first charge-discharge profiles of the graphite and alginate-containing electrode;
"FIG. 23A depicts the Young's modulus of Na-CMC in a dry state. FIG. 23B depicts the Young's modulus of Na-CMC in a wet (impregnated with electrolyte solvent) state;
"FIG. 24 A depicts the XPS characterization (O.sub.1s high resolution spectra) of alginate, carbon black (CB), CB electrode prepared by mixing carbon additives with Na alginate binder, and CB powder extracted from the CB electrode after extensive purification. FIG. 24B depicts the XPS characterization (C.sub.1s high resolution spectra) of alginate, carbon black (CB), CB electrode prepared by mixing carbon additives with Na alginate binder, and CB powder extracted from the CB electrode after extensive purification. FIG. 24C depicts the XPS characterization (O.sub.1s high resolution spectra) of purified exfoliated graphite (PEG), alginate, PEG electrode prepared by mixing PEG with Na alginate binder, and PEG powder extracted from the PEG electrode after extensive purification. FIG. 24D depicts the XPS characterization (C.sub.1s high resolution spectra) of PEG powder, alginate, PEG electrode, and PEG powder extracted from the PEG electrode after extensive purification; and
"FIG. 25 depicts the electrochemical performance of alginate-based nanoSi electrodes (electrode density=0.50 g cm-3, weight ratio of Si:C=3:1).
"FIG. 26 depicts the electrochemical performance of a Si anode with PVDF and Na-CMC.
"While the invention may be susceptible to various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. The drawings may not be to scale. It should be understood, however, that the drawings and detailed description thereto are not intended to limit the invention to the particular form disclosed, but to the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the present invention as defined by the appended claims."
For additional information on this patent application, see:
Keywords for this news article include: Chemicals, Chemistry, Electrochemical, Emerging Technologies,
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