Poly(anhydride)-based polymer electrolytes for high voltage lithium ion batteries

Abstract

New poly(anhydride)-based polymers have been synthesized. When these polymers are combined with electrolyte salts, such polymer electrolytes have shown excellent electrochemical oxidation stability in lithium battery cells. Their stability along with their excellent ionic transport properties make them especially suitable as electrolytes in high energy density lithium battery cells.

Claims

1. A positive electrode comprising: a positive electrode active material comprising lithium iron phosphate; and a catholyte comprising an anhydride-based polymer electrolyte having a structure described by: ##STR00023## wherein a is an integer that ranges from 1 to 5, n is an integer from 1 to 1,000, R is ##STR00024## c is 0 to 10, and d is 0 to 10, wherein c or d is greater than 0; and wherein the positive electrode active material and the catholyte are mixed together, and the catholyte further comprises glass ceramic electrolyte particles mixed with the anhydride-based polymer electrolyte.

2. The positive electrode of claim 1 wherein the catholyte further comprises a solid polymer electrolyte.

3. The positive electrode of claim 1 wherein the catholyte is crosslinked.

4. The positive electrode of claim 1 wherein the catholyte further comprises an electrolyte salt comprising a lithium salt.

5. The positive electrode of claim 1, wherein the glass ceramic electrolyte particles are selected from the group consisting of oxynitride glass, sulfide glass, oxysulfide glass, lithium thionitride glass, lithium lanthanum titanate perovskite glass material, lisicon phosphate-based glass material, and combinations thereof.

6. An electrochemical cell, comprising: an anode configured to absorb and release lithium ions the anode comprises a lithium metal material; a cathode comprising cathode active material particles, an electronically-conductive additive of carbon black, and a catholyte; a current collector adjacent to an outside surface of the cathode; and a separator region between the anode and the cathode, the separator region comprising a solid polymer electrolyte configured to facilitate movement of lithium ions back and forth between the anode and the cathode; wherein the catholyte comprises an anhydride-based polymer structure described by: ##STR00025## wherein a is an integer that ranges from 1 to 5, n is an integer from 1 to 1,000, R is ##STR00026## c is 0 to 10, and d is 0 to 10, is wherein c or d is greater than 0; and the electrolyte salt is a lithium salt, and the catholyte further comprises glass ceramic electrolyte particles mixed with the anhydride-based polymer electrolyte.

7. The electrochemical cell of claim 6 wherein the catholyte further comprises a solid polymer electrolyte.

8. The electrochemical cell of claim 6 wherein the catholyte and the separator electrolyte are the same material.

9. The electrochemical cell of claim 6 further comprising an overlayer between the cathode and the separator region.

10. The electrochemical cell of claim 6 wherein the catholyte is crosslinked.

11. The positive electrolyte of claim 6, wherein the glass ceramic electrolyte particles are selected from the group consisting of oxynitride glass, sulfide glass, oxysulfide glass, lithium thionitride glass, lithium lanthanum titanate perovskite glass material, lisicon phosphate-based glass material, and combinations thereof.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The foregoing aspects and others will be readily appreciated by the skilled artisan from the following description of illustrative embodiments when read in conjunction with the accompanying drawings.

(2) FIG. 1 is a graph that shows ionic conductivities of poly(butenoic anhydride) electrolytes with various concentrations of LiTFSI at 80 C., according to an embodiment of the invention.

(3) FIG. 2 is a graph that shows cyclic voltammetry data for 0.1M of 4-pentenoic anhydride and 0.1M of LiBF.sub.4 in propylene carbonate, according to an embodiment of the invention.

(4) FIG. 3 is a schematic illustration of one configuration of a lithium battery cell that contains an electrolyte that is used in both the cathode and the separator, according to an embodiment of the invention.

(5) FIG. 4 is a schematic illustration of another configuration of a lithium battery cell that contains a catholyte and a separator electrolyte different from the catholyte, according to an embodiment of the invention.

(6) FIG. 5 is a schematic illustration of another configuration of a lithium battery cell that contains a catholyte and a cathode overlayer, according to an embodiment of the invention.

DETAILED DESCRIPTION

(7) The embodiments of the invention are illustrated in the context of anhydride polymers that can be used as electrolytes or electrolyte additives in lithium battery cells and the like. The skilled artisan will readily appreciate, however, that the materials and methods disclosed herein will have application in a number of other contexts where high-voltage electrolytes are desirable, particularly where long-term stability is important.

(8) These and other objects and advantages of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings.

(9) All publications referred to herein are incorporated by reference in their entirety for all purposes as if fully set forth herein.

(10) In this disclosure, the terms negative electrode and anode are both used to describe a negative electrode. Likewise, the terms positive electrode and cathode are both used to describe a positive electrode.

(11) It is to be understood that the terms lithium metal or lithium foil, as used herein with respect to negative electrodes, describe both pure lithium metal and lithium-rich metal alloys as are known in the art. Examples of lithium rich metal alloys suitable for use as anodes include LiAl, LiSi, LiSn, LiHg, LiZn, LiPb, LiC or any other Li-metal alloy suitable for use in lithium metal batteries. Other negative electrode materials that can be used in the embodiments of the invention include materials in which lithium can intercalate, such as graphite, and other materials that can absorb and release lithium ions, such as silicon, germanium, tin, and alloys thereof. Many embodiments described herein are directed to batteries with solid polymer electrolytes, which serve the functions of both electrolyte and separator. As it is well known in the art, batteries with liquid electrolytes use an inactive separator material that is distinct from the liquid electrolyte.

(12) The following construction is used throughout this disclosure: each variable is chosen independently from a list that is provided. An example of this usage can be found with reference to X groups in some of the inventive polymer structures in which there are many X's. The example is, each X may be chosen independently from hydrogen, fluorine, methyl, ethyl, isopropyl, and trifluoromethyl groups. This construction is used to mean that for a particular X in the structure, any of the groups in the list may be used. In choosing a group to use for another X in the structure, any of the groups in the list may be used with no regard to the choices that have been made for other X groups. Thus, the following arrangements are all possible: all the X's may be the same, all the X's may be different, or some X's may be the same and some may be different.

(13) The molecular weights given herein are number-averaged molecular weights.

(14) In this disclosure, ranges of values are given for many variables. It should be understood that the possible values for any variable also include any range subsumed within the given range.

(15) Based on repeated observation of Li.sup.+ interaction with other atoms in molecular dynamics (MD) simulations, it seems that Li.sup.+ coordinates with partially-negatively-charged atoms in a polymer electrolyte or, when the Li-salt is not soluble in the polymer, with negatively charged anions of the salt that has been added to a polymer to form the electrolyte. With polyethylene oxide (PEO), Li.sup.+ coordinates with partially-negatively-charged oxygen atoms in the PEO. Similarly, in poly(anhydride)s, Li.sup.+ coordinates with partially-negatively charged oxygens in the carbonyl groups.

(16) Poly(anhydride)s exhibit high oxidative stability. One reason for this is the stability of the keto isomer of the anhydride. Other carbonyl-containing molecular structures, such as ketones, may undergo isomerization to form an enol tautomer. Yet in anhydrides, the lack of an acidic methylene or proton group prevents such tautomerization. For example, a poly(anhydride) with 3 oxygen atoms per repeat unit as shown below cannot form an enol isomer via an active methylene group route as there is no strongly acidic methylene group in the structure. A proton transfer from an inactive methylene group will result in a high energy enol structure, which is not likely to form and would quickly revert back to the stable keto form, as shown below.

(17) ##STR00006##
Poly(anhydride), Poly(thioanhydride), and Poly(imide):

(18) In some embodiments of the invention, two general structures for poly(anhydride)-based polymers are shown below. Structure A shows the general structure for poly(anhydride) when Y is oxygen (O) and for poly(thioanhydride) when Y is sulfur (S). Structure B is an imide-based polymer with nitrogen atom (N) in place of the oxygen or sulfur atoms shown in structure A. Structure B has functional side chains Z that can be attached either directly as shown or through extendable alkyl chains (not shown).

(19) ##STR00007##

(20) Each Z and R is chosen independently from the lists below, a is an integer that ranges from 1 to 5, and n is an integer that ranges from 1 to 1000.

(21) ##STR00008##

(22) In the Z groups, b is an integer that ranges from 1 to 10, and each R.sub.1 may be chosen independently from hydrogen, methyl, ethyl, propyl, or isopropyl groups. In the R groups; c, d, and e are integers, and each ranges independently from 1 to 10; and each X may be chosen independently from hydrogen, fluorine, methyl, ethyl, isopropyl, and trifluoromethyl groups.

(23) In another embodiment of the invention, Structure A and Structure B include crosslinkable Z groups and/or R groups, which make it possible for such poly(anhydride)-based polymers to be crosslinked. Examples of such crosslinkable Z groups include, but are not limited to, vinyl and allyl groups. Examples of such crosslinkable R groups include, but are not limited to, unsaturated polyolefins such as polybutadiene and polyisoprene. When Structure A or Structure B includes one or more such crosslinkable group(s), it is possible to crosslink the structures using a number of approaches including thermal or UV generation of radicals, click chemistries, hydrosilylation, transesterification, or any other commonly used crosslinking strategy.

(24) Alternatively, Structure A and Structure B may be shown combined as one condensed Structure C as follows:

(25) ##STR00009##
wherein E may be, as for Structure A, O, or S, or as for Structure B, N with a substituent Z. All other values are as described above in reference to Structures A and B.

(26) In another embodiment of the invention, particles of ceramic electrolyte are mixed into a poly(anhydride)-based polymer electrolyte to form an enhanced composite electrolyte with superior ionic transport and mechanical properties. Such a composite electrolyte may be used in a lithium battery cell in the separator region or in the cathode. Examples of ceramic electrolytes that are useful for mixing with poly(anhydride)-based polymer electrolytes include, but are not limited to, those shown in Table 1 below.

(27) TABLE-US-00001 TABLE 1 Exemplary Ceramic Conductors for Use as Additives in Poly(anhydride)-Based Polymer Electrolytes Electrolyte Type Exemplary Formulas Mixture Proportion Oxynitride glass Li.sub.xPO.sub.yN.sub.z x = 2.9, y = 3.3, z = 0.46 0.24 < z < 1.2 Li.sub.xBO.sub.yN.sub.z Sulfide and oxysulfide Li.sub.2SP.sub.2S.sub.5 0.75:0.25 glass Li.sub.2SSiS.sub.2 0.6:0.4 Li.sub.2SSiS.sub.2Li.sub.xMO.sub.4 M = Si, P, Ge 0.57:0.38:0.05 Li.sub.2SSiS.sub.2Li.sub.3PO.sub.4 0.63:0.36:0.01 Li.sub.2SSiS.sub.2xMS.sub.y M = Sn, Ta, Ti 0.6:0.4:0.01-0.05 Li.sub.2SSiS.sub.2Li.sub.3N 0.55:0.40:0.03 Li thionitride glass Li.sub.3NSiS.sub.2 0.4:0.6 LLTO Perovskite La.sub.2/3xLi.sub.3xTiO.sub.3 0.03 x 0.167 structure (Ohara type) La.sub.1/3xLi.sub.3xTaO.sub.3 0.025 x 0.167 La.sub.1/3xLi.sub.3xNbO.sub.3 0 x 0.06 Nasicon-type (Lisicon) Li.sub.1.3Ti.sub.1.7Al.sub.0.3(PO.sub.4).sub.3 phosphate LiAlTa(PO.sub.4).sub.3 LiAl.sub.0.4Ge.sub.1.6(PO.sub.4).sub.3 Li.sub.1.4Ti.sub.1.6Y.sub.0.4(PO.sub.4).sub.3 Li.sub.32x(Sc.sub.1xM.sub.x).sub.2(PO.sub.4).sub.3 M = Zr, Ti, x = 0.1, 0.2 Li.sub.3Sc.sub.1.5Fe.sub.0.5(PO.sub.4).sub.3 denotes that components are mixed together

(28) Table 2 below shows lithium ion transport properties for polyethylene oxide (PEO), and various poly(anhydride)-based polymers based on MD simulation. It is clear that poly(heptanoic anhydride) has a higher conductivity than some of the other structures. Examples of other variations of poly(anhydride)-based polymers include, but are not limited to, poly(thioanhydride) and poly(imide), which are shown in the table below. These variations are obtained by substituting nitrogen and sulfur atoms for oxygen in anhydride repeat units. Other structural variations include, but are not limited to, substituting one or all oxygen atoms with nitrogen and/or sulfur, changing the alkyl chain length, and changing the alkyl groups on the nitrogen atoms of the imides.

(29) TABLE-US-00002 TABLE 2 Lithium Transport Properties of PEO, PPM, and Poly(anhydride)-Based Polymers LiTFSI Concen- tration Polymer Chemical Structure (wt %) (S/cm) t.sub.+ Polyethylene oxide 0 30 8.2 2.2 10.sup.4 0.18 0.07 Poly(pentylmalonate) 30 4.4 10.sup.4 0.66 Poly(heptanoicanhydride) 30 9.7 10.sup.4 0.67 Poly(heptimide) 30 8.2 10.sup.6 0.09 Poly(N- methylheptimide) Poly(thioheptanoicanhydride) 30 3.5 10.sup.5 0.36 Poly(2,4-dioxo-1,3,5- triketononane) 30 5.2 10.sup.4 0.77 Poly(2,4-diamino- 1,3,5-triketononane) Poly(2,4-dithio-1,3,5- triketononane) Poly(cis-hept-4- enoicanhydride) 30 1.26 10.sup.3 0.79
Anhydride Group Chemical Stability

(30) Table 3 shows ionization potentials (IP) and the energy difference between tautomers of anhydride groups as simulated using quantum chemistry (QC) (method: M06-HF/aug-cc-pvtz//PBEO/aug-cc-pvtz). The enol-form of an anhydride group is difficult to form as shown by the 0.66 eV energy required to convert the keto- to the enol-form; however, if formed, it is easier to oxidize the enol-form (lower IP) than it is to oxidize the keto-form. Due to the high energy required to form the enol-form, as well as the relatively high IP of both the keto- and enol-forms, QC predicts that the anhydride group is quite stable against oxidation.

(31) TABLE-US-00003 TABLE 3 Ionization potentials (IP) and energy difference between tautomers of anhydride groups Group Keto-form Enol-form E.sub.Enol-E.sub.Keto Anhydride 0 IP = 11.06 eV IP = 8.88 eV 0.66 eV
Anhydride Conductivity

(32) Symmetric cells were built by sandwiching various poly(butenoic anhydride) electrolytes between two aluminum electrodes. The poly(butenoic anhydride) electrolytes had different LiTFSI lithium salt concentrations. The ionic conductivities of the electrolytes were measured at 80 C. using impedance spectroscopy and are shown in the graph of ionic conductivity as a function of salt concentration in FIG. 1. The data clearly show that poly(butenoic anhydride) electrolytes have substantial lithium ion conductivities at 80 C.

(33) Anhydride Group Electrochemical Stability

(34) Cyclic voltammetry was measured using a three-electrode system that included a Pt button working electrode, a Pt wire counter electrode, and a quasi-reference electrode constructed from an Ag wire dipped in a 10 mM AgNO.sub.3 in 0.1 M tetrabutylammonium hexafluorophosphate solution in glass tubing with an attached Vycor frit. The quasi-reference electrode was first calibrated against a 10 mM ferrocene solution in 0.1 M lithium tetrafluoroborate (LiBF.sub.4) in propylene carbonate, to give E.sub.ox (ferrocene/ferrocenium)=0.058 V (vs. Ag/Ag.sup.+). Then the same ferrocene solution was used to calibrate a lithium reference electrode (E.sub.ox (ferrocene/ferrocenium)=3.35-3.39 V (vs. Li/Li.sup.+)). The cyclic voltammetry was carried out on 0.1M solution of 4-pentenoic anhydride in 0.1M LiBF.sub.4 in propylene carbonate and at a scan rate of 5 mV/s. The cyclic voltammetry data were then standardized for Li/Li.sup.+ to reflect oxidation stability in a lithium cell, as electrolyte materials made from 4-pentenoic anhydride can interact with electrodes in an actual battery cell. The results are shown in the graph in FIG. 2. As shown in FIG. 2, 4-pentenoic anhydride had electrochemical oxidation stability up to at least 4.5 V with insignificant current density response even at 4.5 V. This clearly indicates that this type of anhydride-based system is stable at high voltages and can be used as an electrolyte in high energy density lithium ion batteries.

(35) Cell Designs that Include Anhydride-Based Polymers

(36) In one embodiment of the invention, a lithium battery cell 300 has an anode 320 that is configured to absorb and release lithium ions, as shown in FIG. 3. The anode 320 may be a lithium or lithium alloy foil or it may be made of a material into which lithium ions can be absorbed such as graphite or silicon. Other choices for the anode 320 include, but are not limited to, lithium titanate, and lithium-silicon alloys. The lithium battery cell 300 also has a cathode 340 that includes cathode active material particles 342, an electronically-conductive additive such as carbon black (not shown), a current collector 344, a catholyte (electrolyte in the cathode) 346, and an optional binder (not shown). In one arrangement, the catholyte 346 includes any of the anhydride-based polymer electrolytes disclosed above. In another arrangement, the catholyte 346 includes mixtures or combinations of other solid polymer electrolytes with anhydride-based polymer electrolytes. There is a separator region 360 between the anode 320 and the cathode 340. The catholyte 346 extends all the way into the separator region 360 and facilitates movement of lithium ions back and forth between the anode 320 and the cathode 340 as the cell 300 cycles. The electrolyte 346 in the separator region 360 and the catholyte 346 in the cathode 340 are the same.

(37) In another embodiment of the invention, a lithium battery cell 400 has an anode 420 that is configured to absorb and release lithium ions as shown in FIG. 4. The anode 420 may be a lithium or lithium alloy foil or it may be made of a material into which lithium ions can be absorbed such as graphite or silicon. Other choices for the anode 420 include, but are not limited to, lithium titanate, and lithium-silicon alloys. The lithium battery cell 400 also has a cathode 440 that includes cathode active material particles 442, an electronically-conductive additive such as carbon black (not shown), a current collector 444, a catholyte 446, and an optional binder (not shown). In one arrangement, the catholyte 446 includes any of the anhydride-based polymer electrolytes disclosed above. In another arrangement, the catholyte 446 includes mixtures or combinations of other solid polymer electrolytes with anhydride-based polymer electrolytes. There is a separator electrolyte 460 between the anode 420 and the cathode 440. The separator electrolyte 460 facilitates movement of lithium ions back and forth between the anode 420 and the cathode 440 as the cell 400 cycles. The separator electrolyte 460 may include any electrolyte that is suitable for use in a lithium battery cell. In one arrangement, the separator electrolyte 460 contains a liquid electrolyte that is soaked into a porous plastic material (not shown). In another arrangement, the separator electrolyte 460 contains a viscous liquid or gel electrolyte. In another arrangement, the separator region 460 contains a solid polymer electrolyte in which the anhydride-based polymer is immiscible.

(38) In another embodiment of the invention, a battery cell with a third configuration is described. With reference to FIG. 5, a lithium battery cell 500 has an anode 520 that is configured to absorb and release lithium ions. The anode 520 may be a lithium or lithium alloy foil or it may be made of a material into which lithium ions can be absorbed such as graphite or silicon. Other choices for the anode 520 include, but are not limited to, lithium titanate, and lithium-silicon alloys. The lithium battery cell 500 also has a cathode 550 that includes cathode active material particles 552, an electronically-conductive additive (not shown), a current collector 554, a catholyte 556, an optional binder (not shown), and an overcoat layer 558. In one arrangement, the electrolyte in the overcoat layer 558 and the catholyte 556 are the same. In another arrangement, the electrolyte in the overcoat layer 558 and the catholyte 556 are different. The overcoat layer 558 and/or the catholyte 556 may contain any of the anhydride-based polymer electrolytes or mixtures or combinations of other solid polymer electrolytes with anhydride-based polymer electrolytes or electrolyte additives (in a solid polymer electrolyte host) disclosed herein. In one arrangement, the overcoat layer 558 is a solid electrolyte layer. There is a separator region 560 between the anode 520 and the cathode 550. The separator region 560 contains an electrolyte that facilitates movement of lithium ions back and forth between the anode 520 and the cathode 550 as the cell 500 cycles. The separator region may include any electrolyte that is suitable for such use in a lithium battery cell. In one arrangement, the separator electrolyte 560 contains a liquid electrolyte that is soaked into a porous plastic material (not shown). In another arrangement, the separator electrolyte 560 contains a viscous liquid or gel electrolyte. In another arrangement, the separator region 560 contains a solid polymer electrolyte in which the anhydride-based polymer is immiscible.

(39) A solid polymer electrolyte for use in separator region, such as separator regions 460 or 560, can be any electrolyte that is appropriate for use in a Li battery. Of course, many such electrolytes also include electrolyte salt(s) that help to provide ionic conductivity. Examples of such electrolytes include, but are not limited to, block copolymers that contain ionically-conductive blocks and structural blocks that make up ionically-conductive phases and structural phases, respectively. The ionically-conductive phase may contain one or more linear polymers such as polyethers, polyamines, polyimides, polyamides, poly alkyl carbonates, polynitriles, perfluoro polyethers, fluorocarbon polymers substituted with high dielectric constant groups such as nitriles, carbonates, and sulfones, and combinations thereof. In one arrangement, the ionically-conductive phase contains one or more anhydride-based polymer, as disclosed herein. The linear polymers can also be used in combination as graft copolymers with polysiloxanes, polyalkoxysiloxanes, polyphosphazines, polyolefins, and/or polydienes to form the conductive phase. The structural phase can be made of polymers such as polystyrene, hydrogenated polystyrene, polymethacrylate, poly(methyl methacrylate), polyvinylpyridine, polyvinylcyclohexane, polyimide, polyamide, polypropylene, polyolefins, poly(t-butyl vinyl ether), poly(cyclohexyl methacrylate), poly(cyclohexyl vinyl ether), poly(t-butyl vinyl ether), polyethylene, poly(phenylene oxide), poly(2,6-dimethyl-1,4-phenylene oxide), poly(phenylene sulfide), poly(phenylene sulfide sulfone), poly(phenylene sulfide ketone), poly(phenylene sulfide amide), polysulfone, fluorocarbons, such as polyvinylidene fluoride, or copolymers that contain styrene, methacrylate, or vinylpyridine. It is especially useful if the structural phase is rigid and is in a glassy or crystalline state.

(40) With respect to the embodiments described in FIGS. 3, 4, and 5, suitable cathode active materials include, but are not limited to, LFP (lithium iron phosphate), LMP (lithium metal phosphate in which the metal can be Mn, Co, or Ni), V.sub.2O.sub.5 (divanadium pentoxide), NCA (lithium nickel cobalt aluminum oxide), NCM (lithium nickel cobalt manganese oxide), high energy NCM (HE-NCMmagnesium-rich lithium nickel cobalt manganese oxide), lithium manganese spinel, lithium nickel manganese spinel, and combinations thereof. Suitable electronically-conductive additives include, but are not limited to, carbon black, graphite, vapor-grown carbon fiber, graphene, carbon nanotubes, and combinations thereof. A binder can be used to hold together the cathode active material particles and the electronically conductive additive. Suitable binders include, but are not limited to, PVDF (polyvinylidene difluoride), PVDF-HFP poly (vinylidene fluoride-co-hexafluoropropylene), PAN (polyacrylonitrile), PAA (polyacrylic acid), PEO (polyethylene oxide), CMC (carboxymethyl cellulose), and SBR (styrene-butadiene rubber).

Examples

(41) The following examples provide details relating to composition, fabrication and performance characteristics of polymer electrolytes in accordance with the present invention. It should be understood the following is representative only, and that the invention is not limited by the detail set forth in these examples.

(42) In one example, a synthetic route using acyclic diene metathesis (ADMET) to produce poly(anhydride)s, specifically poly(butenoic anhydride), is depicted below. Hoveyda-Grubb's second-generation catalyst (0.06 g, 0.1 mmol) was added to a sample of 4-pentenoic anhydride (4 g, 22 mmol) and subjected to high vacuum (1 torr approx.). Bubbling of the reaction mixture was seen due to evolution of ethylene gas. The solution was slowly heated to 60 C. and stirred under high vacuum for 16 hours. After that, the reactor was back-filled with argon, and the polymerization was quenched using a solution of ethyl vinyl ether (0.78 g, 10.8 mmol) in toluene (5 mL) and stirred for half an hour. Slow addition of the polymer solution to petroleum ether (500 mL) afforded poly(butenoic anhydride) as an amber-colored waxy solid, which was dried under high vacuum to obtain 2.6 g of dry polymer in 90% yield. Mn (GPC)=80,000 g/mol.

(43) ##STR00022##

(44) This invention has been described herein in considerable detail to provide those skilled in the art with information relevant to apply the novel principles and to construct and use such specialized components as are required. However, it is to be understood that the invention can be carried out by different equipment, materials and devices, and that various modifications, both as to the equipment and operating procedures, can be accomplished without departing from the scope of the invention itself.