Single-layer lithium ion battery separator

Abstract

The present invention relates to a microporous polymeric battery separator comprised of a single layer of enmeshed microfibers and nanofibers. Such a separator accords the ability to attune the porosity and pore size to any desired level through a single nonwoven fabric. As a result, the inventive separator permits a high strength material with low porosity and low pore size to levels unattained. The combination of polymeric nanofibers within a polymeric microfiber matrix and/or onto such a substrate through high shear processing provides such benefits, as well. The separator, a battery including such a separator, the method of manufacturing such a separator, and the method of utilizing such a separator within a battery device, are all encompassed within this invention.

Claims

1. A nonconductive microporous polymeric battery separator consisting of a single layer of enmeshed microfibers and nanofibers, wherein said microfibers have an average fiber diameter greater than 3000 nm, wherein said nanofibers have an average fiber diameter of less than 700 nm, wherein said microfibers are entangled with one another within said single layer, wherein said single layer exhibits interstices between each entangled microfiber such that said interstices include nanofibers present therein, wherein said single layer exhibits a mean flow pore size of less than 1000 nm, a Gurley air resistance of less than 566 seconds/100 cc, a thickness of less than 100 microns, and an ionic resistance when present with LiPF.sub.6 in EC:DMC:DEC mixture (1:1:1 volume) within a lithium ion battery of between 2 and 6 ohms.

2. The battery separator of claim 1, wherein said microfibers comprise fibrillated microfibers.

3. The battery separator of claim 1, exhibiting a porosity greater than 68%.

4. The battery separator of claim 2 comprising nanofibers with a transverse aspect ratio greater than 1.5:1.

5. The battery separator of claim 1, wherein said microfibers are comprised of at least one polymer selected from the group consisting of polyacrylonitrile, cellulose, polypropylene, polyethylene, polybutylene, polyamide, polyvinyl alcohol, polyethylene terephthalalte, polybutylene terephthalate, polysulfone, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl penetene, polyphenylene sulfide, polyacetyl, polyurethane, aromatic polyamide, semi-aromatic polyamide, polypropylene terephthalate, polymethyl methacrylate, polystyrene, and blends, mixtures, and copolymers including these polymers.

6. The battery separator of claim 2, wherein said microfibers are comprised of at least one polymer selected from the group consisting of polyacrylonitrile, cellulose, polypropylene, polyethylene, polybutylene, polyamide, polyvinyl alcohol, polyethylene terephthalalte, polybutylene terephthalate, polysulfone, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl penetene, polyphenylene sulfide, polyacetyl, polyurethane, aromatic polyamide, semi-aromatic polyamide, polypropylene terephthalate, polymethyl methacrylate, polystyrene, and blends, mixtures, and copolymers including these polymers.

7. The battery separator of claim 5, wherein said microfibers are comprised of at least one polymer selected from the group consisting of polyacrylonitrile, cellulose, polyamide, polyethylene terephthalalte, polysulfone, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl penetene, polyphenylene sulfide, aromatic polyamide, semi-aromatic polyamide, and blends, mixtures, and copolymers including these polymers.

8. The battery separator of claim 6, wherein said microfibers are comprised of at least one polymer selected from the group consisting of polyacrylonitrile, cellulose, polyamide, polyethylene terephthalalte, polysulfone, polyvinyl fluoride, polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polymethyl penetene, polyphenylene sulfide, aromatic polyamide, semi-aromatic polyamide, and blends, mixtures, and copolymers including these polymers.

9. The battery separator of claim 5, wherein said nanofibers are selected from fibrillated nanofibers and islands-in-the-sea nanofibers.

10. The battery separator of claim 6, wherein said nanofibers are selected from fibrillated nanofibers and islands-in-the-sea nanofibers.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is an SEM microphotograph of a prior art expanded film battery separator.

(2) FIG. 2 is an SEM microphotograph of a prior art nanofiber nonwoven fabric battery separator.

(3) FIGS. 3 and 4 are SEM microphotographs of one potentially preferred embodiment of an inventive microfiber/nanofiber nonwoven fabric battery separator structure.

(4) FIGS. 5, 6, and 7 are SEM microphotographs of another potentially preferred embodiment of an inventive microfiber/nanofiber nonwoven fabric battery separator structure.

(5) FIG. 8 shows an exploded view of an inventive rechargeable lithium ion battery including an inventive battery separator.

DETAILED DESCRIPTION OF THE DRAWINGS AND PREFERRED EMBODIMENTS

(6) All the features of this invention and its preferred embodiments will be described in full detail in connection with the following illustrative, but not limiting, drawings and examples.

Microfiber and Nanofiber Production

(7) As noted above, the microfiber may be constructed from any polymer (or polymer blend) that accords suitable chemical and heat resistance in conjunction with internal battery cell conditions, as well as the capability to form suitable fiber structures within the ranges indicated, and further the potential to be treated through a fibrillation or like technique to increase the surface area of the fibers themselves for entanglement facilitation during nonwoven fabrication. Such fibers may be made from longstanding fiber manufacturing methods such as melt spinning, wet spinning, solution spinning, melt blowing and others. In addition, such fibers may begin as bicomponent fibers and have their size and/or shape reduced or changed through further processing, such as splittable pie fibers, islands-in-the-sea fibers and others. Such fibers may be cut to an appropriate length for further processing, such lengths may be less than 1 inch, or less than ½ inch, or less than ¼ inch even. Such fibers may also be fibrillated into smaller fibers or fibers that advantageously form wetlaid nonwoven fabrics.

(8) Nanofibers for use in the current invention may be made through several longstanding techniques, such as islands-in-the-sea, centrifugal spinning, electrospinning, film or fiber fibrillation, and the like. Teijin and Hills both market potentially preferred islands-in-the-sea nanofibers (Teijin's is marketed as NanoFront fiber polyethylene terephthalate fibers with a diameter of 70 nm). Dienes and FiberRio are both marketing equipment which would provide nanofibers using the centrifugal spinning technique. Electrospinning nanofiber production is practiced by duPont, E-Spin Technologies, or on equipment marketed for this purpose by Elmarco. Nanofibers fibrillated from films are disclosed in U.S. Pat. Nos. 6,110,588, 6,432,347 and 6,432,532, which are incorporated herein in their entirety by reference. Nanofibers fibrillated from other fibers may be done so under high shear, abrasive treatment. Nanofibers made from fibrillated cellulose and acrylic fibers are marketed by Engineered Fiber Technologies under the brand name EFTEC™. Any such nanofibers may also be further processed through cutting and high shear slurry processing to separate the fibers an enable them for wet laid nonwoven processing. Such high shear processing may or may not occur in the presence of the required microfibers.

(9) Nanofibers that are made from fibrillation in general have a transverse aspect ratio that is different from one, such transverse aspect ratio described in full in U.S. Pat. No. 6,110,588, which is incorporated herein by reference. As such, in one preferred embodiment, the nanofibers have a transverse aspect ratio of greater than 1.5:1, preferably greater than 3.0:1, more preferably greater than 5.0:1.

(10) As such, acrylic, polyester, and polyolefin fibers are particularly preferred for such a purpose, with fibrillated acrylic fibers, potentially most preferred. Again, however, this is provided solely as an indication of a potentially preferred type of polymer for this purpose and is not intended to limit the scope of possible polymeric materials or polymeric blends for such a purpose.

(11) FIGS. 1 and 2 provide photomicrographs of the typical structures of the Celgard expanded film materials and the duPont nanofiber nonwoven battery separator materials, respectively, and as discussed above. Noticeably, the film structure of the Celgard separator shows similarity in pore sizes, all apparently formed through film extrusion and resultant surface disruptions in a rather uniform format. The duPont separator is made strictly from nanofibers alone as the uniformity in fiber size and diameter is evident. Being a nonwoven structure of such nanofibers themselves, the overall tensile strengths of this separator in both machine and cross directions are very low, although roughly uniform in both directions. Thus, such a material may be handled uniformly, as a result, although overall strength lends itself to other difficulties a manufacturer must face, ultimately, if introducing such a separator into a battery cell. To the contrary, then, the FIG. 1 separator, showing the striations for pore generation in the same direction (and thus extrusion of the film in one direction), provides extremely high machine direction tensile strength; unfortunately, the tensile strength of the same material in the cross direction is very close to nonexistent, leaving, as discussed previously, a very difficult and highly suspect battery separator material to actually utilize in a battery manufacturing setting.

(12) The inventive materials, shown in photomicrograph form in FIGS. 3 and 4, are of totally different structure from these two prior art products. One potentially preferred embodiment of the initial combination of microfiber and nanofibers is the EFTEC™ A-010-4 fibrillated polyacrylonitrile fibers, which have high populations of nanofibers as well as microfibers. The resultant nanofibers present within such a combination are residual as a result of the fibrillation of the initial microfibers. Nonwoven sheets made of these materials are shown in FIGS. 3 and 4. By way of example, these fibers can be used as a base material, to which can be added further microfibers or further nanofibers as a way of controlling the pore size and other properties of the nonwoven fabric, or such a material may be utilized as the nonwoven fabric battery separator itself. Examples of such sheets with additional microfibers added are shown in FIGS. 5, 6 and 7. Typical properties of the acrylic Micro/Nanofibers are shown below.

(13) TABLE-US-00001 TABLE 1 Acrylic Micro/Nanofiber Properties Density, g/cm.sup.3 1.17 Tensile Strength, MPa 450 Modulus, GPa 6.0 Elongation, % 15 Typical Fiber Length, mm 4.5-6.5 Canadian Standard Freeness, ml  10-700 BET Surface Area, m.sup.2/g 50 Moisture Regain, % <2.0 Surface Charge Anionic

(14) Such fibers are actually present, as discussed above, in a pulp-like formulation, thereby facilitating introduction within a wetlaid nonwoven fabric production scheme.

Nonwoven Production Method

(15) Material combinations were then measured out to provide differing concentrations of both components prior to introduction together into a wetlaid manufacturing process. Handsheets were made according to TAPPI Test Method T-205, which is incorporated here by reference (basically, as described above, mixing together in a very high aqueous solvent concentration formulation and under high shear conditions as are typically used in wet laid manufacturing and described as “refining” of fibers, ultimately laying the wet structure on a flat surface to allow for solvent evaporation). Several different combinations were produced to form final nonwoven fabric structures. The method was adjusted only to accommodate different basis weights by adjusting the initial amount of material incorporated into each sheet. Materials and ratios are shown in Table 2.

(16) FIGS. 5, 6, and 7 correlate in structure to Example 3 below, as well. The similarity in structure (larger microfibers and smaller nanofibers) are clarified, and the presence of fewer amounts of nanofibers in these structures is evident from these photomicrographs, as well.

(17) The fabric was measured for thickness and then cut into suitable sizes and shapes for introduction within lithium ion rechargeable battery cells. Prior to any such introduction, however, samples of the battery separator fabrics were analyzed and tested for various properties in relation to their capability as suitable battery separators. Furthermore, comparative examples of battery separator nanofiber membranes according to U.S. Pat. No. 7,112,389, which is hereby incorporated by reference, as well as battery separator films from Celgard, are reported from the tests in the patent and from Celgard product literature.

Examples

(18) Examples 1-21 were made according to TAPPI Test Method T205 using Engineered Fiber Technologies EFTEC™ A-010-04 fibrillated acrylic fiber (combination of microfiber and nanofiber)(listed as Base Fabric) and FiberVisions T426 fiber, which is 2 denier per filament, cut to 5 mm length, and a bicomponent fiber made from polypropylene and polyethylene, and has a diameter of approximately 17 microns (listed as Added Fiber). The amount of each fiber, conditioned basis weight, caliper (or thickness), apparent density and porosity of the examples are shown in Table 2. Conditioned Basis Weight, Caliper, Apparent Density, and Tensile were tested according to TAPPI T220, which is hereby incorporated by reference.

(19) TABLE-US-00002 TABLE 2 Separator Materials Production % Conditioned Apparent Ex- % Base Added Basis Wt Caliper Density Porosity ample Fabric Fiber g/m.sup.2 mm g/cm.sup.3 % 1 100% 0% 62.4 0.141 0.442 68% 2 70% 30% 61.5 0.197 0.312 75% 3 50% 50% 66.3 0.244 0.272 76% 4 30% 70% 61.2 0.256 0.239 77% 5 20% 80% 64.0 0.288 0.222 78% 6 100% 0% 30.0 0.079 0.380 73% 7 90% 10% 32.1 0.096 0.334 75% 8 80% 20% 31.4 0.103 0.305 77% 9 70% 30% 30.6 0.109 0.280 78% 10 60% 40% 30.5 0.118 0.259 79% 11 50% 50% 30.2 0.135 0.223 81% 12 100% 0% 42.2 0.103 0.409 71% 13 90% 10% 41.8 0.119 0.352 74% 14 80% 20% 42.3 0.131 0.323 75% 15 70% 30% 41.8 0.145 0.288 77% 16 60% 40% 41.6 0.157 0.265 78% 17 50% 50% 41.7 0.165 0.253 78% 18 100% 0% 24.6 0.081 0.303 78% 19 90% 10% 23.8 0.085 0.281 79% 20 80% 20% 24.9 0.093 0.268 79% 21 70% 30% 24.5 0.094 0.261 79%

(20) The higher the porosity, the higher the peak power output within the subject battery. With such high results, theoretically, at least, the number of batteries necessary to accord the necessary power levels to run certain devices (such as automobiles, for instance) would be reduced through an increase in the available power from individual batteries. Such a benefit would be compounded with an effective air resistance barrier as well. The porosity of the inventive separator may also be controlled by the ratio of nanofiber to microfibers, the types of nanofibers, and also by post processing such as calendaring, as can be seen below.

Battery Separator Base Analysis and Testing

(21) The test protocols were as follows:

(22) Porosity was calculated according to the method in U.S. Pat. No. 7,112,389, which is hereby incorporated by reference. Results are reported in %, which related to the portion of the bulk of the separator that is filled with air or non-solid materials, such as electrolyte when in a battery.

(23) Gurley Air Resistance was tested according to TAPPI Test Method T460, which is hereby incorporated by reference. The instrument used for this test is a Gurley Densometer Model 4110. To run the test, a sample is inserted and fixed within the densometer. The cylinder gradient is raised to the 100 cc (100 ml) line and then allowed to drop under its own weight. The time (in seconds) it takes for 100 cc of air to pass through the sample is recorded. Results are reported in seconds/100 cc, which is the time required for 100 cubic centimeters of air to pass through the separator.

(24) Mean Flow Pore Size was tested according to ASTM E-1294 “Standard Test Method for Pore Size Characteristics of Membrane Filters Using Automated Liquid Porosimeter” which uses an automated bubble point method from ASTM F 316 using a capillary flow porosimeter. Tests were performed by Porous Materials, Inc., Ithaca, N.Y.

(25) The air permeability of a separator is a measurement of the time required for a fixed volume of air to flow through a standard area under light pressure. The procedure is described in ASTM D-726-58.

(26) Tensile properties, Gurley Air Resistance and Mean Flow Pore Size are shown in Table 3.

(27) TABLE-US-00003 TABLE 3 Physical Properties of Battery Separator Materials MD CD Gurley Air Mean Flow Tensile Tensile Resistance Pore Size Example kg/cm.sup.2 kg/cm.sup.2 sec/100 cc mm 1 1407 1407 566 0.46 2 539 539 235 0.96 3 249 249 41 2.13 4 170 170 10 5.96 5 31 31 0.3 11.76 6 1015 1015 162 0.72 7 642 642 81 0.83 8 522 522 64 1.50 9 396 396 39 10 289 289 20 11 132 132 6 12 1128 1128 218 0.61 13 778 778 153 0.71 14 579 579 94 0.79 15 419 419 46 16 292 292 29 17 201 201 12 18 354 354 351 0.78 19 296 296 212 0.89 20 224 224 145 21 161 161 79

(28) The inventive example thus shows a very small pore size mean, indicating a capability to permit a large number of recharge cycles for the subject battery. In addition, the ability to control the pore size is indicated by the change in pore size with the proportional change in the ratio of nanofiber and microfiber materials. This is a key advantage that is not present in any previous art, such that with this technology the pore size can be dialed in by the battery manufacturer depending on the requirements of the end user. Thus, a separator can be designed for a power tool or automotive application to have different characteristics from a rechargeable watch battery, cell phone or laptop computer.

(29) The tensile properties in the examples given are isotropic, that is, the same in all directions, with no distinction between machine and cross directions. Comparative examples show tensile properties that vary considerably between machine direction (MD) and cross direction (CD) tensile strength. In general, nanofiber-based battery separators are quite weak. Thus, one advantage of the current invention is the tensile strength, which allows faster processing in battery manufacture, tighter winding of the batteries, and more durability in battery use. Such MD tensile strength is preferably greater than 250 kg/cm.sup.2, more preferably greater than 500 kg/cm.sup.2, and most preferably greater than 1000 kg/cm.sup.2. The requirements on the CD tensile strength are lower, preferably being greater than 100 kg/cm.sup.2, more preferably being greater than 250 kg/cm.sup.2, and most preferably greater than 500 kg/cm.sup.2.

(30) As noted above, calendaring and an increased population of nanofibers relative to microfibers will reduce the overall pore size mean, even further, thus indicating, again, the ability to target certain measurements on demand for the inventive technology.

(31) Test results for two comparative examples are given to show the state of the prior art. The first CE1 is an electrospun nanofiber example from U.S. Pat. No. 7,112,389, where example 4 is taken as a typical example for comparison purposes. The second example is Celgard 2325 membrane separator. The test results are from Polypore, the manufacturer, as reported on their product literature. The results reported for these materials are shown in Table 4, below.

(32) TABLE-US-00004 TABLE 4 Conditioned MD CD Gurley Air Mean Flow Sample Basis Wt Caliper Porosity Tensile Tensile Resistance Pore Size Units g/m.sup.2 mm % kg/cm.sup.2 kg/cm.sup.2 sec/100 cc mm CE 1 28.5 0.091 73% 25 0.4 2.65 CE 2 0.025 39% 1700 150 620 0.028

(33) The isotropic properties of the inventive separator show the potential for even thinner materials to be made without compromising strength in either direction. Such a result permits lighter, thinner, and less expensive batteries with greater amounts of electrolyte present and, presumably greater surface area for electrodes for improved power generation as well. Furthermore, tensile strength is necessary for processing to prevent electrodes from touching as the battery electrodes are pressed into each other. The CE2 tensile strength is high in the machine direction (MD), but very low in the cross direction (CD). The CE1 MD tensile strength is very low, and was not reported in the CD, limiting the usefulness of the overall product from a manufacturing and handling perspective.

(34) The lower the air resistance, the greater the available usable power within the battery and the lower the energy loss on recharging. As well, the effect of heat on the battery overall is reduced with reduced air resistance characteristics. The inventive example shows a relatively low result when compared, especially, to the CE2 Comparative. The CE1 Comparative is very low; however, in combination with the porosity and pore sizes, as well as the tensile strength measurements noted above, the drawbacks of such a battery separator are evident. The inventive technology provides a better overall effect from all perspectives. Additionally, with thickness control, as well as the amount of nanofibers present within the overall fabric structure, the air resistance of the inventive separator may be modified to a lower level more in line with the CE1 materials, further evincing the unexpectedly good and beneficial results accorded by the inventive technology employed herein.

(35) Battery separators range in thickness from 15 microns to over 100 microns. With the high strength, it is likely that a sheet of 12 gsm can be made without difficulty, and calendaring can reduce the thickness such that the full range of useful sheet thicknesses can be made with this technology. For example, a sheet of 12 gsm may have a thickness equal to one half of the sheets made at 25 gsm, or approximately 40 microns. Calendaring or otherwise compressing the sheet may reduce this thickness by 50%, bringing the resultant thickness to 20 microns. Processing improvements may allow even thinner sheets to be made and compressed to even thinner sheets, all of which would be encompassed within the current invention.

Battery Formation and Actual Battery Testing Results

(36) FIG. 8 shows the typical battery 10 structure with the outside housing 12 which includes al of the other components and being securely sealed to prevent environmental contamination into the cell as well as any leakage of electrolyte from the cell. An anode 14 is thus supplied in tandem with a cathode 16, with at least one battery separator 18 between the two. An electrolyte 20 is added to the cell prior to sealing to provide the necessary ion generation. The separator 18 thus aids in preventing contact of the anode 14 and cathode 16, as well as to allow for selected ion migration from the electrolyte 20 therethrough. The general format of a battery cell follows this structural description, albeit with differing structures sizes and configurations for each internal component, depending on the size and structure of the battery cell itself. In this situation, button battery of substantially circular solid components were produced for proper testing of separator effectiveness within such a cell.

(37) To that end, electrical properties of the separator were tested first by making symmetric lithium foil-separator-lithium foil 2016 coin cells and testing for electrical resistance, and then by making asymmetric carbon electrode-separator-lithium foil 2016 coin cells. Testing was done at the Nanotechnology Laboratory in the Georgia Institute of Technology School of Materials Science and Engineering. For the symmetric lithium-separator-lithium 2016 coin cells, ⅝″ rounds were cut from selected separators, dried in a vacuum chamber of an Ar-filled glove box at 70° C. for approximately 12 hours and assembled into:

(38) (a) symmetric lithium foil-separator-lithium foil 2016 coin cells and

(39) (b) asymmetric carbon electrode-separator-lithium foil 2016 coin cells.

(40) The electrolyte used was 1 M LiPF.sub.6 in EC:DMC:DEC mixture (1:1:1 by volume). Lithium foil was rolled to thickness 0.45 mm and one or two layers of separator were used in this study. Celgard 2325 separator, CE2, was the specific comparative example for test purposes as well.

(41) After 2 days of storage, the potentiostatic electrochemical impedance spectroscopy (EIS) measurements in the frequency range from 0.01 Hz to 100 kHz were carried out on each of the assembled two electrode Li-separator-Li coin cells.

(42) Each cell included the following contributors to the total resistance: (i) Li ion transport in the electrolyte/separator; (ii) Li ion transport in a solid-electrolyte-interphase (SEI) layer on each of the Li electrodes; (iii) electron transport in Li/cell/contacts. Among these components of the resistance the (iii) electron transport can generally be neglected, while (i) Li ion transport in electrolyte usually gives no semicircle in the present frequency region due to their high characteristic frequencies.

(43) Being primarily interested in (i) Li ion transport in the electrolyte/separator, attention was centered on the high frequency region of the Nyquist plot associated therewith. The total resistance of the ion transport across the separator was approximated as the value of the Real part of the total resistance Z at high frequency where the imaginary component of the complex impedance becomes zero. As previously mentioned, the electrical resistance of the interfaces and the electrodes is much smaller than the ionic resistance and thus could be neglected.

(44) The results of the AC EIS analysis are summarized in a Table 5 below. Ionic Resistivity is the resistance value of the electrolyte in the separator, and is calculated from the formula Ri=I*A/t, where Ri is the Ionic Impedance, I is the impedance in ohms, A is the area of the cell in square centimeters, and t is the thickness of the separator in centimeters. As can be seen, the Ionic Impedance of the cell can be reduced by greater than 70% by using the proper combination of microfibers and nanofibers, as shown with a single layer of Example 19. In addition, by choosing the appropriate combination, the impedance can be dialed in to any number within a wide range of impedances. This ability to tune the properties is a key advantage of this invention.

(45) TABLE-US-00005 TABLE 5 Battery Test Results Ionic Impedance Resistivity Example Separator # layers Ohms Ohm-cm 22 18 1 3 733 23 18 2 7.5 916 24 19 1 2 466 25 19 2 26 12 1 6 1153 27 12 2 12 1153 28 13 1 9 1497 29 13 2 11.5 956 30 CE2 1 2 1583 31 CE2 2 4 1583

(46) The ionic resistance of the separator/electrolyte layer was in the range of 2-6 Ohm per layer. Comparative study suggests that Examples 18 and 19 was very close to that of Celgard 2325 separator, CE2.

(47) For asymmetric carbon electrode-separator-lithium foil 2016 coin cells, carbon electrodes were based on Pureblack® carbon and carboxymethyl cellulose (CMC) binder. Electrode composition is:

(48) Pureblack®—88.85 wt. %

(49) CMC (MM 250 kDa, DS 0.9)—11.15 wt. %

(50) Prior to cell assembling the electrode was dried in vacuum at 100° C. for two days. The same type of electrolyte [1 M LiPF.sub.6 in EC:DMC:DEC mixture (1:1:1 by volume)] utilized above was introduced here as well. The results of the 1st Li insertion-extraction cycle collected at a slow rate of C/20 is presented in Table 6 below:

(51) TABLE-US-00006 TABLE 6 Further Battery Testing Intercalation Deintercalation Capacity of Capacity Separator 1st Cycle of 1st Cycle Coulombic Example Example # mAh/g mAh/g Efficiency % 32 18 511 193 37.69 33 12 489 184 37.68 34 19 339 156 46.04 35 CE2 470 176 37.49

(52) The capacity of the electrode and the Coulombic efficiency at the 1st cycle is similar for the cells with Examples 18, 12 and Celgard separator CE2. At a moderate rate, then, the inventive separators provided effective and similar results to the anisotropic Celgard materials. In actuality, though, a 15% increase was noted by Example 34, far above any expectation regarding performance of such a separator. Thus, the overall inventive materials are either similar to or exceed the performance of the standard used in the industry as of today.

(53) It should be understood that various modifications within the scope of this invention can be made by one of ordinary skill in the art without departing from the spirit thereof. It is therefore wished that this invention be defined by the scope of the appended claims as broadly as the prior art will permit, and in view of the specification if need be.