Shutdown and non-shutdown separators for electrochemical devices

Abstract

The present invention provides a novel process that involves a reliable, robust, reproducible, and cost effective casting technique for a shutdown separator with, for example, a combination of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer, polysulfonamide (PSA)/polyether imide (PEI), and CaCO3 powder, and for a non-shutdown separator with, for example, a combination of polysulfonamide (PSA)/polyether imide (PEI), filler/plasticizer, and metal oxide nanostructures (SiO2, TiO2, and Al2O3).

Claims

1. A single layer, fire-resistant shutdown separator for an electrochemical device, comprising: a single film, amorphous porous planar cast structure defining curved and rounded-like shaped pores uniformly distributed throughout a sponge-like structure of the single film, amorphous porous planar cast structure providing mechanical strength in both machine and transverse directions, comprising: a plurality of polymeric materials comprising at least a first polymeric material having a relatively lower melting point, wherein the first polymeric material comprises a poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer, and a second polymeric material having a relatively higher melting point, wherein the second polymeric material comprises polysulfonamide (PSA); and a filler material comprising calcium carbonate; wherein the filler material has a particle size of between about 0.1 micron and about 1 micron and the amorphous porous planar cast structure has a thickness of between about 10μ and about 100μ, a pore size between about 0.0161 micron and about 1 micron, and a porosity of between about 50% and about 80% forming the single layer, fire-resistant shutdown separator, wherein the separator has a wettability of at least about 167% as measured by a two hour immersion in 1 M LiPF6 solution of ethylene carbonate and dimethyl carbonate (50:50).

2. The shutdown separator of claim 1, wherein the second polymeric material further comprises one or more of polyether imide (PEI) and polystyrene (PS).

3. The shutdown separator of claim 1, wherein the plurality of polymeric materials comprise polymeric materials selected from the group consisting of: a poly(vinylidene fluoride) polyolefin, a polysulfone, polyvinyl chloride, polyvinyl fluoride, a polytetrafluoroethylene-polystyrene copolymer, a polyamide, a polyphenyleneoxide-polysterene copolymer, and a polycarbonate.

4. The shutdown separator of claim 1, wherein the filler material comprises one or more of calcium stearate, silica, alumina, titanium oxide, and antimony oxide.

5. The shutdown separator of claim 1, wherein the filler material comprises one or more of mica, barium carbonate, barium sulfate, calcium oxide, calcium sulfate, clay, diatomaceous earth, glass powder, kaolin, magnesium carbonate, magnesium sulfate, magnesium oxide, silica clay, talc, zinc oxide, a poly(hexamethylene adipamide) powder, a polyethylene terephthalate powder, and beads of polystyrene divinyl benzene.

6. The shutdown separator of claim 1, wherein the first polymeric material is configured to melt to fill pores in the porous planar structure at a temperature of between about 100° C. and about 160° C.

7. The shutdown separator of claim 6, wherein the first polymeric material is configured to melt to fill pores in the porous planar structure at a temperature of about 140° C.

8. The shutdown separator of claim 1, further comprising a metal oxide.

9. The shutdown separator of claim 1, wherein the porous planar structure is disposed within an electrolyte solution disposed with the electrochemical device, and wherein the electrochemical device further comprises a housing containing the porous planar structure, the electrolyte solution, an anode, and a cathode.

10. An electrochemical device, comprising: a housing; an electrolyte solution disposed within the housing; an anode disposed within the electrolyte solution in the housing; a cathode disposed within the electrolyte solution in the housing; and one of a single layer, fire-resistant shutdown separator and a non-shutdown separator disposed within the electrolyte solution in the housing; wherein, when used, the single layer, fire resistant shutdown separator comprises a single film, amorphous porous planar cast structure defining curved and rounded-like shaped pores uniformly distributed throughout a sponge-like structure of the single film, amorphous porous planar cast structure providing mechanical strength in both machine and transverse directions, comprising: a plurality of polymeric materials comprising at least a first polymeric material having a relatively lower melting point, wherein the first polymeric material comprises a poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer, and a second polymeric material having a relatively higher melting point, wherein the second polymeric material comprises polysulfonamide (PSA); and a filler material comprising calcium carbonate; wherein the filler material has a particle size of between about 0.1 micron and about 1 micron and the amorphous porous planar cast structure has a thickness of between about 10μ and about 100μ, a pore size between about 0.0161 micron and about 1 micron, and a porosity of between about 50% and about 80% forming the single layer, fire-resistant shutdown separator, wherein the separator has a wettability of at least about 167% as measured by a two hour immersion in 1 M LiPF6 solution of ethylene carbonate and dimethyl carbonate (50:50); and wherein, when used, the non-shutdown separator comprises an amorphous porous planar cast structure defining curved pores uniformly distributed throughout a sponge-like structure providing mechanical strength in both machine and transverse directions, comprising: a polymeric material; and an inorganic particulate filler material; wherein the filler material has a particle size of between about 0.1 micron and about 1 micron and the amorphous porous planar cast structure has a thickness of between about 10μ and about 70μ, a pore size between about 0.0161 micron and about 1 micron, and a porosity of between about 60% and about 200%.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The present invention is illustrated and described herein with reference to the various drawings, in which like reference numbers are used to denote like device components/method steps, as appropriate, and in which:

(2) FIG. 1 is a schematic diagram illustrating one exemplary embodiment of a conventional electrochemical device (battery) utilizing the shutdown or non-shutdown separator of the present invention;

(3) FIG. 2 is a SEM image of an exemplary non-shutdown separator of the present invention;

(4) FIG. 3 is a SEM image of an exemplary shutdown separator of the present invention;

(5) FIG. 4 is a plot of a TGA curve of an exemplary shutdown separator of the present invention;

(6) FIG. 5 is a plot of a TGA curve of an exemplary non-shutdown separator of the present invention;

(7) FIG. 6 is a plot of a DSC curve of an exemplary non-shutdown separator of the present invention;

(8) FIG. 7 is a plot of a DSC curve of an exemplary shutdown separator of the present invention;

(9) FIG. 8 shows digital images of shutdown and non-shutdown separators before and after heating at 200° C. for 30 min in an oven;

(10) FIG. 9 illustrates a Sample 1 voltage vs. capacity profile;

(11) FIG. 10 illustrates a Sample 4 voltage vs. capacity profile;

(12) FIG. 11 illustrates a Sample 14 voltage vs. capacity profile; and

(13) FIG. 12 illustrates a Sample 49 voltage vs. capacity profile.

DETAILED DESCRIPTION OF THE INVENTION

(14) FIG. 1 is a schematic diagram illustrating one exemplary embodiment of a conventional electrochemical device (battery) utilizing the shutdown or non-shutdown separator of the present invention. In general, the battery 10 includes a housing 12 containing an electrolyte solution 14 enabling the transport of ions from an anode 16 to a cathode 18 through a separator 20, such as the shutdown or non-shutdown separator of the present invention, in the discharge of electrical current.

(15) As described herein above, the present invention finds a solution to the problem plaguing the industry for many years to obtain shutdown and non-shutdown separators that have both high mechanical strength (machine and transverse direction), good ionic conductivity, thermal stability, high porosity, and better wettability. The solution is accomplished through a novel process that involves a reliable, robust, reproducible, and cost effective casting technique for a shutdown separator with, for example, a combination of poly(vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) copolymer, polysulfonamide (PSA)/polyether imide (PEI), and CaCO3 powder, and for a non-shutdown separator with, for example, a combination of polysulfonamide (PSA)/polyether imide (PEI), filler/plasticizer, and metal oxide nanostructures (SiO2, TiO2, and Al2O3).

(16) In an exemplary casting process, 0.70 g metal oxide particles and 0.50 g CaCO3 (filler) were dispersed in Acetone (2.60 g) by ultrasonication for 1 h. 2.50 g of 12 wt % PSA solution was added to 0.70 g metal oxide and 0.50 g filler dispersed solution and then stirred for 1 h followed by vortexing for 10 min, continuous stirring for 3 h, and sonication for 30 min, followed by stirring for 20 h. The uniformly mixed solution was cast on a glass plate using a doctor blade. Cast samples were then dried at room temperature for 12 h. The dried samples were soaked in 0.1M HCl for 3 h followed by washing with distilled water several times and then dried at room temperature for 12 h. The room temperature dried sample was dried for 24 h at 100° C. in a vacuum. Afterwards, the separator material was kept in a desiccator until used.

(17) In another exemplary casting process, the metal oxide particles (0.60 g) and 0.50 g PEG-400 (pore farmer) were dispersed in acetone (2.60 g) by ultrasonication for 1 h. 3.32 g of 12 wt % PSA solution was added to 0.60 g of metal oxide and 0.50 g pore farmer dispersed solution and then stirred for 1 h followed by vortexing for 10 min, and continued stirring for 23 h. The uniformly mixed solution was cast on a glass plate using a doctor blade. Cast samples were then dried at room temperature for 12 h. The dried sample was soaked in 20 wt % glycerol and 80 wt % distilled water for 3 h followed by washing with distilled water several times and then drying at room temperature for 6 h. The room temperature dried sample was dried for 24 h at 100° C. in a vacuum. Afterwards, the separator was kept in a desiccator until used.

(18) In a further exemplary casting process, the metal oxide particles (0.40 g) and 0.50 g CaCO.sub.3 (filler) were dispersed in Acetone (2.60 g) by ultrasonication for 1 h. 3.6 g of 20 wt % PEI solution (0.6 g of PEI solid content) was added to 0.40 g of metal oxide and 0.50 g filler dispersed solution and then stirred for 1 h followed by vortexing for 10 min, continuous stirring for 3 h, sonication for 30 min followed by stirring for 20 h. The uniformly mixed solution was cast on a glass plate using a doctor blade. Cast samples were then dried at room temperature for 12 h. The dried samples were soaked in 0.1M HCl for 3 h followed by washing with distilled water several times and then drying at room temperature for 12 h. The room temperature dried sample was dried for 24 h at 100° C. in a vacuum. Afterwards, the separator was kept in a desiccator until used.

(19) In a still further exemplary casting process, various compositions of cellulose acetate (CA) and polysulfonamide (PSA) polymers were homogenized in a minimum amount of N,N-dimethylacetamide (DMAc) and acetone, e.g., 0.75 g of CA and 0.25 g of PSA in 4.5 g DMAc and 1.41 g acetone, until a viscous solution formed. The Sb.sub.2O.sub.3 (20 wt %, particle size 5 μm) was introduced, gently, mixed, and sonicated for homogenization before casting on glass plate using a doctor blade and then dried at 75° C. for 5 h in an oven, and at 80° C. for 15 h in vacuum. Triethyl citrate was used as a plasticizer to decrease the brittleness of the separators. Afterwards, the separator was kept in a desiccator until used.

(20) In a still further exemplary casting process, various compositions of PVDF-HFP and PVP polymers were homogenized in a minimum amount of dry dimethylformamide (DMF), e.g., 0.65 g of PVDF-HFP and 0.35 g of PVP in 2.5 mL DMF, until a viscous solution was formed. The Sb.sub.2O.sub.3 (30 wt %, particle size 5 μm) was introduced, gently, mixed, and sonicated for homogenization before casting on PTFE cloth using a blade and then dried at 80° C. for 48 h. Afterwards, the separator was kept in a desiccator until used.

(21) In an another approach casting process, a measured amount of PVDF-HFP and PS powder (85/15, w/w) was homogeneously dissolved in a mixture of acetone/N, N-dimethylacetamide (3:1, w/w) forming a 20 wt % solution. Various compositions of metal oxides (SiO.sub.2, Al.sub.2O.sub.3 and TiO.sub.2) were introduced, gently, mixed, and sonicated for homogenization before casting on glass plate using a doctor blade and then dried at 75° C. for 5 h in an oven, and at 80° C. for 15 h in vacuum. The thickness of the nonwoven films used was about 20-30 μm. Afterwards, the separator was kept in a desiccator until used.

(22) Prior to fabrication of the lithium ion battery, shutdown and non-shutdown separators were subjected to Scanning Electron Microscopy (SEM), porosity, wettability, DSC-TGA, dimensional stability, permeability, conductivity, and cyclic voltammetry analysis to confirm the porosity, wettability, thermal stability, Gurley value, ionic conductivity, and electrochemical stability window of the separators.

(23) SEM was done by placing the separators on to a carbon tape and subjecting them to SEM analysis. As expected, a typical highly symmetric sponge-like structure was formed and uniformly distributed throughout the non-shutdown separators. This is illustrated in FIG. 2. The pore size ranged from 0.5˜1.0 μm and the porosity was determined to be >70%. High porosity is deemed to be favorable for high electrolyte uptake and high ion conductivity. A highly rough surface with pores formed throughout the surface of the shutdown separators, as illustrated in FIG. 3.

(24) To investigate the ability of the experimental separators to absorb electrolyte, the samples were immersed in a 1M LiPF6 solution of ethylene carbonate and dimethyl carbonate (50:50) for 2 h. Samples were removed from the electrolyte immersion and blotted dry with a Kimwipe to remove excess surface liquids. Each sample was weighed prior to and following the electrolyte immersion and the amount of electrolyte absorbed was collected. Table 1 below contains the results of the electrolyte wettability experiment.

(25) TABLE-US-00001 TABLE 1 The wettability of each separator following 2 h immersion in 1M LiPF6 solution of EC/DMC. Wettability Sample (wt. %/wt. %) W.sub.dry (g) W.sub.wet (g) (%) PVDF-HFP/PS (85/15) 0.0141 0.0283 101 PVDF-HFP/PS/TiO.sub.2 (45/15/40) 0.0127 0.0272 114 PVDF-HFP/PS/SiO.sub.2 (65/15/20) 0.0149 0.0232 56 PVDF-HFP/PS/Al.sub.2O.sub.3 (65/15/20) 0.0137 0.0217 58 PVDF-HFP/PSA (50/50) 0.0039 0.0088 125 PVDF-HFP/PSA/CaCO.sub.3 (50/50/50) 0.0052 0.0147 167 PVDF-HFP/PVP/PSA (40/10/50) 0.0054 0.0090 67 PVDF-HFP/PVP/PSA/ 0.0071 0.0124 75 CaCO.sub.3 (40/10/50/50) SiO.sub.2/PSA/TEC (70/20/10) 0.0032 0.0055 72 SiO.sub.2/PSA/CaCO.sub.3 (50/50/50) 0.0049 0.0111 126 SiO.sub.2/PSA/CaCO.sub.3 (60/40/50) 0.0080 0.0168 110 SiO.sub.2/PSA/CaCO.sub.3 (50/50/75) 0.0051 0.0141 176 SiO.sub.2/PSA/CaCO.sub.3 (50/50/100) 0.0079 0.0161 111 SiO.sub.2/PSA/PEG400 (60/40/50) 0.0064 0.0112 75 PSA/CaCO.sub.3 (50/50) 0.0061 0.0119 95 Al.sub.2O.sub.3/PSA/CaCO.sub.3 (50/50/50) 0.0070 0.0141 101 Al.sub.2O.sub.3/PSA/CaCO.sub.3/ (60/40/50) 0.0055 0.0113 78 Al.sub.2O.sub.3/PSA/CaCO.sub.3 (70/30/50) 0.0064 0.0156 144 Al.sub.2O.sub.3/PSA/TEC (75/20/5) 0.0062 0.0115 85 Al.sub.2O.sub.3/PSA/PEG400 (60/40/50) 0.0093 0.0155 66 TiO.sub.2/PSA/PEG400 (60/40/50) 0.0051 0.0118 105 TiO.sub.2/PSA/CaCO.sub.3 (60/40/50) 0.0054 0.0096 77 TiO.sub.2/PSA/CaCO.sub.3 (70/30/50) 0.0040 0.0083 107 TiO.sub.2/PSA/CaCO.sub.3 (40/60/50) 0.0066 0.0131 98 TiO.sub.2/PSA/TEC (75/20/5) 0.0030 0.0063 110 TiO.sub.2/PSA/TEC (70/20/10) 0.0099 0.0154 55 PSA/PEG400 (50/50) 0.0045 0.0083 84 PSA/PEG400/CaCO.sub.3 (50/50/50) 0.0041 0.0074 80 PSA/PEG400/CaCO.sub.3 (75/25/25) 0.0060 0.0099 65

(26) The porosity of the shutdown and non-shutdown separators was determined using an n-butanol method after soaking 2 h in n-butanol. The porosity of each separator is shown in Table 2. Results show that all of the separators exhibited porosity comparable with the commercially available separators porosity (>50%).

(27) TABLE-US-00002 TABLE 2 The porosity of each separator following 2 h immersion in 1-butanol. Volume Porosity Sample (wt. %/wt. %) W.sub.dry (g) W.sub.wet (g) (cm.sup.3) (%) PEI/CaCO.sub.3 (50/50) 0.0024 0.0067 0.004 133 SiO.sub.2/PEI/CaCO.sub.3 (40/60/50) 0.0023 0.0046 0.004 71 TiO.sub.2/PEI/CaCO.sub.3 (40/60/50) 0.0044 0.0084 0.004 124 Al.sub.2O.sub.3/PEI/CaCO.sub.3 (40/60/100) 0.0042 0.0102 0.006 123 PEI/PVDF-HFP/PVP (50/40/10) 0.0054 0.0089 0.006 86 PEI/PVDF-HFP (50/50) 0.0065 0.0084 0.006 74 PEI/PSA/CaCO3 (50/50/50) 0.0063 0.0127 0.006 185 PSA/CaCO.sub.3 (50/50) 0.0041 0.0058 0.004 52 SiO.sub.2/PSA/CaCO.sub.3 (50/50/50) 0.0053 0.0073 0.004 62 SiO.sub.2/PSA/CaCO.sub.3 (50/50/75) 0.0081 0.0120 0.004 120 SiO.sub.2/PSA/CaCO.sub.3 (50/50/100) 0.0050 0.0110 0.004 185 SiO.sub.2/PSA/CaCO.sub.3 (60/40/50) 0.0078 0.0109 0.004 81 SiO.sub.2/PSA/PEG400 (60/40/50) 0.0064 0.0096 0.004 83 Al.sub.2O.sub.3/PSA/CaCO.sub.3 (50/50/50) 0.0060 0.0112 0.004 160 Al.sub.2O.sub.3/PSA/CaCO.sub.3 (60/40/50) 0.0093 0.0131 0.006 78 Al.sub.2O.sub.3/PSA/CaCO.sub.3 (70/30/50) 0.0055 0.0122 0.004 174 Al.sub.2O.sub.3/PSA/PEG400 (60/40/50) 0.0053 0.0095 0.004 130 Al.sub.2O.sub.3/PSA/TEC (75/20/5) 0.0059 0.0105 0.004 142 TiO.sub.2/PSA/CaCO.sub.3 (60/40/50) 0.0050 0.0073 0.004 71 TiO.sub.2/PSA/CaCO.sub.3 (70/30/50) 0.0038 0.0083 0.004 117 TiO.sub.2/PSA/CaCO.sub.3 (40/60/50) 0.0063 0.0080 0.004 52 TiO.sub.2/PSA/PEG400 (60/40/50) 0.0045 0.0065 0.004 62 TiO.sub.2/PSA/TEC (75/20/5) 0.0055 0.0071 0.003 66 TiO.sub.2/PSA/TEC (70/20/10) 0.0090 0.0105 0.004 46 PSA/PEG400 (50/50) 0.0051 0.0078 0.002 83 PSA/PEG400/CaCO.sub.3 (75/25/25) 0.0055 0.0076 0.002 64 PSA/PEG400/CaCO.sub.3 (50/50/50) 0.0047 0.0082 0.002 108 PSA/PVDF- 0.0055 0.0075 0.004 62 HFP/CaCO.sub.3 (50/50/50) PSA/PVDF- 0.0063 0.0081 0.004 55 HFP/PVP/CaCO.sub.3 (50/40/10/50)

(28) Thermal degradation studies were conducted on shutdown and non-shutdown separators from 30-600° C. under N2 gas atmosphere using a Perkin Elmer TGA instrument. FIGS. 4 and 5 show the TGA curves of shutdown and non-shutdown separators, respectively. The first and second weight loss results are shown in Table 3. The higher thermal stability of the separator is attributed to the presence of the metal oxide, which can enforce a limit on the mobilization of polymer macromolecules and conduct heat homogeneously, thereby avoiding any heat concentration in the composite.

(29) TABLE-US-00003 TABLE 3 The first & second weight loss of each separator in the temperature range 30-400° C. First Second First weight loss Second weight weight weight temp. range loss temp. range Sample (wt. %/wt. %) loss (mg) loss (mg) (° C.) (° C.) PVDF-HFP/PS (85/15) 0.025 0.046 30-150 150-300 (PVDF-HFP/PS)/SiO.sub.2 (80/20) 0.018 0.124 30-150 150-300 (PVDF-HFP/PS)/TiO.sub.2 (80/20) 0.019 0.051 30-150 150-300 PSA/CaCO.sub.3 (50/50) 0.270 0.134 30-150 150-400 SiO.sub.2/PSA/CaCO.sub.3 (50/50/50) 0.240 0.138 30-150 150-400 SiO.sub.2/PSA/PEG400 (60/40/50) 0.131 0.369 30-150 150-400 TiO.sub.2/PSA/CaCO.sub.3 (70/30/50) 0.093 0.084 30-150 150-400 Al.sub.2O.sub.3/PSA/CaCO.sub.3 (70/30/50) 0.147 0.131 30-150 150-400

(30) Based on the above results, we have achieved highly thermal stability (>200° C.) in comparison with commercially available separators' thermal stability (<200° C.). TiO2 filled separators show higher thermal stability as compared to the SiO2 and Al2O3 filled separators due to TiO2 having a less hydrophilic nature as compared to silica and alumina.

(31) Melting temperature studies were conducted on shutdown and non-shutdown separators from 30-400° C. under N2 gas atmosphere using a Perkin Elmer DSC instrument. FIGS. 6 and 7 show the DSC curves of non-shutdown and shutdown separators. Thermograms show no peaks present, indicating that the polymer exists in an amorphous phase. The non-shutdown separator possesses superior thermal stability over 350° C., evidently, as no melting temperature peak is identified in the range of 30 to 350° C. These separators can be used as non-shutdown separators. The shutdown separators exhibit two melting temperature peaks at 108° C. and 140° C. in the first cycle, where as one peak at 140° C. in the second cycle. This separator could be used as a shutdown separator. At 140° C., PVDF-HFP is melting and fills the pores of the separator and stops the ion transport, current flow in the cell, and also prevents shortening of electrodes due to high thermal stability and dimensional stability of polysulfonamide at increased temperatures of the cell. Similar features are observed in polyethylene (135° C.) and polypropylene (165° C.) separators, except the prevention of shortening the anode and cathode due to high thermal shrinkage at elevated temperatures.

(32) Both TGA and DSC profiles show that no unusual phase changes or weight losses occur in the temperature range between 30 and 400° C., which makes the material thermally stable and useful as a separator under standard operating conditions in real battery configurations.

(33) FIG. 8 shows the digital images of shutdown and non-shutdown separators before and after heating at 200° C. for 30 min in an oven. No dimensional changes were observed after heating. This confirms that the separator maintains dimensional stability.

(34) This unique thermal property of the PSA/Metal Oxide and PVDF-HFP/PS/Metal Oxide separators can effectively prevent the potential short circuit in lithium ion batteries. Conventional separators can easily catch fire, leading to explosion. Since PSA and PVDF-HFP/PS are fire resistant, PSA/Metal Oxide and PVDF-HFP/PS/Metal Oxide separators are fire-safe.

(35) The sample 11A separator shows the highest tensile strength (in both directions) in comparison with the other separators. Better mechanical strength comes from relatively higher crystallinity and the orientation of polymer segments driven by the biaxial stretching process during separators preparation.

(36) TABLE-US-00004 TABLE 4 Tensile Strength of each separator. Maximum Tensile Max Specimen Manufacturing Load Strength Elongation Type Direction [N] [kgf/cm 2] [%] 1A MD 3.43 116.43 2.66 1A TD 4.28 145.39 3.06 2A MD 14.51 493.12 5.44 2A TD 16.56 562.88 8.87 3A MD 7.10 361.77 3.40 3A TD 9.13 465.52 3.69 4A MD 14.48 492.06 4.78 4A TD 16.09 546.88 6.60 5A MD 7.34 62.38 6.69 5A TD 8.66 73.60 10.19 6A MD 4.75 484.59 3.81 6A TD 2.66 271.00 4.28 7A MD 12.68 646.41 12.25 7A TD 15.06 768.08 13.78 8A MD 6.96 101.38 6.24 8A TD 5.36 78.15 4.40 9A MD 2.86 583.24 5.65 9A TD 2.21 450.50 3.75 10A  MD 6.07 206.32 7.10 10A  TD 3.49 118.68 1.92 11A  MD 8.84 1803.23 8.24 11A  TD 8.75 1784.25 10.02 12A  MD 3.86 786.73 2.85 12A  TD 1.95 397.55 1.33

(37) The air permeability (Gurley value) study was conducted on non-shutdown separators using a 4340N Permeometer at 23° C. and 70% relative humidity. This is determined by measuring the time for a settled volume of air to pass through the separator with a fixed area under the pressure of 0.02 MPa. Gurley values of the separators are given in the Table 5. In general, high Gurley value corresponds to low air permeability and a long tortuous path for air transportation, implying higher curvature for pores. The Gurley value of the some of the separators is higher than that of a referenced separator. This kind of pore structure is believed to own high curvature to provide effective internal short circuit protection and to reduce liquid electrolyte. The high curvature pore structure is believed to transport lithium ions and help the battery to effectively avoid internal short circuit, at the same time.

(38) TABLE-US-00005 TABLE 5 Gurley values and pore size of each separator. Sample Gurley value No: Sample (wt. %/wt. %) sec/100 mL Pore size (μm) 1 PSA/CaCO.sub.3 (50/50) 175.26 0.0625 2 TiO.sub.2/PSA/CaCO.sub.3 (70/30/50) 58.10 — 3 SiO.sub.2/PSA/CaCO.sub.3 (50/50/50) 360 — 4 SiO.sub.2/PSA/CaCO.sub.3 (60/40/50) 210 — 5 SiO.sub.2/PEI/CaCO.sub.3 (60/40/50) 38.15 0.0928 6 TiO.sub.2/PEI/CaCO.sub.3 (60/40/50) 400.26 0.0374 7 PEI/CaCO.sub.3 (50/50) 552.90 0.0161 8 SiO.sub.2/PSA/CaCO.sub.3 (60/40/50) 834.35 0.0224 9 TiO.sub.2/PSA/CaCO.sub.3 (40/60/50) 420.35 0.0331 10 SiO.sub.2/PSA/CaCO.sub.3 (50/50/75) 125.39 0.0720 13 Celgard 2500 200 0.064

(39) At high frequencies, where the imaginary impedance response approaches zero, the real impedance is a representative value of resistance for the membrane. Using the below equation, the bulk resistivity was then used to calculate the ionic conductivity for each sample membrane as well as for two control separator membranes.

(40) $\begin{array}{cc}\delta =\frac{d}{R*A}& \left(1\right)\end{array}$
in which, δ is the ionic conductivity (mS/cm), d is the thickness of the membrane, R is the bulk resistivity, and A is the area of the membrane.

(41) TABLE-US-00006 TABLE 6 Ionic conductivity of prospective separator candidates. Ionic Conductivity Candidate Thickness (mm) Resistance (Ω) (mS/cm) Sample 1 0.100666667 3.6 1.58 Sample 4 0.105 4.55 1.30 Sample 15 0.077 5.7 0.76

(42) Table 6 above lists the calculated ionic conductivities of the three separator samples when swollen with a standard LiPF6 in EC:DEC electrolyte. When compared to a typical porous polypropylene separator (˜0.8 mS/cm) and glass fiber separators (3.4 mS/cm), the separator samples tested here display similar ionic conductivities. While sample 15 has close to the same conductivity as polypropylene, samples 1 and 4 are closer to that of the nonwoven glass fiber separators (when swollen with the same electrolyte). For reference, the liquid electrolyte used has an ionic conductivity of ˜12 mS/cm. Although each cell has been tested in a coin cell, the ionic conductivity data supports the legitimacy of the samples to perform acceptably in energy storage devices.

(43) During the electrochemical investigation, several prospective samples showed promising performance when utilized as separator materials in lithium cathode ½-coin cells. Each sample was dried in an oven at 80° C. for 24 h prior to testing. Following drying, samples were immersed in a standard electrolyte (1M LiPF6 EC/DEC ( 3/7)) for 2 h to allow full electrolyte impregnation. ½-cell cathode coin cells were assembled by first drying a Lithium Cobalt Oxide (LCO) cathode material at 80° C. for 12 h. LCO cathode punches (1.77 cm2) were placed into Hoshen coin cells followed by 75 μl of electrolyte, the separator samples to be evaluated, a lithium chip (Gelon), two 0.5 mm stainless steel spacers (1.5 cm diameter), a wave spring washer, and finally the anode coin cell lid, resulting in a 4.4 mAh coin cell. Each sample was prepared in a dry room with a relative humidity <1% (dew point −46° C. and a room temperature of 68° F.). The cells were subjected to a C/20 charge and discharge cycle, followed by several C/10 cycles. FIGS. 9-12 are the initial cycle voltage profiles for the four promising cells along with the cycle life for each cell.

(44) As shown in FIGS. 9-12, the Sample 1 separator candidate showed a relatively level voltage plateau during both charge and discharge with a nominal operational voltage of 3.7 V during discharge. Sample 4 displayed similar voltage characteristics during the first charge and discharge cycle, achieving very close to the calculated expected capacity. Sample 4 cells also were able to cycle close to 100 cycles before beginning to lose capacity. Sample 15 has undergone a handful of cycles. However, the initial voltage profile, and the first 4 cycles suggest that this candidate has a strong potential to perform well as a separator for lithium batteries. Sample 49 had higher initial coulombic efficiency. However, the initial voltage profile and cycles suggest that these candidates have a strong potential to perform well as a separator for lithium batteries.

(45) Sample 1# PVDF-HFP+PVP (0.65 g: 0.35 g)

(46) Sample 4# PVDF-HFP+PVP+Sb2O3 (0.50 g: 0.20 g: 0.3 g)

(47) Sample 14# TiO2+PSA+TEC (0.70 g: 0.20 g: 0.10 g)

(48) Sample 49# Al2O3+PEG400+PSA (0.6 g: 0.5 g: 0.4 g)

(49) Although the present invention is illustrated and described herein with reference to preferred embodiments and specific examples thereof, it will be readily apparent to those of ordinary skill in the art that other embodiments and examples may perform similar functions and/or achieve like results. All such equivalent embodiments and examples are within the spirit and scope of the present invention, are contemplated thereby, and are intended to be covered by the following non-limiting claims.