CO-EXTRUDED, MULTI-LAYERED BATTERY SEPARATOR

Abstract

A battery separator comprises a co-extruded, microporous membrane having at least two layers made of extrudable polymers and having: a uniform thickness defined by a standard deviation of <0.80 microns (m); or an interply adhesion as defined by a peel strength >60 grams.

Claims

1. A battery separator comprising: a co-extruded, microporous membrane having at least two layers made of extrudable polymers and having a uniform thickness defined by a standard deviation of <0.80 m, wherein the co-extruded, microporous membrane has a thickness from 8 to 25 microns.

2. (canceled)

3. (canceled)

4. The battery separator of claim 1 wherein an extrudable polymer of one of said at least two layers is the same or different than an extrudable polymer of another of said at least two layers.

5. The battery separator according to claim 1 wherein at least one of said extrudable polymers is a thermoplastic polymer.

6. The battery separator according to claim 1 wherein at least one of said extrudable polymers is selected from the group consisting of: polyolefins, polyamides, polyvinylidenes, copolymers of the foregoing, and blends thereof.

7. The battery separator according to claim 1 wherein at least one of said extrudable polymers further comprises a material added thereto.

8. The battery separator according to claim 7 wherein said material is selected from the group of materials adapted to do at least one of the following: lower the melting temperature of the extrudable polymers; improve the melt integrity of the membrane; improve the strength of toughness of the membrane; improve the antistatic properties of the membrane; improve the surface wettability of the separator; improve the surface tribology performance of the separator; improve the processing of the extrudable polymers; improve the flame of the membrane; facilitate nucleation of the extrudable polymers; color the layer of the membrane; and combinations thereof.

9. A battery separator comprising: a co-extruded, microporous membrane having at least two layers made of extrudable polymers and having an interply adhesion as defined by a peel strength >60 grams.

10. The battery separator according to claim 9 wherein at least one of said extrudable polymers is a thermoplastic polymer.

11. The battery separator of claim 9 wherein an extrudable polymer of one of said at least two layers is the same or different than an extrudable polymer of another of said at least two layers.

12. The battery separator according to claim 9 wherein at least one of said extrudable polymers is selected from the group consisting of: polyolefins, polyacetals, polyamides, polyesters, polysulfides, polyvinyl alcohols, polyvinyl esters, polyvinylidenes, copolymers of the foregoing, and blends thereof.

13. The battery separator according to claim 9 wherein at least one of said extrudable polymers further comprises a material added thereto.

14. The battery separator according to claim 13 wherein said material is selected from the group of materials adapted to do at least one of the following: lower the melting temperature of the extrudable polymers; improve the melt integrity of the membrane; improve the strength of toughness of the membrane; improve the antistatic properties of the membrane; improve the surface wettability of the separator; improve the surface tribology performance of the separator; improve the processing of the extrudable polymers; improve the flame retardancy of the membrane; facilitate nucleation of the extrudable polymers; color the layer of the membrane; and combinations thereof.

15.-18. (canceled)

19. The battery separator according to claim 1 wherein said membrane is a dry-stretched membrane.

20. The battery separator according to claim 9 wherein said membrane is a dry-stretched membrane.

21. A lithium ion battery comprising the battery separator of claim 1.

22. A lithium ion battery comprising the battery separator of claim 9.

23. (canceled)

24. The battery separator of claim 4 wherein the extrudable polymer of one of said at least two layers is different than an extrudable polymer of another of said at least two layers, and wherein dissimilar polymer refers to: polymers having dissimilar chemical natures (e.g., PE and PP, or PE and a co-polymer of PE are polymers having dissimilar chemical natures), and/or polymer having the same chemical nature (e.g., PP1 and PP2, or PP and a co-polymer of PP are polymers having similar chemical natures) but dissimilar properties (e.g., two PE's or PP's having differing properties (e.g., density, molecular weights, molecular weight distributions, rheology, additives (composition and/or percentage), etc.).

25. The battery separator of claim 4 wherein an extrudable polymer of one of said at least two layers is polymerically dissimilar from an extrudable polymer of another of said at least two layers.

26. The battery separator of claim 4, wherein the extrudable polymer of the one of said at least two layers comprises a first polypropylene, and wherein the extrudable polymer of the another of said at least two layers comprises a second polypropylene, said second polypropylene having a density, molecular weight, molecular weight distribution, rheology, additives (composition and/or percentage), and/or the like different from said first polypropylene.

27. The battery separator of claim 11 wherein the extrudable polymer of one of said at least two layers is different than an extrudable polymer of another of said at least two layers, and wherein dissimilar polymer refers to: polymers having dissimilar chemical natures (e.g., PE and PP, or PE and a co-polymer of PE are polymers having dissimilar chemical natures), and/or polymer having the same chemical nature (e.g., PP1 and PP2, or PP and a co-polymer of PP are polymers having similar chemical natures) but dissimilar properties (e.g., two PE's or PP's having differing properties (e.g., density, molecular weights, molecular weight distributions, rheology, additives (composition and/or percentage), etc.).

28. The battery separator of claim 11 wherein an extrudable polymer of one of said at least two layers is polymerically dissimilar from an extrudable polymer of another of said at least two layers.

29. The battery separator of claim 11, wherein the extrudable polymer of the one of said at least two layers comprises a first polypropylene, and wherein the extrudable polymer of the another of said at least two layers comprises a second polypropylene, said second polypropylene having a density, molecular weight, molecular weight distribution, rheology, additives (composition and/or percentage), and/or the like different from said first polypropylene.

30. The battery separator according to claim 4 wherein said membrane is a dry-stretched membrane.

31. The battery separator according to claim 11 wherein said membrane is a dry-stretched membrane.

32. A lithium ion battery comprising the battery separator of claim 4.

33. A lithium ion battery comprising the battery separator of claim 11.

34. A membrane comprising: a co-extruded, microporous membrane having at least two layers made of extrudable polymers and having a uniform thickness defined by a standard deviation of <0.80 m, wherein the co-extruded, microporous membrane has a thickness from 8 to 25 microns.

35. The membrane of claim 34 wherein an extrudable polymer of one of said at least two layers is the same or different than an extrudable polymer of another of said at least two layers.

36. The membrane according to claim 34 wherein at least one of said extrudable polymers is a thermoplastic polymer.

37. The membrane according to claim 34 wherein at least one of said extrudable polymers is selected from the group consisting of: polyolefins, polyvinylidenes, copolymers of the foregoing, and blends thereof.

38. The membrane according to claim 34 wherein at least one of said extrudable polymers further comprises a material added thereto.

39. The membrane according to claim 38 wherein said material is selected from the group of materials adapted to do at least one of the following: lower the melting temperature of the extrudable polymers; improve the melt integrity of the membrane; improve the strength of toughness of the membrane; improve the antistatic properties of the membrane; improve the surface wettability of the separator; improve the surface tribology performance of the separator; improve the processing of the extrudable polymers; improve the flame of the membrane; facilitate nucleation of the extrudable polymers; color the layer of the membrane; and combinations thereof.

40. A membrane comprising: a co-extruded, microporous membrane having at least two layers made of extrudable polymers and having an interply adhesion as defined by a peel strength >60 grams.

41. The membrane according to claim 40 wherein at least one of said extrudable polymers is a thermoplastic polymer.

42. The membrane of claim 40 wherein an extrudable polymer of one of said at least two layers is the same or different than an extrudable polymer of another of said at least two layers.

43. The membrane according to claim 40 wherein at least one of said extrudable polymers is selected from the group consisting of: polyolefins, polyacetals, polyamides, polyesters, polysulfides, polyvinyl alcohols, polyvinyl esters, polyvinylidenes, copolymers of the foregoing, and blends thereof.

44. The membrane according to claim 40 wherein at least one of said extrudable polymers further comprises a material added thereto.

45. The membrane according to claim 44 wherein said material is selected from the group of materials adapted to do at least one of the following: lower the melting temperature of the extrudable polymers; improve the melt integrity of the membrane; improve the strength of toughness of the membrane; improve the antistatic properties of the membrane; improve the surface wettability of the separator; improve the surface tribology performance of the separator; improve the processing of the extrudable polymers; improve the flame retardancy of the membrane; facilitate nucleation of the extrudable polymers; color the layer of the membrane; and combinations thereof.

46. The membrane according to claim 34 wherein said membrane is a dry-stretched membrane.

47. The membrane according to claim 40 wherein said membrane is a dry-stretched membrane.

48. A lithium ion battery comprising the membrane of claim 34.

49. A lithium ion battery comprising the membrane of claim 40.

50. The membrane of claim 35 wherein the extrudable polymer of one of said at least two layers is different than an extrudable polymer of another of said at least two layers, and wherein dissimilar polymer refers to: polymers having dissimilar chemical natures (e.g., PE and PP, or PE and a co-polymer of PE are polymers having dissimilar chemical natures), and/or polymer having the same chemical nature (e.g., PP1 and PP2, or PP and a co-polymer of PP are polymers having similar chemical natures) but dissimilar properties (e.g., two PE's or PP's having differing properties (e.g., density, molecular weights, molecular weight distributions, rheology, additives (composition and/or percentage), etc.).

51. The membrane of claim 35 wherein an extrudable polymer of one of said at least two layers is polymerically dissimilar from an extrudable polymer of another of said at least two layers.

52. The membrane of claim 35, wherein the extrudable polymer of the one of said at least two layers comprises a first polypropylene, and wherein the extrudable polymer of the another of said at least two layers comprises a second polypropylene, said second polypropylene having a density, molecular weight, molecular weight distribution, rheology, additives (composition and/or percentage), and/or the like different from said first polypropylene.

53. The membrane of claim 42 wherein the extrudable polymer of one of said at least two layers is different than an extrudable polymer of another of said at least two layers, and wherein dissimilar polymer refers to: polymers having dissimilar chemical natures (e.g., PE and PP, or PE and a co-polymer of PE are polymers having dissimilar chemical natures), and/or polymer having the same chemical nature (e.g., PP1 and PP2, or PP and a co-polymer of PP are polymers having similar chemical natures) but dissimilar properties (e.g., two PE's or PP's having differing properties (e.g., density, molecular weights, molecular weight distributions, rheology, additives (composition and/or percentage), etc.).

54. The membrane of claim 42 wherein an extrudable polymer of one of said at least two layers is polymerically dissimilar from an extrudable polymer of another of said at least two layers.

55. The membrane of claim 42, wherein the extrudable polymer of the one of said at least two layers comprises a first polypropylene, and wherein the extrudable polymer of the another of said at least two layers comprises a second polypropylene, said second polypropylene having a density, molecular weight, molecular weight distribution, rheology, additives (composition and/or percentage), and/or the like different from said first polypropylene.

56. The membrane according to claim 35 wherein said membrane is a dry-stretched membrane.

57. The membrane according to claim 42 wherein said membrane is a dry-stretched membrane.

58. A lithium ion battery comprising the membrane of claim 35.

59. A lithium ion battery comprising the membrane of claim 42.

Description

EXAMPLES

[0024] The foregoing invention is further illustrated in the following examples. Table 1 illustrates 11 samples made according to the foregoing discussion of the invention. Table 2 illustrates the use of various materials to improve the melt integrity of the separator to a separator without such material. Table 3 illustrates the use of other of the foregoing materials to improve various properties of the separator. The test procedures used in compiling the information in the Tables is set out below.

Test Procedures

[0025] Gurley: Gurley was measured by two methods. In the first method defined as the Japanese Industrial Standard Gurley (JIS Gurley), Gurley is measured using the OHKEN permeability tester. JIS Gurley is defined as the time in seconds required for 100 cc of air to pass through one square inch of film at constant pressure of 4.8 inches of H.sub.2O. In the second method, Gurley is measured according to the ASTM D-726 procedure and is defined as the time in seconds required for 10 cc of air to pass through one square inch of film at constant pressure of 4.8 inches of H.sub.2O.

[0026] Tensile properties: MD and TD Tensile strength is measured using Instron Model 4201 according to ASTM-882 procedure.

[0027] Puncture strength: Puncture strength is measured using Instron Model 4442 based on ASTM D3763. The units of puncture strength are newtons. The measurements are made across the width of stretched product and the averaged puncture energy (puncture strength) is defined as the force required to puncture the test sample.

[0028] Peel Strength or Adhesion: Intra-layer adhesion is tested using the Chatillon TCD-200 Peel Force Tester.

[0029] Shrinkage: Shrinkage is measured at 90 C. for 60 minutes using a modified ASTM D-2732-96 procedure.

[0030] Thickness: The membrane thickness values are measured using the Emveco Microgage 210-A precision micrometer according to ASTM D374. Thickness values are reported in units of micrometers (m). 20 individual micrometer readings taken across the width of the sample are averaged.

[0031] Porosity: The porosity of the microporous film is measured by method ASTM D2873.

[0032] High Temperature Melt Integrity: High Temperature Melt Integrity is measured using Thermal Mechanical Analysis (TMA). The TMA compression probe is used to measure the thickness change of a separator under compression at a constant load of 125 gm as the temperature is scanned from 25 to 300 C. at a rate of 5 C./min. The percentage of thickness retained at 250 C. is defined as the high temperature melting integrity.

[0033] Wettability: One drop of a typical lithium ion electrolyte is placed on a sample of the membrane. The change in appearance of sample from opaque to nearly transparent is recorded. For the wettable separator, appearance should be nearly uniform translucent with no opaque areas. A non-wettable sample retains its opacity.

[0034] ER (Electrical Resistance): The units of electrical resistance are ohm-cm.sup.2. The separator resistance is characterized by cutting small pieces of separators from the finished material and then placing them between two blocking electrodes. The separators are completely saturated with the battery electrolyte with 1.0M LiPF.sub.6 salt in EC/EMC solvent of 3:7 ratio by volume. The resistance, R () of the separator is measured by 4-probe AC impedance technique. In order to reduce the measurement error on the electrode/separator interface, multiple measurements are needed by adding more separator layers. Based on the multiple layer measurements, the electrical (ionic) resistance, R.sub.s () of the separator saturated with electrolyte is then calculated by the formula,

[00001]$\begin{array}{cc}{R}_s=\frac{{}_s.Math.l}{A}& \left(1\right)\end{array}$

where .sub.s is the ionic resistivity of the separator in -cm, A is the electrode area in cm.sup.2 and / is the thickness of the separator membrane in cm. The ratio .sub.s/A is the slope calculated for the variation of separator resistance (R) with multiple separator layers () which is given by,

[00002]$\begin{array}{cc}\mathrm{slope}=\frac{{}_s}{A}=\frac{.Math.R}{.Math.}.& \left(2\right)\end{array}$

Also see U.S. patent application Ser. No. 11/400,465 filed Apr. 7, 2006, test procedure related to ionic resistance, incorporated herein by reference.

[0035] Pin Removal: The pin removal test simulates the cell winding process. Pin Removal force is the force in grams required to pull the pin from the center of jelly roll after winding. A battery winding machine was used to wind the separator around a pin (or core or mandrel). The pin is a two (2) piece cylindrical mandrel with a 0.16 inch diameter and a smooth exterior surface. Each piece has a semicircular cross section. The separator, discussed below, is taken up on the pin. The initial force (tangential) on the separator is 0.5 kgf and thereafter the separator is wound at a rate of ten (10) inches in twenty four (24) seconds. During winding, a tension roller engages the separator being wound on the mandrel. The tension roller comprises a diameter roller located on the side opposite the separator feed, a pneumatic cylinder to which 1 bar of air pressure is applied (when engaged), and a rod interconnecting the roller and the cylinder. The separator consists of two (2) 30 mm (width)10 pieces of the membrane being tested. Five (5) of these separators are tested, the results averaged, and the averaged value is reported. Each piece is spliced onto a separator feed roll on the winding machine with a 1 overlap. From the free end of the separator, i.e., distal the spliced end, ink marks are made at and 7. The mark is aligned with the far side of the pin (i.e., the side adjacent the tension roller), the separator is engaged between the pieces of the pin, and winding is begun with the tension roller engaged. When the 7 mark is about from the jellyroll (separator wound on the pin), the separator is cut at that mark, and the free end of the separator is secured to the jellyroll with a piece of adhesive tape (1 wide, overlap). The jellyroll (i.e., pin with separator wound thereon) is removed from the winding machine. An acceptable jellyroll has no wrinkles and no telescoping. The jellyroll is placed in a tensile strength tester (i.e., Chatillon Model TCD 500-MS from Chatillon Inc., Greensboro, N.C.) with a load cell (50 lbs0.02b; Chatillon DFGS 50). The strain rate is 2.5 inches per minute and data from the load cell is recorded at a rate of 100 points per second. The peak force is reported as the pin removal force. Also see: U.S. Pat. No. 6,692,867, incorporated herein by reference.

[0036] Dielectric Breakdown: Voltage is increased on a sample until a dielectric breakdown of the material is observed. Dielectric Breakdown is expressed in volts. A separator is placed between two electrodes and a voltage is applied across the electrodes. The voltage is increased until dielectric breakdown of the separator is observed. Strong separators show high failure voltage. Any non-uniformity can lead to a low failure voltage.

[0037] Aquapore Size: Pore size is measured using the Aquapore available through PMI (Porous Materials Inc.). Pore size is expressed in microns, m.

[0038] Mixed Penetration: Mixed penetration is the force required to create a short through a separator and is expressed in kilogram-force, kgf. Mixed penetration is the force required to create a short through a separator due to mixed penetration. In this test one starts with a base of a first metal plate, on top of this plate is placed a sheet of cathode material, on top of cathode is placed a separator, and on top of the separator is placed a sheet of anode material. A ball tip of 3 mm is then provided attached to a force gauge. The ball tip is connected to the first metal plate by a resistance meter. Pressure is applied to the ball tip, which is recorded on the force gauge. Once force is applied, there builds up an anode mix and a cathode mix on either side of the separator. When the resistance falls dramatically it indicates a short through the separator due to mixed penetration. Mixed penetration measures the strength of the separator and resistance towards mixed penetration. This has been found to more accurately simulate the behavior of a real cell. It is a better indicator than puncture strength of how a separator will behave in a cell. This test is used to indicate the tendency of separators to allow short-circuits during battery assembly. Also see U.S. patent application Ser. No. 11/400,465 filed Apr. 7, 2006, incorporated herein by reference.

TABLE-US-00001 TABLE 1 Examples of Bilayer & Trilayer Microporous Membrane Sample Celgard Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Sample Number 2300 #1 #2 #3 #4 #5 #6 #7 #8 #9 #10 #11 PP/PE/P PP/PE/ PP/PE PP/PE/PP PP/PE/PP PP/PE/PP PP/PE/PP PP/PE/PP PE/PP/PE PE/PP/PE PE/PP/PE PE/PP/PE PE/PE/PE Des- PP 60% PP 65% PP 65% PP 65% PP 65% PP 65% PP 58% PP 42% PP 42% PP 42% PP 0% PP cription Thickness, 26.9 15.7 9.5 13.0 15.7 18.6 19.9 9.4 9.8 16.5 17.2 17.1 m Thickness 0.72 0.46 0.37 0.46 0.45 0.65 0.55 0.49 0.45 0.51 0.60 0.54 std dev JIS Gurley, 540 485 391 427 550 560 283 195 373 517 364 second Shrinkage 2.7 0.8 0.7 0.9 1.6 1.6 1.5 2.8 5.4 1.7 3.7 7.2 @ 90 C. for 1 hour, % Elongation 52/ 73/ 88/ 90/ 79/ 73/ 99/ 87/ 63/ 68/ 77/ 75/ at break in 478 928 36 93 416 963 116 964 869 1031 967 1022 MD/TD, % Modulus in 5170/ 5425/ 5166/ 4724/ 5764/ 5959/ 2969/ 2957/ 3645/ 2833/ 3846/ 2979/ MD/TD, 2421 3413 5880 5507 4431 4021 2348 1866 2409 1766 1973 2266 kg/cm.sup.2 Tensile 1925 2133 2115 1749 2075 2006 1830 2077 1891 1923 1740 1925 strength in MD, kg/cm.sup.2 Tensile 146 193 187 181 154 170 163 199 188 176 157 120 strength in TD, kg/cm.sup.2 Puncture 502 373 for 177 252 365 421 357 183 154 255 243 283 Strength, g PP side/ 218 for PE side ER, ohm- 1.92 2.05 1.31 1.87 1.70 2.00 2.30 1.11 0.89 1.42 1.81 1.63 cm.sup.2 Mixed 130 110 89 112 105 123 122 70 67 104 118 103 Pene- tration, kgf Dielectric 2900 2082 823 1563 2337 2,341 2,568 754 1040 1476 1769 1564 Break- down, volts Porosity, 40.3 38 30 38 34 41 40 36 43 43 37 44 %

TABLE-US-00002 TABLE 2 Examples of Polymer Blends with Ceramic TiO.sub.2 to Improve Melting Integrity Comparison #1 Sample #1 Sample #2 Sample #3 Sample #4 Description PE/PE/PE PE/PP/PE PP/PE/PP PP/PE/PP PE/PE/PE trilayer trilayer PE trilayer PE trilayer PE trilayer 65% in 35% 58% thickness in thickness in thickness Additive no additives 30% TiO2 in 20% TiO2 in 20% TiO2 in 20% TiO2 in the middle the middle the middle the middle layer layer layer layer Thickness, m/thickness 17.1/0.54 17.8/0.40 15.3/0.61 15.9/0.44 15.5/0.46 std dev JIS Gurley, sec 364 500 400 267 193 Shrinkage @ 90 C. for 1 7.2 5.3 2.2 1.6 4.6 hour, % Tensile strength in TD, 120 110 148 180 100 kg/cm.sup.2 Puncture strength, g 283 310 288 257 265 ER, ohm-cm.sup.2 1.63 1.76 2.60 1.53 1.08 Mix Penetration, kgf 103 102 99 104 87 Dielectric Breakdown, volts 1564 1586 1973 1643 1179 Porosity, % 43.5 43.5 41.5 45.0 46.6 Aquapore Size, m 0.055 0.030/0.057 0.035/0.091 0.064 Peel Strength or Adhesion, >60 >60 >60 >60 >60 g High Temperature Melt 0% 13% 15% 20% 10% Integrity @250 C. by TMA

TABLE-US-00003 TABLE 3 Examples of Polymer Blends Comparison Sample Sample Sample Sample Sample Sample Sample Sample Sample Number #1 #1 #2 #3 #4 #5 #6 #7 #8 Description PP/PE/PP PP/PE/PP PP/PE/PP PP/PE/PP PE/PE/PE PE/PE/PE PP/PE/PP PP/PE/PP PP/PE/PP trilayer trilayer with trilayer with trilayer trilayer with trilayer with trilayer trilayer trilayer without 5% 5000 ppm with 2% 15% PE wax 30% PE with 10% with 20% with 10% additives ethoxylated Kemamide antistatic in the middle wax in the talc in talc in talc in alcohols in in the outside additive layer to middle outside outside outside the middle layers to Pelestat lower the layer to PP layer PP layer PP layer layer to improve pin 300 in the shutdown lower shut and 20% and 25% and 25% improve removal outside temperature down TiO2 in TiO2 in TiO2 in wettability performance layer temperature the the the middle middle middle PE layer PE layer PE layer to to to improve improve improve melt melt melt integrity integrity integrity Thickness, (m) 16.0 15.5 15.5 17.3 20.6 20.3 18.3 18.0 17.5 Gurley, sec 35 35 35 37 13 13-25 56 60 44 Wettable No Yes Shutdown 130 130 130 130 127 124 130 130 130 Temp, C. High 0% 0% 0% 0% 0% 0% >20% >20% >20% Temperature Melt Integrity @ 250 C. Pin Removal, g 9100 8400

[0039] The present invention may be embodied in other forms without departing from the spirit and the essential attributes thereof, and, accordingly, reference should be made to the appended claims, rather than to the foregoing specification, as indicated the scope of the invention.