Non-porous separator and use thereof

Abstract

The present invention belongs to the technical fields of macromolecular materials and batteries, and particularly relates to a non-porous separator and the use thereof, more particularly to a non-porous separator having a gelation function and the use thereof. This non-porous separator is composed of two or more macromolecular materials, wherein at least one of the macromolecular materials can be gelled by an organic solvent. This non-porous separator can be used in batteries having an organic solvent-based electrolyte and a high energy density, such that not only can a micro-short circuit, generated due to the introduction of foreign matters such as metals, be prevented, leading to an improved qualification rate for the product, but also the safety performance and the cycle life of such a battery can be improved significantly.

Claims

1. A non-porous separator, characterized in that the non-porous separator comprises two or more separate macromolecular materials, wherein at least one of the macromolecular materials can be gelled by an organic solvent; the two or more macromolecular materials refer to any mixture of molecular, nanometer or micron scales; the separator is non-porous, and has a gas permeability of 0 ml/min.

2. The non-porous separator according to claim 1, characterized in that the macromolecular material that can be gelled by an organic solvent is a synthetic macromolecular compound or a natural macromolecular compound, or a blend, copolymer, modified product and complex of a synthetic macromolecular compound and a natural macromolecular compound.

3. The non-porous separator according to claim 2, characterized in that the synthetic macromolecular material is one member or a blend, copolymer, modified product and complex of two and more members selected from the group consisting of polyethers, polysiloxane, polyester, polyacrylonitrile, fluoropolymer, polymers of acrylic acid and its esters, polyvinyl chloride, polyvinyl acetate, phenolic resin, epoxy resin, polyurethane, polyarenes, polyamide, and polyimide.

4. The non-porous separator according to claim 2, characterized in that the synthetic macromolecular material further comprise fillers and additives, and the weight proportion of the fillers and additives is 0.01 wt. % to 20 wt. % of the synthetic macromolecular material.

5. The non-porous separator according to claim 4, characterized in that the weight proportion of the fillers and additives is 1 wt. % to 5 wt. % of the synthetic macromolecular material.

6. The non-porous separator according to claim 4, characterized in that the fillers and additives comprise one member or a mixture of two and more members selected from the group consisting of alumina, silica, titania, zirconia, compounds composed of aLi.sub.2O-bAl.sub.2O.sub.3-cTiO.sub.2-dP.sub.2O.sub.5 (where a, b, c, d are between 1 and 100), compounds composed of aLi.sub.2O-bLa.sub.2O.sub.3-cZrO.sub.2-dTa.sub.2O.sub.5 (where a, b, c, d are between 1 and 100), compounds composed of aLi.sub.2S-bSiS.sub.2-cP.sub.2S.sub.5 (where a, b, c are between 1 and 100), montmorillonite, and molecular sieves.

7. The non-porous separator according to claim 2, characterized in that the natural macromolecular material is one member or a blend, modified product and complex of two and more members selected from the group consisting of cellulose, starch, chitin, chitosan, collagen, gelatin, natural silk, and spider silk.

8. The non-porous separator according to claim 7, characterized in that the modified product of the natural macromolecular material is one member or a mixture of two and more members selected from the group consisting of their alkylates, carboxylates, sulfonated compounds, carboxymethyl compounds, grafted compounds, and crosslinked compounds.

9. The non-porous separator according to claim 7, characterized in that the natural macromolecular material further comprise fillers and additives, and the weight proportion of the fillers and additives is 0.01 wt. % to 20 wt. % of the natural macromolecular material.

10. The non-porous separator according to claim 9, characterized in that the weight proportion of the fillers and additives is 1 wt. % to 5 wt. % of the natural macromolecular material.

11. The non-porous separator according to claim 1, characterized in that the thickness of the non-porous separator is 1-200 μm.

12. The non-porous separator according to claim 11, characterized in that the thickness of the non-porous separator is 5-40 μm.

13. The non-porous separator according to claim 1, characterized in that the non-porous separator further comprises, as matrix, at least one macromolecular material that cannot be gelled by an organic solvent.

14. The non-porous separator according to claim 13, characterized in that the matrix is polyolefin; polyesters; polyimide; or polyvinylidene fluoride.

15. The non-porous separator according to claim 14, characterized in that the polyesters is polyethylene terephthalate or polybutylene terephthalate.

16. The non-porous separator according to claim 15, characterized in that the polyesters is polyethylene terephthalate.

17. The non-porous separator according to claim 14, characterized in that the polyolefin is polyethylene, polypropylene or combinations thereof.

18. The non-porous separator according to claim 17, characterized in that the polyolefin is polypropylene or polypropylene/polyethylene/polypropylene.

19. Use of the non-porous separator according to claim 1, as a separator for primary or secondary batteries that employ an organic solvent type electrolyte.

20. A battery comprising the non-porous separator according to claim 1.

21. A process for preparing a non-porous separator comprising two or more macromolecular materials, wherein at least one of the macromolecular materials can be gelled by an organic solvent, and at least one of the macromolecular materials cannot be gelled by an organic solvent, that is, a matrix; wherein the process comprises dissolving the macromolecular materials that can be gelled by an organic solvent in a solvent, thereby forming a solution; immersing the matrix into the solution, evaporating the solvent, allowing the macromolecular materials that can be gelled by an organic solvent to be precipitated from the solution and deposited on the matrix; wherein the separator is non-porous, and has a gas permeability of 0 ml/min.

Description

SPECIFIC EMBODIMENTS

(1) In order to better illustrate the present invention, the present invention will be further described below with reference to specific examples, but shall not be limited to the following examples.

Example 1

(2) A polypropylene membrane with a thickness of 15 μm and a porosity of 60% was put into a 10 wt. % polyvinylidene fluoride solution in acetone and heated to 30° C. The acetone was continuously evaporated, and the polyvinylidene fluoride was precipitated from the solution, and filled into the pores of polypropylene. Thus, a separator comprising polypropylene and polyvinylidene fluoride in a weight ratio of 39:61 was obtained. The gas permeability was found to be 0 ml/min, as detected by gas permeability test (where the area of the separator was 10 cm.sup.2, the gas pressure difference between the two sides was 1 atm, and the time was 10 minutes), no obvious pore structure was found when observed with a scanning electron microscope, and the thickness was 15 μm as detected with a spiral micrometer. This shows that the separator is non-porous.

(3) A mixture of LiFePO.sub.4, a conductive carbon black and a binder PVDF (in a weight ratio of 9:0.4:0.6) was used as the positive electrode, on the surface of which three iron microspheres having a particle size of 0.1 mm were fixed per ampere-hour; a mixture of an artificial graphite (Shanghai Shanshan Co., Ltd., CMS), a conductive carbon black and a binder PVDF (in a weight ratio of 9:0.4:0.6) was used as the negative electrode; LB-315 (Guotai Huarong Chemical Co., Ltd., Zhangjiagang City, Jiangsu Province, China) was used as the electrolyte; and the above non-porous separator was used as the separator. The positive electrode, negative electrode, electrolyte and separator were rolled up in accordance with a conventional method into a lithium ion battery. The batteries were subjected to formation and then capacity grading to determine the qualification rate of the batteries. Afterwards, charge and discharge cycles were performed at a discharge depth of 100% between 2.5-4.0V at 1 C, the changes in the appearance and the capacity of the batteries after 2000 cycles were observed. Some of the data are shown in Table 1.

Comparative Example 1

(4) The conditions were as same as those in Example 1, except that the material used as the separator was polypropylene having a thickness of 13-18 μm, a porosity of 40%, and a pore size of 0.1-0.3 μm. Then the relevant performances of the batteries were measured according to the method as described in Example 1, and the relevant data are summarized in Table 1.

Example 2

(5) A polypropylene/polyethylene/polypropylene composite membrane with a thickness of 30 μm and a porosity of 50% was put into a 10 wt. % polyacrylonitrile solution in N,N-dimethylformamide and heated to 100° C. The N,N-dimethylformamide was continuously evaporated, and the polyacrylonitrile was precipitated from the solution, and filled into the pores of polypropylene/polyethylene/polypropylene. Thus, a separator comprising polypropylene/polyethylene/polypropylene and polyacrylonitrile in a weight ratio of 49:51 was obtained. The gas permeability was found to be 0 ml/min, as detected by gas permeability test (the same method as in Example 1), no obvious pore structure was found when observed with a scanning electron microscope, and the thickness was 31 μm as detected with a spiral micrometer. This shows that the separator is non-porous.

(6) A mixture of a high pressure LiCoO.sub.2 (Hunan Shanshan Co., Ltd., LC800S), a conductive carbon black and a binder PVDF (in weight ratio of 9:0.4:0.6) was used as the positive electrode, on the surface of which three iron microspheres having a particle size of 0.1 mm were fixed per ampere-hour; a mixture of a modified natural graphite (Shanghai Shanshan Co., Ltd., LA1), a conductive carbon black and a binder PVDF (in a weight ratio of 9:0.3:0.7) was used as the negative electrode; LB-315 (Guotai Huarong Chemical Co., Ltd., Zhangjiagang City, Jiangsu Province, China) was used as the electrolyte; and the above non-porous separator was used as the separator. The positive electrode, negative electrode, electrolyte and separator were rolled up in accordance with a conventional method into a square lithium ion battery. The batteries were subjected to formation and then capacity grading to determine the qualification rate of the batteries. Afterwards, charge and discharge cycles were performed at a discharge depth of 100% between 2.5-4.40V at 1 C, the changes in the appearance and the capacity of the batteries after 500 cycles were observed. Some of the data are shown in Table 1.

Comparative Example 2

(7) The conditions were as same as those in Example 2, except that the material used as the separator was polypropylene having a thickness of 28-32 μm, a porosity of 43%, a pore size of 0.1-0.3 μm, and both sides thereof were coated with a composite film of SiO.sub.2 with a thickness of about 2 microns and a particle size of 100 nm. Then the relevant performances of the batteries were measured according to the method as described in Example 1, and the relevant data are summarized in Table 1.

Example 3

(8) A polyethylene terephthalate membrane with a thickness of 20 μm and a porosity of 45% was put into a 20 wt. % polyvinyl acetate solution in butyl acetate containing 5 wt. % of uniformly dispersed TiO.sub.2 having a particle size of 50 nm, and heated to 70° C., The butyl acetate was continuously evaporated, and the TiO.sub.2-containing polyvinyl acetate was precipitated from the solution, and filled into the pores of polyethylene terephthalate. Thus, a separator comprising polyethylene terephthalate, polyvinyl acetate and TiO.sub.2 in a weight ratio of 46:44:11 was obtained. The gas permeability was found to be 0 ml/min, as detected by gas permeability test (the same method as in Example 1), no obvious pore structure was found when observed with a scanning electron microscope, and the thickness was 20 μm as detected with a spiral micrometer. This shows that the separator is non-porous.

(9) A mixture of a high pressure LiCoO.sub.2 (Hunan Shanshan Co., Ltd., LC800S), a conductive carbon black and a binder PVDF (in a weight ratio of 9:0.4:0.6) was used as the positive electrode, on the surface of which three iron microspheres having a particle size of 0.1 mm were fixed per ampere-hour; a mixture of a modified natural graphite (Shanghai Shanshan Co., Ltd., LA1), a conductive carbon black and a binder PVDF (in a weight ratio of 9:0.3:0.7) was used as the negative electrode; LB-315 (Guotai Huarong Chemical Co., Ltd., Zhangjiagang City, Jiangsu Province, China) was used as the electrolyte; and the above non-porous separator was used as the separator. The positive electrode, negative electrode, electrolyte and separator were rolled up in accordance with a conventional method into a lithium ion battery packaged with a laminated aluminum foil. The batteries were subjected to formation and then capacity grading to determine the qualification rate of the batteries. Afterwards, charge and discharge cycles were performed at a discharge depth of 100% between 2.5-4.40V at 1 C, the changes in the appearance and the capacity of the batteries after 500 cycles were observed. Some of the data are shown in Table 1.

Comparative Example 3

(10) The conditions were as same as those in Example 3, except that the material used as the separator was a three-layered structure of polypropylene/polyethylene/polypropylene having a thickness of 18-22 μm, a porosity of 38%, and a pore size of 0.1-0.3 μm. Then the relevant performances of the batteries were measured according to the method as described in Example 3, and the relevant data are summarized in Table 1.

Example 4

(11) A polyimide fiber cloth with a thickness of 50 μm and a diameter of 200 nm was put into a 2 wt. % aqueous solution of carboxymethyl cellulose containing 0.4 wt. % of uniformly dispersed 20Li.sub.2O-19Al.sub.2O.sub.3—SiO.sub.2-30P.sub.2O.sub.5-25TiO.sub.2-3GeO.sub.2 having a particle size of 50 nm, and heated to 80° C.

(12) The water was continuously evaporated, and the carboxymethyl cellulose containing 20Li.sub.2O-19Al.sub.2O.sub.3—SiO.sub.2-30P.sub.2O.sub.5-25TiO.sub.2-3GeO.sub.2 was precipitated from the solution, and filled into the pores of the polyimide fiber cloth. Thus, a separator comprising a polyimide fiber cloth, carboxymethyl cellulose and 20Li.sub.2O-19Al.sub.2O.sub.3—SiO.sub.2-30P.sub.2O.sub.5-25TiO.sub.2-3GeO.sub.2 in a weight ratio of 30:40:8 was obtained. The gas permeability was found to be 0 ml/min, as detected by gas permeability test (the same method as in Example 1), no obvious pore structure was found when observed with a scanning electron microscope, and the thickness was 20 μm as detected with a spiral micrometer. This shows that the separator is non-porous.

(13) A mixture of Li.sub.1.05Ni.sub.0.8Co.sub.0.1Mn.sub.0.1O.sub.2, a conductive carbon black and a binder PVDF (in a weight ratio of 9:0.4:0.6) was used as the positive electrode, on the surface of which three iron microspheres having a particle size of 0.1 mm were fixed per ampere-hour; a mixture of an artificial graphite (Shanghai Shanshan Co., Ltd., CMS), a conductive carbon black and a binder PVDF (in a weight ratio of 9:0.3:0.7) was used as the negative electrode; LB-315 (Guotai Huarong Chemical Co., Ltd., Zhangjiagang City, Jiangsu Province, China) was used as the electrolyte; and the above non-porous separator was used as the separator. The positive electrode, negative electrode, electrolyte and separator were rolled up in accordance with a conventional method into a square lithium ion battery packaged with a metal aluminum shell. The batteries were subjected to formation and then capacity grading to determine the qualification rate of the batteries. Afterwards, charge and discharge cycles were performed at a discharge depth of 100% between 2.5-4.40V at 1 C, the changes in the appearance and the capacity of the batteries after 1000 cycles were observed. Some of the data are shown in Table 1.

Comparative Example 4

(14) The conditions were as same as those in Example 4, except that the separator used had a thickness of about 50 μm, a porosity of 55%, a pore size of 0.1-0.3 μm, with the middle material being a three-layered structure of polypropylene/polyethylene/polypropylene, and both sides thereof were coated with a polyvinylidene fluoride porous membrane having a thickness of about 5 microns, wherein the polyvinylidene fluoride porous membrane contains Al.sub.2O.sub.3 with a mass ratio of 3 wt. % and a particle size of 60 nm. Then the relevant performances of the batteries were measured according to the method as described in Example 4, and the relevant data are summarized in Table 1.

Example 5

(15) A polyvinylidene fluoride membrane with a thickness of 30 μm, a porosity of 35% and an average pore diameter of 400 nm was put into a 20 wt. % polyacrylonitrile solution in acetonitrile containing 0.2 wt. % of uniformly dispersed Li.sub.2S-3SiS.sub.2-5P.sub.2S.sub.5 having a particle size of 50 nm, and heated to 120° C. The acetonitrile was continuously evaporated, and the Li.sub.2S-3SiS.sub.2-5P.sub.2S.sub.5-containing polyacrylonitrile was precipitated from the solution, and filled into the pores of polyvinylidene fluoride. Thus, a separator comprising a polyvinylidene fluoride membrane, polyacrylonitrile and Li.sub.2S-3SiS.sub.2-5P.sub.2S.sub.5 in a weight ratio of 65:35:0.35 was obtained. The gas permeability was found to be 0 ml/min, as detected by gas permeability test (the same method as in Example 1), no obvious pore structure was found when observed with a scanning electron microscope, and the thickness was 30 μm as detected with a spiral micrometer. This shows that the separator is non-porous.

(16) A mixture of Li.sub.1.05Mn.sub.0.98Co.sub.0.02O.sub.2, a conductive carbon black and a binder PVDF (in a weight ratio of 92:4:4) was used as the positive electrode, on the surface of which three iron microspheres having a particle size of 0.1 mm were fixed per ampere-hour; a mixture of an artificial graphite (Shanghai Shanshan Co., Ltd., CMS), a conductive carbon black and a binder PVDF (in a weight ratio of 9:0.3:0.7) was used as the negative electrode; LB-315 (Guotai Huarong Chemical Co., Ltd., Zhangjiagang City, Jiangsu Province, China) was used as the electrolyte; and the above non-porous separator was used as the separator. The positive electrode, negative electrode, electrolyte and separator were rolled up in accordance with a conventional method into a square lithium ion battery packaged with a laminated aluminum foil. The batteries were subjected to formation and then capacity grading to determine the qualification rate of the batteries. Afterwards, charge and discharge cycles were performed at a discharge depth of 100% between 2.5-4.20V at 1 C, the changes in the appearance and the capacity of the batteries after 500 cycles were observed. Some of the data are shown in Table 1.

Comparative Example 5

(17) The conditions were as same as those in Example 5, except that the separated used was a polyvinylidene fluoride porous membrane having a thickness of about 30 μm, a porosity of 35%, and an average pore diameter of 400 nm. Then the relevant performances of the batteries were measured according to the method as described in Example 5, and the relevant data are summarized in Table 1.

(18) TABLE-US-00001 TABLE 1 Electrochemical performance testing results of Examples 1-5 and Comparative Examples 1-5 Capacity retention Battery Thickness change in rate in the qualification the qualified batteries qualified batteries rate (%) after cycles (%) after cycles (%) Example 1 100 3.2 (2000 cycles) 92 (2000 cycles) Comparative 52 36 (2000 cycles) 65 (2000 cycles) example 1 Example 2 100 4.3 (500 cycles) 86 (500 cycles) Comparative 38 42 (500 cycles) 43 (500 cycles) example 2 Example 3 100 4.2 (500 cycles) 87 (500 cycles) Comparative 39 40 (500 cycles) 46 (500 cycles) example 3 Example 4 100 6.1 (1000 cycles) 83 (1000 cycles) Comparative 61 13.2 (1000 cycles) 71 (1000 cycles) example 4 Example 5 100 2.1 (500 cycles) 88 (1000 cycles) Comparative 31 9.3 (1000 cycles) 61 (1000 cycles) example 5

(19) The comparison between the Examples and Comparative examples with regard to the preparation of lithium ion batteries shows that when used in high energy density batteries, the non-porous separator employed by the present invention not only prevents the micro-short circuit of the batteries and yields a high qualification rate of the battery products, but also results in products having a long cycle life and a small volume change.

(20) The non-porous separator of the present invention is mainly used as a separator for a primary or secondary battery that employs an organic solvent type electrolyte. The negative electrode of the battery is an alkali metal, an alloy of alkali metal, a carboneous material, tin, an alloy of tin, silicon or an alloy of silicon, the positive electrode is MNO.sub.2 (M=one of Li, Na, K, or two or more elements thereof, N=one of Co, Ni, Mn, Co, or two or more elements thereof), MN′PO.sub.4 (N=one of Fe, Mn, Co, or two or more elements thereof) or their dopants or covering materials.