CN115810874A - Isolating membrane, preparation method thereof, secondary battery comprising isolating membrane and electricity utilization device - Google Patents
Isolating membrane, preparation method thereof, secondary battery comprising isolating membrane and electricity utilization device Download PDFInfo
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- CN115810874A CN115810874A CN202210810267.1A CN202210810267A CN115810874A CN 115810874 A CN115810874 A CN 115810874A CN 202210810267 A CN202210810267 A CN 202210810267A CN 115810874 A CN115810874 A CN 115810874A
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- 229940093499 ethyl acetate Drugs 0.000 description 1
- JBTWLSYIZRCDFO-UHFFFAOYSA-N ethyl methyl carbonate Chemical compound CCOC(=O)OC JBTWLSYIZRCDFO-UHFFFAOYSA-N 0.000 description 1
- CYEDOLFRAIXARV-UHFFFAOYSA-N ethyl propyl carbonate Chemical compound CCCOC(=O)OCC CYEDOLFRAIXARV-UHFFFAOYSA-N 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- DWYMPOCYEZONEA-UHFFFAOYSA-L fluoridophosphate Chemical compound [O-]P([O-])(F)=O DWYMPOCYEZONEA-UHFFFAOYSA-L 0.000 description 1
- 239000011737 fluorine Substances 0.000 description 1
- 229910052731 fluorine Inorganic materials 0.000 description 1
- 229910002804 graphite Inorganic materials 0.000 description 1
- 239000010439 graphite Substances 0.000 description 1
- 229910021385 hard carbon Inorganic materials 0.000 description 1
- 230000001939 inductive effect Effects 0.000 description 1
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 1
- DCYOBGZUOMKFPA-UHFFFAOYSA-N iron(2+);iron(3+);octadecacyanide Chemical compound [Fe+2].[Fe+2].[Fe+2].[Fe+3].[Fe+3].[Fe+3].[Fe+3].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-].N#[C-] DCYOBGZUOMKFPA-UHFFFAOYSA-N 0.000 description 1
- 239000003350 kerosene Substances 0.000 description 1
- 238000004898 kneading Methods 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 239000007791 liquid phase Substances 0.000 description 1
- XGZVUEUWXADBQD-UHFFFAOYSA-L lithium carbonate Chemical compound [Li+].[Li+].[O-]C([O-])=O XGZVUEUWXADBQD-UHFFFAOYSA-L 0.000 description 1
- 229910052808 lithium carbonate Inorganic materials 0.000 description 1
- 229910000625 lithium cobalt oxide Inorganic materials 0.000 description 1
- 229910002102 lithium manganese oxide Inorganic materials 0.000 description 1
- FRMOHNDAXZZWQI-UHFFFAOYSA-N lithium manganese(2+) nickel(2+) oxygen(2-) Chemical compound [O-2].[Mn+2].[Ni+2].[Li+] FRMOHNDAXZZWQI-UHFFFAOYSA-N 0.000 description 1
- MHCFAGZWMAWTNR-UHFFFAOYSA-M lithium perchlorate Chemical compound [Li+].[O-]Cl(=O)(=O)=O MHCFAGZWMAWTNR-UHFFFAOYSA-M 0.000 description 1
- 229910001486 lithium perchlorate Inorganic materials 0.000 description 1
- 229910001496 lithium tetrafluoroborate Inorganic materials 0.000 description 1
- IGILRSKEFZLPKG-UHFFFAOYSA-M lithium;difluorophosphinate Chemical compound [Li+].[O-]P(F)(F)=O IGILRSKEFZLPKG-UHFFFAOYSA-M 0.000 description 1
- BFZPBUKRYWOWDV-UHFFFAOYSA-N lithium;oxido(oxo)cobalt Chemical compound [Li+].[O-][Co]=O BFZPBUKRYWOWDV-UHFFFAOYSA-N 0.000 description 1
- VLXXBCXTUVRROQ-UHFFFAOYSA-N lithium;oxido-oxo-(oxomanganiooxy)manganese Chemical compound [Li+].[O-][Mn](=O)O[Mn]=O VLXXBCXTUVRROQ-UHFFFAOYSA-N 0.000 description 1
- URIIGZKXFBNRAU-UHFFFAOYSA-N lithium;oxonickel Chemical class [Li].[Ni]=O URIIGZKXFBNRAU-UHFFFAOYSA-N 0.000 description 1
- MCVFFRWZNYZUIJ-UHFFFAOYSA-M lithium;trifluoromethanesulfonate Chemical compound [Li+].[O-]S(=O)(=O)C(F)(F)F MCVFFRWZNYZUIJ-UHFFFAOYSA-M 0.000 description 1
- 238000005259 measurement Methods 0.000 description 1
- 239000002931 mesocarbon microbead Substances 0.000 description 1
- 229940017219 methyl propionate Drugs 0.000 description 1
- KKQAVHGECIBFRQ-UHFFFAOYSA-N methyl propyl carbonate Chemical compound CCCOC(=O)OC KKQAVHGECIBFRQ-UHFFFAOYSA-N 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- YKYONYBAUNKHLG-UHFFFAOYSA-N n-Propyl acetate Natural products CCCOC(C)=O YKYONYBAUNKHLG-UHFFFAOYSA-N 0.000 description 1
- UUIQMZJEGPQKFD-UHFFFAOYSA-N n-butyric acid methyl ester Natural products CCCC(=O)OC UUIQMZJEGPQKFD-UHFFFAOYSA-N 0.000 description 1
- JOUIQRNQJGXQDC-AXTSPUMRSA-N namn Chemical compound O1[C@@H](COP(O)([O-])=O)[C@H](O)[C@@H](O)[C@@H]1[N+]1=CC=CC(C(O)=O)=C1 JOUIQRNQJGXQDC-AXTSPUMRSA-N 0.000 description 1
- 229910021382 natural graphite Inorganic materials 0.000 description 1
- FPBMTPLRBAEUMV-UHFFFAOYSA-N nickel sodium Chemical compound [Na][Ni] FPBMTPLRBAEUMV-UHFFFAOYSA-N 0.000 description 1
- 239000003921 oil Substances 0.000 description 1
- 238000004806 packaging method and process Methods 0.000 description 1
- 230000000149 penetrating effect Effects 0.000 description 1
- 150000008301 phosphite esters Chemical class 0.000 description 1
- 229920001495 poly(sodium acrylate) polymer Polymers 0.000 description 1
- 229920002961 polybutylene succinate Polymers 0.000 description 1
- 239000004631 polybutylene succinate Substances 0.000 description 1
- 229910000027 potassium carbonate Inorganic materials 0.000 description 1
- 229940090181 propyl acetate Drugs 0.000 description 1
- RUOJZAUFBMNUDX-UHFFFAOYSA-N propylene carbonate Chemical compound CC1COC(=O)O1 RUOJZAUFBMNUDX-UHFFFAOYSA-N 0.000 description 1
- 229960003351 prussian blue Drugs 0.000 description 1
- 239000013225 prussian blue Substances 0.000 description 1
- 238000007789 sealing Methods 0.000 description 1
- 239000002153 silicon-carbon composite material Substances 0.000 description 1
- 229910000029 sodium carbonate Inorganic materials 0.000 description 1
- 235000019812 sodium carboxymethyl cellulose Nutrition 0.000 description 1
- 229920001027 sodium carboxymethylcellulose Polymers 0.000 description 1
- IKULXUCKGDPJMZ-UHFFFAOYSA-N sodium manganese(2+) oxygen(2-) Chemical compound [O-2].[Mn+2].[Na+] IKULXUCKGDPJMZ-UHFFFAOYSA-N 0.000 description 1
- NNMHYFLPFNGQFZ-UHFFFAOYSA-M sodium polyacrylate Chemical compound [Na+].[O-]C(=O)C=C NNMHYFLPFNGQFZ-UHFFFAOYSA-M 0.000 description 1
- 229910021384 soft carbon Inorganic materials 0.000 description 1
- 239000010959 steel Substances 0.000 description 1
- 229920003048 styrene butadiene rubber Polymers 0.000 description 1
- 238000006467 substitution reaction Methods 0.000 description 1
- HXJUTPCZVOIRIF-UHFFFAOYSA-N sulfolane Chemical compound O=S1(=O)CCCC1 HXJUTPCZVOIRIF-UHFFFAOYSA-N 0.000 description 1
- 230000001360 synchronised effect Effects 0.000 description 1
- 239000004250 tert-Butylhydroquinone Substances 0.000 description 1
- 235000019281 tert-butylhydroquinone Nutrition 0.000 description 1
- 239000002562 thickening agent Substances 0.000 description 1
- 239000010936 titanium Substances 0.000 description 1
- NQPDZGIKBAWPEJ-UHFFFAOYSA-N valeric acid Chemical compound CCCCC(O)=O NQPDZGIKBAWPEJ-UHFFFAOYSA-N 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Chemical compound O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
- 238000003466 welding Methods 0.000 description 1
Images
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
- Y02E60/10—Energy storage using batteries
Landscapes
- Cell Separators (AREA)
Abstract
The invention relates to an isolating membrane, a preparation method thereof, a secondary battery and an electric device comprising the isolating membrane, wherein the isolating membrane is a porous isolating membrane; the porosity gradient of the separator film decreases in a direction perpendicular to a thickness direction of the separator film, along a center-to-edge direction of the separator film. After the isolating membrane is assembled into a secondary battery cell, the extruding and refluxing efficiency of electrolyte in a central area can be increased, so that the wettability of the electrolyte to the holes of the pole pieces is enhanced, the problem of lithium precipitation at the center of the pole pieces caused by poor electrolyte infiltration due to insufficient standing time between the charging and discharging processes of the battery is prevented, and the safety performance and the cycle performance of the cell are improved.
Description
Technical Field
The invention relates to the technical field of secondary batteries, in particular to an isolating membrane, a preparation method thereof, a secondary battery comprising the isolating membrane and an electric device comprising the isolating membrane.
Background
Nonaqueous secondary batteries represented by lithium ion batteries have advantages such as high energy density and high operating voltage, and have been widely used in portable electronic devices (mobile phones, computers, cameras) and power battery automobiles.
At present, a common monomer lithium ion battery is assembled by a naked battery cell, and the production mode of the naked battery cell mainly comprises a laminated type and a winding type. In the naked electric core of coiling formula, the two great faces of side area are called big face, and two other side are called the narrow face. In the battery cycle process, the phenomenon of lithium precipitation at the center of the large-area pole piece can be found out easily, and the cycle capacity retention rate of the battery is influenced. In the naked electric core of lamination formula or other types, there is similar phenomenon also in pole piece center.
Disclosure of Invention
The invention aims to provide an isolating membrane, a preparation method thereof, a secondary battery comprising the isolating membrane and an electric device.
To this end, in a first aspect, the present invention provides a separator, which is a porous separator; the porosity gradient of the separator film decreases in a direction perpendicular to a thickness direction of the separator film, along a center-to-edge direction of the separator film.
According to the technical scheme of the invention, the central area of the isolating membrane has better electrolyte extrusion and backflow efficiency compared with the edge area, so that the wettability of electrolyte on the pores of the central area of the pole piece can be enhanced, the problem of lithium precipitation at the center of the pole piece caused by poor electrolyte wettability in the charging and discharging processes of a battery is prevented, and the safety performance and the cycle performance of a battery cell are improved.
In some embodiments, the separator includes a length direction and a width direction in a direction perpendicular to a thickness direction of the separator, and the porosity gradient of the separator decreases along a center-to-edge direction of the separator in the length direction and/or the width direction of the separator.
In some embodiments, the porosity gradient of the separator decreases in a width direction of the separator along a center-to-edge direction of the separator.
In some embodiments, the porosity gradient of the separator decreases along the center-to-edge direction of the separator in the length direction of the separator.
In some embodiments, the porosity gradient of the separator decreases along the center-to-edge direction of the separator in both the width direction and the length direction of the separator.
In some embodiments, the isolation film is sequentially divided into n regions along the direction from the center to the edge of the isolation film in the width direction and/or the length direction of the isolation film, wherein n is a positive integer greater than or equal to 2; for any two regions, the region closer to the center of the separator has a greater porosity than the region farther from the center of the separator.
In some embodiments, the isolation film is sequentially divided into n regions along the direction from the center to the edge of the isolation film in the width direction and/or the length direction of the isolation film, wherein n is a positive integer greater than or equal to 2; wherein a region closest to the center of the separation film is a first region, and a region farthest from the center of the separation film is an nth region; the difference between the porosity of the first region and the porosity of the nth region is 2-20%.
In some embodiments, the porosity of the first region is 30% to 60% and the porosity of the nth region is 20% to 50%.
In some embodiments, the distance from the center to the edge of the isolation film is W, the isolation film is sequentially divided into two regions along the direction from the center to the edge of the isolation film, the range from 0 to 1/3W away from the center of the isolation film is taken as a first region, and the porosity of the first region is 30% to 60%; and taking the range of 1/3W-W away from the center of the isolating membrane as a second area, wherein the porosity of the second area is 20% -50%.
In some embodiments, the thickness of the separation film is 5 to 60 μm.
In some embodiments, the separator is a single layer film or a composite film of two or more layers.
In some embodiments, the material of the isolation film includes one or a combination of two or more selected from the following group: glass fibers, non-woven fabrics, polyvinylidene fluoride, polyolefins (e.g. polyethylene, polypropylene).
In some embodiments, the material of the isolation film is a combination of polyethylene and polypropylene.
In some embodiments, the release film is made of polyolefin and has a molecular weight of 80 to 160 ten thousand.
In a second aspect of the present invention, there is provided a method for preparing the separator according to the first aspect of the present invention, comprising: weighing raw materials for preparing the isolating membrane, wherein the raw materials comprise a substrate, a pore-forming agent and an antioxidant; after uniformly mixing the raw materials, sequentially carrying out extrusion, stretching, extraction and shaping; wherein the stretching step comprises: and stretching in a direction perpendicular to the thickness direction of the separator, wherein the gradient of the stretching ratio is reduced in a direction from the center to the edge of the separator so that the gradient of the porosity is reduced.
According to the technical scheme of the invention, the isolating membrane with gradient change of porosity can be prepared by applying different stretching ratios in the stretching process. The preparation method can be carried out by adopting the existing isolation film production equipment, and has the advantages of simple operation, no increase of cost, good stability and the like.
In some embodiments, the stretching step comprises: stretching along the width direction of the isolating film, and reducing the gradient of stretching multiplying power along the direction from the center to the edge of the isolating film so as to reduce the gradient of porosity; and/or the presence of a gas in the gas,
and stretching along the length direction of the isolating membrane, wherein the gradient of stretching multiplying power is reduced along the direction from the center to the edge of the isolating membrane so as to reduce the gradient of porosity.
In some embodiments, the stretching step comprises: stretching along the width direction of the isolating film, and reducing the gradient of stretching multiplying power along the direction from the center to the edge of the isolating film so as to reduce the gradient of porosity; and, stretching uniformly along the length direction of the separator.
In some embodiments, the stretching step comprises: stretching along the length direction of the isolating membrane, and reducing the gradient of stretching multiplying power along the direction from the center to the edge of the isolating membrane so as to reduce the gradient of porosity; and, stretching uniformly in the width direction of the separator.
In some embodiments, the stretching is performed in the width direction and/or the length direction of the separation film, and the separation film is sequentially divided into n regions in the direction from the center to the edge, where n is a positive integer greater than or equal to 2; for any two regions, a greater stretch ratio is applied to a region closer to the center of the separator than to a region farther from the center of the separator.
In some embodiments, the distance from the center to the edge of the separator is W, and the range of 0 to 1/3W from the center of the separator is a first region, and the first region is stretched at a magnification of 4 to 8 times in the stretching step; and a second region having a range of 1/3W-W from the center of the separator, wherein the second region is stretched at a magnification of 2-4 times in the stretching step.
In some embodiments, the raw materials comprise, in parts by weight: 30-65 parts of base material, 10-40 parts of pore-forming agent and 5-10 parts of antioxidant.
In some embodiments, the substrate comprises one or a combination of two or more selected from the group consisting of: glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride.
In some embodiments, the pore former is an organic pore former and/or an inorganic pore former.
In some embodiments, the antioxidant comprises one or a combination of two or more selected from the group consisting of: 4, 4-thiobis (6-t-butyl-m-cresol), dibutylhydroxytoluene, phosphite, t-butylhydroquinone, N-octadecylcarbonate β - (3, 5-di-t-butyl-4-hydroxyphenyl) propionate, 1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 2-t-butyl-6-methylphenol, N, N' -di- β -naphthylp-phenylenediamine, dilaurylthiodipropionate, tris (nonylphenyl) phosphite, triphenyl phosphite.
The third aspect of the present invention provides a secondary battery, which comprises a positive electrode plate, a negative electrode plate, an electrolyte, and an isolation film located between the positive electrode plate and the negative electrode plate, wherein the isolation film is the isolation film of the first aspect of the present invention.
In some embodiments, the secondary battery is one of a lithium ion battery, a sodium ion battery, or a potassium ion battery.
A fourth aspect of the invention provides a battery module including the secondary battery according to the third aspect of the invention.
A fifth aspect of the invention provides a battery pack including the battery module according to the fourth aspect of the invention.
A sixth aspect of the present invention provides an electric device including at least one of the secondary battery according to the third aspect of the present invention, the battery module according to the fourth aspect of the present invention, or the battery pack according to the fifth aspect of the present invention.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
the isolating membrane provided by the invention has gradient distribution porosity in the length direction and/or the width direction, and the porosity is gradually reduced from the center to the edge direction. After the battery cell is assembled, the extruding efficiency and the backflow efficiency of electrolyte in the central area can be increased, so that the wettability of the electrolyte to the holes of the pole pieces is enhanced, the problem of lithium precipitation in the center of the pole pieces caused by poor electrolyte infiltration due to insufficient standing time between the charging and discharging processes of the battery is prevented, and the safety performance and the cycle performance of the battery cell are improved.
Drawings
Various additional advantages and benefits will become apparent to those of ordinary skill in the art upon reading the following detailed description of the preferred embodiments. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention. Also, like reference numerals are used to refer to like parts throughout the drawings. In the drawings:
FIG. 1 is a schematic view of a separator according to an embodiment of the present invention;
fig. 2 is a schematic view of a secondary battery according to an embodiment of the present invention;
fig. 3 is an exploded view of the secondary battery according to one embodiment of the present invention shown in fig. 2;
fig. 4 is a schematic view of a battery module according to an embodiment of the present invention;
fig. 5 is a schematic view of a battery pack according to an embodiment of the present invention;
fig. 6 is an exploded view of the battery pack according to the embodiment of the present invention shown in fig. 5;
fig. 7 is a schematic diagram of an electric device in which a secondary battery according to an embodiment of the present invention is used as a power source;
description of reference numerals:
1, a battery pack; 2, putting the box body on the box body; 3, a lower box body; 4 a battery module; 5, a lithium ion battery; 51 a housing; 52 an electrode assembly; 53 a cap assembly; 6, isolating membrane; 61 a first region; 62 second region.
Detailed Description
Exemplary embodiments of the present disclosure will be described in more detail below with reference to the accompanying drawings. While exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be embodied in various forms and should not be limited by the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.
The "ranges" disclosed herein are defined in terms of lower limits and upper limits, with a given range being defined by a selection of one lower limit and one upper limit that define the boundaries of the particular range. Ranges defined in this manner are inclusive and combinable in any manner, i.e., any lower limit may be combined with any upper limit to form a range.
All embodiments and alternative embodiments of the invention may be combined with each other to form new solutions, if not specified otherwise.
All technical and optional features of the invention may be combined with each other to form new solutions, if not otherwise specified.
All steps of the present invention may be performed sequentially or randomly, preferably sequentially, if not specifically stated. For example, the method comprises steps (a) and (b), meaning that the method may comprise steps (a) and (b) performed sequentially, and may also comprise steps (b) and (a) performed sequentially.
In the prior art, a secondary battery, for example, a lithium ion battery, is a common single lithium ion battery assembled from bare cells, and the production method of the bare cells mainly includes a lamination type and a winding type. In the naked electric core of coiling formula, the two great faces of side area are called big face, and two other side are called the narrow face. In the battery cycle process, the phenomenon of lithium precipitation can be found easily to occur in the center of the large-area pole piece, and the cycle capacity retention rate of the battery is influenced. In the naked electric core of lamination formula or other types, there is similar phenomenon also in pole piece center.
In order to solve the above problems, the present invention has been made by first exploring and analyzing the causes of the above defects. The pole piece of the lithium ion battery has a porous structure, a skeleton of the porous structure is formed by solids such as active substances, conductive agents, binding agents and the like, and electrolyte is filled in pores. In the charge-discharge cycle process of the lithium ion battery, the active substances on the positive pole piece and the negative pole piece are subjected to lithium desorption and can cause the shrinkage or expansion of the volume of the pole pieces, and because the lithium ion battery is subjected to certain pretightening force in a module or a battery pack, the expansion of the volume of the pole pieces is limited to a certain extent, the expansion of solids on the pole pieces can cause the reduction of the volume of pores of the pole pieces, and therefore electrolyte in the pores of the pole pieces is extruded out of the outer space of the pole pieces. Based on similar principle, when the pole piece contracts, the pore volume of the pole piece is increased, and the electrolyte in the outer space of the pole piece is sucked into the pores of the pole piece. During the circulation process of the lithium ion battery, the phenomena of contraction and expansion of the pole piece along with extrusion and absorption of electrolyte are always generated.
Taking a winding type battery cell as an example, in the battery circulation process, because the volume change of the central area of the large-area pole piece is larger than the volume change of the side of the large-area pole piece provided with the pole lug and the opposite side edge area thereof, the amount of the electrolyte extruded or sucked from the central area of the large-area pole piece is also higher than that of the two side edge areas. If the standing time of the battery cell during charge and discharge cycles is too short, the extruded electrolyte cannot be sucked into the pores of the pole piece, so that the electrolyte is poorly infiltrated, the retention rate of the circulating capacity is influenced slightly, and lithium is separated from the center of the large surface of the battery cell heavily.
In addition, similar situations exist for the laminated cell, and the volume change of the central area of the pole piece is larger than the volume change of the side, provided with the pole lug, of the pole piece and the opposite side edge area of the pole piece, so that poor electrolyte infiltration is easily caused in the central area of the pole piece, the retention rate of the circulating capacity is influenced, and the phenomenon of lithium precipitation is caused.
Based on this, the invention proposes the following technical solutions and specific embodiments.
In some embodiments, there is provided a separator, the separator being a porous separator; the porosity gradient of the separator decreases in a direction perpendicular to the thickness direction of the separator, along the center-to-edge direction of the separator.
The following terms are defined and/or interpreted to better understand the invention:
"width direction", also known as transverse direction, abbreviated as TD; the "length direction" is also called machine direction, abbreviated as MD. In the case of a film-like separator having a three-dimensional (XYZ) structure, which has a structure in which the Z dimension is significantly smaller than the X dimension and the Y dimension thereof, the X dimension is defined as the thickness direction, the X dimension is defined as the length direction, the Y dimension is defined as the width direction, and Z < Y ≦ X. It should be noted that, since the separator is generally used for preparing a folded or wound cell, it has the feature of Y < X, that is, in some embodiments, the length of the separator is greater than the width of the separator; in addition, according to the technical solution of the present invention, when the separation film is used for preparing other kinds of battery cells, the separation film may also have a characteristic of Y = X, that is, in some embodiments, the length of the separation film is equal to the width of the separation film.
Therefore, the porosity distribution characteristics of the separator can be described from the length direction, the width direction, and the thickness direction, respectively. According to the technical scheme of the invention, the porosity distribution of the separation film is defined along the direction vertical to the thickness direction (namely the length direction and/or the width direction) of the separation film; the separator of the present invention may have uniform porosity in the thickness direction, without being limited in the thickness direction of the separator.
"center" refers to a point along a selected dimension of the separator that is equidistant from both edges of the separator.
The central area of the isolating film has higher porosity compared with the edge area, so that the isolating film can be beneficial to the extrusion and backflow of electrolyte, and the wettability of the electrolyte on the pores of the central area of the pole piece is enhanced, thereby preventing the problem of lithium precipitation at the center of the large-area pole piece caused by poor electrolyte wettability in the circulating process.
In some embodiments, the porosity gradient of the separator decreases in the width direction and/or the length direction of the separator along the center-to-edge direction of the separator.
In some embodiments, the porosity gradient of the separator decreases along the center-to-edge direction of the separator in the width direction of the separator.
In some embodiments, the porosity gradient of the separator decreases along the center-to-edge direction of the separator in the width direction of the separator; the separator has uniform porosity along its length.
The person skilled in the art knows that, no matter for coiled battery cell or laminated battery cell, the barrier film with length greater than width is adopted for assembly. The winding type battery cell comprises a positive pole piece, an isolating film and a negative pole piece which are sequentially laminated, then winding is carried out, and a pole lug is arranged; this makes two edges of the isolating film along the width direction, the side provided with the pole ear of the large-face pole piece and the opposite side edge thereof oppositely arranged. When the isolating film has the porosity which is reduced in gradient from the center to the edge direction in the width direction, the porosity of the central area of the isolating film is larger than that of the edge area, so that the extruding and the refluxing of electrolyte can be facilitated, the wettability of the electrolyte to the pores of the central area of the large-area pole piece is enhanced, and the problem of lithium precipitation in the center of the large-area pole piece caused by poor electrolyte wetting in the circulating process is solved.
In the laminated cell, positive and negative single sheets are alternately placed on a Z-shaped folded isolating membrane to be stacked, and tabs are arranged; this makes the two edges of the isolating film along the width direction, the side of the pole piece provided with the pole ear and the opposite side edge thereof oppositely arranged. When the isolating membrane has the porosity which is reduced in gradient from the center to the edge direction in the width direction, the porosity of the central area of the isolating membrane is larger than that of the edge area, so that the extruding and the refluxing of electrolyte can be facilitated, the wettability of the electrolyte to the pores of the central area of the pole piece is enhanced, and the problem of lithium precipitation at the center of the pole piece caused by poor electrolyte wetting in the circulating process is prevented.
In some embodiments, the porosity gradient of the separator decreases in the width direction and the length direction of the separator along the center-to-edge direction of the separator.
There are other types of cells in the art, such as cells assembled by stacking a positive electrode monolith, a separator monolith, and a negative electrode monolith in this order, and providing tabs. When the isolating film has the porosity which is reduced in gradient from the center to the edge direction in the width direction and the length direction, the porosity of the central area of the isolating film is larger than that of the edge area, so that the electrolyte can be extruded and reflowed, the wettability of the electrolyte to the pores of the central area of the pole piece is enhanced, and the problem of lithium precipitation at the center of the pole piece caused by poor electrolyte infiltration in the circulating process is solved.
In some embodiments, the separator has a porosity gradient that decreases along a center-to-edge direction of the separator in a length direction of the separator. When the isolating membrane is applied to the battery core, the wettability of electrolyte on the holes of the central area of the pole piece can be enhanced to a certain degree, so that the problem of lithium precipitation at the center of the pole piece caused by poor electrolyte wetting in the circulating process is solved.
In some embodiments, the isolation film is sequentially divided into n regions along a center-to-edge direction of the isolation film in a width direction of the isolation film, wherein n is a positive integer greater than or equal to 2; wherein a region closest to the center of the separation film is a first region, and a region farthest from the center of the separation film is an nth region; for any two regions, the region closer to the center of the separator has greater porosity relative to the region farther from the center of the separator. Wherein n can take values of 2, 3, 4, 5, etc., and is preferably 2 or 3 for processing.
In some embodiments, the isolation film is sequentially divided into n regions along the direction from the center to the edge of the isolation film in the length direction of the isolation film, wherein n is a positive integer greater than or equal to 2; wherein a region closest to the center of the separation film is a first region, and a region farthest from the center of the separation film is an nth region; for any two regions, the region closer to the center of the separator has a greater porosity than the region farther from the center of the separator. Wherein n can take the values of 2, 3, 4, 5 and the like, and is preferably 2 or 3 for the convenience of processing.
In some embodiments, the isolation film is sequentially divided into n regions along the direction from the center to the edge of the isolation film in the width direction and the length direction of the isolation film, wherein n is a positive integer greater than or equal to 2; wherein a region closest to the center of the separation film is a first region, and a region farthest from the center of the separation film is an nth region; for any two regions, the region closer to the center of the separator has greater porosity relative to the region farther from the center of the separator. Wherein n can take the values of 2, 3, 4, 5 and the like.
In some embodiments, the difference between the porosity of the first region and the porosity of the nth region is from 2% to 20%; for example, 2%, 4%, 5%, 8%, 10%, 12%, 15%, 17%, 20%, etc.
According to the technical scheme of the invention, if the difference value of the porosity of the first area and the porosity of the nth area is too small, the difference of ions in electrolyte penetrating through the central area and the edge area of the isolating membrane cannot be reflected; if the difference is too large, the difference between the concentrations of electrolyte ions in the pores of the central region and the edge region of the separator is too large, which results in a large polarization difference and thus non-uniform lithium intercalation.
In some embodiments, the first region has a porosity of 30% to 60%, e.g., 30%, 35%, 40%, 45%, 50%, 55%, 60%, etc.; the nth region has a porosity of 20% to 50%, such as 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc.
According to the technical scheme of the invention, the porosity of the first region is 30-60%; the porosity of the nth region is 20-50%. During charging, because the lithium intercalation kinetics of the negative electrode are slow, if the porosity is too large (for example, greater than 60%), the lithium ion concentration on the surface of the negative electrode is too high, and lithium precipitation is easy to occur; if the porosity is too small (for example, less than 20%), the resistance of lithium ions passing through the separator is too large, and the liquid phase polarization is large, which causes the voltage to reach the cut-off voltage earlier, resulting in a reduction in the capacity actually exerted, but the risk of negative electrode lithium deposition during charging is reduced.
Fig. 1 is a separator 6 as an example. Referring to fig. 1, in the width direction of the separator 6, the distance from the center to the edge of the separator 6 is W, the range of 0 to 1/3W from the center of the separator is a first region 61, and the porosity of the first region 61 is 30% to 60%; the range of 1/3W-W from the center of the separator 6 is a second region 62, and the porosity of the second region 62 is 20% -50%.
In some embodiments, the separator has a thickness of 5 to 60 μm; for example, 5 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 55 μm, 60 μm, etc.
According to the technical scheme of the invention, if the thickness of the isolating membrane is too thin and the mechanical strength is low, the isolating membrane is easy to pierce to cause short circuit in the battery cell during lithium precipitation, so that thermal runaway is caused; if the thickness of the isolating film is too thick, the energy density of the cell volume is reduced.
In some embodiments, the separator is a single layer film or a composite film of two or more layers.
In some embodiments, the material of the isolation film includes one or a combination of two or more selected from the following group: glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride.
In some embodiments, there is provided a method for preparing the separator of the present invention, comprising: weighing raw materials for preparing the isolating membrane, wherein the raw materials comprise a base material, a pore-forming agent and an antioxidant; after the raw materials are uniformly mixed, sequentially carrying out extrusion, stretching, extraction and shaping; wherein the stretching step comprises: and stretching in a direction perpendicular to the thickness direction of the separator, wherein the gradient of the stretching magnification is reduced in a direction from the center to the edge of the separator to reduce the gradient of the porosity.
The isolating membrane with gradient change of porosity can be prepared by applying different stretching multiplying powers in the stretching process. The preparation method can be carried out by adopting the existing isolation film production equipment, and has the advantages of simple operation, no increase of cost, good stability and the like.
In some embodiments, the stretching step comprises: stretching along the width direction of the isolating film, and reducing the gradient of stretching multiplying power along the direction from the center to the edge of the isolating film so as to reduce the gradient of porosity; and (c) and (d),
and stretching along the length direction of the isolating membrane, wherein the gradient of stretching multiplying power is reduced along the direction from the center to the edge of the isolating membrane so as to reduce the gradient of porosity.
In some embodiments, the stretching step comprises: stretching along the width direction of the isolating film, and reducing the gradient of stretching multiplying power along the direction from the center to the edge of the isolating film so as to reduce the gradient of porosity; and the combination of (a) and (b),
and uniformly stretching along the length direction of the isolating membrane.
In some embodiments, the stretching step comprises: stretching along the length direction of the isolating membrane, and reducing the gradient of stretching multiplying power along the direction from the center to the edge of the isolating membrane so as to reduce the gradient of porosity; and uniformly stretching along the width direction of the separation film.
In some embodiments, the isolation film is sequentially divided into n regions along a direction from the center to the edge of the isolation film in a width direction of the isolation film, wherein n is a positive integer greater than or equal to 2; wherein a region closest to the center of the separation film is a first region, and a region farthest from the center of the separation film is an nth region; the stretching is performed in the width direction of the separator, and for any two regions, a region closer to the center of the separator is applied with a larger stretch ratio than a region farther from the center of the separator.
In some embodiments, the isolation film is sequentially divided into n regions along the direction from the center to the edge of the isolation film in the length direction of the isolation film, wherein n is a positive integer greater than or equal to 2; wherein a region closest to the center of the separation film is a first region, and a region farthest from the center of the separation film is an nth region; the stretching is performed in the longitudinal direction of the separator, and for any two regions, a region closer to the center of the separator is applied with a greater stretch ratio than a region farther from the center of the separator.
In some embodiments, the isolation film is sequentially divided into n regions along the direction from the center to the edge of the isolation film in the width direction and the length direction of the isolation film, wherein n is a positive integer greater than or equal to 2; wherein a region closest to the center of the separation film is a first region, and a region farthest from the center of the separation film is an nth region; the stretching is performed in the width direction and the length direction of the separator, and for any two regions, a region closer to the center of the separator is applied with a larger stretch ratio than a region farther from the center of the separator.
In some embodiments, the first region is stretched 4 to 8 times, e.g., 4 times, 5 times, 6 times, 7 times, 8 times, etc., in the stretching step; the nth region is stretched at a magnification of 2 to 4 times, for example, 2 times, 2.5 times, 3 times, 3.5 times, 4 times, etc. in the stretching step.
In some embodiments, the distance from the center to the edge of the separator in the width direction of the separator is W, and the range of 0 to 1/3W from the center of the separator is a first region, the first region being stretched at a magnification of 4 to 8 times in the stretching step; the range of 1/3W-W from the center of the separation film is used as a second area, and the magnification of the second area which is stretched in the stretching step is 2-4 times.
In some embodiments, the raw materials comprise, in parts by weight: 30-65 parts of base material, 10-40 parts of pore-forming agent and 5-10 parts of antioxidant. For example, the weight parts of the substrate may be selected from 30 parts, 40 parts, 50 parts, 60 parts, 65 parts, etc.; the weight portion of the pore-forming agent can be selected from 10 portions, 20 portions, 30 portions, 40 portions and the like; the weight parts of the antioxidant can be selected from 5 parts, 6 parts, 8 parts, 10 parts and the like.
In some embodiments, the substrate comprises one or a combination of two or more selected from the group consisting of: glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride.
In some embodiments, the pore former is an organic pore former and/or an inorganic pore former. For example, the organic pore former may include one or a combination of two or more selected from the group consisting of: white oil, paraffin oil, kerosene or dioctyl phthalate (DOP). For example, the inorganic pore former may include one or a combination of two or more selected from the group consisting of: sodium carbonate, potassium carbonate, lithium carbonate, cobalt carbonate, ammonium bicarbonate, ammonium chloride and ammonium nitrate.
In some embodiments, the antioxidant comprises one or a combination of two or more selected from the group consisting of: 4, 4-thiobis (6-tert-butyl-m-cresol), dibutylhydroxytoluene, phosphite, tert-butylhydroquinone, N-octadecylcarbonate β - (3, 5-di-tert-butyl-4-hydroxyphenyl) propionate, 1, 3-tris (2-methyl-4-hydroxy-5-tert-butylphenyl) butane, 2-tert-butyl-6-methylphenol, N, N' -di-beta-naphthylp-phenylenediamine, dilaurylthiodipropionate, tris (nonylphenyl) phosphite, triphenyl phosphite.
In some embodiments, there is provided a method for preparing a separator according to the present invention, comprising:
1) Feeding: weighing raw materials including a substrate, a pore-forming agent and an antioxidant, uniformly mixing the raw materials, and conveying the mixture to an extrusion system.
2) Extruding: the raw materials in the step 1) are processed by a twin-screw extruder at the temperature of 160-200 ℃ to obtain high-temperature melt, then the high-temperature melt is accurately metered by a melt pump and then is sent into a die head to be extruded from a slit opening of the die head, and the extruded high-temperature melt is processed by a chilling roller to obtain an extruded cast sheet.
3) Stretching: feeding the extruded cast sheet obtained in the step 2) into a synchronous stretcher or an asynchronous stretcher, and synchronously or asynchronously stretching in the extension direction (MD) and the width direction (TD) to obtain a film containing a pore-forming agent;
4) And (3) extraction: soaking the film containing the pore-forming agent obtained in the step 3) in an organic solvent for 10-20 minutes to fully remove the pore-forming agent in the film, and then drying to volatilize the organic solvent to form the film containing micropores, wherein the drying temperature is 35-45 ℃.
5) Shaping: and 4) fully eliminating internal stress of the film containing the micropores obtained in the step 4) at the temperature of 120-150 ℃, and shaping to obtain the isolating membrane.
In some embodiments, step 6) of slitting is further included after step 5): cutting the isolating membrane prepared in the step 5) into a finished membrane according to the specification requirement of the battery cell.
In some embodiments, a secondary battery is provided, which comprises a positive electrode plate, a negative electrode plate, an electrolyte and the isolating membrane of the invention; the isolation film is positioned between the positive pole piece and the negative pole piece. The secondary battery may be, for example, a lithium ion battery, a sodium ion battery, or a potassium ion battery.
[ Positive electrode sheet ]
The positive pole piece comprises a positive pole current collector and a positive pole material arranged on at least one surface of the positive pole current collector, wherein the positive pole material comprises a positive pole active material.
In some embodiments, the positive electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, aluminum foil may be used. The composite current collector may include a polymer material base layer and a metal layer formed on at least one surface of the polymer material base layer. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a base material of a polymer material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, when the secondary battery is a lithium ion battery, the positive active material may be a positive active material for a lithium ion battery, which is well known in the art. As an example, the positive electrode active material may include at least one of the following materials: olivine structured lithium-containing phosphates, lithium transition metal oxides and their respective modified compounds. However, the present invention is not limited to these materials, and other conventional materials that can be used as a positive electrode active material of a battery may be used. These positive electrode active materials may be used alone or in combination of two or more. Among them, examples of the lithium transition metal oxide may include, but are not limited to, lithium cobalt oxide (e.g., liCoO) 2 ) Lithium nickel oxides (e.g., liNiO) 2 ) Lithium manganese oxide (e.g., liMnO) 2 、LiMn 2 O 4 ) Lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide (e.g., liNi) 1/3 Co 1/ 3 Mn 1/3 O 2 (may also be abbreviated as NCM) 333 )、LiNi 0.5 Co 0.2 Mn 0.3 O 2 (may also be abbreviated as NCM) 523 )、LiNi 0.5 Co 0.25 Mn 0.25 O 2 (may also be abbreviated as NCM) 211 )、LiNi 0.6 Co 0.2 Mn 0.2 O 2 (may also be abbreviated as NCM) 622 )、LiNi 0.8 Co 0.1 Mn 0.1 O 2 (may also be abbreviated as NCM) 811 ) Lithium nickel cobalt aluminum oxides (e.g., liNi) 0.85 Co 0.15 Al 0.05 O 2 ) And modified compounds thereof, and the like. Examples of olivine structured lithium-containing phosphates may include, but are not limited to, lithium iron phosphate (e.g., liFePO) 4 (also referred to as LFP), a composite material of lithium iron phosphate and carbon, and lithium manganese phosphate (e.g., lithium manganese phosphate)LiMnPO 4 ) At least one of a composite material of lithium manganese phosphate and carbon, lithium iron manganese phosphate, and a composite material of lithium iron manganese phosphate and carbon.
In some embodiments, when the secondary battery is a sodium ion battery, the positive active material may be a positive active material for a sodium ion battery, which is well known in the art. As an example, only one kind of the positive electrode active material may be used alone, or two or more kinds may be combined. Wherein the positive electrode active material is selected from sodium-iron composite oxide (NaFeO) 2 ) Sodium cobalt composite oxide (NaCoO) 2 ) Sodium chromium composite oxide (NaCrO) 2 ) Sodium manganese oxide (NaMnO) 2 ) Sodium nickel composite oxide (NaNiO) 2 ) Sodium nickel titanium composite oxide (NaNi) 1/2 Ti 1/2 O 2 ) Sodium nickel manganese composite oxide (NaNi) 1/2 Mn 1/2 O 2 ) Sodium-iron-manganese composite oxide (Na) 2/3 Fe 1/3 Mn 2/3 O 2 ) Sodium nickel cobalt manganese complex oxide (NaNi) 1/3 Co 1/3 Mn 1/3 O 2 ) Sodium iron phosphate compound (NaFePO) 4 ) Sodium manganese phosphate compound (NaMn) P O 4 ) Sodium cobalt phosphate compound (NaCoPO) 4 ) Prussian blue-based material, polyanionic material (phosphate, fluorophosphate, pyrophosphate, sulfate), etc., but the present invention is not limited to these materials, and other conventionally known materials that can be used as a positive electrode active material for a sodium ion battery may be used in the present invention.
In some embodiments, the positive electrode material further optionally comprises a binder. For example, the binder may include one or a combination of two or more selected from the group consisting of: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer and fluorine-containing acrylate resin.
In some embodiments, the positive electrode material further optionally includes a conductive agent. For example, the conductive agent may include one or a combination of two or more selected from the group consisting of: super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers.
In some embodiments, the positive electrode sheet may be prepared by: dispersing the above-mentioned positive electrode material, such as a positive electrode active material, a conductive agent, a binder, and any other components, in a solvent (such as N-methylpyrrolidone) to form a positive electrode slurry; and coating the positive electrode slurry on a positive electrode current collector, and drying, cold pressing and the like to obtain the positive electrode piece.
[ negative electrode sheet ]
The negative pole piece comprises a negative pole current collector and a negative pole material arranged on at least one surface of the negative pole current collector, wherein the negative pole material comprises a negative pole active material.
In some embodiments, the negative electrode current collector may employ a metal foil or a composite current collector. For example, as the metal foil, a copper foil can be used. The composite current collector may include a polymer base layer and a metal layer formed on at least one surface of the polymer base material. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel alloy, titanium alloy, silver alloy, etc.) on a polymer base material (e.g., a base material of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).
In some embodiments, the negative active material may employ a negative active material for a battery known in the art. For example, the anode active material includes one or a combination of two or more selected from the group consisting of: natural graphite, artificial graphite, mesophase micro carbon spheres (MCMB), hard carbon, soft carbon, silicon-carbon composite, li-Sn alloy, li-Sn-O alloy, sn, snO 2 、TiO 2 -Li 4 Ti 5 O 12 And Li-Al alloy. However, the present invention is not limited to these materials, and other conventional materials that can be used as a negative active material for a lithium ion battery may be used. These negative electrode active materials may be used alone or in combination of two or more.
In some embodiments, the anode material further optionally includes a binder. For example, the binder may include one or a combination of two or more selected from the group consisting of: styrene Butadiene Rubber (SBR), polyacrylic acid (PAA), sodium Polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium Alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).
In some embodiments, the anode material further optionally includes a conductive agent. For example, the conductive agent may include one or a combination of two or more selected from the group consisting of: super P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, carbon nanofibers.
In some embodiments, the anode material may also optionally include other adjuvants. For example, the other adjuvant may be a thickener such as sodium carboxymethylcellulose (CMC-Na).
In some embodiments, the negative electrode sheet can be prepared by: dispersing the above-mentioned negative electrode material, for example, a negative electrode active material, a conductive agent, a binder, and any other components in a solvent (for example, deionized water) to form a negative electrode slurry; and coating the negative electrode slurry on a negative electrode current collector, and drying, cold pressing and the like to obtain the negative electrode pole piece.
[ electrolyte ]
The electrolyte plays a role in conducting ions between the positive pole piece and the negative pole piece. The electrolyte includes an electrolyte salt and a solvent.
In some embodiments, the electrolyte salt can be selected from at least one of lithium hexafluorophosphate, lithium tetrafluoroborate, lithium perchlorate, lithium hexafluoroarsenate, lithium bis-fluorosulfonylimide, lithium bis-trifluoromethanesulfonylimide, lithium trifluoromethanesulfonate, lithium difluorophosphate, lithium difluorooxalato borate, lithium dioxaoxalato borate, lithium difluorooxalato phosphate, and lithium tetrafluorooxalato phosphate.
In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, ethyl methyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, propyl methyl carbonate, propyl ethyl carbonate, butylene carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1, 4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.
In some embodiments, the electrolyte further optionally includes an additive. For example, the additives may include a negative electrode film-forming additive, a positive electrode film-forming additive, and may further include additives capable of improving certain properties of the battery, such as an additive for improving overcharge properties of the battery, an additive for improving high-temperature or low-temperature properties of the battery, and the like.
[ isolation film ]
The isolating membrane of the invention is applied.
[ production of Secondary Battery ]
In some embodiments, the positive electrode tab, the negative electrode tab, and the separator may be manufactured into an electrode assembly through a winding process or a lamination process.
In some embodiments, the secondary battery may include an exterior package. The exterior package may be used to enclose the electrode assembly and the electrolyte.
In some embodiments, the outer package of the secondary battery may be a hard case, such as a hard plastic case, an aluminum case, a steel case, or the like. The outer package of the secondary battery may also be a pouch, such as a pouch-type pouch. The material of the soft bag may be plastic, and examples of the plastic include polypropylene, polybutylene terephthalate, polybutylene succinate, and the like.
The shape of the secondary battery is not particularly limited in the present invention, and may be a cylindrical shape, a square shape, or any other arbitrary shape. For example, fig. 2 is a secondary battery 5 of a square structure as an example.
In some embodiments, referring to fig. 3, the outer package may include a housing 51 and a cover plate 53. The housing 51 may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose to form an accommodating cavity. The housing 51 has an opening communicating with the accommodating chamber, and a cover plate 53 can be provided to cover the opening to close the accommodating chamber. The positive electrode tab, the negative electrode tab, and the separator may be formed into the electrode assembly 52 through a winding process or a lamination process. An electrode assembly 52 is enclosed within the receiving cavity. The electrolyte is impregnated into the electrode assembly 52. The number of electrode assemblies 52 contained in the secondary battery 5 may be one or more, and those skilled in the art can select them according to the actual needs.
In some embodiments, the secondary batteries may be assembled into a battery module, and the number of the secondary batteries contained in the battery module may be one or more, and the specific number may be selected by those skilled in the art according to the application and capacity of the battery module.
Fig. 4 is a battery module 4 as an example. Referring to fig. 4, in the battery module 4, a plurality of secondary batteries 5 may be arranged in series along the longitudinal direction of the battery module 4. Of course, the arrangement may be in any other manner. The plurality of secondary batteries 5 may be further fixed by a fastener.
Alternatively, the battery module 4 may further include a case having an accommodation space in which the plurality of secondary batteries 5 are accommodated.
In some embodiments, the battery modules 4 may be assembled into a battery pack, and the number of the battery modules contained in the battery pack may be one or more, and the specific number may be selected by one skilled in the art according to the application and the capacity of the battery pack.
Fig. 5 and 6 are a battery pack 1 as an example. Referring to fig. 5 and 6, a battery pack 1 may include a battery case and a plurality of battery modules 4 disposed in the battery case. The battery box comprises an upper box body 2 and a lower box body 3, wherein the upper box body 2 can be covered on the lower box body 3 and forms a closed space for accommodating the battery module 4. A plurality of battery modules 4 may be arranged in any manner in the battery box.
In addition, the invention also provides an electric device which comprises the secondary battery provided by the invention. In some embodiments, the powered device comprises at least one of a battery module or a battery pack provided by the present invention. The secondary battery, the battery module, or the battery pack may be used as a power source of the electric device, and may also be used as an energy storage unit of the electric device. The powered device may include a mobile device (e.g., a mobile phone, a laptop computer, etc.), an electric vehicle (e.g., a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc.), an electric train, a ship, a satellite, an energy storage system, etc., but is not limited thereto.
As the electricity-using device, a secondary battery, a battery module, or a battery pack may be selected according to the use requirement thereof.
Fig. 7 is an electric device as an example. The electric device is a pure electric vehicle, a hybrid electric vehicle or a plug-in hybrid electric vehicle and the like. In order to meet the demand of the electric device for high power and high energy density of the secondary battery, a battery pack or a battery module may be used.
As another example, the device may be a cell phone, tablet, laptop, etc. The device is generally required to be thin and light, and a secondary battery may be used as a power source.
Example 1
(1) Weighing the following raw materials in parts by weight and uniformly mixing: 62 parts of polyethylene with the average molecular weight of 120 ten thousand, 30 parts of paraffin oil and 8 parts of phosphite ester.
(2) The raw materials uniformly mixed in the step (1) are processed by a double-screw extruder at 180 ℃ to obtain a high-temperature melt, the high-temperature melt is accurately metered by a melt pump and then is fed into a die head, the high-temperature melt fed into the die head flows out from a die head slit, and the high-temperature melt flowing out from the die head slit is processed by a chill roll to obtain an extruded cast sheet;
(3) Feeding the extruded casting sheet into a bidirectional asynchronous stretching machine, and stretching by 3 times along the length direction (MD); stretching the film in different regions along the width direction (TD), wherein the region close to the center is stretched by 1.6 times, and the region close to the edge is stretched by 1.5 times to obtain a film containing a pore-forming agent; the pore-forming agent-containing film has a distance W between the center and the edge in the width direction (TD), a region 0 to 1/3W from the center is stretched 1.6 times in the width direction, and a region 1/3W to W from the center is stretched 1.5 times in the width direction;
(4) Fully soaking the film containing the pore-forming agent obtained in the step (3) for 20min by using dichloromethane, removing the pore-forming agent, and drying at 40 ℃ to volatilize the organic solvent to prepare a microporous film;
(5) And (5) preserving the heat of the microporous isolating membrane obtained in the step (4) in a high-temperature shaping device at the temperature of 130 ℃ for 6 hours, and fully removing membrane stress to obtain the isolating membrane I-1 with the thickness of 20 microns. And cutting the prepared isolating membrane into a finished membrane according to the specification requirement of the battery cell.
Example 2
A separator I-2 was obtained in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film was stretched 5.9 times in the width direction (TD) in the region of 0 to 1/3W from the center and 5.3 times in the width direction in the region of 1/3W to W from the center at a distance W from the center.
Example 3
A separator I-3 was produced in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film is stretched in the width direction (TD) by a distance W from the center to the edge, by a factor of 2.5 in the width direction in a region of 0 to 1/3W from the center, and by a factor of 2 in the width direction in a region of 1/3W to W from the center.
Example 4
A separator I-4 was obtained in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film was stretched in the width direction (TD) by 3.6 times in the width direction in the region of 0 to 1/3W from the center and 2.4 times in the width direction in the region of 1/3W to W from the center at a distance W from the center.
Example 5
A separator I-5 was prepared in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film was stretched in the width direction (TD) by 4.2 times in the width direction in a region of 0 to 1/3W from the center and 2.9 times in the width direction in a region of 1/3W to W from the center at a distance W from the center.
Example 6
A separator I-6 was obtained in the same manner as in example 1, except for the following parameters.
In the step (3), the pore-forming agent-containing film is stretched in the width direction (TD) by a distance W between the center and the edge of the film, 4.2 times in the width direction for a region 0 to 1/3W from the center, and 2.4 times in the width direction for a region 1/3W to W from the center.
Example 7
A separator I-7 was produced in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film was stretched in the width direction (TD) by a distance W between the center and the edge, 4.8 times in the width direction for the region 0 to 1/3W from the center, and 2.9 times in the width direction for the region 1/3W to W from the center.
Example 8
A separator I-8 was obtained in the same manner as in example 1, except for the following parameters.
In the step (3), the pore-forming agent-containing film is stretched 7 times in the width direction (TD) in a region of 0 to 1/3W from the center and 5.3 times in the width direction in a region of 1/3W to W from the center at a distance W from the center.
Example 9
A separator I-9 was obtained in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film was stretched in the width direction (TD) by a distance W from the center to the edge, by 5.9 times in the width direction in a region of 0 to 1/3W from the center, and by 3.5 times in the width direction in a region of 1/3W to W from the center.
Example 10
A separator I-10 was produced in the same manner as in example 1, except for the following parameters.
In the step (3), the pore-forming agent-containing film is stretched 5.3 times in the width direction (TD) in a region of 0 to 1/3W from the center and 2.9 times in the width direction in a region of 1/3W to W from the center at a distance W from the center.
Example 11
A separator I-7 was produced in the same manner as in example 1, except for the following parameters.
In the step (3), the pore-forming agent-containing film is stretched by 7 times in the width direction (TD) in a region of 0 to 1/3W from the center and 4.1 times in the width direction in a region of 1/3W to W from the center at a distance W from the center.
Comparative example 1
A separator II-1 was produced in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film was stretched in the width direction (TD) by 1.6 times in the width direction in the region of 0 to 1/3W from the center and 1.7 times in the width direction in the region of 1/3W to W from the center at a distance W from the center.
Comparative example 2
A separator II-2 was produced in the same manner as in example 1, except for the following parameters.
In the step (3), the pore-forming agent-containing film is stretched 2.5 times in the width direction (TD) in a region of 0 to 1/3W from the center and 2.4 times in the width direction in a region of 1/3W to W from the center at a distance W from the center.
Comparative example 3
A separator II-3 was produced in the same manner as in example 1, except for the following parameters.
In the step (3), the pore-forming agent-containing film is stretched 3.6 times in the width direction (TD) in a region of 0 to 1/3W from the center and 3.5 times in the width direction in a region of 1/3W to W from the center at a distance W from the center.
Comparative example 4
A separator II-4 was produced in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film was stretched in the width direction (TD) by 3.6 times in the width direction in the region of 0 to 1/3W from the center and 4.7 times in the width direction in the region of 1/3W to W from the center at a distance W from the center.
Comparative example 5
A separator II-5 was produced in the same manner as in example 1, except for the following parameters.
In the step (3), the pore-forming agent-containing film is stretched 3.6 times in the width direction (TD) in a region of 0 to 1/3W from the center and 5.3 times in the width direction in a region of 1/3W to W from the center at a distance W from the center.
Comparative example 6
A separator II-6 was produced in the same manner as in example 1, except for the following parameters.
In step (3), the pore-forming agent-containing film was stretched in the width direction (TD) by a distance W between the center and the edge, 4.8 times in the width direction for the region 0 to 1/3W from the center, and 4.7 times in the width direction for the region 1/3W to W from the center.
Comparative example 7
A separator II-7 was produced in the same manner as in example 1, except for the following parameters.
In the step (3), the pore-forming agent-containing film is stretched 6.5 times in the width direction (TD) in a region of 0 to 1/3W from the center and 6.6 times in the width direction in a region of 1/3W to W from the center at a distance W from the center.
Examples of the experiments
The separators prepared in examples 1 to 11 and comparative examples 1 to 7 were tested.
Test (1):
the porosity of the separator was measured as follows: kneading the isolating membrane into a cluster and inserting the cluster into a sample cup, and placing the sample cup with the isolating membrane into a true density tester; and (3) sealing the test system, introducing helium according to a program, detecting the pressure of gas in the sample chamber and the expansion chamber, and calculating the real volume according to the Bohr's law (PV = nRT), so as to obtain the porosity of the isolation membrane sample to be tested. Volume of sample cup: 3.5cm 3 Analyzing the gas: helium gas. The result of the detectionAs shown in table 1, the region from 0 to 1/3W from the center in the width direction (TD) of the separator is simply referred to as "first region", and the region from 1/3W to W from the center in the width direction of the separator is simply referred to as "second region".
TABLE 1 stretch ratio and porosity of separator film
Test (2):
3 parallel samples were respectively selected from the separators of examples 1 to 11 and comparative examples 1 to 7, and assembled into small pouch batteries, specifically as follows: laminating the NCM523 positive pole piece, the isolating film and the graphite negative pole piece in sequence to enable the isolating film to be positioned between the positive pole piece and the negative pole piece to play a role in isolating the positive pole and the negative pole, winding to obtain a bare cell, welding a tab, and placing the bare cell in an outer package; and injecting the electrolyte into the dried battery cell, and carrying out packaging, standing, formation and shaping to obtain the lithium ion battery.
And (3) performing constant-current 1C charging/1C discharging circulation on the prepared lithium ion battery in a constant temperature box at 25 ℃, and circulating for 600cls. Then, the battery is disassembled, an anode large-surface pole piece (in a winding type battery cell, a surface with a larger side surface area is called a large surface) is taken, the content of Li element is measured in a large-surface central area and an area close to the edge of a tab through an ICP (Inductive Coupled Plasma Emission Spectrometer), the difference value of the content of Li in the large-surface center minus the content of Li in the large-surface edge is calculated, and the detection result is shown in table 2.
TABLE 2 analysis result of Li element content in anode large-area pole piece
| Sample (I) | Percent of large face center Li content-large face edge Li content wt% |
| Example 1 | 0.45 |
| Example 2 | 0.37 |
| Example 3 | 0.32 |
| Example 4 | 0.19 |
| Example 5 | 0.06 |
| Example 6 | 0.13 |
| Example 7 | 0.34 |
| Example 8 | 0.58 |
| Example 9 | 0.46 |
| Example 10 | 0.4 |
| Example 11 | 0.83 |
| Comparative example 1 | 0.62 |
| Comparative example 2 | 0.54 |
| Comparative example 3 | 0.41 |
| Comparative example 4 | 0.23 |
| Comparative example 5 | 0.03 |
| Comparative example 6 | 0.56 |
| Comparative example 7 | 0.87 |
Test (3):
and (3) preparing the lithium ion battery according to the method in the test (2), and testing the cycle performance of the lithium ion battery. The method for measuring the circulating capacity is as follows: and fully charging the battery monomer at constant current of 1/3C and constant voltage of 4.35V until the current is less than 0.05C, discharging at constant current of 1/3C until the current is 2.5V after standing for 30min, and stopping, wherein the measured capacity is the actual measurement capacity of the current cycle number. The capacity retention rate at the n-th cycle = measured discharge capacity at the n-th week/measured discharge capacity at the first week × 100%. The test results are shown in table 3.
TABLE 3
The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the protection scope of the appended claims.
Claims (19)
1. A separator, characterized in that the separator is a porous separator; the porosity gradient of the separator film decreases in a direction perpendicular to a thickness direction of the separator film, along a center-to-edge direction of the separator film.
2. The separator of claim 1, wherein a direction perpendicular to a thickness direction of the separator comprises a length direction and a width direction; the separator has a porosity gradient that decreases in a width direction of the separator along a center-to-edge direction of the separator.
3. The separation film according to claim 1 or 2, wherein the separation film is sequentially divided into n regions in a direction from the center to the edge, wherein n is a positive integer of 2 or more; for any two regions, the region closer to the center of the separator has greater porosity relative to the region farther from the center of the separator.
4. The separation film according to claim 3, wherein a region closest to a center of the separation film is a first region, and a region farthest from the center of the separation film is an nth region; the difference between the porosity of the first region and the porosity of the nth region is 2-20%.
5. The separator of claim 4, wherein the porosity of the first region is 30% to 60% and the porosity of the nth region is 20% to 50%.
6. The separator according to claim 4, wherein the distance from the center to the edge of the separator is W, the separator is sequentially divided into two regions in the direction from the center to the edge of the separator, the first region is defined as a range of 0 to 1/3W from the center of the separator, and the porosity of the first region is 30% to 60%; and taking the range of 1/3W-W away from the center of the isolating membrane as a second area, wherein the porosity of the second area is 20% -50%.
7. The separator of claim 1 or 2, wherein the separator has a thickness of 5 to 60 μm.
8. The separator of claim 1 or 2, wherein the separator is a single layer film or a composite film of two or more layers.
9. The separator according to claim 1 or 2, wherein the material of the separator comprises one or a combination of two or more selected from the group consisting of: glass fiber, non-woven fabric, polyethylene, polypropylene, polyvinylidene fluoride.
10. The method for producing the separator according to any one of claims 1 to 9, comprising: weighing raw materials for preparing the isolating membrane, wherein the raw materials comprise a base material, a pore-forming agent and an antioxidant; after uniformly mixing the raw materials, sequentially carrying out extrusion, stretching, extraction and shaping; wherein the stretching step comprises: and stretching in a direction perpendicular to the thickness direction of the separator, wherein the gradient of the stretching ratio is reduced in a direction from the center to the edge of the separator so that the gradient of the porosity is reduced.
11. The method of claim 10, wherein the stretching step comprises: stretching along the width direction of the separation film, and reducing the gradient of stretching multiplying power along the direction from the center to the edge of the separation film so as to reduce the gradient of porosity; and/or the presence of a gas in the gas,
and stretching along the length direction of the isolating membrane, wherein the gradient of stretching multiplying power is reduced along the direction from the center to the edge of the isolating membrane so as to reduce the gradient of porosity.
12. The production method according to claim 10 or 11, wherein the separator is sequentially divided into n regions in a direction from the center to the edge of the separator, and n is a positive integer of 2 or more; for any two regions, a greater stretch ratio is applied to a region closer to the center of the separator than to a region farther from the center of the separator.
13. The production method according to claim 12, wherein the distance from the center to the edge of the separator is W, a first region is defined as a range of 0 to 1/3W from the center of the separator, and the first region is stretched at a magnification of 4 to 8 times in the stretching step; and a second region having a range of 1/3W-W from the center of the separator, wherein the second region is stretched at a magnification of 2-4 times in the stretching step.
14. The process according to any one of claims 10 or 11, wherein the starting materials comprise, in parts by weight: 30-65 parts of base material, 10-40 parts of pore-forming agent and 5-10 parts of antioxidant;
preferably, the substrate comprises one or a combination of two or more selected from the group consisting of: glass fibers, non-woven fabrics, polyethylene, polypropylene, polyvinylidene fluoride;
preferably, the pore-forming agent is an organic pore-forming agent and/or an inorganic pore-forming agent;
preferably, the antioxidant comprises one or a combination of two or more selected from the group consisting of: 4, 4-thiobis (6-t-butyl-m-cresol), dibutylhydroxytoluene, phosphite, t-butylhydroquinone, N-octadecylcarbonate β - (3, 5-di-t-butyl-4-hydroxyphenyl) propionate, 1, 3-tris (2-methyl-4-hydroxy-5-t-butylphenyl) butane, 2-t-butyl-6-methylphenol, N, N' -di- β -naphthylp-phenylenediamine, dilaurylthiodipropionate, tris (nonylphenyl) phosphite, triphenyl phosphite.
15. A secondary battery comprising a positive electrode sheet, a negative electrode sheet, an electrolyte, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the separator is the separator according to any one of claims 1 to 9.
16. The secondary battery of claim 15, wherein the secondary battery is one of a lithium ion battery, a sodium ion battery, or a potassium ion battery.
17. A battery module comprising the secondary battery of claim 15 or 16.
18. A battery pack comprising the battery module of claim 17.
19. An electric device comprising at least one of the secondary battery of claim 15 or 16, the battery module of claim 17, or the battery pack of claim 18.
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