WO2018166143A1

WO2018166143A1 - Separator and energy storage device prepared therefrom

Info

Publication number: WO2018166143A1
Application number: PCT/CN2017/099374
Authority: WO
Inventors: 程跃; 鲍晋珍; 陈永乐; 王伟强
Original assignee: 上海恩捷新材料科技股份有限公司
Priority date: 2017-03-15
Filing date: 2017-08-29
Publication date: 2018-09-20
Also published as: CN108630868A

Abstract

Disclosed are a separator and an energy storage device prepared therefrom. The separator comprises a porous base film layer and a functional layer, wherein the functional layer comprises a high-temperature-resistant layer and a binder; and the binder is a polymer containing lithium ions.

Description

Isolation membrane and energy storage device thereof

Technical field

The invention relates to the field of electrochemistry, and in particular to an electrochemical energy storage device isolation membrane.

Background technique

Electrochemical energy storage devices often require high safety and good dynamic performance, which puts high demands on the barrier and permeability of the separator of one of its key components. For example, at present, many technicians improve the safety performance and insulation effect of the battery separator by increasing the thickness of the battery separator or reducing the porosity of the separator, but at the same time, the technician finds that the permeability of the battery separator is degraded. This not only affects the liquid storage capacity of the battery separator, but also increases the internal resistance of the battery separator, which ultimately affects the dynamic performance of the battery. Some technicians, in order to better use the separator on the fast charge battery, improve the permeability by reducing the thickness of the battery separator or increasing its porosity, although the internal resistance is reduced to some extent, but The inside of the battery is extremely prone to internal short-circuit or even thermal runaway, which eventually leads to a safety accident in which the battery burns or explodes.

In recent years, in order to solve this problem, a multilayer coated battery separator has been introduced on the market, and a high-temperature ceramic coating is applied on a thin porous separator, wherein the base film layer is designed to maintain a battery separator. The skeleton and good permeability, the ceramic coating layer design can improve the high temperature resistance and liquid storage of the battery separator to improve the safety of its use in the battery. However, the increase of ceramic coating can not solve the problem of large internal resistance of the battery separator, and even the introduction of the key component of the polymer in the coating, the overall internal resistance of the separator and the battery is further increased. The problem also causes low battery charging and discharging efficiency, poor dynamic performance, and even a safety hazard that causes the battery to overheat.

Therefore, there is a need in the art to provide a battery separator that improves both barrier properties and ion conduction.

Summary of the invention

SUMMARY OF THE INVENTION The present invention is directed to a battery separator which can improve barrier properties while promoting ion conduction.

In a first aspect of the invention, an electrochemical energy storage device separator is provided, the separator film package The porous base film layer and the functional layer, the functional layer containing a high temperature resistant functional material and a binder; the binder is a lithium ion containing polymer; and the lithium ion containing polymer is a lithium ion containing acrylic acid Resin.

In another preferred embodiment, the lithium ion-containing polymer is selected from one or more of the following: lithium polyacrylate, lithium polyacrylate, lithium polymethacrylate, polymethyl methacrylate, Lithium polyacrylonitrile, lithium polyacrylamide; preferably self-polylithium acrylate, lithium polyacrylate, or polymethyl methacrylate.

In another preferred embodiment, the high temperature resistant functional material is selected from one or more of the following: alumina, silica, titania, cerium oxide, calcium carbonate, calcium oxide, zinc oxide, magnesium oxide, titanium Barium acid, calcium titanate, barium titanate, lithium phosphate, lithium titanium phosphate, lithium aluminum aluminum phosphate, lithium nitride, lithium strontium titanate; preferably from alumina or silica.

In another preferred embodiment, the functional layer further contains an additive; the additive is selected from one or more of the following: sodium carboxymethylcellulose, glucose, starch, cellulose; more preferably carboxymethylcellulose Sodium.

In another preferred embodiment, the high temperature functional material is contained in an amount of 90 to 98% by weight, the binder is 2 to 8% by weight, and the balance is an additive.

In another preferred embodiment, the porous base film layer is a porous base film or at least one coated porous base film; the porous base film is a layer multilayer or a single layer; the porous base film layer has a thickness of 3 to 50 μm; more preferably 10 to 15 μm.

In another preferred embodiment, the functional layer is located on one or both sides of the porous base film layer; the functional layer has a thickness of from 1 to 5 μm; more preferably from 1.5 to 3 μm.

In a second aspect of the present invention, there is provided an electrochemical energy storage device comprising a positive electrode, a negative electrode, an electrolyte, and a separator provided by the present invention as described above between the positive electrode and the negative electrode .

Accordingly, the present invention provides a battery separator which can improve barrier properties while promoting ion conduction.

detailed description

As used herein, an "electrochemical energy storage device" includes a lithium secondary battery, a lithium ion secondary battery, a super capacitor, a fuel cell, a solar cell, etc.; the lithium ion secondary battery includes a polymer lithium Ion secondary battery.

As used herein, a "porous base film" material is selected from one or more of the group consisting of polyolefins, aramids, polyimides, polyester fibers, acrylic fibers, and polyvinylidene fluoride.

In the present invention, the numerical range "a-b" denotes an abbreviated representation of any real combination between a and b unless otherwise stated, where a and b are both real numbers. For example, a numerical range of "0-5" means that all real numbers between "0-5" have been listed in this document, and "0-5" is only an abbreviated representation of these numerical combinations.

The term "a" as used in this specification means "at least one" unless otherwise specified.

The "scope" disclosed herein is in the form of a lower limit and an upper limit. It may be one or more lower limits, respectively, and one or more upper limits. The given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges that can be defined in this manner are inclusive and combinable, that is, any lower limit can be combined with any upper limit to form a range. For example, ranges of 60-120 and 80-110 are listed for specific parameters, and ranges of 60-110 and 80-120 are also contemplated. In addition, if the minimum range values listed are 1 and 2, and if the maximum range values 3, 4 and 5 are listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2- 3, 2-4, and 2-5.

The inventors have conducted extensive and intensive research and found that a porous base film or at least one coated porous base film is used as a main structure, and a separator formed by coating a functional layer on either or both sides is used, since a lithium salt is used in the functional layer. The binder makes the separator exhibit low internal resistance, and the prepared lithium ion battery has high fast charge capacity, long cycle life and good safety performance. On the basis of this, the present invention has been completed.

Isolation film

The separator provided by the present invention comprises a porous base film layer and a functional layer coated thereon, the functional layer comprising at least one layer structure, and the functional layer is located on one side or both sides of the porous base film layer.

The porous base film layer in the present invention may be a single layer, that is, a porous base film, or may be a plurality of layers, that is, a porous base film coated on at least one side. The coated material can be conventionally used in the art such as, but not limited to, PVDF (polyvinylidene fluoride). The porous base film layer has a thickness of from 3 to 50 μm, preferably from 10 to 15 μm, and a porosity of from 10% to 80%. The porous base film layer serves as a skeleton structure of the separator, supports the functional layer, and provides an insulating material between the positive and negative electrodes in the battery, and the porous structure provides a channel for ion migration in the battery. The functional layer in the present invention comprises a high temperature resistant functional material and is viscous Conjunction. The high temperature resistant functional material is basically an inorganic material selected from the group consisting of alumina, silica, titania, cerium oxide, calcium carbonate, calcium oxide, zinc oxide, magnesium oxide, barium titanate, calcium titanate, barium titanate. At least one of lithium phosphate, lithium titanium phosphate, lithium aluminum aluminum phosphate, lithium nitride, and lithium strontium titanate. The binder is selected from a binder containing lithium ions, preferably an acrylic resin containing lithium ions. The binder may be at least one selected from the group consisting of lithium acrylate, lithium polyacrylate, lithium polymethacrylate, lithium polymethyl methacrylate, lithium polyacrylonitrile, lithium polyacrylamide, preferably lithium polyacrylate, At least one of lithium polyacrylate and lithium polymethacrylate. The functional layer may also contain other additives, one or more of sodium carboxymethylcellulose, glucose, starch, cellulose, preferably sodium carboxymethylcellulose.

The mass percentage of the high temperature resistant functional material is from 90% to 98%, the mass percentage of the binder is from 2% to 8%, and the balance is an additive, based on the total weight of the functional layer. The single layer thickness of the functional layer ranges from 1 to 5 μm, preferably from 1.5 to 3 μm.

The high temperature resistant functional material in the functional layer can improve the overall high temperature resistance of the separator and improve the safety of the battery; and can improve the insulation performance of the separator and improve the puncture resistance; and can also improve the mechanical strength of the separator and resist oxidation. Sex; the electrolyte storage capacity of the separator can be increased to extend the cycle life of the battery.

The binder in the functional layer can provide the bonding between the high temperature resistant functional material and the porous base film, and also can provide the bonding between the particles of the high temperature resistant functional material, and can also increase the ion migration rate during the charging and discharging process of the battery, thereby improving The dynamic performance of the battery.

Electrochemical energy storage device

The electrochemical energy storage device provided by the present invention comprises a positive electrode, a negative electrode, an electrolyte, and a separator provided by the present invention between the positive electrode and the negative electrode. In an embodiment of the invention, the electrochemical energy storage device may further comprise a package shell.

The above-mentioned features mentioned in the present invention, or the features mentioned in the embodiments, may be arbitrarily combined. All of the features disclosed in the present specification can be used in combination with any of the compositions, and the various features disclosed in the specification can be substituted for any alternative feature that provides the same, equal or similar purpose. Therefore, unless otherwise stated, the disclosed features are only general examples of equal or similar features.

The main advantages of the invention are:

1. The lithium ion-containing binder used in the separator provided by the present invention can exchange lithium ions in the electrolyte to increase the ion migration rate, thereby improving the dynamic performance of the battery.

2. The lithium ion-containing binder used in the separator provided by the present invention During the long-term circulation of the battery, lithium ions in the binder can be taken out to supplement the battery circulation requirement, thereby prolonging the cycle life.

3. The separator provided by the invention solves the dilemma that the internal resistance of the diaphragm is large, and the dynamic performance and safety performance of the battery cannot be balanced.

The invention is further illustrated below in conjunction with specific embodiments. It is to be understood that the examples are not intended to limit the scope of the invention. The experimental methods in the following examples which do not specify the specific conditions are usually carried out according to conventional conditions or according to the conditions recommended by the manufacturer. All percentages, ratios, ratios, or parts are by weight unless otherwise indicated.

The units in the weight percent by volume in the present invention are well known to those skilled in the art and, for example, refer to the weight of the solute in a 100 ml solution.

Unless otherwise defined, all professional and scientific terms used herein have the same meaning as those skilled in the art. In addition, any methods and materials similar or equivalent to those described may be employed in the methods of the invention. The preferred embodiments and materials described herein are for illustrative purposes only.

Comparative example 1

The separator used in the electrochemical device is a single-layer polyethylene film with a thickness of 12 μm and a porosity of 41%. No other functional layers are provided on the base film. The positive electrode, the separator and the negative electrode are sequentially wound to form a bare cell, and assembled into Model 353286 lithium ion battery.

Comparative example 2

The electrochemical device was the same as that of Comparative Example 1, except that the separator used was a single-layer polyethylene-based film coated with a thickness of 2 μm, a base film thickness of 12 μm, a porosity of 41%, and the inorganic material of the functional layer was oxidized. Aluminum, the binder is sodium polyacrylate, and the additive is sodium carboxymethyl cellulose. The ratio of the three is 95:4:1.

Example 1

The electrochemical device was the same as in Comparative Example 2 except that the separator used was a single-layer polyethylene film. The side coating thickness is 2μm functional layer, the base film thickness is 12μm, the porosity is 41%, the inorganic material of the functional layer is alumina, the binder is lithium polyacrylate, and the additive is sodium carboxymethyl cellulose. The ratio of the three is 95:4:1.

Example 2

The electrochemical device was the same as in Comparative Example 2 except that the separator used was a single-layer polyethylene-based film coated with a thickness of 2 μm, a base film thickness of 12 μm, a porosity of 41%, and the inorganic material of the functional layer was oxidized. Aluminum, the binder is lithium polyacrylate, the additive is sodium carboxymethyl cellulose, and the ratio of the three is 95:4:1.

Example 3

The electrochemical device was the same as in Comparative Example 2 except that the separator used was a single-layer polyethylene-based film coated with a thickness of 3 μm, a base film thickness of 12 μm, a porosity of 41%, and the inorganic material of the functional layer was oxidized. Aluminum, the binder is polymethyl methacrylate, the additive is sodium carboxymethyl cellulose, and the ratio of the three is 95:4:1.

Example 4

The electrochemical device was the same as in Example 1, except that the separator used was a single-layer polyethylene film coated on one side with a thickness of 2 μm, a base film thickness of 12 μm, a porosity of 41%, and the inorganic material of the functional layer was oxidized. Aluminum, the binder is lithium polyacrylate, the additive is sodium carboxymethyl cellulose, and the ratio of the three is 93:5:2.

Example 5

The electrochemical device was the same as in Comparative Example 2 except that the separator used was a single-layer polyethylene-based film coated with a thickness of 2 μm, a base film thickness of 12 μm, a porosity of 41%, and the inorganic material of the functional layer was oxidized. Silicon, the binder is lithium polyacrylate, and the additive is sodium carboxymethyl cellulose. The ratio of the three is 95:4:1.

Example 6

The electrochemical device was the same as in Comparative Example 2 except that the separator used was a single layer of a polypropylene-based film coated with a thickness of 2 μm, a base film thickness of 12 μm, a porosity of 41%, and an inorganic material of a functional layer. It is alumina, the binder is lithium polyacrylate, and the additive is sodium carboxymethyl cellulose. The ratio of the three is 95:4:1.

Example 7

The electrochemical device was the same as in Comparative Example 2 except that the separator used was a single-layer polyethylene film coated on both sides with a thickness of 2 μm, a base film thickness of 12 μm, a porosity of 41%, and the functional layer of the inorganic material was Alumina, the binder is lithium polyacrylate, and the additive is sodium carboxymethyl cellulose, the ratio of the three is 95:4:1.

Example 8

The electrochemical device was the same as in Comparative Example 2 except that the separator used was a three-layer polypropylene-based film coated with a thickness of 2 μm, a base film thickness of 12 μm, a porosity of 41%, and the inorganic material of the functional layer was oxidized. Aluminum, the binder is lithium polyacrylate, and the additive is sodium carboxymethyl cellulose, the ratio of the three is 95:4:1.

Example 9

The electrochemical device was the same as in Comparative Example 2 except that the separator used was a single layer of a polypropylene-based film coated with a thickness of 2 μm, and the other side of the base film was provided with a 1 μm PVDF coating layer. The thickness is 12um, the porosity is 41%, the inorganic material of the functional layer is alumina, the binder is lithium polyacrylate, and the additive is sodium carboxymethyl cellulose. The ratio of the three is 95:4:1.

Performance Testing

The following performance tests were performed on the separators of Comparative Examples 1-2 and Examples 1-9 and lithium ion batteries:

1) Air permeability test of the separator: tested with a Gurley permeability tester;

2) isolation film breakdown voltage test: using the breakdown voltage tester test, voltage 6KV, test time 10s;

3) Isolation film internal resistance test: The isolation film is assembled into a CR2016 button battery (without positive and negative electrodes), and the electrochemical impedance workstation is used to test the AC impedance spectrum of the deduction. The focal point value of the horizontal axis is the isolation film. Internal resistance value;

4) The liquid holding capacity test of the battery: the weight of the battery after the liquid injection - the weight of the battery before the liquid injection;

5) 4C charging capacity: a battery with a designed capacity of 1900mAh, at 23 ° C, 7600mA current is charged to record the charging capacity;

6) Cycle life: The battery with a design capacity of 1900 mAh is cyclically charged and discharged at a rate of 0.5 C/0.5 C at 23 ° C. When the battery capacity is only 80%, the number of cycles of the battery is recorded;

7) Overcharge test: At room temperature, charge the battery at 1 C for 120 min to observe whether the battery is on fire or explode.

The separators 1-2 and the separators of Examples 1-9 and the lithium ion battery performance test results are shown in Table 1.

Table 1, Comparative Example and Examples of separator and battery performance test results

The results show that the separator of the functional layer using the lithium salt binder of the present invention exhibits low internal resistance, and the prepared battery has high fast charge capacity, long cycle life and good safety performance. In Comparative Example 1, only the separator with no functional layer was used. Although the internal resistance was small and the permeability was good, on the one hand, the breakdown voltage was low, and the high temperature resistance was poor, resulting in poor safety of the prepared battery. It is characterized by burning phenomenon in overcharge test, on the other hand, ion conductivity is still insufficient, 4C charging capacity and cycle life are not advantageous; Comparative Example 2 uses a high temperature resistant functional layer, but the binder in its functional layer It is an ordinary sodium polyacrylate adhesive, which not only increases the gas permeability value and internal resistance of the separator, but also affects the system. The dynamic performance and cycle life of the backup battery did not pass the overcharge safety test. Compared with Comparative Example 2, Examples 1-3 used lithium polyacrylate, lithium polyacrylate and lithium methacrylate instead of ordinary sodium polyacrylate adhesive, which not only effectively reduced the internal resistance of the separator, but also The kinetic performance of the battery is significantly improved (about 20%), and the cycle life and safety performance of the battery are also significantly improved, mainly because the lithium ions in the lithium-containing binder are effectively exchanged with the lithium ions in the electrolyte. The lithium ions in the electrolyte are replenished later in the cycle. Example 5 increased the mass percentage of the lithium-containing binder by 1% within the feasible range, and the effects of the present invention were also achieved. Example 5 and Example 6 respectively used silicon oxide as a high temperature resistant material and polypropylene as an insulating material, and the binder in the functional layer was a lithium-containing binder, which can improve the internal resistance of the separator and the battery. , kinetic performance, cycle life and safety effects. Embodiment 7 is a double-coated functional layer. Although the gas permeability of the separator increases, the proportion of lithium ions increases correspondingly, so that the internal resistance of the separator decreases significantly, and the 4C charging capacity and cycle life of the battery also increase. In the embodiment 8, the functional layer is provided on the insulating layer of the three-layer structure, and the effect of the present invention can also be achieved. In addition to the insulating layer and the functional layer, the separator of Embodiment 9 is provided with a PVDF coating layer on the opposite side of the functional layer, and the PVDF coating layer functions to bond the separator and the pole piece without affecting the functional layer. High temperature performance and contribution to battery dynamics, cycle life and safety.

The above is only the preferred embodiment of the present invention, and is not intended to limit the scope of the technical scope of the present invention. The technical content of the present invention is broadly defined in the scope of the claims of the application, and any technical entity completed by others. The method or method, if it is identical to the scope of the claims, or equivalents, is considered to be within the scope of the claims.

Claims

An electrochemical energy storage device isolation membrane, the separation membrane comprising a porous base membrane layer and a functional layer, wherein the functional layer comprises a high temperature resistant functional material and a binder; the binder is lithium ion-containing Polymer.
The separator according to claim 1, wherein the lithium ion-containing polymer is an acrylic resin containing lithium ions.
The separator according to claim 1, wherein the lithium ion-containing polymer is one or more selected from the group consisting of lithium polyacrylate, lithium polyacrylate, lithium polymethacrylate, and poly Lithium methyl methacrylate, lithium polyacrylonitrile, lithium polyacrylamide; preferably self-polylithium acrylate, lithium polyacrylate, or polymethyl methacrylate.
The separator according to claim 1, wherein the high temperature resistant functional material is selected from one or more of the following: alumina, silica, titania, cerium oxide, calcium carbonate, calcium oxide, Zinc oxide, magnesium oxide, barium titanate, calcium titanate, barium titanate, lithium phosphate, lithium titanium phosphate, lithium aluminum aluminum phosphate, lithium nitride, lithium strontium titanate; preferably from alumina or silica.
The separator according to any one of claims 1 to 4, wherein the functional layer further contains an additive; and the additive is selected from one or more of the following: sodium carboxymethylcellulose, glucose Starch, cellulose; sodium carboxymethylcellulose is preferred.
The separator according to claim 1, wherein said functional layer has 90% to 98% by weight of said high temperature resistant functional material, 2-8% by weight of said binder, and the balance is additive.
The separator according to claim 1, wherein said porous base film layer is a porous base film or a coated porous base film on at least one side.
The separator according to claim 1, wherein said porous base film is a layer of a plurality of layers or a single layer; The porous base film layer has a thickness of from 3 to 50 μm; preferably from 10 to 15 μm.
The separator according to any one of claims 1 to 4, wherein the functional layer is located on one side or both sides of the porous base film layer; the functional layer has a thickness of 1-5 μm; preferably 1.5-3 μm .
An electrochemical energy storage device, comprising: a positive electrode, a negative electrode, an electrolyte, and a separator according to any one of claims 1 to 9 between the positive electrode and the negative electrode.