Current collector and preparation method thereof, and lithium ion battery

Abstract

In view of the problem that the safety performance of the battery cell needs to be improved while the energy density or fast charging performance of the lithium-ion battery is improved, the present invention provides a current collector, including a first conductive layer, a second conductive layer and an insulating layer, wherein the insulating layer is arranged between the first conductive layer and the second conductive layer; the insulating layer is composed of a plurality of capsule units, the capsule unit includes a shell and a core body, and the shell is wrapped around the core body; the core body is composed of a first polymer; the shell is composed of a second polymer, the glass transition temperature of the second polymer is greater than the glass transition temperature of the first polymer, and the glass transition temperature of the first polymer is ‑60°C to ‑10°C; the glass transition temperature of the second polymer is 25°C to 50°C. At the same time, the present invention also discloses a preparation method and a lithium-ion battery including the above-mentioned current collector. The current collector provided by the present invention has a certain mechanical tensile strength, avoids fracture, and simultaneously achieves insulation and improves safety.

Description

Technical Field

[0001] The present invention belongs to the technical field of secondary batteries, and in particular relates to a current collector and a preparation method thereof, and a lithium ion battery. Background Art

[0002] Lithium-ion batteries are widely used in electric vehicles and consumer electronics due to their advantages such as high energy density, high output power, long cycle life and low environmental pollution. As the application scope of lithium-ion batteries continues to expand, people's requirements for the energy density of lithium-ion batteries are getting higher and higher. With the increase in energy density and the acceleration of charging speed, the safety performance of the battery cell is particularly important. Under the premise of improving energy density or fast charging performance, safety performance cannot be sacrificed.

[0003] At present, the improvement of safety performance is mainly to coat a layer of insulating safety coating on the surface of the positive or negative electrode. This coating is an inert material. On the one hand, it will hinder the transmission of lithium ions and have a deteriorating effect on the charging speed. On the other hand, this coating will increase the thickness of the entire electrode, which will cause a certain loss in battery energy density. In addition, this coating requires an additional process to apply the safety coating after the electrode is coated, which will affect the production efficiency of the entire battery production process. Summary of the invention

[0004] In view of the problem that the safety performance of the battery cell needs to be improved while the energy density or fast charging performance of the existing lithium ion batteries is improved, the present invention provides a current collector and a lithium ion battery.

[0005] The technical solution adopted by the present invention to solve the above technical problems is as follows:

[0006] On the one hand, the present invention provides a current collector, comprising a first conductive layer, a second conductive layer and an insulating layer, wherein the insulating layer is arranged between the first conductive layer and the second conductive layer; the insulating layer is composed of a plurality of capsule units, wherein the capsule unit comprises a shell and a core body, wherein the shell is wrapped around the outer periphery of the core body; the core body is composed of a first polymer; the shell is composed of a second polymer, wherein the glass transition temperature of the second polymer is greater than the glass transition temperature of the first polymer, and the glass transition temperature of the first polymer is -60°C to -10°C; the glass transition temperature of the second polymer is 25°C to 50°C.

[0007] Optionally, the thickness of the insulating layer is 1-20 μm, the thickness of the first conductive layer is 2-10 μm, and the thickness of the second conductive layer is 2-10 μm.

[0008] Optionally, the first conductive layer and the second conductive layer are aluminum layers or copper layers.

[0009] On the other hand, the present invention also provides a method for preparing a current collector, wherein the first polymer is formed by polymerizing a first monomer and a second monomer; and the second polymer is formed by polymerizing a third monomer; and the method for preparing the current collector comprises the following steps:

[0010] Add water, surfactant and first monomer into the reactor, stir with a stirrer for 30-120 min, and raise the reaction temperature to 40-85° C.;

[0011] The second monomer is added dropwise to the reactor. After the second monomer is added dropwise, the reaction temperature is lowered to 25-40° C. and stirred for 120 minutes to obtain the first polymer.

[0012] Raising the reaction temperature to 60-85° C., adding an initiator and dripping the third monomer into the reactor containing the first polymer, raising the reaction temperature to 85-90° C. after the dripping of the third monomer is completed, stirring with a stirrer for 120 min to obtain a solution containing the capsule unit;

[0013] The solution containing the capsule units is laid into a film to form the insulating layer, and the first conductive layer and the second conductive layer are respectively plated on both sides of the insulating layer to obtain the current collector.

[0014] Optionally, the first monomer is selected from one or more of acrylic acid, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, tert-butyl acrylate, methyl methacrylate, styrene, dibornene, hexamethylene diisocyanate and polydimethylsiloxane.

[0015] Optionally, the second monomer is selected from one or more of tris(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate) and thioglycolic acid.

[0016] Optionally, the third monomer is selected from one or more of acrylic acid, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, tert-butyl acrylate, methyl methacrylate, styrene, dibornene, hexamethylene diisocyanate, polydimethylsiloxane, glycidyl methacrylate, methacrylate phosphate and 1,4-butanediol acrylate.

[0017] Optionally, the molar ratio of the first polymer to the second polymer is (1:4) to (4:1).

[0018] Optionally, the initiator is selected from one or more of ammonium persulfate, sodium persulfate, potassium persulfate and azobisisobutyronitrile.

[0019] In another aspect, the present invention provides a lithium-ion battery comprising any one of the current collectors described above.

[0020] According to the current collector provided by the present invention, when the battery cell is damaged, the insulating layer between the first conductive layer and the second conductive layer increases the mechanical tensile strength of the current collector, avoiding the first conductive layer or the second conductive layer from breaking, thereby avoiding short circuit, fire and explosion of the battery cell. If the first conductive layer or the second conductive layer breaks, the second polymer of the capsule unit ruptures or melts in an environment with increased external temperature, releasing the first polymer, and the first polymer covers the cross section of the first conductive layer or the second conductive layer to insulate it, avoiding short circuit and fire of the battery cell, and effectively improving the safety performance of the battery cell. The glass transition temperature of the second polymer is higher than the transition temperature of the second polymer, and the glass transition temperatures of the first polymer and the second polymer differ greatly, so that the second polymer can cover the first polymer when solidified. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 It is a schematic diagram of the structure of the current collector provided by one embodiment of the utility model;

[0022] Figure 2 It is a structural schematic diagram of a current collector capsule unit provided in one embodiment of the utility model.

[0023] The reference numerals in the drawings of the specification are as follows:

[0024] 1. First conductive layer; 2. Second conductive layer; 3. Capsule unit; 31. Shell; 32. Core. DETAILED DESCRIPTION

[0025] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention more clearly understood, the present invention is further described in detail below in conjunction with the embodiments and drawings. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0026] like Figure 1 and Figure 2 As shown, an embodiment of the present invention provides a current collector, including a first conductive layer 1, a second conductive layer 2 and an insulating layer, wherein the insulating layer is arranged between the first conductive layer 1 and the second conductive layer 2. The insulating layer is composed of a plurality of capsule units 3, and the capsule unit 3 includes a shell 31 and a core 32, wherein the shell 31 is wrapped around the periphery of the core 32. The core 32 is composed of a first polymer. The shell 31 is composed of a second polymer, and the glass transition temperature of the second polymer is greater than the glass transition temperature of the first polymer, and the glass transition temperature of the first polymer is -60°C to -10°C. The glass transition temperature of the second polymer is 25°C to 50°C.

[0027] In this embodiment, when the battery cell is damaged, the insulating layer between the first conductive layer 1 and the second conductive layer 2 increases the mechanical tensile strength of the current collector, preventing the first conductive layer 1 or the second conductive layer 2 from breaking, thereby preventing the battery cell from short circuiting, catching fire, and exploding. If the first conductive layer 1 or the second conductive layer 2 breaks, the second polymer of the capsule unit 3 ruptures or melts in an environment with an increased external temperature, releasing the first polymer, which covers the cross section of the first conductive layer 1 or the second conductive layer 2 to insulate it, preventing the battery cell from short circuiting and catching fire, and effectively improving the safety performance of the battery cell. The glass transition temperature of the second polymer is higher than the transition temperature of the second polymer, and the glass transition temperatures of the first polymer and the second polymer differ greatly, so that the second polymer can cover the first polymer when solidified.

[0028] In some embodiments, the thickness of the insulating layer is 1-20 μm, the thickness of the first conductive layer 1 is 2-10 μm, and the thickness of the second conductive layer 2 is 2-10 μm. While improving safety, the thickness of the current collector is kept within a certain range to avoid affecting the energy density, lithium ion transmission speed and fast charging performance of the battery cell.

[0029] In some embodiments, the first conductive layer 1 and the second conductive layer 2 are aluminum layers or copper layers. When the first conductive layer 1 and the second conductive layer 2 are aluminum layers, the current collector is a positive electrode current collector. When the first conductive layer 1 and the second conductive layer 2 are copper layers, the current collector is a negative electrode current collector.

[0030] On the other hand, an embodiment of the present invention further provides a method for preparing a current collector, wherein the first polymer is formed by polymerizing a first monomer and a second monomer. The second polymer is formed by polymerizing a third monomer. The method for preparing the current collector comprises the following steps:

[0031] Water, a surfactant and a first monomer are added to the reactor, and the agitator is stirred for 30-120 minutes, and the reaction temperature is increased to 40-85° C. Specifically, the stirring speed is 200-500 r / min to uniformly disperse the first monomer.

[0032] The second monomer is added dropwise to the reactor, and after the second monomer is added dropwise, the reaction temperature is lowered to 25-40° C., and the agitator is stirred for 120 minutes to obtain the first polymer. Specifically, the second monomer is added dropwise to the reactor, and the stirring speed is set at 10-100 r / min, so that the first monomer and the second monomer are fully polymerized.

[0033] The reaction temperature is raised to 60-85° C., an initiator is added to the reactor containing the first polymer and the third monomer is added dropwise. After the third monomer is added dropwise, the reaction temperature is raised to 85-90° C., and the agitator is stirred for 120 min to obtain a solution containing the capsule unit 3. Specifically, the stirring speed is 10-100 r / min, so that the second polymer formed by the third monomer fully wraps the first polymer.

[0034] The solution containing the capsule units 3 is laid into a film to form the insulating layer, and the first conductive layer 1 and the second conductive layer 2 are respectively plated on both sides of the insulating layer to obtain the current collector.

[0035] In some embodiments, the first monomer is selected from one or more of acrylic acid, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, tert-butyl acrylate, methyl methacrylate, styrene, dibornene, hexamethylene diisocyanate and polydimethylsiloxane.

[0036] In some embodiments, the surfactant is one or more of sodium dodecyl sulfate, sodium dodecylbenzene sulfonate, OP-10, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose and polyvinyl alcohol.

[0037] In some embodiments, the second monomer is selected from one or more of tris(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate), and thioglycolic acid.

[0038] In a preferred embodiment, based on 100% of the total weight of the solution containing the capsule unit 3, the first monomer includes 10%-30% of butyl acrylate and 1%-10% of polydimethylsiloxane. The second monomer includes 2%-5% of trimethylolpropane tris(3-mercaptopropionate) and 3%-5% of pentaerythritol tetrakis(3-mercaptopropionate).

[0039] In some embodiments, the third monomer is selected from one or more of acrylic acid, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, tert-butyl acrylate, methyl methacrylate, styrene, dibornene, hexamethylene diisocyanate, polydimethylsiloxane, glycidyl methacrylate, methacrylate phosphate, and 1,4-butanediol acrylate.

[0040] In a preferred embodiment, based on 100% of the total weight of the solution containing the capsule unit 3, the third monomer includes 10%-50% of acrylonitrile and 5%-20% of glycidyl methacrylate.

[0041] In some embodiments, the molar ratio of the first polymer to the second polymer is (1:4) to (4:1).

[0042] In some embodiments, the initiator is selected from one or more of ammonium persulfate, sodium persulfate, potassium persulfate and azobisisobutyronitrile.

[0043] In a preferred embodiment, based on the total weight of the solution containing the capsule unit 3 being 100%, the content of the initiator is 0.1%-2%.

[0044] In another aspect, the present invention provides a lithium-ion battery comprising any one of the current collectors described above.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a current collector, characterized in that: The capsule comprises a first conductive layer, a second conductive layer and an insulating layer, wherein the insulating layer is arranged between the first conductive layer and the second conductive layer; the insulating layer is composed of a plurality of capsule units, wherein the capsule unit comprises a shell and a core body, wherein the shell is wrapped around the core body; the core body is composed of a first polymer; the shell is composed of a second polymer, wherein the glass transition temperature of the second polymer is greater than the glass transition temperature of the first polymer, wherein the glass transition temperature of the first polymer is -60°C to -10°C; and the glass transition temperature of the second polymer is 25°C to 50°C; The first polymer is formed by polymerizing a first monomer and a second monomer; the second polymer is formed by polymerizing a third monomer; and the preparation method of the current collector comprises the following steps: Add water, surfactant and first monomer into the reactor, stir with a stirrer for 30-120 min, and raise the reaction temperature to 40-85° C.; The second monomer is added dropwise to the reactor. After the second monomer is added dropwise, the reaction temperature is lowered to 25-40° C. and stirred for 120 minutes to obtain the first polymer. Raising the reaction temperature to 60-85° C., adding an initiator and dripping the third monomer into the reactor containing the first polymer, raising the reaction temperature to 85-90° C. after the dripping of the third monomer is completed, stirring with a stirrer for 120 min to obtain a solution containing the capsule unit; The solution containing the capsule units is laid into a film to form the insulating layer, and the first conductive layer and the second conductive layer are respectively plated on both sides of the insulating layer to obtain the current collector.

2. The method for preparing a current collector according to claim 1, characterized in that: The thickness of the insulating layer is 1-20 μm, the thickness of the first conductive layer is 2-10 μm, and the thickness of the second conductive layer is 2-10 μm.

3. The method for preparing a current collector according to claim 1, characterized in that: The first conductive layer and the second conductive layer are aluminum layers or copper layers.

4. The method for preparing a current collector according to claim 1, characterized in that: The first monomer is selected from one or more of acrylic acid, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, tert-butyl acrylate, methyl methacrylate, styrene, dibornene, hexamethylene diisocyanate and polydimethylsiloxane.

5. The method for preparing a current collector according to claim 1, characterized in that: The second monomer is selected from one or more of tris(2-hydroxyethyl)isocyanurate triacrylate, pentaerythritol tetrakis(3-mercaptopropionate), trimethylolpropane tris(3-mercaptopropionate) and thioglycolic acid.

6. The method for preparing a current collector according to claim 1, characterized in that: The third monomer is selected from one or more of acrylic acid, sodium acrylate, acrylonitrile, methyl acrylate, ethyl acrylate, tert-butyl acrylate, methyl methacrylate, styrene, dibornene, hexamethylene diisocyanate, polydimethylsiloxane, glycidyl methacrylate, methacrylate phosphate and 1,4-butanediol acrylate.

7. The method for preparing a current collector according to claim 1, characterized in that: The molar ratio of the first polymer to the second polymer is (1:4) to (4:1).

8. The method for preparing a current collector according to claim 1, characterized in that: The initiator is selected from one or more of ammonium persulfate, sodium persulfate, potassium persulfate and azobisisobutyronitrile.

9. A lithium ion battery, characterized in that: Comprising a current collector prepared by the current collector preparation method according to any one of claims 1 to 8.

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