High-strength low-elongation bipolar current collector and method for manufacturing the same

Abstract

This invention relates to the field of current collector technology, specifically a high-strength, low-elongation bipolar current collector and its preparation method. The high-strength, low-elongation bipolar current collector has a five-layer structure, sequentially comprising: an aluminum layer, a substrate layer I, a polymer film layer, a substrate layer II, and a copper layer. The current collector is prepared by crosslinking and modifying polymer film I and polymer film II, then sequentially depositing substrate layer I and an aluminum layer on one side of polymer film I, and sequentially depositing substrate layer II and a copper layer on one side of polymer film II. Finally, the untreated surfaces of polymer film I and polymer film II are bonded together by heating and pressing. The bipolar current collector prepared by this invention exhibits excellent tensile strength, elongation, and thermal shrinkage, effectively avoiding the through-hole pinholes that may occur with single-layer films, and essentially eliminating the short-circuit problem between the positive and negative electrodes caused by the current collector itself, thus offering better application advantages.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of current collectors, in particular to a high-strength low-elongation bipolar current collector and a preparation method thereof. BACKGROUND

[0002] Composite current collectors provide a new breakthrough point for the development of existing lithium batteries, and can improve the safety performance of lithium batteries and increase the energy density of lithium batteries, and also have potential cost advantages due to the reduced use of metal. Based on the special characteristics of the composite current collector, a new bipolar current collector has recently appeared. The difference between the bipolar current collector and the traditional composite current collector is that the metal layers on both sides of the base film are respectively an aluminum layer for bearing the role of the positive current collector and a copper layer for bearing the role of the negative current collector, and the base film layer in the middle is equivalent to the separator layer of the traditional battery, which serves to prevent short circuit between the positive and negative electrodes.

[0003] The bipolar current collector can realize higher power output by shortening the current transmission path and reducing the internal resistance, and also provides more space for active materials to improve the energy density. In addition, the bipolar current collector structure can realize series connection inside the battery cell, so that the single battery cell can realize high-voltage output.

[0004] At present, the research on bipolar current collectors in the lithium battery industry is still in its infancy, and the preparation and application of bipolar current collectors are still not mature. There are still the following defects: (1) the metal layers on both sides of the base film of the bipolar current collector pole piece and the active material layer are different, and there are differences in compaction and extension of the materials on both sides in the rolling process, which will cause different internal stresses on both sides of the base film, causing the pole piece to curl and poor alignment; (2) the bipolar current collector with traditional high polymer material as the base material is prone to warping, MD lines, wrinkles and other problems under the influence of coating tension and baking zone temperature due to the high elongation; (3) the bipolar current collector is mostly prepared by physical deposition method, which causes the middle polymer layer to easily produce pinholes in the production process, forming a channel through the positive and negative electrodes, resulting in battery short circuit.

[0005] Therefore, it is of great significance to provide a high-strength low-elongation bipolar current collector and a preparation method thereof. SUMMARY

[0006] The purpose of the present application is to provide a high-strength low-elongation bipolar current collector and a preparation method thereof to solve the problems in the prior art.

[0007] To achieve the above-mentioned purpose, the present application provides the following technical scheme:

[0008] The high-strength low-elongation bipolar current collector is divided into a five-layer structure, and sequentially comprises an aluminum layer, a primer layer I, a polymer film layer, a primer layer II, and a copper layer; the polymer film I and the polymer film II are subjected to cross-linking modification treatment, a primer layer I and an aluminum layer are sequentially deposited on one side surface of the polymer film I, a primer layer II and a copper layer are sequentially deposited on one side surface of the polymer film II, and finally the other side surfaces of the polymer film I and the polymer film II which are not subjected to deposition treatment are bonded by heating and pressing to obtain the high-strength low-elongation bipolar current collector.

[0009] Further, the preparation method of the high-strength low-elongation bipolar current collector specifically comprises the following steps.

[0010] S1: preparing a single-side aluminum layer-composite current collector

[0011] S11. depositing a primer layer I on one side surface of the polymer film I by using a physical deposition method;

[0012] S12. depositing an aluminum layer on the surface of the primer layer I by using a vacuum evaporation method to obtain a single-side aluminum layer-composite current collector;

[0013] S2: preparing a single-layer copper layer-composite current collector

[0014] S21. depositing a primer layer II on one side surface of the polymer film II by using a physical deposition method;

[0015] S22. depositing a copper layer on the surface of the primer layer II by using a water electroplating method to obtain a single-side copper layer-composite current collector;

[0016] S3: mutually adhering the other side surfaces of the single-side aluminum layer-composite current collector and the single-side copper layer-composite current collector which are not subjected to deposition treatment, and obtaining a high-strength low-elongation bipolar current collector by heating and pressing.

[0017] Further, the physical deposition method in the present application includes but is not limited to any one of a magnetron sputtering and a vacuum evaporation.

[0018] Preferably, if the physical deposition method is a magnetron sputtering, the process parameters of the magnetron sputtering are: a vacuum degree ≤ 1 × 10 -2 Pa, and a sputtering power is 0.5-2 KW; if the physical deposition method is a vacuum evaporation, the process parameters of the vacuum evaporation are: a vacuum degree ≤ 1 × 10 -2 Pa, and an evaporation temperature is 1400-1600℃.

[0019] Further, the polymer film I and the polymer film II are subjected to cross-linking modification treatment before being subjected to physical deposition.

[0020] The crosslinking modification treatment method is as follows: immerse polymer film I and / or polymer II in an organic solution of crosslinking agent, soak them at 20-60°C for 15-90 seconds, remove them, dry them, and the crosslinking modification treatment is completed.

[0021] Because of the low thickness of the polymer film, it swells slightly in organic solvents, allowing small-molecule crosslinking agents to penetrate into the molecular chains, resulting in uniform modification of the polymer film.

[0022] Furthermore, the polymer film I and polymer film II are, but are not limited to, any one of polypropylene film, polyethylene film, polyethylene terephthalate film, polyimide film, polyphenylene sulfide film, and polystyrene film; their thickness is 3 to 20 μm.

[0023] Furthermore, the crosslinking agent is a low-temperature crosslinking agent, specifically including but not limited to any one of organic peroxide crosslinking agents and multifunctional acrylate crosslinking agents;

[0024] The organic peroxide crosslinking agents include, but are not limited to, dicumyl peroxide and di-tert-butyl peroxide;

[0025] The multifunctional acrylate crosslinking agents include, but are not limited to, trimethylolpropane triacrylate.

[0026] Furthermore, the parameters of the polymer film II and the polymer film I used, as well as the crosslinking agent used in the crosslinking modification treatment, may differ.

[0027] Furthermore, the material of the base layer I is a metal or metal oxide, specifically including but not limited to any one of aluminum oxide, chromium oxide, and chromium, and its thickness is 1 to 20 nm.

[0028] Furthermore, the process parameters for the vacuum evaporation are: vacuum degree ≤ 1 × 10⁻⁶. -2 Pa, evaporation temperature is 1400~1600℃

[0029] Furthermore, the thickness of the aluminum layer is 0.5–2 μm.

[0030] Furthermore, the material of the underlayer II is a metal, specifically including but not limited to one or a combination of nickel, chromium, and copper, with a thickness of 5–40 nm.

[0031] Furthermore, the process parameters for the electroplating are: copper sulfate concentration of 180–220 g / L, and current density of 2.5–3.5 A / dm³. 2 The voltage is 8-12V and the temperature is 45-55℃.

[0032] Furthermore, the thickness of the copper layer is 0.5–2 μm.

[0033] Furthermore, the process parameters for the heating and pressing are: temperature of 60-150℃, pressure of 0.05-0.5MPa, and roller speed of 2-5m / min.

[0034] After hot pressing, the polymer films on both sides are bonded together by chemical bonds, and cross-linking occurs inside the base film, which increases the current collector strength and reduces the tensile elongation.

[0035] Compared with the prior art, the beneficial effects of the present invention are:

[0036] 1. In this invention, the polymer film is modified by crosslinking modification; on the one hand, it can ensure the interfacial bonding strength with the substrate, which improves the strength of the composite current collector; on the other hand, it can reduce the elongation of the composite current collector and improve the processing performance of the bipolar current collector.

[0037] 2. The intermediate polymer film layer of the bipolar current collector prepared by the present invention is obtained by heating and pressing a single-sided aluminum layer-composite current collector and a single-sided copper layer-composite current collector together. On the one hand, it can effectively prevent the appearance of holes in the single-layer film, which could cause short circuits to the positive and negative electrodes, thus greatly improving the safety performance of the battery. On the other hand, it can effectively eliminate the internal stress of the polymer film and prevent the electrode from curling.

[0038] 3. The process for preparing bipolar current collectors in this invention is simple, economical, and has significant advantages in product application. Attached Figure Description

[0039] Figure 1 This is a schematic diagram of the structure of a bipolar current collector. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0041] It should be noted that there are no special restrictions on the suppliers of the raw materials involved in this invention; exemplarily, they include:

[0042] Polyethylene terephthalate film (PET film), with thicknesses of 10μm, 6μm, and 4.5μm, model XR40H, purchased from Toray Industries, South Korea;

[0043] Polypropylene film (PP film), 4.5μm thick, model XT-002-005, purchased from Wenzhou Xintai New Material Co., Ltd.

[0044] The purity of dicumyl peroxide is 99%, CAS number: 80-43-3; the purity of di-tert-butyl peroxide is 99%, CAS number: 110-05-4, both of which are commercially available.

[0045] Example 1: A method for preparing a high-strength, low-elongation bipolar current collector:

[0046] S1: Preparation of a single-sided aluminum layer-composite current collector:

[0047] S11. Take a 6μm thick PET film I, immerse it in a 1mol / L dicumyl peroxide ethanol solution, soak it at 50℃ for 60s, take it out, and dry it at 80℃ to obtain modified PET film I; finally, use vacuum evaporation to deposit a 5nm thick aluminum oxide layer (underlayer I) on one side of the modified PET film I.

[0048] The process parameters for vacuum evaporation are: vacuum degree 0.8 × 10⁻⁶. -2 Pa, evaporation temperature is 1450℃;

[0049] S12. A 1 μm thick aluminum layer is deposited on the surface of the alumina layer of the thin film obtained in S1 by vacuum evaporation to obtain a single-sided aluminum layer-composite current collector.

[0050] The process parameters for vacuum evaporation are: vacuum degree 0.8 × 10⁻⁶. -2 Pa, evaporation temperature is 1550℃;

[0051] S2: Preparation of a single-layer copper composite current collector:

[0052] S21. Take a 4.5 μm thick PET film II, immerse it in a 1 mol / L dicumyl peroxide ethanol solution, soak it at 50 °C for 40 s, take it out, and dry it at 80 °C to obtain modified PET film II; finally, use magnetron sputtering to deposit a 10 nm thick nickel-chromium layer (underlayer II) on one side surface of modified PET film II.

[0053] The process parameters for magnetron sputtering are: vacuum degree of 0.8 × 10⁻⁶. -2 Pa, sputtering power is 1KW;

[0054] S22. A 1 μm thick copper layer is deposited on the surface of the nickel-chromium layer of the thin film obtained in S2 by electroplating to obtain a single-sided copper layer-composite current collector;

[0055] The electroplating process parameters are as follows: copper sulfate concentration 200 g / L, current density 3 A / dm³. 2 The voltage is 10V and the temperature is 50℃.

[0056] S3: The undeposited surfaces of the single-sided aluminum layer-composite current collector obtained in S1 and the single-sided copper layer-composite current collector obtained in S2 are bonded together and heated and pressed at a temperature of 120℃, a pressure of 0.2MPa, and a roller speed of 3m / min to obtain a high-strength, low-elongation bipolar current collector.

[0057] Example 2: A method for preparing a high-strength, low-elongation bipolar current collector:

[0058] S1: Preparation of a single-sided aluminum layer-composite current collector:

[0059] S11. Take a 6μm thick PET film I, immerse it in a 1mol / L dicumyl peroxide ethanol solution, soak it at 30℃ for 60s, take it out, and dry it at 80℃ to obtain modified PET film I; finally, use vacuum evaporation to deposit a 5nm thick aluminum oxide layer (underlayer I) on one side surface of modified PET film I.

[0060] The process parameters for vacuum evaporation are: vacuum degree 0.8 × 10⁻⁶. -2 Pa, evaporation temperature is 1450℃;

[0061] S12. A 1 μm thick aluminum layer is deposited on the surface of the alumina layer of the thin film obtained in S1 by vacuum evaporation to obtain a single-sided aluminum layer-composite current collector.

[0062] The process parameters for vacuum evaporation are: vacuum degree 0.8 × 10⁻⁶. -2 Pa, evaporation temperature is 1550℃;

[0063] S2: Preparation of a single-layer copper composite current collector:

[0064] S21. Take a 4.5 μm thick PP film II, immerse it in an acetone solution of 1 mol / L di-tert-butyl peroxide, soak it at 50 °C for 40 s, take it out, and dry it at 80 °C to obtain modified PET film II; finally, use magnetron sputtering to deposit a 10 nm thick nickel-chromium layer (underlayer II) on one side of the modified PET film II.

[0065] The process parameters for magnetron sputtering are: vacuum degree of 0.8 × 10⁻⁶. -2 Pa, sputtering power is 1KW;

[0066] S22. A 1 μm thick copper layer is deposited on the surface of the nickel-chromium layer of the thin film obtained in S2 by electroplating to obtain a single-sided copper layer-composite current collector;

[0067] The electroplating process parameters are as follows: copper sulfate concentration 200 g / L, current density 3 A / dm³. 2 The voltage is 10V and the temperature is 50℃.

[0068] S3: The undeposited surfaces of the single-sided aluminum layer-composite current collector obtained in S1 and the single-sided copper layer-composite current collector obtained in S2 are bonded together and heated and pressed at a temperature of 120℃, a pressure of 0.2MPa, and a roller speed of 3m / min to obtain a high-strength, low-elongation bipolar current collector.

[0069] Based on Example 1, the following control experiments were conducted, specifically Comparative Examples 1 and 2, as described below:

[0070] Comparative Example 1: Comparative Example 1 is based on Example 1, with the following adjustment: only one PET base film is used, and deposition treatment is performed on both surfaces of the film, while other processes remain unchanged. Specifically:

[0071] A method for preparing a high-strength, low-elongation bipolar current collector:

[0072] S1. Take a 10μm thick PET film, immerse it in a 1mol / L dicumyl peroxide ethanol solution, soak it at 50℃ for 60s, take it out, and then dry it at 80℃ to obtain a modified PET film.

[0073] S2. A 5nm thick aluminum oxide layer is deposited on one side of the modified PET film using vacuum evaporation (underlying layer I); then a 1μm thick aluminum layer is deposited on the surface of the aluminum oxide layer using vacuum evaporation to obtain a single-sided aluminum layer-composite current collector.

[0074] S3. A 10 nm thick nickel-chromium layer (underlayer II) is deposited on the other side of the modified PET film using magnetron sputtering; then a 1 μm thick copper layer is deposited on the surface of the nickel-chromium layer using electroplating to obtain a high-strength, low-elongation bipolar current collector.

[0075] The process parameters for vacuum evaporation are: vacuum degree 0.8 × 10⁻⁶. -2 Pa, evaporation temperature is 1550℃;

[0076] The process parameters for magnetron sputtering are: vacuum degree of 0.8 × 10⁻⁶. -2 Pa, sputtering power is 1KW;

[0077] The electroplating process parameters are: copper sulfate concentration of 200 g / L, current density of 3 A / dm³.2 The voltage is 10V and the temperature is 50℃.

[0078] Comparative Example 2: Comparative Example 2 is based on Example 1, but with the following adjustment: instead of using a heat-pressing method to bond the single-sided aluminum layer-composite current collector and the single-sided copper layer-composite current collector, a polyurethane adhesive is used to bond them together. All other processes remain unchanged. Specifically:

[0079] A method for preparing a high-strength, low-elongation bipolar current collector:

[0080] S1: Preparation of a single-sided aluminum layer-composite current collector:

[0081] S11. Take a 6μm thick PET film I, immerse it in a 1mol / L dicumyl peroxide ethanol solution, soak it at 50℃ for 60s, take it out, and dry it at 80℃ to obtain modified PET film I; finally, use vacuum evaporation to deposit a 5nm thick aluminum oxide layer (underlayer I) on one side of the modified PET film I.

[0082] The process parameters for vacuum evaporation are: vacuum degree 0.8 × 10⁻⁶. -2 Pa, evaporation temperature is 1450℃;

[0083] S12. A 1 μm thick aluminum layer is deposited on the surface of the alumina layer of the thin film obtained in S1 by vacuum evaporation to obtain a single-sided aluminum layer-composite current collector.

[0084] The process parameters for vacuum evaporation are: vacuum degree 0.8 × 10⁻⁶. -2 Pa, evaporation temperature is 1550℃;

[0085] S2: Preparation of a single-layer copper composite current collector:

[0086] S21. Take a 4.5 μm thick PET film II, immerse it in a 1 mol / L dicumyl peroxide ethanol solution, soak it at 50 °C for 40 s, take it out, and dry it at 80 °C to obtain modified PET film II; finally, use magnetron sputtering to deposit a 10 nm thick nickel-chromium layer (underlayer II) on one side surface of modified PET film II.

[0087] The process parameters for magnetron sputtering are: vacuum degree of 0.8 × 10⁻⁶. -2 Pa, sputtering power is 1KW;

[0088] S22. A 1 μm thick copper layer is deposited on the surface of the nickel-chromium layer of the thin film obtained in S2 by electroplating to obtain a single-sided copper layer-composite current collector;

[0089] The electroplating process parameters are as follows: copper sulfate concentration 200 g / L, current density 3 A / dm³. 2 The voltage is 10V and the temperature is 50℃.

[0090] S3: After coating the undeposited surfaces of the single-sided aluminum layer-composite current collector obtained in S1 and the single-sided copper layer-composite current collector obtained in S2 with polyurethane adhesive, the two are bonded together to obtain a high-strength, low-elongation bipolar current collector.

[0091] Performance testing: The bipolar current collectors prepared in Examples 1-2 and Comparative Examples 1-2 were subjected to relevant performance tests, as follows:

[0092] (1) The tensile strength and elongation of the bipolar current collector were tested according to the standard GB / T 1040.3-2006;

[0093] (2) After baking the bipolar current collector at 150°C for 30 minutes, the heat shrinkage rate was tested.

[0094] (3) Perform density and light transmittance tests on the bipolar current collector.

[0095] (4) Cut the bipolar current collector into 10cm×10cm size, place it naturally on a flat table, and measure the maximum height of the edge of the bipolar current collector.

[0096] The specific test results are shown in Table 1 below:

[0097] Table 1

[0098]

[0099]

[0100] Results Analysis: As can be seen from the data in the table above, the tensile strength, elongation and thermal shrinkage of the bipolar current collector prepared by the present invention are far superior to those of the bipolar current collector prepared by the traditional method, and there is no risk of light transmission. The internal stress of the material is smaller and the edge warping is also smaller.

[0101] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, all variations falling within the meaning and scope of equivalents of the claims are intended to be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for preparing a high-strength, low-elongation bipolar current collector, characterized in that: Specifically, the following steps are included: S1: Preparation of a single-sided aluminum layer-composite current collector: S11. A base layer I is deposited on one side surface of polymer film I using a physical deposition method; S12. An aluminum layer is deposited on the surface of the base layer I by vacuum evaporation to obtain a single-sided aluminum layer-composite current collector; S2: Preparation of a single-layer copper composite current collector: S21. A base layer II is deposited on one side surface of polymer film II using a physical deposition method; S22. A copper layer is deposited on the surface of the base layer II by electroplating to obtain a single-sided copper layer-composite current collector; S3: The undeposited surfaces of the single-sided aluminum layer-composite current collector and the single-sided copper layer-composite current collector are bonded together and heated and pressed to obtain a high-strength, low-elongation bipolar current collector; Before physical deposition, both polymer film I and polymer film II undergo crosslinking modification treatment. The method for crosslinking modification is as follows: immerse polymer film I and / or polymer II in an organic solution of crosslinking agent, soak them at 20-60℃ for 15-90 seconds, remove them, dry them, and the crosslinking modification is completed. The crosslinking agent is a low-temperature crosslinking agent, specifically including any one of organic peroxide crosslinking agents and multifunctional acrylate crosslinking agents; The process parameters for heating and pressing are: temperature 60-150℃, pressure 0.05-0.5MPa, and roller speed 2-5m / min. The organic peroxide crosslinking agent includes dicumyl peroxide and di-tert-butyl peroxide; the multifunctional acrylate crosslinking agent includes trimethylolpropane triacrylate.

2. The method for preparing a high-strength, low-elongation bipolar current collector according to claim 1, characterized in that: The polymer film I and polymer film II are of any one of polypropylene film, polyethylene film, polyethylene terephthalate film, polyimide film, polyphenylene sulfide film, and polystyrene film, and their thickness is 3 to 20 μm.

3. The method for preparing a high-strength, low-elongation bipolar current collector according to claim 1, characterized in that: The parameters of the polymer film II and the polymer film I used, as well as the crosslinking agent used in the crosslinking modification treatment, may differ.

4. The method for preparing a high-strength, low-elongation bipolar current collector according to claim 1, characterized in that: The physical deposition method includes either magnetron sputtering or vacuum evaporation; if the physical deposition method is magnetron sputtering, the process parameters for magnetron sputtering are: vacuum degree ≤ 1 × 10⁻⁶. -2 Pa, sputtering power is 0.5~2KW; If the physical deposition method is vacuum evaporation, the process parameters for vacuum evaporation are: vacuum degree ≤ 1 × 10⁻⁶. -2 Pa, evaporation temperature is 1400~1600℃.

5. The method for preparing a high-strength, low-elongation bipolar current collector according to claim 1, characterized in that: The material of the underlayer I is a metal or metal oxide, specifically including any one of aluminum oxide, chromium oxide, and chromium, with a thickness of 1 to 20 nm; the material of the underlayer II is a metal, specifically including one or a combination of nickel, chromium, and copper, with a thickness of 5 to 40 nm.

6. The method for preparing a high-strength, low-elongation bipolar current collector according to claim 1, characterized in that: The process parameters for the vacuum evaporation are: vacuum degree ≤ 1×10⁻⁶ -2 Pa, evaporation temperature is 1400~1600℃; the thickness of the aluminum layer is 0.5~2μm; the electroplating process parameters are: copper sulfate concentration is 180~220g / L, current density is 2.5~3.5A / dm³ 2 The voltage is 8–12V and the temperature is 45–55℃; the thickness of the copper layer is 0.5–2μm.

7. A high-strength, low-elongation bipolar current collector prepared by the preparation method according to any one of claims 1 to 6, characterized in that: The high-strength, low-elongation bipolar current collector is sequentially configured with: an aluminum layer, a base layer I, a polymer film layer, a base layer II, and a copper layer.

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