Irregularly shaped composite current collector and its preparation method, positive electrode sheet

Abstract

This invention provides an irregularly shaped composite current collector and its preparation method, as well as a positive electrode sheet. The preparation method includes the following steps: adding a dispersant, a conductive agent, and an inorganic filler sequentially to water, followed by sand milling to obtain a first mixture; mixing a binder and a wetting agent into the first mixture to obtain a second mixture; vacuuming, degassing, and filtering the second mixture to obtain a base coating slurry; applying the base coating slurry to the surface of the current collector in a single coating operation, forming a first base coating portion, a second base coating portion, and a third base coating portion arranged sequentially side by side along the width of the current collector. The first and third base coating portions are located on opposite sides of the second base coating portion, and their thicknesses are all greater than those of the second base coating portion. This preparation method employs a specific dispersion process to ensure more uniform dispersion of the conductive agent, reducing resistance differences. By completing two coating operations in a single coating operation, the thickness zoning is achieved, which can reduce heat generation during short circuits, lower the risk of short circuits, and improve the pass rates of thermal abuse, drop, and needle penetration tests.

Description

Technical Field

[0001] This invention relates to the field of new energy battery technology, and in particular to the preparation of key materials for new energy batteries, and even more so to a shaped composite current collector and its preparation method, and a positive electrode sheet. Background Technology

[0002] With the rapid iteration of consumer digital electronics products and the increasing demand for high energy density, the safety performance of lithium-ion batteries has become a core technical indicator in the industry. Needle penetration, thermal abuse, and drop tests are key items in the mandatory safety testing of lithium batteries, and their failure and fire issues have long constrained the safety upgrades and large-scale application of digital lithium batteries. Meanwhile, existing base coating technologies and double-coating processes used to improve battery safety performance generally suffer from poor resistance stability, poor batch consistency, and significant defects in mass production processes, failing to simultaneously address cell safety performance, electrochemical performance, and production feasibility.

[0003] During the nail penetration test, after the needle pierces the positive and negative electrode plates, it directly causes the positive and negative active materials to come into contact, triggering an internal short circuit and rapid temperature rise in the battery. As the penetration depth increases, the positive current collector aluminum foil comes into direct contact with the negative active material, and the two undergo a violent exothermic reaction, further aggravating the battery temperature rise and ultimately causing a fire and explosion. In particular, the probability of fire in lithium cobalt oxide batteries can reach 100% in conventional nail penetration tests, posing an extremely high safety hazard.

[0004] During thermal abuse testing, the separator at the top and bottom edges of the cell is prone to thermal shrinkage after being heated. After shrinkage, the separator cannot effectively insulate and isolate the cells, causing the positive and negative electrodes in the edge area to directly contact and short-circuit. The heat generated by the short circuit will continue to aggravate the degree of separator shrinkage, expand the short circuit range, and in severe cases, directly cause the battery to catch fire.

[0005] During drop testing, the impact of the drop will cause the electrode plates on the upper and lower edges of the cell to be squeezed and bent, which can easily cause the active material on the electrode surface to fall off. The fallen active material particles can easily pierce the separator and form an internal short circuit. If the aluminum foil comes into contact with the negative electrode active material during the short circuit, it will also quickly trigger thermal runaway and fire.

[0006] To address the aforementioned fire issues, existing technologies typically apply a safety undercoat to the surface of the aluminum foil current collector. Utilizing the high adhesion between the undercoat and the current collector, the undercoat remains intact even when the active material detaches. This undercoat encapsulates and isolates the aluminum foil, preventing direct contact between the aluminum foil and the negative electrode active material, thus reducing the risk of violent reactions and fire. Furthermore, existing technologies employ a two-coating process to prepare the electrode sheet. By controlling the thickness, the electrode sheet's thickness at the edges on both sides of the current collector surface is greater than the thickness in the middle area. The proportion of conductive agent in the second coating slurry is reduced to increase coating resistance, which is used to improve the lithium plating problem at the electrode edges. However, this process is only applied to carbon-coated battery cells, with the core purpose of improving fast-charging performance. It is not a specific improvement solution for needle penetration, thermal abuse, or drop safety tests, and therefore cannot solve the problem of battery fire failure in multiple scenarios.

[0007] Furthermore, existing technologies have significant and insurmountable drawbacks in practical applications: First, the resistance stability of the base coating is poor, with large resistance deviations between different production batches, mainly due to the uneven dispersion of conductive agents such as SP. Some manufacturers try to reduce the overall coating resistance to minimize resistance differences, but this reduction in resistance can exacerbate the reaction after a battery short circuit, significantly increasing the probability of fire. It is impossible to simultaneously ensure both resistance consistency and battery safety performance. Second, the double coating process increases production steps, production cycle, and production costs in mass production. Because different slurry formulations are used for the two coatings, mixing problems are very likely to occur during production. At the same time, the alignment accuracy during the second coating is difficult to control, easily leading to coating misalignment, overlapping areas, and localized missed coatings, which seriously affect the quality of electrode products and mass production yield.

[0008] In summary, existing digital lithium battery technologies cannot effectively solve the problems of fire and explosion in needle penetration, thermal abuse, and drop tests. They also suffer from multiple technical defects, such as unstable bottom coating resistance, poor batch consistency, easy misalignment and mixing of materials in the two coating processes, high production costs, and insufficient mass production stability. These shortcomings make it difficult to meet the safety and production requirements of high-end digital lithium batteries. Therefore, developing a lithium battery technology solution that can solve the above problems at the same time is of great practical significance. Summary of the Invention

[0009] Based on the above problems, the purpose of this invention is to provide an irregularly shaped composite current collector and its preparation method, as well as a positive electrode sheet. The preparation method adopts a specific dispersion process to make the conductive agent more uniformly dispersed, reduce the resistance difference, and achieve the purpose of thickness partitioning by completing two coatings in one coating, thereby effectively reducing the heat generation during short circuits, reducing the risk of short circuits, and improving the battery pass rate of thermal abuse, drop, and nail penetration tests.

[0010] To achieve the above objectives, the first aspect of the present invention provides a method for preparing an irregularly shaped composite current collector, comprising the steps of: (1) Preparation of primer slurry A first mixture is obtained by adding a dispersant, a conductive agent, and an inorganic filler sequentially to water and then milling it. A binder and a wetting agent are then mixed into the first mixture to obtain a second mixture. The second mixture is then vacuumed, degassed, and filtered to obtain a primer slurry. The inorganic filler is selected from alumina and / or boehmite, and the conductive agent is selected from conductive carbon black and / or conductive agent materials with PTC effect. The milling conditions are as follows: the number of milling cycles is 3 to 5, the milling speed is 2000 to 2800 rpm, and the diameter of the milling media is 1000 to 1500 times that of the primer slurry Dv50. (2) Coating of current collector The primer slurry is applied to the surface of the current collector in one step, and a first primer portion, a second primer portion, and a third primer portion are formed in parallel along the width direction of the current collector. The first primer portion and the third primer portion are disposed on the opposite side of the second primer portion and their thicknesses are both higher than those of the second primer portion.

[0011] In the preparation method of the irregular composite current collector of the present invention, during the preparation of the primer slurry, a specific dispersion process can be used to make the components disperse evenly, which can not only reduce the resistance difference, but also avoid the risks of material damage, resistance increase, and large polarization.

[0012] Specifically, in the preparation process of the primer slurry, before adding the binder, the dispersant, conductive agent, inorganic filler, and water are first milled to ensure that the conductive agent, inorganic filler, and other powder particles are fully wetted, deagglomerated, and uniformly dispersed. This prevents the binder from prematurely encapsulating the powder particles, causing agglomeration and poor dispersion, and avoids the high shear force of milling damaging the molecular chains of the binder. Furthermore, based on the fact that the inorganic filler in the slurry is alumina and / or boehmite, and the conductive agent is conductive carbon black and / or a conductive agent material with PTC effect, the inventors of this invention control the milling conditions as follows: 3-5 milling cycles, a milling speed of 2000-2800 rpm, a milling media diameter 1000-1500 times that of the primer slurry Dv50, and the milling media occupying 50-70% of the milling chamber volume. This avoids excessive milling cycles (too long a time) and excessively fast milling speeds, which could lead to the destruction of the conductive agent, a rapid increase in resistance, and the destruction of the inorganic filler, resulting in reverse agglomeration. If the diameter of the grinding media is too large, the grinding shear force will be insufficient, and the particle size distribution will be widened (Dv10 / Dv90 will increase). If the diameter is too small, the energy input will be insufficient, the grinding efficiency will decrease, the risk of batch-to-batch fluctuations will increase, and the media will be prone to agglomeration or encapsulation by boehmite colloids (especially under high solids content and weak dispersion conditions), leading to grinding stagnation and difficulty in discharging. Therefore, this invention, based on specific conductive agents and specific inorganic fillers, creatively selects specific grinding parameters to ensure uniform dispersion and rheological stability of the slurry components, reduce the extreme difference in resistivity, and avoid the risks of increased resistance due to material damage.

[0013] This invention enables a single-coat application of a uniformly dispersed primer slurry onto the current collector, eliminating the need for multiple coatings and various coating slurries. This shortens production time and avoids misalignment issues associated with multiple coatings. Furthermore, this single-coat application achieves a primer layer that is thicker at the edges and thinner in the center (the thickness of the first and third primer layers is greater than that of the second primer layer). The resistance at the edges is significantly higher than in the center, reducing heat generation during short circuits at the electrode edges. Additionally, the thicker primer layer at the edges, after electrode slitting, also provides some encapsulation for the cut current collector. Therefore, the irregularly shaped composite current collector prepared using this method reduces the risk of short circuits, thereby improving battery pass rates in thermal abuse, drop, and nail penetration tests.

[0014] As one technical solution of the present invention, the solid content of the primer slurry is 10-15%, the viscosity is 100-500 mPa·s, and based on the total mass of the dispersant, the binder, the conductive agent, the inorganic filler, and the wetting agent being 100%, the proportion of the dispersant is 0.1-0.5 wt.%, the proportion of the binder is 6-15 wt.%, the proportion of the conductive agent is 1.5-2.5 wt.%, the proportion of the inorganic filler is 81-93 wt.%, and the proportion of the wetting agent is 0.1-0.5 wt.

[0015] As one technical solution of the present invention, the dispersant is selected from polyether polymers, the binder is selected from polyacrylic acid polymers or polyamide polymers, and the wetting agent is selected from polyether-modified polysiloxane compounds.

[0016] As a technical solution of the present invention, the Dv10 of the primer slurry is 0.05~0.20μm, the Dv50 is 0.2~0.8μm, the Dv90 is 0.80~1.99μm, and the resistance difference is ≤2Ω under a pressure of 60MPa.

[0017] As a technical solution of the present invention, the dispersant, the conductive agent, the inorganic filler, the binder and the wetting agent are first mixed using a planetary ball mill when added. The media of the planetary ball mill are a combination of agate balls with the same mass ratio and diameters of 1 mm and 3 mm, respectively. The revolution speed of each ball is 100~500 r / min, the rotation speed is 200~1000 rpm, and the milling time is 10~60 min.

[0018] As one technical solution of the present invention, the grinding medium is zirconium beads with a diameter of 0.5~1.0mm, and the medium occupies 50~70% of the grinding chamber volume.

[0019] As a technical solution of the present invention, the vacuum is drawn to a vacuum degree of -70~-90Kpa and maintained for 30~60min, and the filtration adopts a 120~150 mesh filter screen.

[0020] As a technical solution of the present invention, the concave roller used for coating includes a first roller section, a second roller section, and a third roller section arranged in parallel. The first roller section is coated to form the first base coating section, the second roller section is coated to form the second base coating section, and the third roller section is coated to form the third base coating section. The mesh count on the roller surface of the first roller section and the third roller section is 40-80 mesh, and the mesh depth is 150-200 μm. The mesh count on the roller surface of the second roller section is 100-180 mesh, and the mesh depth is 50-100 μm.

[0021] A second aspect of the present invention provides an irregularly shaped composite current collector prepared by the aforementioned method, comprising a current collector and a first base coating portion, a second base coating portion, and a third base coating portion disposed on the surface of the current collector. The thickness of the second base coating portion is 3~5 μm, and the resistivity of the second base coating portion is 0.5~5.0 Ω / cm. 2 The thickness of the first and third base coating portions is 8~20μm, and the resistivity of the first and third base coating portions is 10~100Ω / cm. 2 .

[0022] The irregularly shaped composite current collector of the present invention has high resistance and thickness at the edges and low resistance and thickness in the middle. Therefore, during thermal abuse, drop and nail penetration tests, it can avoid contact between the current collector and the active material layer of the other electrode, reduce heat generation during short circuit, reduce the risk of short circuit, improve the battery test pass rate and expand its application range.

[0023] A third aspect of the present invention provides a positive electrode sheet, comprising a positive current collector and an active material layer, wherein the positive current collector is a aforementioned irregularly shaped composite current collector, and the first base coating portion, the second base coating portion and the third base coating portion are all disposed between the active material layer and the current collector. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the irregular composite current collector of the present invention.

[0025] Figure 2 The image shows the appearance of the irregularly shaped composite current collector of Example 1 magnified 100 times using a magnifying glass.

[0026] Figure 3 The image shows the appearance of the irregularly shaped composite current collector of Comparative Example 2 after being magnified 100 times using a magnifying glass. Detailed Implementation

[0027] The irregularly shaped composite current collector of the present invention can be used as a positive electrode current collector or a negative electrode current collector in the electrode sheet. Preferably, it is applied to the positive electrode sheet, which can effectively avoid contact with the negative electrode active material to reduce the risk of internal short circuit, thereby improving the pass rate of the battery in thermal abuse, drop and nail penetration tests.

[0028] The positive electrode of this invention includes a positive current collector and an active material layer. For example... Figure 1 As shown, the irregularly shaped composite current collector 100 used in the positive electrode current collector includes a current collector 10 and a first base coating portion 31, a second base coating portion 33, and a third base coating portion 35 disposed on the surface of the current collector 10. The first base coating portion 31, the second base coating portion 33, and the third base coating portion 35 are arranged side by side along the width direction of the current collector 10. The first base coating portion 31 and the third base coating portion 35 are disposed on opposite sides of the second base coating portion 33 and are both thicker than the second base coating portion 33. An active material layer is disposed on the first base coating portion 31, the second base coating portion 33, and the third base coating portion 35. The thickness of the second base coating portion 33 is 3~5μm, and the resistivity of the second base coating portion 33 is 0.5~5.0Ω / cm. 2 The thickness of the first primer layer 31 and the third primer layer 35 is 8~20μm, and the resistivity of the first primer layer 31 and the third primer layer 35 is 10~100Ω / cm. 2 The irregularly shaped composite current collector of this invention can be a single unit or multiple units. Multiple irregularly shaped composite current collectors can be further slitting later. For example... Figure 1 As shown, there are two irregularly shaped composite current collectors, which can be produced by slitting the third primer portion 35 to obtain two independent irregularly shaped composite current collectors. The positional error of the slitting determines the width of the third primer portion 35 in the two irregularly shaped composite current collectors. If the slitting position is exactly in the middle, the width of the third primer portion 35 of the two irregularly shaped composite current collectors will be the same, which can be 5mm. The allowable deviation of the slitting position is ±3mm, and the minimum requirement is not less than 2mm.

[0029] The method for preparing the irregularly shaped composite current collector of the present invention includes the following steps: (1) Preparation of primer slurry Dispersant, conductive agent and inorganic filler are added to water in sequence and then sand milled to obtain a first mixture. Binder and wetting agent are then mixed into the first mixture to obtain a second mixture. The second mixture is vacuumed, degassed and filtered to obtain a primer slurry. (2) Coating of current collector A primer slurry is applied to the surface of the current collector in one pass, and a first primer portion, a second primer portion, and a third primer portion are formed in parallel along the width direction of the current collector. The first primer portion and the third primer portion are disposed on the opposite side of the second primer portion and their thicknesses are both higher than those of the second primer portion.

[0030] The primer slurry has a Dv10 of 0.05~0.20μm, a Dv50 of 0.2~0.8μm, and a Dv90 of 0.80~1.99μm. A lower Dv50 indicates uniform dispersion of the components in the slurry. The shaped composite current collector exhibits a resistivity difference ≤2Ω under 60MPa pressure, further confirming the relatively uniform dispersion of the conductive agent. The primer slurry has a solid content of 10~15% and a viscosity of 100~500mpa.s.

[0031] Based on the total mass of dispersant, binder, conductive agent, inorganic filler, and wetting agent as 100%, the proportion of dispersant is 0.1~0.5 wt.%, binder is 6~15 wt.%, conductive agent is 1.5~2.5 wt.%, inorganic filler is 81~93 wt.%, and wetting agent is 0.1~0.5 wt.%. The dispersant is selected from polyether polymers, and the binder is selected from polyacrylic acid polymers or polyamide polymers. The conductive agent is selected from conductive carbon black and / or conductive agent materials with PTC effect. Conductive agent materials with PTC effect exhibit PTC effect, where the resistance becomes infinite at high temperatures during short circuits, physically isolating electron conduction and reducing thermal failure reactions. Conductive agent materials with PTC effect can be N550 carbon black, methyl methacrylate-grafted carbon black, or modified carbon black. The inorganic filler is selected from alumina and / or boehmite, with a Dv10 of 0.05~0.20μm, a Dv50 of 0.2~0.8μm, and a Dv90 of 0.80~1.99μm. The wetting agent is selected from polyether-modified polysiloxane compounds. The dispersant, conductive agent, inorganic filler, binder and wetting agent are first mixed in a planetary ball mill before being added. The media of the planetary ball mill are a combination of agate balls with the same mass ratio and diameters of 1 mm and 3 mm. The revolution speed of each ball is 100~500 r / min, the rotation speed is 200~1000 rpm, and the milling time is 10~60 min.

[0032] The sand milling conditions are as follows: 3-5 milling cycles, a milling speed of 2000-2800 rpm, and a milling media diameter 1000-1500 times that of D1. Furthermore, the milling media consists of zirconium beads with a diameter of 0.5-1.0 mm, occupying 50-70% of the milling chamber volume. Excessive media content can damage the media and cause significant overall heat generation; insufficient content will result in inadequate dispersion of the slurry. A vacuum is applied to -70 to -90 kPa and maintained for 30-60 minutes. Filtration is performed using a 120-150 mesh filter.

[0033] The coating process utilizes a concave roller comprising a first roller section, a second roller section, and a third roller section arranged in parallel. The first roller section forms the first primer coating, the second roller section forms the second primer coating, and the third roller section forms the third primer coating. The mesh count on the roller surfaces of the first and third roller sections is 40-80 mesh, and the cell depth is 150-200 μm. The mesh count on the roller surface of the second roller section is 100-180 mesh, and the cell depth is 50-100 μm. The concave roller can employ a 45° oblique groove design to reduce the appearance of coating lines. Multiple sets of first, second, and third roller sections can be arranged in parallel on the concave roller, allowing for the simultaneous coating of multiple sets of irregularly shaped composite current collectors. These can then be slited to produce multiple independent irregularly shaped composite current collectors, or coated with active material and then slited to produce multiple independent electrode sheets. After coating, the irregularly shaped composite current collectors can be obtained through conventional drying processes, with drying parameters adjusted according to the solid content of the slurry.

[0034] To better illustrate the purpose, technical solution, and beneficial effects of this invention, the invention will be further described below with reference to specific embodiments. It should be noted that the methods described below are further explanations of this invention and should not be construed as limiting it.

[0035] Example 1 This embodiment describes a method for preparing an irregularly shaped composite current collector, which includes the following steps.

[0036] (1) Preparation of primer slurry The raw materials include 0.3 wt.% polyether dispersant 2383, 12 wt.% PAA binder, 1.5 wt.% conductive carbon black, 86 wt.% boehmite (Dv50 is 0.5 μm), and 0.2 wt.% polyether-modified polydimethylsiloxane.

[0037] Polyether dispersant 2383 was added to water and mixed using a planetary ball mill. The media in the planetary ball mill consisted of agate balls (a combination of 1mm diameter and 3mm diameter agate balls in equal mass ratio). Dispersion was carried out for 10 minutes at a rotation speed of 300 rpm and a revolution speed of 200 rpm. Then, conductive carbon black was added and dispersed for 60 minutes at a rotation speed of 450 rpm and a revolution speed of 300 rpm. Finally, boehmite was added and dispersed at high speed for 80 minutes at a rotation speed of 550 rpm and a revolution speed of 300 rpm. The mixture was then subjected to sand milling to obtain the first mixture. The sand milling conditions were as follows: three milling cycles, a milling speed of 2500 rpm, and zirconium beads as the milling media. The zirconium beads had a diameter of 0.8mm and occupied 60% of the sand milling chamber volume.

[0038] The first mixture was poured back into the planetary ball mill, and PAA binder was added. The mixture was stirred and dispersed for 60 minutes at a rotation speed of 400 rpm and a revolution speed of 300 rpm. Then, polyether-modified polydimethylsiloxane was added and stirred for 10 minutes at 500 rpm to obtain the second mixture. The second mixture was then evacuated to a vacuum of -80 kPa and maintained for 45 minutes to remove bubbles. The mixture was then filtered through a 120-150 mesh filter to obtain the primer slurry. The primer slurry had a Dv10 of 0.10 μm, a Dv50 of 0.56 μm, a Dv90 of 1.34 μm, a solid content of 13%, and a viscosity of 270 mPa·s.

[0039] (2) Coating of current collector A primer slurry is applied to the surface of the aluminum foil in a single coat, forming a first primer layer, a second primer layer, and a third primer layer arranged sequentially side-by-side along the width of the current collector. The first and third primer layers are located on opposite sides of the second primer layer. The mesh count on the roller surfaces of the first and third roller layers is 50 mesh, and the cell depth is 180 μm. The mesh count on the roller surface of the second roller layer is 150 mesh, and the cell depth is 80 μm. After coating, the material is dried at 100°C for 15 min to obtain a shaped composite current collector.

[0040] The irregularly shaped composite current collector prepared by this method includes a current collector and a first primer layer, a second primer layer, and a third primer layer disposed on the surface of the current collector. Testing showed that the thickness of the first primer layer is 12 μm and its resistivity is 74.9 Ω / cm. 2 The thickness of the second primer layer is 4 μm, and the resistivity of the second primer layer is 3.0 Ω / cm. 2 The thickness of the third primer layer is 12 μm and its resistivity is 73.2 Ω / cm. 2 The resistance range is 1.7Ω / cm. 2 The morphology was observed using a magnifying glass, and the results are as follows: Figure 2 As shown, there are no black spots visible to the naked eye on the surface.

[0041] Example 2 This embodiment describes a method for preparing an irregularly shaped composite current collector, which includes the following steps.

[0042] (1) Preparation of primer slurry The raw materials include 0.2 wt.% polyether dispersant F68, 15 wt.% PAI binder, 2.0 wt.% carbon black / HDPE composite conductive material, 82.5 wt.% alumina (Dv50 is 0.3 μm), and 0.3 wt.% polyether modified polydimethylsiloxane.

[0043] Polyether dispersant F68 and N550 carbon black were added to water and mixed using a planetary ball mill. The media in the planetary ball mill consisted of agate balls (a combination of 1mm and 3mm diameter agate balls in equal mass ratio). Dispersion was carried out for 20 minutes at a rotation speed of 600 rpm and a revolution speed of 300 rpm. Then, alumina was added and dispersed at high speed for 60 minutes at a rotation speed of 800 rpm and a revolution speed of 400 rpm. The mixture was then subjected to sand milling to obtain the first mixture. The sand milling conditions were as follows: 5 milling cycles, a sand milling speed of 2200 rpm, and zirconium beads as the milling media. The zirconium beads had a diameter of 0.6mm and occupied 55% of the sand milling chamber volume.

[0044] The first mixture was poured back into the planetary ball mill, and PAI binder was added. The mixture was stirred and dispersed for 30 minutes at a rotation speed of 600 rpm and a revolution speed of 300 rpm. Then, polyether-modified polydimethylsiloxane was added and stirred for 20 minutes at 600 rpm to obtain the second mixture. The second mixture was then evacuated to a vacuum of -90 kPa and maintained for 30 minutes to remove bubbles. The mixture was then filtered through a 120-mesh filter to obtain the primer slurry. The primer slurry had a Dv10 of 0.09 μm, a Dv50 of 0.54 μm, a Dv90 of 1.28 μm, a solid content of 15%, and a viscosity of 450 mPa·s.

[0045] (2) Coating of current collector A primer slurry is applied to the surface of the aluminum foil in a single coat, forming a first primer layer, a second primer layer, and a third primer layer arranged sequentially side-by-side along the width of the current collector. The first and third primer layers are located on opposite sides of the second primer layer. The mesh count on the roller surfaces of the first and third roller layers is 70 mesh, and the cell depth is 160 μm. The mesh count on the roller surface of the second roller layer is 180 mesh, and the cell depth is 55 μm. After coating, the material is dried at 120°C for 10 min to obtain a shaped composite current collector.

[0046] The irregularly shaped composite current collector prepared by this method includes a current collector and a first primer layer, a second primer layer, and a third primer layer disposed on the surface of the current collector. Testing showed that the thickness of the first primer layer is 10 μm and its resistivity is 60.1 Ω / cm. 2 The thickness of the second primer layer is 3 μm, and the resistivity of the second primer layer is 2.5 Ω / cm. 2 The thickness of the third primer layer is 10 μm and its resistivity is 61.7 Ω / cm. 2 The resistance range is 1.6Ω / cm. 2 .

[0047] Comparative Example 1 This comparative example illustrates a method for preparing an irregularly shaped composite current collector, comprising the following steps.

[0048] (1) Preparation of primer slurry The raw materials include 0.3 wt.% polyether dispersant 2383, 12 wt.% PAA binder, 1.5 wt.% conductive carbon black, 86 wt.% boehmite (Dv50 is 0.5 μm), and 0.2 wt.% polyether-modified polydimethylsiloxane.

[0049] Polyether dispersant 2383 was added to water and mixed using a planetary ball mill. The media in the planetary ball mill were agate balls (a combination of 1mm diameter and 3mm diameter agate balls in equal mass ratio). The mixture was dispersed for 10 minutes at a rotation speed of 300 rpm and a revolution speed of 200 rpm. Conductive carbon black was then added and dispersed for 60 minutes at a rotation speed of 450 rpm and a revolution speed of 300 rpm. Boehmite was then added and dispersed at high speed for 80 minutes at a rotation speed of 550 rpm and a revolution speed of 300 rpm. PAA binder was then added and stirred and dispersed for 60 minutes at a rotation speed of 400 rpm and a revolution speed of 300 rpm. Polyether-modified polydimethylsiloxane was then added and stirred for 10 minutes at a speed of 500 rpm to obtain a second mixture. The second mixture was then evacuated to a vacuum of -80 kPa and maintained for 45 minutes to remove bubbles. The mixture was then filtered through a 120-150 mesh filter to obtain the primer slurry. The primer has a Dv10 of 0.21 μm, a Dv50 of 0.98 μm, a Dv90 of 2.25 μm, a solid content of 13%, and a viscosity of 288 mPa·s.

[0050] (2) Coating of current collector A primer slurry is applied to the surface of the aluminum foil in a single coat, forming a first primer layer, a second primer layer, and a third primer layer arranged sequentially side-by-side along the width of the current collector. The first and third primer layers are located on opposite sides of the second primer layer. The mesh count on the roller surfaces of the first and third roller layers is 50 mesh, and the cell depth is 180 μm. The mesh count on the roller surface of the second roller layer is 150 mesh, and the cell depth is 80 μm. After coating, the material is dried at 100°C for 15 min to obtain a shaped composite current collector.

[0051] The irregularly shaped composite current collector prepared by this method includes a current collector and a first primer layer, a second primer layer, and a third primer layer disposed on the surface of the current collector. Testing showed that the thickness of the first primer layer is 12 μm and its resistivity is 35.8 Ω / cm. 2 The second primer layer has a thickness of 4 μm and a resistivity of 2.2 Ω / cm. 2 The thickness of the third primer layer is 12 μm and its resistivity is 40.6 Ω / cm. 2 The resistance range is 4.8Ω / cm. 2 .

[0052] Comparative Example 2 This comparative example illustrates a method for preparing an irregularly shaped composite current collector, comprising the following steps.

[0053] (1) Preparation of primer slurry The raw materials include 0.3 wt.% polyether dispersant 2383, 12 wt.% PAA binder, 1.5 wt.% conductive carbon black, 86 wt.% boehmite (Dv50 is 0.5 μm), and 0.2 wt.% polyether-modified polydimethylsiloxane.

[0054] Polyether dispersant 2383 was added to water and mixed using a planetary ball mill. The media in the planetary ball mill consisted of agate balls (a combination of 1mm diameter and 3mm diameter agate balls in equal mass ratio). Dispersion was carried out for 10 minutes at a rotation speed of 300 rpm and a revolution speed of 200 rpm. Then, conductive carbon black was added and dispersed for 60 minutes at a rotation speed of 450 rpm and a revolution speed of 300 rpm. Finally, boehmite was added and dispersed at high speed for 80 minutes at a rotation speed of 550 rpm and a revolution speed of 300 rpm. The mixture was then subjected to sand milling to obtain the first mixture. The sand milling conditions were as follows: 10 milling cycles, a milling speed of 2500 rpm, and zirconium beads as the milling media. The zirconium beads had a diameter of 0.8mm and occupied 60% of the milling chamber volume.

[0055] The first mixture was poured back into the planetary ball mill, and PAA binder was added. The mixture was stirred and dispersed for 60 minutes at a rotation speed of 400 rpm and a revolution speed of 300 rpm. Then, polyether-modified polydimethylsiloxane was added and stirred for 10 minutes at 500 rpm to obtain the second mixture. The second mixture was then evacuated to a vacuum of -80 kPa and maintained for 45 minutes to remove bubbles. The mixture was then filtered through a 120-150 mesh filter to obtain the primer slurry. The primer slurry had a Dv10 of 0.09 μm, a Dv50 of 0.69 μm, a Dv90 of 1.77 μm, a solid content of 13%, and a viscosity of 263 mPa·s.

[0056] (2) Coating of current collector A primer slurry is applied to the surface of the aluminum foil in a single coat, forming a first primer layer, a second primer layer, and a third primer layer arranged sequentially side-by-side along the width of the current collector. The first and third primer layers are located on opposite sides of the second primer layer. The mesh count on the roller surfaces of the first and third roller layers is 50 mesh, and the cell depth is 180 μm. The mesh count on the roller surface of the second roller layer is 150 mesh, and the cell depth is 80 μm. After coating, the material is dried at 100°C for 15 min to obtain a shaped composite current collector.

[0057] This preparation method can produce an irregularly shaped composite current collector, comprising a current collector and a first primer layer, a second primer layer, and a third primer layer disposed on the surface of the current collector. Testing showed that the thickness of the first primer layer is 12 μm and its resistivity is 96.1 Ω / cm. 2 The thickness of the second primer layer is 4 μm, and the resistivity of the second primer layer is 8.4 Ω / cm. 2The thickness of the third primer layer is 12 μm and its resistivity is 103.7 Ω / cm. 2 The resistance range is 7.6Ω / cm. 2 The morphology was observed using a magnifying glass, and the results are as follows: Figure 3 As shown, there are visible black spots on the surface.

[0058] Comparative Example 3 This comparative example illustrates a method for preparing an irregularly shaped composite current collector, comprising the following steps.

[0059] (1) Preparation of primer slurry The raw materials include 0.3 wt.% polyether dispersant 2383, 12 wt.% PAA binder, 1.5 wt.% conductive carbon black, 86 wt.% boehmite (Dv50 is 0.5 μm), and 0.2 wt.% polyether-modified polydimethylsiloxane.

[0060] Polyether dispersant 2383 was added to water and mixed using a planetary ball mill. The media in the planetary ball mill consisted of agate balls (a combination of 1mm diameter and 3mm diameter agate balls in equal mass ratio). Dispersion was carried out for 10 minutes at a rotation speed of 300 rpm and a revolution speed of 200 rpm. Then, conductive carbon black was added and dispersed for 60 minutes at a rotation speed of 450 rpm and a revolution speed of 300 rpm. Finally, boehmite was added and dispersed at high speed for 80 minutes at a rotation speed of 550 rpm and a revolution speed of 300 rpm. The mixture was then subjected to sand milling to obtain the first mixture. The sand milling conditions were as follows: three milling cycles, a milling speed of 2500 rpm, and zirconium beads as the milling media. The zirconium beads had a diameter of 0.1mm and occupied 60% of the sand milling chamber volume.

[0061] The first mixture was poured back into the planetary ball mill, and PAA binder was added. The mixture was stirred and dispersed for 60 minutes at a rotation speed of 400 rpm and a revolution speed of 300 rpm. Then, polyether-modified polydimethylsiloxane was added and stirred for 10 minutes at 500 rpm to obtain the second mixture. The second mixture was then evacuated to a vacuum of -80 kPa and maintained for 45 minutes to remove bubbles. The mixture was then filtered through a 120-150 mesh filter to obtain the primer slurry. The primer slurry had a Dv10 of 0.08 μm, a Dv50 of 0.62 μm, a Dv90 of 2.50 μm, a solid content of 13%, and a viscosity of 259 mPa·s.

[0062] (2) Coating of current collector A primer slurry is applied to the surface of the aluminum foil in a single coat, forming a first primer layer, a second primer layer, and a third primer layer arranged sequentially side-by-side along the width of the current collector. The first and third primer layers are located on opposite sides of the second primer layer. The mesh count on the roller surfaces of the first and third roller layers is 50 mesh, and the cell depth is 180 μm. The mesh count on the roller surface of the second roller layer is 150 mesh, and the cell depth is 80 μm. After coating, the material is dried at 100°C for 15 min to obtain a shaped composite current collector.

[0063] This preparation method can produce an irregularly shaped composite current collector, comprising a current collector and a first primer layer, a second primer layer, and a third primer layer disposed on the surface of the current collector. Testing showed that the thickness of the first primer layer is 12 μm and its resistivity is 42.3 Ω / cm. 2 The thickness of the second primer layer is 4 μm, and the resistivity of the second primer layer is 2.6 Ω / cm. 2 The thickness of the third primer layer is 12 μm and its resistivity is 39.4 Ω / cm. 2 The resistance range is 2.9Ω / cm. 2 .

[0064] Comparative Example 4 This comparative example illustrates a method for preparing an irregularly shaped composite current collector, comprising the following steps.

[0065] (1) Preparation of primer slurry The raw materials include 0.3 wt.% polyether dispersant 2383, 12 wt.% PAA binder, 1.5 wt.% conductive carbon black, 86 wt.% boehmite (Dv50 is 0.5 μm), and 0.2 wt.% polyether-modified polydimethylsiloxane.

[0066] Polyether dispersant 2383 was added to water and mixed using a planetary ball mill. The media in the planetary ball mill consisted of agate balls (a combination of 1mm diameter and 3mm diameter agate balls in equal mass ratio). Dispersion was carried out for 10 minutes at a rotation speed of 300 rpm and a revolution speed of 200 rpm. Conductive carbon black was then added and dispersed for 60 minutes at a rotation speed of 450 rpm and a revolution speed of 300 rpm. Boehmite was then added and dispersed at high speed for 80 minutes at a rotation speed of 550 rpm and a revolution speed of 300 rpm. The mixture was then subjected to sand milling to obtain the first mixture. The sand milling conditions were as follows: three milling cycles, a milling speed of 2500 rpm, and zirconium beads as the milling media. The zirconium beads had a diameter of 3.0mm and occupied 60% of the sand milling chamber volume.

[0067] The first mixture was poured back into the planetary ball mill, and PAA binder was added. The mixture was stirred and dispersed for 60 minutes at a rotation speed of 400 rpm and a revolution speed of 300 rpm. Then, polyether-modified polydimethylsiloxane was added and stirred for 10 minutes at 500 rpm to obtain the second mixture. The second mixture was then evacuated to a vacuum of -80 kPa and maintained for 45 minutes to remove bubbles. The mixture was then filtered through a 120-150 mesh filter to obtain the primer slurry. The primer slurry had a Dv10 of 0.31 μm, a Dv50 of 0.88 μm, a Dv90 of 3.11 μm, a solid content of 13%, and a viscosity of 285 mPa·s.

[0068] (2) Coating of current collector A primer slurry is applied to the surface of the aluminum foil in a single coat, forming a first primer layer, a second primer layer, and a third primer layer arranged sequentially side-by-side along the width of the current collector. The first and third primer layers are located on opposite sides of the second primer layer. The mesh count on the roller surfaces of the first and third roller layers is 50 mesh, and the cell depth is 180 μm. The mesh count on the roller surface of the second roller layer is 150 mesh, and the cell depth is 80 μm. After coating, the material is dried at 100°C for 15 min to obtain a shaped composite current collector.

[0069] This preparation method can produce an irregularly shaped composite current collector, comprising a current collector and a first primer layer, a second primer layer, and a third primer layer disposed on the surface of the current collector. Testing showed that the thickness of the first primer layer is 12 μm and its resistivity is 29.5 Ω / cm. 2 The thickness of the second primer layer is 4 μm, and the resistivity of the second primer layer is 2.1 Ω / cm. 2 The thickness of the third primer layer is 12 μm and its resistivity is 33.2 Ω / cm. 2 The resistance range is 3.7Ω / cm. 2 .

[0070] A comparison of Examples 1-2 and Comparative Examples 1-4 shows that by milling the dispersant, conductive agent, and inorganic filler before adding the binder, and controlling the milling conditions as follows: 3-5 milling cycles, a milling speed of 2000-2800 rpm, and a milling media diameter 1000-1500 times that of D1, a primer slurry with a smaller Dv50 and a resistivity difference of less than 2.0 Ω / cm can be obtained. 2 Furthermore, the absence of visible black spots on the electrode surface indicates that the components in the base coating slurry are evenly dispersed. Moreover, the resistance values ​​of the first and third base coating parts in the prepared irregular composite current collector are close, and the resistance is much greater than that of the second base coating part. Therefore, the risk of micro-short circuit at the electrode edge can be effectively reduced when performing drop and thermal abuse tests.

[0071] Lithium cobalt oxide, PVDF binder, and SuperP conductive agent were mixed uniformly in NVP at a mass ratio of 96:2.5:1.5 to prepare a positive electrode slurry of a certain viscosity. The irregularly shaped composite current collectors of Examples 1-2 and Comparative Examples 1-4 were used as positive electrode current collectors, and the slurries were coated onto the positive electrode slurries. After drying and rolling, positive electrode sheets were obtained. Artificial graphite, conductive carbon black SP, SBR, and CMC were dispersed in water at a mass ratio of 96:2.0:1.0:1.0 and mixed uniformly to prepare a negative electrode slurry of a certain viscosity. This slurry was coated onto copper foil, dried, and rolled to obtain a negative electrode sheet. The electrolyte was a 1 mol / L LiPF6 solution (the solvent was a mixture of EC, DMC, and EMC in a volume ratio of 1:1:1), and the separator was a polypropylene microporous membrane. The positive electrode sheet, separator, and negative electrode sheet were wound to form a soft-pack battery cell, packaged in aluminum-plastic film, filled with electrolyte, and after formation and capacity testing, lithium-ion batteries (sizes 1-6) were manufactured. The lithium-ion batteries #1 to #6 were subjected to thermal abuse, drop, and nail penetration tests, and the pass rate was calculated. The results are shown in Table 1.

[0072] Thermal abuse test conditions: After the battery cell is fully charged to 1 ItA, it is placed in a forced-air drying oven and heated from room temperature to (130±2)℃ at a rate of (5℃±2℃) / min and held at that temperature for 30 minutes. After the test, the battery cell is disassembled and the shrinkage distance of the separator at the edge of the electrode is observed.

[0073] Drop test conditions: After one cycle of 0.5ItA, the battery cell is fully charged. It is then dropped from a height (lowest point height) of 1000mm along a guide rail onto a concrete surface, with one free drop each in the X, Y, and Z directions (positive and negative). After the test, the battery cell is disassembled, and the condition of the electrode edges (including any signs of slurry loss) and short circuits are observed.

[0074] The needle penetration test conditions are as follows: after the battery cell is discharged to 3.0V at 1ItA, it is charged to 4.80V at 3C constant current and then switched to constant voltage charging. The charging time of the battery cell reaches 7 hours or the battery cell surface temperature drops to 20% lower than the peak value. The battery cell does not catch fire or explode, indicating that it has passed the test.

[0075] Table 1 Test results of lithium-ion batteries #1-#6

[0076] The results in Table 1 further illustrate that the irregularly shaped composite current collector prepared by the method of the present invention can improve the pass rate of the battery in the nail penetration test and reduce the degree of short circuit at the electrode edge in the thermal abuse and drop tests when used in battery electrodes. Although the thermal abuse, drop, and nail penetration test results of lithium-ion battery #4 are better, its resistance is relatively high and the resistance range is large, making it unsuitable for use in high-rate batteries such as fast-charging batteries.

[0077] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, it is not limited to those listed in the embodiments. Those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A method for preparing an irregularly shaped composite current collector, characterized in that, Including the following steps: (1) Preparation of primer slurry A first mixture is obtained by adding a dispersant, a conductive agent, and an inorganic filler sequentially to water and then milling it. A binder and a wetting agent are then mixed into the first mixture to obtain a second mixture. The second mixture is then vacuumed, degassed, and filtered to obtain a primer slurry. The inorganic filler is selected from alumina and / or boehmite, and the conductive agent is selected from conductive carbon black and / or conductive agent materials with PTC effect. The milling conditions are as follows: the number of milling cycles is 3 to 5, the milling speed is 2000 to 2800 rpm, and the diameter of the milling media is 1000 to 1500 times that of the primer slurry Dv50. (2) Coating of current collector The primer slurry is applied to the surface of the current collector in one step, and a first primer portion, a second primer portion, and a third primer portion are formed in parallel along the width direction of the current collector. The first primer portion and the third primer portion are disposed on the opposite side of the second primer portion and their thicknesses are both higher than those of the second primer portion.

2. The method for preparing the irregularly shaped composite current collector according to claim 1, characterized in that, The primer slurry has a solid content of 10-15% and a viscosity of 100-500 mPa·s. Based on the total mass of the dispersant, binder, conductive agent, inorganic filler, and wetting agent as 100%, the proportion of the dispersant is 0.1-0.5 wt.%, the proportion of the binder is 6-15 wt.%, the proportion of the conductive agent is 1.5-2.5 wt.%, the proportion of the inorganic filler is 81-93 wt.%, and the proportion of the wetting agent is 0.1-0.5 wt.

3. The method for preparing the irregularly shaped composite current collector according to claim 1, characterized in that, The dispersant is selected from polyether polymers, the binder is selected from polyacrylic acid polymers or polyamide polymers, and the wetting agent is selected from polyether-modified polysiloxane compounds.

4. The method for preparing the irregularly shaped composite current collector according to claim 1, characterized in that, The primer slurry has a Dv10 of 0.05~0.20μm, a Dv50 of 0.2~0.8μm, and a Dv90 of 0.80~1.99μm, and a resistivity difference of ≤2Ω under a pressure of 60MPa.

5. The method for preparing the irregularly shaped composite current collector according to claim 1, characterized in that, The dispersant, the conductive agent, the inorganic filler, the binder, and the wetting agent are first mixed using a planetary ball mill before being added. The media in the planetary ball mill are a combination of agate balls with the same mass ratio and diameters of 1 mm and 3 mm, respectively. The revolution speed of each ball is 100~500 r / min, the rotation speed is 200~1000 rpm, and the milling time is 10~60 min.

6. The method for preparing the irregularly shaped composite current collector according to claim 1, characterized in that, The grinding medium is zirconium beads with a diameter of 0.5~1.0 mm, and the medium occupies 50~70% of the grinding chamber volume.

7. The method for preparing the irregularly shaped composite current collector according to claim 1, characterized in that, The vacuum is drawn to a vacuum level of -70 to -90 kPa and maintained for 30 to 60 minutes, and the filtration uses a 120 to 150 mesh filter.

8. The method for preparing the irregularly shaped composite current collector according to claim 1, characterized in that, The coating process uses a concave roller comprising a first roller section, a second roller section, and a third roller section arranged in parallel. The first roller section is coated to form the first base coat, the second roller section is coated to form the second base coat, and the third roller section is coated to form the third base coat. The mesh count on the roller surfaces of the first and third roller sections is 40-80 mesh, and the mesh depth is 150-200 μm. The mesh count on the roller surface of the second roller section is 100-180 mesh, and the mesh depth is 50-100 μm.

9. The irregularly shaped composite current collector prepared by the method for preparing the irregularly shaped composite current collector according to any one of claims 1 to 8, characterized in that, It includes a current collector and a first primer layer, a second primer layer, and a third primer layer disposed on the surface of the current collector. The thickness of the second primer layer is 3~5μm, and the resistivity of the second primer layer is 0.5~5.0Ω / cm. 2 The thickness of the first and third base coating portions is 8~20μm, and the resistivity of the first and third base coating portions is 10~100Ω / cm. 2 .

10. A positive electrode plate, characterized in that, It includes a positive electrode current collector and an active material layer. The positive electrode current collector adopts the irregularly shaped composite current collector as described in claim 9. The first base coating, the second base coating, and the third base coating are all disposed between the active material layer and the current collector.

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