Cylindrical battery containing low-expansion multilayer current collector and preparation method thereof

Abstract

The invention discloses a cylindrical battery containing a low-expansion multi-layer current collector and a preparation method of the cylindrical battery, and relates to the technical field of preparation of multi-layer current collectors. According to the invention, the expansion buffer structures are arranged in the welding areas of the multi-layer current collector tabs at intervals, so that the repeated dragging of welding marks caused by expansion is relieved, the welding reliability is improved, and the expansion buffer areas and the anti-tearing structures can retain the effective overflowing area of the tabs as much as possible when the battery cell expands; the anti-interference chamfer is arranged at one end, far away from the multi-layer current collector, of the tab, so that the tab is prevented from being wrinkled due to mutual interference when the tab is bundled after the pole piece is wound, and the welding of the bundled tab and a battery shell is influenced; according to the invention, a composite material with high heat-conducting property and low expansion property is prepared by compounding graphene and ZrW2O8, and then is prepared into negative active slurry, and the negative active slurry is coated on a high-molecular base membrane containing a metal conductive layer, so that the material is endowed with low expansion property.

Description

Technical Field

[0001] The present invention relates to the technical field of multilayer current collector preparation, and in particular to a cylindrical battery containing a low-expansion multilayer current collector and a preparation method thereof. Background Art

[0002] The multilayer current collector has a "sandwich" structure, with the inner layer being a polymer layer (such as PET, PP or PI) and the two sides being metal conductive layers (such as Al or Cu). Since the multilayer current collector is not conductive in the thickness direction, it is impossible to directly form a tab. The current tab welding of the multilayer current collector is to weld two pieces of pure metal foil to the metal layers on both sides of the multilayer current collector by ultrasonic roll welding.

[0003] Cylindrical batteries currently offer the highest energy density among power batteries, and they are typically paired with high-energy-density silicon anodes. Multilayer current collectors can further enhance battery energy density. However, these batteries present new challenges, such as balancing the current flow capacity of the tabs in cylindrical batteries due to their unique structure, and the impact of expansion caused by the structural characteristics of cylindrical batteries on the tab welding strength. However, since the current collector and tabs of the multilayer current collector are not integrally formed but ultrasonically welded, the cylindrical battery undergoes repeated expansion-contraction-expansion-contraction cycles during charge and discharge, causing the current collector to stretch and repeatedly pull on the metal foil welded to its edges. This can lead to weld failure or a reduction in the effective flow area, potentially causing battery power outages or severe tab heating.

[0004] Therefore, we propose a cylindrical battery containing a low-expansion multi-layer current collector and a preparation method thereof to solve the above problems. Summary of the Invention

[0005] The object of the present invention is to provide a cylindrical battery containing a low-expansion multi-layer current collector and a preparation method thereof, so as to solve the problems raised in the prior art.

[0006] To achieve the above objectives, the present invention provides the following technical solutions: a cylindrical battery containing a low-expansion multi-layer current collector, comprising a cylindrical battery cell, a shell, and a cover plate, wherein the cylindrical battery cell comprises a pole piece and a separator, and the pole piece comprises a multi-layer current collector;

[0007] The multi-layer current collector includes a polymer base film, a metal conductive layer and an active material layer.

[0008] Furthermore, a metal foil is welded to one end of the metal conductive layer to form a welding area; the welding area and the metal foil together form a tab.

[0009] Furthermore, the welding area is provided with expansion buffer structures at intervals; the expansion buffer structures are cutouts or openings;

[0010] The expansion buffer structure is provided with an anti-tear structure;

[0011] The anti-tear structure is a round hole or a duckbill-shaped through hole.

[0012] Furthermore, when the expansion buffer structure is a cutout, the anti-tear structure is located at the end of the cutout between the welding area and the active material layer; the anti-tear structure is a circular hole;

[0013] When the expansion buffer structure is an open hole, the anti-tear structure is located at the top and bottom of the open hole; the anti-tear structure is a duckbill-shaped through hole.

[0014] Furthermore, the tab is a full tab; an anti-interference chamfer is provided at one end of the tab away from the multi-layer current collector;

[0015] The length of the tab is the same as the length of the multi-layer current collector.

[0016] Furthermore, the welding area is provided with a plurality of arranged welding points; the cylindrical battery cell is formed by stacking and winding the pole piece and the diaphragm in the order of "pole piece-diaphragm-pole piece";

[0017] The spacing between the welding spots wound on the inner side is greater than the spacing between the welding spots wound on the outer side.

[0018] Furthermore, the metal conductive layer is provided on the upper surface and / or lower surface of the polymer base film;

[0019] The active material layer is arranged on a side of the metal conductive layer away from the polymer base film.

[0020] In the above technical solution, the expansion buffer structure can alleviate the repeated pulling of the welding mark caused by expansion, thereby improving welding reliability; the expansion buffer and anti-tear structure can retain the effective flow area of ​​the tab as much as possible when the battery cell expands; the anti-interference chamfer can prevent the tabs from interfering with each other when they are bundled after the electrode sheet is wound, resulting in wrinkles on the tabs, thereby affecting the welding of the tabs with the battery case after the tabs are bundled;

[0021] When the metal foil is welded to the multi-layer current collector, the current collector is in a flat state, and the metal foils on both sides are the same length. However, since the current collector itself has a certain thickness, after the electrode is wound, for each circle of the electrode, the circumference of the metal foil on the outer side is greater than the circumference of the metal foil on the inner side. Therefore, if the metal foil on the outer side of the multi-layer current collector is guaranteed to be in a non-stretched state, then the metal foil on the inner side must have a certain redundancy. Therefore, the spacing between the weld points on the inner side is designed to be larger to release stress and avoid wrinkling and protrusion of the inner metal sheet.

[0022] A method for preparing a cylindrical battery containing a low-expansion multilayer current collector comprises the following steps:

[0023] Step 1: Mix the low expansion composite material, a binder, a dispersant and deionized water, and stir them evenly to obtain a negative electrode active material slurry;

[0024] Step 2: Take the polymer base film, magnetron sputter a metal material on its surface to form a metal conductive layer, and then apply the negative electrode active material slurry to form a negative electrode active material layer to obtain a multi-layer current collector to form a negative electrode plate;

[0025] Step 3: Mix lithium iron phosphate, carbon nanotubes, Super P and PVDF, stir evenly to obtain a positive electrode active material slurry; take aluminum foil, apply the positive electrode active material slurry on the upper surface and / or lower surface to form a positive electrode active material layer, and obtain a positive electrode sheet;

[0026] Step 4: Stack and wind the positive electrode sheet, negative electrode sheet and separator in the order of "negative electrode sheet-separator-positive electrode sheet-separator" to form a cylindrical battery cell, abut the cylindrical battery cell with the inner wall of the shell and the cover plate, perform laser welding, and then inject liquid to seal it to obtain a cylindrical battery containing a low-expansion multi-layer current collector.

[0027] Furthermore, in step 1, the mass ratio of the low expansion composite material, the mixed binder, the dispersant and the deionized water is 10: (0.5-1): (0.3-0.5): (20-40).

[0028] Furthermore, in step 1, the binder is obtained by mixing a water-based binder and an elastic binder in a mass ratio of 1: (0.5-2.5);

[0029] The water-based binder is a mixture of one or more of polyacrylate, polyvinyl alcohol, and water-based polyurethane;

[0030] The elastic adhesive is one of styrene-butadiene rubber emulsion and nitrile-butadiene rubber emulsion.

[0031] In step 1, the dispersant is one or more of sodium polyacrylate, carboxymethyl cellulose, and hydroxypropyl methyl cellulose.

[0032] Furthermore, in step 2, the polymer base film is one of PET film (polyethylene terephthalate), PP film (polypropylene), and PI film (polyimide);

[0033] In step 2, the metal material is one of an aluminum target and a copper target.

[0034] Furthermore, in step 2, the thickness of the metal conductive layer is 0.5 nm to 1 nm;

[0035] In step 2, the negative electrode active material slurry is coated to a thickness of 1 μm to 3 μm.

[0036] Furthermore, in step 2, the process conditions of magnetron sputtering are: sputtering power density 20W / cm 2 ~40W / cm 2 , vacuum degree 3×10 -4 Pa~5×10 -4 Pa.

[0037] Furthermore, in step 3, the mass ratio of the lithium iron phosphate, carbon nanotubes, Super P (conductive carbon black) and PVDF (polyvinylidene fluoride) is 1: (0.3-0.5): (0.1-0.3): (0.1-0.3).

[0038] Furthermore, in step 3, the coating thickness of the positive electrode active material slurry is 1 μm to 3 μm.

[0039] Furthermore, in step 4, the process conditions of the laser welding are: laser wavelength 600 μm to 1200 μm, and laser input energy 300 J to 500 J.

[0040] Furthermore, in step 4, the electrolyte used for the liquid injection seal is prepared by mixing LiPF6 (lithium hexafluorophosphate), EC (ethylene carbonate) and DEC (diethyl carbonate);

[0041] The electrolyte concentration is 1M;

[0042] The volume ratio of EC to DEC is 1:1.

[0043] Furthermore, in step 1, the low expansion composite material is prepared by the following process:

[0044] S1: mixing composite graphene powder with deionized water and dispersing by ultrasonication to obtain a composite graphene dispersion;

[0045] S2: Mixing ZrW2O8 (zirconium tungstate) with a composite graphene dispersion, adjusting the pH to 4-5, hydrothermally reacting, and drying to obtain composite graphene-coated ZrW2O8;

[0046] S3: The composite graphene-coated ZrW2O8 is ball-milled, sieved, microwave-sintered, and crushed to obtain a low-expansion composite material.

[0047] Furthermore, in S1, the mass ratio of the composite graphene powder to deionized water is 1:(40-60);

[0048] In S1, the process conditions of the ultrasonic dispersion are: power 300W to 600W, time 20min to 40min.

[0049] Furthermore, in S2, the mass ratio of ZrW2O8 to composite graphene dispersion is 1:(5-10);

[0050] In S2, the process conditions of the hydrothermal reaction are: temperature 150° C. to 200° C., and time 10 h to 20 h.

[0051] Furthermore, in S3, the process conditions of the microwave sintering are: sintering temperature 500° C. to 600° C., time 20 min to 40 min, and power 1 kW to 3 kW.

[0052] Furthermore, in S1, the preparation method of the composite graphene powder is as follows:

[0053] The copper powder is mixed with polyvinyl alcohol, stirred for reaction, centrifuged, and the precipitate is collected. The precipitate is mixed with a graphene dispersion, stirred until no black precipitate is left, and dried to obtain a composite graphene powder.

[0054] Furthermore, the mass ratio of the copper powder to polyvinyl alcohol is 1:(5-10);

[0055] The mass ratio of the precipitate to the graphene dispersion is 1:(3-5).

[0056] Furthermore, the process conditions of the stirring reaction are: temperature 45°C to 65°C, time 30min to 60min;

[0057] The process conditions for centrifugation are: rotation speed 2000 rpm to 3000 rpm, time 5 min to 10 min.

[0058] Furthermore, the polyvinyl alcohol is added in the form of a solution, and the concentration of the polyvinyl alcohol solution is 1% to 3%.

[0059] Furthermore, the graphene dispersion is obtained by mixing graphene powder and deionized water, and the mass ratio of graphene powder to deionized water is 1:(10-20).

[0060] Furthermore, the average particle size of the copper powder is 0.3 μm;

[0061] The average particle size of the graphene powder is 3 nm.

[0062] In the above technical solution, a composite material with both high thermal conductivity and low expansion performance is prepared by compounding graphene and ZrW2O8, which is then made into a slurry and coated on a polymer base film. ZrW2O8 has an isotropic negative expansion coefficient, which gives the composite material low expansion performance. The composite graphene is obtained by compounding copper powder and graphene, and has good thermal conductivity and electrical conductivity. The two-dimensional graphene sheets can be filled between the copper powder particles to form a conductive path, reduce the contact resistance between the particles, and improve the overall conductivity.

[0063] However, when sintered at a high temperature of 700°C, ZrW2O8 will react with copper to generate oxides, causing the material to lose its negative expansion properties. Therefore, the microwave sintering process is selected. Microwaves can directly penetrate the material, rapidly heat up, inhibit the oxidation side reactions produced by the sintering of the material, enhance the thermal conductivity continuity of the material, and further reduce the expansion.

[0064] Compared with the prior art, the present invention has the following beneficial effects:

[0065] 1. The expansion buffer structure provided in the present application can alleviate the repeated pulling of the welding mark caused by expansion and improve the welding reliability; the expansion buffer zone and the anti-tear structure can retain the effective flow area of ​​the tab as much as possible when the battery cell expands; the anti-interference chamfer can avoid mutual interference when the tabs are bundled after the pole pieces are wound, resulting in wrinkling of the tabs, thereby affecting the welding of the tabs with the battery shell after they are bundled; when the metal foil is welded to the multi-layer current collector, the current collector is in a flat state, and the metal foils on both sides are the same length, but because the current collector itself has a certain thickness, after the pole piece is wound, for each circle of the pole piece, the circumference of the metal foil on the outer side is greater than the circumference of the metal foil on the inner side. Therefore, if the metal foil on the outer side of the multi-layer current collector facing the winding is guaranteed to be in a non-stretched state, then the metal foil on the inner side must have a certain redundancy, so the welding point spacing on the inner side is designed to be larger to release stress and avoid wrinkling and protrusion of the inner metal sheet.

[0066] 2. A composite material with both high thermal conductivity and low expansion properties is prepared by combining graphene and ZrW2O8, which is then made into a slurry and coated on a polymer base film. ZrW2O8 has an isotropic negative expansion coefficient, which gives the composite material low expansion properties. Composite graphene is a composite of copper powder and graphene, and has good thermal conductivity and electrical conductivity. The two-dimensional graphene sheets can be filled between copper powder particles to form a conductive path, reduce the contact resistance between particles, and improve the overall conductivity. Microwaves can directly penetrate the material, rapidly heat up, inhibit the oxidation side reaction caused by the sintering of the material, enhance the thermal conductivity continuity of the material, and further reduce the expansion. BRIEF DESCRIPTION OF THE DRAWINGS

[0067] Figure 1 Schematic diagram of the cross-sectional structure of the multi-layer current collector electrode in Example 1 of the present invention;

[0068] Figure 2 Schematic diagram of the flattened structure of the multi-layer current collector electrode in Example 1 of the present invention;

[0069] Figure 3 This is a schematic diagram of the incision-type expansion buffer structure in Example 1 of the present invention;

[0070] Figure 4 This is a schematic diagram of an open-hole expansion buffer structure in Example 2 of the present invention;

[0071] Figure 5 This is a schematic diagram of the anti-tear optimization structure of the incision-type expansion buffer structure in Example 1 of the present invention;

[0072] Figure 6 This is a structural schematic diagram of the anti-interference chamfer design of the tab structure of the notch-type expansion buffer structure in Example 1 of the present invention;

[0073] Figure 7 Schematic diagram of the pole piece winding method in Example 1 of the present invention;

[0074] Figure 8 This is a physical picture of the welding area in Example 1 of the present invention.

[0075] In the figure, 1. Polymer base film, 2. Metal conductive layer, 3. Active material layer, 4. Welding area, 5. Tab, 6. Expansion buffer structure, 7. Anti-tear structure, 8. Multi-layer current collector, 9. Anti-interference chamfer. DETAILED DESCRIPTION

[0076] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0077] In the following specific embodiments,

[0078] The polymer base film is PET film with a thickness of 4 μm;

[0079] The metal material is copper target with a purity of 99.99%;

[0080] Aluminum foil, thickness 6 μm;

[0081] The water-based binder is polyvinyl alcohol;

[0082] The elastic binder is styrene-butadiene rubber latex, model SN-307R;

[0083] The dispersant is carboxymethyl cellulose;

[0084] Copper powder, average particle size 0.3 μm;

[0085] Graphene powder, average particle size 3nm;

[0086] The diaphragm is a polyethylene diaphragm with a thickness of 0.5 mm;

[0087] Prepare the electrolyte: mix LiPF6, EC and DEC to prepare an electrolyte with a concentration of 1M; the volume ratio of EC to DEC is 1:1.

[0088] Example 1: A cylindrical battery containing a low-expansion multilayer current collector, comprising a cylindrical cell, a housing, and a cover; the cylindrical cell comprises a pole piece and a separator, and the pole piece comprises a multilayer current collector 8;

[0089] like Figures 1 to 3 As shown, the multilayer current collector 8 includes a polymer base film 1, a metal conductive layer 2 and an active material layer 3; a metal foil is welded to one end of the metal conductive layer 2 to form a welding area 4; the welding area 4 and the metal foil together form a pole ear 5; an expansion buffer structure 6 is provided at intervals in the welding area 4; the expansion buffer structure 6 is a cutout; an anti-tear structure 7 is provided in the expansion buffer structure 6, and the anti-tear structure 7 is a circular hole. The anti-tear structure 7 is located at the end of the cutout between the welding area 4 and the active material layer 3; the pole ear 5 is a full pole ear; an anti-interference chamfer 9 is provided at one end of the pole ear 5 away from the multilayer current collector 8; the length of the pole ear 5 is the same as that of the multilayer current collector 8;

[0090] like Figures 5 to 8 As shown, the welding area 4 is provided with a plurality of arranged welding points; the cylindrical battery cell is formed by stacking and winding the electrode and the diaphragm in the order of "electrode-diaphragm-electrode"; the spacing of the welding points wound on the inner side is greater than the spacing of the welding points wound on the outer side; the metal conductive layer 2 is provided on the upper surface and / or lower surface of the polymer base film 1; the active material layer 3 is provided on the side of the metal conductive layer 2 away from the polymer base film 1.

[0091] Example 2: A cylindrical battery containing a low-expansion multilayer current collector, comprising a cylindrical cell, a housing, and a cover; the cylindrical cell comprises a pole piece and a separator, and the pole piece comprises a multilayer current collector 8;

[0092] like Figures 1 to 3As shown, the multilayer current collector 8 includes a polymer base film 1, a metal conductive layer 2 and an active material layer 3; a metal foil is welded to one end of the metal conductive layer 2 to form a welding area 4; the welding area 4 and the metal foil together form a pole ear 5; the welding area 4 is provided with an expansion buffer structure 6; the expansion buffer structure 6 is an opening; an anti-tear structure 7 is provided in the expansion buffer structure 6, and the anti-tear structure 7 is a duckbill-shaped through hole, and the anti-tear structure 7 is located at the top and bottom of the opening; the pole ear 5 is a full pole ear; an anti-interference chamfer 9 is provided at one end of the pole ear 5 away from the multilayer current collector 8; the length of the pole ear 5 is the same as that of the multilayer current collector 8;

[0093] like Figures 5 to 8 As shown, the welding area 4 is provided with a plurality of arranged welding points; the cylindrical battery cell is formed by stacking and winding the electrode and the diaphragm in the order of "electrode-diaphragm-electrode"; the spacing of the welding points wound on the inner side is greater than the spacing of the welding points wound on the outer side; the metal conductive layer 2 is provided on the upper surface and / or lower surface of the polymer base film 1; the active material layer 3 is provided on the side of the metal conductive layer 2 away from the polymer base film 1.

[0094] Example 3: Similar to Example 1, when the expansion buffer structure is a cutout, a method for preparing a cylindrical battery containing a low-expansion multilayer current collector comprises the following steps:

[0095] (1) Preparation of low expansion composite materials:

[0096] The graphene powder was mixed with deionized water in a mass ratio of 1:10 to obtain a graphene dispersion;

[0097] Copper powder was mixed with a 3% polyvinyl alcohol solution in a mass ratio of 1:5, the mixture was stirred at 65°C for 60 minutes, and centrifuged at 3000 rpm for 10 minutes to collect the precipitate. The precipitate was mixed with a graphene dispersion in a mass ratio of 1:5, stirred until no black precipitate was formed, and dried to obtain a composite graphene powder.

[0098] S1: The composite graphene powder and deionized water were mixed in a mass ratio of 1:40, and ultrasonically dispersed to obtain a composite graphene dispersion liquid; S2: ZrW2O8 was mixed with the composite graphene dispersion liquid in a mass ratio of 1:10, the pH was adjusted to 5, and the mixture was hydrothermally reacted at 200°C for 20 hours, and dried to obtain composite graphene-coated ZrW2O8; S3: The composite graphene-coated ZrW2O8 was ball-milled, sieved, and then microwave-sintered and pulverized to obtain a low-expansion composite material; in S1, the process conditions for ultrasonic dispersion were: power 600W, time 40 minutes; in S3, the process conditions for microwave sintering were: sintering temperature 600°C, time 40 minutes, and power 3kW;

[0099] (2) Preparation of cylindrical batteries:

[0100] The polyvinyl alcohol and the styrene-butadiene rubber latex are mixed in a mass ratio of 1:2.5 to obtain a binder;

[0101] Lithium iron phosphate, carbon nanotubes, Super P and PVDF were mixed in a mass ratio of 1:0.5:0.3:0.3 to obtain a positive electrode active material slurry;

[0102] Step 1: Mix the low expansion composite material, binder, carboxymethyl cellulose and deionized water in a mass ratio of 10:1:0.5:40 and stir evenly to obtain a negative electrode active material slurry; Step 2: Take a PET film 1, magnetron sputter a copper target on its surface to form a metal conductive layer 2 with a thickness of 1nm, and then apply the negative electrode active material slurry to form a negative electrode active material layer 3 with a thickness of 3μm, obtain a multilayer current collector 8, and form a negative electrode sheet; Step 3: Take aluminum foil and coat it on the upper surface and / or lower surface. Apply the positive electrode active material slurry to form a positive electrode active material layer to obtain a positive electrode sheet; Step 4, stack and wind the positive electrode sheet, the negative electrode sheet and the polyethylene separator in the order of "negative electrode sheet-polyethylene separator-positive electrode sheet-polyethylene separator" to form a cylindrical battery cell, abut the cylindrical battery cell with the inner wall of the shell and the cover plate, perform laser welding, and then inject and seal to obtain a cylindrical battery containing a low-expansion multilayer current collector; In step 2, the process conditions of magnetron sputtering are: sputtering power density 40W / cm 2 , vacuum degree 5×10 -4 Pa; in step 4, the process conditions of laser welding are: laser wavelength 600μm, laser input energy 300J.

[0103] Example 4: Similar to Example 1, when the expansion buffer structure is a cutout, a method for preparing a cylindrical battery containing a low-expansion multilayer current collector comprises the following steps:

[0104] (1) Preparation of low expansion composite materials:

[0105] The graphene powder was mixed with deionized water in a mass ratio of 1:15 to obtain a graphene dispersion;

[0106] Copper powder was mixed with a 2% polyvinyl alcohol solution in a mass ratio of 1:7, stirred at 55°C for 450 minutes, centrifuged at 2500 rpm for 7 minutes, and the precipitate was collected. The precipitate was mixed with a graphene dispersion in a mass ratio of 1:4, stirred until no black precipitate was left, and dried to obtain a composite graphene powder.

[0107] S1: The composite graphene powder and deionized water were mixed in a mass ratio of 1:50, and ultrasonically dispersed to obtain a composite graphene dispersion liquid; S2: ZrW2O8 was mixed with the composite graphene dispersion liquid in a mass ratio of 1:7, the pH was adjusted to 4, and the mixture was hydrothermally reacted at 170°C for 15 hours, and dried to obtain composite graphene-coated ZrW2O8; S3: The composite graphene-coated ZrW2O8 was ball-milled, sieved, and then microwave-sintered and pulverized to obtain a low-expansion composite material; in S1, the process conditions for ultrasonic dispersion were: power 400W, time 30 minutes; in S3, the process conditions for microwave sintering were: sintering temperature 550°C, time 30 minutes, and power 2kW;

[0108] (2) Preparation of cylindrical batteries:

[0109] The polyvinyl alcohol and the styrene-butadiene rubber latex are mixed in a mass ratio of 1:1.5 to obtain a binder;

[0110] Lithium iron phosphate, carbon nanotubes, Super P and PVDF were mixed in a mass ratio of 1:0.4:0.2:0.2 to obtain a positive electrode active material slurry;

[0111] Step 1: Mix the low expansion composite material, binder, carboxymethyl cellulose and deionized water in a mass ratio of 10:0.7:0.4:30 and stir evenly to obtain a negative electrode active material slurry; Step 2: Take a PET film 1, magnetron sputter a copper target on its surface to form a metal conductive layer 2 with a thickness of 0.7nm, and then apply the negative electrode active material slurry to form a negative electrode active material layer 3 with a thickness of 2μm, obtain a multilayer current collector 8, and form a negative electrode sheet; Step 3: Take aluminum foil and The surface is coated with a positive electrode active material slurry to form a positive electrode active material layer to obtain a positive electrode sheet; in step 4, the positive electrode sheet, the negative electrode sheet and the polyethylene separator are stacked and wound in the order of "negative electrode sheet-polyethylene separator-positive electrode sheet-polyethylene separator" to form a cylindrical battery cell, the cylindrical battery cell is abutted against the inner wall of the shell and the cover plate, laser welded, and then sealed by injection to obtain a cylindrical battery containing a low-expansion multilayer current collector; in step 2, the process conditions of magnetron sputtering are: sputtering power density 30W / cm 2 , vacuum degree 4×10 -4 Pa; in step 4, the process conditions of laser welding are: laser wavelength 900μm, laser input energy 400J.

[0112] Example 5: Similar to Example 1, when the expansion buffer structure is a cutout, a method for preparing a cylindrical battery containing a low-expansion multilayer current collector comprises the following steps:

[0113] (1) Preparation of low expansion composite materials:

[0114] The graphene powder was mixed with deionized water in a mass ratio of 1:20 to obtain a graphene dispersion;

[0115] Copper powder was mixed with a 1% polyvinyl alcohol solution in a mass ratio of 1:5, stirred at 45°C for 30 minutes, centrifuged at 2000 rpm for 5 minutes, and the precipitate was collected. The precipitate was mixed with a graphene dispersion in a mass ratio of 1:3, stirred until no black precipitate was left, and dried to obtain a composite graphene powder.

[0116] S1: The composite graphene powder and deionized water were mixed in a mass ratio of 1:60, and ultrasonically dispersed to obtain a composite graphene dispersion liquid; S2: ZrW2O8 was mixed with the composite graphene dispersion liquid in a mass ratio of 1:5, the pH was adjusted to 4, and the mixture was hydrothermally reacted at 150°C for 10 hours, and dried to obtain composite graphene-coated ZrW2O8; S3: The composite graphene-coated ZrW2O8 was ball-milled, sieved, and then microwave-sintered and pulverized to obtain a low-expansion composite material; in S1, the process conditions for ultrasonic dispersion were: power 300W, time 20 minutes; in S3, the process conditions for microwave sintering were: sintering temperature 500°C, time 20 minutes, and power 1kW;

[0117] (2) Preparation of cylindrical batteries:

[0118] The polyvinyl alcohol and the styrene-butadiene rubber latex are mixed in a mass ratio of 1:0.5 to obtain a binder;

[0119] Lithium iron phosphate, carbon nanotubes, Super P and PVDF were mixed in a mass ratio of 1:0.3:0.1:0.1 to obtain a positive electrode active material slurry;

[0120] Step 1: Mix the low expansion composite material, binder, carboxymethyl cellulose and deionized water in a mass ratio of 10:0.5:0.3:20 and stir evenly to obtain a negative electrode active material slurry; Step 2: Take a PET film 1, magnetron sputter a copper target on its surface to form a metal conductive layer 2 with a thickness of 0.5nm, and then apply the negative electrode active material slurry to form a negative electrode active material layer 3 with a thickness of 1μm, obtain a multilayer current collector 8, and form a negative electrode sheet; Step 3: Take aluminum foil and The surface is coated with a positive electrode active material slurry to form a positive electrode active material layer to obtain a positive electrode sheet; in step 4, the positive electrode sheet, the negative electrode sheet and the polyethylene separator are stacked and wound in the order of "negative electrode sheet-polyethylene separator-positive electrode sheet-polyethylene separator" to form a cylindrical battery cell, the cylindrical battery cell is abutted against the inner wall of the shell and the cover plate, laser welded, and then sealed by injection to obtain a cylindrical battery containing a low-expansion multilayer current collector; in step 2, the process conditions of magnetron sputtering are: sputtering power density 20W / cm 2 , vacuum degree 3×10 -4Pa; in step 4, the process conditions of laser welding are: laser wavelength 600μm, laser input energy 300J.

[0121] Comparative Example 1: Using Example 3 as a comparison, the composite graphene powder was replaced with graphene powder, and the other conditions remained unchanged.

[0122] Comparative Example 2: Compared with Example 3, no graphene powder and copper powder were added to the active material slurry, and other conditions remained unchanged.

[0123] Comparative Example 3: Using Example 3 as a comparison, the composite graphene powder was replaced with graphene powder, while graphene powder and copper powder were not added, and other conditions remained unchanged.

[0124] experiment:

[0125] Battery performance test: The cylindrical batteries obtained in the examples and comparative examples were tested using the 1C / 1C charge-discharge cycle performance test method at room temperature, with a charge cut-off voltage of 3.65V and a cut-off current of 0.05C; a discharge cut-off voltage of 2.5V and a cut-off current of 0.05C, for 500 cycles, and the thickness expansion rate of the battery was tested.

[0126] Multilayer current collector peel strength test: The multilayer current collectors obtained in the examples and comparative examples were subjected to a peel strength test using an intelligent tensile testing machine in a 180° peel mode.

[0127] The following table shows the performance test results of cylindrical batteries;

[0128]

[0129] Based on the data in the above table, we can draw the following conclusions:

[0130] Compared with Example 3, in Comparative Example 1, the composite graphene powder is replaced with graphene powder. The expansion rate of the battery increases and the discharge capacity decreases. This is because the composite graphene is a composite of copper powder and graphene, and has good thermal conductivity and electrical conductivity. The two-dimensional sheets of graphene can be filled between the copper powder particles to form a conductive path, reduce the contact resistance between the particles, and improve the overall conductivity.

[0131] Compared with Example 3, in Comparative Example 2, where no graphene powder and copper powder were added to the active material slurry, the battery expansion rate increased and the discharge capacity decreased. This is because graphene powder has good thermal conductivity and copper powder has good electrical conductivity. If only ZrW2O8 is added, the composite material does not have complete thermal and electrical conductivity pathways, resulting in a decrease in cycle performance.

[0132] Compared with Example 3, Comparative Example 3 replaces the composite graphene powder with graphene powder, and does not add graphene powder and copper powder. The expansion rate of the battery increases significantly and the discharge capacity decreases significantly, indicating that the setting of the materials and the selection of the process used in the preparation of the multilayer current collector of the present invention can improve the performance of the cylindrical battery prepared in the embodiment of the present invention in all aspects.

[0133] 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 embodied in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered in all respects as illustrative and non-restrictive, and the scope of the invention is defined by the appended claims, not the foregoing description, and all variations within the meaning and range of equivalents of the claims are intended to be included therein. Any reference sign in a claim should not be construed as limiting the claim to which it relates.

Claims

1. A cylindrical battery containing a low-expansion multilayer current collector, characterized in that: The invention comprises a cylindrical battery cell, a shell and a cover plate, wherein the cylindrical battery cell comprises a pole piece and a diaphragm, wherein the pole piece comprises a multi-layer current collector (8); the multi-layer current collector comprises a polymer base film (1), a metal conductive layer (2) and an active material layer (3); One end of the metal conductive layer (2) is welded with a metal foil to form a welding area (4); the welding area (4) and the metal foil together form a tab (5); The welding areas (4) are provided with expansion buffer structures (6) at intervals; the expansion buffer structures (6) are cutouts or openings.

2. A cylindrical battery with a low-expansion multi-layer current collector according to claim 1, characterized in that: The expansion buffer structure (6) is provided with an anti-tear structure (7); The anti-tear structure (7) is a round hole or a duckbill-shaped through hole.

3. A cylindrical battery with a low-expansion multi-layer current collector according to claim 1, characterized in that: When the expansion buffer structure (6) is a cutout, the tear-proof structure (7) is located at the end of the cutout between the welding area (4) and the active material layer (3); the tear-proof structure (7) is a circular hole; When the expansion buffer structure (6) is an open hole, the tear-proof structure (7) is located at the top and bottom of the open hole; the tear-proof structure (7) is a duckbill-shaped through hole.

4. A cylindrical battery with a low-expansion multi-layer current collector according to claim 1, characterized in that: The pole tab (5) is a full pole tab; an anti-interference chamfer (9) is provided at one end of the pole tab (5) away from the multi-layer current collector (8); The length of the tab (5) is the same as that of the multi-layer current collector (8).

5. The cylindrical battery with a low-expansion multi-layer current collector according to claim 1, characterized in that: The welding area (4) is provided with a plurality of arranged welding points; the cylindrical battery core is formed by stacking and winding the pole piece and the diaphragm in the order of "pole piece-diaphragm-pole piece"; The spacing between the welding spots wound on the inner side is greater than the spacing between the welding spots wound on the outer side.

6. The cylindrical battery with a low-expansion multi-layer current collector according to claim 1, characterized in that: The metal conductive layer (2) is arranged on the upper surface and / or lower surface of the polymer base film (1); The active material layer (3) is arranged on the side of the metal conductive layer (2) facing away from the polymer base film (1).

7. A method for preparing a cylindrical battery containing a low-expansion multilayer current collector, characterized in that: The following steps are involved: Step 1: Mix the low expansion composite material, a binder, a dispersant and deionized water, and stir them evenly to obtain a negative electrode active material slurry; Step 2: Take the polymer base film, magnetron sputter a metal material on its surface to form a metal conductive layer, and then apply the negative electrode active material slurry to form a negative electrode active material layer to obtain a multi-layer current collector to form a negative electrode plate; Step 3: Mix lithium iron phosphate, carbon nanotubes, Super P and PVDF, stir evenly to obtain a positive electrode active material slurry; take aluminum foil, apply the positive electrode active material slurry on the upper surface and / or lower surface to form a positive electrode active material layer, and obtain a positive electrode sheet; Step 4: Stack and wind the positive electrode sheet, negative electrode sheet and separator in the order of "negative electrode sheet-separator-positive electrode sheet-separator" to form a cylindrical battery cell, abut the cylindrical battery cell with the inner wall of the shell and the cover plate, perform laser welding, and then inject liquid to seal it to obtain a cylindrical battery containing a low-expansion multi-layer current collector.

8. The method for preparing a cylindrical battery containing a low-expansion multi-layer current collector according to claim 7, characterized in that: In step 1, the low expansion composite material is prepared by the following process: S1: mixing composite graphene powder with deionized water and dispersing by ultrasonication to obtain a composite graphene dispersion; S2: mixing ZrW2O8 with a composite graphene dispersion, adjusting the pH to 4-5, hydrothermally reacting, and drying to obtain composite graphene-coated ZrW2O8; S3: The composite graphene-coated ZrW2O8 is ball-milled, sieved, microwave-sintered, and crushed to obtain a low-expansion composite material.

9. The method for preparing a cylindrical battery containing a low-expansion multi-layer current collector according to claim 7, characterized in that: In S1, the preparation method of the composite graphene powder is as follows: The copper powder is mixed with polyvinyl alcohol, stirred for reaction, centrifuged, and the precipitate is collected. The precipitate is mixed with a graphene dispersion, stirred until no black precipitate is left, and dried to obtain a composite graphene powder.

10. The method for preparing a cylindrical battery containing a low-expansion multi-layer current collector according to claim 7, characterized in that: In step 1, the mass ratio of the low-expansion composite material, the mixed binder, the dispersant and the deionized water is 10: (0.5-1): (0.3-0.5): (20-40).

Images