Current collector, secondary battery and electric equipment

Abstract

The embodiment of the invention provides a current collector, a secondary battery and electric equipment, the current collector provided by the embodiment of the invention comprises a metal matrix and a composite layer arranged on the surface of at least one side of the metal matrix, and the composite layer comprises a conductive polymer grid layer and a metal grid layer; on the surface of the same side of the metal matrix, the conductive polymer grid layer and the metal grid layer are stacked, and grid lines in the conductive polymer grid layer intersect with grid lines in the metal grid layer, so that the contact area between an active material coating coated on the surface of the current collector and the current collector is increased; and the interface bonding force between the active material coating and the current collector in the pole piece is improved, so that the internal resistance of the secondary battery is reduced, the falling proportion of the active material coating in the charge-discharge cycle process of the secondary battery is reduced, and the cycle performance of the secondary battery is improved.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a current collector, a secondary battery, and an electrical device. Background Art

[0002] With the rapid development of pure electric vehicles and hybrid electric vehicles, higher requirements are placed on the energy density of lithium-ion batteries.

[0003] In related technologies, in order to increase the energy density of lithium-ion batteries, the thickness of the electrodes in lithium-ion batteries is made thinner and thinner; however, as the thickness of the electrodes continues to decrease, the interfacial bonding force between the current collector and the active material coating in the electrodes continues to decrease, which not only leads to an increase in the internal resistance of the lithium-ion battery, but also during the charge and discharge cycle of the lithium-ion battery, the active material coating in the electrode is very easy to fall off from the current collector, resulting in a decrease in the cycle performance of the lithium-ion battery. Summary of the Invention

[0004] The technical problem to be solved by the present application is to provide a current collector, a secondary battery and an electrical device to solve the problem in the related art that the interface bonding force between the current collector and the active material coating in the electrode sheet decreases due to the continuous thinning of the electrode sheet thickness in the secondary battery.

[0005] In order to solve the above problems, this application is implemented through the following technical solutions:

[0006] The present application proposes a current collector, which includes a metal substrate and a composite layer provided on at least one surface of the metal substrate, wherein the composite layer includes a conductive polymer grid layer and a metal grid layer;

[0007] The conductive polymer grid layer and the metal grid layer are stacked on the same side surface of the metal substrate, and the grid lines in the conductive polymer grid layer intersect with the grid lines in the metal grid layer.

[0008] Furthermore, the current collector includes a hollow foil area and a coated area; in the conductive polymer grid layer, the width of the grid lines in the hollow foil area is greater than the width of the grid lines in the coated area; and / or, in the metal grid layer, the width of the grid lines in the coated area is greater than the width of the grid lines in the hollow foil area.

[0009] Furthermore, in the current collector, in the conductive polymer grid layer, the ratio of the width of the grid lines in the empty foil area to the width of the grid lines in the coated area is 2 to 4; and / or, in the metal grid layer, the ratio of the width of the grid lines in the empty foil area to the width of the grid lines in the coated area is 0.2 to 0.5.

[0010] Furthermore, the current collector includes a hollow foil area and a coated area; in the conductive polymer grid layer, the spacing between adjacent grid lines in the hollow foil area is smaller than the spacing between adjacent grid lines in the coated area; and / or, in the metal grid layer, the spacing between adjacent grid lines in the coated area is smaller than the spacing between adjacent grid lines in the hollow foil area.

[0011] Furthermore, the current collector has a first direction and a second direction perpendicular to each other; the conductive polymer grid layer includes a first grid line arranged along the first direction and a second grid line arranged along the second direction, and the first grid line and the second grid line intersect; the metal grid layer includes a third grid line arranged along the first direction and a fourth grid line arranged along the second direction, and the third grid line and the fourth grid line intersect; the first grid line and the third grid line are arranged at intervals, and the second grid line and the fourth grid line are arranged at intervals;

[0012] And / or, the current collector includes a hollow foil area and a coating area; in the coating area, the conductive polymer grid layer is located between the metal substrate and the metal grid layer; in the hollow foil area, the metal grid layer is located between the metal substrate and the conductive polymer grid layer.

[0013] The present application provides a secondary battery, which includes the current collector described above.

[0014] Furthermore, the secondary battery comprises a wound cell, the wound cell comprising a positive electrode sheet, a separator and a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material coating provided on the surface of the negative electrode current collector, the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material coating provided on the surface of the positive electrode current collector; the negative electrode current collector and / or the positive electrode current collector are the current collectors described above;

[0015] In which, the wound battery core includes a corner section and a straight section; the thickness of the conductive polymer grid layer in the current collector in the corner section is greater than the thickness of the conductive polymer grid layer in the straight section, and / or the thickness of the metal grid layer in the current collector in the corner section is greater than the thickness of the metal grid layer in the straight section.

[0016] Furthermore, in the secondary battery, in the straight section of the wound battery cell, the thickness of the conductive polymer grid layer in the current collector is less than or equal to the thickness of the metal substrate, and / or the thickness of the metal grid layer in the current collector is less than or equal to the thickness of the metal substrate.

[0017] Furthermore, in the secondary battery, at the corner section of the wound battery cell, an adhesive layer is provided on the surface of the conductive polymer grid layer and / or the metal grid layer in the current collector facing the separator, and the current collector is bonded to the separator via the adhesive layer;

[0018] The meshes of the conductive polymer mesh layer and the metal mesh layer are filled with active material coatings.

[0019] The present application also proposes an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0020] Compared with the related art, the embodiments of the present application have the following advantages:

[0021] In an embodiment of the present application, a current collector is provided that includes a metal substrate and a composite layer provided on at least one side surface of the metal substrate, the composite layer including a conductive polymer grid layer and a metal grid layer; on the same side surface of the metal substrate, the conductive polymer grid layer and the metal grid layer are stacked and the grid lines in the conductive polymer grid layer intersect with the grid lines in the metal grid layer, which is beneficial to increasing the surface area of ​​the current collector, thereby increasing the contact area between the active material coating coated on the surface of the current collector and the current collector, and improving the interfacial bonding force between the active material coating and the current collector in the electrode piece; when the interfacial bonding force between the active material coating and the current collector in the electrode piece is improved, the internal resistance of the secondary battery prepared based on the current collector provided in the embodiment of the present application can be reduced, and the proportion of active material coating falling off during the charge and discharge cycle of the secondary battery can be reduced, thereby improving the cycle performance of the secondary battery; further, in the embodiment of the present application, the conductive polymer grid layer and the metal grid layer provided on the surface of the metal substrate are arranged as a grid structure, which can reduce the increase in the volume and weight of the current collector, and is beneficial to improving the interfacial bonding force between the active material coating and the current collector while improving the energy density of the secondary battery.

[0022] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic diagram of a top view of a current collector provided in an embodiment of the present application. Figure 1 ;

[0024] Figure 2 This is a schematic diagram of a top view of a current collector provided in an embodiment of the present application. Figure 2 ;

[0025] Figure 3 This is a schematic diagram of a top view of a current collector provided in an embodiment of the present application. Figure 3 ;

[0026] Figure 4 1 is a schematic diagram of the cross-sectional structure of a current collector provided in an embodiment of the present application;

[0027] Figure 5 This is a schematic diagram of a top view of a current collector provided in an embodiment of the present application. Figure 4 ;

[0028] Figure 6 This is a schematic diagram of a top view of a current collector provided in an embodiment of the present application. Figure 5 ;

[0029] Figure 7 This is a schematic diagram of a top view of a current collector provided in an embodiment of the present application. Figure 6 .

[0030] Description of reference numerals:

[0031] 10 - current collector; 101 - metal substrate; 102 - conductive polymer grid layer; 102a - first grid line; 102b - second grid line; 103 - metal grid layer; 103a - third grid line; 103b - fourth grid line; 104 - tab. DETAILED DESCRIPTION

[0032] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0033] In related technologies, in order to improve the interfacial bonding strength between the current collector and the active material coating in the electrode, the proportion of the binder in the active material coating formula is generally increased; however, the introduction of a high proportion of binder will lead to an increase in the ion conduction resistance of the secondary battery, which in turn will lead to an increase in the internal resistance of the secondary battery, a decrease in the charge and discharge capacity and rate performance of the secondary battery, and a decrease in the cycle stability of the secondary battery.

[0034] In addition, as the thickness of the electrode continues to decrease, the brittleness of the electrode also increases. In the process of rolling the electrode using a roller press, the electrode is prone to cracks and breakage, resulting in a decrease in the finished product yield and preparation efficiency of the electrode.

[0035] In order to solve the above problems, the present invention provides a current collector. Figure 1 The current collector 10 includes a metal substrate 101 and a composite layer provided on at least one surface of the metal substrate 101 , wherein the composite layer includes a conductive polymer grid layer 102 and a metal grid layer 103 .

[0036] On the same side surface of the metal substrate 101 , the conductive polymer grid layer 102 and the metal grid layer 103 are stacked, and the grid lines in the conductive polymer grid layer 102 intersect with the grid lines in the metal grid layer 103 .

[0037] The current collector 10 provided in the embodiment of the present application may be a negative electrode current collector and / or a positive electrode current collector.

[0038] In some embodiments, the current collector 10 is a negative electrode current collector, and the metal substrate 101 can be a negative electrode foil for secondary batteries available to those skilled in the art. The negative electrode foil for secondary batteries can include but is not limited to copper foil, nickel foil, and stainless steel foil.

[0039] In some embodiments, the current collector 10 is a positive electrode current collector, and the metal substrate 101 can be a positive electrode foil for secondary batteries that can be obtained by those skilled in the art. The positive electrode foil for secondary batteries can include but is not limited to aluminum foil, nickel foil, stainless steel foil, and titanium foil.

[0040] The metal substrate 101 serves as the base layer of the current collector 10 , and is used to support the conductive polymer grid layer 102 and the metal grid layer 103 . It also conducts electrons, loads active material coatings, and ensures electrical connections within the secondary battery.

[0041] The conductive polymer grid layer 102 is a conductive polymer layer having a grid structure formed by photolithography, masking, or inkjet printing of a conductive polymer film. The polymer material of the conductive polymer grid layer 102 has high toughness. In the embodiment of the present application, the conductive polymer grid layer 102 provided on the surface of the metal substrate 101 can reduce the brittleness of the current collector 10, improve the toughness of the current collector 10, and further improve the toughness of the electrode prepared based on the current collector 10. During the process of rolling the electrode using a roller press, the probability of the electrode breaking can be reduced, thereby improving the finished product yield and production efficiency of the electrode.

[0042] Specifically, the conductive polymer grid layer 102 can be prepared by the following process:

[0043] First, the surface of the flexible substrate is cleaned and then activated; wherein the flexible substrate can be selected from polyethylene terephthalate (PET).

[0044] Then, the monomers used to prepare the conductive polymer grid layer 102 are prepared into a monomer solution; wherein the solvent in the monomer solution can be selected from pure water or ethanol; and the concentration of the monomer solution is 0.1M to 0.5M.

[0045] Then, an oxidant is added to the monomer solution to obtain a mixed solution; wherein the molar ratio between the oxidant and the monomer is 1:1 to 2:1; the oxidant can be selected from ferric chloride (FeCl3) or ammonium persulfate ((NH4)2S2O8, APS).

[0046] Then, the mixed solution is coated on the surface of the activated flexible substrate, and a polymerization reaction is carried out at 0° C. to 25° C. to obtain a conductive polymer film.

[0047] Finally, a grid structure is formed on the conductive polymer film by photolithography, masking, or inkjet printing to obtain the conductive polymer grid layer 102 .

[0048] The metal mesh layer 103 is a metal layer having a mesh structure formed by screen printing metal particles. The material of the metal mesh layer 103 can be the same as or different from that of the metal substrate 101, and this embodiment of the application does not specifically limit this.

[0049] Specifically, the metal mesh layer 103 can be prepared by the following process:

[0050] The metal particles are printed into a mesh layer by screen printing metal, and the mesh layer is sintered under preset temperature conditions to obtain the metal mesh layer 103; wherein the preset temperature can be determined according to the material of the metal mesh layer 103. For example, when the material of the metal mesh layer 103 is copper, the preset temperature can be 200°C to 300°C, and the atmosphere for sintering the mesh layer is an inert atmosphere to prevent the metal mesh layer 103 from oxidizing during the sintering process.

[0051] In some embodiments, reference Figure 1 , the conductive polymer grid layer 102 is arranged on at least one side surface of the metal substrate 101, and the metal grid layer 103 is stacked on the surface of the conductive polymer grid layer 102; the metal grid layer 103 and the metal substrate 101 sandwich the conductive polymer grid layer 102 in the middle, which can not only prevent the conductive polymer grid layer 102 from falling off the surface of the metal substrate 101, but also improve the mechanical strength of the current collector 10, and further reduce the probability of the pole piece breaking during the rolling process; in addition, the metal grid layer 103 is stacked on the surface of the conductive polymer grid layer 102, and the grid lines in the conductive polymer grid layer 102 and the metal grid layer 103 are intersected, which can increase the surface area of ​​the current collector 10, thereby increasing the contact area between the active material coating coated on the surface of the current collector 10 and the current collector 10, and improving the interface bonding force between the active material coating in the pole piece and the current collector 10.

[0052] It can be understood that when the current collector 10 is a negative electrode current collector, the active material coating coated on the surface of the current collector 10 is a negative electrode active material coating, and the electrode sheet prepared based on the current collector 10 is a negative electrode electrode sheet; when the current collector 10 is a positive electrode current collector, the active material coating coated on the surface of the current collector 10 is a positive electrode active material coating, and the electrode sheet prepared based on the current collector 10 is a positive electrode electrode sheet.

[0053] In the embodiment of the present application, the metal substrate 101, the conductive polymer grid layer 102, and the metal grid layer 103 can be first stacked in a predetermined stacking manner to obtain a laminate; the laminate can then be roll-pressed to obtain the current collector 10. The temperature for rolling the laminate is 80° C. to 150° C., the pressure is 5 MPa to 20 MPa, and the rolling speed is 0.1 m / min to 1 m / min. The roller used to roll the laminate can be made of a metal roller, and the surface of the metal roller is polished to prevent adhesion between the roller and the laminate.

[0054] In some embodiments, the preset stacking method is: the conductive polymer grid layer 102 and the metal grid layer 103 are stacked in sequence on the upper surface of the metal substrate 101, and the conductive polymer grid layer 102 and the metal grid layer 103 are stacked in sequence on the lower surface of the metal substrate 101; in this scenario, in the current collector 10 obtained by rolling, the upper and lower surfaces of the metal substrate 101 are both provided with a conductive polymer grid layer 102, and the metal grid layer 103 is stacked on the conductive polymer grid layer 102.

[0055] In other embodiments, the preset stacking method is: a conductive polymer grid layer 102 and a metal grid layer 103 are stacked in sequence on the upper surface of the metal substrate 101; in this scenario, in the current collector 10 obtained by rolling, a conductive polymer grid layer 102 is provided on the upper surface of the metal substrate 101, and a metal grid layer 103 is stacked on the conductive polymer grid layer 102.

[0056] In some other embodiments, the preset stacking method is: a conductive polymer grid layer 102 and a metal grid layer 103 are stacked in sequence on the lower surface of the metal substrate 101; in this scenario, in the current collector 10 obtained by rolling, a conductive polymer grid layer 102 is provided on the lower surface of the metal substrate 101, and a metal grid layer 103 is stacked on the conductive polymer grid layer 102.

[0057] In the embodiment of the present application, on the same side surface of the metal substrate 101, the grid lines in the conductive polymer grid layer 102 and the grid lines in the metal grid layer 103 can be interwoven with each other (eg, Figure 2 ), or they can be independent of each other (as shown in Figure 1 This embodiment of the present application does not specifically limit this.

[0058] The current collector 10 provided in the embodiment of the present application includes a metal substrate 101, and a conductive polymer grid layer 102 and a metal grid layer 103 provided on at least one side surface of the metal substrate 101. On the same side surface of the metal substrate 101, the conductive polymer grid layer 102 and the metal grid layer 103 are stacked and the grid lines in the conductive polymer grid layer 102 are intersected with the grid lines in the metal grid layer 103. In the embodiment of the present application, by arranging the conductive polymer grid layer 102 on the surface of the metal substrate 101, the toughness of the conductive polymer grid layer 102 can be utilized to improve the toughness of the current collector 10, thereby improving the toughness of the electrode piece, reducing the probability of the electrode piece breaking during the rolling process, and improving the finished product yield and preparation efficiency of the electrode piece. In addition, the metal grid layer 103 and the metal substrate 101 sandwich the conductive polymer grid layer 102 in the middle, which not only prevents the conductive polymer grid layer 102 from falling off the surface of the metal substrate 101, but also improves the mechanical strength of the current collector 10, further reducing the occurrence of electrode piece breaking during the rolling process. probability; in addition, the metal grid layer 103 is stacked on the surface of the conductive polymer grid layer 102, and the grid lines in the conductive polymer grid layer 102 are arranged to intersect with the grid lines in the metal grid layer 103, which is beneficial to increasing the surface area of ​​the current collector 10, thereby increasing the contact area between the active material coating coated on the surface of the current collector 10 and the current collector 10, and improving the interface bonding force between the active material coating and the current collector 10 in the electrode piece; when the interface bonding force between the active material coating and the current collector 10 in the electrode piece is improved, the internal resistance of the secondary battery can be reduced, and the proportion of active material coating falling off during the charge and discharge cycle of the secondary battery can be reduced, thereby improving the cycle performance of the secondary battery; further, the embodiment of the present application sets the conductive polymer grid layer 102 and the metal grid layer 103 provided on the surface of the metal substrate 101 as a grid structure, which can reduce the increase in the volume and weight of the current collector 10, and is beneficial to improving the interface bonding force between the active material coating and the current collector 10 while improving the energy density of the secondary battery.

[0059] In the related art, the rollers of the roller press have the problem of severe wear in the middle area due to long-term use. In the process of using the rollers of the roller press to roll the pole pieces, the edge of the pole piece will be subjected to excessive force, exacerbating the problem of pole piece breakage.

[0060] In some embodiments of the present application, reference is made to Figure 3 and Figure 4 , Figure 4 is Figure 3A schematic cross-sectional view of the current collector 10 taken along its thickness at the O-O' position. The current collector 10 includes a hollow foil region and a coated region. In the conductive polymer mesh layer 102, the width w1 of the grid lines in the hollow foil region is greater than the width w2 of the grid lines in the coated region. By increasing the width w1 of the grid lines in the hollow foil region of the conductive polymer mesh layer 102, the embodiments of the present application can increase the toughness of the hollow foil region at the edge of the current collector 10. The highly tough hollow foil region can reduce the problem of electrode breakage caused by excessive force on the electrode edge, further reducing the probability of electrode breakage during rolling.

[0061] In some embodiments, in the conductive polymer mesh layer 102, the ratio of the width w1 of the mesh lines in the hollow foil area to the width w2 of the mesh lines in the coated area is 2 to 4; specifically, in the conductive polymer mesh layer 102, the width w1 of the mesh lines in the hollow foil area and the width w2 of the mesh lines in the coated area satisfy:

[0062] w1=α×w2 (1)

[0063] Wherein, w1 represents the width of the grid lines in the hollow foil area of ​​the conductive polymer grid layer 102; w2 represents the width of the grid lines in the coated area of ​​the conductive polymer grid layer 102; α represents the ratio of the width w1 of the grid lines in the hollow foil area of ​​the conductive polymer grid layer 102 to the width w2 of the grid lines in the coated area, and the value of α is 2 to 4.

[0064] In some embodiments, in the conductive polymer grid layer 102 , the ratio of the width w1 of the grid lines in the blank foil area to the width w2 of the grid lines in the coated area may be in the range of 2, 2.5, 3, 3.5, and 4, or any two thereof.

[0065] In the embodiment of the present application, the ratio of the width w1 of the grid lines in the empty foil area of ​​the conductive polymer grid layer 102 to the width w2 of the grid lines in the coating area is controlled to be 2 to 4. This can reduce the probability of the pole piece breaking while reducing the increase in the volume and weight of the current collector 10, thereby improving the energy density of the secondary battery.

[0066] In some embodiments, the width of the grid lines in the conductive polymer grid layer 102 is 1 mm to 5 mm. Specifically, the width of the grid lines in the conductive polymer grid layer 102 can be within the range of one or any two of 1 mm, 2 mm, 3 mm, 4 mm, and 5 mm. In the embodiments of the present application, the width of the grid lines in the conductive polymer grid layer 102 is controlled within the range of 1 mm to 5 mm. This can reduce the risk of the conductive polymer grid layer 102 breaking due to excessively small widths of the grid lines in the conductive polymer grid layer 102, thereby improving the quality of the conductive polymer grid layer 102. Furthermore, controlling the width of the grid lines in the conductive polymer grid layer 102 within the range of 1 mm to 5 mm can also help the conductive polymer grid layer 102 fully play its role in improving the toughness of the current collector 10.

[0067] In some embodiments, the spacing between adjacent grid lines in the conductive polymer grid layer 102 is 1 mm to 20 mm; specifically, the spacing between adjacent grid lines in the conductive polymer grid layer 102 can be one or any two of 1 mm, 5 mm, 10 mm, 13 mm, 18 mm and 20 mm. Within this range, while ensuring that the conductive polymer grid layer 102 plays a full role in improving the toughness of the current collector 10, the processability of the conductive polymer grid layer 102 is also improved.

[0068] In some embodiments, reference Figure 5 The current collector 10 includes a hollow foil area and a coated area; in the conductive polymer grid layer 102, the spacing L1 of adjacent grid lines in the hollow foil area is smaller than the spacing L2 of adjacent grid lines in the coated area; the embodiment of the present application reduces the spacing of adjacent grid lines in the hollow foil area in the conductive polymer grid layer 102, thereby increasing the density of grid lines in the hollow foil area in the conductive polymer grid layer 102, which is beneficial to increasing the toughness of the hollow foil area at the edge of the current collector 10. The hollow foil area with high toughness can reduce the problem of pole piece breakage caused by excessive force on the edge of the pole piece, which is beneficial to further reduce the probability of pole piece breakage during rolling.

[0069] In some embodiments, reference Figure 3 and Figure 4The current collector 10 includes a hollow foil area and a coated area; in the metal grid layer 103, the width w4 of the grid line in the coated area is greater than the width w3 of the grid line in the hollow foil area; the embodiment of the present application increases the width w4 of the grid line in the coated area in the metal grid layer 103, thereby increasing the contact area between the coated area and the active material coating in the current collector 10, which is beneficial to further improve the interface bonding force between the active material coating in the electrode and the current collector 10, reduce the internal resistance of the secondary battery, and reduce the proportion of the active material coating falling off during the charge and discharge cycle of the secondary battery, thereby improving the cycle performance of the secondary battery.

[0070] In some embodiments, in the metal mesh layer 103, the ratio of the width w3 of the mesh lines in the empty foil area to the width w4 of the mesh lines in the coated area is 0.2 to 0.5; specifically, in the metal mesh layer 103, the width w3 of the mesh lines in the empty foil area and the width w4 of the mesh lines in the coated area satisfy:

[0071] w3=β×w4 (2)

[0072] Among them, w3 represents the width of the grid line in the empty foil area of ​​the metal grid layer 103; w4 represents the width of the grid line in the coating area of ​​the metal grid layer 103; β represents the ratio of the width w3 of the grid line in the empty foil area of ​​the metal grid layer 103 to the width w1 of the grid line in the coating area, and the value of β is 0.2~0.5.

[0073] In some embodiments, in the metal grid layer 103 , the ratio of the width w3 of the grid lines in the empty foil area to the width w4 of the grid lines in the coated area may be in the range of one or any two of 0.2, 0.3, 0.35, 0.4 and 0.5.

[0074] In the embodiment of the present application, the ratio of the width w3 of the grid lines in the empty foil area of ​​the metal grid layer 103 to the width w4 of the grid lines in the coating area is controlled to be 0.2 to 0.5. This can increase the contact area between the coating area and the active material coating in the current collector 10, improve the interfacial bonding force between the active material coating in the electrode and the current collector 10, and at the same time reduce the increase in the volume and weight of the current collector 10, thereby improving the energy density of the secondary battery.

[0075] In some embodiments, the width of the grid lines in the metal grid layer 103 is 2 mm to 10 mm; specifically, the width of the grid lines in the metal grid layer 103 can be within the range of one or any two of 2 mm, 4 mm, 5 mm, 7 mm, 9 mm, and 10 mm. In the embodiment of the present application, the width of the grid lines in the metal grid layer 103 is controlled within the range of 2 mm to 10 mm, which can reduce the risk of the metal grid layer 103 being broken due to the width of the grid lines in the metal grid layer 103 being too small, thereby improving the quality of the metal grid layer 103. Furthermore, controlling the width of the grid lines in the metal grid layer 103 within the range of 2 mm to 10 mm can also help the metal grid layer 103 to fully play its role in improving the interfacial bonding strength between the current collector 10 and the active material coating.

[0076] It should be noted that the width of the grid lines in the conductive polymer grid layer 102 may be equal to or different from the width of the grid lines in the metal grid layer 103 , and this embodiment of the present application does not specifically limit this.

[0077] In some embodiments, the spacing between adjacent grid lines in the metal grid layer 103 is 1 mm to 20 mm; specifically, the spacing between adjacent grid lines in the metal grid layer 103 can be a range of one or any two of 1 mm, 5 mm, 10 mm, 13 mm, 18 mm and 20 mm. Within this range, while ensuring that the metal grid layer 103 plays a full role in improving the interfacial bonding force between the current collector 10 and the active material coating, the processability of the metal grid layer 103 is also improved.

[0078] It should be noted that, in the embodiment of the present application, the spacing between adjacent grid lines in the conductive polymer grid layer 102 may be the same as or different from the spacing between adjacent grid lines in the metal grid layer 103 , and this embodiment of the present application does not specifically limit this.

[0079] In some embodiments, reference Figure 5 The current collector 10 includes a hollow foil area and a coated area; in the metal grid layer 103, the spacing L3 between adjacent grid lines in the coated area is smaller than the spacing L4 between adjacent grid lines in the hollow foil area; the embodiment of the present application reduces the spacing between adjacent grid lines in the coated area in the metal grid layer 103, thereby increasing the density of grid lines in the coated foil area in the metal grid layer 103, thereby further increasing the contact area between the coated area and the active material coating in the current collector 10, improving the interface bonding force between the active material coating in the electrode and the current collector 10, reducing the internal resistance of the secondary battery, and reducing the proportion of active material coating falling off during the charge and discharge cycle of the secondary battery, thereby improving the cycle performance of the secondary battery.

[0080] In some embodiments, the length of the grid lines in the conductive polymer grid layer 102 is less than or equal to the length of the current collector 10 ; in some embodiments, the length of the grid lines in the metal grid layer 103 is less than or equal to the length of the current collector 10 .

[0081] In some embodiments, reference Figure 6 The current collector 10 includes a hollow foil area and a coating area; in the coating area, the conductive polymer grid layer 102 is located between the metal substrate 101 and the metal grid layer 103; in the hollow foil area, the metal grid layer 103 is located between the metal substrate 101 and the conductive polymer grid layer 102.

[0082] Specifically, in the coating area, the conductive polymer grid layer 102 is provided on at least one side surface of the metal substrate 101, and the metal grid layer 103 is provided on the surface of the conductive polymer grid layer 102; in the empty foil area, the metal grid layer 103 is provided on at least one side surface of the metal substrate 101, and the conductive polymer grid layer 102 is provided on the surface of the metal grid layer 103; wherein, on the same side surface of the metal substrate 101, the grid lines in the conductive polymer grid layer 102 and the grid lines in the metal grid layer 103 are arranged to intersect.

[0083] In an embodiment of the present application, in the coating area of ​​the current collector 10, the conductive polymer grid layer 102 is located between the metal substrate 101 and the metal grid layer 103, which can prevent the conductive polymer grid layer 102 from falling off the surface of the metal substrate 101, and the metal grid layer 103 is stacked on the surface of the conductive polymer grid layer 102, and the grid lines in the conductive polymer grid layer 102 and the grid lines in the metal grid layer 103 are arranged to intersect, which is beneficial to increase the surface area of ​​the coating area in the current collector 10, and then increase the contact area between the active material coating coated on the surface of the coating area and the coating area, thereby improving the interface bonding force between the active material coating in the electrode and the current collector 10.

[0084] In addition, in the embodiment of the present application, in the hollow foil area of ​​the current collector 10, the metal grid layer 103 is located between the metal substrate 101 and the conductive polymer grid layer 102, so that the exposed upper surface of the hollow foil area can be the surface of the conductive polymer grid layer 102, thereby reducing the exposure amount of the metal surface in the hollow foil area, which is beneficial to reducing the burrs generated on the metal surface in the hollow foil area, and reducing the penetration hazard of the burrs generated on the surface of the current collector 10 to the diaphragm in the secondary battery and the local decomposition of the electrolyte caused by the tip effect of the burrs, which is beneficial to improving the safety of the secondary battery.

[0085] In some embodiments, the empty foil area in the current collector 10 is used to prepare the tab; Figure 6In the hollow foil area, the area between adjacent grid lines in the conductive polymer grid layer 102 serves as the tab 104 obtained after cutting; thereby, the exposure amount of the metal surface in the hollow foil area of ​​the current collector 10 can be further reduced, and the burrs generated on the metal surface in the hollow foil area can be reduced, thereby reducing the penetration hazard of the burrs to the diaphragm in the secondary battery and the local decomposition of the electrolyte caused by the tip effect of the burrs, thereby improving the safety of the secondary battery.

[0086] In some embodiments, the thickness of the conductive polymer grid layer 102 is less than or equal to the thickness of the metal substrate 101, which can ensure that the conductive polymer grid layer 102 fully plays its role in improving the toughness of the current collector 10 while improving the mechanical strength of the current collector 10 and the reliability of the electrical connection of the current collector 10 in the secondary battery.

[0087] In some embodiments, the thickness of the metal grid layer 103 is less than or equal to the thickness of the metal substrate 101, which can ensure that the metal grid layer 103 fully plays its role in improving the interfacial bonding force between the current collector 10 and the active material coating, while improving the mechanical strength of the current collector 10 and the reliability of the electrical connection of the current collector 10 in the secondary battery.

[0088] In some embodiments, the thickness of the metal substrate 101 is 5 μm to 15 μm; specifically, the thickness of the metal substrate 101 can be one or any two of 5 μm, 8 μm, 10 μm, 12 μm and 15 μm. Within this range, the metal substrate 101 is conducive to fully playing its role in carrying the conductive polymer grid layer 102 and the metal grid layer 103, conducting electrons, loading the active material coating and ensuring the electrical connection inside the secondary battery.

[0089] In some embodiments, the thickness of the conductive polymer grid layer 102 is 1 μm to 10 μm; specifically, the thickness of the conductive polymer grid layer 102 can be in the range of one or any two of 1 μm, 3 μm, 5 μm, 8 μm and 10 μm. Within this range, while the conductive polymer grid layer 102 can fully play its role in improving the toughness of the current collector 10, it can also improve the energy density of the secondary battery.

[0090] In some embodiments, the thickness of the metal grid layer 103 is 1 μm to 10 μm; specifically, the thickness of the metal grid layer 103 can be a range of one or any two of 1 μm, 3 μm, 5 μm, 8 μm and 10 μm. Within this range, while the metal grid layer 103 plays a full role in improving the interfacial bonding force between the current collector 10 and the active material coating, the energy density of the secondary battery can also be improved.

[0091] It should be noted that, in the embodiment of the present application, the thickness of the conductive polymer grid layer 102 may be the same as or different from the thickness of the metal grid layer 103 , and this embodiment of the present application does not specifically limit this.

[0092] In some embodiments, the conductive polymer grid layer 102 can be selected from at least one of polyacetylene (PA) type copolymers, polyaniline (PANI) type copolymers, polypyrrole (PPy) type copolymers, polythiophene (PT) type copolymers, polyphenylene sulfide (PPS) type copolymers and polyquinoline (PQ) type copolymers.

[0093] In some embodiments, as Figure 7 As shown, the current collector has a first and second perpendicular directions, such as the length and width of the current collector. The conductive polymer grid layer 102 includes first grid lines 102a arranged along the first direction and second grid lines 102b arranged along the second direction, with the first grid lines 102a and the second grid lines 102b intersecting. The metal grid layer 103 includes third grid lines 103a arranged along the first direction and fourth grid lines 103b arranged along the second direction, with the third grid lines 103a and the fourth grid lines 103b intersecting. The first grid lines 102a and the third grid lines 103a are spaced apart, while the second grid lines 102b and the fourth grid lines 103b are spaced apart. The grid lines are arranged along the length and width of the current collector and can extend along the rolling direction of the current collector, which helps the current collector to stretch the grid lines during rolling, thereby improving the toughness of the current collector edge. In addition, it also helps to cut the tab along the extended path of the grid lines, improving the consistency of the tab edge size.

[0094] The present application also provides a secondary battery including the current collector 10 described above. Specifically, in some embodiments, the negative electrode current collector in the secondary battery is the current collector 10 described above; in other embodiments, the positive electrode current collector in the secondary battery is the current collector 10 described above; and in still other embodiments, both the negative electrode current collector and the positive electrode current collector in the secondary battery are the current collector 10 described above.

[0095] In which case, when both the negative electrode current collector and the positive electrode current collector in the secondary battery are the current collectors 10 described above, the negative electrode current collector and the positive electrode current collector can be independently selected from the current collectors 10 described in any of the above items. The material types of the metal matrix 101, the conductive polymer grid layer 102, and the metal grid layer 103 in the negative electrode current collector can be adaptively adjusted to the material types suitable for the application scenario of the negative electrode current collector. Correspondingly, the material types of the metal matrix 101, the conductive polymer grid layer 102, and the metal grid layer 103 in the positive electrode current collector can be adaptively adjusted to the material types suitable for the application scenario of the positive electrode current collector.

[0096] In some embodiments, the secondary battery includes a wound battery cell, the wound battery cell includes a positive electrode sheet, a separator and a negative electrode sheet, the negative electrode sheet includes a negative electrode collector and a negative electrode active material coating provided on the surface of the negative electrode collector, and the positive electrode sheet includes a positive electrode collector and a positive electrode active material coating provided on the surface of the positive electrode collector.

[0097] The negative electrode current collector and / or the positive electrode current collector in the wound battery cell may be the current collector 10 as described above.

[0098] In the embodiment of the present application, the wound cell includes corner sections and straight sections. The current collector 10 includes a metal substrate 101, and a conductive polymer grid layer 102 and a metal grid layer 103 disposed on at least one side of the metal substrate 101. The conductive polymer grid layer 102 and the metal grid layer 103 are stacked on the same side of the metal substrate 101, with the grid lines in the conductive polymer grid layer 102 intersecting with the grid lines in the metal grid layer 103.

[0099] In some embodiments, the thickness of the conductive polymer grid layer 102 in the current collector 10 at the corners of the wound cell is greater than the thickness of the conductive polymer grid layer 102 in the straight sections of the wound cell. Specifically, when the negative electrode current collector in the wound cell is the current collector 10 described above, the thickness of the conductive polymer grid layer 102 in the negative electrode current collector at the corners is greater than the thickness of the conductive polymer grid layer 102 in the straight sections; when the positive electrode current collector in the wound cell is the current collector 10 described above, the thickness of the conductive polymer grid layer 102 in the positive electrode current collector at the corners is greater than the thickness of the conductive polymer grid layer 102 in the straight sections.

[0100] In some embodiments, the thickness of the metal grid layer 103 in the current collector 10 at the corners of the wound cell is greater than the thickness of the metal grid layer 103 in the straight sections of the wound cell. Specifically, when the negative electrode current collector in the wound cell is the current collector 10 described above, the thickness of the metal grid layer 103 in the negative electrode current collector at the corners is greater than the thickness of the metal grid layer 103 in the straight sections; when the positive electrode current collector in the wound cell is the current collector 10 described above, the thickness of the metal grid layer 103 in the positive electrode current collector at the corners is greater than the thickness of the metal grid layer 103 in the straight sections.

[0101] In related technologies, the corner sections of wound battery cells have a smaller curvature radius, which will cause local current density concentration. According to the "tip effect" in electromagnetism, the greater the curvature, the more obvious the charge accumulation is, resulting in faster electrochemical reaction rates in the corner sections of the wound battery cells and higher lithium ion diffusion requirements. If the charge transfer rate is insufficient, lithium ions will be deposited on the surface of the negative electrode to form lithium dendrites.

[0102] In the secondary battery provided in the embodiment of the present application, the thickness of the conductive polymer grid layer 102 in the corner section of the current collector 10 is greater than the thickness of the conductive polymer grid layer 102 in the straight section, and / or the thickness of the metal grid layer 103 in the corner section of the current collector 10 is greater than the thickness of the metal grid layer 103 in the straight section, so that the cross-sectional area of ​​the conductive structure for transmitting charge in the corner section of the wound battery cell is increased. According to Ohm's law, when the cross-sectional area of ​​the conductive structure for transmitting charge in the corner section is increased, the resistance of the corner section in the wound battery cell will be significantly reduced, which is beneficial to improving the charge transfer rate of the corner section, alleviating the high polarization problem caused by charge concentration in the corner section, reducing the risk of lithium plating caused by lithium ion accumulation in the corner section, and thereby reducing the short circuit, capacity attenuation and other problems caused by lithium dendrite growth piercing the diaphragm, which is beneficial to improving the safety of the secondary battery and extending the service life of the secondary battery.

[0103] In some embodiments, in the straight section of the wound battery cell, the thickness of the conductive polymer grid layer 102 in the current collector 10 is less than or equal to the thickness of the metal substrate 101. Thus, the energy density of the secondary battery can be improved while ensuring that the conductive polymer grid layer 102 fully plays its role in improving the toughness of the current collector 10.

[0104] In some embodiments, in the straight section of the wound battery cell, the thickness of the metal grid layer 103 in the current collector 10 is less than or equal to the thickness of the metal substrate 101. Thus, the energy density of the secondary battery can be improved while ensuring that the metal grid layer 103 fully plays its role in improving the interfacial bonding force between the current collector 10 and the active material coating.

[0105] In some embodiments, in the corner section of the wound battery cell, the surface of the conductive polymer grid layer and / or metal grid layer in the current collector 10 facing the diaphragm is provided with an adhesive layer (the adhesive used in the adhesive layer includes polyacrylic acid or polyurethane adhesive, etc.), and the current collector 10 is bonded to the diaphragm through the adhesive layer; specifically, the adhesive layer includes a first adhesive layer and a second adhesive layer; in the case where the negative current collector in the wound battery cell is the current collector 10 as described above, in the corner section of the wound battery cell, the surface of the conductive polymer grid layer and / or metal grid layer in the negative current collector facing the diaphragm is provided with a first adhesive layer, and the negative current collector is bonded to the diaphragm through the first adhesive layer; in the case where the positive current collector in the wound battery cell is the current collector 10 as described above, in the corner section of the wound battery cell, the surface of the conductive polymer grid layer and / or metal grid layer in the positive current collector facing the diaphragm is provided with a second adhesive layer, and the positive current collector is bonded to the diaphragm through the second adhesive layer. And the grids of the conductive polymer grid layer and the metal grid layer are filled with active material coatings, that is, in the positive electrode current collector, the grids of the conductive polymer grid layer and the metal grid layer of the positive electrode current collector in the corner section are filled with positive electrode active material coatings, so that the positive electrode current collector is connected to the diaphragm through the second adhesive layer of the corner section, so that the positive electrode active material coating of the corner section has good interface contact with the diaphragm; in the negative electrode current collector, the grids of the conductive polymer grid layer and the metal grid layer of the negative electrode current collector in the corner section are filled with negative electrode active material coatings, so that the negative electrode current collector is connected to the diaphragm through the first adhesive layer of the corner section, so that the negative electrode active material coating of the corner section has good interface contact with the diaphragm; that is, the positive electrode active material coating and the negative electrode active material coating on both sides of the diaphragm are in good interface contact with the diaphragm, respectively, reducing the risk of gaps between the positive and negative electrodes in the corner section.

[0106] In the embodiment of the present application, in the corner section of the wound battery cell, an adhesive layer is provided on the surface of the conductive polymer grid layer and / or metal grid layer in the current collector 10 facing the diaphragm, so that the current collector 10 is bonded to the diaphragm through the adhesive layer. This can improve the adhesion between the positive electrode sheet, the diaphragm, and the negative electrode sheet in the corner section, reduce the gap between the positive electrode sheet, the diaphragm, and the negative electrode sheet in the corner section, and reduce the risk of lithium plating caused by excessive gaps between the positive and negative electrodes at the corner, which is beneficial to improving the interface contact quality between the positive electrode sheet, the diaphragm, and the negative electrode sheet in the corner section, improving the safety of the secondary battery, and extending the service life of the secondary battery.

[0107] In some embodiments, the negative electrode plate includes the current collector 10 as described above and a negative electrode active material coating provided on the current collector 10. The negative electrode active material coating can be made of a negative electrode active material for a secondary battery. The negative electrode active material can be selected from a metal negative electrode active material or a non-metallic negative electrode active material; the metal negative electrode active material can be selected from metal foil or alloy compounds such as metallic sodium, sodium alloy, tin, antimony, etc.; the non-metallic negative electrode active material can be selected from any one of hard carbon, soft carbon, graphite, and silicon oxide, or a combination of at least two of them.

[0108] The negative electrode plate also includes a conductive agent and a binder; the conductive agent includes one or more of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, and graphene; the binder includes a carboxymethyl cellulose (Sodium Carboxymethyl Cellulose, CMC)-based binder and a resin binder.

[0109] Optionally, the carboxymethyl cellulose-based binder includes one or more of sodium carboxymethyl cellulose and lithium carboxymethyl cellulose; and / or the resin binder includes one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and polyacrylonitrile (PAN).

[0110] In some embodiments, the negative electrode sheet is prepared as follows: the components for preparing the negative electrode sheet, such as the negative electrode active material, binder and conductive agent, are dispersed in a solvent such as deionized water to form a negative electrode slurry; the negative electrode slurry is coated on both sides of the current collector 10; and after baking, rolling, cutting, striping and other processes, the negative electrode sheet can be obtained.

[0111] The positive electrode sheet includes the current collector 10 as described above and a positive electrode active material coating disposed on the current collector 10. The positive electrode active material coating includes a positive electrode active material, a conductive agent, and a binder. The positive electrode active material includes a lithium ion transition metal oxide, a ternary positive electrode material, etc. The lithium ion transition metal oxide includes at least one of lithium cobalt oxide, lithium manganese oxide, and lithium iron phosphate; the conductive agent may include at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes, graphene, hard carbon, carbon fiber, and carbon microspheres; and the binder includes at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, and a tetrafluoroethylene-hexafluoropropylene copolymer.

[0112] In some embodiments, the positive electrode sheet is prepared as follows: the components for preparing the positive electrode sheet, such as the positive electrode active material, the binder and the conductive agent including the positive electrode material, are dispersed in a solvent such as N-methylpyrrolidone to form a positive electrode slurry; the positive electrode slurry is coated on both sides of the current collector 10; and after drying, rolling, die-cutting and other processes, the positive electrode sheet can be obtained.

[0113] The secondary battery provided in the present application also includes a positive electrolyte. The electrolyte plays the role of conducting ions between the positive electrode plate and the negative electrode plate. The electrolyte can be liquid, gel or all-solid. In some embodiments, the above-mentioned electrolyte adopts a liquid electrolyte, and the electrolyte includes an electrolyte salt and a solvent. The electrolyte salt is a lithium salt, and the solvent includes a cyclic ester solvent and a chain ester solvent. In some embodiments, the cyclic ester solvent includes at least one of ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate and γ-butyrolactone; the chain ester solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate and diphenyl carbonate. In some embodiments, the organic solvent includes ethylene carbonate, propylene carbonate and ethyl methyl carbonate.

[0114] In practical applications, the negative electrode sheet, separator and positive electrode sheet are stacked in order and wound to obtain a wound battery cell, which is then packaged to obtain a bare battery cell. The bare battery cell is baked and then injected with liquid, formed, repackaged and sorted to obtain the above-mentioned secondary battery.

[0115] The present application also proposes an electrical device, which includes the above-mentioned secondary battery, and the secondary battery serves as a power supply for the electrical device.

[0116] For the above-mentioned electrical equipment embodiment, it includes the above-mentioned secondary battery and can achieve the same technical effect. In order to avoid repetition, it will not be described here. For relevant details, please refer to the partial description of the secondary battery embodiment.

[0117] In order to make the invention purpose, technical solution and beneficial effects of this application clearer, the present application is further described below in conjunction with examples. It should be understood that these examples are only used to illustrate this application and are not used to limit the scope of this application.

[0118] The present application is described in detail below through examples.

[0119] Example 1

[0120] (1) Obtaining a metal matrix:

[0121] A battery-grade copper foil with a thickness of 10 μm was used as the metal substrate.

[0122] (2) Obtaining a conductive polymer grid layer:

[0123] First, the surface of the PET flexible substrate is cleaned and then activated;

[0124] Then, the pyrrole monomer was dissolved in anhydrous ethanol to prepare a monomer solution with a concentration of 0.3 M;

[0125] Then, an oxidant FeCl3 is added to the monomer solution to obtain a mixed solution; wherein the molar ratio between FeCl3 and the pyrrole monomer is 1:1.

[0126] Then, the mixed solution was coated on the surface of the activated PET flexible substrate and polymerized at 20°C to obtain a conductive polymer film;

[0127] Finally, a grid structure is formed on the conductive polymer film by photolithography technology to obtain a conductive polymer grid layer; wherein, the thickness of the conductive polymer grid layer in the straight section of the wound battery cell is 5μm, and the thickness of the conductive polymer grid layer in the corner section of the wound battery cell is 10μm; the grid line width of the conductive polymer grid layer in the coating area of ​​the negative electrode current collector is 2mm, and the grid line width in the empty foil area of ​​the negative electrode current collector is 4mm; the spacing between adjacent grid lines in the conductive polymer grid layer is 10mm.

[0128] (3) Get the metal grid layer:

[0129] A slurry made of copper nanoparticles is printed into a grid layer by screen printing, and the grid layer is sintered at 250°C in an argon atmosphere to obtain a metal grid layer; wherein, the thickness of the metal grid layer in the straight section of the wound battery cell is 5μm, and the thickness of the metal grid layer in the corner section of the wound battery cell is 10μm; the grid line width of the metal grid layer in the coating area of ​​the negative electrode current collector is 6mm, and the grid line width in the empty foil area of ​​the negative electrode current collector is 3mm; the spacing between adjacent grid lines in the metal grid layer is 10mm.

[0130] (4) Obtaining the negative electrode current collector:

[0131] First, a conductive polymer grid layer and a metal grid layer are sequentially stacked on the upper surface of a metal substrate, and a conductive polymer grid layer and a metal grid layer are sequentially stacked on the lower surface of the metal substrate to obtain a stack; then, the stack is rolled at 100°C and a pressure of 10 MPa at a rolling speed of 0.5 m / min to obtain a negative electrode current collector.

[0132] (5) Preparation of negative electrode sheet:

[0133] First, the negative electrode active material graphite, the conductive agent acetylene black, and the binder styrene-butadiene rubber and sodium carboxymethyl cellulose were mixed with deionized water in a mass ratio of 96.5:1.5:1.8:0.2 to obtain a negative electrode slurry;

[0134] Then, the negative electrode slurry is evenly coated on the surface of the negative electrode current collector obtained through step (4) provided with a conductive polymer grid layer and a metal grid layer through a coating machine, and then placed in an oven for drying at 90° C., and a negative electrode plate can be prepared through processes such as rolling, cutting, and slitting; the negative electrode plate includes the negative electrode current collector obtained through step (4) and a negative electrode active material coating provided on the surface of the negative electrode current collector, and the negative electrode active material coating is a coating formed after the negative electrode slurry coated on the surface of the negative electrode current collector is dried.

[0135] (6) Preparation of positive electrode sheet:

[0136] First, the positive electrode active material lithium iron phosphate, the conductive agent conductive carbon black and the binder polyvinylidene fluoride were mixed uniformly in a mass ratio of 96.5:2:1.5 and evenly dispersed in N-methylpyrrolidone to prepare a uniform positive electrode slurry;

[0137] Then, the positive electrode slurry is evenly coated on both sides of the aluminum foil through a coating machine, and then the positive electrode sheet is prepared through processes such as vacuum drying at 90°C, rolling, cutting, and slitting. The positive electrode sheet includes aluminum foil and a positive electrode active material coating provided on the surface of the aluminum foil. The positive electrode active material coating is a coating formed after the positive electrode slurry coated on the surface of the aluminum foil is dried.

[0138] (7) Preparation of secondary batteries:

[0139] The negative electrode sheet prepared by step (5), the separator, and the positive electrode sheet prepared by step (6) are wound in a predetermined order to obtain a wound cell, the wound cell is packaged, and a lithium salt electrolyte is injected to prepare a lithium ion battery with a thickness of 4.0±0.05mm, a height of 105±2mm, a width of 115±1mm, and a capacity of 3700±100mAh; wherein the wound cell includes a corner section and a straight section; the thickness of the conductive polymer grid layer in the corner section of the negative electrode current collector is 10μm, and the thickness of the conductive polymer grid layer in the straight section of the negative electrode current collector is 10μm. The thickness of the conductive polymer grid layer in the segment is 5 μm; the thickness of the metal grid layer in the corner segment of the negative current collector is 10 μm, and the thickness of the metal grid layer in the straight segment of the negative current collector is 5 μm; in the corner segment of the wound battery cell, the conductive polymer grid layer and the metal grid layer of the negative current collector are provided with an adhesive layer on the side facing the diaphragm (the adhesive used in the adhesive layer includes polyacrylic acid), the negative current collector is bonded to the diaphragm through the adhesive layer, and the grids of the conductive polymer grid layer and the metal grid layer of the negative current collector are filled with a negative electrode active material coating.

[0140] Examples 2-3

[0141] The difference between Examples 2 and 3 and Example 1 is that:

[0142] In step (1), the thickness of the metal substrates is 5 μm and 15 μm, respectively.

[0143] Examples 4-5

[0144] The difference between Examples 4 and 5 and Example 1 is that:

[0145] In step (2), the thickness of the conductive polymer grid layer is 1 μm and 10 μm respectively;

[0146] In step (3), the thickness of the metal mesh layer is 1 μm and 10 μm, respectively.

[0147] Example 6

[0148] The difference between Example 6 and Example 1 is that:

[0149] In step (2), the width of the grid lines in the conductive polymer grid layer in the coating area of ​​the negative electrode current collector is 1 mm.

[0150] Example 7

[0151] The difference between Example 7 and Example 1 is that:

[0152] In step (2), the width of the grid lines in the conductive polymer grid layer in the coating area of ​​the negative electrode current collector is 1 mm, and the width of the grid lines in the empty foil area of ​​the negative electrode current collector is 3 mm.

[0153] Examples 8-9

[0154] The difference between Examples 8 and 9 and Example 1 is that:

[0155] In step (2), the spacing between adjacent grid lines in the conductive polymer grid layer is 1 mm and 20 mm, respectively.

[0156] Example 10

[0157] The difference between Example 10 and Example 1 is that:

[0158] In step (2), the spacing between adjacent grid lines in the empty foil area of ​​the negative electrode current collector in the conductive polymer grid layer is 5 mm.

[0159] Example 11

[0160] The difference between Example 11 and Example 1 is that:

[0161] In step (3), the width of the grid lines in the metal grid layer in the coating area of ​​the negative electrode current collector is 10 mm, and the width of the grid lines in the empty foil area of ​​the negative electrode current collector is 2 mm.

[0162] Example 12

[0163] The difference between Example 12 and Example 1 is that:

[0164] In step (3), the width of the grid lines in the metal grid layer in the coating area of ​​the negative electrode current collector is 10 mm, and the width of the grid lines in the empty foil area of ​​the negative electrode current collector is 3 mm.

[0165] Examples 13-14

[0166] The difference between Examples 13 and 14 and Example 1 is that:

[0167] In step (3), the spacing between adjacent grid lines in the metal grid layer is 1 mm and 20 mm, respectively.

[0168] Example 15

[0169] The difference between Example 15 and Example 1 is that:

[0170] In step (3), the spacing between adjacent grid lines in the metal grid layer in the coating area of ​​the negative electrode current collector is 5 mm.

[0171] Example 16

[0172] The difference between Example 16 and Example 1 is that:

[0173] In step (4), in the coating area of ​​the negative electrode current collector, a conductive polymer grid layer and a metal grid layer are sequentially stacked on the upper surface of the metal substrate, and the conductive polymer grid layer and the metal grid layer are sequentially stacked on the lower surface of the metal substrate. In the empty foil area of ​​the negative electrode current collector, a metal grid layer and a conductive polymer grid layer are sequentially stacked on the upper surface of the metal substrate, and the metal grid layer and the conductive polymer grid layer are sequentially stacked on the lower surface of the metal substrate to obtain a laminated part.

[0174] Example 17

[0175] The difference between Example 17 and Example 1 is that:

[0176] In step (1), the thickness of the metal substrate is 8 μm;

[0177] In step (2), the thickness of the conductive polymer grid layer is 2 μm; the width of the grid lines in the coated area of ​​the negative electrode current collector in the conductive polymer grid layer is 1 mm, and the width of the grid lines in the empty foil area of ​​the negative electrode current collector is 2 mm; the spacing between adjacent grid lines in the conductive polymer grid layer is 3 mm;

[0178] In step (3), the thickness of the metal grid layer is 2 μm; the width of the grid lines in the coating area of ​​the negative electrode current collector in the metal grid layer is 2 mm, and the width of the grid lines in the empty foil area of ​​the negative electrode current collector is 1 mm; the spacing between adjacent grid lines in the metal grid layer is 4 mm.

[0179] Example 18

[0180] The difference between Example 18 and Example 17 is that:

[0181] In step (2), the thickness of the conductive polymer grid layer is 3 μm;

[0182] In step (3), the thickness of the metal mesh layer is 3 μm.

[0183] Example 19

[0184] The difference between Example 19 and Example 17 is that:

[0185] In step (2), the spacing between adjacent grid lines in the conductive polymer grid layer is 4 mm;

[0186] In step (3), the spacing between adjacent grid lines in the metal grid layer is 6 mm.

[0187] Comparative Example 1

[0188] The difference between Comparative Example 1 and Example 1 is:

[0189] Steps (1) to (3) are not included;

[0190] In step (4), a battery-grade copper foil with a thickness of 20 μm is used as the negative electrode current collector;

[0191] In step (5), the negative electrode slurry is evenly coated on both sides of the negative electrode current collector obtained in step (4) by a coating machine, and then placed in an oven at 90° C. for drying. After rolling, cutting, and slitting, the negative electrode sheet can be prepared;

[0192] In step (7), no adhesive layer is provided on the surface of the negative electrode current collector facing the separator.

[0193] Comparative Example 2

[0194] The difference between Comparative Example 2 and Comparative Example 1 is:

[0195] In step (4), a battery-grade copper foil with a thickness of 12 μm was used as the negative electrode current collector.

[0196] The parameters of the negative electrode sheets prepared in various embodiments and comparative examples are shown in Table 1.

[0197] Table 1

[0198]

[0199] Test method:

[0200] (1) Peeling force test of negative electrode sheet: First, cut the negative electrode sheet into small pieces of 4cm×26cm in size; then, wipe the auxiliary steel sheet and roller of the universal tensile testing machine clean with a dust-free cloth; then, stick a 2.5cm wide double-sided tape on the auxiliary steel sheet, stick the small piece of negative electrode sheet on the double-sided tape, and leave a 10mm length of negative electrode sheet not on the double-sided tape; use the roller to roll back and forth on the surface of the small piece of negative electrode sheet 3 times; finally, use the universal tensile testing machine to clamp the bonding structure after rolling to the reserved 10mm length of negative electrode sheet, and click the test to perform the peeling force test.

[0201] (2) Test of the number of negative electrode strip breaks: Count the number of negative electrode strip breaks that occur every 2000m.

[0202] (3) DC internal resistance (DCR) test of secondary battery: First, place the secondary battery in a constant temperature box at 25°C for 4 hours; then, use a current of 3700mAh to discharge at a constant current rate of 1C for 30 minutes; after leaving it for 2 hours, use a current of 7400mAh to discharge at a constant current rate of 1C for 10 seconds; leave it for 1 minute; calculate DCR = (voltage before constant current discharge - voltage after constant current discharge) / discharge current * 1000.

[0203] (4) Cycling performance test of secondary batteries: Step 1. Place the secondary battery in a constant temperature box at 25°C and 45°C for 4 hours respectively; Step 2. Use a current of 4000mAh to charge at a constant current and constant voltage of 1C to 3.6V, with a cut-off current of 200mA; Step 3. Leave it for 30 minutes; Step 4. Use a current of 4000mAh to discharge at a constant current of 1C to 2.0V; Step 5. Leave it for 30 minutes; Cycle steps 2 to 5, stop charging and discharging when the number of cycles is equal to 2000, record the first discharge specific capacity of the secondary battery and the discharge specific capacity when the number of cycles is equal to 2000, and calculate the cycle capacity retention rate of the secondary battery when the number of cycles is equal to 2000 = discharge specific capacity when the number of cycles is equal to 2000 / first discharge specific capacity*100%. In addition, referring to the national standard GBT 31467.3-2015, a secondary battery with a cycle number equal to 2000 cycles was disassembled, the electrolyte in the secondary battery was filtered, and the residue obtained after filtration was dried and weighed to obtain the amount of powder loss of the negative electrode sheet. The material loss ratio of the negative electrode sheet was calculated = the amount of powder loss of the negative electrode sheet / the total weight of the negative electrode active material in the negative electrode sheet * 100%.

[0204] The negative electrode sheets obtained by the above embodiments and comparative examples were subjected to the above-mentioned peeling force test and the number of broken belt tests, and the secondary batteries obtained by the above embodiments and comparative examples were subjected to the above-mentioned DCR test and the cycle performance test. The test results are shown in Table 2.

[0205] Table 2

[0206]

[0207] From the test data of Example 1 and Comparative Example 1 in Table 2, and the test data of Example 17 and Comparative Example 2, it can be seen that for negative electrode current collectors with the same thickness, the number of broken strips of the negative electrode sheets prepared by the embodiments of the present application is significantly reduced, and the peeling force is significantly improved. It can be seen that the embodiments of the present application can improve the toughness of the negative electrode sheets, reduce the probability of broken strips of the negative electrode sheets during the rolling process, and improve the interface bonding force between the negative electrode active material in the negative electrode sheets and the negative electrode current collector; further, the material drop ratio of the negative electrode sheets in the secondary battery prepared by the embodiments of the present application and the DC internal resistance of the secondary battery are significantly reduced, and the cycle capacity retention rate of the secondary battery is significantly improved. It can be seen that the embodiments of the present application can reduce the internal resistance of the secondary battery and reduce the charge and discharge of the secondary battery by improving the interface bonding force between the negative electrode active material in the negative electrode sheets and the negative electrode current collector. The proportion of negative electrode active material falling during the cycle process is improved, and the cycle performance of the secondary battery is improved; by controlling the thickness of the conductive polymer grid layer in the negative electrode collector at the corner section of the wound battery cell to be greater than the thickness of the conductive polymer grid layer in the straight section of the wound battery cell, controlling the thickness of the metal grid layer in the negative electrode collector at the corner section to be greater than the thickness of the metal grid layer in the straight section, and providing an adhesive layer on the surface of the conductive polymer grid layer and the metal grid layer of the negative electrode collector facing the diaphragm in the corner section of the wound battery cell, so that the negative electrode collector is bonded to the diaphragm through the adhesive layer, and filling the gap between the conductive polymer grid layer and the metal grid layer of the negative electrode collector with a negative electrode active material coating, the risk of lithium dendrite growth in the corner section of the wound battery cell can be reduced, which is beneficial to improving the cycle capacity retention rate of the secondary battery and the safety of the secondary battery during the charge and discharge cycle, and extending the service life of the secondary battery.

[0208] Specifically, referring to the test data of Examples 1 to 3 in Table 2, as the thickness of the metal substrate gradually increases, the number of broken strips of the negative electrode sheet gradually decreases, the peeling force gradually increases, and the material drop ratio of the negative electrode sheet in the secondary battery and the DC internal resistance of the secondary battery gradually decrease, and the cycle capacity retention rate of the secondary battery gradually increases. It can be seen that as the thickness of the metal substrate increases, the toughness of the negative electrode sheet is improved, and the interfacial bonding force between the negative electrode current collector and the negative electrode active material is improved, which reduces the internal resistance of the secondary battery, reduces the proportion of negative electrode active material drop, and improves the cycle performance of the secondary battery, but the energy density of the secondary battery decreases accordingly.

[0209] Referring to the test data of Example 1, Example 4 and Example 5 in Table 2, as the thickness of the conductive polymer grid layer and the metal grid layer gradually increases, the number of times the negative electrode sheet is broken gradually decreases, the peeling force gradually increases, and the material drop ratio of the negative electrode sheet in the secondary battery and the DC internal resistance of the secondary battery are gradually reduced, and the cycle capacity retention rate of the secondary battery is gradually improved. It can be seen that as the thickness of the conductive polymer grid layer and the metal grid layer increases, the role of the conductive polymer grid layer and the metal grid layer is fully exerted, so that the toughness of the negative electrode sheet is improved, and the interface bonding force between the negative electrode current collector and the negative electrode active material is improved, thereby gradually reducing the number of times the negative electrode sheet is broken, the internal resistance of the secondary battery is reduced, the proportion of negative electrode active material drop is reduced, and the cycle performance of the secondary battery is improved. However, as the thickness of the conductive polymer grid layer and the metal grid layer gradually increases, the energy density of the secondary battery decreases accordingly.

[0210] Referring to the test data of Example 1, Example 6 and Example 7 in Table 2, the ratio of the width of the grid lines in the hollow foil area of ​​the conductive polymer grid layer to the width of the grid lines in the coating area is gradually increased from 2 in Example 1 to 3 in Example 7 and 4 in Example 6. As the ratio of the width of the grid lines in the hollow foil area of ​​the conductive polymer grid layer to the width of the grid lines in the coating area gradually increases, the number of broken negative electrode sheets is 0 times / 2000m, the peeling force of the negative electrode sheet is maintained above 10N / m, the material drop ratio of the negative electrode sheet in the secondary battery is below 15%, the DC internal resistance of the secondary battery is below 6mΩ, and the cyclic capacity retention rate of the secondary battery is above 83%. It can be seen that by controlling the ratio of the width of the grid lines in the hollow foil area of ​​the conductive polymer grid layer to the width of the grid lines in the coating area within the range of 2 to 4, the probability of broken negative electrode sheets can be reduced while maintaining the electrochemical performance of the secondary battery in a relatively stable state.

[0211] Referring to the test data of Example 1, Example 8 and Example 9 in Table 2, by controlling the spacing between adjacent grid lines in the conductive polymer grid layer within the range of 1 mm to 20 mm, the number of negative electrode sheet breaks can be reduced to 0 times / 2000 m and the proportion of negative electrode sheet dropout can be reduced to 0%. In addition, as the spacing between adjacent grid lines in the conductive polymer grid layer decreases, the peeling force of the negative electrode sheet increases, the DC internal resistance of the secondary battery decreases, and the cycle capacity retention rate of the secondary battery increases.

[0212] Referring to the test data of Example 1 and Example 10 in Table 2, when the spacing between adjacent grid lines in the empty foil area of ​​the conductive polymer grid layer is smaller than the spacing between adjacent grid lines in the coated area, the toughness of the empty foil area at the edge of the negative electrode current collector can be increased, and the interfacial bonding force between the negative electrode current collector and the negative electrode active material can be improved, so that the number of negative electrode sheet breaks can be reduced to 0 times / 2000m and the material drop ratio of the negative electrode sheet can be reduced to 0%, while the electrochemical performance of the secondary battery can be maintained in a relatively stable state.

[0213] Referring to the test data of Example 1, Example 11 and Example 12 in Table 2, the ratio of the width of the grid lines in the empty foil area of ​​the metal grid layer to the width of the grid lines in the coating area is gradually reduced from 0.5 in Example 1 to 0.3 in Example 12 and 0.2 in Example 11. As the ratio of the width of the grid lines in the empty foil area of ​​the metal grid layer to the width of the grid lines in the coating area is gradually reduced, the width of the grid lines in the coating area of ​​the metal grid layer can be increased, thereby increasing the contact area between the coating area and the negative electrode active material in the negative electrode current collector, and improving the contact area between the negative electrode active material and the negative electrode in the negative electrode sheet. The interfacial bonding strength between the electrode and current collector is such that the peeling force of the negative electrode sheet is increased from 11.2 N / m in Example 1 to more than 12.3 N / m, while the number of broken strips of the negative electrode sheet is maintained at 0 times / 2000m and the material drop ratio of the negative electrode sheet is maintained at 0%, and the DC internal resistance of the secondary battery is reduced from 5.6 mΩ in Example 1 to 5.2 mΩ, and the cycle capacity retention rate of the secondary battery at 25°C is increased from 87.2% in Example 1 to more than 89%, and the cycle capacity retention rate of the secondary battery at 45°C is increased from 83.6% in Example 1 to more than 84%.

[0214] Referring to the test data of Example 1, Example 13 and Example 14 in Table 2, by controlling the spacing between adjacent grid lines in the metal grid layer within the range of 1 mm to 20 mm, the number of broken strips of the negative electrode sheet can be reduced to 0 times / 2000 m, and the proportion of material drop of the negative electrode sheet can be reduced to 0%. In addition, as the spacing between adjacent grid lines in the metal grid layer decreases, the peeling force of the negative electrode sheet gradually increases, the DC internal resistance of the secondary battery gradually decreases, and the cycle capacity retention rate of the secondary battery gradually improves.

[0215] Referring to the test data of Example 1 and Example 15 in Table 2, when the spacing between adjacent grid lines in the coated foil area in the metal grid layer is smaller than the spacing between adjacent grid lines in the empty foil area, the peeling force of the negative electrode sheet can be increased, the DC internal resistance of the secondary battery can be reduced, and the cycle capacity retention rate of the secondary battery can be improved. At the same time, it is possible to ensure that the empty foil area of ​​the negative electrode sheet has good toughness, so that the number of broken strips of the negative electrode sheet is 0 times / 2000m.

[0216] Referring to the test data of Example 1 and Example 16 in Table 2, when the conductive polymer grid layer in the coating area is located between the metal substrate and the metal grid layer, and when the metal grid layer in the hollow foil area is located between the metal substrate and the conductive polymer grid layer, the toughness of the negative electrode sheet, the interfacial bonding strength between the negative electrode active material and the negative electrode current collector, and the DC internal resistance and cycle capacity retention rate of the secondary battery can be ensured while reducing the probability of burrs on the metal surface in the hollow foil area, which is beneficial to improving the safety of the secondary battery.

[0217] In summary, in the embodiment of the present application, the current collector provided includes a metal substrate, and a conductive polymer grid layer and a metal grid layer provided on at least one side surface of the metal substrate; on the same side surface of the metal substrate, the conductive polymer grid layer and the metal grid layer are stacked and the grid lines in the conductive polymer grid layer are intersected with the grid lines in the metal grid layer, which is beneficial to increase the surface area of ​​the current collector, thereby increasing the contact area between the active material coating coated on the surface of the current collector and the current collector, and improving the interfacial bonding force between the active material coating and the current collector in the electrode piece; when the interfacial bonding force between the active material coating and the current collector in the electrode piece is improved, the internal resistance of the secondary battery prepared based on the current collector provided in the embodiment of the present application can be reduced, and the proportion of active material coating falling off during the charge and discharge cycle of the secondary battery can be reduced, thereby improving the cycle performance of the secondary battery; further, the embodiment of the present application sets the conductive polymer grid layer and the metal grid layer provided on the surface of the metal substrate as a grid structure, which can reduce the increase in the volume and weight of the current collector, which is beneficial to improve the interfacial bonding force between the active material coating and the current collector while improving the energy density of the secondary battery.

[0218] Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they become aware of the basic inventive concepts. Therefore, the claims are intended to include the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0219] The above is a detailed introduction to a current collector, secondary battery and electrical equipment provided by the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for general technical personnel in this field, based on the ideas of the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A current collector, characterized in that: The current collector includes a metal substrate and a composite layer provided on at least one surface of the metal substrate, wherein the composite layer includes a conductive polymer grid layer and a metal grid layer; The conductive polymer grid layer and the metal grid layer are stacked on the same side surface of the metal substrate, and the grid lines in the conductive polymer grid layer intersect with the grid lines in the metal grid layer.

2. The current collector according to claim 1, characterized in that The current collector includes a hollow foil area and a coated area; in the conductive polymer grid layer, the width of the grid lines in the hollow foil area is greater than the width of the grid lines in the coated area; and / or, in the metal grid layer, the width of the grid lines in the coated area is greater than the width of the grid lines in the hollow foil area.

3. The current collector according to claim 2, characterized in that In the conductive polymer grid layer, the ratio of the width of the grid lines in the empty foil area to the width of the grid lines in the coated area is 2 to 4; and / or, in the metal grid layer, the ratio of the width of the grid lines in the empty foil area to the width of the grid lines in the coated area is 0.2 to 0.

5.

4. The current collector according to claim 1, characterized in that The current collector includes a hollow foil area and a coating area; in the conductive polymer grid layer, the spacing between adjacent grid lines in the hollow foil area is smaller than the spacing between adjacent grid lines in the coating area; And / or, in the metal grid layer, a distance between adjacent grid lines in the coating area is smaller than a distance between adjacent grid lines in the blank foil area.

5. The current collector according to claim 1, characterized in that The current collector has a first direction and a second direction perpendicular to each other; the conductive polymer grid layer includes a first grid line arranged along the first direction and a second grid line arranged along the second direction, and the first grid line and the second grid line intersect; the metal grid layer includes a third grid line arranged along the first direction and a fourth grid line arranged along the second direction, and the third grid line and the fourth grid line intersect; the first grid line and the third grid line are arranged at intervals, and the second grid line and the fourth grid line are arranged at intervals; And / or, the current collector includes a hollow foil area and a coating area; in the coating area, the conductive polymer grid layer is located between the metal substrate and the metal grid layer; in the hollow foil area, the metal grid layer is located between the metal substrate and the conductive polymer grid layer.

6. A secondary battery, characterized in that: The secondary battery includes the current collector according to any one of claims 1 to 5.

7. The secondary battery according to claim 6, characterized in that The secondary battery comprises a wound cell, the wound cell comprising a positive electrode sheet, a separator and a negative electrode sheet, the negative electrode sheet comprising a negative electrode current collector and a negative electrode active material coating provided on the surface of the negative electrode current collector, and the positive electrode sheet comprising a positive electrode current collector and a positive electrode active material coating provided on the surface of the positive electrode current collector; the negative electrode current collector and / or the positive electrode current collector is the current collector according to any one of claims 1 to 5; In which, the wound battery core includes a corner section and a straight section; the thickness of the conductive polymer grid layer in the current collector in the corner section is greater than the thickness of the conductive polymer grid layer in the straight section, and / or the thickness of the metal grid layer in the current collector in the corner section is greater than the thickness of the metal grid layer in the straight section.

8. The secondary battery according to claim 7, wherein: In the straight section of the wound battery core, the thickness of the conductive polymer grid layer in the current collector is less than or equal to the thickness of the metal substrate, and / or the thickness of the metal grid layer in the current collector is less than or equal to the thickness of the metal substrate.

9. The secondary battery according to claim 7, wherein At the corner section of the wound battery core, an adhesive layer is provided on a surface of the conductive polymer grid layer and / or the metal grid layer in the current collector facing the separator, and the current collector is bonded to the separator via the adhesive layer; The meshes of the conductive polymer mesh layer and the metal mesh layer are filled with active material coatings.

10. An electrical device, characterized in that: The device comprises the secondary battery according to any one of claims 6 to 9, wherein the secondary battery serves as a power supply for the electrical device.

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