Composite current collector, positive electrode plate, negative electrode plate and lithium ion battery

Abstract

The composite current collector comprises a macromolecule layer and metal layers arranged on the upper side face and the lower side face of the macromolecule layer, a plurality of hollowed-out structures are arranged on the macromolecule layer, and the two metal layers are connected into a whole at the hollowed-out structures. According to the utility model, the two metal layers are mutually contacted and fused into one layer at the hollow part, so that the problem that the polymer layer and the metal layers are easy to peel off and fall off is solved.

Description

Technical Field

[0001] The utility model relates to the technical field of electrode sheets, and in particular to a composite current collector, a positive electrode sheet, a negative electrode sheet and a lithium ion battery. Background Art

[0002] The battery collector is an important component of lithium-ion batteries. It can carry active substances, collect and conduct current. At present, the main material of the battery collector is metal foil, such as copper foil and aluminum foil. However, metal foil has the disadvantages of heavy weight, high cost, and easy thermal runaway. In order to overcome these disadvantages, composite current collectors have been studied and applied more and more. The composite current collector is a "sandwich" structure composed of a metal film layer and a polymer material layer (such as a composite current collector, electrode plate and electrochemical device disclosed in patent document CN110943227B), which has the advantages of light weight, low cost and high safety. However, due to the large difference between the molecular bonds inside the polymer material and the atomic bonds inside the metal film layer, the surface adhesion of the metal layer and the polymer material layer is poor, the bonding is not tight, and it is easy to peel off, and it is easy to produce a false weld during the welding of the pole ear, causing safety hazards.

[0003] Therefore, it is necessary to develop a composite current collector, a positive electrode sheet, a negative electrode sheet and a lithium ion battery. Utility Model Content

[0004] The utility model aims to provide a composite current collector, a positive electrode sheet, a negative electrode sheet and a lithium ion battery, which can improve the problem that a polymer layer and a metal layer are easily peeled off.

[0005] The composite current collector described in the utility model comprises a polymer layer and metal layers arranged on the upper and lower sides of the polymer layer. The polymer layer is provided with a plurality of hollow structures, and two metal layers are connected as a whole at the hollow structures.

[0006] Optionally, a plurality of first pits are provided on the metal layer; since the thickness of the composite current collector at the hollowed-out part of the polymer layer is small and is in the shape of a pit, the adhesion between the positive / negative electrode material and the composite current collector can be enhanced, thereby improving the bonding strength of the positive / negative electrode sheets (i.e., electrode peeling force).

[0007] Optionally, the depth of the first pit is 1.6 μm to 4 μm. Setting the first pit within the range of 1.6 μm to 4 μm can better meet the requirement of the electrode sheet for bonding strength.

[0008] Optionally, the area of ​​the hollow structure is 0.2 square microns to 10 square microns. Setting the area of ​​the hollow structure to 0.2 square microns to 10 square microns can not only ensure that the polymer layer supports the composite current collector and is not easy to break, but also ensure the connection area of ​​the two metal layers at the hollow structure, thereby improving the problem of easy peeling and falling off of the polymer layer and the metal layer.

[0009] Optionally, the distance between adjacent hollow structures in the lateral direction is 1 μm to 100 μm, and the distance between adjacent hollow structures in the longitudinal direction is 1 μm to 100 μm, so as to ensure the integrity of the polymer layer and prevent it from being easily broken, and to provide good support for the metal layer.

[0010] In a second aspect, a positive electrode sheet described in the present invention comprises a composite current collector as described in the present invention, and active material layers arranged on upper and lower sides of the composite current collector, wherein the metal layer of the composite current collector is an aluminum foil layer.

[0011] Optionally, a plurality of second pits are provided on the active material layer; the provision of the second pits can buffer the expansion of the pole piece during the charge and discharge process and release part of the expansion stress, thereby reducing battery expansion and improving battery life and safety.

[0012] In a third aspect, a negative electrode sheet described in the present invention comprises the composite current collector described in the present invention, and active material layers arranged on the upper and lower sides of the composite current collector, wherein the metal layer of the composite current collector is a copper foil layer.

[0013] Optionally, a plurality of second pits are provided on the active material layer; the provision of the second pits can buffer the expansion of the pole piece during the charge and discharge process and release part of the expansion stress, thereby reducing battery expansion and improving battery life and safety.

[0014] In a fourth aspect, the present invention provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery adopts the positive electrode sheet described in the present invention, and / or the negative electrode of the lithium-ion battery adopts the negative electrode sheet described in the present invention.

[0015] Beneficial effects of the utility model: The polymer layer of the composite current collector described in the utility model has a plurality of hollow structures, and the two metal layers contact and fuse into one layer at the hollow part, thereby improving the problem of easy peeling and falling off of the polymer layer and the metal layer. At the same time, since the thickness of the composite current collector at the hollow part of the polymer layer is small and pit-shaped, it can enhance the adhesion between the positive / negative electrode material and the composite current collector, thereby improving the bonding strength of the positive / negative electrode sheet (i.e., the electrode sheet peeling force), and there are also uniform pits on the surface of the positive / negative electrode sheet after coating with the composite current collector. The setting of the pits can buffer the expansion of the electrode sheet during charging and discharging and release part of the expansion stress, thereby reducing battery expansion and improving battery life and safety. In addition, compared with conventional composite current collectors, the composite current collector using this structure can be made smaller in mass, which is beneficial to improving the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 is a schematic diagram of the structure of the composite current collector in this embodiment;

[0017] Figure 2 for Figure 1 Sectional view along line AA;

[0018] Figure 3 for Figure 1 The cross section along line BB;

[0019] Figure 4 Schematic diagram of the structure of the polymer layer in this embodiment;

[0020] Figure 5 Schematic diagram of the structure of the positive electrode sheet or the negative electrode sheet in this embodiment;

[0021] In the figure: 1-composite current collector, 11-metal layer, 111-first pit, 12-polymer layer, 121-hollow structure, 2-active material layer, 21-second pit. DETAILED DESCRIPTION

[0022] The following will refer to the accompanying drawings and preferred embodiments to illustrate the implementation of the technical solution of the utility model. Those skilled in the art can easily understand other advantages and effects of the utility model from the contents disclosed in this specification. The utility model can also be implemented or applied through other different specific implementations, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the utility model. It should be understood that the preferred embodiments are only for illustrating the utility model, not for limiting the scope of protection of the utility model.

[0023] The following will refer to the accompanying drawings and preferred embodiments to illustrate the implementation of the technical solution of the utility model. Those skilled in the art can easily understand other advantages and effects of the utility model from the contents disclosed in this specification. The utility model can also be implemented or applied through other different specific implementations, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the utility model. It should be understood that the preferred embodiments are only for illustrating the utility model, not for limiting the scope of protection of the utility model.

[0024] like Figures 1 to 5 As shown, in this embodiment, a composite current collector includes a polymer layer 12 and a metal layer 11 disposed on the upper and lower sides of the polymer layer 12, wherein the polymer layer 12 is provided with a plurality of hollow structures 121, the plurality of hollow structures 121 are relatively evenly distributed on the polymer layer 12, and the two metal layers 11 are connected as a whole at the hollow structures 121. The metal layer 11 is provided with a plurality of first pits 111.

[0025] In a possible implementation, the polymer layer 12 of the composite current collector 1 has a plurality of hollow structures 121, and the two metal layers 11 contact each other at the hollows and fuse into one layer, thereby improving the problem of easy peeling and falling off of the polymer layer 12 and the metal layer 11. At the same time, since the composite current collector 1 has a small thickness at the hollow of the polymer layer 12 and is in the shape of a pit (i.e., the first pit 111), the adhesion between the positive / negative electrode material and the composite current collector 1 can be enhanced, thereby improving the bonding strength of the positive / negative electrode sheets (i.e., the electrode sheet peeling force).

[0026] In a possible implementation, the depth of the first pit 111 is 1.6 μm to 4 μm. Setting the first pit 111 within the range of 1.6 μm to 4 μm can better meet the requirement of the electrode sheet for bonding strength.

[0027] In a possible implementation, the hollow structure 121 uses a circular hole or a square hole for easy processing. The area of ​​the hollow structure 121 is 0.2 square microns to 10 square microns. Setting the area of ​​the hollow structure to 0.2 square microns to 10 square microns can not only ensure that the polymer layer supports the composite current collector and is not easy to break, but also ensure the connection area of ​​the two metal layers at the hollow structure, thereby improving the problem of easy peeling and shedding of the polymer layer and the metal layer.

[0028] In a possible implementation, the distance between adjacent hollow structures 121 in the lateral direction is 1 μm to 100 μm, and the distance between adjacent hollow structures 121 in the longitudinal direction is 1 μm to 100 μm, so as to ensure the integrity of the polymer layer 12 and ensure good support for the metal layer 11 .

[0029] In one possible implementation, the composite current collector 1 is prepared in a substantially similar manner to a conventional current collector, using a polymer material film such as PET or PP as a support layer, and forming nanoscale metal on both sides of the polymer support layer through vacuum evaporation, magnetron sputtering, etc., and then depositing and thickening the metal layer 11 to more than 1 micron through water electroplating.

[0030] In a possible implementation, a composite current collector 1 for a positive electrode sheet has a thickness of 12 μm. The polymer layer 12 is made of PET material, and the thickness of the polymer layer 12 is 4 μm. The polymer layer 12 has uniformly distributed hollow structures 121, and the hollow shape is rectangular, the rectangle width is 0.5 μm, the rectangle length is 1.5 μm, and the longitudinal spacing between adjacent hollow structures 121 is 1 μm, and the lateral spacing is 10 μm. The upper and lower sides of the polymer layer 12 are both aluminum foil layers, and the two aluminum foil layers are fused into one layer at the hollow part. The thickness of the metal layer 11 at the hollow part is 8 μm, and the depth of the first pit 111 is 2 μm.

[0031] In a possible implementation, a composite current collector 1 for a negative electrode sheet has a thickness of 8 μm. The polymer layer 12 is made of PET material, and the thickness of the polymer layer 12 is 4 μm. The polymer layer 12 has a uniformly distributed hollow structure 121, and the hollow shape is a rectangle with a rectangle width of 0.5 μm and a rectangle length of 1.5 μm. The longitudinal spacing between adjacent hollows is 1 μm, and the lateral spacing is 10 μm. The upper and lower sides of the polymer layer 12 are both copper foil layers, and the two metal layers 11 are fused into one layer at the hollow part. The thickness of the metal layer 11 at the hollow part is 4 μm, and the depth of the first pit 111 is 2 μm.

[0032] In this embodiment, a positive electrode sheet includes a composite current collector 1 as described in this embodiment, and an active material layer 2 disposed on the upper and lower sides of the composite current collector 1, wherein the metal layer 11 of the composite current collector 1 is an aluminum foil layer. A plurality of second pits 21 are disposed on the active material layer 2 (uniform second pits 21 are present on the surface of the positive / negative electrode sheet after coating with the composite current collector 1); the second pits 21 can buffer the expansion of the electrode sheet during charging and discharging and release part of the expansion stress, thereby reducing battery expansion and improving battery life and safety.

[0033] In one possible implementation, the positive electrode sheet is prepared as follows:

[0034] Using NMP as solvent, the positive electrode active material LiFePO4, the binder PVDF, and the conductive agent carbon black are uniformly dispersed into a positive electrode slurry at a ratio of 97:2.2:0.8, and then the slurry is uniformly coated on the aluminum foil layer of the composite current collector 1, and the positive electrode sheet is obtained after drying. Since the slurry has a certain self-leveling property before drying, the second pit 21 on the surface of the positive electrode sheet after drying is smaller than the first pit 111 on the composite current collector 1, and the depth of the micro-pit on the surface of the positive electrode sheet is about 1μm.

[0035] In one possible implementation, the negative electrode sheet is prepared as follows:

[0036] Using water as solvent, graphite, anode active material, SBR, CMC, and carbon black, anode conductive agent, are uniformly dispersed into cathode slurry at a ratio of 96.5:1.5:1.4:0.6, and then the slurry is uniformly coated on the copper foil layer on the composite current collector 1, and the negative electrode sheet is obtained after drying. Since the slurry has a certain self-leveling property before drying, the second pit 21 on the surface of the negative electrode sheet after drying is smaller than the first pit 111 of the composite current collector 1, and the depth of the micro-pit on the surface of the negative electrode sheet is about 1 μm.

[0037] In this embodiment, a negative electrode sheet includes a composite current collector 1 as described in this embodiment, and an active material layer 2 disposed on the upper and lower sides of the composite current collector 1, wherein the metal layer 11 of the composite current collector 1 is a copper foil layer. A plurality of second pits 21 are disposed on the active material layer 2; the second pits 21 can buffer the expansion of the electrode sheet during the charge and discharge process and release part of the expansion stress, thereby reducing battery expansion and improving battery life and safety.

[0038] In this embodiment, a lithium ion battery is provided, and the positive electrode of the lithium ion battery adopts the positive electrode sheet as described in this embodiment.

[0039] In this embodiment, a lithium ion battery is provided, and the negative electrode of the lithium ion battery adopts the negative electrode sheet described in this embodiment.

[0040] In this embodiment, a lithium-ion battery is provided. The positive electrode of the lithium-ion battery adopts the positive electrode sheet described in this embodiment, and the negative electrode of the lithium-ion battery adopts the negative electrode sheet described in this embodiment.

[0041] In one possible implementation, the preparation of lithium-ion batteries:

[0042] The positive and negative electrode sheets are rolled, cut, assembled and wound with the isolation film, and the tabs are welded before being packaged in an aluminum-plastic film, baked at 85°C to remove water, injected with commercial non-aqueous electrolyte, and then sealed, formed, and vented to obtain a finished 2Ah soft-pack lithium-ion battery.

[0043] Comparative data analysis: As shown in Table 1, the electrode sheet using the composite current collector 1 in this embodiment is compared with the electrode sheet using a conventional current collector, and the comparative data are as follows:

[0044]

[0045] It can be seen from Table 1 that the electrode sheet using the composite current collector 1 has a higher electrode sheet peeling force, and the battery cell expansion and cycle performance are significantly improved.

[0046] In this embodiment, “ / ” means “or”.

[0047] The above-mentioned embodiments are preferred implementation modes of the present invention, but the implementation modes of the present invention are not limited by the above-mentioned embodiments. Any other changes, modifications, substitutions, combinations and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement modes and shall be included in the protection scope of the present invention.

Claims

1. A composite current collector, characterized in that: It comprises a polymer layer (12) and a metal layer (11) arranged on the upper and lower sides of the polymer layer (12), wherein a plurality of hollow structures (121) are arranged on the polymer layer (12), and the two metal layers (11) are connected as a whole at the hollow structures (121).

2. The composite current collector according to claim 1, characterized in that: A plurality of first pits (111) are provided on the metal layer (11).

3. The composite current collector according to claim 2, characterized in that: The depth of the first pit (111) is 1.6 μm to 4 μm.

4. The composite current collector according to claim 1, characterized in that: The area of ​​the hollow structure (121) is 0.2 square micrometers to 10 square micrometers.

5. The composite current collector according to claim 4, characterized in that: The distance between adjacent hollow structures (121) in the transverse direction is 1 μm to 100 μm, and the distance between adjacent hollow structures (121) in the longitudinal direction is 1 μm to 100 μm.

6. A positive electrode sheet, characterized in that: It comprises a composite current collector (1) as claimed in any one of claims 1 to 5, and active material layers (2) arranged on the upper and lower sides of the composite current collector (1), wherein the metal layer (11) of the composite current collector (1) is an aluminum foil layer.

7. The positive electrode sheet according to claim 6, characterized in that: A plurality of second pits (21) are provided on the active material layer (2).

8. A negative electrode sheet, characterized in that: It comprises a composite current collector (1) as claimed in any one of claims 1 to 5, and an active material layer (2) arranged on the upper and lower sides of the composite current collector (1); the metal layer (11) of the composite current collector (1) is a copper foil layer.

9. The negative electrode sheet according to claim 8, characterized in that: A plurality of second pits (21) are provided on the active material layer (2).

10. A lithium ion battery, characterized in that: The positive electrode of the lithium ion battery adopts the positive electrode sheet as claimed in claim 6 or 7, and / or the negative electrode of the lithium ion battery adopts the negative electrode sheet as claimed in claim 8 or 9.

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