Secondary battery, method for manufacturing the same, polymer-based current collector, and electric device

Abstract

The application provides a secondary battery, a preparation method thereof, a polymer-based current collector, and an electric device. The secondary battery comprises an electrode tab, the electrode tab comprises a polymer-based current collector, the polymer-based current collector comprises a polymer film layer and a graphene-based material arranged in the polymer film layer, the polymer film layer comprises a polymer, and the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction is less than or equal to 1:10, so that the cycle performance of the secondary battery can be improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery, a preparation method thereof, a polymer-based current collector, and an electric device. BACKGROUND

[0002] In recent years, the application range of secondary batteries such as lithium ion batteries is more and more extensive, which are widely used in energy storage power supply systems such as hydraulic, thermal, wind and solar power stations, and in many fields such as electric tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, aerospace, etc. The secondary battery has made great development, and therefore higher requirements are put forward for its cycle performance. SUMMARY

[0003] In view of the above problems, the present application provides a secondary battery, a preparation method thereof, a polymer-based current collector, and an electric device, aiming to improve the cycle performance of the secondary battery.

[0004] In a first aspect of the present application, a secondary battery is provided, comprising an electrode tab, wherein the electrode tab comprises a polymer-based current collector, and the polymer-based current collector comprises a polymer film layer and a graphene-based material arranged in the polymer film layer, the polymer film layer comprises a polymer, and the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction of the polymer film layer is less than or equal to 1:10.

[0005] Since the graphene-based material has excellent electrical conductivity, by introducing the graphene-based material into the polymer film layer and controlling the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction of the polymer film layer to be less than or equal to 1:10, the electrical conductivity of the polymer film layer in the direction perpendicular to the thickness direction, i.e. the planar direction, can be effectively improved, so that the electrical conductivity of the polymer-based current collector in the planar direction is higher, and the voltage uniformity and current uniformity on the polymer-based current collector are better, thereby facilitating the improvement of the cycle performance of the secondary battery.

[0006] In some embodiments, the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer is 1x10 -6 Ω·m~100Ω·m.

[0007] In some embodiments, the resistivity of the polymer film layer in the thickness direction of the polymer film layer is 10Ω·m~5x10 5 Ω·m.

[0008] The resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer and / or the resistivity of the polymer film layer in the thickness direction of the polymer film layer is controlled to be within the above range, which can improve the conductivity of the polymer film layer, and further improve the conductivity, voltage uniformity and current uniformity of the polymer-based current collector, and further improve the cycle performance of the secondary battery.

[0009] In some embodiments, the mass percentage of the graphene-based material in the polymer film layer is 3% to 40%. Controlling the mass percentage of the graphene-based material in the polymer film layer to be within the above range is beneficial to further improve the cycle performance of the secondary battery.

[0010] In some embodiments, the mass percentage of the polymer in the polymer film layer is 60% to 97%. Controlling the mass percentage of the polymer in the polymer film layer to be within the above range is beneficial to further improve the cycle performance of the secondary battery.

[0011] In some embodiments, the mass percentage of the graphene-based material in the polymer film layer is 3% to 22%. Controlling the mass percentage of the graphene-based material in the polymer film layer to be within the above range is beneficial to further improve the cycle performance of the secondary battery.

[0012] In some embodiments, the mass percentage of the polymer in the polymer film layer is 78% to 97%. Controlling the mass percentage of the polymer in the polymer film layer to be within the above range is beneficial to further improve the cycle performance of the secondary battery.

[0013] In some embodiments, the graphene-based material includes one or more of graphene, graphene oxide and redox graphene.

[0014] In some embodiments, the polymer includes one or more of polyethylene oxide, polyethylene terephthalate, polypropylene, polyimide, polypyrrole and polyaniline. The above-mentioned types of polymers have relatively stable structures and are not prone to react with electrolyte or solid electrolyte.

[0015] In some embodiments, the average flake diameter of the graphene-based material is 20 μm to 300 μm. Controlling the average flake diameter of the graphene-based material to be within the above range can improve the orientation of the graphene-based material in the polymer film layer, thereby controlling the resistivity of the polymer film layer in the thickness direction.

[0016] In some embodiments, the average thickness of the graphene-based material is 0.3 nm to 20 nm. Controlling the average thickness of the graphene-based material to be within the above range can improve the distribution uniformity and orientation of the graphene-based material in the polymer film layer, thereby controlling the resistivity of the polymer film layer in the thickness direction.

[0017] In some embodiments, the percentage of the number of the graphene-like materials with the thickness direction being the same as the thickness direction of the polymer film layer in the number of the graphene-like materials is 70% to 100%. In this way, the graphene-like materials in the polymer film layer can construct a conductive network, which is conducive to improving the conductivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer, thereby improving the conductivity of the polymer-based current collector in any direction perpendicular to the thickness direction of the polymer-based current collector.

[0018] In some embodiments, the average flake diameter of the graphene-like materials is 100 μm to 300 μm. Controlling the average flake diameter of the graphene-like materials in the above range can improve the orientation of the graphene-like materials in the polymer film layer, thereby controlling the resistivity of the polymer film layer in the thickness direction.

[0019] In some embodiments, the average thickness of the graphene-like materials is 0.3 nm to 7 nm. Controlling the average thickness of the graphene-like materials in the above range can improve the uniformity and orientation of the graphene-like materials in the polymer film layer, thereby controlling the resistivity of the polymer film layer in the thickness direction.

[0020] In some embodiments, the polymer-based current collector further comprises a conductive layer disposed on at least one side of the polymer film layer, and the conductive layer comprises one or more of a metal material and a carbon material. In this way, the conductivity of the polymer-based current collector can be further improved.

[0021] In some embodiments, the thickness of the polymer-based current collector is 5 μm to 25 μm.

[0022] In some embodiments, the thickness of the polymer film layer accounts for 30% to 100% of the thickness of the polymer-based current collector.

[0023] In a second aspect of the present application, a preparation method of a secondary battery is provided, which comprises an electrode tab, the electrode tab comprising a polymer-based current collector, the polymer-based current collector comprising a polymer film layer and graphene-like materials disposed in the polymer film layer, the polymer film layer comprising a polymer, and the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction being less than or equal to 1:10; the preparation method of the polymer-based current collector comprising the following steps:

[0024] applying a first electric field to a polymer film layer slurry containing a polymer and graphene-like materials to orient and arrange the graphene-like materials;

[0025] forming a film piece from the obtained slurry, applying a second electric field to the film piece, and solidifying; wherein the direction of the second electric field is perpendicular to the thickness direction of the film piece.

[0026] The preparation method is simple in operation and is conducive to large-scale production. The first electric field can cause the graphene-based material in the polymer film layer slurry to be pre-oriented, and the second electric field can further improve the orientation of the graphene-based material in the film sheet. Thus, the graphene-based material can be arranged along the direction of the electric field to a certain extent to form a conductive network, thereby regulating the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer and the resistivity of the polymer film layer in the thickness direction.

[0027] Since the graphene-based material has excellent electrical conductivity, the introduction of the graphene-based material into the polymer film layer and the control of the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction to be less than or equal to 1:10 can effectively improve the electrical conductivity of the polymer film layer in the direction perpendicular to the thickness direction, i.e., the planar direction, so that the polymer-based current collector has higher electrical conductivity in the planar direction, and the voltage uniformity and current uniformity on the polymer-based current collector are better, thereby facilitating the improvement of the cycle performance of the secondary battery.

[0028] In some embodiments, the intensity of the first electric field and the second electric field is independently 10 V / m to 100 V / m.

[0029] In some embodiments, the application time of the first electric field and the second electric field is independently 0.5 h to 12 h.

[0030] In some embodiments, the solid content of the polymer film layer slurry is 3 wt% to 8 wt%.

[0031] Controlling at least one of the intensity of the first electric field, the application time of the first electric field, the intensity of the second electric field, and the application time of the second electric field can regulate the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer and the resistivity of the polymer film layer in the thickness direction.

[0032] In a third aspect, the present application provides a polymer-based current collector, comprising a polymer film layer and a graphene-based material arranged in the polymer film layer, wherein the polymer film layer comprises a polymer, and the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction is less than or equal to 1:10.

[0033] Due to the excellent electrical conductivity of graphene-based materials, by introducing graphene-based materials into the polymer film layer and controlling the ratio of the electrical resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the electrical resistivity of the polymer film layer in the thickness direction of the polymer film layer to be less than or equal to 1:10, the electrical conductivity of the polymer film layer in the direction perpendicular to the thickness direction, i.e. the planar direction, can be effectively improved, the planar electrical conductivity of the polymer-based current collector is higher, and the voltage uniformity and current uniformity on the polymer-based current collector are better, thereby facilitating the improvement of the cycle performance of the secondary battery.

[0034] In a fourth aspect of the present application, a power utilization device is provided, which comprises at least one of the secondary battery of the first aspect of the present application, the secondary battery prepared by the preparation method of the secondary battery of the second aspect of the present application, and the polymer-based current collector of the third aspect of the present application.

[0035] The power utilization device of the present application comprises at least one of the secondary battery provided by the present application, the secondary battery prepared by the preparation method of the secondary battery provided by the present application, and the polymer-based current collector provided by the present application, and thus at least has the same advantages as the at least one of the secondary battery, the secondary battery prepared by the preparation method of the secondary battery, and the polymer-based current collector.

[0036] The details of one or more embodiments of the present application are set forth in the accompanying drawings and the description below. Other features, objects, and advantages of the present application will be apparent from the description, drawings, and claims. BRIEF DESCRIPTION OF DRAWINGS

[0037] In order to better describe and illustrate the embodiments or examples provided by the present application, one or more drawings can be referred to. Additional details or examples used to describe the drawings should not be considered as limiting the scope of the disclosed application, the presently described embodiments or examples, and any one of the best modes of these applications presently understood. Moreover, the same reference numbers are used to represent the same components throughout the drawings. In the drawings:

[0038] Figure 1 is a schematic diagram of a battery cell of a secondary battery according to an embodiment of the present application.

[0039] Figure 2 is Figure 1 is an exploded view of the battery cell according to an embodiment of the present application.

[0040] Figure 3 is a schematic diagram of a battery device according to an embodiment of the present application.

[0041] Figure 4 is a schematic diagram of a battery pack according to an embodiment of the present application.

[0042] Figure 5 isFigure 4 exploded view of the battery pack according to an embodiment of the present application.

[0043] Figure 6 is a schematic view of an electric device using a secondary battery as a power source according to an embodiment of the present application.

[0044] BRIEF DESCRIPTION OF DRAWINGS

[0045] 1: battery pack; 2: upper case; 3: lower case; 4: battery device; 5: battery cell; 51: case; 52: electrode assembly; 53: cover plate; 6: electric device. DETAILED DESCRIPTION

[0046] The technical solutions in the embodiments of the present application will be apparently and completely described below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without any creative work fall within the scope of protection of the present application.

[0047] The "range" disclosed in the present application can be limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit limit the boundary of the particular range. The range limited in this way can be inclusive or exclusive of the end values, either end value can be independently included or excluded, and can be arbitrarily combined, i.e. any lower limit can be combined with any upper limit to form a range. For example, if the ranges of 60~120 and 80~110 are listed for a particular parameter, it is understood that the ranges of 60~110 and 80~120 are also anticipated. In addition, if the minimum range values of 1 and 2 are listed, and if the maximum range values of 3, 4 and 5 are also listed, the following ranges are all anticipated: 1~3, 1~4, 1~5, 2~3, 2~4 and 2~5. In the present application, unless otherwise specified, the numerical range "a~b" represents a shorthand representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "0~5" means that all the real numbers between "0~5" have been listed herein, and "0~5" is only a shorthand representation of these numerical combinations. In addition, when it is stated that a parameter is an integer ≥2, it is equivalent to disclose that the parameter is, for example, an integer 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc. For example, when it is stated that a parameter is an integer selected from "2~10", it is equivalent to list the integers 2, 3, 4, 5, 6, 7, 8, 9 and 10.

[0048] In the present application, "a plurality of", "a plurality of kinds", etc. refer to more than 2 or equal to 2 in quantity, unless otherwise specified. For example, "one or more" means one or more than two.

[0049] If not otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form new technical solutions.

[0050] Reference herein to "an embodiment" means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment or implementation of the application. The appearances of the phrase that the phrase in various places in the specification are not necessarily all referring to the same embodiment, nor are they necessarily mutually exclusive of other embodiments. It is explicitly contemplated that embodiments described herein can be combined with other embodiments. It is explicitly understood that the reference herein to "an implementation" is to be interpreted similarly.

[0051] It is understood by those skilled in the art that in the method of each embodiment or example, the order of writing each step does not mean a strict execution order and does not constitute any limitation on the implementation process, and the detailed execution order of each step should be determined by its function and possible internal logic. If not otherwise specified, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method comprises steps (a) and (b), which means that the method can comprise steps (a) and (b) performed sequentially, or steps (b) and (a) performed sequentially. For example, the method can also comprise step (c), which means that step (c) can be added to the method in any order, for example, the method can comprise steps (a), (b) and (c), or steps (a), (c) and (b), or steps (c), (a) and (b), etc.

[0052] In the present application, A (such as B) means that B is one non-limiting example of A, and it can be understood that A is not limited to B.

[0053] In the present application, "optionally", "optional" and "optional" mean that it can or can not be present, that is, it means to select from two parallel schemes of "have" or "have" any one. If there are multiple "options" in a technical solution, if not otherwise specified, and there is no contradiction or mutual restriction, each "option" is independent.

[0054] Polymer-based current collectors can reduce the risk of thermal runaway of secondary batteries and improve the safety performance of batteries compared to traditional current collectors. However, the conductivity of the traditional polymer film layer in the polymer-based current collector is poor. In order to solve this problem, nano-conductive agents such as nano-metal powder are usually added to the polymer film layer to improve the conductivity of the polymer film layer. However, due to the size and shape limitations of the nano-conductive agent, the nano-conductive agent cannot form a continuous conductive network in the polymer film layer, which is not conducive to the cycle performance of the battery. When carbon powder is added to the polymer film layer, the conductivity of the obtained polymer-based current collector is isotropic, and the surface voltage uniformity and surface current uniformity of the current collector are easily affected by the structure and performance of the opposite side. When the voltage distribution on the polymer-based current collector is uneven, overcharging easily occurs in the high-voltage area, leading to the collapse of the structure of the electrode active material, the decomposition of the electrolyte, etc. Over-discharge easily occurs in the low-voltage area, leading to the growth of lithium dendrites. When the current distribution is uneven, a local high-temperature area is formed in the current-concentrated area, which may accelerate the pulverization of the electrode active material and exacerbate the oxidation-reduction reaction of the electrolyte. With the continuous cycling of the battery, the battery capacity may quickly decay, thereby affecting the cycle performance of the battery.

[0055] Based on this, in a first aspect of the present application, a secondary battery is provided, comprising an electrode tab, the electrode tab comprising a polymer-based current collector, the polymer-based current collector comprising a polymer film layer and a graphene-based material disposed in the polymer film layer, the polymer film layer comprising a polymer, and a ratio of an electrical resistivity of the polymer film layer in any direction perpendicular to a thickness direction of the polymer film layer to an electrical resistivity of the polymer film layer in the thickness direction of the polymer film layer is less than or equal to 1:10.

[0056] Since the graphene-based material has excellent conductivity, by introducing the graphene-based material into the polymer film layer and controlling the ratio of the electrical resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the electrical resistivity of the polymer film layer in the thickness direction of the polymer film layer to be less than or equal to 1:10, the conductivity of the polymer film layer in the direction perpendicular to the thickness direction, i.e., the planar direction, can be effectively improved. The planar direction of the polymer-based current collector has higher conductivity, and the voltage uniformity and current uniformity on the polymer-based current collector are better, thereby facilitating the improvement of the cycle performance of the secondary battery.

[0057] As non-limiting examples, the ratio of the electrical resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the electrical resistivity of the polymer film layer in the thickness direction of the polymer film layer includes but is not limited to: 1:10, 1:50, 1:100, 1:500, 1:1000, 1:5000, 1:10000, 1:50000, 1:100000, 1:1000000, 1:1000000, or a range between any two of the foregoing.

[0058] Without limitation, the polymer-based current collector can be obtained by disassembling a secondary battery, peeling off the electrode tab, and etching the surface metal conductive layer using dilute hydrochloric acid. The polymer film layer's resistivity in a direction perpendicular to its thickness (four probes on the same side of the polymer film layer) and the polymer film layer's resistivity in a thickness direction (two probes on one side of the polymer film layer and the other two probes on the other side of the polymer film layer) can be tested using a four-probe method. A cross-section of the polymer-based current collector can be imaged using a scanning electron microscope (SEM), and the presence of polymer and graphene-like material in the polymer film layer of the polymer-based current collector can be determined using SEM in conjunction with an energy dispersive spectrometer (EDS).

[0059] In some embodiments, the polymer film layer has a resistivity in any direction perpendicular to its thickness of 1 x 10 -6 Ω·m~100Ω·m. As non-limiting examples, the above resistivity includes, but is not limited to, 1 x 10 -6 Ω·m, 5 x 10 -6 Ω·m, 1 x 10 -5 Ω·m, 5 x 10 -5 Ω·m, 1 x 10 -4 Ω·m, 5 x 10 -4 Ω·m, 1 x 10 -3 Ω·m, 5 x 10 -3 Ω·m, 1 x 10 -2 Ω·m, 5 x 10 -2 Ω·m, 0.1Ω·m, 0.5Ω·m, 1Ω·m, 5Ω·m, 10Ω·m, 30Ω·m, 50Ω·m, 80Ω·m, 100Ω·m, or a range between any two of the foregoing.

[0060] In some embodiments, the polymer film layer has a resistivity in a thickness direction of 10Ω·m~5 x 10 5 Ω·m. As non-limiting examples, the polymer film layer's resistivity in a thickness direction includes, but is not limited to, 10Ω·m, 50Ω·m, 100Ω·m, 500Ω·m, 1 x 10 3 Ω·m, 5 x 10 3 Ω·m, 1 x 10 4 Ω·m, 5 x 10 4 Ω·m, 1 x 10 5 Ω·m, 5 x 10 5 Ω·m, or a range between any two of the foregoing.

[0061] The resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer and / or the resistivity of the polymer film layer in the thickness direction of the polymer film layer is controlled to be within the above range, which can improve the conductivity of the polymer film layer, and further improve the conductivity, voltage uniformity and current uniformity of the polymer-based current collector, and further improve the cycle performance of the secondary battery.

[0062] In some embodiments, the mass percentage of the graphene-based material in the polymer film layer is 3% to 40%. As non-limiting examples, the mass percentage of the graphene-based material in the polymer film layer includes, but is not limited to, 3%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, or a range between any two of the foregoing. Further, the mass percentage of the graphene-based material in the polymer film layer is 3% to 22%.

[0063] In some embodiments, the mass percentage of the polymer in the polymer film layer is 60% to 97%. As non-limiting examples, the mass percentage of the polymer in the polymer film layer includes, but is not limited to, 60%, 62%, 65%, 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 97%, or a range between any two of the foregoing. Further, the mass percentage of the polymer in the polymer film layer is 78% to 97%.

[0064] Controlling the mass percentage of the graphene-based material in the polymer film layer and / or the mass percentage of the polymer in the polymer film layer to be within the above range is beneficial to further improve the cycle performance of the secondary battery.

[0065] In some embodiments, the graphene-based material includes one or more of graphene, graphene oxide, and redox graphene.

[0066] In some embodiments, the polymer includes one or more of polyethylene oxide (PEO), polyethylene terephthalate, polypropylene, polyimide, polypyrrole, and polyaniline. The above-mentioned types of polymers have relatively stable structures and are less likely to react with electrolyte or solid electrolyte.

[0067] In some embodiments, the average flake size of the graphene-based material is in the range of 20 pm to 300 pm. Controlling the average flake size of the graphene-based material in the above range can improve the orientation of the graphene-based material in the polymer film layer, thereby controlling the resistivity of the polymer film layer in the thickness direction. As non-limiting examples, the average flake size of the graphene-based material includes, but is not limited to, 20 pm, 50 pm, 80 pm, 100 pm, 120 pm, 140 pm, 160 pm, 180 pm, 200 pm, 220 pm, 240 pm, 260 pm, 280 pm, 300 pm, or a range between any two of the foregoing. Further, the average flake size of the graphene-based material is in the range of 100 pm to 300 pm.

[0068] Non-limitingly, the average flake size of the graphene-based material can be obtained by disassembling a secondary battery to obtain an electrode tab, peeling off the polymer-based current collector from the electrode tab, randomly cutting a cross section of the polymer film layer in the polymer-based current collector that is perpendicular to the thickness direction of the polymer film layer, and measuring the flake size of the graphene-based material in the cross section using an optical microscope, and taking an average value.

[0069] In some embodiments, the average thickness of the graphene-based material is in the range of 0.3 nm to 20 nm. Controlling the average thickness of the graphene-based material in the above range can improve the uniformity and orientation of the graphene-based material in the polymer film layer, thereby controlling the resistivity of the polymer film layer in the thickness direction. As non-limiting examples, the average thickness of the graphene-based material includes, but is not limited to, 0.3 nm, 0.5 nm, 1 nm, 2 nm, 3 nm, 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, 15 nm, 16 nm, 17 nm, 18 nm, 19 nm, 20 nm, or a range between any two of the foregoing. Further, the average thickness of the graphene-based material is in the range of 0.3 nm to 7 nm.

[0070] Non-limitingly, the average thickness of the graphene-based material can be obtained by disassembling a secondary battery to obtain an electrode tab, peeling off the polymer-based current collector from the electrode tab, randomly cutting a cross section of the polymer film layer in the polymer-based current collector that is parallel to the thickness direction of the polymer film layer, and measuring the thickness of the graphene-based material in the cross section using a transmission electron microscope (TEM), and taking an average value.

[0071] In some embodiments, the percentage of the number of graphene-like materials having the thickness direction identical to the thickness direction of the polymer film layer to the total number of graphene-like materials in the graphene-like materials is 70% to 100%. In this way, the graphene-like materials in the polymer film layer can construct a conductive network, which is beneficial to improve the conductivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer, thereby improving the conductivity of the polymer-based current collector in any direction perpendicular to the thickness direction of the polymer-based current collector. As non-limiting examples, the percentage of the number of graphene-like materials having the thickness direction identical to the thickness direction of the polymer film layer to the total number of graphene-like materials in the graphene-like materials includes, but is not limited to, 70%, 72%, 75%, 78%, 80%, 82%, 85%, 88%, 90%, 92%, 95%, 98%, 100%, or a range between any two of the foregoing.

[0072] Non-limitingly, the percentage of the number of graphene-like materials having the thickness direction identical to the thickness direction of the polymer film layer to the total number of graphene-like materials in the graphene-like materials can be obtained by disassembling a secondary battery, obtaining an electrode tab, peeling off the polymer-based current collector from the electrode tab, randomly cutting a cross section of the polymer film layer in the polymer-based current collector parallel to the thickness direction of the polymer film layer, and observing the total number of graphene-like materials and the number of graphene-like materials having the thickness direction identical to the thickness direction of the polymer film layer in the cross section using TEM.

[0073] In some embodiments, the polymer-based current collector further comprises a conductive layer disposed on at least one side of the polymer film layer, and the conductive layer comprises one or more of a metal material and a carbon material. In this way, the conductivity of the polymer-based current collector can be further improved. It can be understood that the conductive layer can be disposed on only one side of the polymer film layer, or on opposite sides of the polymer film layer.

[0074] It should be noted that when the polymer-based current collector comprises a conductive layer, the polymer-based current collector can also be referred to as a composite current collector.

[0075] In some embodiments, the thickness of the polymer-based current collector is 5 μm to 25 μm. As non-limiting examples, the thickness of the polymer-based current collector includes, but is not limited to, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, 21 μm, 22 μm, 23 μm, 24 μm, 25 μm, or a range between any two of the foregoing.

[0076] In some embodiments, the thickness of the polymer film layer is 30% to 100% of the thickness of the polymer-based current collector. As non-limiting examples, the thickness of the polymer film layer is 30%, 40%, 50%, 60%, 70%, 80%, 90%, 100%, or a range between any two of the foregoing, of the thickness of the polymer-based current collector.

[0077] In some embodiments, the electrode tab further includes an electrode active layer, the electrode active layer including an electrode active material.

[0078] In some embodiments, the electrode tab includes one or more of a positive electrode tab and a negative electrode tab.

[0079] In some embodiments, the electrode tab is a positive electrode tab, the electrode active layer is a positive electrode active layer, the electrode active material is a positive electrode active material, and the polymer-based current collector is a positive current collector.

[0080] As non-limiting examples, the positive current collector has two opposing surfaces in the thickness direction of the positive current collector, and the positive electrode active layer is disposed on either one or both of the opposing surfaces of the positive current collector.

[0081] In some embodiments, the positive electrode active material can be any of the positive electrode active materials known in the art. As non-limiting examples, the positive electrode active material can include one or more of a lithium-containing phosphate having an olivine structure, a lithium transition metal oxide, and a modified compound of each thereof. However, the present application is not limited to these materials, and other conventional materials that can be used as a positive electrode active material for a battery can also be used. These positive electrode active materials can be used alone or in combination with two or more.

[0082] Examples of the lithium transition metal oxide can include, but are not limited to, one or more of lithium cobalt oxide (e.g., LiCoO2), lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and a modified compound thereof. Non-limiting examples of the lithium-containing phosphate having an olivine structure can include, but are not limited to, one or more of lithium iron phosphate, a composite of lithium iron phosphate and carbon, lithium manganese phosphate, a composite of lithium manganese phosphate and carbon, lithium manganese iron phosphate, and a composite of lithium manganese iron phosphate and carbon.

[0083] Non-limiting examples of the lithium cobalt oxide can include LiCoO2; non-limiting examples of the lithium nickel oxide can include LiNiO2; non-limiting examples of the lithium manganese oxide can include LiMnO2, LiMn2O4, and the like; non-limiting examples of the lithium nickel cobalt manganese oxide can include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3O2(also can be referred to as NCM 333 LiNi 0.5 Co 0.2 Mn 0.3 O2(also can be referred to as NCM 523 LiNi 0.5 Co 0.25 Mn 0.25 O2(also can be referred to as NCM 211 LiNi 0.6 Co 0.2 Mn 0.2 O2(also can be referred to as NCM 622 LiNi 0.8 Co 0.1 Mn 0.1 O2(also can be referred to as NCM 811 LiNi 0.8 Co 0.15 Al 0.05 O2.

[0084] In some embodiments, the positive electrode active material comprises lithium-containing phosphates.

[0085] It can be understood that the battery will be accompanied by lithium (Li) deintercalation and consumption during charging and discharging, and the content of Li in the positive electrode active material is different when the battery is discharged to different states. In the enumeration of the positive electrode active material in the present application, the content of Li is the initial state of the material unless otherwise specified. When the positive electrode active material is applied to the positive electrode sheet in the battery system, the content of Li in the positive electrode active material contained in the sheet will usually change after charging and discharging cycles. The content of Li can be quantified by molar content, but is not limited thereto. As for "the content of Li is the initial state of the material", the initial state of the material refers to the state before being fed into the positive electrode slurry. It can be understood that new materials obtained by proper modification of the listed positive electrode active materials are also within the scope of positive electrode active materials, and the foregoing proper modification refers to acceptable modification methods for positive electrode active materials, and non-limiting examples include coating modification.

[0086] In the enumeration of the positive electrode active material in the present application, the content of oxygen (O) is only the theoretical state value, and the release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual content of O will fluctuate. The content of O can be quantified by molar content, but is not limited thereto.

[0087] In some embodiments, the positive electrode active layer optionally further includes a binder. As non-limiting examples, the binder can include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), a vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, a vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, a tetrafluoroethylene-hexafluoropropylene copolymer, and a fluorine-containing acrylate resin.

[0088] In some embodiments, the positive electrode active layer optionally further includes a conductive agent. As non-limiting examples, the conductive agent can include one or more of super-P, acetylene black, carbon black, ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0089] In some embodiments, the positive electrode tab can be prepared by dispersing the above-mentioned components for preparing the positive electrode tab, such as the positive electrode active material, the conductive agent, the binder, and any other components, in a solvent to form a positive electrode slurry; coating the positive electrode slurry on at least one side surface of the positive electrode current collector, and after processes such as drying, cold pressing, etc., the positive electrode tab can be obtained. The type of the solvent can be selected from, but is not limited to, any of the aforementioned embodiments, such as N-methyl pyrrolidone (NMP). The surface of the positive electrode current collector to which the positive electrode slurry is coated can be on a single surface of the positive electrode current collector, or on both surfaces of the positive electrode current collector. The solid content of the positive electrode slurry can be 40wt% to 80wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000mPa·s to 25000mPa·s.

[0090] When coating the positive electrode slurry, the unit area density of single-sided coating (excluding the solvent) on a dry basis can be 15mg / cm 2 to 35mg / cm 2 . The compaction density of the positive electrode tab can be 3.0g / cm 3 to 3.6g / cm 3 , optionally 3.3g / cm 3 to 3.5g / cm 3 .

[0091] In some embodiments, the electrode tab is a negative electrode tab, the electrode active layer is a negative electrode active layer, the electrode active material is a negative electrode active material, and the polymer-based current collector is a negative electrode current collector.

[0092] As non-limiting examples, the negative electrode current collector has two opposite surfaces in the thickness direction of the negative electrode current collector itself, and the negative electrode active layer is disposed on either one or both of the two opposite surfaces of the negative electrode current collector.

[0093] In some embodiments, the negative active material can employ a negative active material for a battery known in the art. As non-limiting examples, the negative active material can include one or more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based material, tin-based material, and lithium titanate, etc. The silicon-based material can include one or more of elemental silicon, silicon oxide compound, silicon-carbon composite, silicon-nitrogen composite, and silicon alloy. The tin-based material can include one or more of elemental tin, tin oxide compound, and tin alloy. However, the present application is not limited to these materials, and other conventional materials that can be used as a negative active material for a battery can also be used. These negative active materials can be used alone or in combination of two or more.

[0094] In some embodiments, the negative active layer can also optionally include a binder. The binder can include one or more of styrene butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0095] In some embodiments, the negative active layer can also optionally include a conductive agent. The conductive agent can include one or more of super P, acetylene black, carbon black, ketjen black, carbon dot, carbon nanotube, graphene, and carbon nanofiber.

[0096] In some embodiments, the negative active layer can also optionally include other auxiliary agents, such as thickening agents (e.g., sodium carboxymethyl cellulose (CMC-Na)) and the like.

[0097] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as the negative active material, the conductive agent, the binder, and any other components, in a solvent (a non-limiting example of the solvent is deionized water) to form a negative electrode slurry; coating the negative electrode slurry on at least one side surface of the negative current collector, and after processes such as drying, cold pressing, and the like, the negative electrode sheet can be obtained. The surface of the negative current collector coated with the negative electrode slurry can be on a single surface of the negative current collector, or on both surfaces of the negative current collector. The solid content of the negative electrode slurry can be 40 wt% to 60 wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s.

[0098] When coating the negative electrode slurry, the unit area density of one side coating (excluding the solvent) on a dry basis can be 7.5 mg / cm 2 ~22 mg / cm 2 . The compaction density of the negative electrode sheet can be 1.0 g / cm 3 ~ 1.8 g / cm 3 .

[0099] The compaction density of the positive or negative electrode sheet can be tested by charging the battery to 100% state of charge, disassembling the battery to take the electrode sheet, and punching into a small disc with an area S = 1540.25 mm 2 , measuring the weight M and thickness L of the small disc, taking another electrode sheet, wiping off the film layer on the surface to leave the empty current collector foil, and punching into a small disc with an area S = 1540.25 mm 2 , weighing the mass M0 of the empty aluminum foil, and then the compaction density PD = (M - M0) / S / (L - L0). L0 is the thickness of the current collector foil.

[0100] The surface density of the positive or negative electrode sheet of the battery cell at 100% state of charge can be tested by charging the battery to 100% state of charge, disassembling the battery to take the electrode sheet, and punching into a small disc with an area S = 1540.25 mm 2 , measuring the weight M of the small disc, taking another electrode sheet, wiping off the film layer on the surface to leave the empty current collector foil, and punching into a small disc with an area S = 1540.25 mm 2 , weighing the mass M0 of the empty aluminum foil, and then the surface density = (M - M0) / S / n, where n is the number of film layers coated on the current collector, which is 1 or 2, corresponding to single-sided coating or double-sided coating.

[0101] The electrolyte has the function of conducting ions between the positive electrode sheet and the negative electrode sheet. The type of electrolyte is not particularly limited in the present application, and can be selected according to the needs. For example, the electrolyte can be liquid, gel or all-solid-state.

[0102] In some embodiments, the electrolyte uses an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0103] In some embodiments, the electrolyte salt can include a lithium electrolyte salt. Without limitation, the electrolyte salt can include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bisfluorosulfonylimide (LiFSI), lithium bis-trifluoromethanesulfonylimide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluoro-oxalato-borate (LiDFOB), lithium bis-oxalato-borate (LiBOB), lithium difluoro-bis-oxalato-phosphate (LiDFOP), and lithium tetrafluoro-oxalato-phosphate (LiTFOP).

[0104] In some embodiments, the solvent includes at least one of an ether solvent, an ester solvent, and a sulfone solvent.

[0105] As an example, the ether solvent can include at least one of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), tetraethylene glycol dimethyl ether (TEGDME), and 1,3-dioxolane (DOL).

[0106] As an example, the ester solvent can include at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylene carbonate (VC), fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), γ-butyrolactone (BL), 1,3-propane sultone (1,3-PS), methyl propionate (MP), methyl butyrate (MB), ethyl acetate (EA), ethyl propionate (EP), propyl propionate (PP), and ethyl butyrate (EB).

[0107] In some embodiments, the electrolyte solution can further optionally include an additive. For example, the additive can include a negative electrode film-forming additive, a positive electrode film-forming additive, and can further include an additive capable of improving certain properties of the battery, such as an additive for improving overcharge performance of the battery, an additive for improving high-temperature or low-temperature performance of the battery, etc.

[0108] In some embodiments, the secondary battery further includes a separator. The type of the separator is not particularly limited in the present application, and any known porous separator having good chemical stability and mechanical stability can be used.

[0109] In some embodiments, the separator can include one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can be a single layer film or a multi-layer composite film, and is not particularly limited. When the separator is a multi-layer composite film, the materials of the respective layers can be the same or different, and are not particularly limited.

[0110] In some embodiments, the thickness of the separator is 6 μm to 40 μm of the active layer, and can be 12 μm to 20 μm of the active layer.

[0111] In some embodiments, the positive electrode tab, the negative electrode tab, and the separator can be manufactured into an electrode assembly through a winding process or a stacking process. The electrolyte solution is used to impregnate the electrode assembly.

[0112] In some embodiments, the secondary battery includes one or more of a solid-state battery and a liquid battery. When the secondary battery is a solid-state battery, the separator can be replaced with a solid electrolyte layer.

[0113] It is understood that the solid electrolyte layer includes a solid electrolyte. The solid electrolyte in the solid electrolyte layer can be a solid electrolyte known in the art that can be used in solid-state batteries.

[0114] As a non-limiting example, in different film layers of a solid-state battery, the solid electrolyte may include one or more of the following: sulfide solid electrolyte, halide solid electrolyte, oxide solid electrolyte, polymer solid electrolyte, etc.

[0115] As another non-limiting example, in different film layers of a solid-state battery, the solid electrolyte can be, but is not limited to, one or more of oxide-based solid electrolytes, sulfide-based solid electrolytes, and halide-based solid electrolytes. In some embodiments, the solid electrolyte can independently include, but is not limited to, one or more of Argyrodite-type sulfide electrolytes and halide electrolytes. Non-limiting examples of oxide-based solid electrolytes may include LISICON-type oxide electrolytes (such as γ-Li3PO4), NASICON-type oxide electrolytes (such as Li... 1+x Al x Ge 2-x (PO4)3,Li 1+x Al x Ti 2-x (PO4)3, etc., 0≤x≤1), Garnet type (such as Li7La3Zr2O) 12 (etc.), perovskite-type oxide electrolytes (such as Li, etc.) 3x La 2 / 3-x One or more of the following: TiO3, etc. (0≤x≤0.5). Non-limiting examples of sulfide solid electrolytes may include Li. 10 GeP2S 12 Li₂S-P₂S₅, Argyrodite type (such as Li₆PS₅Cl, Li 5.5 PS 5.5 Cl 1.5 One or more of the following (etc.). Non-limiting examples of halide solid electrolytes may include one or more of the following: Li3InCl6, Li3YCl6, Li3ScCl6, Li3ErCl6, Li2ZrCl6, etc.

[0116] Solid electrolyte membranes or solid electrolyte layers can be prepared using dry methods. In some embodiments, the solid electrolyte layer can be formed by pressing solid electrolyte materials into a solid electrolyte membrane. In other embodiments, the solid electrolyte layer is formed by pressing the constituent raw materials of the solid electrolyte layer onto an electrode layer. In still other embodiments, the solid electrolyte membrane can also be prepared using methods such as fibrosis combined with calendering, melt extrusion, or spraying.

[0117] In the present application, the solid electrolyte film sheet can also be referred to as a solid electrolyte film.

[0118] The solid electrolyte layer can also be prepared by a wet method, and the electrolyte slurry used includes at least a solid electrolyte and an organic solvent, and usually further includes one or more of a binder and a dispersant.

[0119] In some embodiments, the solid-state battery includes a semi-solid-state battery and a full solid-state battery.

[0120] In some embodiments, the solid-state battery includes a full solid-state battery. Further, the solid-state battery is a full solid-state battery.

[0121] It can be understood that the liquid-state battery refers to a battery in which the electrolyte in the battery is a liquid. The semi-solid-state battery is a battery between the liquid-state battery and the full solid-state battery, which mainly replaces part of the electrolyte with a solid electrolyte on the basis of the liquid-state battery.

[0122] In the present application, unless otherwise specified, the "full solid-state battery" refers to a solid-state battery in which the electrolyte in the battery is a solid electrolyte. At this time, the positive electrode layer, the negative electrode layer, the functional layer and the electrolyte part all use solid materials, and there is no liquid-state electrolyte in the battery, so it can be referred to as a "full solid-state battery".

[0123] In some embodiments, the solid-state battery includes a solid-state battery with a stacked structure.

[0124] In some embodiments, the negative electrode sheet in the solid-state battery can not contain a negative electrode active layer, at which time it corresponds to a negative electrode-free solid-state battery.

[0125] The secondary battery includes at least one battery cell. The secondary battery can include one or more battery cells.

[0126] In the present application, unless otherwise specified, the "battery cell" refers to a basic unit capable of realizing the mutual conversion of chemical energy and electrical energy. Further, in general, the battery cell includes at least a positive electrode sheet, a negative electrode sheet and an electrolyte. During the charging and discharging process of the battery, active ions are embedded and extracted between the positive electrode sheet and the negative electrode sheet. The electrolyte plays a role in conducting active ions between the positive electrode sheet and the negative electrode sheet. The battery cell includes one or more electrode assemblies, and the electrolyte is used to soak the above-mentioned electrode assemblies.

[0127] The shape of the battery cell is not particularly limited in the present application, and it can be cylindrical, square or any other shape. For example, Figure 1 The battery cell shown is an example of a square structure of the battery cell as an example.

[0128] In some embodiments, the battery cell can include an outer package. The outer package can be used to encapsulate the electrode assembly and the electrolyte as described above. In some embodiments, the outer package of the battery cell can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, etc. The outer package of the battery cell can also be a soft package, such as a pouch soft package. The material of the soft package can be plastic, and further, non-limiting examples of the plastic can include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate, etc.

[0129] In some embodiments, referring to Figure 2 , the outer package can include a shell 51 and a cover plate 53. The shell 51 can include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell 51 has an opening in communication with the receiving cavity, and the cover plate 53 can be arranged on the opening to close the receiving cavity. The positive electrode sheet, the negative electrode sheet, and the separator film can form the electrode assembly 52 through a winding process or a stacking process. The electrode assembly 52 is encapsulated in the receiving cavity. The electrode assembly 52 is soaked in the electrolyte. The number of the electrode assemblies 52 contained in the battery cell 5 can be one or more, which can be selected by a person skilled in the art according to actual needs.

[0130] In some embodiments, the secondary battery can be a battery device or a battery pack. The battery device includes at least one battery cell. The number of the battery cells contained in the battery device can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery device.

[0131] Figure 3 The battery device 4 is an example. Referring to Figure 3 , in the battery device 4, the plurality of battery cells 5 can be arranged in sequence along the length direction of the battery device 4. Of course, other arbitrary arrangements can also be used. Further, the plurality of battery cells 5 can be fixed by fasteners.

[0132] Optionally, the battery device 4 can further include a housing having a receiving space, and the plurality of battery cells 5 are received in the receiving space.

[0133] In some embodiments, the above-mentioned battery device can also be assembled into a battery pack, and the number of the battery devices contained in the battery pack can be one or more, which can be selected by a person skilled in the art according to the application and capacity of the battery pack.

[0134] Figure 4 And Figure 5 The battery pack 1 is an example. Referring to Figure 4 And Figure 5In the battery pack 1, a battery box and a plurality of battery devices 4 disposed in the battery box can be included. The battery box includes an upper box body 2 and a lower box body 3, and the upper box body 2 can be disposed on the lower box body 3 to form an enclosed space for accommodating the battery devices 4. The plurality of battery devices 4 can be arranged in the battery box in any manner.

[0135] In some embodiments, a plurality of battery cells 5 can also be arranged in the battery box in any manner to directly obtain the battery pack 1.

[0136] In a second aspect of the present application, a preparation method of a secondary battery is provided, including an electrode tab, the electrode tab including a polymer-based current collector, the polymer-based current collector including a polymer film layer and a graphene-based material disposed in the polymer film layer, the polymer film layer including a polymer, and a ratio of an electrical resistivity of the polymer film layer in any direction perpendicular to a thickness direction of the polymer film layer to an electrical resistivity of the polymer film layer in the thickness direction being less than or equal to 1:10; the preparation method of the polymer-based current collector including the following steps:

[0137] applying a first electric field to a polymer film layer slurry containing a polymer and a graphene-based material to cause the graphene-based material to be oriented and arranged;

[0138] forming a film piece from the obtained slurry, applying a second electric field to the film piece, and solidifying; wherein a direction of the second electric field is perpendicular to a thickness direction of the film piece.

[0139] The above preparation method is simple to operate and is conducive to large-scale production. The graphene-based material in the polymer film layer slurry can be pre-oriented and arranged by the applied first electric field, and the orientation of the graphene-based material in the film piece can be further improved by the applied second electric field. Thus, the graphene-based material can be arranged to a certain extent along the direction of the electric field to construct a conductive network, so that the electrical resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer and the electrical resistivity of the polymer film layer in the thickness direction can be controlled.

[0140] Since the graphene-based material has excellent electrical conductivity, the introduction of the graphene-based material into the polymer film layer and the control of the ratio of the electrical resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the electrical resistivity of the polymer film layer in the thickness direction being less than or equal to 1:10 can effectively improve the electrical conductivity of the polymer film layer in the direction perpendicular to the thickness direction, i.e., the planar direction, so that the planar direction of the polymer-based current collector has higher electrical conductivity, and the voltage uniformity and current uniformity on the polymer-based current collector are better, thereby being conducive to the improvement of the cycle performance of the secondary battery.

[0141] In some embodiments, the intensity of the first electric field and the second electric field are each independently 10 V / m to 100 V / m. As non-limiting examples, the intensity of the first electric field and the second electric field each independently include 10 V / m, 20 V / m, 30 V / m, 40 V / m, 50 V / m, 60 V / m, 70 V / m, 80 V / m, 90 V / m, 100 V / m, or a range between any two of the foregoing.

[0142] In some embodiments, the application time of the first electric field and the second electric field are each independently 0.5 h to 12 h. As non-limiting examples, the application time of the first electric field and the second electric field each independently include 0.5 h, 1 h, 2 h, 3 h, 4 h, 5 h, 6 h, 7 h, 8 h, 9 h, 10 h, 11 h, 12 h, or a range between any two of the foregoing.

[0143] In some embodiments, the first electric field is applied on both sides of the polymer film layer slurry.

[0144] In some embodiments, the solid content of the polymer film layer slurry is 3 wt% to 8 wt%. As non-limiting examples, the solid content of the polymer film layer slurry includes, but is not limited to, 3 wt%, 4 wt%, 5 wt%, 6 wt%, 7 wt%, 8 wt%, or a range between any two of the foregoing.

[0145] In some embodiments, the temperature of the solidification is 80 °C to 150 °C. As non-limiting examples, the temperature of the solidification includes, but is not limited to, 80 °C, 90 °C, 100 °C, 110 °C, 120 °C, 130 °C, 140 °C, 150 °C, or a range between any two of the foregoing.

[0146] In some embodiments, the time of the solidification is 5 min to 120 min. As non-limiting examples, the time of the solidification includes, but is not limited to, 5 min, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, or a range between any two of the foregoing.

[0147] Adjusting at least one of the intensity of the first electric field, the application time of the first electric field, the intensity of the second electric field, and the application time of the second electric field can adjust the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer and the resistivity of the polymer film layer in the thickness direction of the polymer film layer.

[0148] In some embodiments, the step of forming the obtained slurry into a film sheet includes one or more of a solution casting method and an in-situ polymerization method.

[0149] By regulating the process conditions in the above preparation method, the secondary battery of the first aspect of the present application can be obtained.

[0150] In the third aspect of the present application, a polymer-based current collector is provided, which comprises a polymer film layer and a graphene-based material arranged in the polymer film layer, the polymer film layer comprising a polymer, and the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction of the polymer film layer being less than or equal to 1:10.

[0151] Since the graphene-based material has excellent electrical conductivity, by introducing the graphene-based material into the polymer film layer and controlling the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction of the polymer film layer to be less than or equal to 1:10, the electrical conductivity of the polymer film layer in the direction perpendicular to the thickness direction, i.e., the planar direction, can be effectively improved, so that the polymer-based current collector has higher electrical conductivity in the planar direction, and the voltage uniformity and current uniformity on the polymer-based current collector are better, thereby facilitating the improvement of the cycle performance of the secondary battery.

[0152] In some embodiments, the polymer-based current collector is as defined in the secondary battery of the first aspect of the present application.

[0153] In the fourth aspect of the present application, a power-using device is provided, which comprises at least one of the secondary battery of the first aspect of the present application, the secondary battery prepared by the preparation method of the second aspect of the present application, and the polymer-based current collector of the third aspect of the present application.

[0154] The secondary battery can be used as a power source of the power-using device, or as an energy storage unit of the power-using device. The power-using device can include mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc., but is not limited thereto. Among them, the mobile device can be a mobile phone, a notebook computer, etc.; the electric vehicle can be a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, etc., but is not limited thereto.

[0155] As the power-using device, the secondary battery can be selected according to the use requirements thereof.

[0156] Figure 6 The power-using device 6 is an example. The power-using device 6 is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. In order to meet the high power and high energy density requirements of the secondary battery for the power-using device, the above battery pack or battery device can be used as a power source.

[0157] As another example, the device can be a mobile phone, a tablet computer, a notebook computer, etc. The device generally requires thinning, and the above-mentioned battery monomer can be used as a power supply.

[0158] Hereinafter, some embodiments of the present application will be described. The embodiments described below are exemplary and are for the purpose of explanation of the present application only, and should not be understood as limiting the present application. In the embodiments, the techniques or conditions not mentioned are performed according to the description above, or according to the techniques or conditions described in the literature in the art, or according to the product instructions. The reagents or instruments not mentioned by the manufacturer are all conventional products that can be obtained commercially, or can be synthesized according to the conventional method of commercially available products.

[0159] The test methods of each embodiment and comparative example are as follows:

[0160] (1) Test of resistivity of polymer film layer in the direction perpendicular to its thickness and resistivity of polymer film layer in the thickness direction

[0161] The sheet resistance of the polymer-based current collector is tested using the four-terminal method, the resistivity of the polymer-based current collector in the direction perpendicular to its thickness is obtained (the four terminals are on the same side of the polymer film layer), and then the resistivity of the polymer-based current collector in the thickness direction is tested using the four-terminal method (two terminals are on one side of the polymer-based current collector, and the other two terminals are on the other side of the polymer-based current collector), thereby obtaining the resistivity of the polymer film layer in the direction perpendicular to its thickness and the resistivity of the polymer film layer in the thickness direction.

[0162] (2) Test of average flake diameter of graphene-based material

[0163] The secondary battery is disassembled, the negative electrode sheet is obtained, the polymer-based current collector is peeled off from the negative electrode sheet, and the cross section of the polymer film layer in the polymer-based current collector in the direction perpendicular to its thickness is obtained by random cutting. The flake diameter of the graphene-based material in the cross section is measured by an optical microscope, and the average value is obtained to obtain the average flake diameter of the graphene-based material.

[0164] (3) Test of average thickness of graphene-based material and percentage of the number of graphene-based materials in the thickness direction same as the thickness direction of the polymer film layer to the number of graphene-based materials

[0165] The secondary battery is disassembled to obtain a negative electrode sheet, and a polymer-based current collector is peeled off from the negative electrode sheet. A cross section of the polymer film layer in the polymer-based current collector is obtained by random cutting. The thickness of the graphene-like material in the cross section is measured by TEM. The average thickness of the graphene-like material is obtained by averaging. The total number of the graphene-like material in the cross section and the number of the graphene-like material with the thickness direction being the same as the thickness direction of the polymer film layer are observed by TEM. Thus, the percentage of the number of the graphene-like material with the thickness direction being the same as the thickness direction of the polymer film layer in the number of the graphene-like material is obtained.

[0166] (4) Cycle performance test

[0167] At 25°C, the solid-state battery is charged to 4.3V (vs. Li + / Li) at a constant current of 0.1C and a constant voltage, and then discharged to 2.5V (vs. Li + / Li) at a constant current of 0.5C. The charge capacity (mAh) and discharge capacity (mAh) are recorded. After 200 cycles, the cycle capacity retention rate is tested. The calculation formula is as follows: capacity retention rate after 200 cycles = (discharge capacity of the 200th cycle / first discharge capacity) x 100%. The higher the capacity retention rate, the better the cycle performance of the solid-state battery.

[0168] Example 1

[0169] The preparation method of the solid-state battery comprises the following steps:

[0170] (1) Preparation of the negative electrode sheet

[0171] The graphene-like material (graphene) is added to the polymer (PEO) solution dissolved in acetonitrile to obtain a polymer film layer slurry, and the solid content of the polymer film layer slurry is 5wt%; wherein the mass ratio of graphene and polymer is 5:44.

[0172] A first electric field is applied to both sides of the polymer film layer slurry to promote the oriented arrangement of graphene, and the strength of the first electric field is 50V / m, and the application time of the first electric field is 1h.

[0173] The obtained slurry is made into a film sheet by solution casting method. Subsequently, a second electric field parallel to the film sheet is applied during the solidification process of the polymer in the film sheet, that is, the direction of the second electric field is perpendicular to the thickness direction of the film sheet, so that the graphene remains uniformly oriented during the solidification process. The strength of the second electric field is 70V / m, and the application time of the second electric field is 10h. Thus, a polymer-based current collector with a thickness of 10μm is obtained.

[0174] Lithium metal is rolled on the double-sided surface of the polymer-based current collector to form a negative active layer, thereby obtaining a negative electrode sheet; wherein the thickness of the negative active layer on both sides of the polymer-based current collector is the same.

[0175] (2) Preparation of the functional layer

[0176] The porous carbon black and the binder PVDF are mixed in a weight ratio of 95:5, a solvent NMP is added, and the mixture is fully stirred and uniformly mixed to obtain a functional layer slurry.

[0177] (3) Preparation of the positive electrode sheet

[0178] The positive active material NCM 811 , the sulfide solid electrolyte Li6PS5Cl, and the conductive agent vapor-grown carbon fiber (VGCF) are uniformly mixed in a mass ratio of 70:27:3 for 10 min to obtain a composite positive electrode powder;

[0179] The binder PTFE is added to the composite positive electrode powder in a mass ratio of 1% of the composite positive electrode powder, and the composite positive electrode powder is rolled into a positive electrode film (positive active layer). Then, the positive electrode film is compounded on the double-sided surface of the positive current collector (aluminum foil) by a hot roller to obtain a positive electrode sheet.

[0180] (4) Preparation of the solid electrolyte layer

[0181] The sulfide solid electrolyte Li6PS5Cl and the binder PTFE in a mass ratio of 1% (the mass of PTFE is 1% of the mass of Li6PS5Cl) are fully mixed, and a solid electrolyte film (solid electrolyte layer) is rolled.

[0182] (5) Battery assembly

[0183] The negative electrode sheet, the functional layer, the solid electrolyte layer, and the positive electrode sheet are sequentially stacked in a bottom-up order, and the obtained electrode assembly is packaged in an aluminum plastic bag after being subjected to warm isostatic pressing at 600 MPa, thereby obtaining a solid-state battery.

[0184] Examples 2-4

[0185] The preparation method of the solid-state battery is basically the same as that in Example 1, except that the mass ratio of graphene and polymer in the polymer film layer slurry in step (1) is changed, thereby changing the mass proportion of graphene-based materials in the polymer film layer. The specific conditions are shown in Table 1.

[0186] Comparative Example 1

[0187] The preparation method of the solid-state battery is basically the same as that in Example 1, except that step (1) is different.

[0188] Specifically, the graphene-based material (graphene) is added into the acetonitrile-dissolved polymer (PEO) solution to obtain a polymer film layer slurry; wherein the mass ratio of the graphene and the polymer is 5:44.

[0189] The obtained polymer film layer slurry is made into a film sheet by a solution casting method, and is cured to obtain a polymer-based current collector with a thickness of 10 μm.

[0190] The lithium metal is rolled on the double-sided surfaces of the polymer-based current collector to form negative electrode active layers, and a negative electrode sheet is obtained; wherein the thicknesses of the negative electrode active layers on the two sides of the polymer-based current collector are the same.

[0191] Comparative Example 2

[0192] The preparation method of the solid-state battery is basically the same as that in Embodiment 1, except that step (1) is different.

[0193] Specifically, the nano metal powder (nano silver, with an average particle size of 50 nm) is added into the acetonitrile-dissolved polymer (PEO) solution to obtain a polymer film layer slurry; wherein the mass ratio of the nano metal powder and the polymer is 5:44.

[0194] The obtained polymer film layer slurry is made into a film sheet by a solution casting method, and is cured to obtain a polymer-based current collector with a thickness of 10 μm.

[0195] The lithium metal is rolled on the double-sided surfaces of the polymer-based current collector to form negative electrode active layers, and a negative electrode sheet is obtained; wherein the thicknesses of the negative electrode active layers on the two sides of the polymer-based current collector are the same.

[0196] The test results of Embodiments 1-4 and Comparative Examples 1-2 are shown in Table 1. In Table 1, since the polymer film layer contains a small amount of acetonitrile and the purity of the polymer is lower than 100%, the sum of the mass ratio of the graphene-based material in the polymer film layer and the mass ratio of the polymer in the polymer film layer is not 100%.

[0197] Table 1

[0198]

[0199] In Table 1, " / " represents that the substance or the parameter does not exist.

[0200] As can be seen from Table 1, the capacity retention rate of the battery of Examples 1-4 after 200 cycles is higher than that of the batteries of Comparative Examples 1-2, indicating that the battery in Examples 1-4, which comprises the negative electrode sheet comprising the polymer-based current collector comprising the polymer film layer and the graphene-based material disposed in the polymer film layer, and the ratio of the resistivity of the polymer film layer in any direction perpendicular to the thickness direction of the polymer film layer to the resistivity of the polymer film layer in the thickness direction is less than or equal to 1:10, can effectively improve the cycle performance of the battery.

[0201] Examples 5-7

[0202] The preparation method of the solid-state battery is basically the same as that of Example 1, except that the average flake diameter of the graphene-based material in the polymer film layer slurry of step (1) is changed, as shown in Table 2.

[0203] The test results of Example 1 and Examples 5-7 are shown in Table 2.

[0204] Table 2

[0205]

[0206] As can be seen from Table 2, adjusting the average flake diameter of the graphene-based material within an appropriate range can further improve the cycle performance of the battery.

[0207] Examples 8-11

[0208] The preparation method of the solid-state battery is basically the same as that of Example 1, except that the average thickness of the graphene-based material in the polymer film layer slurry of step (1) is changed, as shown in Table 3.

[0209] The test results of Example 1 and Examples 8-11 are shown in Table 3.

[0210] Table 3

[0211]

[0212] As can be seen from Table 3, adjusting the average thickness of the graphene-based material within an appropriate range can further improve the cycle performance of the battery.

[0213] Example 12

[0214] The preparation method of the solid-state battery is basically the same as that of Example 1, except that the type of the graphene-based material in the polymer film layer slurry of step (1) is changed to redox graphene, as shown in Table 4.

[0215] The test results of Example 1 and Example 12 are shown in Table 4.

[0216] Table 4

[0217]

[0218] As can be seen from Table 4, the cycle performance of the battery can be improved by changing the type of graphene-based material.

[0219] The above description of the various embodiments and examples tends to emphasize differences between the various embodiments and examples, and the same or similar parts can be referred to each other, and for the sake of brevity, will not be described herein. Each of the technical features of the above-described embodiments and examples can be combined arbitrarily, and for the sake of brevity, each of the technical features of the above-described embodiments and examples will not be described, and however, as long as the combination of the technical features does not contradict, it should be considered as within the scope of the present disclosure.

[0220] It should be noted that the present application is not limited to the above-described embodiments and examples. The above-described embodiments and examples are merely examples, and embodiments and examples having substantially the same configuration and playing the same role and effect as the technical idea within the scope of the technical solution of the present application are all included in the technical scope of the present application. The above-described embodiments and examples only express several embodiments and examples of the present application, and the description is relatively detailed, but it should not be construed as limiting the scope of the patent. In addition, within the scope of the gist of the present application, various modifications that can be thought of by those skilled in the art, other modes constructed by combining part of the elements of the embodiments or examples are also included in the scope of the present application.

Claims

1. A secondary battery characterized by comprising: An electrode tab includes a polymer-based current collector including a polymer film layer and a graphene-based material disposed in the polymer film layer, the polymer film layer including a polymer, a ratio of an electrical resistivity of the polymer film layer in any direction perpendicular to a thickness direction of the polymer film layer to an electrical resistivity of the polymer film layer in the thickness direction being less than or equal to 1:10, the electrical resistivity of the polymer film layer in the thickness direction being 10 Ω·m to 5 x 10 5 Ω·m.

2. The secondary battery according to claim 1, characterized by The polymer film layer has an electrical resistivity of 1 x 10 -6 Ω·m~100Ω·m in any direction perpendicular to the thickness direction thereof.

3. The secondary battery according to claim 1 or 2, characterized by The secondary battery has one or more of the following features: (1) The mass percentage of the graphene-based material in the polymer film layer is 3% to 40%; (2) The graphene-based material includes one or more of graphene, graphene oxide, and redox graphene; (3) The mass percentage of the polymer in the polymer film layer is 60% to 97%; (4) The polymer includes one or more of polyethylene oxide, polyethylene terephthalate, polypropylene, polyimide, polypyrrole, and polyaniline.

4. The secondary battery according to claim 3, characterized by The secondary battery has one or more of the following features: (1) The mass percentage of the graphene-based material in the polymer film layer is 3% to 22%; (2) The mass percentage of the polymer in the polymer film layer is 78% to 97%.

5. The secondary battery according to claim 1 or 2, characterized by The secondary battery has one or more of the following features: (1) The average flake diameter of the graphene-based material is 20 μm to 300 μm; (2) The average thickness of the graphene-based material is 0.3 nm to 20 nm; (3) The percentage of the number of graphene-based materials with the same thickness direction as the thickness direction of the polymer film layer to the total number of graphene-based materials is 70% to 100%.

6. The secondary battery according to claim 5, characterized by The secondary battery has one or more of the following features: (1) The average flake diameter of the graphene-based material is 100 μm to 300 μm; (2) The average thickness of the graphene-based material is 0.3 nm to 7 nm.

7. The secondary battery according to claim 1 or 2, characterized by The secondary battery has one or more of the following features: (1) The polymer-based current collector further includes a conductive layer disposed on at least one side of the polymer film layer, and the conductive layer includes one or more of a metal material and a carbon material; (2) The thickness of the polymer-based current collector is 5 μm to 25 μm; (3) The thickness of the polymer film layer accounts for 30% to 100% of the thickness of the polymer-based current collector.

8. A method for producing a secondary battery, characterized by, An electrode tab including a polymer-based current collector including a polymer film layer and a graphene-based material disposed in the polymer film layer, the polymer film layer including a polymer, a ratio of an electrical resistivity of the polymer film layer in any direction perpendicular to a thickness direction of the polymer film layer to an electrical resistivity of the polymer film layer in the thickness direction being less than or equal to 1:10, the electrical resistivity of the polymer film layer in the thickness direction being 10 Ω·m to 5 × 10 5 Ω·m; and a method of manufacturing the polymer-based current collector including the steps of: A first electric field is applied to a polymer film layer slurry containing a polymer and a graphene-based material to orient the graphene-based material; The obtained slurry is made into a film, a second electric field is applied to the film, and the film is cured; wherein the direction of the second electric field is perpendicular to the thickness direction of the film.

9. The method of claim 8, wherein the method further comprises the step of: The preparation method satisfies one or more of the following conditions: (1) The intensity of the first electric field and the second electric field is independently 10 V / m to 100 V / m; (2) The application time of the first electric field and the second electric field is independently 0.5 h to 12 h; (3) The solid content of the polymer film layer slurry is 3 wt% to 8 wt%.

10. A polymer-based current collector characterized by, The material includes a polymer film and a graphene-like material disposed in the polymer film. The polymer film comprises a polymer, and the ratio of the resistivity of the polymer film in any direction perpendicular to its thickness direction to the resistivity in the thickness direction of the polymer film is less than or equal to 1:

10. The resistivity in the thickness direction of the polymer film is 10 Ω·m to 5 × 10⁻⁶. 5 Ω·m.

11. An electrical device, characterized by At least one of the secondary battery of any one of claims 1 to 7, the secondary battery prepared by the preparation method of any one of claims 8 to 9, and the polymer-based current collector of claim 10.

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