Positive plate, sodium ion battery and application of sodium ion battery

Abstract

The invention relates to a positive plate, a sodium ion battery and application of the positive plate, the positive plate comprises a current collector, and a first coating and a second coating which are sequentially attached to at least one surface of the current collector, one of the first coating and the second coating is selected from a layered metal oxide active material layer, and the other one is selected from a polyanion active material layer. And the layered metal oxide active material layer contains a one-dimensional ceramic material. According to the invention, the layered metal oxide positive electrode material and the polyanionic positive electrode material are coated in a layered manner, and the one-dimensional ceramic material is compounded in the layered metal oxide active material layer to construct the three-dimensional heat-conducting network, so that the heat conductivity and the mechanical strength of the layered metal oxide active material layer can be improved at the same time; therefore, the thermal diffusivity and stability of the positive plate can be remarkably improved, the thermal management efficiency of the sodium ion battery using the positive plate is further remarkably improved, generation of local hot spots is inhibited, and the sodium ion battery cannot cause thermal runaway under extreme abuse working conditions such as needling.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a positive electrode sheet, a sodium ion battery and applications thereof. Background Art

[0002] Sodium-ion batteries (SIBs) are considered a potential alternative to lithium-ion batteries due to their abundant sodium resources and low cost. However, among the cathode materials for SIBs, layered metal oxide cathode materials have poor thermal and cycling stability, and a high risk of thermal runaway. While polyanionic cathode materials offer excellent safety, they lack energy density. Therefore, existing technologies primarily coat polyanionic cathode materials onto layered metal oxide cathode materials to create composite materials with relatively balanced overall performance. However, this composite material is limited by the cell structure and cannot effectively eliminate local hot spots under extreme abuse conditions such as needle puncture, making it prone to thermal runaway. Summary of the Invention

[0003] Based on this, it is necessary to provide a positive electrode sheet, a sodium ion battery and its application to address the above problems, so that the sodium ion battery using the positive electrode sheet will not cause thermal runaway under extreme abuse conditions such as needle puncture.

[0004] A positive electrode sheet comprises a current collector and a first coating and a second coating sequentially attached to at least one surface of the current collector, wherein one of the first coating and the second coating is selected from a layered metal oxide active material layer, and the other is selected from a polyanion active material layer, and the layered metal oxide active material layer contains a one-dimensional ceramic material.

[0005] In one embodiment, the first coating layer is selected from a layered metal oxide active material layer, and the second coating layer is selected from a polyanion active material layer;

[0006] And / or, the polyanion active material layer contains a one-dimensional ceramic material.

[0007] In one embodiment, the mass fraction of the one-dimensional ceramic material in the layered metal oxide active material layer is 0.1%-1%;

[0008] And / or, the one-dimensional ceramic material is selected from ceramic nanowires and / or ceramic nanotubes.

[0009] In one embodiment, when the one-dimensional ceramic material is selected from ceramic nanowires, the ceramic nanowires have a length of 1 μm-10 μm, a diameter of 100 nm-500 nm, and an aspect ratio of 5-15;

[0010] And / or, the one-dimensional ceramic material is selected from at least one of silicon carbide nanowires, boron nitride nanowires, aluminum nitride nanowires, silicon carbide nanotubes, boron nitride nanotubes, and aluminum nitride nanotubes.

[0011] In one embodiment, the thickness of the layered metal oxide active material layer is 20 μm-40 μm;

[0012] And / or, the compacted density of the layered metal oxide active material layer is 3.2 g / cm 3 -3.4g / cm 3 ;

[0013] And / or, the thickness of the polyanion active material layer is 60 μm-120 μm;

[0014] And / or, the compaction density of the polyanion active material layer is 2.0 g / cm 3 -2.1g / cm 3 .

[0015] In one embodiment, a conductive carbon layer is further sandwiched between the first coating layer and the second coating layer.

[0016] In one embodiment, the thickness of the conductive carbon layer is 1 μm-3 μm;

[0017] And / or, the compaction density of the conductive carbon layer is 0.5 g / cm 3 -0.7g / cm 3 .

[0018] A sodium ion battery using the positive electrode sheet.

[0019] In one embodiment, the sodium ion battery uses a ceramic coated separator.

[0020] A sodium ion battery is used in a battery module or a battery pack.

[0021] One-dimensional ceramic materials have extremely high thermal conductivity coefficients and fiber reinforcement effects. Therefore, the present invention coats the layered metal oxide positive electrode material and the polyanion positive electrode material in layers, and then composites the one-dimensional ceramic material in the layered metal oxide active material layer. This can construct a three-dimensional thermal conductive network in the layered metal oxide active material layer, while improving the thermal conductivity and mechanical strength of the layered metal oxide active material layer, thereby significantly improving the thermal diffusion capacity and stability of the positive electrode sheet, and further significantly improving the thermal management efficiency of the sodium ion battery using the positive electrode sheet, inhibiting the generation of local hot spots, and preventing the sodium ion battery from causing thermal runaway under extreme abuse conditions such as needle puncture. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To more clearly illustrate the technical solutions in the embodiments of the present application or in the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0023] Figure 1 Structural schematic diagram of a positive electrode sheet according to an embodiment of the present invention;

[0024] Figure 2 Structural schematic diagram of a positive electrode sheet according to another embodiment of the present invention.

[0025] In the figure: 100, current collector; 101, first coating; 102, second coating; 103, conductive carbon layer. Detailed implementation manners

[0026] To facilitate the understanding of the present invention, the present invention will be described in more detail below. However, it should be understood that the present invention can be implemented in many different forms and is not limited to the embodiments or examples described herein. On the contrary, the purpose of providing these embodiments or examples is to make the understanding of the disclosure of the present invention more thorough and comprehensive.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those of ordinary skill in the technical field to which the present invention belongs. The terms used in the description of the present invention in this specification are only for the purpose of describing specific embodiments or examples and are not intended to limit the present invention. The optional range of the term "and / or" used herein includes any one of two or more related listed items, and also includes any and all combinations of the related listed items. The said any and all combinations include any two related listed items, any more related listed items, or all combinations of the related listed items.

[0028] In the present invention, when it comes to numerical ranges, unless otherwise specified, the above numerical ranges are considered continuous and include the minimum and maximum values of the range, as well as each value between such minimum and maximum values. Further, when the range refers to integers, it includes each integer between the minimum and maximum values of the range. In addition, when multiple ranges are provided to describe features or characteristics, the ranges can be combined. In other words, unless otherwise specified, all ranges disclosed herein should be understood to include any and all sub-ranges subsumed therein.

[0029] Such as Figure 1As shown, the positive electrode sheet of an embodiment provided by the present invention includes a current collector 100, and a first coating layer 101 and a second coating layer 102 sequentially attached to at least one surface of the current collector 100. For example, the first coating layer 101 and the second coating layer 102 are sequentially attached only on any one surface of the current collector 100, or the first coating layer 101 and the second coating layer 102 are sequentially attached on both surfaces of the current collector 100.

[0030] Specifically, one of the first coating layer 101 and the second coating layer 102 is selected from a layered metal oxide active material layer, and the other is selected from a polyanion active material layer. For example, the first coating layer 101 is a layered metal oxide active material layer, and the second coating layer 102 is a polyanion active material layer, or the first coating layer 101 is a polyanion active material layer, and the second coating layer 102 is a layered metal oxide active material layer. Considering that the safety and stability of the polyanion-based cathode material are better than those of the layered metal oxide cathode material, it is preferred that the first coating layer 101 is a layered metal oxide active material layer, and the second coating layer 102 is a polyanion active material layer. Thus, the polyanion active material layer can greatly isolate the direct contact between the layered metal oxide active material layer and the electrolyte and inhibit side reactions.

[0031] Among them, the layered metal oxide active material layer of the present invention contains one-dimensional ceramic materials. The one-dimensional ceramic materials have extremely high thermal conductivity. At the same time, the one-dimensional ceramic materials have a fiber reinforcement effect. Therefore, the present invention coats the layered metal oxide cathode material and the polyanion-based cathode material in layers, and then composes one-dimensional ceramic materials in the layered metal oxide active material layer, which can construct a three-dimensional thermal conduction network in the layered metal oxide active material layer, and at the same time improve the defects of insufficient cycle stability and thermal stability of the layered metal oxide cathode material, and enhance the thermal conductivity and mechanical strength of the layered metal oxide active material layer. Thereby, the thermal diffusion ability and stability of the positive electrode sheet can be significantly improved, and further, the thermal management efficiency of the sodium-ion battery using the positive electrode sheet can be significantly improved, the generation of local hot spots can be inhibited, and the sodium-ion battery will not cause thermal runaway under extreme abuse conditions such as pinprick.

[0032] It can be understood that when introducing one-dimensional ceramic materials into the positive electrode sheet, the proportion of the active material in the positive electrode sheet decreases, which will inevitably affect the electrical properties such as energy density. In the present invention, the layered metal oxide positive electrode material and the polyanion-type positive electrode material are coated in layers to form a layered metal oxide active material layer and a polyanion active material layer, which can effectively exert the respective performance advantages of the layered metal oxide positive electrode material and the polyanion-type positive electrode material. Then, only the one-dimensional ceramic material is compounded in the layered metal oxide active material layer, which can minimize the impact on the electrical properties when introducing the one-dimensional ceramic material and hardly affect the electrical properties. Compared with the positive electrode sheet made by first coating the polyanion-type positive electrode material on the layered metal oxide positive electrode material to form a composite material and then using this composite material for coating, the positive electrode sheet of the present invention has better rate performance and other aspects and has better electrical properties. Therefore, when there is a need to further improve the thermal diffusion ability and stability of the positive electrode sheet, the one-dimensional ceramic material can also be compounded in the polyanion active material layer.

[0033] As described above, the proportion of the one-dimensional ceramic material will affect the electrical properties such as the energy density of the positive electrode sheet. Therefore, in order to make the positive electrode sheet have both excellent thermal diffusion ability and stability and excellent electrical properties, the mass fraction of the one-dimensional ceramic material in the layered metal oxide active material layer is preferably 0.1%-1%.

[0034] Optionally, the one-dimensional ceramic material is selected from ceramic nanowires and / or ceramic nanotubes, further preferably ceramic nanowires. The length of the ceramic nanowires is preferably 1 μm-10 μm, the diameter is preferably 100 nm-500 nm, and the aspect ratio is preferably 5-15, which can take into account the dispersibility and mechanical strength, form a more effective heat conduction path, and thus can better improve the thermal conductivity and mechanical strength of the layered metal oxide active material layer.

[0035] Optionally, the one-dimensional ceramic material is selected from at least one of silicon carbide nanowires, boron nitride nanowires, aluminum nitride nanowires, silicon carbide nanotubes, boron nitride nanotubes, and aluminum nitride nanotubes, which not only has a high thermal conductivity coefficient but also has a wide source and low cost.

[0036] It can be understood that the layered metal oxide active material layer of the present invention, in addition to containing one-dimensional ceramic materials, also includes conventional layered metal oxide cathode materials, conductive agents, binders, etc. The mass fraction of the layered metal oxide cathode material in the layered metal oxide active material layer is 92% - 97%, the mass fraction of the conductive agent in the layered metal oxide active material layer is 1% - 5%, and the mass fraction of the binder in the layered metal oxide active material layer is 1% - 3%. Similarly, the polyanion active material layer includes polyanion-type cathode materials, conductive agents, binders, etc. The mass fraction of the polyanion-type cathode material in the polyanion active material layer is 92% - 98%, the mass fraction of the conductive agent in the polyanion active material layer is 1% - 5%, and the mass fraction of the binder in the polyanion active material layer is 1% - 3%.

[0037] In the present invention, there are no special requirements for the selection of the layered metal oxide cathode material, polyanion-type cathode material, conductive agent, and binder, and they can be selected and controlled according to the conventional method. For example, the layered metal oxide cathode material is selected from Na x MO2 (M is selected from at least one or a combination of Fe, Co, Ni, Mn, V, 0 < x ≤ 1), the polyanion-type cathode material is selected from one or a combination of NaFePO4, Na4Fe3(PO4)2P2O7, Na3V2(PO4)3, the conductive agent is selected from carbon nanotubes (CNT), conductive carbon black (Super P), acetylene black, Ketjen black, and conductive graphite, etc., and the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), etc. The present invention will not elaborate here.

[0038] It can be understood that if one-dimensional ceramic materials are also compounded in the polyanion active material layer, the selection and mass fraction of the one-dimensional ceramic materials in the polyanion active material layer can refer to those of the layered metal oxide active material layer.

[0039] Optionally, the thickness of the layered metal oxide active material layer of the present invention is preferably 20 μm - 40 μm, and the thickness of the polyanion active material layer is preferably 40 μm - 80 μm; in addition, the tap density of the layered metal oxide active material layer is preferably 3.2 g / cm 3 - 3.4 g / cm 3 , and the tap density of the polyanion active material layer is preferably 2.0 g / cm 3 - 2.1 g / cm 3Thus, the thermal conductivity between particles within the layer can be improved, as well as the thermal conductivity between the layered metal oxide active material layer and the polyanion active material layer. At the same time, when the second coating layer 102 is a polyanion active material layer, the high compaction density of the polyanion active material layer can also protect the layered metal oxide active material layer, thereby further improving the thermal diffusion capacity and stability of the positive electrode sheet.

[0040] like Figure 2 As shown, the present invention also provides another embodiment of a positive electrode sheet. In this embodiment, a conductive carbon layer 103 is sandwiched between the first coating layer 101 and the second coating layer 102. The conductive carbon layer 103 not only improves the thermal conductivity between the first coating layer 101 and the second coating layer 102, but also serves as an intermediate heat dissipation layer, thereby further enhancing the thermal diffusion capacity of the positive electrode sheet. In addition, the conductive carbon layer 103 also helps to improve the electronic conductivity between the first coating layer 101 and the second coating layer 102, thereby improving the thermal diffusion capacity of the positive electrode sheet while also enhancing its capacity and other performance.

[0041] Optionally, the carbon material of the conductive carbon layer 103 may be at least one of carbon nanotubes (CNTs), conductive carbon black (Super P), acetylene black, Ketjen black, and conductive graphite.

[0042] Furthermore, the thickness of the conductive carbon layer 103 is 1 μm-3 μm, and the compaction density of the conductive carbon layer 103 is 0.5 g / cm 3 -0.7g / cm 3 .

[0043] The present invention also provides a sodium ion battery using the positive electrode sheet. Since the positive electrode sheet of the present invention has excellent thermal diffusion capability and stability, the sodium ion battery using the positive electrode sheet can suppress the generation of local hot spots, so that the sodium ion battery will not cause thermal runaway under extreme abuse conditions such as needle puncture.

[0044] It can be understood that the sodium-ion battery further includes a negative electrode sheet, a separator, an electrolyte, etc. The present invention has no special requirements for the negative electrode sheet, separator, and electrolyte of the sodium-ion battery, and conventional designs can be selected. For example, the active material of the negative electrode sheet is selected from hard carbon materials, soft carbon materials, graphite, etc.; the conductive agent is selected from carbon nanotubes (CNT), conductive carbon black (Super P), acetylene black, Ketjen black, and conductive graphite, etc.; the binder is selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), sodium alginate, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), etc.; the separator is selected from polypropylene separators (PP), polyimide separators (PI), polyethylene separators (PE), ceramic-coated separators, etc.; the electrolyte contains sodium salts and organic solvents, where the sodium salts are selected from NaPF6, etc., and the organic solvents are selected from ethylene carbonate (EC), dimethyl carbonate (DMC), etc. The present invention will not elaborate further herein.

[0045] Furthermore, the ceramic-coated separator can not only improve the heat resistance of the separator but also assist in heat diffusion. Therefore, the separator is preferably a ceramic-coated separator.

[0046] The present invention does not impose any requirements on the form of the sodium-ion battery, which can be a cylindrical battery, a square battery, etc.

[0047] The present invention also provides an application of a sodium-ion battery in a battery module or a battery pack. Thus, the battery module or battery pack applying the sodium-ion battery of the present invention has more reliable safety.

[0048] Hereinafter, the technical solution of the present invention will be further described through the following specific examples. However, those skilled in the art will understand that the following examples are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the examples, the operations are carried out under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments not specified by the manufacturer can all be obtained as conventional products through commercial purchase.

[0049] Example 1

[0050] Take NaNi 0.3 Mn 0.3 Fe 0.4O2, Super P, MWCNT, PVDF, and silicon carbide nanowires (with a length of 2 μm and a diameter of 200 nm) were added to NMP solvent in a mass ratio of 95.9:2:1:1:0.1. First, it was dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT, and PVDF were added to NMP solvent in a mass ratio of 96:2:1:1. First, it was dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form the second slurry. Then, the first slurry was used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then the second slurry was used to prepare a polyanion active material layer on the first coating as the second coating to obtain the positive electrode sheet. Among them, the thickness of the first coating was 30 μm, and the tap density was 3.3 g / cm 3 , the thickness of the second coating was 90 μm, and the tap density was 2.1 g / cm 3 .

[0051] Hard carbon materials, Super P, and CMC were mixed in a mass ratio of 97:1.5:1.5, coated on the carbon-coated aluminum foil, and roll-pressed to a tap density of 0.95 g / cm³ to obtain the negative electrode sheet.

[0052] A 3-μm-thick Al2O3@BN composite ceramic coating was coated on a 9-μm-thick PE-based film. Among them, the mass fraction of BN in the composite ceramic coating was 30 wt% to obtain the ceramic-coated separator.

[0053] NaPF6 was used as the sodium salt. NaPF6 was dissolved in a mixed solvent of EC / DMC with a volume ratio of 4:6, and then 1 wt% of fluoroethylene carbonate (FEC) was added as a film-forming additive to obtain the electrolyte. Among them, the concentration of the sodium salt in the electrolyte was 1.0 mol / L, and the conductivity of the electrolyte was ~12 mS / cm (25 °C).

[0054] The full-tab design was adopted. The positive electrode sheet, negative electrode sheet, and separator were alternately wound. After being flattened, the tabs were welded. After being put into the shell, the electrolyte was injected, and the battery was sealed to form a 32700 cylindrical battery.

[0055] Example 2

[0056] The difference between Example 2 and Example 1 was only that NaNi 0.3 Mn 0.3 Fe 0.4O2, Super P, MWCNT, PVDF, and silicon carbide nanowires (1 μm in length and 100 nm in diameter) were added to NMP solvent in a mass ratio of 95.7:2:1:1:0.3. First, ultrasonic dispersion was carried out at 500 W for 30 minutes, and then mechanical stirring was carried out at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT, and PVDF were added to NMP solvent in a mass ratio of 96:2:1:1. First, ultrasonic dispersion was carried out at 500 W for 30 minutes, and then mechanical stirring was carried out at 800 rpm for 2 hours to form the second slurry. Then, the first slurry was used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then the second slurry was used to prepare a polyanion active material layer on the first coating as the second coating to obtain the positive electrode sheet. Among them, the thickness of the first coating is 25 μm, and the tap density is 3.3 g / cm 3 , and the thickness of the second coating is 95 μm, and the tap density is 2.1 g / cm 3 .

[0057] Example 3

[0058] The difference between Example 3 and Example 1 is only that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, PVDF, and silicon carbide nanowires (3 μm in length and 300 nm in diameter) were added to NMP solvent in a mass ratio of 95.5:2:1:1:0.5. First, ultrasonic dispersion was carried out at 500 W for 30 minutes, and then mechanical stirring was carried out at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT, and PVDF were added to NMP solvent in a mass ratio of 96:2:1:1. First, ultrasonic dispersion was carried out at 500 W for 30 minutes, and then mechanical stirring was carried out at 800 rpm for 2 hours to form the second slurry. Then, the first slurry was used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then the second slurry was used to prepare a polyanion active material layer on the first coating as the second coating to obtain the positive electrode sheet. Among them, the thickness of the first coating is 30 μm, and the tap density is 3.3 g / cm 3 , and the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 .

[0059] Example 4

[0060] The difference between Example 4 and Example 1 is only that NaNi 0.3 Mn 0.3 Fe 0.4O2, Super P, MWCNT, PVDF, and silicon carbide nanowires (4 μm in length and 400 nm in diameter) were added to NMP solvent in a mass ratio of 95.2:2:1:1:0.8. First, they were ultrasonically dispersed at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT, and PVDF were added to NMP solvent in a mass ratio of 96:2:1:1. First, they were ultrasonically dispersed at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form the second slurry. Then, the first slurry was used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then the second slurry was used to prepare a polyanion active material layer on the first coating as the second coating to obtain the positive electrode sheet. Among them, the thickness of the first coating is 30 μm, and the tap density is 3.3 g / cm 3 , and the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 .

[0061] Example 5

[0062] The difference between Example 5 and Example 1 is only that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, PVDF, and silicon carbide nanowires (2 μm in length and 200 nm in diameter) were added to NMP solvent in a mass ratio of 95:2:1:1:1. First, they were ultrasonically dispersed at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT, and PVDF were added to NMP solvent in a mass ratio of 96:2:1:1. First, they were ultrasonically dispersed at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form the second slurry. Then, the first slurry was used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then the second slurry was used to prepare a polyanion active material layer on the first coating as the second coating to obtain the positive electrode sheet. Among them, the thickness of the first coating is 30 μm, and the tap density is 3.3 g / cm 3 , and the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 .

[0063] Example 6

[0064] Example 6 is only different from Example 1 in that a first slurry is used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, then MWCNT and Super P are mixed at a mass ratio of 1:1, a conductive carbon layer is prepared on the first coating, and then a second slurry is used to prepare a polyanion active material layer on the conductive carbon layer as the second coating to obtain a positive electrode sheet. Among them, the thickness of the first coating is 30 μm, and the tap density is 3.3 g / cm 3 , the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 , the thickness of the conductive carbon layer is 1 μm, and the tap density is 0.7 g / cm 3 .

[0065] Example 7

[0066] Example 7 is only different from Example 3 in that a first slurry is used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, then MWCNT and Super P are mixed at a mass ratio of 1:1, a conductive carbon layer is prepared on the first coating, and then a second slurry is used to prepare a polyanion active material layer on the conductive carbon layer as the second coating to obtain a positive electrode sheet. Among them, the thickness of the first coating is 30 μm, and the tap density is 3.3 g / cm 3 , the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 , the thickness of the conductive carbon layer is 1 μm, and the tap density is 0.7 g / cm 3 .

[0067] Example 8

[0068] Example 8 is only different from Example 5 in that a first slurry is used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, then MWCNT and Super P are mixed at a mass ratio of 1:1, a conductive carbon layer is prepared on the first coating, and then a second slurry is used to prepare a polyanion active material layer on the conductive carbon layer as the second coating to obtain a positive electrode sheet. Among them, the thickness of the first coating is 30 μm, and the tap density is 3.3 g / cm 3 , the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 , the thickness of the conductive carbon layer is 1 μm, and the tap density is 0.7 g / cm 3 .

[0069] Example 9

[0070] Example 9 is only different from Example 1 in that the separator is a PE separator.

[0071] Example 10

[0072] Example 10 is only different from Example 1 in that the thickness of the first coating is 40 μm and the compaction density is 3.0 g / cm 3 , the thickness of the second coating is 100 μm and the compaction density is 1.8 g / cm 3 .

[0073] Comparative Example 1

[0074] Comparative Example 1 is only different from Example 1 in that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, and PVDF are added to the NMP solvent in a mass ratio of 96:2:1:1. First, ultrasonic dispersion is carried out at 500 W for 30 minutes, and then mechanical stirring is carried out at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT, and PVDF are added to the NMP solvent in a mass ratio of 96:2:1:1. First, ultrasonic dispersion is carried out at 500 W for 30 minutes, and then mechanical stirring is carried out at 800 rpm for 2 hours to form the second slurry. Then, the first slurry is used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then the second slurry is used to prepare a polyanion active material layer on the first coating as the second coating to obtain a positive electrode sheet. Among them, the thickness of the first coating is 30 μm and the compaction density is 3.3 g / cm 3 , the thickness of the second coating is 90 μm and the compaction density is 2.1 g / cm 3 .

[0075] Comparative Example 2

[0076] Comparative Example 2 is only different from Example 1 in that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, and PVDF are added to the NMP solvent in a mass ratio of 96:2:1:1. First, ultrasonic dispersion is carried out at 500 W for 30 minutes, and then mechanical stirring is carried out at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT, and PVDF are added to the NMP solvent in a mass ratio of 96:2:1:1. First, ultrasonic dispersion is carried out at 500 W for 30 minutes, and then mechanical stirring is carried out at 800 rpm for 2 hours to form the second slurry.

[0077] The first slurry is used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then MWCNT and Super P are mixed in a mass ratio of 1:1 to prepare a conductive carbon layer on the first coating. Then, the second slurry is used to prepare a polyanion active material layer on the conductive carbon layer as the second coating to obtain a positive electrode sheet. Among them, the thickness of the first coating is 30 μm and the compaction density is 3.3 g / cm 3, the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 , the thickness of the conductive carbon layer is 1 μm, and the tap density is 0.7 g / cm 3 .

[0078] Comparative Example 3

[0079] The difference between Comparative Example 3 and Example 1 is only that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, PVDF and silicon carbide nanosheets are added to NMP solvent in a mass ratio of 95.9:2:1:1:0.1. First, ultrasonic dispersion is carried out at 500 W for 30 minutes, and then mechanical stirring is carried out at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT and PVDF are added to NMP solvent in a mass ratio of 96:2:1:1. First, ultrasonic dispersion is carried out at 500 W for 30 minutes, and then mechanical stirring is carried out at 800 rpm for 2 hours to form the second slurry. Then, the first slurry is used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then the second slurry is used to prepare a polyanion active material layer on the first coating as the second coating to obtain a positive electrode sheet. Among them, the thickness of the first coating is 30 μm, and the tap density is 3.3 g / cm 3 , the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 .

[0080] Comparative Example 4

[0081] The difference between Comparative Example 4 and Example 1 is only that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, PVDF and silicon carbide particles are added to NMP solvent in a mass ratio of 95.9:2:1:1:0.1. First, ultrasonic dispersion is carried out at 500 W for 30 minutes, and then mechanical stirring is carried out at 800 rpm for 2 hours to form the first slurry. NaFePO4, Super P, MWCNT and PVDF are added to NMP solvent in a mass ratio of 96:2:1:1. First, ultrasonic dispersion is carried out at 500 W for 30 minutes, and then mechanical stirring is carried out at 800 rpm for 2 hours to form the second slurry. Then, the first slurry is used to prepare a layered metal oxide active material layer on the aluminum foil as the first coating, and then the second slurry is used to prepare a polyanion active material layer on the first coating as the second coating to obtain a positive electrode sheet. Among them, the thickness of the first coating is 30 μm, and the tap density is 3.3 g / cm 3 , the thickness of the second coating is 90 μm, and the tap density is 2.1 g / cm 3 .

[0082] Comparative Example 5

[0083] The difference between Comparative Example 5 and Example 1 is only that NaNi 0.3 Mn 0.3 Fe 0.4 O2@NaFePO4, Super P, MWCNT, PVDF and silicon carbide nanowires (with a length of 2 μm and a diameter of 200 nm) were added to NMP solvent in a mass ratio of 95.9:2:1:1:0.1. First, ultrasonic dispersion was carried out at 500 W for 30 minutes, and then mechanical stirring was carried out at 800 rpm for 2 hours to form a slurry. Then, the slurry was used to prepare an active material layer on the aluminum foil to obtain a positive electrode sheet. Among them, the thickness of the active material layer was 40 μm, and the compaction density was 3.3 g / cm 3 .

[0084] The sodium-ion batteries of Examples 1 - 10 and Comparative Examples 1 - 5 were subjected to a needle puncture test. The needle puncture test standard was: a 5 mm tungsten steel needle was used to vertically puncture the battery at a speed of 25 mm / s and stay for 15 s. The results are shown in Table 1.

[0085] Table 1 Results of needle puncture test of sodium-ion batteries

[0086]

[0087] It can be seen from the examples and comparative examples that by compounding one-dimensional ceramic materials in the layered metal oxide active material layer, the thermal diffusion ability and stability of the positive electrode sheet can be significantly improved, and further the thermal management efficiency of the sodium-ion battery using this positive electrode sheet can be significantly improved. The peak temperature of the sodium-ion battery during needle puncture is below 200 °C, so that the sodium-ion battery will not cause thermal runaway under extreme abuse conditions such as needle puncture.

[0088] In addition, it can be seen from Examples 6 - 8 that the introduction of a conductive carbon layer can effectively reduce the internal resistance and the peak temperature of the needle puncture test. It can be seen from Example 9 that although the ordinary separator can pass the needle puncture test, the peak temperature is relatively high. It can be seen from Example 10 that increasing the compaction density can reduce the peak temperature.

[0089] The technical features of the above-described embodiments can be combined arbitrarily. For the sake of concise description, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, it should be considered to be within the scope described in this specification.

[0090] The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation on the scope of the invention patent. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several modifications and improvements can still be made, and these all fall within the protection scope of the present invention. Therefore, the protection scope of the present invention patent shall be subject to the appended claims.

Claims

1. A positive electrode sheet, characterized in that, The positive electrode sheet includes a current collector, and a first coating layer and a second coating layer sequentially attached to at least one surface of the current collector. One of the first coating layer and the second coating layer is selected from a layered metal oxide active material layer, and the other is selected from a polyanion active material layer. And the layered metal oxide active material layer contains a one-dimensional ceramic material.

2. The positive electrode sheet according to claim 1, characterized in that, The first coating layer is selected from a layered metal oxide active material layer, and the second coating layer is selected from a polyanion active material layer; and / or, the polyanion active material layer contains a one-dimensional ceramic material.

3. The positive electrode sheet according to claim 1, characterized in that, The mass fraction of the one-dimensional ceramic material in the layered metal oxide active material layer is 0.1% - 1%; and / or, the one-dimensional ceramic material is selected from ceramic nanowires and / or ceramic nanotubes.

4. The positive electrode sheet according to claim 3, characterized in that, When the one-dimensional ceramic material is selected from ceramic nanowires, the length of the ceramic nanowires is 1 μm - 10 μm, the diameter is 100 nm - 500 nm, and the aspect ratio is 5 - 15; and / or, the one-dimensional ceramic material is selected from at least one of silicon carbide nanowires, boron nitride nanowires, aluminum nitride nanowires, silicon carbide nanotubes, boron nitride nanotubes, and aluminum nitride nanotubes.

5. The positive electrode sheet according to claim 1, wherein The thickness of the layered metal oxide active material layer is 20 μm - 40 μm; And / or, the tap density of the layered metal oxide active material layer is 3.2 g / cm 3 - 3.4 g / cm 3 ; and / or, the thickness of the polyanion active material layer is 60 μm - 120 μm; And / or, the tap density of the polyanion active material layer is 2.0 g / cm 3 - 2.1 g / cm 3 .

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that, A conductive carbon layer is further interposed between the first coating layer and the second coating layer.

7. The positive electrode sheet according to claim 6, characterized in that, The thickness of the conductive carbon layer is 1 μm - 3 μm; And / or, the compacted density of the conductive carbon layer is 0.5 g / cm 3 - 0.7 g / cm 3 .

8. A sodium-ion battery, characterized in that, The sodium ion battery uses the positive electrode sheet according to any one of claims 1 to 7.

9. The sodium ion battery according to claim 8, characterized in that, The sodium ion battery uses a ceramic-coated separator.

10. An application of the sodium ion battery according to claim 8 or 9 in a battery module or a battery pack.

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