Positive electrode sheet, sodium-ion battery and application thereof

Abstract

The application relates to a positive plate, a sodium ion battery and application thereof, the positive plate comprising a current collector and a first coating and a second coating attached to at least one surface of the current collector in sequence, one of the first coating and the second coating is selected from a layered metal oxide active material layer, the other is selected from a polyanion active material layer, and the layered metal oxide active material layer contains a one-dimensional ceramic material. The application coats the layered metal oxide positive material and the polyanion positive material in layers, and composites the one-dimensional ceramic material in the layered metal oxide active material layer to construct a three-dimensional heat conduction network, so that the thermal conductivity and the mechanical strength of the layered metal oxide active material layer can be improved at the same time, the heat diffusion capacity and the stability of the positive plate can be significantly improved, the thermal management efficiency of the sodium ion battery using the positive plate can be significantly improved, local hot spots are inhibited, and the sodium ion battery will not cause thermal runaway under extreme abuse conditions such as needle puncture.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a positive electrode sheet, a sodium-ion battery and application thereof. BACKGROUND

[0002] Sodium-ion batteries are considered as potential substitutes for lithium-ion batteries due to abundant sodium resources and low cost. However, the thermal stability and cycle stability of layered metal oxide positive electrode materials in the positive electrode materials of sodium-ion batteries are poor, and the risk of thermal runaway is high. Although the polyanion positive electrode material has excellent safety, the energy density is insufficient. Therefore, the prior art mainly coats the polyanion positive electrode material on the layered metal oxide positive electrode material to obtain a composite material with relatively balanced comprehensive performance. However, this composite material is limited by the structure of the battery cell and cannot effectively lead out the local hot spot under extreme abuse conditions such as needle puncture, which easily leads to thermal runaway. SUMMARY

[0003] Therefore, it is necessary to provide a positive electrode sheet, a sodium-ion battery and application thereof to solve the above problems. 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, comprising a current collector and a first coating layer and a second coating layer attached to at least one surface of the current collector in sequence, 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.

[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 length of the ceramic nanowires is 1-10 microns, the diameter is 100-500 nanometers, and the aspect ratio is 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 compaction density of the layered metal oxide active material layer is 3.2 g / cm³. 3 -3.4g / cm 3 ;

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

[0014] And / or, the compaction density of the polyanionic active material layer is 2.0 g / cm³. 3 -2.1g / cm 3 .

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

[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 / cm³. 3 -0.7g / cm 3 .

[0018] A sodium-ion battery, wherein the sodium-ion battery uses the aforementioned positive electrode.

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

[0020] An application of a sodium-ion battery in a battery module or battery pack.

[0021] One-dimensional ceramic materials possess extremely high thermal conductivity and a fiber-reinforced effect. Therefore, this invention involves layering layered metal oxide cathode materials and polyanionic cathode materials, then composites one-dimensional ceramic materials within the layered metal oxide active material layer. This constructs a three-dimensional thermally conductive network within the layered metal oxide active material layer, simultaneously enhancing its thermal conductivity and mechanical strength. Consequently, it significantly improves the thermal diffusion capability and stability of the cathode sheet, thereby significantly improving the thermal management efficiency of sodium-ion batteries using this cathode sheet. It also suppresses the generation of localized hot spots, preventing thermal runaway in sodium-ion batteries under extreme abuse conditions such as needle penetration. Attached Figure Description

[0022] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the accompanying drawings needed to be used in the description of the embodiments or the prior art will be briefly introduced. Obviously, the accompanying drawings in the following description only represent some embodiments of the present application, and for those skilled in the art, other drawings can be obtained from these drawings without any creative effort.

[0023] Figure 1 Structure schematic diagram of a positive electrode sheet according to an embodiment of the present application.

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

[0025] In the drawings: 100, current collector; 101, first coating layer; 102, second coating layer; 103, conductive carbon layer. DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the present application, the present application will be described in more detail below. However, it should be understood that the present application can be realized 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 disclosure of the present application more thorough and comprehensive.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terminology used in the description of the present application herein is for the purpose of describing particular embodiments or examples only and is not intended to be limiting of the present application. As used herein, the term "and / or" is an optional range that includes any one of two or more related listed items, and also includes any and all combinations of the related listed items, including a combination of any two related listed items, a combination of any more related listed items, or a combination of all related listed items.

[0028] In the present application, when a numerical interval is involved, unless otherwise specified, the numerical interval is considered to be continuous and includes the minimum value and the maximum value of the range, and each value between the minimum value and the maximum value. Further, when the range is an integer, each integer between the minimum value and the maximum value of the range is included. In addition, when multiple ranges are provided to describe a feature or a characteristic, 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 included therein.

[0029] As Figure 1As shown, the positive electrode sheet provided by the present application includes a current collector 100 and a first coating layer 101 and a second coating layer 102 attached to at least one surface of the current collector 100 in sequence, such as the first coating layer 101 and the second coating layer 102 attached to any surface of the current collector 100 in sequence, or the first coating layer 101 and the second coating layer 102 attached to both surfaces of the current collector 100 in sequence.

[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, such as the first coating layer 101 being a layered metal oxide active material layer and the second coating layer 102 being a polyanion active material layer, or the first coating layer 101 being a polyanion active material layer and the second coating layer 102 being a layered metal oxide active material layer. Considering that the safety and stability of the polyanion positive electrode material are better than those of the layered metal oxide positive electrode 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, so that the polyanion active material layer can greatly isolate the layered metal oxide active material layer from direct contact with the electrolyte and inhibit side reactions.

[0031] Among them, the layered metal oxide active material layer of the present application contains one-dimensional ceramic material. The one-dimensional ceramic material has very high thermal conductivity, and at the same time, the one-dimensional ceramic material has fiber reinforcement effect, so that the present application 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, which can construct a three-dimensional heat conduction network in the layered metal oxide active material layer, and at the same time improve the defects of poor cycle stability and thermal stability of the layered metal oxide positive electrode material, and improve the thermal conductivity and mechanical strength of the layered metal oxide active material layer, so that the heat diffusion capacity and stability of the positive electrode sheet can be significantly improved, and the thermal management efficiency of the sodium ion battery using the positive electrode sheet can be significantly improved, and the generation of local hot spots can be inhibited, so that the sodium ion battery will not cause thermal runaway under extreme abuse conditions such as needle puncture.

[0032] It can be understood that when the one-dimensional ceramic material is introduced 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. The layered metal oxide positive electrode material and the polyanion positive electrode material are layered and coated to form a layered metal oxide active material layer and a polyanion active material layer in the present application, which can effectively exert the performance advantages of the layered metal oxide positive electrode material and the polyanion positive electrode material. Then, only in the layered metal oxide active material layer, the one-dimensional ceramic material is compounded, which can minimize the impact on the electrical properties when the one-dimensional ceramic material is introduced, and almost does not affect the electrical properties. Compared with the positive electrode sheet made of the composite material formed by coating the polyanion positive electrode material on the layered metal oxide positive electrode material, the positive electrode sheet of the present application is better in terms of rate performance and has better electrical properties. Therefore, when there is a demand to further improve the thermal diffusion capacity 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 energy density and other electrical properties of the positive electrode sheet. Therefore, in order to make the positive electrode sheet have excellent thermal diffusion capacity and stability, and at the same time have 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, and is further preferably ceramic nanowires. The length of the ceramic nanowires is preferably 1-10 μm, the diameter is preferably 100-500 nm, and the aspect ratio is preferably 5-15. The dispersibility and mechanical strength can be considered, and a more effective heat conduction path can be formed, so that the thermal conductivity and mechanical strength of the layered metal oxide active material layer can be better improved.

[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. It not only has a high thermal conductivity, 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 application comprises, in addition to the one-dimensional ceramic material, conventional layered metal oxide positive electrode material, conductive agent and binder, etc., the mass fraction of the layered metal oxide positive electrode 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 comprises polyanion positive electrode material, conductive agent and binder, etc., the mass fraction of the polyanion positive electrode 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 application, there is no special requirement for the selection of the layered metal oxide positive electrode material, the polyanion positive electrode material, the conductive agent and the binder, and they can be selected and controlled according to the conventional method. For example, the layered metal oxide positive electrode material is selected from Na x MO2 (M is selected from at least one or a combination of Fe, Co, Ni, Mn and V, and 0

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

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

[0040] As shown in FIG. 1, the present application provides a positive electrode sheet, which comprises a layered metal oxide active material layer 100, a first coating layer 101 and a second coating layer 102. Figure 2 As shown in FIG. 2, the present application also provides a positive electrode sheet of another embodiment, in which a conductive carbon layer 103 is further arranged between the first coating layer 101 and the second coating layer 102. The conductive carbon layer 103 can improve the heat conduction efficiency between the first coating layer 101 and the second coating layer 102, and also serve as an intermediate heat dissipation layer, thereby further improving the heat diffusion capacity of the positive electrode sheet. In addition, the conductive carbon layer 103 is also conducive to improving the electronic conduction between the first coating layer 101 and the second coating layer 102, thereby improving the capacity and other properties of the positive electrode sheet while improving the heat diffusion capacity.

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

[0042] Further, the thickness of the conductive carbon layer 103 is 1-3 μm, and the tap density of the conductive carbon layer 103 is 0.5-1.5 g / cm 3 -0.7 g / cm 3 .

[0043] The present application also provides a sodium ion battery using the positive electrode sheet. Since the positive electrode sheet has excellent heat diffusion capacity and stability, the sodium ion battery using the positive electrode sheet can inhibit 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 also comprises a negative electrode sheet, a separator and an electrolyte, etc., and the present application does not have special requirements for the negative electrode sheet, the separator and the electrolyte of the sodium ion battery, and a conventional design can be selected. For example, the active material of the negative electrode sheet is selected from hard carbon material, soft carbon material, graphite, etc., the conductive agent is selected from carbon nanotube (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, butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), etc., the separator is selected from polypropylene separator (PP), polyimide separator (PI), polyethylene separator (PE), ceramic coated separator, etc., and the electrolyte comprises sodium salt and organic solvent, wherein the sodium salt is selected from NaPF6, etc., and the organic solvent is selected from ethylene carbonate (EC), dimethyl carbonate (DMC), etc., and the present application will not be described here.

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

[0046] The present application does not have requirements for the form of the sodium ion battery, which can be a cylindrical battery, a square battery, etc.

[0047] The present application also provides an application of the sodium ion battery in a battery module or a battery pack, so that the battery module or the battery pack using the sodium ion battery of the present application is more reliable in safety.

[0048] Hereinafter, the technical solutions of the present application 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 application, and should not be regarded as limiting the scope of the present application. If the specific conditions are not specified in the examples, the conventional conditions or the conditions recommended by the manufacturer are used. If the reagents or instruments used are not specified by the manufacturer, they are all conventional products that can be obtained by purchase.

[0049] Example 1

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

[0051] The hard carbon material, Super P and CMC are mixed at a mass ratio of 97:1.5:1.5, coated on a carbon-coated aluminum foil, and rolled to a compacted density of 0.95 g / cm³ to obtain a negative electrode sheet.

[0052] An Al2O3@BN composite ceramic coating layer with a thickness of 3 μm is coated on a PE-based film with a thickness of 9 μm, wherein the mass fraction of BN in the composite ceramic coating layer is 30 wt%, to obtain a ceramic-coated separator.

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

[0054] A full-tab design is used, the positive electrode sheet, the negative electrode sheet and the separator are alternately wound, the tabs are welded after being rubbed flat, the electrolyte is injected after being put into the shell, and the 32700 cylindrical battery is formed after being sealed.

[0055] Example 2

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

[0057] Example 3

[0058] Example 3 is different from Example 1 only in that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, PVDF and silicon carbide nanowires (length of 1 μm, diameter of 100 nm) are added into NMP solvent in a mass ratio of 95.7:2:1:1:0.3, first dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a first slurry. NaFePO4, Super P, MWCNT and PVDF are added into NMP solvent in a mass ratio of 96:2:1:1, first dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a second slurry. Then, the first slurry is used to prepare a layered metal oxide active material layer on an aluminum foil as a first coating layer, and then the second slurry is used to prepare a polyanion active material layer on the first coating layer as a second coating layer to obtain a positive electrode sheet. The thickness of the first coating layer is 25 μm, and the compacted density is 3.3 g / cm 3 The thickness of the second coating layer is 95 μm, and the compacted density is 2.1 g / cm 3 .

[0059] Example 4

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

[0061] Example 5

[0062] Example 5 is only different from Example 1 in that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, PVDF and silicon carbide nanowires (length of 4 μm, diameter of 400 nm) are added into NMP solvent in a mass ratio of 95.2:2:1:1:0.8, first dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a first slurry. NaFePO4, Super P, MWCNT and PVDF are added into NMP solvent in a mass ratio of 96:2:1:1, first dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a second slurry. Then, the first slurry is used to prepare a layered metal oxide active material layer on an aluminum foil as a first coating layer, and then the second slurry is used to prepare a polyanion active material layer on the first coating layer as a second coating layer to obtain a positive electrode sheet. The thickness of the first coating layer is 30 μm, and the compacted density is 3.3 g / cm 3 The thickness of the second coating layer is 90 μm, and the compacted density is 2.1 g / cm 3 .

[0063] Example 6

[0064] Example 6 differs from Example 1 only in that a layered metal oxide active material layer is prepared on the aluminum foil as a first coating layer using a first slurry, then a conductive carbon layer is prepared on the first coating layer by mixing MWCNT and Super P at a mass ratio of 1:1, and then a polyanion active material layer is prepared on the conductive carbon layer as a second coating layer using a second slurry, to obtain the positive electrode sheet. The thickness of the first coating layer is 30 μm, the tap density is 3.3 g / cm 3 , the thickness of the second coating layer is 90 μm, 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 differs from Example 3 only in that a layered metal oxide active material layer is prepared on the aluminum foil as a first coating layer using a first slurry, then a conductive carbon layer is prepared on the first coating layer by mixing MWCNT and Super P at a mass ratio of 1:1, and then a polyanion active material layer is prepared on the conductive carbon layer as a second coating layer using a second slurry, to obtain the positive electrode sheet. The thickness of the first coating layer is 30 μm, the tap density is 3.3 g / cm 3 , the thickness of the second coating layer is 90 μm, 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 differs from Example 5 only in that a layered metal oxide active material layer is prepared on the aluminum foil as a first coating layer using a first slurry, then a conductive carbon layer is prepared on the first coating layer by mixing MWCNT and Super P at a mass ratio of 1:1, and then a polyanion active material layer is prepared on the conductive carbon layer as a second coating layer using a second slurry, to obtain the positive electrode sheet. The thickness of the first coating layer is 30 μm, the tap density is 3.3 g / cm 3 , the thickness of the second coating layer is 90 μm, 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 differs from Example 1 only in that the separator is a PE separator.

[0071] Example 10

[0072] Example 10 differs from Example 1 only in that the first coating layer has a thickness of 40 μm and a compacted density of 3.0 g / cm 3 , and the second coating layer has a thickness of 100 μm and a compacted density of 1.8 g / cm 3 .

[0073] Comparative Example 1

[0074] Comparative Example 1 differs from Example 1 only in that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT and PVDF are added to NMP solvent in a mass ratio of 96:2:1:1, first dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a first slurry. NaFePO4, Super P, MWCNT and PVDF are added to NMP solvent in a mass ratio of 96:2:1:1, first dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a second slurry. Then a layered metal oxide active material layer is prepared on an aluminum foil using the first slurry as a first coating layer, and then a polyanion active material layer is prepared on the first coating layer using the second slurry as a second coating layer to obtain a positive electrode sheet. The thickness of the first coating layer is 30 μm, and the compacted density is 3.3 g / cm 3 , and the thickness of the second coating layer is 90 μm, and the compacted density is 2.1 g / cm 3 .

[0075] Comparative Example 2

[0076] Comparative Example 2 differs from Example 1 only in that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT and PVDF are added to NMP solvent in a mass ratio of 96:2:1:1, first dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a first slurry. NaFePO4, Super P, MWCNT and PVDF are added to NMP solvent in a mass ratio of 96:2:1:1, first dispersed by ultrasonic wave at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a second slurry.

[0077] A layered metal oxide active material layer is prepared on an aluminum foil using the first slurry as a first coating layer, then a conductive carbon layer is prepared on the first coating layer by mixing MWCNT and Super P in a mass ratio of 1:1, and then a polyanion active material layer is prepared on the conductive carbon layer using the second slurry as a second coating layer to obtain a positive electrode sheet. The thickness of the first coating layer is 30 μm, and the compacted density is 3.3 g / cm 3, the thickness of the second coating layer is 90 pm, and the compacted density is 2.1 g / cm 3 , the thickness of the conductive carbon layer is 1 pm, and the compacted density is 0.7 g / cm 3 .

[0078] Comparative Example 3

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

[0080] Comparative Example 4

[0081] Comparative Example 4 differs from Example 1 only in that NaNi 0.3 Mn 0.3 Fe 0.4 O2, Super P, MWCNT, PVDF and silicon carbide nanosheets are added into NMP solvent at a mass ratio of 95.9:2:1:1:0.1, first ultrasonic dispersed at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a first slurry. NaFePO4, Super P, MWCNT and PVDF are added into NMP solvent at a mass ratio of 96:2:1:1, first ultrasonic dispersed at 500 W for 30 minutes, and then mechanically stirred at 800 rpm for 2 hours to form a second slurry. Then, the first slurry is used to prepare a layered metal oxide active material layer on an aluminum foil as a first coating layer, and then the second slurry is used to prepare a polyanion active material layer on the first coating layer as a second coating layer to obtain a positive electrode sheet. The thickness of the first coating layer is 30 pm, and the compacted density is 3.3 g / cm 3 , the thickness of the second coating layer is 90 pm, and the compacted density is 2.1 g / cm 3 .

[0082] Comparative Example 5

[0083] Comparative Example 5 differs from Example 1 only in that NaNi 0.3 Mn 0.3 Fe 0.4 O2@NaFePO4, Super P, MWCNT, PVDF and silicon carbide nanowires (2 μm in length and 200 nm in diameter) were added into NMP solvent at a mass ratio of 95.9:2:1:1:0.1, and were first dispersed by ultrasonic waves at 500 W for 30 minutes, and then were mechanically stirred at 800 rpm for 2 hours to form a slurry. Then the slurry was used to prepare an active material layer on an aluminum foil to obtain a positive electrode sheet. The thickness of the active material layer was 40 μm, and the compacted 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 that a 5 mm tungsten steel needle was vertically punctured into the battery at a speed of 25 mm / s, and was stopped for 15 s. The results are shown in Table 1.

[0085] Table 1 Needle puncture test results of sodium ion batteries

[0086]

[0087] From the examples and comparative examples, it can be seen that the one-dimensional ceramic material can be combined in the layered metal oxide active material layer to significantly improve the thermal diffusion capacity and stability of the positive electrode sheet, and further significantly improve the thermal management efficiency of the sodium ion battery using the positive electrode sheet. 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, from Examples 6-8, it can be seen that the introduction of the conductive carbon layer can effectively reduce the internal resistance and the peak temperature of the needle puncture test. From Example 9, it can be seen that although the ordinary separator can pass the needle puncture test, the peak temperature is high. From Example 10, it can be seen that the increase of the compacted density can reduce the peak temperature.

[0089] The technical features of the above-described examples can be combined in any manner. In order to make the description simple, all possible combinations of the technical features in the above-described examples are not described, however, as long as the combinations of the technical features do not exist contradictions, they should be considered as the scope of the present disclosure.

[0090] The above embodiments only express several implementation manners of the present application, and the description is more specific and detailed, but it should not be understood as a limitation on the scope of the patent. It should be noted that for ordinary skilled persons in the art, without departing from the concept of the present application, several modifications and improvements can be made, which are within the scope of protection of the present application. Therefore, the protection scope of the patent of the present application should be subject to the appended claims.

Claims

1. A positive electrode sheet, characterized by, The positive electrode sheet comprises a current collector and a first coating layer and a second coating layer attached to at least one surface of the current collector in sequence, 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, the layered metal oxide active material layer consists of 92%-97% of a layered metal oxide positive electrode material, 1%-5% of a conductive agent, 1%-3% of a binder, and 0.1%-1% of a one-dimensional ceramic material 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, and the thickness of the layered metal oxide active material layer is 20-40 μm, and the thickness of the polyanion active material layer is 60-120 μm.

2. The positive electrode sheet according to claim 1, characterized by 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 by When the one-dimensional ceramic material is selected from ceramic nanowires, the length of the ceramic nanowires is 1-10 μm, the diameter is 100-500 nm, and the aspect ratio is 5-15.

4. The positive electrode sheet according to claim 1, characterized by The compacted density of the layer of layered metal oxide active material is 3.2 g / cm 3 - 3.4 g / cm 3 ; and / or the compacted density of the polyanion active material layer is 2.0 g / cm 3 - 2.1 g / cm 3 .

5. The positive electrode sheet according to any one of claims 1 to 4, characterized by, A conductive carbon layer is further sandwiched between the first coating layer and the second coating layer.

6. The positive electrode sheet according to claim 5, characterized by The thickness of the conductive carbon layer is 1-3 μm. and / or the compacted density of the electrically conductive carbon layer is 0.5 g / cm 3 -0.7 g / cm 3 .

7. A sodium-ion battery, characterized in that, The sodium ion battery uses the positive electrode sheet according to any one of claims 1-6.

8. The sodium-ion battery of claim 7, wherein, The sodium ion battery uses a ceramic-coated separator.

9. Use of the sodium ion battery according to claim 7 or 8 in a battery module or a battery pack.

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