Secondary battery and application thereof

Abstract

The invention belongs to the technical field of secondary batteries, and particularly relates to a secondary battery. According to the secondary battery disclosed by the invention, the structure of the negative pole piece is optimally designed, namely, the first negative active coating, the first conductive layer, the second negative active coating and the second conductive layer are arranged on the surface of at least one side of the negative current collector, and the metal sulfide or the metal oxide is selected as the first negative active material; and the carbon-containing material is used as a second negative electrode active material. The secondary battery provided by the invention effectively improves the problems of short cycle life and poor rate capability, and has a better application prospect.

Description

Technical Field

[0001] The present application belongs to the field of secondary battery technology, specifically relates to a secondary battery, especially a sodium ion secondary battery, and further discloses its application. Background Art

[0002] With the rapid development of the new energy industry, the demand for high-performance energy storage devices is increasing. Sodium-ion batteries, due to their abundant sodium resources and low cost, hold broad application prospects in large-scale energy storage. However, practical applications have shown that the performance of sodium-ion batteries still needs to be improved. In particular, the performance of their anode materials is one of the key factors limiting their development.

[0003] In sodium-ion batteries, the performance of the anode material plays a key role in the overall performance of the battery. Currently, commonly used sodium-ion battery anode materials include carbon materials, alloys, and transition metal compounds. Hard carbon materials, as a common sodium-ion battery anode material, offer advantages such as widespread availability, low cost, and structural stability. Furthermore, hard carbon has a complex microstructure, typically containing disordered graphite crystallites and numerous defects. This provides abundant sites for sodium ion storage, resulting in high specific capacity and good cycling stability. However, hard carbon also has some shortcomings, such as relatively low electronic conductivity, which limits the battery's rate capability. Furthermore, the specific capacity of hard carbon still needs to be further improved, and it cannot meet the requirements for high energy density performance. Although transition metal compounds have high theoretical specific capacity, they experience significant volume changes during charge and discharge, leading to electrode powder shedding and ultimately poor cycling performance. Therefore, there is a need in the art to develop anode electrodes with improved cycling and rate performance to meet the demands of high-performance batteries. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present application is to provide a secondary battery to solve the problems of short cycle life and poor rate performance of negative electrode materials of sodium ion batteries in the prior art.

[0005] The second technical problem to be solved by this application is to provide applications of the above-mentioned secondary battery.

[0006] In order to solve the above technical problems, the secondary battery described in the present application includes a negative electrode plate;

[0007] The negative electrode plate includes a negative electrode current collector, and a first negative electrode active coating, a first conductive layer, a second negative electrode active coating, and a second conductive layer provided on at least one side of the negative electrode current collector; the first negative electrode active coating is close to the negative electrode current collector, and the second conductive layer is away from the negative electrode current collector; the first conductive layer is provided between the first negative electrode active coating and the second negative electrode active coating, wherein,

[0008] The first negative electrode active coating layer comprises a first negative electrode active material, wherein the first negative electrode active material comprises at least one of a metal sulfide or a metal oxide;

[0009] The second negative electrode active coating layer includes a second negative electrode active material, and the second negative electrode active material includes a carbon material.

[0010] Furthermore, the second negative electrode active coating is disposed between the first conductive layer and the second conductive layer.

[0011] Furthermore, the thickness Tb of the second negative electrode active coating layer is greater than the thickness Ta of the first negative electrode active coating layer, and the thickness T1 of the first conductive layer is greater than the thickness T2 of the second conductive layer.

[0012] Furthermore, the first conductive layer comprises a first conductive material; the second conductive layer comprises a second conductive material; and the conductivity of the first conductive material is greater than the conductivity of the second conductive material.

[0013] Furthermore, the thickness of the second negative electrode active coating layer Tb>the thickness of the first negative electrode active coating layer Ta>the thickness of the first conductive layer T1>the thickness of the second conductive layer T2.

[0014] Furthermore, the negative electrode plate has at least one of the following features (a) to (d):

[0015] (a) the thickness Ta of the first negative electrode active coating is 10-30 μm;

[0016] (b) the thickness Tb of the second negative electrode active coating is 50-130 μm;

[0017] (c) the thickness T1 of the first conductive layer is 1.5-8 μm;

[0018] (d) The thickness T2 of the second conductive layer is 1-3 μm.

[0019] Furthermore, based on the total mass of the first negative electrode active material and the second negative electrode active material, the mass content of the first negative electrode active material is 5-30 wt %, and the mass content of the second negative electrode active material is 70-95 wt %.

[0020] Further, the metal sulfide includes at least one of titanium disulfide (TiS2), molybdenum disulfide (MoS2), tungsten disulfide (WS2), tin disulfide (SnS2), and vanadium disulfide (VS2);

[0021] The metal oxide includes at least one of iron oxide (Fe2O3), nickel oxide (NiO), cobalt oxide (Co3O4), molybdenum oxide (MoO3), and manganese oxide (MnO2);

[0022] The average particle size of the metal oxide or metal sulfide is 100-1000 nm;

[0023] The carbon material includes hard carbon, soft carbon or graphite, or a mixture of the hard carbon, soft carbon or graphite.

[0024] Furthermore, based on the total amount of the first conductive material and the second conductive material, the mass content of the first conductive material is 60-70 wt %, and the mass content of the second conductive material is 30-40 wt %.

[0025] Furthermore, the first conductive material includes at least one of multilayer graphene, conductive graphite, multi-walled CNT, carbon nanotube or carbon nanofiber; and / or,

[0026] The second conductive material includes at least one of single-walled CNT, single-layer graphene, or acetylene black.

[0027] Furthermore, the secondary battery further includes a positive electrode plate, wherein the positive electrode plate includes a positive electrode active coating containing a positive electrode active material, and the positive electrode active material includes a sodium transition metal oxide.

[0028] The present application also discloses an electric device, comprising the secondary battery, wherein the secondary battery serves as a power supply for the electric device.

[0029] The secondary battery described in this application utilizes an optimized design of the negative electrode sheet structure, namely, a first negative electrode active coating, a first conductive layer, a second negative electrode active coating, and a second conductive layer structure disposed on at least one side of the negative electrode current collector, and selects a metal sulfide or metal oxide as the first negative electrode active material and a carbonaceous material as the second negative electrode active material. The metal sulfide or metal oxide, when used as a negative electrode material for a sodium ion battery, can provide a high theoretical capacity, while also exhibiting good cycle stability and capacity retention. Furthermore, the further provision of the first and second conductive layers effectively addresses the issues of poor conductivity and large volume expansion during charge and discharge of metal sulfides or metal oxides, which lead to rapid performance degradation over long charge and discharge cycles. Furthermore, the material's conductivity is effectively enhanced, and the volume expansion of the metal oxide or metal sulfide is suppressed, effectively resolving the short cycle life and poor rate performance of negative electrode materials for sodium ion batteries in the prior art. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to make the content of this application easier to understand, the following further describes this application in detail based on the specific embodiments of this application and in conjunction with the accompanying drawings, wherein:

[0031] Figure 1 This is a schematic structural diagram of the negative electrode sheet described in this application;

[0032] Figure 2 Graph showing the cycling performance of the sodium ion battery tested in Example 1 and Comparative Example 1 of the present application;

[0033] The reference numerals in the figure are as follows: 1-negative electrode current collector, 2-first negative electrode active coating, 3-first conductive layer, 4-second negative electrode active coating, 5-second conductive layer. DETAILED DESCRIPTION

[0034] The following will be combined with the drawings in the embodiments of this application to clearly and completely describe the technical solutions in the embodiments of this application. Obviously, the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0035] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" and any variations thereof in the specification of this application and the above-mentioned drawings are intended to cover non-exclusive inclusions.

[0036] In the description of the embodiments of this application, the technical terms "first," "second," etc. are used only to distinguish different objects and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, the meaning of "plurality" is more than two, unless otherwise specifically defined.

[0037] References herein to "embodiments" mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it constitute an independent or alternative embodiment that is mutually exclusive of other embodiments. It is understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0038] As used herein, "ranges" are defined in terms of lower and upper limits. A given range is defined by selecting a lower limit and an upper limit, the selected lower and upper limits defining the boundaries of the particular range. Ranges defined in this manner may be inclusive or exclusive and may be combined arbitrarily, i.e., any lower limit may be combined with any upper limit to form a range.

[0039] In order to solve the problems of short cycle life and poor rate performance of negative electrode materials in traditional sodium ion batteries, the first aspect of the present application provides a secondary battery, the secondary battery comprising a negative electrode plate;

[0040] The negative electrode plate includes a negative electrode current collector, and a first negative electrode active coating, a first conductive layer, a second negative electrode active coating, and a second conductive layer provided on at least one side of the negative electrode current collector; the first negative electrode active coating is close to the negative electrode current collector, and the second conductive layer is away from the negative electrode current collector; the first conductive layer is provided between the first negative electrode active coating and the second negative electrode active coating, wherein,

[0041] The first negative electrode active coating layer comprises a first negative electrode active material, wherein the first negative electrode active material comprises at least one of a metal sulfide or a metal oxide;

[0042] The second negative electrode active coating layer includes a second negative electrode active material, and the second negative electrode active material includes a carbon material.

[0043] In the secondary battery described in this application, the negative electrode plate adopts a multi-layer negative electrode and uses a carbon material and a metal compound (i.e., a metal sulfide or metal oxide) as the negative electrode active material. The metal sulfide or metal oxide can provide a higher theoretical capacity, while also giving the secondary battery good cycle stability and capacity retention; while the carbon material can give the secondary battery a higher specific capacity and good cycle stability. The negative electrode plate described in this application, by providing a conductive layer on the surface of the metal sulfide or metal oxide and the carbon material, can effectively enhance the conductivity of the negative electrode plate, while also helping to suppress the volume expansion of the metal compound, further improving the cycle life and rate performance of the battery.

[0044] In an optional embodiment, the second negative electrode active coating is disposed between the first conductive layer and the second conductive layer. That is, the second conductive layer serves as the outermost layer of the negative electrode plate. This allows the second conductive layer to absorb the expansion stress of the second active material, thereby reducing the expansion rate of the plate and improving battery cycle performance.

[0045] In the secondary battery described in the present application, the thickness Tb of the second negative electrode active coating layer is greater than the thickness Ta of the first negative electrode active coating layer, and the thickness T1 of the first conductive layer is greater than the thickness T2 of the second conductive layer. By setting the thickness Tb of the second negative electrode active coating layer greater than the thickness Ta of the first negative electrode active coating layer, the cycle performance of the second negative electrode active coating layer formed of the carbon material is more outstanding. At the same time, the thickness setting of the first negative electrode active layer also effectively guarantees the performance of the negative electrode plate. By setting the thickness T1 of the first conductive layer greater than the thickness T2 of the second conductive layer, the conductive layer can effectively suppress the volume expansion of the transition metal compound during the cycle, which is beneficial to improving the stability of the material. The thickness of the first conductive layer disposed between the first negative electrode active layer and the second negative electrode active coating layer is greater, which also helps to improve the problem of insufficient conductivity of the transition metal compound and improve the overall performance of the negative electrode plate.

[0046] In an optional embodiment, in the negative electrode sheet of the secondary battery described in the present application, the first conductive layer contains a first conductive material, and the second conductive layer contains a second conductive material; wherein the conductivity of the first conductive material is greater than the conductivity of the second conductive material.

[0047] The negative electrode sheet of the secondary battery described in this application achieves improved overall performance of the negative electrode sheet by adjusting the conductivity of the first and second conductive layers to form a matching conductive structure, thereby optimizing the application performance of the secondary battery. In particular, setting the conductivity of the first conductive material to be greater than that of the second conductive material effectively mitigates the poor conductivity of transition metal compounds. Placing a highly conductive material between the two layers of the negative electrode active coating accelerates the mobility of electrons and sodium ions within the electrode material, thereby improving overall performance of the negative electrode sheet.

[0048] In an optional embodiment, for the negative electrode plate of the secondary battery described in the present application, the thickness of the second negative electrode active coating layer Tb>the thickness of the first negative electrode active coating layer Ta>the thickness of the first conductive layer T1>the thickness of the second conductive layer T2.

[0049] The negative electrode plate of the secondary battery described in the present application is formed by further adjusting the thickness of the second negative electrode active coating, the first negative electrode active coating, the first conductive layer and the second conductive layer to match each other, thereby forming a negative electrode plate with an adaptive thickness structure, effectively improving the expansion of the negative electrode plate, and thus improving the cycle performance of the battery.

[0050] In an optional embodiment, the thickness Ta of the first negative electrode active coating layer is 10-30 μm. As an exemplary embodiment, the thickness Ta of the first negative electrode active coating layer is adjusted to 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, 22 μm, 24 μm, 26 μm, 28 μm, 30 μm, or the like, or within a range consisting of any of the above values. The thickness of the first negative electrode active coating layer in the present application is set within the above range. While ensuring the thickness of the entire negative electrode sheet, this thickness setting ensures the usage of the first negative electrode active material, fully realizing the theoretical capacity contribution of the metal sulfide or metal oxide, while also avoiding the problem of the metal sulfide or metal oxide affecting the overall conductive performance due to excessive thickness.

[0051] In an optional embodiment, the thickness Tb of the second negative electrode active coating layer is 50-130 μm. As an exemplary embodiment, the thickness Tb of the second negative electrode active coating layer is adjusted to 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 130 μm, or the like, or within a range comprised of any of the above values. The thickness of the second negative electrode active coating layer in the present application is set within the above range. While ensuring the thickness of the entire negative electrode sheet, this thickness setting ensures the amount of second negative electrode active material used, fully utilizing the advantages of the carbon material in terms of specific capacity and cycle stability, while also avoiding the problem of insufficient energy density of the negative electrode sheet due to excessive carbon material due to excessive thickness.

[0052] In an optional embodiment, the thickness T1 of the first conductive layer is 1.5-8 μm; as an exemplary embodiment, the thickness T1 of the first conductive layer is adjusted to 1.5 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, etc., or within the range of any of the above values. The thickness of the first conductive layer of the present application is set within the above range. While ensuring the thickness of the entire negative electrode sheet, the conductive advantage of the first conductive layer is maximized. The first conductive layer is located between the first negative electrode active coating and the second negative electrode active coating. With its higher conductivity, it can compensate for the unsatisfactory conductivity of the metal sulfide / metal oxide and carbon material itself. At the same time, it also avoids the problem of the first conductive layer being thicker and affecting the synergistic performance between the first negative electrode active coating and the second negative electrode active coating.

[0053] In an optional embodiment, the thickness T2 of the second conductive layer is 1-3 μm; as an exemplary embodiment, the thickness T2 of the second conductive layer is adjusted to 1 μm, 1.2 μm, 1.5 μm, 1.8 μm, 2 μm, 2.2 μm, 2.5 μm, 2.8 μm, 3 μm, etc., or within the range of any of the above values. The thickness of the second conductive layer of the present application is set within the above range, which effectively guarantees the conductive performance of the second conductive layer while ensuring the thickness of the entire negative electrode sheet. At the same time, it can form a certain conductivity difference with the first conductive layer, which is more conducive to promoting electron transfer; at the same time, it also avoids the problem of the entire electrode sheet being too thick due to the thick size of the second conductive layer.

[0054] In an optional embodiment, in the negative electrode sheet of the secondary battery, the mass content of the first negative electrode active material is 5-30wt%, and the mass content of the second negative electrode active material is 70-95wt%, based on the total amount of the first negative electrode active material and the second negative electrode active material. As an exemplary embodiment, the mass content of the first negative electrode active material is adjusted to 5wt%, 8wt%, 10wt%, 12wt%, 15wt%, 18wt%, 20wt%, 22wt%, 25wt%, 28wt%, 30wt%, or the like, or within any range thereof; and the mass content of the second negative electrode active material is correspondingly 70wt%, 72wt%, 75wt%, 78wt%, 80wt%, 82wt%, 85wt%, 88wt%, 90wt%, 92wt%, 95wt%, or the like, or within any range thereof. The reasonable ratio between the first negative electrode active material and the second negative electrode active material in the present application is more conducive to achieving a "balance" between the better cycle stability and capacity retention of the transition metal compound and the higher specific capacity and good cycle stability of the carbon material, thereby offsetting the defective effects of the two to the greatest extent.

[0055] In an optional embodiment, the metal sulfide in the negative electrode of the secondary battery includes at least one of titanium disulfide (TiS2), molybdenum disulfide (MoS2), tungsten disulfide (WS2), tin disulfide (SnS2), and vanadium disulfide (VS2), or a mixture thereof. These metal sulfides have the advantage of being readily available and can provide the negative electrode with a higher theoretical capacity, while also enabling the secondary battery to have better cycling stability and capacity retention.

[0056] In an optional embodiment, the metal oxide in the negative electrode of the secondary battery includes at least one of, or a mixture of, iron oxide (Fe2O3), nickel oxide (NiO), cobalt oxide (Co3O4), molybdenum oxide (MoO3), and manganese oxide (MnO2). These metal oxides have the advantage of being readily available and can provide the negative electrode with a higher theoretical capacity, while also enabling the secondary battery to have better cycle stability and capacity retention.

[0057] In an optional embodiment, in the negative electrode plate of the secondary battery, the average particle size of the metal oxide or metal sulfide is 100-1000 nm, and preferably the average particle size is 400-500 nm. As an exemplary embodiment, the average particle size of the metal oxide or metal sulfide is selected to be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm, 800 nm, 850 nm, 900 nm, 950 nm, 1000 nm, etc., or within a range consisting of any of the above values.

[0058] In an optional embodiment, the carbon material in the negative electrode of the secondary battery includes one or a mixture of hard carbon, soft carbon, or graphite. This carbon material has the advantage of being readily available and can provide the negative electrode with a high specific capacity and good cycling stability, thereby improving the cycling stability of the secondary battery.

[0059] The negative electrode plate of the secondary battery described in the present application is made of nano-porous metal oxide or metal sulfide material. The particle size of the selected metal oxide or metal sulfide material is 100-1000nm. During the charge and discharge process, its internal porous structure can not only buffer the volume change caused by the charge and discharge process, but also increase the contact area between the electrode and the electrolyte, and has high capacity, excellent cycle and rate performance.

[0060] In an optional embodiment, in the negative electrode sheet of the secondary battery, based on the total amount of the first conductive material and the second conductive material, the mass content of the first conductive material is 60-70wt%, and the mass content of the second conductive material is 30-40wt%. As an exemplary embodiment, the mass content of the first conductive material is adjusted to 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, etc., or within the range of any of the above values; and the mass content of the second conductive material is correspondingly 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, 40wt%, etc., or within the range of any of the above values. In the negative electrode sheet, by setting the amount of the first conductive material to be higher than the second conductive material, on the one hand, the "conductor" function of the first conductive layer between the first negative electrode active coating and the second negative electrode active coating is ensured, and on the other hand, the synergistic effect between the first conductive layer and the second conductive layer ensures the balanced "conductivity" performance of the entire negative electrode sheet.

[0061] In an optional embodiment, in the negative electrode of the secondary battery, the first conductive material comprises at least one of multilayer graphene, conductive graphite, multi-walled CNTs, carbon nanotubes, or carbon nanofibers, or a mixture thereof. Selecting a material with higher conductivity as the first conductive material can effectively improve the poor conductivity of transition metal compounds. Placing a highly conductive material between the two layers of the negative electrode active coating can accelerate the mobility of electrons and sodium ions in the electrode material, thereby improving the overall performance of the negative electrode.

[0062] In an optional embodiment, the second conductive material in the negative electrode of the secondary battery includes at least one of single-walled carbon nanotubes (CNTs), single-layer graphene, or acetylene black, or a mixture thereof. The second conductive material is selected from the aforementioned conductive agents, and due to its difference in conductivity from the first conductive material, it helps to accelerate the movement of electrons within the entire electrode, thereby improving the overall performance of the negative electrode.

[0063] In an optional embodiment, in the negative electrode sheet of the secondary battery, the mass content of the first negative electrode active material is 80-95wt% based on the mass of the first negative electrode active coating. As an exemplary embodiment, the mass content of the first negative electrode active material is adjusted to 80wt%, 82wt%, 85wt%, 88wt%, 90wt%, 92wt%, 95wt%, etc., or within a range consisting of any of the above values. In the first negative electrode active coating of the present application, the mass content of the first negative electrode active material reaches 80-95wt%, ensuring the active effect of the entire negative electrode active coating. At the same time, the stability of the active coating can also be ensured by adding other components such as a binder.

[0064] In an optional embodiment, in the negative electrode sheet of the secondary battery, the mass content of the second negative electrode active material is 80-95wt% based on the mass of the second negative electrode active coating. As an exemplary embodiment, the mass content of the second negative electrode active material is adjusted to 80wt%, 82wt%, 85wt%, 88wt%, 90wt%, 92wt%, 95wt%, etc., or within a range consisting of any of the above values. In the second negative electrode active coating of the present application, the mass content of the second negative electrode active material reaches 80-95wt%, ensuring the active effect of the entire negative electrode active coating. At the same time, the stability of the active coating can be ensured by adding other ingredients such as a binder.

[0065] In an optional embodiment, in the negative electrode sheet of the secondary battery, based on the mass of the first conductive layer, the mass content of the first conductive material is 90-97wt%; as an exemplary embodiment, the mass content of the first conductive material is adjusted to 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, etc., or within a range consisting of any of the above values. The mass content of the first conductive material in the first conductive layer of the present application is as high as 90-97wt%. The higher amount of conductive material added effectively guarantees the performance requirements of the conductive layer. At the same time, the stability of the conductive layer can also be guaranteed by adding other components such as binders.

[0066] In an optional embodiment, in the negative electrode sheet of the secondary battery, based on the mass of the second conductive layer, the mass content of the second conductive material is 90-97wt%; as an exemplary embodiment, the mass content of the second conductive material is adjusted to 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, 95wt%, 96wt%, 97wt%, etc., or within a range consisting of any of the above values. The mass content of the second conductive material in the second conductive layer of the present application is as high as 90-97wt%. The higher amount of conductive material added effectively guarantees the performance requirements of the conductive layer. At the same time, the stability of the conductive layer can also be guaranteed by adding other components such as binders.

[0067] In an optional embodiment, the secondary battery further comprises a positive electrode sheet, wherein the positive electrode sheet comprises a positive electrode active coating containing a positive electrode active material, wherein the positive electrode active material comprises a sodium transition metal oxide. The sodium transition metal oxide comprises Na a Ni b Fe c Mn d X e Y fO2, wherein 0.90≤a≤1.10, 0.10≤b≤0.60, 0.10≤c≤0.40, 0.10≤d≤0.40, 0≤e≤0.02, 0≤f≤0.01, X includes at least one of Cu and B, and Y includes at least one of Ca, Ti, Sr, and Cr.

[0068] In a second aspect, the present application further discloses an electric device, namely comprising the secondary battery of the first party, wherein the secondary battery serves as a power supply for the electric device.

[0069] The present application is further described in detail below with reference to specific embodiments and the accompanying drawings. Those skilled in the art will be able to implement the present application based on these descriptions. Furthermore, the embodiments of the present application described below are generally only a portion of the embodiments of the present application, rather than all of the embodiments. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments in the present application without creative effort should fall within the scope of protection of the present application.

[0070] In the following embodiments of the present application, the secondary battery includes a negative electrode sheet and a positive electrode sheet, wherein the structure of the negative electrode sheet is as follows Figure 1 shown.

[0071] like Figure 1 In the structure shown, the negative electrode sheet includes a negative electrode current collector 1, and a first negative electrode active coating 2, a first conductive layer 3, a second negative electrode active coating 4, and a second conductive layer 5 stacked in sequence on at least one side surface of the negative electrode current collector 1; the first negative electrode active coating 2 is close to the negative electrode current collector, and the second conductive layer 5 is far away from the negative electrode current collector. The first conductive layer 3 is arranged between the first negative electrode active coating 2 and the second negative electrode active coating 4, and the second negative electrode active coating 4 is arranged between the first conductive layer 3 and the second conductive layer 5.

[0072] The present application is further described in detail below with reference to specific embodiments. These embodiments should not be construed as limiting the scope of protection claimed in this application.

[0073] Example 1

[0074] In this embodiment, a sodium ion secondary battery is prepared, and the specific preparation process is as follows.

[0075] Preparation of negative electrode sheet

[0076] S1. A transition metal compound Fe2O3 (average particle size 400 nm), a binder PVDF, and a conductive carbon black were mixed in water at a mass ratio of 8:1:1 and stirred evenly to prepare a first negative electrode slurry. The first negative electrode slurry was then coated on both sides of the negative electrode current collector copper foil and baked to form a first negative electrode active coating with a thickness of 20 μm. The surface density of the first negative electrode active coating was 46 mg / 1540.25 cm 2 ;

[0077] S2. Conductive graphite and binder CMC are mixed and dispersed in water in a mass ratio of 10:1 to prepare a first conductive slurry. The first conductive slurry is then coated on the first negative electrode active coating and dried to obtain a first conductive layer with a thickness of 2 μm. The surface density of the first conductive layer is 5 mg / 1540.25 cm 2 ;

[0078] S3, hard carbon, binder PVDF, and conductive agent were mixed in water at a mass ratio of 8:1:1, stirred evenly, and a second negative electrode slurry was prepared. The second negative electrode slurry was then coated on the first conductive layer and dried to obtain a second negative electrode active coating with a thickness of 100 μm. The surface density of the first negative electrode active coating was 230 mg / 1540.25 cm 2 ;

[0079] S4. Mix and disperse the monolayer graphene and the adhesive CMC in water at a mass ratio of 10:1 to prepare a second conductive slurry. Then, apply the second conductive slurry on the second negative electrode active coating and dry it to obtain a second conductive layer with a thickness of 1 μm. The surface density of the second conductive layer is 6 mg / 1540.25 cm 2 .

[0080] Preparation of positive electrode

[0081] The positive electrode active material (NaNi 0.5 Fe 0.3 Mn 0.2 O2), conductive carbon black, and binder PVDF are mixed in a mass ratio of 95:3.2:1.8, and N-methylpyrrolidone is used as a solvent to prepare the above mixture into a positive electrode active material slurry; the positive electrode active material slurry is coated on both surfaces of an aluminum foil, and the positive electrode sheet is obtained after drying, rolling, slitting and sheeting.

[0082] Preparation of secondary batteries:

[0083] The negative electrode sheet, PP separator layer, and positive electrode sheet were stacked and wound in sequence to form a core. The dry core was encapsulated in aluminum-plastic film and baked at 105°C. Then, 16g of electrolyte (electrolyte formula: 1M NaPF6 + a 1:1 EC:DME mixed organic solvent by mass ratio + 5% FEC) was injected. The core was then allowed to stand at 45°C and sealed at 45°C for formation. After formation, the air bag was removed and the core was vacuum-sealed. After volume separation at room temperature, a sodium-ion secondary battery was prepared.

[0084] Example 2

[0085] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0086] In the first negative electrode active coating, the first negative electrode active material is NiO (average particle size 500 nm);

[0087] In the first conductive layer, the first conductive material is multilayer graphene;

[0088] In the second conductive layer, the second conductive material is single-walled CNT.

[0089] Example 3

[0090] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0091] In the first negative electrode active coating, the first negative electrode active material is selected from Co3O4 (average particle size 600nm);

[0092] In the first conductive layer, the first conductive material is carbon nanotubes, with a coating thickness of 1.5 μm;

[0093] In the second conductive layer, the second conductive material is acetylene black.

[0094] Example 4

[0095] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0096] In the first negative electrode active coating, the first negative electrode active material is MoO3 (average particle size 100 nm);

[0097] In the first conductive layer, the first conductive material is carbon nanofiber, with a coating thickness of 2.5 μm;

[0098] In the second conductive layer, the second conductive material is a single layer of graphene with a coating thickness of 2 μm.

[0099] Example 5

[0100] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0101] In the first negative electrode active coating, the first negative electrode active material is selected from MnO2 (average particle size 700 nm);

[0102] In the first conductive layer, the first conductive material is multilayer graphene with a coating thickness of 5 μm;

[0103] In the second conductive layer, the second conductive material is a single layer of graphene with a coating thickness of 3 μm.

[0104] Example 6

[0105] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0106] In the first negative electrode active coating, the first negative electrode active material is selected from TiS2 (average particle size 250 nm);

[0107] In the first conductive layer, the first conductive material is conductive graphite, with a coating thickness of 6 μm;

[0108] In the second conductive layer, the second conductive material is a single layer of graphene with a coating thickness of 3 μm.

[0109] Example 7

[0110] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0111] In the first negative electrode active coating, the first negative electrode active material is selected from MoS2 (average particle size 800nm);

[0112] In the first conductive layer, the first conductive material is multilayer graphene with a coating thickness of 7 μm;

[0113] In the second conductive layer, the second conductive material is single-walled CNT, with a coating thickness of 3 μm.

[0114] Example 8

[0115] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0116] In the first negative electrode active coating, the first negative electrode active material is selected from WS2 (average particle size 300 nm);

[0117] In the first conductive layer, the first conductive material is carbon nanotubes, with a coating thickness of 7 μm;

[0118] In the second conductive layer, the second conductive material is acetylene black, and the coating thickness is 2.5 μm.

[0119] Example 9

[0120] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0121] In the first negative electrode active coating, the first negative electrode active material is selected from SnS2 (average particle size 900 nm);

[0122] In the first conductive layer, the first conductive material is carbon nanofiber, and the coating thickness is 4 μm;

[0123] In the second conductive layer, the second conductive material is a single layer of graphene with a coating thickness of 1.5 μm.

[0124] Example 10

[0125] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0126] In the first negative electrode active coating, the first negative electrode active material is selected from VS2 (average particle size 1000 nm);

[0127] In the first conductive layer, the first conductive material is multilayer graphene with a coating thickness of 6 μm;

[0128] In the second conductive layer, the second conductive material is a single layer of graphene with a coating thickness of 2 μm.

[0129] Example 11

[0130] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0131] In the first negative electrode active coating layer, the coating thickness of the first negative electrode active material is 10 μm;

[0132] In the second negative electrode active coating, the second negative electrode active material is soft carbon, and the coating thickness is 50 μm.

[0133] Example 12

[0134] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0135] In the first negative electrode active coating, the coating thickness of the first negative electrode active material is 12 μm;

[0136] In the second negative electrode active coating, the second negative electrode active material is soft carbon, and the coating thickness is 80 μm.

[0137] Example 13

[0138] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0139] In the first negative electrode active coating, the coating thickness of the first negative electrode active material is 15 μm;

[0140] In the second negative electrode active coating, the second negative electrode active material is soft carbon, and the coating thickness is 60 μm.

[0141] Example 14

[0142] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0143] In the first negative electrode active coating, the coating thickness of the first negative electrode active material is 18 μm;

[0144] In the second negative electrode active coating, the second negative electrode active material is soft carbon, and the coating thickness is 80 μm.

[0145] Example 15

[0146] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0147] In the first negative electrode active coating, the coating thickness of the first negative electrode active material is 22 μm;

[0148] In the second negative electrode active coating, the second negative electrode active material is graphite, and the coating thickness is 90 μm.

[0149] Example 16

[0150] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0151] In the first negative electrode active coating, the coating thickness of the first negative electrode active material is 25 μm;

[0152] In the second negative electrode active coating layer, the second negative electrode active material is graphite, and the coating thickness is 100 μm.

[0153] Example 17

[0154] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0155] In the first negative electrode active coating, the coating thickness of the first negative electrode active material is 25 μm;

[0156] In the second negative electrode active coating, the second negative electrode active material is graphite, and the coating thickness is 110 μm.

[0157] Example 18

[0158] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0159] In the first negative electrode active coating, the coating thickness of the first negative electrode active material is 25 μm;

[0160] In the first conductive layer, the coating thickness of the first conductive material is 8 μm;

[0161] In the second negative electrode active coating, the second negative electrode active material is graphite, and the coating thickness is 120 μm.

[0162] Example 19

[0163] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being:

[0164] In the first negative electrode active coating layer, the coating thickness of the first negative electrode active material is 30 μm;

[0165] In the second negative electrode active coating, the second negative electrode active material is graphite, and the coating thickness is 130 μm.

[0166] Comparative Example 1

[0167] The structure and system of the secondary battery in this embodiment are the same as those in embodiment 1, with the only difference being that the first conductive layer and the second conductive layer are not provided.

[0168] The features involved in the above-mentioned embodiments and comparative examples of the present application are summarized in Table 1 below.

[0169] Table 1

[0170]

[0171]

[0172] The indicators based on the secondary battery performance test include cycle performance, rate performance, and expansion performance.

[0173] 1) The specific test process of the secondary battery cycle performance is as follows: the test is carried out under constant temperature conditions at room temperature (25°C), the battery is charged to 3.5V at a constant current of 0.1C, then charged to 4.0V at a constant current of 0.33C, then charged to a cut-off current of 0.05C at a constant voltage of 4.0V, and finally discharged at a constant current of 0.33C to obtain the initial charge and discharge capacity of the battery. After that, the battery is charged to 4.0V at 1C and discharged to 2.8V at 1C for 1000 cycles to obtain the discharge capacity of 1000 cycles, and the battery capacity retention rate of 1000 cycles at a rate of 1C is calculated. Similarly, the battery is cyclically charged and discharged at a rate of 8C (8C charging to 4.0V, 8C discharging to 2.8V), and the battery capacity retention rate of 1000 cycles at a rate of 8C is calculated.

[0174] 2) The specific test process of the secondary battery expansion performance is as follows: during the cyclic charge and discharge process of the secondary battery, after 1000 cycles, the thickness of the secondary battery in a fully charged state is tested to obtain the battery thickness after 1000 cycles, and the battery thickness before the first cycle is used as a reference value to calculate the battery thickness expansion rate.

[0175] In this experimental example, the specific test results of each secondary battery are shown in Table 2 and Figure 2 .

[0176] Table 2

[0177]

[0178]

[0179] It can be seen from the results of the above embodiments and comparative examples that providing a double-layer conductive layer can not only effectively improve the conductivity of the overall material, but also effectively suppress the volume expansion caused by the cycle of transition metal oxides or sulfides, thereby effectively improving the cycle performance of the battery.

[0180] Obviously, the above embodiments are merely examples for clarity of explanation and are not intended to limit the implementation methods. Those skilled in the art will appreciate that other variations or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation methods here. Obvious variations or modifications arising therefrom remain within the scope of protection of this application.

Claims

1. A secondary battery, characterized in that: Including negative electrode plate; The negative electrode plate includes a negative electrode current collector, and a first negative electrode active coating, a first conductive layer, a second negative electrode active coating, and a second conductive layer provided on at least one side of the negative electrode current collector; the first negative electrode active coating is close to the negative electrode current collector, and the second conductive layer is away from the negative electrode current collector; the first conductive layer is provided between the first negative electrode active coating and the second negative electrode active coating, wherein, The first negative electrode active coating layer comprises a first negative electrode active material, wherein the first negative electrode active material comprises at least one of a metal sulfide or a metal oxide; The second negative electrode active coating layer includes a second negative electrode active material, and the second negative electrode active material includes a carbon material.

2. The secondary battery according to claim 1, wherein: The second negative electrode active coating layer is disposed between the first conductive layer and the second conductive layer.

3. The secondary battery according to claim 1, wherein: The thickness Tb of the second negative electrode active coating layer is greater than the thickness Ta of the first negative electrode active coating layer; The thickness T1 of the first conductive layer is greater than the thickness T2 of the second conductive layer.

4. The secondary battery according to claim 1, wherein: The first conductive layer comprises a first conductive material; The second conductive layer comprises a second conductive material; The electrical conductivity of the first conductive material is greater than the electrical conductivity of the second conductive material.

5. The secondary battery according to claim 3, wherein: The thickness of the second negative electrode active coating layer Tb>the thickness of the first negative electrode active coating layer Ta>the thickness of the first conductive layer T1>the thickness of the second conductive layer T2.

6. The secondary battery according to claim 5, characterized in that: The negative electrode plate has at least one of the following features (a) to (d): (a) the thickness Ta of the first negative electrode active coating is 10-30 μm; (b) the thickness Tb of the second negative electrode active coating is 50-130 μm; (c) the thickness T1 of the first conductive layer is 1.5-8 μm; (d) The thickness T2 of the second conductive layer is 1-3 μm.

7. The secondary battery according to any one of claims 1 to 6, characterized in that: Based on the total amount of the first negative electrode active material and the second negative electrode active material, the mass content of the first negative electrode active material is 5-30 wt %, and the mass content of the second negative electrode active material is 70-95 wt %.

8. The secondary battery according to claim 1, wherein: The metal sulfide includes at least one of titanium disulfide (TiS2), molybdenum disulfide (MoS2), tungsten disulfide (WS2), tin disulfide (SnS2), and vanadium disulfide (VS2); The metal oxide includes at least one of iron oxide (Fe2O3), nickel oxide (NiO), cobalt oxide (Co3O4), molybdenum oxide (MoO3), and manganese oxide (MnO2); The average particle size of the metal oxide or metal sulfide is 100-1000 nm; The carbon material includes hard carbon, soft carbon or graphite, or a mixture of the hard carbon, soft carbon or graphite.

9. The secondary battery according to claim 4, characterized in that: Based on the total mass of the first conductive material and the second conductive material, the mass content of the first conductive material is 60-70 wt %, and the mass content of the second conductive material is 30-40 wt %.

10. The secondary battery according to claim 9, wherein: The first conductive material comprises at least one of multilayer graphene, conductive graphite, multi-walled CNT, carbon nanotube or carbon nanofiber; and / or, The second conductive material includes at least one of single-walled CNT, single-layer graphene, or acetylene black.

11. The secondary battery according to any one of claims 1 to 6, characterized in that: The invention also includes a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active coating containing a positive electrode active material, and the positive electrode active material includes sodium transition metal oxide.

12. An electrical device, characterized in that: The secondary battery comprises the secondary battery according to any one of claims 1 to 11, wherein the secondary battery serves as a power supply for the electrical device.

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