Negative pole piece and sodium ion battery

Abstract

The invention discloses a negative pole piece and a sodium ion battery, and relates to the technical field of batteries. The negative pole piece comprises a current collector and a negative active material layer coating the current collector, the negative active material layer comprises a negative material, a binder and a conductive agent, the negative active material layer comprises a first sub-layer and a second sub-layer which are stacked, the first sub-layer is connected to the current collector, and the second sub-layer is connected to the conductive agent. The second sub-layer is arranged on the side, away from the current collector, of the first sub-layer, the mass fraction of the binder in the first sub-layer is larger than that of the binder in the second sub-layer, and the mass fraction of the conductive agent in the first sub-layer is larger than that of the conductive agent in the second sub-layer. According to the invention, by increasing the proportion of the binder and the conductive agent in the first sub-layer directly connected with the current collector, the reliability and the electrical performance of the negative pole piece can be improved.

Description

TECHNICAL FIELD

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

[0002] The overall process flow of a sodium-ion battery is similar to that of a lithium battery, but Na and Al do not alloy at low voltage, so aluminum foil can be used as the current collector for the negative electrode of a sodium-ion battery. However, the negative electrode material used in a sodium-ion battery is hard carbon, which mainly uses water as the solvent, and the hydrophobicity of aluminum foil is relatively large. If the amount of binder used in the negative electrode formula is small, the adhesion of the negative electrode active material layer will be poor, which will cause the negative electrode active material layer to peel off easily, thereby affecting the electrical performance of the battery. Although increasing the amount of binder can improve the adhesion of the negative electrode active material layer, it also reduces the electrical conductivity of the electrode sheet and the proportion of the negative electrode material. Therefore, the negative electrode sheet of the sodium-ion battery in the related art cannot balance the electrical conductivity and reliability.

[0003] In view of this, the present application is proposed. SUMMARY

[0004] The purpose of the present application is to provide a negative electrode sheet and a sodium-ion battery, which has better electrical conductivity and reliability.

[0005] The present application is implemented as follows: In a first aspect, the present application provides a negative electrode sheet, comprising a current collector and a negative electrode active material layer coated on the current collector, the components of the negative electrode active material layer comprising a negative electrode material, a binder and a conductive agent, the negative electrode active material layer comprising a first sub-layer and a second sub-layer stacked, the first sub-layer being connected to the current collector, the second sub-layer being arranged on the side of the first sub-layer away from the current collector, the mass fraction of the binder in the first sub-layer being greater than the mass fraction of the binder in the second sub-layer, and the mass fraction of the conductive agent in the first sub-layer being greater than the mass fraction of the conductive agent in the second sub-layer.

[0006] In an optional embodiment, the mass fraction of the binder in the first sub-layer is A1, the mass fraction of the binder in the second sub-layer is A2, and A1 = (1.1~2) × A2.

[0007] In an optional embodiment, the mass fraction of the conductive agent in the first sub-layer is B1, the mass fraction of the binder in the second sub-layer is B2, and B1 = (1.1~2) × B2.

[0008] In an optional embodiment, the areal density of the negative electrode active material layer is C, the areal density of the first sub-layer is 0.05C~0.2C, and the areal density of the second sub-layer is 0.8C~0.95C.

[0009] In an optional embodiment, the areal density of the negative electrode active material layer is 50~250 g / m2 .

[0010] In an optional embodiment, the binder is selected from at least one of sodium carboxymethyl cellulose, polyacrylic acid, sodium alginate, polytetrafluoroethylene, butylphenyl, benzene propyl.

[0011] In an optional embodiment, the conductive agent is selected from at least one of SP, carbon black, KS-6, carbon nanotubes, and graphene.

[0012] In an optional embodiment, the material of the current collector is aluminum.

[0013] In an optional embodiment, the negative electrode material is selected from hard carbon or soft carbon.

[0014] In a second aspect, the application provides a sodium ion battery, comprising the negative electrode sheet of any one of the preceding embodiments.

[0015] The application has the following beneficial effects: The application provides a negative electrode sheet, comprising a current collector and a negative electrode active material layer coated on the current collector, the components of the negative electrode active material layer comprising a negative electrode material, a binder, and a conductive agent, the negative electrode active material layer comprising a first sublayer and a second sublayer arranged in layers, the first sublayer being connected to the current collector, the second sublayer being arranged on the side of the first sublayer away from the current collector, the mass fraction of the binder in the first sublayer being greater than the mass fraction of the binder in the second sublayer, and the mass fraction of the conductive agent in the first sublayer being greater than the mass fraction of the conductive agent in the second sublayer. In the application, by increasing the proportion of the binder and the conductive agent in the first sublayer directly connected to the current collector, the adhesion and the electrical conductivity between the negative electrode active material layer and the current collector can be significantly improved without changing the overall components of the negative electrode active material layer, thereby improving the reliability and the electrical performance of the negative electrode sheet. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions of the embodiments of the application, the following will briefly introduce the drawings needed to be used in the embodiments. It should be understood that the following drawings only show some of the embodiments of the application, and therefore should not be considered as a limitation to the scope. For those skilled in the art, other related drawings can also be obtained without creative labor.

[0017] Figure 1 FIG. 1 is a schematic diagram of the negative electrode sheet in an embodiment of the application.

[0018] Main element symbol explanation: 100 - current collector; 200 - negative electrode active material layer; 210 - first sublayer; 220 - second sublayer. DETAILED DESCRIPTION

[0019] In existing sodium ion batteries, the adhesion between the negative electrode material and the current collector is poor, which leads to easy peeling and powdering, and the reliability of the negative electrode sheet is poor. However, if a large amount of binder is added, the conductivity of the electrode sheet and the proportion of the negative electrode material will be reduced. Therefore, in the related art, the negative electrode sheet of the sodium ion battery is difficult to balance the reliability and the better electrical performance.

[0020] Therefore, the embodiment of the present application provides a negative electrode sheet, by setting the negative electrode active material layer as a double-layer structure, increasing the mass fraction of the binder and the conductive agent in the first sub-layer directly contacting the current collector, so that the reliability and electrical performance of the negative electrode sheet can be improved without changing the overall formula of the negative electrode active material layer.

[0021] In order to make the purpose, technical scheme and advantages of the embodiments of the present application more clear, the technical scheme in the embodiments of the present application will be described clearly and completely below. If the specific conditions are not specified in the embodiments, 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 purchased on the market.

[0022] The features and properties of the present application are further described in detail below.

[0023] Figure 1 A schematic diagram of the negative electrode sheet in an embodiment of the present application is shown. As shown in Figure 1 The negative electrode sheet provided by the embodiment of the present application can be applied in a sodium ion battery, and the negative electrode sheet includes a current collector 100 and a negative electrode active material layer 200 coated on the surface of the current collector 100. The components of the negative electrode active material layer 200 include a negative electrode material, a binder and a conductive agent, and the negative electrode active material layer 200 includes a first sub-layer 210 and a second sub-layer 220 stacked. The first sub-layer 210 is connected to the current collector 100, and the second sub-layer 220 is arranged on the side of the first sub-layer 210 away from the current collector 100. The mass fraction of the binder in the first sub-layer 210 is greater than the mass fraction of the binder in the second sub-layer 220, and the mass fraction of the conductive agent in the first sub-layer 210 is greater than the mass fraction of the conductive agent in the second sub-layer 220. By setting the mass fraction of the binder and the conductive agent in the first sub-layer 210 to be greater than the mass fraction of the binder and the conductive agent in the second sub-layer 220, the negative electrode active material layer of the negative electrode sheet provided by the embodiment of the present application has stronger adhesion and conductivity between the negative electrode active material layer and the current collector 100 compared with the negative electrode sheet of the existing negative electrode active material layer 200 with uniform components, so that the negative electrode sheet has better reliability and electrical performance.

[0024] It should be understood that in the embodiments of the present application, the first sub-layer 210 and the second sub-layer 220 each include a negative electrode material, a binder and a conductive agent. The mass fraction of the binder in the first sub-layer 210 is the percentage of the mass of the binder in the first sub-layer 210 in the total mass of the first sub-layer 210, and the mass fraction of the conductive agent in the first sub-layer 210 is the percentage of the mass of the conductive agent in the first sub-layer 210 in the total mass of the first sub-layer 210; the mass fraction of the binder in the second sub-layer 220 is the percentage of the mass of the binder in the second sub-layer 220 in the total mass of the second sub-layer 220, and the mass fraction of the conductive agent in the second sub-layer 220 is the percentage of the mass of the conductive agent in the second sub-layer 220 in the total mass of the second sub-layer 220.

[0025] In the embodiments of the present application, the areal density of the first sub-layer 210 is less than the areal density of the second sub-layer 220. The areal density of the first sub-layer 210 refers to the mass of the first sub-layer 210 covering a unit area of the current collector 100, and the areal density of the second sub-layer 220 refers to the mass of the second sub-layer 220 covering a unit area of the current collector 100 (or the first sub-layer 210). Macroscopically, the thickness of the first sub-layer 210 is less than the thickness of the second sub-layer 220. By so doing, when the mass fractions of the binder and the conductive agent in the first sub-layer 210 are significantly greater than the mass fractions of the binder and the conductive agent in the entire negative electrode active material layer 200, the content of each component in the second sub-layer 220 is close to the content of each component in the entire negative electrode active material layer 200, thereby avoiding performance degradation due to a large difference between the content of each component in the second sub-layer 220 and the content of each component in the negative electrode active material layer 200.

[0026] Optionally, the areal density of the negative electrode active material layer 200 is C, the areal density of the first sub-layer 210 is 0.05C-0.2C, and the areal density of the second sub-layer 220 is 0.8C-0.95C. Further, the areal density of the negative electrode active material layer 200 can be optionally 100-250 g / m 2 , such as 100 g / m 2 , 110 g / m 2 , 120 g / m 2 , 130 g / m 2 , 140 g / m 2 , 150 g / m 2 , 160 g / m 2 , 170 g / m 2 , 180 g / m 2 , 190 g / m 2 , 200 g / m 2 , 210 g / m 2 , 220 g / m 2 , 230 g / m 2 , 240 g / m 2, 250 g / m 2 Any value in the range or any two points in the range.

[0027] Optionally, the mass fraction of the binder in the first sub-layer 210 is A1, and the mass fraction of the binder in the second sub-layer 220 is A2, wherein A1 = (1.1-2) x A2. By increasing the binder in the first sub-layer 210 by 10-100% relative to the second sub-layer 220, the adhesion between the first sub-layer 210 and the current collector 100 can be significantly improved, thereby effectively reducing the risk of the negative active material layer 200 peeling off from the current collector 100.

[0028] Further, the mass fraction of the conductive agent in the first sub-layer 210 is B1, and the mass fraction of the conductive agent in the second sub-layer 220 is B2, wherein B1 = (1.1-2) x B2. By increasing the conductive agent in the first sub-layer 210 by 10-100% relative to the second sub-layer 220, the electrical conductivity between the first sub-layer 210 and the current collector 100 can be significantly improved, thereby improving the electrical performance of the negative electrode tab.

[0029] Optionally, the mass ratio of the negative electrode material, the binder, and the conductive agent in the first sub-layer 210 is 90-95:4-8:1.3-2.2, and the mass ratio of the negative electrode material, the binder, and the conductive agent in the second sub-layer 220 is 94-95.8:3.3-4.0:0.9-1.1.

[0030] Optionally, the binder is selected from at least one of sodium carboxymethyl cellulose (CMC), polyacrylic acid (PAA), sodium alginate (ALG), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), and styrene propylene. The above high molecular compounds can enhance the contact between the negative electrode material and the conductive agent, and also enhance the contact between the negative electrode material and the current collector 100.

[0031] Optionally, the material of the current collector 100 is aluminum. At the working potential of the sodium-ion battery negative electrode, aluminum will not alloy with sodium. A dense aluminum oxide (Al2O3) passivation film will be formed on the surface of aluminum, which can effectively prevent the current collector 100 from being further corroded by sodium or electrolyte. Therefore, the aluminum current collector 100 maintains structural integrity and stable electrical performance throughout the battery cycle, ensuring long life and high reliability of the battery. The price of aluminum is much lower than that of copper, and the density of aluminum is small and the texture is softer, so the processing difficulty and energy consumption are lower than those of copper foil when it is rolled into an ultra-thin foil (such as 10-12 μm). Therefore, the material cost and processing cost of the aluminum current collector 100 are relatively low. The density of aluminum (2.7 g / cm 3 ) is much lower than that of copper (8.96 g / cm 3), so the same volume of aluminum foil is used, which is much lighter than copper foil, so using an aluminum current collector 100 helps to reduce the weight of the non-active components of the battery, thereby improving the weight energy density of the battery to some extent.

[0032] Optionally, the negative electrode material is selected from hard carbon or soft carbon. Hard carbon is suitable for scenarios that pursue high energy density (especially mass energy density) due to its higher reversible capacity, such as electric vehicles and high-end energy storage systems. Soft carbon has the advantages of excellent rate performance, high initial efficiency, low cost, and high compaction density.

[0033] Optionally, the conductive agent is selected from at least one of SP (Super P, acetylene black), carbon black, KS-6 (artificial graphite), carbon nanotubes, and graphene. The conductive agent can build an electron conduction path, with small conductive agent particles filling between the negative electrode material particles to form a continuous three-dimensional electron conduction network, ensuring that each negative electrode material particle can maintain good electrical contact with the current collector 100, allowing electrons to flow quickly and smoothly. The conductive agent is beneficial to improve the rate performance of the battery, promote uniform current distribution, and reduce polarization.

[0034] The embodiments of the present application also provide a sodium ion battery, which includes the negative electrode sheet provided by the above embodiments. The sodium ion battery further includes a positive electrode sheet, a shell, a separator, and an electrolyte. The positive electrode sheet, the negative electrode sheet, the separator, and the electrolyte are arranged in the shell, and the separator separates the positive electrode sheet and the negative electrode sheet. The specific structure and working principle of the sodium ion battery can refer to the prior art, which will not be described here.

[0035] In order to verify the performance of the negative electrode sheet provided by the embodiments of the present application, the following tests are performed on Example 1, Example 2, and Comparative Example 1. Specifically, the adhesion of the negative electrode sheet of Example 1, Example 2, and Comparative Example 1 is tested to represent the difficulty of peeling the negative electrode active material layer 200 from the current collector 100. Furthermore, a sodium ion battery with a model number of 40105105 and a capacity of 2.5 Ah is prepared, and the 3C discharge capacity retention rate and the 1C / 1C 1000 cycle retention rate at 25°C are tested. When manufacturing the sodium ion battery, the same positive electrode sheet, separator, and electrolyte are used in each example and comparative example, and the positive electrode sheet, separator, and electrolyte are all made of conventional materials. The specific parameters and test results are shown in the following table. The binder ratio in the following table refers to the ratio of the content of the binder in the first sublayer and the second sublayer; the conductive agent ratio in the following table refers to the ratio of the content of the conductive agent in the first sublayer and the second sublayer.

[0036]

[0037] From the comparison of the above examples 1-6 and comparative example 1, it can be seen that the adhesion of the negative electrode tab of the present application is improved compared with the negative electrode tab with uniform components, and the electrical performance and cycle of the sodium ion battery produced are also greatly improved.

[0038] In summary, the present application provides a negative electrode tab, which comprises a current collector 100 and a negative electrode active material layer 200 coated on the current collector 100, the components of the negative electrode active material layer 200 comprising a negative electrode material, a binder and a conductive agent, the negative electrode active material layer 200 comprising a first sub-layer 210 and a second sub-layer 220 arranged in layers, the first sub-layer 210 being connected to the current collector 100, the second sub-layer 220 being arranged on the side of the first sub-layer 210 away from the current collector 100, the mass fraction of the binder in the first sub-layer 210 being greater than that in the second sub-layer 220, and the mass fraction of the conductive agent in the first sub-layer 210 being greater than that in the second sub-layer 220. In the present application, by increasing the proportion of the binder and the conductive agent in the first sub-layer 210 directly connected to the current collector 100, the adhesion and the electrical conductivity between the negative electrode active material layer 200 and the current collector 100 can be significantly improved without changing the overall components of the negative electrode active material layer 200, thereby improving the reliability and the electrical performance of the negative electrode tab.

[0039] The above only describes the preferred embodiments of the present application and is not intended to limit the present application. Various modifications and changes can be made by those skilled in the art based on the principles and technical solutions of the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A negative electrode sheet, characterized in that, The device includes a current collector and a negative electrode active material layer coated on the current collector. The negative electrode active material layer comprises a negative electrode material, a binder, and a conductive agent. The negative electrode active material layer includes a first sublayer and a second sublayer stacked together. The first sublayer is connected to the current collector, and the second sublayer is disposed on the side of the first sublayer opposite to the current collector. The mass fraction of the binder in the first sublayer is greater than the mass fraction of the binder in the second sublayer, and the mass fraction of the conductive agent in the first sublayer is greater than the mass fraction of the conductive agent in the second sublayer.

2. The negative electrode sheet according to claim 1, characterized in that, The mass fraction of the adhesive in the first sublayer is A1, and the mass fraction of the adhesive in the second sublayer is A2, where A1 = (1.1~2) × A2.

3. The negative electrode sheet according to claim 1, characterized in that, The mass fraction of the conductive agent in the first sub-layer is B1, and the mass fraction of the binder in the second sub-layer is B2, where B1 = (1.1~2) × B2.

4. The negative electrode sheet according to claim 1, characterized in that, The areal density of the negative electrode active material layer is C, the areal density of the first sublayer is 0.05C~0.2C, and the areal density of the second sublayer is 0.8C~0.95C.

5. The negative electrode sheet according to claim 1, characterized in that, The areal density of the negative electrode active material layer is 50~250 g / m³. 2 .

6. The negative electrode sheet according to any one of claims 1-5, characterized in that, The adhesive is selected from at least one of sodium carboxymethyl cellulose, polyacrylic acid, sodium alginate, polytetrafluoroethylene, styrene-butadiene, and styrene-acrylic acid.

7. The negative electrode sheet according to any one of claims 1-5, characterized in that, The conductive agent is selected from at least one of SP, carbon black, KS-6, carbon nanotubes, and graphene.

8. The negative electrode sheet according to any one of claims 1-5, characterized in that, The current collector is made of aluminum.

9. The negative electrode sheet according to any one of claims 1-5, characterized in that, The negative electrode material is selected from hard carbon or soft carbon.

10. A sodium-ion battery, characterized in that, Includes the negative electrode sheet according to any one of claims 1-9.

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