Negative electrode binder and negative electrode sheet, preparation method and battery

Abstract

The present invention discloses a negative electrode binder and a negative electrode sheet, a preparation method and a battery, wherein the negative electrode binder is an SBR-M binder emulsion containing both SBR and M elements, wherein M is Na or Li, and the pH of the negative electrode binder is 7.0 to 9.0. The negative electrode binder of the present invention can not only effectively improve the first efficiency of the battery, reduce the loss of active sodium / lithium, thereby improving the battery capacity and energy density, but also improve the negative electrode sheet peeling force, capture the free acid in the electrolyte, thereby improving the cycle life.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a negative electrode binder and a negative electrode sheet, a preparation method and a battery. Background Art

[0002] In recent years, sodium-ion batteries and lithium-ion batteries have been widely used in the field of electric vehicles. However, with the continuous development of electric vehicles, people have put forward higher requirements for their endurance, which requires batteries to have higher energy density. The existing technology has mostly improved from the aspects of increasing the gram capacity of positive and negative electrode materials and pre-lithiation, but it still faces the technical problem of difficulty in improving the energy density of sodium / lithium-ion batteries. Summary of the invention

[0003] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, one object of the present invention is to provide a negative electrode binder and a negative electrode sheet, a preparation method and a battery, which can improve the battery capacity and energy density.

[0004] According to the negative electrode binder of the first embodiment of the present invention, the negative electrode binder is an SBR-M binder emulsion containing both SBR and M elements, M is Na or Li, and the pH of the negative electrode binder is 7.0-9.0.

[0005] According to the second aspect of the present invention, the method for preparing a negative electrode binder comprises the following steps: mixing an SBR emulsion and an MOH solution until the pH is 7.0 to 9.0 and does not change within a preset time to obtain an SBR-M binder emulsion, wherein M is Na or Li.

[0006] Optionally, the pH of the SBR emulsion is 2.5 to 7.0.

[0007] Optionally, the solid content of the SBR emulsion is 20% to 60%.

[0008] Optionally, the concentration of the MOH solution is 0.05M to 1.0M.

[0009] The negative electrode sheet according to the third embodiment of the present invention includes the negative electrode binder described above.

[0010] According to the fourth aspect of the present invention, the method for preparing a negative electrode sheet comprises the following steps: mixing a negative electrode active material, a conductive agent, a thickener, SBR-M and solvent water to obtain a mixture; coating the mixture on a metal foil to obtain the negative electrode sheet according to claim 6.

[0011] Optionally, the negative electrode active material is one of graphite, hard carbon, silicon carbon or phosphorus carbon or any combination thereof, and / or the metal foil is aluminum foil or copper foil.

[0012] Optionally, the mass ratio of the active material, the conductive agent, the thickener and the binder is (92.5-97.7): (0.5-2.0): (0.8-2.0): (1.0-3.5).

[0013] According to the battery of the fourth embodiment of the present invention, the battery includes the above-mentioned negative electrode sheet.

[0014] The negative electrode binder of the embodiment of the present invention is a high-performance negative electrode binder, specifically comprising SBR-M (M = Na or Li), which can effectively improve the first efficiency of the battery, reduce the loss of active sodium / lithium, and thus improve the battery capacity and energy density. In addition, the SBR-M binder can improve the peeling force of the negative electrode sheet, capture the free acid (H+) in the electrolyte, and thus improve the cycle life. Moreover, by adopting a pH value of 7 to 9, the stability of the emulsion can also be guaranteed.

[0015] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0017] FIG. 1( a ) is a comparison diagram of the negative electrode sheet peeling force according to Example 1 of the present invention and Comparative Example 1;

[0018] FIG. 1( b ) is a comparison diagram of the peeling force of the negative electrode sheets according to Example 2 of the present invention and Comparative Example 2;

[0019] FIG2( a ) is a comparison diagram of the first effects of Example 1 and Comparative Example 1 according to the present invention;

[0020] FIG2( b ) is a comparison diagram of the first effects of Example 2 and Comparative Example 2 according to the present invention;

[0021] FIG3( a ) is a comparison chart of 1C1C cycle capacity retention rates between Example 1 of the present invention and Comparative Example 1;

[0022] FIG3( b ) is a comparison chart of the 1C1C cycle capacity retention rates of Example 2 according to the present invention and Comparative Example 2. DETAILED DESCRIPTION

[0023] The negative electrode binder according to an embodiment of the present invention will be described below with reference to FIGS. 1( a ) to 3 ( b ).

[0024] The negative electrode binder according to the embodiment of the present invention is an SBR-M binder emulsion containing both SBR and M elements, M is Na or Li, and the pH of the negative electrode binder is 7.0-9.0. It should be noted that, compared with conventional SBR, the SBR-M binder provided by the present invention introduces active elements Na / Li, which can effectively reduce the loss of active Na / Li, thereby significantly improving the initial efficiency of the battery. At the same time, the carboxyl group in the negative electrode binder molecule can also form a stronger chemical bond with the foil, thereby increasing the peeling force of the negative electrode sheet and improving the cycle performance. In addition, the functional group -COOM can also capture free acid (H + ), alleviate the acid damage to the positive electrode material, and further improve the battery long cycle life. In addition, in this embodiment, by using a pH value of 7 to 9, for example, the pH of the negative electrode binder is 7.0, 7.5, 8.0, 8.5 or 9.0, it can be ensured that SBR is basically completely converted into SBR-M, while ensuring the stability of the emulsion.

[0025] Therefore, the negative electrode binder of the embodiment of the present invention is a high-performance negative electrode binder, specifically comprising SBR-M (M = Na or Li), which can effectively improve the first efficiency of the battery, reduce the loss of active sodium / lithium, and thus improve the battery capacity and energy density. In addition, the SBR-M binder can improve the peeling force of the negative electrode sheet, capture the free acid (H+) in the electrolyte, and thus improve the cycle life. Moreover, by adopting a pH value of 7 to 9, the stability of the emulsion can also be guaranteed.

[0026] The present invention also discloses a method for preparing the negative electrode binder of any of the above embodiments, comprising the following steps:

[0027] The SBR emulsion and the MOH solution are mixed until the pH is 7.0 to 9.0 and does not change within a preset time, thereby obtaining an SBR-M binder emulsion, wherein M is Na or Li. For example, a certain amount of carboxylated styrene butadiene emulsion is weighed and placed in a stirrer, and a certain concentration of MOH solution is added while slowly stirring until the solution pH is about 8.0 and does not change significantly within 20 minutes, at which point the SBR-M binder emulsion is obtained. Optionally, the stirring speed is 30 r / min to 120 r / min.

[0028] It can be seen that the preparation method of the negative electrode binder has the advantages of simple synthesis and simple steps.

[0029] According to one embodiment of the present invention, the pH of the SBR emulsion is 2.5-7.0, for example, the pH of the SBR emulsion is 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 6.5 or 7.0, etc. In this embodiment, the pH of the SBR emulsion is 2.5-7.0, and the SBR with a pH of 2.5-7.0 contains more carboxyl groups, so it can provide effective reaction sites, which is conducive to the formation of SBR-M binder.

[0030] In some specific embodiments of the present invention, the solid content of the SBR emulsion is 20% to 60%, for example, the solid content of the SBR emulsion is 20%, 25%, 30%, 35%, 40%, 45%, 50% or 60%, etc. Conventional SBR emulsion can be used to reduce costs.

[0031] According to one embodiment of the present invention, the concentration of the MOH solution is 0.05M-1.0M, for example, the concentration of the MOH solution is 0.05M, 0.06M, 0.08M, 0.1M, 0.2M, 0.3M, 04M, 0.5M, 0.6M, 0.7M, 0.8M, 0.9M or 1.0M, etc. In this embodiment, the concentration of the MOH solution is 0.05M-1.0M, which can take into account both the controllability and production efficiency of the reaction.

[0032] The present invention also discloses a negative electrode sheet, which includes any of the negative electrode binders described above. The carboxyl groups in the negative electrode binder molecules can also form stronger chemical bonds with the foil, thereby increasing the peeling force of the negative electrode sheet and thus improving the cycle performance.

[0033] The present invention also discloses a method for preparing a negative electrode sheet, which comprises the following steps:

[0034] The negative electrode active material, the conductive agent, the thickener, the SBR-M binder and the solvent water are mixed to obtain a mixture. The mixture is coated on a metal foil to obtain a negative electrode sheet of any of the above embodiments. That is to say, the negative electrode active material, the conductive agent, the thickener, the negative electrode binder and the solvent water are mixed, wherein the negative electrode binder is the negative electrode binder of any of the above embodiments. Specifically, the negative electrode binder according to the embodiment of the present invention is an SBR-M binder emulsion containing both SBR and M elements, M is Na or Li, and the pH of the negative electrode binder is 7.0 to 9.0. During implementation, the negative electrode active material, the conductive agent, the thickener, the SBR-M binder and the solvent water can be uniformly mixed in a certain amount and then coated on a metal foil, and then rolled to a certain thickness to obtain the desired negative electrode sheet, which is conducive to obtaining negative electrode sheets of various thicknesses.

[0035] It can be seen that the method for preparing the negative electrode sheet of the embodiment of the present invention also has the advantages of easy operation and simple process.

[0036] According to one embodiment of the present invention, the negative electrode active material is one of graphite, hard carbon, silicon carbon or phosphorus carbon, etc. or any combination thereof, which can be applicable to the selection of negative electrode materials for various batteries, expanding the scope of application, and / or, the metal foil is aluminum foil or copper foil, etc., among which aluminum foil can be used in sodium ion batteries and copper foil can be used in lithium ion batteries.

[0037] In some specific embodiments of the present invention, the ratio of the amount of active material, conductive agent, thickener, and binder is (92.5-97.7): (0.5-2.0): (0.8-2.0): (1.0-3.5). For example, the ratio of the amount of active material, conductive agent, thickener, and binder is 93.0: 0.6: 1.0: 2.0. In this embodiment, by using the ratio of the amount of active material, conductive agent, thickener, and binder as (92.5-97.7): (0.5-2.0): (0.8-2.0): (1.0-3.5), the reaction can be ensured to be sufficient.

[0038] The present invention also discloses a battery, including the negative electrode sheet of any of the above embodiments. When preparing the battery, the negative electrode sheet of any of the above embodiments can be used in combination with the corresponding positive electrode, separator, electrolyte, etc. to assemble the required battery. By synthesizing a high-performance negative electrode binder SBR-M binder (M = Na or Li), the negative electrode sheet peeling force and the battery first efficiency are effectively improved, and the battery cycle life is also improved.

[0039] The negative electrode binder, negative electrode sheet and battery of the embodiments of the present invention are described in detail below in conjunction with specific embodiments.

[0040] Example 1

[0041] Example 1 provides a high-performance negative electrode binder SBR-Na for a sodium ion battery, a negative electrode sheet containing the binder and a corresponding sodium ion battery, specifically comprising the following steps:

[0042] (1) Synthesis of SBR-Na

[0043] Weigh 100g of carboxylated styrene butadiene emulsion with a solid content of 30% and pH = 3.5 and place it in a stirrer, and set the speed to 100r / min. While stirring, slowly add 0.5M NaOH solution, and use a pH meter to monitor the pH change of the emulsion until pH = 8.0 and there is no obvious change within 20 minutes, then stop adding NaOH, and the SBR-Na binder emulsion can be obtained.

[0044] (2) Preparation of negative electrode sheet

[0045] 3 kg of hard carbon was weighed and prepared into negative electrode slurry according to the mass ratio of hard carbon: SP: CMC: SBR-Na = 94.7: 1.5: 1.3: 2.5 and the corresponding process, and then coated on aluminum foil and rolled to obtain a negative electrode sheet containing SBR-Na.

[0046] (3) Preparation of sodium ion batteries

[0047] The above-mentioned negative electrode sheet is used in combination with the corresponding positive electrode, separator, electrolyte and other auxiliary materials to assemble the required sodium ion battery.

[0048] Example 2

[0049] Example 2 provides a high-performance negative electrode binder SBR-Li for lithium-ion batteries, a negative electrode sheet containing the binder and a corresponding lithium-ion battery, which specifically includes the following steps:

[0050] (1) Synthesis of SBR-Li

[0051] Weigh 100g of carboxylated styrene butadiene emulsion with a solid content of 30% and pH = 3.5 and place it in a stirrer, and set the speed to 100r / min. While stirring, slowly add 0.5M LiOH solution, and use a pH meter to monitor the pH change of the emulsion until pH = 8.0 and there is no obvious change within 20 minutes, then stop adding LiOH, and the SBR-Li binder emulsion can be obtained.

[0052] (2) Preparation of negative electrode sheet

[0053] 3 kg of graphite was weighed and prepared into a negative electrode slurry according to the mass ratio of graphite: SP: CMC: SBR-Na = 95.5: 1.2: 1.3: 2.0 and the corresponding process, and then coated on a copper foil and rolled to obtain a negative electrode sheet containing SBR-Li.

[0054] (3) Preparation of lithium-ion batteries

[0055] The above-mentioned negative electrode sheet is used in combination with the corresponding positive electrode, separator, electrolyte and other auxiliary materials to assemble the required lithium-ion battery.

[0056] Comparative Example 1

[0057] Comparative Example 1 uses conventional SBR (the solid content of conventional SBR is between 25% and 55%, and the pH value is between 6 and 8) to prepare a conventional negative electrode sheet and a corresponding sodium ion battery, which specifically includes the following steps:

[0058] (1) Preparation of negative electrode

[0059] Weigh 3 kg of hard carbon and prepare it into negative electrode slurry according to the mass ratio of hard carbon: SP: CMC: SBR = 94.7: 1.5: 1.3: 2.5 and the corresponding process, then coat it on aluminum foil and roll it to obtain a conventional negative electrode sheet, in which SBR is a conventional product.

[0060] (2) Preparation of sodium ion batteries

[0061] The above-mentioned negative electrode sheet is used in combination with the corresponding positive electrode, separator, electrolyte and other auxiliary materials to assemble the required sodium ion battery.

[0062] Comparative Example 2

[0063] Comparative Example 2 uses the same conventional SBR as that in Comparative Example 1 to prepare a conventional negative electrode sheet and a corresponding lithium-ion battery, which specifically includes the following steps:

[0064] (1) Preparation of negative electrode

[0065] 3 kg of graphite was weighed and prepared into negative electrode slurry according to the mass ratio of graphite: SP: CMC: SBR = 95.5: 1.2: 1.3: 2.0 and the corresponding process, and then coated on aluminum foil and rolled to obtain a conventional negative electrode sheet, wherein SBR is a conventional product.

[0066] (2) Preparation of lithium-ion batteries

[0067] The above-mentioned negative electrode sheet is used in combination with the corresponding positive electrode, separator, electrolyte and other auxiliary materials to assemble the required lithium-ion battery.

[0068] It should be noted that the size and shape of the negative electrode sheets of the above-mentioned embodiments and comparative examples are the same. Specifically, the shape of the negative electrode sheet is rectangular, the thickness is 0.150 mm, and the length is 1500 mm; the shape of the positive electrode sheet is also rectangular, the thickness is 0.115 mm, and the length is 1430 mm; the diaphragm is a PE diaphragm with a thickness of 0.012 mm; and the electrolyte is an electrolyte matching sodium electrolyte.

[0069] The negative electrode sheet peeling force, battery initial efficiency and cycle life of Example 1 and Comparative Example 1 were tested below.

[0070] Among them, the battery's first effect is tested at room temperature using a 0.2C charge and discharge current test; the cycle life is tested at room temperature using a 1C1C standard test.

[0071] The test results are as follows Figure 1(a) to Figure 3(a)As shown, it can be seen that in Example 1, M = Na, carboxylated styrene butadiene emulsion pH = 3.5, solid content is 30%, NaOH solution concentration is 0.5M, active material in slurry: conductive agent: thickener: SBR-Na = 94.7:1.5:1.3:2.5. For example, in Example 1, the negative electrode sheet peeling force is increased from 6.3N / m to 8.6N / m; the battery first efficiency is increased from 83.5% to 85.6%; 1000cycle cycle capacity retention rate is increased from 88.6% to 93.2%. However, the various test results of Comparative Example 1 are not as good as those of Example 1.

[0072] A similar pattern is also shown for lithium batteries. Figure 1(b) to Figure 3(b) It can be seen that under the same test conditions, Example 2 has better performance than Comparative Example 2. The negative electrode sheet peeling force is increased from 9.5 N / m to 12.5 N / m; the lithium battery first efficiency is increased from 88.5% to 90.1%; and the 1000 cycle capacity retention rate is increased from 85.4% to 88.5%.

[0073] It can be seen that the negative electrode binder of the embodiment of the present invention is a high-performance negative electrode binder, specifically comprising SBR-Na or SBR-Li, which can effectively improve the first efficiency of the battery, reduce the loss of active sodium, and thus improve the battery capacity and energy density. In addition, SBR-Na or SBR-Li can improve the negative electrode sheet peeling force, capture free acid (H+) in the electrolyte, and thus improve the cycle life.

[0074] In summary, the negative electrode binder, negative electrode sheet, preparation method and battery according to the embodiments of the present invention have the advantages of simple synthesis and obvious effect, and are very suitable for industrial promotion.

[0075] Other structures and operations of the battery according to the embodiment of the present invention are known to those skilled in the art and will not be described in detail here.

[0076] In the description of the present invention, it is necessary to understand that the terms "center", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "inside", "outside", "circumferential" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0077] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0078] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "illustrative embodiments", "examples", "specific examples", or "some examples" means that the specific features, structures, materials, or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example.

[0079] Although the embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the claims and their equivalents.

Claims

1. A negative electrode binder, characterized in that: The negative electrode binder is an SBR-M binder emulsion containing both SBR and M elements, M is Na or Li, and the pH of the negative electrode binder is 7.0-9.

0.

2. A method for preparing a negative electrode binder, characterized in that: The steps include: The SBR emulsion and the MOH solution are mixed until the pH is 7.0 to 9.0 and does not change within a preset time to obtain an SBR-M binder emulsion, wherein M is Na or Li.

3. The method for preparing a negative electrode binder according to claim 2, characterized in that: The pH of the SBR emulsion is 2.5-7.

0.

4. The method for preparing a negative electrode binder according to claim 2, characterized in that: The solid content of the SBR emulsion is 20% to 60%.

5. The method for preparing a negative electrode binder according to claim 2, characterized in that: The concentration of the MOH solution is 0.05M to 1.0M.

6. A negative electrode sheet, characterized in that: The negative electrode binder according to claim 1 is included.

7. A method for preparing a negative electrode sheet, characterized in that: The steps include: The negative electrode active material, the conductive agent, the thickener, the SBR-M binder and the solvent water are mixed to obtain a mixture; The mixture is coated on a metal foil to obtain the negative electrode sheet according to claim 6.

8. The method for preparing a negative electrode sheet according to claim 7, characterized in that: The negative electrode active material is one of graphite, hard carbon, silicon carbon or phosphorus carbon or any combination thereof, and / or the metal foil is aluminum foil or copper foil.

9. The method for preparing a negative electrode sheet according to claim 7, characterized in that: The mass ratio of the negative electrode active material, the conductive agent, the thickener, and the SBR-M binder is (92.5-97.7): (0.5-2.0): (0.8-2.0): (1.0-3.5).

10. A battery, characterized in that: Includes the negative electrode sheet as described in claim 6.

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