Negative plate, preparation method of negative plate, sodium ion battery and preparation method of sodium ion battery

Abstract

The invention discloses a negative plate and a preparation method thereof, and a sodium ion battery and a preparation method thereof, and belongs to the technical field of batteries. According to the preparation method of the negative electrode plate, the initial electrode plate is pretreated by an electrochemical method, so that the ether-based electrolyte pre-constructs a layer of interfacial film on the surface of the negative electrode plate of the sodium-ion battery, and the interfacial film is excellent in stability, can promote rapid transmission of sodium ions and has better dynamic performance. When being applied to subsequent preparation of the sodium-ion battery, the ether-based electrolyte and the ester-based electrolyte have a synergistic effect, so that the dual advantages of the ether-based electrolyte and the ester-based electrolyte can be fully realized, the corresponding adverse effects of the two electrolytes can be avoided, the interface stability of the sodium-ion battery can be improved, rapid transmission of sodium ions at the interface can be ensured, and the service life of the sodium-ion battery can be prolonged. And the sodium ion battery has excellent dynamic performance and cycle performance, and the problems of solvation co-embedding and poor stability do not exist.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a negative electrode sheet and a preparation method thereof, a sodium ion battery and a preparation method thereof. Background Art

[0002] Sodium-ion batteries have great application prospects in the fields of energy storage and small power due to their unique performance advantages in low-temperature performance, rate performance and safety performance, as well as their cost advantages. Sodium-ion batteries are mainly composed of positive electrode materials, negative electrode materials, electrolytes, diaphragms and shells. The electrolyte plays an important role in the battery system. It is not only a medium for the transmission of active ions in the battery, but also participates in the formation of the electrode / electrolyte interface film. Therefore, a suitable electrolyte can greatly improve the electrochemical performance of the battery.

[0003] Currently in commercial use, the common types of electrolytes are mainly carbonate electrolytes and ether electrolytes. Ether-based electrolytes form a thin, uniform and dense SEI film on the surface of the negative electrode, which can improve the interface stability of sodium-ion batteries while ensuring the rapid transmission of sodium ions at the interface and have better kinetic performance. However, ether-based electrolytes have the problem of solvation co-embedding, which will destroy the electrode structure during recycling and are not suitable for long-cycle scenarios. Ester-based electrolytes do not have the problem of solvation co-embedding and have better cycle performance. However, ester-based electrolytes have poor stability and high sodium ion solubility, resulting in unstable film formation and poor rate performance under high-rate test conditions.

[0004] Therefore, developing a simple and feasible battery preparation method that takes into account both cycle and rate performance is of great significance to promoting the practical application and industrialization of sodium-ion batteries.

[0005] Application Contents

[0006] In view of this, the present application provides a negative electrode sheet and a preparation method thereof, a sodium ion battery and a preparation method thereof, aiming to provide a negative electrode sheet and a sodium ion battery that can take into account both cycle and rate performance.

[0007] The embodiment of the present application is implemented as follows: a method for preparing a negative electrode sheet is provided, comprising: providing an initial sodium ion battery, wherein the initial sodium ion battery comprises an initial negative electrode sheet, an initial positive electrode sheet, a first separator and an ether-based electrolyte; performing charge and discharge treatment on the initial sodium ion battery to pre-treat the initial negative electrode sheet; and taking out the initial negative electrode sheet that has been pre-filmed from the initial sodium ion battery to obtain a negative electrode sheet.

[0008] In some embodiments, the main salt of the ether-based electrolyte is one or more of NaPF6 and NaClO4; and / or, the solvent of the ether-based electrolyte is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; and / or, the ether-based electrolyte is a commercial electrolyte.

[0009] In some embodiments, the material of the initial negative electrode sheet includes one or more of hard carbon, graphite, porous carbon, soft carbon, mesophase carbon microspheres, tin alloys, bismuth alloys, and metallic sodium; and / or, the initial positive electrode sheet includes a positive electrode active substance, a conductive agent, and a binder, wherein the positive electrode active substance includes any one or more of layered oxides, polyanions, and Prussian blue; and / or, the first diaphragm is selected from polyethylene, polypropylene, a glass fiber diaphragm, or polytetrafluoroethylene.

[0010] In some embodiments, the charging and discharging treatment of the initial sodium ion battery includes: charging and discharging the initial sodium ion battery in cycles with a current of 0.1C to 1C, with the number of cycles being 1 to 20 times.

[0011] In some embodiments, removing the initial negative electrode sheet that has undergone the pre-filming from the initial sodium ion battery comprises: disassembling the initial sodium ion battery in a glove box filled with inert gas and removing the initial negative electrode sheet that has undergone the pre-filming, and then drying it.

[0012] Correspondingly, an embodiment of the present application also provides a negative electrode sheet, which is prepared by the above-mentioned preparation method.

[0013] Correspondingly, an embodiment of the present application also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a second separator and an ester-based electrolyte, wherein the negative electrode sheet is prepared by the above-mentioned preparation method.

[0014] In some embodiments, the main salt of the ester-based electrolyte is one or more of NaPF6 and NaClO4; and / or, the solvent of the ester-based electrolyte is one or more of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; and / or, the ester-based electrolyte is a commercial electrolyte; and / or, the positive electrode sheet includes a positive electrode active material, a conductive agent, and a binder, wherein the positive electrode active material includes any one or more of layered oxides, polyanions, and Prussian blue; and / or, the second diaphragm is selected from polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene; and / or, the first diaphragm and the second diaphragm are diaphragms made of the same material.

[0015] Correspondingly, an embodiment of the present application also provides a method for preparing a sodium ion battery, comprising: providing an initial sodium ion battery, the initial sodium ion battery comprising an initial negative electrode sheet, an initial positive electrode sheet, a first diaphragm and an ether-based electrolyte; performing charge and discharge treatment on the initial sodium ion battery to pre-treat the initial negative electrode sheet and the initial positive electrode sheet; removing the initial negative electrode sheet and the initial positive electrode sheet from the initial sodium ion battery after the charge and discharge treatment to obtain a negative electrode sheet and a positive electrode sheet; preparing a sodium ion battery, wherein the sodium ion battery comprises the positive electrode sheet, the negative electrode sheet, a second diaphragm and an ester-based electrolyte.

[0016] In some embodiments, the main salt of the ether-based electrolyte is one or more of NaPF6 and NaClO4; and / or, the solvent of the ether-based electrolyte is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; and / or, the ether-based electrolyte is a commercial electrolyte; and / or, the initial negative electrode sheet includes one or more of hard carbon, graphite, porous carbon, soft carbon, mesophase carbon microspheres, tin alloy, bismuth alloy, and metallic sodium; and / or, the initial positive electrode sheet includes a positive electrode active material, a conductive agent, and a binder, wherein the The positive electrode active material includes any one or more of layered oxides, polyanions, and Prussian blue; and / or, the first diaphragm is selected from polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene; and / or, the second diaphragm is selected from polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene; and / or, the first diaphragm and the second diaphragm are made of the same material; and / or, the charge and discharge treatment of the initial sodium ion battery includes: charging and discharging the initial sodium ion battery with a current of 0.1C to 1C, and the number of cycles is 1 to 20 times.

[0017] The preparation method of the negative electrode sheet of the present application is to pre-treat the initial electrode sheet by an electrochemical method, wherein the ether-based electrolyte will pre-construct a layer of interface film on the surface of the negative electrode sheet of the sodium ion battery, and this interface film has excellent stability, and can promote the rapid transmission of sodium ions, and has better kinetic performance. When applied to the subsequent preparation of sodium ion batteries, through the synergistic effect with the ester-based electrolyte, the dual advantages of the ether-based electrolyte and the ester-based electrolyte can be fully realized and the corresponding adverse effects of the two electrolytes can be avoided, which can improve the interface stability of the sodium ion battery, ensure the rapid transmission of sodium ions at the interface, and make the kinetic performance and cycle performance of the sodium ion battery excellent, and there is no problem of solvation co-embedding and poor stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For those skilled in the art, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 It is a schematic flow chart of an embodiment of a method for preparing a hard carbon negative electrode material provided in the present application;

[0020] Figure 2 1 is a graph of cycle capacity retention rates of Example 3, Comparative Example 1 and Comparative Example 2;

[0021] Figure 3 This is a graph showing the 5C discharge capacity retention rates of Example 3, Comparative Examples 1 and 2. DETAILED DESCRIPTION

[0022] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without making creative work belong to the scope of protection of the present application. In addition, it should be understood that the specific implementation methods described herein are only used to illustrate and explain the present application and are not used to limit the present application. In the present application, unless otherwise stated, the directional words used, such as "upper" and "lower", are specifically the directions of the drawings in the accompanying drawings. In addition, in the description of the present application, the term "including" means "including but not limited to".

[0023] Various embodiments of the present application may be presented in the form of a range; it should be understood that the description in the form of a range is only for convenience and brevity, and should not be understood as a rigid limitation on the scope of the present application; therefore, the range description should be considered to have specifically disclosed all possible sub-ranges and single numerical values ​​within the range. For example, the range description from 1 to 6 should be considered to have specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., as well as single numbers within the range, such as 1, 2, 3, 4, 5 and 6, which apply regardless of the range. In addition, whenever a numerical range is indicated herein, it is meant to include any cited number (fractional or integer) within the indicated range.

[0024] In this application, "and / or" describes the association relationship of associated objects, indicating that there may be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. A and B can be singular or plural.

[0025] In the present application, "at least one" means one or more, and "plurality" means two or more. "At least one", "at least one of the following" or similar expressions refer to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0026] The present application provides a method for preparing a negative electrode sheet, referring to Figure 1 , Figure 1 This is a flow chart of an embodiment of a method for preparing a hard carbon negative electrode material provided by the present application, which specifically includes the following steps:

[0027] Step S1: providing an initial sodium ion battery, wherein the initial sodium ion battery comprises an initial negative electrode sheet, an initial positive electrode sheet, a first separator and an ether-based electrolyte;

[0028] Step S2: performing charge and discharge treatment on the initial sodium ion battery to pre-treat the initial negative electrode sheet;

[0029] Step S3: taking out the initial negative electrode sheet after the pre-film formation from the initial sodium ion battery to obtain a negative electrode sheet.

[0030] In this embodiment, the initial electrode sheet is pretreated by an electrochemical method, wherein the ether-based electrolyte pre-constructs an interface film on the surface of the negative electrode sheet of the sodium ion battery. This interface film has excellent stability, can promote the rapid transmission of sodium ions, and has better kinetic performance.

[0031] The negative electrode sheet prepared by the method of this embodiment, when applied to the subsequent preparation of sodium ion batteries, can fully realize the dual advantages of ether-based electrolytes and ester-based electrolytes through synergistic effect with ester-based electrolytes and avoid the corresponding adverse effects of the two electrolytes, which can improve the interface stability of sodium ion batteries, ensure the rapid transmission of sodium ions at the interface, and make the kinetic performance and cycle performance of sodium ion batteries excellent, and there is no problem of solvation co-embedding and poor stability.

[0032] In step S1:

[0033] The initial positive electrode sheet may be a common positive electrode sheet in sodium ion batteries, and is generally prepared from a positive electrode active material, a conductive agent, a binder, and the like. The positive electrode active material may include any one or more of layered oxides, polyanions, Prussian blue, and the like. It is understandable that the initial positive electrode sheet may be purchased commercially, or may be made from commercially available materials.

[0034] In a specific embodiment, the positive electrode active material, the conductive agent (SuperP), and the binder (such as polyvinylidene fluoride, PVDF) are homogenously mixed in a mass ratio of 90:5:5, wherein the solvent is N-methylpyrrolidone (NMP) and the solid content is 40-50%; after forming a uniform mixed slurry, it is coated on the current collector aluminum foil, and after vacuum drying at 70-90°C, it is cut into an initial positive electrode sheet.

[0035] The first diaphragm can be made of polyethylene, polypropylene, glass fiber diaphragm, or polytetrafluoroethylene.

[0036] The material of the initial negative electrode sheet may include one or more of hard carbon, graphite, porous carbon, soft carbon, mesophase carbon microspheres, tin alloy, bismuth alloy, and metallic sodium. In a specific embodiment, the material of the negative electrode sheet is selected from hard carbon.

[0037] In a specific embodiment, the preparation method of the initial negative electrode sheet includes: selecting a commercial hard carbon material of any precursor, mixing the negative electrode active material hard carbon (HC), the conductive agent (SuperP), and the binder polyvinylidene fluoride (PVDF) in a mass ratio of 92:4:4, the solvent is N-methylpyrrolidone (NMP), and the solid content is 30-40%. After forming a uniform mixed slurry, it is coated on the current collector aluminum foil, and after vacuum drying at 70-90°C, it is cut into an initial negative electrode sheet.

[0038] The ether-based electrolyte can be any electrolyte known in the art, and can be a commercially available ether-based electrolyte. Using a commercial electrolyte can save costs and improve the wide applicability of the negative electrode sheet preparation method.

[0039] In one embodiment, the main salt of the ether-based electrolyte may be one or more sodium salts such as NaPF6, NaClO4, etc.; the solvent may be one or more of ethylene glycol dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), triethylene glycol dimethyl ether (TRGDME), and tetraethylene glycol dimethyl ether (TEGDME).

[0040] The assembly steps of the initial sodium ion battery specifically include: in a glove box filled with argon, using a glass fiber membrane as a battery separator, assembling and sealing the pre-cut initial positive electrode sheet, initial negative electrode sheet, separator and commercial ether-based electrolyte into an initial sodium ion battery.

[0041] In step S2:

[0042] The charge and discharge treatment can be performed using a battery testing platform, such as a Xinwei constant temperature battery testing stand. The charge and discharge treatment is specifically: the battery is charged and discharged at a current of 0.1C to 1C for 1 to 20 cycles, thereby pre-treating the initial negative electrode sheet for pre-film formation.

[0043] It is understandable that during the charge and discharge process, the initial positive electrode sheet is also processed accordingly.

[0044] In step S3:

[0045] The taking out of the initial negative electrode sheet after the pre-filming from the initial sodium ion battery can be carried out in a glove box filled with an inert gas such as argon, and the pre-treated negative electrode sheet and positive electrode sheet can be obtained after drying.

[0046] The present application provides a negative electrode sheet prepared by the above preparation method.

[0047] The present application also provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet, a second diaphragm and an ester-based electrolyte, wherein the negative electrode sheet is the negative electrode sheet provided in the present application.

[0048] The present application also provides a sodium ion battery, which is assembled from a positive electrode sheet, a negative electrode sheet, a second diaphragm and an ester-based electrolyte, wherein the negative electrode sheet is the negative electrode sheet provided in the present application.

[0049] Specifically, the main salt of the selected ester-based electrolyte is one or more of NaPF6, NaClO4, etc.; the solvent is one or more of ethylene carbonate (EC), diethyl carbonate (DEC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC). The ester-based electrolyte can be a commercial electrolyte, which can save costs and improve the wide applicability of the sodium ion battery preparation method.

[0050] The second diaphragm is selected from polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene. In a specific embodiment, the second diaphragm is selected from a diaphragm of the same material as the first diaphragm.

[0051] The positive electrode sheet comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material comprises any one or more of layered oxides, polyanions and Prussian blue.

[0052] In one embodiment, the positive electrode sheet may be the positive electrode sheet prepared in step S3, or the initial positive electrode sheet prepared in step S1, or other commonly used positive electrode sheets of sodium ion batteries.

[0053] It can be understood that the sodium ion battery is compared with the initial sodium ion battery:

[0054] a. The electrolytes used are different, specifically: the ether-based electrolyte used in the initial sodium-ion battery and the ester-based electrolyte used in the sodium-ion battery;

[0055] b. The negative electrode sheet of the sodium ion battery is removed from the initial sodium ion battery after being processed;

[0056] c. The separator used in the sodium ion battery can be the same as that in the initial sodium ion battery;

[0057] d. The positive electrode sheet used in the preparation process of the sodium ion battery can be the same as the positive electrode sheet used in the preparation of the initial sodium ion battery, or the positive electrode sheet removed from the initial sodium ion battery after the treatment in step 2 can be used.

[0058] In one embodiment, the preparation method of the sodium ion battery includes: assembling and sealing the negative electrode sheet prepared by the preparation method provided in the present application, the positive electrode sheet prepared by the preparation method provided in the present application, the second diaphragm and the ester-based electrolyte into a sodium ion battery.

[0059] In one embodiment, the method for preparing a sodium ion battery provided in the present application comprises:

[0060] Providing an initial sodium ion battery, the initial sodium ion battery comprising an initial negative electrode sheet, an initial positive electrode sheet, a first separator and an ether-based electrolyte;

[0061] Performing charge and discharge treatment on the initial sodium ion battery to pre-treat the initial negative electrode sheet and the initial positive electrode sheet;

[0062] Taking out the initial negative electrode sheet and the initial positive electrode sheet from the initial sodium ion battery after the charge and discharge treatment to obtain a negative electrode sheet and a positive electrode sheet;

[0063] A sodium ion battery is prepared, wherein the sodium ion battery comprises the positive electrode sheet, the negative electrode sheet, a second separator and an ester-based electrolyte.

[0064] The main salt of the ether-based electrolyte is one or more of NaPF6 and NaClO4. The solvent of the ether-based electrolyte is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether. The ether-based electrolyte can be a commercial electrolyte.

[0065] The initial negative electrode sheet includes one or more of hard carbon, graphite, porous carbon, soft carbon, mesophase carbon microspheres, tin alloy, bismuth alloy, and metallic sodium.

[0066] The initial positive electrode sheet comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material comprises any one or more of layered oxides, polyanions and Prussian blue.

[0067] The first diaphragm is made of polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene. The second diaphragm is made of polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene. Specifically, the first diaphragm and the second diaphragm can be made of the same material.

[0068] The charging and discharging treatment of the initial sodium ion battery includes: charging and discharging the initial sodium ion battery in cycles with a current of 0.1C to 1C, with the number of cycles being 1 to 20 times.

[0069] The sodium ion battery provided in the present application includes a negative electrode sheet on which a stable interface film has been pre-constructed through electrochemical treatment, which can effectively isolate the contact between the ester-based electrolyte and the negative electrode active material, inhibit the occurrence of side reactions, and promote the rapid transmission of sodium ions, and has better kinetic performance; at the same time, the ester-based electrolyte improves the solvation co-embedding problem of the ether-based electrolyte, thereby improving the cycle performance of the battery.

[0070] The sodium ion battery and its preparation method provided in the present application can significantly improve the kinetic performance and cycle performance of the battery, and the preparation method has a simple process and high adaptability, and is suitable for various hard carbon battery systems.

[0071] The technical scheme and technical effects of the present application are described in detail below through specific embodiments, comparative examples and experimental examples. The following embodiments are only some embodiments of the present application and do not specifically limit the present application. Unless otherwise specified, the raw materials, reagents, equipment, etc. used in the following examples can be purchased through conventional commercial channels or prepared under conventional conditions in accordance with regulations.

[0072] Example 1

[0073] Step 1: Preparation of initial sodium ion battery

[0074] The commercial layered sodium oxide positive electrode, conductive agent (Super P), and binder polyvinylidene fluoride (PVDF) are homogenized and mixed at a mass ratio of 90:5:5, the solvent is N-methylpyrrolidone (NMP), and the solid content is 40-50%. After forming a uniform mixed slurry, it is coated on the current collector aluminum foil, vacuum dried at 70-90°C, and cut into the preset positive electrode sheet. The commercial hard carbon negative electrode (HC), conductive agent (Super P), and binder polyvinylidene fluoride (PVDF) are homogenized and mixed at a mass ratio of 92:4:4, using N-methylpyrrolidone (NMP) as the solvent, and mixed at a solid content of 30-40% to form a uniform mixed slurry, which is then coated on the current collector aluminum foil, vacuum dried at 70-90°C, and cut into the preset negative electrode sheet. In a glove box filled with argon, a glass fiber membrane is used as the battery separator, and an ether-based electrolyte with NaPF6 as the main salt and diethylene glycol dimethyl ether (DEGDME) as the solvent is selected. The pre-cut positive electrode sheet, negative electrode sheet, separator and commercial ether-based electrolyte are assembled and sealed into a sodium-ion battery.

[0075] Step 2: Charge and discharge the initial sodium ion battery

[0076] The assembled battery was tested on the Xinwei constant temperature battery test stand, and the battery was charged and discharged once with a current of 0.5C, and a pre-film treatment was performed on the negative electrode surface.

[0077] Step 3, in a glove box filled with argon, take out the positive electrode and negative electrode sheets after the pre-filming treatment, and dry them naturally to obtain the positive electrode sheets and negative electrode sheets after the filming;

[0078] Step 4, using glass fiber membrane as battery separator, selecting NaPF6 as main salt, and commercial ester-based electrolyte with ethylene carbonate (EC) and diethyl carbonate (DEC) in a volume ratio of 1:1 as solvent, assembling and sealing the film-formed positive electrode sheet, negative electrode sheet, separator and commercial ester-based electrolyte to form a sodium ion battery.

[0079] Example 2

[0080] The difference from Example 1 is that in step 2, the battery is charged and discharged in a cycle at a current of 0.5C for 5 times.

[0081] Example 3

[0082] The difference from Example 1 is that in step 2, the battery is charged and discharged in a cycle at a current of 0.5 C for 10 times.

[0083] Example 4

[0084] The difference from Example 1 is that in step 2, the battery is charged and discharged in a cycle at a current of 0.5 C for 20 times.

[0085] Comparative Example 1

[0086] The difference from Example 1 is that only ether-based electrolyte is used for assembly, that is, only step 1 is performed to prepare the initial sodium ion battery, and the subsequent steps are not performed.

[0087] Comparative Example 2

[0088] The difference from Example 1 is that only an ester-based electrolyte is used for assembly, that is, during the process of preparing the initial sodium-ion battery in step 1, the ester-based electrolyte in step 4 is used to replace the ether-based electrolyte in step 1 to prepare a sodium-ion battery, and the subsequent steps 2-4 are not performed.

[0089] Comparative Example 3

[0090] The difference from Example 1 is that an ester-based electrolyte is first used to charge and discharge the battery at a current of 0.5C for 1 cycle. After the battery electrodes are pretreated, an ether-based electrolyte is used for assembly; that is, the electrolytes used in steps 1 and 4 are replaced, that is, an ester-based electrolyte is used in step 1, and an ether-based electrolyte is used in step 4.

[0091] Comparative Example 4

[0092] The difference from Example 1 is that an ester-based electrolyte is first used to charge and discharge the battery at a current of 0.5C for 5 cycles, and after the battery electrodes are pretreated, an ether-based electrolyte is used for assembly; or the difference from Comparative Example 3 is that in step 2, the battery is charged and discharged at a current of 0.5C for 5 cycles.

[0093] Comparative Example 5

[0094] The difference from Example 1 is that an ester-based electrolyte is first used to charge and discharge the battery at a current of 0.5C for 10 cycles, and after the battery electrodes are pretreated, an ether-based electrolyte is used for assembly; or the difference from Comparative Example 3 is that in step 2, the battery is charged and discharged at a current of 0.5C for 10 cycles.

[0095] Comparative Example 6

[0096] The difference from Example 1 is that an ester-based electrolyte is first used to charge and discharge the battery at a current of 0.5C for 20 cycles, and after the battery electrodes are pretreated, an ether-based electrolyte is used for assembly; or the difference from Comparative Example 3 is that in step 2, the battery is charged and discharged at a current of 0.5C for 20 cycles.

[0097] test:

[0098] The sodium ion batteries prepared in the various embodiments and comparative examples were tested on a Xinwei constant temperature battery test stand at a test temperature of 25°C. The test steps were as follows: after being left for 4 hours, they were charged to 3.95V at a constant current of 0.33C, left for 5 minutes, discharged to 2.0V at a constant current, left for 5 minutes, and cycled 3 times; they were charged to 3.95V at a constant current of 1C, left for 5 minutes, discharged to 2.0V at a constant current, and the battery was cycled and rate tested based on the constant capacity. The test results are shown in Tables 1 and Figure 2 , Figure 3 , Figure 2 is the cycle capacity retention rate of Example 3 and Comparative Example 1 / Comparative Example 2, Figure 3 5C discharge capacity retention rate of Example 3 and Comparative Example 1 / Comparative Example 2.

[0099] Table 1. Battery cycle and rate test data

[0100] First effect / % 500 cycles retention rate / % 5C discharge capacity retention rate / % Example 1 86.8 96.3 96.12 Example 2 86.9 97.5 97.53 Example 3 87.4 99.8 98.47 Example 4 87.2 99.4 97.37 Comparative Example 1 87.8 82.5 95.81 Comparative Example 2 85.2 95.6 85.42 Comparative Example 3 85.4 83.6 87.46 Comparative Example 4 85.3 84.9 86.93 Comparative Example 5 85.5 87.3 86.42 Comparative Example 6 84.7 86.2 86.01

[0101] From the above Table 1 and Figure 2 , Figure 3 It can be seen that the sodium ion battery formed by the negative electrode sheet prepared by the method provided in the present application has good initial efficiency as well as good cycle performance and rate performance.

[0102] The negative electrode sheet and its preparation method, sodium ion battery and its preparation method provided in the embodiments of the present application are introduced in detail above. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for technical personnel in this field, according to the idea of ​​the present application, there will be changes in the specific implementation method and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A method for preparing a negative electrode sheet, characterized in that: include: Providing an initial sodium ion battery, the initial sodium ion battery comprising an initial negative electrode sheet, an initial positive electrode sheet, a first separator and an ether-based electrolyte; Performing charge and discharge treatment on the initial sodium ion battery to pre-treat the initial negative electrode sheet; The initial negative electrode sheet that has undergone the pre-filming is taken out from the initial sodium ion battery to obtain a negative electrode sheet.

2. The preparation method according to claim 1, characterized in that: include: The main salt of the ether-based electrolyte is one or more of NaPF6 and NaClO4; and / or, The solvent of the ether-based electrolyte is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; and / or, The ether-based electrolyte is a commercial electrolyte.

3. The preparation method according to claim 1, characterized in that: include: The material of the initial negative electrode sheet includes one or more of hard carbon, graphite, porous carbon, soft carbon, mesophase carbon microspheres, tin alloy, bismuth alloy, and metallic sodium; and / or, The initial positive electrode sheet comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material comprises any one or more of layered oxides, polyanions and Prussian blue; and / or, The first diaphragm is selected from polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene.

4. The preparation method according to claim 1, characterized in that: The charging and discharging process of the initial sodium ion battery comprises: The initial sodium ion battery is charged and discharged in cycles at a current of 0.1C to 1C, with the number of cycles being 1 to 20 times.

5. The preparation method according to claim 1, characterized in that: The method of taking out the initial negative electrode sheet after the pre-filming from the initial sodium ion battery comprises: The initial sodium ion battery is disassembled in a glove box filled with inert gas, and the initial negative electrode sheet after the pre-filming is taken out and then air-dried.

6. A negative electrode sheet, characterized in that: Prepared by the preparation method according to any one of claims 1 to 5.

7. A sodium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet, a second separator and an ester-based electrolyte, wherein the negative electrode sheet is prepared by the preparation method according to any one of claims 1 to 5.

8. The sodium ion battery according to claim 7, characterized in that: The main salt of the ester-based electrolyte is one or more of NaPF6 and NaClO4; and / or, The solvent of the ester-based electrolyte is one or more of ethylene carbonate, diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate; and / or, The ester-based electrolyte is a commercial electrolyte; and / or, The positive electrode sheet comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material comprises any one or more of layered oxides, polyanions and Prussian blue; and / or, The second diaphragm is selected from polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene; and / or, The first diaphragm and the second diaphragm are made of the same material.

9. A method for preparing a sodium ion battery, characterized in that: include: Providing an initial sodium ion battery, the initial sodium ion battery comprising an initial negative electrode sheet, an initial positive electrode sheet, a first separator and an ether-based electrolyte; Performing charge and discharge treatment on the initial sodium ion battery to pre-treat the initial negative electrode sheet and the initial positive electrode sheet; Taking out the initial negative electrode sheet and the initial positive electrode sheet from the initial sodium ion battery after the charge and discharge treatment to obtain a negative electrode sheet and a positive electrode sheet; A sodium ion battery is prepared, wherein the sodium ion battery comprises the positive electrode sheet, the negative electrode sheet, a second separator and an ester-based electrolyte.

10. The preparation method according to claim 9, characterized in that: The main salt of the ether-based electrolyte is one or more of NaPF6 and NaClO4; and / or, The solvent of the ether-based electrolyte is one or more of ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether; and / or, The ether-based electrolyte is a commercial electrolyte; and / or, The initial negative electrode sheet comprises one or more of hard carbon, graphite, porous carbon, soft carbon, mesophase carbon microspheres, tin alloy, bismuth alloy, and metallic sodium; and / or, The initial positive electrode sheet comprises a positive electrode active material, a conductive agent and a binder, wherein the positive electrode active material comprises any one or more of layered oxides, polyanions and Prussian blue; and / or, The first diaphragm is selected from polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene; and / or, The second diaphragm is selected from polyethylene, polypropylene, glass fiber diaphragm or polytetrafluoroethylene; and / or, The first diaphragm and the second diaphragm are made of the same material; and / or, The charging and discharging treatment of the initial sodium ion battery includes: charging and discharging the initial sodium ion battery in cycles with a current of 0.1C to 1C, with the number of cycles being 1 to 20 times.

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