A method and application for continuously supplementing sodium to improve circulatory performance

Abstract

This application proposes a method and application for continuously replenishing sodium to improve cycle performance. The method includes: obtaining a first mass content of the sodium replenisher in a first cathode material when the theoretical specific capacity of the sodium replenisher is equal to the capacity consumed in forming the SEI film; determining, based on the theoretical specific capacity, a first capacity required by a second cathode material containing a second mass content of sodium replenisher to compensate for the capacity consumed by the SEI film, thus obtaining the remaining capacity; dividing the remaining capacity into at least two segments of second capacity, and replenishing each segment of second capacity sequentially during the cycle. This method for continuously replenishing sodium to improve cycle performance achieves segmented release of the sodium replenisher by precisely controlling the full-cell voltage. Specifically, the first released active sodium is used to improve the initial efficiency, while the remaining active sodium is stored in the sodium-ion replenishment station (cathode material) and released when the cycle retention rate decays to compensate for the sodium consumed throughout the sodium-ion battery's lifespan.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a method and application for continuously supplementing sodium to improve cycle performance. Background Technology

[0002] With the increasing global demand for clean energy, sodium-ion batteries, as a novel energy storage device, have attracted widespread attention due to their abundant resources, low cost, and high safety. However, the loss of active sodium during the charging and discharging process of sodium-ion batteries is a significant issue, mainly due to two factors: 1) active sodium loss caused by SEI formation; and 2) repeated SEI breakage and growth caused by continuous side reactions. Previous research has primarily focused on using pre-sodiumization to compensate for the sodium ions consumed by SEI formation, thereby improving initial efficiency and energy density.

[0003] Currently, sodium-ion batteries suffer from irreversible capacity loss during cycling, mainly due to: 1) the formation of a solid electrolyte membrane (SEI) leading to irreversible loss of active sodium ions; 2) changes in the structure of the sodium-ion cathode material resulting in capacity loss; and 3) severe consumption of active sodium ions by side reactions during cycling.

[0004] To improve initial efficiency and cycle life, pre-sodiuming is required. Traditional cathode pre-sodiuming involves adding extra active sodium to the cathode material, releasing the sodium replenishment capacity all at once to compensate for irreversible capacity loss during the first charge-discharge cycle, thereby improving the overall battery energy density and cycle life. However, releasing the sodium replenishment capacity all at once results in excessive and active sodium ions being stored at the negative electrode for a long time, which can exacerbate side reactions with the electrolyte and consume more active sodium during cycling.

[0005] Therefore, there is an urgent need for a method that can continuously replenish sodium during the cycle to improve cycle performance and avoid side reactions and other defects. Summary of the Invention

[0006] In view of this, one objective of this application is to provide a method for continuously replenishing sodium to improve cycle performance. This method achieves the segmented release of sodium replenishment agent by precisely controlling the full cell voltage. Specifically, the active sodium released initially is used to improve the first efficiency, while the remaining active sodium is stored in the sodium ion replenishment station (positive electrode material) and released when the cycle retention rate decays, thereby compensating for the sodium consumed throughout the entire life cycle of the sodium-ion battery.

[0007] Another objective of this application is to provide a method for continuously supplementing sodium to improve circulatory performance.

[0008] To achieve the above objectives, the first aspect of this application proposes a method for continuously supplementing sodium to improve circulatory performance, comprising:

[0009] Obtain the charging capacity and voltage curves of the sodium supplement;

[0010] The first mass content of the sodium supplement in the first cathode material is obtained when the theoretical specific capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film.

[0011] Based on the theoretical specific capacity, a first capacity required by the second cathode material containing the second mass content of the sodium-replenishing agent to compensate for the capacity consumed by the SEI film is determined, and the difference between the theoretical specific capacity and the first capacity is taken as the remaining capacity of the sodium-replenishing agent in the second cathode material; the second mass content is greater than the first mass content, and the second cathode material is the same as the first cathode material except for the content of the sodium-replenishing agent; both the first cathode material and the second cathode material include cathode active material;

[0012] By combining the charging capacity and voltage curves, the first charging cutoff voltage corresponding to the first capacity is obtained;

[0013] The remaining capacity is divided into at least two segments of second capacity, and the second capacity segments are gradually added to the cycle process of the first full cell containing the second cathode material, taking into account the cycle retention rate decay.

[0014] In some embodiments, obtaining a first mass ratio of the sodium replenishing agent in the first cathode material when the theoretical specific capacity of the sodium replenishing agent is equal to the capacity consumed in forming the SEI film includes:

[0015] A coin cell was prepared using a sodium supplement as the positive electrode active material.

[0016] Prepare a second full cell containing the first cathode material;

[0017] The first mass content is calculated based on the charging specific capacity of the positive electrode active material in the first positive electrode material, the first efficiency of the second full cell, the first-cycle sodium replenishment capacity of the coin half cell (i.e., the theoretical specific capacity of the sodium replenishment agent), and the mass content of the positive electrode active material in the first positive electrode material.

[0018] In some embodiments, the first mass content ratio is calculated according to the following formula:

[0019] a*b%*(dx)%+c*x%=a*(dx)%,

[0020] Wherein, a is the charge capacity of the positive active material in the first positive electrode material, in mAh / g; b% is the first efficiency of the second full cell; c is the first-cycle sodium replenishment capacity of the coin cell (i.e., the theoretical charge capacity of the sodium replenishment agent), in mAh / g; d% is the sum of the mass content of the positive active material in the first positive electrode material and the first mass content; x% is the first mass content.

[0021] In some embodiments, the coin cell is a coin cell used to obtain the charge capacity and voltage curve of the sodium supplement.

[0022] In some embodiments, the cycling process of progressively adding the second capacity segment by segment to the first full cell containing the second positive electrode material includes:

[0023] For each decay of the first full-cell cycle capacity retention rate, the second capacity is used to replenish the cycle decomposition capacity once.

[0024] In some implementations, the required replenishment of the cyclic decomposition capacity each time is calculated using the following formula:

[0025] C i+1 =i*(C / n),

[0026] Among them, C i+1 The cyclic decomposition capacity replenished for the i-th time is expressed in mAh / g; C is the remaining capacity expressed in mAh / g; C / n is the second capacity; n is the number of segments into which the remaining capacity is divided equally, expressed in segments; n is an integer greater than 1 and less than 2000; i is the number of times the cyclic decomposition capacity is replenished, expressed as an integer greater than 0 and less than n.

[0027] In some embodiments, the method for continuously supplementing sodium to improve circulation performance further includes:

[0028] Based on the charging capacity and voltage curves, the voltage corresponding to the total capacity released by the sodium replenishing agent after each replenishment of the cycle decomposition capacity is determined, and this voltage is used as the corresponding second cutoff voltage for capacity recovery replenishment of the first full cell.

[0029] In some embodiments, the cycle retention rate decay includes a cycle decay ratio below R%, and a capacity retention rate decrease of mR% after a certain number of cycles; where R ≤ 20%, and m is greater than 0 and less than 1.

[0030] In some embodiments, the method for continuously replenishing sodium to improve cycle performance further includes: after each replenishment of the second capacity, continuing to cycle the first full cell.

[0031] In some embodiments, both the first mass content and the second mass content are 1-10%.

[0032] In some embodiments, the sodium supplement includes at least one of Na2O, NaNO2, Na2CO3, Na2NiO2, NaCrO2, Na5FeO4, NaBH4, NaNH2, Na2C6O6, Na2C6H2O6, CH3COONa, PABZ-Na, EDTA-4Na, DTPA-5Na, Na2C4O4, Na2C2O4, and Na2C3O5.

[0033] In some embodiments, both the first positive electrode material and the second positive electrode material further include a first positive electrode conductive agent, a second positive electrode conductive agent, a positive electrode binder, and the sodium supplement agent, and the mass ratio of the positive electrode active material, the first positive electrode conductive agent, the second positive electrode conductive agent, and the positive electrode binder is (87-99):(1-5):(1-4):(1-4).

[0034] In some embodiments, the positive electrode active material in both the first and second positive electrode materials includes at least one of sodium ion layered oxide, sodium-containing sulfate, sodium-containing phosphate, sodium-containing fluorinated polyanion, sodium-containing mixed polyanion, sodium-containing silicate, and sodium-containing borate.

[0035] In some embodiments, the negative electrode material of the first full cell includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener and a negative electrode binder, wherein the mass ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode thickener and the negative electrode binder is (90-99):(1-3):(1-4):(1-4).

[0036] In some embodiments, the first positive electrode conductive agent, the second positive electrode conductive agent, and the negative electrode conductive agent all include at least one of Super P, Ketjen Black, acetylene black, carbon nanotubes, graphene, conductive graphite, carbon fiber, conductive carbon nanotubes, or ordered mesoporous carbon.

[0037] In some embodiments, the separator of the first full cell includes at least one of a polymer separator, a ceramic separator, and a polymer / ceramic composite separator.

[0038] The second aspect of this application relates to the application of the method for continuously replenishing sodium to improve cycle performance as described in this application during the use of sodium-ion batteries.

[0039] The method for continuously supplementing sodium to improve circulatory performance described in this application can bring at least the following beneficial effects:

[0040] 1. By precisely regulating the full-cell voltage, the release of active sodium in the sodium storage layer is controlled, which can both ensure the initial efficiency and continuously replenish sodium to improve the cycle.

[0041] 2. Excess sodium ions are stored at the positive electrode. Compared with the traditional sodium replenishment method where all excess sodium ions are stored at the negative electrode, the side reactions that consume sodium during the cycle process are reduced.

[0042] Additional aspects and advantages of this application will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of this application. Attached Figure Description

[0043] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the following description of the embodiments taken in conjunction with the accompanying drawings.

[0044] in:

[0045] Figure 1 The flowchart illustrates a method for continuously supplementing sodium to improve cycle performance, which is an exemplary embodiment of this application.

[0046] Figure 2 The charging curve of the coin cell with sodium supplement Na2O in Example 1 is shown. It is also the charging capacity and voltage curve (Call & V curve) of the second full cell (sodium-ion coin cell) with the optimal addition ratio (i.e., the first mass content) of 3% sodium supplement Na2O.

[0047] Figure 3 The charging curve (also known as the charging capacity & voltage curve (Call & V curve)) of the first full cell (sodium-ion coin cell) with an excess of 5% sodium supplement Na2O in Example 1 (i.e., the second mass content) is shown.

[0048] Figure 4 This is a cycle decay diagram of the full cell (i.e., the first full cell in this application).

[0049] Figure 5 The charging curve of the coin cell with sodium supplement Na2NiO2 in Example 3 is shown. It is also the charging capacity and voltage curve (referred to as the Call & V curve) of the second full cell (sodium-ion coin cell) with the optimal addition ratio (i.e., the first mass content) of 3.85% sodium supplement Na2NiO2.

[0050] Figure 6 The charging curve (also known as the charging capacity & voltage curve (Call & V curve)) of the first full cell (sodium-ion coin cell) with an excess ratio (i.e., the second mass content) of 6.4% sodium supplement Na2NiO2 in Example 3 is shown. Detailed Implementation

[0051] The embodiments of this application are described in detail below, with examples of these embodiments illustrated in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this application, and should not be construed as limiting this application.

[0052] In this application, the disclosure of numerical ranges includes all values ​​throughout the range and the disclosure of further subdivisions of the range, including the endpoints and subranges given for these ranges.

[0053] Unless otherwise specified, all raw materials and equipment involved in this application are self-made through commercial means or known methods; and all methods involved are conventional methods unless otherwise specified.

[0054] In this application, room temperature refers to 20-30℃.

[0055] The following describes a method for continuously supplementing sodium to improve circulation performance according to an embodiment of this application, with reference to the accompanying drawings.

[0056] Figure 1 This is a flowchart illustrating a method for continuously supplementing sodium to improve cycle performance, as shown in an exemplary embodiment of this application. Figure 1 As shown, the method includes the following steps:

[0057] S101. Obtain the charging capacity and voltage curves of the sodium supplement.

[0058] In some embodiments, the sodium replenishing agent includes, but is not limited to, at least one of Na₂O, NaNO₂, Na₂CO₃, Na₂NiO₂, NaCrO₂, Na₅FeO₄, NaBH₄, NaNH₂, Na₂C₆O₆, Na₂C₆H₂O₆, CH₃COONa, PABZ-Na, EDTA-4Na, DTPA-5Na, Na₂C₄O₄, Na₂C₂O₄, and Na₂C₃O₅. These sodium replenishing agents have high sodium replenishment capacity, are compatible with existing common manufacturing processes and battery systems, and exhibit good environmental stability, remaining stable in air or relatively dry environments.

[0059] As a preferred example, the sodium supplement is at least one of Na2O, Na2NiO2, Na5FeO4, Na2C6O6, and Na2CO3, more preferably Na2O.

[0060] It should be noted that different sodium supplements have different charging capacity and voltage curves.

[0061] In the embodiments of this application, when obtaining the charging specific capacity and voltage curve of the sodium supplement, it is necessary to use the sodium supplement as the positive electrode active material to prepare a coin cell, and then obtain the charging specific capacity and voltage curve of the sodium supplement in the coin cell.

[0062] It should be noted that, in the embodiments of this application, the coin cell used to obtain the above-mentioned charging capacity and voltage curve is the same as the coin cell involved in calculating the first mass ratio later.

[0063] As an alternative example, the assembly method of the above-mentioned sodium-supplemented coin cell is as follows:

[0064] Conductive agent, binder, and sodium supplement agent were mixed in a mass ratio of 10:5:85, and an appropriate amount of N-methylpyrrolidone (NMP) was added to form a slurry. The slurry was then uniformly coated onto the surface of a 13μm thick aluminum foil using a scraper. After drying in a vacuum drying oven at 120℃ for 10 hours, a positive electrode sheet was obtained. A sodium sheet was used as the negative electrode, and the sodium supplement agent coin cell was assembled in a glove box in the following order: negative electrode shell - spring sheet - gasket - negative electrode (sodium sheet) - electrolyte - separator - electrolyte - positive electrode - positive electrode shell. The sodium supplement agent Na2O was charged to 4.2V using a constant current and constant voltage of 0.05C and the cutoff current was 0.02C. The specific capacity and voltage curves of the sodium supplement agent Na2O were obtained. The electrolyte composition is as follows: the solute can be 1 mol / L NaClO4, the solvent is ethylene carbonate / diethyl carbonate (volume ratio 1:1); the diaphragm is a 12 μm thick polyethylene (PE) diaphragm; the conductive agent is Super P, and the binder is polyvinylidene fluoride.

[0065] S102. Obtain the first mass content of the sodium replenishing agent in the first cathode material when the theoretical specific capacity of the sodium replenishing agent is equal to the capacity consumed in forming the SEI film. The first cathode material includes a cathode active material.

[0066] It is understood that in the embodiments of this application, when the mass content of the sodium supplement in the first positive electrode material is the first mass content, the theoretical specific capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film. That is, the first mass ratio is the optimal mass ratio that makes the theoretical specific capacity of the sodium supplement equal to the capacity consumed in forming the SEI film. If the amount of sodium supplement added is greater than the first mass ratio, it is considered an excessive addition.

[0067] In some embodiments, obtaining a first mass ratio of the sodium replenishing agent in the first cathode material when the theoretical specific capacity of the sodium replenishing agent is equal to the capacity consumed in forming the SEI film includes:

[0068] A coin cell was prepared using the sodium supplement as the positive electrode active material.

[0069] Prepare a second full cell containing the first cathode material;

[0070] The first mass content is calculated based on the charging specific capacity of the positive electrode active material in the first positive electrode material, the first efficiency of the second full cell, the first-cycle sodium replenishment capacity of the coin half cell (i.e., the theoretical specific capacity of the sodium replenishment agent), and the mass content of the positive electrode active material in the first positive electrode material.

[0071] It should be noted that the order of the steps for preparing the coin cell half-cell and the steps for preparing the second full cell can be interchanged.

[0072] In some embodiments, the coin cell is a coin cell used to obtain the charge capacity and voltage curve of the sodium supplement.

[0073] In some embodiments, the method for preparing the second full cell is as follows:

[0074] The positive electrode active material, the first positive electrode conductive agent, the second positive electrode conductive agent, the positive electrode binder, and the sodium supplement agent, which constitute the formulation amount of the first positive electrode material, are combined into a positive electrode slurry and prepared into a positive electrode sheet.

[0075] The negative electrode active material, negative electrode conductive agent, negative electrode thickener, and negative electrode binder are mixed in the formula to form a negative electrode slurry and then prepared into a negative electrode sheet.

[0076] The positive electrode, negative electrode, and separator are stacked and assembled, with the separator positioned between the positive and negative electrode sheets. After being welded with tabs and sealed, the electrolyte is injected after baking to ensure the moisture content is within acceptable limits.

[0077] In some embodiments, in the second full cell, the first positive electrode material includes a positive electrode active material, a first positive electrode conductive agent, a second positive electrode conductive agent, a positive electrode binder, and the sodium supplement agent, and the mass ratio of the positive electrode active material, the first positive electrode conductive agent, the second positive electrode conductive agent, and the positive electrode binder is (87-99):(1-5):(1-4):(1-4), including but not limited to 90:2:1:1, 90:1:2:1, 90:1:1:2.5, 90:3:1:1, 95:2:2:2.5, 99:2:2:2.5, 95:2:1:4, or 99:1:1:2.5, etc.

[0078] As an optional example, in the first positive electrode material of the second full cell, the ratio by mass is: positive electrode active material: first positive electrode conductive agent: second positive electrode conductive agent: positive electrode binder: sodium supplement agent = 92%: 1.5%: 1.0%: 2.5%: 3%.

[0079] In some embodiments, the first positive electrode material of the second full cell includes at least one of sodium-ion layered oxide, sodium-containing sulfate, sodium-containing phosphate, sodium-containing fluorinated polyanion, sodium-containing mixed polyanion, sodium-containing silicate, and sodium-containing borate.

[0080] For example, sodium ion layered oxides include, but are not limited to, at least one of O3-phase sodium ion layered oxides and P2-phase sodium ion layered oxides. The O3-phase sodium ion layered oxides include, but are not limited to, Na... 2 / 3 Ni 1 / 3 Mn 1 / 3Ti 1 / 3 O2, Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na[Ni 0.25 Fe 0.5 Mn 0.25 At least one of O2, etc.; sodium ion layered oxides of the P2 phase, including but not limited to Na. 0.5 VO2, Na 2 / 3 Mn 1 / 2 Fe 1 / 2 O2, Na 0.85 Li 0.12 Ni 0.22 Mn 0.66 At least one of O2, etc.

[0081] For example, sodium-containing sulfates include, but are not limited to, Na2Fe2(SO4)3 and Na2Fe(SO4). 2.2 At least one of H2O, etc.

[0082] For example, sodium-containing phosphates include, but are not limited to, at least one of Na3V2(PO3), Na3MnTi(PO3)3, Na2FeP2O7, and Na2CoP2O7.

[0083] For example, sodium-containing fluorinated polyanions include, but are not limited to, at least one of Na3(VPO4)2F3, Na3(VOPO4)2F, and Na2FePO4F.

[0084] For example, sodium-containing mixed polyanions include, but are not limited to, at least one of Na4Fe3(PO4)2P2O7, Na4Co3(PO4)2P2O7, Na7V4(P2O7)4(PO4).

[0085] For example, sodium-containing silicates include, but are not limited to, at least one of Na2MnSiO4, Na2FeSiO4, etc.

[0086] For example, sodium-containing borates include, but are not limited to, Na3CoB5O. 10 Na3FeB5O 10 At least one of the following.

[0087] As a preferred example, in the first positive electrode material of the second full cell, the positive electrode active material is Na4Fe3(PO4)2P2O7, Na 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3 O2, Na 2 / 3 Mn 1 / 2 Fe 1 / 2 At least one of O2, etc.

[0088] In some embodiments, the negative electrode material of the second full cell includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder, wherein the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode thickener, and negative electrode binder is (90-99):(1-3):(1-4):(1-4), including but not limited to 90:2:2.5:2.5, 90:1:3:2, 99:2:2.5:2.5, 99:1:1:2, 95:2:2.5:2.5, 95:1:1:1, or 95:3:1:2, etc.

[0089] As an alternative example, in the negative electrode material of the second full cell, the mass ratio of negative electrode active material: negative electrode conductive agent: negative electrode thickener: negative electrode binder is 94.6%: 0.8%: 1.6%: 3.0%.

[0090] In some embodiments, in the second full cell, the first positive electrode conductive agent, the second positive electrode conductive agent, and the negative electrode conductive agent are all, but are not limited to, at least one of Super P, Ketjen Black, acetylene black, carbon nanotubes, graphene, conductive graphite, carbon fiber, conductive carbon nanotubes, or ordered mesoporous carbon.

[0091] It should be noted that, in the embodiments of this application, the selection of materials such as positive electrode binder, negative electrode active material, negative electrode thickener and negative electrode binder in the second full cell is not limited, and they can all be any positive electrode binder, negative electrode active material, negative electrode thickener and negative electrode binder known in the art.

[0092] In some embodiments, the electrolyte in the second full cell comprises: a solute of 1 mol / L NaClO4 or 1 mol / L NaPF4, and a solvent of two or more of EC, PC, FEC, and DMC.

[0093] As an alternative example, the electrolyte preparation method in the second full cell is as follows: dissolve 1 mol / L of solute NaClO4 in a solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1).

[0094] In some embodiments, the separator of the second full cell includes, but is not limited to, at least one of polymer separators, ceramic separators, polymer / ceramic composite separators, etc.

[0095] For example, polymer membranes include, but are not limited to, at least one of single-layer polymer membranes and multi-layer polymer membranes. Single-layer polymer membranes include, but are not limited to, polyethylene (PE) membranes or polypropylene (PP) membranes.

[0096] As an alternative example, the diaphragm is a polyethylene (PE) diaphragm with a thickness of 12 μm.

[0097] In some embodiments, the first mass content ratio is calculated according to the following formula:

[0098] a*b%*(dx)%+c*x%=a*(dx)%,

[0099] Wherein, a is the charge capacity of the positive active material in the first positive electrode material, in mAh / g; b% is the first efficiency of the second full cell; c is the first-cycle sodium replenishment capacity of the coin cell (i.e., the theoretical charge capacity of the sodium replenishment agent), in mAh / g; d% is the sum of the mass content of the positive active material and the mass content of the sodium replenishment agent in the first positive electrode material (i.e., the first mass content); x% is the first mass content.

[0100] It should be noted that, in the embodiments of this application, the sodium replenishment capacity of the coin cell in the first week involved in the calculation of the first mass content is also the theoretical specific capacity in step S102. Furthermore, when calculating the first mass content using the above formula, the contents of the positive electrode conductive agent (i.e., the aforementioned first and second positive electrode conductive agents) and the positive electrode binder in the first positive electrode material of the second full cell can generally be preset according to conventional techniques in the art. That is, the mass content of the positive electrode conductive agent and the mass content of the positive electrode binder in the first positive electrode material of the second full cell are known. Therefore, by subtracting the mass content of the positive electrode binder and the mass content of the positive electrode conductive agent from 100% of the total mass content of the first positive electrode material of the second full cell, the sum d of the mass content of the positive electrode active material and the mass content of the sodium replenishment agent in the first positive electrode material of the second full cell can be obtained. For example, when the positive electrode conductive agent is SP and CNT, the positive electrode binder is PVDF, and their mass contents in the first positive electrode material of the second full cell are 1.5%, 1.0%, and 2.5%, respectively, d% = 100% - SP% - CNT% - PVDF% = 100% - 1.5% - 1% - 2.5% = 95%, the mass content of sodium supplementer in the first positive electrode material of the second full cell—the first mass ratio—can be calculated according to the above formula.

[0101] In the embodiments of this application, the first mass content varies depending on the choice of the sodium supplementer. Generally, the first mass content of the sodium supplementer in the first cathode material is 1-10%, including but not limited to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, or 10%.

[0102] As an optional example, the sodium replenishing agent is Na2O, whose theoretical specific capacity (i.e., the initial sodium replenishment capacity in step S102) c is 510 mAh / g; the charging specific capacity a of the first positive electrode material in the second full cell is 113.7 mAh / g, and the discharging specific capacity is 101.6 mAh / g; the positive electrode active material in the first positive electrode material of the second full cell is Na4Fe3(PO4)2P2O7, and its mass content in the first positive electrode material is 92%; the initial efficiency b of the second full cell is 85.4%; the first mass content x% of the sodium replenishing agent Na2O in the first positive electrode material of the second full cell is 3%.

[0103] S103. Based on the theoretical specific capacity, determine the first capacity required by the second cathode material containing the second mass content of the sodium replenishing agent to compensate for the capacity consumed by the SEI film, and use the difference between the theoretical specific capacity and the first capacity as the remaining capacity of the sodium replenishing agent in the second cathode material; the second mass content is greater than the first mass content, and the second cathode material is the same as the first cathode material except for the content of the sodium replenishing agent.

[0104] In the embodiments of this application, the theoretical specific capacity in step S102 can be determined by charging the second full cell to the target voltage V0 (the method for determining V0 is combined with a curve (e.g., hereinafter). Figure 2 After calculating x%*CA=y%*CB, it is confirmed that the first full cell, for example, requires 306mAh / g for SEI. The horizontal and vertical axes correspond to V0, so that the sodium replenishment capacity is fully released to compensate for SEI consumption. At this time, the sodium replenishment capacity released is exactly equal to the capacity consumed by SEI. The theoretical specific capacity of the sodium replenishment corresponding to the target voltage V0 can be obtained according to the charging specific capacity and voltage curve, which is the theoretical specific capacity in step S102.

[0105] In some embodiments, the method for determining the first capacity required by the second cathode material containing the second mass content of the sodium-supplementing agent to compensate for the capacity consumed by the SEI membrane, based on the theoretical specific capacity, is as follows:

[0106] Based on the theoretical specific capacity, the first capacity is calculated using the following formula:

[0107] x%*C A =y%*C B

[0108] Wherein: x% is the first mass content; y% is the second mass content; C A The theoretical specific capacity of the sodium supplement is expressed in mAh / g; C B The first capacity is expressed in mAh / g.

[0109] For example, when the sodium supplement is Na2O, the theoretical specific capacity of Na2O is 510 mAh / g, the first mass content is 3%, and the second mass content is 5%, the first capacity calculated according to the above formula is 306 mAh / g. That is, when the amount of sodium supplement added in the second cathode material is 5 wt%, the capacity required to compensate for the consumption of the SEI film is 306 mAh / g.

[0110] It is understood that in the embodiments of this application, the second mass content is greater than the first mass content, that is, the sodium supplement is added in excess in the second cathode material compared to the first cathode material. Except for the content of the sodium supplement, the second cathode material is identical to the first cathode material; that is, the only difference between the first and second cathode materials is the different content of the sodium supplement.

[0111] It should be noted that, similar to the first mass content, the second mass content varies depending on the choice of the sodium supplement agent in the embodiments of this application. It should also be emphasized that, although the main purpose of the sodium supplement agent in the embodiments of this application is to improve cycle life, it is not necessarily true that the more sodium supplement agent added, the better. Increasing the amount of sodium supplement agent added to the second positive electrode material will lead to increased Na re-intercalation at the negative electrode during discharge. + If there are not enough sites for the positive electrode to receive the discharge, the discharge capacity will be reduced to varying degrees.

[0112] Based on the above, in the embodiments of this application, the content of the sodium supplement in the second positive electrode material exceeds the content of the sodium supplement in the first positive electrode material by no more than 2 / 3. That is, the difference between the second mass content and the first mass content does not exceed 2 / 3 of the first mass ratio.

[0113] In some embodiments, the second mass content is 1-10%, including but not limited to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%.

[0114] As an optional example, when the sodium supplement is Na2O, the first mass content is 3% and the second mass content is 5%.

[0115] In the embodiments of this application, the remaining capacity is stored in the sodium ion replenishment station, that is, stored in the second positive electrode material.

[0116] In the embodiments of this application, if the theoretical specific capacity is defined as C all The first capacity is C SEI If the remaining capacity is C, then C = C all -C SEI .

[0117] S104. Based on the charging capacity and voltage curve, obtain the first charging cutoff voltage corresponding to the first capacity.

[0118] In the embodiments of this application, based on the first capacity corresponding to the horizontal axis of the charging capacity and voltage curve, the corresponding voltage on the vertical axis can be found, which is the corresponding first charging cutoff voltage.

[0119] In the embodiments of this application, the purpose of confirming the first capacity and the first charging cutoff voltage is to just make up for the fact that the first discharge capacity of the full-charge cycle will not be low when SEI is used; it can take into account both the first discharge and the remaining capacity.

[0120] S105. The remaining capacity is divided into at least two segments of second capacity, and in combination with the cycle retention rate decay, each segment of the second capacity is gradually added to the cycle process of the first full cell containing the second cathode material.

[0121] It is understood that in the embodiments of this application, the remaining capacity is divided into multiple segments, each segment being a second capacity used to compensate for capacity loss during the cyclic process. It should be noted that in the embodiments of this application, the remaining capacity (referred to as formula C below) is... i+1 = (i-1)*(C / n) where C) is the number of segments into which the components are divided (C in the formula below) i+1 = (i-1)*(C / n) where n can be infinitely many, and the second capacity corresponding to each segment (C in the formula below) i+1 = (i-1)*(C / n) where C / n can be infinitely small.

[0122] In some embodiments, the cycle retention rate decay includes a cycle decay ratio below R%, and a capacity retention rate decrease of mR% after a certain number of cycles; where R ≤ 20%, and m is greater than 0 and less than 1.

[0123] For example, R includes, but is not limited to, 2%.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, 6.5%, 7%, 7.5%, 8%, 8.5%, 9%, 9.5%, 10%, 10.5%, 11%, 11.5%, 12%, 12.5%, 13%, 13.5%, 14%, 14.5%, 15%, 15.5%, 16%, 16.5%, 17%, 17.5%, 18%, 18.5%, 19%, 19.5%, 20%, etc.

[0124] For example, m may include, but is not limited to, 0.1, 0.25, 0.5, 0.75, or 0.95.

[0125] In some embodiments, the cycling process of progressively adding the second capacity segment by segment to the first full cell containing the second positive electrode material includes:

[0126] For each decay of the first full-cell cycle capacity retention rate, the second capacity is used to replenish the cycle decomposition capacity once.

[0127] In the embodiments of this application, replenishing the capacity after one cycle refers to performing a charge-discharge cycle on the first full battery within a preset voltage range each time the capacity retention rate of the first full battery decreases, thereby achieving a replenishment of the capacity after one cycle. For example, taking Embodiment 1 below as an example, combined with... Figure 3 When the cycle capacity retention rate of the first full battery decreases by 3%, the first full battery is charged to 3.7V (V2) and then discharged to -1.5V to replenish the capacity after the first cycle breakdown. Then, the 1C / 1C cycle performance is tested again at room temperature within a voltage range of 1.5V-3.4V. When the cycle capacity retention rate of the first full battery decreases by 3% again, the first full battery is charged to V3 (V2). Figure 3 (Not shown), then discharge to -1.5V to replenish the capacity for the second cycle decomposition, and then continue to test the 1C / 1C cycle performance in the voltage range of 1.5V-3.4V at room temperature.

[0128] In some implementations, the required replenishment of the cyclic decomposition capacity each time is calculated using the following formula:

[0129] C i+1 =i*(C / n),

[0130] Among them, C i+1The cyclic decomposition capacity replenished for the i-th time is expressed in mAh / g; C is the remaining capacity expressed in mAh / g; C / n is the second capacity; n is the number of segments into which the remaining capacity is divided equally, expressed in segments; n is an integer greater than 1 and less than 2000; i is the number of times the cyclic decomposition capacity is replenished, expressed as an integer greater than 0 and less than n.

[0131] For example, when replenishing capacity for the first time, i = 1, and the replenished cyclic decomposition capacity C2 = C / n; when replenishing capacity for the second time, i = 2, and the replenished cyclic decomposition capacity C3 = 2*(C / n); when replenishing capacity for the third time, i = 3, and the replenished cyclic decomposition capacity C4 = 3*(C / n); and so on. At this time, the aforementioned theoretical capacity (C...) all ), the first capacity (C) SEI ) and the required replenishment of the cycle decomposition capacity (C) for each iteration i+1 The relationship between C and C is: all =C SEI +C2+……C n .

[0132] In some embodiments, the method for continuously supplementing sodium to improve circulation performance further includes:

[0133] Based on the charging capacity and voltage curves, the voltage corresponding to the total capacity released by the sodium replenishing agent after each replenishment of the cycle decomposition capacity is determined, and this voltage is used as the corresponding second cutoff voltage for capacity recovery replenishment of the first full cell.

[0134] In some embodiments, the total sodium release capacity after each replenishment of the cyclic decomposition capacity is calculated using the following formula:

[0135] C' i =C SEI +C i+1

[0136] Among them, C' i Ci is the total capacity released by the sodium supplement after the i-th replenishment of the cyclic decomposition capacity, in mAh / g; Ci is the cyclic decomposition capacity replenished after the i-th replenishment, in mAh / g; i is the number of times the cyclic decomposition capacity is replenished, i is an integer greater than 0 and less than n; n is the number of segments into which the remaining capacity is divided, in segments; n is an integer greater than 1 and less than 2000.

[0137] It should be noted that, in the embodiments of this application, C SEIThe first capacity required for the second cathode material containing the second mass content of the sodium replenishing agent to compensate for the capacity consumed by the SEI membrane can be regarded as the capacity released by the sodium replenishing agent for the first time, and each subsequent replenishment of the cyclic decomposition capacity is equivalent to the capacity released by the sodium replenishing agent for the second, third... nth time.

[0138] For example, according to Figure 3 The Call & V curve shows the total release capacity of the sodium supplement after the first replenishment of the cyclic decomposition capacity, C'1 = C. SEI +C2, whose corresponding voltage is V2, is set as the charging cutoff voltage (i.e., the second cutoff voltage); similarly, after the second replenishment of the cycle decomposition capacity, the total capacity released by the sodium supplement is C'2 = C SEI +C3, whose corresponding voltage is V3, is set as the charging cutoff voltage (i.e., the second cutoff voltage); and so on, to obtain C'3, C'4...C' n The corresponding voltages V4, V5...Vn are used to set V3, V4...Vn as the charging cutoff voltage (i.e., the second cutoff voltage) for small current capacity replenishment.

[0139] In some embodiments, the method for continuously replenishing sodium to improve cycle performance further includes: after each replenishment of the second capacity, continuing to cycle the first full cell.

[0140] In some embodiments, in the first full cell, the second positive electrode material includes a positive electrode active material, a first positive electrode conductive agent, a second positive electrode conductive agent, a positive electrode binder, and the sodium supplement agent, and the mass ratio of the positive electrode active material, the first positive electrode conductive agent, the second positive electrode conductive agent, and the positive electrode binder is (87-99):(1-5):(1-4):(1-4), including but not limited to 90:2:1:1, 90:1:2:1, 90:1:1:2.5, 90:3:1:1, 95:2:2:2.5, 99:2:2:2.5, 95:2:1:4, or 99:1:1:2.5, etc.

[0141] In some embodiments, the second positive electrode material of the first full cell includes at least one of sodium-ion layered oxide, sodium-containing sulfate, sodium-containing fluorinated polyanion, sodium-containing mixed polyanion, sodium-containing silicate, and sodium-containing borate.

[0142] For example, sodium ion layered oxides include, but are not limited to, at least one of O3-phase sodium ion layered oxides and P2-phase sodium ion layered oxides. The O3-phase sodium ion layered oxides include, but are not limited to, Na... 2 / 3 Ni 1 / 3 Mn 1 / 3Ti1 / 3 O2, Na[Ni 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, Na[Ni 0.25 Fe 0.5 Mn 0.25 At least one of O2, etc.; sodium ion layered oxides of the P2 phase, including but not limited to Na. 0.5 VO2, Na 2 / 3 Mn 1 / 2 Fe 1 / 2 O2, Na 0.85 Li 0.12 Ni 0.22 Mn 0.66 At least one of O2, etc.

[0143] For example, sodium-containing sulfates include, but are not limited to, Na2Fe2(SO4)3 and Na2Fe(SO4). 2.2 At least one of H2O, etc.

[0144] For example, sodium-containing phosphates include, but are not limited to, at least one of Na3V2(PO3), Na3MnTi(PO3)3, Na2FeP2O7, and Na2CoP2O7.

[0145] For example, sodium-containing fluorinated polyanions include, but are not limited to, at least one of Na3(VPO4)2F3, Na3(VOPO4)2F, and Na2FePO4F.

[0146] For example, sodium-containing mixed polyanions include, but are not limited to, at least one of Na4Fe3(PO4)2P2O7, Na4Co3(PO4)2P2O7, Na7V4(P2O7)4(PO4).

[0147] For example, sodium-containing silicates include, but are not limited to, at least one of Na2MnSiO4, Na2FeSiO4, etc.

[0148] For example, sodium-containing borates include, but are not limited to, Na3CoB5O. 10 Na3FeB5O 10 At least one of the following.

[0149] As a preferred example, in the second positive electrode material of the first full cell, the positive electrode active material is Na4Fe3(PO4)2P2O7, Na 2 / 3 Ni 1 / 3 Mn 1 / 3 Ti 1 / 3 O2, Na 2 / 3 Mn 1 / 2 Fe1 / 2 At least one of O2, etc.

[0150] In some embodiments, the negative electrode material of the first full cell includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener, and a negative electrode binder, wherein the mass ratio of the negative electrode active material, negative electrode conductive agent, negative electrode thickener, and negative electrode binder is (90-99):(1-3):(1-4):(1-4), including but not limited to 90:2:2.5:2.5, 90:1:3:2, 99:2:2.5:2.5, 99:1:1:2, 95:2:2.5:2.5, 95:1:1:1, or 95:3:1:2, etc.

[0151] In some embodiments, in the first full cell, the first positive electrode conductive agent, the second positive electrode conductive agent, and the negative electrode conductive agent are all, but are not limited to, at least one of Super P, Ketjen Black, acetylene black, carbon nanotubes, graphene, conductive graphite, carbon fiber, conductive carbon nanotubes, or ordered mesoporous carbon.

[0152] It should be noted that, in the embodiments of this application, the selection of materials such as positive electrode binder, negative electrode active material, negative electrode thickener and negative electrode binder in the first full cell is not limited, and they can all be any positive electrode binder, negative electrode active material, negative electrode thickener and negative electrode binder known in the art.

[0153] In some embodiments, the separator of the first full cell includes, but is not limited to, at least one of polymer separators, ceramic separators, and polymer / ceramic composite separators.

[0154] For example, polymer membranes include, but are not limited to, at least one of single-layer polymer membranes and multi-layer polymer membranes. Single-layer polymer membranes include, but are not limited to, polyethylene (PE) membranes or polypropylene (PP) membranes.

[0155] As an alternative example, in the first full cell, the separator is a polyethylene (PE) separator with a thickness of 12 μm.

[0156] In some embodiments, the electrolyte in the first full cell comprises:

[0157] The electrolyte used is the same as that used in coin cells. The solute can be 1 mol / L NaClO4 or 1 mol / L NaPF4, and the solvent includes, but is not limited to, two or more of the following: ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), and dimethyl carbonate (DMC).

[0158] As an alternative example, the electrolyte in the first full cell is prepared by dissolving 1 mol / L of solute NaClO4 in a solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1).

[0159] It should be noted that in the embodiments of this application, the first full cell and the second full cell are identical in composition except for the mass content of sodium supplement in the cathode material. Furthermore, the preparation methods of the first full cell and the second full cell are also the same, and will not be repeated here.

[0160] The method for continuously supplementing sodium to improve circulatory performance described in this application can bring at least the following beneficial effects:

[0161] 1. By precisely regulating the full-cell voltage, the release of active sodium in the sodium storage layer is controlled, which can both ensure the initial efficiency and continuously replenish sodium to improve the cycle.

[0162] 2. Excess sodium ions are stored at the positive electrode. Compared with the traditional sodium replenishment method where all excess sodium ions are stored at the negative electrode, the side reactions that consume sodium during the cycle process are reduced.

[0163] The method for continuously replenishing sodium to improve cycle performance according to the embodiments of this application can be used in the use of sodium-ion batteries to achieve continuous sodium replenishment during the cycle process.

[0164] The following non-limiting embodiments further illustrate certain features of the present technology.

[0165] The ambient temperature used in the following examples and comparative examples is 25°C.

[0166] Example 1

[0167] The method for continuously supplementing sodium to improve circulation performance in this embodiment includes the following steps:

[0168] (1) Using Na2O as the positive electrode active material, a coin cell with sodium supplementation was prepared, and the charging specific capacity and voltage curves of the sodium supplementation agent Na2O were obtained, as follows: Figure 2 As shown. Wherein:

[0169] The preparation method of Na2O coin cell is as follows: SP:PVDF:Na2O is mixed in a mass ratio of 10:5:85, and an appropriate amount of NMP is added to make a slurry. This slurry is then uniformly coated onto the surface of a 13μm thick aluminum foil using a scraper. After drying in a vacuum drying oven at 120℃ for 10 hours, a positive electrode is obtained. A sodium sheet is used as the negative electrode, and the Na2O coin cell is assembled in a glove box in the following order: negative electrode shell - spring sheet - gasket - negative electrode (sodium sheet) - electrolyte - separator - electrolyte - positive electrode - positive electrode shell. The electrolyte solute is 1mol / L NaClO4, and the solvent is ethylene carbonate / diethyl carbonate (volume ratio 1:1). The separator is a 12μm thick polyethylene (PE) membrane.

[0170] The method for obtaining the charging capacity and voltage curves of Na2O is as follows: charge to 4.2V using a constant current and constant voltage of 0.05C, cut off current of 0.02C, and obtain the charging capacity and voltage curves of the sodium supplement Na2O.

[0171] (2) Obtain the theoretical specific capacity of sodium supplement Na2O (which can be obtained through...) Figure 2 The sodium replenishing agent is obtained at a first mass content in the first cathode material that is equal to the capacity consumed in forming the SEI film. Specifically, this includes the following steps:

[0172] 1) Prepare a second full cell containing a first positive electrode material. Specifically, the method for preparing the second full cell includes the following steps:

[0173] A. Preparation of positive electrode sheet containing sodium supplement Na2O: The positive electrode slurry was prepared according to the following mass ratio: positive active material: first positive conductive agent: second positive conductive agent: positive binder: sodium supplement = Na4Fe3(PO4)2P2O7:Super P:CNT:PVDF:Na2O = 92%:1.5%:1.0%:2.5%:3%, and then formed into a positive electrode sheet. The positive current collector is an aluminum foil with a thickness of 13μm.

[0174] B. Negative Electrode Preparation: A negative electrode slurry was prepared by mixing the negative active material, negative conductive agent, negative thickener, and negative binder in a mass ratio of 94.6% to 0.8% to 1.6% to 3.0% for hard carbon, Super P, CMC, and SBR. The negative electrode current collector was a 13μm thick aluminum foil.

[0175] C. Separator selection: The diaphragm is a 12um thick polyethylene (PE) diaphragm.

[0176] D. Electrolyte preparation: 1 mol / L NaClO4 solute is dissolved in a solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1).

[0177] E. Assembly: The positive electrode, negative electrode, and separator are stacked and assembled, with the separator positioned between the positive and negative electrode. After the tabs are welded and the assembly is sealed, the electrolyte can be injected after the moisture content is qualified by baking.

[0178] 2) Calculate the first mass content according to the following formula:

[0179] a*b%*(dx)%+c*x%=a*(dx)%,

[0180] Wherein, a is the charging specific capacity of the positive electrode active material in the first positive electrode material, which is 113.7 mAh / g; b% is the first-cycle efficiency of the second full cell, which is 85.4%; c is the first-cycle sodium replenishment capacity of the coin cell prepared in step (1) (that is, the theoretical specific capacity of Na2O, within the voltage range of 2.5-4.2V), which is 510 mAh / g; d% is the sum of the mass content of the positive electrode active material and the mass content of the sodium replenishment agent (that is, the first mass content) in the first positive electrode material of the second full cell, which is 95%; x% is the first mass content.

[0181] The calculated content of the first mass is 3%.

[0182] (3) The sodium replenishment capacity of the coin cell prepared in step (1) in the first week is the capacity of the sodium replenishing agent used in step (2) to compensate for the consumption of the SEI film, that is, the theoretical specific capacity of the sodium replenishing agent Na2O in step (2); based on the theoretical specific capacity, in Figure 2 Find the corresponding charging cutoff voltage V0 from the charging capacity and voltage curves, and charge the second full cell to the cutoff voltage V0, so that the sodium replenishment capacity is fully released to compensate for SEI consumption. Where V0 = 4.2V.

[0183] (4) Based on the theoretical specific capacity of sodium replenisher Na2O in step (2), determine the first capacity required by the second cathode material containing the second mass content of sodium replenisher Na2O to compensate for the capacity consumed by the SEI film. The difference between the theoretical specific capacity of sodium replenisher Na2O and the first capacity is taken as the remaining capacity of the sodium replenisher in the second cathode material, and this remaining capacity is stored in the sodium ion replenishment station (i.e., in the second cathode material). The second mass content is 5%. Specifically:

[0184] i) To prepare a positive electrode sheet by making the sodium supplement Na2O in the second positive electrode material to a second mass content of 5%, and then to prepare a first full cell, the method for preparing the first full cell includes the following steps:

[0185] F. Preparation of the positive electrode sheet: The positive electrode slurry was prepared according to the mass ratio of positive active material: first positive conductive agent: second positive conductive agent: positive binder: sodium supplement = Na4Fe3(PO4)2P2O7:Super P:CNT:PVDF:Na2O = 90%:1.5%:1.0%:2.5%:5% to form the positive electrode sheet. The positive current collector is an aluminum foil with a thickness of 13μm.

[0186] G. Preparation of negative electrode sheet: The negative electrode slurry was prepared according to the mass ratio of negative electrode active material: negative electrode conductive agent: negative electrode thickener: negative electrode binder = hard carbon: Super P: CMC: SBR = 94.6%: 0.8%: 1.6%: 3.0% to form a negative electrode sheet. The negative electrode current collector is an aluminum foil with a thickness of 13μm.

[0187] H. Diaphragm selection: The diaphragm is a 12µm thick polyethylene (PE) diaphragm.

[0188] I. Electrolyte preparation: Dissolve 1 mol / L NaClO4 in a solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1).

[0189] G. Assembly: The positive electrode, negative electrode, and separator are stacked and assembled, with the separator positioned between the positive and negative electrode. After the electrodes are welded together and sealed, the electrolyte is injected after baking to ensure the moisture content is within acceptable limits.

[0190] ii) Calculate the first capacity according to the theoretical specific capacity of sodium supplement Na2O in step (2) using the following formula:

[0191] x%*C A =y%*C B

[0192] Where: x% is the first mass content, which is 3%; y% is the second mass content, which is 5%; C A The theoretical specific capacity of the sodium supplement Na2O in step (2) (within a voltage range of 2.5-4.2V) is 510mAh / g; C B The first capacity is expressed in mAh / g.

[0193] Calculations show that the first capacity C required by the second cathode material, containing a second mass content of sodium replenishing agent Na2O, to compensate for the capacity consumed by the SEI membrane. B It is 306mAh / g.

[0194] iii) Define the theoretical specific capacity of sodium supplement Na2O in step (2) as C all The first capacity is C SEI If the remaining capacity is C, then C = C all -C SEI=510-306=204mAh / g.

[0195] (5) Combination Figure 2 The charging capacity and voltage curves of Na2O shown are used to obtain the first charging cutoff voltage V1 corresponding to the first capacity in step (4), where V1 = 3.6V (e.g., ...). Figure 3 (As shown). Specifically:

[0196] The first full cell in step (4) is charged with a constant current of 0.02C, and the cutoff voltage is set to 2.0V. Then, it is charged with a constant current of 0.1C to 3.4V to completely decompose the second positive electrode material in the first full cell. Finally, it is charged with a constant current and constant voltage of 0.05C to V1, and the cutoff current is 0.02C to achieve the first decomposition of the sodium storage layer C. SEI (C SEI =306mAh / g) is just enough to compensate for the loss of the SEI film.

[0197] (6) Divide the remaining capacity obtained in step (5) into 6 equal segments, each segment being labeled as the second capacity. Based on the cycle retention rate decay, gradually replenish the second capacity of each segment to the cycle life of the first full cell. Specifically, this includes the following steps:

[0198] a) When the first full-cell cycle capacity retention rate decreases by 3%, the corresponding second-capacity capacity is used to replenish the cycle capacity once. The required replenishment capacity for each cycle is calculated using the following formula:

[0199] C i+1 =i*(C / n),

[0200] Among them, C i+1 The cyclic decomposition capacity replenished for the i-th time is expressed in mAh / g; C is the remaining capacity, which is 204 mAh / g; C / n is the second capacity; n is the number of segments into which the remaining capacity is divided, which is 6 segments; i is the number of times the cyclic decomposition capacity is replenished, which is an integer greater than 0 and less than 6.

[0201] Calculations show that during the first capacity replenishment (i=1), the replenished cyclic decomposition capacity is C2=C / 6=204 / 6=34mAh / g; during the second capacity replenishment (i=2), the replenished cyclic decomposition capacity is C3=2*(C / 6)=68mAh / g; during the third capacity replenishment (i=3), the replenished cyclic decomposition capacity is C4=3*(C / n)=102mAh / g; during the fourth capacity replenishment (i=4), the replenished cyclic decomposition capacity is C5=4*(C / n)=136mAh / g; during the fifth capacity replenishment (i=5), the replenished cyclic decomposition capacity is C6=5*(C / n)=170mAh / g; and during the sixth capacity replenishment (i=6), the replenished cyclic decomposition capacity is C7=6*(C / n)=204mAh / g.

[0202] b) According to Figure 2 The charging capacity and voltage curves of Na2O shown are used to determine the voltage corresponding to the total capacity released by the sodium supplement Na2O after each replenishment cycle decomposition capacity, and this voltage is used as the corresponding second cutoff voltage for capacity recovery replenishment of the first full cell.

[0203] Specifically, the total release capacity of sodium supplement Na2O after each replenishment of the cycle decomposition capacity is calculated using the following formula:

[0204] C' i =C SEI +C i+1

[0205] Among them, C' i The total release capacity of sodium supplement Na2O after the i-th replenishment of the cyclic decomposition capacity is expressed in mAh / g; Ci is the cyclic decomposition capacity replenished in the i-th replenishment, expressed in mAh / g; i is the number of replenishments of the cyclic decomposition capacity, an integer greater than 0 and less than n; n is the number of segments into which the remaining capacity is divided equally, which is 6 segments.

[0206] according to Figure 3 The Call & V curve shows the total release capacity C'1 = C after the first replenishment of the cycle decomposition capacity and the subsequent addition of sodium supplement Na2O. SEI +C2=306+34=340mAh / g, corresponding to a voltage of V2. This voltage is set as the charging cutoff voltage (i.e., the second cutoff voltage). The first full battery is charged to 3.7V (V2) and then discharged to -1.5V to replenish the first cycle decomposition capacity. Then, the 1C / 1C cycle performance is tested for 2000 cycles within the 1.5V-3.4V voltage range at room temperature. When the cycle capacity retention rate of the first full battery decreases again by 3%, a second cycle decomposition capacity replenishment is performed. At this time, the total capacity released by the sodium supplement after the second cycle decomposition capacity replenishment is C'2=C SEI +C3 = 306 + 68 = 374 mAh / g, corresponding to a voltage of 3.8V (V3). This voltage is set as the charging cutoff voltage (i.e., the second cutoff voltage). The first full battery is charged to V3, then discharged to -1.5V to replenish capacity for the second cycle decomposition. Then, the 1C / 1C cycle performance is tested within the 1.5V-3.4V voltage range at room temperature. Similarly, the voltages V4, V5, V6, and V7 corresponding to C'3, C'4, C'5, and C'6 are obtained. V4, V5, V6, and V7 are set as the charging cutoff voltage (i.e., the second cutoff voltage) for small-current capacity replenishment—V4 = 3.9V releases C'3 (C'3 = C...). SEI+C4=306+102=408mAh / g), V5=4.0V releases C'4 (C'4=C SEI +C5=306+136=442mAh / g), V6=4.1V releases C'5 (C'5=C SEI +C6=306+170=476mAh / g), V7=4.2V releases C'6 (C'6=C SEI (+C7=306+204=510mAh / g) There are 6 segments in total, until the sodium supplement Na2O capacity is fully released.

[0207] Example 2

[0208] This embodiment is basically the same as embodiment 1, except that:

[0209] In step (6), in step a), when the first full-cell cycle capacity retention rate decreases by 5% (m = 0.25, based on the actual cycle requirement of 2000 cycles for the cell, R ≤ 20%, here R = 20, so mR% is 5%), the corresponding second capacity is used to supplement the cycle decomposition capacity once. The 1C / 1C cycle performance for 2000 cycles is tested in the voltage range of 1.5V-3.4V at room temperature.

[0210] Example 3

[0211] The method for continuously supplementing sodium to improve circulation performance in this embodiment includes the following steps:

[0212] (1) A coin cell was prepared using Na2NiO2 as the positive electrode active material, and the charging specific capacity and voltage curves of Na2NiO2 were obtained, as follows: Figure 5 As shown. Wherein:

[0213] The preparation method of coin cell half-cell is as follows:

[0214] The preparation method of Na2NiO2 coin cell is as follows: SP:PVDF:Na2NiO2 is mixed in a mass ratio of 10:5:85, and an appropriate amount of NMP is added to make a slurry. This slurry is then uniformly coated onto a 13μm thick aluminum foil surface using a scraper. After drying in a vacuum drying oven at 120℃ for 10 hours, a positive electrode is obtained. A sodium sheet is used as the negative electrode, and the Na2NiO2 coin cell is assembled in a glove box in the following order: negative electrode shell - spring sheet - gasket - negative electrode (sodium sheet) - electrolyte - separator - electrolyte - positive electrode - positive electrode shell. The electrolyte solute can be 1mol / L NaClO4, and the solvent is ethylene carbonate / diethyl carbonate (volume ratio 1:1). The separator is a 12μm thick polyethylene (PE) membrane.

[0215] The method for obtaining the charging specific capacity and voltage curves of Na2NiO2 is as follows: charge to 3.6V using a constant current and constant voltage of 0.05C, cut off current of 0.02C, and obtain the charging specific capacity and voltage curves of the sodium supplement Na2NiO2.

[0216] (2) Obtain the first mass content of the sodium supplement Na2NiO2 in the first cathode material when the theoretical specific capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film. Specifically, this includes the following steps:

[0217] 1) Prepare a second full cell containing a first positive electrode material. Specifically, the method for preparing the second full cell includes the following steps:

[0218] A. Preparation of positive electrode sheet containing sodium supplement Na2NiO2: The positive electrode slurry was prepared according to the following mass ratio: positive active material: first positive conductive agent: second positive conductive agent: positive binder: sodium supplement = Na4Fe3(PO4)2P2O7:Super P:CNT:PVDF:Na2NiO2 = 91.15%: 1.5%: 1.0%: 2.5%: 3.85%, and then formed into a positive electrode sheet. The positive current collector is a 13μm thick aluminum foil.

[0219] B. Negative Electrode Preparation: A negative electrode slurry was prepared by mixing the negative active material, negative conductive agent, negative thickener, and negative binder in a mass ratio of 94.6% to 0.8% to 1.6% to 3.0% for hard carbon, Super P, CMC, and SBR. The negative electrode current collector was a 13μm thick aluminum foil.

[0220] C. Separator selection: The diaphragm is a 12um thick polyethylene (PE) diaphragm.

[0221] D. Electrolyte preparation: 1 mol / L NaClO4 solute is dissolved in a solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1).

[0222] E. Assembly: The positive electrode, negative electrode, and separator are stacked and assembled, with the separator positioned between the positive and negative electrode. After the tabs are welded and the assembly is sealed, the electrolyte can be injected after the moisture content is qualified by baking.

[0223] 2) Calculate the first mass content according to the following formula:

[0224] a*b%*(dx)%+c*x%=a*(dx)%,

[0225] Wherein, a is the charge capacity of the positive active material in the first positive electrode material, which is 113.7 mAh / g; b% is the first efficiency of the second full cell, which is 85.4%; c is the first-cycle sodium replenishment capacity of the coin cell prepared in step (1) (within the voltage range of 2.0-3.6V), which is 393 mAh / g; d% is the sum of the mass content of the positive active material and the mass content of the sodium replenishment agent (i.e., the first mass content) in the first positive electrode material of the second full cell, which is 95%; x% is the first mass content.

[0226] The calculated content of the first mass is 3.85%.

[0227] (3) The sodium replenishment capacity of the coin cell prepared in step (1) in the first week is the capacity of the sodium replenishing agent used in step (2) to compensate for the SEI film consumption, which is also the theoretical specific capacity of the sodium replenishing agent Na2NiO2 in step (2); based on the theoretical specific capacity, in Figure 5 Find the corresponding charging cutoff voltage V0 from the charging capacity and voltage curves, and charge the second full cell to the cutoff voltage V0, so that the sodium replenishment capacity is fully released to compensate for SEI consumption. Where V0 = 3.6V.

[0228] (4) Based on the theoretical specific capacity of the sodium replenishing agent Na2NiO2 in step (2), determine the first capacity required by the second cathode material containing the second mass content of sodium replenishing agent Na2NiO2 to compensate for the capacity consumed by the SEI film. The difference between the theoretical specific capacity of the sodium replenishing agent Na2NiO2 and the first capacity is taken as the remaining capacity of the sodium replenishing agent in the second cathode material, and the remaining capacity is stored in the sodium ion replenishment station (i.e., in the second cathode material). The second mass content is 6.4%. Specifically:

[0229] i) The second mass content of sodium supplement Na2NiO2 in the second positive electrode material is 6.4% to prepare the positive electrode sheet, and then to prepare the first full cell. The method for preparing the first full cell includes the following steps:

[0230] F. Preparation of the positive electrode sheet: The positive electrode slurry was prepared according to the mass ratio of positive active material: first positive conductive agent: second positive conductive agent: positive binder: sodium supplement = Na4Fe3(PO4)2P2O7:Super P:CNT:PVDF:Na2NiO2 = 88.6%:1.5%:1.0%:2.5%:6.4% to form the positive electrode sheet. The positive current collector is an aluminum foil with a thickness of 13μm.

[0231] G. Preparation of negative electrode sheet: The negative electrode slurry was prepared according to the mass ratio of negative electrode active material: negative electrode conductive agent: negative electrode thickener: negative electrode binder = hard carbon: Super P: CMC: SBR = 94.6%: 0.8%: 1.6%: 3.0% to form a negative electrode sheet. The negative electrode current collector is an aluminum foil with a thickness of 13μm.

[0232] H. Diaphragm selection: The diaphragm is a 12µm thick polyethylene (PE) diaphragm.

[0233] I. Electrolyte preparation: Dissolve 1 mol / L NaClO4 in a solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1).

[0234] G. Assembly: The positive electrode, negative electrode, and separator are stacked and assembled, with the separator positioned between the positive and negative electrode. After the electrodes are welded together and sealed, the electrolyte is injected after baking to ensure the moisture content is within acceptable limits.

[0235] ii) Based on the theoretical specific capacity of the sodium supplement Na2NiO2 in step (2), calculate the first capacity using the following formula:

[0236] x%*C A =y%*C B

[0237] Wherein: x% is the first mass content, which is 3.85%; y% is the second mass content, which is 6.4%; C A The theoretical specific capacity (within the voltage range of 2.0-3.6V) of the sodium supplement Na2NiO2 in step (2) is 393mAh / g; C B The first capacity is expressed in mAh / g.

[0238] Calculations show that the first capacity C required by the second cathode material containing the second mass content of sodium replenishing agent Na2NiO2 to compensate for the capacity consumed by the SEI film is... B It is 236.4 mAh / g.

[0239] iii) Define the theoretical specific capacity of sodium supplement Na2NiO2 in step (2) as C all The first capacity is C SEI If the remaining capacity is C, then C = C all -C SEI =393-236.4=156.6mAh / g.

[0240] (5) Combination Figure 5 The charging specific capacity and voltage curve of Na2NiO2 shown is used to obtain the first charging cutoff voltage V1 corresponding to the first capacity in step (4), where V1 = 3.4V (e.g., ...). Figure 6 (As shown). Specifically:

[0241] The first full cell in step (4) is charged with a constant current of 0.02C, and the cutoff voltage is set to 2.0V. Then, it is charged with a constant current of 0.05C to 3.4V to completely decompose the second positive electrode material in the first full cell. At the same time, the initial decomposition amount C of the sodium storage layer is... SEI (CSEI =236.4mAh / g) is just enough to compensate for the loss of the SEI film.

[0242] (6) Divide the remaining capacity obtained in step (5) into two equal segments, each labeled as the second capacity. Based on the cycle retention rate decay, gradually replenish the second capacity of each segment to the cycle life of the first full cell. Specifically, this includes the following steps:

[0243] a) When the first full-cell cycle capacity retention rate decreases by 5%, the corresponding second-capacity capacity is used to replenish the cycle capacity once. The required replenishment capacity for each cycle is calculated using the following formula:

[0244] C i+1 =i*(C / n),

[0245] Among them, C i+1 The cyclic decomposition capacity replenished for the i-th time is expressed in mAh / g; C is the remaining capacity, which is 90 mAh / g; C / n is the second capacity; n is the number of segments into which the remaining capacity is divided, which is 2 segments; i is the number of times the cyclic decomposition capacity is replenished, where i is an integer greater than 0 and less than 2.

[0246] Calculations show that when the capacity is replenished for the first time, i = 1, the replenished cyclic decomposition capacity is C2 = C / 2 = 156.6 / 2 = 78.3 mAh / g; when the capacity is replenished for the second time, i = 2, the replenished cyclic decomposition capacity is C3 = 2*(C / 2) = 156.6 mAh / g.

[0247] b) According to Figure 6 The charging capacity and voltage curves of Na2NiO2 shown are used to determine the voltage corresponding to the total capacity released by the sodium replenisher Na2NiO2 after each replenishment cycle decomposition capacity, and this voltage is used as the corresponding second cutoff voltage for capacity recovery replenishment of the first full cell.

[0248] Specifically, the total release capacity of sodium supplement Na2NiO2 after each replenishment of the decomposition capacity is calculated using the following formula:

[0249] C' i =C SEI +C i+1

[0250] Among them, C' i The total release capacity of sodium supplement Na2NiO2 after the i-th replenishment of the cyclic decomposition capacity is expressed in mAh / g; Ci is the cyclic decomposition capacity replenished in the i-th replenishment, expressed in mAh / g; i is the number of times the cyclic decomposition capacity is replenished, which is an integer greater than 0 and less than n; n is the number of segments into which the remaining capacity is divided equally, which is 2 segments.

[0251] according to Figure 6 The Call & V curves show the total release capacity of sodium supplement Na2NiO2 after the first replenishment of the decomposition capacity, C'1 = C. SEI +C2=236.4+78.3=314.7mAh / g, corresponding to a voltage of V2. This voltage is set as the charging cutoff voltage (i.e., the second cutoff voltage). The first full battery is charged to 3.5V (V2) and then discharged to -1.5V to replenish the first cycle decomposition capacity. Then, the 1C / 1C cycle performance is tested for 2000 cycles within the 1.5V-3.4V voltage range at room temperature. When the cycle capacity retention rate of the first full battery decreases by 5% again, a second cycle decomposition capacity replenishment is performed. At this time, the total capacity released by the sodium supplement after the second cycle decomposition capacity replenishment is C'2=C SEI +C3=236.4+156.6=393mAh / g, which corresponds to a voltage of 3.6V (V3). This voltage is set as the charging cutoff voltage (i.e., the second cutoff voltage). The first full cell is charged to V3 and then discharged to -1.5V to replenish the capacity for the second cycle decomposition, so that the capacity of the sodium replenishing agent Na2NiO2 is fully released.

[0252] Comparative Example 1

[0253] The cathode material of this comparative full-cell battery does not contain sodium supplementation agent. The preparation method of the full-cell battery includes the following steps:

[0254] A. Preparation of positive electrode sheet: The positive electrode slurry is prepared according to the mass ratio of positive active material: first positive conductive agent: second positive conductive agent: positive binder: sodium supplement = Na4Fe3(PO4)2P2O7:Super P:CNT:PVDF:Na2O = 95%:1.5%:1.0%:2.5%:0% and then the positive electrode sheet is prepared.

[0255] B. Preparation of negative electrode sheet: The negative electrode slurry is prepared according to the mass ratio of negative electrode active material: negative electrode conductive agent: negative electrode thickener: negative electrode binder = hard carbon: Super P: CMC: SBR = 94.6%: 0.8%: 1.6%: 3.0% and then the negative electrode sheet is prepared.

[0256] C. Separator selection: The diaphragm is a 12um thick polyethylene (PE) diaphragm.

[0257] D. Electrolyte preparation: 1 mol / L NaClO4 solute is dissolved in a solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1).

[0258] E. Assembly: The positive electrode, negative electrode, and separator are stacked and assembled, with the separator positioned between the positive and negative electrode. After the tabs are welded and the assembly is sealed, the electrolyte can be injected after the moisture content is qualified by baking.

[0259] The full battery was first charged with a constant current of 0.02C, with the cutoff voltage set to 2.0V. Then it was charged with a constant current and constant voltage of 0.2C to 3.4V, with the cutoff current at 0.05C. Its performance of 2000 cycles at 1C / 1C was tested in the voltage range of 1.5V-3.4V at room temperature.

[0260] Comparative Example 2

[0261] The positive electrode material of the full cell in this comparative example contains sodium supplement Na2O. The preparation method of the full cell includes the following steps:

[0262] A. Preparation of positive electrode sheet: The positive electrode slurry is prepared according to the mass ratio of positive active material: first positive conductive agent: second positive conductive agent: positive binder: sodium supplement = Na4Fe3(PO4)2P2O7:Super P:CNT:PVDF:Na2O = 92%:1.5%:1.0%:2.5%:3% and then the positive electrode sheet is prepared.

[0263] B. Preparation of negative electrode sheet: The negative electrode slurry is prepared according to the mass ratio of negative electrode active material: negative electrode conductive agent: negative electrode thickener: negative electrode binder = hard carbon: Super P: CMC: SBR = 94.6%: 0.8%: 1.6%: 3.0% and then the negative electrode sheet is prepared.

[0264] C. Separator selection: The diaphragm is a 12um thick polyethylene (PE) diaphragm.

[0265] D. Electrolyte preparation: 1 mol / L NaClO4 solute is dissolved in a solvent of ethylene carbonate / diethyl carbonate (volume ratio 1:1).

[0266] E. Assembly: The positive electrode, negative electrode, and separator are stacked and assembled, with the separator positioned between the positive and negative electrode. After the tabs are welded and the assembly is sealed, the electrolyte can be injected after the moisture content is qualified by baking.

[0267] The full cell was first charged with a constant current of 0.02C, with the cutoff voltage set to 2.0V. Then, it was charged with a constant current of 0.1C to 3.4V to ensure complete decomposition of the sodium electrode material. Finally, it was charged with a constant current and voltage of 0.05C to V0, where V0 = 4.2V, with a cutoff current of 0.02C to completely decompose the 3% sodium supplement. The capacity C was then determined. all (Optimal sodium supplement ratio C) all Equivalent to C SEI It was used to compensate for SEI consumption and its 1C / 1C cycle performance was tested in the voltage range of 1.5V-3.4V at room temperature.

[0268] The electrochemical performance of the first full cell in Examples 1-3 and the full cells in Comparative Examples 1-2 was tested. Specifically, the method for testing the discharge capacity in the first week was as follows: The prepared sodium-ion battery was placed on a testing instrument in a testing environment of (25±1)℃. Charging method: After resting for 10 min, constant current charging at 0.02C was used, with the cutoff voltage set to 2.0V. After resting for 10 min, constant current charging at 0.1C was used to reach 3.4V. After resting for 10 min, constant current charging at 0.05C was used to reach V1, with the cutoff current at 0.02C to obtain the charging capacity. Discharging method: The full cell was discharged at 0.05C to 1.5V to obtain the discharge capacity in the first week.

[0269] The first-efficiency test method is: first-week discharge capacity / first-week charging capacity * 100% to obtain the first-efficiency data.

[0270] The method for testing the capacity of the sodium supplement in the first week is as follows: The sodium supplement is placed on the testing instrument and placed in a testing environment of (25±1)℃. Charging method: After standing for 10 minutes, it is charged with a constant current of 0.05C to V0, and then charged with a constant voltage to 0.02C to obtain the charge capacity of the sodium supplement in the first week.

[0271] The original method for testing capacity retention after 2000 cycles at 1C is as follows: At (25±1)℃, the second full cell is charged at a constant current of 1C to 3.4V within the range of 1.5-3.4V, and then charged at a constant voltage to 0.05C; followed by constant current discharge at 1C, with a cutoff voltage of 1.5V. The above charge and discharge steps are repeated for 2000 cycles.

[0272] The electrochemical performance test results are shown in Table 1.

[0273] Table 1. Electrochemical performance of the first full cell in Examples 1-3 and the full cells in Comparative Examples 1-2

[0274]

[0275] As can be seen from Table 1:

[0276] The embodiments of this application achieve segmented release of sodium replenishment by precisely controlling the full battery voltage. The active sodium released initially is used to improve the initial efficiency, and the remaining active sodium is released in segments through the sodium ion replenishment station to compensate for the sodium consumed throughout the entire life cycle of the sodium-ion battery.

[0277] Comparative Example 1 was without sodium supplementation, and Comparative Example 2 was with appropriate sodium supplementation Na2O. With appropriate sodium supplementation Na2O, the initial efficiency increased from 85.42% to 91.13%, and the cycle life increased from 2000cls@92.4% to 94.8% (that is, the cycle retention rate corresponding to 2000 cycles was 92.4%).

[0278] Examples 1 and 2 involve adding an excess of sodium supplement Na₂O. By controlling the full-cell voltage, the initial decomposition capacity C of the sodium supplement is maximized. SEI This perfectly compensates for the SEI film consumption, and the remaining capacity is released in stages. In Examples 1 and 2, charge and discharge were performed when the cycle capacity retention rate decreased by 3% and 5%, respectively, to release the remaining capacity (C). all -C SEI The method described in this application improves the retention rate by 4% compared to the original method.

[0279] In this application, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0280] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this application, "multiple" means at least two, such as two, three, etc., unless otherwise explicitly specified.

[0281] Although embodiments of this application have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting this application. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of this application.

Claims

1. A method for continuously supplementing sodium to improve circulatory performance, characterized in that, include: Obtain the charging capacity and voltage curves of the sodium supplement; The first mass content of the sodium supplement in the first cathode material is obtained when the theoretical specific capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film. Based on the theoretical specific capacity, a first capacity required by the second cathode material containing the second mass content of the sodium-replenishing agent to compensate for the capacity consumed by the SEI film is determined, and the difference between the theoretical specific capacity and the first capacity is taken as the remaining capacity of the sodium-replenishing agent in the second cathode material; the second mass content is greater than the first mass content, and the second cathode material is the same as the first cathode material except for the content of the sodium-replenishing agent; both the first cathode material and the second cathode material include cathode active material; By combining the charging capacity and voltage curves, the first charging cutoff voltage corresponding to the first capacity is obtained; The remaining capacity is divided into at least two segments of second capacity, and the second capacity of each segment is gradually added to the cycle process of the first full cell containing the second cathode material, taking into account the cycle retention rate decay. The first mass content of the sodium replenishing agent in the first cathode material when the theoretical specific capacity of the sodium replenishing agent is equal to the capacity consumed in forming the SEI film includes: A coin cell was prepared using a sodium supplement as the positive electrode active material. Prepare a second full cell containing the first cathode material; The first mass content is calculated based on the charging specific capacity of the positive electrode active material in the first positive electrode material, the first efficiency of the second full cell, the first-cycle sodium replenishment capacity of the coin half cell, and the mass content of the positive electrode active material in the first positive electrode material. The first mass content is calculated according to the following formula: a*b%*(dx)%+c*x%= a*(dx)% Wherein, a is the charge capacity of the positive electrode active material in the first positive electrode material, in mAh / g; b% is the first-cycle efficiency of the second full cell; c is the first-cycle sodium replenishment capacity of the coin cell half cell, in mAh / g; d% is the sum of the mass content of the positive electrode active material in the first positive electrode material and the first mass content; x% is the first mass content; The method for determining the first capacity required by the second cathode material containing the second mass content of the sodium supplement to compensate for the capacity consumed by the SEI membrane, based on the theoretical specific capacity, is as follows: Based on the theoretical specific capacity, the first capacity is calculated using the following formula: x%*C A =y%*C B Where: x% is the first mass content; y% is the second mass content; C A The theoretical granular capacity of the sodium supplement is expressed in mAh / g; C B The first capacity is expressed in mAh / g.

2. The method according to claim 1, characterized in that, The coin cell is the coin cell used to obtain the charging capacity and voltage curve of the sodium supplement.

3. The method according to claim 1, characterized in that: The process of gradually adding the second capacity of each segment to the first full cell containing the second positive electrode material during cycling includes: For each decay of the first full-cell cycle capacity retention rate, the second capacity is used to replenish the cycle decomposition capacity once.

4. The method according to claim 3, characterized in that, The required replenishment of the cyclic decomposition capacity each time is calculated using the following formula: C i+1 = i *(C / n), Among them, C i+1 The cyclic decomposition capacity replenished for the i-th time is expressed in mAh / g; C is the remaining capacity expressed in mAh / g; C / n is the second capacity; n is the number of segments into which the remaining capacity is divided equally, expressed in segments; n is an integer greater than 1 and less than 2000; i is the number of times the cyclic decomposition capacity is replenished, expressed as an integer greater than 0 and less than n. And / or, the method for continuously supplementing sodium to improve cyclic performance further includes: Based on the charging capacity and voltage curves, the voltage corresponding to the total capacity released by the sodium replenishing agent after each replenishment of the cycle decomposition capacity is determined, and this voltage is used as the corresponding second cutoff voltage for capacity recovery replenishment of the first full cell.

5. The method according to claim 1, characterized in that, The cycle retention rate decay includes a cycle decay ratio below R%, and a capacity retention rate decrease of mR% after a certain number of cycles; where R is ≤20%, and m is greater than 0 and less than 1.

6. The method according to claim 1, characterized in that, The first mass content and the second mass content are both 1-10%.

7. The method according to claim 1, characterized in that, The sodium supplement includes at least one of Na2O, NaNO2, Na2CO3, Na2NiO2, NaCrO2, Na5FeO4, NaBH4, NaNH2, Na2C6O6, Na2C6H2O6, CH3COONa, PABZ-Na, EDTA-4Na, DTPA-5Na, Na2C4O4, Na2C2O4, and Na2C3O5. And / or, both the first positive electrode material and the second positive electrode material further include a first positive electrode conductive agent, a second positive electrode conductive agent, a positive electrode binder and the sodium supplement agent, and the mass ratio of the positive electrode active material, the first positive electrode conductive agent, the second positive electrode conductive agent and the positive electrode binder is (87-99):(1-5):(1-4):(1-4); And / or, the negative electrode material of the first full cell includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener and a negative electrode binder, wherein the mass ratio of the negative electrode active material, the negative electrode conductive agent, the negative electrode thickener and the negative electrode binder is (90-99):(1-3):(1-4):(1-4); And / or, the separator of the first full cell includes at least one of a polymer separator, a ceramic separator, and a polymer / ceramic composite separator.

8. The method according to claim 7, characterized in that, In both the first and second positive electrode materials, the positive electrode active material includes at least one of sodium ion layered oxide, sodium-containing sulfate, sodium-containing phosphate, sodium-containing fluorinated polyanion, sodium-containing mixed polyanion, sodium-containing silicate, and sodium-containing borate. And / or, the first positive electrode conductive agent, the second positive electrode conductive agent, and the negative electrode conductive agent each include at least one of Super P, Ketjen Black, acetylene black, carbon nanotubes, graphene, conductive graphite, carbon fiber, or ordered mesoporous carbon.

9. The application of the method as described in any one of claims 1 to 8 in the use of sodium-ion batteries.

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