Method for continuously supplementing sodium to improve cycle performance and application

Abstract

The invention provides a method for continuously supplementing sodium to improve the cycle performance and application. The method for continuously supplementing sodium to improve the cycle performance comprises the following steps: acquiring the first mass content of a sodium supplementing agent in a first positive electrode material when the theoretical gram volume of the sodium supplementing agent is equal to the capacity consumed for forming an SEI membrane; according to the theoretical gram capacity, determining a first capacity required by a second positive electrode material containing a second mass content of a sodium supplementing agent to make up the capacity consumed by the SEI membrane, and obtaining a residual capacity; and averagely dividing the residual capacity into at least two sections of second capacity, and supplementing each section of second capacity to the circulation process section by section. According to the method for continuously supplementing sodium to improve the cycle performance, the total battery voltage is accurately controlled, the sodium supplementing agent is released in a segmented mode, namely active sodium released for the first time is used for improving the first efficiency, the remaining active sodium is stored in a sodium ion supply station (positive electrode material) and released when the cycle retention rate is attenuated, and the cycle performance is improved. The sodium consumed by the sodium ion battery in the whole life cycle is made up.

Description

Technical Field

[0001] The present application relates to the technical field of secondary batteries, and in particular to a method and application of continuously supplementing sodium to improve cycle performance. Background Art

[0002] As the global demand for clean energy grows, sodium-ion batteries, as a new type of energy storage device, have attracted widespread attention due to their abundant resources, low cost, and high safety. However, the loss of active sodium is an important issue during the charge and discharge process of sodium-ion batteries. The loss of active sodium mainly has two aspects: 1) loss of active sodium caused by SEI formation; 2) continuous side reactions will cause repeated breakage and growth of SEI. Previous studies have mainly focused on using pre-sodiumization to compensate for the sodium ions consumed by SEI formation and improve the initial efficiency and energy density.

[0003] At present, sodium-ion batteries have the problem of irreversible capacity loss during the cycle process, mainly due to: 1) the formation of solid electrolyte membrane (SEI) leading to irreversible loss of active sodium ions; 2) structural changes in sodium battery positive electrode materials leading to capacity loss; 3) side reactions during the cycle process seriously consume active sodium ions.

[0004] In order to improve the first efficiency and cycle life, the pre-sodiumization method is required. The traditional positive electrode pre-sodiumization is to add additional active sodium to the positive electrode material to release the capacity of the sodium supplement agent in one go, which is used to compensate for the irreversible capacity loss during the first cycle of charge and discharge, and to achieve the improvement of the energy density and cycle life of the whole battery. However, if the capacity of the sodium supplement agent is released in one go, the excessive and active sodium ions will be stored in the negative electrode for a long time, which will aggravate the side reactions caused by contact with the electrolyte, and more active sodium will be consumed during the cycle.

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

[0006] In view of this, an object of the present application is to provide a method for continuously supplementing sodium to improve cycle performance, which realizes the segmented release of the sodium supplement by precisely controlling the voltage of the entire battery, that is, the active sodium released for the first time is used to improve the initial efficiency, and the remaining active sodium is stored in the sodium ion supply station (positive electrode material), and is released when the cycle retention rate decays, thereby making up for the sodium consumed during the entire life cycle of the sodium ion battery.

[0007] Another object of the present application is to provide a method for continuously supplementing sodium to improve cycle performance.

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

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

[0010] Obtaining a first mass content of the sodium supplement in the first positive electrode material when the theoretical gram capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film;

[0011] According to the theoretical gram capacity, determining the first capacity required for the second positive electrode material containing the second mass content of the sodium supplement to make up for the capacity consumed by the SEI film, and taking the difference between the theoretical gram capacity and the first capacity as the remaining capacity of the sodium supplement in the second positive electrode material; the second mass content is greater than the first mass content, and the second positive electrode material is the same as the first positive electrode material except for the content of the sodium supplement; the first positive electrode material and the second positive electrode material both include positive electrode active substances;

[0012] Combining the charging capacity and voltage curve, obtaining a first charging cut-off voltage corresponding to the first capacity;

[0013] The remaining capacity is evenly divided into at least two sections of second capacity, and the second capacity of each section is replenished step by step during the cycle of the first full battery containing the second positive electrode material in combination with the attenuation of the cycle retention rate.

[0014] In some embodiments, obtaining a first mass ratio of the sodium supplement in the first positive electrode material when the theoretical gram capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film comprises:

[0015] A button-type half-cell was prepared using a sodium supplement as the positive electrode active material;

[0016] preparing a second full battery containing the first cathode material;

[0017] The first mass content is calculated according to the charged gram capacity of the positive electrode active substance in the first positive electrode material, the first efficiency of the second full battery, the first week sodium replenishment capacity of the button half-cell (that is, the theoretical gram capacity of the sodium replenisher), and the mass content of the positive electrode active substance 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] Among them, a is the charging gram capacity of the positive electrode active substance in the first positive electrode material, in mAh / g; b% is the first efficiency of the second full battery; c is the first week sodium replenishment capacity of the button half-cell (that is, the theoretical gram capacity of the sodium replenisher), in mAh / g; d% is the sum of the mass content of the positive electrode active substance in the first positive electrode material and the first mass content; x% is the first mass content.

[0021] In some embodiments, the button-type half-cell is a button-type half-cell used to obtain the charging gram capacity and voltage curve of the sodium supplement.

[0022] In some embodiments, replenishing each segment of the second capacity to a cycle of a first full battery containing the second cathode material segment by segment comprises:

[0023] Each time the first full-battery cycle capacity retention rate decays, the second capacity is used to supplement the cycle decomposition capacity accordingly.

[0024] In some embodiments, the cyclic decomposition capacity required to be supplemented each time is calculated according to the following formula:

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

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

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

[0028] According to the charging gram capacity and voltage curve, the voltage corresponding to the total released capacity of the sodium supplement agent after each replenishment of the cyclic decomposition capacity is determined, and the voltage is used as the corresponding second cut-off voltage to restore and replenish the capacity of the first full battery.

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

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

[0031] In some embodiments, the first mass content and the second mass content are both 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, the first positive electrode material and the second positive electrode material also include a first positive electrode conductor, a second positive electrode conductor, a positive electrode binder and the sodium supplement, and the mass ratio of the positive electrode active material, the first positive electrode conductor, the second positive electrode conductor and the positive electrode binder is (87-99): (1-5): (1-4): (1-4).

[0034] In some embodiments, in the first positive electrode material and the second positive electrode material, the positive electrode active material includes at least one of sodium ion layered oxides, sodium-containing sulfates, sodium-containing phosphates, sodium-containing fluorinated polyanions, sodium-containing mixed polyanions, sodium-containing silicates, and sodium-containing borates.

[0035] In some embodiments, the negative electrode material of the first full battery includes a negative electrode active material, a negative electrode conductor, a negative electrode thickener and a negative electrode binder, and the mass ratio of the negative electrode active material, the negative electrode conductor, 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 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 the present application relates to the application of the method for continuous sodium supplementation to improve cycle performance described in the present application during the use of sodium ion batteries.

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

[0040] 1. By precisely regulating the voltage of the entire battery, the release of active sodium in the sodium storage layer is controlled, which not only takes into account the initial effect but also can continuously replenish sodium to improve the circulation.

[0041] 2. Excess sodium ions are stored in the positive electrode. Compared with the traditional sodium replenishment method in which all excess sodium ions are stored in the negative electrode, the sodium consumption by side reactions in the cycle process is reduced.

[0042] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

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

[0044] in:

[0045] Figure 1 This is a flow chart of a method for improving cycle performance by continuous sodium supplementation, shown as an exemplary embodiment of the present application.

[0046] Figure 2 It is the charging curve of the button half-cell containing the sodium supplement Na2O in Example 1, and is also the charging capacity & voltage curve (referred to as Call & V curve) of the second full cell (sodium ion battery button full cell) when the optimal addition ratio (i.e., the first mass content) of the sodium supplement Na2O is 3%.

[0047] Figure 3 The first full battery (sodium ion battery button-type full battery) charging curve (also known as the charging gram capacity & voltage curve (referred to as Call & V curve)) when the excess addition ratio (also known as the second mass content) of 5% sodium supplement Na2O in Example 1 is used.

[0048] Figure 4 This is a cycle attenuation diagram of a full battery (that is, the first full battery in this application).

[0049] Figure 5 It is the charging curve of the button-type half-cell of the sodium supplement Na2NiO2 in Example 3, and also the charging capacity & voltage curve (referred to as Call & V curve) of the second full cell (sodium ion battery button-type full cell) when the optimal addition ratio (that is, the first mass content) of the sodium supplement Na2NiO2 is 3.85%.

[0050] Figure 6 The first full cell (sodium ion battery button-type full cell) charging curve (also known as the charging gram capacity & voltage curve (referred to as Call & V curve)) when the excess addition ratio (also known as the second mass content) of the sodium supplement Na2NiO2 in Example 3 is 6.4%. DETAILED DESCRIPTION

[0051] The embodiments of the present application are described in detail below, and examples of the embodiments are shown in the accompanying drawings. The embodiments described below with reference to the accompanying drawings are exemplary and are intended to be used to explain the present application, but cannot be understood as limiting the present application.

[0052] In this application, the disclosure of numerical ranges includes all values ​​within the entire range and the disclosure of further subdivided ranges, including the endpoints and sub-ranges given in these ranges.

[0053] In this application, the raw materials, equipment, etc. involved, unless otherwise specified, are all raw materials and equipment that can be made through commercial channels or known methods; the methods involved, unless otherwise specified, are all conventional methods.

[0054] In this application, normal temperature refers to 20-30°C.

[0055] A method for continuously supplementing sodium to improve cycle performance according to an embodiment of the present application is described below with reference to the accompanying drawings.

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

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

[0058] In some embodiments, the sodium supplement 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, Na2C3O5, etc. These sodium supplements have a high sodium supplement capacity, are compatible with existing general manufacturing processes and battery systems, have good environmental stability, and can remain stable in air or a relatively dry environment.

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

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

[0061] In the embodiments of the present application, when obtaining the charge gram capacity and voltage curve of the sodium supplement agent, the sodium supplement agent needs to be used as the positive electrode active material to prepare a button-type half-cell, and then the charge gram capacity and voltage curve of the sodium supplement agent in the button-type half-cell are obtained.

[0062] It should be noted that, in the embodiments of the present application, the button-type half-cell used to obtain the above-mentioned charging capacity and voltage curve is consistent with the button-type half-cell involved in calculating the first mass ratio later.

[0063] As an optional example, the assembly method of the above sodium supplement button half-cell is as follows:

[0064] Conductive agent: binder: sodium supplement agent were mixed in a mass ratio of 10:5:85, and an appropriate amount of N-methylpyrrolidone (NMP) was added to make a slurry, which was evenly coated on the surface of an aluminum foil with a thickness of 13 μm using a scraper, and dried at 120°C in a vacuum drying oven for 10 h to obtain a positive electrode sheet; a sodium sheet was used as a negative electrode, and was assembled into a sodium supplement agent button half-cell in a glove box in the order of negative electrode shell-spring-gasket-negative electrode (sodium sheet)-electrolyte-diaphragm-electrolyte-positive electrode-positive electrode shell; a constant current and constant voltage of 0.05C was used to charge to 4.2V, with a cut-off current of 0.02C, and the charging gram capacity & voltage curve of the sodium supplement agent Na2O was obtained. The electrolyte is composed of: the solute is 1 mol / L NaClO4, the solvent is ethylene carbonate / diethyl carbonate (volume ratio 1:1); the diaphragm is a polyethylene (PE) diaphragm with a thickness of 12 μm; the conductive agent is Super P, and the binder is polyvinylidene fluoride.

[0065] S102, obtaining a first mass content of the sodium supplement in the first positive electrode material when the theoretical gram capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film. The first positive electrode material includes a positive electrode active substance.

[0066] It can be understood that in the embodiments of the present application, when the mass content of the sodium supplement in the first positive electrode material is the first mass content, the theoretical gram 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 gram 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 excessive addition.

[0067] In some embodiments, obtaining a first mass ratio of the sodium supplement in the first positive electrode material when the theoretical gram capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film comprises:

[0068] Using the sodium supplement as the positive electrode active material, a button-type half-cell is prepared;

[0069] preparing a second full battery containing the first cathode material;

[0070] The first mass content is calculated according to the charging gram capacity of the positive electrode active substance in the first positive electrode material, the first efficiency of the second full battery, the first week sodium replenishment capacity of the button half-cell (that is, the theoretical gram capacity of the sodium replenisher), and the mass content of the positive electrode active substance in the first positive electrode material.

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

[0072] In some embodiments, the button-type half-cell is a button-type half-cell used to obtain the charging gram capacity and voltage curve of the sodium supplement.

[0073] In some embodiments, the preparation method of the second full battery is:

[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 supplementing agent in the formulated amount of the first positive electrode material are mixed into a positive electrode slurry to prepare a positive electrode sheet;

[0075] Mixing the negative electrode active material, negative electrode conductive agent, negative electrode thickener and negative electrode binder in a negative electrode slurry to prepare a negative electrode sheet;

[0076] The positive electrode sheet, the negative electrode sheet and the diaphragm are stacked and assembled, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet. After the tabs are welded and packaged, the electrolyte can be injected after the moisture content is qualified after baking.

[0077] In some embodiments, in the second full battery, the first positive electrode material includes a positive electrode active material, a first positive electrode conductor, a second positive electrode conductor, a positive electrode binder and the sodium supplement, and the mass ratio of the positive electrode active material, the first positive electrode conductor, the second positive electrode conductor 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 battery, the mass ratio is: positive electrode active material: first positive electrode conductive agent: second positive electrode conductive agent: positive electrode binder: sodium supplement = 92%: 1.5%: 1.0%: 2.5%: 3%.

[0079] In some embodiments, in the first positive electrode material of the second full battery, the positive electrode active material includes at least one of sodium ion layered oxides, sodium-containing sulfates, sodium-containing phosphates, sodium-containing fluorinated polyanions, sodium-containing mixed polyanions, sodium-containing silicates, and sodium-containing borates.

[0080] Exemplarily, the sodium ion layered oxide includes but is not limited to at least one of an O3 phase sodium ion layered oxide and a P2 phase sodium ion layered oxide. Among them, the O3 phase sodium ion layered oxide includes but is 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.; the sodium ion layered oxide of the P2 phase includes but is 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] Exemplary sodium sulfates include, but are not limited to, Na2Fe2(SO4)3, Na2Fe(SO4) 2.2 At least one of H2O, etc.

[0082] Exemplarily, the sodium-containing phosphate includes, but is not limited to, at least one of Na3V2(PO3), Na3MnTi(PO3)3, Na2FeP2O7, Na2CoP2O7, and the like.

[0083] Exemplarily, the sodium-containing fluorinated polyanion includes, but is not limited to, at least one of Na3(VPO4)2F3, Na3(VOPO4)2F, Na2FePO4F, and the like.

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

[0085] Exemplarily, the sodium-containing silicate includes, but is not limited to, at least one of Na2MnSiO4, Na2FeSiO4, and the like.

[0086] Exemplary sodium-containing borates include, but are not limited to, Na3CoB5O 10 、Na3FeB5O 10 At least one of the above.

[0087] As a preferred example, in the first positive electrode material of the second full battery, 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 battery includes a negative electrode active material, a negative electrode conductor, a negative electrode thickener and a negative electrode binder, and the mass ratio of the negative electrode active material, the negative electrode conductor, the negative electrode thickener and the 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 optional example, in the negative electrode material of the second full battery, the mass ratio is negative electrode active material: negative electrode conductive agent: negative electrode thickener: negative electrode binder = 94.6%: 0.8%: 1.6%: 3.0%.

[0090] In some embodiments, in the second full battery, the first positive electrode conductive agent, the second positive electrode conductive agent and the negative electrode conductive agent all include but are not limited to at least one of Super P, Ketjen black, acetylene black carbon 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 the present application, there is no limitation on the material selection of the positive electrode binder, negative electrode active material, negative electrode thickener and negative electrode binder in the second full battery, and they can all adopt any positive electrode binder, negative electrode active material, negative electrode thickener and negative electrode binder known in the art.

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

[0093] As an optional example, the method for preparing the electrolyte in the second full battery is: dissolving 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 a polymer separator, a ceramic separator, a polymer / ceramic composite separator, and the like.

[0095] Exemplarily, the polymer separator includes but is not limited to at least one of a single-layer polymer separator and a multi-layer polymer separator, etc. The single-layer polymer separator includes but is not limited to a polyethylene (PE) separator or a polypropylene (PP) separator, etc.

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

[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] Among them, a is the charging gram capacity of the positive electrode active substance in the first positive electrode material, in mAh / g; b% is the first efficiency of the second full battery; c is the first week sodium replenishment capacity of the button half-cell (that is, the theoretical gram capacity of the sodium replenisher), in mAh / g; d% is the sum of the mass content of the positive electrode active substance in the first positive electrode material and the mass content of the sodium replenisher (that is, the first mass content); x% is the first mass content.

[0100] It should be noted that, in the embodiment of the present application, the first week sodium supplement capacity of the button half-cell involved in the calculation of the first mass content is also the theoretical gram capacity in step S102. In addition, when applying the above formula to calculate the first mass content, the contents of the positive electrode conductor (that is, the first positive electrode conductor and the second positive electrode conductor) and the positive electrode binder in the first positive electrode material of the second full battery can be preset according to conventional techniques in the art, that is, the mass content of the positive electrode conductor and the mass content of the positive electrode binder in the first positive electrode material of the second full battery are known, so the mass content of the positive electrode binder and the mass content of the positive electrode conductor can be subtracted from the total mass content of the first positive electrode material of the second battery by 100%, and the sum of the mass content of the positive active material and the mass content of the sodium supplement in the first positive electrode material of the second full battery, d%, 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 battery are 1.5%, 1.0% and 2.5% respectively, d%=100%-SP%-CNT%-PVDF%=100%-1.5%-1%-2.5%=95%, and then the mass content of the sodium supplement in the first positive electrode material of the second full battery can be calculated according to the above formula - the first mass ratio.

[0101] In the embodiments of the present application, different sodium supplements are selected and the first mass content is different. Generally, the first mass content of the sodium supplement in the first positive electrode material is 1-10%, including but not limited to 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 10%, etc.

[0102] As an optional example, the sodium supplement is Na2O, and its theoretical gram capacity (that is, the first week sodium supplement capacity in step S102) c is 510 mAh / g; the charging gram capacity of the first positive electrode material in the second full battery is a=113.7 mAh / g, and the discharge gram capacity is 101.6 mAh / g; the positive electrode active substance in the first positive electrode material of the second full battery is Na4Fe3(PO4)2P2O7, and its mass content in the first positive electrode material is 92%; the first efficiency of the second full battery is b=85.4%; the first mass content x% of the sodium supplement Na2O in the first positive electrode material of the second full battery is 3%.

[0103] S103. Determine, based on the theoretical gram capacity, the first capacity required for a second positive electrode material containing a second mass content of the sodium supplement to compensate for the capacity consumed by the SEI film, and use the difference between the theoretical gram capacity and the first capacity as the remaining capacity of the sodium supplement in the second positive electrode material; the second mass content is greater than the first mass content, and except for the content of the sodium supplement in the second positive electrode material, the rest are the same as the first positive electrode material.

[0104] In the embodiment of the present application, the theoretical gram capacity in step S102 can be obtained by charging the second full battery to the target voltage V0 ((the determination method of V0 is to combine the curve (for example, as follows, Figure 2 ), after calculating x%*CA=y%*CB, it is confirmed that the full battery requires 306mAh / g for the first time, for example, SEI, and the horizontal and vertical coordinates correspond, and V0)) can be obtained, so that the capacity of the sodium supplement agent is fully released to make up for the SEI consumption. At this time, the released capacity of the sodium supplement agent is exactly equal to the capacity consumed by SEI. The theoretical gram capacity of the sodium supplement agent corresponding to the target voltage V0 can be obtained according to the charging gram capacity and voltage curve, that is, the theoretical gram capacity in step S102.

[0105] In some embodiments, the method for determining the first capacity required for the second positive electrode material containing the second mass content of the sodium supplement to make up for the capacity consumed by the SEI film according to the theoretical gram capacity is:

[0106] According to the theoretical gram capacity, the first capacity is calculated according to 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 is the theoretical gram capacity of the sodium supplement, in mAh / g; C B is the first capacity, and the unit is mAh / g.

[0109] Exemplarily, when the sodium supplement is Na2O, the theoretical gram 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 the sodium supplement added in the second positive electrode material is 5 wt%, the capacity required to compensate for the consumption of the SEI film is 306 mAh / g.

[0110] It can be understood that in the embodiment of the present application, the second mass content is greater than the first mass content, that is, the sodium supplement is added in excess in the second positive electrode material relative to that in the first positive electrode material. Except for the content of the sodium supplement, the rest of the second positive electrode material is the same as the first positive electrode material, that is, the only difference between the first positive electrode material and the second positive electrode material is the different addition content of the sodium supplement.

[0111] It should be noted that, similar to the first mass content, in the embodiments of the present application, the material selection of the sodium supplement is different, and the second mass content is also different. It should also be emphasized that in the embodiments of the present application, although the main purpose of the sodium supplement is to improve the cycle life, it is not the case that the more excessive addition of the sodium supplement, the better. The amount of sodium supplement added to the second positive electrode material increases, and the Na embedded back in the negative electrode during discharge increases. + If there are not enough sites for the positive electrode to receive, the discharge capacity will be reduced to varying degrees.

[0112] Based on the above, in the embodiment of the present 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 of the content of the sodium supplement in the first positive electrode material. 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%, etc.

[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 an embodiment of the present application, the remaining capacity is stored in the sodium ion supply station, that is, stored in the second positive electrode material.

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

[0117] S104: Acquire a first charging cut-off voltage corresponding to the first capacity in combination with the charging capacity and voltage curve.

[0118] In the embodiment of the present application, according to 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 accordingly, and the voltage is the corresponding first charging cut-off voltage.

[0119] In the embodiment of the present application, the purpose of confirming the first capacity and the first charging cut-off voltage is to ensure that when SEI is just compensated, the full-power first-cycle discharge capacity will not be low; it can take into account both the first-cycle discharge and the remaining capacity for circulation.

[0120] S105, dividing the remaining capacity into at least two sections of second capacity on average, and replenishing each section of the second capacity step by step during the cycle of the first full battery containing the second positive electrode material in combination with the attenuation of the cycle retention rate.

[0121] It is understandable that in the embodiment of the present application, the remaining capacity is evenly divided into multiple sections, each section is a second capacity, which is used to supplement the capacity loss during the cycle. It should be noted that in the embodiment of the present application, the remaining capacity (hereinafter referred to as Formula C i+1 = (i-1)*(C / n) where C is evenly divided into the number of segments (hereinafter referred to as C in the formula i+1 =(i-1)*(C / n) where n) can be infinite, and the second capacity corresponding to each segment (the formula C in the following text) i+1 =(i-1)*(C / n) where C / n) can be infinitely small.

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

[0123] Exemplarily, the R includes but is not limited to 2%, 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] Exemplarily, m includes but is not limited to 0.1, 0.25, 0.5, 0.75 or 0.95, etc.

[0125] In some embodiments, replenishing each segment of the second capacity to a cycle of a first full battery containing the second cathode material segment by segment comprises:

[0126] Each time the first full-battery cycle capacity retention rate decays, the second capacity is used to supplement the cycle decomposition capacity accordingly.

[0127] In the embodiment of the present application, replenishing the cycle decomposition capacity means that each time the first full battery capacity retention rate decays once, the first full battery is charged and discharged once within a preset voltage range, thereby achieving a cycle capacity decomposition replenishment. Figure 3 , when the first full battery cycle capacity retention rate decays by 3%, the first full battery is charged to 3.7V (V2), and then discharged to -1.5V to replenish the first cycle decomposition capacity, and then the 1C / 1C cycle performance is continued to be tested in the voltage range of 1.5V-3.4V at room temperature; when the first full battery cycle capacity retention rate decays by 3% again, the first full battery is charged to V3 ( Figure 3 The battery was then discharged to -1.5 V to replenish the decomposition capacity for the second cycle, and then the 1C / 1C cycle performance was tested in the voltage range of 1.5 V to 3.4 V at room temperature.

[0128] In some embodiments, the cyclic decomposition capacity required to be supplemented each time is calculated according to the following formula:

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

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

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

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

[0133] According to the charging gram capacity and voltage curve, the voltage corresponding to the total released capacity of the sodium supplement agent after each replenishment of the cyclic decomposition capacity is determined, and the voltage is used as the corresponding second cut-off voltage to restore and replenish the capacity of the first full battery.

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

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

[0136] Among them, C' i is the total released capacity of the sodium supplement after the cyclic decomposition capacity is replenished for the i-th time, in mAh / g; Ci is the cyclic decomposition capacity replenished for the i-th time, 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 evenly divided, in segments; n is an integer greater than 1 and less than 2000.

[0137] It should be noted that in the embodiments of the present application, C SEIThe first capacity required for the second positive electrode material containing the second mass content of the sodium supplement to make up for the capacity consumed by the SEI film can be regarded as the capacity released by the sodium supplement for the first time, and each subsequent replenishment of the cyclic decomposition capacity is equivalent to the second, third...nth release capacity of the sodium supplement.

[0138] For example, according to Figure 3 The Call & V curve shows that after the first replenishment of the cycle decomposition capacity, the total release capacity of the sodium supplement is C'1 = C SEI +C2, the corresponding voltage is V2, and the voltage is set as the charging cut-off voltage (ie, the second cut-off voltage); similarly, after the second replenishment of the cycle decomposition capacity, the total release capacity of the sodium supplement agent is C'2 = C SEI +C3, its corresponding voltage is V3, which is set as the charging cut-off voltage (that is, the second cut-off voltage); and so on, obtain C'3, C'4...C' n The corresponding voltages V4, V5...Vn set V3, V4...Vn as the charging cut-off voltage (ie, the second cut-off voltage) respectively to supplement the small current capacity.

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

[0140] In some embodiments, in the first full battery, the second positive electrode material includes a positive electrode active material, a first positive electrode conductor, a second positive electrode conductor, a positive electrode binder and the sodium supplement, and the mass ratio of the positive electrode active material, the first positive electrode conductor, the second positive electrode conductor 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, in the second positive electrode material of the first full battery, the positive electrode active material includes at least one of sodium ion layered oxides, sodium-containing sulfates, sodium-containing fluorinated polyanions, sodium-containing mixed polyanions, sodium-containing silicates, and sodium-containing borates.

[0142] Exemplarily, the sodium ion layered oxide includes but is not limited to at least one of an O3 phase sodium ion layered oxide and a P2 phase sodium ion layered oxide. Among them, the O3 phase sodium ion layered oxide includes but is 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.; the sodium ion layered oxide of the P2 phase includes but is 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] Exemplary sodium sulfates include, but are not limited to, Na2Fe2(SO4)3, Na2Fe(SO4) 2.2 At least one of H2O, etc.

[0144] Exemplarily, the sodium-containing phosphate includes, but is not limited to, at least one of Na3V2(PO3), Na3MnTi(PO3)3, Na2FeP2O7, Na2CoP2O7, and the like.

[0145] Exemplarily, the sodium-containing fluorinated polyanion includes, but is not limited to, at least one of Na3(VPO4)2F3, Na3(VOPO4)2F, Na2FePO4F, and the like.

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

[0147] Exemplarily, the sodium-containing silicate includes, but is not limited to, at least one of Na2MnSiO4, Na2FeSiO4, and the like.

[0148] Exemplary sodium-containing borates include, but are not limited to, Na3CoB5O 10 、Na3FeB5O 10 At least one of the above.

[0149] As a preferred example, in the second positive electrode material of the first full battery, 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 battery includes a negative electrode active material, a negative electrode conductor, a negative electrode thickener and a negative electrode binder, and the mass ratio of the negative electrode active material, the negative electrode conductor, the negative electrode thickener and the 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 battery, the first positive electrode conductive agent, the second positive electrode conductive agent and the negative electrode conductive agent all include but are not limited to at least one of Super P, Ketjen black, acetylene black carbon 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 the present application, there is no limitation on the material selection of the positive electrode binder, negative electrode active material, negative electrode thickener and negative electrode binder in the first full battery, and they can all adopt 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 a polymer separator, a ceramic separator, a polymer / ceramic composite separator, and the like.

[0154] Exemplarily, the polymer separator includes but is not limited to at least one of a single-layer polymer separator and a multi-layer polymer separator, etc. The single-layer polymer separator includes but is not limited to a polyethylene (PE) separator or a polypropylene (PP) separator, etc.

[0155] As an optional example, in the first full battery, the separator is a polyethylene (PE) separator with a thickness of 12 um.

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

[0157] The electrolyte used in the button half-cell is consistent with that used in the button half-cell. The solute may be 1 mol / L NaClO4 or 1 mol / L NaPF4. The solvent includes but is not limited to two or more of ethylene carbonate (EC), propylene carbonate (PC), fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), etc.

[0158] As an optional example, the method for preparing the electrolyte in the first full battery is: 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 embodiment of the present application, the first full battery and the second full battery have the same composition except for the different mass content of the sodium supplement in the positive electrode material. In addition, the preparation methods of the first full battery and the second full battery are also the same, which will not be repeated here.

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

[0161] 1. By precisely regulating the voltage of the entire battery, the release of active sodium in the sodium storage layer is controlled, which not only takes into account the initial effect but also can continuously replenish sodium to improve the circulation.

[0162] 2. Excess sodium ions are stored in the positive electrode. Compared with the traditional sodium replenishment method in which all excess sodium ions are stored in the negative electrode, the sodium consumption by side reactions in the cycle process is reduced.

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

[0164] Certain features of the present technology are further illustrated in the following non-limiting examples.

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

[0166] Example 1

[0167] The method of continuously supplementing sodium to improve cycle performance in this embodiment comprises the following steps:

[0168] (1) Using Na2O as the positive electrode active material, a sodium supplement button half-cell was prepared, and the charging capacity and voltage curve of the sodium supplement Na2O were obtained, such as Figure 2 As shown. Among them:

[0169] The preparation method of Na2O button half-cell is as follows: SP:PVDF:Na2O is mixed in a mass ratio of 10:5:85, an appropriate amount of NMP is added to make a slurry, and the slurry is evenly coated on the surface of an aluminum foil with a thickness of 13 μm using a scraper, and the positive electrode sheet is obtained after being placed in a vacuum drying oven at 120°C for 10 hours; the sodium sheet is used as the negative electrode, and the Na2O button half-cell is assembled in the glove box in the order of negative electrode shell-spring-gasket-negative electrode (sodium sheet)-electrolyte-diaphragm-electrolyte-positive electrode-positive electrode shell. The electrolyte solute is 1 mol / L NaClO4, and the solvent is ethylene carbonate / diethyl carbonate (volume ratio 1:1); the diaphragm is a polyethylene (PE) diaphragm with a thickness of 12 μm.

[0170] The method for obtaining the charging gram capacity and voltage curve of Na2O is: use 0.05C constant current and constant voltage to charge to 4.2V, cut off current 0.02C, and obtain the charging gram capacity & voltage curve of the sodium supplement Na2O.

[0171] (2) Obtain the theoretical gram capacity of the sodium supplement Na2O (which can be obtained by Figure 2 The method further comprises the following steps:

[0172] 1) Preparing a second full battery containing the first positive electrode material. Specifically, the preparation method of the second full battery includes the following steps:

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

[0174] B. Preparation of negative electrode sheet: negative electrode slurry is mixed and prepared into negative electrode sheet 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%. Among them, the negative electrode current collector is aluminum foil with a thickness of 13 μm.

[0175] C. Diaphragm selection: The diaphragm is a polyethylene (PE) diaphragm with a thickness of 12um.

[0176] D. Preparation of electrolyte: 1 mol / L NaClO4 solute was dissolved in ethylene carbonate / diethyl carbonate (volume ratio 1:1) solvent.

[0177] E. Assembly: The positive electrode sheet, the negative electrode sheet and the diaphragm are stacked and assembled, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet. After the tabs are welded and packaged, the electrolyte can be injected after the moisture content is qualified after baking.

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

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

[0180] Among them, a is the charging gram capacity of the positive electrode active substance in the first positive electrode material, which is 113.7 mAh / g; b% is the first efficiency of the second full battery, which is 85.4%; c is the first week sodium replenishment capacity of the button half-battery prepared in step (1) (that is, the theoretical gram 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 substance in the first positive electrode material of the second full battery and the mass content of the sodium replenisher (that is, the first mass content), which is 95%; x% is the first mass content.

[0181] After calculation, the first mass content is 3%.

[0182] (3) The first week sodium replenishment capacity of the button half-cell prepared in step (1) is taken as the capacity of the sodium replenisher used to compensate for the SEI film consumption in step (2), that is, the theoretical gram capacity of the sodium replenisher Na2O in step (2); according to the theoretical gram capacity, Figure 2 The corresponding charging cut-off voltage V0 is found in the charging capacity and voltage curve, and the second full battery is charged to the cut-off voltage V0, so that the capacity of the sodium supplement is fully released to compensate for the SEI consumption. Wherein, V0 = 4.2V.

[0183] (4) According to the theoretical gram capacity of the sodium supplement Na2O in step (2), determine the first capacity required for the second positive electrode material containing the second mass content of the sodium supplement Na2O to make up for the capacity consumed by the SEI film, and use the difference between the theoretical gram capacity of the sodium supplement Na2O and the first capacity as the remaining capacity of the sodium supplement in the second positive electrode material, and store the remaining capacity in the sodium ion supply station (i.e., in the second positive electrode material). The second mass content is 5%. Specifically:

[0184] i) making the second mass content of the sodium supplement Na2O in the second positive electrode material 5%, preparing a positive electrode sheet, and then preparing a first full battery, the preparation method of the first full battery comprising the following steps:

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

[0186] G. Preparation of negative electrode sheet: 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% to prepare the negative electrode sheet. The negative electrode current collector is an aluminum foil with a thickness of 13 μm.

[0187] H. Diaphragm selection: The diaphragm is a polyethylene (PE) diaphragm with a thickness of 12um.

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

[0189] G. Assembly: The positive electrode sheet, the negative electrode sheet and the diaphragm are stacked and assembled, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet. After the tabs are welded and packaged, the electrolyte can be injected after the moisture content is qualified after baking.

[0190] ii) According to the theoretical gram capacity of the sodium supplement Na2O in step (2), the first capacity is calculated according to the following formula:

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

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

[0193] After calculation, the first capacity C required for the second cathode material containing the second mass content of the sodium supplement Na2O to make up for the capacity consumed by the SEI film is B It is 306mAh / g.

[0194] iii) Define the theoretical gram capacity of the sodium supplement Na2O in step (2) as C all , the first capacity is C SEI , then 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 curve of Na2O shown in FIG. 4 is used to obtain the first charging cut-off voltage V1 corresponding to the first capacity in step (4), V1 = 3.6 V (as shown in FIG. Figure 3 Specific:

[0196] The first full battery in step (4) is charged at 0.02C constant current, with the cut-off voltage set to 2.0V, and then charged at 0.1C constant current to 3.4V to completely decompose the second positive electrode material in the first full battery, and finally charged at 0.05C constant current and constant voltage to V1, with the cut-off current of 0.02C, to decompose the first decomposition amount C of the sodium storage layer. SEI (C SEI =306mAh / g) is just used to make up for the SEI film loss.

[0197] (6) The remaining capacity obtained in step (5) is evenly divided into 6 sections, each of which is marked as the second capacity. Combined with the attenuation of the cycle retention rate, each section of the second capacity is added to the cycle process of the first full battery step by step. Specifically, the following steps are included:

[0198] a) When the first full battery cycle capacity retention rate decays by 3%, the cycle decomposition capacity is supplemented once using each second capacity. The cycle decomposition capacity required to be supplemented each time is calculated according to the following formula:

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

[0200] Among them, C i+1 is the cycle decomposition capacity replenished for the i-th time, 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 evenly divided, which is 6 segments; i is the number of times the cycle decomposition capacity is replenished, and i is an integer greater than 0 and less than 6.

[0201] After calculation, when the capacity is replenished for the first time, i=1, the replenished cycle decomposition capacity C2=C / 6=204 / 6=34mAh / g; when the capacity is replenished for the second time, i=2, the replenished cycle decomposition capacity C3=2*(C / 6)=68mAh / g; when the capacity is replenished for the third time, i=3, the replenished cycle decomposition capacity C4=3*(C / n)=102mAh / g; when the capacity is replenished for the fourth time, i=4, the replenished cycle decomposition capacity C5=4*(C / n)=136mAh / g; when the capacity is replenished for the fifth time, i=5, the replenished cycle decomposition capacity C6=5*(C / n)=170mAh / g; when the capacity is replenished for the sixth time, i=6, the replenished cycle decomposition capacity C7=6*(C / n)=204mAh / g.

[0202] b) According to Figure 2 The charging gram capacity and voltage curve of Na2O shown in the figure determines the voltage corresponding to the total released capacity of the sodium supplement agent Na2O after each replenishment cycle decomposition capacity, and uses this voltage as the corresponding second cut-off voltage to restore and replenish the capacity of the first full battery.

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

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

[0205] Among them, C' i is the total released capacity of the sodium supplement agent Na2O after the i-th replenishment of the cycle decomposition capacity, in mAh / g; Ci is the cycle decomposition capacity replenished for the i-th time, in mAh / g; i is the number of times the cycle 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 evenly divided, which is 6 segments.

[0206] according to Figure 3 Call & V curve, after the first replenishment cycle decomposition capacity, the total release capacity of the sodium supplement Na2O is C'1=C SEI +C2=306+34=340mAh / g, and its corresponding voltage is V2, which is set as the charging cut-off voltage (i.e., the second cut-off voltage), and the first full battery is charged to 3.7V (V2), and then discharged to -1.5V, which is the first cycle decomposition capacity replenishment, and then the 1C / 1C cycle 2000 cycle performance is continued to be tested in the voltage range of 1.5V-3.4V at room temperature; when the cycle capacity retention rate of the first full battery decays by 3% again, the second cycle decomposition capacity replenishment is performed, and at this time, after the second replenishment of the cycle decomposition capacity, the total released capacity of the sodium supplement agent is C'2=C SEI +C3=306+68=374mAh / g, and its corresponding voltage is 3.8V (V3). Set this voltage as the charge cutoff voltage (also the second cutoff voltage), charge the first full battery to V3, and then discharge it 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. And so on, obtain the voltages V4, V5, V6, and V7 corresponding to C'3, C'4, C'5, and C'6, set V4, V5, V6, and V7 as the charge cutoff voltage (also the second cutoff voltage) respectively, and perform small current capacity replenishment - V4=3.9V to release 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 = 510 mAh / g) for a total of 6 stages until the capacity of the sodium supplement Na2O is fully released.

[0207] Example 2

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

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

[0210] Example 3

[0211] The method of continuously supplementing sodium to improve cycle performance in this embodiment comprises the following steps:

[0212] (1) Using Na2NiO2 as the positive electrode active material, a button half-cell was prepared, and the charging capacity and voltage curve of Na2NiO2 were obtained, such as Figure 5 As shown. Among them:

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

[0214] The preparation method of Na2NiO2 button half-cell is as follows: SP:PVDF:Na2NiO2 is mixed in a mass ratio of 10:5:85, an appropriate amount of NMP is added to make a slurry, and the slurry is evenly coated on the surface of an aluminum foil with a thickness of 13μm by a scraper, and the positive electrode sheet is obtained after being placed in a vacuum drying oven at 120℃ for 10h; the sodium sheet is used as the negative electrode, and the Na2NiO2 button half-cell is assembled in a glove box in the order of negative electrode shell-spring-gasket-negative electrode (sodium sheet)-electrolyte-diaphragm-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 diaphragm is a polyethylene (PE) diaphragm with a thickness of 12μm.

[0215] The method for obtaining the charging gram capacity and voltage curve of Na2NiO2 is: use 0.05C constant current and constant voltage to charge to 3.6V, cut off current 0.02C, and obtain the charging gram capacity & voltage curve of the sodium supplement Na2NiO2.

[0216] (2) Obtaining a first mass content of the sodium supplement agent Na2NiO2 in the first positive electrode material when the theoretical gram capacity of the sodium supplement agent is equal to the capacity consumed in forming the SEI film. Specifically, the following steps are included:

[0217] 1) Preparing a second full battery containing the first positive electrode material. Specifically, the preparation method of the second full battery includes the following steps:

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

[0219] B. Preparation of negative electrode sheet: negative electrode slurry is mixed and prepared into negative electrode sheet 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%. Among them, the negative electrode current collector is aluminum foil with a thickness of 13 μm.

[0220] C. Diaphragm selection: The diaphragm is a polyethylene (PE) diaphragm with a thickness of 12um.

[0221] D. Preparation of electrolyte: 1 mol / L NaClO4 solute was dissolved in ethylene carbonate / diethyl carbonate (volume ratio 1:1) solvent.

[0222] E. Assembly: The positive electrode sheet, the negative electrode sheet and the diaphragm are stacked and assembled, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet. After the tabs are welded and packaged, the electrolyte can be injected after the moisture content is qualified after baking.

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

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

[0225] Among them, a is the charge gram capacity of the positive electrode active substance in the first positive electrode material, which is 113.7 mAh / g; b% is the first efficiency of the second full battery, which is 85.4%; c is the first week sodium replenishment capacity of the button half-battery prepared in step (1) (within the voltage range of 2.0-3.6 V), which is 393 mAh / g; d% is the sum of the mass content of the positive electrode active substance in the first positive electrode material of the second full battery and the mass content of the sodium replenisher (that is, the first mass content), which is 95%; x% is the first mass content.

[0226] After calculation, the first mass content is 3.85%.

[0227] (3) The first week sodium replenishment capacity of the button half-cell prepared in step (1) is taken as the capacity of the sodium replenisher used to compensate for the SEI film consumption in step (2), that is, the theoretical gram capacity of the sodium replenisher Na2NiO2 in step (2); according to the theoretical gram capacity, Figure 5 The corresponding charging cut-off voltage V0 is found in the charging capacity and voltage curve, and the second full battery is charged to the cut-off voltage V0, so that the capacity of the sodium supplement is fully released to compensate for the SEI consumption. Wherein, V0 = 3.6V.

[0228] (4) According to the theoretical gram capacity of the sodium supplement Na2NiO2 in step (2), determine the first capacity required for the second positive electrode material containing the second mass content of the sodium supplement Na2NiO2 to make up for the capacity consumed by the SEI film, and use the difference between the theoretical gram capacity of the sodium supplement Na2NiO2 and the first capacity as the remaining capacity of the sodium supplement in the second positive electrode material, and store the remaining capacity in the sodium ion supply station (i.e., in the second positive electrode material). The second mass content is 6.4%. Specifically:

[0229] i) making the second mass content of the sodium supplement Na2NiO2 in the second positive electrode material 6.4%, preparing a positive electrode sheet, and then preparing a first full battery, the preparation method of the first full battery comprising the following steps:

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

[0231] G. Preparation of negative electrode sheet: 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% to prepare the negative electrode sheet. The negative electrode current collector is an aluminum foil with a thickness of 13 μm.

[0232] H. Diaphragm selection: The diaphragm is a polyethylene (PE) diaphragm with a thickness of 12um.

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

[0234] G. Assembly: The positive electrode sheet, the negative electrode sheet and the diaphragm are stacked and assembled, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet. After the tabs are welded and packaged, the electrolyte can be injected after the moisture content is qualified after baking.

[0235] ii) According to the theoretical gram capacity of the sodium supplement Na2NiO2 in step (2), the first capacity is calculated according to 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 gram capacity (in the voltage range of 2.0-3.6V) of the sodium supplement Na2NiO2 in step (2) is 393mAh / g; C B is the first capacity, and the unit is mAh / g.

[0238] After calculation, the first capacity C required for the second cathode material containing the second mass content of the sodium supplement Na2NiO2 to make up for the capacity consumed by the SEI film B It is 236.4mAh / g.

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

[0240] (5) Combination Figure 5 The charging capacity and voltage curve of Na2NiO2 shown in FIG. 4 is used to obtain the first charging cut-off voltage V1 corresponding to the first capacity in step (4), V1 = 3.4 V (as shown in FIG. Figure 6 Specific:

[0241] The first full battery in step (4) is charged at a constant current of 0.02C, with the cut-off voltage set to 2.0V, and then charged at a constant current of 0.05C to 3.4V so that the second positive electrode material in the first full battery is completely decomposed. At the same time, the first decomposition amount C of the sodium storage layer is SEI (CSEI =236.4 mAh / g) is just used to make up for the SEI film loss.

[0242] (6) Divide the remaining capacity obtained in step (5) into two sections, each of which is marked as the second capacity. Combined with the attenuation of the cycle retention rate, each section of the second capacity is added to the cycle of the first full battery step by step. Specifically, the following steps are included:

[0243] a) When the first full battery cycle capacity retention rate decays by 5%, the cycle decomposition capacity is supplemented once using each second capacity. The cycle decomposition capacity required to be supplemented each time is calculated according to the following formula:

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

[0245] Among them, C i+1 is the cycle decomposition capacity replenished for the i-th time, 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 evenly divided, which is 2 segments; i is the number of times the cycle decomposition capacity is replenished, and i is an integer greater than 0 and less than 2.

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

[0247] b) According to Figure 6 The charging gram capacity and voltage curve of Na2NiO2 shown in the figure determines the voltage corresponding to the total released capacity of the sodium supplement agent Na2NiO2 after each replenishment cycle decomposition capacity, and uses this voltage as the corresponding second cut-off voltage to restore and replenish the capacity of the first full battery.

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

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

[0250] Among them, C' i is the total released capacity of the sodium supplement agent Na2NiO2 after the i-th replenishment of the cycle decomposition capacity, in mAh / g; Ci is the cycle decomposition capacity replenished for the i-th time, in mAh / g; i is the number of times the cycle 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 evenly divided, which is 2 segments.

[0251] according to Figure 6 Call&V curve, after the first replenishment cycle decomposition capacity, the total release capacity of the sodium supplement Na2NiO2 is C'1=C SEI +C2=236.4+78.3=314.7mAh / g, and its corresponding voltage is V2, which is set as the charging cut-off voltage (i.e., the second cut-off voltage), and the first full battery is charged to 3.5V (V2), and then discharged to -1.5V, which is the first cycle decomposition capacity replenishment, and then the 1C / 1C cycle 2000 cycle performance is continued to be tested in the voltage range of 1.5V-3.4V at room temperature; when the cycle capacity retention rate of the first full battery decays by 5% again, the second cycle decomposition capacity replenishment is performed, and at this time, after the second replenishment of the cycle decomposition capacity, the total released capacity of the sodium supplement agent is C'2=C SEI +C3=236.4+156.6=393mAh / g, and the corresponding voltage is 3.6V (V3). This voltage is set as the charging cut-off voltage (i.e., the second cut-off voltage), and the first full battery is charged to V3, and then discharged to -1.5V to replenish the decomposition capacity for the second cycle, so that the capacity of the sodium supplement Na2NiO2 is fully released.

[0252] Comparative Example 1

[0253] The full battery positive electrode material of this comparative example does not contain a sodium supplement, and the preparation method of the full battery comprises the following steps:

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

[0255] B. Preparation of negative electrode sheets: negative electrode slurry is mixed and prepared into negative electrode sheets 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%.

[0256] C. Diaphragm selection: The diaphragm is a polyethylene (PE) diaphragm with a thickness of 12um.

[0257] D. Preparation of electrolyte: 1 mol / L NaClO4 solute was dissolved in ethylene carbonate / diethyl carbonate (volume ratio 1:1) solvent.

[0258] E. Assembly: The positive electrode sheet, the negative electrode sheet and the diaphragm are stacked and assembled, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet. After the tabs are welded and packaged, the electrolyte can be injected after the moisture content is qualified after baking.

[0259] The full battery is first charged with a 0.02C constant current with the cut-off voltage set to 2.0V, then charged with a 0.2C constant current and constant voltage to 3.4V with a cut-off current of 0.05C, and its 1C / 1C cycle performance for 2000 weeks is tested in the voltage range of 1.5V-3.4V at room temperature.

[0260] Comparative Example 2

[0261] The full battery positive electrode material of this comparative example contains a sodium supplement Na2O, and the preparation method of the full battery comprises the following steps:

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

[0263] B. Preparation of negative electrode sheets: negative electrode slurry is mixed and prepared into negative electrode sheets 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%.

[0264] C. Diaphragm selection: The diaphragm is a polyethylene (PE) diaphragm with a thickness of 12um.

[0265] D. Preparation of electrolyte: 1 mol / L NaClO4 solute was dissolved in ethylene carbonate / diethyl carbonate (volume ratio 1:1) solvent.

[0266] E. Assembly: The positive electrode sheet, the negative electrode sheet and the diaphragm are stacked and assembled, wherein the diaphragm is located between the positive electrode sheet and the negative electrode sheet. After the tabs are welded and packaged, the electrolyte can be injected after the moisture content is qualified after baking.

[0267] The whole battery was first charged with a constant current of 0.02C, with the cut-off voltage set to 2.0V, then charged with a constant current of 0.1C to 3.4V to completely decompose the sodium positive electrode material, and finally charged with a constant current and constant voltage of 0.05C to V0, V0 = 4.2V, with a cut-off current of 0.02C, to completely decompose the 3% sodium supplement. all (The best sodium supplement ratio C all Equivalent to C SEI ) is used to compensate for SEI consumption and test its 1C / 1C cycle performance in the voltage range of 1.5V-3.4V at room temperature.

[0268] The electrochemical performance of the first full battery in Example 1-3 and the full battery in Comparative Example 1-2 was tested, wherein: the test method for the first week discharge gram capacity is: place the prepared sodium ion battery on the test instrument and place it in a (25±1)℃ test environment. Charging method: let it stand for 10 minutes, use 0.02C constant current charging, set the cut-off voltage to 2.0V, let it stand for 10 minutes, then 0.1C constant current charging to 3.4V, let it stand for 10 minutes, and finally use 0.05C constant current constant voltage charging to V1, and the cut-off current is 0.02C to obtain the charging gram capacity; Discharging method: discharge the full battery to 1.5V at 0.05C to obtain the first week discharge gram capacity.

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

[0270] The test method for the capacity of the sodium supplement in the first week is: place the sodium supplement on the test instrument and place it in a (25±1)℃ test environment. Charging method: let it stand for 10 minutes, charge to V0 with a constant current of 0.05C, and charge to 0.02C with a constant voltage to obtain the first week charging capacity of the sodium supplement;

[0271] The original method 1C cycle 2000-cycle capacity retention test method is: (25±1)℃, charge the second full battery in the range of 1.5-3.4V, 1C constant current to 3.4V, constant voltage charge to 0.05C; 1C constant current discharge, cut-off voltage 1.5V. Repeat the above charge and discharge steps 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 cell in Comparative Examples 1-2

[0274]

[0275] From Table 1 we can see that:

[0276] The embodiments of the present application achieve segmented release of the sodium supplement by precisely controlling the voltage of the entire battery. The active sodium released for the first time is used to improve the initial effect, and the remaining active sodium is released segmentedly through the sodium ion supply station to make up for the sodium consumed during the entire life cycle of the sodium ion battery.

[0277] Comparative Example 1 is without adding sodium supplement, and Comparative Example 2 is with adding appropriate amount of sodium supplement Na2O. The initial effect of adding appropriate amount of sodium supplement Na2O is increased from 85.42% to 91.13%, and the cycle life is increased from 2000cls@92.4% to 94.8% (that is, the cycle retention rate corresponding to 2000 weeks is 92.4%).

[0278] In embodiments 1 and 2, excessive amounts of sodium supplement Na2O are added, and the first decomposition capacity of the sodium supplement C is controlled by controlling the full battery voltage. SEI Just to make up for the SEI film consumption, the remaining capacity is released in stages. In Examples 1 and 2, the charge and discharge are performed when the cycle capacity retention rate decays by 3% and 5%, respectively, and the remaining capacity (C all -C SEI ) improves the cycle retention rate. The results show that the method of the embodiment of the present application improves the retention rate by 4% compared with the original method.

[0279] In the present application, the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the described specific features, structures, materials or characteristics may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0280] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In the description of this application, the meaning of "plurality" is at least two, such as two, three, etc., unless otherwise clearly and specifically defined.

[0281] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A method for continuously supplementing sodium to improve cycle performance, characterized in that: include: Obtain the charging gram capacity and voltage curve of the sodium supplement; Obtaining a first mass content of the sodium supplement in the first positive electrode material when the theoretical gram capacity of the sodium supplement is equal to the capacity consumed in forming the SEI film; According to the theoretical gram capacity, determining the first capacity required for the second positive electrode material containing the second mass content of the sodium supplement to make up for the capacity consumed by the SEI film, and taking the difference between the theoretical gram capacity and the first capacity as the remaining capacity of the sodium supplement in the second positive electrode material; the second mass content is greater than the first mass content, and the second positive electrode material is the same as the first positive electrode material except for the content of the sodium supplement; the first positive electrode material and the second positive electrode material both include positive electrode active substances; Combining the charging capacity and voltage curve, obtaining a first charging cut-off voltage corresponding to the first capacity; The remaining capacity is evenly divided into at least two sections of second capacity, and the second capacity of each section is replenished step by step during the cycle of the first full battery containing the second positive electrode material in combination with the attenuation of the cycle retention rate.

2. The method according to claim 1, characterized in that Obtaining a first mass ratio of the sodium supplement agent in the first positive electrode material when the theoretical gram capacity of the sodium supplement agent is equal to the capacity consumed in forming the SEI film comprises: A button-type half-cell was prepared using a sodium supplement as the positive electrode active material; preparing a second full battery containing the first cathode material; The first mass content is calculated according to the charge gram capacity of the positive electrode active substance in the first positive electrode material, the first efficiency of the second full battery, the first week sodium replenishment capacity of the button half battery, and the mass content of the positive electrode active substance in the first positive electrode material.

3. The method according to claim 2, characterized in that The first mass content ratio is calculated according to the following formula: a*b%*(dx)%+c*x%=a*(dx)%, Wherein, a is the charge gram capacity of the positive electrode active substance in the first positive electrode material, in mAh / g; b% is the first efficiency of the second full battery; c is the first week sodium replenishment capacity of the button half-battery, in mAh / g; d% is the sum of the mass content of the positive electrode active substance in the first positive electrode material and the first mass content; x% is the first mass content; And / or, the button-type half-cell is a button-type half-cell used to obtain the charging gram capacity and voltage curve of the sodium supplement agent.

4. The method according to claim 1, characterized in that: The method of replenishing each section of the second capacity step by step to a cycle of a first full battery containing the second positive electrode material comprises: Each time the first full-battery cycle capacity retention rate decays, the second capacity is used to supplement the cycle decomposition capacity accordingly.

5. The method according to claim 4, characterized in that The cycle decomposition capacity required to be supplemented each time is calculated according to the following formula: C i+1 =i*(C / n), Among them, C i+1 is the cycle decomposition capacity replenished for the i-th time, in mAh / g; C is the remaining capacity, in mAh / g; C / n is the second capacity; n is the number of segments into which the remaining capacity is evenly divided, in segments; n is an integer greater than 1 and less than 2000; i is the number of times the cycle decomposition capacity is replenished, i is an integer greater than 0 and less than n; And / or, the method for continuously supplementing sodium to improve circulation performance further comprises: According to the charging gram capacity and voltage curve, the voltage corresponding to the total released capacity of the sodium supplement agent after each replenishment of the cyclic decomposition capacity is determined, and the voltage is used as the corresponding second cut-off voltage to restore and replenish the capacity of the first full battery.

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

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

8. 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, the first positive electrode material and the second positive electrode material both further include a first positive electrode conductor, a second positive electrode conductor, a positive electrode binder and the sodium supplement, and the mass ratio of the positive electrode active material, the first positive electrode conductor, the second positive electrode conductor and the positive electrode binder is (87-99): (1-5): (1-4): (1-4); And / or, the negative electrode material of the first full battery includes a negative electrode active material, a negative electrode conductive agent, a negative electrode thickener and a negative electrode binder, and 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 battery includes at least one of a polymer separator, a ceramic separator, and a polymer / ceramic composite separator.

9. The method according to claim 8, characterized in that In the first positive electrode material and the second positive electrode material, 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 all include at least one of Super P, Ketjen black, acetylene black carbon black, carbon nanotubes, graphene, conductive graphite, carbon fiber, conductive carbon nanotubes or ordered mesoporous carbon.

10. Use of the method according to any one of claims 1 to 9 in the use of sodium ion batteries.

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