A sodium supplement method of a sodium ion battery and a sodium ion battery after sodium supplement

Abstract

The application provides a sodium supplement method for a sodium ion battery and a sodium-supplemented sodium ion battery, and the sodium supplement method comprises the following steps: (1) coating an initial negative electrode sheet with a sodium supplement agent slurry to obtain a coated negative electrode sheet; the sodium supplement agent in the sodium supplement agent slurry comprises sodium nitride; (2) performing heat treatment on the coated negative electrode sheet obtained in step (1), and then performing battery assembly to obtain a sodium-supplemented sodium ion battery; or performing bare battery assembly on the coated negative electrode sheet obtained in step (1) to obtain a bare battery, performing thermal formation on the obtained bare battery, and then preparing the sodium-supplemented sodium ion battery by using the bare battery after thermal formation. The sodium-supplemented sodium ion battery obtained by the sodium supplement method has high initial coulomb efficiency and cycle stability, and also has high energy density.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of batteries, and relates to a sodium supplement method for a sodium ion battery, in particular to a sodium supplement method for a sodium ion battery and a sodium ion battery after sodium supplement. BACKGROUND

[0002] In the initial cycle of the sodium ion battery, some irreversible reactions such as the formation of the SEI film on the negative electrode surface will cause the loss of sodium in the system, resulting in a low first coulombic efficiency of the negative electrode material, which is one of the main obstacles affecting the energy density of the sodium ion battery. Compared with half cells, this consumption is particularly obvious in full cells. This is because the SEI film formed during the first charge and discharge will consume sodium ions, and this part of consumption is irreversible. Therefore, the key to restricting the cycle stability and energy density of the full cell is the irreversible consumption of limited sodium. At present, researchers have done a lot of work from the aspects of material and electrolyte design to reduce the irreversible capacity loss in the sodium ion battery, but the sodium consumption is difficult to completely eliminate. Therefore, pre-sodium of the sodium ion battery becomes an important solution to the above problems. At present, pre-sodium has been widely studied in sodium ion batteries, sodium ion capacitors and dual-ion batteries.

[0003] The positive electrode additive pre-sodium method has the advantages of low cost, high performance, simple operation, high safety and the like, and is the most commercially potential pre-sodium method at present. However, the positive electrode additive pre-sodium method is inevitably affected by the “dead mass”, “dead volume” or harmful gas released by the positive electrode additive, which affects the utilization rate of the positive electrode active material, reduces the overall energy density of the battery, and causes the capacity attenuation of the battery in the long cycle process. In addition, the compatibility of the sodium additive and the positive electrode material also needs to be considered, which limits the selection of the positive electrode material.

[0004] The negative electrode pre-sodium can also effectively compensate for the sodium ions consumed by the reaction such as the formation of the SEI film, more significantly improve the initial coulombic efficiency (ICE), and alleviate the problem of insufficient sodium content of the positive electrode material, providing flexibility for the development of high-energy-density batteries.

[0005] The physical method based on sodium metal powder or sodium foil is the most direct pre-sodium method, but the atmosphere requirement is the most stringent; moreover, due to the extremely high activity of sodium metal, it will react violently when exposed to air, so that the safety of the method is low and it is difficult to realize large-scale commercial application. In addition, the pre-sodium by physical method will also lead to the formation of sodium dendrites and the risk of thermal runaway of the battery. The electrochemical pre-sodium method can form a uniform SEI film and obtain good pre-sodium effect, but the complicated process greatly increases the cost of the method. The pre-sodium of sodium ion battery negative electrode by liquid immersion and chemical spraying method shows good ability to compensate for the loss of active sodium ions, but anions will be formed in the electrolyte during the pre-sodium process, which will affect the uniformity and density of the SEI film.

[0006] CN116365047A discloses a preparation method of a sodium ion battery with negative electrode sodium supplement, which is suitable for sodium ion battery, comprising the following steps: S01, under gas protection, adding sodium salt into conductive carbon black, ball milling uniformly to obtain ball milling material; after water washing, the ball milling material is dried to obtain sodium supplement carbon black; the mass ratio of the sodium salt and the conductive carbon black is (0.5-3):1; S02, adding the sodium supplement carbon black of step S01 into negative electrode material, stirring uniformly to obtain sodium supplement negative electrode material; S03, preparing a negative electrode sodium supplement sodium ion battery with positive electrode material and the sodium supplement negative electrode material of step S02.

[0007] CN108878780A discloses a sodium ion battery negative electrode sodium supplement method and a sodium ion battery, comprising: in an inert atmosphere, melting solid sodium metal at a certain temperature to obtain liquid sodium metal; uniformly adding the liquid sodium metal to the surface of the negative electrode sheet, so that the liquid sodium metal penetrates into the gap between the negative electrode materials of the negative electrode sheet; drying the negative electrode sheet.

[0008] The sodium supplement methods of the sodium ion battery disclosed in the prior art have certain defects, and there are problems of low stability, generation of harmful gas, poor compatibility, high requirement for the environment atmosphere during the sodium supplement process, low safety, complex process flow, risk of sodium dendrite formation and thermal runaway, and formation of anions in the electrolyte, which affects the uniformity and density of the SEI film. Therefore, it is crucial to develop and design a new sodium supplement method for sodium ion battery and a sodium ion battery after sodium supplement. SUMMARY

[0009] In view of the deficiencies of the prior art, the purpose of the present application is to provide a sodium ion battery sodium supplement method and a sodium ion battery after sodium supplement, the sodium supplement method provided by the present application can effectively supplement the sodium ion loss caused by the formation of SEI film or other side reactions during the first charging, the stability of the sodium supplement method is higher, harmful gas will not be generated during the sodium supplement process, the compatibility is higher, the requirement for the environment atmosphere during the sodium supplement process is lower, the safety is higher and the process flow is simple, the risk of forming dendrites during the sodium supplement process is lower and the risk of thermal runaway is lower, and anions will not be formed in the electrolyte, thereby avoiding the adverse effects on the uniformity and density of the SEI film, therefore, the sodium ion battery after sodium supplement obtained by the sodium supplement method not only has higher first coulomb efficiency and cycle stability, but also has higher energy density.

[0010] To achieve this purpose, the present application adopts the following technical solutions:

[0011] In a first aspect, the present application provides a sodium supplement method for a sodium ion battery, the sodium supplement method comprising:

[0012] (1) coating an initial negative electrode sheet with a sodium supplement agent slurry to obtain a coated negative electrode sheet; the sodium supplement agent in the sodium supplement agent slurry comprises sodium nitride;

[0013] (2) performing heat treatment on the coated negative electrode sheet obtained in step (1), and then performing battery assembly to obtain a sodium ion battery after sodium supplement;

[0014] or

[0015] performing bare battery assembly on the coated negative electrode sheet obtained in step (1) to obtain a bare battery, and then performing thermal formation on the obtained bare battery, and then preparing a sodium ion battery after sodium supplement by using the bare battery after thermal formation.

[0016] The reactions in the sodium supplement method provided by the present application are all mild reactions, and no materials with very active chemical properties are used, so the stability is higher.

[0017] The sodium supplement method provided by the present application supplements sodium in the negative electrode, and the sodium supplement agent used is sodium nitride (Na3N), the sodium supplement agent is decomposed by heat in step (2) or thermal formation, the thermal decomposition reaction is: 2Na3N→6Na+N2, and the generated gas is nitrogen gas instead of harmful gas.

[0018] The compatibility of the sodium supplement agent with the negative electrode material in the sodium supplement method provided by the present application is higher, so the sodium supplement method has higher compatibility.

[0019] The sodium replenishment method provided by this invention includes sodium nitride as the sodium replenishing agent. Compared with metallic sodium, sodium nitride has lower activity, a milder thermal decomposition reaction, lower requirements for the environmental atmosphere, and higher safety. It is less likely to form dendrites during sodium replenishment, and the risk of thermal runaway is lower.

[0020] The sodium supplementation method provided by this invention has fewer steps, all of which are easy to implement, and therefore has the advantage of a simple process flow.

[0021] In the sodium replenishment method provided by this invention, the sodium replenishing agent decomposes before the bare battery is inserted into the casing, and the generated gas has been eliminated. After being inserted into the casing and injected with electrolyte, it will not form anions in the electrolyte, thereby avoiding adverse effects on the uniformity and density of the SEI film.

[0022] In the sodium replenishment method provided by this invention, the sodium replenishing agent decomposes before the bare battery is inserted into the casing, leaving no non-active solid residue. After the battery is inserted into the casing and injected with electrolyte, the sodium-ion battery will not suffer any loss in energy density after sodium replenishment.

[0023] The sodium replenishment method provided by this invention can effectively compensate for sodium ion loss caused by the formation of the SEI film or other side reactions during the first charge. The sodium replenishment method has high stability, does not generate harmful gases during the process, has strong compatibility, low requirements for the environmental atmosphere during the process, high safety, and a simple process flow. The risk of dendrite formation and thermal runaway during the sodium replenishment process is low, and it does not form anions in the electrolyte, thus avoiding adverse effects on the uniformity and density of the SEI film. Therefore, the sodium-ion battery obtained by the sodium replenishment method not only has high initial coulombic efficiency and cycle stability, but also high energy density.

[0024] Preferably, the mass concentration of sodium supplement in the sodium supplement slurry in step (1) is 0.05~0.5wt%, for example, it can be 0.05wt%, 0.01wt%, 0.15wt%, 0.2wt%, 0.25wt%, 0.3wt%, 0.4wt% or 0.5wt%, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0025] Preferably, the method for preparing the sodium supplement slurry in step (1) includes: mixing the sodium supplement with a solvent, wherein the mixing method includes stirring.

[0026] Preferably, the boiling point of the solvent in the sodium supplement slurry is lower than the decomposition temperature of the sodium supplement, the solvent is soluble in the sodium supplement, and the solvent does not react with the sodium supplement.

[0027] Preferably, the solvent comprises any one or a combination of at least two of tetrahydrofuran, methyltetrahydrofuran, acetonitrile or acetone, typical but non-limiting combinations include a combination of tetrahydrofuran and methyltetrahydrofuran, a combination of methyltetrahydrofuran and acetonitrile, a combination of acetonitrile and acetone, or a combination of tetrahydrofuran, methyltetrahydrofuran and acetonitrile.

[0028] Preferably, the coating in step (1) comprises spraying, and the spraying speed is 0.2-0.8 m / s, for example, it can be 0.2 m / s, 0.3 m / s, 0.4 m / s, 0.5 m / s, 0.6 m / s, 0.7 m / s or 0.8 m / s, but not only limited to the listed values, other values not listed in the range are also applicable.

[0029] Preferably, the spraying of the sodium supplement agent slurry in the spraying has a spraying area density of 1.5-100 g / m 2 , for example, it can be 1.5 g / m 2 , 3 g / m 2 , 5 g / m 2 , 10 g / m 2 , 15 g / m 2 , 20 g / m 2 , 30 g / m 2 , 40 g / m 2 , 50 g / m 2 , 60 g / m 2 , 70 g / m 2 , 80 g / m 2 , 90 g / m 2 or 100 g / m 2 , but not only limited to the listed values, other values not listed in the range are also applicable.

[0030] Preferably, the coating in step (1) further comprises drying, and the drying temperature is 80-100°C, and the drying time is 10-60 min.

[0031] The drying temperature in the present application is 80-100°C, for example, it can be 80°C, 82°C, 85°C, 88°C, 90°C, 92°C, 95°C, 98°C or 100°C, but not only limited to the listed values, other values not listed in the range are also applicable, preferably 80-90°C.

[0032] The drying time in the present application is 10-60 min, for example, it can be 10 min, 20 min, 30 min, 40 min, 50 min or 60 min, but not only limited to the listed values, other values not listed in the range are also applicable.

[0033] In the present application, although the sodium nitride will decompose during the drying, the decomposition of the sodium nitride is relatively small due to the short drying time.

[0034] Preferably, the drying in step (1) further comprises die cutting.

[0035] Preferably, the initial negative electrode sheet in step (1) comprises a current collector and a negative active material.

[0036] Preferably, the negative active material comprises any one of carbon material, metal element, non-metal element, alloy or metal compound or a combination of at least two of them, typically but not limitedly, the combination includes a combination of carbon material and metal element, a combination of metal element and non-metal element, a combination of alloy and metal compound, or a combination of carbon material, metal element and non-metal element.

[0037] Preferably, the carbon material comprises any one of hard carbon, soft carbon, active carbon, expanded graphite, carbon nanotube, carbon nanowire or graphene or a combination of at least two of them, typically but not limitedly, the combination includes a combination of hard carbon and soft carbon, a combination of active carbon and expanded graphite, a combination of carbon nanotube and carbon nanowire, a combination of carbon nanowire and graphene.

[0038] Preferably, the metal element comprises any one of Sn, Ge or Bi.

[0039] Preferably, the non-metal element comprises P or S.

[0040] Preferably, the alloy comprises any one of Sn alloy, Ge alloy or Bi alloy or a combination of at least two of them, typically but not limitedly, the combination includes a combination of Sn alloy and Ge alloy, a combination of Ge alloy and Bi alloy, or a combination of Sn alloy, Ge alloy and Bi alloy.

[0041] Preferably, the metal compound comprises any one of oxide, fluoride or nitride or a combination of at least two of them, typically but not limitedly, the combination includes a combination of oxide and fluoride, a combination of fluoride and nitride, or a combination of oxide, fluoride and nitride.

[0042] Preferably, the water content of the initial negative electrode sheet is not more than 100 ppm, for example, it can be 100 ppm, 99 ppm, 95 ppm, 90 ppm, 85 ppm, 80 ppm, 75 ppm, 70 ppm, 60 ppm, 50 ppm or 20 ppm, but is not limited to the listed values, and other values not listed in this range are also applicable.

[0043] Preferably, the temperature of the heat treatment in step (2) is 90-150℃ and the time is 30-120 min.

[0044] In this invention, the heat treatment temperature in step (2) is 90~150℃, for example, it can be 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃, 130℃, 135℃, 140℃, 145℃ or 150℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0045] In this invention, the heat treatment time in step (2) is 30~120min, for example, it can be 30min, 40min, 50min, 60min, 70min, 80min, 90min or 100min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0046] Preferably, the battery assembly in step (2) includes:

[0047] The coated negative electrode obtained after heat treatment in step (1) is assembled with the separator and positive electrode to form a bare battery. The bare battery is then subjected to casing, electrolyte injection and battery formation in sequence to obtain a sodium-ion battery after sodium supplementation.

[0048] In this invention, a bare battery is first prepared using the coated negative electrode sheet obtained in step (1). After thermal formation of the bare battery, it is then encased and injected with electrolyte. The sodium replenishment process occurs during the thermal formation of the bare cell. After sodium replenishment, there is no non-active solid residue, and the energy density of the battery itself will not be lost. At the same time, the original sodium-ion battery preparation process is not changed. The process is simple, easy to operate, and low in cost, and has extremely high practical value.

[0049] Preferably, the bare battery assembly in step (2) includes:

[0050] The coated negative electrode obtained in step (1) is assembled with the separator and positive electrode to form a bare battery.

[0051] Preferably, the temperature of the thermalization in step (2) is 80~90℃ and the time is 300~600min.

[0052] The temperature of thermalization in step (2) of this invention is 80~90℃, for example, it can be 80℃, 81℃, 82℃, 83℃, 84℃, 85℃, 86℃, 87℃, 88℃, 89℃ or 90℃, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0053] The thermal transformation time in step (2) of this invention is 300~600 min, for example, it can be 300 min, 350 min, 400 min, 450 min, 500 min or 600 min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0054] Preferably, the method for preparing a sodium-added sodium-ion battery from a thermally formed bare battery in step (2) includes:

[0055] The bare battery after thermal formation is sequentially subjected to casing, electrolyte injection, and battery formation to obtain a sodium-ion battery after sodium supplementation.

[0056] Preferably, both steps (1) and (2) are carried out in an inert atmosphere with an ambient humidity of less than 3%. The ambient humidity can be, for example, 2.9%, 2.7%, 2.5%, 2.3%, 2%, 1.5%, 1%, 0.5% or 0.1%, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] As a preferred embodiment of the sodium supplementation method of the present invention, the sodium supplementation method includes:

[0058] (1) In an inert atmosphere with an ambient humidity of less than 3%, the sodium supplement agent and solvent are mixed by stirring to obtain a sodium supplement agent slurry with a mass concentration of 0.05~0.5wt%. The sodium supplement agent slurry is then sprayed onto the initial negative electrode with a water content of no more than 100ppm at a speed of 0.2~0.8m / s. The spraying surface density of the sodium supplement agent slurry is 1.5~100g / m². 2 After drying at 80~100℃ for 10~60min, the material is die-cut to obtain the coated negative electrode sheet.

[0059] The sodium supplement in the sodium supplement slurry includes sodium nitride. The boiling point of the solvent in the sodium supplement slurry is lower than the decomposition temperature of the sodium supplement. The solvent is soluble in the sodium supplement and does not react with the sodium supplement.

[0060] (2) In an inert atmosphere with an ambient humidity of less than 3%, the coated negative electrode obtained in step (1) is heat-treated at 90~150℃ for 30~120 minutes. The heat-treated coated negative electrode is then assembled with the separator and positive electrode to form a bare battery. The bare battery is then sequentially subjected to casing, electrolyte injection and battery formation to obtain a sodium-ion battery with sodium supplementation.

[0061] or

[0062] In an inert atmosphere with an ambient humidity of less than 3%, the coated negative electrode obtained in step (1) is assembled with the separator and positive electrode to form a bare battery. The bare battery is then thermally formed at 80~90℃ for 300~600 minutes. The thermally formed bare battery is then sequentially subjected to casing, electrolyte injection and battery formation to obtain a sodium-ion battery with added sodium.

[0063] In a second aspect, the present invention provides a sodium-ion battery after sodium replenishment, wherein the sodium-ion battery after sodium replenishment is obtained by the sodium replenishment method described in the first aspect.

[0064] Preferably, the sodium-added sodium-ion battery includes a sodium-added negative electrode, a separator, a positive electrode, an electrolyte, and a casing.

[0065] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0066] Compared with the prior art, the present invention has the following beneficial effects:

[0067] The sodium replenishment method provided by this invention can effectively compensate for sodium ion loss caused by the formation of the SEI film or other side reactions during the first charge. The sodium replenishment method has high stability, does not generate harmful gases during the process, has strong compatibility, low requirements for the environmental atmosphere during the process, high safety, and a simple process flow. The risk of dendrite formation and thermal runaway during the sodium replenishment process is low, and it does not form anions in the electrolyte, thus avoiding adverse effects on the uniformity and density of the SEI film. Therefore, the sodium-ion battery obtained by the sodium replenishment method not only has high initial coulombic efficiency and cycle stability, but also high energy density. Attached Figure Description

[0068] Figure 1 These are the first charge-discharge curves of the sodium-ion battery obtained in Example 1 after sodium replenishment and the sodium-ion battery obtained in Comparative Example 1.

[0069] Figure 2 These are the cycle curves of the sodium-ion battery obtained in Example 1 after sodium supplementation and the sodium-ion battery obtained in Comparative Example 1. Detailed Implementation

[0070] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention in any way.

[0071] Example 1

[0072] This embodiment provides a method for replenishing sodium in a sodium-ion battery, the method comprising:

[0073] (1) In a nitrogen atmosphere with an ambient humidity of 2%, Na3N and tetrahydrofuran were mixed by stirring to obtain a sodium supplement slurry with a mass concentration of 0.2wt%. The sodium supplement slurry was then sprayed onto the surface of an initial HC negative electrode with a water content of 80ppm at a speed of 0.5m / s. The spraying surface density of the sodium supplement slurry was 4g / m². 2 After drying at 80℃ for 30 minutes, the material is die-cut to obtain the coated negative electrode sheet.

[0074] The method for preparing the initial negative electrode of HC is as follows:

[0075] A slurry was prepared by uniformly mixing the negative electrode active material (hard carbon, HC), binder (sodium polyacrylate), conductive agent (conductive carbon black), and deionized water. The mass ratio of hard carbon, sodium polyacrylate, and conductive carbon black was 8:1:1. The slurry was then coated on both sides of an aluminum foil. After drying, the coating weight on each side of the negative electrode was 7 mg / cm². 2 Then, after cold pressing, the initial negative electrode sheet of HC is obtained;

[0076] (2) In a nitrogen atmosphere with an ambient humidity of 2%, the coated negative electrode obtained in step (1) is assembled with the separator and NFPP positive electrode to form a bare battery. The bare battery is then thermally formed at 85°C for 400 minutes. The thermally formed bare battery is then sequentially inserted into the casing, injected with electrolyte and formed into the battery to obtain a sodium-ion battery after sodium supplementation.

[0077] The method for preparing the NFPP positive electrode sheet is as follows:

[0078] A slurry was prepared by uniformly mixing the positive electrode active material (NFPP composite), binder (PVDF), conductive agent (SP), and solvent (N-methylpyrrolidone). The mass ratio of NFPP, PVDF, and SP was 8:1:1. The resulting slurry was then coated onto both sides of a carbon-coated aluminum foil. After drying, the coating weight on each side of the positive electrode was 20 mg / cm². 2 The electrode has a water content of 80ppm, and after cold pressing and die cutting, NFPP positive electrode is obtained.

[0079] Example 2

[0080] This embodiment provides a method for replenishing sodium in a sodium-ion battery, the method comprising:

[0081] (1) In an inert atmosphere with an ambient humidity of 2.5%, Na3N and methyltetrahydrofuran were mixed by stirring to obtain a sodium supplement slurry with a mass concentration of 0.05wt%. The sodium supplement slurry was then sprayed onto an initial negative electrode with a water content of 70ppm at a speed of 0.8m / s. The spraying surface density of the sodium supplement slurry was 16.5g / m². 2 After drying at 85℃ for 30 minutes, the coated negative electrode sheet is die-cut to obtain the coated negative electrode sheet.

[0082] The method for preparing the initial negative electrode of HC is as follows:

[0083] A slurry was prepared by uniformly mixing the negative electrode active material (hard carbon, HC), binder (sodium polyacrylate), conductive agent (conductive carbon black), and deionized water. The mass ratio of hard carbon, sodium polyacrylate, and conductive carbon black was 8:1:1. The slurry was then coated on both sides of an aluminum foil. After drying, the coating weight on each side of the negative electrode was 7 mg / cm². 2 Then, after cold pressing, the initial negative electrode sheet of HC is obtained;

[0084] (2) In an inert atmosphere with an ambient humidity of 2.5%, the coated negative electrode obtained in step (1) is assembled with the separator and NFPP positive electrode to form a bare battery. The bare battery is then thermally formed at 85°C for 300 minutes. The thermally formed bare battery is then sequentially inserted into the casing, injected with electrolyte and formed into the battery to obtain a sodium-ion battery with added sodium.

[0085] The method for preparing the positive electrode sheet is as follows:

[0086] A slurry was prepared by uniformly mixing the positive electrode active material (NFPP composite), binder (PVDF), conductive agent (SP), and solvent (N-methylpyrrolidone). The mass ratio of NFPP, PVDF, and SP was 8:1:1. The resulting slurry was then coated onto both sides of a carbon-coated aluminum foil. After drying, the coating weight on each side of the positive electrode was 20 mg / cm². 2 The electrode has a water content of 90 ppm, and the positive electrode is obtained after cold pressing and die cutting.

[0087] Example 3

[0088] This embodiment provides a method for replenishing sodium in a sodium-ion battery, the method comprising:

[0089] (1) In an inert atmosphere with an ambient humidity of 1%, Na3N and acetone were mixed by stirring to obtain a sodium supplement slurry with a mass concentration of 0.3wt%. The sodium supplement slurry was then sprayed onto an initial negative electrode with a water content of not 90ppm at a speed of 0.2m / s. The spraying surface density of the sodium supplement slurry was 2.8g / m². 2 After drying at 80℃ for 60 minutes, the coated negative electrode sheet is obtained by die cutting.

[0090] The method for preparing the initial negative electrode of HC is as follows:

[0091] A slurry was prepared by uniformly mixing the negative electrode active material (hard carbon, HC), binder (sodium polyacrylate), conductive agent (conductive carbon black), and deionized water. The mass ratio of hard carbon, sodium polyacrylate, and conductive carbon black was 8:1:1. The slurry was then coated on both sides of an aluminum foil. After drying, the coating weight on each side of the negative electrode was 7 mg / cm². 2 Then, after cold pressing, the initial negative electrode sheet of HC is obtained;

[0092] (2) In an inert atmosphere with an ambient humidity of 1%, the coated negative electrode obtained in step (1) is assembled with the separator and NFPP positive electrode to form a bare battery. The bare battery is then thermally formed at 85°C for 400 minutes. The thermally formed bare battery is then sequentially inserted into the casing, injected with electrolyte and formed into the battery to obtain a sodium-ion battery with added sodium.

[0093] The method for preparing the NFPP positive electrode sheet is as follows:

[0094] A slurry was prepared by uniformly mixing the positive electrode active material (NFPP composite), binder (PVDF), conductive agent (SP), and solvent (N-methylpyrrolidone). The mass ratio of NFPP, PVDF, and SP was 8:1:1. The resulting slurry was then coated onto both sides of a carbon-coated aluminum foil. After drying, the coating weight on each side of the positive electrode was 20 mg / cm². 2 The electrode has a water content of 60ppm, and after cold pressing and die cutting, an NFPP positive electrode is obtained.

[0095] Example 4

[0096] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for step (2), in which the obtained bare battery is thermally formed at 80°C for 600 min, the rest is the same as in embodiment 1.

[0097] Example 5

[0098] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for step (2), in which the obtained bare battery is thermally formed at 90°C for 300 minutes, the rest is the same as in embodiment 1.

[0099] Example 6

[0100] This embodiment provides a method for replenishing sodium in a sodium-ion battery, except that the NFPP positive electrode in step (2) is replaced with O3-NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 Except for the O2 positive electrode, everything else is the same as in Example 1;

[0101] Preparation of the O3-NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The method for using the O2 positive electrode is as follows:

[0102] The positive electrode active material O3-NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, binder polyvinylidene fluoride (PVDF), conductive agent conductive carbon black (SP), and solvent N-methylpyrrolidone are mixed evenly to form a slurry. O3-NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The mass ratio of O2, PVDF, and SP was 8:1:1. The resulting slurry was then coated on both sides of a carbon-coated aluminum foil. After drying, the coating weight on each side of the positive electrode was 20 mg / cm². 2 The water content of the electrodes is ≤100ppm, and O3-NaNi is obtained after cold pressing and die cutting. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 positive electrode plate.

[0103] Example 7

[0104] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for replacing the NFPP positive electrode with an NVP positive electrode in step (2), the rest is the same as in embodiment 1.

[0105] The method for preparing the NVP positive electrode sheet is as follows:

[0106] A slurry was prepared by uniformly mixing sodium vanadium phosphate (NVP), polyvinylidene fluoride (PVDF), conductive carbon black (SP), and N-methylpyrrolidone as the positive electrode active material. The mass ratio of NVP, PVDF, and SP was 8:1:1. The resulting slurry was then coated onto both sides of a carbon-coated aluminum foil. After drying, the coating weight on each side of the positive electrode was 10 mg / cm². 2 The water content of the electrode sheets is ≤100ppm, and after cold pressing and die cutting, NVP positive electrode sheets are obtained.

[0107] Example 8

[0108] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for replacing the NFPP positive electrode in step (2) with a Prussian white positive electrode, the rest is the same as in embodiment 1.

[0109] The method for preparing the Prussian white positive electrode sheet is as follows:

[0110] A slurry was prepared by uniformly mixing Prussian white (positive electrode active material), polyvinylidene fluoride (PVDF) binder, conductive carbon black (SP) conductive agent, and N-methylpyrrolidone (NMP) solvent. The mass ratio of NVP, PVDF, and SP was 7:1:2. The resulting slurry was then coated on both sides of a carbon-coated aluminum foil. After drying, the coating weight on each side of the positive electrode was 10 mg / cm². 2 The water content of the electrode sheets is ≤100ppm, and after cold pressing and die cutting, Prussian white positive electrode sheets are obtained.

[0111] Example 9

[0112] This embodiment provides a method for replenishing sodium in a sodium-ion battery. Except for replacing the NFPP positive electrode in step (2) with a sodium iron sulfate positive electrode, the rest is the same as in embodiment 1.

[0113] The method for preparing the sodium ferric sulfate positive electrode sheet is as follows:

[0114] A slurry was prepared by uniformly mixing sodium ferric sulfate (NVP), polyvinylidene fluoride (PVDF), conductive carbon black (SP), and N-methylpyrrolidone (N-Methylpyrrolidone) as the positive electrode active material, with a mass ratio of NVP, PVDF, and SP of 7:1:2. The resulting slurry was then coated onto both sides of a carbon-coated aluminum foil. After drying, the coating weight on each side of the positive electrode was 12 mg / cm². 2 The water content of the electrode sheets is ≤100ppm, and after cold pressing and die cutting, sodium ferric sulfate positive electrode sheets are obtained.

[0115] Example 10

[0116] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for replacing the HC initial negative electrode sheet in step (1) with a pure aluminum initial negative electrode sheet, the rest is the same as in embodiment 1.

[0117] The pure aluminum initial negative electrode sheet is prepared by drying aluminum foil using existing technology.

[0118] Example 11

[0119] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for replacing the HC initial negative electrode sheet in step (1) with a carbon-coated aluminum foil initial negative electrode sheet, the rest is the same as in embodiment 1.

[0120] The initial negative electrode sheet with carbon-coated aluminum foil is prepared by drying carbon-coated aluminum foil in the prior art.

[0121] Example 12

[0122] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for replacing the HC initial negative electrode sheet with the AC initial negative electrode sheet in step (1), the rest is the same as in embodiment 1.

[0123] The method for preparing the initial negative electrode of AC is as follows:

[0124] A slurry was prepared by uniformly mixing activated carbon (AC), a thickener (carboxymethyl cellulose), a binder (styrene-butadiene rubber), and a conductive agent (conductive carbon black) with deionized water. The mass ratio of activated carbon, carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black was 8:0.2:0.8:1. The slurry was then coated on both sides of an aluminum foil, and after drying, the coating weight on each side was 2 mg / cm². 2 The initial negative electrode sheet of AC was prepared.

[0125] Example 13

[0126] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for replacing the HC initial negative electrode sheet in step (1) with a foamed nickel initial negative electrode sheet, the rest is the same as in embodiment 1.

[0127] The initial negative electrode sheet of the nickel foam is prepared by drying nickel foam in the prior art.

[0128] Example 14

[0129] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for replacing the HC initial negative electrode sheet in step (1) with the Sn initial negative electrode sheet, the rest is the same as in embodiment 1.

[0130] The method for preparing the initial Sn negative electrode is as follows:

[0131] A slurry was prepared by uniformly mixing tin powder (Sn), a thickener (carboxymethyl cellulose), a binder (styrene-butadiene rubber), a conductive agent (conductive carbon black), and deionized water. The mass ratio of tin powder, carboxymethyl cellulose, styrene-butadiene rubber, and conductive carbon black was 7:0.5:1.5:1. The resulting slurry was then coated on both sides of an aluminum foil. After drying, the coating weight on each side was 2 mg / cm². 2 Sn electrode sheets were prepared.

[0132] Example 15

[0133] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except that the mass concentration of sodium replenishing agent in the sodium replenishing agent slurry in step (1) is 0.01wt%, and the mass of sodium replenishing agent Na3N coated on the surface of the initial negative electrode remains unchanged, the rest is the same as in Example 1.

[0134] Example 16

[0135] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except that the mass concentration of sodium replenishing agent in the sodium replenishing agent slurry in step (1) is 0.8wt%, and the mass of sodium replenishing agent Na3N coated on the surface of the initial negative electrode remains unchanged, the rest is the same as in Example 1.

[0136] Example 17

[0137] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for the spraying speed of the sodium replenishment slurry in step (1) being 0.1 m / s, the rest is the same as in embodiment 1.

[0138] Example 18

[0139] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for the spraying speed of the sodium replenishment slurry in step (1) being 1 m / s, the rest is the same as in embodiment 1.

[0140] Example 19

[0141] This embodiment provides a sodium replenishment method for a sodium-ion battery. Except for replacing step (2), the rest is the same as in Embodiment 1. Step (2) is replaced with:

[0142] In an inert atmosphere with an ambient humidity of 2.5%, the coated negative electrode obtained in step (1) is heat-treated at 120°C for 70 minutes. The heat-treated coated negative electrode is then assembled with the separator and positive electrode to form a bare battery. The bare battery is then sequentially subjected to casing, electrolyte injection and battery formation to obtain a sodium-ion battery with sodium supplementation.

[0143] Example 20

[0144] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for the temperature of heat treatment of the coated negative electrode in step (2) being 70°C, the rest is the same as in embodiment 21.

[0145] Example 21

[0146] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for the temperature of heat treatment of the coated negative electrode in step (2) being 200°C, the rest is the same as in embodiment 21.

[0147] Example 22

[0148] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for the temperature of 70°C for thermal formation of the bare battery in step (2), the rest is the same as in embodiment 1.

[0149] Example 23

[0150] This embodiment provides a sodium replenishment method for sodium-ion batteries. Except for the temperature of 100°C for thermal formation of the bare battery in step (2), the rest is the same as in embodiment 1.

[0151] Comparative Example 1

[0152] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode in step (2) with an initial HC negative electrode, the rest is the same as in Example 1.

[0153] Comparative Example 2

[0154] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode in step (2) with an initial HC negative electrode, the rest is the same as in Example 6.

[0155] Comparative Example 3

[0156] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode in step (2) with an initial HC negative electrode, the rest is the same as in Example 7.

[0157] Comparative Example 4

[0158] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode in step (2) with an initial HC negative electrode, the rest is the same as in Example 8.

[0159] Comparative Example 5

[0160] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode in step (2) with an initial HC negative electrode, the rest is the same as in Example 9.

[0161] Comparative Example 6

[0162] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode sheet in step (2) with a pure aluminum initial negative electrode sheet, the rest is the same as in Example 10.

[0163] Comparative Example 7

[0164] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode in step (2) with an initial negative electrode sheet coated with carbon aluminum foil, the rest is the same as in Example 11.

[0165] Comparative Example 8

[0166] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode in step (2) with the initial AC negative electrode, the rest is the same as in Example 12.

[0167] Comparative Example 9

[0168] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode sheet in step (2) with a foamed nickel initial negative electrode sheet, the rest is the same as in Example 13.

[0169] Comparative Example 10

[0170] This comparative example provides a method for preparing a sodium-ion battery. Except for omitting step (1), i.e., directly replacing the coated negative electrode in step (2) with an initial Sn negative electrode, the rest is the same as in Example 14.

[0171] The sodium-ion battery with sodium replenishment provided in the above embodiments and the sodium-ion battery provided in the comparative examples were subjected to first-efficiency test, cycle life test and energy density test.

[0172] The method for initial efficiency testing is as follows: the battery is left to stand in a 25°C environment for 30 minutes; then it is charged at a constant current of 0.1C to 3.5V to obtain the charging capacity (AGCO), followed by constant voltage charging at 3.5V until the current decreases to 0.05C to obtain the constant voltage capacity (ICCO); after standing for 30 minutes, it is discharged at a constant current of 0.1C to 1.5V to obtain the initial discharge capacity (DO); the initial coulombic efficiency of the battery is then calculated using the formula: Initial coulombic efficiency = DO / (ICCO + AGCO), and the initial coulombic efficiency is shown in Table 1; among them, the first charge-discharge curves of the sodium-ion battery after sodium replenishment obtained in Example 1 and the sodium-ion battery obtained in Comparative Example 1 are shown in Table 1. Figure 1 As shown.

[0173] The cycle life test method is as follows: the battery is cycled at 1C / 1C until the battery capacity is 80% of the initial capacity. The number of cycles at this point is the cycle life, and the obtained cycle counts are shown in Table 1. The cycle curves of the sodium-ion battery obtained in Example 1 after sodium replenishment and the sodium-ion battery obtained in Comparative Example 1 are shown in Table 1. Figure 2 As shown.

[0174] The method for testing energy density is as follows: Energy density of sodium battery = battery discharge energy / battery weight; The method for testing discharge energy is: charge at 0.2C constant current and constant voltage to 3.5V, then discharge at 0.2C to 1.5V, cycle for 3 weeks, and obtain the discharge energy. The calculated energy density is shown in Table 1.

[0175] Table 1

[0176]

[0177]

[0178] From Table 1, we can obtain:

[0179] (1) The sodium-ion batteries prepared by the sodium-supplementation method provided in Examples 1 to 5 of the present invention have a large initial coulombic efficiency, excellent cycle stability and high energy density.

[0180] (2) By comparing Example 1 with Examples 6-9, it can be seen that the positive electrode in step (2) of the sodium replenishment method described in this invention will affect the performance of the sodium-ion battery after sodium replenishment. The positive electrode is an NFPP positive electrode or an O3-NaNi positive electrode. 1 / 3 Fe 1 / 3 Mn 1 / When using 3O2 positive electrode and NVP positive electrode, sodium-ion batteries have a longer cycle life after sodium is added.

[0181] (3) By comparing Example 1 with Examples 10-14, it can be seen that the initial negative electrode used in step (1) of the sodium replenishment method described in this invention will affect the performance of the sodium-ion battery after sodium replenishment. When the initial negative electrode is HC initial negative electrode, carbon-coated aluminum foil initial negative electrode, AC initial negative electrode, foamed nickel initial negative electrode and Sn initial negative electrode, the sodium-ion battery after sodium replenishment exhibits a large initial coulombic efficiency and excellent cycle stability.

[0182] (4) By comparing Example 1 with Examples 15 and 16, it can be seen that the mass concentration of sodium supplement in the sodium supplement slurry in step (1) of the present invention will affect the performance of sodium-ion battery after sodium supplementation. When the mass concentration of sodium supplement is 0.05~0.5wt%, the sodium-ion battery after sodium supplementation has better cycle life. This is because the appropriate concentration of sodium supplement is conducive to its uniform distribution in the initial negative electrode, thereby promoting uniform sodium supplementation inside the negative electrode and improving the cycle life of the battery.

[0183] (5) By comparing Example 1 with Examples 17 and 18, it can be seen that the spraying speed of the sodium replenishing agent slurry in step (1) of the present invention will affect the performance of the sodium-ion battery after sodium replenishment. When the spraying speed of the sodium replenishing agent is 0.2~0.8m / s, the sodium-ion battery after sodium replenishment has a better cycle life. This is because when the spraying speed is too fast, the sodium replenishing agent cannot fully penetrate into the material, thus causing the initial negative electrode bottom to be unable to replenish sodium. When the spraying speed is too slow, the efficiency is low, which will lead to the accumulation of local sodium replenishing agent.

[0184] (6) By comparing Example 1 and Example 19, it can be seen that the technical solution in step (2) of the present invention, "assembling bare batteries by coating the negative electrode sheet obtained in step (1), then thermally forming the bare battery, and then preparing a sodium-ion battery after sodium supplementation with the bare battery after thermal forming", is better than the technical solution of "heat-treating the negative electrode sheet obtained in step (1) and then assembling the battery to obtain a sodium-ion battery after sodium supplementation". This is because in the present invention, the bare battery is first prepared by coating the negative electrode sheet obtained in step (1), and after thermal forming of the bare battery, it is then put into the casing and injected with liquid. The sodium supplementation process occurs during the thermal forming process of the bare cell. After sodium supplementation, there is no non-active solid residue, and the energy density of the battery itself will not be lost. At the same time, the original sodium-ion battery preparation process is not changed. The process is simple, easy to operate, and low in cost, and has extremely high practical value.

[0185] (7) By comparing Example 1 with Examples 20 and 21, it can be seen that when the technical solution of step (2) is "the coated negative electrode sheet obtained in step (1) is heat-treated and then the battery is assembled to obtain a sodium-ion battery after sodium replenishment", the temperature of heat treatment will affect the performance of the sodium-ion battery after sodium replenishment. When the temperature of heat treatment is 90~150℃, the sodium-ion battery after sodium replenishment has better coulombic efficiency and cycle life. This is because when the heat treatment temperature is too low, the sodium replenishing agent is not completely decomposed and the expected sodium replenishment effect cannot be achieved, and the coulombic efficiency is reduced. When the heat treatment temperature is too high, it will cause the decomposition of the binder in the initial negative electrode, resulting in a weakening of the adhesion of the electrode itself, thus shortening the cycle life.

[0186] (8) By comparing Example 1 with Examples 22 and 23, it can be seen that when the technical solution of step (2) is "to assemble the coated negative electrode sheet obtained in step (1) into a bare battery, to obtain a bare battery, to perform thermal formation on the obtained bare battery, and to prepare a sodium-ion battery after sodium supplementation with the bare battery after thermal formation", the temperature of thermal formation will affect the performance of the sodium-ion battery after sodium supplementation. When the temperature of thermal formation is 80~90℃, the sodium-ion battery after sodium supplementation has better coulombic efficiency and cycle life. This is because when the thermal formation temperature is too low, the sodium supplement agent is not completely decomposed and the expected sodium supplementation effect cannot be achieved. When the thermal formation temperature is too high, it will cause the separator to shrink thermally, thus shortening the cycle life and battery safety.

[0187] (9) By comparing Examples 1, 6-14 with Comparative Examples 1-10, it can be seen that the initial coulombic efficiency and cycle life of the sodium-ion battery after sodium replenishment, which includes a sodium-replenished negative electrode, are better than those of the corresponding comparative examples. The sodium replenishment method provided by the present invention can effectively replenish the sodium ion loss caused by the formation of SEI film or other side reactions during the first charge. The sodium replenishment method has high stability, does not generate harmful gases during the sodium replenishment process, has strong compatibility, low requirements for the environmental atmosphere during the sodium replenishment process, high safety, and simple process flow. The risk of dendrite formation and thermal runaway during the sodium replenishment process is low, and it does not form anions in the electrolyte, thereby avoiding adverse effects on the uniformity and density of the SEI film. Therefore, the sodium replenishment method provided by the present invention can effectively improve the initial coulombic efficiency and cycle life of the sodium-ion battery.

[0188] The above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A method for replenishing sodium in a sodium-ion battery, characterized in that, The sodium supplementation method includes: (1) The initial negative electrode sheet is coated with a sodium-supplementing slurry to obtain a coated negative electrode sheet; the sodium-supplementing agent in the sodium-supplementing slurry is sodium nitride; The sodium-supplementing agent slurry has a sodium-supplementing agent concentration of 0.05~0.5wt%; the coating includes spraying, the spraying speed is 0.2~0.8m / s, and the spraying surface density of the sodium-supplementing agent slurry is 1.5~100g / m². 2 ; The boiling point of the solvent in the sodium supplement slurry is lower than the decomposition temperature of the sodium supplement, the solvent is soluble in the sodium supplement, and the solvent does not react with the sodium supplement. (2) After heat treatment of the coated negative electrode sheet obtained in step (1) at 90~150℃ for 30~120min, the battery is then assembled to obtain a sodium-ion battery after sodium supplementation. The battery assembly includes: The coated negative electrode obtained after heat treatment in step (1) is assembled with the separator and positive electrode to form a bare battery. The bare battery is then subjected to casing, electrolyte injection and battery formation in sequence to obtain a sodium-ion battery after sodium supplementation. or The coated negative electrode obtained in step (1) is used to assemble a bare battery. The bare battery is then subjected to thermal formation at 80~90℃ for 300~600 min. The sodium-added sodium-ion battery is then prepared from the thermally formed bare battery. Methods for preparing sodium-ion batteries with sodium supplementation from bare cells after thermal formation include: The bare battery after thermal formation is sequentially subjected to casing, electrolyte injection, and battery formation to obtain a sodium-ion battery after sodium supplementation.

2. The sodium supplementation method according to claim 1, characterized in that, Step (1) after coating also includes drying, the drying temperature is 80~100℃ and the time is 10~60min.

3. The sodium supplementation method according to claim 1, characterized in that, The sodium supplementation method includes: (1) In an inert atmosphere with an ambient humidity of less than 3%, the sodium supplement agent and solvent are mixed by stirring to obtain a sodium supplement agent slurry with a mass concentration of 0.05~0.5wt%. The sodium supplement agent slurry is then sprayed onto the initial negative electrode with a water content of no more than 100ppm at a speed of 0.2~0.8m / s. The spraying surface density of the sodium supplement agent slurry is 1.5~100g / m². 2 After drying at 80~100℃ for 10~60min, the material is die-cut to obtain the coated negative electrode sheet. The sodium supplement in the sodium supplement slurry includes sodium nitride. The boiling point of the solvent in the sodium supplement slurry is lower than the decomposition temperature of the sodium supplement. The solvent is soluble in the sodium supplement and does not react with the sodium supplement. (2) In an inert atmosphere with an ambient humidity of less than 3%, the coated negative electrode obtained in step (1) is heat-treated at 90~150℃ for 30~120 minutes. The heat-treated coated negative electrode is then assembled with the separator and positive electrode to form a bare battery. The bare battery is then sequentially subjected to casing, electrolyte injection and battery formation to obtain a sodium-ion battery with sodium supplementation. or In an inert atmosphere with an ambient humidity of less than 3%, the coated negative electrode obtained in step (1) is assembled with the separator and positive electrode to form a bare battery. The bare battery is then thermally formed at 80~90℃ for 300~600 minutes. The thermally formed bare battery is then sequentially subjected to casing, electrolyte injection and battery formation to obtain a sodium-ion battery with added sodium.

4. A sodium-ion battery that can be replenished with sodium, characterized in that, The sodium-ion battery after sodium replenishment is obtained by the sodium replenishment method according to any one of claims 1 to 3.

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