Sodium supplement additive for sodium-ion battery, preparation method of sodium supplement additive, positive pole piece and sodium-ion battery

Abstract

The invention provides a sodium ion battery sodium supplement additive, a preparation method and application thereof, and relates to the technical field of sodium ion batteries. The sodium ion battery sodium supplement additive comprises a sodium fluoride / polyacrylonitrile (NaF / PAN) composite material, the mass of the PAN accounts for 0.1%-50% of the mass of the sodium fluoride / polyacrylonitrile composite material, and preferably 5%-35% of the mass of the sodium fluoride / polyacrylonitrile composite material. According to the invention, the NaF / PAN composite material is used as the sodium supplement additive of the sodium-ion battery, so that the activity and efficiency of the sodium supplement additive are improved, the conductivity of the positive electrode material is improved, the formation of a compact SEI film with high conductivity is facilitated, and the capacity, the cycle performance and the coulombic efficiency of the battery are improved.

Description

Technical Field

[0001] The present application relates to the technical field of sodium ion batteries, and in particular to a sodium supplement additive and a preparation method thereof, a positive electrode sheet and a sodium ion battery. Background Art

[0002] Lithium-ion batteries are currently the most researched type on the market, and their commercialization technology is relatively mature, but sodium-ion batteries also have their own advantages. For example, sodium reserves are more abundant than lithium, which has price advantages, and the conductivity of sodium salts is higher than that of lithium salts, so lower concentrations of electrolytes can be used. Therefore, the research and development of sodium-ion batteries has become a new trend in the battery industry.

[0003] Although sodium-ion batteries and lithium-ion batteries have similar working principles, the requirements for electrode materials are completely different due to the different radii of the metal ions that are embedded and deintercalated. Many electrode materials that are widely used in lithium-ion batteries cannot function in sodium batteries. The cycle life of a general battery is related to the stability of the interface (such as the interface between the electrode and the electrolyte). The formation of the interface is often accompanied by the irreversible consumption of sodium ions, especially for the interface between the negative electrode and the electrolyte. Therefore, compared with the sodium-ion half-cell, this consumption is particularly evident in the sodium-ion full battery, because the SEI film formed during the first charge and discharge will consume sodium ions, and this part of the consumption is irreversible. Therefore, the key to restricting the battery cycle stability and energy density in the full battery is to suppress or reduce the irreversible consumption of limited sodium ions. In response to the above problems, researchers have found that introducing sodium-supplementing additives in the positive electrode can provide effective compensation for the above-mentioned irreversible consumption.

[0004] Patent CN108878780A is to melt solid sodium metal and then add liquid sodium metal uniformly to the surface of the negative electrode sheet, so that the sodium metal penetrates into the gap between the negative electrode materials, and the sodium ion battery is supplemented with sodium. However, this melting method is uneven in the penetration of electrode materials, the consistency is poor, the performance of the battery fluctuates greatly, and it is not suitable for industrial production. The negative electrode sodium supplementation of CN1068848388A is to spray or drip an organic sodium solution on the surface of the negative electrode sheet under an inert atmosphere and dry the negative electrode sheet. This method directly uses sodium, which has extremely high requirements for personnel operation and environment, otherwise there are great safety hazards. The current frequent chemical safety accidents have extremely strict restrictions on this flammable and explosive material. Therefore, the above two direct sodium supplementation methods using sodium metal do not have industrial practical value. At present, the positive electrode sodium supplementation additives are more studied and are mainly inorganic compounds, such as sodium nickelate (NaNiO2), sodium chromate (NaCrO2) and sodium carbonate (Na2CO3). However, from a practical point of view, they all have more or less shortcomings. For example, NaNiO2 and NaCrO2 leave residues after formation, which is not conducive to capacity calculation, and sodium salts containing heavy metals also have potential environmental problems such as toxicity; Na2CO3 will release oxygen and affect battery performance. Summary of the invention

[0005] The purpose of the present application is to provide a sodium supplement additive and a preparation method thereof, a positive electrode sheet and a preparation method thereof, and a sodium ion battery. By using a NaF / PAN composite material as a sodium supplement additive in the positive electrode of a sodium ion battery, PAN is used as a conductive skeleton to load the NaF material to improve the utilization rate of NaF. Compared with ordinary sodium supplement additives, this NaF / PAN composite material greatly improves the activity and utilization rate of the sodium supplement additive. PAN as a conductive skeleton is more efficient and uniform than sodium supplement additives with ordinary conductive agents. NaF can participate in the formation of SEI film, which helps to form a high-conductivity, dense SEI film, high safety, low cost, and can significantly improve the capacity and coulomb efficiency of sodium ion batteries.

[0006] To achieve the above objectives, the technical solution of this application is as follows:

[0007] In a first aspect, the present application provides a sodium supplement additive, including a sodium fluoride / polyacrylonitrile (NaF / PAN) composite material;

[0008] Preferably, the mass of PAN accounts for 0.1%-50% of the mass of the sodium fluoride / polyacrylonitrile composite material, preferably 5%-35%.

[0009] In a second aspect, the present application provides a method for preparing the sodium supplement additive described in the first aspect, comprising the following steps: mixing PAN and NaF materials in proportion and subjecting them to heat treatment.

[0010] Preferably, the mixing method includes spray drying, calcination, and hydrothermal method.

[0011] Preferably, the inlet air temperature of the spray drying method is 250-400°C, and the atomizer speed is 30-50Hz.

[0012] Preferably, the sintering temperature of the calcination method is 300-400° C., and the sintering time is 1-10 h.

[0013] Preferably, the hydrothermal temperature of the hydrothermal method is 300-400° C., and the hydrothermal time is 1-10 h.

[0014] In a third aspect, the present application also provides a positive electrode plate, comprising the sodium supplement additive described in the first aspect.

[0015] Preferably, the amount of the sodium supplement additive added is 0.1%-30% of the mass of the positive electrode active material, preferably 1%-10%.

[0016] In a fourth aspect, the present application provides a method for preparing the positive electrode sheet according to the third aspect, comprising:

[0017] The sodium supplement additive, the positive electrode active material, the conductive agent and the binder are mixed to obtain a positive electrode slurry;

[0018] The positive electrode slurry is coated on a positive electrode current collector to obtain the positive electrode sheet.

[0019] Preferably, the preparation method satisfies at least one of the following conditions:

[0020] a. The positive electrode active material comprises at least one of a layered oxide positive electrode material, a polyanion positive electrode material and a Prussian blue positive electrode material;

[0021] b. The conductive agent includes at least one of conductive carbon black, conductive graphite and graphene;

[0022] c. The binder includes one or more of PVDF, LA132, LA133, CMC, and SBR;

[0023] d. The mass ratio of the positive electrode active material, the sodium supplement additive, the conductive agent and the binder is 100:0.1-30:0.1-20:0.1-20, preferably 100:1-10:0.5-2:1-5.

[0024] Preferably, the coating has a thickness of 10 μm-500 μm, preferably 100 μm-300 μm.

[0025] In a fifth aspect, the present application also provides a sodium ion battery, comprising the positive electrode plate of the third aspect above.

[0026] The beneficial effects of this application are:

[0027] By using sodium fluoride / polyacrylonitrile (NaF / PAN) composite material as the sodium supplement additive in the positive electrode of sodium ion battery, PAN is used as the conductive skeleton to load NaF material to improve the utilization rate of NaF. Compared with ordinary sodium supplement additives, this NaF / PAN composite material greatly improves the activity and utilization rate of sodium supplement additives. NaF can participate in the formation of SEI film, which helps to form a high conductivity and dense SEI film. It has high safety, low cost, and can significantly improve the capacity and coulomb efficiency of sodium ion batteries.

[0028] By using the above-mentioned sodium supplement additive in the positive electrode plate of the present application, the amount of conductive agent used in the slurry preparation process of the positive electrode plate is reduced, the conductivity of the sodium battery positive electrode material, especially the NFPP positive electrode material, is improved, and the formation of SEI film of NaF during the first charge and discharge process of the battery is efficiently promoted, thereby improving the cycle performance and safety performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments will be briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope of the present invention.

[0030] Figure 1 The figure is a comparison chart of the battery cycle performance of the embodiment of the present invention and the comparative example. DETAILED DESCRIPTION

[0031] The embodiments of the present application will be described in detail below in conjunction with specific examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. In the examples, if specific conditions are not specified, they are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0032] Electrochemical test methods

[0033] Capacity test: The button half-cell was placed in a thermostat for testing at a temperature of 25±1°C. A new battery tester was used, the process step was set to "constant current and constant voltage charging", the voltage was set to 4V, first charged to 4.0V at a rate of 0.2C, then the constant voltage charging current was reduced to 0.02C, the initial charging capacity C1 of the sodium ion battery was tested, and then the constant current was discharged to 2.0V at a current of 0.2C, the initial discharge capacity C2 of the sodium ion battery was tested, and the first efficiency (Eff.) was calculated as: Eff. = C2 / C1*100%. The capacity retention rate of the 30th cycle is the discharge capacity C3 after 30 cycles of charge and discharge, 30th = C3 / C1*100%.

[0034] Rate performance (rate discharge): Discharge the fully charged battery at 0.2C and 2.0C to the cut-off voltage, and calculate the capacity retention rate, which is the value of 2C / 0.2C.

[0035] Example 1

[0036] This embodiment provides a NaF / PAN composite material as a sodium supplement additive, and the NaF / PAN composite material is prepared by sintering NaF and PAN at 350° C. for 5 hours through a calcination method, wherein the mass of PAN accounts for 20% of the total mass of the sodium supplement additive.

[0037] The present embodiment provides a positive electrode plate, including the sodium supplement additive NaF / PAN composite material in the present embodiment. The specific preparation method includes: at room temperature, 91% NFPP positive electrode material, 5% NaF / PAN composite material, 1% SuperP conductive agent, and 3% PVDF binder are made into a uniformly mixed positive electrode slurry, and then the positive electrode slurry is coated on aluminum foil with a coating thickness of 150um to obtain a positive electrode plate.

[0038] This embodiment provides a sodium ion battery, including the positive electrode sheet of this embodiment, and the electrochemical performance of the battery is tested.

[0039] Example 2

[0040] This embodiment provides a NaF / PAN composite material as a sodium supplement additive, and the NaF / PAN composite material is prepared by sintering NaF and PAN at 350° C. for 5 hours through a calcination method, wherein the mass of PAN accounts for 20% of the total mass of the sodium supplement additive.

[0041] The present embodiment provides a positive electrode plate, including the sodium supplement additive NaF / PAN composite material in the present embodiment. The specific preparation method includes: at room temperature, 91% NFPP positive electrode material, 1% NaF / PAN composite material, 1% SuperP conductive agent, and 3% PVDF binder are made into a uniformly mixed positive electrode slurry, and then the positive electrode slurry is coated on aluminum foil with a coating thickness of 150um to obtain a positive electrode plate.

[0042] This embodiment provides a sodium ion battery, including the positive electrode sheet of this embodiment, and the electrochemical performance of the battery is tested.

[0043] Example 3

[0044] This embodiment provides a NaF / PAN composite material as a sodium supplement additive, and the NaF / PAN composite material is prepared by sintering NaF and PAN at 350° C. for 5 hours through a calcination method, wherein the mass of PAN accounts for 20% of the total mass of the sodium supplement additive.

[0045] The present embodiment provides a positive electrode plate, including the sodium supplement additive NaF / PAN composite material in the present embodiment. The specific preparation method includes: at room temperature, 91% NFPP positive electrode material, 10% NaF / PAN composite material, 1% SuperP conductive agent, and 3% PVDF binder are made into a uniformly mixed positive electrode slurry, and then the positive electrode slurry is coated on aluminum foil with a coating thickness of 150um to obtain a positive electrode plate.

[0046] This embodiment provides a sodium ion battery, including the positive electrode sheet of this embodiment, and the electrochemical performance of the battery is tested.

[0047] Example 4

[0048] This embodiment provides a NaF / PAN composite material as a sodium supplement additive, and the NaF / PAN composite material is prepared by sintering NaF and PAN at 350° C. for 5 hours through a calcination method, wherein the mass of PAN accounts for 35% of the total mass of the sodium supplement additive.

[0049] The present embodiment provides a positive electrode plate, including the sodium supplement additive NaF / PAN composite material in the present embodiment. The specific preparation method includes: at room temperature, 91% NFPP positive electrode material, 5% NaF / PAN composite material, 1% SuperP conductive agent, and 3% PVDF binder are made into a uniformly mixed positive electrode slurry, and then the positive electrode slurry is coated on aluminum foil with a coating thickness of 150um to obtain a positive electrode plate.

[0050] This embodiment provides a sodium ion battery, including the positive electrode sheet of this embodiment, and the electrochemical performance of the battery is tested.

[0051] Example 5

[0052] This embodiment provides a NaF / PAN composite material as a sodium supplement additive, and the NaF / PAN composite material is prepared by sintering NaF and PAN at 350° C. for 5 hours through a calcination method, wherein the mass of PAN accounts for 5% of the total mass of the sodium supplement additive.

[0053] The present embodiment provides a positive electrode plate, including the sodium supplement additive NaF / PAN composite material in the present embodiment. The specific preparation method includes: at room temperature, 91% NFPP positive electrode material, 5% NaF / PAN composite material, 1% SuperP conductive agent, and 3% PVDF binder are made into a uniformly mixed positive electrode slurry, and then the positive electrode slurry is coated on aluminum foil with a coating thickness of 150um to obtain a positive electrode plate.

[0054] This embodiment provides a sodium ion battery, including the positive electrode sheet of this embodiment, and the electrochemical performance of the battery is tested.

[0055] Comparative Example 1

[0056] This comparative example provides a positive electrode plate, which does not contain a sodium supplement additive. The specific preparation method includes: at room temperature, 91% of NFPP positive electrode material, 1% of Super P conductive agent, and 3% of PVDF binder are prepared by high-energy ball milling to form a uniformly mixed positive electrode slurry, and then the positive electrode slurry is coated on an aluminum foil with a coating thickness of 150um to obtain a positive electrode plate.

[0057] This comparative example provides a sodium ion battery, including the positive electrode sheet of this comparative example, and tests the electrochemical performance of the battery.

[0058] Comparative Example 2

[0059] This comparative example provides a positive electrode sheet, in which NaF is added as a sodium supplement additive. The specific preparation method includes: at room temperature, 91% of NFPP positive electrode material, 5% of NaF sodium supplement additive, 1% of Super P conductive agent, and 3% of PVDF binder are mixed to form a uniformly mixed positive electrode slurry, and then the positive electrode slurry is coated on aluminum foil with a coating thickness of 150um to obtain a positive electrode sheet.

[0060] This comparative example provides a sodium ion battery, including the positive electrode sheet of this comparative example, and tests the electrochemical performance of the battery.

[0061] Comparative Example 3

[0062] This comparative example provides a positive electrode sheet, in which PAN is added as a sodium supplement additive. The specific preparation method includes: at room temperature, 91% of NFPP positive electrode material, 5% of PAN sodium supplement additive, 1% of Super P conductive agent, and 3% of PVDF binder are made into a uniformly mixed positive electrode slurry, and then the positive electrode slurry is coated on aluminum foil with a coating thickness of 150um to obtain a positive electrode sheet.

[0063] This comparative example provides a sodium ion battery, including the positive electrode sheet of this comparative example, and tests the electrochemical performance of the battery.

[0064] Table 1: 0.2C discharge capacity, first efficiency (2.0-4.0V), 2C capacity and 30th cycle capacity retention rate of Examples 1-5 and Comparative Examples 1-3

[0065] 0.2C First effect 2C / 0.2C 30th% Example 1 113.4 94.70％ 88.20％ 96.30％ Example 2 109.8 91.60％ 84.70％ 93.20％ Example 3 112.9 94.50％ 87.90％ 96.70％ Example 4 111.7 93.10％ 86.40％ 94.30％ Example 5 109.2 92.90％ 82.50％ 92.80％ Comparative Example 1 107.9 90.60％ 80.60％ 88.50％ Comparative Example 2 108.4 92.10％ 81.90％ 91.30％ Comparative Example 3 108.1 90.90％ 82.30％ 90.40％

[0066] Comparative Example 1 does not add sodium supplement additives, Comparative Example 2 only adds NaF as a sodium supplement additive, and Comparative Example 3 only adds PAN to replace the sodium supplement additive; By comparing Example 1 with Comparative Examples 1, 2, and 3, it can be seen that the NaF / PAN sodium supplement additive can significantly improve the discharge capacity and coulomb efficiency. Thanks to the conductive skeleton structure of PAN, the rate performance has been significantly improved, and the improvement in the 30-cycle retention rate is due to PAN promoting the formation of a dense and stable SEI film. By comparing Example 1 with Comparative Examples 1 and 2, it can be seen that PAN plays a key role in the sodium supplement additive, greatly improving the activity and sodium supplement effect of NaF. By comparing Examples 1, 2, 3, 4, and 5, it can be seen that the amount of NaF / PAN sodium supplement additive and the proportion of PAN will also significantly affect the electrochemical performance. When the amount of NaF / PAN sodium supplement additive is 5% and PAN accounts for 20%, the effect is best.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

[0068] In addition, those skilled in the art will appreciate that, although some embodiments herein include certain features included in other embodiments but not other features, the combination of features of different embodiments is meant to be within the scope of the present invention and to form different embodiments. For example, in the above claims, any one of the claimed embodiments may be used in any combination. The information disclosed in this background technology section is intended only to deepen the understanding of the overall background technology of the present invention and should not be regarded as an admission or in any form of implication that the information constitutes prior art known to those skilled in the art.

Claims

1. A sodium supplement additive, comprising a sodium fluoride / polyacrylonitrile (NaF / PAN) composite material; the mass of the PAN accounts for 0.1%-50% of the mass of the sodium fluoride / polyacrylonitrile composite material, preferably 5%-35%.

2. The preparation method of the sodium supplement additive according to claim 1, characterized in that, The method comprises the following steps: performing mixed heat treatment on PAN and NaF materials in proportion, wherein the mixed heat treatment method comprises spray drying method, calcination method and hydrothermal method.

3. The preparation method of the sodium supplement additive as claimed in claim 2, characterized in that, The spray drying method has an air inlet temperature of 250-400°C and an atomizer speed of 30-50Hz; and / or the calcination method has a sintering temperature of 300-400°C and a sintering time of 1-10h; and / or the hydrothermal method has a hydrothermal temperature of 300-400°C and a hydrothermal time of 1-10h.

4. A positive electrode sheet, characterized in that: The invention comprises the sodium supplement additive according to claim 1 or the sodium supplement additive prepared by the preparation method according to claim 2 or 3.

5. The positive electrode sheet according to claim 4, characterized in that: The amount of the sodium supplement additive added is 0.1%-30% of the mass of the positive electrode active material, preferably 1%-10%.

6. The method for preparing a positive electrode sheet according to claim 4 or 5, characterized in that: include: The sodium supplement additive, the positive electrode active material, the conductive agent and the binder are mixed to obtain a positive electrode slurry; The positive electrode slurry is coated on a positive electrode current collector to obtain the positive electrode sheet.

7. The preparation method according to claim 6, characterized in that: The positive electrode active material includes at least one of a layered oxide type positive electrode material, a polyanion type positive electrode material and a Prussian blue type positive electrode material; and / or the conductive agent includes at least one of conductive carbon black, conductive graphite and graphene.

8. The preparation method according to claim 6 or 7, characterized in that: The binder includes one or more of PVDF, LA132, LA133, CMC, and SBR; and / or the mass ratio of the positive electrode active material, the sodium supplement additive, the conductive agent, and the binder is 100:0.1-30:0.1-20:0.1-20, preferably 100:1-10:0.5-2:1-5.

9. The preparation method according to any one of claims 6 to 8, characterized in that: The coating thickness is 10 μm-500 μm, preferably 100 μm-300 μm.

10. A sodium ion battery, comprising the positive electrode sheet according to claim 4 or 5 or the positive electrode sheet prepared by the preparation method according to any one of claims 6 to 9.

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