Positive pole piece of sodium ion battery, preparation method of positive pole piece and battery

Abstract

The invention relates to a sodium-ion battery positive pole piece, a preparation method thereof and a battery, belongs to the technical field of sodium-ion batteries, and aims to solve the problems that the existing layered oxide is easy to crack due to stress release in the charge-discharge process, so that side reaction of electrolyte is caused, the pole piece is expanded, the internal resistance of a battery cell is increased, and the service life of the battery cell is prolonged. And the cycle life of the battery cell is shortened. The steric hindrance agent is added into the sodium ion battery positive pole piece, the steric hindrance agent can relieve stress release of the layered oxide in the charging and discharging process, the cracking problem of the layered oxide is effectively inhibited, then expansion of the pole piece in the circulating process can be reduced, side reaction of the layered oxide and electrolyte is reduced, and the service life of the sodium ion battery positive pole piece is prolonged. Therefore, the cycle life of the battery cell is prolonged. In addition, the steric hindrance agent can also reduce the resistance of the pole piece diaphragm, thereby reducing the internal resistance of the battery cell and prolonging the cycle life of the battery cell.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a sodium-ion battery positive electrode sheet, its preparation method, and the battery itself. Background Technology

[0002] Sodium-ion batteries offer advantages such as abundant sodium resources, low cost, and high safety performance. Currently, they show great potential in the market for replacing lead-acid batteries and complementing lithium-ion batteries. As a major component of sodium-ion batteries, the positive electrode plays a crucial role in cell performance.

[0003] Currently, the mainstream sodium-ion battery cathodes on the market mainly include two categories: layered oxides and polyanionic oxides. Layered oxides occupy a considerable market share due to their advantages such as high capacity, high average voltage, and ease of synthesis. However, layered oxides also suffer from particle cracking and expansion caused by frequent phase transitions during charging and discharging, which leads to severe electrolyte side reactions and electrode expansion, increasing the internal resistance of the cell and ultimately causing a sharp decline in the cell's cycle life. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a sodium-ion battery positive electrode sheet, its preparation method, and the battery itself, in order to solve at least one of the following problems: existing layered oxides are prone to cracking due to stress release during charging and discharging, causing side reactions in the electrolyte, and electrode sheet expansion, which increases the internal resistance of the cell and reduces the cycle life of the cell.

[0005] In a first aspect, the present invention provides a positive electrode sheet for a sodium-ion battery, the positive electrode sheet comprising the following raw materials: layered oxide, steric hindrance agent, conductive agent, binder and inhibitor;

[0006] The steric hindrance agent includes at least one of 3-propanolamine, 2-amino-2-methyl-1,3-propanediol, N,N-dimethylethanolamine, and N,N-diethylethanolamine.

[0007] Furthermore, the steric hindrance agent has a mass percentage of a% in the positive electrode sheet, and the areal density of the positive electrode sheet is b mg / cm³. 2 If the expansion rate of the positive electrode is α%, then a, b, and α satisfy the following relationship:

[0008] 0.0005≤a / b≤0.5, α≤10;

[0009] Among them, the expansion rate refers to the expansion rate of the positive electrode after the battery cell is charged at 1C constant current and constant voltage at room temperature and discharged at 1C constant current for 300 cycles.

[0010] Furthermore, a ranges from 0.1 to 5, and b ranges from 10 to 20.

[0011] Furthermore, by mass percentage, the layered oxide comprises 90–97%, the steric hindrance 0.1–5%, the conductive agent 1–6%, the binder 1–4%, and the inhibitor 0.1–0.6%.

[0012] Furthermore, the conductive agent is at least one of Super-P, CNTs, graphene, VGCF and Ketjen Black.

[0013] The adhesive is at least one of polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer, and polyimide;

[0014] The inhibitor is at least one of oxalic acid, acetic acid, and citric acid.

[0015] Secondly, the present invention provides a method for preparing the positive electrode sheet of a sodium-ion battery, comprising: homogenizing the positive electrode sheet raw material in a solvent to obtain a slurry, coating the slurry onto a current collector, drying, rolling, and cutting to obtain the positive electrode sheet.

[0016] Furthermore, the areal density of the coating is 10–20 mg / cm³. 2 .

[0017] Furthermore, the solvent is N-methylpyrrolidone.

[0018] Thirdly, the present invention provides a sodium-ion battery, including the aforementioned sodium-ion positive electrode sheet.

[0019] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0020] 1. The sodium-ion battery positive electrode of the present invention incorporates a steric retardant. This steric retardant mitigates stress release in the layered oxide during charging and discharging, effectively suppressing cracking of the layered oxide. This, in turn, reduces electrode expansion during cycling and minimizes side reactions between the layered oxide and the electrolyte, thereby improving the cycle life of the battery cell. Furthermore, the steric retardant also reduces the electrode film resistance, thereby lowering the internal resistance of the battery cell and further improving its cycle life.

[0021] 2. Since the expansion of the electrode during cycling is mainly caused by the phase transition of the positive electrode material, the uniform dispersion of steric hindrance on the surface of the material particles can effectively suppress the expansion of the electrode during subsequent cycles. The areal density of the electrode is also a factor affecting the electrode expansion rate. Since more than 90% of the electrode is composed of positive electrode active material, the higher the areal density, the greater the expansion rate during subsequent cycles. Therefore, the steric hindrance and areal density need to satisfy 0.0005 ≤ a / b ≤ 0.5.

[0022] 3. The amount of steric retardant added in this invention is 0.1-5%. The addition amount within this range is positively improved, which can reduce the electrode film resistance, suppress the expansion of the electrode during cycling, and improve the cycle performance of the battery cell. If too little is added (<0.1%), the improvement effect will not be obvious, and if too much is added (>5%), it will cause the film resistance to be too high. Because the steric retardant is an organic material that is non-conductive, it will lead to an increase in the internal resistance of the battery cell and reduce the cycle life.

[0023] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0024] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0025] Figure 1 This is a SEM image of the layered oxide formed by the electrode prepared in Example 1 after 300 battery cycles.

[0026] Figure 2 This is a SEM image of the layered oxide formed by the electrode prepared in Comparative Example 1 after 300 battery cycles. Detailed Implementation

[0027] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0028] A specific embodiment of the present invention discloses a positive electrode sheet for a sodium-ion battery, wherein the positive electrode sheet comprises the following raw materials: layered oxide, steric hindrance agent, conductive agent, binder and inhibitor;

[0029] The steric hindrance agent includes at least one of 3-propanolamine, 2-amino-2-methyl-1,3-propanediol, N,N-dimethylethanolamine, and N,N-diethylethanolamine.

[0030] Compared with existing technologies, the sodium-ion battery positive electrode of this invention incorporates a steric retardant. This steric retardant can mitigate the stress release of layered oxides during charging and discharging, effectively suppressing the cracking problem of layered oxides. This, in turn, reduces electrode expansion during cycling and minimizes side reactions between layered oxides and the electrolyte, thereby improving the cycle life of the battery cell. Furthermore, the steric retardant can also reduce the electrode film resistance, thereby reducing the internal resistance of the battery cell and improving its cycle life.

[0031] Specifically, the steric hindrance agent has a mass percentage of a% in the positive electrode sheet, and the areal density of the positive electrode sheet is b mg / cm³. 2 If the expansion rate of the positive electrode is α%, then a, b, and α satisfy the following relationship:

[0032] 0.0005≤a / b≤0.5, α≤10; a / b is for example 0.0005, 0.01, 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, and α is for example 10, 9.5, 9, 8.5, 8, 7.5, 7, 6.5, 6, 5.5, 5, 4.5, 4, 3.5, 3, 2.5, 2, 1.5, 1, 0.5, 0.

[0033] Among them, the expansion rate refers to the expansion rate of the positive electrode after the battery cell is charged at 1C constant current and constant voltage at room temperature and discharged at 1C constant current for 300 cycles.

[0034] It should be noted that the expansion rate is calculated as follows in this invention: (electrode thickness after 300 cycles - electrode thickness during assembly) / electrode thickness during assembly. The assembly thickness is the electrode thickness measured during the winding / stacking process of the battery cell.

[0035] Since the expansion of the electrode during cycling is mainly caused by the phase transition of the positive electrode material, the uniform dispersion of steric hindrance on the surface of the material particles can effectively suppress the expansion of the electrode during subsequent cycling. The areal density of the electrode is also a factor affecting the electrode expansion rate. Because more than 90% of the electrode is composed of positive electrode active material, the higher the areal density, the greater the expansion rate during subsequent cycling. Therefore, the steric hindrance and areal density need to satisfy 0.0005 ≤ a / b ≤ 0.5.

[0036] Specifically, a ranges from 0.1 to 5, for example, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5; b ranges from 10 to 20, for example, 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.

[0037] It should be noted that the proportion of steric retardant is 0.1% to 5%. Adding an amount within this range has a positive effect, which can reduce the resistance of the electrode film, suppress the expansion of the electrode during cycling, and improve the cycle performance of the cell. If too little is added (<0.1%), the improvement effect will not be obvious, and if too much is added (>5%), it will cause the film resistance to be too high. This is because the steric retardant is an organic material that is non-conductive, which will lead to an increase in the internal resistance of the cell and reduce the cycle life.

[0038] Specifically, by mass percentage, the layered oxide is 90-97% (e.g., 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%), the steric hindrance is 0.1-5% (e.g., 0.1%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%), the conductive agent is 1-6% (e.g., 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%), the binder is 1-4% (1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%), and the inhibitor is 0.1-0.6% (e.g., 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%).

[0039] It should be noted that the layered oxides of the present invention are all commercially available or prepared using existing methods. For example, the general formula of the layered oxides is NaT. x O2, wherein T is at least one of Ni, Fe, Mn, Cu, Ti, and V, and 0.5 ≤ x ≤ 1, for example, 0.5, 0.6, 0.7, 0.8, 0.9, and 1. Specifically, the conductive agent is at least one of Super-P (conductive carbon black), CNTs (carbon nanotubes), graphene, VGCF (vapor-grown carbon fiber), and Ketjen black;

[0040] The adhesive is at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), and polyimide (PI);

[0041] The inhibitor is at least one of oxalic acid, acetic acid, and citric acid.

[0042] Secondly, the present invention provides a method for preparing the above-mentioned sodium-ion battery positive electrode sheet, comprising: homogenizing the positive electrode sheet raw material in a solvent to obtain a slurry, coating the slurry onto a current collector, drying, rolling, and cutting to obtain the positive electrode sheet.

[0043] Specifically, the surface density of the coating is 10–20 mg / cm³. 2 For example, 10 mg / cm 211mg / cm 2 12mg / cm 2 13mg / cm 2 14mg / cm 2 15mg / cm 2 16mg / cm 2 17mg / cm 2 18mg / cm 2 19mg / cm 2 20mg / cm 2 .

[0044] It should be noted that electrode areal density is a factor affecting electrode expansion rate. Since over 90% of the electrode is composed of positive electrode active material, a higher areal density results in a greater expansion rate during subsequent cycling. Therefore, in this invention, the coating areal density is controlled to be 10–20 mg / cm³. 2 .

[0045] Specifically, the solvent is N-methylpyrrolidone.

[0046] Specifically, the mass fraction of the positive electrode raw material in the solvent is 55-75%.

[0047] Thirdly, the present invention provides a sodium-ion battery, including the sodium-ion positive electrode sheet described above.

[0048] The present invention employs the following embodiments to further explain and illustrate the technical solution of the present invention.

[0049] The layered oxides described in this invention are commercially available products or prepared using existing methods. In the following examples, the layered oxides are all existing products, and in this invention, the general formula is NaNi. 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 is used for explanation, but the scope of protection of this invention is not limited to layered oxides of this general formula, but may also include layered oxides of other general formulas.

[0050] Example 1

[0051] According to the embodiment of the positive electrode sheet of a sodium-ion battery, the electrode sheet comprises the following raw materials by mass percentage: layered oxide: 93.1%, steric hindrance agent: 3%, conductive agent: 2%, binder: 1.5% and inhibitor: 0.4%;

[0052] The steric hindrance agent is 3-propanolamine, the conductive agent is Super-P, the binder is PVDF, and the inhibitor is oxalic acid.

[0053] The preparation method of the positive electrode sheet in this embodiment is as follows: The raw materials are homogenized in the solvent N-methylpyrrolidone to obtain a slurry, wherein the mass fraction of the positive electrode sheet raw material in the solvent is 65%; the slurry is then prepared according to a single-sided surface density of 15 mg / cm³. 2 The coating is applied to aluminum foil, dried, rolled, slit, and cut to obtain the positive electrode sheet.

[0054] Example 2

[0055] The raw materials and preparation method of the positive electrode sheet in this embodiment are similar to those in Example 1, except that the amount of steric hindrance added to the raw materials is 0.1% and the amount of layered oxide added is 96%.

[0056] Example 3

[0057] The raw materials and preparation method of the positive electrode sheet in this embodiment are similar to those in Example 1, except that the amount of steric hindrance added to the raw materials is 5%, and the amount of layered oxide added is 91.1%.

[0058] Example 4

[0059] The raw materials and preparation method of the positive electrode sheet in this embodiment are similar to those in Example 1, except that the surface density of the slurry coating on one side is 10 mg / cm² in the preparation method. 2 .

[0060] Example 5

[0061] The raw materials and preparation method of the positive electrode sheet in this embodiment are similar to those in Example 1, except that the surface density of the slurry coating on one side is 20 mg / cm² in the preparation method. 2 .

[0062] Example 6

[0063] The raw materials and preparation method of the positive electrode in this embodiment are similar to those in Example 1, except that the steric hindrance is 2-amino-2-methyl-1,3-propanediol.

[0064] Example 7

[0065] The raw materials and preparation method of the positive electrode sheet in this embodiment are similar to those in Example 1, except that the steric hindrance agent in the raw materials is N,N-dimethylethanolamine.

[0066] Example 8

[0067] The raw materials and preparation method of the positive electrode sheet in this embodiment are similar to those in Example 1, except that the steric hindrance agent in the raw materials is N,N-diethylethanolamine.

[0068] Example 9

[0069] According to the embodiment of the positive electrode sheet of a sodium-ion battery, the electrode sheet comprises the following raw materials by mass percentage: layered oxide: 90%, steric hindrance agent: 2.9%, conductive agent: 4%, binder: 2.5%, and inhibitor: 0.6%.

[0070] The steric hindrance is 3-propanolamine, the conductive agent is graphene, the binder is PVDF, and the inhibitor is acetic acid.

[0071] The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1.

[0072] Example 10

[0073] According to the embodiment of the positive electrode sheet of a sodium-ion battery, the electrode sheet comprises the following raw materials by mass percentage: layered oxide: 90%, steric hindrance agent: 2.9%, conductive agent: 6%, binder: 1%, and inhibitor: 0.1%.

[0074] The steric hindrance is 3-propanolamine, the conductive agent is CNTs, the binder is PVDF, and the inhibitor is citric acid.

[0075] The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1.

[0076] Comparative Example 1

[0077] The raw materials and preparation method of the sodium-ion battery positive electrode sheet in this comparative example are similar to those in Example 1, except that no steric hindrance is added to the raw materials, and the amount of layered oxide added is 96.1%.

[0078] Comparative Example 2

[0079] The raw materials and preparation method of the sodium-ion battery positive electrode sheet in this comparative example are similar to those in Example 1, except that the amount of steric hindrance added to the raw materials is 8%, and the amount of layered oxide added is 88.1%.

[0080] Comparative Example 3

[0081] The raw materials and preparation method of the sodium-ion battery positive electrode sheet in this comparative example are similar to those in Example 1, except that the areal density on one side is 23 mg / cm³ in the preparation method. 2 .

[0082] Example 1: Preparation of a Sodium-ion Battery

[0083] The positive electrode sheets prepared in the examples and comparative examples were used to fabricate sodium-ion batteries. The specific preparation methods are as follows:

[0084] (1) Preparation of negative electrode sheet: Amorphous carbon negative electrode, conductive agent SP, CMC and SBR were homogenized with deionized water at a mass ratio of 94.3:1.5:1.6:2.6, with a solid content of 54% and a single-sided surface density of 8.5 mg / cm³. 2 The slurry is evenly coated onto aluminum foil and then thoroughly dried in an oven. The electrode sheet is then rolled to the desired thickness according to the designed compaction method, followed by slitting and cutting to obtain the negative electrode sheet, with a specific size of 70mm × 700mm.

[0085] (2) Cell Assembly: The negative electrode sheet obtained in step 1 and the positive electrode sheet obtained in the examples and comparative examples are welded together with tabs. Then, the positive and negative electrodes and the separator are wound into a core and then hot-pressed into an aluminum-plastic shell. After baking to remove moisture, the electrolyte is injected. The electrolyte salt is sodium hexafluorophosphate with a concentration of 1 mol / L, and the solvent is an ester solvent. After subsequent pre-charging, aging and formation, a sodium-ion battery is finally obtained.

[0086] The capacity retention and expansion rate of sodium batteries made using the positive electrode sheets of the examples and comparative examples were tested after 300 cycles, and the results are shown in Table 1.

[0087] Cell cycle system: At room temperature (25℃), charge at 1C constant current and constant voltage to 0.05C, let stand for 10 minutes, and then discharge at 1C constant current.

[0088] Capacity retention rate = discharge capacity at week 300 / discharge capacity at week 3 × 100%.

[0089] The expansion rate is the expansion rate of the positive electrode after 300 cycles of 1C constant current and constant voltage charging and 1C constant current discharging at room temperature. The calculation method is as follows: (electrode thickness after 300 cycles - electrode thickness at assembly) / electrode thickness at assembly. The assembly thickness is the electrode thickness measured during the winding / stacking process of the battery cell.

[0090] Table 1

[0091]

[0092] As shown in Table 1, the battery made using the positive electrode sheet of the present invention retains a capacity of 93.2% to 96.8% after 300 cycles.

[0093] As can be seen from Examples 1-3, as the amount of steric hindrance added increases, the expansion rate of the electrode gradually decreases and the cycle capacity retention rate increases.

[0094] As can be seen from Examples 1 and 4-5, as the surface density of a single side increases, the electrode expansion rate gradually increases, while the capacity retention rate gradually decreases.

[0095] As shown in Example 1 and Comparative Example 1, without the addition of a steric hindrance, the electrode expansion rate increases and the capacity retention rate decreases. This is because the interlayer slip cracking of the layered oxide is severe. After 300 cycles, the SEM image of the layered oxide is as follows: Figure 1 As shown, after 300 battery cycles, the SEM images of the layered oxide in Comparative Example 1 are as follows: Figure 2 As shown.

[0096] As can be seen from Example 1 and Comparative Example 2, when an excessive amount of steric hindrance is added, although the electrode expansion rate decreases, the capacity retention rate also decreases.

[0097] As can be seen from Example 1 and Comparative Example 3, if the surface density of a single side is too high, the expansion rate of the electrode is as high as 12% under the same amount of steric retardant, which is detrimental to cycling, and the capacity retention rate is only 90.6% after 300 cycles.

[0098] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode sheet for a sodium-ion battery, characterized in that, The positive electrode sheet comprises the following raw materials: layered oxide, steric hindrance agent, conductive agent, binder, and inhibitor; The steric hindrance agent includes at least one of 3-propanolamine, 2-amino-2-methyl-1,3-propanediol, N,N-dimethylethanolamine, and N,N-diethylethanolamine.

2. The sodium-ion battery positive electrode sheet according to claim 1, characterized in that, The steric hindrance has a mass percentage of a% in the positive electrode and a single-sided areal density of b mg / cm³. 2 If the expansion rate of the positive electrode is α%, then a, b, and α satisfy the following relationship: 0.0005≤a / b≤0.5, α≤10; Among them, the expansion rate refers to the expansion rate of the positive electrode after the battery cell is charged at 1C constant current and constant voltage at room temperature and discharged at 1C constant current for 300 cycles.

3. The sodium-ion battery positive electrode sheet according to claim 2, characterized in that, a is 0.1 to 5, and b is 10 to 20.

4. The sodium-ion battery positive electrode sheet according to any one of claims 1-3, characterized in that, By mass percentage, the layered oxide is 90–97%, the steric hindrance is 0.1–5%, the conductive agent is 1–6%, the binder is 1–4%, and the inhibitor is 0.1–0.6%.

5. The sodium-ion battery positive electrode sheet according to claim 4, characterized in that, The conductive agent is at least one of Super-P, CNTs, graphene, VGCF and Ketjen Black.

6. The sodium-ion battery positive electrode sheet according to claim 4, characterized in that, The adhesive is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinylidene fluoride-hexafluoropropylene copolymer and polyimide; The inhibitor is at least one of oxalic acid, acetic acid, and citric acid.

7. A method for preparing a sodium-ion battery positive electrode sheet according to any one of claims 1-6, characterized in that, include: The positive electrode material is homogenized in a solvent to obtain a slurry. The slurry is then coated onto a current collector, dried, rolled, and cut to obtain the positive electrode.

8. The preparation method according to claim 7, characterized in that, The surface density of the coating is 10–20 mg / cm³. 2 .

9. The preparation method according to claim 7, characterized in that, The solvent is N-methylpyrrolidone.

10. A sodium-ion battery, characterized in that, Includes the sodium ion positive electrode sheet as described in any one of claims 1-6.

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