A positive electrode pre-sodium composite current collector, its preparation method and application

Abstract

This invention belongs to the field of sodium-ion battery materials and discloses a positive electrode pre-sodium composite current collector, its preparation method, and its application, to achieve safe and controllable sodium replenishment. The positive electrode pre-sodium composite current collector includes a porous current collector, a positive electrode pre-sodium filling layer filling the pores of the porous current collector, and a conductive carbon layer located on the surface of the current collector. The positive electrode pre-sodium filling layer includes a positive electrode pre-sodium additive (at least one of Na2C2O4, Na2C6O6, Na4C6O6, NaN3, Na2S, Na2CO3, and Na3P). This pre-sodium additive is an organic or inorganic sodium salt with a high dissociation potential and gas production upon high-temperature heating. When applied to sodium-ion batteries, it allows for real-time and controllable sodium replenishment according to actual needs, improving the battery's initial efficiency and energy density, while also enhancing the battery's cycle life and safety performance.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery materials, and more particularly to a positive electrode pre-sodium composite current collector. Background Technology

[0002] Low-cost, long-life, highly safe, and controllable large-scale energy storage systems are essential for achieving sustainable development in modern society and meeting the requirements for carbon peaking and carbon neutrality. With the rapid development of large-scale electrochemical energy storage systems, global demand for lithium resources has increased, leading to a supply shortage. Therefore, finding a new type of battery to replace lithium-ion batteries is of profound significance. Sodium-ion batteries, with similar mechanisms, identical equipment, and compatible production lines to lithium-ion batteries, are considered potentially commercially viable rechargeable batteries. However, many problems remain in practical applications, such as low initial charge / discharge efficiency, short cycle life, and low energy density. These can be addressed by supplementing sodium at the positive or negative electrode to improve electrical performance. Traditional sodium supplementation methods are similar to lithium supplementation methods, including electrochemical sodium supplementation, chemical sodium supplementation, and sodium supplementation with additives. Electrochemical methods involve pre-treating the electrodes to add sodium before reassembling them into batteries. This method is complex, increases production steps and costs, and is rarely used in commercial technologies. Chemical sodium addition, such as in application CN 115050968 A, involves bonding active sodium powder or sodium foil to the negative electrode. This method has stringent environmental requirements, poses safety hazards, and the amount of sodium added and the reaction process are difficult to control. Additive sodium addition involves adding a sodium-adding agent to the positive electrode side. A common example is patent application CN118039844 A, which directly adds a pre-sodium additive to the positive electrode slurry. Since pre-sodium additives are mostly non-conductive materials, their presence in the slurry will undoubtedly increase the electrode layer impedance, reduce the proportion of active material, and make the reaction uncontrollable. Therefore, a better pre-sodium method is urgently needed to overcome the current technological bottlenecks. Summary of the Invention

[0003] To address the aforementioned technical problems and achieve safe and controllable sodium supplementation, this invention proposes a positive electrode pre-sodium composite current collector, its preparation method, and its application.

[0004] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0005] A positive electrode pre-sodium composite current collector includes a porous current collector, a positive electrode pre-sodium filling layer filled in the pores of the porous current collector, and a conductive carbon layer located on the surface of the current collector; wherein the positive electrode pre-sodium filling layer includes a positive electrode pre-sodium additive; the positive electrode pre-sodium additive is at least one of Na2C2O4, Na2C6O6, Na4C6O6, NaN3, Na2S, Na2CO3 and Na3P.

[0006] This invention fills a porous current collector with a positive electrode pre-sodium additive (at least one of Na2C2O4, Na2C6O6, Na4C6O6, NaN3, Na2S, Na2CO3, and Na3P) that has a dissociation potential higher than 3.65V and produces gas upon heating. After drying and rolling, a conductive carbon layer is then coated on the surface to prepare a highly safe and controllable positive electrode pre-sodium composite current collector. When applied to sodium-ion batteries, on the one hand, according to actual needs, by intermittently increasing the charging cutoff potential in real time, the filling layer releases sodium ions to replenish the irreversible sodium source loss in the battery, meeting the sodium replenishment needs throughout the battery's entire life cycle, significantly improving the battery's initial efficiency and energy density, while also extending the battery's cycle life. On the other hand, before a safety hazard occurs in the battery, the pre-sodium additive produces gas upon heating, causing the current collector and the material layer to separate, promptly preventing failure and deterioration, and improving the battery's safety performance. In addition, the conductive carbon layer acts as a buffer and reduces interfacial tension, which is beneficial for the subsequent coating of positive electrode active materials on the composite current collector.

[0007] The aforementioned positive electrode pre-sodium filling layer also includes a binder, conductive carbon, and additives; the conductive carbon layer includes conductive carbon and a binder.

[0008] Furthermore, the aforementioned positive electrode pre-sodium filler layer comprises 70wt%-96wt% of positive electrode pre-sodium additives, 1wt%-10wt% of binder, 2wt%-10wt% of conductive carbon, and 1wt%-10wt% of auxiliary agents; the conductive carbon layer comprises 90wt%-98wt% of conductive carbon and 2wt%-10wt% of binder.

[0009] The binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylamide, and hydroxyethyl cellulose; the conductive carbon is at least one of carbon black, conductive graphite, carbon nanotubes, graphene, and acetylene black.

[0010] The above-mentioned additives are at least one of polyvinylpyrrolidone, dipropylene glycol, polyethylene glycol, triglycerides, and decaglycerides.

[0011] The aforementioned porous current collector is made of aluminum foil or PET aluminum foil, with a thickness of 5-50 μm and a pore size of 1-100 μm; the thickness of the conductive carbon layer is 0.05 μm-20 μm.

[0012] A method for preparing a positive electrode pre-sodium composite current collector, comprising the following steps:

[0013] (1) Add the adhesive to the solvent and stir to prepare an adhesive solution;

[0014] (2) After dry mixing the positive electrode pre-sodium additive and conductive carbon, add the adhesive and additives prepared in step (1) and stir to obtain slurry I; fill the slurry into the pores of the porous current collector, bake and roll to obtain a porous current collector containing a positive electrode pre-sodium filling layer.

[0015] (3) Add conductive carbon to the adhesive solution obtained in step (1), stir evenly to obtain slurry II, and apply it to the porous current collector obtained in step (2) by scraping or spraying to obtain the positive electrode pre-sodium composite current collector.

[0016] Furthermore, the solvent is at least one of N-methylpyrrolidone, tetramethylurea, trimethyl phosphate, and dimethyl sulfoxide; the thickness of the positive electrode pre-sodium filling layer is not greater than the thickness of the porous current collector.

[0017] Furthermore, the viscosity of slurry I is 1000-9000 mPa·s; the viscosity of slurry II is 4000-20000 mPa·s.

[0018] Specifically, the preparation method of the above-mentioned positive electrode pre-sodium composite current collector includes the following steps:

[0019] 1. The positive electrode pre-sodium filling layer is filled in the porous current collector.

[0020] S1. At room temperature (25℃), add the adhesive to the solvent and stir for 6-12 hours to prepare a transparent adhesive solution with a solid content between 1% and 10%. Remove and set aside for later use.

[0021] S2. Dry mix the positive electrode pre-sodium additive and conductive carbon in a certain proportion for 0.5h-3h, and use a homogenizer to rotate at 20-40 rpm and 500-2000 rpm to ensure uniform mixing.

[0022] S3. Add the prepared adhesive and additives in sequence, maintain the revolution speed of 30-50 rpm and the rotation speed of 3000-5000 rpm, and stir for 3-6 hours;

[0023] S4. Adjust the slurry viscosity to 1000-9000 mPa·s and uniformly fill it into the pores of the porous current collector.

[0024] 2. Preparation of porous current collectors containing a positive electrode pre-sodium filling layer

[0025] The positive electrode sodium supplement additive is filled into the porous current collector, and then dried and rolled. The drying temperature is 25℃-60℃.

[0026] 3. Preparation of conductive carbon layer

[0027] S1. At room temperature (25°C), add the adhesive to the solvent and stir for 6-12 hours to prepare a transparent adhesive solution.

[0028] S2. Add conductive carbon in multiple steps, maintaining a revolution speed of 40-70 rpm and a rotation speed of 4000-8000 rpm, and stir for 6-10 hours;

[0029] S3. Adjust the slurry viscosity to 4000-20000 mPa·s, and apply it to the current collector by scraping or spraying.

[0030] A sodium-ion battery includes the aforementioned positive electrode pre-sodium composite current collector.

[0031] The beneficial effects of this invention are:

[0032] (1) The present invention provides a positive electrode pre-sodium composite current collector. The pre-sodium agent is filled into the porous current collector, which is different from the traditional method of directly mixing it into the active material slurry. This pre-sodium method is different from the traditional method. It will not increase the electrode impedance or reduce the proportion of active material. It is simple to operate, environmentally friendly, controllable in real time, and easy to engineer.

[0033] (2) In this invention, organic or inorganic sodium salts (at least one of Na2C2O4, Na2C6O6, Na4C6O6, NaN3, Na2S, Na2CO3 and Na3P) with a dissociation potential higher than 3.65V are preferred as positive electrode pre-sodium additives. They do not dissociate under normal battery operating voltage. According to actual needs, the charging cut-off voltage can be increased intermittently, the charging current and charging time can be controlled to release sodium ions, replenish the irreversibly lost sodium source, and realize controllable sodium replenishment throughout the entire life cycle.

[0034] (3) The positive electrode pre-sodium additive of the present invention will generate gas when heated at high temperature, which will force the current collector and the coating layer to separate, thus forming an open circuit in time, slowing down or avoiding failure deterioration, and improving battery safety performance.

[0035] (4) The present invention fills the positive electrode pre-sodium additive into the porous current collector, which can improve the first charge and discharge efficiency, energy density and cycle life of the battery.

[0036] (5) The conductive carbon layer in this invention has good sodium ion / electron channels, dynamics and structural stability, plays a buffer role between the filling layer and the subsequent active material layer, and improves the current collector interface after filling, which facilitates the coating of the subsequent active material. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 SEM image of the positive electrode pre-sodium composite current collector prepared in Example 1 of this invention.

[0039] Figure 2The charging curve of the sodium-ion battery prepared using the positive electrode pre-sodium composite current collector of Example 1 is shown to be charged to 4.2V.

[0040] Figure 3 The normal discharge curve of the sodium-ion battery prepared using the positive electrode pre-sodium composite current collector of Example 1 is shown.

[0041] Figure 4 The normal discharge curve of the sodium-ion battery prepared using the positive electrode pre-sodium composite current collector of Example 2 is shown.

[0042] Figure 5 The normal discharge curve of the sodium-ion battery prepared using the positive electrode pre-sodium composite current collector of Example 3 is shown.

[0043] Figure 6 The normal discharge curve of the sodium-ion battery prepared using the positive electrode pre-sodium composite current collector of Example 4 is shown.

[0044] Figure 7 The normal discharge curve of the sodium-ion battery prepared using the positive electrode pre-sodium composite current collector of Example 5 is shown.

[0045] Figure 8 The normal discharge curve of the sodium-ion battery prepared using the positive electrode pre-sodium composite current collector of Example 6 is shown.

[0046] Figure 9 The normal discharge curve of the sodium-ion battery prepared using the positive electrode pre-sodium composite current collector of Example 7 is shown.

[0047] Figure 10 The curves show the cycle number and capacity of the sodium-ion battery prepared with the positive electrode pre-sodium composite current collector of Example 1 after 500 cycles of pre-sodium charging and discharging.

[0048] Figure 11 The normal discharge curve of the sodium-ion battery prepared using the composite current collector of Comparative Example 1 is shown. Detailed Implementation

[0049] The technical solution of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0050] Example 1

[0051] This embodiment describes a method for preparing a positive electrode pre-sodium composite current collector, comprising three stages: the first stage involves filling a porous current collector with a pre-sodium additive; the second stage involves baking and rolling the current collector after filling; and the third stage involves coating the surface with a conductive carbon layer. The specific steps are as follows:

[0052] Phase 1: Pre-sodium additives are filled into porous current collectors.

[0053] (1) At room temperature of 25°C, weigh 10wt% of the adhesive polyvinylidene fluoride (444.4g) and dissolve it in 4L of N-methylpyrrolidone solvent. Stir for 12h to prepare a transparent adhesive solution with a solid content of 10%. Take it out and set it aside.

[0054] (2) 70wt% positive electrode pre-sodium additive Na2C2O4 (3111.11g) and 10wt% conductive agent carbon nanotubes (444.4g) were dry-mixed for 3h, and the homogenizer was kept rotating at 40 rpm and 2000 rpm to ensure uniform mixing.

[0055] (3) Add the prepared adhesive solution and 10wt% of the auxiliary agent polyvinylpyrrolidone (444.4g) in sequence, keep the revolution at 50 rpm and the rotation at 5000 rpm, and stir for 6 hours;

[0056] (4) Adjust the viscosity of the slurry to 1000 mPa·s and fill it evenly into a porous aluminum foil current collector with a thickness of 12 μm and a pore size of 50 μm. The thickness of the pre-sodium filling layer is 12 μm.

[0057] Second stage: Preparation of porous current collector containing positive electrode pre-sodium filling layer

[0058] After drying at 45℃ and rolling, a smooth positive electrode pre-sodium composite current collector precursor (a porous current collector containing a positive electrode pre-sodium filling layer) is obtained.

[0059] Phase 3: Preparation of the surface conductive carbon layer

[0060] (1) At room temperature of 25°C, 2wt% adhesive (40g of polyvinylidene fluoride) was added to 2L of N-methylpyrrolidone solvent and stirred for 12h to prepare a transparent adhesive solution.

[0061] (2) Add 98wt% conductive carbon black (1960g) in multiple steps, maintain the revolution at 70 rpm and the rotation at 8000 rpm, and stir for 10 hours;

[0062] (3) Adjust the slurry viscosity to 10000 mPa·s and spray it onto the current collector;

[0063] (4) The thickness of the conductive carbon coating is 1 μm, and the positive electrode pre-sodium composite current collector is finally obtained.

[0064] SEM image of the positive electrode pre-sodium composite current collector prepared in this embodiment, as shown below. Figure 1 As shown, from Figure 1 As can be seen, the coating surface is smooth and the conductive agent is evenly distributed.

[0065] Example 2

[0066] This embodiment describes a method for preparing a positive electrode pre-sodium composite current collector, comprising three stages: the first stage involves filling a porous current collector with a pre-sodium additive; the second stage involves baking and rolling the current collector after filling; and the third stage involves coating the surface with a conductive carbon layer. The specific steps are as follows:

[0067] Phase 1: Pre-sodium additives are filled into porous current collectors.

[0068] (1) At room temperature of 25°C, weigh 5 wt% of the adhesive polyvinylidene fluoride (210.5 g) and dissolve it in 4 L of N-methylpyrrolidone solvent. Stir for 6 h to prepare a transparent adhesive solution with a solid content of 5%. Take it out and set it aside.

[0069] (2) 85wt% positive electrode pre-sodium additive Na2C6O6 (3578.9g) and 5wt% conductive agent carbon nanotubes (210.5g) were dry-mixed for 0.5h, and the homogenizer was kept rotating at 20 rpm and 500 rpm to ensure uniform mixing.

[0070] (3) Add the prepared adhesive solution and 5wt% polyvinylpyrrolidone (210.5g) in sequence, keep the revolution at 50 rpm and the rotation at 5000 rpm, and stir for 6 hours;

[0071] (4) Adjust the viscosity of the slurry to 9000 mPa·s and fill it evenly in a porous aluminum foil current collector with a thickness of 12 μm and a pore size of 50 μm. The thickness of the pre-sodium filling layer is 6 μm.

[0072] Second stage: Preparation of porous current collector containing positive electrode pre-sodium filling layer

[0073] After drying at 60℃ and rolling, a smooth positive electrode pre-sodium composite current collector precursor (a porous current collector containing a positive electrode pre-sodium filling layer) is obtained.

[0074] Phase 3: Preparation of the surface conductive carbon layer

[0075] (1) At room temperature of 25°C, 4wt% of adhesive (80g of polyvinylidene fluoride) was added to 2L of N-methylpyrrolidone solvent and stirred for 6h to prepare a transparent adhesive solution.

[0076] (2) Add 96wt% conductive carbon black (1920g) in multiple steps, maintain the revolution at 40 rpm and the rotation at 4000 rpm, and stir for 6 hours;

[0077] (3) Adjust the slurry viscosity to 20000 mPa·s and spray it onto the current collector;

[0078] (4) The conductive carbon coating thickness is 5μm, and the positive electrode pre-sodium composite current collector is finally obtained.

[0079] Example 3

[0080] This embodiment describes a method for preparing a positive electrode pre-sodium composite current collector, comprising three stages: the first stage involves filling a porous current collector with a pre-sodium additive; the second stage involves baking and rolling the current collector after filling; and the third stage involves coating the surface with a conductive carbon layer. The specific steps are as follows:

[0081] Phase 1: Pre-sodium additives are filled into porous current collectors.

[0082] (1) At room temperature of 25°C, weigh 1 wt% of the adhesive polyvinylidene fluoride (40.4 g) and dissolve it in 4 L of N-methylpyrrolidone solvent. Stir for 6 h to prepare a transparent adhesive solution with a solid content of 1%. Take it out and set it aside.

[0083] (2) 96wt% positive electrode pre-sodium additive Na2S (3878.8g) and 2wt% conductive agent carbon nanotubes (80.8g) were dry-mixed for 0.5h, and the homogenizer was kept rotating at 20 rpm and 500 rpm to ensure uniform mixing.

[0084] (3) Add the prepared adhesive solution and 1wt% of the auxiliary agent polyvinylpyrrolidone (40.4g) in sequence, keep the revolution at 30 rpm and the rotation at 3000 rpm, and stir for 3 hours;

[0085] (4) Adjust the slurry viscosity to 9000 mPa·s and fill it evenly in a porous aluminum foil current collector with a thickness of 12 μm and a pore size of 50 μm. The pre-sodium filling layer has a thickness of 12 μm.

[0086] Second stage: Preparation of porous current collector containing positive electrode pre-sodium filling layer

[0087] After drying at 60℃ and rolling, a smooth positive electrode pre-sodium composite current collector precursor (a porous current collector containing a positive electrode pre-sodium filling layer) is obtained.

[0088] Phase 3: Preparation of the surface conductive carbon layer

[0089] (1) At room temperature of 25°C, 2wt% of adhesive (40g of polyvinylidene fluoride) was added to 2L of N-methylpyrrolidone solvent and stirred for 6h to prepare a transparent adhesive solution.

[0090] (2) Add 98wt% conductive carbon black (1960g) in multiple steps, maintain the revolution at 40 rpm and the rotation at 4000 rpm, and stir for 6 hours;

[0091] (3) Adjust the slurry viscosity to 20000 mPa·s and spray it onto the current collector;

[0092] (4) The thickness of the conductive carbon coating is 5μm, and the positive electrode pre-sodium composite current collector is finally obtained.

[0093] Example 4

[0094] The method for preparing a positive electrode pre-sodium composite current collector in this embodiment differs from that in Example 1 in that the positive electrode pre-sodium additive is Na4C6O6, while the other steps are the same.

[0095] Example 5

[0096] The method for preparing a positive electrode pre-sodium composite current collector in this embodiment differs from that in Example 1 in that the positive electrode pre-sodium additive is NaN3, while the other steps are the same.

[0097] Example 6

[0098] The method for preparing a positive electrode pre-sodium composite current collector in this embodiment differs from that in Example 1 in that the positive electrode pre-sodium additive is Na2CO3, while the other steps are the same.

[0099] Example 7

[0100] The method for preparing a positive electrode pre-sodium composite current collector in this embodiment differs from that in Example 1 in that the positive electrode pre-sodium additive is Na3P, while the other steps are the same.

[0101] Example 8

[0102] The preparation method of the positive electrode pre-sodium composite current collector in this embodiment includes the following steps:

[0103] Phase 1: Pre-sodium additives are filled into porous current collectors.

[0104] (1) At room temperature of 25°C, weigh 8 wt% of the adhesive polyvinylidene fluoride (347.8 g) and dissolve it in 4 L of N-methylpyrrolidone solvent. Stir for 8 h to prepare a transparent adhesive solution with a solid content of 8%. Take it out and set it aside.

[0105] (2) 72wt% positive electrode pre-sodium additive Na2C2O4 (3130.4g) and 10wt% conductive agent conductive graphite (434.8g) were dry-mixed for 1.5h, and the homogenizer was kept rotating at 30 rpm and 1000 rpm to ensure uniform mixing.

[0106] (3) Add the prepared adhesive solution and 10wt% of the auxiliary agent polyvinylpyrrolidone (434.8g) in sequence, keep the revolution at 40 rpm and the rotation at 4000 rpm, and stir for 4.5h;

[0107] (4) Adjust the viscosity of the slurry to 4000 mPa·s and fill it evenly into a porous PET aluminum foil current collector with a thickness of 50 μm and a pore size of 1 μm. The thickness of the pre-sodium filling layer is 50 μm.

[0108] Second stage: Preparation of porous current collector containing positive electrode pre-sodium filling layer

[0109] After natural drying at 25℃ and roller pressing, a smooth positive electrode pre-sodium composite current collector precursor (a porous current collector containing a positive electrode pre-sodium filling layer) is obtained.

[0110] Phase 3: Preparation of the surface conductive carbon layer

[0111] (1) At room temperature of 25°C, 10wt% of adhesive (200g of polyvinylidene fluoride) was added to 2L of N-methylpyrrolidone solvent and stirred for 7h to prepare a transparent adhesive solution.

[0112] (2) Add 90wt% conductive agent conductive graphite (1800g) in multiple steps, maintain the revolution at 50 rpm and the rotation at 6000 rpm, and stir for 8 hours;

[0113] (3) Adjust the viscosity of the slurry to 4000 mPa·s and scrape it onto the current collector;

[0114] (4) The conductive carbon coating thickness is 20 μm, and the positive electrode pre-sodium composite current collector is finally obtained.

[0115] Example 9

[0116] The preparation method of the positive electrode pre-sodium composite current collector in this embodiment includes the following steps:

[0117] Phase 1: Pre-sodium additives are filled into porous current collectors.

[0118] (1) At room temperature of 25°C, weigh 8 wt% of the adhesive polyvinylidene fluoride (347.8 g) and dissolve it in 4 L of N-methylpyrrolidone solvent. Stir for 8 h to prepare a transparent adhesive solution with a solid content of 8%. Take it out and set it aside.

[0119] (2) 80wt% positive electrode pre-sodium additive Na2C2O4 (3478g) and 8wt% conductive agent acetylene black (347.8g) were dry-mixed for 1.5h, and the homogenizer was kept rotating at 30 rpm and 1000 rpm to ensure uniform mixing.

[0120] (3) Add the prepared adhesive solution and 4wt% polyvinylpyrrolidone (173.9g) in sequence, keep the revolution at 40 rpm and the rotation at 4000 rpm, and stir for 4.5h;

[0121] (4) Adjust the slurry viscosity to 6000 mPa·s and fill it evenly into a porous PET aluminum foil current collector with a thickness of 5 μm and a pore size of 100 μm. The pre-sodium filling layer has a thickness of 5 μm.

[0122] Second stage: Preparation of porous current collector containing positive electrode pre-sodium filling layer

[0123] After natural drying at 25℃ and roller pressing, a smooth positive electrode pre-sodium composite current collector precursor (a porous current collector containing a positive electrode pre-sodium filling layer) is obtained.

[0124] Phase 3: Preparation of the surface conductive carbon layer

[0125] (1) At room temperature of 25°C, 5wt% adhesive (100g of polyvinylidene fluoride) was added to 2L of N-methylpyrrolidone solvent and stirred for 7h to prepare a transparent adhesive solution.

[0126] (2) Add 95wt% conductive agent conductive graphite (1900g) in multiple steps, maintain the revolution at 50 rpm and the rotation at 6000 rpm, and stir for 8 hours;

[0127] (3) Adjust the viscosity of the slurry to 4000 mPa·s and scrape it onto the current collector;

[0128] (4) The thickness of the conductive carbon coating is 0.05 μm, and the positive electrode pre-sodium composite current collector is finally obtained.

[0129] Comparative Example 1

[0130] In this comparative example, carbon-coated aluminum foil was used as the current collector. The substrate aluminum foil was 12 μm thick, and the conductive carbon coating was 5 μm thick graphene. The specific preparation method is as follows:

[0131] (1) At room temperature of 25°C, 2wt% of adhesive (40g of polyvinylidene fluoride) was added to 2L of N-methylpyrrolidone solvent and stirred for 6h to prepare a transparent adhesive solution.

[0132] (2) Add 98wt% conductive carbon black (1960g) in multiple steps, maintain the revolution at 40 rpm and the rotation at 4000 rpm, and stir for 6 hours;

[0133] (3) Adjust the slurry viscosity to 20000 mPa·s and spray it onto the current collector;

[0134] (4) The thickness of the conductive carbon coating is 5μm, and the composite current collector is finally obtained.

[0135] Application examples

[0136] The positive electrode pre-sodium composite current collectors prepared in Examples 1-7 and the composite current collector prepared in Comparative Example 1 were applied to sodium-ion batteries. The specific preparation method of the sodium-ion battery is as follows:

[0137] (1) Preparation of positive electrode sheet: N-methylpyrrolidone (NMP) and polyvinylidene fluoride (PVDF) were prepared into a gel solution for later use. Polyanionic positive electrode material and conductive carbon black (SP) were dry-mixed and then multi-walled carbon nanotube (CNT) slurry and gel solution were added stepwise. The proportion of each component was NFM111:PVDF:SP:CNT = 96:2:1.5:0.5. The mixture was stirred at high speed for 120 min, vacuumed to remove bubbles, sieved, and discharged. The sheet was prepared with a single-sided surface density of 15 mg / cm³. 2 The positive electrode sheet is prepared by coating it onto a pre-sodium composite current collector or a composite current collector.

[0138] (2) Preparation of negative electrode sheet: Sodium carboxymethyl cellulose (CMC) was added to water to prepare a glue solution for later use. Hard carbon and conductive carbon black (SP) were dry-mixed and then added stepwise to single-walled carbon nanotube (CNT) slurry and glue solution. The mixture was stirred at high speed for 180 min, vacuumed to remove air bubbles, and the viscosity was adjusted before adding styrene-butadiene rubber (SBR). The proportions of each component were hard carbon:SP:CNT:CMC:SBR = 91.2:2.5:0.05:2.5:3.75. The mixture was stirred slowly for 30 min, sieved, and discharged. The material was coated onto copper foil with an N / P ratio of 1.15, corresponding to a single-sided areal density of 8.38 mg / cm³. 2 A negative electrode sheet was prepared.

[0139] (3) Battery assembly: The positive and negative electrode plates are pressed to a density of 1.9 g / cm³. 3 1g / cm 3 The finished battery cell is produced through processes such as roll forming, die cutting, baking, stacking, hot pressing, tab welding, packaging, secondary baking, electrolyte injection, aging, and formation.

[0140] Electrochemical performance tests were performed on the sodium-ion batteries prepared above. The sodium-ion batteries prepared in the examples required pre-sodium charging and discharging, where the purpose of pre-sodium charging was to replenish the sodium source lost during SEI film formation; the sodium-ion batteries prepared in Comparative Example 1 were directly charged and discharged normally.

[0141] (1) Use a stepped current for pre-sodium discharge and then discharge normally. The specific steps are as follows:

[0142] a. Charge the battery with a stepped current to 4.2V; b. Discharge to 2.0V; c. Then charge the battery normally to 3.65V; d. Discharge again to 2.0V.

[0143] Figure 2The figure shows the charging curve of a sodium-ion battery when the positive electrode pre-sodium composite current collector prepared in Example 1 is applied to a sodium-ion battery, with the battery being charged to 4.2V. As can be seen from the figure, there is a small plateau of dissociation of the pre-sodium additive at a voltage higher than 3.65V and close to 4.0V, indicating that the sodium source is released at this stage.

[0144] Figure 3 The normal discharge curve of the positive electrode pre-sodium composite current collector prepared in Example 1 applied to a sodium-ion battery shows that the first discharge capacity is 5.9 Ah.

[0145] Figure 4 The normal discharge curve of the positive electrode pre-sodium composite current collector prepared in Example 2 applied to a sodium-ion battery shows that the first discharge capacity is 5.802 Ah.

[0146] Figure 5 The normal discharge curve of the positive electrode pre-sodium composite current collector prepared in Example 3 applied to a sodium-ion battery shows that the first discharge capacity is 5.888 Ah.

[0147] Figure 6 The normal discharge curve of the positive electrode pre-sodium composite current collector prepared in Example 4 applied to a sodium-ion battery shows that the first discharge capacity is 5.84 Ah.

[0148] Figure 7 The normal discharge curve of the positive electrode pre-sodium composite current collector prepared in Example 5 applied to a sodium-ion battery shows that the first discharge capacity is 5.828 Ah.

[0149] Figure 8 The normal discharge curve of the positive electrode pre-sodium composite current collector prepared in Example 6 applied to a sodium-ion battery shows that the first discharge capacity is 5.884 Ah.

[0150] Figure 9 The normal discharge curve of the positive electrode pre-sodium composite current collector prepared in Example 7 applied to a sodium-ion battery shows that the first discharge capacity is 5.861 Ah.

[0151] Figure 10 When the positive electrode pre-sodium composite current collector prepared in Example 1 is applied to a sodium-ion battery, the battery's cycle life is improved by controllably releasing sodium sources after 500 cycles by increasing the charging cut-off voltage to 4.2V. This further illustrates that during battery use, sodium ions can be released at any time to replenish sodium simply by increasing the charging voltage, demonstrating a controllable characteristic.

[0152] (2) The sodium-ion battery prepared in the comparative example discharged normally. The specific process is as follows:

[0153] a. Charge the battery normally to 3.65V; b. Discharge it to 2.0V. Figure 11 The normal discharge curve of the composite current collector prepared in Comparative Example 1 applied to a sodium-ion battery shows that the first discharge capacity is 5.561 Ah.

[0154] The results of discharge capacity, first charge-discharge efficiency, and energy density of different embodiments and comparative examples are shown in Table 1.

[0155] Table 1

[0156]

[0157] As can be seen from Table 1, the present invention fills the positive electrode pre-sodium additive into the porous current collector. By pre-sodium treatment, the first charge and discharge efficiency and energy density of the battery can be improved.

[0158] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A positive electrode pre-sodium composite current collector, characterized in that, The positive electrode pre-sodium composite current collector includes a porous current collector, a positive electrode pre-sodium filling layer filled in the pores of the porous current collector, and a conductive carbon layer located on the surface of the current collector; wherein, the positive electrode pre-sodium filling layer includes a positive electrode pre-sodium additive; the positive electrode pre-sodium additive is at least one of Na2C2O4, Na2C6O6, Na4C6O6, NaN3, Na2S, Na2CO3, and Na3P; the thickness of the positive electrode pre-sodium filling layer is not greater than the thickness of the porous current collector.

2. The positive electrode pre-sodium composite current collector according to claim 1, characterized in that, The positive electrode pre-sodium filling layer further includes a binder, conductive carbon, and additives; the conductive carbon layer includes conductive carbon and a binder.

3. The positive electrode pre-sodium composite current collector according to claim 2, characterized in that, The positive electrode pre-sodium filler layer comprises 70wt%-96wt% positive electrode pre-sodium additive, 1wt%-10wt% binder, 2wt%-10wt% conductive carbon, and 1wt%-10wt% auxiliary agent; the conductive carbon layer comprises 90wt%-98wt% conductive carbon and 2wt%-10wt% binder.

4. The positive electrode pre-sodium composite current collector according to claim 2 or 3, characterized in that, The binder is at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl alcohol, polyacrylamide, polyacrylamide and hydroxyethyl cellulose; the conductive carbon is at least one of carbon black, conductive graphite, carbon nanotubes, graphene and acetylene black.

5. The positive electrode pre-sodium composite current collector according to claim 4, characterized in that, The additive is at least one of polyvinylpyrrolidone, dipropylene glycol, polyethylene glycol, triglycerides, and decaglycerides.

6. The positive electrode pre-sodium composite current collector according to claim 5, characterized in that, The porous current collector is made of aluminum foil or PET aluminum foil, with a thickness of 5-50 μm and a pore size of 1-100 μm; the thickness of the conductive carbon layer is 0.05 μm-20 μm.

7. A method for preparing the positive electrode pre-sodium composite current collector as described in claim 1, characterized in that, The steps are as follows: (1) Add the adhesive to the solvent and stir to prepare an adhesive solution; (2) After dry mixing the positive electrode pre-sodium additive and conductive carbon, add the adhesive and additives prepared in step (1) and stir to obtain slurry I; fill the pores of the porous current collector with slurry I, bake and roll to obtain a porous current collector containing a positive electrode pre-sodium filling layer. (3) Add conductive carbon to the adhesive solution obtained in step (1), stir evenly to obtain slurry II, and apply it to the porous current collector obtained in step (2) by scraping or spraying to obtain the positive electrode pre-sodium composite current collector.

8. The method for preparing the positive electrode pre-sodium composite current collector according to claim 7, characterized in that, The solvent is at least one selected from N-methylpyrrolidone, tetramethylurea, trimethyl phosphate, and dimethyl sulfoxide.

9. The method for preparing the positive electrode pre-sodium composite current collector according to claim 8, characterized in that, The viscosity of slurry I is 1000-9000 mPa·s; the viscosity of slurry II is 4000-20000 mPa·s.

10. A sodium-ion battery, characterized in that, Includes the positive electrode pre-sodium composite current collector as described in claim 1.

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