Method for modifying positive electrode of sodium-ion battery based on high-performance positive electrode sodium-supplementing additive

Abstract

The invention discloses a sodium ion battery positive electrode modification method based on a high-performance positive electrode sodium supplement additive, which is characterized in that a proper amount of sodium carboxymethyl cellulose (CMC) is introduced as the positive electrode sodium supplement additive in a positive electrode material preparation process, an ultrahigh electronic conductive network can be established, and a channel beneficial to sodium ion transmission can be formed in a positive electrode material; the migration resistance of sodium ions in the electrode material is reduced, so that the sodium ion conductivity of the electrode is improved, the sodium ions are embedded and separated more smoothly in the charging and discharging process of the battery, and the charging and discharging efficiency and the rate capability of the battery are improved. In addition, the sodium carboxymethyl cellulose serving as a positive sodium supplement additive can stabilize the electrode structure and reduce damage and structural collapse of the material in the circulation process, so that the cycle life of the battery is prolonged. A series of characterization tests prove that the rate, cycle and other electrochemical properties of the modified ferric sodium pyrophosphate material are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the field of new energy materials, sodium ion battery positive electrodes, and relates to a method for modifying sodium ion battery positive electrodes, and specifically to a method for modifying sodium ion battery positive electrodes by using a high-performance positive electrode sodium supplement additive. Background Art

[0002] Sodium-ion batteries (SIBs) are gaining popularity in the energy storage market due to their numerous advantages, including abundant resources, low cost, environmental friendliness, high safety, excellent fast-charging performance, and outstanding wide-temperature performance. While SIBs offer significant advantages in energy storage power stations, low-speed electric vehicles, and backup power supplies, they still face challenges in electric vehicles and consumer electronics, which demand high energy density. With technological advancements and scale-up, SIBs are expected to become a key complementary technology for energy transition. To date, mainstream SIBs can be categorized into three types: Prussian blue, layered oxides, and polyanions. Prussian blue-based materials have an open framework and multiple pores, allowing for rapid sodium ion intercalation and deintercalation, improving the battery's rate capability and cycling stability. However, residual crystalline water in their structure is difficult to remove, which can lead to structural collapse during cycling and compromise electrochemical performance. Layered oxide-based materials offer high theoretical specific capacity and can provide high energy density, but they suffer from poor air stability and prone to degradation and gassing, which can impact safety. Polyanion-based materials offer excellent structural stability and minimal volume change during charge and discharge, effectively suppressing structural collapse or phase transitions, thereby extending the battery's cycle life. In addition, the newly developed composite sodium iron pyrophosphate (NFPP) positive electrode material has the advantages of good structural stability, long cycle life, low cost, excellent low-temperature performance, safety and environmental friendliness, and has great potential in the field of communication energy storage.

[0003] However, the intrinsic electronic conductivity of NFPP is poor, which limits its performance under high-rate charge and discharge conditions. It is usually necessary to improve the conductivity through methods such as carbon coating or element doping. The theoretical specific capacity of NFPP is 129mAh / g. Compared with the positive electrode materials of lithium batteries, its energy density is lower, which limits its application in scenarios with high energy density requirements. In addition, NFPP easily generates impurities during the synthesis process and is sensitive to temperature. The preparation process has high requirements, which affects its large-scale production and application. Therefore, in order to improve the defects of NFPP, a highly conductive network can be constructed by surface carbon coating to improve the conductivity and structural stability of the material, and element doping can be used to reduce the diffusion energy barrier of sodium ions and improve the diffusion kinetics of sodium ions. The particle size of the material can be reduced by nano-processing of the material, the diffusion path of sodium ions can be shortened, and the electrochemical performance can be improved. Summary of the Invention

[0004] To address the low electronic conductivity and slow lithium ion diffusion rate of sodium ferric pyrophosphate (SFP) cathode materials, the present invention provides a method for modifying the cathode of a sodium-ion battery using a high-performance cathode sodium supplement. This method introduces an appropriate amount of sodium carboxymethyl cellulose (CMC) as a cathode sodium supplement during the cathode formulation process. This method establishes an ultra-high electronic conductive network, forming channels within the cathode material that facilitate sodium ion transport, reducing sodium ion migration resistance within the electrode material, thereby improving the electrode's sodium ion conductivity and facilitating smoother sodium ion insertion and extraction during the battery's charge and discharge processes, thereby enhancing the battery's charge and discharge efficiency and rate performance. Furthermore, the SFP cathode sodium supplement stabilizes the electrode structure, reducing material damage and structural collapse during cycling, thereby extending the battery's cycle life. A series of characterization tests demonstrated significant improvements in the electrochemical performance of the modified SFP material, including rate and cycling performance.

[0005] The purpose of the present invention is achieved through the following technical solutions: A method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive comprises the following steps: Step S1, dissolving the positive electrode sodium supplement additive in a solvent, and sonicating until there is no agglomeration, wherein: The positive electrode sodium supplement additive is one of sodium carboxymethyl cellulose (CMC), sodium dodecyl sulfate, sodium alginate, sodium acetate, sodium hydroxide, sodium peroxide, sodium gluconate, and sodium ascorbate, preferably sodium carboxymethyl cellulose (CMC), with a degree of substitution of 0.8-1.2 and a purity of >99%.

[0006] The ultrasonic power is 50-60W, the time is 10-30 minutes, and the temperature is 25-35°C; The solvent is N-methylpyrrolidone (NMP) with a solid content of 3-5%; Step S2: adding the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder to the solution obtained in step S1 in sequence, stirring evenly, to obtain a positive electrode slurry, wherein: The mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 94-96:3-2:3-2, and the amount of the positive electrode sodium supplement additive is 0.5-1.5wt% of the positive electrode active material, preferably 1wt%; The positive electrode active material is one of layered metal oxides, Prussian blue (white) materials, polyanion materials and sulfate materials; The positive electrode conductive agent is one of Super P, acetylene black, carbon nanotubes, Ketjen black, conductive graphite, modified graphene and modified carbon fiber; The positive electrode binder is one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyether resin, and polyurethane; The stirring rate is 200-300 rpm and the temperature is 25-35°C; Step S3: coating the positive electrode slurry obtained in step S2 on the positive electrode current collector, drying, rolling, and cutting to obtain a positive electrode sheet, wherein: The positive electrode current collector is aluminum foil; The thickness of the positive electrode current collector is 13 to 15 microns; The drying process adopts a vacuum drying method, and the drying temperature is 80-85°C.

[0007] The positive electrode sheet prepared by the above method is used in a sodium ion battery. The positive electrode sheet is assembled with a die-cut negative electrode sheet and a separator to form a battery cell, shell, inject liquid and seal the battery to form a sodium ion battery.

[0008] Compared with the prior art, the present invention has the following advantages: 1. The present invention modifies the sodium ferric pyrophosphate cathode material by introducing a high-performance cathode sodium supplement additive. The Na⁺ released by the high-performance cathode sodium supplement additive can compensate for the sodium loss during the first charge of the cathode material, while improving the sodium ion diffusion kinetics, thereby achieving excellent rate, cycle, and charge-discharge electrochemical properties.

[0009] 2. The positive electrode sodium supplement additive in the present invention is biomass-based, and sodium carboxymethyl cellulose is degradable, meets green manufacturing requirements, and is environmentally friendly.

[0010] 3. In the present invention, sodium carboxymethyl cellulose forms hydrogen bonds with the hydroxyl groups on the surface of the positive electrode material through the carboxyl group, thereby improving the bonding effect and enhancing the peeling strength of the electrode.

[0011] 4. The high molecular chains of sodium carboxymethyl cellulose in the present invention can be adsorbed on the surface of active material particles, reducing agglomeration and improving electrode kinetics. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The figure is a rate performance diagram of the sodium iron pyrophosphate material of Example 1, Example 2, Example 3 and Comparative Example 1; Figure 2 These are the charge and discharge diagrams of the sodium iron pyrophosphate materials of Example 1 and Comparative Example 1. DETAILED DESCRIPTION

[0013] The technical solution of the present invention is further described below with reference to the embodiments, but is not limited thereto. Any modification or equivalent replacement of the technical solution of the present invention that does not depart from the spirit and scope of the technical solution of the present invention should be included in the scope of protection of the present invention.

[0014] Example 1 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) dissolving sodium carboxymethyl cellulose as a positive electrode sodium supplement in NMP and ultrasonically dispersing the mixture for 15 minutes until no agglomerates are observed. The ultrasonic power is 50 W and the temperature is 25 °C. Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0015] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0016] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0017] Example 2 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium dodecyl sulfate as a positive electrode sodium supplement additive is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0018] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0019] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0020] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0021] Example 3 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium alginate as a positive electrode sodium supplement was dissolved in NMP and ultrasonically dispersed for 15 minutes until there was no agglomeration. The ultrasonic power was 50 W and the temperature was 25 °C.

[0022] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0023] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0024] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0025] Example 4 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium acetate was dissolved in NMP as a positive electrode sodium supplement, and ultrasonic dispersion was performed for 15 minutes until there was no agglomeration. The ultrasonic power was 50 W and the temperature was 25 °C.

[0026] Step (2) weighing sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, uniformly mixing them in the NMP of step (1) and stirring evenly, the stirring rate is 250rmp, the temperature is 25 ° C, wherein the total amount of the positive electrode material, the conductive agent and the binder is 100%, and sodium acetate is added as a positive electrode sodium supplement additive, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0027] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0028] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0029] Example 5 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium peroxide as a positive electrode sodium supplement additive is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50W and the temperature is 25°C.

[0030] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0031] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter.2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0032] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0033] Example 6 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium gluconate was dissolved in NMP as a positive electrode sodium supplement, and ultrasonically dispersed for 15 minutes until there was no agglomeration. The ultrasonic power was 50 W and the temperature was 25 °C.

[0034] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0035] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 microns using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100cm area using a circle cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0036] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0037] Example 7 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium ascorbate as a positive electrode sodium supplement additive is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0038] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0039] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0040] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0041] Example 8 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium hydroxide as a positive electrode sodium supplement additive is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0042] Step (1) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, uniformly mix them in the NMP of step (1) and stir evenly, the stirring rate is 250rmp, the temperature is 25°C, wherein the total amount of the positive electrode material, the conductive agent and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0043] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0044] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0045] Example 9 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium carboxymethyl cellulose as a positive electrode sodium supplement is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0046] Step (1) Weigh the sodium nickel iron manganese oxide positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 95:2:3, uniformly mix them in the NMP of step (1), and stir them evenly. The stirring rate is 250 rpm, and the temperature is 25 ° C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium nickel iron manganese oxide positive electrode material to obtain a positive electrode slurry.

[0047] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0048] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0049] Example 10 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium carboxymethyl cellulose as a positive electrode sodium supplement is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0050] Step (2) weigh Na2MnFe(CN)6 positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 96:2:2, uniformly mix them in the NMP of step (1) and stir them evenly. The stirring rate is 250rmp and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the Na2MnFe(CN)6 positive electrode material to obtain a positive electrode slurry.

[0051] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 13 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0052] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0053] Example 11 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium carboxymethyl cellulose as a positive electrode sodium supplement is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0054] Step (2) weighing sodium ferric pyrophosphate positive electrode material, acetylene black conductive agent, and PVDF binder according to a mass ratio of 95:3:2, uniformly mixing them in the NMP of step (1) and stirring evenly, the stirring rate is 250rmp, the temperature is 25°C, wherein the total amount of the positive electrode material, the conductive agent and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0055] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 14 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a circle cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0056] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0057] Example 12 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium carboxymethyl cellulose as a positive electrode sodium supplement is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0058] Step (2) weighing sodium ferric pyrophosphate positive electrode material, carbon nanotube conductive agent, and PVDF binder according to a mass ratio of 94:3:3, uniformly mixing them in the NMP of step (1) and stirring evenly, the stirring rate is 250rmp, the temperature is 25°C, wherein the total amount of the positive electrode material, the conductive agent and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0059] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0060] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0061] Example 13 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium carboxymethyl cellulose as a positive electrode sodium supplement is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0062] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and polytetrafluoroethylene binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0063] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0064] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0065] Example 14 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium carboxymethyl cellulose as a positive electrode sodium supplement is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0066] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and polyacrylate binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0067] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on a positive electrode aluminum foil current collector with a thickness of 15 μm using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0068] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0069] Comparative Example 1 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Weigh sodium iron pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in NMP and stir them evenly. The stirring rate is 250 rpm and the temperature is 25 °C. The total amount of the positive electrode material, conductive agent and binder is 100%. No sodium supplement additive is added here to obtain a positive electrode slurry.

[0070] Step (2) The positive electrode slurry obtained in step (1) is evenly coated on the positive electrode aluminum foil current collector using an extrusion coating machine, baked in a segmented high-temperature oven, and cut into a 100 cm area using a circle cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0071] In step (3), hard carbon is used as the negative electrode of the sodium ion battery, and is matched with the sodium battery positive electrode prepared in step (2) to assemble a full battery, and then the battery assembly is performed (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0072] Comparative Example 2 This embodiment provides a method for preparing a sodium ion battery, and the specific steps are as follows: Step (1) Sodium carboxymethyl cellulose as a positive electrode sodium supplement is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0073] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 0.5wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0074] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on the positive electrode aluminum foil current collector using an extrusion coater, baked in a segmented high-temperature oven, and cut into a 100 cm area using a round cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0075] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0076] Comparative Example 3 This embodiment provides a method for preparing a sodium ion battery, which is as follows: Step (1) Sodium carboxymethyl cellulose as a positive electrode sodium supplement is dissolved in NMP and ultrasonically dispersed for 15 minutes until there is no agglomeration. The ultrasonic power is 50 W and the temperature is 25 °C.

[0077] Step (2) Weigh the sodium ferric pyrophosphate positive electrode material, Super P conductive agent, and PVDF binder according to a mass ratio of 94:3:3, mix them evenly in the NMP of step (1), and stir them evenly. The stirring rate is 250rmp, and the temperature is 25°C. The total amount of the positive electrode material, the conductive agent, and the binder is 100%, and the amount of the sodium supplement additive is 1.5wt% of the sodium ferric pyrophosphate positive electrode material to obtain a positive electrode slurry.

[0078] Step (3) The positive electrode slurry obtained in step (2) is evenly coated on the positive electrode aluminum foil current collector using an extrusion coating machine, baked in a segmented high-temperature oven, and cut into a 100 cm area using a circle cutter. 2 The disc was weighed and the weight of the positive electrode single side was 0.0197 g / cm 2 The double-sided weight of the positive electrode is 0.0359 g / cm 2 After coating, slitting, rolling and die-cutting, the sodium battery positive electrode sheet is obtained.

[0079] Step (4) uses hard carbon as the negative electrode of the sodium ion battery, and assembles a full battery by matching it with the sodium battery positive electrode prepared in step (3), and then performs battery assembly (components include: positive electrode sheet, negative electrode sheet, diaphragm, gasket, spring sheet, electrolyte).

[0080] Performance test: The positive electrode materials of the embodiment and the comparative example were made into button batteries, and the electrochemical performance was tested on a high-performance battery testing system, Blue Electric. The test conditions were: voltage range: 2.0-3.8 V, temperature: 25°C, current size: 0.1 C. The results are shown in Table 1 below: It can be found from Table 1 that by comparing Example 1 with Examples 2-8, and Example 1 with Comparative Examples 1-3, it is proved that sodium carboxymethyl cellulose as a positive electrode sodium supplement additive and its content at 1wt% has the best discharge specific capacity and capacity retention rate as well as high first effect.

[0081] Figure 1 The rate spectra of Example 1 and Comparative Examples 1 to 3 are shown. It can be found that the sodium ferric pyrophosphate material in which an appropriate amount of sodium carboxymethyl cellulose is introduced as a sodium supplement additive in Example 1 exhibits excellent rate performance at a current density of 0.1-2 C. This is mainly because sodium carboxymethyl cellulose as a positive electrode sodium supplement additive can establish an ultra-high electronic conductive network, form a channel in the positive electrode material that is conducive to sodium ion transmission, reduce the migration resistance of sodium ions in the electrode material, thereby improving the sodium ion conductivity of the electrode, making the insertion and extraction of sodium ions in the battery during the charge and discharge process smoother, which helps to improve the charge and discharge efficiency and rate performance of the battery. Figure 2 The charge and discharge curves of the sodium iron pyrophosphate material of Example 1 and Comparative Example 1 at 0.5 C are shown. The sodium iron pyrophosphate material to which an appropriate amount of sodium carboxymethyl cellulose is introduced as a sodium supplement additive in Example 1 exhibits a smaller charge and discharge voltage platform spacing than the sodium iron pyrophosphate material to which no sodium supplement additive is added in Comparative Example 1, which means that a smaller polarization is generated, and also reflects its high discharge specific capacity. This is mainly attributed to the fact that sodium carboxymethyl cellulose, as a positive electrode sodium supplement additive, improves the electronic conductivity and ion transfer rate of the sodium iron pyrophosphate material, can optimize the interfacial wettability between the electrode and the electrolyte, allows the electrolyte to better penetrate into the interior of the electrode, increases the contact area between the electrode and the electrolyte, and reduces the interface resistance. At the same time, it can also inhibit the corrosion of the electrolyte on the electrode material to a certain extent, improve the stability of the interface, and is beneficial to the performance of the battery performance.

Claims

1. A method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive, characterized in that The method comprises the following steps: Step S1, dissolving a positive electrode sodium supplement additive in a solvent, and sonicating until no agglomerates are formed, wherein the positive electrode sodium supplement additive is one of sodium carboxymethyl cellulose, sodium dodecyl sulfate, sodium alginate, sodium acetate, sodium hydroxide, sodium peroxide, sodium gluconate, and sodium ascorbate; Step S2, sequentially adding a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder to the solution obtained in step S1, and stirring uniformly to obtain a positive electrode slurry, wherein: the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is 94-96:3-2:3-2, and the amount of the positive electrode sodium supplement additive is 0.5-1.5wt% of the positive electrode active material; Step S3: coating the positive electrode slurry obtained in step S2 on the positive electrode current collector, and obtaining the positive electrode sheet after drying, rolling and cutting.

2. The method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive according to claim 1, characterized in that The positive electrode sodium supplement additive is sodium carboxymethyl cellulose with a degree of substitution of 0.8-1.2 and a purity of >99%; the solvent is N-methylpyrrolidone with a solid content of 3-5%.

3. The method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive according to claim 1, characterized in that The ultrasonic power is 50-60W, the time is 10-30 minutes, and the temperature is 25-35°C.

4. The method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive according to claim 1 or 2, characterized in that The amount of the positive electrode sodium supplement additive is 1 wt % of the positive electrode active material.

5. The method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive according to claim 1, characterized in that The positive electrode active material is one of layered metal oxides, Prussian blue materials, Prussian white materials, polyanion materials and sulfate materials; the positive electrode conductive agent is one of Super P, acetylene black, carbon nanotubes, Ketjen black, conductive graphite, modified graphene and modified carbon fiber; the positive electrode binder is one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylate, polyether resin and polyurethane.

6. The method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive according to claim 1 or 5, characterized in that The positive electrode active material is sodium iron pyrophosphate positive electrode material.

7. The method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive according to claim 1, characterized in that The stirring speed is 200-300 rpm and the temperature is 25-35°C.

8. The method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive according to claim 1, characterized in that The positive electrode current collector is aluminum foil with a thickness of 13 to 15 microns.

9. The method for modifying the positive electrode of a sodium ion battery based on a high-performance positive electrode sodium supplement additive according to claim 1, characterized in that The drying process adopts a vacuum drying method, and the drying temperature is 80-85°C.

10. Use of a positive electrode modified by the method according to any one of claims 1 to 9 in a sodium ion battery.

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