Positive electrode sodium supplementing method of sodium-ion battery and sodium-ion battery

Abstract

The invention belongs to the related technical field of electrochemical sodium ion batteries, and discloses a sodium ion battery positive electrode sodium supplementing method and a lithium ion battery, and the method comprises the following steps: coating a sodium supplementing slurry on a diaphragm of a sodium ion battery to form a sodium supplementing layer; wherein the raw materials of the sodium supplementing slurry comprise halogen sodium salt, a conductive agent and a binder; the halogen sodium salt is a sodium supplementing material and comprises one or more of sodium fluoride, sodium chloride, sodium bromide and sodium iodide. According to the invention, halogen sodium salt is homogenized as a sodium supplementing material and then is coated on the diaphragm to serve as a sodium supplementing layer of the positive electrode, and when the battery is charged in the first circle, additional sodium ions are provided by decomposition, irreversible capacity loss caused by the sodium ions consumed by the negative electrode is made up, and the reversible capacity of the sodium ion battery is effectively improved.

Description

Technical Field

[0001] The present invention belongs to the technical field related to electrochemical sodium ion batteries, and more specifically, relates to a method for replenishing sodium at a positive electrode of a sodium ion battery and a lithium ion battery. Background Art

[0002] Sodium has abundant reserves on Earth, is widely distributed, has a simple extraction process, and is much cheaper than lithium. More importantly, as elements of the same main group, the two have similar physical and chemical properties. + The standard potential of -2.71V vs. Li / Li + The standard potential of -3.04V is close to that of lithium-ion batteries, which work on the same principle as the "rocking chair battery". + It can also be charged and discharged by intercalation between the positive and negative electrodes. This battery system is called a sodium ion battery.

[0003] However, during the first week of battery charging, the solid electrolyte membrane (SEI) formed on the surface of the negative electrode consumes part of the Na released from the positive electrode. + , which reduces the reversible capacity of the battery and directly affects the energy density of the battery. In order to solve this problem, it is necessary to find an additional sodium source to supplement the sodium battery system in advance to make up for the Na consumed in it. + Therefore, sodium supplementation technology is of great significance to improving the capacity and energy density of sodium batteries. Summary of the invention

[0004] In view of the above defects or improvement needs of the prior art, the present invention provides a method for replenishing sodium at the positive electrode of a sodium ion battery and a lithium ion battery, which aims to solve the problem of sodium loss during the first week of charging and discharging of the sodium ion battery.

[0005] To achieve the above object, according to one aspect of the present invention, a method for replenishing sodium at a positive electrode of a sodium ion battery is provided, the method comprising the following steps:

[0006] A sodium supplement slurry is applied on the diaphragm of a sodium ion battery to form a sodium supplement layer; wherein the raw materials of the sodium supplement slurry include a halogen sodium salt, a conductive agent and a binder; the halogen sodium salt is a sodium supplement material, which includes one or more of sodium fluoride, sodium chloride, sodium bromide and sodium iodide.

[0007] Furthermore, the halogen sodium salt is sodium chloride.

[0008] Furthermore, the sodium chloride and the conductive agent are ball-milled at a mass ratio of 9:1 for 6 hours.

[0009] Furthermore, the conductive agent includes one or more of Ketjen black, acetylene black, Super P, and carbon nanotubes.

[0010] Furthermore, the conductive agent is Ketjen black.

[0011] Furthermore, the mass ratio of the sodium supplement material, the conductive agent and the binder is 8:1:1 and they are evenly stirred to obtain a sodium supplement slurry.

[0012] Furthermore, the diaphragm is a polyethylene diaphragm or a polypropylene diaphragm.

[0013] Furthermore, the mass of the NaCl sodium supplement material on the diaphragm is 1% to 50% of the mass of the positive electrode.

[0014] Furthermore, the mass of the NaCl sodium-supplementing material on the diaphragm is 20% of the mass of the positive electrode; and the binder includes one or more of polytetrafluoroethylene, polytetrafluoroethylene, and sodium alginate.

[0015] The present invention also provides a sodium ion battery, which comprises a positive electrode, a sodium supplement layer, a separator and a negative electrode arranged from bottom to top, and the sodium supplement layer is obtained by adopting the positive electrode sodium supplement method of the sodium ion battery as described above.

[0016] In general, compared with the prior art, the above technical solutions conceived by the present invention mainly have the following beneficial effects:

[0017] 1. Halogen sodium salt is used as a sodium supplement material and then applied to the diaphragm as a sodium supplement layer for the positive electrode. It decomposes and provides additional sodium ions during the first cycle of charging of the battery to make up for the irreversible capacity loss caused by the sodium ions lost at the negative electrode, effectively improving the reversible capacity of the sodium ion battery.

[0018] 2. Loading NaCl material on commercial diaphragms, which can store more NaCl, can greatly increase the initial charge capacity of the positive electrode, and effectively avoid the damage of NaCl decomposition to the positive electrode structure, ensuring the stability of the electrode structure and battery performance. At the same time, in sodium-ion batteries, NaCl supplements sodium ions, making up for the sodium ions that are inevitably consumed on the positive and negative electrode sides, effectively increasing the initial discharge capacity of sodium-ion batteries and increasing the Na in the positive electrode active material. + The utilization rate of sodium-ion batteries is greatly improved, which effectively improves the initial efficiency and energy density of sodium-ion batteries.

[0019] 3. The present invention provides a non-toxic, harmless, low-cost halogen sodium salt as a positive electrode sodium supplement material, which improves the reversible capacity and energy density of the sodium ion full battery, and the method is safe, practical and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 (a) and (b) are surface scanning electron micrographs of commercial NaCl and ball-milled NaCl / KB materials in Example 1, respectively;

[0021] Figure 2 are the first cycle charge and discharge curves of NaCl and NaCl / KB as the positive electrode of the sodium ion battery in Example 1;

[0022] Figure 3 (a) and (b) are the surface scanning electron microscope images and electron images of the commercial polyethylene separator and the NaCl loaded commercial polyethylene separator in Example 1, respectively;

[0023] Figure 4 It is the first cycle charge and discharge curve diagram of NVP-PP@%NaCl in Example 1 and comparative example NVP as the positive electrode half-cell of sodium ion battery;

[0024] Figure 5 It is the first cycle charge and discharge curve of the sodium ion full battery with NVP-PP@NaCl and the comparative example NVP matching hard carbon negative electrode in Example 1;

[0025] Figure 6 It is the sodium ion full battery cycle performance diagram of NVP-PP@NaCl in Example 1 and the comparative example NVP matching hard carbon negative electrode;

[0026] Figure 7 It is the sodium ion full battery rate performance diagram of NVP-PP@NaCl in Example 1 and the comparative example NVP matching hard carbon negative electrode;

[0027] Figure 8 It is a structural schematic diagram of a sodium ion battery provided by the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0029] The present invention provides a method for replenishing sodium in a positive electrode of a sodium ion battery. The method mainly comprises the following steps: applying a sodium replenishing slurry on a diaphragm of the sodium ion battery to form a sodium replenishing layer; wherein the raw materials of the sodium replenishing slurry include a halogen sodium salt, a conductive agent and a binder.

[0030] The halogen sodium salt is a sodium supplement material, which includes one or more of sodium fluoride (NaF), sodium chloride (NaCl), sodium bromide (NaBr), and sodium iodide (NaI), preferably sodium chloride. The sodium supplement material is mixed with a conductive agent and ball milled to reduce the particle size of the sodium supplement material so that it is completely decomposed in the first cycle of charging; in one embodiment, the sodium chloride and the conductive agent are ball milled at a mass ratio of 9:1 for 6 hours.

[0031] The conductive agent includes one or more of Ketjen black, acetylene black, Super P, and carbon nanotubes, preferably Ketjen black.

[0032] In one embodiment, the mass ratio of the sodium supplement material, the conductive agent, and the binder is 8:1:1, and the mixture is evenly stirred to obtain a sodium supplement slurry, which is then applied to the diaphragm and placed in an oven for drying.

[0033] The diaphragm is a polyethylene diaphragm or a polypropylene diaphragm; the mass of the NaCl sodium supplement material on the diaphragm is 1% to 50% of the mass of the positive electrode, preferably 20%; the positive electrode active material of the positive electrode includes one or more of sodium vanadium phosphate, sodium vanadium phosphate fluoride, Prussian blue, Prussian white and layered oxides, preferably, the positive electrode active material is sodium vanadium phosphate.

[0034] The binder includes one or more of polytetrafluoroethylene, polytetrafluoroethylene, and sodium alginate. Preferably, the binder includes polytetrafluoroethylene (PVDF).

[0035] The present invention also provides a sodium ion battery, the sodium ion battery comprising a positive electrode, a sodium supplement layer, a diaphragm and a negative electrode arranged from bottom to top, the sodium supplement layer is obtained by adopting the positive electrode sodium supplement method of the sodium ion battery as described above, such as Figure 8 shown.

[0036] The present invention is further described in detail below with reference to specific embodiments.

[0037] Example 1

[0038] Commercial NaCl material and Ketjen black (KB) were ball-milled in a mass ratio of 9:1 to obtain a NaCl / KB composite material as a positive electrode sodium supplement material. The ratio of sodium supplement material, conductive agent, and binder was 8:1:1, stirred evenly, applied on the diaphragm and placed in an oven for drying. Cut into 19mm discs, recorded as PP@NaCl. The positive electrode uses commercial sodium vanadium phosphate material, and the negative electrode uses commercial hard carbon material. The positive and negative electrode N / P ratio is controlled at 1.05-1.1 for pairing.

[0039] Example 2

[0040] Commercial NaCl material and Ketjen black (KB) were ball-milled in a mass ratio of 9:1 to obtain a NaCl / KB composite material as a positive electrode sodium supplement material. The ratio of sodium supplement material, conductive agent, and binder was 7:2:1, stirred evenly, applied on the diaphragm and placed in an oven for drying. Cut into 19mm discs, recorded as PP@NaCl. The positive electrode uses commercial sodium vanadium phosphate material, and the negative electrode uses commercial hard carbon material. The positive and negative electrode N / P ratio is controlled at 1.05-1.1 for pairing.

[0041] Example 3

[0042] Commercial NaCl material and Ketjen black (KB) were ball-milled in a mass ratio of 9:1 to obtain a NaCl / KB composite material as a positive electrode sodium supplement material. The ratio of sodium supplement material, conductive agent, and binder was 90:5:5, stirred evenly, applied on the diaphragm and placed in an oven for drying. Cut into 19mm discs, recorded as PP@NaCl. The positive electrode uses commercial sodium vanadium phosphate material, and the negative electrode uses commercial hard carbon material. The positive and negative electrode N / P ratio is controlled at 1.05-1.1 for pairing.

[0043] Comparative Example

[0044] The comparative example of the present invention is a sodium ion battery without a NaCl sodium-supplementing diaphragm (a NaCl sodium-supplementing layer is provided on the diaphragm), and the other steps are consistent with those of Application Example 1.

[0045] Application Examples

[0046] The positive electrode sodium supplement material NaCl in Example 1 was used as the test object, wherein Comparative Example 1 does not contain NaCl as a control example, and NaCl was coated on the diaphragm and applied to the sodium ion battery for performance testing. The battery was assembled in an argon-protected glove box, the test battery model was a 2032 coin battery, and the tested electrolyte was NaClO4 dissolved in DEC and EC, with 5% FEC added. The voltage window of the positive electrode half-cell was set to 2.5-4.2V. It was matched with a commercial hard carbon negative electrode, the hard carbon model was LN-0001, and the full battery voltage window was set to 2-4.2V.

[0047] Test results see Figure 1 to Figure 6 shown.

[0048] Figure 1 The scanning electron microscope photos of commercial NaCl and NaCl / KB obtained by ball milling in Example 1 are as follows: Figure 1 It can be seen that the particle size of commercial NaCl material is about 100 μm, and after mixing with KB and ball milling, the size of NaCl particles is reduced to about 1 μm.

[0049] Figure 2 Figure 1 is the first cycle charge and discharge curve of NaCl and NaCl / KB as sodium ion batteries in Example 1. Figure 2 As shown, at 23mA g -1 At a current density of 200 mAh g, its first charge / discharge specific capacity is 438 / 20 mAh g -1 and 457 / 14mAh g -1 , indicating that the ball-milled NaCl / KB can be completely decomposed during the first cycle of charging, releasing enough Na + .

[0050] Figure 3 The following are the surface scanning electron microscope photos and electron photos of the commercial polyethylene separator and the NaCl loaded commercial polyethylene separator in Example 1. Figure 3 It can be seen that the surface of the modified diaphragm is NaCl particles with a size of about 1 micron.

[0051] Figure 4 The first cycle charge and discharge curves of NVP-PP@%NaCl in Example 1 and NVP in the comparative example as the positive electrode half-cell of the sodium ion battery are shown in FIG. Figure 4 As shown, at a current density of 0.2C (23mA g -1 ), the first cycle charge and discharge capacity of NVP is 116 mAh g -1 and 112mAh g -1 The first cycle charge-discharge capacity of NVP-10%NaCl is 221mAh g -1 and 119mAh g -1 For the NVP half-cell containing PP@NaCl, the first charge specific capacity of the positive electrode is increased by 105 mAh g -1 .

[0052] Figure 5 The first cycle charge and discharge curves of the sodium ion full battery with NVP-PP@NaCl in Example 1 and the comparative example NVP matched with hard carbon (HC) negative electrode. Figure 5 As shown, at a current density of 0.2C (23mA g -1 ) under the condition of NVP matching hard carbon full battery, the first cycle charge and discharge specific capacity is 115 mAh g -1 and 80mAh g -1 The first cycle charge-discharge capacity of NVP-PP@NaCl||HC is 215 mAh g -1 and 115mAh g -1 For NVP||HC full battery containing PP@NaCl, the first discharge capacity of the full battery positive electrode is increased by 35 mAh g -1 , indicating that the decomposition of NaCl provides additional sodium ions, which make up for the solid electrolyte membrane formed by the first discharge of the positive and negative electrodes of the full battery and all the sodium ions consumed by irreversible side reactions. The initial efficiency after sodium replenishment is 100%.

[0053] Figure 6 The sodium ion full battery cycle performance diagram of NVP-PP@NaCl in Example 1 and the comparative example NVP matched with hard carbon (HC) negative electrode. Figure 5 As shown, at a current density of 0.2C (23mA g -1 ), after 50 cycles, the charge specific capacities of NVP||HC and NVP-NVP-PP@NaCl||HC full batteries are 88 mAh g -1 and 58mAh g -1 The capacity retention rates are 76% and 73%, respectively, indicating that the sodium replenishment layer containing PP@NaCl not only has a good sodium replenishment effect, but also does not affect the subsequent cycle stability of the battery.

[0054] Figure 7 The figure is the rate performance diagram of the sodium ion full battery of NVP-PP@NaCl in Example 1 and the comparative example NVP matched with hard carbon (HC) negative electrode. Figure 7 As shown, at a maximum current density of 585 mA g -1 At (5C), the discharge specific capacities of NVP||HC and NVP-PP@NaCl||HC full batteries are 80 mAh g -1 and 60mAh g -1 This indicates that the sodium-replenishing layer containing PP@NaCl has good rate performance.

[0055] It will be easily understood by those skilled in the art that 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 and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for replenishing sodium in the positive electrode of a sodium ion battery, characterized in that: The method comprises the following steps: A sodium supplement slurry is applied on the diaphragm of a sodium ion battery to form a sodium supplement layer; wherein the raw materials of the sodium supplement slurry include a halogen sodium salt, a conductive agent and a binder; the halogen sodium salt is a sodium supplement material, which includes one or more of sodium fluoride, sodium chloride, sodium bromide and sodium iodide.

2. The method for replenishing sodium at the positive electrode of a sodium ion battery according to claim 1, wherein: The halogen sodium salt is sodium chloride.

3. The method for replenishing sodium at the positive electrode of a sodium ion battery according to claim 2, characterized in that: The sodium chloride and the conductive agent are ball-milled at a mass ratio of 9:1 for 6 hours.

4. The method for replenishing sodium at the positive electrode of a sodium ion battery according to claim 1, wherein: The conductive agent includes one or more of Ketjen black, acetylene black, Super P, and carbon nanotubes.

5. The method for replenishing sodium at the positive electrode of a sodium ion battery according to claim 4, characterized in that: The conductive agent is Ketjen black.

6. The method for replenishing sodium at the positive electrode of a sodium ion battery according to claim 1, characterized in that: The mass ratio of the sodium supplement material, the conductive agent and the binder is 8:1:1 and they are evenly stirred to obtain a sodium supplement slurry.

7. The method for replenishing sodium at the positive electrode of a sodium ion battery according to claim 1, characterized in that: The diaphragm is a polyethylene diaphragm or a polypropylene diaphragm.

8. The method for replenishing sodium at the positive electrode of a sodium ion battery according to claim 7, characterized in that: The mass of the NaCl sodium supplement material on the diaphragm is 1% to 50% of the mass of the positive electrode.

9. The method for replenishing sodium at the positive electrode of a sodium ion battery according to claim 8, characterized in that: The mass of the NaCl sodium supplement material on the diaphragm is 20% of the mass of the positive electrode; the binder includes one or more of polytetrafluoroethylene, polytetrafluoroethylene, and sodium alginate.

10. A sodium ion battery, characterized in that: The sodium ion battery comprises a positive electrode, a sodium supplement layer, a separator and a negative electrode arranged from bottom to top, and the sodium supplement layer is obtained by adopting the positive electrode sodium supplement method of a sodium ion battery according to any one of claims 1 to 9.

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