Negative-electrode-free sodium ion battery

Abstract

The invention discloses a negative-electrode-free sodium ion battery, which comprises a positive plate, a negative plate, a diaphragm and an electrolyte, the positive plate comprises a positive current collector, the surface of the positive current collector is coated with a positive active material, a positive conductive agent and a positive binder, the negative plate comprises a negative current collector, the surface of the negative current collector is coated with a carbon nanotube and polyvinylidene fluoride, the negative electrode current collector is a copper foil, the electrolyte comprises sodium salt and an organic solvent, the sodium salt is sodium nitrate, and the organic solvent comprises fluoroethylene carbonate, 1, 3-propane sultone and dimethyl sulfoxide. The negative-electrode-free sodium ion battery has the beneficial effects that the negative electrode does not use active materials and only uses CNT and PVDF, so that more positive electrode active substances can be accommodated in the battery, more electric energy can be stored under the same volume, and the energy density of the negative-electrode-free sodium ion battery is improved. No negative electrode active material is introduced, so that the cost is reduced and the manufacturing process is simplified. And meanwhile, by optimizing an electrolyte system, the growth of sodium dendrites is effectively inhibited, and the cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium-ion batteries, and particularly relates to a sodium-ion battery without a negative electrode. Background Art

[0002] As a potential alternative energy storage technology, sodium-ion batteries have received extensive attention and research in recent years. Compared with lithium-ion batteries, sodium-ion batteries have many advantages, such as rich raw materials, low cost, high safety, etc. These advantages make sodium-ion batteries have broad application prospects in the field of energy storage.

[0003] However, traditional sodium-ion batteries still face many challenges in terms of energy density, cost, and cycle life. Low energy density is one of the key factors restricting the wide application of sodium-ion batteries. Due to the low energy density, the electric energy that can be stored by sodium-ion batteries under the same volume or weight is relatively small, which limits their application in fields such as electric vehicles and portable devices. At the same time, although sodium raw materials are rich, the manufacturing process of traditional sodium-ion batteries is complex, resulting in still high costs. In addition, short cycle life is also an important factor restricting the wide application of sodium-ion batteries. Summary of the Invention

[0004] The purpose of the present invention is to overcome the deficiencies of the prior art and provide a sodium-ion battery without a negative electrode. The negative electrode only uses a conductive agent CNT and a binder PVDF without using active materials, so that more positive active materials can be accommodated inside the battery, thereby storing more electric energy under the same volume and improving the energy density of the sodium-ion battery without a negative electrode. Moreover, the introduction of negative active materials is not required, which can reduce costs and simplify the manufacturing process. At the same time, by optimizing the electrolyte system, the growth of sodium dendrites is effectively inhibited, and the cycle life of the battery is improved.

[0005] The purpose of the present invention is achieved by the following technical measures: A sodium-ion battery without a negative electrode includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet includes a positive electrode current collector, and the surface of the positive electrode current collector is coated with a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode sheet includes a negative electrode current collector, and the surface of the negative electrode current collector is coated with carbon nanotubes and polyvinylidene fluoride. The negative electrode current collector is a copper foil. The electrolyte includes a sodium salt and an organic solvent. The sodium salt is sodium nitrate, and the organic solvent includes fluoroethylene carbonate, 1,3-propane sultone, and dimethyl sulfoxide.

[0006] In some embodiments, the concentration of the sodium nitrate is 0.5 - 1.0 mol·L -1 .

[0007] In some embodiments, the volume ratio of the fluoroethylene carbonate is 4 - 8 vol%, and the volume ratio of the 1,3-propane sultone is 5 - 10 vol%.

[0008] In some embodiments, the volume ratio of fluoroethylene carbonate / 1,3 - propanesultone / dimethyl sulfoxide is 5:5:90.

[0009] In some embodiments, based on the total weight of the coating slurry, the weight percentage of the carbon nanotubes is 1 - 20%.

[0010] In some embodiments, the mass ratio of carbon nanotubes / polyvinylidene fluoride is 9:1.

[0011] In some embodiments, the negative electrode current collector is also coated with N - methylpyrrolidone.

[0012] In some embodiments, the positive electrode active material is sodium fluorophosphate vanadate.

[0013] In some embodiments, the positive electrode conductive agent is carbon nanotubes and Super P.

[0014] In some embodiments, the positive electrode binder is polyvinylidene fluoride.

[0015] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0016] The sodium - ion battery without a negative electrode of the present invention overcomes the restriction of the negative electrode material of traditional sodium - ion batteries on the energy density. The negative electrode of the present invention does not use active materials, such as hard carbon, and only uses a conductive agent CNT and a binder PVDF, enabling more positive electrode active substances to be accommodated inside the battery, so that more electric energy can be stored under the same volume, improving the energy density of the sodium - ion battery without a negative electrode. At the same time, the introduction of negative electrode active materials is avoided, which can reduce costs and simplify the manufacturing process.

[0017] The electrolyte of the present invention uses sodium nitrate as the sodium salt and a mixture of FEC, PS and DMSO as the organic solvent, which not only provides good ion conduction performance for the battery, but also can form a stable and dense (rich in NaF and organic and inorganic components containing S) electrode / electrolyte interface film on the surface of the positive electrode during charge and discharge, not only making the positive electrode interface have a lower impedance, but also further enhancing the stability and cycle life of the battery.

[0018] The present invention uses NVOPF as the positive electrode active material, and is equipped with Super P and CNT as the conductive agent, and PVDF as the binder, making full use of the high - energy - density characteristics of NVOPF, and the excellent electrical conductivity of Super P and CNT, ensuring the high - efficiency performance of the battery during charge and discharge.

[0019] This patent achieves excellent cycle stability through a lithium-free anode design and optimized electrolyte formulation. The lithium-free sodium-ion battery has a cycle life of over 1000 times with low capacity fade, which means that the battery can maintain a high performance level during long-term use, reducing the frequency and cost of battery replacement.

[0020] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 is Figure 1 XPS spectra of the CEI film components on the surface of the NVOPF cathode in Example 1 of the present invention: (a) N 1s and (b) S2p.

[0022] Figure 2 TEM image of the CNT anode after formation in Example 1 of the present invention.

[0023] Figure 3 Cycling performance graph of the lithium-free sodium-ion battery in Example 1 of the present invention.

[0024] Figure 4 EIS graph of the lithium-free sodium-ion coin cell in Example 16 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0025] An embodiment of the present invention provides a lithium-free sodium-ion battery, which includes a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte. The positive electrode sheet includes a positive electrode current collector, and the surface of the positive electrode current collector is coated with a positive electrode active material, a positive electrode conductive agent, and a positive electrode binder. The negative electrode sheet includes a negative electrode current collector, and the surface of the negative electrode current collector is coated with carbon nanotubes (CNT) and polyvinylidene fluoride (PVDF). The negative electrode current collector is a copper foil. The electrolyte includes a sodium salt and an organic solvent. The sodium salt is sodium nitrate, and the organic solvent includes fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), and dimethyl sulfoxide (DMSO).

[0026] In the lithium-free sodium-ion battery of the present invention, no active material such as hard carbon is used for the negative electrode, and only the conductive agent CNT and the binder PVDF are used. This allows more positive electrode active material to be accommodated inside the battery, thereby storing more electrical energy in the same volume and improving the energy density of the lithium-free sodium-ion battery. At the same time, the absence of negative electrode active material can greatly reduce the cost and simplify the manufacturing process.

[0027] During charging of the lithium-free sodium-ion battery of the present invention, Na + is removed from the positive electrode and migrates to the negative electrode. At the same time, NO3 - in the electrolyte undergoes a reduction reaction on the surface of the negative electrode to generate NO2 - and O2- 。O2 - combines with Na + to form Na2O nanoparticles adsorbed on the surface of CNT, while NO2 - dissolves in the electrolyte. During discharge, NO2 - undergoes an oxidation reaction on the surface of the negative electrode, and at the same time, the Na2O particles on the surface of CNT dissolve and release O2 - and Na + , and these ions combine with NO2 - and undergo an oxidation reaction to form NO3 - , while Na + re-migrates to the positive electrode and embeds therein. This charge-discharge mechanism ensures the efficient and stable operation of the battery.

[0028] In some embodiments, the concentration of sodium nitrate is 0.5 - 1.0 mol·L -1 , preferably, the concentration of sodium nitrate is 0.5 mol·L -1 .

[0029] In some embodiments, the volume ratio of FEC is 4 - 8 vol%, and the volume ratio of PS is 5 - 10 vol%. Preferably, the ratio of FEC is 5 vol%, and the ratio of PS is 5 vol%.

[0030] In some embodiments, the volume ratio of FEC / PS / DMSO is 5:5:90.

[0031] In some embodiments, based on the total weight of the coating slurry, the weight ratio of CNT is 1 - 20%.

[0032] In some embodiments, the mass ratio of CNT / PVDF is 9:1.

[0033] In some embodiments, the CNT loading on the negative electrode current collector is 0.2 mg cm -2 .

[0034] In some embodiments, the negative electrode current collector is further coated with N-methylpyrrolidone (NMP). Preferably, based on the total weight of the coating slurry, the weight ratio of NMP is 60%.

[0035] In some embodiments, the positive electrode active material is sodium vanadium fluorophosphate (NVOPF), making full use of the high energy density characteristics of NVOPF.

[0036] In some embodiments, the positive electrode conductive agent is CNT and Super P.

[0037] In some embodiments, the positive electrode binder is PVDF.

[0038] In some embodiments, the weight ratio of NVOPF / Super P / CNT / PVDF in the positive electrode coating slurry is 95:1:1:3.

[0039] To better understand the technical solution provided by the present invention, many specific details are set forth in the following description for a thorough understanding of the present invention. However, the present invention can also be implemented in other ways different from those described herein. Obviously, the embodiments in the specification are only a part of the embodiments of the present invention, rather than all of the embodiments.

[0040] Example 1

[0041] This example discloses a sodium-ion battery without a negative electrode, and its specific preparation method is as follows:

[0042] Positive electrode preparation: The active material is NVOPF, the conductive agent 1 is Super P, the conductive agent 2 is CNT, and the binder is PVDF. The specific addition ratio of NVOPF / Super P / CNT / PVDF is 95:1:1:3. Finally, an appropriate amount of solvent NMP is added, and NMP accounts for 40% of the total weight of the slurry. The slurry is prepared and coated on the surface of carbon-coated aluminum foil to serve as the positive electrode of the sodium-ion battery.

[0043] Negative electrode preparation: No active material is used, only the conductive agent CNT and the binder PVDF are used. The specific addition ratio of CNT / PVDF is 9:1. Finally, an appropriate amount of solvent NMP is added, and NMP accounts for 60% of the total weight of the slurry. The slurry is prepared and coated on the surface of copper foil to serve as the negative electrode of the sodium-ion battery, where the CNT loading is 0.2 mg cm -2 .

[0044] Preparation of the soft-pack battery: The above positive electrode and negative electrode are roll-pressed, cut, and assembled with a separator into a soft-pack battery.

[0045] Electrolyte preparation: Under the protection of an inert gas, 0.5 mol·L -1 NaNO3 is added to an organic solvent with a volume ratio of FEC / PS / DMSO of 5:5:90.

[0046] Filling the soft-pack battery with electrolyte: The electrolyte is added to the soft-pack battery, and the filling coefficient is 3.0 g / Ah.

[0047] High-temperature infiltration: The soft-pack battery after filling is placed at 45 °C for 24 h to ensure that the electrolyte fully infiltrates the battery core.

[0048] Formation: The battery is formed at 25 °C. Formation process: The battery is charged to 4.3 V with a constant current of 0.05C.

[0049] Secondary final sealing: Release the gas in the formed soft-pack battery, and perform secondary sealing on the side of the soft-pack battery.

[0050] Aging: Place the soft-pack battery at 45 °C for 48 h for high-temperature aging, and finally obtain the finished soft-pack battery.

[0051] Cycling test: Place the finished soft-pack battery at 25 °C for long cycling tests. The test voltage range is 2.5 - 4.3 V, and the cycling rate is 0.5 C.

[0052] Figure 1 These are the (a) N 1s and (b) S2p spectra of the CEI film components on the surface of the NVOPF cathode in Example 1 of the present invention. In the electrolyte system of the present invention, a CEI film rich in inorganic components is naturally formed on the surface of the NVOPF cathode, which not only greatly promotes the rapid conduction of Na + at the cathode interface, ensures the structural stability of the NVOPF material, but also effectively suppresses the harmful side reactions between the electrolyte and the NVOPF cathode, slows down the accumulation of interfacial impedance, thereby greatly enhancing the cycling durability and rate response ability of the battery. In addition, this CEI film rich in inorganic components acts as a solid barrier, effectively blocking the intrusion of moisture and harmful impurities, and further extending the service life of the battery.

[0053] Figure 2 This is the TEM image of the CNT anode after formation in Example 1 of the present invention. The Na2O nanoparticles are within the red frame, indicating that during the charging process of the battery, Na + is removed from the cathode and migrates to the anode, while NO3 - in the electrolyte undergoes a reduction reaction on the surface of the anode to form NO2 - and O2 - . O2 - combines with Na + to form Na2O nanoparticles, which are adsorbed on the surface of the CNT.

[0054] Examples 2 - 15 were used to prepare the anode-free battery using the same method as in Example 1, except that the electrolyte formulation ratio was adjusted, and the cycling performance was tested. The details are shown in Table 1 as follows:

[0055] Table 1

[0056]

[0057]

[0058] Figure 3This is the cycling performance graph of the sodium-ion battery without a negative electrode in Example 1 of the present invention. Combining the data in Table 1, it can be seen that the sodium-ion battery without a negative electrode of the present invention exhibits excellent cycling stability. The cycling life of this sodium-ion battery without a negative electrode can reach 1000 times, and the capacity decay is small, which means that the battery can maintain a high performance level during long-term use, reducing the frequency and cost of battery replacement.

[0059] It should be noted that since redox reactions occur at the negative electrode interface, NaNO3 in the electrolyte serves as both an ionic conductor and an active substance. However, in the calculation of the cell capacity, the present invention still uses the number of active sodium ions in the positive electrode material NVOPF as the benchmark for the cell capacity. - In the negative electrode interface, redox reactions occur, so NaNO3 in the electrolyte serves as both an ionic conductor and an active substance. However, in the calculation of the cell capacity, the present invention still uses the number of active sodium ions in the positive electrode material NVOPF as the benchmark for the cell capacity.

[0060] Example 16

[0061] In Example 16, the negative electrode, positive electrode, and electrolyte were prepared using the same method as in Example 1. The battery in Example 16 is a button cell assembled from small round wafers with a diameter of 14 mm for both the positive and negative electrodes.

[0062] Figure 4 This is the EIS graph of the sodium-ion button battery without a negative electrode in Example 16 of the present invention. The impedance of the SEI film is approximately 70 Ω, while the impedance range of a conventional SEI film is about 120 - 200 Ω. It can be seen that the impedance of the SEI film of the button battery of the present invention is much smaller than that of the SEI film in a conventional full-cell button battery.

[0063] In the description of the present invention, it should be understood that terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0064] Although the above embodiments have been shown and described, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions, and variations made by those of ordinary skill in the art to the above embodiments are within the protection scope of the present invention.

Claims

1. A sodium-ion battery without a negative electrode, characterized in that: It includes a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte. The positive electrode sheet includes a positive electrode current collector, and the surface of the positive electrode current collector is coated with a positive electrode active material, a positive electrode conductive agent and a positive electrode binder. The negative electrode sheet includes a negative electrode current collector, and the surface of the negative electrode current collector is coated with carbon nanotubes and polyvinylidene fluoride. The negative electrode current collector is a copper foil. The electrolyte includes a sodium salt and an organic solvent. The sodium salt is sodium nitrate. The organic solvent includes fluoroethylene carbonate, 1,3 - propanesultone and dimethyl sulfoxide.

2. The non-aqueous sodium-ion battery according to claim 1, characterized in that: The concentration of the sodium nitrate is 0.5 - 1.0 mol·L -1 .

3. The non-aqueous sodium-ion battery according to claim 1, characterized in that: The volume ratio of fluoroethylene carbonate is 4 - 8 vol%, and the volume ratio of 1,3 - propanesultone is 5 - 10 vol%.

4. The non-lithium anode sodium ion battery according to claim 1, characterized in that: The volume ratio of fluoroethylene carbonate / 1,3 - propanesultone / dimethyl sulfoxide is 5:5:

90.

5. The non-aqueous sodium-ion battery according to claim 1, characterized in that: Based on the total weight of the coating slurry, the weight ratio of the carbon nanotubes is 1 - 20%.

6. The non-aqueous sodium-ion battery according to claim 1, characterized in that: The mass ratio of carbon nanotubes / polyvinylidene fluoride is 9:

1.

7. The non-aqueous sodium-ion battery according to claim 1, wherein: The negative electrode current collector is also coated with N - methylpyrrolidone.

8. The non-aqueous sodium-ion battery according to claim 1, characterized in that: The positive electrode active material is sodium fluorophosphate vanadate.

9. The non-aqueous sodium-ion battery according to claim 1, characterized in that: The positive electrode conductive agent is carbon nanotubes and Super P.

10. The sodium-ion battery without a negative electrode according to claim 1, wherein: The positive electrode binder is polyvinylidene fluoride.

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