Sodium-ion battery positive electrode and preparation method and application thereof

Abstract

The invention relates to the technical field of sodium batteries, in particular to a sodium ion battery positive electrode and a preparation method and application thereof. A lithium-containing compound or a potassium-containing compound is added into the positive electrode, compared with a sodium-containing compound, due to the fact that the Na < + > / Na standard hydrogen reduction potential is-2.71 V, the Na < + > / Na standard hydrogen reduction potential is-3.04 V higher than the Li < + > / Li standard hydrogen reduction potential, and the K < + > / K standard hydrogen reduction potential is-2.97 V higher than the sodium-containing compound, when the sodium-ion battery is charged to the high voltage of 4.1 V, the lithium-containing compound or the potassium-containing compound of the positive electrode is oxidized and decomposed; a certain amount of lithium ions or potassium ions enter the electrolyte, and meanwhile, a certain amount of sodium ions in the electrolyte participate in a negative electrode reaction to achieve the purpose of supplementing sodium; lithium ions and potassium ions do not generate dendritic crystals in a sodium-ion battery system, and are in an electrolyte in an ion form, so that the SEI of a negative electrode is improved; the sodium-ion battery positive electrode is compatible with the current sodium-ion battery process technology, and can supplement sodium, improve a negative electrode SEI film and improve the cycle stability of the battery at the same time.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium batteries, in particular to a sodium ion battery positive electrode and a preparation method and application thereof. Background Art

[0002] Due to the rapid development of various electronic devices, the demand for high energy density chemical batteries is increasing. Due to the limitation of lithium resources of lithium-ion batteries, sodium-ion batteries have become a strong alternative to lithium-ion batteries due to the higher abundance of sodium in the earth's crust, the moderate energy density of sodium-ion batteries, and excellent performance. However, the existing sodium-ion batteries have the problem of low initial coulombic efficiency of the negative electrode and the continuous attenuation of capacity due to the dissolution of the SEI film. To address this problem, researchers and engineers use the method of sodium supplementation to compensate for the irreversible capacity loss during the initial cycle and improve the quality of the SEI film through electrolyte design.

[0003] At present, the most common processes for sodium replenishment are divided into positive electrode sodium replenishment and negative electrode sodium replenishment. Negative electrode sodium replenishment uses sodium metal to supplement the irreversible capacity loss of the negative electrode during the first cycle, but the high reactivity of sodium will cause safety problems, while the positive electrode sodium replenishment process, adding sodium-containing compounds such as NaNO2 and Na2C2O4 is irreversible during the first charge and discharge, and the excess sodium is used to supplement the sodium loss during the first discharge. Huawei patent CN117810379A discloses a method for adding NamEaJbGcOn to the positive electrode to replenish sodium, which compensates for the irreversible capacity of the negative electrode, but the amount of sodium replenishment is insufficient. In the article Doi:10.1002 / adma.202001419, Guo Yuguo's research group used Na2C2O4 as a sodium replenishment material to effectively compensate for the sodium loss of the negative electrode.

[0004] The overall performance of the battery can be effectively improved through the design of sodium ion battery electrolyte. Patent CN202410844842.9 uses sacrificial additives to improve the high temperature performance of the battery. Patent CN202410300701.0 uses molecular formula C x H y O 3z P z R m The material is used as an additive to inhibit gas production and improve the rate performance and cycle performance of the battery. Article Doi:10.1021 / jacs.3c08224, Chen Shimou's research group used LiTFSI salt as a sacrificial lithium salt to improve the sodium ion SEI film, and the cycle life retention rate exceeded 92% at 2000 cycles at 10C

[0005] However, there is currently no sodium-ion battery design that can simultaneously meet the needs of sodium replenishment and improvement of the negative electrode SEI film. Summary of the invention

[0006] In order to solve the above technical problems existing in the prior art, the present invention provides a sodium ion battery positive electrode and a preparation method and application thereof, which are specifically achieved through the following technical solutions.

[0007] A sodium ion battery positive electrode contains a lithium-containing compound or a potassium-containing compound.

[0008] Furthermore, the lithium-containing compound is LiF, Li2CO3, Li2C4O4, Li2C2O4, Li2C3O5, Li2C5O5, Li2C4O6, Li2C6O6, Li2C3O3, Li5FeO4, Li2NiO2, Li2O, Li2O 2、 Li3N, Li2CO3, Li2N4O2C2 one or more are mixed in any proportion 、 .

[0009] Furthermore, the potassium-containing compound is KF, K2CO3, K2C4O4, K2C2O4, K2C3O5, K2C5O5, K2C4O6, K2C6O6, K2C3O3, K5FeO4, K2NiO2, K2O, K2O 2、 One or more of K3N, K2CO3, and K2N4O2C2 are mixed in any proportion.

[0010] Furthermore, the sodium ion battery positive electrode also contains a positive electrode active material, a binder, and a conductive agent.

[0011] Furthermore, the positive electrode active material is NaxM[M(CN)6]y·zH2O Prussian blue (white) material, sodium vanadium phosphate, sodium pyrophosphate and other polyanion positive electrode materials, layered oxide positive electrode material NaxMO2, wherein M is a transition metal element such as Fe, Co, Ni, Mn, Cr, Ti, etc.

[0012] The method for preparing the positive electrode of a sodium ion battery comprises mixing a positive electrode active material, a binder, a conductive agent and a lithium-containing compound or a potassium-containing compound to prepare the positive electrode.

[0013] Application of the sodium ion battery positive electrode in sodium ion batteries or sodium metal batteries.

[0014] A sodium ion battery comprises the above-mentioned sodium ion battery positive electrode.

[0015] Furthermore, it also includes: electrolyte, diaphragm and negative electrode. It can also include spring pieces and gaskets.

[0016] Furthermore, the electrolyte sodium salt of the electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(oxalatoborate), sodium bis(trifluoromethanesulfonate imide), and sodium bis(fluorosulfonate imide) mixed in any proportion, and the molar concentration of the electrolyte lithium salt in the electrolyte is 0.3 to 10 mol / L; the solvent of the electrolyte is a carbonate solvent or an ether solvent, specifically one or more of cyclic esters ethylene carbonate, propylene carbonate, fluoroethylene carbonate and linear esters dimethyl carbonate, diethyl carbonate, methyl ethyl carbonate, dioxolane, ethylene glycol dimethyl ether, and diethylene glycol dimethyl ether mixed in any proportion.

[0017] Furthermore, the material used for the negative electrode is hard carbon, soft carbon, natural graphite, artificial graphite, metallic sodium, alloy negative electrode material, silicon oxide negative electrode material, silicon carbon material, silicon oxide / carbon material; the diaphragm is a single-layer polypropylene diaphragm.

[0018] Compared with the prior art, the technical effects created by the present invention are embodied in:

[0019] (1) The present invention utilizes the decomposition of positive lithium-containing compounds or potassium-containing compounds to achieve the purpose of supplementing the sodium loss during the formation of the negative electrode and improving the SEI film, and prepares the positive electrode sheet by mixing the positive electrode active material, adhesive, conductive agent and lithium-containing compounds or potassium-containing compounds. This method achieves the purpose of compensating the sodium loss of the negative electrode and improving the negative electrode SEI at the same time through the design of the positive electrode sheet.

[0020] (2) The present invention adopts the method of adding a positive electrode lithium-containing compound or a potassium-containing compound to the positive electrode. Compared with the sodium-containing compound, the Na + / Na standard hydrogen reduction potential -2.71V, higher than Li + / Li standard hydrogen reduction potential -3.04V, higher than K + / K standard hydrogen reduction potential is -2.97V, the positive electrode lithium-containing compound or potassium-containing compound is more easily oxidized and decomposed in the sodium battery. According to Faraday's law, a certain amount of lithium ions or potassium ions enter the electrolyte, and a certain amount of sodium ions in the electrolyte will participate in the negative electrode reaction to achieve the purpose of sodium supplementation; at the same time, lithium ions and potassium ions will not produce dendrites in the sodium ion battery system, and will be in the electrolyte in the form of ions to improve the negative electrode SEI; and the sodium ion battery positive electrode of the present invention is compatible with the current sodium ion battery process technology, and can take into account sodium supplementation, improve the negative electrode SEI film, and enhance the battery cycle stability.

[0021] (3) The present application also uses the positive electrode of the sodium ion battery to prepare a battery, the separator is a polyethylene film and a polypropylene film, the electrolyte is an organic solvent containing sodium salt, and the negative electrode is a carbon-based material or a non-carbon-based material or sodium metal. The design advantage of the sodium ion battery is that when the positive electrode contains lithium compounds or potassium compounds, the sodium salt in the electrolyte decomposes to form the SEI of the negative electrode, which serves the purpose of sodium supplementation. At the same time, the lithium or potassium ions entering the electrolyte help the negative electrode to form a composite SEI film, thereby improving the cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is the charge and discharge curve of the first cycle of lithium oxalate in Example 1.

[0023] Figure 2 NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2|Na and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2(Li2C2O4)|Na full battery cycle performance diagram.

[0024] Figure 3 NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2|Na and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2(Li2C2O4)|Na full battery first cycle charge and discharge curve.

[0025] Figure 4 is NaNi in Example 3 1 / 3 Fe 1 / 3 Mn 1 / 3 O2|HG and NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2(Li2C2O4)|HG full battery cycle performance diagram. DETAILED DESCRIPTION

[0026] The technical solution of the present invention is further defined below in conjunction with specific implementation methods, but the scope of protection required is not limited to the description.

[0027] Example 1

[0028] In an argon glove box with oxygen and water pressures less than 0.1 ppm, electrolyte, lithium salt: 1.0 mol·L -1Lithium hexafluorophosphate; organic solvent: ethylene carbonate and dimethyl carbonate with a volume ratio of 3:7 as the electrolyte, lithium metal as the negative electrode, lithium oxalate as the positive electrode, and a single-layer polypropylene film as the separator. The first cycle charge and discharge curve at 0.1C (1C = 200mAh / g) is as follows: Figure 1 The experimental group's specific capacity reached 275 mAh / g when charged to 4.5 V, which is equivalent to charging to 4.2 V to provide a specific capacity of more than 275 mAh / g in sodium batteries.

[0029] Example 2

[0030] Using NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2(NFM) material was used as the positive electrode material, Li2C2O4 was used as the positive electrode material additive, and NFM pole pieces and NFM(Li2C2O4) pole pieces (Li2C2O4 mass percentage was 5%) were prepared. Sodium metal sheet was used as the negative electrode, and a single-layer polypropylene film was used as the separator. -1 Sodium hexafluorophosphate was dissolved in organic solvents ethylene carbonate and dimethyl carbonate (volume ratio 3 / 7) as electrolyte. After assembling into a battery, the voltage range was 2.0-4.1V, 0.1C (1C = 120mAh / g) for three cycles, and 1C cycled 100 times. Figure 2 and 3 The first coulombic efficiency of NFM pole piece is 91.3%, and the discharge capacity is 135.9mAh / g. The first coulombic efficiency of NFM (Li2C2O4) pole piece is 82%, and the discharge capacity is 137.6mAh / g. The low coulombic efficiency comes from the decomposition of lithium oxalate to provide additional charge capacity. Under 1C, the first discharge capacity of NFM pole piece is 122.1mAh / g, and the discharge capacity after 100 cycles is 92.4mAh / g, the capacity retention rate is 75.6%, and the average coulombic efficiency is 99.1%. The first discharge capacity of NFM (Li2C2O4) pole piece is 123.3mAh / g, and the discharge capacity after 100 cycles is 109.3mAh / g, the capacity retention rate is 88.6%, and the average coulombic efficiency is 99.6%. This shows that after the decomposition of lithium oxalate, lithium enters the electrolyte, which can effectively improve SEI and improve the coulombic efficiency and capacity retention rate of the battery.

[0031] Example 3

[0032] Using NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2(NFM) material was used as the positive electrode material, Li2C2O4 was used as the positive electrode material additive, and NFM pole pieces and NFM(Li2C2O4) pole pieces (Li2C2O4 mass percentage was 5%) were prepared. Hard carbon was used as the negative electrode, and 1.0 mol·L -1 Sodium hexafluorophosphate was dissolved in organic solvents ethylene carbonate and dimethyl carbonate (volume ratio 3 / 7) as electrolyte, and a single-layer polypropylene film was used as a separator. After assembling into a soft-pack battery, the voltage range was 2.0-4.1V, and the full battery cycle performance was as follows Figure 4 ,NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The discharge capacity of O2|HG in the first cycle is 0.975Ah, and the discharge capacity after 70 cycles is 0.896Ah. 1 / 3Fe 1 / 3 Mn 1 / 3 The first cycle discharge capacity of the O2(Li2C2O4)|HG full battery is 1.02Ah, and the discharge capacity after 100 cycles is 0.928Ah.

[0033] Finally, it should be pointed out that the above embodiments are only representative examples of the present invention. Obviously, the technical solution of the present invention is not limited to the above embodiments, and there are many variations. All variations that can be directly derived or associated with the content disclosed by ordinary technicians in this field should be considered as the protection scope of the present invention.

Claims

1. A sodium ion battery positive electrode, characterized in that: It contains a lithium-containing compound or a potassium-containing compound.

2. The sodium ion battery positive electrode according to claim 1, characterized in that The lithium-containing compound is LiF, Li2CO3, Li2C4O4, Li2C2O4, Li2C3O5, Li2C5O5, Li2C4O6, Li2C6O6, Li2C3O3, Li5FeO4, Li2NiO2, Li2O, Li2O 2、 Li3N, Li2CO3, Li2N4O2C2 one or more are mixed in any proportion 、 .

3. The sodium ion battery positive electrode according to claim 1, characterized in that The potassium-containing compound is KF, K2CO3, K2C4O4, K2C2O4, K2C3O5, K2C5O5, K2C4O6, K2C6O6, K2C3O3, K5FeO4, K2NiO2, K2O, K2O 2、 One or more of K3N, K2CO3, and K2N4O2C2 are mixed in any proportion.

4. The sodium ion battery positive electrode according to claim 1, characterized in that It also contains positive electrode active material, binder and conductive agent.

5. The sodium ion battery positive electrode according to claim 4, characterized in that The positive electrode active material is NaxM[M(CN)6]y·zH2O Prussian blue (white) material, sodium vanadium phosphate, sodium pyrophosphate and other polyanion positive electrode materials, layered oxide positive electrode material NaxMO2, wherein M is a transition metal element.

6. The method for preparing the positive electrode of a sodium ion battery according to claim 1, characterized in that: The positive electrode active material, the binder, the conductive agent and the lithium-containing compound or the potassium-containing compound are mixed to prepare the product.

7. Application of the sodium ion battery positive electrode according to claim 1 in sodium ion batteries or sodium metal batteries.

8. A sodium ion battery, characterized in that: A sodium ion battery positive electrode comprising any one of claims 1 to 5.

9. The sodium ion battery according to claim 8, characterized in that: Also includes: Electrolyte, separator and negative electrode.

10. The sodium ion battery according to claim 8, characterized in that: The electrolyte sodium salt of the electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bis(oxalatoborate), sodium bis(trifluoromethanesulfonate imide), and sodium bis(fluorosulfonate imide) mixed in any proportion, and the molar concentration of the electrolyte lithium salt in the electrolyte is 0.3 to 10 mol / L; the solvent of the electrolyte is a carbonate solvent or an ether solvent.

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