A negative electrode for a sodium-ion battery and a sodium-ion battery

Abstract

The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a negative electrode of a sodium-ion battery and a sodium-ion battery. The negative electrode of the sodium-ion battery of the present invention comprises a negative current collector and a negative active material layer coated on the negative current collector. The negative active material layer comprises a main material for the negative electrode of a sodium-ion battery, a conductive agent, a binder, and a weakly basic alkali metal salt; the mass ratio of the main material for the negative electrode of a sodium-ion battery, the conductive agent, the binder, and the weakly basic alkali metal salt is 90-98:1-9:1-9:0.5-2. The present invention adds a weakly basic alkali metal salt to the negative electrode of the battery. This alkali metal salt can wrap the negative particles in the slurry, reduce the contact area between the electrolyte and the negative particles, thereby reducing the side reaction between the negative electrode material of the sodium-ion battery and the electrolyte, reducing the generation of gas, and further improving the cycle performance and high-temperature performance of the sodium-ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium-ion batteries, and particularly relates to a negative electrode of a sodium-ion battery and a sodium-ion battery. Background Art

[0002] Lithium-ion batteries are particularly favored due to their high energy density and compliance with environmental requirements. However, the lithium element necessary for lithium-ion batteries is not abundant in the earth's crust. With the rapid development of the lithium-ion battery industry, lithium has become a bottleneck in the development of lithium-ion batteries. How to solve the lithium source has become the biggest problem in this industry. Subsequently, the raw materials of the lithium-ion battery industry have risen sharply, creating huge pressure on the entire industrial chain.

[0003] The crustal abundance of sodium is more than 1300 times that of lithium, and it is cheap. Moreover, sodium is in the same main group as lithium, making it the best material to replace lithium. Sodium-ion batteries have also become a focus of the industry. Sodium-ion batteries have excellent cycling performance and a wide temperature window. However, due to the high reactivity of sodium, it is extremely easy to reduce the electrolyte solvent on the surface of the negative electrode, resulting in gas generation in current sodium-ion batteries. Gas generation will cause continuous deterioration of battery performance and ultimately lead to battery failure. Therefore, gas generation is a problem that must be solved for sodium-ion batteries. Many technologies in the industry have improved the cathode material and electrolyte. For example, Chinese invention patent CN109786827A discloses an electrolyte additive for a sodium-ion battery, an electrolyte, and a sodium-ion battery. The electrolyte additive for the sodium-ion battery can form a stable and dense interfacial film on the surfaces of the positive and negative electrodes, reduce the side reactions between the positive and negative electrodes and the electrolyte, and reduce gas generation.

[0004] However, as an important part and the main gas generation source of sodium-ion batteries, the negative electrode should also be an important way to control gas in sodium-ion batteries. There is currently no report on improving the negative electrode material of sodium-ion batteries to reduce gas generation in sodium-ion batteries. Therefore, it is of great significance to develop a negative electrode material for sodium-ion batteries that can reduce gas generation. Summary of the Invention

[0005] The purpose of the present invention is to provide a negative electrode of a sodium-ion battery, and the negative electrode material can reduce gas generation during the use of the sodium-ion battery, and solve the problem of gas generation during the cyclic use of existing sodium-ion batteries, which leads to deterioration of battery performance.

[0006] The second purpose of the present invention is to provide a sodium-ion battery including the above-mentioned negative electrode of the sodium-ion battery, and the sodium-ion battery has good cycling performance and high-temperature performance.

[0007] In order to achieve the above purposes, the technical solutions adopted by the present invention are as follows:

[0008] A negative electrode of a sodium-ion battery includes a negative current collector and a negative active material layer coated on the negative current collector. The negative active material layer includes a main material for the negative electrode of a sodium-ion battery, a conductive agent, a binder, and a weakly basic alkali metal salt. The mass ratio of the main material for the negative electrode of a sodium-ion battery, the conductive agent, the binder, and the weakly basic alkali metal salt is 90-98:1-9:1-9:0.5-2.

[0009] The important reasons for gas generation in sodium-ion batteries at high temperatures and during cycling are the insufficient formation of the SEI film on the negative electrode, which leads to continuous reduction reactions of solvents, etc. on the negative electrode surface, resulting in gas generation and thus deterioration of battery performance. In the present invention, an alkali metal salt is added to the negative electrode slurry. The alkali metal salt added during the processing of the negative electrode of the battery can wrap the negative electrode particles in the slurry. Since the partially unformed SEI film is pre-covered with an alkali metal salt layer, the contact area between the electrolyte and the negative electrode particles is reduced, compensating for the deficiency in forming the SEI film during formation, reducing gas generation, and being beneficial to improving battery performance.

[0010] Preferably, the main material for the negative electrode of the sodium-ion battery is hard carbon. The hard carbon is one or more of biomass hard carbon, organic matter hard carbon, and coal-based hard carbon.

[0011] Preferably, the weakly basic alkali metal salt is one or more of sodium salts, lithium salts, and potassium salts.

[0012] Preferably, the lithium salt is one or more of Li2CO3, Li2C2O4, and ROLi, the sodium salt is one or more of Na2CO3, Na2C2O4, Na3PO4, RONa, and NaF, and the potassium salt is one or more of K4SiO4 and ROK, where R is an alkyl group.

[0013] Preferably, the weakly basic alkali metal salt uses a sodium salt, and the sodium salt is preferably NaF or Na3PO4 or Na2CO3.

[0014] Preferably, the binder is one or more of styrene-butadiene rubber, acrylonitrile, acrylate, LA133, PVDF, and CMC; the conductive agent is one or more of conductive graphite, carbon nanotubes, acetylene black, and SP.

[0015] Preferably, the negative current collector is aluminum foil or copper foil.

[0016] A sodium-ion battery includes a negative electrode, a positive electrode, a separator, an electrolyte, and a housing; the negative electrode is the negative electrode of the sodium-ion battery as described above.

[0017] The sodium-ion battery of the present invention uses the negative electrode of the sodium-ion battery as described above. When the sodium-ion battery is used cyclically, gas generation can be reduced, and it has good battery cycling performance and high-temperature performance.

[0018] Preferably, the positive electrode of the sodium-ion battery includes a positive current collector and a positive active material layer coated on the positive current collector. The positive active material layer includes a main material for the positive electrode of the sodium-ion battery, a conductive agent, and a binder. The mass ratio of the main material for the positive electrode of the sodium-ion battery, the conductive agent, and the binder is 93-98:1-5:2-5.

[0019] Preferably, the main material of the positive electrode is a layered oxide Na x MO2, Prussian blue structure Na x MM’(CN)6, or one or more of them; in the Na x MO2, M is at least one of Ni, Co, Mn, Fe, Cu, Mg, Zr, Al, Ti, V, and 0 < x ≤ 1; in the Na x MM’(CN)6, M is at least one of Mn and Fe, M’ is at least one of Fe, Co, Mn, Ni, Cu, V, and Ti, and x ≥ 1.

[0020] Preferably, the positive current collector is aluminum foil or copper foil.

[0021] Preferably, the separator is a PP film, a PE film, or a composite film of PP and PE.

[0022] Preferably, the electrolyte solute is NaPF6, and the solvent is one or more of carbonates and ethers; the carbonate is one or more of EC, PC, DMC, DEC, and EMC; the ether is DME.

[0023] Preferably, the housing material is one of an aluminum-plastic film, a square aluminum case, a square steel case, a cylindrical steel case, a cylindrical aluminum case, and a plastic case. Description of the Drawings

[0024] Figure 1 It is a schematic diagram of reducing gas generation in the negative electrode of the sodium-ion battery of the present invention;

[0025] Figure 2 It is the test of the volume growth rate of the sodium-ion battery in Example 3 before and after baking;

[0026] Figure 3 It is the test of the volume growth rate of the sodium-ion battery in Example 4 before and after baking;

[0027] Figure 4 It is the test of the volume growth rate of the sodium-ion battery in Comparative Example 2 before and after baking. Detailed Embodiments

[0028] The technical solutions of the present invention will be further described below in conjunction with the drawings and specific embodiments, but the embodiments of the present invention are not limited thereto.

[0029] I. Specific embodiments of the negative electrode of the sodium-ion battery of the present invention are as follows:

[0030] Example 1

[0031] The negative electrode of the sodium-ion battery in this example includes a negative current collector and a negative active material layer coated on the negative current collector. The negative active material layer includes the main material of the sodium-ion battery negative electrode, a conductive agent, a binder, and a weakly basic alkali metal salt. The negative main material hard carbon (purchased from Kureha, Japan, Type2), conductive agent SP, binder LA133, and weakly basic alkali metal salt NaF are dispersed in water as a solvent according to a mass ratio of 94.5:1:4:0.5. After mixing and stirring evenly under the action of a double planetary mixer, the solid content is adjusted to make the slurry meet the viscosity requirements for coating (2000 - 4000 mPa·s, controlled at 3000 mPa·s in this example) and the solid content (40 - 60%, controlled at 60% in this example). After defoaming, demagnetization, and filtration, a qualified negative electrode slurry is obtained. The slurry is transferred to a coater through an automatic feeding system and coated on aluminum foil. After coating, it is rolled, slit, and die-cut to produce a negative electrode sheet.

[0032] Example 2

[0033] The negative electrode of the sodium-ion battery in this example is different from that in Example 1 in that the weakly basic alkali metal salt in this example is Na2CO3.

[0034] II. Specific embodiments of the sodium-ion battery of the present invention are as follows:

[0035] Example 3

[0036] 1) Negative electrode of the sodium-ion battery: The negative electrode of the sodium-ion battery in this example is the negative electrode of the sodium-ion battery in Example 1.

[0037] 2) Positive electrode of the sodium-ion battery: The positive electrode of the sodium-ion battery includes a positive current collector and a positive active material layer coated on the positive current collector. The positive main material NaNi 0.3 Mn 0.4 Fe 0.2 Cu 0.1O2, binder PVDF, conductive agent 1 (SP), and conductive agent 2 (KS6) are dispersed into NMP organic solvent in a ratio of 94:3:1:2. After being mixed and stirred evenly under the action of a double planetary mixer, the solid content is adjusted to make the slurry meet the viscosity requirements for coating (2000 - 10000 mPa·s, controlled at 6000 mPa·s in this example) and solid content (60 - 80%, controlled at 70% in this example). After defoaming, demagnetization, and filtration, qualified positive electrode slurry is obtained. The slurry is transferred to a coater through an automatic feeding system and coated onto aluminum foil. After coating, it is roll-pressed, slit, and die-cut to produce positive electrode sheets.

[0038] 3) The separator is a 25-μm-thick PP separator, and the electrolyte is an organic system with NaPF6 as the solute. The concentration of NaPF6 is 1 mol / L. -1 , and the organic system is a mixed system of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC). The volume ratio of EC, EMC, and DEC is 1:1:1.

[0039] 4) Sodium-ion battery: The positive electrode sheet, negative electrode sheet, and separator are stacked into an electric core on a stacker; after the electric core is welded with a pole handle, it is installed into a shell made of aluminum-plastic film and heat-sealed to form a semi-finished electric core. After baking the semi-finished electric core, it is made into a 5-Ah liquid soft-packaged sodium-ion battery through liquid injection, formation, and grading.

[0040] Example 4

[0041] The sodium-ion battery in this example is different from that in Example 3 in that the negative electrode of the sodium-ion battery in this example is the negative electrode of the sodium-ion battery in Example 2.

[0042] III. Comparative Examples of the Negative Electrode of Sodium-Ion Batteries

[0043] Comparative Example 1

[0044] The negative electrode of the sodium-ion battery in this comparative example is different from that in Example 1 in that the negative active material layer does not include a weakly basic alkali metal salt, and the mass ratio of the main negative electrode material hard carbon, conductive agent SP, and binder LA133 is 95:1:4.

[0045] IV. Comparative Examples of Sodium-Ion Batteries

[0046] Comparative Example 2

[0047] The sodium-ion battery in this comparative example is different from that in Example 3 in that the negative electrode of the sodium-ion battery in this comparative example is the negative electrode of the sodium-ion battery in Comparative Example 1.

[0048] V. Experimental Examples

[0049] After fully charging the sodium-ion batteries in Examples 3-4 and Comparative Example 2, they were placed in an oven at 55 °C for 7 days, and the volume change of the batteries before and after placement was measured. The results are as Figure 2-4 shown in Table 1.

[0050] Table 1 Volume change of sodium-ion batteries before and after baking

[0051] <![CDATA[Volume before baking, cm 3 > <![CDATA[Volume after baking, cm 3 > Volume growth rate, % Example 3 71.71 73.15 2.08 Example 4 70.71 73.37 2.66 Comparative Example 2 71.12 80.10 12.61

[0052] As can be seen from Figures 2 to 4 Table 1, after high-temperature baking, the volume growth rate of the sodium-ion batteries in Examples 3-4 of the present invention is much smaller than that of the sodium-ion batteries in Comparative Example 2 after high-temperature baking, indicating that the sodium-ion batteries of the present invention have less gas evolution at high temperatures and good battery performance. The principle of reducing gas production in the negative electrode of the sodium-ion battery of the present invention is as Figure 1 shown. By adding an alkali metal salt during the processing of the negative electrode of the battery, the alkali metal salt can wrap the negative electrode particles in the slurry. Since the part where the SEI film is not fully formed is covered with an alkali metal salt layer in advance, the contact area between the electrolyte and the negative electrode particles is reduced, making up for the deficiency in forming the SEI film during formation, reducing gas generation, and being beneficial to improving battery performance.

[0053] The above is only a preferred embodiment of the present invention and does not impose any formal limitations on the technical solutions of the present invention. Any simple modifications, equivalent changes, and decorations made to the above embodiments based on the technical essence of the present invention all fall within the protection scope of the present invention.

Claims

1. A negative electrode of a sodium-ion battery, characterized in that, It includes a negative current collector and a negative active material layer coated on the negative current collector. The negative active material layer includes a main material for the negative electrode of a sodium-ion battery, a conductive agent, a binder, and a weakly basic alkali metal salt; the mass ratio of the main material for the negative electrode of the sodium-ion battery, the conductive agent, the binder, and the weakly basic alkali metal salt is 90-98:1-9:1-9:0.5-2; the weakly basic alkali metal salt is NaF.

2. The negative electrode of the sodium-ion battery according to claim 1, characterized in that The main material for the negative electrode of the sodium-ion battery is hard carbon.

3. The negative electrode of the sodium-ion battery according to claim 1, characterized in that The binder is one or more of styrene-butadiene rubber, acrylonitrile, acrylate, LA133, PVDF, and CMC; the conductive agent is one or more of conductive graphite, carbon nanotubes, acetylene black, and SP.

4. The negative electrode of the sodium-ion battery according to claim 1, characterized in that, The negative current collector is aluminum foil or copper foil.

5. A sodium-ion battery, characterized in that, It includes a negative electrode, a positive electrode, a separator, an electrolyte, and a housing; the negative electrode is the negative electrode of the sodium-ion battery according to any one of claims 1-4.

6. The sodium ion battery according to claim 5, wherein, The main material of the positive electrode is a layered oxide Na x MO2, Prussian blue structure Na x MM’(CN)6, or one or more of them; the Na x In MO2, M is at least one of Ni, Co, Mn, Fe, Cu, Mg, Zr, Al, Ti, V, and 0 < x ≤ 1; the Na x In MM’(CN)6, M is at least one of Mn, Fe, and M’ is at least one of Fe, Co, Mn, Ni, Cu, V, Ti, and x ≥ 1.

7. The sodium ion battery according to claim 5, characterized in that, The separator is a PP film, a PE film, or a composite film of PP and PE.

8. The sodium ion battery according to claim 5, wherein, The solute of the electrolyte is NaPF6, and the solvent is one or a mixture of several of carbonates and ethers; the carbonate is one or more of EC, PC, DMC, DEC, and EMC; the ether is DME.

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