Sodium ion battery

Abstract

The invention discloses a sodium ion battery, which comprises a positive electrode, a negative electrode and an electrolyte, the electrolyte comprises a non-aqueous organic solvent, a sodium salt and an additive, the additive comprises a compound A and a compound B, the structure of the compound A is shown as a formula 1, the structure of the compound B is shown as a formula 2: # imgabs0, one of X, Y and Z is sulfonyl, and the other one of X, Y and Z is sulfonyl. The rest two of X, Y and Z are independently selected from sulfonyl or carbonyl respectively, and the rest two of X, Y and Z are not sulfonyl at the same time; r is fluorine-containing alkane containing 1-6 carbon atoms. Wherein the compound A and the compound B can form a uniform, compact and thermodynamically stable SEI film on the surface of the negative electrode through a synergistic effect, and the film also has lower impedance at a low temperature, so that further precipitation of sodium ions can be effectively inhibited. Therefore, the sodium ion battery provided by the invention has relatively good high-temperature storage performance, high-temperature cycle performance and low-temperature performance.

Description

Technical Field

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

[0002] Due to the abundant sodium resources, rechargeable sodium-ion batteries (SIBs) have always been considered as ideal candidates for large-scale energy storage systems. Although sodium-ion batteries have significant theoretical advantages, their electrochemical performance at low temperatures has always been unsatisfactory. Especially when the temperature drops below 0 °C, this is mainly due to the low ion transport efficiency in the electrolyte, the difficulty of cation desolvation at the electrode-electrolyte interface, and the kinetic barriers of electron and ion transport inside the electrode materials, etc.

[0003] Among them, one of the greatest challenges faced by sodium-ion batteries at low temperatures is that the interfacial Na + desolvation process becomes particularly slow and becomes a key factor limiting the charge transfer rate. This not only increases the dominant charge transfer impedance but also causes Na + to accumulate near the SEI layer, thereby triggering the deposition of Na metal. In addition, the ideal SEI film formed by additives in the electrolyte should be electronically insulating and ionically conductive, and should be insoluble and inert relative to the electrolyte to avoid side reactions that cause irreversible capacity loss. Compared with lithium-ion batteries, the solubility of alkyl sodium and alkyl sodium carbonate in the Na-SEI film of sodium-ion batteries is 70-80 times higher than that of inorganic NaF, Na2CO3, etc. in carbonate, and the solubility of inorganic components NaF, Na2CO3 in Na-SEI is 30-40 times higher than that of inorganic components LiF, Li2CO3 in Li-SEI. This means that the Na-SEI film is more easily eroded by the electrolyte, resulting in an increase in the instability of Na-SEI, further exacerbating the side reaction with the electrolyte, and ultimately affecting the high-temperature storage and cycling performance of sodium-ion batteries.

[0004] Therefore, there is an urgent need for a sodium-ion battery to solve the deficiencies of the existing technology. Summary of the Invention

[0005] In view of the above problems, the purpose of the present invention is to provide a sodium-ion battery, which has good high-temperature storage performance, high-temperature cycling performance and low-temperature performance.

[0006] To achieve the above purpose, the present invention provides a sodium-ion battery, including a positive electrode, a negative electrode and an electrolyte. The electrolyte includes a non-aqueous organic solvent, a sodium salt and an additive. The additive includes compound A and compound B. The structure of compound A is shown in formula 1, and the structure of compound B is shown in formula 2:

[0007]

[0008] Among them, one of X, Y, and Z is a sulfonyl group, and the other two of X, Y, and Z are each independently selected from a sulfonyl group or a carbonyl group, and the other two of X, Y, and Z are not both sulfonyl groups at the same time; R is a fluorinated alkane containing 1 to 6 carbon atoms.

[0009] Compared with the prior art, the present invention introduces compound A into the electrolyte of the sodium-ion battery. Compound A contains a cyclic sulfonyl compound, which helps to form compounds such as Na2S and Na2SO3 with good thermodynamic stability at the electrode interface, thereby inhibiting the reaction between the electrode material and the electrolyte and significantly improving the high-temperature storage and high-temperature cycling performance of the sodium-ion battery; in addition, although the cyclic sulfonyl compound contained in compound A can reduce the electron cloud density of C=O in the carbonate solvent through its strong electronegativity, thereby weakening the + binding strength with solvent molecules and promoting the + desolvation process, the wettability of compound A on the surface of the hard carbon negative electrode is poor, resulting in uneven distribution on the electrode surface. This uneven distribution will cause the thickness of the SEI film to be inconsistent, with local regions rich in insulating components and insufficient conductive components, resulting in an increase in the interfacial impedance. Under high-impedance conditions, the + migration rate of Na decreases significantly, leading to the accumulation of charges at the interface and ultimately triggering the sodium deposition phenomenon. Based on this, the present application also introduces compound B, which is a sodium fluorosulfinate compound. Due to the high electronegativity and electron-withdrawing properties of its fluorine atoms, compound B has high solubility and dissociation degree in non-aqueous solvents, improving the uniform distribution of compound A on the surface of the negative electrode. Therefore, compound A and compound B can form a uniform, dense and thermodynamically stable SEI film on the surface of the negative electrode through synergistic effects. This film also has a lower impedance at low temperatures and can effectively inhibit the further precipitation of sodium ions and reduce the "sodium deposition" phenomenon. Therefore, the sodium-ion battery of the present invention has good high-temperature storage performance, high-temperature cycling performance and low-temperature performance.

[0010] Furthermore, the fluorinated alkane containing 1 to 6 carbon atoms in the present invention refers to an alkane derivative with a carbon chain length of 1 to 6 carbon atoms and part or all of the hydrogen atoms replaced by fluorine (F). According to the degree of fluorination, it can be divided into perfluoroalkanes (all hydrogens are replaced by fluorine) and partially fluorinated alkanes (part of the hydrogens are replaced by fluorine). Specifically, the fluorinated alkane containing 1 to 6 carbon atoms can be but not limited to tetrafluoromethane (CF4), difluoromethane (CH2F2), octafluoropropane (C3F8), hexafluoroethane (C2F6).

[0011] Furthermore, the mass percentage of Compound A of the present invention in the electrolyte is 0.1-2%. Specifically, the mass percentage of Compound A in the electrolyte may be, but is not limited to, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%.

[0012] Furthermore, the mass percentage of Compound B of the present invention in the electrolyte is 0.1-1%. Specifically, the mass percentage of Compound B in the electrolyte may be, but is not limited to, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 0.9%, 1.0%.

[0013] Furthermore, Compound A of the present invention is selected from at least one of Compound A1 to Compound A3:

[0014]

[0015] Furthermore, Compound B of the present invention is selected from at least one of Compound B1, Compound B2, and Compound B3:

[0016]

[0017] Furthermore, the sodium salt of the present invention is selected from at least one of NaPF6 (sodium hexafluorophosphate), NaBF4 (sodium tetrafluoroborate), NaClO4 (sodium perchlorate), NaBOB (sodium bis(oxalato)borate), NaODFB (sodium difluoro(oxalato)borate), NaFAP (sodium trifluoromethanesulfonate), NaAsF6 (sodium hexafluoroarsenate), NaSbF6 (sodium hexafluoroantimonate), NaCF3SO3 (sodium trifluoromethanesulfonate), NaN(SO2CF3)2 (sodium bis(trifluoromethylsulfonyl)imide), NaN(SO2C2F5)2 (sodium bis(pentafluoroethylsulfonyl)imide), NaN(SO2C4F9)2 (sodium bis(nonafluorobutylsulfonyl)imide), NaC(SO2CF3)3 (sodium tris(trifluoromethylsulfonyl)methide), NaPF2(C2O4)2 (sodium difluorobis(oxalato)phosphate), NaPF4(C2O4) (sodium tetrafluoro(oxalato)phosphate), NaB(CF3)4 (sodium tetra(trifluoromethyl)borate), and NaBF3(C2F5) (sodium trifluoroethyltrifluoroborate).

[0018] Furthermore, the concentration of the sodium salt of the present invention in the electrolyte is 0.5-2.5 mol / L. Specifically, the concentration of the sodium salt in the electrolyte may be, but is not limited to, 0.5 mol / L, 0.8 mol / L, 1.2 mol / L, 1.6 mol / L, 1.9 mol / L, 2.2 mol / L, 2.5 mol / L.

[0019] Furthermore, the non-aqueous organic solvent of the present invention is selected from carbonate compounds and / or carboxylate compounds.

[0020] Furthermore, the non-aqueous organic solvent of the present invention is selected from at least one of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), γ-butyrolactone (GBL), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), butyl acetate (BA), ethyl propionate (EP), propyl propionate (PP), and butyl propionate (BP).

[0021] Furthermore, the active material of the positive electrode of the present invention is a layered oxide, and the chemical formula of the layered oxide is Na x M 1-y-z Fe y Mn z O2, where M includes at least one of Co, Ni, Cu, Mg, Zn, Al, Sn, Ga, Cr, Sr, V, and Ti, 0 < x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1, and y + z ≤ 1. Of course, the active material of the positive electrode material can also be other materials that can undergo ion deintercalation with sodium ions.

[0022] Furthermore, the active material of the negative electrode of the present invention includes hard carbon materials. Specific Embodiments

[0023] To better illustrate the purpose, technical solution, and beneficial effects of the present invention, the present invention will be further described below in conjunction with specific embodiments. It should be noted that the following described methods are further explanatory descriptions of the present invention and should not be construed as limitations on the present invention.

[0024] Example 1

[0025] (1) Preparation of the electrolyte solution:

[0026] In an argon atmosphere, an electrolyte solution was prepared in a vacuum glove box with a moisture content < 1 ppm. In a dry argon atmosphere glove box, propylene carbonate (PC), diethyl carbonate (DEC), propyl acetate (PA), and butyl acetate (BA) were mixed in a weight ratio of PC:DEC:PA:BA = 5:4:2:1. Then, an additive was added, dissolved, and thoroughly stirred, and then the electrolyte salt NaPF6 was added. After mixing evenly, the electrolyte solution was obtained.

[0027] (2) Preparation of the positive electrode sheet:

[0028] The positive electrode active material NaNi 1 / 3 Mn 1 / 3 Fe 1 / 3O2, binder PVDF, and conductive agent SuperP are mixed evenly in a mass ratio of 95:1:4 to make a sodium-ion battery cathode slurry with a certain viscosity. After coating the mixed slurry on both sides of the aluminum foil, it is dried and roll-pressed to obtain the cathode sheet.

[0029] (3) Preparation of the anode sheet: Hard carbon (Kuraray Type1), conductive agent SuperP, thickener CMC, and binder SBR (styrene-butadiene rubber emulsion) are made into a slurry in a mass ratio of 95:1.5:1.0:2.5, mixed evenly, and the mixed slurry is coated on both sides of the copper foil. After drying and roll-pressing, the anode sheet is obtained.

[0030] (4) Preparation of the sodium-ion battery: The cathode sheet, separator membrane, and anode sheet are made into a square battery cell in a stacked manner, packaged with a polymer, filled with the above-prepared electrolyte, and after processes such as formation and grading, a sodium-ion battery with a capacity of 1000 mAh is made.

[0031] The electrolyte formulations of Examples 1-8 and Comparative Examples 1-3 are shown in Table 1, and the preparation steps of the sodium-ion battery are the same as those of Example 1.

[0032] Table 1 Electrolyte formulations of examples and comparative examples

[0033]

[0034]

[0035] The following test methods are used to test the performance of the sodium-ion batteries prepared in Examples 1-8 and Comparative Examples 1-3, and the test results are shown in Table 2.

[0036] Initial Coulomb efficiency test:

[0037] The sodium-ion battery is placed in a high-temperature and high-pressure formation cabinet, and the battery is subjected to three-step formation at a pressure of 25 °C and 0.28 Mpa (4 PCS batteries). In the first step, a constant current of 0.05C is applied for 60 min, and the charging capacity C1 is recorded. In the second step, a constant current of 0.1C is applied for 120 min, and the charging capacity C2 is recorded. In the third step, a constant current of 0.2C is applied for 240 min, and the charging capacity C3 is recorded. The upper limit voltage is 3.9V. Then, the battery is second-sealed using a rotary sealer. Then, at room temperature, it is charged at a constant current of 0.5C until the voltage reaches 4.25V, then charged at a constant voltage of 4.25V until the current reaches 0.05C, and then discharged at a constant current of 1C until the voltage reaches 2.5V. The initial discharge capacity C0 is recorded, and the initial Coulomb efficiency = C0 / (C1 + C2 + C3) × 100%.

[0038] High-temperature cycle performance test of sodium-ion battery:

[0039] Place the sodium-ion battery in an incubator at 45 °C and let it stand for 30 min to bring the sodium-ion battery to a constant temperature. Charge it at a constant current of 1C until the voltage reaches 4.25V, then charge it at a constant voltage of 4.25V until the current reaches 0.05C, and then discharge it at a constant current of 1C until the voltage reaches 2.0V. Record the initial discharge capacity of the battery, which is one charge-discharge cycle. Repeat this cycle 400 times, record the discharge capacity of the first cycle and the last cycle, and calculate the capacity retention rate according to the following formula.

[0040] Capacity retention rate = (Discharge capacity of the last cycle / Discharge capacity of the first cycle) × 100%

[0041] High-temperature storage performance test of sodium-ion battery:

[0042] Under normal temperature (25 °C) conditions, perform one charge and discharge of 0.5C / 0.5C on the sodium-ion battery (the discharge capacity of the battery is recorded as C0), with the upper limit voltage of 4.25V. Then charge the battery to 4.25V under the condition of constant current and constant voltage of 0.5C, and measure the thickness of the battery (the thickness is recorded as D0); place the battery in an oven at 60 °C for 30 days, take it out and measure the thickness of the battery (the thickness is recorded as D1), and calculate the thickness expansion rate.

[0043] Thickness expansion rate = (D1 / D0) × 100%

[0044] Low-temperature discharge test:

[0045] Under normal temperature (25 °C) conditions, perform one charge and discharge of 0.5C / 0.5C on the sodium-ion battery (the discharge capacity of the battery is recorded as C0), with the upper limit voltage of 4.25V; then place the battery in a low-temperature chamber at -10 °C, and then discharge it at a constant current of 0.1C until the voltage reaches 2.0V. Record the initial discharge capacity C1 of the battery, which is one charge-discharge cycle. Continue to perform one charge and discharge of 0.5C / 0.5C on the sodium-ion battery under normal temperature (25 °C) conditions (the discharge capacity of the battery is recorded as C2). After 10 cycles, disassemble the battery and observe the sodium deposition on the electrode.

[0046] Capacity recovery rate = (C2 / C0) × 100%

[0047] Table 2 Performance test results of sodium-ion batteries in examples and comparative examples

[0048]

[0049] As can be seen from Table 2, compared with Comparative Examples 1 to 3, the sodium-ion batteries of Examples 1 to 8 have better high-temperature cycle performance, high-temperature storage performance, and low-temperature discharge performance. This is because the sodium-ion batteries of Examples 1 to 8 contain Compound A and Compound B. Compound A contains a cyclic sulfonyl compound, which helps to form compounds such as Na2S and Na2SO3 with better thermodynamic stability at the electrode interface, thereby inhibiting the reaction between the electrode material and the electrolyte and significantly improving the high-temperature storage and high-temperature cycle performance of the sodium-ion battery. At the same time, due to the high electronegativity and electron-withdrawing properties of the fluorine atoms in Compound B, it has a high solubility and dissociation degree in non-aqueous solvents, improving the distribution uniformity of Compound A on the negative electrode surface. Therefore, Compound A and Compound B can form a uniform, dense, and thermodynamically stable SEI film on the negative electrode surface through synergistic effects. This film also has a lower impedance at low temperatures and can effectively inhibit the further precipitation of sodium ions, reducing the "sodium precipitation" phenomenon. Therefore, the sodium-ion battery of the present invention has good high-temperature storage performance, high-temperature cycle performance, and low-temperature performance.

[0050] Comparing Example 2 with Comparative Examples 1 to 2, it can be seen that Compound A and Compound B can form a uniform, dense, and thermodynamically stable SEI film on the negative electrode surface through synergistic effects. This film also has a lower impedance at low temperatures. In short, removing either Compound A or Compound B cannot ensure that the sodium-ion battery has good high-temperature storage performance, high-temperature cycle performance, and low-temperature performance at the same time.

[0051] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the present invention and not to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, it is not limited to only the examples listed. Those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A sodium-ion battery, comprising a positive electrode, a negative electrode and an electrolyte, wherein the electrolyte comprises a non-aqueous organic solvent, a sodium salt and an additive, characterized in that, The additive includes compound A and compound B. The structure of compound A is shown in Formula 1, and the structure of compound B is shown in Formula 2: Among them, one of X, Y, and Z is a sulfonyl group, and the other two of X, Y, and Z are each independently selected from a sulfonyl group or a carbonyl group, and the other two of X, Y, and Z are not both sulfonyl groups at the same time; R is a fluoroalkane containing 1 to 6 carbon atoms.

2. The sodium-ion battery according to claim 1, characterized in that, The mass percentage of compound A in the electrolyte is 0.1 to 2%.

3. The sodium ion battery according to claim 1, characterized in that, The mass percentage of compound B in the electrolyte is 0.1 to 1%.

4. The sodium ion battery according to claim 1, characterized in that, Compound A is selected from at least one of compound A1 to compound A3:

5. The sodium-ion battery according to claim 1, characterized in that, Compound B is selected from at least one of compound B1, compound B2, and compound B3:

6. The sodium ion battery according to claim 1, wherein The sodium salt is selected from at least one of NaPF6, NaBF4, NaClO4, NaBOB, NaODFB, NaFAP, NaAsF6, NaSbF6, NaCF3SO3, NaN(SO2CF3)2, NaN(SO2C2F5)2, NaN(SO2C4F9)2, NaC(SO2CF3)3, NaPF2(C2O4)2, NaPF4(C2O4), NaB(CF3)4, and NaBF3(C2F5).

7. The sodium ion battery according to claim 1, wherein, The concentration of the sodium salt in the electrolyte is 0.5 to 2.5 mol / L.

8. The sodium ion battery according to claim 1, wherein, The non-aqueous organic solvent is selected from carbonate compounds and / or carboxylate compounds.

9. The sodium-ion battery according to claim 8, wherein The non-aqueous organic solvent is selected from at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, γ-butyrolactone, methyl acetate, ethyl acetate, propyl acetate, butyl acetate, ethyl propionate, propyl propionate, and butyl propionate.

10. The sodium-ion battery according to claim 1, wherein, The active material of the negative electrode includes hard carbon material, and the active material of the positive electrode is a layered oxide. The chemical formula of the layered oxide is Na x M 1-y-z Fe y Mn z O2, where M includes at least one of Co, Ni, Cu, Mg, Zn, Al, Sn, Ga, Cr, Sr, V, and Ti, 0 < x ≤ 1, 0 ≤ y < 1, 0 ≤ z < 1, and y + z ≤ 1.

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