A sodium-ion battery

Abstract

The application discloses a kind of sodium ion battery, including positive pole, negative pole and electrolyte, the negative pole includes negative pole active material, the negative pole active material includes carbon material, the crystallinity of the carbon material is X%;The electrolyte includes electrolyte salt, solvent and additive, the mass percentage content of the additive in the electrolyte is Y%;Wherein, X and Y satisfy the relationship formula 25≤X*Y≤120.The sodium ion battery of the application controls sodium ion battery negative pole sodium storage site and interface reaction by the crystallinity of negative pole carbon material and electrolyte additive content, when the crystallinity X% of carbon material and the mass percentage content Y% of additive in electrolyte satisfy the relationship formula 25≤X*Y≤120, the initial efficiency and capacity performance of sodium ion battery can be simultaneously improved.

Description

Technical Field

[0001] This invention relates to the field of energy storage device technology, and more specifically, to a sodium-ion battery. Background Technology

[0002] Lithium-ion batteries use graphite as the negative electrode. Graphite has a regular structure, high crystallinity, and high coulombic efficiency. Unlike commercial lithium-ion batteries, sodium-ion batteries use carbon materials containing some amorphous regions as the negative electrode. The lower coulombic efficiency of sodium-ion batteries is mainly due to the reaction between the negative electrode and the electrolyte, forming an unstable interfacial film that consumes a limited sodium source. The electrolyte reacts on the surface of the carbon material to form an interfacial film. The formation of this film depends on the structure of the carbon material and the electrolyte, significantly affecting the battery's coulombic efficiency and capacity. Therefore, to improve the coulombic efficiency and capacity of sodium-ion batteries, in-depth research on sodium-ion batteries and improving the quality of the interfacial film are necessary. Summary of the Invention

[0003] This invention is based on the inventor's discovery and understanding of the following facts and problems: Currently, sodium-ion batteries suffer from low coulombic efficiency and capacity. Therefore, it is necessary to improve sodium-ion batteries to increase their coulombic efficiency and capacity.

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. To this end, this invention provides a sodium-ion battery, comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative electrode active material, which is a carbon material, and the crystallinity of the carbon material is X%. The electrolyte comprises an electrolyte salt, a solvent, and an additive, and the mass percentage of the additive in the electrolyte is Y%. Wherein, X and Y satisfy the relationship 25 ≤ X * Y ≤ 120.

[0005] Optional, 50≤X*Y≤110.

[0006] Optionally, the crystallinity X% of the carbon material satisfies 15≤X≤50; preferably, 18≤X≤35.

[0007] Optionally, the mass percentage Y% of the additive in the electrolyte satisfies 0.1≤Y≤10; preferably, 2≤Y≤8.

[0008] Optionally, the additive includes cyclic compounds.

[0009] Optionally, the additive includes at least one of fluorocarbonate compounds, cyclic sulfonate compounds, cyclic sulfate compounds, and cyclic borate compounds.

[0010] Optionally, the additive includes at least one of fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, ethylene sulfate, and sodium difluorooxalate borate.

[0011] Optionally, the solvent includes at least one of C3-C8 carbonates, C2-C6 carboxylic esters, and C4-C10 ethers.

[0012] Optionally, the electrolyte salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethane)sulfonamide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, and sodium perchlorate.

[0013] Optionally, the positive electrode includes a positive electrode active material, which is selected from at least one of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds.

[0014] In the sodium-ion battery provided by this invention, during the electrochemical process, an interfacial film forms at the interface between the negative electrode carbon material and the electrolyte. Electrolyte consumption leads to capacity loss and reduces coulombic efficiency. Since the amorphous regions of the carbon material have more defect sites than the crystalline regions, the probability of side reactions at the interface between the electrolyte and the carbon material is higher in the amorphous regions. The crystallinity of the carbon material affects sodium storage behavior, thus affecting battery capacity; excessively high crystallinity adversely affects sodium storage, reducing capacity. For low-crystallinity carbon materials with more amorphous regions, adding a high content of additives can adjust the interfacial reaction between the negative electrode and the electrolyte, improving the battery's coulombic efficiency.

[0015] Experiments have shown that the crystallinity of the negative electrode carbon material and the content of electrolyte additives can regulate the sodium storage sites and interfacial reactions in sodium-ion batteries. When the crystallinity X% and the mass percentage of additives Y% in the electrolyte satisfy the relationship 25≤X*Y≤120, both the initial efficiency and capacity performance of the sodium-ion battery can be improved. When X*Y<25, low crystallinity leads to intensified interfacial reactions in the amorphous regions of the electrolyte, and low additive content cannot effectively suppress these reactions, resulting in a decrease in the battery's initial efficiency. When X*Y>120, high crystallinity leads to lower negative electrode capacity, and high additive content increases interfacial film impedance, further reducing battery capacity performance. Detailed Implementation

[0016] The embodiments of the present invention are described in detail below. These embodiments are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0017] In this embodiment of the invention, the crystallinity of carbon material refers to the ratio of the area of ​​the C(002) crystal plane diffraction peak in the XRD of carbon material to the sum of the areas of the amorphous peak and the C(002) crystal plane diffraction peak.

[0018] An embodiment of the present invention provides a sodium-ion battery comprising a positive electrode, a negative electrode, and an electrolyte. The negative electrode comprises a negative electrode active material, which is a carbon material, and the crystallinity of the carbon material is X%. The electrolyte comprises an electrolyte salt, a solvent, and an additive, and the mass percentage of the additive in the electrolyte is Y%. Wherein, X and Y satisfy the relationship 25≤X*Y≤120.

[0019] In the electrochemical process, an interfacial film forms at the interface between the negative electrode carbon material and the electrolyte. Electrolyte consumption leads to capacity loss and reduces coulombic efficiency. Since the amorphous regions of carbon materials have more defect sites than the crystalline regions, the probability of side reactions at the interface between the electrolyte and carbon material is higher in the amorphous regions. The crystallinity of the carbon material affects sodium storage behavior, thus affecting battery capacity; excessively high crystallinity negatively impacts sodium storage and reduces capacity. For low-crystallinity carbon materials with more amorphous regions, adding high amounts of additives can regulate the interfacial reaction between the negative electrode and the electrolyte, thereby improving battery coulombic efficiency.

[0020] Experiments have shown that the crystallinity of the negative electrode carbon material and the content of electrolyte additives can regulate the sodium storage sites and interfacial reactions in sodium-ion batteries. When the crystallinity X% and the mass percentage of additives Y% in the electrolyte satisfy the relationship 25≤X*Y≤120, both the initial efficiency and capacity performance of the sodium-ion battery can be improved. When X*Y<25, low crystallinity leads to intensified interfacial reactions in the amorphous regions of the electrolyte, and low additive content cannot effectively suppress these reactions, resulting in a decrease in the battery's initial efficiency. When X*Y>120, high crystallinity leads to lower negative electrode capacity, and high additive content increases interfacial film impedance, further reducing battery capacity performance.

[0021] In specific embodiments, X*Y can be 25, 30, 35, 40, 45, 50, 64, 70, 90, 100, 104.5, 105, 110, 115, 120.

[0022] In a preferred embodiment, 50 ≤ X*Y ≤ 110.

[0023] In some embodiments, the crystallinity X% of the carbon material satisfies 15 ≤ X ≤ 50.

[0024] In a specific embodiment, X can be 15, 16, 17, 18, 19, 19.5, 20, 22, 25, 30, 35, 40, 45, 50.

[0025] In a preferred embodiment, 18 ≤ X ≤ 35.

[0026] In this invention, the crystallinity of the carbon material is closely related to the heating rate, carbonization temperature, and holding time during the carbon material preparation process. For example, increasing the carbonization temperature increases the crystallinity of the carbon material; decreasing the heating rate increases the crystallinity of the carbon material. By controlling conditions such as the heating rate and carbonization temperature, the crystallinity of the carbon material can be controlled. The crystallinity of the carbon material affects sodium storage behavior, thereby affecting battery capacity. In the amorphous regions of the carbon material, the probability of side reactions at the contact surface between the electrolyte and the carbon material is relatively high. Optimizing the crystallinity of the carbon material is beneficial for further improving the initial efficiency and capacity of sodium-ion batteries.

[0027] In some embodiments, the mass percentage Y% of the additive in the electrolyte satisfies 0.1 ≤ Y ≤ 10.

[0028] In specific embodiments, Y can be 0.1, 0.2, 0.5, 1, 1.5, 2, 2.5, 3, 4, 5, 5.5, 6, 7, 8, 9, 10.

[0029] In a preferred embodiment, 2≤Y≤8.

[0030] In this embodiment of the invention, by optimizing the amount of additives added, the interfacial reaction between the negative electrode and the electrolyte is adjusted, which is beneficial to further improve the coulombic efficiency and capacity of sodium-ion batteries.

[0031] In some embodiments, the additive comprises a cyclic compound.

[0032] In specific embodiments, the additive includes at least one of fluorocarbonate compounds, cyclic sulfonate compounds, cyclic sulfate compounds, and cyclic borate compounds.

[0033] In a preferred embodiment, the additive includes at least one of fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, ethylene sulfate, and sodium difluorooxalate borate.

[0034] In a more preferred embodiment, the additive includes two of the following: fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, ethylene sulfate, and sodium difluorooxalate borate, with a mass ratio of the two additives being 3:2 to 2:3.

[0035] In this embodiment of the invention, the preferred additive is a cyclic compound, more preferably ethylene sulfate and sodium difluorooxalate borate, etc. Simultaneously, the crystallinity X% and the mass fraction Y% of the additive in the electrolyte satisfy the relationship 25≤X*Y≤120, which can improve the initial efficiency and capacity performance of sodium-ion batteries. Cyclic compounds can preferentially react with solvents and electrolyte salts, thereby participating in the reaction at the negative electrode interface to form a sodium-containing interfacial component, improving the interface density and facilitating the reversible insertion / extraction of sodium ions, thus improving the battery's coulombic efficiency and capacity. The preferred cyclic compound additive contains heteroatoms, which can regulate the interaction between interfacial carbonate or carbonate and heteroatom-containing salt components, further improving interfacial stability and enhancing battery performance.

[0036] In some embodiments, the solvent includes at least one of carbonates having 3 to 8 carbon atoms, carboxylic acid esters having 2 to 6 carbon atoms, and ethers having 4 to 10 carbon atoms. Preferably, the carbon atoms have a C / C hybridization type of SP3 hybridization, meaning that the solvent does not contain carbon-carbon double bonds or carbon-carbon triple bonds.

[0037] In a preferred embodiment, the carbonate with 3 to 8 carbon atoms includes at least one of cyclic carbonates or chain carbonates with 3 to 8 carbon atoms; the cyclic carbonate with 3 to 8 carbon atoms does not contain halogen atoms and includes at least one of γ-butyrolactone (GBL), butylene carbonate (BC), and ethylene carbonate; the chain carbonate with 3 to 8 carbon atoms includes at least one of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), and dipropyl carbonate (DPC).

[0038] Preferably, the carboxylic acid ester having 2 to 6 carbon atoms includes at least one of methyl acetate (MA), ethyl acetate (EA), propyl acetate (EP), butyl acetate, and propyl propionate (PP);

[0039] Preferably, the ether having 4 to 10 carbon atoms includes at least one of cyclic ethers or chain ethers having 4 to 10 carbon atoms; the cyclic ether having 4 to 10 carbon atoms includes at least one of 1,3-dioxolane (DOL), 1,4-dioxane (DX), tetrahydrofuran (THF), 2-methyltetrahydrofuran (2-CH3-THF), and 2-trifluoromethyltetrahydrofuran (2-CF3-THF); the chain ether having 4 to 10 carbon atoms includes at least one of dimethoxymethane (DMM), 1,2-dimethoxyethane (DME), and diethylene glycol dimethyl ether (TEGDME).

[0040] In some embodiments, the electrolyte salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethane)sulfonamide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, and sodium perchlorate.

[0041] In some embodiments, the positive electrode includes a positive electrode active material selected from at least one of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds.

[0042] In a preferred embodiment, the chemical formula of the layered transition metal oxide is Na x M y O z , 0 < x ≤ 1, 0 < y ≤ 1, 1 < z ≤ 2, M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, V; preferably, the layered transition metal oxide is NaNi m Fe n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1) or NaNi m Co n Mn p O2 (m + n + p = 1, 0 ≤ m ≤ 1, 0 ≤ n ≤ 1, 0 ≤ p ≤ 1); specifically, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2;

[0043] The chemical formula of the Prussian compound is Na x M[M′(CN)6] y ·zH2O, M and M′ are transition metals, 0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20; preferably, the Prussian compound is Na x Mn[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20) or Na x Fe[Fe(CN)6] y ·zH2O (0 < x ≤ 2, 0 < y ≤ 1, 0 < z ≤ 20);

[0044] The chemical formula of the phosphate compound is Na3(MO 1-x PO4)2F 1+2x , 0 ≤ x ≤ 1, M is selected from at least one of Al, V, Ge, Fe, Ga, preferably, the phosphate compound is at least one of Na3(VPO4)2F3 or Na3(VOPO4)2F; or, the chemical formula of the phosphate compound is Na2MPO4F, M is selected from at least one of Fe, Mn, preferably, the phosphate compound is at least one of Na2FePO4F or Na2MnPO4F;

[0045] The chemical formula of the sulfate compound is Na2M(SO4)2·2H2O, where M is selected from at least one of Cr, Fe, Co, Ni, Cu, Mn, Sn, Mo, Sb, and V.

[0046] In some embodiments, the preparation method of the positive electrode includes: mixing the positive electrode active material, binder, conductive agent, and solvent, coating the mixture onto a substrate, and removing the solvent to obtain the positive electrode; the preparation method of the negative electrode includes: mixing the negative electrode active material, binder, conductive agent, and solvent, coating the mixture onto a substrate, and removing the solvent to obtain the negative electrode. In these embodiments of the invention, there are no particular limitations on the conductive agent, binder, and solvent; commonly used conductive agents, binders, and solvents in the art can all be employed.

[0047] The present invention will now be described with reference to specific embodiments. It should be noted that these embodiments are merely descriptive and do not limit the present invention in any way.

[0048] Example 1

[0049] Sodium-ion batteries include:

[0050] (1) Electrolyte: The non-aqueous electrolyte is prepared by mixing the solvent ethylene carbonate, the solvent ethyl methyl carbonate, the electrolyte salt NaPF6, and the additives in a mass ratio of 25:57:13:5. The additives are ethylene sulfate and sodium difluorooxalate borate, and the mass ratio of ethylene sulfate to sodium difluorooxalate borate is 3:2.

[0051] (2) Negative electrode: The negative electrode carbon material is hard carbon, and the crystallinity of hard carbon is 18%.

[0052] (3) Sodium-ion battery: the electrolyte, negative electrode, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 The battery consists of an O2 positive electrode and a PP separator.

[0053] Example 2-17

[0054] Examples 2-17 illustrate the sodium-ion battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:

[0055] The crystallinity of the negative electrode carbon material used in Examples 2-17, as well as the types and mass percentages of additives in the electrolyte, are shown in Table 1.

[0056] Comparative Examples 1-6

[0057] Comparative Examples 1-6 are used to illustrate the sodium-ion battery disclosed in this invention, including most of the operating steps in Example 1, with the following differences:

[0058] The crystallinity of the negative electrode carbon material used in Comparative Examples 1-6, as well as the types and mass percentages of additives in the electrolyte, are shown in Table 1.

[0059] Performance testing

[0060] The sodium-ion batteries described above underwent the following performance tests:

[0061] (1) First-time test: The unformed battery was charged at a constant current of 0.1C to 3.9V, and then charged at a constant voltage until the current dropped to 0.03C. The charging capacity D1 of the battery was recorded. Then the battery was discharged at a constant current of 0.1C to 1.5V. The discharge capacity D2 of the battery was recorded.

[0062] First-time efficiency (%) = Discharge capacity D2 / Charge capacity D1 × 100%.

[0063] (2) Capacity test: The battery is prepared by combining the negative electrode sheet after formation, sodium metal, and the above electrolyte. It is discharged to 0V with a constant current of 0.1C, and then charged to 1.5V with a constant current of 0.1C. The charging capacity D3 of the battery is recorded. The mass of the negative electrode sheet after removing the current collector is m.

[0064] Battery capacity = D3 / m.

[0065] Table 1

[0066]

[0067]

[0068] As can be seen from Table 1, the sodium-ion batteries prepared in Examples 1-17 have a crystallinity of X% and an additive mass percentage of Y% that satisfy the relationship 25≤X*Y≤120, which can simultaneously improve the initial efficiency and capacity performance of sodium-ion batteries.

[0069] When X and Y further satisfy the relationship 50 ≤ X * Y ≤ 110, it is beneficial to further improve the initial efficiency and specific capacity of sodium-ion batteries. Further optimization of crystallinity (X%) and / or additive mass percentage (Y%) results in even better sodium-ion battery performance.

[0070] Comparative Examples 1-4 do not satisfy the condition 25 ≤ X*Y ≤ 120, resulting in lower initial efficiency and specific capacity of the sodium-ion batteries. In Comparative Example 1, X*Y is 400, higher than 120. High crystallinity leads to lower negative electrode capacity, and high additive content increases interfacial film impedance, resulting in relatively low battery specific capacity. In Comparative Example 3, X*Y is 9, lower than 25. Low crystallinity exacerbates electrolyte interfacial reactions in amorphous regions, and low additive content cannot effectively suppress these reactions, leading to lower initial efficiency.

[0071] As can be seen from Examples 1 and 13-17, for different additives in this invention, under the condition that the relationship 25≤X*Y≤120 is satisfied, they all have a good effect on improving the first efficiency and capacity performance of sodium-ion batteries.

[0072] As can be seen from the test results of Examples 1, 13-17 and Comparative Examples 5-6, replacing the additives in this invention with other additives does not improve the performance of sodium-ion batteries as much as the additives in this invention, under the same conditions. This is because cyclic compounds can preferentially react with electrolyte salts before solvents, thereby participating in the reaction at the negative electrode interface to form sodium-containing interfacial components, improving the interface density, which is beneficial to the reversible insertion / extraction of sodium ions, thereby improving the battery coulombic efficiency and capacity. Comparative Examples 7-8 are linear compounds containing heteroatoms, which cannot achieve the effect of the additives described in this invention.

[0073] In this invention, the terms "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment or example, which is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0074] Although the above embodiments have been shown and described, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Any changes, modifications, substitutions and variations made to the above embodiments by those skilled in the art are within the protection scope of the present invention.

Claims

1. A sodium-ion battery, characterized in that, The electrolyte comprises a positive electrode, a negative electrode, and an electrolyte solution. The negative electrode includes a negative electrode active material, which is a carbon material with a crystallinity of X%. The electrolyte comprises an electrolyte salt, a solvent, and an additive, with the additive having a mass percentage of Y%. X and Y satisfy the relationship 25 ≤ X. Y≤120; The crystallinity of the carbon material refers to the ratio of the area of ​​the C(002) crystal plane diffraction peak in the XRD of the carbon material to the sum of the areas of the amorphous peak and the C(002) crystal plane diffraction peak; The additive is a cyclic compound; the additive is composed of two of the following: fluoroethylene carbonate, 1,3-propanesulfonate lactone, 1,3-propenesulfonate lactone, ethylene sulfate, and sodium difluorooxalate borate, with a mass ratio of the two additives of 3:2 to 2:

3. The crystallinity X% of the carbon material satisfies 15≤X≤50; The mass percentage Y% of the additive in the electrolyte satisfies 0.1≤Y≤10.

2. The sodium-ion battery according to claim 1, characterized in that, 50≤X Y≤110。 3. The sodium-ion battery according to claim 1, characterized in that, The crystallinity X% of the carbon material satisfies 18 ≤ X ≤ 35.

4. The sodium-ion battery according to claim 1, characterized in that, The mass percentage Y% of the additive in the electrolyte satisfies 2≤Y≤8.

5. The sodium-ion battery according to claim 1, characterized in that, The solvent includes at least one of C3-C8 carbonates, C2-C6 carboxylic esters, and C4-C10 ethers.

6. The sodium-ion battery according to claim 1, characterized in that, The electrolyte salt includes at least one of sodium hexafluorophosphate, sodium bis(trifluoromethane)sulfonamide, sodium trifluoromethanesulfonate, sodium tetrafluoroborate, and sodium perchlorate.

7. The sodium-ion battery according to claim 1, characterized in that, The positive electrode includes a positive electrode active material, which is selected from at least one of layered transition metal oxides, Prussian compounds, phosphate compounds, and sulfate compounds.

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