Sodium ion battery and electric equipment

Abstract

The sodium ion battery provided by the embodiment of the invention comprises a positive electrode, a negative electrode, an electrolyte and a diaphragm, the negative electrode comprises a carbon material, the specific surface area of the carbon material is a, and the unit is m < 2 > / g; the electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a sodium salt additive and an organic additive, the mass percentage content of the sodium salt additive in the electrolyte is e, the unit is%, and the numerical ratio of e to a meets the condition that e / a is greater than or equal to 0.01 and less than or equal to 3.5; the mass percentage content of the organic additive in the electrolyte is f, the unit is%, and the numerical ratio of f to a meets the condition that f / a is larger than or equal to 0.05 and smaller than or equal to 10. According to the sodium-ion battery, the reasonable use amount of the additive required in the electrolyte is determined according to the physicochemical properties of the electrode material, and a proper amount of sodium salt additive and organic additive are added into the electrolyte, so that the battery performance can be better improved. The embodiment of the invention also provides a preparation method of the sodium ion battery and electric equipment.

Description

Technical Field

[0001] The embodiments of the present application relate to the technical field of sodium ion batteries, and in particular to sodium ion batteries and electrical equipment. Background Art

[0002] Sodium-ion batteries are considered to be very promising candidates in energy storage scenarios because of their advantages such as abundant sodium resources and low cost. However, sodium-ion batteries currently have disadvantages such as poor cycle performance, high-temperature storage and cycle flatulence, which restrict their widespread application. The performance of sodium-ion batteries mainly depends on the positive electrode material, negative electrode material and electrolyte. Among them, some additives are usually added to the electrolyte to improve the electrochemical properties of the electrolyte and improve the quality of negative electrode deposition. Taking the sodium-ion battery with sodium-nickel-iron-manganese as the positive electrode material and hard carbon as the negative electrode material as an example, the commonly used additives in the electrolyte form a SEI (Solid Electrolyte Interphase) film covering the surface of the hard carbon negative electrode during the formation or volume separation stage, and the additives are basically consumed at this stage. However, the SEI film of sodium-ion batteries is not stable, and the SEI film cannot be effectively repaired later; in addition, since the additives are basically consumed, the positive electrode cannot effectively form and repair the CEI (Cathode Electrolyte Interphase, cathode electrolyte interface) film, which affects the long cycle performance and high temperature performance of the battery system. Summary of the invention

[0003] In view of this, an embodiment of the present application provides a sodium ion battery, the electrolyte of which contains specific additives, which can improve the film formation quality on the surface of the negative electrode, effectively avoid the continuous rupture and dissolution of the SEI film during the cycle, and reduce the occurrence of side reactions; at the same time, it is also beneficial to form an effective CEI film on the surface of the positive electrode, inhibiting the dissolution of positive electrode metal ions; so as to achieve the purpose of improving the battery cycle performance, high and low temperature storage performance and reducing gas production.

[0004] Specifically, the first aspect of the embodiment of the present application provides a sodium ion battery, the sodium ion battery includes a positive electrode, a negative electrode, an electrolyte and a separator, the negative electrode includes a negative electrode active material, the negative electrode active material includes a carbon material, and the specific surface area of ​​the carbon material is a, in units of m 2 / g; the electrolyte includes an electrolyte salt, an organic solvent and an additive, the additive includes a sodium salt additive and an organic additive, the mass percentage of the sodium salt additive in the electrolyte is e, the unit is %, and the numerical ratio of e to a satisfies: 0.01≤e / a≤3.5; the mass percentage of the organic additive in the electrolyte is f, the unit is %, and the numerical ratio of f to a satisfies: 0.05≤f / a≤10.

[0005] It should be noted that the numerical ratio of e to a refers to the ratio of the two without considering the unit. For example, e is 1% and a is 0.5 m 2 / g, then the numerical ratio of e to a is e / a=1 / 0.5=2.

[0006] Similarly, the numerical ratio of f to a refers to the ratio of the two without considering the unit, for example, f is 2% and a is 0.5 m 2 / g, then the numerical ratio of f and a is f / a=2 / 0.5=4.

[0007] The sodium ion battery of the embodiment of the present application adds two types of additives, sodium salt additives and organic additives, to the electrolyte, and controls the ratio of the amount of the two types of additives added to the specific surface area of ​​the carbon material of the negative electrode within a suitable range. In this way, a reasonable amount of additives is selected according to the specific surface area of ​​the negative electrode carbon material, which can guide the design of the electrode material and electrolyte collocation, avoid the problem that the improper amount of additives in the electrolyte cannot effectively reduce the side reaction between the electrolyte and the electrode material, reduce the internal resistance, etc., and better achieve a good balance between the performance of the carbon material and the effect of the additives, thereby better ensuring the electrochemical performance of the battery; Among them, the sodium salt additive can react with the negative electrode before the organic additive to passivate the negative electrode surface, thereby improving the film quality of the organic additive on the negative electrode surface, effectively avoiding the continuous rupture and dissolution of the SEI film during the cycle, reducing the contact between the negative electrode and the electrolyte, and reducing the probability of side reactions; at the same time, it can enable the battery to have an appropriate amount of additives to form an effective CEI film on the positive electrode surface, thereby inhibiting the dissolution of positive electrode metal ions; in addition, the addition of an appropriate amount of sodium salt additive can also reduce the consumption and consumption rate of organic additives, improve battery cycle performance, improve high and low temperature storage performance and reduce battery gas production.

[0008] In the embodiment of the present application, the mass percentage of the sodium salt additive in the electrolyte is 0.05%-3%. The addition of an appropriate amount of the sodium salt additive in the electrolyte can better passivate the surface of the negative electrode, improve the film-forming quality of the SEI film of the negative electrode, and enable the SEI film to be effectively repaired during the battery cycle. It is also more conducive to the formation of an effective CEI film on the surface of the positive electrode of the battery during the cycle, thereby better improving the long cycle performance of the battery; the addition of an appropriate amount of the sodium salt additive can also reduce the consumption and consumption rate of the organic additive, improve the high and low temperature storage performance of the battery, and reduce the gas production of the battery.

[0009] In the embodiment of the present application, the organic additive includes a fluorocarbonate, and the mass percentage of the fluorocarbonate in the electrolyte is 0.1%-10%. Fluorinated carbonates have a lower lowest unoccupied molecular orbital (LUMO) energy and are easily reduced before other electrolyte solvents. Using fluorocarbonates as organic additives can form a highly crystalline and inorganic component-rich SEI film on the surface of the negative electrode of the sodium ion battery, thereby effectively protecting the negative electrode and ensuring uniform and rapid migration of sodium ions at the interface. Controlling the amount of fluorocarbonates within the above range can better play the film-forming advantages of fluorocarbonates and better improve the cycle performance of the battery.

[0010] The mass percentage e of the sodium salt additive in the electrolyte and the mass percentage f of the fluorocarbonate directly affect the film-forming performance of the positive and negative electrodes of the sodium ion battery. In order to better form a film on the surface of the positive and negative electrodes and improve the battery performance, in the embodiment of the present application, the numerical ratio of the e to the f satisfies: 0.01≤e / f≤8.

[0011] In the embodiment of the present application, the specific surface area of ​​the carbon material is 0.5 m 2 / g-15m 2 / g. The negative electrode carbon material with a suitable specific surface area is conducive to the negative electrode having a better ability to accept and release sodium ions, so that the battery has relatively better kinetic performance; at the same time, the negative electrode carbon material with a suitable specific surface area means that adding a suitable amount of additives can form a stable SEI film, avoiding improper use of additives.

[0012] In the embodiment of the present application, the sodium salt additive includes one or more of sodium bis(oxalatoborate) (NaBOB), sodium difluoro(oxalatoborate) (NaDFOB), sodium difluorobis(oxalatophosphate) (NaDFOP), and sodium difluorophosphate (NaPO2F2). The above sodium salt additive has a higher reduction film-forming potential, and can react with the negative electrode before the organic additive, passivate the negative electrode surface, thereby improving the film-forming quality of the organic additive on the negative electrode surface, effectively avoiding the continuous rupture and dissolution of the SEI film during the cycle, reducing the contact between the negative electrode and the electrolyte, and reducing the probability of side reactions.

[0013] In the embodiment of the present application, the fluorocarbonate includes at least one of fluoroethylene carbonate (FEC) and bisfluoroethylene carbonate (DFEC). The above two fluorocarbonates have good film-forming properties on the electrode surface, can effectively protect the electrode, and ensure the uniform and rapid migration of sodium ions at the interface between the electrode and the electrolyte, thereby improving the battery kinetics and cycle performance.

[0014] In the embodiment of the present application, the positive electrode includes a positive electrode active material, and the positive electrode active material includes at least one of a layered sodium transition metal oxide, a Prussian blue (white) compound, and a sodium polyanion compound. The positive electrode active material can be a combination of one or more of the above materials, wherein the layered sodium transition metal oxide positive electrode material and the Prussian blue (white) compound positive electrode material both have a high specific capacity; the sodium polyanion compound has a high electrochemical reaction stability.

[0015] In some embodiments of the present application, the positive electrode active material includes a layered sodium transition metal oxide, and the specific surface area of ​​the layered sodium transition metal oxide is 0.1 m 2 / g-1.0m 2 / g, denoted as b; the numerical ratio of said e to said b satisfies: 0.1≤e / b≤15. Controlling the specific surface area of ​​the layered sodium transition metal oxide within a suitable range is conducive to better balancing the battery rate performance with the battery cycle and storage performance. Controlling the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area b of the positive electrode active material layered sodium transition metal oxide within a suitable range can better achieve a good balance between the performance of the layered sodium transition metal oxide and the effect of the additive, and better improve the battery performance.

[0016] In the embodiment of the present application, the mass percentage of the layered sodium transition metal oxide in the positive electrode material layer is ≥ 92%; the 0.1C gram capacity of the layered sodium transition metal oxide material is greater than or equal to 100 mAh / g; the compaction density of the positive electrode is 2.9 g / cm 3 -3.6g / cm 3 . Controlling the mass content of layered sodium transition metal oxide in the positive electrode material layer to a higher proportion is conducive to improving the battery capacity. Selecting a positive electrode active material with a larger capacity is conducive to improving the overall capacity of the battery and improving the charge and discharge performance. A suitable positive electrode compaction density is conducive to the battery having better other properties while obtaining a higher energy density.

[0017] In some other embodiments of the present application, the positive electrode active material includes a Prussian blue (white) compound, and the specific surface area of ​​the Prussian blue (white) compound is 0.1 m 2 / g-1.0m 2 / g, denoted as c; the numerical ratio of said e to said c satisfies: 0.1≤e / c≤15. Controlling the specific surface area of ​​the positive electrode active material within a suitable range is conducive to better balancing the battery rate performance with the battery cycle and storage performance. Controlling the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area c of the positive electrode active material Prussian blue (white) compound within a suitable range can better achieve a good balance between the performance of the Prussian blue (white) compound and the effect of the additive, and better improve the battery performance.

[0018] In the embodiment of the present application, the mass percentage of the Prussian blue (white) compound in the positive electrode material layer is ≥92%; the 0.1C gram capacity of the Prussian blue (white) compound material is greater than or equal to 130mAh / g; the compaction density of the positive electrode is 1.2g / cm 3 -1.8g / cm 3 . Controlling the mass content of Prussian blue (white) compounds in the positive electrode material layer to a higher proportion is conducive to improving the battery capacity. Selecting a positive electrode active material with a larger capacity is conducive to improving the overall capacity of the battery and improving the charge and discharge performance. A suitable positive electrode compaction density is conducive to the battery having better other properties while obtaining a higher energy density.

[0019] In some other embodiments of the present application, the positive electrode active material includes a sodium polyanion compound, and the specific surface area of ​​the sodium polyanion compound is 5m 2 / g-25m 2 / g, denoted as d; the numerical ratio of said e to said d satisfies: 0.005≤e / d≤0.4. Controlling the specific surface area of ​​the positive electrode active material within a suitable range is conducive to better balancing the battery rate performance with the battery cycle and storage performance. Controlling the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area d of the positive electrode active material sodium polyanion compound within a suitable range can better achieve a good balance between the performance of the sodium polyanion compound and the effect of the additive, and better improve the battery performance.

[0020] In the embodiment of the present application, the mass percentage of the sodium polyanion compound in the positive electrode material layer is ≥92%; the 0.1C gram capacity of the sodium polyanion compound material is greater than or equal to 100 mAh / g; the compaction density of the positive electrode is 1.8 g / cm 3 -2.8g / cm 3 . Controlling the mass content of sodium polyanion compounds in the positive electrode material layer to a higher proportion is beneficial to improving the battery capacity. Selecting a positive electrode active material with a larger capacity is beneficial to improving the overall capacity of the battery and improving the charge and discharge performance. A suitable positive electrode compaction density is beneficial for the battery to have better other properties while obtaining a higher energy density.

[0021] In the embodiment of the present application, the 0.1C gram capacity of the carbon material is greater than or equal to 230 mAh / g. Selecting a carbon material with a larger capacity as the negative electrode active material is beneficial to increasing the overall capacity of the battery and improving the charge and discharge performance.

[0022] In the embodiment of the present application, the carbon material includes at least one of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, and porous carbon materials. The negative electrode of the sodium ion battery of the present application may include one or more of the above carbon materials.

[0023] In the embodiment of the present application, the mass percentage of the carbon material in the negative electrode material layer is ≥ 93%; the compaction density of the negative electrode is 0.9 g / cm 3 -1.6g / cm 3 The appropriate negative electrode compaction density is conducive to the battery having higher energy density and better other properties.

[0024] In the embodiment of the present application, the electrolyte further comprises one or more of sulfur-containing ester compounds, nitrile compounds, and acid anhydride compounds. The sulfur-containing ester compounds can form high-quality interface films on the surfaces of positive and negative electrode materials, improve the high-temperature performance of sodium ion batteries and inhibit gas production; the nitrile compounds can complex transition metal ions in positive electrode materials, reduce the catalytic activity of transition metal ions, reduce the dissolution of transition metal ions and improve the oxidation resistance of the electrolyte; the acid anhydride compounds can form films on the surfaces of positive and negative electrode materials, reducing the problems caused by the high alkalinity of the positive electrode materials.

[0025] In the embodiment of the present application, the mass percentage of the sulfur-containing ester compound in the electrolyte is 1%-5%; the mass percentage of the nitrile compound in the electrolyte is 1%-6%; the mass percentage of the acid anhydride compound in the electrolyte is 0.05%-1%. Controlling the above-mentioned different additives to a suitable content is conducive to not reducing other performances of the battery when they exert their beneficial effects.

[0026] In the embodiment of the present application, the sulfur-containing ester compound includes but is not limited to one or more of dimethyl sulfite, diethyl sulfite, vinyl sulfite, vinyl sulfate, propylene sulfate, methylene methanedisulfonate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate.

[0027] In the present application embodiment, the nitrile compound includes a mononitrile compound and / or a polynitrile compound. In some embodiments, the mononitrile compound includes but is not limited to at least one of acetonitrile and p-methylbenzonitrile. In some embodiments, the polynitrile compound includes but is not limited to one or more of succinonitrile, glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,6-hexanetrinitrile.

[0028] In the embodiment of the present application, the acid anhydride compound includes but is not limited to one or more of succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride, and cyclic phosphoric anhydride.

[0029] In the embodiment of the present application, the electrolyte salt includes but is not limited to NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, NaTDI, Na[(CF3SO2)2N], Na[(FSO2)2N] and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], wherein m and n are natural numbers.

[0030] In the embodiment of the present application, the molar concentration of the electrolyte salt in the electrolyte solution is 0.01 mol / L-5.0 mol / L.

[0031] In the embodiment of the present application, the organic solvent includes one or more of carbonate solvents, ether solvents, and carboxylate solvents.

[0032] A second aspect of an embodiment of the present application provides a method for preparing a sodium ion battery, comprising:

[0033] A positive electrode sheet, a negative electrode sheet, a separator and an electrolyte are provided; wherein the negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprises a carbon material, and the specific surface area of ​​the carbon material is a, in m 2 / g; the electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a sodium salt additive and an organic additive, the mass percentage of the sodium salt additive in the electrolyte is e, in %; the mass percentage of the organic additive in the electrolyte is f, in %;

[0034] Wherein, the numerical ratio of the e to the a is controlled to satisfy: 0.01≤e / a≤3.5, and the numerical ratio of the f to the a is controlled to satisfy: 0.05≤f / a≤10;

[0035] The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are assembled to obtain a sodium ion battery.

[0036] An embodiment of the present application also provides an electrical device, which includes a shell, and electronic components and a battery housed in the shell, wherein the battery supplies power to the electronic components, and the battery includes the sodium ion battery described in the first aspect of the embodiment of the present application, or the sodium ion battery prepared by the preparation method described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 A schematic diagram of the structure of a sodium ion battery 100 provided in an embodiment of the present application;

[0038] Figure 2 A schematic diagram of the structure of an electric device 200 provided in an embodiment of the present application;

[0039] Figure 3 This is a comparison chart of the cycle performance of the sodium ion battery of Example 3 of the present application and Comparative Example 2 after 300 cycles at 0.5C / 0.5C;

[0040] Figure 4 This is a comparison chart of the cycle performance of the sodium ion battery of Example 23 of the present application and Comparative Example 8 after 300 cycles at 0.5C / 0.5C;

[0041] Figure 5 This is a comparison chart of the cycle performance of the sodium ion battery of Example 31 of the present application and the comparative example 11 after 300 cycles of 0.5C / 0.5C;

[0042] Figure 6 This is a film forming potential diagram of the sodium ion battery of Example 10 of the present application and Comparative Example 1. DETAILED DESCRIPTION

[0043] The embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application.

[0044] The performance of sodium ion batteries mainly depends on the positive electrode material, the negative electrode material and the electrolyte. Among them, some additives are usually added to the electrolyte to improve the electrochemical properties of the electrolyte and improve the quality of negative electrode deposition. Taking the sodium ion battery with sodium nickel iron manganese as the positive electrode material and hard carbon as the negative electrode material as an example, the common additives in the electrolyte form an SEI film covering the surface of the hard carbon negative electrode during the formation or capacity separation stage, and the additives are basically consumed at this stage. However, the SEI film of the sodium ion battery has poor stability, and the SEI film cannot be effectively repaired later; in addition, since the additives are basically consumed, the positive electrode cannot effectively form and repair the CEI film, affecting the long cycle performance and high temperature performance of the battery system. In view of this, the embodiment of the present application provides a sodium ion battery, the electrolyte of which contains specific additives, which can improve the film quality of the negative electrode surface, effectively avoid the continuous rupture and dissolution of the SEI film during the cycle process, and reduce the occurrence of side reactions; at the same time, it is also conducive to the formation of an effective CEI film on the positive electrode surface, inhibiting the dissolution of positive electrode metal ions; so as to achieve the purpose of improving the battery cycle performance, high and low temperature storage performance and reducing gas production.

[0045] like Figure 1 As shown, an embodiment of the present application provides a sodium ion battery 100, which includes a positive electrode 10, a negative electrode 20, a separator 30 and an electrolyte 40, wherein the separator 30 is disposed between the positive electrode 10 and the negative electrode 20, and the electrolyte 40 is filled between the positive electrode 10 and the negative electrode 20 and infiltrates the separator 30. The negative electrode 20 includes a negative electrode active material 202, and the negative electrode active material 202 includes a carbon material, wherein, during charging, sodium ions are released from the positive electrode active material 102 of the positive electrode 10, and are embedded in the negative electrode active material 202 of the negative electrode 20 after passing through the electrolyte 40; during discharging, sodium ions are released from the negative electrode active material 202, and are inserted into the positive electrode active material 102 after passing through the electrolyte 40. In the embodiment of the present application, the specific surface area of ​​the carbon material is a, and the unit is m 2 / g; the electrolyte 40 includes electrolyte salt, organic solvent and additives, the additives include sodium salt additives and organic additives, the mass percentage of the sodium salt additive in the electrolyte 40 is e, the unit is %, wherein the numerical ratio of e to a satisfies: 0.01≤e / a≤3.5; the mass percentage of the organic additive in the electrolyte 40 is f, the unit is %, wherein the numerical ratio of f to a satisfies: 0.05≤f / a≤10. Under this condition, the electrode material and the electrolyte in the battery have a good matching effect, which can effectively reduce the side reaction between the electrolyte and the electrode material, reduce impedance and improve the battery cycle performance, and improve the high temperature performance of the battery.

[0046] It should be noted that the numerical ratio of e to a refers to the ratio of e to a without considering the unit. For example, e is 1% and a is 0.5 m 2 / g, then the numerical ratio of e to a is e / a = 1 / 0.5 = 2. Similarly, the numerical ratio of f to a refers to the ratio of the two without considering the unit, for example, f is 2% and a is 0.5m 2 / g, then the numerical ratio of f and a is f / a=2 / 0.5=4.

[0047] It should be noted that the sodium ion battery 100 of the embodiment of the present application may be a battery in various stages: before formation, after formation, after capacity separation, and after cycling.

[0048] The sodium ion battery of the embodiment of the present application adds two types of additives, sodium salt additives and organic additives, to the electrolyte, and controls the ratio of the amount of the two types of additives added to the specific surface area of ​​the carbon material of the negative electrode within a suitable range. In this way, a reasonable amount of additives is selected according to the specific surface area of ​​the negative electrode carbon material, which can guide the design of the electrode material and electrolyte collocation, avoid the problem that the improper amount of additives in the electrolyte cannot effectively reduce the side reaction between the electrolyte and the electrode material, reduce the internal resistance, etc., and better achieve a good balance between the performance of the carbon material and the effect of the additives, thereby better ensuring the electrochemical performance of the battery Among them, the sodium salt additive can react with the negative electrode before the organic additive, passivate the negative electrode surface, thereby improving the film quality of the organic additive on the negative electrode surface, effectively avoiding the continuous rupture and dissolution of the SEI film during the cycle, reducing the contact between the negative electrode and the electrolyte, and reducing the probability of side reactions; at the same time, it can enable an appropriate amount of additives to form an effective CEI film on the positive electrode surface, thereby inhibiting the dissolution of positive electrode metal ions; in addition, the addition of an appropriate amount of sodium salt additive can also reduce the consumption and consumption rate of organic additives, improve battery cycle performance, improve high and low temperature storage performance and reduce battery gas production.

[0049] The positive electrode 10, the negative electrode 20, the separator 30 and the electrolyte 40 of the sodium ion battery 100 will be described in detail below.

[0050] positive electrode

[0051] like Figure 1As shown, in the embodiment of the present application, the positive electrode 10 includes a positive electrode collector 101 and a positive electrode material layer provided on the surface of the positive electrode collector 101, wherein the positive electrode collector 101 may be a metal foil, such as aluminum foil, gold foil, platinum foil, etc. The positive electrode material layer includes a positive electrode active material 102, and the positive electrode active material 102 can reversibly embed / de-embed sodium ions. In the embodiment of the present application, the positive electrode active material may be at least one of a layered sodium transition metal oxide, a Prussian blue (white) compound, and a sodium polyanion compound. The positive electrode active material may be a combination of one or more (two or more) of the above materials. Among them, the layered sodium transition metal oxide positive electrode material and the Prussian blue (white) compound positive electrode material both have a high specific capacity; the sodium polyanion compound has a high electrochemical reaction stability. In the embodiment of the present application, the layered sodium transition metal oxide may be, for example, sodium nickel iron manganese (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, abbreviated as NFM), Prussian blue (white) compounds can be, for example, Prussian white (Na2Mn[Fe(CN)6], abbreviated as PBA), and sodium polyanion compounds can be, for example, sodium iron phosphate (NaFePO4, abbreviated as NFP). In some embodiments of the present application, the positive electrode active material includes one or more of sodium nickel iron manganese, Prussian white, and sodium iron phosphate materials.

[0052] In some embodiments of the present application, the positive electrode active material includes a layered sodium transition metal oxide, and the specific surface area of ​​the layered sodium transition metal oxide is denoted as b, where b can be 0.1 m 2 / g-1.0m 2 In some embodiments, the specific surface area b of the layered sodium transition metal oxide is 0.2 m 2 / g-0.8m 2 In some embodiments, the specific surface area b of the layered sodium transition metal oxide may be, for example, 0.1 m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 Controlling the specific surface area of ​​the positive electrode active material within a suitable range is conducive to better balancing the battery rate performance and the battery cycle and storage performance.

[0053] In the embodiment of the present application, the 0.1C gram capacity of the layered sodium transition metal oxide material is greater than or equal to 100 mAh / g. Selecting a positive electrode active material with a larger capacity is beneficial to increasing the overall capacity of the battery and improving the charge and discharge performance.

[0054] In the embodiment of the present application, the mass percentage of the layered sodium transition metal oxide in the positive electrode material layer is ≥ 92%. In the embodiment of the present application, the compaction density of the positive electrode is 2.9 g / cm 3 -3.6g / cm 3 Controlling the mass content of layered sodium transition metal oxide in the positive electrode material layer to a higher proportion is beneficial to improving the battery capacity. A suitable positive electrode compaction density is beneficial for the battery to have better other properties while obtaining a higher energy density.

[0055] In some embodiments of the present application, the positive electrode active material includes a Prussian blue (white) compound, and the specific surface area of ​​the Prussian blue (white) compound is denoted as c, where c can be 0.1 m 2 / g-1.0m 2 In some embodiments, the specific surface area c of the Prussian blue (white) compound may be 0.3 m 2 / g-0.8m 2 In some embodiments, the specific surface area c of the Prussian blue (white) compound may be, for example, 0.1 m 2 / g, 0.2m 2 / g, 0.3m 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 Controlling the specific surface area of ​​the positive electrode active material within a suitable range is conducive to better balancing the battery rate performance and the battery cycle and storage performance.

[0056] In the embodiment of the present application, the 0.1C gram capacity of the Prussian blue (white) compound material is greater than or equal to 130 mAh / g. Selecting a positive electrode active material with a larger capacity is beneficial to increasing the overall capacity of the battery and improving the charge and discharge performance.

[0057] In the embodiment of the present application, the mass percentage of the Prussian blue (white) compound material in the positive electrode material layer is ≥ 92%. In the embodiment of the present application, the compaction density of the positive electrode is 1.2 g / cm 3 -1.8g / cm 3Controlling the mass content of Prussian blue (white) compounds in the positive electrode material layer to a higher proportion is beneficial to improving the battery capacity. A suitable positive electrode compaction density is beneficial for the battery to have better other properties while obtaining a higher energy density.

[0058] In some embodiments of the present application, the positive electrode active material includes a sodium polyanion compound, and the specific surface area of ​​the sodium polyanion compound is denoted as d, where d can be 5m 2 / g-25m 2 / g. In some embodiments, the specific surface area d of the sodium polyanionic compound may be 8m 2 / g-18m 2 In some embodiments, the specific surface area d of the sodium polyanionic compound may be, for example, 5 m 2 / g, 8m 2 / g, 10m 2 / g, 12m 2 / g, 15m 2 / g, 18m 2 / g, 20m 2 / g, 22m 2 / g, 25m 2 Controlling the specific surface area of ​​the positive electrode active material within a suitable range is conducive to better balancing the battery rate performance and the battery cycle and storage performance.

[0059] In the embodiment of the present application, the 0.1C gram capacity of the sodium polyanion compound material is greater than or equal to 100 mAh / g. Selecting a positive electrode active material with a larger capacity is beneficial to increasing the overall capacity of the battery and improving the charge and discharge performance.

[0060] In the embodiment of the present application, the mass percentage of the sodium polyanion compound in the positive electrode material layer is ≥ 92%. In the embodiment of the present application, the compaction density of the positive electrode is 1.8 g / cm 3 -2.8g / cm 3 Controlling the mass content of sodium polyanion compounds in the positive electrode material layer to a higher proportion is beneficial to improving the battery capacity. A suitable positive electrode compaction density is beneficial for the battery to have better other properties while obtaining a higher energy density.

[0061] It can be understood that the values ​​of b, c, and d mentioned above may have a certain influence on the specific surface area test of the material after actual battery formation, capacity division or cycling due to the formation of the interface film, and a certain measurement and testing error may be allowed. The values ​​within the error range may be understood as the range defined in the embodiments of the present application, or the numerical range of the specific surface area of ​​the material tested after formation, capacity division or cycling is still within the above range and may be understood as the range defined in the embodiments of the present application.

[0062] The 0.1C gram capacity of the above-mentioned positive electrode materials, such as layered sodium transition metal oxides, Prussian blue (white) compounds, and sodium polyanion compounds, refers to the discharge gram capacity at 0.1C in terms of a half cell.

[0063] In the embodiment of the present application, the positive electrode material layer may further include a certain amount of binder, conductive agent and other components. The binder may be, for example, polyvinylidene fluoride (PVDF). The conductive agent may be, for example, amorphous carbon, carbon nanotubes, carbon fiber, graphene, etc. The above binder and conductive agent are only exemplary and are not limited thereto.

[0064] negative electrode

[0065] like Figure 1 As shown, in an embodiment of the present application, the negative electrode 20 includes a negative electrode current collector 201 and a negative electrode material layer provided on the surface of the negative electrode current collector 201, wherein the negative electrode current collector 201 may be a metal foil, such as copper foil, aluminum foil, gold foil, platinum foil, etc. The negative electrode material layer includes a negative electrode active material 202, and the negative electrode active material 202 can accept and release sodium ions. In an embodiment of the present application, the negative electrode active material 202 includes a carbon material. In an embodiment of the present application, the carbon material may be one or more of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, and porous carbon materials. The negative electrode of the sodium ion battery of the present application may include one or more of the above-mentioned carbon materials. In some embodiments, the carbon material includes, for example, hard carbon and / or soft carbon.

[0066] In the embodiment of the present application, the specific surface area a of the carbon material can be 0.5 m 2 / g-15m 2 / g. In some embodiments, the specific surface area a of the carbon material may be 1.0 m 2 / g-8.0m 2 In some embodiments, the specific surface area a of the carbon material may be, for example, 0.5 m 2 / g, 1m 2 / g, 1.5m 2 / g, 2m 2 / g, 3m 2 / g, 4m 2 / g, 5m 2 / g, 6m 2 / g, 7m 2 / g, 8m 2 / g, 9m 2 / g, 10m 2 / g, 12m 2 / g, 15m 2 / g. The negative electrode carbon material with a suitable specific surface area is conducive to the negative electrode having a better ability to accept and release sodium ions, so that the battery has relatively better kinetic performance; at the same time, the negative electrode carbon material with a suitable specific surface area means that adding a suitable amount of additives can form a stable SEI film, avoiding improper use of additives.

[0067] It can be understood that the value of a mentioned above, after actual battery formation, capacity division or cycle, will have a certain impact on the material specific surface area test due to the formation of the interface film, and a certain measurement test error can be allowed. The values ​​within the error range can be understood as the range defined in the embodiments of the present application, or the numerical range of the specific surface area of ​​the material test after formation, capacity division or cycle is still within the above range and can be understood as the range defined in the embodiments of the present application.

[0068] In the embodiment of the present application, the 0.1C gram capacity of the carbon material is greater than or equal to 230 mAh / g. Selecting a carbon material with a larger capacity as the negative electrode active material is beneficial to increasing the overall capacity of the battery and improving the charge and discharge performance. The 0.1C gram capacity of the carbon material, in terms of a half-cell, refers to the charge gram capacity at 0.1C.

[0069] In the embodiment of the present application, the mass percentage of the carbon material in the negative electrode material layer is ≥ 93%; the compaction density of the negative electrode is 0.9 g / cm 3 -1.6g / cm 3 The appropriate negative electrode compaction density is conducive to the battery having higher energy density and better other properties.

[0070] In the embodiment of the present application, the negative electrode material layer may further include a certain amount of binder, conductive agent and other components. The binder may be, for example, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (NaPAA), etc., and the conductive agent may be, for example, amorphous carbon, carbon nanotubes, carbon fiber, graphene, etc. The above binder and conductive agent are only exemplary and are not limited thereto.

[0071] Diaphragm

[0072] like Figure 1 As shown, in the sodium ion battery 100, the separator 30 blocks the passage of electrons and allows the passage of sodium ions. In some embodiments of the present application, the separator 30 includes but is not limited to single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, three-layer PP / PE / PP and ceramic-coated PE.

[0073] Electrolyte

[0074] like Figure 1As shown, in the sodium ion battery 100, the electrolyte 40 is a transmission medium when sodium ions are transmitted between the positive electrode 10 and the negative electrode 20. In the embodiment of the present application, the electrolyte 40 includes an organic solvent, an electrolyte salt and an additive, wherein the electrolyte salt and the additive are both dissolved in the organic solvent.

[0075] In the embodiment of the present application, the organic solvent includes but is not limited to one or more of carbonate solvents, ether solvents, and carboxylate solvents. Among them, carbonate solvents include but are not limited to dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, trifluoromethyl ethylene carbonate, bis (2,2,2-trifluoroethyl) carbonate, (2,2,2-trifluoroethyl) methyl carbonate. One or more of ether solvents include but are not limited to tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis (2,2,2-trifluoroethyl) ether. Carboxylate solvents include but are not limited to one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, methyl difluoroacetate, and methyl trifluoroacetate.

[0076] In the embodiment of the present application, the electrolyte salt includes but is not limited to NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, NaTDI, Na[(CF3SO2)2N], Na[(FSO2)2N] and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], wherein m and n are natural numbers. In some embodiments of the present application, the molar concentration of the electrolyte salt in the electrolyte may be 0.01mol / L-5.0mol / L. In some embodiments, in the electrolyte, the molar concentration of the electrolyte salt may be, for example, 0.01mol / L, 0.1mol / L, 0.5mol / L, 0.8mol / L, 1.0mol / L, 1.2mol / L, 1.5mol / L, 1.8mol / L, 2.0mol / L, 3.0mol / L, 4.0mol / L, 5.0mol / L.

[0077] In the embodiment of the present application, the additive includes a sodium salt additive and an organic additive.

[0078] In the embodiment of the present application, the mass percentage of the sodium salt additive in the electrolyte 40 is e, and the numerical ratio of e to a satisfies: 0.01≤e / a≤3.5. In some embodiments, the numerical ratio of e / a is 0.1-3.0. As an example, the numerical ratio of e / a can typically but not limitatively be 0.01, 0.02, 0.05, 0.1, 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 1.8, 2.0, 2.1, 2.2, 2.5, 2.7, 2.8, 3.0, 3.2, 3.5, and numbers between any two of the above values, all of which are possible ranges of e / a. For example, e / a can be any value between 0.01-0.1, any value between 0.1-0.8, any value between 0.5-1.5, any value between 2.1-3.5, or any other number between any two values. The ratio e / a represents the relationship between the specific surface area of ​​the sodium salt additive and the negative electrode active material. When the e / a value is too large, there are too many sodium salt additives, which will cause excess sodium salt additives to form a film on the negative electrode surface, increase impedance, and deteriorate battery storage performance. When the e / a value is too low, the sodium salt additive is not sufficient to effectively passivate the hard carbon negative electrode surface, and FEC is not easy to form an effective SEI film or the stability of the SEI film is reduced, resulting in a shortened battery cycle life and a decrease in storage performance.

[0079] In the embodiment of the present application, the mass percentage e of the sodium salt additive in the electrolyte may be 0.05%-3%. In some embodiments, the mass percentage e of the sodium salt additive in the electrolyte may be 0.1%-2%. As an example, the mass percentage e of the sodium salt additive in the electrolyte may be, for example, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.7%, 0.9%, 1.0%, 1.2%, 1.4%, 1.6%, 1.8%, 2.0%, 2.2%, 2.5%, 2.7% or 3%. The addition of an appropriate amount of sodium salt additives to the electrolyte can better passivate the negative electrode surface, improve the quality of the SEI film formation of the negative electrode, and enable the SEI film to be effectively repaired during the battery cycle. It is also more conducive to the formation of an effective CEI film on the surface of the positive electrode of the battery during the cycle, thereby better improving the long-cycle performance of the battery; the addition of an appropriate amount of sodium salt additives can also reduce the consumption and consumption rate of organic additives, improve the high and low temperature storage performance of the battery, and reduce battery gas production.

[0080] In the embodiment of the present application, the mass percentage of the organic additive in the electrolyte 40 is f, and the numerical ratio of f to a satisfies: 0.05≤f / a≤10. In some embodiments, the numerical ratio of f / a is 0.1-5. As an example, the value of f / a can be typically but not restrictively 0.05, 0.07, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and the number between any two of the above values, which are all the range values ​​of f / a. For example, f / a can be any value between 0.05-0.5, any value between 0.1-5, any value between 1-10, and any other number between any two values.

[0081] In the embodiment of the present application, the organic additive includes a fluorocarbonate, and the mass percentage f of the fluorocarbonate in the electrolyte is 0.1%-10%. In some embodiments, f can be 0.5%-5%. As an exemplary illustration, f can be, for example, 0.1%, 0.3%, 0.5%, 0.7%, 1%, 3%, 5%, 7%, 10%. Fluorinated carbonates have a lower lowest unoccupied molecular orbital (LUMO) energy and are easily reduced before other electrolyte solvents. Using fluorocarbonates as organic additives can form a highly crystalline and inorganic component-rich SEI film on the surface of the negative electrode of the sodium ion battery, thereby effectively protecting the negative electrode and ensuring uniform and rapid migration of sodium ions at the interface. Controlling the amount of fluorocarbonates within the above range can better play the film-forming advantages of fluorocarbonates and better improve the cycle performance of the battery.

[0082] In the embodiment of the present application, the mass percentage e of the sodium salt additive in the electrolyte and the mass percentage f of the fluorocarbonate directly affect the film-forming performance of the positive and negative electrodes of the sodium ion battery. In order to better form a film on the surface of the positive and negative electrodes and improve the battery performance, in the embodiment of the present application, the numerical ratio of e to f satisfies: 0.01≤e / f≤8. In some embodiments, the numerical ratio of e / f is 0.02-5. As an example, the numerical ratio of e / f can be typically but not limitatively, for example, 0.01, 0.02, 0.05, 0.1, 0.5, 1.0, 2.0, 3.0, 4.0, 5.0, 6.0, 7.0, 8.0, and the number between any two of the above values, which are all the range values ​​of e / f, for example, e / f can be taken from any value between 0.01-0.1, and can also be taken from any value between 0.05-5.0, and can also be taken from any value between 1.0-8.0, and can also be taken from any other number between any two values. The e / f ratio represents the competition and consumption of sodium salt additives and organic additives to form a film. Controlling the e / f ratio within a suitable range can better avoid excessive sodium salt additives, which will cause excess sodium salt additives to form a film on the negative electrode surface, increase impedance, and deteriorate battery storage performance; and better avoid high FEC content, which will lead to poor high-temperature storage performance and aggravate the problem of high-temperature gas production.

[0083] It can be understood that the above-mentioned values ​​of a, e, and f, as well as the calculated values ​​of e / a, f / a, and e / f, in specific embodiments, in batteries at various stages such as before formation, after formation, after capacity division, and after cycling, may be allowed to have certain measurement test system errors during actual test operations, and the values ​​within the system error range may be understood as the range defined in the embodiments of the present application.

[0084] In the embodiment of the present application, the sodium salt additive may be one or more of sodium bis(oxalatoborate) (NaBOB), sodium difluorooxalatoborate (NaDFOB), sodium difluorobis(oxalatophosphate) (NaDFOP), and sodium difluorophosphate (NaPO2F2). The above sodium salt additive has a higher reduction film-forming potential, and can react with the negative electrode before the organic additive, passivate the negative electrode surface, thereby improving the film-forming quality of the organic additive on the negative electrode surface, effectively avoiding the continuous rupture and dissolution of the SEI film during the cycle, reducing the contact between the negative electrode and the electrolyte, and reducing the probability of side reactions.

[0085] In the embodiment of the present application, the fluorinated carbonate may be at least one of fluorinated ethylene carbonate (FEC) and bis-fluorinated ethylene carbonate (DFEC). The above two fluorinated carbonates have good film-forming properties on the electrode surface, can effectively protect the electrode, and ensure the uniform and rapid migration of sodium ions at the interface between the electrode and the electrolyte, thereby improving the battery kinetics and cycle performance.

[0086] In the embodiment of the present application, the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area b of the layered sodium transition metal oxide satisfies: 0.1≤e / b≤15. In some embodiments, the numerical ratio of e / b can be 0.2-10. As an example, the numerical ratio of e / b can be typically but not limitatively 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, and the number between any two of the above values, which are all the range values ​​of e / b, for example, e / b can be any value between 0.1-1, any value between 0.2-5, any value between 1-10, any value between 5-15, and any other number between any two values. By controlling the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area b of the positive electrode active material layered sodium transition metal oxide within a suitable range, a good balance between the performance of the layered sodium transition metal oxide and the effect of the additive can be better achieved, thereby better improving the battery performance.

[0087] In the embodiment of the present application, the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area c of the Prussian blue (white) compound satisfies: 0.1≤e / c≤15. In some embodiments, the numerical ratio of e / c can be 0.2-10. As an example, the numerical ratio of e / c can be typically but not limitatively, for example, 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, and the number between any two of the above values, which are all the range values ​​of e / c, for example, e / c can be taken from any value between 0.1-1, and can also be taken from any value between 0.2-5, and can also be taken from any value between 1-10, and can also be taken from any value between 5-15, and can also be taken from any other number between any two values. By controlling the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area c of the positive electrode active material Prussian blue (white) compound within a suitable range, a good balance between the performance of the Prussian blue (white) compound and the effect of the additive can be better achieved, thereby better improving the battery performance.

[0088] In the embodiment of the present application, the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area d of the sodium polyanionic compound satisfies: 0.005≤e / d≤0.4. In some embodiments, the numerical ratio of e / d can be 0.01-0.3. As an example, the numerical ratio of e / d can be typically but not limitatively 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, and the number between any two of the above values, which are all the range values ​​of e / d, for example, e / d can be taken from a value between 0.005-0.05, or any value between 0.01-0.2, or any value between 0.1-0.3, or any value between 0.2-0.4, or any other number between any two values. By controlling the numerical ratio of the mass percentage e of the sodium salt additive to the specific surface area d of the positive electrode active material sodium polyanion compound within a suitable range, a good balance between the performance of the sodium polyanion compound and the effect of the additive can be better achieved, thereby better improving the battery performance.

[0089] It can be understood that the calculated values ​​of e / b, e / c, and e / d mentioned above may allow for certain measurement test system errors during actual test operations, and the values ​​within the system error range may be understood as the range specified in the embodiments of the present application.

[0090] It should be noted that the numerical ratio of e to b refers to the ratio of e to b without considering the unit. For example, e is 1% and b is 0.5 m 2 / g, then the numerical ratio of e to b is e / b = 1 / 0.5 = 2. Similarly, the numerical ratio of e to c refers to the ratio of the two without considering the unit, for example, e is 1% and c is 0.5m 2 / g, then the numerical ratio of e to c is e / c = 1 / 0.5 = 2. Similarly, the numerical ratio of e to d refers to the ratio of the two without considering the unit, for example, e is 1% and d is 10m 2 / g, then the numerical ratio of e and d is e / d=1 / 10=0.1.

[0091] In the embodiment of the present application, the electrolyte may also include one or more of sulfur-containing ester compounds, nitrile compounds, and acid anhydride compounds. The sulfur-containing ester compounds can form high-quality interface films on the surfaces of positive and negative electrode materials, improve the high-temperature performance of sodium ion batteries and inhibit gas production; the nitrile compounds can complex transition metal ions in positive electrode materials, reduce the catalytic activity of transition metal ions, reduce the dissolution of transition metal ions and improve the oxidation resistance of the electrolyte; the acid anhydride compounds can form films on the surfaces of positive and negative electrode materials, reducing the problems caused by the high alkalinity of the positive electrode materials.

[0092] In some embodiments of the present application, the mass percentage of the sulfur-containing ester compound in the electrolyte may be 1%-5%, for example, 1%, 2%, 3%, 4%, 5%. Controlling the sulfur-containing ester compound to a suitable content is conducive to not reducing other performances of the battery when it exerts its beneficial effects.

[0093] In the embodiment of the present application, the sulfur-containing ester compound includes but is not limited to at least one of dimethyl sulfite, diethyl sulfite, vinyl sulfite, vinyl sulfate (DTD), propylene sulfate (TS), methylene methanedisulfonate (MMDS), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), 1,4-butane sultone (BS), dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate.

[0094] In some embodiments of the present application, the mass percentage of the nitrile compound in the electrolyte may be 1%-6%, for example, 1%, 2%, 3%, 4%, 5%, 6%. Controlling the nitrile compound to a suitable content is conducive to not reducing other performances of the battery when it exerts its beneficial effects.

[0095] In the embodiments of the present application, the nitrile compound includes a mononitrile compound and / or a polynitrile compound. In some embodiments, the mononitrile compound includes but is not limited to at least one of acetonitrile and p-methylbenzonitrile. In some embodiments, the polynitrile compound includes one or more of succinonitrile (SN), glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane (DENE), and 1,3,6-hexanetrinitrile (HTCN).

[0096] In some embodiments of the present application, the mass percentage of the acid anhydride compound in the electrolyte may be 0.05%-1%, and for example, it may be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1.0%. Controlling the acid anhydride compound to a suitable content is conducive to not reducing other performances of the battery when it exerts its beneficial effects.

[0097] In the embodiment of the present application, the acid anhydride compound includes, but is not limited to, one or more of succinic anhydride (SA), glutaric anhydride, adipic anhydride, maleic anhydride, and cyclic phosphoric anhydride.

[0098] The specific shape or type of the sodium ion battery in the embodiment of the present application is not limited, and can be a square battery, a button battery, a cylindrical battery, a soft-pack battery, etc.; it can be a wound battery or a stacked battery.

[0099] The sodium ion battery provided by the embodiment of the present application, by adding two types of additives, sodium salt additives and organic additives, to the electrolyte, and controlling the ratio of the addition amount of the two types of additives to the specific surface area of ​​the carbon material of the negative electrode within a suitable range, so that the amount of additives is reasonably designed according to the specific surface area of ​​the negative electrode carbon material, and a good balance between the performance of the carbon material and the effect of the additives can be achieved, and the improper amount of additives in the electrolyte can be avoided, resulting in the inability to effectively reduce the side reactions between the electrolyte and the electrode material, reduce the internal resistance, and other problems, thereby better ensuring the electrochemical performance of the battery; and further controlling the addition amount ratio of the two types of additives, sodium salt additives and organic additives, can better take into account the performance of the battery in all aspects; further adjusting the addition amount of sodium salt additives according to the specific surface area of ​​the positive electrode active material can better balance the performance of the positive electrode active material and the effect of the sodium salt additive. This application can significantly improve the comprehensive performance of the battery cell by accurately regulating the relationship between the parameters of the electrolyte and the positive and negative electrode active materials, reduce the trial and error of DOE (Design Of Experiment) experiments, shorten the research and development cycle, and has a practical guiding role. Among them, the sodium salt additive can react with the negative electrode before the organic additive to passivate the negative electrode surface, thereby improving the film quality of the organic additive on the negative electrode surface, effectively avoiding the continuous rupture and dissolution of the SEI film during the cycle, reducing the contact between the negative electrode and the electrolyte, and reducing the probability of side reactions; at the same time, it can enable an appropriate amount of additives to form an effective CEI film on the positive electrode surface, thereby inhibiting the dissolution of positive electrode metal ions; in addition, the addition of an appropriate amount of sodium salt additive can also reduce the consumption and consumption rate of organic additives, improve battery cycle performance, improve high and low temperature storage performance and reduce battery gas production.

[0100] The sodium ion battery provided in the embodiments of the present application can be used in terminal devices, for example, consumer electronic products, such as mobile phones, tablet computers, mobile power supplies, portable computers, laptop computers and other wearable or portable electronic devices, and can also be used in vehicles, energy storage devices, base stations and other equipment products to improve product safety and reliability.

[0101] The present application also provides a method for preparing a sodium ion battery, comprising:

[0102] A positive electrode sheet, a negative electrode sheet, a separator and an electrolyte are provided; wherein the negative electrode sheet comprises a negative electrode active material, the negative electrode active material comprises a carbon material, and the specific surface area of ​​the carbon material is a, and the unit is m 2 / g; the electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a sodium salt additive and an organic additive, the mass percentage of the sodium salt additive in the electrolyte is e, in %, and the mass percentage of the organic additive in the electrolyte is f, in %;

[0103] Among them, the numerical ratio of e to a is controlled to satisfy: 0.01≤e / a≤3.5, and the numerical ratio of f to a is controlled to satisfy: 0.05≤f / a≤10;

[0104] The positive electrode sheet, negative electrode sheet, separator and electrolyte are assembled to obtain a sodium ion battery.

[0105] It can be understood that the relevant features involved in the preparation method can be found in the above description of the sodium ion battery and will not be repeated here.

[0106] The method for preparing a sodium ion battery provided in an embodiment of the present application can effectively improve the cycle performance and storage performance of the battery by controlling the ratio of the added amount of two types of additives, namely, sodium salt additives and organic additives, to the specific surface area of ​​the carbon material of the negative electrode within a suitable range.

[0107] See also Figure 2 , the embodiment of the present application also provides an electric device 200, which includes a housing 211, and electronic components and a battery 212 contained in the housing 211, the battery 212 supplies power to the electronic components, and the battery 212 includes the sodium ion battery described above in the embodiment of the present application. In the present application, the electric device 200 can be a consumer electronic product, such as a mobile phone, a tablet computer, a desktop computer, a laptop computer, a mobile power supply, a portable computer, a smart screen, a display, an audio system, a vehicle-mounted product, and other wearable or movable electronic devices (such as glasses, watches, bracelets, headphones, etc.), or it can be a vehicle, an energy storage device, a base station, and other equipment products.

[0108] The embodiments of the present application are further described below with reference to a plurality of embodiments.

[0109] In the sodium ion batteries of the following examples and comparative examples, the positive electrode active material is NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 (abbreviated as NFM), Na2Mn[Fe(CN)6] (abbreviated as PBA), and NaFePO4 (abbreviated as NFP) materials; the negative electrode active materials use hard carbon and soft carbon materials.

[0110] Sodium ion battery production:

[0111] Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent Super P and 96% positive electrode active materials (NFM, PBA, NFP) by weight, add them into N-methylpyrrolidone (NMP) in sequence, stir and mix them evenly, apply the slurry on an aluminum foil current collector, dry, cold press and cut to obtain positive electrode sheets;

[0112] Weigh 1.5% CMC, 2.5% SBR, 1% Super P and 95% negative electrode active material (hard carbon, soft carbon) by weight, add them into deionized water in sequence, stir and mix them evenly, apply the slurry on the copper foil current collector, dry, cold press and cut to obtain negative electrode sheets;

[0113] The positive electrode sheet, negative electrode sheet and commercial PE separator prepared above are made into battery cells, packaged with polymer, infused with the sodium ion battery electrolyte prepared above, and processed through processes such as chemical formation to produce a 2Ah soft-pack sodium ion battery.

[0114] Example 1

[0115] Preparation of electrolyte: Ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of EC:PC:EMC=10:25:65, and then sodium hexafluorophosphate (NaPF6) was added to the resulting mixture to a molar concentration of 1 mol / L, and then additives of different types and contents were added (see Table 1).

[0116] The sodium salt additive A is NaDFOB, and the sodium salt additive B is NaPO2F2. The FEC content f in the original electrolyte refers to the FEC content in the electrolyte prepared as above, that is, the FEC content in the electrolyte before battery formation.

[0117] Examples 2-41 and Comparative Examples 1-13 were all carried out according to the method of Example 1, except that the types of positive active materials and negative active materials of the sodium ion battery, the specific surface areas a, b, c, and d of the positive active materials and negative active materials were different, the types and contents of additives in the electrolyte were different, e / a, e / f, and f / a were different, and e / b, e / c, or e / d were different, as shown in Table 1. In addition, 2% sulfur-containing ester compounds (2% PS) were added to the electrolyte of Example 37, 2% nitrile compounds (2% DENE) were added to the electrolyte of Example 38, and 0.1% acid anhydride compounds (0.1% SA) were added to the electrolyte of Example 39.

[0118] 25℃ Cyclic Performance Test:

[0119] The sodium ion batteries prepared in Examples 1-41 and Comparative Examples 1-13 were placed in an oven at a constant temperature of 2523°C, charged to 3.95V at a constant current of 0.5C, then charged at a constant voltage until the current dropped to 0.05C, left to rest for 10 minutes, and then discharged to 2.0V at a constant current of 0.5C. This cycle was repeated 300 times, and the discharge capacities of the 1st and 300th cycles were recorded. The capacity retention rate of the cycle was calculated according to the following formula, and the results are recorded in Table 1.

[0120] Capacity retention rate (%)=discharge capacity at the 300th cycle / discharge capacity at the 1st cycle×100%.

[0121] Performance test at 60℃ for 30 days:

[0122] The sodium ion batteries prepared in Examples 1-41 and Comparative Examples 1-13 were placed in an oven at a constant temperature of 2523°C, charged to 3.95V at a constant current of 0.2C, then charged at a constant voltage until the current dropped to 0.05C, and rested for 10 minutes, and then discharged to 2.0V at a constant current of 0.2C, and the capacity was recorded as the initial capacity; the battery was charged to 3.95V at a constant current of 0.2C again, and then charged at a constant voltage until the current dropped to 0.05C, and rested for 10 minutes. The charged battery was placed at 60°C for 30 days, and then placed in an open circuit at room temperature for 2 hours, and discharged to 2.0V at a constant current of 0.2C, which was recorded as the residual capacity. The residual capacity retention rate of the cycle was calculated according to the following formula, and the results are recorded in Table 1.

[0123] Record remaining capacity retention rate (%) = remaining capacity / initial capacity × 100%.

[0124] The specific surface area of ​​the positive electrode active material and the specific surface area of ​​the negative electrode active material are measured by a specific surface area analyzer. The content of the sodium salt additive in the electrolyte can be measured by an ion chromatograph, and the organic additives such as FEC in the electrolyte can be measured by gas chromatography.

[0125] Table 1 Parameter details and battery performance of Examples 1-41 and Comparative Examples 1-13

[0126]

[0127]

[0128] It can be seen from the results in Table 1 that the cycle performance of the sodium ion batteries prepared in Examples 1-41 of the present application is significantly better than that of the sodium ion batteries prepared in Comparative Examples 1-13.

[0129] Figure 3 This is a comparison chart of the cycle performance of the sodium ion battery of Example 3 and Comparative Example 2 after 300 cycles at 0.5C / 0.5C; Figure 4 This is a comparison chart of the cycle performance of the sodium ion batteries of Example 23 and Comparative Example 8 after 300 cycles at 0.5C / 0.5C; Figure 5 This is a comparison chart of the cycle performance of the sodium ion batteries of Example 31 and Comparative Example 11 after 300 cycles at 0.5C / 0.5C.

[0130] (1) From Table 1, and Figures 3 to 5The results show that the sodium ion batteries prepared in Examples 1 to 41 of the present application simultaneously add appropriate amounts of FEC additives and sodium salt additives when preparing the electrolyte, and an appropriate amount of FEC is retained in the electrolyte after the battery is formed. The sodium ion battery thus obtained has a capacity retention rate of 81.1%-90.6% after 300 cycles of 0.5C / 0.5C, and a capacity retention rate of 90.1%-96.8% after 30 days of storage at 60°C, which is significantly higher than the capacity retention rate (70.2%-75.2%) of the sodium ion battery (Comparative Example 1, Comparative Example 10) obtained without adding sodium salt additives to the electrolyte, and a capacity retention rate of 85.1%-85.3% after 30 days of storage at 60°C. This is attributed to the following: during the battery formation process, the FEC additive and the sodium salt additive competitively bind to the surface of the hard carbon / soft carbon negative electrode to form a better quality SEI film; and after formation, an appropriate amount of FEC remains in the electrolyte, which is beneficial to repair the rupture of the SEI film during the cycle process and to form a CEI film on the positive electrode surface, thereby improving the cycle performance of the sodium ion battery.

[0131] (2) Comparison: The positive electrode active material is the same as NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 In Examples 1-21 and Comparative Examples 1-6 of O2(NFM), when the FEC, hard carbon / soft carbon specific surface area a and NFM positive electrode material specific surface area b are fixed, the ratio e / a of the mass percentage content e of the sodium salt additive in the electrolyte to the specific surface area a of the hard carbon / soft carbon, the ratio f / a of the mass percentage content f of the fluorocarbonate in the electrolyte to the specific surface area a of the hard carbon / soft carbon, the ratio e / f of the mass percentage content e of the sodium salt additive in the electrolyte to the mass percentage content f of the fluorocarbonate in the electrolyte, and / or the ratio e / b of the mass percentage content e of the sodium salt additive in the electrolyte to the specific surface area b of the NFM material are within a suitable range, which can significantly improve the battery cycle performance and high temperature storage performance. This is attributed to: According to the specific surface area of ​​the negative electrode active material, the content of sodium salt additives and organic additives in the electrolyte is controlled within a suitable range, which is conducive to the formation of high-quality CEI film and SEI film on the surface of the positive and negative electrodes respectively, effectively reducing the side reactions between the electrolyte and the electrode materials, inhibiting the dissolution of metal ions in the positive electrode material, reducing the internal resistance, controlling the consumption and consumption rate of additives, and ultimately improving the cycle life and storage performance of the battery.

[0132] For example, in the sodium ion batteries provided in Comparative Example 3 and Comparative Example 2, 1.0% FEC is also added to the electrolyte, but the sodium ion battery provided in Example 3 further adds 1.0% by mass of a sodium salt additive NaPO2F2 to the electrolyte during the preparation of the electrolyte, maintaining e / a=0.2, f / a=0.2, e / f=1.0, and e / b=2.0. In the sodium ion battery obtained by chemical formation in Example 3, the mass percentage of FEC in the electrolyte is 0.58%, and the capacity retention rate of the final sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 89.3%, and the capacity retention rate after storage at 60°C for 30 days is 96.6%; while in Comparative Example 2, only 0.02% of the sodium salt additive NaPO2F2 is added to the electrolyte, at this time e / a=0.004, f / a=0.2, e / f=0.02, e / b=0.04, and the mass percentage of FEC in the electrolyte obtained by chemical formation is only 0.18%, and the capacity retention rate of the final sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 76.4% and the capacity retention rate after storage at 60°C for 30 days is 87.6%, which is significantly lower than Example 3. By comparing the sodium ion batteries provided in Example 3 (e / a=0.2, e / b=2.0) and Comparative Example 2 (e / a=0.004, e / b=0.04), it can be seen that: when e / a<0.01, e / b<0.1, the content of the sodium salt additive is too little to effectively passivate the surface of the hard carbon negative electrode, resulting in excessive consumption of fluorocarbonate (FEC) in the film formation, and the inability to effectively inhibit the side reactions in the late stage of the battery cycle. Therefore, although the sodium ion battery of Comparative Example 2 has both the sodium salt additive and FEC added to the electrolyte, it has little effect on improving the battery cycle performance and high temperature storage performance.

[0133] For example, by comparing the sodium ion batteries provided in Example 9 and Comparative Example 3, it can be seen that even though a sodium salt additive and FEC are added to the electrolyte at the same time in Comparative Example 3, since the ratio of the mass percentage f of the fluorocarbonate in the electrolyte to the specific surface area a of the hard carbon is f / a<0.05, the amount of fluorocarbonate added is relatively too small, and therefore the battery in Comparative Example 3 cannot obtain higher cycle performance and high temperature storage performance.

[0134] For example, from the sodium ion batteries provided by Comparative Example 17 and Comparative Example 6, it can be seen that even though the sodium salt additive and FEC are added to the electrolyte at the same time in Comparative Example 6, since the ratio of the mass percentage e of the sodium salt additive in the electrolyte to the specific surface area a of the hard carbon (e / a>3.5), the amount of sodium salt additive added is relatively too much, and therefore the battery in Comparative Example 6 cannot obtain higher cycle performance and high temperature storage performance.

[0135] The sodium ion batteries of Example 10 and Comparative Example 1 were charged to 3.1V at 0.05C and hot pressed at 45°C. The voltage and capacity data during the charging process were read, and the capacity was differentiated with respect to the voltage to obtain the dQ / dV data. A graph was drawn with the voltage as the horizontal axis and the dQ / dV data as the vertical axis to obtain Figure 6 The film formation potential diagram of the sodium ion battery shown in Figure 1. Figure 6 It can be seen that a new peak appears at about 2200 mV, indicating that NaDFOB can form a film on the surface of the hard carbon negative electrode material before FEC.

[0136] (3) By comparing Examples 22-30 and Comparative Examples 7-9 in which the positive electrode active material is the same Na2Mn[Fe(CN)6](PBA), when the FEC, hard carbon / soft carbon specific surface area a and PBA positive electrode material specific surface area c are fixed, the ratio e / a of the mass percentage e of the sodium salt additive in the electrolyte to the specific surface area a of the hard carbon / soft carbon, the ratio f / a of the mass percentage f of the fluorocarbon ester in the electrolyte to the specific surface area a of the hard carbon / soft carbon, the ratio e / f of the mass percentage e of the sodium salt additive in the electrolyte to the mass percentage f of the fluorocarbon ester in the electrolyte, and / or the ratio e / c of ​​the mass percentage e of the sodium salt additive in the electrolyte to the specific surface area c of the PBA material are within a suitable range, which can significantly improve the battery cycle performance and high temperature storage performance. This is attributed to: According to the specific surface area of ​​the negative electrode active material, the content of sodium salt additives and organic additives in the electrolyte is controlled within a suitable range, which is conducive to the formation of high-quality CEI film and SEI film on the surface of the positive and negative electrodes respectively, effectively reducing the side reactions between the electrolyte and the electrode materials, inhibiting the dissolution of metal ions in the positive electrode material, reducing the internal resistance, controlling the consumption and consumption rate of additives, and ultimately improving the cycle life and storage performance of the battery.

[0137] Specifically, the sodium ion batteries provided in Comparative Example 23 and Comparative Example 8 also added 1% FEC to the electrolyte, but the sodium ion battery provided in Example 23 also added 1.0% by mass of a sodium salt additive NaDFOB to the electrolyte during the preparation of the electrolyte, maintaining e / a=0.2, f / a=0.2, e / f=1.0, and e / c=1.25. In the sodium ion battery obtained by chemical formation in Example 23, the mass percentage of FEC in the electrolyte is 0.45%, and the capacity retention rate of the final sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 87.9% and the capacity retention rate after storage at 60°C for 30 days is 95.3%; while in Comparative Example 8, only 0.02% of the sodium salt additive NaDFOB is added to the electrolyte, at this time e / a=0.004, f / a=0.2, e / f=0.02, e / c=0.025, and the mass percentage of FEC in the sodium ion battery obtained by chemical formation is only 0.15%, and the capacity retention rate of the final sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 76.1% and the capacity retention rate after storage at 60°C for 30 days is 87.2%, which is significantly lower than Example 23. By comparing the sodium ion batteries provided in Example 23 (e / a=0.2, e / c=1.25) and Comparative Example 8 (e / a=0.004, e / c=0.025), it can be seen that: when e / a<0.01 and e / c<0.1, the content of the sodium salt additive is too little to effectively passivate the surface of the hard carbon negative electrode, resulting in excessive consumption of fluorocarbonate (FEC) in the film formation, and unable to effectively inhibit the side reactions in the late stage of the battery cycle. Therefore, although the sodium ion battery of Comparative Example 8 has both sodium salt additives and FEC added to the electrolyte, it has little effect on improving the battery cycle performance and high-temperature storage performance.

[0138] (4) By comparing Examples 31-34 and Comparative Examples 10-13 in which the positive electrode active material is the same NaFePO4 (NFP), when the FEC, hard carbon / soft carbon specific surface area a and NFP positive electrode material specific surface area d are fixed, the ratio e / a of the mass percentage e of the sodium salt additive in the electrolyte to the specific surface area a of the hard carbon / soft carbon, the ratio f / a of the mass percentage f of the fluorocarbon ester in the electrolyte to the specific surface area a of the hard carbon / soft carbon, the ratio e / f of the mass percentage e of the sodium salt additive in the electrolyte to the mass percentage f of the fluorocarbon ester in the electrolyte, and / or the ratio e / d of the mass percentage e of the sodium salt additive in the electrolyte to the specific surface area d of the NFP material are within a suitable range, which can significantly improve the battery cycle performance and high temperature storage performance. This is attributed to: According to the specific surface area of ​​the negative electrode active material, the content of sodium salt additives and organic additives in the electrolyte is controlled within a suitable range, which is conducive to the formation of high-quality CEI film and SEI film on the surface of the positive and negative electrodes respectively, effectively reducing the side reactions between the electrolyte and the electrode materials, inhibiting the dissolution of metal ions in the positive electrode material, reducing the internal resistance, controlling the consumption and consumption rate of additives, and ultimately improving the cycle life and storage performance of the battery.

[0139] For example, in the sodium ion battery provided in Example 31 and Comparative Example 11, 1% FEC is also added to the electrolyte. In the sodium ion battery provided in Example 31, 1.0% of the sodium salt additive NaPO2F2 is also added to the electrolyte during the preparation of the electrolyte, e / a=0.25, f / a=0.25, e / f=1.0, e / d=0.1. In the sodium ion battery obtained by chemical formation in Example 31, the mass percentage of FEC in the electrolyte is 0.42%, and the capacity retention rate of the finally obtained sodium ion battery after 300 cycles of 0.5C / 0.5C is 88.6% and the capacity retention rate after 30 days of storage at 60°C is 95.9%. In Comparative Example 11, only 0.01% by mass of the sodium salt additive NaPO2F2 was added to the electrolyte, e / a=0.0025, f / a=0.25, e / f=0.01, e / d=0.001, and in the sodium ion battery obtained after chemical formation, the mass percentage of FEC in the electrolyte was only 0.15%. The capacity retention rate of the final sodium ion battery after 300 cycles of 0.5C / 0.5C was 78.7% and the capacity retention rate after storage at 60°C for 30 days was 87.4%, which was significantly lower than that in Example 31. By comparing the sodium ion batteries provided by Example 31 (e / a=0.25, e / d=0.1) and Comparative Example 11 (e / a=0.0025, e / d=0.001), it can be seen that: when e / a<0.01, e / d<0.005, the content of the sodium salt additive is too little to effectively passivate the surface of the hard carbon negative electrode, resulting in excessive consumption of fluorocarbonate (FEC) in the film formation, and unable to effectively inhibit the side reactions in the late stage of the battery cycle. Therefore, although the sodium ion battery of Comparative Example 11 has both sodium salt additives and FEC added to the electrolyte, it has little effect on improving the battery cycle performance and high-temperature storage performance.

[0140] For example, from the sodium ion batteries provided by Comparative Example 14 and Comparative Example 13, it can be seen that even though the sodium salt additive and FEC are added to the electrolyte at the same time in Comparative Example 13, since the ratio of the mass percentage f of the fluorocarbonate in the electrolyte to the specific surface area a of the soft carbon is f / a>10.0, the amount of fluorocarbonate added is relatively too much, and therefore the battery of Comparative Example 13 cannot obtain higher cycle performance and high temperature storage performance.

[0141] (5) Comparing the sodium ion batteries provided in Example 35 and Example 14, 10.0% FEC was also added to the electrolyte. However, in the sodium ion battery provided in Example 14, 3.0% by weight of the sodium salt additive NaDFOB was added to the electrolyte during the preparation of the electrolyte, maintaining e / a=3.0, f / a=10.0, e / f=0.3, and e / b=6.0. In the sodium ion battery obtained by chemical formation in Example 14, the mass percentage of FEC in the electrolyte is 4.96%, and the capacity retention rate of the final sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 85.1% and the capacity retention rate after storage at 60°C for 30 days is 93.2%; while in Example 35, a sodium salt additive NaDFOB with a mass percentage of 0.08% is added to the electrolyte, at this time e / a=0.08, f / a=10.0, e / f=0.008, e / b=0.16, and the mass percentage of FEC in the sodium ion battery obtained by chemical formation is 2.82%, and the capacity retention rate of the final sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 81.1% and the capacity retention rate after storage at 60°C for 30 days is 90.1%, which is lower than Example 14. By comparing the sodium ion batteries provided in Example 14 (e / f=0.3) and Example 35 (e / f=0.008), it can be seen that when e / f>0.01 is controlled, it is beneficial to improve the battery cycle performance and high temperature storage performance.

[0142] Comparing the sodium ion batteries provided in Example 36 and Example 17, 2.8% of the sodium salt additive was also added to the electrolyte. However, in the sodium ion battery provided in Example 17, 0.6% by weight of the organic additive FEC was added to the electrolyte during the preparation of the electrolyte, maintaining e / a=3.5, e / f=4.67, f / a=0.75, and e / b=5.6. In the sodium ion battery obtained by chemical formation in Example 17, the mass percentage of FEC in the electrolyte is 0.27%, and the capacity retention rate of the final sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 84.6% and the capacity retention rate after storage at 60°C for 30 days is 94.3%; while in Example 36, an organic additive FEC with a mass percentage of 0.3% is added to the electrolyte, at this time e / a=3.5, e / f=9.33, f / a=0.38, e / b=5.6, and the mass percentage of FEC in the sodium ion battery obtained by chemical formation is 0.08%, and the capacity retention rate of the final sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 81.7% and the capacity retention rate after storage at 60°C for 30 days is 90.7%, which is lower than Example 17. By comparing the sodium ion batteries provided in Example 17 (e / f=4.67) and Example 35 (e / f=9.33), it can be seen that when e / f≤8.0 is controlled, it is beneficial to improve the battery cycle and high temperature storage performance.

[0143] (6) Comparing the sodium ion batteries provided in Examples 37-39 and Example 10, 2.0% of the organic additive FEC and 0.5% of the sodium salt additive NaDFOB were also added to the electrolyte. However, in the sodium ion batteries provided in Examples 37-39, 2% of PS (Example 37), 2% of DENE (Example 38) and 0.1% of SA (Example 39) were added to the electrolyte during the preparation of the electrolyte, respectively, and e / a=0.25, e / f=0.25, f / a=1.0, and e / b=1.0 were maintained. Finally, the capacity retention rate of the sodium ion battery obtained in Examples 37-39 after 300 cycles of 0.5C / 0.5C and the capacity retention rate after 30 days of storage at 60°C were slightly higher than those in Example 10, which indicates that the addition of appropriate amounts of sulfur-containing ester compounds, nitrile compounds, and anhydride compounds is beneficial to further improve the cycle performance and high temperature storage performance of the battery.

[0144] (7) Comparing the sodium ion batteries provided in Example 40 and Example 10, 2.0% of the organic additive FEC was also added to the electrolyte. However, in the sodium ion battery provided in Example 10, 0.5% by weight of the sodium salt additive NaDFOB was added to the electrolyte during the preparation of the electrolyte, maintaining e / a=0.25, e / f=0.25, f / a=1.0, and e / b=1.0. In the sodium ion battery obtained by chemical formation in Example 10, the mass percentage of FEC in the electrolyte is 0.95%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 86.8%, and the capacity retention rate after storage at 60°C for 30 days is 95.2%; while in Example 40, a sodium salt additive NaDFOB with a mass percentage of 0.08% is added to the electrolyte, at this time e / a=0.04, e / f=0.04, f / a=1.0, e / b=0.08, and the mass percentage of FEC in the electrolyte obtained by chemical formation is 0.57%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 82.3%, and the capacity retention rate after storage at 60°C for 30 days is 91.3%, which is lower than Example 10. By comparing the sodium ion batteries provided in Example 10 (e / b=1.0) and Example 40 (e / b=0.08), it can be seen that when e / b>0.1 is controlled, it is beneficial to improve the battery cycle and high temperature storage performance.

[0145] (8) Comparing the sodium ion batteries provided in Example 41 and Example 10, 2.0% of the organic additive FEC was also added to the electrolyte. However, in the sodium ion battery provided in Example 10, 0.5% by weight of the sodium salt additive NaDFOB was added to the electrolyte during the preparation of the electrolyte, maintaining e / a=0.25, e / f=0.25, f / a=1.0, and e / b=1.0. In the sodium ion battery obtained by chemical formation in Example 10, the mass percentage of FEC in the electrolyte is 0.95%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 86.8% and the capacity retention rate after storage at 60°C for 30 days is 95.2%; while in Example 41, a sodium salt additive NaDFOB with a mass percentage of 2.5% is added to the electrolyte, at this time e / a=1.25, e / f=1.25, f / a=1.0, e / b=16.67, and the mass percentage of FEC in the electrolyte obtained by chemical formation is 1.05%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles is 82.5% and the capacity retention rate after storage at 60°C for 30 days is 91.8%, which is lower than Example 10. By comparing the sodium ion batteries provided in Example 10 (e / b=1.0) and Example 41 (e / b=16.67), it can be seen that when e / b≤15.0 is controlled, it is beneficial to improve the battery cycle and high temperature storage performance.

[0146] In summary, adding sodium salt additives and organic additives to the electrolyte of the sodium ion battery at the same time and controlling the sodium salt additives and organic additives to a suitable content according to the specific surface area of ​​the negative electrode carbon material can improve the capacity retention rate of the sodium ion battery after 300 cycles of 0.5C / 0.5C and the capacity retention rate after storage at 60°C for 30 days.

[0147] It should be understood that the first, second and various numerical numbers involved in this document are only distinguished for the convenience of description and are not used to limit the scope of the present application.

[0148] In this application, "and / or" describes the association relationship of associated objects, indicating that there can be three relationships. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects are in an "or" relationship.

[0149] In this application, "at least one" means one or more, and "plurality" means two or more. "At least one of the following" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, "at least one of a, b, or c", or "at least one of a, b, and c" can all mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, c can be single or multiple, respectively.

[0150] In this application, “-” represents a range value, including the endpoint values ​​at both ends. For example, the value of a can be 0.5-15, which means that the value of a can be between 0.5 and 15, and includes the endpoint values ​​0.5 and 15.

[0151] It should be understood that in the various embodiments of the present application, the size of the serial numbers of the above-mentioned processes does not mean the order of execution, some or all of the steps can be executed in parallel or sequentially, and the execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present application.

Claims

1. A sodium ion battery, characterized in that: The sodium ion battery comprises a positive electrode, a negative electrode, an electrolyte and a separator, the negative electrode comprises a negative electrode active material, the negative electrode active material comprises a carbon material, and the specific surface area of ​​the carbon material is a, in units of m 2 / g; the electrolyte includes an electrolyte salt, an organic solvent and an additive, the additive includes a sodium salt additive and an organic additive, the mass percentage of the sodium salt additive in the electrolyte is e, the unit is %, and the numerical ratio of e to a satisfies: 0.01≤e / a≤3.5; the mass percentage of the organic additive in the electrolyte is f, the unit is %, and the numerical ratio of f to a satisfies: 0.05≤f / a≤10.

2. The sodium ion battery according to claim 1, characterized in that The mass percentage of the sodium salt additive in the electrolyte is 0.05%-3%.

3. The sodium ion battery according to claim 1 or 2, characterized in that: The organic additive comprises fluorinated carbonate, and the mass percentage of the fluorinated carbonate in the electrolyte is 0.1%-10%.

4. The sodium ion battery according to any one of claims 1 to 3, characterized in that: The numerical ratio of the e to the f satisfies: 0.01≤e / f≤8.

5. The sodium ion battery according to any one of claims 1 to 4, characterized in that: The specific surface area of ​​the carbon material is 0.5 m 2 / g-15m 2 / g.

6. The sodium ion battery according to any one of claims 1 to 5, characterized in that: The sodium salt additive includes one or more of sodium bis(oxalatoborate), sodium difluorooxalatoborate, sodium difluorobis(oxalatophosphate), and sodium difluorophosphate.

7. The sodium ion battery according to claim 3, characterized in that: The fluorinated carbonate includes at least one of fluorinated ethylene carbonate and bis-fluorinated ethylene carbonate.

8. The sodium ion battery according to any one of claims 1 to 7, characterized in that: The positive electrode includes a positive electrode active material, and the positive electrode active material includes at least one of a layered sodium transition metal oxide, a Prussian blue (white) compound, and a sodium polyanion compound.

9. The sodium ion battery according to claim 8, characterized in that The positive electrode active material comprises a layered sodium transition metal oxide, wherein the specific surface area of ​​the layered sodium transition metal oxide is 0.1 m 2 / g-1.0m 2 / g, denoted as b; the numerical ratio of e to b satisfies: 0.1≤e / b≤15.

10. The sodium ion battery according to claim 9, characterized in that: The mass percentage of the layered sodium transition metal oxide in the positive electrode material layer is ≥92%; the 0.1C gram capacity of the layered sodium transition metal oxide material is greater than or equal to 100 mAh / g; the compaction density of the positive electrode is 2.9 g / cm 3 -3.6g / cm 3 .

11. The sodium ion battery according to claim 8, characterized in that The positive electrode active material includes a Prussian blue (white) compound, and the specific surface area of ​​the Prussian blue (white) compound is 0.1 m 2 / g-1.0m 2 / g, denoted as c; the numerical ratio of said e to said c satisfies: 0.1≤e / c≤15.

12. The sodium ion battery according to claim 11, characterized in that The mass percentage of the Prussian blue (white) compound in the positive electrode material layer is ≥92%; the 0.1C gram capacity of the Prussian blue (white) compound material is greater than or equal to 130mAh / g; the compaction density of the positive electrode is 1.2g / cm 3 -1.8g / cm 3 .

13. The sodium ion battery according to claim 8, characterized in that The positive electrode active material comprises a sodium polyanion compound, and the specific surface area of ​​the sodium polyanion compound is 5 m 2 / g-25m 2 / g, denoted as d; the numerical ratio of the e to the d satisfies: 0.005≤e / d≤0.

4.

14. The sodium ion battery according to claim 13, characterized in that: The mass percentage of the sodium polyanion compound in the positive electrode material layer is ≥92%; the 0.1C gram capacity of the sodium polyanion compound material is greater than or equal to 100 mAh / g; the compaction density of the positive electrode is 1.8 g / cm 3 -2.8g / cm 3 .

15. The sodium ion battery according to any one of claims 1 to 14, characterized in that: The carbon material includes at least one of natural graphite, artificial graphite, mesophase micro carbon beads, hard carbon, soft carbon, and porous carbon materials.

16. The sodium ion battery according to any one of claims 1 to 15, characterized in that: The mass percentage of the carbon material in the negative electrode material layer is ≥ 93%; the 0.1C gram capacity of the carbon material is greater than or equal to 230 mAh / g; the compaction density of the negative electrode is 0.9 g / cm 3 -1.6g / cm 3 .

17. The sodium ion battery according to any one of claims 1 to 16, characterized in that: The electrolyte also includes one or more of sulfur-containing ester compounds, nitrile compounds, and acid anhydride compounds.

18. The sodium ion battery according to claim 17, characterized in that The mass percentage of the sulfur-containing ester compound in the electrolyte is 1%-5%; the mass percentage of the nitrile compound in the electrolyte is 1%-6%; and the mass percentage of the acid anhydride compound in the electrolyte is 0.05%-1%.

19. The sodium ion battery according to claim 17 or 18, characterized in that: The sulfur-containing ester compound includes one or more of dimethyl sulfite, diethyl sulfite, vinyl sulfite, vinyl sulfate, propylene sulfate, methylene methanedisulfonate, 1,3-propane sultone, 1,3-propylene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate.

20. The sodium ion battery according to claim 17 or 18, characterized in that: The nitrile compounds include mononitrile compounds and / or polynitrile compounds; the mononitrile compounds include at least one of acetonitrile and p-methylbenzonitrile; the polynitrile compounds include one or more of succinonitrile, glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, and 1,3,6-hexanetrinitrile.

21. The sodium ion battery according to claim 17 or 18, characterized in that: The acid anhydride compound includes one or more of succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride, and cyclic phosphoric anhydride.

22. The sodium ion battery according to any one of claims 1 to 21, characterized in that: The electrolyte salts include NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, NaTDI, Na[(CF3SO2)2N], Na[(FSO2)2N] and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], wherein m and n are natural numbers.

23. The sodium ion battery according to any one of claims 1 to 22, characterized in that: The molar concentration of the electrolyte salt in the electrolyte solution is 0.01 mol / L-5.0 mol / L.

24. The sodium ion battery according to any one of claims 1 to 23, characterized in that: The organic solvent includes one or more of carbonate solvents, ether solvents, and carboxylate solvents.

25. A method for preparing a sodium ion battery, characterized in that: include: Provide positive electrode sheets, negative electrode sheets, separators and electrolytes; The negative electrode sheet includes a negative electrode active material, the negative electrode active material includes a carbon material, and the specific surface area of ​​the carbon material is a, in units of m 2 / g; the electrolyte comprises an electrolyte salt, an organic solvent and an additive, the additive comprises a sodium salt additive and an organic additive, the mass percentage of the sodium salt additive in the electrolyte is e, in %; the mass percentage of the organic additive in the electrolyte is f, in %; The numerical ratio of e to a is controlled to satisfy: 0.01≤e / a≤3.5, and the numerical ratio of f to a is controlled to satisfy: 0.05≤f / a≤10; The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are assembled to obtain a sodium ion battery.

26. An electrical equipment, characterized in that: The electrical equipment includes a shell, and electronic components and a battery housed in the shell, the battery supplies power to the electronic components, and the battery includes the sodium ion battery described in any one of claims 1 to 24, or the sodium ion battery prepared by the preparation method described in claim 25.

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