Sodium-ion battery and electrical device

Abstract

A sodium-ion battery, a preparation method therefor, and an electrical device comprising the sodium-ion battery. The sodium-ion battery comprises a positive electrode, a negative electrode, an electrolytic solution, and a separator, the negative electrode comprises a carbon material, the specific surface area of the carbon material is a, and the unit is m2 / g; the electrolytic solution 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 electrolytic solution is e, the unit is %, and the numerical ratio of e to a satisfies: 0.01≤e / a≤3.5; the mass percentage content of the organic additive in the electrolytic solution is f, the unit is %, and the numerical ratio of f to a satisfies: 0.05≤f / a≤10. In the sodium-ion battery, the reasonable usage amount of an additive required in an electrolytic solution is determined on the basis of physical and chemical characteristics of an electrode material, and a proper amount of sodium salt additives and organic additives are added into the electrolytic solution, so that the battery performance can be better improved.

Description

Sodium ion batteries and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on June 14, 2023, with application number 202310710192.4 and application name “Sodium Ion Batteries and Electrical Equipment”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] 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

[0003] Sodium-ion batteries (SIBs), with their abundant sodium resources and low cost, are considered a promising candidate for energy storage applications. However, their widespread application is currently hampered by shortcomings such as poor cycling performance, high-temperature storage, and cyclic flatulence. The performance of SIBs depends primarily on the cathode and anode materials, as well as the electrolyte. Additives are often added to the electrolyte to improve its electrochemical properties and enhance the quality of the anode deposition. For example, in a SIB with a sodium-nickel-iron-manganese cathode and hard carbon anode, common electrolyte additives form a solid electrolyte interface (SEI) film covering the hard carbon anode surface during the formation or volume separation phase, and the additives are largely consumed during this phase. However, the SEI film in SIBs is not stable and cannot be effectively repaired. Furthermore, due to the depletion of additives, the cathode cannot effectively form and repair the cathode electrolyte interface (CEI), affecting the long-term cycling and high-temperature performance of the battery system.

[0004] Summary of the Invention

[0005] 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 negative electrode surface, 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 positive electrode surface, inhibiting the dissolution of positive electrode metal ions; so as to achieve the purpose of improving battery cycle performance, high and low temperature storage performance and reducing gas production.

[0006] Specifically, the first aspect of the embodiment of the present application provides a sodium ion battery, the sodium ion battery comprising a positive electrode, a negative electrode, an electrolyte and a separator, the negative electrode comprising a negative electrode active material, the negative electrode active material comprising a carbon material, the specific surface area of ​​the carbon material is a, the unit is 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.

[0007] It should be noted that the numerical ratio of e to a refers to the ratio of the two without considering the units. For example, e is 1% and a is 0.5m 2 / g, then the numerical ratio of e to a is e / a=1 / 0.5=2.

[0008] Similarly, the numerical ratio of f to a refers to the ratio of the two without considering the units, for example, f is 2% and a is 0.5m 2 / g, then the numerical ratio of f to a is f / a=2 / 0.5=4.

[0009] 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 combination, avoid the problem of ineffective reduction of side reactions between the electrolyte and the electrode material and internal resistance due to improper addition of additives in the electrolyte, 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 formation 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.

[0010] In the embodiment of the present application, the sodium salt additive is present in the electrolyte in an amount of 0.05% to 3% by weight. The addition of an appropriate amount of the sodium salt additive to the electrolyte can better passivate the negative electrode surface, improve the quality of the SEI film formed on the negative electrode, and effectively repair the SEI film during battery cycling. It also facilitates the formation of an effective CEI film on the positive electrode surface during cycling, thereby further 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 rate of organic additives, improve the battery's high and low temperature storage performance, and reduce battery gassing.

[0011] In an 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 low lowest unoccupied molecular orbital (LUMO) energy and are easily reduced before other electrolyte solvents. Using fluorocarbons as organic additives can form a highly crystalline, inorganic-rich SEI film on the surface of the negative electrode of a 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 fluorocarbonate within the above range can better utilize the film-forming advantages of the fluorocarbonate and better improve the battery's cycle performance.

[0012] 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 battery performance, in the embodiment of the present application, the numerical ratio of the e to the f satisfies: 0.01≤e / f≤8.

[0013] In the embodiment of the present application, the specific surface area of ​​the carbon material is 0.5m 2 / g-15m 2 / g. A suitable specific surface area of ​​the negative electrode carbon material is conducive to the negative electrode's ability to better accept and release sodium ions, giving the battery relatively better kinetic performance. At the same time, a suitable specific surface area of ​​the negative electrode carbon material means that adding an appropriate amount of additives can form a stable SEI film, avoiding the improper use of additives.

[0014] In an embodiment of the present application, the sodium salt additive includes one or more of sodium bis(oxalatoborate) (NaBOB), sodium difluorooxalatoborate (NaDFOB), sodium difluorobis(oxalatophosphate) (NaDFOP), and sodium difluorophosphate (NaPO2F2). The above sodium salt additives have a high reduction film-forming potential and can react with the negative electrode before the organic additives, passivating the negative electrode surface, thereby improving the film formation quality of the organic additives on the negative electrode surface, effectively preventing 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.

[0015] In the embodiments of the present application, the fluorocarbonate comprises at least one of fluoroethylene carbonate (FEC) and bisfluoroethylene carbonate (DFEC). These two fluorocarbonates have good film-forming properties on electrode surfaces, effectively protecting the electrodes and ensuring uniform and rapid migration of sodium ions at the interface between the electrode and the electrolyte, thereby improving battery kinetics and cycling performance.

[0016] In an embodiment of the present application, the positive electrode includes a positive electrode active material, which 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 may be a combination of one or more of the aforementioned materials, wherein both the layered sodium transition metal oxide positive electrode material and the Prussian blue (white) compound positive electrode material have high specific capacity, and the sodium polyanion compound has high electrochemical reaction stability.

[0017] 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 0.1m 2 / g-1.0m 2 / g, denoted as b; the numerical ratio of e to b satisfies the following: 0.1 ≤ e / b ≤ 15. Controlling the specific surface area of ​​the layered sodium transition metal oxide within a suitable range helps to better balance battery rate performance with cycling 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 layered sodium transition metal oxide, the positive electrode active material, 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, thereby improving battery performance.

[0018] 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 compacted density of the positive electrode is 2.9 g / cm 3 -3.6g / cm 3 Controlling the mass content of layered sodium transition metal oxides in the positive electrode material layer to a high ratio is beneficial for increasing battery capacity. Selecting a high-capacity positive electrode active material is beneficial for increasing the overall battery capacity and improving charge and discharge performance. A suitable positive electrode compaction density helps the battery achieve higher energy density while also achieving better other performance characteristics.

[0019] 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 0.1m 2 / g-1.0m2 / g, denoted as c; the numerical ratio of e to c satisfies: 0.1≤e / c≤15. Controlling the specific surface area of ​​the positive electrode active material within a suitable range is beneficial for better balancing battery rate performance with battery cycling 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 Prussian blue (white) compound of the positive electrode active material 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, thereby further improving battery performance.

[0020] 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 130 mAh / g; the compacted density of the positive electrode is 1.2 g / cm 3 -1.8g / cm 3 Controlling the mass content of Prussian blue (white) compounds in the positive electrode material layer to a high ratio is beneficial for increasing battery capacity. Selecting a positive electrode active material with a larger capacity is beneficial for increasing the overall capacity of the battery and improving charge and discharge performance. A suitable positive electrode compaction density helps the battery achieve higher energy density while also having better other performance characteristics.

[0021] 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 e to d satisfies the following: 0.005 ≤ e / d ≤ 0.4. Controlling the specific surface area of ​​the positive electrode active material within a suitable range helps to better balance battery rate performance with battery cycling 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 sodium polyanionic compound of the positive electrode active material within a suitable range can better achieve a good balance between the performance of the sodium polyanionic compound and the effect of the additive, thereby further improving battery performance.

[0022] 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 compacted density of the positive electrode is 1.8 g / cm 3 -2.8g / cm 3 Controlling the mass content of sodium polyanionic compounds in the positive electrode material layer to a high ratio is beneficial for increasing battery capacity. Selecting a high-capacity positive electrode active material is beneficial for increasing the overall capacity of the battery and improving charge and discharge performance. A suitable positive electrode compaction density helps the battery achieve higher energy density while also having better other performance characteristics.

[0023] 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.

[0024] 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 material. The negative electrode of the sodium ion battery of the present application may include one or more of the above carbon materials.

[0025] In the embodiment of the present application, the mass percentage of the carbon material in the negative electrode material layer is ≥93%; the compacted density of the negative electrode is 0.9 g / cm 3 -1.6g / cm 3 The appropriate negative electrode compaction density is beneficial for the battery to obtain higher energy density while having better other performance.

[0026] In an embodiment of the present application, the electrolyte further comprises one or more of a sulfur-containing ester compound, a nitrile compound, and an anhydride compound. The sulfur-containing ester compound can form a high-quality interfacial film on the surface of the positive and negative electrode materials, improving the high-temperature performance of the sodium-ion battery and inhibiting gas production; the nitrile compound can complex the transition metal ions in the positive electrode material, reducing the catalytic activity of the transition metal ions, reducing the dissolution of the transition metal ions, and improving the oxidation resistance of the electrolyte; and the anhydride compound can form a film on the surface of the positive and negative electrode materials, reducing the problems caused by the high alkalinity of the positive electrode material.

[0027] In the embodiment of the present application, the sulfur-containing ester compound comprises 1% to 5% by weight of the electrolyte; the nitrile compound comprises 1% to 6% by weight of the electrolyte; and the anhydride compound comprises 0.05% to 1% by weight of the electrolyte. Controlling the amounts of these various additives to appropriate levels allows them to exert their beneficial effects without degrading other battery properties.

[0028] 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, ethylene sulfite, ethylene sulfate, propylene sulfate, methylene methanedisulfonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] In the embodiment of the present application, the organic solvent includes one or more of carbonate solvents, ether solvents, and carboxylate solvents.

[0034] A second aspect of an embodiment of the present application provides a method for preparing a sodium ion battery, comprising:

[0035] 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 %;

[0036] 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;

[0037] The positive electrode sheet, the negative electrode sheet, the separator and the electrolyte are assembled to obtain a sodium ion battery.

[0038] 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. 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

[0039] FIG1 is a schematic structural diagram of a sodium ion battery 100 provided in an embodiment of the present application;

[0040] FIG2 is a schematic structural diagram of an electric device 200 provided in an embodiment of the present application;

[0041] FIG3 is a comparison of the cycle performance of the sodium ion batteries of Example 3 of the present application and Comparative Example 2 after 300 cycles at 0.5C / 0.5C;

[0042] FIG4 is a comparison of the cycling performance of the sodium ion batteries of Example 23 of the present application and Comparative Example 8 after 300 cycles at 0.5C / 0.5C;

[0043] FIG5 is a comparison of the cycling performance of the sodium ion batteries of Example 31 of the present application and Comparative Example 11 after 300 cycles at 0.5C / 0.5C;

[0044] FIG6 is a diagram of the film formation potential of the sodium ion batteries of Example 10 and Comparative Example 1 of the present application. DETAILED DESCRIPTION

[0045] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0046] 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 a sodium-ion battery with a positive electrode material of sodium-nickel-iron-manganese and a negative electrode material of hard carbon 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 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 subsequently; in addition, because the additives are basically consumed, the positive electrode cannot effectively form and repair the CEI film, which affects 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 formation 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 battery cycle performance, high and low temperature storage performance and reducing gas production.

[0047] As shown in FIG1 , 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 provided 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; electrolyte 40 includes an electrolyte salt, an organic solvent, and additives, including a sodium salt additive and an organic additive. The mass percentage of the sodium salt additive in electrolyte 40 is e, expressed in %, where the ratio of e to a satisfies the following: 0.01 ≤ e / a ≤ 3.5; the mass percentage of the organic additive in electrolyte 40 is f, expressed in %, where the ratio of f to a satisfies the following: 0.05 ≤ f / a ≤ 10. Under these conditions, the electrode materials and electrolyte in the battery are well matched, effectively reducing side reactions between the electrolyte and electrode materials, lowering impedance, improving battery cycle performance, and improving high-temperature performance.

[0048] 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 0.5m 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 to a is f / a=2 / 0.5=4.

[0049] It should be noted that the sodium ion battery 100 of the embodiment of the present application can be a battery in various stages: before formation, after formation, after capacity separation, and after cycling.

[0050] 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 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 combination, 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 formation 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.

[0051] 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.

[0052] positive electrode

[0053] As shown in Figure 1, in an embodiment of the present application, the positive electrode 10 includes a positive electrode current collector 101 and a positive electrode material layer provided on the surface of the positive electrode current collector 101, wherein the positive electrode current 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-intercalate sodium ions. In an embodiment of the present application, the positive electrode active material may be at least one of layered sodium transition metal oxides, Prussian blue (white) compounds, and sodium polyanion compounds. The positive electrode active material may be a combination of one or more (two or more) materials selected from the above. 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 an 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.

[0054] 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 recorded as b, which can be 0.1m 2 / g-1.0m 2 / g. 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 beneficial to better balance the battery rate performance with the battery cycle and storage performance.

[0055] 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.

[0056] 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 compacted 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 cathode material layer to a high ratio is beneficial for improving battery capacity. A suitable cathode compaction density helps the battery achieve higher energy density while also having better other performance properties.

[0057] 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, which can be 0.1m 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 beneficial to better balance the battery rate performance with the battery cycle and storage performance.

[0058] 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.

[0059] 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 compacted density of the positive electrode is 1.2 g / cm 3 -1.8g / cm 3 Controlling the mass content of Prussian blue (white) compounds in the positive electrode material layer to a high ratio is beneficial for improving battery capacity. A suitable positive electrode compaction density helps the battery achieve higher energy density while also having better other performance properties.

[0060] 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, which can be 5m 2 / g-25m 2 / g. In some embodiments, the specific surface area d of the sodium polyanionic compound can 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 beneficial to better balance the battery rate performance with the battery cycle and storage performance.

[0061] 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.

[0062] 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 compacted density of the positive electrode is 1.8 g / cm 3 -2.8g / cm 3 Controlling the mass content of sodium polyanionic compounds in the positive electrode material layer to a high ratio is beneficial for improving battery capacity. A suitable positive electrode compaction density helps the battery achieve higher energy density while also having better other performance properties.

[0063] It can be understood that the values ​​of b, c, and d mentioned above may have a certain impact on the specific surface area test of the material after actual battery formation, capacity separation or cycling due to the formation of the interface film. A certain measurement 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 specific surface area value range of the material test after formation, capacity separation or cycling is still within the above range and may be understood as the range defined in the embodiments of the present application.

[0064] 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.

[0065] In embodiments of the present application, the positive electrode material layer may further include a certain amount of a binder, a 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 fibers, graphene, and the like. The above binders and conductive agents are merely illustrative and are not intended to be limiting.

[0066] negative electrode

[0067] As shown in Figure 1, 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 is capable of accepting and releasing 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 material. 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.

[0068] In the embodiment of the present application, the specific surface area a of the carbon material can be 0.5m 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. A suitable specific surface area of ​​the negative electrode carbon material is conducive to the negative electrode's ability to better accept and release sodium ions, giving the battery relatively better kinetic performance. At the same time, a suitable specific surface area of ​​the negative electrode carbon material means that adding an appropriate amount of additives can form a stable SEI film, avoiding the improper use of additives.

[0069] It can be understood that the value of the above-mentioned a, after actual battery formation, capacity separation or cycling, 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 specific surface area value range of the material test after formation, capacity separation or cycling is still within the above range and can be understood as the range defined in the embodiments of the present application.

[0070] In the embodiments of this 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 helps increase the overall capacity of the battery and improve charge and discharge performance. The 0.1C gram capacity of the carbon material, for a half-cell, refers to the gram capacity at 0.1C.

[0071] In the embodiment of the present application, the mass percentage of carbon material in the negative electrode material layer is ≥93%; the compacted density of the negative electrode is 0.9 g / cm 3 -1.6g / cm 3 The appropriate negative electrode compaction density is beneficial for the battery to obtain higher energy density while having better other performance.

[0072] In embodiments of the present application, the negative electrode material layer may further include a certain amount of a binder, a conductive agent, and other components. Examples of the binder include sodium carboxymethylcellulose (CMC-Na), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), and sodium polyacrylate (NaPAA). Examples of the conductive agent include amorphous carbon, carbon nanotubes, carbon fibers, and graphene. The aforementioned binders and conductive agents are merely illustrative and are not intended to be limiting.

[0073] diaphragm

[0074] As shown in FIG1 , in a sodium-ion battery 100 , a separator 30 blocks electrons while allowing sodium ions to pass through. In some embodiments of the present application, separator 30 includes, but is not limited to, single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, and ceramic-coated PE.

[0075] electrolyte

[0076] As shown in Figure 1, in a sodium ion battery 100, the electrolyte 40 is the 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.

[0077] In the embodiment of the present application, organic solvent includes but is not limited to one or more of carbonate solvents, ether solvents, and carboxylate solvents.Wherein, 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.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, bis (2,2,2-trifluoroethyl) ether one or more.Carboxylate solvents include but are not limited to one or more of methyl formate, ethyl formate, ethyl acetate, propyl acetate, propyl propionate, methyl difluoroacetate, methyl trifluoroacetate.

[0078] In the embodiment of the present application, the electrolyte salts include but are 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 0.01 mol / L-5.0 mol / L. In some embodiments, in the electrolyte, the molar concentration of the electrolyte salt may be, for example, 0.01 mol / L, 0.1 mol / L, 0.5 mol / L, 0.8 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.8 mol / L, 2.0 mol / L, 3.0 mol / L, 4.0 mol / L, or 5.0 mol / L.

[0079] In the embodiment of the present application, the additive includes a sodium salt additive and an organic additive.

[0080] 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, 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 decline in storage performance.

[0081] In an 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 SEI film formation quality 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 positive electrode surface 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.

[0082] 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 limited to 0.05, 0.07, 0.1, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, and numbers between any two of the above values, all of which are 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, or any other number between any two values.

[0083] In an 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 example, f can be 0.1%, 0.3%, 0.5%, 0.7%, 1%, 3%, 5%, 7%, or 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 SEI film rich in inorganic components 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 exert the film-forming advantages of fluorocarbonates and better improve the cycle performance of the battery.

[0084] 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 limited to 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 numbers between any two of the above values, all of which are the range values ​​of e / f. For example, e / f can be any value between 0.01-0.1, any value between 0.05-5.0, any value between 1.0-8.0, or 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 an appropriate 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 worsen the high-temperature gas production problem.

[0085] 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 separation, and after cycling, may be subject to certain measurement and test system errors during actual testing operations, and the values ​​within the system error range may be understood as the range defined in the embodiments of the present application.

[0086] 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 additives have a high reduction film-forming potential and can react with the negative electrode before the organic additives, passivating the negative electrode surface, thereby improving the film formation quality of the organic additives on the negative electrode surface, effectively preventing 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.

[0087] In the embodiments of the present application, the fluorocarbonate may be at least one of fluoroethylene carbonate (FEC) and bisfluoroethylene carbonate (DFEC). These two fluorocarbonates have good film-forming properties on electrode surfaces, effectively protecting the electrodes and ensuring uniform and rapid migration of sodium ions at the interface between the electrode and the electrolyte, thereby improving battery kinetics and cycling 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 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 typically but not limitatively be 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, and numbers between any two of the above values, all of which are 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, 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 b of the positive electrode active material layered sodium transition metal oxide within an appropriate 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 battery performance.

[0089] 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 typically but not limitatively be 0.1, 0.2, 0.5, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, and numbers between any two of the above values, all of which are the range values ​​of e / c, for example, e / c can be any value between 0.1-1, any value between 0.2-5, any value between 1-10, any value between 5-15, 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 c of the positive electrode active material Prussian blue (white) compound within an appropriate 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.

[0090] 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 typically but not limitatively be 0.005, 0.01, 0.05, 0.1, 0.2, 0.3, 0.4, and numbers between any two of the above values, all of which are 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 an appropriate 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 battery performance.

[0091] 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 can be understood as the range specified by the embodiments of this application.

[0092] 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 0.5m 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%, 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 to d is e / d=1 / 10=0.1.

[0093] In embodiments of the present application, the electrolyte may further include one or more of sulfur-containing ester compounds, nitrile compounds, and acid anhydride compounds. The sulfur-containing ester compounds can form high-quality interfacial films on the surfaces of the positive and negative electrode materials, improving the high-temperature performance of the sodium-ion battery and inhibiting gas production. The nitrile compounds can complex transition metal ions in the positive electrode material, reducing the catalytic activity of the transition metal ions, reducing the dissolution of the transition metal ions, and improving the oxidation resistance of the electrolyte. The acid anhydride compounds can form films on the surfaces of the positive and negative electrode materials, reducing problems caused by the high alkalinity of the positive electrode material.

[0094] In some embodiments of the present application, the mass percentage of the sulfur-containing ester compound in the electrolyte can be 1%-5%, for example, 1%, 2%, 3%, 4%, or 5%. Controlling the sulfur-containing ester compound to an appropriate content is beneficial for achieving its beneficial effects without degrading other battery properties.

[0095] 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, ethylene sulfite, ethylene sulfate (DTD), propylene sulfate (TS), methylene methanedisulfonate (MMDS), 1,3-propane sultone (PS), 1,3-propene sultone (PST), 1,4-butane sultone (BS), dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate.

[0096] In some embodiments of the present application, the mass percentage of the nitrile compound in the electrolyte can be 1%-6%, for example, 1%, 2%, 3%, 4%, 5%, or 6%. Controlling the nitrile compound to an appropriate content helps to achieve its beneficial effects without degrading other battery properties.

[0097] 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).

[0098] In some embodiments of the present application, the weight percentage of the acid anhydride compound in the electrolyte can be 0.05%-1%. For example, it can be 0.05%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, or 1.0%. Controlling the acid anhydride compound to an appropriate content is beneficial for achieving its beneficial effects without degrading other battery properties.

[0099] 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.

[0100] 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 laminated battery.

[0101] The sodium ion battery provided by 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 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. In this way, the amount of the additive is reasonably designed according to the specific surface area of ​​the negative electrode carbon material, which can better achieve a good balance between the performance of the carbon material and the effect of the additive, 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 and reduce the internal resistance, 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 all aspects of the battery performance; further adjusting the addition amount of the sodium salt additive 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 precisely controlling the relationship between the various parameters of the electrolyte and the positive and negative electrode active materials, reduce DOE (Design Of Experiment) trial and error, 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, passivate the negative electrode surface, thereby improving the film formation 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.

[0102] 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 mobile electronic devices, and can also be used in vehicles, energy storage devices, base stations and other equipment products to improve product safety and reliability.

[0103] The present invention also provides a method for preparing a sodium ion battery, comprising:

[0104] Provide a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; wherein 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 comprising 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 %;

[0105] 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;

[0106] The positive electrode sheet, negative electrode sheet, separator and electrolyte are assembled to obtain a sodium ion battery.

[0107] It can be understood that the relevant features involved in the preparation method can be found in the above description of sodium ion batteries and will not be repeated here.

[0108] The preparation method of the sodium ion battery provided in the embodiment of the present application can effectively improve the cycle performance and storage performance of the battery by controlling the ratio of the addition amount of two types of additives, sodium salt additives and organic additives, to the specific surface area of ​​the carbon material of the negative electrode within a suitable range.

[0109] Referring to Figure 2, an embodiment of the present application further provides an electric device 200, which includes a housing 211, and electronic components and a battery 212 housed 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 this 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, energy storage device, base station and other equipment products.

[0110] The embodiments of the present application are further described below with reference to a number of embodiments.

[0111] In the following examples and comparative examples, the sodium ion battery uses NaNi as the positive electrode active material. 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.

[0112] Fabrication of sodium-ion batteries:

[0113] Weigh 2% polyvinylidene fluoride (PVDF), 2% conductive agent Super P, and 96% positive electrode active materials (NFM, PBA, NFP) in order, add them to N-methylpyrrolidone (NMP), stir and mix thoroughly, and coat the slurry on an aluminum foil current collector. Dry, cold press, and cut to produce positive electrode sheets.

[0114] Weigh 1.5% CMC, 2.5% SBR, 1% Super P, and 95% negative electrode active material (hard carbon, soft carbon) in mass percentage, add them to deionized water in sequence, stir and mix thoroughly, coat the slurry on a copper foil current collector, dry, cold press, and cut to produce negative electrode sheets;

[0115] The positive electrode sheet, negative electrode sheet and commercial PE separator prepared above are made into battery cells, which are packaged with polymers and filled with the sodium ion battery electrolyte prepared above. After chemical formation and other processes, a 2Ah soft-pack sodium ion battery is produced.

[0116] Example 1

[0117] Preparation of the electrolyte: Ethylene carbonate (EC), propylene carbonate (PC) and ethyl methyl carbonate (EMC) were mixed in 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).

[0118] 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 above, that is, the FEC content in the electrolyte before battery formation.

[0119] Examples 2-41 and Comparative Examples 1-13 were all carried out according to the method of Example 1, except that the types of the positive and negative active materials of the sodium ion batteries, the specific surface areas a, b, c, and d of the positive and negative active materials were different, and the types and contents of the additives in the electrolyte were different, including e / a, e / f, and f / a, and e / b, e / c, or e / d, as shown in Table 1. Furthermore, 2% of a sulfur-containing ester compound (2% PS) was added to the electrolyte of Example 37, 2% of a nitrile compound (2% DENE) was added to the electrolyte of Example 38, and 0.1% of an acid anhydride compound (0.1% SA) was added to the electrolyte of Example 39.

[0120] 25℃ cycle performance test:

[0121] The sodium ion batteries prepared in Examples 1-41 and Comparative Examples 1-13 were placed in an oven at a constant temperature of 25±3°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 capacity of the 1st and 300th cycles was recorded. The capacity retention rate of the cycle was calculated according to the following formula, and the results are recorded in Table 1.

[0122] Capacity retention rate (%)=discharge capacity at the 300th cycle / discharge capacity at the 1st cycle×100%.

[0123] Performance test after 30 days storage at 60℃:

[0124] The sodium ion batteries prepared in Examples 1-41 and Comparative Examples 1-13 were placed in an oven at a constant temperature of 25±3°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. Then, the batteries were discharged to 2.0V at a constant current of 0.2C, and the capacity was recorded as the initial capacity. The batteries were again charged to 3.95V at a constant current of 0.2C, and then charged at a constant voltage until the current dropped to 0.05C, and rested for 10 minutes. The charged batteries were placed at a temperature of 60°C for 30 days, then placed in an open circuit at room temperature for 2 hours, and discharged to 2.0V at a constant current of 0.2C. The residual capacity was recorded, and the residual capacity retention rate of the cycle was calculated according to the following formula. The results are recorded in Table 1.

[0125] The remaining capacity retention rate (%) was recorded as: remaining capacity / initial capacity×100%.

[0126] The specific surface area of ​​the positive electrode active material and the specific surface area of ​​the negative electrode active material are measured using a specific surface area analyzer. The content of sodium salt additives in the electrolyte can be measured using an ion chromatograph, and the content of organic additives such as FEC in the electrolyte can be measured using gas chromatography.

[0127] Table 1 Parameter details and battery performance of Examples 1-41 and Comparative Examples 1-13

[0128] From the results in Table 1, it can be seen 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 is a comparison of the cycle performance of the sodium ion batteries of Example 3 and Comparative Example 2 after 300 cycles at 0.5C / 0.5C; Figure 4 is a comparison of the cycle performance of the sodium ion batteries of Example 23 and Comparative Example 8 after 300 cycles at 0.5C / 0.5C; and Figure 5 is a comparison 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) As shown in Table 1 and the results of Figures 3 to 5, 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 remains in the electrolyte after the battery is formed. The sodium ion batteries thus obtained have a capacity retention rate of 81.1%-90.6% after 300 cycles at 0.5C / 0.5C, and a capacity retention rate of 90.1%-96.8% after 30 days of storage at 60°C, which are significantly higher than the capacity retention rate (70.2%-75.2%) of the sodium ion batteries obtained without adding sodium salt additives to the electrolyte (Comparative Example 1 and Comparative Example 10) after 300 cycles at 0.5C / 0.5C, 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 repairing the rupture of the SEI film during the cycle and is beneficial to the formation of the CEI film on the positive electrode surface, thereby improving the cycle performance of the sodium ion battery.

[0131] (2) Comparison of the positive electrode active materials: 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 values ​​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 an appropriate range, which can significantly improve the battery cycle performance and high-temperature storage performance. This is attributed to the following: 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 positive and negative electrode surfaces 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 was also added to the electrolyte, but the sodium ion battery provided in Example 3 further added a sodium salt additive NaPO2F2 with a mass percentage of 1.0% to the electrolyte during the electrolyte preparation process, 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 was 0.58%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 89.3%, and the capacity retention rate after storage at 60°C for 30 days was 96.6%; while in Comparative Example 2, only 0.02% of the sodium salt additive NaPO2F2 was added to the electrolyte. At this time, e / a=0.004, f / a=0.2, e / f=0.02, and e / b=0.04, in the sodium ion battery obtained by chemical formation, the mass percentage of FEC in the electrolyte was only 0.18%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 76.4% and the capacity retention rate after storage at 60°C for 30 days was 87.6%, which was significantly lower than that of 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 and e / b<0.1, the content of the sodium salt additive is too small to effectively passivate the surface of the hard carbon negative electrode, resulting in excessive consumption of the fluorocarbonate (FEC) 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 contains both the sodium salt additive and FEC in 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 in Comparative Example 3 at the same time, 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 is e / a>3.5, the amount of sodium salt additive added is relatively too much, and therefore the battery of Comparative Example 6 cannot obtain higher cycle performance and high-temperature storage performance.

[0135] The sodium-ion batteries from 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 charging were recorded, and the capacity was differentiated against the voltage to obtain dQ / dV data. The dQ / dV data were plotted against the voltage on the horizontal axis to produce the film formation potential diagram for the sodium-ion battery shown in Figure 6. Figure 6 shows a new peak at approximately 2200 mV, indicating that NaDFOB can form a film on the hard carbon anode material before FEC.

[0136] (3) 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 values ​​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 / c of ​​the mass percentage content e of the sodium salt additive in the electrolyte to the specific surface area c of the PBA material are within an appropriate range, which can significantly improve the battery cycle performance and high temperature storage performance. This is attributed to the following: 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 positive and negative electrode surfaces 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, in the sodium ion batteries provided in Comparative Example 23 and Comparative Example 8, 1% FEC was also added to the electrolyte, but the sodium ion battery provided in Example 23 further added a sodium salt additive NaDFOB with a mass percentage content of 1.0% to the electrolyte during the electrolyte preparation process, 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 was 0.45%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 87.9% and the capacity retention rate after storage at 60°C for 30 days was 95.3%; while in Comparative Example 8, only 0.02% of the sodium salt additive NaDFOB was added to the electrolyte. At this time, e / a=0.004, f / a=0.2, e / f=0.02, and e / c=0.025. In the sodium ion battery obtained by chemical formation, the mass percentage of FEC in the electrolyte was only 0.15%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 76.1% and the capacity retention rate after storage at 60°C for 30 days was 87.2%, which was significantly lower than that of 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 small to effectively passivate the surface of the hard carbon negative electrode, resulting in excessive consumption of fluorocarbonate (FEC) film formation, and inability to effectively inhibit side reactions in the late stage of the battery cycle. Therefore, although the sodium ion battery of Comparative Example 8 contains both the sodium salt additive and FEC in the electrolyte, it has little effect on improving the battery cycle performance and high-temperature storage performance.

[0138] (4) 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 values ​​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 / d of the mass percentage content e of the sodium salt additive in the electrolyte to the specific surface area d of the NFP material are within an appropriate range, which can significantly improve the battery cycle performance and high-temperature storage performance. This is attributed to the following: 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 positive and negative electrode surfaces 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 was also added to the electrolyte. In the sodium ion battery provided in Example 31, 1.0% by weight of a sodium salt additive NaPO2F2 was further added to the electrolyte during the electrolyte preparation process, with e / a = 0.25, f / a = 0.25, e / f = 1.0, and e / d = 0.1. In the sodium ion battery obtained by chemical formation in Example 31, the mass percentage of FEC in the electrolyte was 0.42%. The resulting sodium ion battery had a capacity retention rate of 88.6% after 300 cycles at 0.5C / 0.5C and a capacity retention rate of 95.9% after storage at 60°C for 30 days. 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, and e / d=0.001. 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 sodium ion battery finally obtained 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 of Example 31. By comparing the sodium ion batteries provided in 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 and 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) film formation, and inability to effectively inhibit 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, a sodium salt additive NaDFOB with a mass percentage of 3.0 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 was 4.96%, and the capacity retention rate of the sodium ion battery finally obtained after 0.5C / 0.5C cycle 300 cycles was 85.1% and the capacity retention rate after storage at 60°C for 30 days was 93.2%; while in Example 35, a sodium salt additive NaDFOB with a mass percentage of 0.08% was added to the electrolyte. At this time, e / a=0.08, f / a=10.0, e / f=0.008, and e / b=0.16, and the mass percentage of FEC in the sodium ion battery obtained by chemical formation was 2.82%, and the capacity retention rate of the sodium ion battery finally obtained after 0.5C / 0.5C cycle 300 cycles was 81.1% and the capacity retention rate after storage at 60°C for 30 days was 90.1%, which was 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 mass 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 was 0.27%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 84.6%, and the capacity retention rate after storage at 60°C for 30 days was 94.3%; while in Example 36, an organic additive FEC with a mass percentage of 0.3% was added to the electrolyte. At this time, e / a=3.5, e / f=9.33, f / a=0.38, and e / b=5.6, and the mass percentage of FEC in the sodium ion battery obtained by chemical formation was 0.08%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 81.7% and the capacity retention rate after storage at 60°C for 30 days was 90.7%, which was lower than that of 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 is controlled to be ≤8.0, 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 batteries obtained in Examples 37-39 after 300 cycles of 0.5C / 0.5C and 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 acid 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 was 0.95%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 86.8%, and the capacity retention rate after storage at 60°C for 30 days was 95.2%; while in Example 40, a sodium salt additive NaDFOB with a mass percentage of 0.08% was added to the electrolyte. At this time, e / a=0.04, e / f=0.04, f / a=1.0, and e / b=0.08, and the mass percentage of FEC in the electrolyte was 0.57% in the sodium ion battery obtained by chemical formation. The capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 82.3%, and the capacity retention rate after storage at 60°C for 30 days was 91.3%, which was lower than that of 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 was 0.95%, and the capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 86.8% and the capacity retention rate after storage at 60°C for 30 days was 95.2%; while in Example 41, a sodium salt additive NaDFOB with a mass percentage of 2.5% was added to the electrolyte. At this time, e / a=1.25, e / f=1.25, f / a=1.0, and e / b=16.67, and the mass percentage of FEC in the electrolyte obtained by chemical formation was 1.05%. The capacity retention rate of the finally obtained sodium ion battery after 0.5C / 0.5C cycle 300 cycles was 82.5% and the capacity retention rate after storage at 60°C for 30 days was 91.8%, which was lower than that of 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 is controlled to be ≤15.0, 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 sodium ion batteries at the same time and controlling the sodium salt additives and organic additives to an appropriate content according to the specific surface area of ​​the negative electrode carbon material can improve the capacity retention rate of sodium ion batteries after 300 cycles of 0.5C / 0.5C and the capacity retention rate after 30 days of storage at 60°C.

[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 intended to limit the scope of this application.

[0148] In this application, "and / or" describes the relationship between related objects, indicating that three possible relationships exist. For example, "A and / or B" can mean: A exists alone, A and B exist simultaneously, and B exists alone. A and B can be singular or plural. The character " / " generally indicates that the related objects are in an "or" relationship.

[0149] In this application, "at least one" means one or more, and "more than one" 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, and c can be single or multiple.

[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. 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is 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, It is characterized in that The electrolyte salt includes NaClO 4 , NaBF 4 、NaPF 6 、NaAsF 6 、NaCF 3 SO 3 、NaTDI、Na[(CF 3 SO 2 ) 2 N]、Na[(FSO 2 ) 2 N] and Na[(C m F 2m+1 SO 2 )(C n F 2n+1 SO 2 )N], where m and n are natural numbers.

23. The sodium ion battery according to any one of claims 1 to 22, It is 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, It is 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, It is 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 device, It is 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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