Sodium ion battery and electric equipment

Abstract

The embodiment of the invention provides a sodium-ion battery and electric equipment, the sodium-ion battery comprises a positive electrode, a negative electrode, a diaphragm and an electrolyte, and the electrolyte comprises a cyclic carbonate solvent and / or a carboxylic ester solvent; the ratio of the mass ratio of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle size of the positive electrode active material and the D50 particle size of the negative electrode active material is (0.005: 1)-(0.2: 1); the ratio of the mass ratio of the carboxylic ester solvent in the electrolyte to the sum of the D50 particle size of the positive electrode active material and the D50 particle size of the negative electrode active material is 0.002: 1 to 0.1: 1; wherein the unit of the D50 particle size is [mu] m. According to the sodium-ion battery, by reasonably designing the specific incidence relation between the D50 particle size of the positive and negative electrode active materials and the electrolyte solvent, the ion transmission and ion diffusion capability in the charging and discharging process of the battery can be effectively balanced, the low-temperature dynamic performance of the battery is improved, and meanwhile, the high-temperature performance is considered.

Description

Technical Field

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

[0002] With the shortage and uneven distribution of lithium resources, sodium-ion batteries are considered to be very potential candidates in energy storage scenarios due to their advantages such as rich sodium resources and low cost. The low-temperature characteristics are the highlights for sodium-ion batteries to create differentiation. However, at present, the low-temperature charge kinetic performance of sodium-ion batteries is poor, and sodium deposition is easy to occur, resulting in serious side reactions and poor cycle performance, which has become a bottleneck for sodium-ion batteries to create a differentiated competition route. The electrolyte, the positive and negative electrode materials, etc. all have an impact on the low-temperature performance of sodium-ion batteries. However, it is still unclear how to design the correlation between the electrolyte and the positive and negative electrode materials so that the low-temperature characteristics of sodium-ion batteries can be better exerted while taking into account the high-temperature performance. Therefore, it is necessary to clarify the structure-activity relationship between the electrolyte and the positive and negative electrode materials. Summary of the Invention

[0003] In view of this, the embodiments of the present application provide a sodium-ion battery and an electrical device. By reasonably designing the specific correlation between the D50 particle size of the positive and negative electrode active materials and the electrolyte solvent, the sodium-ion battery can effectively balance the ion transport and ion diffusion capabilities during the charge and discharge process of the battery, improve the low-temperature kinetic performance of the battery, and at the same time take into account the high-temperature performance.

[0004] In the first aspect of the embodiments of the present application, a sodium-ion battery is provided. The sodium-ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode. The electrolyte includes an electrolyte salt and an organic solvent. The organic solvent includes a cyclic carbonate solvent and / or a carboxylate solvent; the positive electrode includes a positive electrode active material; the negative electrode includes a negative electrode active material;

[0005] The mass ratio of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.005:1 to 0.2:1;

[0006] The mass ratio of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.002:1 to 0.1:1; wherein, the unit of the D50 particle size is μm.

[0007] The sodium-ion battery provided by the embodiments of the present application establishes a correlation between the D50 particle size of the positive and negative electrode active materials and the electrolyte solvent, and controls the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material within a suitable specific range, and controls the numerical ratio of the mass percentage of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material within a suitable specific range, so as to reasonably regulate physical properties such as the viscosity and conductivity of the electrolyte, effectively balance the ion transport and ion diffusion capabilities during the charge and discharge process of the battery, improve the low-temperature kinetic performance of the positive and negative electrode active materials, and take into account the high-temperature performance at the same time, thereby obtaining a sodium-ion battery with both good low-temperature performance and excellent high-temperature performance.

[0008] The D50 particle size refers to the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%, and the D50 is also called the median diameter or median particle size.

[0009] In the embodiment of the present application, the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.01:1 to 0.1:1. Controlling the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material within a suitable range can better take into account the high-temperature performance of the battery while using the cyclic carbonate solvent to improve the low-temperature performance, make the electrolyte have a suitable conductivity as a whole, and obtain a higher ion transport ability.

[0010] In the embodiment of the present application, the numerical ratio of the mass percentage of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.005:1 to 0.05:1. By controlling the numerical ratio of the mass percentage of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material within a suitable range, the high-temperature performance of the battery can be better taken into account while using the carboxylate solvent to improve the low-temperature performance, make the electrolyte have a suitable viscosity as a whole, and obtain a faster ion transport ability.

[0011] In the embodiment of the present application, the cyclic carbonate solvent includes one or more of ethylene carbonate and propylene carbonate; the mass percentage of the cyclic carbonate solvent in the electrolyte is 10%-40%. The addition of a suitable content of the cyclic carbonate solvent in the electrolyte is beneficial to giving full play to its advantages to improve the low-temperature performance of the battery, and can also cooperate with other solvents to better improve the comprehensive performance of the battery.

[0012] In the embodiments of the present application, the mass percentage of ethylene carbonate in the electrolyte is 0%-20%, and the mass percentage of propylene carbonate in the electrolyte is 10%-40%.

[0013] In the embodiments of the present application, the carboxylic ester solvent includes one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, methyl difluoroacetate, and methyl trifluoroacetate; the mass percentage of the carboxylic ester solvent in the electrolyte is 5%-25%.

[0014] In the embodiments of the present application, the D50 particle size of the positive electrode active material is 0.7 μm-20 μm. A suitable particle size is beneficial to improving the electrochemical performance of the battery.

[0015] In the embodiments of the present application, the D50 particle size of the negative electrode active material is 0.7 μm-20 μm. A suitable particle size is beneficial to improving the electrochemical performance of the battery.

[0016] In the embodiments of the present application, the organic solvent further includes a linear carbonate solvent. The addition of the linear carbonate solvent is beneficial to reducing the viscosity of the electrolyte and improving the ion transport ability of the electrolyte.

[0017] In the embodiments of the present application, the mass percentage of the linear carbonate solvent in the electrolyte is 20%-50%. The addition of an appropriate amount of the linear carbonate solvent is beneficial to making the electrolyte obtain a suitable viscosity and better improving the comprehensive performance of the electrolyte together with other solvents such as cyclic carbonate solvents and carboxylic ester solvents.

[0018] In the embodiments of the present application, the linear carbonate solvent includes one or more of diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the mass percentage of diethyl carbonate in the electrolyte is 0%-40%, the mass percentage of ethyl methyl carbonate in the electrolyte is 0%-40%, and the mass percentage of dimethyl carbonate in the electrolyte is 0%-20%.

[0019] In the embodiments of the present application, the organic solvent further includes an ether solvent, and the mass percentage of the ether solvent in the electrolyte is less than or equal to 20%. The stable solvation structure of the ether solvent can realize a highly reversible solvent-cocodoping reaction and form a thin and stable SEI film (Solid Electrolyte Interphase), which is beneficial to the stable cycling of the electrode and fast sodium storage kinetics.

[0020] In the embodiments of the present application, the ether solvent includes one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether.

[0021] In the embodiments of the present application, the electrolyte further includes an additive, and the additive includes at least one of a sodium salt additive and an organic additive; the mass percentage of the sodium salt additive in the electrolyte is 0.05%-3%; the mass percentage of the organic additive in the electrolyte is 0.1%-15%. The addition of the sodium salt additive can improve the film-forming quality of the SEI film on the negative electrode and reduce the contact between the negative electrode and the electrolyte; the addition of the organic additive is beneficial to forming a high-quality SEI film on the surface of the negative electrode of the sodium-ion battery, thereby effectively protecting the negative electrode and ensuring the uniform and rapid migration of sodium ions at the interface. The addition of an appropriate amount of sodium salt additive and organic additive in the electrolyte is beneficial to better improving the comprehensive performance of the battery.

[0022] In the embodiments of the present application, the sodium salt additive includes one or more of sodium bis(oxalato)borate (NaBOB), sodium difluoro(oxalato)borate (NaDFOB), sodium difluoro bis(oxalato)phosphate (NaDFOP), and sodium difluorophosphate (NaPO2F2); the organic additive includes one or more of sulfur-containing ester compounds, fluorinated carbonate compounds, nitrile compounds, and anhydride compounds.

[0023] In the embodiments of the present application, the mass percentage of the sulfur-containing ester compound in the electrolyte is 0.5%-5%; the mass percentage of the fluorinated carbonate compound in the electrolyte is 0.5%-5%; the mass percentage of the nitrile compound in the electrolyte is 0.5%-5%; the mass percentage of the anhydride compound in the electrolyte is 0.05%-1%.

[0024] In the embodiments of the present application, the sulfur-containing ester compounds include 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 ethyl methyl sulfate; the fluorinated carbonate compounds include one or more of fluorinated ethylene carbonate and difluorinated ethylene carbonate; 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, 1,3,6-hexanetricarbonitrile, and 1,4-dicyano-2-butene; the anhydride compounds include one or more of succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride, cyclic phosphoric anhydride, and 1-butyl phosphoric anhydride.

[0025] In the embodiments of the present application, in the electrolyte, the molar concentration of the electrolyte salt is 0.05 mol / L - 5 mol / L; the electrolyte salts include one or more of NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, sodium 4,5-dicyano-2-trifluoromethylimidazole (NaTDI), Na[(CF3SO2)2N], Na[(FSO2)2N], and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], where m and n are natural numbers.

[0026] In the embodiments of the present application, the positive electrode active material includes at least one of layered sodium transition metal oxides, Prussian blue (white) compounds, and sodium polyanion-type compounds.

[0027] In the embodiments of the present application, the negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase microbeads, hard carbon, soft carbon, and porous carbon materials.

[0028] The sodium ion battery provided by the embodiments of the present application can be used in terminal devices, such as consumer electronic products, such as mobile phones, tablet computers, mobile power supplies, portable computers, laptop computers, and other wearable or movable electronic devices, or can also be used in devices such as vehicles, energy storage devices, and base stations, so as to improve the safety and reliability of the products.

[0029] In the second aspect of the embodiments of the present application, a method for preparing a sodium ion battery is provided, including:

[0030] Provide a positive electrode sheet, a negative electrode sheet, a separator and an electrolyte; wherein the positive electrode sheet includes a positive electrode active material, the negative electrode sheet includes a negative electrode active material, the electrolyte includes an electrolyte salt and an organic solvent, and the organic solvent includes a cyclic carbonate solvent and / or a carboxylic acid ester solvent;

[0031] Wherein, control the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material to be 0.005:1 to 0.2:1;

[0032] Control the numerical ratio of the mass percentage of the carboxylic acid ester solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material to be 0.002:1 to 0.1:1; wherein, the unit of the D50 particle size is μm;

[0033] Assemble the above positive electrode sheet, negative electrode sheet, separator and electrolyte to obtain a sodium ion battery.

[0034] The preparation method of the sodium ion battery provided by the embodiment of the present application can effectively balance the ion transport and ion diffusion capabilities during the charge and discharge process of the battery, improve the low-temperature kinetic performance of the battery, and at the same time take into account the high-temperature performance by reasonably designing the specific correlation between the D50 particle sizes of the positive and negative electrode active materials and the electrolyte solvent, so as to improve the battery cycle, improve the high-temperature storage performance and low-temperature charging performance.

[0035] The embodiment of the present application also provides an electrical device, the electrical device includes a housing, and electronic components and a battery accommodated in the housing, the battery supplies power to the electronic components, and the battery includes the sodium ion battery described in the first aspect or the sodium ion battery prepared by the preparation method described in the second aspect. Description of the Drawings

[0036] Figure 1 It is a schematic structural diagram of the sodium ion battery 100 provided by the embodiment of the present application;

[0037] Figure 2 It is a schematic structural diagram of the electrical device 200 provided by the embodiment of the present application;

[0038] Figure 3 It is a comparison chart of the cycle performance of the sodium ion batteries of Example 5 and Comparative Examples 1-2 of the present application. Detailed Embodiments

[0039] Next, the embodiments of the present application will be described with reference to the drawings in the embodiments of the present application.

[0040] In a sodium-ion battery, the electrolyte, the positive and negative electrode materials, etc. all have an impact on the low-temperature performance of the sodium-ion battery. However, it is currently unclear how to design the correlation between the electrolyte and the positive and negative electrode materials so as to better exert the low-temperature characteristics of the sodium-ion battery while taking into account the high-temperature performance. In view of this, the embodiments of the present application provide a sodium-ion battery and an electrical device. By reasonably designing the specific correlation between the D50 particle size of the positive and negative electrode active materials and the electrolyte solvent, this sodium-ion battery can effectively balance the ion transport and ion diffusion capabilities during the charge and discharge processes of the battery, improve the low-temperature kinetic performance of the battery, and at the same time take into account the high-temperature performance.

[0041] As Figure 1 shown, the embodiments of the present application provide a sodium-ion battery 100. The sodium-ion battery 100 includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte 40. The separator 30 is disposed between the positive electrode 10 and the negative electrode 20, and the electrolyte 40 is filled between the positive electrode 10 and the negative electrode 20 and infiltrates the separator 30; the positive electrode 10 includes a positive electrode active material 102, the negative electrode 20 includes a negative electrode active material 202, the electrolyte 40 includes an electrolyte salt and an organic solvent, and the organic solvent includes a cyclic carbonate solvent and / or a carboxylate solvent;

[0042] Among them, the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte 40 to the sum of the D50 particle sizes of the positive electrode active material 102 and the negative electrode active material 202 is 0.005:1 to 0.2:1; the numerical ratio of the mass percentage of the carboxylate solvent in the electrolyte 40 to the sum of the D50 particle sizes of the positive electrode active material 102 and the negative electrode active material 202 is 0.002:1 to 0.1:1; wherein, the unit of the D50 particle size is μm.

[0043] When the sodium-ion battery 100 is charged, sodium ions are removed from the positive electrode active material 102 of the positive electrode 10 and embedded in the negative electrode active material 202 of the negative electrode 20 after passing through the electrolyte 40; when discharging, sodium ions are removed from the negative electrode active material 202 and inserted into the positive electrode active material 102 after passing through the electrolyte 40. When the positive and negative electrode active materials of the sodium-ion battery 100 and the electrolyte solvent meet the above conditions, the ion transport and ion diffusion capabilities during the charge and discharge processes of the battery can be effectively balanced, the low-temperature kinetic performance of the battery can be improved, and the high-temperature performance can be taken into account at the same time, so as to obtain a sodium-ion battery product with both good low-temperature performance and excellent high-temperature performance, thereby enhancing the market competitiveness of electrical devices such as electronic devices and electric vehicles.

[0044] Among them, the D50 particle size refers to the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%, and the D50 is also called the median diameter or the median particle size.

[0045] The inventors of the present application have found that in the sodium-ion battery 100, the particle size of the positive and negative active materials and the solvent system of the electrolyte both play important roles in the performance at low temperatures. However, unilaterally adjusting and changing the particle size of the positive and negative active materials or the solvent system of the electrolyte will deteriorate the performance in other aspects such as the high-temperature performance of the battery. The sodium-ion battery provided by the embodiments of the present application establishes a correlation between the D50 particle size of the positive and negative active materials and the electrolyte solvent, and controls the mass ratio of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive active material and the negative active material within a suitable specific range, and controls the mass ratio of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive active material and the negative active material within a suitable specific range, which can reasonably regulate the physical properties such as the viscosity and conductivity of the electrolyte, effectively balance the ion transport and ion diffusion capabilities during the charge and discharge process of the battery, improve the low-temperature kinetic performance of the positive and negative active materials, and take into account the high-temperature performance at the same time, so as to obtain a sodium-ion battery with both good low-temperature performance and excellent high-temperature performance.

[0046] It should be noted that the numerical ratio of the mass ratio of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive active material and the negative active material is a numerical ratio calculated without considering the unit of the D50 particle size. For example, if the mass ratio of the cyclic carbonate solvent is 30%, the D50 particle size of the positive active material is 5 μm, and the D50 particle size of the negative active material is 5 μm, then the numerical ratio = 30% / (5 + 5) = 0.03.

[0047] Similarly, the numerical ratio of the mass ratio of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive active material and the negative active material is also a numerical ratio calculated without considering the unit of the D50 particle size. For example, if the mass ratio of the carboxylate solvent is 10%, the D50 particle size of the positive active material is 5 μm, and the D50 particle size of the negative active material is 5 μm, then the numerical ratio = 10% / (5 + 5) = 0.01.

[0048] In this application, the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte 40 to the sum of the D50 particle sizes of the positive electrode active material 102 and the negative electrode active material 202 is 0.005:1 to 0.2:1. The cyclic carbonate solvent has a high dielectric constant, which is beneficial to the dissociation of sodium salts, improves the conductivity of the electrolyte, is beneficial to ion transport, and has a wide liquid temperature range, strong dissolution ability, high safety and stability, which is beneficial to improving the low-temperature performance of sodium-ion batteries; by controlling the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material within a suitable range, while utilizing the cyclic carbonate solvent to improve the low-temperature performance, the high-temperature performance of the battery can be better taken into account, so that the electrolyte as a whole has a suitable conductivity and obtains a high ion transport ability. In some embodiments, specific examples of the numerical ratio are, for example, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, 0.12:1, 0.15:1, 0.18:1, 0.2:1, and numbers between any two of the above values are all within the acceptable range. For example, the numerical ratio can be taken from the values between 0.005:1 and 0.02:1, or from the values between 0.01:1 and 0.07:1, or from the values between 0.03:1 and 0.1:1, or from the values between 0.08:1 and 0.2:1, or can take other numbers between any two values. In some embodiments of this application, the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte 40 to the sum of the D50 particle sizes of the positive electrode active material 102 and the negative electrode active material 202 is 0.01:1 to 0.1:1.

[0049] In this application, the numerical ratio of the mass percentage of the carboxylic acid ester solvent in the electrolyte 40 to the sum of the D50 particle sizes of the positive electrode active material 102 and the negative electrode active material 202 is 0.002:1 to 0.1:1. The carboxylic acid ester solvent has a relatively low freezing point and a relatively low melting point, and a relatively small viscosity, which is beneficial to improving the low-temperature performance of the sodium-ion battery. By controlling the numerical ratio of the mass percentage of the carboxylic acid ester solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material within a suitable range, while improving the low-temperature performance by using the carboxylic acid ester solvent, the high-temperature performance of the battery can be better balanced. In some embodiments, specific examples of the numerical ratio are, for example, 0.002:1, 0.003:1, 0.004:1, 0.005:1, 0.006:1, 0.007:1, 0.008:1, 0.009:1, 0.01:1, 0.015:1, 0.02:1, 0.025:1, 0.03:1, 0.035:1, 0.04:1, 0.045:1, 0.05:1, 0.06:1, 0.07:1, 0.08:1, 0.09:1, 0.1:1, and numbers between any two of the above values, all of which are acceptable range values. For example, the numerical ratio can be taken from the values between 0.002:1 and 0.02:1, or from the values between 0.01:1 and 0.06:1, or from the values between 0.04:1 and 0.08:1, or from the values between 0.07:1 and 0.1:1, or can also take values between any other two values. In some embodiments of this application, the numerical ratio of the mass percentage of the carboxylic acid ester solvent in the electrolyte 40 to the sum of the D50 particle sizes of the positive electrode active material 102 and the negative electrode active material 202 is 0.005:1 to 0.05:1.

[0050] It should be noted that for the calculated values of the above numerical ratios, in actual test operations, a certain measurement test system error is allowed, and the values within the system error range can be understood as the range defined by the embodiments of this application.

[0051] In the embodiments of this application, the cyclic carbonate solvents include, but are not limited to, one or more of ethylene carbonate (EC) and propylene carbonate (PC). In some embodiments, the cyclic carbonate solvent in the electrolyte only includes ethylene carbonate (EC); in some embodiments, the cyclic carbonate solvent in the electrolyte only includes propylene carbonate (PC); in some embodiments, the cyclic carbonate solvent in the electrolyte includes both ethylene carbonate (EC) and propylene carbonate (PC). Among them, propylene carbonate (PC) has a relatively wider liquid temperature range, and adding propylene carbonate (PC) to the electrolyte is more beneficial to balancing the performance at high and low temperatures.

[0052] In the embodiments of the present application, the mass percentage of the cyclic carbonate solvent in the electrolyte can be 10% - 40%. The addition of a suitable content of the cyclic carbonate solvent in the electrolyte is beneficial to exert its advantages to improve the conductivity of the electrolyte, enhance the ion transport ability, thereby improving the low-temperature performance of the battery, and can also cooperate with other solvents to better improve the comprehensive performance of the battery. In some embodiments, the mass percentage of the cyclic carbonate solvent in the electrolyte is, for example, 10%, 15%, 20%, 25%, 30%, 35%, 40%, etc.

[0053] In some embodiments of the present application, the mass percentage of ethylene carbonate in the electrolyte is 0% - 20%, specifically, for example, it can be 0%, 1%, 5%, 8%, 10%, 12%, 14%, 15%, 18%, 20%, etc., and the mass percentage of propylene carbonate in the electrolyte is 10% - 40%, specifically, for example, it can be 10%, 12%, 15%, 16%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc.

[0054] In the embodiments of the present application, the carboxylic acid ester solvents include, but are not limited to, one or more of methyl formate (MA), ethyl formate, methyl acetate (EA), ethyl acetate, propyl acetate (EP), ethyl propionate, propyl propionate (PP), methyl difluoroacetate, and methyl trifluoroacetate.

[0055] In the embodiments of the present application, the mass percentage of the carboxylic acid ester solvent in the electrolyte can be 5% - 25%. The addition of a suitable content of the carboxylic acid ester solvent in the electrolyte is beneficial to exert its advantages to improve the low-temperature kinetics, thereby improving the low-temperature performance of the battery, and can also cooperate with other solvents to better improve the comprehensive performance of the battery. In some embodiments, the mass percentage of the carboxylic acid ester solvent in the electrolyte is, for example, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, etc.

[0056] In some embodiments of the present application, the organic solvent further includes linear carbonate solvents. The addition of linear carbonate solvents is beneficial to reducing the viscosity of the electrolyte and enhancing the ion transport ability of the electrolyte. In the embodiments of the present application, the mass percentage of the linear carbonate solvents in the electrolyte can be 20%-50%. The addition of an appropriate amount of linear carbonate solvents is beneficial to making the electrolyte obtain a suitable viscosity and better enhancing the comprehensive performance of the electrolyte together with other solvents such as cyclic carbonate solvents and carboxylic ester solvents. In some embodiments, the mass percentage of the linear carbonate solvents in the electrolyte is, for example, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, 42%, 45%, 48%, 50%, etc. In some embodiments, the mass percentage of the linear carbonate solvents in the electrolyte can be 30%-50%.

[0057] In the embodiments of the present application, the linear carbonate solvents include, but are not limited to, one or more of diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC). In some embodiments of the present application, the mass percentage of diethyl carbonate in the electrolyte is 0%-40%, and can be, for example, 0%, 2%, 5%, 8%, 10%, 12%, 15%, 20%, 25%, 30%, 35%, 40%, etc.; the mass percentage of ethyl methyl carbonate in the electrolyte is 0%-40%, and can be, for example, 0%, 5%, 10%, 12%, 15%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc.; the mass percentage of dimethyl carbonate in the electrolyte is 0%-20%, and can be, for example, 0%, 2%, 5%, 8%, 10%, 12%, 15%, 20%, etc. In some embodiments, the linear carbonate solvents in the electrolyte include both diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) at the same time. In some embodiments, the mass percentage of diethyl carbonate in the electrolyte is 5%-20%; the mass percentage of ethyl methyl carbonate in the electrolyte is 20%-40%.

[0058] In some embodiments of the present application, the organic solvent further includes ether solvents. The stable solvation structure of ether solvents can achieve a highly reversible solvent-cocodoping reaction and form a thin and stable SEI film (Solid Electrolyte Interphase), which is beneficial to the stable cycling of the electrode and fast sodium storage kinetics. In the embodiments of the present application, the mass percentage of the ether solvents in the electrolyte can be less than or equal to 20%. In some embodiments, the mass percentage of the ether solvents in the electrolyte is, for example, 0%, 2%, 5%, 8%, 10%, 12%, 15%, 20%, etc.

[0059] In the embodiments of the present application, the ether solvents include, but are not limited to, one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether.

[0060] It can be understood that for the values of the mass percentages of the above solvents, after actual battery formation, formation and capacity separation, or cycling, due to the formation of the interface film, it will have a certain impact on the measurement of the mass percentage of the electrolyte solvent. A certain measurement error is allowed, and the values within the error range can be understood as the range defined in the embodiments of the present application, or the numerical range of the mass percentage of the electrolyte solvent measured after formation, formation and capacity separation, or cycling is still within the above range can be understood as the range defined in the embodiments of the present application.

[0061] In the embodiments of the present application, the electrolyte further includes additives, and the additives include, but are not limited to, at least one of sodium salt additives and organic additives. The addition of sodium salt additives can improve the film-forming quality of the SEI film on the negative electrode and reduce the contact between the negative electrode and the electrolyte; the addition of organic additives is beneficial to forming a quality SEI film on the surface of the negative electrode of the sodium-ion battery, thereby effectively protecting the negative electrode and ensuring the uniform and rapid migration of sodium ions at the interface. In some embodiments, the additives include both sodium salt additives and organic additives at the same time. In this way, the sodium salt additives have a higher reduction film-forming potential and can react with the negative electrode prior to the organic additives to passivate the surface of the negative electrode, thereby improving the film-forming quality of the organic additives on the surface of the negative electrode, effectively avoiding the continuous rupture and dissolution of the SEI film during cycling, reducing the contact between the negative electrode and the electrolyte, and reducing the probability of side reactions.

[0062] In the embodiments of the present application, the sodium salt additives include, but are not limited to, one or more of sodium bis(oxalato)borate (NaBOB), sodium difluoro(oxalato)borate (NaDFOB), sodium difluoro bis(oxalato)phosphate (NaDFOP), and sodium difluorophosphate (NaPO2F2). In the embodiments of the present application, the mass percentage of the sodium salt additives in the electrolyte can be 0.05% - 3%. In some embodiments, the mass percentage of the sodium salt additives in the electrolyte can be, for example, 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.7%, 0.9%, 1.0%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2.0%, 2.2%, 2.5%, 2.7%, 3%, etc. The addition of an appropriate amount of sodium salt additives in the electrolyte is beneficial to better improving the comprehensive performance of the battery.

[0063] In the embodiments of the present application, the organic additives include, but are not limited to, one or more of sulfur-containing ester compounds, fluorinated carbonate compounds, nitrile compounds, and anhydride compounds. In the embodiments of the present application, the sulfur-containing ester compounds include, but are not limited to, one or more of dimethyl sulfite, diethyl sulfite, ethylene sulfite, vinylene sulfate (DTD), propylene sulfate (TS), methylene methanedisulfonate (MMDS), 1,3-propane sultone (PS), 1,3-propylene sultone (PST), 1,4-butane sultone (BS), dimethyl sulfate, diethyl sulfate, and ethyl methyl sulfate. In the embodiments of the present application, the fluorinated carbonate compounds include, but are not limited to, one or more of fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC). In the embodiments of the present application, the nitrile compounds include, but are not limited to, mononitrile compounds and / or polynitrile compounds. Among them, the mononitrile compounds include, but are not limited to, at least one of acetonitrile and p-methylbenzonitrile; the polynitrile compounds include, but are not limited to, one or more of succinonitrile (SN), glutarodinitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane (DENE), 1,3,6-hexanetricarbonitrile (HTCN), and 1,4-dicyano-2-butene. In the embodiments of the present application, the anhydride compounds include, but are not limited to, one or more of succinic anhydride (SA), glutaric anhydride, adipic anhydride, maleic anhydride, cyclic phosphoric anhydride (CA), and 1-butyl phosphoric anhydride.

[0064] In the embodiments of the present application, the mass percentage of the organic additive in the electrolyte can be 0.1%-15%. In some embodiments, the mass percentage of the organic additive in the electrolyte can be 0.1%-15%, for example, it can be 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, etc. The addition of an appropriate amount of the organic additive in the electrolyte is beneficial to better improving the comprehensive performance of the battery.

[0065] In some embodiments of the present application, the mass percentage of the sulfur-containing ester compound in the electrolyte is 0.5%-5%; for example, it can be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc. In some embodiments of the present application, the mass percentage of the fluorinated carbonate compound in the electrolyte is 0.5%-5%; for example, it can be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc. In some embodiments of the present application, the mass percentage of the nitrile compound in the electrolyte is 0.5%-5%; for example, it can be 0.5%, 1.0%, 2.0%, 3.0%, 4.0%, 5.0%, etc. In some embodiments of the present application, the mass percentage of the anhydride compound in the electrolyte is 0.05%-1%, for example, it can be 0.05%, 0.1%, 0.2%, 0.4%, 0.6%, 0.8%, 1.0%, etc. In some embodiments, the organic additives added to the electrolyte include two types: sulfur-containing ester compounds and fluorinated carbonate compounds; in some embodiments, the organic additives added to the electrolyte include three types: sulfur-containing ester compounds, fluorinated carbonate compounds, and nitrile compounds; in some embodiments, the organic additives added to the electrolyte include three types: sulfur-containing ester compounds, fluorinated carbonate compounds, and anhydride compounds; in some embodiments, the organic additives added to the electrolyte include four types: sulfur-containing ester compounds, fluorinated carbonate compounds, nitrile compounds, and anhydride compounds.

[0066] In the embodiments of the present application, in the electrolyte, the molar concentration of the electrolyte salt is 0.05 mol / L - 5 mol / L. In some embodiments, in the electrolyte, the molar concentration of the electrolyte salt can be, for example, 0.05 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, 5.0 mol / L, etc. The electrolyte salt includes but is not limited to one or more of NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, sodium 4,5-dicyano-2-trifluoromethylimidazole (NaTDI), Na[(CF3SO2)2N], Na[(FSO2)2N], and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], where m and n are natural numbers.

[0067] In the sodium-ion battery 100, the electrolyte 40 is a transmission medium for sodium ions during transmission between the positive electrode 10 and the negative electrode 20. In the electrolyte 40, both the electrolyte salt and the additive are dissolved in the organic solvent.

[0068] As shown in Figure 1 , in some embodiments 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. Among them, the positive electrode current collector 101 can 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 intercalate / deintercalate sodium ions. In the embodiments of the present application, the positive electrode active material 102 can be at least one of a layered sodium transition metal oxide, a Prussian blue (white) compound, and a sodium polyanion compound. The positive electrode active material can be a combination of one or more (two or more) of the above materials. Among them, both the layered sodium transition metal oxide positive electrode material and the Prussian blue (white) compound positive electrode material have a relatively high specific capacity; the sodium polyanion compound has a relatively high electrochemical reaction stability. In the embodiments of the present application, the layered sodium transition metal oxide can be, for example, sodium nickel iron manganese (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, abbreviated as NFM), the Prussian blue (white) compound can be, for example, Prussian white (Na2Mn[Fe(CN)6], abbreviated as PBA), and the sodium polyanion compound can be, for example, sodium iron phosphate (NaFePO4, abbreviated as NFP), sodium iron sulfate (Na2Fe2(SO4)3, abbreviated as NFS), etc. In some embodiments of the present application, the positive electrode active material includes at least one of sodium nickel iron manganese, Prussian white, sodium iron phosphate, and sodium iron sulfate.

[0069] In the embodiments of the present application, the D50 particle size of the positive electrode active material is 0.7 μm - 20 μm. A suitable particle size is beneficial to improving the electrochemical performance of the battery. The D50 particle size of the positive electrode active material can be, for example, 0.7 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, and numbers between any two of the above values; in some embodiments, the D50 particle size of the positive electrode active material is 2 μm - 10 μm. It can be understood that for the above D50 values, after actual battery formation, grading, or cycling, due to the formation of the interface film, it will have a certain impact on the measurement of the median particle size of the material. A certain measurement error is allowed, and the values within the error range can be understood as the range defined in the embodiments of the present application, or the median particle size value range of the material after formation, grading, or cycling is still within the above range can be understood as the range defined in the embodiments of the present application.

[0070] In the embodiments of the present application, in addition to the positive electrode active material 102, the positive electrode material layer may further include a certain amount of components such as a binder and a conductive agent. The binder may be, for example, polyvinylidene fluoride (PVDF). The conductive agent may be, for example, conductive carbon black Super P, amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. The above-mentioned binder and conductive agent are only exemplary illustrations and are not limited thereto.

[0071] As Figure 1 shown, in some embodiments 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. Among them, the negative electrode current collector 201 may be a metal foil, such as copper foil, aluminum foil, gold foil, platinum foil, etc. The negative electrode material layer includes a negative electrode active material 202, and the negative electrode active material 202 can accept and release sodium ions. In some embodiments of the present application, the negative electrode active material 202 includes a carbon material. In the embodiments of the present application, the carbon material may be one or more of natural graphite, artificial graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, and porous carbon materials.

[0072] In the embodiments of the present application, the D50 particle size of the negative electrode active material is 0.7 μm - 20 μm. A suitable particle size is beneficial to improving the electrochemical performance of the battery. The D50 particle size of the negative electrode active material may be, for example, 0.7 μm, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm, 10 μm, 12 μm, 14 μm, 15 μm, 16 μm, 18 μm, 20 μm, and the numbers between any two of the above values; in some embodiments, the D50 particle size of the negative electrode active material is 2 μm - 10 μm. It can be understood that for the above-mentioned D50 values, after the actual battery formation, formation and grading, or cycling, due to the formation of the interface film, it will have a certain impact on the measurement of the median particle size of the material. A certain measurement error is allowed, and the values within the error range can be understood as the range defined by the embodiments of the present application, or the median particle size value range of the material after formation, formation and grading, or cycling is still within the above range can be understood as the range defined by the embodiments of the present application.

[0073] In the embodiments of the present application, the negative electrode material layer may further include a certain amount of components such as a binder and a conductive agent. The binder may be, for example, sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (NaPAA), etc., and the conductive agent may be, for example, conductive carbon black Super P, amorphous carbon, carbon nanotubes, carbon fibers, graphene, etc. The above-mentioned binder and conductive agent are only exemplary illustrations and are not limited thereto.

[0074] As Figure 1As shown, in the sodium-ion battery 100, the separator 30 is located between the positive electrode 10 and the negative electrode 20, which is used to block the passage of electrons and allow the passage of sodium ions. In some embodiments of the present application, the separator 30 includes, but is not limited to, single-layer polypropylene (PP), single-layer polyethylene (PE), double-layer PP / PE, double-layer PP / PP, triple-layer PP / PE / PP, and ceramic-coated PE separators.

[0075] The specific shape or type of the sodium-ion battery according to the embodiments of the present application is not limited. It 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.

[0076] The sodium-ion battery provided by the embodiments of the present application can be used in terminal devices, such as consumer electronic products, such as mobile phones, tablet computers, mobile power supplies, portable computers, laptop computers, and other wearable or movable electronic devices, and can also be device products such as vehicles, energy storage devices, and base stations, so as to improve the safety and reliability of the products.

[0077] The embodiments of the present application also provide a method for preparing a sodium-ion battery, including:

[0078] Providing a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; wherein the positive electrode sheet includes a positive electrode active material, the negative electrode sheet includes a negative electrode active material, the electrolyte includes an electrolyte salt and an organic solvent, and the organic solvent includes a cyclic carbonate solvent and / or a carboxylate solvent;

[0079] Wherein, controlling the numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.005:1 to 0.2:1;

[0080] Controlling the numerical ratio of the mass percentage of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.002:1 to 0.1:1; wherein the unit of the D50 particle size is μm;

[0081] Assembling the above positive electrode sheet, negative electrode sheet, separator, and electrolyte to obtain a sodium-ion battery.

[0082] It can be understood that the relevant features involved in this preparation method can be referred to the description of the sodium-ion battery above, and will not be elaborated here.

[0083] The preparation method of the sodium-ion battery provided by the embodiments of the present application can effectively balance the ion transport and ion diffusion capabilities during the charge and discharge process of the battery by reasonably designing the specific correlation between the D50 particle size of the positive and negative electrode active materials and the electrolyte solvent, improve the low-temperature kinetic performance of the battery, and take into account the high-temperature performance at the same time, so as to improve the battery cycle, and improve the high-temperature storage performance and low-temperature charging performance.

[0084] Refer to Figure 2 , the embodiments of the present application also provide an electrical 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 embodiments of the present application. In the present application, the electrical 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, a speaker, a vehicle-mounted product, and other wearable or movable electronic devices (such as glasses, watches, bracelets, earphones, etc.), or can also be equipment products such as vehicles, energy storage devices, and base stations. By using the sodium-ion battery provided by the embodiments of the present application, the safety and reliability of the product can be improved.

[0085] The embodiments of the present application will be further described in multiple embodiments below.

[0086] The sodium-ion batteries in the following embodiments and comparative examples are prepared according to the following method:

[0087] Weigh 2% by mass of polyvinylidene fluoride (PVDF), 2% of conductive agent Super P, and 96% of positive electrode active material, and add them to N-methylpyrrolidone (NMP) in sequence. Stir well and mix evenly. Coating the slurry on an aluminum foil current collector, drying, cold pressing, and slitting to obtain a positive electrode sheet;

[0088] Weigh 1.5% by mass of CMC-Na, 2.5% of SBR, 1% of Super P, and 95% of negative electrode active material, and add them to deionized water in sequence. Stir well and mix evenly. Coating the slurry on a copper foil current collector, drying, cold pressing, and slitting to obtain a negative electrode sheet;

[0089] Add sodium hexafluorophosphate (NaPF6) to an organic solvent, and then add different types and contents of additives to obtain an electrolyte; the molar concentration of NaPF6 in the electrolyte is 1 mol / L;

[0090] Make the positive electrode sheet, negative electrode sheet and commercial PE separator prepared above into an electric core, use polymer packaging, pour the sodium-ion battery electrolyte prepared above, and make a 2 Ah soft-pack sodium-ion battery after processes such as formation.

[0091] Among them, the types and D50 particle sizes of the positive electrode active materials, the types and D50 particle sizes of the negative electrode active materials, the types and mass percentages of the organic solvents in the electrolyte, and the types and mass percentages of the additives added are shown in Table 1.

[0092] The performances of each example and comparative example were tested according to the following methods, and the test results are shown in Table 1:

[0093] 1. 45°C cycling performance test:

[0094] The sodium-ion batteries prepared in the examples and comparative examples were placed in an oven at a constant temperature of 45 ± 3°C, charged at a constant current of 0.5C to 3.95V, then charged at a constant voltage until the current dropped to 0.05C, rested for 10 min, and then discharged at a constant current of 0.5C to 2.0V. After 250 such cycles, the discharge capacities of the first and 250th cycles were recorded, and the capacity retention rate after 250 cycles was calculated according to the following formula:

[0095] Capacity retention rate (%) = Discharge capacity of the 250th cycle / Discharge capacity of the first cycle × 100%.

[0096] 2. -40°C low-temperature performance test:

[0097] Under the condition of an ambient temperature of 25 ± 3°C, the battery was charged at a constant current of 0.2C to 3.95V, then charged at a constant voltage until the current dropped to 0.05C, rested for 10 min, and then discharged at a constant current of 0.2C to 2.0V. The discharge capacity at this time was the initial capacity; the battery was left at -40°C for 4 hours, then charged at a constant current of 0.2C to 3.95V, then charged at a constant voltage until the current dropped to 0.05C, rested for 10 min, and then discharged at a constant current of 0.2C to 2.0V. The discharge capacity at this time was recorded as the remaining capacity, and the remaining capacity retention rate was calculated. The remaining capacity retention rate = (Remaining capacity / Initial capacity) × 100%.

[0098] Table 1 Parameter details and battery performances of Examples 1 - 45 and Comparative Examples 1 - 9

[0099]

[0100]

[0101]

[0102]

[0103]

[0104] As can be seen from the data in Table 1, when comparing the sodium-ion batteries prepared in Examples 1-25, Examples 39-45 and Comparative Examples 1-3, the low-temperature remaining capacity retention rate of the sodium-ion batteries obtained in Examples 1-25 and Examples 39-45 at -40°C is 45.4%-51.9%, and the capacity retention rate after 250 cycles at 45°C is 94.7%-97.2%, which is significantly higher than the low-temperature remaining capacity retention rate (37.1%-37.6%) and the capacity retention rate after 250 cycles at 45°C (94.0%-94.3%) of the sodium-ion batteries obtained in Comparative Examples 1-3. This is attributed to the fact that in Examples 1-25 and Examples 39-45, the numerical ratio of the cyclic carbonate to the sum of the median particle sizes of the positive electrode active material (NFM) and the median particle sizes of the negative electrode active materials (hard carbon, soft carbon) satisfies 0.005:1 to 0.2:1; the numerical ratio of the carboxylic acid ester to the sum of the median particle sizes of the positive electrode active material (NFM) and the median particle sizes of the negative electrode active materials (hard carbon, soft carbon) satisfies 0.002:1 to 0.1:1. While in Comparative Examples 1-3, the above numerical ratios are not satisfied. Specifically, in Example 5, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFM (D50: 6 μm) and the median particle size of hard carbon (D50: 5 μm) is 0.027:1; the numerical ratio of the mass percentage of propyl acetate (EP) in the electrolyte to the sum of the median particle size of NFM (D50: 6 μm) and the median particle size of hard carbon (D50: 5 μm) is 0.014:1. While in Comparative Example 1, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFM (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0.7 μm) is 0.214:1 (greater than 0.2:1); the numerical ratio of the mass percentage of propyl acetate (EP) in the electrolyte to the sum of the median particle size of NFM (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0.7 μm) is 0.107:1 (greater than 0.1:1); in Comparative Example 2, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFM (D50: 20 μm) and the median particle size of hard carbon (D50: 20 μm) is 0.004:1 (less than 0.005:1). This results in the inability to balance ion transport and ion diffusion, and the battery performance is not well exerted. Figure 3 Figure for comparing the cycling performance of the sodium-ion batteries of Example 5 with Comparative Example 1 and Comparative Example 2. From Figure 3 it can be seen that the cycling performance of the sodium-ion battery of Example 5 after 250 cycles at 45°C is significantly better than that of Comparative Example 1 and Comparative Example 2.

[0105] It can also be learned by comparing Example 5 with Examples 39-41 and Examples 43-45 that adding an appropriate amount of sodium salt additive and / or organic additive to the electrolyte is beneficial to further improve the performance of the battery, and adding both sodium salt additive and organic additive at the same time is beneficial to improving the battery performance.

[0106] As can be seen from the data in Table 1, when comparing the sodium-ion batteries prepared in Examples 26-30 of this application with Comparative Examples 4-5, the low-temperature remaining capacity retention rate of the sodium-ion batteries obtained in Examples 26-30 at -40 °C is 51.8%-52.7%, and the capacity retention rate after 250 cycles at 45 °C is 96.2%-96.8%, which are significantly higher than the low-temperature remaining capacity retention rate (38.3%-38.8%) and the capacity retention rate after 250 cycles at 45 °C (94.3%-94.5%) of the sodium-ion batteries obtained in Comparative Examples 4-5. This is attributed to the fact that in Examples 26-30, the numerical ratio of the mass percentage of cyclic carbonate in the electrolyte to the sum of the median particle sizes of the positive electrode active material (PBA) and the negative electrode active material (hard carbon) satisfies 0.005:1 to 0.2:1; the numerical ratio of the mass percentage of carboxylic acid ester in the electrolyte to the sum of the median particle sizes of the positive electrode active material (PBA) and the negative electrode active material (hard carbon) satisfies 0.002:1 to 0.1:1. While in Comparative Examples 4-5, the above numerical ratios are not satisfied. Specifically, in Example 30, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of PBA (D50: 6 μm) and the median particle size of hard carbon (D50: 5 μm) is 0.027:1; the numerical ratio of the mass percentage of ethyl propionate (EP) in the electrolyte to the sum of the median particle size of PBA (D50: 6 μm) and the median particle size of hard carbon (D50: 5 μm) is 0.014:1. While in Comparative Example 4, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of PBA (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0.7 μm) is 0.214:1 (greater than 0.2:1); the numerical ratio of the mass percentage of ethyl propionate (EP) in the electrolyte to the sum of the median particle size of PBA (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0.7 μm) is 0.107:1 (greater than 0.1:1); in Comparative Example 5, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of PBA (D50: 20 μm) and the median particle size of hard carbon (D50: 20 μm) is 0.004:1 (less than 0.005:1), resulting in the inability to balance ion transport and ion diffusion, and the battery performance is not well exerted.

[0107] As can be seen from the data in Table 1, by comparing the sodium-ion batteries prepared in Examples 31-34 and Comparative Examples 6-7 of the present application, it can be known that the low-temperature remaining capacity retention rate of the sodium-ion batteries obtained in Examples 31-34 at -40 °C is 50.6%-51.2%, and the capacity retention rate after 250 cycles at 45 °C is 97.1%-97.5%, which is significantly higher than the low-temperature remaining capacity retention rate (36.8%-37.5%) and the capacity retention rate after 250 cycles at 45 °C (94.1%-94.5%) of the sodium-ion batteries obtained in Comparative Examples 6-7. This is attributed to the fact that in Examples 31-34, the numerical ratio of the mass percentage of cyclic carbonate in the electrolyte to the sum of the median particle sizes of the positive electrode active material (NFP) and the negative electrode active material (hard carbon) satisfies 0.005:1 to 0.2:1; the numerical ratio of the mass percentage of carboxylic acid ester in the electrolyte to the sum of the median particle sizes of the positive electrode active material (NFP) and the negative electrode active material (hard carbon) satisfies 0.002:1 to 0.1:1. While in Comparative Examples 6-7, the above numerical ratios are not satisfied. Specifically, in Example 32, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFP (D50: 6 μm) and the median particle size of hard carbon (D50: 5 μm) is 0.027:1; the numerical ratio of the mass percentage of ethyl propionate (EP) in the electrolyte to the sum of the median particle size of NFP (D50: 6 μm) and the median particle size of hard carbon (D50: 5 μm) is 0.014:1. While in Comparative Example 6, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFP (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0.7 μm) is 0.214:1 (greater than 0.2:1); the numerical ratio of the mass percentage of ethyl propionate (EP) in the electrolyte to the sum of the median particle size of NFP (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0.7 μm) is 0.107:1 (greater than 0.1:1); in Comparative Example 7, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFP (D50: 20 μm) and the median particle size of hard carbon (D50: 20 μm) is 0.004:1 (less than 0.005:1), resulting in the inability to balance ion transport and ion diffusion, and the battery performance is not well exerted.

[0108] As can be seen from the data in Table 1, when comparing the sodium-ion batteries prepared in Examples 35-38 with those in Comparative Examples 8-9, the low-temperature remaining capacity retention rate of the sodium-ion batteries obtained in Examples 31-34 at -40°C is 50.1%-50.7%, and the capacity retention rate after 250 cycles at 45°C is 96.1%-96.6%, which are significantly higher than the low-temperature remaining capacity retention rate (40.3%-40.9%) and the capacity retention rate after 250 cycles at 45°C (94.1%-94.5%) of the sodium-ion batteries obtained in Comparative Examples 8-9. This is attributed to the fact that in Examples 35-38, the numerical ratio of the mass percentage of cyclic carbonate in the electrolyte to the sum of the median particle sizes of the positive electrode active material (NFS) and the negative electrode active material (hard carbon) satisfies 0.005:1 to 0.2:1; the numerical ratio of the mass percentage of carboxylate in the electrolyte to the sum of the median particle sizes of the positive electrode active material (NFS) and the negative electrode active material (hard carbon) satisfies 0.002:1 to 0.1:1. While in Comparative Examples 8-9, the above numerical ratios are not satisfied. Specifically, in Example 35, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFS (D50: 6 μm) and the median particle size of hard carbon (D50: 5 μm) is 0.027:1; the numerical ratio of the mass percentage of ethyl propionate (EP) in the electrolyte to the sum of the median particle size of NFS (D50: 6 μm) and the median particle size of hard carbon (D50: 5 μm) is 0.014:1. While in Comparative Example 8, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFS (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0.7 μm) is 0.214:1 (greater than 0.2:1); the numerical ratio of the mass percentage of ethyl propionate (EP) in the electrolyte to the sum of the median particle size of NFS (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0.7 μm) is 0.107:1 (greater than 0.1:1); in Comparative Example 9, the numerical ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to the sum of the median particle size of NFS (D50: 20 μm) and the median particle size of hard carbon (D50: 20 μm) is 0.004:1 (less than 0.005:1), resulting in the inability to balance ion transport and ion diffusion, and the battery performance is not well exerted.

[0109] In summary, it can be known that: under the condition that other conditions remain unchanged, by regulating the numerical ratio of the mass percentages of cyclic carbonate solvents and carboxylate solvents in the electrolyte of sodium-ion batteries to the sum of the median particle sizes of positive and negative active materials within a suitable range, the low-temperature performance of sodium-ion batteries can be improved while taking into account the high-temperature performance.

[0110] It should be understood that the first, second, and various numerical numbers involved herein are only for the convenience of description and are not used to limit the scope of this application.

[0111] In this application, "and / or" describes the relationship between associated objects and indicates that there can be three relationships. For example, A and / or B can represent: A exists alone, A and B exist simultaneously, or B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects before and after are in an "or" relationship.

[0112] In this application, "at least one" means one or more, and "a plurality" means two or more. "At least one of the following" or similar expressions refer 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 both represent: a, b, c, a - b (i.e., a and b), a - c, b - c, or a - b - c, where a, b, and c can be single or multiple respectively.

[0113] 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, indicating that the value of a can be between 0.5 and 15, and includes the endpoint values 0.5 and 15.

[0114] It should be understood that in various embodiments of this application, the magnitude of the sequence numbers of the above processes does not imply 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 to the implementation process of the embodiments of this application.

Claims

1. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode, a negative electrode, a separator and an electrolyte located between the positive electrode and the negative electrode. The electrolyte includes an electrolyte salt and an organic solvent. The organic solvent includes a cyclic carbonate solvent and / or a carboxylate solvent; the positive electrode includes a positive electrode active material; the negative electrode includes a negative electrode active material; The numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.005:1 to 0.2:1; The numerical ratio of the mass percentage of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.002:1 to 0.1:1; wherein, the unit of the D50 particle size is μm.

2. The sodium ion battery according to claim 1, wherein The numerical ratio of the mass percentage of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.01:1 to 0.1:

1.

3. The sodium-ion battery according to claim 1, characterized in that, The numerical ratio of the mass percentage of the carboxylate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.005:1 to 0.05:

1.

4. The sodium ion battery according to claim 1, characterized in that, The cyclic carbonate solvent includes one or more of ethylene carbonate and propylene carbonate; the mass percentage of the cyclic carbonate solvent in the electrolyte is 10%-40%.

5. The sodium-ion battery according to claim 4, wherein, The mass percentage of ethylene carbonate in the electrolyte is 0%-20%, and the mass percentage of propylene carbonate in the electrolyte is 10%-40%.

6. The sodium-ion battery according to claim 1, characterized in that, The carboxylate solvent includes one or more of methyl formate, ethyl formate, methyl acetate, ethyl acetate, propyl acetate, ethyl propionate, propyl propionate, methyl difluoroacetate, and methyl trifluoroacetate; the mass percentage of the carboxylate solvent in the electrolyte is 5%-25%.

7. The sodium ion battery according to any one of claims 1-6, characterized in that, The D50 particle size of the positive electrode active material is 0.7 μm - 20 μm.

8. The sodium-ion battery according to any one of claims 1-7, characterized in that, The D50 particle size of the negative electrode active material is 0.7 μm - 20 μm.

9. The sodium ion battery according to any one of claims 1-8, characterized in that, The organic solvent further includes a linear carbonate solvent.

10. The sodium ion battery according to claim 9, wherein The mass percentage of the linear carbonate solvent in the electrolyte is 20%-50%.

11. The sodium-ion battery according to claim 10, characterized in that, The linear carbonate solvent includes one or more of diethyl carbonate, ethyl methyl carbonate, and dimethyl carbonate; the mass percentage of diethyl carbonate in the electrolyte is 0%-40%, the mass percentage of ethyl methyl carbonate in the electrolyte is 0%-40%, and the mass percentage of dimethyl carbonate in the electrolyte is 0%-20%.

12. The sodium-ion battery according to any one of claims 9-11, characterized in that, The organic solvent further includes an ether solvent, and the mass percentage of the ether solvent in the electrolyte is less than or equal to 20%.

13. The sodium ion battery according to claim 12, wherein The ether solvent includes one or more of tetrahydrofuran, 2-methyltetrahydrofuran, 1,3-dioxolane, dimethoxymethane, 1,2-dimethoxyethane, diethylene glycol dimethyl ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and bis(2,2,2-trifluoroethyl) ether.

14. The sodium ion battery according to any one of claims 1-13, characterized in that, The electrolyte further includes an additive, and the additive includes at least one of a sodium salt additive and an organic additive; the mass percentage of the sodium salt additive in the electrolyte is 0.05%-3%; the mass percentage of the organic additive in the electrolyte is 0.1%-15%.

15. The sodium-ion battery according to claim 14, wherein The sodium salt additive includes one or more of sodium bis(oxalato)borate, sodium difluoro(oxalato)borate, sodium difluoro bis(oxalato)phosphate, and sodium difluorophosphate; the organic additive includes one or more of sulfur-containing ester compounds, fluorinated carbonate compounds, nitrile compounds, and acid anhydride compounds.

16. The sodium-ion battery according to claim 15, wherein, The mass percentage of the sulfur-containing ester compound in the electrolyte is 0.5%-5%; the mass percentage of the fluorinated carbonate compound in the electrolyte is 0.5%-5%; the mass percentage of the nitrile compound in the electrolyte is 0.5%-5%; the mass percentage of the acid anhydride compound in the electrolyte is 0.05%-1%.

17. The sodium ion battery according to claim 15 or 16, characterized in that, The sulfur-containing ester compounds include one or more of dimethyl sulfite, diethyl sulfite, vinylene sulfite, ethylene sulfate, propylene sulfate, methylene methanedisulfonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, and ethyl methyl sulfate; the fluorinated carbonate compounds include one or more of fluoroethylene carbonate and difluoroethylene carbonate; 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, 1,3,6-hexanetricarbonitrile, and 1,4-dicyano-2-butene; the acid anhydride compounds include one or more of succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride, cyclic phosphoric anhydride, and 1-butyl phosphoric anhydride.

18. The sodium ion battery according to any one of claims 1-17, characterized in that, In the electrolyte, the molar concentration of the electrolyte salt is 0.05 mol / L - 5 mol / L; the electrolyte salt includes one or more of NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, sodium 4,5-dicyano-2-trifluoromethylimidazole (NaTDI), Na[(CF3SO2)2N], Na[(FSO2)2N], and Na[(C m F 2m+1 SO2)(C n F 2n+1 SO2)N], where m and n are natural numbers.

19. The sodium-ion battery according to any one of claims 1-18, characterized in that, The positive electrode active material includes at least one of layered sodium transition metal oxides, Prussian blue (white) compounds, and sodium polyanionic compounds.

20. The sodium ion battery according to any one of claims 1-19, characterized in that, The negative electrode active material includes at least one of natural graphite, artificial graphite, mesocarbon microbeads, hard carbon, soft carbon, and porous carbon materials.

21. A method for preparing a sodium ion battery, comprising: providing a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte; wherein the positive electrode sheet includes a positive electrode active material, the negative electrode sheet includes a negative electrode active material, the electrolyte includes an electrolyte salt and an organic solvent, and the organic solvent includes a cyclic carbonate solvent and / or a carboxylic acid ester solvent; wherein, controlling the numerical ratio of the mass fraction of the cyclic carbonate solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.005:1 to 0.2:1; controlling the numerical ratio of the mass fraction of the carboxylic acid ester solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the negative electrode active material is 0.002:1 to 0.1:1; wherein, the unit of the D50 particle size is μm. Assemble the above-mentioned positive electrode sheet, negative electrode sheet, separator and electrolyte to obtain a sodium-ion battery.

22. An electrical device, characterized in that, The electrical device includes a housing, and electronic components and a battery accommodated in the housing. The battery powers the electronic components, and the battery includes the sodium-ion battery according to any one of claims 1-20 or the sodium-ion battery prepared by the preparation method according to claim 21.

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