Sodium-ion battery and electric device

Abstract

A sodium-ion battery and an electric device. The sodium-ion battery comprises a positive electrode, a negative electrode, a separator and an electrolyte; the electrolyte comprises a cyclic carbonate ester solvent and / or a carboxylic ester solvent; the ratio of the mass ratio of the cyclic carbonate ester solvent in the electrolyte to the sum of the D50 particle size of a positive electrode active material and the D50 particle size of a negative electrode active material is 0.005:1 to 0.2:1; and 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 μm. By reasonably designing the specific association relationship between the D50 particle size of the positive and negative electrode active materials and the solvents in the electrolyte, the sodium-ion battery can effectively balance the ion transmission and ion diffusion capabilities in the battery charging and discharging process, thereby improving the low-temperature dynamic performance of the battery, and also considering the high-temperature performance.

Description

Sodium-ion batteries and electrical equipment

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 29, 2023, with application number 202311865528.0 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 field of battery technology, and in particular to a sodium ion battery and electrical equipment. Background Art

[0003] With the shortage and uneven distribution of lithium resources, sodium-ion batteries are considered to be very promising candidates in energy storage scenarios due to their advantages such as abundant sodium resources and low cost. Low-temperature characteristics are the highlight of sodium-ion batteries to create differentiation. However, the current sodium-ion batteries have poor low-temperature charging kinetics and are prone to sodium precipitation, which causes serious side reactions and leads to poor cycle performance. This has become a bottleneck for sodium-ion batteries to create a differentiated competitive route. Electrolytes, positive and negative electrode materials, etc. all have an impact on the low-temperature performance of sodium-ion batteries, but how to design the relationship between electrolytes and positive and negative electrode materials so that the low-temperature characteristics of sodium-ion batteries are better utilized while taking into account high-temperature performance is still unclear. Therefore, it is necessary to clarify the structure-activity relationship between electrolytes and positive and negative electrode materials. Summary of the Invention

[0004] In view of this, the embodiments of the present application provide a sodium ion battery and an electrical device. By rationally designing the specific relationship 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 battery charge and discharge process, improve the battery's low-temperature kinetic performance, and take into account the high-temperature performance.

[0005] In a first aspect, an embodiment of the present application provides a sodium ion battery, comprising a positive electrode, a negative electrode, and a separator and an electrolyte located between the positive electrode and the negative electrode, wherein the electrolyte comprises an electrolyte salt and an organic solvent, wherein the organic solvent comprises a cyclic carbonate solvent and / or a carboxylate solvent; the positive electrode comprises a positive electrode active material; and the negative electrode comprises a negative electrode active material.

[0006] The ratio of the mass proportion 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 to 0.2:1;

[0007] The numerical ratio of the mass proportion of the carboxylate 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 μm.

[0008] The sodium ion battery provided in 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 proportion 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 within a suitable specific range, and controls the numerical ratio of the mass proportion of the carboxylate 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 within a suitable specific range. In this way, the physical properties of the electrolyte, such as viscosity and conductivity, can be reasonably regulated, and the ion transport and ion diffusion capabilities during the battery charge and discharge process can be effectively balanced. The low-temperature kinetic properties of the positive and negative electrode active materials are improved, while taking into account the high-temperature performance, thereby obtaining a sodium ion battery with both good low-temperature performance and excellent high-temperature performance.

[0009] D50 particle size refers to the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%. D50 is also called median diameter or median particle size.

[0010] In an embodiment of the present application, the ratio of the mass proportion 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 0.01:1 to 0.1:1. By controlling the ratio of the mass proportion 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 within a suitable range, it is possible to better balance the high temperature performance of the battery while utilizing the cyclic carbonate solvent to improve the low temperature performance, thereby ensuring that the electrolyte as a whole has suitable conductivity and obtaining a higher ion transport capacity.

[0011] In an embodiment of the present application, the ratio of the mass proportion of the carboxylate 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 to 0.05:1. By controlling the ratio of the mass proportion of the carboxylate 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 within a suitable range, the high-temperature performance of the battery can be better balanced while utilizing the carboxylate solvent to improve low-temperature performance, thereby ensuring that the overall electrolyte has a suitable viscosity and achieving faster ion transport capability.

[0012] In the embodiments 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% to 40%. The addition of a suitable amount of the cyclic carbonate solvent to the electrolyte can help leverage its advantages to enhance the low-temperature performance of the battery and can also be combined with other solvents to further enhance the overall performance of the battery.

[0013] In the embodiment of the present application, the mass percentage of the ethylene carbonate in the electrolyte is 0%-20%, and the mass percentage of the propylene carbonate in the electrolyte is 10%-40%.

[0014] In an embodiment of the present application, 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%.

[0015] In the embodiment 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.

[0016] In the embodiment 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.

[0017] In the embodiment of the present application, the organic solvent further comprises 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 capacity of the electrolyte.

[0018] In the embodiment of the present application, the linear carbonate solvent comprises 20% to 50% by weight of the electrolyte. The addition of an appropriate amount of linear carbonate solvent helps to achieve a suitable viscosity for the electrolyte and, together with other solvents such as cyclic carbonate solvents and carboxylate solvents, further enhances the overall performance of the electrolyte.

[0019] In an embodiment 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%.

[0020] In an embodiment of the present application, the organic solvent further comprises 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 achieve a highly reversible solvent-co-intercalation reaction and form a thin and stable SEI film (Solid Electrolyte Interphase), which is conducive to stable electrode cycling and rapid sodium storage kinetics.

[0021] In an embodiment 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.

[0022] In an embodiment 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 SEI film formation quality of the negative electrode and reduce the contact between the negative electrode and the electrolyte; the addition of the organic additive is conducive to the formation of 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 uniform and rapid migration of sodium ions at the interface. The addition of an appropriate amount of sodium salt additives and organic additives to the electrolyte is conducive to better improving the overall performance of the battery.

[0023] 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 organic additive includes one or more of sulfur-containing ester compounds, fluorocarbonate compounds, nitrile compounds, and acid anhydride compounds.

[0024] In the embodiment 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 fluorocarbonate compound in the electrolyte is 0.5%-5%; the mass percentage of the nitrile compound in the electrolyte is 0.5%-5%; and the mass percentage of the acid anhydride compound in the electrolyte is 0.05%-1%.

[0025] In the embodiment of the present application, the sulfur-containing ester compound includes one or more of dimethyl sulfite, diethyl sulfite, ethylene sulfite, ethylene sulfate, propylene sulfate, methylene disulfonate, 1,3-propane sultone, 1,3-propene sultone, 1,4-butane sultone, dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate; the fluorocarbonate compound includes one or more of fluoroethylene carbonate and difluoroethylene carbonate; the nitrile The compound includes a mononitrile compound and / or a polynitrile compound; the mononitrile compound includes at least one of acetonitrile and p-methylbenzonitrile; the polynitrile compound includes one or more of succinonitrile, glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3,6-hexanetrinitrile, and 1,4-dicyano-2-butene; the acid anhydride compound includes one or more of succinic anhydride, glutaric anhydride, adipic anhydride, maleic anhydride, cyclic phosphoric anhydride, and 1-butylphosphoric anhydride.

[0026] In the embodiment of the present application, in the electrolyte, the molar concentration of the electrolyte salt is 0.05 mol / L-5 mol / L; the electrolyte salt includes NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, 4,5-dicyano-2-trifluoromethylimidazolium sodium (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.

[0027] In an embodiment 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 compounds.

[0028] In an embodiment of the present application, the negative electrode active material includes at least one of natural graphite, artificial graphite, mesophase microcarbon beads, hard carbon, soft carbon, and porous carbon materials.

[0029] 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.

[0030] A second aspect of an embodiment of the present application provides a method for preparing a sodium ion battery, comprising:

[0031] 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;

[0032] The ratio of the mass proportion 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 controlled to be 0.005:1 to 0.2:1;

[0033] The ratio of the mass proportion of the carboxylate 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 controlled to be 0.002:1 to 0.1:1; wherein the unit of the D50 particle size is μm;

[0034] The positive electrode sheet, negative electrode sheet, separator and electrolyte are assembled to obtain a sodium ion battery.

[0035] The preparation method of the sodium ion battery provided in the embodiment of the present application can effectively balance the ion transport and ion diffusion capabilities during the battery charge and discharge process by rationally designing the specific correlation between the D50 particle size of the positive and negative electrode active materials and the electrolyte solvent, improve the battery's low-temperature kinetic performance, and take into account the high-temperature performance at the same time, so as to achieve the purpose of improving the battery cycle, high-temperature storage performance and low-temperature charging performance.

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

[0037] FIG1 is a schematic structural diagram of a sodium ion battery 100 provided in an embodiment of the present application;

[0038] FIG2 is a schematic structural diagram of an electric device 200 provided in an embodiment of the present application;

[0039] FIG3 is a comparison chart of the cycle performance of the sodium ion batteries of Example 5 of the present application and Comparative Examples 1-2. DETAILED DESCRIPTION

[0040] The embodiments of the present application will be described below with reference to the accompanying drawings.

[0041] In sodium-ion batteries, the electrolyte, positive and negative electrode materials, etc. all have an impact on the low-temperature performance of the sodium-ion battery, but it is currently unclear how to design the relationship between the electrolyte and the positive and negative electrode materials to better utilize the low-temperature characteristics of the sodium-ion battery while also taking into account the high-temperature performance. In view of this, the embodiments of the present application provide a sodium-ion battery and electrical equipment. By rationally designing the specific relationship 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 battery's charge and discharge process, improve the battery's low-temperature kinetic performance, and at the same time take into account the high-temperature performance.

[0042] 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 . The separator 30 is disposed between the positive electrode 10 and the negative electrode 20 . 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 , and the electrolyte 40 includes an electrolyte salt and an organic solvent. The organic solvent includes a cyclic carbonate solvent and / or a carboxylic acid ester solvent.

[0043] Among them, the numerical ratio of the mass proportion of the cyclic carbonate solvent in the electrolyte 40 to the sum of the D50 particle size of the positive electrode active material 102 and the D50 particle size of the negative electrode active material 202 is 0.005:1 to 0.2:1; the numerical ratio of the mass proportion of the carboxylate solvent in the electrolyte 40 to the sum of the D50 particle size of the positive electrode active material 102 and the D50 particle size of the negative electrode active material 202 is 0.002:1 to 0.1:1; wherein the unit of D50 particle size is μm.

[0044] During charging, sodium ions in the sodium-ion battery 100 are released from the positive electrode active material 102 of the positive electrode 10, then intercalated into the negative electrode active material 202 of the negative electrode 20 after passing through the electrolyte 40. During discharge, sodium ions are released from the negative electrode active material 202, then intercalated into the positive electrode active material 102 after passing through the electrolyte 40. The positive and negative active materials and the electrolyte solvent of the sodium-ion battery 100 meet the aforementioned conditions, effectively balancing ion transport and ion diffusion during the battery's charge and discharge processes. This improves the battery's low-temperature kinetics while also balancing high-temperature performance. This results in a sodium-ion battery product with both good low-temperature and excellent high-temperature performance, thereby enhancing the market competitiveness of electronic devices, electric vehicles, and other electrical equipment.

[0045] Among them, D50 particle size refers to the particle size corresponding to when the cumulative particle size distribution percentage of a sample reaches 50%. D50 is also called median diameter or median particle size.

[0046] The inventors of the present application have found that in the sodium ion battery 100, the particle size of the positive and negative electrode active materials and the solvent system of the electrolyte play an important role in the low temperature performance of the battery. However, unilateral adjustment of the particle size of the positive and negative electrode active materials or the solvent system of the electrolyte will deteriorate the high temperature performance and other performances of the battery. The sodium ion battery provided in the embodiment of the present application establishes a correlation between the D50 particle size of the positive and negative electrode active materials and the solvent of the electrolyte, and correlates the mass proportion of the cyclic carbonate solvent in the electrolyte with the D50 particle size of the positive electrode active material and the solvent system of the negative electrode active material. By controlling the numerical ratio of the sum of the D50 particle sizes of the materials within a suitable specific range, and controlling the numerical ratio of the mass proportion 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 D50 particle sizes of the negative electrode active material within a suitable specific range, the viscosity, conductivity and other physical properties of the electrolyte can be reasonably regulated, the ion transport and ion diffusion capabilities during the battery charge and discharge process can be effectively balanced, the low-temperature kinetic properties of the positive and negative electrode active materials can be improved, and the high-temperature performance can be taken into account at the same time, thereby obtaining a sodium ion battery with both good low-temperature performance and excellent high-temperature performance.

[0047] It should be noted that the numerical ratio of the mass proportion 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 a numerical ratio calculated without considering the unit of the D50 particle size. For example, if the mass proportion of the cyclic carbonate solvent is 30%, the D50 particle size of the positive electrode active material is 5 μm, and the D50 particle size of the negative electrode active material is 5 μm, then the numerical ratio = 30% / (5+5) = 0.03.

[0048] Similarly, the numerical ratio of the mass proportion of the carboxylate 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 also a numerical ratio calculated without considering the unit of the D50 particle size. For example, if the mass proportion of the carboxylate solvent is 10%, the D50 particle size of the positive electrode active material is 5 μm, and the D50 particle size of the negative electrode active material is 5 μm, then the numerical ratio = 10% / (5+5) = 0.01.

[0049] In the present application, the ratio of the mass fraction of the cyclic carbonate solvent in the electrolyte 40 to the sum of the D50 particle size of the positive electrode active material 102 and the D50 particle size of the negative electrode active material 202 is 0.005:1 to 0.2:1. Cyclic carbonate solvents have a high dielectric constant, which is conducive to the dissociation of sodium salts, improves the conductivity of the electrolyte, and is conducive to ion transport. They also have a wide liquid temperature range, strong solubility, high safety and stability, which are conducive to improving the low-temperature performance of sodium-ion batteries. By controlling the ratio of the mass fraction 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 within a suitable range, the high-temperature performance of the battery can be better taken into account while utilizing the cyclic carbonate solvent to improve the low-temperature performance, so that the electrolyte as a whole has suitable conductivity and obtains a high ion transport capacity. In some embodiments, the numerical ratio is specifically, 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 acceptable ranges. For example, the numerical ratio can be taken from a value between 0.005:1-0.02:1, or from a value between 0.01:1-0.07:1, or from a value between 0.03:1-0.1:1, or from a value between 0.08:1-0.2:1, or from a value between any two other values. In some embodiments of the present application, the numerical ratio of the mass fraction of the cyclic carbonate solvent in the electrolyte 40 to the sum of the D50 particle size of the positive electrode active material 102 and the D50 particle size of the negative electrode active material 202 is 0.01:1 to 0.1:1.

[0050] In the present application, the ratio of the mass proportion of the carboxylate solvent in the electrolyte 40 to the sum of the D50 particle size of the positive electrode active material 102 and the D50 particle size of the negative electrode active material 202 is 0.002:1 to 0.1:1. Carboxylate solvents have a low freezing point and a low melting point, and a low viscosity, which are beneficial for improving the low-temperature performance of sodium-ion batteries. By controlling the ratio of the mass proportion of the carboxylate 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 within a suitable range, it is possible to better balance the high-temperature performance of the battery while utilizing the carboxylate solvent to improve the low-temperature performance. In some embodiments, the numerical ratio is specifically, 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 :1, 0.08:1, 0.09:1, 0.1:1, and numbers between any two of the above values ​​are all acceptable ranges. For example, the numerical ratio can be taken from a value between 0.002:1-0.02:1, a value between 0.01:1-0.06:1, a value between 0.04:1-0.08:1, a value between 0.07:1-0.1:1, or a number between any two other values. In some embodiments of the present application, the numerical ratio of the mass proportion of the carboxylate solvent in the electrolyte 40 to the sum of the D50 particle size of the positive electrode active material 102 and the D50 particle size of the negative electrode active material 202 is 0.005:1 to 0.05:1.

[0051] It should be noted that the calculated values ​​of the above-mentioned numerical ratios may be subject to certain measurement and test system errors during actual test operations, and the values ​​within the system error range may be understood as the range defined by the embodiments of this application.

[0052] In the embodiments of the present application, the cyclic carbonate solvent includes, but is not limited to, one or more of ethylene carbonate (EC) and propylene carbonate (PC). In some embodiments, the cyclic carbonate solvent in the electrolyte includes only ethylene carbonate (EC); in some embodiments, the cyclic carbonate solvent in the electrolyte includes only propylene carbonate (PC); and in some embodiments, the cyclic carbonate solvent in the electrolyte includes both ethylene carbonate (EC) and propylene carbonate (PC). Propylene carbonate (PC) has a relatively wider liquidus temperature range, and the addition of propylene carbonate (PC) to the electrolyte is more conducive to achieving both high and low temperature performance.

[0053] In the embodiment of the present application, the mass percentage of the cyclic carbonate solvent in the electrolyte can be 10%-40%. The addition of a suitable amount of cyclic carbonate solvent in the electrolyte is beneficial to its advantages in improving the conductivity of the electrolyte and enhancing the ion transmission capacity, thereby improving the low-temperature performance of the battery, and can also be combined with other solvents to better improve the overall 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.

[0054] In some embodiments of the present application, the mass percentage of ethylene carbonate in the electrolyte is 0%-20%, 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%, for example, it can be 10%, 12%, 15%, 16%, 20%, 22%, 25%, 28%, 30%, 32%, 35%, 38%, 40%, etc.

[0055] In the embodiment of the present application, the carboxylate solvent includes but is 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.

[0056] In the embodiments of the present application, the mass percentage of the carboxylate solvent in the electrolyte can be 5%-25%. The addition of a suitable amount of carboxylate solvent to the electrolyte is beneficial to leveraging its advantages to improve low-temperature dynamics, thereby improving the low-temperature performance of the battery, and can also be combined with other solvents to better improve the overall performance of the battery. In some embodiments, the mass percentage of the carboxylate solvent in the electrolyte is, for example, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, etc.

[0057] In some embodiments of the present application, the organic solvent also includes a linear carbonate solvent. The addition of a linear carbonate solvent helps reduce the viscosity of the electrolyte and improve the ion transport capacity of the electrolyte. In the embodiments of the present application, the mass percentage of the linear carbonate solvent in the electrolyte can be 20%-50%. The addition of an appropriate amount of linear carbonate solvent helps to obtain a suitable viscosity for the electrolyte and, together with other solvents such as cyclic carbonate solvents and carboxylate solvents, better improves the overall performance of the electrolyte. In some embodiments, the mass percentage of the linear carbonate solvent 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 solvent in the electrolyte can be 30%-50%.

[0058] In embodiments of the present application, 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%, 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%, 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%, for example, 0%, 2%, 5%, 8%, 10%, 12%, 15%, 20%, etc. In some embodiments, the linear carbonate solvent in the electrolyte includes both diethyl carbonate (DEC) and ethyl methyl carbonate (EMC). 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%.

[0059] In some embodiments of the present application, the organic solvent further comprises an ether solvent. The stable solvation structure of the ether solvent can realize a highly reversible solvent-co-intercalation reaction and form a thin and stable SEI film (Solid Electrolyte Interphase, solid electrolyte interface film), which is beneficial to the stable circulation of the electrode and the rapid sodium storage dynamics. In an embodiment of the present application, the mass percentage of the ether solvent in the electrolyte can be less than or equal to 20%. In some embodiments, the mass percentage of the ether solvent in the electrolyte is, for example, 0%, 2%, 5%, 8%, 10%, 12%, 15%, 20%, etc.

[0060] In the embodiment of the present application, the ether solvent includes but is 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.

[0061] It can be understood that the mass percentage values ​​of the above-mentioned solvents will have a certain impact on the mass percentage test of the electrolyte solvent due to the formation of the interface film after actual battery formation, fractionation or circulation, and a certain measurement test error can be allowed. The values ​​within the error range can be understood as the range defined in the embodiments of the present application, or the numerical range of the mass percentage of the electrolyte solvent tested after formation, fractionation or circulation is still within the above range and can be understood as the range defined in the embodiments of the present application.

[0062] In the embodiment 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 of the negative electrode and reduce the contact between the negative electrode and the electrolyte; the addition of organic additives is conducive to the formation of 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. In some embodiments, the additives include both sodium salt additives and organic additives, so that the sodium salt additive has a higher reduction film-forming potential and can react with the negative electrode before the organic additive, passivating the negative electrode surface, thereby improving the film-forming quality of the organic additive on the negative electrode surface, effectively avoiding the continuous rupture and dissolution of the SEI film during the cycle, reducing the contact between the negative electrode and the electrolyte, and reducing the probability of side reactions.

[0063] In the embodiment of the present application, the sodium salt additive includes but is not limited to one or more of sodium bis(oxalatoborate) (NaBOB), sodium difluorooxalatoborate (NaDFOB), sodium difluorobis(oxalatophosphate) (NaDFOP), and sodium difluorophosphate (NaPO2F2). In the embodiment of the present application, the mass percentage of the sodium salt additive in the electrolyte can be 0.05%-3%. In some embodiments, the mass percentage of the sodium salt additive 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 additive to the electrolyte is conducive to better improving the overall performance of the battery.

[0064] In the embodiment of the present application, the organic additive includes but is not limited to one or more of sulfur-containing ester compounds, fluorocarbonate compounds, nitrile compounds, and acid anhydride compounds. In the embodiment of the present application, the sulfur-containing ester compounds include but are not limited to dimethyl sulfite, diethyl sulfite, vinyl sulfite, vinyl sulfate (DTD), propylene sulfate (TS), methylene disulfonate (MMDS), 1,3-propane sultone (PS), 1,3-propene sultone (PST), 1,4-butane sultone (BS), dimethyl sulfate, diethyl sulfate, and 4-methylethylene sulfate. In the embodiment of the present application, the fluorocarbonate compounds include but are not limited to one or more of fluoroethylene carbonate (FEC) and bisfluoroethylene carbonate (DFEC). In the embodiment of the present application, the nitrile compounds include but are not limited to mononitrile compounds and / or polynitrile compounds. Among them, mononitrile compounds include but are not limited to at least one of acetonitrile and p-methylbenzonitrile; polynitrile compounds include but are not limited to one or more of succinonitrile (SN), glutaronitrile, adiponitrile, 1,2-bis(2-cyanoethoxy)ethane (DENE), 1,3,6-hexanetrinitrile (HTCN), and 1,4-dicyano-2-butene. In the embodiments of the present application, acid 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-butylphosphonic anhydride.

[0065] In the embodiments of the present application, the mass percentage of the organic additive in the electrolyte may be 0.1%-15%. In some embodiments, the mass percentage of the organic additive in the electrolyte may be 0.1%-15%, for example, 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 organic additive to the electrolyte is conducive to better improving the overall performance of the battery.

[0066] In some embodiments of the present application, the mass percentage of the sulfur-containing ester compound in the electrolyte is 0.5%-5%, such as 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 fluorocarbonate compound in the electrolyte is 0.5%-5%, such as 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%, such as 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 acid anhydride compound in the electrolyte is 0.05%-1%, such as 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 of compounds: sulfur-containing ester compounds and fluorocarbonate compounds; in some embodiments, the organic additives added to the electrolyte include three types of compounds: sulfur-containing ester compounds, fluorocarbonate compounds, and nitrile compounds; in some embodiments, the organic additives added to the electrolyte include three types of compounds: sulfur-containing ester compounds, fluorocarbonate compounds, and acid anhydride compounds; in some embodiments, the organic additives added to the electrolyte include four types of compounds: sulfur-containing ester compounds, fluorocarbonate compounds, nitrile compounds, and acid anhydride compounds.

[0067] In the embodiment of the present application, in the electrolyte, the molar concentration of the electrolyte salt is 0.05mol / L-5mol / L. In some embodiments, in the electrolyte, the molar concentration of the electrolyte salt can be, for example, 0.05mol / L, 0.1mol / L, 0.5mol / L, 0.8mol / L, 1.0mol / L, 1.2mol / L, 1.5mol / L, 1.8mol / L, 2.0mol / L, 3.0mol / L, 4.0mol / L, 5.0mol / L, etc. The electrolyte salt includes but is not limited to NaClO4, NaBF4, NaPF6, NaAsF6, NaCF3SO3, 4,5-dicyano-2-trifluoromethylimidazolium sodium (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.

[0068] In the sodium ion battery 100, the electrolyte 40 is a transport medium for sodium ions to be transported between the positive electrode 10 and the negative electrode 20. In the electrolyte 40, electrolyte salt and additives are dissolved in an organic solvent.

[0069] 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, 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 the embodiment of the present application, the positive electrode active material 102 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 the embodiment of the present application, the layered sodium transition metal oxide may be, for example, sodium nickel iron manganese (NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2, abbreviated as NFM), Prussian blue (white) compounds can be, for example, Prussian white (Na2Mn[Fe(CN)6], abbreviated as PBA), and sodium polyanion compounds can be, for example, sodium iron phosphate (NaFePO4, abbreviated as NFP), 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.

[0070] In the embodiment of the present application, the D50 particle size of the positive electrode active material is 0.7μm-20μm. 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, 0.7μm, 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 15μm, 16μm, 18μm, 20μm, and numbers between any two of the above values; in some embodiments, the D50 particle size of the positive electrode active material is 2μm-10μm. It can be understood that the above D50 value will have a certain impact on the median particle size test of the material due to the formation of the interface film after actual battery formation, capacity separation or cycling, and a certain measurement test error can be allowed. The values ​​within the error range can be understood as the range defined in the embodiment of the present application, or the median particle size 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 embodiment of the present application.

[0071] In the embodiment of the present application, the positive electrode material layer may include, in addition to the positive electrode active material 102, a certain amount of binder, conductive agent, and other components. The binder may be, for example, polyvinylidene fluoride (PVDF). The conductive agent may be, for example, conductive carbon black Super P, amorphous carbon, carbon nanotubes, carbon fiber, graphene, etc. The above binders and conductive agents are merely exemplary and are not intended to be limiting.

[0072] As shown in Figure 1, 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, wherein the negative electrode current collector 201 can 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 can be one or more of natural graphite, artificial graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, and porous carbon materials.

[0073] In the embodiment of the present application, the D50 particle size of the negative electrode active material is 0.7μm-20μm. A suitable particle size is beneficial to improving the electrochemical performance of the battery. The D50 particle size of the negative electrode active material can be, for example, 0.7μm, 1μm, 2μm, 4μm, 6μm, 8μm, 10μm, 12μm, 14μm, 15μm, 16μm, 18μm, 20μm, and numbers between any two of the above values; in some embodiments, the D50 particle size of the negative electrode active material is 2μm-10μm. It can be understood that the above D50 value will have a certain impact on the median particle size test of the material due to the formation of the interface film after actual battery formation, capacity separation or cycling, and a certain measurement test error can be allowed. The values ​​within the error range can be understood as the range defined in the embodiment of the present application, or the median particle size 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 embodiment of the present application.

[0074] 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 conductive carbon black Super P, amorphous carbon, carbon nanotubes, carbon fibers, and graphene. The aforementioned binders and conductive agents are merely illustrative and are not intended to be limiting.

[0075] As shown in FIG1 , in a sodium-ion battery 100 , a separator 30 is located between the positive electrode 10 and the negative electrode 20 , blocking the passage of electrons while allowing the passage of sodium ions. 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.

[0076] 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.

[0077] 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.

[0078] The present invention also provides a method for preparing a sodium ion battery, comprising:

[0079] 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;

[0080] The ratio of the mass proportion 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 controlled to be 0.005:1 to 0.2:1;

[0081] The ratio of the mass proportion of the carboxylate 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 controlled to be 0.002:1 to 0.1:1; wherein the unit of the D50 particle size is μm;

[0082] The positive electrode sheet, negative electrode sheet, separator and electrolyte are assembled to obtain a sodium ion battery.

[0083] 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.

[0084] The preparation method of the sodium ion battery provided in the embodiment of the present application can effectively balance the ion transport and ion diffusion capabilities during the battery charge and discharge process by rationally designing the specific correlation between the D50 particle size of the positive and negative electrode active materials and the electrolyte solvent, improve the battery's low-temperature kinetic performance, and take into account the high-temperature performance at the same time, so as to achieve the purpose of improving the battery cycle, high-temperature storage performance and low-temperature charging performance.

[0085] 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, an energy storage device, a base station or other equipment product. The sodium ion battery provided in the embodiment of the present application can be used to improve product safety and reliability.

[0086] The embodiments of the present application are further described below with reference to a number of embodiments.

[0087] The sodium ion batteries in the following examples and comparative examples were prepared according to the following method:

[0088] 2% polyvinylidene fluoride (PVDF), 2% conductive agent Super P, and 96% positive electrode active material were weighed and added to N-methylpyrrolidone (NMP) in sequence. The mixture was thoroughly stirred and mixed. The slurry was coated on an aluminum foil current collector, dried, cold pressed, and cut into pieces to produce positive electrode sheets.

[0089] Weigh 1.5% CMC-Na, 2.5% SBR, 1% Super P, and 95% negative electrode active material by weight, add them to deionized water in sequence, stir and mix thoroughly, apply the slurry on a copper foil current collector, dry, cold press, and cut to produce negative electrode sheets;

[0090] Sodium hexafluorophosphate (NaPF6) is added to an organic solvent, and then additives of different types and contents are added to obtain an electrolyte; the molar concentration of NaPF6 in the electrolyte is 1 mol / L;

[0091] 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.

[0092] The types and D50 particle sizes of the positive electrode active materials, negative electrode active materials, organic solvents in the electrolyte, and additives used in the examples and comparative examples are shown in Table 1.

[0093] The performance of each embodiment and comparative example was tested according to the following method, and the test results are shown in Table 1:

[0094] 1. 45℃ cycle performance test:

[0095] 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 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 250 times, and the discharge capacities of the first and 250th cycles were recorded. The capacity retention rate after 250 cycles was calculated as follows:

[0096] Capacity retention (%)=discharge capacity at the 250th cycle / discharge capacity at the 1st cycle×100%.

[0097] 2. -40℃ low temperature performance test:

[0098] Under the condition of ambient temperature of 25±3℃, charge to 3.95V with a constant current of 0.2C, then charge at a constant voltage until the current drops to 0.05C, let it rest for 10 minutes, and then discharge to 2.0V with a constant current of 0.2C. The discharge capacity at this time is the initial capacity; the battery is placed at a temperature of -40℃ for 4 hours, then charged to 3.95V with a constant current of 0.2C, then charged at a constant voltage until the current drops to 0.05C, let it rest for 10 minutes, and then discharged to 2.0V with a constant current of 0.2C. The discharge capacity at this time is recorded as the residual capacity, and the residual capacity retention rate is calculated. Residual capacity retention rate = (residual capacity / initial capacity) × 100%.

[0099] Table 1 Parameter details and battery performance of Examples 1-45 and Comparative Examples 1-9

[0100] As can be seen from the data in Table 1, the sodium ion batteries prepared in Examples 1-25, Examples 39-45 and Comparative Examples 1-3 of the present application are compared. The sodium ion batteries obtained in Examples 1-25 and Examples 39-45 have a -40°C low-temperature residual capacity retention rate of 45.4%-51.9%, and a 45°C cycle 250 cycle capacity retention rate of 94.7%-97.2%, which are significantly higher than the -40°C low-temperature residual capacity retention rate (37.1%-37.6%) and 45°C cycle 250 cycle capacity retention rate (94.0%-94.3%) of the sodium ion batteries obtained in Comparative Examples 1-3. This is attributed to the following: in Examples 1-25 and Examples 39-45, the numerical ratio of the cyclic carbonate to the median particle size of the positive electrode active material (NFM) and the median particle size of the negative electrode active material (hard carbon, soft carbon) satisfies 0.005:1 to 0.2:1; and the numerical ratio of the carboxylate to the median particle size of the positive electrode active material (NFM) and the median particle size of the negative electrode active material (hard carbon, soft carbon) satisfies 0.002:1 to 0.1:1. However, these numerical ratios were not met in Comparative Examples 1-3. 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. 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). As a result, it is impossible to balance ion transport and ion diffusion, resulting in poor battery performance. Figure 3 is a comparison of the cycling performance of the sodium ion batteries of Example 5, Comparative Examples 1, and Comparative Examples 2. As can be seen from Figure 3, the cycling performance of the sodium ion battery of Example 5 after 250 cycles at 45°C is significantly better than that of Comparative Examples 1 and 2.

[0101] By comparing Example 5 with Examples 39-41 and Examples 43-45, it can be seen that adding an appropriate amount of sodium salt additives and / or organic additives to the electrolyte is beneficial to further improving the performance of the battery, and adding sodium salt additives and organic additives at the same time is beneficial to improving the battery performance.

[0102] As can be seen from the data in Table 1, compared with the sodium ion batteries prepared in Examples 26-30 of the present application and Comparative Examples 4-5, the sodium ion batteries obtained in Examples 26-30 have a -40°C low-temperature residual capacity retention rate of 51.8%-52.7%, and a 45°C cycle 250 cycle capacity retention rate of 96.2%-96.8%, which are significantly higher than the -40°C low-temperature residual capacity retention rate (38.3%-38.8%) and 45°C cycle 250 cycle capacity retention rate (94.3%-94.5%) of the sodium ion batteries obtained in Comparative Examples 4-5. This is attributed to the following: in Examples 26-30, the numerical ratio of the mass percentage of the cyclic carbonate in the electrolyte to the sum of the median particle size of the positive electrode active material (PBA) and the median particle size of the negative electrode active material (hard carbon) satisfies 0.005:1 to 0.2:1; and the numerical ratio of the mass percentage of the carboxylate in the electrolyte to the sum of the median particle size of the positive electrode active material (PBA) and the median particle size of the negative electrode active material (hard carbon) satisfies 0.002:1 to 0.1:1. However, these numerical ratios were not met in Comparative Examples 4-5. 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 propyl acetate (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. In Comparative Example 4, the ratio of the mass percentage of propylene carbonate (PC) in the electrolyte to 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 ratio of the mass percentage of propyl acetate (EP) in the electrolyte to the median particle size of PBA (D50: 0.7 μm) and the median particle size of hard carbon (D50: 0 .7μm) 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 (D50:20μm) and the median particle size of hard carbon (D50:20μm) is 0.004:1 (less than 0.005:1), which makes it impossible to take into account both ion transport and ion diffusion, and the battery performance is poor.

[0103] As can be seen from the data in Table 1, by comparing the sodium ion batteries prepared in Examples 31-34 of the present application and Comparative Examples 6-7, the sodium ion batteries obtained in Examples 31-34 have a -40°C low-temperature residual capacity retention rate of 50.6%-51.2% and a 45°C cycle 250 cycle capacity retention rate of 97.1%-97.5%, which are significantly higher than the -40°C low-temperature residual capacity retention rate (36.8%-37.5%) and 45°C cycle 250 cycle capacity retention rate (94.1%-94.5%) of the sodium ion batteries obtained in Comparative Examples 6-7. This is attributed to the following: in Examples 31-34, the numerical ratio of the mass percentage of the cyclic carbonate in the electrolyte to the sum of the median particle size of the positive electrode active material (NFP) and the median particle size of the negative electrode active material (hard carbon) satisfies 0.005:1 to 0.2:1; and the numerical ratio of the mass percentage of the carboxylate in the electrolyte to the sum of the median particle size of the positive electrode active material (NFP) and the median particle size of the negative electrode active material (hard carbon) satisfies 0.002:1 to 0.1:1. However, these numerical ratios were not met in Comparative Examples 6-7. 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 propyl acetate (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. In Comparative Example 6, the 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 ratio of the mass percentage of propyl acetate (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 .7μm) 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 (D50:20μm) and the median particle size of hard carbon (D50:20μm) is 0.004:1 (less than 0.005:1), which makes it impossible to take into account both ion transport and ion diffusion, and the battery performance is poor.

[0104] As can be seen from the data in Table 1, compared with the sodium ion batteries prepared in Examples 35-38 of the present application and Comparative Examples 8-9, the sodium ion batteries obtained in Examples 31-34 have a -40°C low-temperature residual capacity retention rate of 50.1%-50.7% and a 45°C cycle 250 cycle capacity retention rate of 96.1%-96.6%, which are significantly higher than the -40°C low-temperature residual capacity retention rate (40.3%-40.9%) and 45°C cycle 250 cycle capacity retention rate (94.1%-94.5%) of the sodium ion batteries obtained in Comparative Examples 8-9. This is attributed to the following: in Examples 35-38, the numerical ratio of the mass percentage of the cyclic carbonate in the electrolyte to the sum of the median particle size of the positive electrode active material (NFS) and the median particle size of the negative electrode active material (hard carbon) satisfies 0.005:1 to 0.2:1; and the numerical ratio of the mass percentage of the carboxylate in the electrolyte to the sum of the median particle size of the positive electrode active material (NFS) and the median particle size of the negative electrode active material (hard carbon) satisfies 0.002:1 to 0.1:1. However, these numerical ratios were not met in Comparative Examples 8-9. 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 propyl acetate (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. In Comparative Example 8, the 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 ratio of the mass percentage of propyl acetate (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 .7μm) 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 (D50:20μm) and the median particle size of hard carbon (D50:20μm) is 0.004:1 (less than 0.005:1), which makes it impossible to take into account both ion transport and ion diffusion, and the battery performance is poor.

[0105] In summary, when other conditions remain unchanged, regulating the numerical ratio of the mass percentage 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 an appropriate range can improve the low-temperature performance of sodium ion batteries while taking into account the high-temperature performance.

[0106] 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.

[0107] 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.

[0108] 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.

[0109] 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.

[0110] 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, 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 carboxylic ester 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 D50 particle size of the negative electrode active material is 0.005:1 to 0.2:1; The numerical ratio of the mass percentage of the carboxylic ester solvent in the electrolyte to the sum of the D50 particle sizes 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 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 D50 particle size of 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 carboxylic ester solvent in the electrolyte to the sum of the D50 particle sizes of the positive electrode active material and the D50 particle size of the negative electrode active material is 0.005:1 to 0.05:

1.

4. The sodium-ion battery according to claim 1, wherein 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, characterized in that, 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, wherein, 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%.

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 difluorobis(oxalato)phosphate, and sodium difluorophosphate; the organic additive includes one or more of sulfur-containing ester compounds, fluorinated carbonate compounds, nitrile compounds, and anhydride compounds.

16. The sodium ion battery according to claim 15, characterized in that, 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%.

17. The sodium ion battery according to claim 15 or 16, wherein, 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 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 polyanion-type 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, 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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