Sodium-ion battery, preparation method thereof and electric equipment

Abstract

The invention relates to the technical field of sodium ion batteries, in particular to a sodium ion battery, a preparation method thereof and electric equipment. The sodium ion battery comprises a positive pole piece, a negative pole piece and an electrolyte, the negative pole piece comprises a negative active material, and the sodium ion battery meets the following conditions: 300SA sigma / QDgt; 3.5); s is the specific surface area of the negative electrode active material; d is the D50 median particle size of the negative electrode active material; a is the capacity ratio of a discharge slope area of the button cell made of the negative electrode active material; q is the reversible gram capacity of the button cell made of the negative electrode active material; and sigma is the conductivity of the electrolyte. The specific surface area, the particle size and the capacity of the negative electrode active material and the conductivity of the electrolyte are controlled to meet the relational expression 300SA sigma / QDgt; and 3.5, the energy density of the sodium-ion battery is improved, the sodium-ion battery also has relatively good low-temperature charge-discharge performance, and the low-temperature cycle life of the battery is prolonged.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery and a preparation method and electrical equipment thereof. Background Art

[0002] Compared with lithium-ion batteries, sodium-ion batteries have the advantages of low cost, fast charging speed and high safety.

[0003] Existing sodium-ion batteries pursue higher energy density, which requires a positive and negative electrode system with relatively higher gram capacity. However, while the energy density is increased, it is difficult to take into account the low-temperature charging and discharging performance of the battery, resulting in a short charging and discharging cycle life under low-temperature conditions.

[0004] In view of this, the present invention is proposed. Summary of the invention

[0005] The first object of the present invention is to provide a sodium ion battery, which satisfies the relationship 300SAσ / QD>3.5 by controlling the specific surface area, particle size and capacity of the negative electrode active material and the conductivity of the electrolyte, so that the sodium ion battery has good low-temperature charge and discharge performance while improving the energy density, thereby extending the low-temperature cycle life of the battery. The problem that the existing technology is difficult to take into account the low-temperature charge and discharge performance of the battery while improving the energy density, resulting in a short charge and discharge cycle life under low temperature conditions is solved.

[0006] The second object of the present invention is to provide a method for preparing a sodium ion battery.

[0007] The third object of the present invention is to provide an electrical device.

[0008] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are particularly adopted:

[0009] The present invention first provides a sodium ion battery, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet includes a negative electrode active material, and the sodium ion battery satisfies the following conditions: 300SAσ / QD>3.5; wherein S is the specific surface area of ​​the negative electrode active material, in units of m 2 / g; D is the D50 median particle size of the negative electrode active material, in μm; A is the discharge slope capacity ratio of the button battery made of the negative electrode active material; Q is the reversible gram capacity of the button battery made of the negative electrode active material, in mAh / g; σ is the conductivity of the electrolyte, in mS / cm.

[0010] Furthermore, 6m 2 / g≤S≤20m 2 / g.

[0011] Furthermore, 2.5 μm<D<5.5 μm.

[0012] Further, Q>300mAh / g.

[0013] Further, 25%<A<50%.

[0014] Furthermore, the electrolyte includes a carbonate solvent.

[0015] Furthermore, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0016] Furthermore, the negative electrode active material includes at least one of hard carbon, soft carbon and graphite.

[0017] Furthermore, the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes at least one of layered oxides, polyanions and Prussian blue.

[0018] The present invention further provides a method for preparing a sodium ion battery, comprising the following steps: assembling a positive electrode sheet, a negative electrode sheet and a separator, and then injecting an electrolyte.

[0019] The present invention also provides an electrical device, which comprises the above-mentioned sodium ion battery.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention controls the specific surface area, particle size and capacity of the negative electrode active material and the conductivity of the electrolyte to satisfy the relationship 300SAσ / QD>3.5, so that the sodium ion battery can improve the energy density while taking into account good low-temperature charge and discharge performance, thereby extending the low-temperature cycle life of the sodium ion battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a comparison chart of low temperature cycle test results of the sodium ion batteries of various embodiments and comparative examples provided by the present invention. DETAILED DESCRIPTION

[0024] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. If specific conditions are not specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer is not specified in the reagents or instruments used, they are all conventional products that can be purchased commercially.

[0025] If there is no special explanation, in the present invention, "the first aspect", "the second aspect", "the third aspect", "the fourth aspect", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or quantity, nor can they be understood as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "the first", "the second", "the third", "the fourth", etc. only serve the purpose of non-exhaustive enumeration and description, and it should be understood that they do not constitute a closed limitation on quantity.

[0026] If there is no special explanation, the "include" and "comprising" mentioned in the present invention represent open-ended or closed-ended expressions. For example, the "include" and "comprising" may represent that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0027] If there is no special explanation, in the present invention, "one or more" or "at least one" refers to any one, any two or more of the listed items. Among them, "several" refers to any two or more of the listed items.

[0028] In a first aspect, the present invention provides a sodium ion battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte.

[0029] The negative electrode sheet includes a negative electrode active material. That is, the negative electrode active layer of the negative electrode sheet contains a negative electrode active material. The negative electrode active material includes any material commonly used in the art, such as hard carbon, soft carbon, and graphite, etc., and the present invention does not limit this.

[0030] The sodium ion battery satisfies the following condition: 300SAσ / QD>3.5, wherein 300SAσ / QD is 300×S×A×σ / (Q×D), and the value of 300SAσ / QD includes but is not limited to any point value of 3.6, 3.8, 4, 4.3, 4.5, 4.8, 5, 5.5, 6, 7, 8, 9, 10, 12, 13, 15, 16, 17, 18, 20 or a range value between any two of them.

[0031] Wherein, S is the specific surface area of ​​the negative electrode active material, in m 2 / g.

[0032] D is the D50 median particle size of the negative electrode active material, in μm.

[0033] A is the discharge slope capacity ratio of the button battery (hereinafter referred to as button battery) made of the negative electrode active material. The discharge slope capacity ratio refers to the ratio of the 2V-0.1V button battery discharge capacity to the 2V-0V button battery discharge total capacity.

[0034] Q is the reversible gram capacity of the button cell made of the negative electrode active material, in mAh / g.

[0035] It is understandable that the negative electrode active material is first used to assemble a button cell, and after testing to determine its discharge slope capacity ratio and reversible gram capacity, it is assembled into a sodium ion battery. Among them, the preparation method of the button cell is: according to the mass ratio of negative electrode active material: binder PVDF: conductive agent SP = 90:5:5, NMP is used as solvent, mixed into negative electrode slurry, and then the negative electrode slurry is applied to the foil and dried to obtain a negative electrode sheet (4mg / cm 2 ), and then a metal sodium sheet was used as the counter electrode to assemble a button cell in an Ar atmosphere protection glove box. The reversible gram capacity Q can be obtained by taking the first cycle charge and discharge data of the button cell from 2V to 0V at a current density of 0.1C.

[0036] σ is the conductivity of the electrolyte, in mS / cm.

[0037] The present invention controls the specific surface area, particle size and capacity of the negative electrode active material and the conductivity of the electrolyte to satisfy the relationship 300SAσ / QD>3.5, thereby improving the energy density of the sodium ion battery while ensuring that the sodium ion battery has better charge and discharge cycle performance under low temperature conditions and improving the low-temperature cycle life.

[0038] In some specific embodiments, the specific surface area of ​​the negative electrode active material satisfies: 6m 2 / g≤S≤20m 2 / g, including but not limited to 6m 2 / g, 6.5m 2 / g, 7m 2 / g, 7.5m 2 / g, 8m 2 / g, 8.5m 2 / g, 9m 2 / g, 10m 2 / g, 11m 2 / g, 12m 2 / g, 13m 2 / g, 14m 2 / g, 15m 2 / g, 16m 2 / g, 17m 2 / g, 18m 2 / g, 19m 2 / g, or a range of values ​​between them.

[0039] The present invention controls the specific surface area S of the negative electrode active material within a certain range. On the one hand, S is not too small, thereby avoiding insufficient number of reaction active sites and reducing the low-temperature cycle performance of the battery. On the other hand, S is not too large, thereby avoiding poor material processing performance, difficulty in uniform dispersion, and reduced battery consistency. If S is too large, the battery's initial efficiency will be low, the capacity will decrease, and the battery's energy density will be reduced.

[0040] In some specific embodiments, the D50 median particle size of the negative electrode active material satisfies: 2.5 μm<D<5.5 μm, including but not limited to any point value of 2.7 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.3 μm or a range value between any two of them.

[0041] The present invention controls the particle size D50 of the negative electrode active material within a certain range. On the one hand, D is not too large, which avoids the reaction distance being extended and the material rate performance being reduced, thereby reducing the low-temperature cycle performance of the battery. On the other hand, D is not too small, which avoids the compaction of the material being reduced, the thickness of the pole piece being increased, and the energy density of the battery being reduced.

[0042] In some specific embodiments, the reversible gram capacity of the button battery made of the negative electrode active material satisfies: Q>300mAh / g, including but not limited to any point value of 310mAh / g, 320mAh / g, 330mAh / g, 340mAh / g, 350mAh / g, 360mAh / g, 370mAh / g, 380mAh / g or a range value between any two of them.

[0043] In some specific embodiments, the discharge slope capacity ratio of the button battery made of the negative active material satisfies the following: 25%<A<50%, including but not limited to 26%, 27%, 28%, 29%, 30%, 31%, 32%, 33%, 34%, 35%, 36%, 37%, 38%, 40%, 43%, 45%, 47%, 49%, any one of the point values ​​or the range value between any two of them.

[0044] The present invention controls the discharge slope area capacity proportion A of the negative electrode active material within a certain range. On the one hand, A is not too small, which avoids the decrease of the material voltage platform and the deterioration of the rate performance, thereby reducing the low-temperature cycle performance of the battery. On the other hand, A is not too large, which avoids the decrease of the material capacity and thereby reduces the energy density of the battery.

[0045] In some specific embodiments, the electrolyte includes a carbonate solvent, that is, the electrolyte includes a carbonate electrolyte. The carbonate electrolyte refers to an electrolyte using at least one of carbonate solvents such as ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) as a solvent.

[0046] The present invention adopts carbonate electrolyte to form a more stable solid electrolyte interface (SEI) on the negative electrode surface, reduce side reactions, lower the transfer impedance at the interface under low temperature conditions, and extend the low temperature cycle life of the battery.

[0047] In some specific embodiments, the negative electrode active layer of the negative electrode sheet is mainly composed of a negative electrode active material, a binder and a conductive agent. The binder and the conductive agent can be any binder material and conductive material commonly used in the art, and the ratio of the three can also be any ratio commonly used in the art, which is not limited by the present invention.

[0048] It can be understood that the negative electrode active layer is disposed on the surface of the negative electrode current collector.

[0049] In some specific embodiments, the negative electrode active material includes at least one of hard carbon, soft carbon and graphite.

[0050] In some specific embodiments, the positive electrode plate includes a positive electrode active material, and the positive electrode active material includes at least one of a layered oxide, a polyanion, and Prussian blue.

[0051] In some specific implementations, the positive electrode active layer further includes a binder and a conductive agent, which is not limited in the present invention.

[0052] In some specific embodiments, the sodium ion battery further includes a separator, which is not limited in the present invention.

[0053] In a second aspect, the present invention provides a method for preparing a sodium ion battery, comprising the following steps: assembling a positive electrode sheet, a negative electrode sheet and a separator, and then injecting an electrolyte.

[0054] The preparation method has the advantages of simple operation and mass production.

[0055] In some specific embodiments, the preparation method of the sodium ion battery specifically includes: assembling the positive electrode sheet, the negative electrode sheet and the separator in the manner of positive electrode sheet-separator-negative electrode sheet-separator, and obtaining a bare cell after electrode ear welding and gluing treatment, placing the bare cell in an aluminum shell, injecting an electrolyte, and then performing a high-temperature standing treatment, and then performing formation, aging, and capacity separation processes to obtain a sodium ion battery.

[0056] In a third aspect, the present invention provides an electrical device comprising the above-mentioned sodium ion battery.

[0057] The electrical equipment has good low-temperature charging and discharging performance and a high low-temperature cycle life.

[0058] The sodium ion battery provided by the present invention can be applied to various fields, such as the field of transportation, the field of electronic products, the field of aerospace, the field of medical treatment, and the field of energy storage, but is not limited thereto.

[0059] It is to be understood that the electrical equipment includes any equipment or device including the above-mentioned sodium ion battery.

[0060] The electrical equipment of the present invention is not particularly limited, and may include but is not limited to the following types: laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini CDs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, etc.

[0061] The embodiments of the present invention will be described in detail below in conjunction with the examples, but it will be appreciated by those skilled in the art that the following examples are only used to illustrate the present invention and should not be considered as limiting the scope of the present invention. If no specific conditions are specified in the examples, the conditions are carried out according to normal conditions or the conditions recommended by the manufacturer. If the manufacturer is not specified for the reagents or instruments used, they are all conventional products that can be obtained commercially.

[0062] Example 1

[0063] The method for preparing a sodium ion battery provided in this embodiment comprises the following steps:

[0064] (1) Processing of negative electrode sheet: NMP (N-methylpyrrolidone) is used as solvent, PVDF (polyvinylidene fluoride) is used as binder, conductive carbon black SP is used as conductive agent, hard carbon (with D50 median particle size D = 5 μm, specific surface area S = 8 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q=360mAh / g, and the discharge slope capacity of the buckle battery obtained is A=27.5%) as the negative electrode active material, according to the ratio of negative electrode active material: conductive agent: binder = 95%:2%:3% (mass percentage), each raw material is weighed, and the solvent is added thereto and stirred to obtain a uniform negative electrode slurry; aluminum foil is used as the current collector, and the negative electrode slurry is evenly coated on both sides of the current collector, and then dried in an oven, compacted by a roller press, and cut by a die-cutting slitting machine to obtain a negative electrode sheet.

[0065] (2) Processing of positive electrode sheet: NMP is used as solvent, PVDF is used as binder, SP is used as conductive agent, and layered oxide (chemical formula is NaCu 1 / 3 Fe 1 / 3 Mn 1 / 3 O2) is the positive electrode active material, and the raw materials are weighed according to the ratio of positive electrode active material: conductive agent: binder = 96%: 2%: 2% (mass percentage), and the solvent is added thereto and stirred to obtain a uniform positive electrode slurry; aluminum foil is used as a current collector, and the positive electrode slurry is evenly coated on both sides of the current collector, and then dried in an oven, compacted by a roller press, and cut by a die-cutting slitting machine to obtain a positive electrode sheet.

[0066] (3) Preparation of batteries: Control the ambient temperature, humidity and cleanliness to meet the standards (the required temperature is 25±5°C, the humidity is ≤10%RH, and the cleanliness is Class 100,000). The positive electrode sheet, negative electrode sheet and separator obtained by the above processing are assembled in the manner of positive electrode-separator-negative electrode-separator. After the tabs are welded and glued, a bare cell can be obtained. The bare cell is placed in an aluminum shell and injected with a carbonate electrolyte (the conductivity of the injected electrolyte is σ=10mS / cm, and its composition is 1M NaPF6, solvent PC (propylene carbonate) / EMC (ethyl methyl carbonate) / DMC (dimethyl carbonate) in a volume ratio of 3:3:4, and an additive is 2% FEC (fluoroethylene carbonate)). Then, a high-temperature static treatment is performed, and then after the formation, aging and volume separation processes, a finished sodium ion battery is obtained.

[0067] Example 2

[0068] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5 μm and a specific surface area S=11 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q=355mAh / g, the discharge slope capacity proportion A of the buckle battery obtained is A=31.0%, and the conductivity of the electrolyte injected in step (3) is σ=8.6mS / cm, and its composition contains 1M NaPF6, the volume ratio of solvent PC / EMC=1:1, and the additive is 2% VC (vinyl carbonate).

[0069] Example 3

[0070] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5 μm and a specific surface area S=15 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q=350mAh / g, the discharge slope capacity proportion A of the buckle battery obtained is A=34.5%, and the conductivity σ of the injected electrolyte in step (3) is 8.6mS / cm.

[0071] Example 4

[0072] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 1, except that: the hard carbon used in step (1) has a D50 median particle size D=4 μm and a specific surface area S=15 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q=348mAh / g, the discharge slope capacity proportion A of the buckle battery obtained is A=34.5%, and the conductivity σ of the injected electrolyte in step (3) is 8.6mS / cm.

[0073] Example 5

[0074] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 1, except that: the hard carbon used in step (1) has a D50 median particle size D=2.6 μm and a specific surface area S=20 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q=345mAh / g, the discharge slope capacity proportion A of the buckle battery obtained is A=35.5%, and the conductivity σ of the injected electrolyte in step (3) is 8.6mS / cm.

[0075] Example 6

[0076] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 1, except that: the hard carbon used in step (1) has a D50 median particle size D=4.0 μm and a specific surface area S=6 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q = 340 mAh / g, the discharge slope capacity proportion A of the buckle battery obtained is A = 28%; and the σ of the injected electrolyte in step (3) is 10 mS / cm.

[0077] Example 7

[0078] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5.4 μm and a specific surface area S=8 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q = 320 mAh / g, the discharge slope capacity proportion A of the buckle battery obtained is A = 30%; and the σ of the injected electrolyte in step (3) is 8.6 mS / cm.

[0079] Example 8

[0080] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5.0 μm and a specific surface area S=13 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q=330mAh / g, the discharge slope capacity of the buckle battery obtained is A=33%; and the σ of the injected electrolyte in step (3) is 5mS / cm, and its composition contains 0.6M NaPF6, the volume ratio of solvent PC / DEC is 1:1, and the additive is 2% VC.

[0081] Example 9

[0082] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 6, except that: the hard carbon used in step (1) has a D50 median particle size D=3.0 μm and a specific surface area S=15 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q=301mAh / g, the discharge slope capacity of the buckle battery obtained is A=40%; and the σ of the injected electrolyte in step (3) is 7mS / cm, and its composition contains 1M NaPF6, the volume ratio of solvent PC / DEC is 1:1, and the additive is 2% VC.

[0083] Example 10

[0084] The preparation method of the sodium ion battery provided in this embodiment is basically the same as that in embodiment 1, except that: the hard carbon used in step (1) has a D50 median particle size D=4 μm and a specific surface area S=12 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q = 380 mAh / g, the discharge slope area capacity proportion A of the buckle battery obtained is A = 25.5%; and the σ of the injected electrolyte in step (3) is 8.6 mS / cm.

[0085] Comparative Example 1

[0086] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that the conductivity σ of the injected electrolyte in step (3) is 8.6 mS / cm.

[0087] Comparative Example 2

[0088] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5.4 μm and a specific surface area S=6 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q=300mAh / g, the discharge slope capacity proportion A of the buckle battery obtained is A=36.5%, and the conductivity σ of the electrolyte injected in step (3) is 8.6mS / cm.

[0089] Comparative Example 3

[0090] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5.0 μm and a specific surface area S=7 m 2 / g, the reversible gram capacity of the buckle battery obtained is Q = 330 mAh / g, the discharge slope capacity proportion A of the buckle battery obtained is A = 27.5%; and the σ of the injected electrolyte in step (3) is 5 mS / cm.

[0091] Comparative Example 4

[0092] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5.5 μm and a specific surface area S=6.0 m 2 / g, the obtained reversible capacity Q = 330 mAh / g, the obtained capacity proportion of the discharge slope zone A = 38.5%; the conductivity σ of the injected electrolyte in step (3) = 8.6 mS / cm.

[0093] Comparative Example 5

[0094] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that: the hard carbon used in step (1) has a D50 median particle size D=4.5 μm and a specific surface area S=6.5 m 2 / g, the obtained reversible capacity of the charge-off discharge is Q = 290 mAh / g, and the capacity proportion of the charge-off discharge slope zone is A = 30%; the conductivity of the injected electrolyte in step (3) is σ = 7 mS / cm.

[0095] Comparative Example 6

[0096] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5 μm and a specific surface area S=8 m 2 / g, the obtained reversible capacity Q = 350 mAh / g, the obtained capacity proportion of the discharge slope zone A = 25%; the conductivity σ of the injected electrolyte in step (3) = 10.0 mS / cm.

[0097] Comparative Example 7

[0098] The preparation method of the sodium ion battery provided in this comparative example is basically the same as that in Example 1, except that: the hard carbon used in step (1) has a D50 median particle size D=5 μm and a specific surface area S=5.5 m 2 / g, the obtained reversible capacity Q = 320 mAh / g, the obtained capacity proportion of the discharge slope zone A = 31%; the conductivity σ of the injected electrolyte in step (3) = 8.6 mS / cm.

[0099] The values ​​of S, A, σ, Q, D and 300SAσ / QD in each embodiment and each comparative example are shown in Table 1.

[0100] Table 1 Summary of data of various embodiments and comparative examples

[0101] Group D(μm) <![CDATA[S(m 2 / g)]]> A Q(mAh / g) σ(mS / cm) 300SAσ / (QD) Example 1 5 8 0.275 360 10.0 3.67 Example 2 5 11 0.310 355 8.6 4.96 Example 3 5 15 0.345 350 8.6 7.63 Example 4 4 15 0.345 348 8.6 9.59 Example 5 2.6 20 0.355 345 8.6 20.42 Example 6 4 6 0.280 340 10.0 3.71 Example 7 5.4 8 0.300 320 8.6 3.58 Example 8 5 13 0.330 330 5.0 3.90 Example 9 3 15 0.400 301 7.0 13.95 Example 10 4 12 0.255 380 8.6 5.19 Comparative Example 1 5 8 0.275 360 8.6 3.15 Comparative Example 2 5.4 6 0.365 300 8.6 3.49 Comparative Example 3 5 7 0.275 330 5.0 1.75 Comparative Example 4 5.5 6 0.385 330 8.6 3.28 Comparative Example 5 4.5 6.5 0.300 290 7.0 3.14 Comparative Example 6 5 8 0.250 350 10.0 3.43 Comparative Example 7 5 5.5 0.310 320 8.6 2.75

[0102] Experimental example

[0103] The sodium ion batteries prepared in each embodiment and each comparative example were subjected to low temperature cycle tests according to the following method: At -20°C, the finished sodium ion batteries were subjected to cycle tests, the charge and discharge rate was 0.1C, the upper and lower limit voltages were 2 to 3.95V, and the low temperature charge and discharge cycle life and capacity retention rate were obtained. The results are shown in Tables 2 and Figure 1 shown.

[0104] Table 2 Low temperature cycle test results of sodium ion batteries of various embodiments and comparative examples

[0105] Group Low temperature cycle number Capacity retention rate Example 1 100 96.55％ Example 2 100 97.39％ Example 3 100 97.99％ Example 4 100 98.36％ Example 5 100 98.66％ Example 6 100 96.79％ Example 7 100 96.24％ Example 8 100 97.15％ Example 9 100 98.58％ Example 10 100 97.69％ Comparative Example 1 100 86.68％ Comparative Example 2 100 95.96％ Comparative Example 3 20 80.00％ Comparative Example 4 100 89.67％ Comparative Example 5 100 86.45％ Comparative Example 6 100 95.32％ Comparative Example 7 64 80.00％

[0106] from Figure 1 From the results in Table 2, it can be seen that the sodium ion battery capacity Q≤300mAh / g of Comparative Examples 2 and 5, and 300SAσ / QD>3.5 are not satisfied, and the low-temperature cycle performance is poor. In addition, although the sodium ion batteries of Comparative Examples 1, 3, 4, 6, and 7 can provide high energy density (Q>300mAh / g), they do not satisfy 300SAσ / QD>3.5, and the low-temperature cycle performance is poor.

[0107] The sodium ion batteries provided in Examples 1 to 10 of the present invention satisfy 300SAσ / QD>3.5, and while the energy density is improved, the low-temperature cycle performance is also significantly improved.

[0108] It can be seen that the present invention controls the specific surface area, particle size and capacity of the negative electrode active material and the conductivity of the electrolyte to satisfy the relationship 300SAσ / QD>3.5, so that the sodium ion battery can improve the energy density while taking into account good low-temperature charge and discharge performance, thereby improving the low-temperature cycle life of the sodium ion battery.

[0109] Although the present invention has been illustrated and described with specific embodiments, it should be appreciated that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Those skilled in the art should understand that the technical solutions described in the above embodiments may be modified, or some or all of the technical features thereof may be replaced by equivalents without departing from the spirit and scope of the present invention. However, these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention. Therefore, this means that all such replacements and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A sodium ion battery, characterized in that: The invention comprises a positive electrode sheet, a negative electrode sheet and an electrolyte, wherein the negative electrode sheet comprises a negative electrode active material, and the sodium ion battery satisfies the following conditions: 300SAσ / QD>3.5; Wherein, S is the specific surface area of ​​the negative electrode active material, in m 2 / g; D is the D50 median particle size of the negative electrode active material, in μm; A is the discharge slope capacity ratio of the button battery made of the negative electrode active material; Q is the reversible gram capacity of the button cell made of the negative electrode active material, in mAh / g; σ is the conductivity of the electrolyte, in mS / cm.

2. The sodium ion battery according to claim 1, characterized in that: 6m 2 / g≤S≤20m 2 / g.

3. The sodium ion battery according to claim 1, characterized in that: 2.5μm<D<5.5μm.

4. The sodium ion battery according to claim 1, characterized in that: Q>300mAh / g.

5. The sodium ion battery according to claim 1, characterized in that: 25％＜A＜50％。 6. The sodium ion battery according to claim 1, characterized in that: The electrolyte includes a carbonate solvent; Preferably, the carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

7. The sodium ion battery according to claim 1, characterized in that: The negative electrode active material includes at least one of hard carbon, soft carbon and graphite.

8. The sodium ion battery according to claim 1, characterized in that: The positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes at least one of layered oxides, polyanions and Prussian blue.

9. The method for preparing a sodium ion battery according to any one of claims 1 to 8, characterized in that: The method comprises the following steps: assembling the positive electrode sheet, the negative electrode sheet and the separator, and then injecting the electrolyte.

10. An electrical device, characterized in that: Comprising the sodium ion battery as claimed in any one of claims 1 to 8.

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