Sodium ion battery and electric device

Abstract

A sodium ion battery and an electric device. The sodium ion battery comprises a positive electrode sheet, a negative electrode sheet, and an electrolyte. The electrolyte comprises an organic solvent, a sodium salt, an organic additive, and a low electrode potential metal salt additive. The standard electrode potential of a low electrode potential metal element in the low electrode potential metal salt additive is less than -2.714 V. The negative electrode sheet is mainly made of a negative active material. The content A of the low electrode potential metal element in the electrolyte, the liquid retention M of the sodium ion battery, and the specific surface area S of the negative electrode active material satisfy the following relational expression: (I). The low electrode potential metal element is introduced into the electrolyte, and parameters are controlled to satisfy the corresponding relational expressions, such that the sodium ion battery has good cycle stability, and has a good capacity retention rate and a low impedance growth rate in the use process, and the problems of sodium precipitation and production of a large amount of gas are less likely to occur.

Description

Sodium ion battery and electrical equipment

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to the Chinese patent application with application number CN202311316359.5 and title “A Sodium Ion Battery and Electrical Equipment” filed with the Patent Office of China on October 12, 2023, the entire contents of which are incorporated by reference into this application. Technical Field

[0003] The present disclosure relates to the technical field of sodium ion batteries, and in particular to a sodium ion battery and an electrical device. Background Art

[0004] Compared to lithium-ion batteries, sodium-ion batteries, with their higher resource abundance, are expected to play a significant role in complementing lithium-ion batteries in areas such as power tools, energy storage, and mobile devices. These applications require sodium-ion batteries to exhibit certain cycling stability, which is largely dependent on the state of the SEI film formed between the anode and the electrolyte. The initial formation of the anode SEI film, as well as its dissolution, fragmentation, and repair during cycling, all affect the battery's electrochemical performance.

[0005] Therefore, it is of great significance to improve the cycling stability of sodium-ion batteries by improving the SEI film.

[0006] In view of this, the present disclosure is proposed.

[0007] Application Contents

[0008] One object of the present disclosure is to provide a sodium ion battery. By introducing a low-potential metal element having a standard electrode potential lower than that of Na into the electrolyte and controlling various parameters in the sodium ion battery to satisfy the above-mentioned relationship, the composition of the inorganic portion of the SEI membrane of the sodium ion battery can be optimized to form a crystalline microphase with a wider interplanar spacing, thereby adjusting the conductivity of sodium ions in the SEI membrane, reducing polarization and initial impedance, improving the long-cycle performance of the sodium ion battery, and reducing the initial impedance and impedance growth rate of the battery.

[0009] Another object of the present disclosure is to provide an electrical device.

[0010] In order to achieve the above-mentioned purpose of the present disclosure, the following technical solutions are adopted:

[0011] A sodium ion battery comprising a positive electrode sheet, a negative electrode sheet and an electrolyte;

[0012] The electrolyte comprises an organic solvent, a sodium salt, an organic additive and a low electrode potential metal salt additive; the standard electrode potential of the low electrode potential metal element in the low electrode potential metal salt additive is less than -2.714V;

[0013] The negative electrode sheet is mainly made of negative electrode active material;

[0014] The total content A of the low electrode potential metal elements in the electrolyte, the liquid retention capacity M of the sodium ion battery, and the specific surface area S of the negative electrode active material satisfy the following relationship:

[0015] Wherein, A = 0.01 to 50 mg / kg;

[0016] M = 1.5 ~ 10g / Ah;

[0017] S=2~8m 2 / g;

[0018] The low electrode potential metal salt additive includes at least one of potassium difluorophosphate, lithium difluorophosphate, rubidium difluorophosphate, cesium difluorophosphate, francium difluorophosphate, barium difluorophosphate, calcium difluorophosphate and potassium hexafluorophosphate;

[0019] The organic solvent comprises a cyclic ester solvent and a chain ester solvent in a mass ratio of 0.1-6:4-10.

[0020] An electrical device comprises the sodium ion battery. DETAILED DESCRIPTION

[0021] In a first aspect, the present disclosure provides a sodium ion battery, specifically a sodium ion secondary battery, which includes a positive electrode sheet, a negative electrode sheet and an electrolyte.

[0022] The electrolyte comprises an organic solvent, a sodium salt, an organic additive and a low electrode potential metal salt additive; the standard electrode potential E of the low electrode potential metal element in the low electrode potential metal salt additive at 25°C is 0 <-2.714V. Among them, the standard electrode potential E 0 The value includes but is not limited to any point value of -2.8V, -2.866V, -2.9V, -2.906V, -2.923V, -2.924V, -2.925V, -3.0V, -3.1V, -3.2V, -3.3V, -3.4V, -3.405V, -3.5V or the range value between any two of them.

[0023] Among them, if the element with a standard electrode potential higher than -2.714V is used, it is easy to be reduced to a metal element, forming dendrites and causing a short circuit.

[0024] Elements with a standard electrode potential lower than -2.714 V are reduced along with anions to form fluoride salts, carbonates, and alkyl carbonates.

[0025] The present invention introduces a low electrode potential metal salt additive with a standard electrode potential lower than that of Na into the electrolyte to participate in film formation at a lower potential, thereby improving the chemical composition of the SEI film to a certain extent, generating an SEI film with lower solubility, higher stability, and faster sodium conduction, thereby ensuring low impedance growth and excellent cycle performance throughout the battery life.

[0026] The negative electrode plate is mainly made of negative electrode active material.

[0027] The total content A of the low electrode potential metal elements in the electrolyte, the liquid retention capacity M of the sodium ion battery, and the specific surface area S of the negative electrode active material satisfy the following relationship:

[0028] Right now, The value of = 0.11 ~ 3.7, Values ​​include, but are not limited to, any one of 0.11, 0.15, 0.20, 0.25, 0.28, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 1.0, 1.5, 2, 2.5, 3, 3.5, 3.7, or a range of values ​​between any two of them.

[0029] In the above relationship, the unit of the total content A of the low electrode potential metal elements in the electrolyte is mg / kg, which means that the total content of the low electrode potential metal elements contained in each kg of the electrolyte is A mg.

[0030] In the above relationship, the unit of the electrolyte retention M of the sodium ion battery is g / Ah, where the electrolyte retention refers to the electrolyte retention. The unit of the specific surface area S of the negative electrode active material is m 2 / g.

[0031] In order to comprehensively improve the electrochemical performance of sodium ion batteries, in the above relationship, A=0.01~50 mg / kg, wherein the value of A includes but is not limited to 0.01 mg / kg, 0.05 mg / kg, 0.1 mg / kg, 0.5 mg / kg, 1 mg / kg, 3 mg / kg, 5 mg / kg, 8 mg / kg, 10 mg / kg, 12 mg / kg, 14 mg / kg, 15 mg / kg, 18 mg / kg, 20 mg / kg, 25 mg / kg, 30 mg / kg, 35 mg / kg, 40 mg / kg, 45 mg / kg, 50 mg / kg, any one of the point values ​​or the range between any two of them.

[0032] In one embodiment, A = 10-20 mg / kg.

[0033] In order to comprehensively improve the electrochemical performance of sodium ion batteries, in the above relationship, M=1.5~10g / Ah, wherein the M value includes but is not limited to any one of 1.5g / Ah, 2g / Ah, 2.5g / Ah, 3g / Ah, 3.5g / Ah, 4g / Ah, 4.5g / Ah, 5g / Ah, 5.5g / Ah, 6g / Ah, 6.3g / Ah, 6.5g / Ah, 7g / Ah, 7.5g / Ah, 8g / Ah, 8.5g / Ah, 9g / Ah, and 10g / Ah, or a range between any two of them.

[0034] The amount of electrolyte injected into sodium-ion secondary batteries is affected by the design capacity of the battery. If the amount of liquid retained per ampere-hour is too little, it is difficult to completely infiltrate the positive and negative electrodes, affecting the degree of sodium ion deintercalation during charging and discharging, and thus affecting the secondary battery's impedance, capacity, cycle and other performance, and there will be problems such as sodium precipitation; if the amount of liquid retained is too much, the degree of side reactions will increase, and the battery will produce gas and expand.

[0035] In order to further improve the electrochemical performance of sodium ion batteries, the present disclosure also optimizes the specific surface area of ​​the negative electrode active material. In the relationship, S = 2 to 8 m 2 / g; S value includes but not limited to 2m 2 / g、3m 2 / g、4m 2 / g、5m 2 / g、6m 2 / g、7m 2 / g、8m 2 / g or any point value or range value between any two of them. When the specific surface area is too high, the contact part between the negative electrode and the electrolyte is too large, the gas production is too much, the initial efficiency is low, and more binder needs to be added, which increases the internal resistance; when the specific surface area is too low, the active sites are small, the material utilization rate is low, and it is not conducive to the migration of sodium ions. In one embodiment, S=3~7m 2 / g.

[0036] The sodium-ion battery disclosed herein improves the SEI membrane composition by introducing a low-electrode-potential metal salt additive with a standard electrode potential lower than that of Na into the electrolyte. By regulating the low-electrode-potential metal element content, electrolyte retention, and specific surface area of ​​the negative electrode active material, the method achieves a denser, less soluble, more stable, and faster sodium-conducting SEI membrane, resulting in a sodium-ion battery with improved cycle stability and reversible capacity. This method is compatible with existing sodium-ion battery production processes and offers low production costs.

[0037] Electrolyte is one of the main materials of sodium ion batteries and one of the important factors affecting the performance of sodium ion secondary batteries. Among them, solvents, sodium salts, and additives are the main components of the electrolyte, which have a great influence on the performance of secondary batteries such as cycle, impedance, and kinetics. This application optimizes the composition of the electrolyte, comprehensively designs the amount of low electrode potential metal elements added, the liquid retention amount of the sodium ion battery, the specific surface area of ​​the negative electrode active material and other parameters to satisfy the above relationship. It can optimize the composition of the inorganic part of the SEI membrane of the sodium ion battery, form a crystalline microphase with a wider interplanar spacing, adjust the conductivity of sodium ions in the SEI membrane, reduce polarization and initial impedance, and thus make the sodium ion battery have good cycle stability, good capacity retention and low impedance growth rate during use, and is not prone to sodium precipitation and large-scale gas production.

[0038] By introducing low electrode potential metal elements in the form of low electrode potential metal salt additives, they migrate to the negative electrode during the first charge to participate in film formation, forming components such as LiF, KF, RbF that are not easily soluble in organic solvents (NaF is more soluble), which helps to reduce the dissolution of SEI during the cycle and optimize the long-cycle performance of the battery.

[0039] In one embodiment, the low electrode potential metal salt additive includes at least one of a lithium salt additive, a potassium salt additive, a rubidium salt additive, a cesium salt additive, a francium salt additive, a barium salt additive, and a calcium salt additive.

[0040] The present disclosure introduces elements such as Li, K, Rb, Cs, Fr, Ca, and Ba (which are not easily reduced to a single-element state) with a standard electrode potential lower than that of Na into the electrolyte, allowing them to participate in film formation at a lower potential, and controlling various parameters to satisfy the above-mentioned relationship. This can optimize the composition of the inorganic portion of the SEI membrane of a sodium ion battery, form a crystalline microphase with a wider interplanar spacing, adjust the conductivity of sodium ions in the SEI membrane, reduce polarization and initial impedance, and ensure that the sodium ion battery has good cycle stability, good capacity retention and low impedance growth rate during use, and is less likely to experience problems such as sodium precipitation and large-scale gas production.

[0041] In one embodiment, the lithium salt additive includes at least one of lithium hexafluorophosphate, lithium bisfluorosulfonyl imide, lithium bistrifluoromethanesulfonyl imide, lithium difluorooxalatoborate, lithium difluorophosphate, and lithium difluorobisoxalatophosphate.

[0042] In one embodiment, the potassium salt additive includes at least one of potassium hexafluorophosphate, potassium bisfluorosulfonyl imide, potassium bistrifluoromethanesulfonyl imide, potassium difluorooxalatoborate, potassium difluorophosphate, and potassium difluorobisoxalatophosphate.

[0043] In one embodiment, the rubidium salt additive includes at least one of rubidium hexafluorophosphate, rubidium bisfluorosulfonyl imide, rubidium bistrifluoromethanesulfonyl imide, rubidium difluorooxalatoborate, rubidium difluorophosphate, and rubidium difluorobisoxalatophosphate.

[0044] In one embodiment, the cesium salt additive includes at least one of cesium hexafluorophosphate, cesium bisfluorosulfonyl imide, cesium bistrifluoromethanesulfonyl imide, cesium difluorooxalatoborate, cesium difluorophosphate, and cesium difluorobisoxalatophosphate.

[0045] In one embodiment, the francium salt additive includes at least one of francium hexafluorophosphate, francium bisfluorosulfonyl imide, francium bistrifluoromethanesulfonyl imide, francium difluorooxalatoborate, francium difluorophosphate, and francium difluorobisoxalatophosphate.

[0046] In one embodiment, the barium salt additive includes at least one of barium hexafluorophosphate, barium bis(fluorosulfonyl)imide, barium bis(trifluoromethanesulfonyl)imide, barium difluorooxalatoborate, barium difluorophosphate, and barium difluorobis(oxalatophosphate).

[0047] In one embodiment, the calcium salt additive includes at least one of calcium hexafluorophosphate, calcium bisfluorosulfonyl imide, calcium bistrifluoromethanesulfonyl imide, calcium difluorooxalatoborate, calcium difluorophosphate, and calcium difluorobisoxalatophosphate.

[0048] In one embodiment, the mass of the low electrode potential metal element accounts for 0.0001% to 2% of the total mass of the electrolyte, including but not limited to any one of 0.0001%, 0.0005%, 0.001%, 0.005%, 0.01%, 0.05%, 0.1%, 0.5%, 1%, 1.5%, and 2%, or a range between any two of them.

[0049] In one embodiment, the sodium salt (which is the main salt in the electrolyte) includes at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium perchlorate (NaClO4), sodium bis(fluorosulfonyl)imide (NaFSI) and sodium bis(trifluoromethanesulfonyl)imide (NaTFSI).

[0050] In one embodiment, the mass of the sodium salt is 4.5% to 20% of the total mass of the electrolyte; including but not limited to any one of 3%, 4.5%, 5%, 6%, 8%, 10%, 12%, 15%, 18%, 20% or a range between any two of them.

[0051] The type and amount of the main salt and low-electrode-potential metal salt additives affect the electrolyte's conductivity and solvation structure; the solvation structure, in turn, influences initial SEI formation and kinetic performance during cycling. By controlling the specific type and amount of the main salt, the present disclosure facilitates the development of sodium-ion secondary batteries with stable film formation and excellent kinetic performance.

[0052] In one embodiment, the positive electrode plate is mainly made of a positive electrode active material. The positive electrode active material can be any conventional positive electrode active material, such as at least one of a layered metal oxide, a polyanion compound, a Prussian compound, a phosphate compound, and a sulfate compound, but is not limited thereto.

[0053] In one embodiment, the organic solvent comprises a cyclic ester solvent and a chain ester solvent in a mass ratio of 0.1-6:4-10, wherein the mass ratio includes but is not limited to any one of 0.1:9.9, 0.5:9.5, 1:9, 2:8, 3:7, 4:6, 5:5, 6:4 or a range between any two of the above.

[0054] Among them, the cyclic ester solvent has a high dielectric constant and a large viscosity, while the chain ester solvent has a low dielectric constant and a low viscosity. The present disclosure controls the mass ratio of the cyclic ester solvent and the chain ester solvent within the above-mentioned suitable range, which is beneficial to improving the kinetic performance of the sodium ion battery, preventing sodium precipitation, and optimizing its impedance performance.

[0055] In one embodiment, the cyclic ester solvent includes at least one of ethylene carbonate (EC), propylene carbonate (PC), and γ-butyrolactone (1,4-butyrolactone).

[0056] By adopting the above mass ratio range, it is also possible to avoid the problem of battery gas production caused by excessive proportion of ethylene carbonate in the cyclic ester solvent due to the singlet oxygen release mechanism.

[0057] In one embodiment, the chain ester solvent includes at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP) and butyl propionate (BP).

[0058] In one embodiment, the organic additive includes at least one of a carbonate additive, a silicon-containing additive, and a sulfur-containing additive.

[0059] In one embodiment, the mass of the organic additive is 0.1% to 5% of the total mass of the electrolyte, including but not limited to any one of 0.1%, 0.3%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, and 5%, or a range between any two of them.

[0060] In one embodiment, the carbonate additive includes at least one of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0061] In one embodiment, the silicon-containing additive includes at least one of tris(trimethylsilyl)phosphite (TMSPi), tris(trimethylsilyl)phosphate (TMSP), and tris(trimethylsilyl)borate (TMSB).

[0062] In one embodiment, the sulfur-containing additive includes at least one of 1,3-propane sultone (PS), 1,3-propylene sultone (PST), ethylene sulfate (DTD), propylene sulfate (PCS), methylene methanedisulfonate (MMDS), 4-methylethylene sulfate (MeDTD), 4-fluoroethylene sulfate (FDTD), 4,4'-bisulfate (BiDTD), spirobidi DTD (1,3,6,8-tetrahydro-2,7-disulfide-spiro[4.4]nonane-2,2,7,7-tetraoxide), pyridine DTD (GS), 4,5-dimethylethylene sulfate (DMeDTD) and 1,2-cyclopentadiene sulfate (CPS).

[0063] In one embodiment, the mass of the silicon-containing additive is 0.1% to 2% of the mass of the electrolyte; including but not limited to any one of 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2% or a range between any two of them.

[0064] In one embodiment, the mass of the sulfur-containing additive is 0.5% to 3% of the mass of the electrolyte, including but not limited to any one of 0.5%, 0.8%, 1%, 1.3%, 1.5%, 1.8%, 2%, 2.3%, 2.5%, 2.8%, 3% or a range between any two of them.

[0065] During formation, additives preferentially form films at lower potentials. This disclosure regulates the main components of the SEI film by adjusting the types and ratios of additives (including organic additives and low-electrode-potential metal salt additives) in the electrolyte and rationally distributes the organic and inorganic components of the SEI, ensuring lower impedance and higher cycling stability for the main SEI components.

[0066] In one embodiment, the electrolyte comprises the following components by mass percentage: 3% to 20% sodium salt, 0.1% to 5% organic additive, 0.0001% to 2% low electrode potential metal element, and the balance being an organic solvent.

[0067] In one embodiment, the negative electrode active material includes any commercially available negative electrode active material and negative electrode active material prepared using existing technology, such as soft carbon, hard carbon, expanded graphite, titanium-based embedded negative electrode material and alloy material, but is not limited thereto.

[0068] In a second aspect, the present disclosure provides an electrical device comprising the sodium ion battery.

[0069] It is understandable that the above-mentioned electrical equipment includes any equipment or device that uses the above-mentioned sodium ion battery, such as electric vehicles, starting power supplies, energy storage systems, electronic products and office equipment, but is not limited thereto.

[0070] The embodiments of the present disclosure will be described in detail below with reference to the examples. However, those skilled in the art will appreciate that the following examples are intended only to illustrate the present disclosure and should not be construed as limiting the scope of the present disclosure. Where specific conditions are not specified in the examples, the experiments were performed under conventional conditions or the conditions recommended by the manufacturer. Where the manufacturer of the reagents or instruments is not specified, all are commercially available conventional products.

[0071] In the following embodiments of the present disclosure, the preparation method of the positive electrode sheet includes: uniformly dispersing the positive electrode active material, Super P and PVDF in a solvent N-methylpyrrolidone in a mass ratio of 96:2.4:1.6 to obtain a positive electrode slurry, and then coating the positive electrode slurry on the positive electrode current collector aluminum foil, drying, and pressing.

[0072] The preparation method of the negative electrode sheet includes: uniformly dispersing the negative electrode active material, Super P, CMC and SBR in a solvent N-methylpyrrolidone according to a mass ratio of 94.3:1.4:1.6:2.7 to obtain a negative electrode slurry, and then coating the negative electrode slurry on the negative electrode current collector aluminum foil, drying and pressing.

[0073] The preparation method of the electrolyte comprises: uniformly mixing various raw materials.

[0074] The assembly method of the sodium ion battery is as follows: stack the positive electrode sheet, the separator, and the negative electrode sheet in order, so that the separator is placed between the positive electrode sheet and the negative electrode sheet to play an isolating role, and then wind to obtain a bare battery cell, place the bare battery cell in an aluminum-plastic film outer packaging, inject the sodium ion battery electrolyte as described above, and encapsulate and form it.

[0075] Example 1-Example 13

[0076] The sodium ion battery provided in Examples 1 to 13 includes a positive electrode sheet, a negative electrode sheet, and an electrolyte. The negative electrode active material used in the negative electrode sheet is hard carbon; the positive electrode active material used in the positive electrode sheet is Cu 0.12 Ni 0.22 Fe 0.33 Mn 0.33 The electrolyte includes an organic solvent, a sodium salt, an organic additive, and a low electrode potential metal salt additive. The specific principles and amounts of each component (in terms of mass percentage) are shown in Table 1. In addition, in each embodiment, the sodium ion battery liquid retention M, the specific surface area S of the negative electrode active material, the total content A of the low electrode potential metal elements in the electrolyte, and The values ​​are shown in Table 1.

[0077] The calculation method of the balance of organic solvent in Table 1 is: 100% - mass percentage of sodium salt - mass percentage of organic additives - mass percentage of low electrode potential metal salt additives.

[0078] Comparative Example 1-Comparative Example 6

[0079] The key parameters of each comparative example are shown in Table 1 (the rest of the conditions are the same as those of the embodiments).

[0080] Among them, the low electrode potential metal element content A was obtained by ICP testing, the liquid retention volume M was measured by balance weighing, and the specific surface area S of the negative electrode active material was obtained by Micromeritics 2020HD88 specific surface and porosity analyzer (nitrogen).

[0081] Table 1 Comparison of key parameters of each embodiment and each comparative example:

[0082] Experimental example: Electrochemical performance test:

[0083] The electrochemical performance tests of the sodium ion batteries provided in the above embodiments and comparative examples were performed, and the results are shown in Table 2 below.

[0084] The gas production test method is the drainage method; the sodium precipitation observation is to disassemble the battery in a dry room with a dew point of about -40℃ and observe the negative electrode with the naked eye.

[0085] Table 2 Electrochemical performance test results of sodium ion batteries:

[0086] As can be seen from Table 2, the sodium ion batteries prepared in each embodiment, due to the combination of the added low electrode potential metal elements and the negative electrode materials corresponding to the appropriate specific surface area, form non-sodium inorganic salt membrane components such as LiF, KF, RbF, Li2O, and Li2CO3 with appropriate content and distribution, optimize the electrical properties of the SEI film throughout the battery life cycle, improve the ability of the membrane to conduct sodium ions, and enable the battery to have good capacity retention, low initial membrane impedance and low impedance growth rate, and is not prone to problems such as sodium precipitation and large-scale gas production.

[0087] However, due to the inappropriate M, S or A values ​​of each comparative example, or the relationship is not satisfied, the electrochemical performance is reduced, the cycle performance is deteriorated, and problems such as sodium precipitation and large-scale gas production are prone to occur. Specifically, Comparative Example 1, which does not add low electrode potential metal elements, cannot achieve the above-mentioned SEI film formation optimization effect. The initial film impedance is high, the growth rate is large, and the cycle retention performance is poor. However, the addition amount of low electrode potential metal elements should not be too much. Comparative Example 2 causes the destruction of the positive electrode crystal structure and deteriorates the cycle performance due to the addition of excessive low electrode potential metal elements. Similarly, an inappropriate injection amount strongly deteriorates the battery performance. In Comparative Example 3, the injection amount is too small, and the negative electrode material has a large specific surface area and many reaction sites. The absolute content and relative content of the low electrode potential metal are insufficient, the film quality is poor, and the negative electrode material cannot be fully protected. Strong side reactions occur during the cycle of this group of batteries, gas production is high, and the cycle is difficult to maintain. On the other hand, the injection amount in Comparative Example 4 is too much, which also leads to frequent interface side reactions, strong gas production, and deteriorated battery performance. Comparative Example 5 demonstrates that exceeding the agreed range for low-electrode potential metal addition, liquid injection volume, and negative electrode specific surface area also fails to achieve excellent battery performance. The high-electrode potential metal element used in Comparative Example 6 is unable to participate in SEI formation and exists as a single element in the battery, forming dendrites that lead to micro-short circuits, significantly degrading battery performance, and increasing gas production.

[0088] Compared with the prior art, the present invention has the following beneficial effects:

[0089] (1) The sodium ion battery provided by the present disclosure introduces a low electrode potential metal element into the electrolyte and comprehensively designs the content of the low electrode potential metal element, the liquid retention capacity of the sodium ion battery, and the specific surface area of ​​the negative electrode active material so that they satisfy the above-mentioned relationship. This can optimize the composition of the inorganic part of the SEI membrane of the sodium ion battery, form a crystalline microphase with a wider interplanar spacing, adjust the conductivity of sodium ions in the SEI membrane, reduce polarization and initial impedance, and enable the sodium ion battery to have good cycle stability, good capacity retention and low impedance growth rate during use, and is not prone to problems such as sodium precipitation and large-scale gas production.

[0090] (2) The present disclosure improves the kinetic performance of sodium-ion batteries, prevents sodium precipitation, and optimizes their impedance performance by controlling the mass ratio of the cyclic ester solvent to the chain ester solvent within a specific range. At the same time, it avoids the problem of battery gassing caused by excessive proportion of ethylene carbonate in the cyclic ester solvent due to the singlet oxygen release mechanism.

[0091] (3) The present invention regulates the main composition of the SEI film by adjusting the types and proportions of organic additives and low electrode potential metal salt additives in the electrolyte and rationally distributes the organic and inorganic components of the SEI, thereby ensuring lower impedance and higher cycle stability of the SEI body. Industrial Applicability

[0092] The sodium-ion battery provided by the present disclosure introduces a low-electrode-potential metal element into the electrolyte and comprehensively designs the content of the low-electrode-potential metal element, the liquid retention capacity of the sodium-ion battery, and the specific surface area of ​​the negative electrode active material to satisfy the above-mentioned relationship. This can optimize the composition of the inorganic part of the SEI membrane of the sodium-ion battery, form a crystalline microphase with a wider interplanar spacing, adjust the conductivity of sodium ions in the SEI membrane, reduce polarization and initial impedance, and enable the sodium-ion battery to have good cycle stability, good capacity retention and low impedance growth rate during use, and is not prone to problems such as sodium precipitation and large-scale gas production. It can be widely used in electrical equipment.

Claims

1. A sodium ion battery, characterized in that: Including positive electrode sheet, negative electrode sheet and electrolyte; Wherein, the electrolyte comprises an organic solvent, a sodium salt, an organic additive and a low electrode potential metal salt additive; the standard electrode potential of the low electrode potential metal element in the low electrode potential metal salt additive is <-2.714V; The negative electrode plate is mainly made of negative electrode active material; The total content A of the low electrode potential metal element in the electrolyte, the liquid retention M of the sodium ion battery and the specific surface area S of the negative electrode active material satisfy the following relationship: Wherein, A = 0.01-50 mg / kg; M = 1.5 ~ 10g / Ah; S=2~8m 2 / g; The low electrode potential metal salt additive includes at least one of potassium difluorophosphate, lithium difluorophosphate, rubidium difluorophosphate, cesium difluorophosphate, francium difluorophosphate, barium difluorophosphate, calcium difluorophosphate and potassium hexafluorophosphate; The organic solvent comprises a cyclic ester solvent and a chain ester solvent in a mass ratio of 0.1-6:4-10.

2. The sodium ion battery according to claim 1, characterized in that The mass of the low electrode potential metal element accounts for 0.0001% to 2% of the total mass of the electrolyte.

3. The sodium ion battery according to claim 1, characterized in that: The sodium salt includes at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium perchlorate, sodium bis(fluorosulfonyl)imide and sodium bis(trifluoromethanesulfonyl)imide.

4. The sodium ion battery according to claim 1, characterized in that The mass of the sodium salt accounts for 3% to 20% of the total mass of the electrolyte.

5. The sodium ion battery according to claim 1, characterized in that: The cyclic ester solvent includes at least one of ethylene carbonate, propylene carbonate and gamma-butyrolactone.

6. The sodium ion battery according to claim 1, characterized in that: The chain ester solvent includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate and butyl propionate.

7. The sodium ion battery according to claim 1, characterized in that: The organic additive includes at least one of a carbonate additive, a silicon-containing additive, and a sulfur-containing additive.

8. The sodium ion battery according to claim 1, characterized in that: The mass of the organic additive accounts for 0.1% to 5% of the total mass of the electrolyte.

9. The sodium ion battery according to claim 7, characterized in that: The organic additive comprises at least one of the following features (1) to (3): (1) The carbonate additive includes at least one of vinylene carbonate and fluoroethylene carbonate; (2) the silicon-containing additive comprises at least one of tris(trimethylsilyl)phosphite, tris(trimethylsilyl)phosphate and tris(trimethylsilyl)borate; (3) The sulfur-containing additive includes at least one of 1,3-propane sultone, 1,3-propylene sultone, ethylene sulfate, propylene sulfate, methylene methanedisulfonate, 4-methylethylene sulfate, 4-fluoroethylene sulfate, 4,4'-diethylene sulfate, spirodiDTD, pyrodiDTD, 4,5-dimethylethylene sulfate and 1,2-cyclopentadiene sulfate.

10. An electrical device, characterized in that: It comprises the sodium ion battery as claimed in any one of claims 1 to 9.

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