Sodium-ion batteries

Abstract

The present invention provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and a sodium ion battery electrolyte, wherein the positive electrode sheet comprises a positive electrode current collector and a positive electrode material layer, and the positive electrode material layer comprises a positive electrode active material and a positive electrode additive Na 2 SiF 6 The sodium ion battery electrolyte includes a sodium salt, a non-aqueous organic solvent and an electrolyte additive, wherein the sodium salt includes a fluorinated sulfonyl imide sodium salt and NaPF 6 The electrolyte additive includes a sulfonic acid electrolyte additive, and the sodium ion battery electrolyte satisfies the following conditions: 0.1≤a≤5, 0.1≤b≤5; a is the mass percentage of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte; b is the mass percentage of the fluorinated sulfonyl imide sodium salt and NaPF 6 The mass ratio in the electrolyte of sodium ion batteries. The sodium salt of fluorinated sulfonyl imide and the sulfonic acid electrolyte additive form a complete, high-temperature stable protective film on the positive electrode material layer, while improving the fast charging performance and high-temperature cycle performance.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and specifically relates to a sodium ion battery with improved fast charging performance and high-temperature cycle performance. Background Art

[0002] Sodium-ion batteries have excellent safety performance. They will not precipitate sodium when charged at low temperatures and high rates, and sodium will not form an alloy with aluminum. Therefore, aluminum foil can be used as both the positive and negative current collectors to further reduce costs. Sodium-ion batteries are considered a strong competitor for the next generation of energy storage systems because of their low cost, good low-temperature performance, and excellent rate performance.

[0003] However, since the redox potential of sodium is higher than that of lithium (about 0.33V), this means that the voltage of the positive electrode material of sodium-ion batteries is higher than that of the positive electrode material of lithium-ion batteries. Therefore, in sodium-ion batteries, the side reactions at the interface between the positive electrode material and the electrolyte will increase greatly. Among them, the hydrofluoric acid generated by the hydrolysis of sodium hexafluorophosphate will destroy the lattice structure and surface solid electrolyte film of the positive electrode material, resulting in the dissolution of positive transition metal ions and the reduction of initial coulomb efficiency; in addition, high voltage will also cause the solvent in the electrolyte to decompose, generating a thicker amorphous organic solid electrolyte film, leading to the deterioration of battery performance. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the present invention provides a sodium ion battery, in which NaPF6 is partially replaced by a fluorinated sodium sulfonyl imide salt in the sodium ion battery electrolyte, and a sulfonic acid-based electrolyte additive is added, so as to improve the conductivity and sodium ion migration number of the sodium ion battery electrolyte; by adding Na2SiF6 to the positive electrode material layer, the sodium ion battery can make the fluorinated sodium sulfonyl imide salt and the sulfonic acid-based electrolyte additive better form a complete, high-temperature stable protective film in the positive electrode material layer, thereby improving the fast charging performance and the high-temperature cycle performance of the sodium ion battery.

[0005] The technical effects to be achieved by the present invention are achieved through the following technical aspects:

[0006] The present invention provides a sodium ion battery, comprising a positive electrode plate, a negative electrode plate and a sodium ion battery electrolyte, wherein the positive electrode plate comprises a positive electrode current collector and a positive electrode material layer coated on at least one surface of the positive electrode current collector, wherein the positive electrode material layer comprises a positive electrode active material and a positive electrode additive Na2SiF6;

[0007] The sodium ion battery electrolyte comprises a sodium salt, a non-aqueous organic solvent and an electrolyte additive, wherein the sodium salt comprises a fluorinated sulfonyl imide sodium salt and NaPF6, the electrolyte additive comprises a sulfonic acid-based electrolyte additive, and the sodium ion battery electrolyte satisfies the following conditions:

[0008] 0.1≤a≤5, 0.1≤b≤5;

[0009] Wherein, a is the mass percentage of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte;

[0010] b is the mass ratio of fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte.

[0011] In some embodiments, the sodium ion battery satisfies the following conditions:

[0012] 0.5≤(a+b) / lgc≤5, 40≤c≤3000;

[0013] Wherein, c is the mass content of the positive electrode additive Na2SiF6 in the positive electrode material layer, unit: ppm.

[0014] In some embodiments, the sodium ion battery satisfies the following condition: 1≤(a+b) / lgc≤3.

[0015] In some embodiments, the fluorine-containing sulfonyl imide sodium salt includes at least one of NaFSI and NaTFSI.

[0016] In some embodiments, the sulfonic acid-based electrolyte additive includes at least one of sodium fluorosulfonate, sodium trifluoromethanesulfonate, trimethylsilyl trifluoromethanesulfonate, 3-butyryl trifluorosulfonate, and sodium benzenesulfonate.

[0017] In some embodiments, the sulfonic acid-based electrolyte additive is preferably trimethylsilyl trifluoromethanesulfonate.

[0018] In some embodiments, the non-aqueous organic solvent includes at least one of a carbonate solvent, a carboxylate solvent, and an ether solvent.

[0019] In some embodiments, the mass percentage a of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte is 1%, 1.2%, 1.4%, 1.7%, 1.9%, 2.1%, 2.2%, 2.4%, 2.7%, 2.9%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5% or 5%.

[0020] In some embodiments, the mass ratio b of the fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte is 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.2, 1.4, 1.7, 1.9, 2.1, 2.4, 2.7, 3, 3.2, 3.5, 4, 4.5 or 5.

[0021] In some embodiments, the positive electrode active material includes at least one of a sodium-containing layered oxide, a sodium-containing polyanion compound, and a sodium-containing Prussian blue compound.

[0022] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer coated on at least one surface of the negative electrode current collector, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of soft carbon, hard carbon, carbon nanotubes, expanded graphite and graphene.

[0023] In summary, the present invention has at least the following benefits:

[0024] 1. The sodium ion battery provided by the present invention partially replaces NaPF6 with a fluorinated sulfonyl imide sodium salt in the sodium ion battery electrolyte, and adds a sulfonic acid-based electrolyte additive with good compatibility with the negative electrode active material, which can improve the conductivity and sodium ion migration number of the sodium ion battery electrolyte.

[0025] 2. The sodium ion battery provided by the present invention adds Na2SiF6 to the positive electrode material layer, so that the fluorinated sodium sulfonyl imide salt and the sulfonic acid-based electrolyte additive can better form a complete, high-temperature stable protective film on the positive electrode material layer; the sodium ion battery satisfies a specific relationship and can give full play to the synergistic effect between the sulfonic acid-based electrolyte additive, the fluorinated sodium sulfonyl imide salt and Na2SiF6, thereby forming a complete, uniform and high-temperature stable protective film on the surface of the positive electrode active material, thereby improving the fast charging performance and the high-temperature cycle performance of the sodium ion battery. DETAILED DESCRIPTION

[0026] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively below in conjunction with specific embodiments. Preferred embodiments of the present invention are provided in the embodiments. However, the present invention can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present invention more thoroughly understood.

[0027] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present invention. The terms used in the specification of the present invention herein are only for the purpose of describing specific embodiments and are not intended to limit the present invention.

[0028] References in the specification to "one embodiment", "embodiment", "exemplary embodiment", etc. mean the embodiment being described, but not every embodiment may include a particular feature, structure, or characteristic. Specific features, structures, or characteristics are included. Moreover, such phrases do not necessarily refer to the same embodiment. In addition, when specific features, structures, or characteristics are described in conjunction with certain embodiments, whether or not explicitly described, it is within the knowledge of those skilled in the art to consider the effects of applying the features, structures, or characteristics to other embodiments.

[0029] Values ​​expressed as ranges should be interpreted in a flexible manner to include not only the values ​​explicitly listed as limits of the range, but also all individual values ​​or sub-ranges included in the range, as if each value and sub-range were clearly stated. For example, a (mass) concentration range of "about 0.1% to about 5%" should be interpreted as including not only the explicitly listed values ​​of about 0.1% to about 5% by weight, but also the individual (mass) concentrations (e.g., 1%, 2%, 3% and 4%) and sub-ranges (e.g., 0.1% to 0.5%, 1.1% to 2.2%, and 3.3% to 4.4%) within the specified range.

[0030] As described herein, unless stated otherwise, the terms "a" and "an" are used to include one or more than one, and the term "or" is used to refer to a non-exclusive "or". In addition, when a term or terms used herein are not otherwise qualified, they should be understood to be used for descriptive purposes only and not for limiting purposes. In addition, all publications, patents, and patent documents mentioned in the specification are incorporated herein by reference in their entirety, as if individually incorporated by introduction. If there is an inconsistency in usage between this document and those documents incorporated by reference, the usage in the cited references should be considered to supplement this document. For irreconcilable inconsistencies, the usage in this document shall prevail.

[0031] The embodiment of the present invention provides a sodium ion battery electrolyte, comprising a sodium salt, a non-aqueous organic solvent and an electrolyte additive, wherein the sodium salt comprises a fluorinated sulfonyl imide sodium salt and NaPF6, and the electrolyte additive comprises a sulfonic acid-based electrolyte additive, and the sodium ion battery electrolyte satisfies the following conditions:

[0032] 0.1≤a≤5, 0.1≤b≤5;

[0033] Wherein, a is the mass percentage of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte, expressed in %;

[0034] b is the mass ratio of fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte.

[0035] The thermal stability of NaPF6 in the sodium ion battery electrolyte is poor, and its decomposition product PF5 will further generate HF in the sodium ion battery electrolyte. HF will destroy the structure of the positive electrode active material of the sodium ion battery and the solid electrolyte membrane, dissolve the transition metal ions, and increase the occurrence of side reactions in the sodium ion battery. In the sodium ion battery electrolyte provided in this embodiment, fluorinated sulfonyl imide sodium salt and NaPF6 are used as sodium salts, wherein the fluorinated sulfonyl imide sodium salt has excellent thermal stability, high dissociation degree and good film-forming properties with the negative electrode active material, and can be applied to fast-charging sodium ion battery systems and high-temperature sodium ion battery systems. When the mass percentage a of the sulfonic acid-based electrolyte additive in the sodium ion battery electrolyte and the mass ratio b of the fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte meet the above-mentioned relationship conditions, the conductivity and electrochemical stability of the sodium ion battery electrolyte can be improved.

[0036] Furthermore, the fluorine-containing sodium sulfonyl imide salt includes at least one of NaFSI and NaTFSI. NaFSI is sodium bis(fluorosulfonyl)imide, and NaTFSI is sodium bis(trifluoromethylsulfonyl)imide.

[0037] The sodium ion battery electrolyte provided in this embodiment partially replaces NaPF6 with fluorinated sulfonyl imide sodium salt, which can improve the conductivity and sodium ion migration number of the sodium ion battery electrolyte, improve the fast charging performance of the sodium ion battery, and reduce the loss of active sodium caused by the high-temperature decomposition of NaPF6, thereby further improving the comprehensive performance of the sodium ion battery.

[0038] Further, the sulfonic acid-based electrolyte additive includes at least one of sodium fluorosulfonate, sodium trifluoromethanesulfonate, trimethylsilyl trifluoromethanesulfonate, 3-butyryl trifluorosulfonate and sodium benzenesulfonate.

[0039] Furthermore, the sulfonic acid-based electrolyte additive is preferably trimethylsilyl trifluoromethanesulfonate.

[0040] Sulfonic acid-based electrolyte additives have good compatibility with negative electrode active materials. They can generate a solid electrolyte membrane with relatively stable performance on the surface of the negative electrode active materials, thereby improving the cycle stability of sodium ion batteries.

[0041] Furthermore, the non-aqueous organic solvent includes at least one of a carbonate solvent, a carboxylate solvent and an ether solvent.

[0042] Furthermore, the mass percentage a of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte is 1%, 1.2%, 1.4%, 1.7%, 1.9%, 2.1%, 2.2%, 2.4%, 2.7%, 2.9%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5% or 5%.

[0043] Furthermore, the mass ratio b of the fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte is 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.2, 1.4, 1.7, 1.9, 2.1, 2.4, 2.7, 3, 3.2, 3.5, 4, 4.5 or 5.

[0044] An embodiment of the present invention further provides a sodium ion battery, comprising a positive electrode sheet, a negative electrode sheet and the above-mentioned sodium ion battery electrolyte.

[0045] In the sodium ion battery of the present embodiment, the sodium salt component of the sodium ion battery electrolyte partially replaces NaPF6 with fluorinated sulfonyl imide sodium salt, which can improve the conductivity and sodium ion migration number of the sodium ion battery electrolyte, improve the fast charging performance of the sodium ion battery, and reduce the loss of active sodium caused by the high temperature decomposition of NaPF6, thereby further improving the comprehensive performance of the sodium ion battery; the electrolyte additive adopts a sulfonic acid-based electrolyte additive, which has good compatibility with the negative electrode active material of the sodium ion battery, and can generate a solid electrolyte membrane with relatively stable performance on the surface of the negative electrode active material, thereby improving the cycle stability of the sodium ion battery.

[0046] Furthermore, the positive electrode plate includes a positive electrode current collector and a positive electrode material layer coated on at least one surface of the positive electrode current collector, and the positive electrode material layer includes a positive electrode active material and a positive electrode additive Na2SiF6.

[0047] The positive electrode material layer includes positive electrode active material and positive electrode additive Na2SiF6. Na2SiF6 contains silicon element and Si-F bond is relatively active, which can react with sulfonic acid electrolyte additive and fluorinated sulfonyl imide sodium salt in sodium ion battery electrolyte to form a solid electrolyte membrane.

[0048] Specifically, the sulfonic acid electrolyte additive reacts with the positive electrode additive Na2SiF6 in the positive electrode material layer to generate SiO3-rich 2- 、SO3 2- and SO4 2- Sodium and semi-sodium salts of groups and NaF, SiO3 contained in solid electrolyte membrane 2- The groups and NaF can improve the mechanical strength of the solid electrolyte membrane, SO3 2- and SO4 2- The group has the effect of reducing the interface impedance, which can increase the migration speed of sodium ions and improve the electrochemical performance and chemical stability of sodium ion batteries. At the same time, the sodium salt of fluorinated sulfonyl imide also reacts with Na2SiF6 to generate SiO3-rich 2- 、SO3 2- and SO4 2- The sodium salt and semi-sodium salt of the group and NaF further enhance the protection ability of the positive electrode active material.

[0049] Furthermore, sodium ion batteries meet the following conditions:

[0050] 0.5≤(a+b) / lgc≤5, 0.1≤a≤5, 0.1≤b≤5, 40≤c≤3000;

[0051] Wherein, a is the mass percentage of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte, expressed in %;

[0052] b is the mass ratio of fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte;

[0053] c is the mass content of the positive electrode additive Na2SiF6 in the positive electrode material layer, unit: ppm.

[0054] Since the positive electrode additive Na2SiF6 is a solid phase additive, and the sulfonic acid electrolyte additive and the fluorinated sulfonyl imide sodium salt are dissolved in the sodium ion battery electrolyte, the reaction between Na2SiF6 and the sulfonic acid electrolyte additive and the fluorinated sulfonyl imide sodium salt is a heterogeneous reaction, and the reaction occurs on the surface of Na2SiF6, so a logarithmic function is used to limit the concentration of Na2SiF6.

[0055] When the sodium ion battery satisfies the following relationship conditions [0.5≤(a+b) / lgc≤5, 0.1≤a≤5, 0.1≤b≤5, 40≤c≤3000], the synergistic effect between the sulfonic acid electrolyte additive, the fluorinated sulfonyl imide sodium salt and Na2SiF6 can be fully utilized, thereby forming a complete, uniform, high-temperature stable protective film on the surface of the positive electrode active material, thereby improving the fast charging performance and the high-temperature cycle performance of the sodium ion battery.

[0056] Preferably, the sodium ion battery satisfies the following condition: 1≤(a+b) / lgc≤3.

[0057] In sodium ion batteries, the mass percentage a of the sulfonic acid-based electrolyte additive in the sodium ion battery electrolyte, the mass ratio b of the fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte, and the mass content c of the positive electrode additive Na2SiF6 in the positive electrode active material layer satisfy the above relationship conditions, thereby obtaining the technical effects of improving the high temperature storage and cycle performance of the sodium ion battery and inhibiting gas production, and further achieving the purpose of synergistically improving the high temperature performance and low impedance of the sodium ion battery.

[0058] Further, the positive electrode active material includes at least one of a sodium-containing layered oxide, a sodium-containing polyanion compound, and a sodium-containing Prussian blue compound.

[0059] Furthermore, the negative electrode plate includes a negative electrode current collector and a negative electrode material layer coated on at least one surface of the negative electrode current collector, the negative electrode material layer includes a negative electrode active material, and the negative electrode active material includes at least one of soft carbon, hard carbon, carbon nanotubes, expanded graphite and graphene.

[0060] Examples 1-24

[0061] A sodium ion battery is prepared by the following preparation method:

[0062] (1) Preparation of sodium ion battery electrolyte

[0063] Ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) are mixed in a mass ratio of EC: PC: DEC = 75:15:10, and the sulfonic acid electrolyte additive and sodium salt (fluorinated sulfonyl imide sodium salt and NaPF6) as shown in Table 1 are added, based on the total weight of the sodium ion battery electrolyte as 100%.

[0064] (2) Preparation of positive electrode

[0065] The positive electrode active material (CAM), conductive carbon black (Super-P), binder polyvinylidene fluoride (PVDF) and sodium fluorosilicate (Na2SiF6) are mixed in a mass ratio of CAM: Super-P: PVDF: Na2SiF6 = 94-x: 3: 3: x to prepare a positive electrode material mixture. Among them, sodium fluorosilicate (Na2SiF6) is added according to the content shown in Table 1. The relationship between x and c satisfies: x = c / 10000.

[0066] The positive electrode material mixture is dispersed in N-methyl-2-pyrrolidone (NMP) to obtain positive electrode slurry. Aluminum foil is used as the positive electrode current collector. The positive electrode slurry is evenly coated on both sides of the aluminum foil. After drying, calendering and vacuum drying, a positive electrode material layer is obtained. After the aluminum lead wire is welded with an ultrasonic welder, the positive electrode sheet is obtained.

[0067] (3) Preparation of negative electrode sheet

[0068] Hard carbon (HC), conductive carbon black (Super-P), binder styrene-butadiene rubber (SBR) and carboxymethyl cellulose (CMC) are mixed in a mass ratio of HC: Super-P: SBR: CMC = 94: 2.5: 2.5: 1, and then dispersed in deionized water to obtain negative electrode slurry. Aluminum foil is used as the negative electrode current collector, and the negative electrode slurry is coated on both sides of the aluminum foil. After drying, calendering and vacuum drying, and welding nickel lead wires with an ultrasonic welder, the negative electrode sheet is obtained.

[0069] (4) Preparation of battery cells

[0070] Three layers of separators are placed between the positive electrode sheet and the negative electrode sheet, and then the sandwich structure consisting of the positive electrode sheet, the negative electrode sheet and the separator is wound. The wound body is flattened and placed in an aluminum foil packaging bag, and vacuum-baked at 85°C for 48 hours to obtain a battery cell ready for liquid injection.

[0071] (5) Battery filling and formation

[0072] In a glove box with a dew point controlled below -40°C, the prepared sodium ion battery electrolyte is injected into a battery cell, vacuum packaged, and left to stand for 24 hours; the battery cell is subjected to a formation operation to prepare a sodium ion battery.

[0073] Table 1 Types and contents of sulfonic acid electrolyte additives, sodium salts and Na2SiF6 of sodium ion batteries of Examples 1-24

[0074]

[0075] Comparative Examples 1-8

[0076] A sodium ion battery is prepared by the following preparation method:

[0077] (1) Preparation of sodium ion battery electrolyte

[0078] Ethylene carbonate (EC), propylene carbonate (PC) and diethyl carbonate (DEC) were mixed in a mass ratio of EC: PC: DEC = 75:15:10, and the sulfonic acid electrolyte additives and sodium salts shown in Table 2 were added, based on the total weight of the sodium ion battery electrolyte as 100%.

[0079] (2) Preparation of positive electrode

[0080] The positive electrode active material (CAM), conductive carbon black (Super-P), binder polyvinylidene fluoride (PVDF) and sodium fluorosilicate (Na2SiF6) are mixed in a mass ratio of CAM: Super-P: PVDF: Na2SiF6 = 94-x: 3: 3: x to prepare a positive electrode material mixture. Among them, sodium fluorosilicate (Na2SiF6) is added according to the content shown in Table 2. The relationship between x and c satisfies: x = c / 10000.

[0081] The positive electrode material mixture is dispersed in N-methyl-2-pyrrolidone (NMP) to obtain positive electrode slurry. Aluminum foil is used as the positive electrode current collector. The positive electrode slurry is evenly coated on both sides of the aluminum foil. After drying, calendering and vacuum drying, a positive electrode material layer is obtained. After the aluminum lead wire is welded with an ultrasonic welder, the positive electrode sheet is obtained.

[0082] For the sodium ion batteries of Comparative Examples 1-8, the remaining preparation steps and operations (preparation of negative electrode plates, preparation of battery cells, injection and formation of battery cells) are the same as those of Examples 1-24.

[0083] Table 2 Types and contents of sulfonic acid electrolyte additives, sodium salts and Na2SiF6 of sodium ion batteries of Comparative Examples 1-8

[0084]

[0085] Performance Testing

[0086] The sodium ion batteries prepared in Examples 1-24 and Comparative Examples 1-8 were subjected to the following performance tests. The test results are shown in Table 3.

[0087] 1. Impedance performance test

[0088] The DC internal resistance of the sodium ion battery is tested after formation.

[0089] 2. 25℃ Cyclic Performance Test

[0090] The formed sodium ion battery was placed at room temperature of 25°C, charged at a constant current of 0.7C to 3.9V, then charged at a constant voltage of 3.9V with a cut-off current of 0.05C, and then discharged at a constant current of 1C to 1.5V, and this cycle was repeated for 400 cycles;

[0091] The capacity retention rate after 400 cycles at 25°C is calculated by the following formula:

[0092] Capacity retention rate after 400 cycles at 25°C (%) = discharge capacity at the 400th cycle / discharge capacity at the 1st cycle × 100%.

[0093] 3. High temperature cycle performance test

[0094] The formed sodium ion battery was placed under high temperature conditions of 45°C, charged at a constant current of 0.7C to 3.9V, then charged at a constant voltage of 3.9V with a cut-off current of 0.05C, and then discharged at a constant current of 1C to 1.5V, and this cycle was repeated for 200 and 400 cycles;

[0095] The gas production rate after 200 cycles at 45°C is calculated by the following formula:

[0096] Gas production rate after 200 cycles at 45°C (%) = (battery volume at the 200th week - battery volume at the 1st week) / battery volume at the 1st week × 100%;

[0097] The capacity retention rate after 400 cycles at 45°C is calculated by the following formula:

[0098] Capacity retention rate after 400 cycles at 45°C (%) = discharge capacity at the 400th cycle / discharge capacity at the 1st cycle × 100%.

[0099] 4. High temperature storage performance test

[0100] The formed sodium ion battery was charged to 3.9V at a constant current of 0.7C, then charged at a constant current and constant voltage until the current dropped to 0.05C, and then discharged to 1.5V at a constant current of 1C. The initial discharge capacity C0 of the battery was measured, and then it was stored in an oven at a constant temperature of 60°C. After storage for 30 days, it was discharged to 1.5V at a standard discharge rate, and the recovery capacity C1 and retention capacity C2 of the battery after 30 days of storage were measured.

[0101] Capacity recovery rate (%) = recovery capacity C1 / initial discharge capacity C0×100%;

[0102] Capacity retention rate (%) = retention capacity C2 / initial discharge capacity C0×100%.

[0103] Table 3 Performance test results of sodium ion batteries prepared in Examples 1-24 and Comparative Examples 1-8

[0104]

[0105] From the test results in Table 3, it can be seen that in the sodium ion batteries prepared in Examples 1-24, sulfonic acid compounds are used as electrolyte additives, fluorinated sulfonyl imide sodium salts are used as electrolyte sodium salts, and sodium fluorosilicate is used as a positive electrode additive.

[0106] When the mass percentage a (unit: %) of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte, the mass ratio b of the fluorinated sulfonyl imide sodium salt and NaPF6 in the sodium ion battery electrolyte, and the mass content c (unit: ppm) of the positive electrode additive Na2SiF6 in the positive electrode material layer meet the relationship conditions: 0.5≤(a+b) / lgc≤5, 0.1≤a≤5, 0.1≤b≤5, 40≤c≤3000, the prepared sodium ion battery has lower impedance and excellent high temperature cycle performance and high temperature storage performance. The main reason is that the sulfonic acid electrolyte additive can react with the positive electrode additive Na2SiF6 in the positive electrode material layer to generate SiO3-rich 2- 、SO3 2- and SO4 2- Sodium and hemi-sodium salts of groups and NaF, SiO3 2- The groups and NaF can improve the mechanical strength of the surface of the positive electrode material layer, SO3 2- and SO4 2-The group can reduce the interfacial impedance of sodium ion batteries and increase the migration speed of sodium ions. The synergistic effect of the two improves the electrochemical performance and chemical stability of sodium ion batteries. At the same time, the sodium salt of fluorinated sulfonyl imide is also reactive with Na2SiF6 and can generate SiO3-rich 2- 、SO3 2- and SO4 2- The sodium salt and semi-sodium salt of the group and NaF further improve the protection ability of the positive electrode active material. Since a protective film is formed on the surface of the positive electrode active material, the side reaction between the positive electrode active material and the sodium ion battery electrolyte is inhibited, and the dissolution of transition metal ions is limited, which improves the cycle and storage stability of the sodium ion battery at high temperature.

[0107] From the test results of the sodium ion batteries prepared in Examples 6-10, it can be seen that the mass percentage a (unit: %) of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte, the mass ratio b of the fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte, and the mass content c (unit: ppm) of the positive electrode additive Na2SiF6 in the positive electrode material layer further satisfy the relationship condition: 1≤(a+b) / lgc≤3, which is beneficial to further inhibit the gas production of the sodium ion battery at high temperature, while improving the storage capacity recovery rate and cycle capacity retention rate of the sodium ion battery at high temperature.

[0108] From the test results of the sodium ion battery prepared in Comparative Examples 1-6, it can be seen that even if the mass percentage a (unit: %) of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte, the mass ratio b of the fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte, and the mass content c (unit: ppm) of the positive electrode additive Na2SiF6 in the positive electrode material layer meet the relationship condition 0.5≤(a+b) / lgc≤5, but when the a value, b value or c value does not meet its range limit, the sodium ion battery still does not have a lower impedance and better high-temperature cycle and storage performance, indicating that the a value, b value, and c value have a strong correlation in improving the performance of the surface protective film of the positive electrode active material of the sodium ion battery. In particular, when the content of sodium fluorosilicate in the positive electrode material layer of the sodium ion battery is too low or too high, the adverse effect on the sodium ion battery is more obvious. Similarly, when the a value, b value or c value meets its range limit, but the (a+b) / lgc value does not meet the above relationship conditions, the improvement in the performance of the sodium ion battery is not obvious.

[0109] The sulfonic acid electrolyte additive used in Examples 18-19 is trimethylsilyl trifluoromethanesulfonate. Comparing the test results of the sodium ion batteries prepared in Example 6 and Example 18, it can be seen that when the mass percentage a (unit: %) of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte, the mass ratio b of the fluorinated sulfonyl imide sodium salt and NaPF6 in the sodium ion battery electrolyte, and the mass content c (unit: ppm) of the positive electrode additive Na2SiF6 in the positive electrode material layer are consistent, the storage and cycle performance of trimethylsilyl trifluoromethanesulfonate is higher than that of sodium fluorosulfonate. The reason is that trimethylsilyl trifluoromethanesulfonate forms a protective film with better performance on the surface of the positive electrode active material, and the trimethylsilyl group can capture HF and H2O, inhibit corrosion of the positive electrode active material, and reduce the occurrence of side reactions.

[0110] The above contents are merely examples and explanations of the structure of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, and these obvious replacement forms all belong to the protection scope of the present invention.

Claims

1. A sodium ion battery, characterized in that It includes a positive electrode sheet, a negative electrode sheet and a sodium ion battery electrolyte, wherein the positive electrode sheet includes a positive electrode current collector and a positive electrode material layer coated on at least one surface of the positive electrode current collector, wherein the positive electrode material layer includes a positive electrode active material and a positive electrode additive Na2SiF6; The sodium ion battery electrolyte comprises a sodium salt, a non-aqueous organic solvent and an electrolyte additive, wherein the sodium salt comprises a fluorinated sulfonyl imide sodium salt and NaPF6, the electrolyte additive comprises a sulfonic acid-based electrolyte additive, and the sodium ion battery satisfies the following conditions: 0.1≤a≤5, 0.1≤b≤5, 0.5≤(a+b) / lgc≤5, 40≤c≤3000; Wherein, a is the mass percentage of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte; b is the mass ratio of fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte; c is the mass content of the positive electrode additive Na2SiF6 in the positive electrode material layer, unit: ppm.

2. The sodium ion battery according to claim 1, characterized in that The sodium ion battery satisfies the following condition: 1≤(a+b) / lgc≤3.

3. The sodium ion battery according to claim 1, characterized in that: The fluorine-containing sulfonyl imide sodium salt includes at least one of NaFSI and NaTFSI.

4. The sodium ion battery according to any one of claims 1 to 3, characterized in that: The sulfonic acid-based electrolyte additive includes at least one of sodium fluorosulfonate, sodium trifluoromethanesulfonate, trimethylsilyl trifluoromethanesulfonate, 3-butyryl trifluorosulfonate and sodium benzenesulfonate.

5. The sodium ion battery according to claim 4, characterized in that: The sulfonic acid electrolyte additive is trimethylsilyl trifluoromethanesulfonate.

6. The sodium ion battery according to claim 1, characterized in that: The mass percentage a of the sulfonic acid electrolyte additive in the sodium ion battery electrolyte is 1%, 1.2%, 1.4%, 1.7%, 1.9%, 2.1%, 2.2%, 2.4%, 2.7%, 2.9%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5% or 5%.

7. The sodium ion battery according to claim 1, characterized in that: The mass ratio b of the fluorinated sulfonyl imide sodium salt to NaPF6 in the sodium ion battery electrolyte is 0.1, 0.3, 0.5, 0.7, 0.9, 1, 1.2, 1.4, 1.7, 1.9, 2.1, 2.4, 2.7, 3, 3.2, 3.5, 4, 4.5 or 5.

8. The sodium ion battery according to claim 1, characterized in that: The positive electrode active material includes at least one of a sodium-containing layered oxide, a sodium-containing polyanion compound, and a sodium-containing Prussian blue compound.

9. The sodium ion battery according to claim 1, characterized in that: The negative electrode plate includes a negative electrode current collector and a negative electrode material layer coated on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode active material.

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