Sodium-ion battery electrolyte and sodium-ion battery

Abstract

The invention belongs to the field of sodium-ion batteries, and discloses a sodium-ion battery electrolyte and a sodium-ion battery. The sodium-ion battery electrolyte comprises sodium salt, an organic solvent and an organic molecular additive shown in the following formula, wherein R1 to R5 are respectively and independently any one of F, Cl, Br, I, CN, H, OH, SH and NO2. A boron atom in the molecular structure of the additive is used as an electron-deficient center and can be preferentially complexed with anions or solvent molecules in the electrolyte to pre-stabilize an electrode interface; the bond energy of the B-O bond is moderate, so that the oxidation potential of the B-O bond is lower than that of a main body carbonate solvent, the B-O bond can be preferentially decomposed in the first charge-discharge process, and a thin, compact and highly stable positive electrode electrolyte interface film is formed on the surface of a positive electrode; the controllable substituent group on the benzene ring further regulates the decomposition potential of molecules through an electronic effect, so that the film forming time and the film property can be precisely regulated and controlled. The stable CEI can effectively inhibit continuous decomposition of the electrolyte at high temperature and high pressure, and the cycling stability of the battery in the high-temperature and high-pressure environment is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of sodium-ion batteries, and particularly relates to a high-temperature, high-pressure sodium-ion battery electrolyte. Background Technology

[0002] In recent years, with the increasing severity of environmental and energy problems, sodium-ion batteries, with their advantages of abundant resources and low cost, have been regarded as a promising next-generation large-scale energy storage technology. As the core medium for ion transport in the battery, the chemical and electrochemical stability of the electrolyte directly determines the overall performance of the battery, while the compatibility between the electrolyte and the cathode material interface is a key factor affecting the energy density, cycle life, and safety of sodium-ion batteries.

[0003] Currently, electrolyte systems suitable for sodium-ion batteries (such as carbonates and ethers) face severe challenges when matching high-capacity or high-voltage cathode materials (such as layered oxides and polyanionic compounds). Under high voltage, the electrolyte is prone to oxidative decomposition at the cathode interface, leading to a surge in interfacial impedance, dissolution of transition metals, and irreversible phase transitions. For example, the prior art CN118486897A discloses a high-temperature resistant lithium-ion battery electrolyte, focusing on improving the high-temperature durability of lithium-ion batteries. Among them, the methoxy carbonyl (ester group) or tert-butyldimethylsiloxy substituents introduced on the benzene ring by the phenylboronic acid pinacol ester additive are prone to electrochemical oxidation or hydrolysis under high voltage, and their silicon-oxygen bonds are also extremely sensitive to acidic substances (such as HF) generated by electrolyte side reactions. These unstable functional groups are not only prone to decomposition themselves, but also interfere with the electronic regulation function of the benzene ring, resulting in insufficient adaptability under high voltage (such as 4.5 V) conditions. In addition, at high temperatures, the side reactions are aggravated, further damaging the stability of the cathode structure, causing rapid capacity decay and safety hazards. Especially for sodium-ion batteries, the larger radius of sodium ions and different interfacial chemical properties make the formation mechanism and stability of the cathode / electrolyte interface (CEI) different from those of lithium battery systems, requiring targeted electrolyte design. Summary of the Invention

[0004] To address the technical problem that existing sodium-ion battery electrolytes are not stable under high temperature and high voltage conditions and are prone to harmful side reactions with high-voltage cathode materials, leading to a sharp decline in battery cycle performance, this invention proposes a sodium-ion battery electrolyte and a sodium-ion battery.

[0005] To achieve the above objectives, the technical solution of the present invention is implemented as follows:

[0006] A sodium-ion battery electrolyte comprises a basic electrolyte consisting of a sodium salt and an organic solvent, and an organic molecular additive; wherein the structural formula of the organic molecular additive is as follows:

[0007] ;

[0008] Among them, R1, R2, R3, R4 and R5 are each independently any one of F, Cl, Br, I, CN, H, OH, SH and NO2.

[0009] Furthermore, the aforementioned organic molecular additive is at least one selected from the following: 5-chloro-2-fluorophenylboronic acid pinacol ester, 4-mercaptophenylboronic acid pinacol ester, 2-nitro-4-fluorophenylboronic acid pinacol ester, and 3,4-difluorophenylboronic acid pinacol ester.

[0010] The mass of the aforementioned organic molecular additives is 0.1-10% of the mass of the basic electrolyte; the concentration of sodium salt in the basic electrolyte is 0.5-3 mol / L.

[0011] Furthermore, the sodium salt is at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(oxalato)borate, sodium trifluoromethanesulfonate, and sodium perchlorate; the organic solvent is any one or more of cyclic carbonates, linear carbonates, carboxylic acid esters, and cyclic lactones.

[0012] The aforementioned cyclic carbonates are any one or two of ethylene carbonate (EC) and propylene carbonate (PC), and the chain linear carbonates are any one or more of dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC).

[0013] More preferably, the organic solvent is ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 1:1, and the sodium salt is sodium hexafluorophosphate with a concentration of 1 mol / L.

[0014] The above-mentioned method for preparing sodium-ion battery electrolyte comprises the following steps: adding sodium salt to an organic solvent to form a mixed solution; adding organic molecular additives to the mixed solution and dissolving them to obtain the electrolyte.

[0015] A sodium-ion battery includes a positive electrode, a negative electrode, a separator, and the aforementioned sodium-ion battery electrolyte.

[0016] The positive electrode contains a positive electrode active material, and the negative electrode contains metallic sodium or an active material that can intercalate / deintercalate sodium ions.

[0017] Furthermore, the aforementioned positive electrode active material is at least one of the following: polyanionic compounds (such as sodium ferrous sulfate, sodium iron phosphate pyrophosphate, etc.), layered transition metal oxides, Prussian blue compounds, sulfides, nitrides, carbides, and titanates. The positive electrode also includes conductive agents (conductive carbon black, Ketjen black, Super P Li, etc.) and binders (including polyvinylidene fluoride (PVDF) and sodium carboxymethyl cellulose (CMC), etc.).

[0018] The beneficial effects of this invention are:

[0019] (1) This invention introduces specific arylboronic acid pinacol esters as functional additives into the electrolyte. The core mechanism of this molecule stems from its ingenious structural design. The molecule has a benzene ring as its core, with boron atoms connected by a sterically hindered and structurally stable cyclic coordination center. Meanwhile, the substituents (R1-R5) on the benzene ring are all electrochemically inert hydrogen, halogens, or stable groups, thus forming a molecular skeleton that is structurally stable in a high-pressure oxidation environment. The key to high performance lies in the ability to precisely control the electron distribution of the entire molecule by accurately selecting the type, position, and number of substituents on the benzene ring, thereby achieving customization of the molecular oxidation decomposition potential. This allows it to preferentially initiate a controllable and mild decomposition reaction when the positive electrode potential rises to the high-voltage region (e.g., 4.5V) and the interface faces severe oxidation challenges. The active species generated during this decomposition process then polymerize in situ to form a thin, dense, and stable CEI film rich in inorganic boron-oxygen networks and also containing flexible organic components. This interface film can effectively block direct contact between the electrolyte and the highly active cathode material, suppressing side reactions and thus significantly improving the high-voltage cycle stability of the battery; at the same time, its unique composite structure also contributes to excellent high-temperature resistance.

[0020] (2) The robust CEI film constructed in this invention can physically block continuous interfacial side reactions, stabilize sodium ion transport, and inhibit cathode particle breakage under harsh conditions. It is particularly suitable for high-voltage cathode material systems represented by sodium ferrous sulfate, thereby significantly improving the long-cycle stability of sodium-ion batteries matched with such cathodes under high temperature and high pressure conditions. Specifically, under a high temperature of 60°C and a voltage window of 2-4.5 V, a long-cycle test was conducted at a rate of 1 C. The electrolyte with this additive still maintained a capacity retention rate of 73.9% after 700 cycles; the electrolyte without this functional component showed that its capacity had almost completely decayed after only 60 cycles under the same conditions. The above results indicate that the arylboronic acid pinacol ester additive introduced in this invention can significantly improve the cycle stability and capacity retention rate of sodium-ion batteries under high temperature and high pressure conditions through the above-mentioned interfacial modification mechanism. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1 The images show the SEM morphology of the spherical and blocky sodium ferrous sulfate used in this invention.

[0023] Figure 2 This is a comparison chart of the first-week charge-discharge curves of the sodium-ion battery prepared in Example 4 of the present invention (Application Example 4) and the sodium-ion battery prepared in Comparative Example 1 (Application Example 17).

[0024] Figure 3 This is a TEM comparison image showing the CEI thickness formed after the first week of charge and discharge of the sodium-ion battery prepared in Example 4 of the present invention (Application Example 4) and the sodium-ion battery prepared in Comparative Example 1 (Application Example 17).

[0025] Figure 4 Cyclic performance test curves of the sodium-ion battery prepared in Example 4 of the present invention (Application Example 4) and the sodium-ion battery prepared in Comparative Example 1 (Application Example 17).

[0026] Figure 5 This is a comparison chart of the first-week charge-discharge curves of the sodium-ion battery prepared in Example 5 of the present invention (Application Example 5) and the sodium-ion battery prepared in Comparative Example 2 (Application Example 18).

[0027] Figure 6 This is a comparison chart of the first-week charge-discharge curves of the sodium-ion battery prepared in Example 8 of the present invention (Application Example 8) and the sodium-ion battery prepared in Comparative Example 5 (Application Example 21).

[0028] Figure 7 This is a comparison chart of the first-week charge-discharge curves of the sodium-ion battery prepared in Example 9 of the present invention (Application Example 9) and the sodium-ion battery prepared in Comparative Example 6 (Application Example 22).

[0029] Figure 8 The first-week charge-discharge curves of the sodium-ion batteries (Application Examples 10-12) prepared in Examples 10-12 of this invention are shown in the comparison diagram.

[0030] Figure 9 This is a comparison chart of the first-week charge-discharge curves of the sodium-ion battery prepared in Example 13 of the present invention (Application Example 13) and the sodium-ion battery prepared in Comparative Example 7 (Application Example 23).

[0031] Figure 10 This is a comparison chart of the first-week charge-discharge curves of the sodium-ion battery prepared in Example 14 of the present invention (Application Example 14) and the sodium-ion battery prepared in Comparative Example 8 (Application Example 24). Detailed Implementation

[0032] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] In the following examples and comparative examples, the electrolyte preparation method includes the following steps: mixing the base electrolyte and the additive evenly. All mixing is carried out in a glove box filled with argon gas.

[0034] Example 1

[0035] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0036] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, organic molecular additives were added, and the mixture was ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 1.0 wt% (as a percentage of the mass of the base electrolyte).

[0037] Application Example 1

[0038] A method for assembling a sodium-ion battery, comprising the following steps:

[0039] Using lumpy sodium ferrous sulfate (morphology as follows) Figure 1 The positive electrode active material (shown) is mixed with a conductive agent (Super P Li) and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture is stirred evenly to form a slurry, which is then coated onto a current collector (aluminum foil). After vacuum drying, the slurry is cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) is used as the negative electrode, a glass fiber membrane (Whatman GF / D) is used as the separator, the electrolyte of this embodiment is used, and a stainless steel shell is used as the outer casing to assemble a CR2025 coin cell.

[0040] Example 2

[0041] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0042] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 5.0 wt% (as a percentage of the mass of the base electrolyte).

[0043] Application Example 2

[0044] A method for assembling a sodium-ion battery, comprising the following steps:

[0045] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0046] Example 3

[0047] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0048] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 7.0 wt% (as a percentage of the mass of the base electrolyte).

[0049] Application Example 3

[0050] A method for assembling a sodium-ion battery, comprising the following steps:

[0051] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0052] Example 4

[0053] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0054] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0055] Application Example 4

[0056] A method for assembling a sodium-ion battery, comprising the following steps:

[0057] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0058] Example 5

[0059] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0060] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0061] Application Example 5

[0062] A method for assembling a sodium-ion battery, comprising the following steps:

[0063] Sodium vanadium fluorophosphate (positive electrode active material) was mixed with a conductive agent (Super P Li) and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was stirred evenly to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) was used as the separator, the electrolyte of this embodiment was used, and a stainless steel shell was used as the outer casing to assemble a CR2025 coin cell.

[0064] Example 6

[0065] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0066] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0067] Application Example 6

[0068] A method for assembling a sodium-ion battery, comprising the following steps:

[0069] Sodium vanadium phosphate (positive electrode active material) was mixed with a conductive agent (Super P Li) and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was stirred evenly to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) was used as the separator, the electrolyte of this embodiment was used, and a stainless steel shell was used as the outer casing to assemble a CR2025 coin cell.

[0070] Example 7

[0071] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0072] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0073] Application Example 7

[0074] A method for assembling a sodium-ion battery, comprising the following steps:

[0075] Sodium iron phosphate pyrophosphate (positive electrode active material) was mixed with a conductive agent (Super P Li) and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was stirred evenly to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) was used as the separator, the electrolyte of this embodiment was used, and a stainless steel shell was used as the outer casing to assemble a CR2025 coin cell.

[0076] Example 8

[0077] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0078] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0079] Application Example 8

[0080] A method for assembling a sodium-ion battery, comprising the following steps:

[0081] Spherical sodium ferrous sulfate (positive electrode active material, morphology as follows) Figure 1 As shown, a conductive agent (Super P Li) and polyvinylidene fluoride are mixed in a mass ratio of 8:1:1. The mixture is then thoroughly mixed to form a slurry, which is applied to a current collector (aluminum foil). After vacuum drying, the slurry is cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) is used as the negative electrode, a glass fiber membrane (Whatman GF / D) is used as the separator, the electrolyte of this embodiment is used, and a stainless steel shell is used as the outer casing to assemble a CR2025 coin cell.

[0082] Example 9

[0083] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0084] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0085] Application Example 9

[0086] A method for assembling a sodium-ion battery, comprising the following steps:

[0087] (1) A lumpy sodium ferrous sulfate (positive electrode active material) is mixed with a conductive agent (Super P Li) and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture is mixed evenly to form a slurry, which is then coated onto a current collector (aluminum foil). After vacuum drying, the slurry is cut to obtain a positive electrode with a diameter of 12 mm.

[0088] (2) Hard carbon (negative electrode active material) is mixed with conductive agent (Super P Li) and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture is mixed evenly to form a slurry and coated onto the current collector (copper foil). After vacuum drying, it is cut to obtain a negative electrode with a diameter of 13 mm.

[0089] (3) Using the positive and negative electrodes prepared in steps (1) and (2) above, the glass fiber membrane (Whatman GF / D) is used as the separator, the electrolyte of this embodiment is used, and the stainless steel shell is used as the outer shell, and the CR2025 button cell is assembled.

[0090] Example 10

[0091] The preparation method of the sodium-ion battery electrolyte in this embodiment uses 4-mercaptophenylboronic acid pinacol ester as an additive, and the specific steps are as follows:

[0092] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 4-mercaptophenylboronic acid pinacol ester (organic molecular additive) was 1.0 wt% (as a percentage of the mass of the base electrolyte).

[0093] Application Example 10

[0094] A method for assembling a sodium-ion battery, comprising the following steps:

[0095] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0096] Example 11

[0097] The preparation method of the sodium-ion battery electrolyte in this embodiment uses 2-nitro-4-fluorophenylboronic acid pinacol ester as an additive, and the specific steps are as follows:

[0098] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, organic molecular additives were added, and the mixture was ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 2-nitro-4-fluorophenylboronic acid pinacol ester (organic molecular additive) was 5.0 wt% (as a percentage of the mass of the base electrolyte).

[0099] Application Example 11

[0100] A method for assembling a sodium-ion battery, comprising the following steps:

[0101] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0102] Example 12

[0103] The preparation method of the sodium-ion battery electrolyte in this embodiment uses 3,4-difluorophenylboronic acid pinacol ester as an additive, and the specific steps are as follows:

[0104] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 3,4-difluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0105] Application Example 12

[0106] A method for assembling a sodium-ion battery, comprising the following steps:

[0107] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0108] Example 13

[0109] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0110] EC and DMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, organic molecular additives were added, and the mixture was ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0111] Application Example 13

[0112] A method for assembling a sodium-ion battery, comprising the following steps:

[0113] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0114] Example 14

[0115] The preparation method of the sodium-ion battery electrolyte in this embodiment uses pinacol 5-chloro-2-fluorophenylboronic acid as an additive, and the specific steps are as follows:

[0116] EC and EMC were mixed evenly at a volume ratio of 1:1, NaClO4 was added and stirred to dissolve, organic molecular additives were added, and the mixture was ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaClO4 was 1 mol / L, and the mass percentage of 5-chloro-2-fluorophenylboronic acid pinacol ester (organic molecular additive) was 3.0 wt% (as a percentage of the mass of the base electrolyte).

[0117] Application Example 14

[0118] A method for assembling a sodium-ion battery, comprising the following steps:

[0119] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 8:1:1. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0120] Example 15

[0121] The preparation method of the sodium-ion battery electrolyte in this embodiment uses 3,4-difluorophenylboronic acid pinacol ester as an additive, and the specific steps are as follows:

[0122] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 3,4-difluorophenylboronic acid pinacol ester (organic molecular additive) was 0.1 wt% (as a percentage of the mass of the base electrolyte).

[0123] Application Example 15

[0124] A method for assembling a sodium-ion battery, comprising the following steps:

[0125] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 80:10:10. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0126] Example 16

[0127] The preparation method of the sodium-ion battery electrolyte in this embodiment uses 3,4-difluorophenylboronic acid pinacol ester as an additive, and the specific steps are as follows:

[0128] EC and EMC were mixed evenly at a volume ratio of 1:1, NaPF6 was added and stirred to dissolve, and then organic molecular additives were added and ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L, and the mass percentage of 3,4-difluorophenylboronic acid pinacol ester (organic molecular additive) was 10.0 wt% (as a percentage of the mass of the base electrolyte).

[0129] Application Example 16

[0130] A method for assembling a sodium-ion battery, comprising the following steps:

[0131] A CR2025 coin cell was assembled using lumpy sodium ferrous sulfate (positive electrode active material), a conductive agent (Super P Li), and polyvinylidene fluoride in a mass ratio of 80:10:10. The mixture was thoroughly mixed to form a slurry, which was then coated onto a current collector (aluminum foil). After vacuum drying, the slurry was cut to obtain a positive electrode with a diameter of 12 mm. A sodium metal sheet (15 mm in diameter) was used as the negative electrode, a glass fiber membrane (Whatman GF / D) as the separator, the electrolyte of this embodiment, and a stainless steel casing.

[0132] Comparative Example 1

[0133] The preparation method of the sodium-ion battery electrolyte in this comparative example differs from that in Example 1 in that no organic molecular additives are added. The specific steps are as follows:

[0134] EC and EMC were mixed evenly at a volume ratio of 1:1, and NaPF6 was added and stirred to dissolve. The mixture was then ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L.

[0135] Application Example 17

[0136] An assembly method for a sodium-ion battery, the steps of which are the same as in Application Example 1.

[0137] Comparative Example 2

[0138] The preparation method of the sodium-ion battery electrolyte in this comparative example differs from that in Example 5 in that no organic molecular additives are added. The specific steps are as follows:

[0139] EC and EMC were mixed evenly at a volume ratio of 1:1, and NaPF6 was added and stirred to dissolve. The mixture was then ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L.

[0140] Application Example 18

[0141] An assembly method for a sodium-ion battery, the steps of which are the same as in Application Example 5.

[0142] Comparative Example 3

[0143] The preparation method of the sodium-ion battery electrolyte in this comparative example differs from that in Example 6 in that no organic molecular additives are added. The specific steps are as follows:

[0144] EC and EMC were mixed evenly at a volume ratio of 1:1, and NaPF6 was added and stirred to dissolve. The mixture was then ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L.

[0145] Application Example 19

[0146] An assembly method for a sodium-ion battery, the steps of which are the same as in Application Example 6.

[0147] Comparative Example 4

[0148] The preparation method of the sodium-ion battery electrolyte in this comparative example differs from that in Example 7 in that no organic molecular additives are added. The specific steps are as follows:

[0149] EC and EMC were mixed evenly at a volume ratio of 1:1, and NaPF6 was added and stirred to dissolve. The mixture was then ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L.

[0150] Application Example 20

[0151] An assembly method for a sodium-ion battery, the steps of which are the same as in Application Example 7.

[0152] Comparative Example 5

[0153] The preparation method of the sodium-ion battery electrolyte in this comparative example differs from that in Example 8 in that no organic molecular additives are added. The specific steps are as follows:

[0154] EC and EMC were mixed evenly at a volume ratio of 1:1, and NaPF6 was added and stirred to dissolve. The mixture was then ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L.

[0155] Application Example 21

[0156] An assembly method for a sodium-ion battery, the steps of which are the same as in Application Example 8.

[0157] Comparative Example 6

[0158] The preparation method of the sodium-ion battery electrolyte in this comparative example differs from that in Example 9 in that no organic molecular additives are added. The specific steps are as follows:

[0159] EC and EMC were mixed evenly at a volume ratio of 1:1, and NaPF6 was added and stirred to dissolve. The mixture was then ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L.

[0160] Application Example 22

[0161] An assembly method for a sodium-ion battery, the steps of which are the same as in Application Example 9.

[0162] Comparative Example 7

[0163] The preparation method of the sodium-ion battery electrolyte in this comparative example differs from that in Example 13 in that no organic molecular additives are added. The specific steps are as follows:

[0164] EC and DMC were mixed evenly at a volume ratio of 1:1, and NaPF6 was added and stirred to dissolve. The mixture was then ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaPF6 was 1 mol / L.

[0165] Application Example 23

[0166] An assembly method for a sodium-ion battery, the steps of which are the same as in Application Example 13.

[0167] Comparative Example 8

[0168] The preparation method of the sodium-ion battery electrolyte in this comparative example differs from that in Example 14 in that no organic molecular additives are added. The specific steps are as follows:

[0169] EC and EMC were mixed evenly at a volume ratio of 1:1, and NaClO4 was added and stirred to dissolve. The mixture was then ultrasonically dispersed to obtain the desired electrolyte. The concentration of NaClO4 was 1 mol / L.

[0170] Application Example 24

[0171] An assembly method for a sodium-ion battery, the steps of which are the same as in Application Example 14.

[0172] Implementation Results Example

[0173] The sodium-ion batteries prepared in Examples 1, 2, 3, 4, 8, 10, 11, 12, 13, 14, 15, 16 and Comparative Examples 1, 5, 7, 8 were tested under a 1 C charge / discharge rate mode, with a charging cutoff voltage of 4.5 V, a discharging cutoff voltage of 2.0 V, and a temperature of 60 °C.

[0174] The sodium-ion batteries prepared in Example 5 and Comparative Example 2 were tested under a 1 C rate charge / discharge mode, with a charging cutoff voltage of 4.4 V, a discharging cutoff voltage of 2.5 V, and a temperature of 60 °C.

[0175] The sodium-ion batteries prepared in Example 6 and Comparative Example 3 were tested under a 1 C rate charge / discharge mode, with a charging cutoff voltage of 4.0 V, a discharging cutoff voltage of 2.5 V, and a temperature of 60 °C.

[0176] The sodium-ion batteries prepared in Example 7 and Comparative Example 4 were tested under a 1 C rate charge / discharge mode, with a charging cutoff voltage of 4.0 V, a discharging cutoff voltage of 1.5 V, and a temperature of 60 °C.

[0177] The sodium-ion batteries prepared in Example 9 and Comparative Example 6 were tested under a 1 C rate charge / discharge mode, with a charging cutoff voltage of 4.5 V, a discharging cutoff voltage of 1.0 V, and a temperature of 60 °C.

[0178] Figure 2 This is a comparison of the first-cycle charge-discharge curves of the sodium-ion battery prepared in Example 4 of this invention and the sodium-ion battery prepared in Comparative Example 1. Figure 2 It can be seen that the comparative example exhibited significant overcharging during the first week of charge and discharge, while the example achieved a coulombic efficiency of 93%. This experimental test demonstrates that organic molecular additives play a crucial role in the high-temperature, high-pressure cycling of sodium-ion batteries.

[0179] Figure 3 This is a TEM comparison image showing the CEI thickness formed after the first charge-discharge cycle of the sodium-ion battery prepared in Example 4 of this invention and the sodium-ion battery prepared in Comparative Example 1. Figure 3 It can be seen that the embodiment formed a thinner and more uniform CEI compared with the comparative example, which effectively suppressed the continuous interfacial side reactions.

[0180] Figure 4 The cycling performance test curves (60°C, 2-4.5 V voltage range, 1 C rate charge / discharge) of the sodium-ion battery prepared in Example 4 and the sodium-ion battery prepared in Comparative Example 1 are shown. Figure 4 It can be seen that the battery with added organic molecular additives has better cycle stability, with a capacity retention rate of up to 73.9% after 700 cycles. In contrast, the sodium-ion battery prepared in Comparative Example 1 has almost zero capacity decay after 60 cycles.

[0181] Figure 5 This is a comparison of the first-cycle charge-discharge curves of the sodium-ion battery prepared in Example 5 of this invention and the sodium-ion battery prepared in Comparative Example 2. Figure 5 As can be seen, the embodiment exhibits a higher coulombic efficiency of 78% compared to the comparative example.

[0182] Figure 6 This is a comparison of the first-cycle charge-discharge curves of the sodium-ion battery prepared in Example 8 of this invention and the sodium-ion battery prepared in Comparative Example 5. Figure 8 As can be seen, the embodiment exhibits a higher coulombic efficiency of 95% compared to the comparative example.

[0183] Figure 7 This is a comparison chart of the first-cycle charge-discharge curves of the sodium-ion battery prepared in Example 9 of this invention and the sodium-ion battery prepared in Comparative Example 6. Figure 9 As can be seen, the embodiment exhibits a higher coulombic efficiency of 97% compared to the comparative example.

[0184] Figure 8 The first-cycle charge-discharge curves of the sodium-ion batteries prepared in Examples 10-12 of this invention are shown in the comparison diagram. It can be seen that all examples exhibit high coulombic efficiency.

[0185] Figure 9This is a comparison chart of the first-cycle charge-discharge curves of the sodium-ion battery prepared in Example 13 of this invention and the sodium-ion battery prepared in Comparative Example 7. Figure 9 As can be seen, the embodiment exhibits a higher coulombic efficiency of 92% compared to the comparative example.

[0186] Figure 10 This is a comparison of the first-cycle charge-discharge curves of the sodium-ion battery prepared in Example 14 of this invention and the sodium-ion battery prepared in Comparative Example 8. Figure 10 As can be seen, the embodiment exhibits a higher coulombic efficiency of 89% compared to the comparative example.

[0187] The above experimental tests demonstrate that organic molecular additives play an important role in the high-temperature and high-pressure cycling of a series of sodium-ion batteries.

[0188] The composition of the sodium-ion battery electrolyte, the type of cathode material, the first-cycle coulombic efficiency, and the capacity retention rate after a certain number of cycles were summarized in Table 1 for the sodium-ion battery prepared in Examples 1-14 and Comparative Examples 1-8.

[0189] Table 1. Electrolyte composition, cathode material type, first-cycle coulombic efficiency, and capacity retention of sodium-ion batteries prepared in the examples and comparative examples.

[0190]

[0191] As shown in Table 1, under the premise that other conditions in the sodium-ion battery electrolyte are kept the same, the capacity retention rates of Examples 1-14 with added organic additives are higher than those of Comparative Examples 1-8 without additives under the same experimental conditions after a certain number of cycles.

[0192] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A sodium-ion battery electrolyte, characterized in that, It includes a basic electrolyte composed of sodium salt and organic solvent, and an organic molecular additive; the structural formula of the organic molecular additive is as follows: ； Among them, R1, R2, R3, R4 and R5 are each independently any one of F, Cl, Br, I, CN, H, OH, SH and NO2.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, The organic molecular additive is at least one selected from 5-chloro-2-fluorophenylboronic acid pinacol ester, 4-mercaptophenylboronic acid pinacol ester, 2-nitro-4-fluorophenylboronic acid pinacol ester, and 3,4-difluorophenylboronic acid pinacol ester.

3. The sodium-ion battery electrolyte according to claim 1 or 2, characterized in that, The organic molecular additive is 0.1-10% of the mass of the base electrolyte; the concentration of sodium salt in the base electrolyte is 0.5-3 mol / L.

4. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt is at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium hexafluoroarsenate, sodium bis(oxalato)borate, sodium trifluoromethanesulfonate, and sodium perchlorate; the organic solvent is any one or more of cyclic carbonates, linear carbonates, carboxylic acid esters, and cyclic lactones.

5. The sodium-ion battery electrolyte according to claim 4, characterized in that, The cyclic carbonate is any one or two of ethylene carbonate and propylene carbonate, and the linear carbonate is any one or more of dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

6. The method for preparing the sodium-ion battery electrolyte according to claim 1, characterized in that, The steps are as follows: add sodium salt to an organic solvent, add organic molecular additives, and dissolve to obtain the product.

7. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode, a negative electrode, a separator, and the sodium-ion battery electrolyte as described in any one of claims 1, 2, or 4-6.

8. The sodium-ion battery according to claim 7, characterized in that, The positive electrode contains a positive electrode active material, and the negative electrode includes metallic sodium or an active material capable of intercalating / deintercalating sodium ions.

9. The sodium-ion battery according to claim 8, characterized in that, The positive electrode active material is at least one of polyanionic compounds, layered transition metal oxides, Prussian blue compounds, sulfides, nitrides, carbides, and titanates.

10. The sodium-ion battery according to claim 8, characterized in that, The positive electrode also includes a conductive agent and a binder.

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