Sodium-ion battery electrolyte containing poly-dtd structure additive, sodium-ion battery and preparation method thereof

Abstract

The application discloses a sodium-ion battery electrolyte containing a multi-DTD structure additive, a sodium-ion battery and a preparation method thereof. The electrolyte comprises a composite sodium salt, a non-aqueous solvent and an additive. The composite sodium salt comprises a first sodium salt and a second sodium salt, and the additive comprises a film-forming additive, a sulfur-containing additive and a multi-DTD structure additive. The second sodium salt is sodium fluorosulfonate. In the electrolyte, the content of the first sodium salt is 0.01-15% by mass percentage, the content of the second sodium salt is 0.01-15% by mass percentage, the content of the film-forming additive is 0.01-5% by mass percentage, the content of the sulfur-containing additive is 0.01-5% by mass percentage, the content of the multi-DTD structure additive is 0.01-5% by mass percentage, and the content of the non-aqueous solvent is 40-90% by mass percentage. By introducing the combination system of sodium fluorosulfonate and the multi-DTD structure additive, the electrode interface characteristics are improved, so that the cycle performance, interface stability and temperature adaptability of the sodium-ion battery containing the combination system are improved.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a sodium-ion battery electrolyte containing multiple DTD structure additives, a sodium-ion battery, and a method for preparing the same. Background Technology

[0002] With the increasing demand for sodium-ion batteries in energy storage, electric transportation, and large-scale energy storage, higher requirements are being placed on the performance of electrolyte systems. Current sodium-ion battery electrolytes typically use sodium hexafluorophosphate (NaPF6) and sodium bis(fluorosulfonyl)imide (NaFSI) as electrolyte salts, combined with carbonate solvent systems. However, this type of system still faces significant challenges in practical applications: (1) Insufficient interfacial stability: NaPF6 is prone to decomposition and electrochemical side reactions during electrochemical processes, resulting in loss of active sodium; (2) The structure of the interface membrane (SEI membrane) is unstable: the solid electrolyte interface (SEI) membrane formed by existing single-function additives (such as FEC, VC, DTD) has a relatively uniform composition and lacks the synergistic protection of multi-dimensional components, resulting in a relatively simple interface membrane structure. (3) Limited cycling and high-temperature performance: The interfacial membrane is prone to rupture or continuous growth under long-term cycling or high-temperature conditions, which leads to increased impedance and affects cycle life; (4) Insufficient low-temperature performance: The low interfacial ion conduction capacity affects the low-temperature discharge performance.

[0003] Although additives such as DTD (ethylene sulfate) can introduce inorganic sulfur species into the negative electrode surface and form an interfacial film containing inorganic components, their molecular structure with single reaction sites makes it difficult to construct a composite interfacial network that combines structural stability and multifunctional properties. Therefore, it is necessary to develop a novel electrolyte system that optimizes molecular structure to achieve precise control of interfacial properties, thereby improving interfacial stability and enhancing the overall electrochemical performance of sodium-ion batteries. Summary of the Invention

[0004] To address the aforementioned technical problems and overcome the shortcomings of existing technologies, this invention provides a sodium-ion battery electrolyte containing multiple DTD structure additives, a sodium-ion battery, and a method for preparing the same. By introducing a combination system of sodium fluorosulfonate and multiple DTD structure additives, the electrode interface characteristics are improved, thereby enhancing the cycle performance, interface stability, and temperature adaptability of the sodium-ion battery containing this combination system.

[0005] To achieve the above objectives, the first aspect of the present invention provides a sodium-ion battery electrolyte containing a multi-DTD structure additive. The electrolyte comprises a composite sodium salt, a non-aqueous solvent, and additives. The composite sodium salt comprises a first sodium salt and a second sodium salt. The additives comprise a film-forming additive, a sulfur-containing additive, and a multi-DTD structure additive. The second sodium salt is sodium fluorosulfonate. By mass percentage, the electrolyte contains 0.01% to 15% of the first sodium salt, 0.01% to 15% of the second sodium salt, 0.01% to 5% of the film-forming additive, 0.01% to 5% of the sulfur-containing additive, 0.01% to 5% of the multi-DTD structure additive, and 40% to 90% of the non-aqueous solvent.

[0006] In some possible implementations, the sodium fluorosulfonate content is preferably 0.3%, and the multi-DTD structure additive content is preferably 1.0%.

[0007] In some possible implementations, the multi-DTD structure additive has the following general formula: R1-(DTD) n -R2; where n is an integer from 2 to 3, DTD represents the vinyl sulfate structural unit, and R1 and R2 are selected from C1-C1 respectively. 10 Hydrocarbon group, fluorinated hydrocarbon group or cyano group.

[0008] In some possible implementations, the first sodium salt is selected from at least one of sodium hexafluorophosphate (NaPF6), sodium tetrafluoroborate (NaBF4), sodium difluorophosphate (NaPO2F2), sodium difluorosulfonamide (NaFSI), sodium bis(oxalate-borate) (NaBOB), sodium difluorooxalate-borate (NaDFOB), and sodium difluorodioxalate-phosphate (NaDFOP).

[0009] In some possible implementations, the sodium fluorosulfonate includes one or more of sodium fluorosulfonate (NaSO3F) and sodium trifluoromethylsulfonate (NaSO3CF3).

[0010] In some implementations, the film-forming additive is selected from one or more of fluoroethylene carbonate (FEC), fluoroethyl methyl carbonate (FEMC), and vinylene carbonate (VC).

[0011] In some implementations, the sulfur-containing additive is selected from one or more of DTD, 1,3-propanesulfonyl lactone (PS), and 1,3-propenesulfonyl lactone (PST).

[0012] In some implementations, the non-aqueous solvent includes one or more of organic esters, sulfones, and dinitrile solvents.

[0013] In some possible implementations, the organic ester is a carbonate and / or carboxylic acid ester, preferably ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4 At least one of butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and ethyl butyrate; the sulfone is at least one of dimethyl sulfoxide, sulfolane, or a derivative thereof; the dinitrile is at least one of adiponitrile, succinic anion, glutaronitrile, or a fluorinated derivative thereof.

[0014] A second aspect of the present invention provides a sodium-ion battery, comprising a positive electrode active material, a separator, and a sodium-ion battery electrolyte containing a multi-DTD structure additive as described in the first aspect.

[0015] In some implementations, the membrane is a porous polymer membrane made of olefin polymers.

[0016] In some implementations, the positive electrode active material includes at least one of layered oxides or polyanionic compounds.

[0017] In some implementations, the layered oxide comprises at least one of sodium nickel iron manganate or sodium copper iron manganate; the polyanionic compound comprises at least one of sodium iron pyrophosphate, sodium vanadium phosphate, and sodium iron pyrophosphate.

[0018] In some implementations, the sodium-ion battery further includes a negative electrode active material, which is at least one of hard carbon, soft carbon, and graphite.

[0019] In some implementations, the sodium-ion battery can also employ a negative electrode-free structure.

[0020] A third aspect of the present invention provides a method for preparing a sodium-ion battery comprising a negative electrode active material, comprising the steps of: S1. Preparation of sodium-ion battery electrolyte containing additives with multiple DTD structures; S2. Prepare the positive and negative electrode plates; S3. Preparation of soft-pack dry cell; S4. The electrolyte prepared in step S1 is injected into the soft-pack dry cell prepared in step S3, and after formation and capacity testing, a sodium-ion soft-pack battery is obtained.

[0021] In some possible implementations, step S1 specifically includes the following steps: under an inert protective atmosphere where the water and oxygen content are both below 10 ppm, a first sodium salt is slowly added to a non-aqueous solvent, followed by the addition of a film-forming additive and a sulfur-containing additive, and the mixture is stirred until a transparent and uniform basic electrolyte is obtained; a second sodium salt and the multi-DTD structure additive are added to the basic electrolyte to obtain a sodium-ion battery electrolyte containing the multi-DTD structure additive.

[0022] In some possible implementations, step S2 specifically includes the following steps for preparing the positive electrode sheet: dispersing the positive electrode active material, positive electrode binder, and conductive agent in an N-methylpyrrolidone (NMP) organic solvent, stirring until stable and uniform, coating it onto an aluminum current collector, drying it, and then preparing an electrode core using a roller press. After cutting and drying, the positive electrode sheet for the soft-pack battery is obtained. The preparation of the negative electrode sheet specifically includes the following steps: uniformly mixing and dispersing the negative electrode active material, first negative electrode binder, second negative electrode binder, and conductive agent in deionized water, then coating it onto an aluminum current collector, drying it, and then preparing an electrode core using a roller press. After cutting and drying, the negative electrode sheet for the soft-pack battery is obtained.

[0023] In some possible implementations, step S3 specifically includes the following steps: stacking the positive electrode, separator, and negative electrode in sequence, so that the separator is positioned between the positive electrode and the negative electrode to provide isolation, and then winding and drying to produce a soft-pack dry cell.

[0024] In some possible implementations, in step S2, the positive electrode binder, the first negative electrode binder, or the second negative electrode binder is selected from at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), or polyethylene oxide (PEO); the conductive agent is selected from one or more of carbon nanotubes (CNT), conductive graphite, conductive carbon fiber, acetylene black, or conductive carbon black.

[0025] In some possible implementations, in step S2, the weight ratio of the positive electrode active material, the positive electrode binder, and the conductive agent is 94~96:1~3:2~4; and the weight ratio of the negative electrode active material, the first negative electrode binder, the second negative electrode binder, and the conductive agent is 92~98:0.1~3:0.1~3:0.1~3.

[0026] Compared with the prior art, the present invention has the following beneficial effects: (1) This invention introduces sodium fluorosulfonate and a multi-DTD structure additive into the electrolyte. Both participate in the interfacial reaction during the electrochemical process, which helps to form a composite interfacial film containing inorganic components and organic structures on the electrode surface. The multi-DTD structure additive has multiple reaction sites and can participate in multi-point reaction processes at the electrode interface, which helps to form a more stable interfacial layer.

[0027] (2) Based on the above-mentioned interface regulation effect, the electrolyte system of the present invention exhibits good electrochemical performance in practical applications, including but not limited to: improving capacity retention during cycling; reducing the growth trend of interface impedance; improving the working stability of the battery under different temperature conditions; wherein, the formation of the composite interface film helps to reduce interface side reactions, thereby improving the overall performance of the sodium-ion battery of the present invention to a certain extent.

[0028] (3) The electrolyte system of the present invention has good applicability over a wide temperature range and can maintain relatively stable electrochemical performance under different temperature environments. Moreover, the electrolyte of the present invention is applicable to a variety of sodium-ion battery systems and has a wide range of applications. Detailed Implementation

[0029] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Where specific conditions are not specified in the examples, they can be performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all commercially available standard products.

[0031] Existing electrolyte systems typically face challenges in practical applications, including insufficient interfacial stability, unstable interfacial film structures, limited cycle performance and high-temperature performance, and insufficient low-temperature performance. In particular, existing single-functional additives (such as FEC, VC, and DTD) form solid electrolyte interphase (SEI) films with relatively homogeneous composition, lacking synergistic protection from multidimensional components. This results in a relatively simple interfacial film structure, leading to insufficient interfacial stability and consequently affecting the overall performance of sodium-ion batteries based on this electrolyte system. Although additives such as DTD (ethylene sulfate) can introduce inorganic sulfur species into the negative electrode surface, forming an interfacial film containing inorganic components, their molecular structure with single reaction sites makes it difficult to construct a composite interfacial network that combines structural stability and multifunctional properties.

[0032] In view of this, the first aspect of the present invention provides a sodium-ion battery electrolyte containing a multi-DTD structure additive, comprising a composite sodium salt, a non-aqueous solvent, and additives; the composite sodium salt comprises a first sodium salt and a second sodium salt; wherein the additives comprise a film-forming additive, a sulfur-containing additive, and a multi-DTD structure additive, and the second sodium salt is sodium fluorosulfonate; wherein the first sodium salt accounts for 0.01% to 15% of the total mass of the electrolyte, the second sodium salt accounts for 0.01% to 15% of the total mass of the electrolyte, the film-forming additive accounts for 0.01% to 5% of the total mass of the electrolyte, the sulfur-containing additive accounts for 0.01% to 5% of the total mass of the electrolyte, the multi-DTD structure additive accounts for 0.01% to 5% of the total mass of the electrolyte, and the non-aqueous solvent accounts for 40% to 90% of the total mass of the electrolyte. Preferably, the sodium fluorosulfonate content accounts for 0.3% of the total mass of the electrolyte, and the multi-DTD structure additive content is preferably 1.0% of the total mass of the electrolyte.

[0033] Therefore, this invention improves the cycle performance, interface stability and temperature adaptability of sodium-ion batteries containing this combination system by the synergistic effect of composite sodium salt and additives, namely by introducing sodium fluorosulfonate into the composite sodium salt system and introducing multi-DTD structure additives into the additive system.

[0034] The principle by which the present invention achieves the above-mentioned effects will be explained below: This invention introduces sodium fluorosulfonate and a multi-DTD structure additive into the electrolyte. Both participate in interfacial reactions during electrochemical processes, facilitating the formation of a composite interfacial film containing inorganic components and organic structures on the electrode surface. The multi-DTD structure additive has multiple reaction sites, participating in multi-point reaction processes at the electrode interface, contributing to a more stable interfacial layer. Compared to a single DTD, the multi-DTD structure is more conducive to maintaining the interfacial structure, improving the instability of the interfacial film structure in traditional single-additive systems, and reducing the likelihood of interfacial film rupture or reconstruction during cycling. Simultaneously, the introduction of sodium fluorosulfonate helps increase the proportion of inorganic components at the interface, further enhancing the stability of the interfacial film. Therefore, the electrolyte system of this invention can maintain a relatively stable interfacial state during charge-discharge cycling. Furthermore, at low temperatures, the stability of the interfacial structure helps maintain ion conduction; at higher temperatures, the composite interfacial film helps suppress side reactions. Therefore, this electrolyte system can maintain relatively stable electrochemical performance under different temperature environments.

[0035] It should also be noted that in this invention, the amount of the second sodium salt and the multi-DTD structure additive has a significant impact on battery performance. Their effects do not increase linearly with increasing amounts, but rather there is an optimal range for addition. When the amounts of the second sodium salt and the multi-DTD structure additive are low, their participation in the reaction at the electrode interface is limited, making it difficult to form a continuous, dense, and stable interfacial film structure on the electrode surface. At this point, the interfacial film coverage is insufficient, leaving a significant amount of exposed active surface. Electrolyte decomposition, side reactions, and active sodium loss are difficult to effectively suppress, resulting in limited improvements in cycle performance, rate performance, and high / low temperature performance.

[0036] When the amounts of the second sodium salt and the multi-DTD structure additive are within a moderate range, they synergistically interact during the electrochemical process: the second sodium salt preferentially decomposes to form an interface structure rich in inorganic components, while the multi-DTD structure additive participates in interfacial polymerization or cross-linking reactions through its multiple reaction sites, thereby constructing a composite interface film on the electrode surface that combines the stability of inorganic components with the flexibility of organic structures. This interface film exhibits good compactness, stability, and ion conductivity, effectively reducing interfacial side reactions, inhibiting impedance growth, and promoting Na+... + Transport at the interface allows the battery to exhibit optimal overall electrochemical performance.

[0037] However, when the amount of the second sodium salt and / or multi-DTD structure additives is too high, the preferential interfacial reaction becomes too vigorous, easily forming an excessively thick or locally enriched interfacial film on the electrode surface. On the one hand, an excessively thick interfacial film will prolong the Na... + Migration pathways increase interfacial impedance, leading to a decrease in rate performance and low-temperature performance. On the other hand, excessive additives may trigger additional side reactions or generate more byproducts, exacerbating interfacial instability under high-temperature conditions, thereby preventing the overall performance of the battery from improving or even causing it to decline.

[0038] Therefore, the amount of the second sodium salt and the multi-DTD structure additive should not be as high as possible, but rather a balance should be achieved between interface stability and ion transport performance within a certain range, so as to achieve the optimal battery performance.

[0039] In some embodiments, the multi-DTD structure additive has the following general formula: R1-(DTD) n -R2; where n is an integer from 2 to 3, DTD represents the vinyl sulfate structural unit, and R1 and R2 are selected from C1-C1 respectively. 10 Hydrocarbon group, fluorinated hydrocarbon group or cyano group.

[0040] In some embodiments, the first sodium salt is selected from at least one of NaPF6, NaBF4, NaPO2F2, NaFSI, NaBOB, NaDFOB, and NaDFOP.

[0041] In some embodiments, sodium fluorosulfonate includes one or more of NaSO3F and NaSO3CF3.

[0042] In some of these embodiments, the film-forming additive is selected from one or more of FEC, FEMC, and VC.

[0043] In some of these embodiments, the sulfur-containing additive is selected from one or more of DTD, PS, and PST.

[0044] In some embodiments, the non-aqueous solvent includes one or more of organic esters, sulfones, and dinitrile solvents. The organic esters are carbonates and / or carboxylic acid esters, preferably ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4 At least one of butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and ethyl butyrate; at least one of dimethyl sulfoxide, sulfolane, or their derivatives; and at least one of adiponitrile, succinic anhydride, glutaronitrile, or their fluorinated derivatives.

[0045] A second aspect of the present invention provides a sodium-ion battery, comprising a positive electrode active material, a separator, and a sodium-ion battery electrolyte containing a multi-DTD structure additive as described in the first aspect.

[0046] In some embodiments, the membrane is a porous polymer membrane made of olefin polymers. Specifically, it is at least one of porous polymer membranes made of olefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, and ethylene / methacrylate copolymer.

[0047] In some embodiments, the positive electrode active material includes at least one of layered oxides or polyanionic compounds. The layered oxides include at least one of sodium nickel iron manganese oxide or sodium copper iron manganese oxide; the polyanionic compounds include at least one of sodium iron pyrophosphate, sodium vanadium phosphate, and sodium iron pyrophosphate.

[0048] In some embodiments, the sodium-ion battery further includes a negative electrode active material, which is at least one of hard carbon, soft carbon, and graphite.

[0049] In some embodiments, the sodium-ion battery may also employ a negative electrode-free structure. This negative electrode-free structure is not "completely without a negative electrode" in the traditional sense, but rather omits the pre-coated negative electrode active material and uses only a current collector (such as copper foil, aluminum foil, or modified aluminum current collector) as the substrate for sodium metal deposition.

[0050] A third aspect of the present invention provides a method for preparing a sodium-ion battery comprising a negative electrode active material, as described in the second aspect, specifically including the following steps: (1) In a glove box filled with argon (O2 < 10 ppm, H2O < 10 ppm), the first sodium salt is slowly added to a non-aqueous solvent; then film-forming additives and sulfur-containing additives are added and stirred evenly to obtain a transparent and uniform basic electrolyte; the second sodium salt and the multi-DTD structure additives are added to the basic electrolyte to prepare an electrolyte. (2) The positive electrode active material, positive electrode binder, and conductive agent are dispersed in N-methylpyrrolidone (NMP) organic solvent, stirred until stable and uniform, coated on aluminum current collector, dried, and then the electrode core is prepared by a roller press. After cutting and drying, the positive electrode sheet of the soft pack battery is obtained. The positive electrode binder is selected from at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), or polyethylene oxide (PEO), preferably polyvinylidene fluoride (PVDF); the conductive agent is selected from one or more of carbon nanotubes (CNT), conductive graphite, conductive carbon fiber, acetylene black, or conductive carbon black; the weight ratio of positive electrode active material, positive electrode binder, and conductive agent is 94 ~ 96:1 ~ 3:2 ~ 4. (3) The negative electrode active material, the first negative electrode binder, the second negative electrode binder, and the conductive agent are uniformly mixed and dispersed in deionized water, then coated on an aluminum current collector, dried, and then the electrode core is prepared by a roller press. After cutting and drying, the negative electrode sheet of the soft-pack battery is obtained; wherein, the first negative electrode binder and the second negative electrode binder are selected from at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), or polyethylene oxide (PEO), wherein the first negative electrode binder is preferably styrene-butadiene rubber (SBR), and the second negative electrode binder is preferably sodium carboxymethyl cellulose (CMC); the conductive agent is selected from one or more of carbon nanotubes (CNT), conductive graphite, conductive carbon fiber, acetylene black, or conductive carbon black; the weight ratio of the negative electrode active material, the first negative electrode binder, the second negative electrode binder, and the conductive agent is 92 ~ 98: 0.1 ~ 3: 0.1 ~ 3: 0.1 ~ 3; (4) Stack the positive electrode, separator and negative electrode in sequence so that the separator is between the positive electrode and the negative electrode to play a role in isolation. Then wind and dry to make a soft-pack dry cell. (5) The electrolyte prepared in step (1) is injected into the soft-pack dry cell prepared in step (4), and after formation and capacity testing, sodium-ion soft-pack battery is obtained.

[0051] The present invention will be further illustrated below through specific embodiments and comparative examples. Example 1 describes the preparation of the basic electrolyte; Examples 2-10 describe the preparation of the sodium-ion battery electrolyte containing multiple DTD structure additives according to the present invention; Comparative Examples 1-4 describe the preparation of sodium-ion battery electrolytes according to comparative examples of the present invention; Examples 11-19 describe the preparation of sodium-ion batteries based on the electrolytes of Examples 2-10; and Comparative Examples 5-8 describe the preparation of sodium-ion batteries based on the electrolytes of Comparative Examples 1-4.

[0052] Example 1 In an argon-filled glove box (O2 < 10 ppm, H2O < 10 ppm), ethylene carbonate (EC), propylene carbonate (PC), and ethyl methyl carbonate (EMC) were mixed uniformly in a mass ratio of 3:3:4 as a non-aqueous solvent. Sodium hexafluorophosphate (NaPF6) and sodium difluorosulfonamide (NaFSI) were added to the above mixed solvent, so that the total content of the two in the electrolyte was 6.0 wt%, wherein the mass ratio of sodium hexafluorophosphate (NaPF6) to sodium difluorosulfonamide (NaFSI) was 6:4. Subsequently, 0.3 wt% sodium difluorophosphate (NaPO2F2), 1.0 wt% fluoroethylene carbonate (FEC), and 0.5 wt% 1,3-propanesulfonyl lactone (PS) were added, and the mixture was stirred evenly to obtain a transparent and homogeneous electrolyte. The non-aqueous solvent was in the balance, and the sum of the mass percentages of all components in the electrolyte was 100%.

[0053] Example 2 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3F and 0.5% 2-DTD were added to obtain the electrolyte of this example.

[0054] Example 3 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3F and 0.5% 3-DTD were added to obtain the electrolyte of this example.

[0055] Example 4 In the basic electrolyte prepared in Example 1 of this invention, 0.1% NaSO3F and 0.5% 3-DTD were added to obtain the electrolyte of this example.

[0056] Example 5 In the basic electrolyte prepared in Example 1 of this invention, 0.5% NaSO3F and 0.5% 3-DTD were added to obtain the electrolyte of this example.

[0057] Example 6 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3F and 1.0% 3-DTD were added to obtain the electrolyte of this example.

[0058] Example 7 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3F and 3.0% 3-DTD were added to obtain the electrolyte of this example.

[0059] Example 8 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3F and 5.0% 3-DTD were added to obtain the electrolyte of this example.

[0060] Example 9 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3CF3 and 1.0% 3-DTD were added to obtain the electrolyte of this example.

[0061] Example 10 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3CF3 and 1.0% 2-DTD were added to obtain the electrolyte of this example.

[0062] Comparative Example 1 The basic electrolyte prepared in Example 1 of this invention is used as Comparative Example 1.

[0063] Comparative Example 2 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3F and 0.5% DTD were added to obtain the electrolyte of this comparative example.

[0064] Comparative Example 3 In the basic electrolyte prepared in Example 1 of this invention, 1.0% of 3-DTD and 0.5% of DTD were added to obtain the electrolyte of this comparative example.

[0065] Comparative Example 4 In the basic electrolyte prepared in Example 1 of this invention, 0.3% NaSO3CF3 and 0.5% DTD were added to obtain the electrolyte of this comparative example.

[0066] Example 11 (1) Preparation of positive electrode: The positive electrode active material sodium iron pyrophosphate, the binder polyvinylidene fluoride (PVDF), and the conductive agent acetylene black are mixed at a mass ratio of 95:2.5:2.5, and NMP (N Methylpyrrolidone (MPP) is used as a solvent to prepare a slurry. The slurry is stirred until it is stable and uniform under the action of a vacuum mixer. Then it is evenly coated on an aluminum current collector, dried, and then the electrode core is prepared by a roller press. After cutting and drying, the positive electrode of the soft pack battery is obtained.

[0067] (2) Negative electrode preparation: The negative electrode active materials hard carbon, conductive carbon black, sodium carboxymethyl cellulose (CMC) and styrene-butadiene rubber (SBR) are mixed in a mass ratio of 94:2:2:2. Deionized water is used as a solvent to prepare a slurry. The slurry is stirred until it is stable and uniform under the action of a vacuum mixer. Then it is evenly coated on aluminum current collector. After drying, the electrode core is prepared by a roller press. After cutting and drying, the negative electrode sheet of soft pack battery is obtained.

[0068] (3) Preparation of soft-pack battery: The above positive electrode, separator and negative electrode are stacked in order, so that the separator is between the positive electrode and the negative electrode to play a role in isolation. Then, they are wound and dried to make soft-pack dry cell, which is convenient for subsequent preparation of electrolyte and liquid injection.

[0069] (4) Sodium-ion battery preparation: The electrolyte prepared in Example 2 of this invention is injected into a soft-pack dry cell, and after formation and capacity testing, a sodium-ion soft-pack battery is obtained, which is the sodium-ion battery of this embodiment.

[0070] Examples 12-19 The steps for preparing the positive electrode, negative electrode, and pouch cell in Examples 12-19 of this invention are the same as in Example 11. The electrolytes prepared in Examples 3-10 of this invention are injected into the pouch cells to obtain sodium-ion pouch batteries, i.e., sodium-ion batteries of Examples 12-19.

[0071] Comparative Examples 5-8 The methods and steps for preparing the positive electrode, negative electrode, and pouch cell in the comparative examples of this invention are the same as in Example 11. The electrolytes prepared in Comparative Examples 1-4 of this invention are injected into the pouch cells to obtain sodium-ion pouch cells, i.e., sodium-ion batteries in Comparative Examples 5-8.

[0072] The sodium-ion batteries prepared in Examples 11-19 and Comparative Examples 5-8 were subjected to room temperature cycling performance tests, rate charging tests, low-temperature discharge performance tests, and high-temperature storage performance tests, respectively, under the following test conditions: (1) Room temperature cycle test: The prepared sodium-ion battery was placed in a constant temperature room with an ambient temperature of 25°C and charged with a constant current and constant voltage of 1C and 3.4V until the cutoff current was 0.05C. Then it was discharged with a constant current of 1C until the voltage was 1.5V. After 500 cycles, the capacity retention rate was recorded. The capacity retention rate of the nth cycle (%) = (specific capacity of the nth cycle discharge / specific capacity of the first cycle discharge) × 100%.

[0073] 2) Rate charging test: The prepared sodium-ion battery was placed in a constant temperature room with an ambient temperature of 25°C. First, a baseline capacity test was performed: the battery was charged at a constant current of 0.2C to the cutoff voltage of 3.4V, and after standing for 10 minutes, it was discharged at a constant current of 0.2C to the cutoff voltage of 1.5V. Then, it was charged at a constant current of 0.2C to the cutoff voltage of 3.4V. The charging capacity was recorded as the baseline capacity Q0.2C.

[0074] Then, a rate charging test was performed: the battery was discharged at a constant current of 0.2C to 1.5V and left to stand for 10 minutes; then, constant current charging was performed sequentially at different charging rates (the charging current was adjusted sequentially to 0.5C, 1C, and 2C, and constant current charging was performed to 3.4V; after each charging, the battery was left to stand for 10 minutes, and then discharged at a constant current of 0.2C to 1.5V, and the corresponding charging capacity Q was recorded). C (x = 0.5, 1, 2). The cycle can be repeated 1-3 times at each leverage, and the average value is taken. Capacity retention rate is calculated as follows: Capacity retention rate (%) at a certain leverage = (Q C / Q0.2C) × 100%.

[0075] (3) Low-temperature discharge test: The prepared sodium-ion battery was placed in a high-low temperature chamber. First, it was charged at 25°C with a current of 0.5C and a voltage of 3.4V under constant current and constant voltage until the cutoff current was 0.05C. Then, it was discharged at a constant current of 0.5C until the voltage was 1.5V, and the discharge capacity was recorded as C0. After fully charging the sodium-ion battery according to the above charging method, the high-low temperature chamber was adjusted to -20°C. After the surface temperature of the sodium-ion battery reached -20°C, it was discharged at a constant current of 0.5C until the voltage was 1.5V, and the discharge capacity was recorded as C1. The low-temperature discharge capacity retention rate of the sodium-ion battery was calculated as follows: Low-temperature discharge capacity retention rate (%) = (C1 / C0) × 100%.

[0076] (4) High-temperature storage performance test: The prepared sodium-ion battery was placed in a high-low temperature chamber. First, it was charged at 25°C with a current of 1C and a voltage of 3.4V under constant current and constant voltage until the cutoff current was 0.05C. Then, it was discharged at a constant current of 1C until the voltage was 1.5V, and the discharge capacity D0 was recorded. After the sodium-ion battery was fully charged according to the above charging method, it was stored at 60°C for 15 days. After the storage was completed, it was discharged at a constant current of 1C until 1.5V, and the discharge capacity D1 was recorded. The capacity retention rate of the sodium-ion battery after 30 days of storage at 60°C was calculated as follows: Capacity retention rate (%) after 30 days of storage at 60°C = (D1 / D0) × 100%.

[0077] The test results are shown in Table 1 below:

[0078] As can be seen from the above test results, compared with Comparative Examples 5-8, the battery of the present invention, after introducing sodium fluorosulfonate and multi-DTD structure additives, exhibits excellent comprehensive performance in terms of cycle performance, rate performance, and high and low temperature performance. Specifically, the room temperature cycle test results show that after 500 cycles at 25°C, the capacity retention rate increased from 60%~73% in the comparative examples to 80%~92%; the rate charging performance test results show that, compared with the 0.2C benchmark, at a charging rate of 2C (discharge holding at 0.2C), the capacity retention rate increased from 53%~64% in the comparative examples to 78%~90%; the low temperature discharge test results show that at -20°C, the discharge capacity retention rate increased from 43%~54% in the comparative examples to 61%~75%; and the high temperature storage performance test results show that after 30 days of storage at 60°C, the capacity retention rate increased from 53%~67% in the comparative examples to 70%~82%.

[0079] Furthermore, the experimental results of Examples 11-12 and 18-19 show that the sodium-ion batteries prepared with the electrolyte system using 3-DTD additives have better performance than those using 2-DTD additives, indicating that the multiple reaction sites of the multi-DTD structure help to improve the interfacial kinetic performance.

[0080] The experimental results of Examples 12-17 show that as the content of sodium fluorosulfonate and multi-DTD structure additives increases, the various performance characteristics of the battery initially improve gradually. However, once the content exceeds a certain value, the improvement gradually decreases, exhibiting a diminishing marginal effect. This indicates that there is a reasonable content window for sodium fluorosulfonate and multi-DTD structure additives.

[0081] In Example 15 of this invention, when the amount of NaSO3F added is 0.3% and the amount of 3-DTD additive added is 1.0%, the battery performance is optimal under the test conditions of this invention.

[0082] Comparative Examples 5-8 show that without the use of sodium fluorosulfonate and multi-DTD structure additives, the performance level of the embodiments of the present invention could not be achieved by using sodium fluorosulfonate or multi-DTD structure additives alone. This indicates that sodium fluorosulfonate and multi-DTD structure have a synergistic effect in the present invention. Only by working together can excellent battery cycle performance, rate performance and high and low temperature performance be achieved. Neither can be omitted. Only by introducing both at the same time can the good comprehensive performance described in the present invention be obtained.

[0083] This invention introduces sodium fluorosulfonate and a multi-DTD structure additive into the electrolyte. Both participate in interfacial reactions during electrochemical processes, facilitating the formation of a composite interfacial film containing inorganic components and organic structures on the electrode surface, thus enhancing the stability of the interfacial film. The electrolyte system of this invention can maintain a relatively stable interfacial state during charge-discharge cycles. Furthermore, at low temperatures, the stability of the interfacial structure helps maintain ion conduction; at higher temperatures, the composite interfacial film helps suppress side reactions. Therefore, this electrolyte system can maintain relatively stable electrochemical performance under different temperature environments.

[0084] The above description is only a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any simple modifications, equivalent changes and alterations made under the inventive concept of the present invention based on the content of the present invention specification, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A sodium-ion battery electrolyte containing additives with multiple DTD structures, characterized in that, The electrolyte comprises a composite sodium salt, a non-aqueous solvent, and additives; the composite sodium salt comprises a first sodium salt and a second sodium salt, the additives comprise a film-forming additive, a sulfur-containing additive, and a multi-DTD structure additive, and the second sodium salt is sodium fluorosulfonate; by mass percentage, the electrolyte contains 0.01% to 15% of the first sodium salt, 0.01% to 15% of the second sodium salt, 0.01% to 5% of the film-forming additive, 0.01% to 5% of the sulfur-containing additive, 0.01% to 5% of the multi-DTD structure additive, and 40% to 90% of the non-aqueous solvent.

2. The sodium-ion battery electrolyte containing multi-DTD structure additives according to claim 1, characterized in that, The sodium fluorosulfonate content is 0.3%, and the multi-DTD structure additive content is 1.0%.

3. The sodium-ion battery electrolyte containing multi-DTD structure additives according to claim 1, characterized in that, The multi-DTD structure additive has the following general formula: R1-(DTD) n -R2; where n is an integer from 2 to 3, DTD represents the vinyl sulfate structural unit, and R1 and R2 are selected from C1-C1 respectively. 10 Hydrocarbon group, fluorinated hydrocarbon group or cyano group.

4. The sodium-ion battery electrolyte containing multi-DTD structure additives according to claim 1, characterized in that, The first sodium salt is selected from at least one of sodium hexafluorophosphate, sodium tetrafluoroborate, sodium difluorophosphate, sodium difluorosulfonamide, sodium bis(oxalate)borate, sodium difluorooxalateborate, and sodium difluorodioxalate phosphate.

5. The sodium-ion battery electrolyte containing multi-DTD structure additives according to claim 1, characterized in that, The sodium fluorosulfonate includes one or more of sodium fluorosulfonate and sodium trifluoromethylsulfonate.

6. The sodium-ion battery electrolyte containing multi-DTD structure additives according to claim 1, characterized in that, The film-forming additive is selected from one or more of fluoroethylene carbonate, fluoroethyl methyl carbonate, and vinylene carbonate.

7. The sodium-ion battery electrolyte containing multi-DTD structure additives according to claim 1, characterized in that, The sulfur-containing additive is selected from one or more of DTD, 1,3-propanesulfonyl lactone, and 1,3-propenesulfonyl lactone.

8. The sodium-ion battery electrolyte containing multi-DTD structure additives according to claim 1, characterized in that, The non-aqueous solvent includes one or more of organic esters, sulfones, and dinitrile solvents.

9. The sodium-ion battery electrolyte containing multi-DTD structure additives according to claim 8, characterized in that, The organic esters are carbonates and / or carboxylic acid esters, preferably ethylene carbonate, propylene carbonate, butene carbonate, dimethyl carbonate, diethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, 1,4 At least one of butyrolactone, methyl formate, ethyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, and ethyl butyrate; the sulfone is at least one of dimethyl sulfoxide, sulfolane, or a derivative thereof; the dinitrile is at least one of adiponitrile, succinic anion, glutaronitrile, or a fluorinated derivative thereof.

10. A sodium-ion battery, characterized in that, Includes positive electrode active material, separator, and sodium-ion battery electrolyte containing multi-DTD structure additives as described in any of claims 1-9.

11. The sodium-ion battery according to claim 10, characterized in that, The diaphragm is a porous polymer membrane made of olefin polymers.

12. The sodium-ion battery according to claim 10, characterized in that, The positive electrode active material includes at least one of layered oxides or polyanionic compounds.

13. The sodium-ion battery according to claim 10, characterized in that, The layered oxide includes at least one of sodium nickel iron manganate or sodium copper iron manganate; the polyanionic compound includes at least one of sodium iron pyrophosphate, sodium vanadium phosphate, and sodium iron pyrophosphate.

14. The sodium-ion battery according to claim 10, characterized in that, It also includes a negative electrode active material, wherein the negative electrode active material is at least one of hard carbon, soft carbon, and graphite.

15. A method for preparing a sodium-ion battery according to claim 14, characterized in that, Including the following steps: S1. Preparation of sodium-ion battery electrolyte containing additives with multiple DTD structures; S2. Prepare the positive and negative electrode plates; S3. Preparation of soft-pack dry cell; S4. The electrolyte prepared in step S1 is injected into the soft-pack dry cell prepared in step S3, and sodium-ion soft-pack battery is obtained through formation and capacity testing.

16. The method for preparing a sodium-ion battery according to claim 15, characterized in that, Step S1 specifically includes the following steps: Under an inert protective atmosphere where the water and oxygen content are both below 10 ppm, the first sodium salt is slowly added to a non-aqueous solvent, followed by the addition of a film-forming additive and a sulfur-containing additive, and the mixture is stirred until a transparent and uniform basic electrolyte is obtained; the second sodium salt and the multi-DTD structure additive are added to the basic electrolyte to obtain a sodium-ion battery electrolyte containing the multi-DTD structure additive.

17. The method for preparing a sodium-ion battery according to claim 15, characterized in that, In step S2, the preparation of the positive electrode sheet specifically includes the following steps: dispersing the positive active material, positive binder, and conductive agent in an N-methylpyrrolidone organic solvent, stirring it until stable and uniform, coating it onto an aluminum current collector, drying it, and then preparing an electrode core using a roller press. After cutting and drying, the positive electrode sheet of the soft-pack battery is obtained. The preparation of the negative electrode sheet specifically includes the following steps: uniformly mixing and dispersing the negative active material, first negative binder, second negative binder, and conductive agent in deionized water, then coating it onto an aluminum current collector, drying it, and then preparing an electrode core using a roller press. After cutting and drying, the negative electrode sheet of the soft-pack battery is obtained.

18. The method for preparing a sodium-ion battery according to claim 15, characterized in that, Step S3 specifically includes the following steps: stacking the positive electrode, separator, and negative electrode in sequence, so that the separator is placed between the positive electrode and the negative electrode to play an isolation role, and then winding and drying to make a soft-pack dry cell.

19. The method for preparing a sodium-ion battery according to claim 17, characterized in that, The positive electrode binder, the first negative electrode binder, or the second negative electrode binder is selected from at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, or polyethylene oxide; the conductive agent is selected from one or more of carbon nanotubes, conductive graphite, conductive carbon fiber, acetylene black, or conductive carbon black.

20. The method for preparing a sodium-ion battery according to claim 17, characterized in that, The weight ratio of the positive electrode active material, positive electrode binder, and conductive agent is 94~96:1~3:2~4; the weight ratio of the negative electrode active material, first negative electrode binder, second negative electrode binder, and conductive agent is 92~98:0.1~3:0.1~3:0.1~3.

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