Electrolyte additive and application thereof

Abstract

The invention provides an electrolyte additive and application thereof, and belongs to the technical field of sodium ion battery manufacturing. According to the invention, an additive a thiophosphoramide compound with a specific structure and a conventional additive are combined as an electrolyte additive; s and N atoms are introduced into a phosphate framework by the additive a thiophosphoramide compound, an inorganic interfacial film rich in Na2S, Na3N and Na3P is generated in the formation stage, the solid electrolyte interfacial film contains more inorganic components and less organic components, has higher high temperature resistance, improves the safety performance of the battery, and is used cooperatively with a conventional additive, so that the battery has a good application prospect. A more uniform and compact SEI film with smaller impedance is formed, so that the safety performance of the battery is further improved, and the obtained sodium ion battery has good flame retardant property and safety performance.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion battery manufacturing, in particular to an electrolyte additive and application thereof. BACKGROUND

[0002] Sodium ion batteries (SIBs) are considered as an important supplement or alternative technology of lithium ion batteries (LIBs) due to their abundant resources and low cost, but their safety performance still has a significant short board, especially in terms of thermal runaway, interface stability and actual application verification. At present, researchers develop flame-retardant electrolytes, such as in-situ polymerization flame-retardant quasi-solid-state electrolyte (TPQSE), which can combine cross-linked network and flame retardant (PFPN) to improve safety performance; in the interface engineering optimization, the desolvation energy barrier is reduced by regulating the solvation structure (such as anion enrichment strategy), and a uniform SEI layer is constructed; and in the multi-dimensional safety evaluation system, a three-dimensional model covering thermal runaway temperature, gas generation characteristics and explosion risk is established.

[0003] In order to improve the safety performance of sodium ion batteries, electrolyte additives are usually introduced into the electrolyte to improve the flame retardant performance and safety performance, and the prior art CN114300745 A discloses a non-aqueous electrolyte, a secondary battery and the application of thiophosphoramide as an electrolyte additive. The invention combines thiophosphoramide and 1,3-propane sulfonate as an electrolyte additive. The thiophosphoramide compound helps to form an SEI film on the negative electrode interface, prevents the electrolyte from entering the negative electrode, and makes the battery have excellent high-temperature cycle and high-temperature storage performance. At the same time, the thiophosphoramide compound substituted by halogen atoms has a good flame-retardant effect on the battery. However, it is mainly suitable for the field of lithium ion batteries, and the improvement of the flame retardant property and safety performance of the battery by the thiophosphoramide compound as an electrolyte additive still needs to be further improved. SUMMARY

[0004] The technical problem to be solved by the present application is to overcome the problem that the effect of improving the flame retardant and safety performance of sodium ion batteries by the electrolyte additive in the prior art needs to be further improved. The present application provides an electrolyte additive, which comprises an additive a thiophosphoramide compound with a specific structure and a conventional additive. The additive a thiophosphoramide compound introduces S and N atoms on the phosphate ester skeleton, participates in the formation of an inorganic interface film rich in Na2S, Na3N and Na3P in the formation stage, has stronger high-temperature resistance, cooperates with the conventional additive to form a more uniform and dense SEI film with smaller impedance, and improves the safety performance of the battery. And using propylene carbonate with good high-temperature stability and good film-forming property as an electrolyte solvent further improves the safety performance, and the obtained sodium ion battery has good flame retardant performance and safety performance.

[0005] Another object of the present application is to provide a sodium ion battery electrolyte.

[0006] Another object of the present application is to provide a sodium ion battery.

[0007] The above object of the present application is achieved by the following technical solutions. The present application provides an electrolyte additive, which comprises an additive a and an additive b; the additive a comprises a thiophosphamide compound shown in structural formula 1:

[0008] Structural formula 1 Wherein, R1, R2, R3, R4, R5 and R6 are independently selected from one of H, halogen atom, alkyl group with carbon atom number of 1-10, and the H of the alkyl group can be partially or totally substituted by one or more of halogen atom, cyano group, carboxyl group and sulfonic acid group; The additive b comprises one or more of ethylene carbonate, fluoroethylene carbonate, vinyl ethylene carbonate, 1,3-propane sulfonic acid lactone, propylene sulfite, vinyl sulfate, 4-methyl ethylene sulfite, sodium difluorophosphate, succinic anhydride, adiponitrile and 1,3,6-hexane tricyanide.

[0009] Preferably, R1, R2, R3, R4, R5 and R6 are independently selected from one of H, alkyl group with carbon atom number of 1-4.

[0010] Preferably, the additive b is fluoroethylene carbonate, vinyl sulfate, sodium difluorophosphate. When sodium difluorophosphate is used as an additive, it can participate in the formation of a more compact solid interface film, and can improve the rate, low temperature, cycle and high temperature performance of the battery.

[0011] Preferably, the weight ratio of the additive a and the additive b is 5:2-5; specifically, it can be 5:2, 5:3, 5:4, 5:5, and further preferably 5:3.

[0012] The present application also protects a sodium ion battery electrolyte, which comprises a sodium salt electrolyte, an electrolyte additive and an electrolyte solvent, and the electrolyte additive is the above-mentioned electrolyte additive.

[0013] Specifically, the electrolyte additive accounts for 7-10% of the total mass of the sodium ion battery electrolyte, specifically, it can be 7%, 8%, 9%, 10%, and preferably 8%.

[0014] Specifically, the sodium salt electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium bisfluorosulfonylimide, sodium tetrafluoroborate, sodium difluorophosphate, sodium bisoxalate borate and sodium bisfluoroxalate borate.

[0015] Specifically, the mass of the sodium salt electrolyte accounts for 10-20% of the total mass of the sodium ion battery electrolyte, and can be 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, 20%, preferably 14%.

[0016] Preferably, the sodium salt electrolyte is sodium hexafluorophosphate and sodium bisfluorosulfonylimide.

[0017] Specifically, the mass ratio of sodium hexafluorophosphate and sodium bisfluorosulfonylimide is 1-3:1, and can be 1:1, 3:2, 2:1, 5:2, 3:1, preferably 1:1 and 5:2.

[0018] Specifically, the electrolyte solvent includes at least one of a cyclic carbonate solvent.

[0019] Specifically, the cyclic carbonate solvent is one or more of vinyl carbonate, propylene carbonate and butylene carbonate.

[0020] Preferably, the electrolyte solvent is propylene carbonate (PC). Propylene carbonate (PC) has good high-temperature stability (boiling point about 240℃), good film-forming properties (participating in forming a stable SEI film), and electrochemical stability (strong oxidation resistance) and other characteristics.

[0021] Specifically, the electrolyte solvent accounts for 70-80% of the total mass of the sodium ion battery electrolyte, and can be 70%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, preferably 78%.

[0022] The application also protects a preparation method of the above-mentioned sodium ion battery electrolyte, including the following steps: stirring and mixing sodium salt electrolyte, electrolyte additives and electrolyte solvent under an inert atmosphere to obtain the sodium ion battery electrolyte.

[0023] Preferably, the inert atmosphere is at least one of a nitrogen atmosphere, an argon atmosphere and a helium atmosphere.

[0024] The application also protects a sodium ion battery including a positive electrode sheet, a negative electrode sheet, an electrolyte and a battery separator, wherein the electrolyte is the above-mentioned sodium ion battery electrolyte.

[0025] Specifically, the battery separator includes at least one of a porous polymer film prepared from ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer and ethylene / methacrylic acid copolymer and other olefin polymers.

[0026] Specifically, the preparation of the positive electrode sheet includes the following steps: dispersing the positive electrode active material, the binder, and the conductive agent in NMP (N-methyl pyrrolidone) organic solvent, stirring them until they are stable and uniform, and coating them on an aluminum foil. The aluminum foil is dried in an oven after being air-dried, and then is cold-pressed and die-cut to form the positive electrode sheet.

[0027] Specifically, the positive electrode active material includes at least one of a layered oxide or a polyanion compound; the layered oxide includes at least one of sodium nickel-iron-manganese acid or sodium copper-iron-manganese acid, and the polyanion compound includes at least one of sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7), sodium vanadium phosphate, or sodium iron pyrophosphate.

[0028] Preferably, the layered oxide is sodium nickel-iron-manganese acid.

[0029] Preferably, the polyanion compound includes at least one of sodium iron phosphate pyrophosphate (Na4Fe3(PO4)2P2O7) or sodium vanadium phosphate.

[0030] Specifically, the binder is selected from one or more of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, or polyethylene oxide.

[0031] Specifically, the conductive agent is selected from one or more of carbon nanotubes (CNT), conductive graphite, conductive carbon fiber, acetylene black, or conductive carbon black.

[0032] Specifically, the weight ratio of the positive electrode active material, the binder, and the conductive agent is 94-96:1-3:2-4.

[0033] Specifically, the preparation of the negative electrode sheet includes the following steps: uniformly mixing and dispersing the negative electrode active material, the binder, and the conductive agent in NMP organic solvent, and then coating them on an aluminum foil. The aluminum foil is dried in an oven after being air-dried at room temperature, and then is cold-pressed and die-cut to form the negative electrode sheet.

[0034] Specifically, the negative electrode active material includes one or more of hard carbon, soft carbon, or graphite.

[0035] Specifically, the binder is selected from at least one of polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose, or polyethylene oxide.

[0036] Specifically, the conductive agent is selected from at least one of conductive carbon black (Super-P), carbon nanotubes (CNT), conductive graphite, conductive carbon fiber, or acetylene black.

[0037] Specifically, the weight ratio of the negative electrode active material, the binder, and the conductive agent is 96-98:1-3:0.5-1.5.

[0038] Compared with the prior art, the present application has the beneficial effects that: The present application provides an electrolyte additive, which is combined with a specific structure of additive a sulfophosphoramide compound and a conventional additive b as an electrolyte additive, and uses propylene carbonate with good high-temperature stability and good film-forming properties as an electrolyte solvent; the additive a sulfophosphoramide compound introduces S and N atoms on the phosphate skeleton, participates in the formation of an inorganic interface film rich in Na2S, Na3N and Na3P in the formation stage, and has more inorganic components and less organic components in the solid electrolyte interface film, and has stronger high-temperature resistance, thereby improving the safety performance of the battery; in summary, the functional electrolyte additive of the present application can significantly improve the safety of the battery, and when used in combination with the conventional additive, a more uniform and dense SEI film with smaller impedance is formed, thereby further improving the safety performance of the battery, and the prepared sodium ion battery has a short self-extinguishing time (1.8-6.8s) and a high thermal runaway triggering temperature (287-350℃), and has a small risk of battery fire or explosion. DETAILED DESCRIPTION

[0039] The present application will be further described below in conjunction with specific embodiments, but the embodiments do not limit the present application in any form. Unless otherwise specified, the raw materials used in the embodiments of the present application are commercially available raw materials.

[0040] Example 1 Positive electrode preparation: the positive electrode material sodium iron pyrophosphate (Na4Fe3(PO4)2P2O7), the binder polyvinylidene fluoride (PVDF), and the conductive agent are dispersed in NMP (N-methyl pyrrolidone) organic solvent at a mass ratio of 95:2:3, and are stirred to be stable and uniform under the action of a vacuum stirrer, and are uniformly coated on an aluminum foil with a thickness of 12 μm. After the aluminum foil is dried at room temperature, it is transferred to a 120℃ air oven for drying for 1h, and then is cold-pressed and die-cut to form a positive electrode sheet; Negative electrode preparation: hard carbon, binder PVDF, and conductive agent Super-P are mixed together at a mass ratio of 97:2:1, and are dispersed in NMP organic solvent to obtain a uniform coating on an aluminum foil with a thickness of 15 μm; after the aluminum foil is dried at room temperature, it is transferred to a 120℃ air oven for drying for 1h, and then is cold-pressed and die-cut to form a negative electrode sheet; Electrolyte preparation: The electrolyte was prepared in a nitrogen-filled glove box (O2<2 ppm, H2O<3 ppm). The sodium salt, solvent and additives were mixed uniformly by magnetic stirring. The sodium salt was NaPF6 and NaFSI, the solvent was propylene carbonate (PC), the additive a was the compound of formula 1, and the additive b was fluoroethylene carbonate, vinyl sulfate, sodium difluorophosphate. The weight ratio of NaPF6 and NaFSI, PC, the compound of formula 1, FEC, DTD and NaPO2F2 was 7:7:78:5:1:1:1. The structure of the compound of formula 1 is as follows:

[0041] Formula 1 (n-butyl thiophosphoric acid triamide CAS No.: 94317-64-3) Preparation of sodium ion battery: The positive electrode, the separator and the negative electrode were stacked in order, and the bare battery was obtained by winding. The sodium ion battery was prepared by packaging with aluminum plastic film, roasting, liquid injection, standing, formation, jig shaping, two-sealing and capacity test.

[0042] Example 2 The difference from Example 1 is that the additive a in the electrolyte additive is:

[0043] Formula 2 (n-propyl thiophosphoric acid triamide CAS No.: 91680-14-8) The other steps are the same as Example 1.

[0044] Example 3 The difference from Example 1 is that the additive a in the electrolyte additive is:

[0045] Formula 3 (thiophosphoric acid triamide CAS No.: 13455-05-5) The other steps are the same as Example 1.

[0046] Example 4 The difference from Example 1 is that the additive a in the electrolyte additive is:

[0047] Formula 4 (triethylenethiophosphoramide CAS No.: 52-24-4) The other steps are the same as Example 1.

[0048] Example 5 The difference from Example 1 is that the additive a in the electrolyte additive is:

[0049] Formula 5 (N,N,N-trimethylthiophosphoric acid triamide CAS number: 6141-78-2) The other steps are the same as Example 1.

[0050] Example 6 The difference from Example 1 is only that the weight ratio of NaPF6 and NaFSI, PC, Formula 1 compound, FEC, DTD and NaPO2F2 is 10:4:78:5:1:1:1; the other steps are the same as Example 1. The other steps are the same as Example 1.

[0051] Example 7 The difference from Example 1 is only that the positive electrode material is sodium nickel iron manganese acid, and the other steps are the same as Example 1.

[0052] The other steps are the same as Example 1.

[0053] Example 8 The difference from Example 1 is only that the positive electrode material is sodium vanadium phosphate, and the other steps are the same as Example 1.

[0054] The other steps are the same as Example 1.

[0055] Example 9 The difference from Example 1 is only that the weight ratio of NaPF6 and NaFSI, PC, Formula 1 compound, FEC, DTD and NaPO2F2 is 7:7:79:5:0:1:1, and the other steps are the same as Example 1.

[0056] The other steps are the same as Example 1.

[0057] Example 10 The difference from Example 1 is only that the weight ratio of NaPF6 and NaFSI, PC, Formula 1 compound, FEC, DTD and NaPO2F2 is 7:7:79:5:1:0:1, and the other steps are the same as Example 1.

[0058] The other steps are the same as Example 1.

[0059] Example 11 The difference from Example 1 is only that the weight ratio of NaPF6 and NaFSI, PC, Formula 1 compound, FEC, DTD and NaPO2F2 is 7:7:79:5:1:1:0, and the other steps are the same as Example 1.

[0060] The other steps are the same as Example 1.

[0061] Example 12 The difference from Example 1 is only that the weight ratio of NaPF6and NaFSI, PC, the compound of Formula 1, FEC, DTD, and NaPO2F2is 7:7:77:5:2:1:1, and the other steps are the same as in Example 1.

[0062] The other steps are the same as in Example 1.

[0063] Example 13 The difference from Example 1 is only that the weight ratio of NaPF6and NaFSI, PC, the compound of Formula 1, FEC, DTD, and NaPO2F2is 7:7:79:5:1:2:1, and the other steps are the same as in Example 1.

[0064] The other steps are the same as in Example 1.

[0065] Comparative Example 1 The difference from Example 1 is only that the weight ratio of NaPF6and NaFSI, the compound of Formula 1, PC, FEC, DTD, and NaPO2F2is 7:7:0:83:1:1:1; The other steps are the same as in Example 1.

[0066] Comparative Example 2 The difference from Example 1 is only that the weight ratio of NaPF6and NaFSI, PC, ethyl methyl carbonate (EMC), the compound of Formula 1, FEC, DTD, and NaPO2F2is 7:7:20:58:5:1:1:1; The other steps are the same as in Example 1.

[0067] Comparative Example 3 The difference from Example 1 is only that the additive a (P:S:N = 1:0:3) in the electrolyte additive is:

[0068] Formula 6 (N-(N-butyl)phosphoric acid triamide CAS No.: 25316-39-6) The other steps are the same as in Example 1.

[0069] Comparative Example 4 The difference from Example 1 is only that the additive a (P:S:N = 1:1:0) in the electrolyte additive is:

[0070] Formula 7 (3,3',3"-thiophosphoryl tripropionic acid CAS No.: 5961-86-4) The other steps are the same as in Example 1.

[0071] Comparative Example 5 The difference from Example 1 is that the additive a (P:S:N = 1:1:2) in the electrolyte additive is:

[0072] Formula 8 (4-S-(propionic acid)thiophosphamide CAS No.: 70396-87-1) The other steps are the same as Example 1.

[0073] Comparative Example 6 The difference from Example 1 is that the additive a (P:S:N = 1:2:0) in the electrolyte additive is:

[0074] Formula 9 (O-ethyl-S-propyl dithiophosphoryl chloride CAS No.: 42069-01-2) The other steps are the same as Example 1.

[0075] Results detection Detection method: the sodium ion battery prepared by the above examples and comparative examples is subjected to the following performance detection: 1. Electrolyte combustion test method The cotton soaked with different electrolytes is placed close to the outer flame of the alcohol lamp, then the cotton is moved away from the outer flame, and the combustion of the cotton is observed, and the self-extinguishing time is recorded. The shorter the time of continuous combustion of the electrolyte after being ignited, the better.

[0076] 2. Thermal runaway test method Sodium ion battery test based on UL 9540A:2025: Step 1: 0.2C constant current charging to 3.25V, cutoff current 0.05C, rest for 12 hours; Step 2: During the test, PI heating film is used to heat the two sides of the battery. Assembly method: the upper and lower sides of the battery are respectively PI heating film, heat insulation cotton and clamp. The temperature rising speed is controlled at 5℃ / min. The temperature of the surface of the battery is monitored (the recording frequency is 1s). If the battery catches fire or explodes, the heating can be stopped immediately.

[0077] Table 1 Composition and proportion of electrolyte prepared in examples and comparative examples

[0078] Table 2 Performance test results of experimental batteries provided by examples and comparative examples

[0079] As can be seen from Table 1 and Table 2, by using the sulfonamide compound with different structural formula, the additive with P:S:N ratio of 1:1:3 combined with the conventional additive as the electrolyte additive, and the cyclic propylene carbonate as the electrolyte solvent, and NaPF6 and NaFSI as the sodium salt electrolyte, the sodium ion battery prepared by the application has good flame retardant performance and safety performance, the self-extinguishing time of the sodium ion battery is short (1.8-6.8s), the thermal runaway triggering temperature is high (287-350℃), and the risk of battery fire or explosion is small; and it can be concluded from Examples 7-8 that the electrolyte formula of the application is also applicable to other layered oxides or polyanion materials. The sulfonamide compound of the additive a introduces S and N atoms on the phosphate skeleton, participates in the formation of an inorganic interfacial film rich in Na2S, Na3N and Na3P, and has more inorganic components and less organic components in the solid electrolyte interfacial film, has stronger high temperature resistance, and cooperates with the conventional additive to form a more uniform and dense SEI film with smaller impedance, thereby improving the safety performance of the battery.

[0080] The electrolyte formula of Comparative Example 1 does not introduce the phosphonamide compound of the additive a, and only uses the cyclic propylene carbonate as the solvent, so that the high temperature resistance is limitedly improved, and the safety performance and flame retardant performance are poor; the electrolyte formula of Comparative Example 2 introduces the phosphonamide compound of the additive a, but the solvent is a mixture of cyclic propylene carbonate (PC) and methyl ethyl carbonate (EMC), which has poorer performance than the pure cyclic propylene carbonate solvent, resulting in poor safety performance and flame retardant performance; the P:S:N ratio of the additive a of Comparative Examples 3-6 is 1:0:3, 1:1:0, 1:1:2 and 1:2:0 respectively, and the effect is optimal after the synergistic effect under the premise of containing P, S and N elements, and the performance is relatively poor if one of the elements is less, and the optimal ratio of the three elements is 1:1:3.

[0081] Obviously, the above examples of the application are only examples for clearly illustrating the application, and are not intended to limit the implementation modes of the application. Based on the above description, other different forms of changes or variations can be made by those skilled in the art. Here, all the implementation modes are not required or can not be exhausted. Any modification, equivalent replacement and improvement made within the spirit and principle of the application shall be included in the protection scope of the claims of the application.

Claims

1. An electrolyte additive, characterized in that, The electrolyte additive includes additive a and additive b; additive a includes a thiophosphoramide compound represented by structural formula 1: Structural Formula 1 R1, R2, R3, R4, R5, and R6 are each independently selected from H, a halogen atom, and an alkane group having 1 to 10 carbon atoms, and the H of the alkane group may be partially or completely replaced by one or more of a halogen atom, a cyano group, a carboxyl group, and a sulfonic acid group; the additive b includes one or more of ethylene carbonate, fluoroethylene carbonate, ethylene ethylene carbonate, 1,3-propanesulfonate lactone, propylene sulfite, ethylene sulfate, 4-methylethylene sulfate, sodium difluorophosphate, succinic anhydride, adiponitrile, and 1,3,6-hexanetrionitrile.

2. The electrolyte additive as described in claim 1, characterized in that, In the structural formula 1, R1, R2, R3, R4, R5, and R6 are each independently selected from H atoms and alkane groups having 1 to 4 carbon atoms.

3. The electrolyte additive as described in claim 1, characterized in that, The additive b is fluoroethylene carbonate, ethylene sulfate, or sodium difluorophosphate; the weight ratio of additive a to additive b is 5:2~5.

4. A sodium-ion battery electrolyte, characterized in that, The sodium-ion battery electrolyte comprises a sodium salt electrolyte, an electrolyte additive, and an electrolyte solvent, wherein the electrolyte additive is the electrolyte additive described in any one of claims 1 to 3.

5. The sodium-ion battery electrolyte as described in claim 4, characterized in that, The electrolyte additive accounts for 7-10% of the total mass of the sodium-ion battery electrolyte.

6. The sodium-ion battery electrolyte as described in claim 4, characterized in that, The sodium salt electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium difluorosulfonamide, sodium difluorophosphate, sodium tetrafluoroborate, sodium dioxalate borate, and sodium dioxalate borate; preferably, the mass of the sodium salt electrolyte accounts for 10-20% of the total mass of the sodium-ion battery electrolyte.

7. The sodium-ion battery electrolyte as described in claim 4, characterized in that, The electrolyte solvent includes at least one of cyclic carbonate solvents; preferably, the cyclic carbonate solvent is one or more of ethylene carbonate, propylene carbonate and butene carbonate; preferably, the electrolyte solvent is propylene carbonate.

8. The sodium-ion battery electrolyte as described in claim 4, characterized in that, The electrolyte solvent accounts for 70-80% of the total mass of the sodium-ion battery electrolyte.

9. A sodium-ion battery, characterized in that, The sodium-ion battery includes a positive electrode, a negative electrode, an electrolyte, and a separator; the electrolyte is the sodium-ion battery electrolyte according to any one of claims 4 to 8.

10. The sodium-ion battery as described in claim 9, characterized in that, The positive electrode active material of the positive electrode sheet includes at least one of layered oxide or polyanionic material; preferably, the layered oxide includes at least one of sodium nickel iron manganese oxide or sodium copper iron manganese oxide; preferably, the polyanionic material includes at least one of sodium iron pyrophosphate, sodium vanadium phosphate, and sodium iron pyrophosphate.

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