Local high-concentration high-voltage electrolyte, preparation method and battery

Abstract

The invention discloses a local high-concentration high-voltage electrolyte, a preparation method and a battery, and belongs to the technical field of electrolytes. The local high-concentration high-voltage electrolyte comprises a sodium salt, a first solvent and a second solvent, the first solvent comprises carbonic ester, the second solvent comprises at least one of a fluoroether solvent and a fluorobenzene solvent, the first solvent and the second solvent are mutually soluble, the solubility of the sodium salt in the first solvent is defined as S1, the solubility of the sodium salt in the second solvent is defined as S2, and S1 is larger than S2. According to the electrolyte, the overall salt concentration can be reduced, the viscosity of the electrolyte can be reduced, the wettability of the electrolyte can be improved, so that the conductivity of ions is improved, in addition, oxygenolysis of the first solvent can be slowed down, and furthermore, the second solvent has high oxidation resistance and oxidation resistance, so that the service life of the electrolyte is prolonged. And the oxygenolysis of the electrolyte under a high-voltage condition can be inhibited, so that the cycling stability of the battery can be improved, the battery capacity is improved, and the battery is suitable for a high-voltage application scene.

Description

Technical Field

[0001] The present invention relates to the technical field of electrolytes, and in particular to a local high-concentration high-voltage electrolyte, a preparation method thereof, and a battery. Background Art

[0002] The current energy density of sodium-ion batteries is relatively low, and the voltage corresponding to high energy density is also relatively high. The electrolyte in sodium-ion batteries often cannot withstand voltages of 4.2V and above. The positive electrode material is prone to dissolution of transition metal ions under high voltage, which eventually leads to the collapse of the material structure and affects the battery performance. At this stage, the improvement of high-voltage resistance mainly focuses on breakthroughs in positive electrode materials and electrolytes. Compared with improving positive electrode materials, improving the high-voltage performance of sodium-ion batteries by modifying the electrolyte is also the most economical and effective way. The research on high-voltage electrolytes has not yet formed a system. The electrolyte is easily oxidized and decomposed under high voltage, and the battery positive electrode interface is relatively poor. Studies have found that high-concentration electrolytes can change the solvation state of sodium ions to give them a wider electrochemical window and better safety. High-concentration electrolytes bring higher viscosity and higher cost. Compared with high-concentration electrolytes, local high-concentration electrolytes have lower cost and viscosity. The combined use of multiple additives can inhibit high-voltage decomposition and improve the problem of poor sodium ion circulation at high voltage. Summary of the invention

[0003] The main purpose of the present invention is to provide a local high-concentration high-voltage electrolyte and a preparation method and a battery to solve the technical problem of poor cycle performance of the battery under high-voltage conditions.

[0004] To achieve the above-mentioned object, the present invention provides a local high-concentration and high-voltage electrolyte, which includes a sodium salt, a first solvent, and a second solvent. The first solvent includes a carbonate, and the second solvent includes a fluoroether and a fluorobenzene solvent. The first solvent and the second solvent are mutually soluble. The solubility of the sodium salt in the first solvent is defined as S1, and the solubility in the second solvent is defined as S2, then S1>S2.

[0005] In some embodiments of the present invention, the sodium salt includes a main salt and a secondary salt, wherein the main salt includes sodium bis(fluorosulfonyl)imide (NaFSI), sodium hexafluorophosphate (NaPF 6 ), sodium perchlorate (NaClO 4 ), sodium tetrafluoroborate (NaBF 4 ) at least one; the auxiliary salt includes sodium difluorooxalatoborate (NaODFB), sodium bis(oxalate)borate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ) at least one of the following.

[0006] In some embodiments of the present invention, the mass ratio of the main salt to the auxiliary salt is (10-60):1.

[0007] In some embodiments of the present invention, the carbonate includes one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate;

[0008] And / or, the fluoroether solvent includes at least one of 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether (HFE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE), and the fluorobenzene solvent includes at least one of 1,2-difluorobenzene and mFT.

[0009] In some embodiments of the present invention, the mass ratio of the first solvent to the second solvent is 1:(1-2.5).

[0010] In some embodiments of the present invention, the mass ratio of the first solvent to the second solvent is 1:(1.2-2).

[0011] In some embodiments of the present invention, the local high-concentration high-voltage electrolyte also includes additives, and the additives include at least one of fluoroethylene carbonate (FEC), propylene sulfite (PS), diethylene sulfate (DTD), tris(trimethylsilyl)borate (TMSB), sodium acesulfame, trimethyl phosphate, triethyl phosphate, dimethyl methyl phosphate, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and ethoxy(pentafluoro)cyclotriphosphazene.

[0012] In some embodiments of the present invention, based on 100% of the total mass of the local high-concentration high-voltage electrolyte, the content of the additive is 2% to 8%.

[0013] The present invention also provides a method for preparing the local high-concentration high-voltage electrolyte as described above, comprising the following steps:

[0014] The sodium salt and the first solvent are mixed, and the second solvent is added and mixed to obtain the local high-concentration high-voltage electrolyte.

[0015] The present invention also provides a use of the high-concentration and high-voltage electrolyte as described above in a sodium ion battery.

[0016] The beneficial effects that can be achieved by the present invention are:

[0017] The local high-concentration high-voltage electrolyte of the present invention comprises a sodium salt, a first solvent and a second solvent, wherein the first solvent comprises a carbonate, and the second solvent comprises a fluoroether solvent and / or a fluorobenzene solvent, wherein the sodium salt is easily soluble in the first solvent and is insoluble in the second solvent, and after mixing, a local high-concentration sodium salt electrolyte can be obtained, and compared with the electrolyte of the high-concentration sodium salt, the electrolyte of the local high-concentration sodium salt can reduce the overall salt concentration on the one hand, thereby reducing the cost, and on the other hand, it can reduce the viscosity of the electrolyte, improve the wettability of the electrolyte, thereby improving the conductivity of the ions, and the local high-concentration sodium salt can also greatly reduce the proportion of the free state of the first solvent, thereby slowing down the oxidative decomposition of the first solvent. In addition, the second solvent fluoroether and fluorobenzene solvents have strong antioxidant and oxidation resistance, and can inhibit the oxidative decomposition of the electrolyte under high-voltage conditions, thereby improving the cycle stability of the battery, improving the battery capacity, and making the battery suitable for high-voltage application scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying creative work.

[0019] Figure 1 The figure is a performance comparison chart of batteries prepared with the electrolytes obtained in the examples of the present invention and the comparative examples after 150 cycles.

[0020] Figure 2 The figure is a performance comparison chart of batteries prepared with the electrolytes obtained in the examples of the present invention and the comparative examples after 200 cycles.

[0021] The realization of the purpose, functional features and advantages of the present invention will be further explained in conjunction with embodiments and with reference to the accompanying drawings. DETAILED DESCRIPTION

[0022] It should be understood that the specific embodiments described herein are only used to explain the present invention, and are not used to limit the present invention.

[0023] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0024] In the present invention, descriptions such as "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0025] The present invention provides a local high-concentration high-voltage electrolyte, which comprises a sodium salt, a first solvent, and a second solvent. The first solvent comprises a carbonate, and the second solvent comprises a fluoroether solvent and a fluorobenzene solvent. The first solvent and the second solvent are mutually soluble. The solubility of the sodium salt in the first solvent is defined as S1, and the solubility in the second solvent is defined as S2, then S1>S2.

[0026] The local high-concentration high-voltage electrolyte of the present invention comprises a sodium salt, a first solvent and a second solvent, wherein the first solvent is a carbonate, and the second solvent is a fluoroether or fluorobenzene solvent. The sodium salt is easily soluble in the first solvent and is difficult to dissolve in the second solvent. The solubility S1 in the first solvent is greater than the solubility S2 in the second solvent. After mixing, a local high-concentration sodium salt electrolyte can be obtained. Compared with the electrolyte of a high-concentration sodium salt, the electrolyte of a local high-concentration sodium salt can reduce the overall salt concentration on the one hand, thereby reducing the cost, and on the other hand, it can reduce the viscosity of the electrolyte, improve the wettability of the electrolyte, thereby improving the conductivity of the ions, and the local high-concentration sodium salt can also greatly reduce the proportion of the free state of the first solvent, thereby slowing down the oxidative decomposition of the first solvent. In addition, the second solvent, the fluoroether or fluorobenzene solvent, has strong antioxidant and oxidation resistance, and can inhibit the oxidative decomposition of the electrolyte under high-voltage conditions, thereby improving the cycle stability of the battery, improving the battery capacity, and making the battery suitable for high-voltage application scenarios.

[0027] In some embodiments, the sodium salt includes a main salt and a secondary salt, the main salt includes sodium bis(fluorosulfonyl)imide (NaFSI), sodium hexafluorophosphate (NaPF 6 ), sodium perchlorate (NaClO 4 ), sodium tetrafluoroborate (NaBF 4 ) at least one; auxiliary salts include sodium difluorooxalatoborate (NaODFB), sodium bis(oxalate)borate (NaBOB), sodium difluorophosphate (NaPO 2 F 2 ) at least one of the following.

[0028] In some embodiments, the mass ratio of the main salt to the auxiliary salt is (10-60): 1, and the mass ratio can be any ratio in the range of (10-60): 1, such as 10: 1, 15: 1, 20: 1, 25: 1, 30: 1, 40: 1, 50: 1, 60: 1, etc. In this embodiment, the main salt and the auxiliary salt are compounded, the main salt can provide Na ions as a solute, and the auxiliary salt can provide anions as an additive, so the main salt has a relatively high proportion, which is beneficial to improve the cycle performance of the battery.

[0029] In some embodiments, the first solvent carbonate includes one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0030] In some embodiments, the fluoroether solvent includes at least one of 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether (HFE), bis(2,2,2-trifluoroethyl) ether (BTFE), 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether (TTE), and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether (OFE).

[0031] In some embodiments, the fluorobenzene solvent includes at least one of 1,2-difluorobenzene and m-fluorotoluene.

[0032] In some embodiments, compounding a fluoroether solvent and a fluorobenzene solvent to obtain a second solvent is beneficial to improving the solubility of the second solvent.

[0033] In some embodiments, the mass ratio of the fluorinated ether solvent to the fluorinated benzene solvent is (1-2): (1-2).

[0034] In some embodiments, the mass ratio of the first solvent to the second solvent is 1:(1-2.5), and the mass ratio can be any ratio within the range of 1:(1-2.5), such as 1:1, 1:2, 1:2.5, etc.

[0035] In some embodiments, the mass ratio of the first solvent to the second solvent is 1:(1.2-2).

[0036] In some embodiments, the local high-concentration high-voltage electrolyte further includes additives, and the additives include at least one of fluoroethylene carbonate (FEC), propylene sulfite (PS), vinyl sulfate (DTD), tris(trimethylsilyl) borate (TMSB), sodium acesulfame, trimethyl phosphate, triethyl phosphate, dimethyl methyl phosphate, triphenyl phosphite, tris(2,2,2-trifluoroethyl) phosphate, and ethoxy(pentafluoro)cyclotriphosphazene. Adding the above additives to the electrolyte can react with sodium salts to decompose on the electrode to form a stable, thin and dense solid electrolyte interface film containing sodium fluoride, and at the same time, it can reduce the interface impedance, show high electronic insulation and high ionic conductivity, promote the transport of sodium ions, and thus improve the cycle performance of the battery under high-voltage conditions.

[0037] In some embodiments, based on 100% of the total mass of the local high-concentration high-voltage electrolyte, the content of the additive is 2% to 8%, and can be any value within the range of 2% to 8%, such as 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc.

[0038] The present invention also provides a method for preparing the local high-concentration high-voltage electrolyte as described above, comprising the following steps:

[0039] The sodium salt and the first solvent are mixed, and the second solvent is added and mixed to obtain the local high-concentration high-voltage electrolyte.

[0040] In the present invention, the sodium salt is easily soluble in the first solvent. Mixing the sodium salt and the first solvent is conducive to the dispersion of the sodium salt to form a high-concentration electrolyte. Then, the second solvent is added. The sodium salt is difficult to dissolve in the second solvent, thereby obtaining a uniform local high-concentration electrolyte.

[0041] In some embodiments, stirring may be used to promote uniform mixing of the sodium salt, the first solvent, the second solvent and other additives.

[0042] In some embodiments, the above additives may be added after the sodium salt, the first solvent, and the second solvent are mixed.

[0043] The viscosity of the electrolyte prepared by the invention is 1.0 mPa·S to 10.0 mPa·S.

[0044] The local high-concentration high-voltage electrolyte of the present invention can be applied to sodium ion batteries to improve the capacity retention rate and cycle performance of the batteries.

[0045] In some embodiments, the sodium ion battery comprises a positive electrode sheet, a negative electrode sheet, a separator and the electrolyte of the present invention.

[0046] In some embodiments, the separator of the sodium ion battery is made of at least one of polypropylene and polyethylene.

[0047] In some embodiments, a sodium ion battery positive electrode sheet includes layered oxides, carbon black, carbon nanotubes, and PVDF.

[0048] In some embodiments, the layered oxide has a chemical formula of Na 2 / 3 [Ni 1 / 3 Mn 2 / 3 ]O 2 .

[0049] In some embodiments, the weight percentages of layered oxide, carbon black, carbon nanotubes and PVDF are 94%, 2%, 1.5% and 2.5% respectively.

[0050] In some embodiments, the negative electrode plate in the sodium ion battery includes hard carbon, carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose.

[0051] In some embodiments, the weight percentages of hard carbon, carbon black, styrene-butadiene rubber, and sodium carboxymethyl cellulose are 94%, 2%, 3%, and 1%, respectively.

[0052] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the following specific embodiments are only used to explain the present invention, and are not used to limit the present invention.

[0053] Example 1

[0054] Preparation of electrolyte

[0055] The present embodiment provides a local high-concentration high-voltage electrolyte prepared by the following preparation method: according to Table 1, sodium salt is added to a first solvent, mixed evenly, and then a second solvent and an additive are added and mixed evenly to obtain a local high-concentration high-voltage electrolyte.

[0056] Example 2 to Example 3

[0057] In Example 2 and Example 3, local high-concentration and high-voltage electrolytes were prepared according to the preparation method of Example 1, with the difference being the type and addition amount of raw materials, as shown in Table 1 for details.

[0058] Comparative Example 1 to Comparative Example 3

[0059] A local high-concentration high-voltage electrolyte was prepared according to the preparation method of Example 1, except for the type and addition amount of raw materials, as shown in Table 1.

[0060] Performance Testing

[0061] The electrolytes prepared in Examples 1 to 3 and Comparative Examples 1 to 3 were respectively applied to sodium ion batteries, and the performance of each group of sodium ion batteries was tested.

[0062] Test method: 1C cycle test at 2.5-4.25V, capacity retention after 150 cycles and 200 cycles. Test results are shown in Figure 1 , Figure 2 and Table 1, where Figure 1 The results of 150 cycles are as follows: Figure 2 The results are for 200 cycles.

[0063] Table 1

[0064]

[0065]

[0066] Combination Figure 1 , Figure 2 As can be seen from Table 1, the capacity of the batteries prepared with the electrolytes of Examples 1 and 3 hardly decays after 150 cycles, and the decay after 200 cycles is less than 3%.

[0067] In Comparative Examples 1 and 2, the mass ratio of the first solvent to the second solvent is 5:1, the content of the first solvent is too high, and the content of the second solvent is too low. When the obtained electrolyte is applied to a sodium ion battery, the cycle performance of the sodium ion battery decreases.

[0068] In Comparative Example 3, no additives were added, and the obtained electrolyte was applied to a sodium ion battery, and the cycle performance of the sodium ion battery also declined.

[0069] The above are only preferred embodiments of the present invention, and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A local high-concentration high-voltage electrolyte, characterized in that: The local high-concentration high-voltage electrolyte includes a sodium salt, a first solvent, and a second solvent. The first solvent includes carbonate, the second solvent includes at least one of a fluoroether solvent and a fluorobenzene solvent, the first solvent and the second solvent are miscible, and the solubility of the sodium salt in the first solvent is defined as S1, and the solubility in the second solvent is defined as S2, then S1>S2.

2. The local high-concentration high-voltage electrolyte according to claim 1, characterized in that: The sodium salt includes a main salt and an auxiliary salt. The main salt includes at least one of sodium bis(fluorosulfonyl)imide, sodium hexafluorophosphate, sodium perchlorate, and sodium tetrafluoroborate; the auxiliary salt includes at least one of sodium difluorooxalatoborate, sodium bis(oxalato)borate, and sodium difluorophosphate.

3. The local high-concentration high-voltage electrolyte according to claim 2, characterized in that: The mass ratio of the main salt to the auxiliary salt is (10-60):

1.

4. The local high-concentration high-voltage electrolyte according to claim 1, characterized in that: The carbonate includes one or more of propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate; And / or, the fluoroether solvent includes at least one of 2,2,2-trifluoroethyl-1,1,2,2-tetrafluoroethyl ether, bis(2,2,2-trifluoroethyl) ether, 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, and 1H,1H,5H-octafluoropentyl-1,1,2,2-tetrafluoroethyl ether; And / or, the fluorobenzene solvent includes at least one of 1,2-difluorobenzene and m-fluorotoluene.

5. The local high-concentration high-voltage electrolyte according to claim 4, characterized in that: The mass ratio of the first solvent to the second solvent is 1:(1-2.5).

6. The local high-concentration high-voltage electrolyte according to claim 5, characterized in that: The mass ratio of the first solvent to the second solvent is 1:(1.2-2).

7. The local high-concentration high-voltage electrolyte according to claim 1, characterized in that: The local high-concentration high-voltage electrolyte also includes additives, and the additives include at least one of fluoroethylene carbonate, propylene sulfite, vinyl sulfate, tris(trimethylsilyl)borate, sodium acesulfame, trimethyl phosphate, triethyl phosphate, dimethyl methyl phosphate, triphenyl phosphite, tris(2,2,2-trifluoroethyl)phosphate, and ethoxy(pentafluoro)cyclotriphosphazene.

8. The local high-concentration high-voltage electrolyte according to claim 7, characterized in that: Based on 100% of the total mass of the local high-concentration high-voltage electrolyte, the content of the additive is 2% to 8%.

9. A method for preparing the local high-concentration high-voltage electrolyte according to any one of claims 1 to 8, characterized in that: The following steps are involved: The sodium salt and the first solvent are mixed, and the second solvent is added and mixed to obtain the local high-concentration high-voltage electrolyte.

10. A battery, characterized in that: The battery comprises the local high-concentration high-voltage electrolyte according to any one of claims 1 to 8.

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