Sodium-ion battery and ester-based electrolyte thereof

Abstract

The invention belongs to the field of electrolytes, and particularly relates to a sodium ion battery and an ester-based electrolyte thereof, the sodium ion battery is composed of NaPF6, a formula 1 (), a formula 2 () and a formula 3 (), wherein R1 is H or alkyl with 1 to 4 carbon atoms; r < 2 > and R < 3 > are C1-C4 alkyl groups; r < 4 > is alkyl with 1 to 4 carbon atoms or alkoxy with 1 to 4 carbon atoms; and R5 is vinyl, ethynyl, ethylene substituted alkyl, ethylene substituted alkoxy or propyne substituted alkoxy. Innovative research shows that components of NaPF6, a formula 1, a formula 2 and a formula 3 are innovatively combined, based on physicochemical characteristics of the components, synergism can be achieved, conduction of Na < + > can be improved based on a weak coordination limiting mechanism of Na < + >, and PF6 <-> can be stabilized. According to the ester-based electrolyte disclosed by the invention, the high-temperature long-acting stability and fast-charging stability of the ester-based electrolyte can be effectively improved.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of sodium ion batteries, in particular to an electrolyte. BACKGROUND

[0002] Sodium ion batteries (SIBs) have similar working mechanisms as lithium ion batteries (LIBs), have high energy density, abundant and low-cost sodium resources, and are considered to be the most promising next-generation large-scale energy storage technology. SIBs combining polyanion compounds such as Na3V2(PO4)3 (NVP), Na3V2(PO4)2O2F (NVPF), layered transition metal oxides and Prussian blue analogues positive electrodes and hard carbon (HC) negative electrodes are considered to be the most promising high-energy-density SIBs for large-scale energy storage. Among the key components of the SIBs system, the interface layer (CEI) formed at the positive electrode and the interface layer (SEI) formed at the negative electrode of the electrolyte significantly affect the overall performance of the battery.

[0003] Ester electrolytes generally have advantages such as high oxidation stability, high boiling point and high dielectric constant, making them have wide commercial application prospects in SIBs. However, the compatibility of ester electrolytes with electrodes, especially with HC negative electrodes, is poor, and an organic-rich, unstable and uneven SEI layer is formed during charging and discharging, which increases the overpotential of SIBs, reduces the coulombic efficiency (CE), and seriously reduces the cycle life and safety of the battery.

[0004] In view of the above problems, the prior art also provides some reports on adding additives to the electrolyte to improve its performance. For example, the patent document with publication number CN106920988A discloses a sodium ion battery electrolyte, which comprises a sodium salt, a non-aqueous organic solvent and an additive; wherein the additive is a sulfuric acid ester compound, a sulfonic acid lactone compound and fluoroethylene carbonate (FEC). For another example, the patent document with publication number CN107171020A discloses a sodium ion battery non-aqueous electrolyte, which comprises a dinitrile or polynitrile functional additive in the electrolyte. The patent document with publication number CN107171021A discloses a sodium ion battery electrolyte, which adds an acid anhydride additive in the electrolyte.

[0005] In summary, although improving the performance of the electrolyte by adding additives is a common idea, the commonly used fluorine-containing additives not only have potential environmental pollution problems, but also increase the cost of the electrolyte, which is not conducive to commercial promotion and application. In addition, the research on optimizing the high-temperature stability and high-temperature rate of sodium ion batteries by adding additives is relatively scarce, and the development of related ideal additives is of great significance. SUMMARY

[0006] In view of the problem that the ester-based electrolyte for sodium ion battery is difficult to balance excellent high-temperature stability and high-temperature fast charging, the first object of the present application is to provide an ester-based electrolyte for sodium ion battery, which aims to reduce the coordination limitation of sodium ions and improve the high-temperature stability and high-temperature rate performance of sodium ion battery.

[0007] The second object of the present application is to provide a sodium ion battery comprising the ester-based electrolyte.

[0008] An ester-based electrolyte for sodium ion battery, which is composed of NaPF6, formula 1, formula 2 and formula 3.

[0009] Formula 1

[0010] Formula 2

[0011] Formula 3

[0012] R1 is H or C1-C4 alkyl;

[0013] R2 and R3 are C1-C4 alkyl;

[0014] R4 is C1-C4 alkyl or C1-C4 alkoxy; and R5 is vinyl, ethynyl, vinyl-substituted alkyl, vinyl-substituted alkoxy or propynyl-substituted alkoxy.

[0015] The present application innovatively studies that the combination of NaPF6, formula 1, formula 2 and formula 3 can achieve synergy based on the physicochemical characteristics between the components, can improve the conduction of Na + based on the weak coordination limitation mechanism of Na + , and can stabilize PF6 - . The ester-based electrolyte of the present application can effectively improve the high-temperature long-term stability and fast charging stability of the ester-based electrolyte.

[0016] In the present application, in formula 1, R1 is H.

[0017] In the present application, in formula 2, R2 and R3 are both methyl or ethyl.

[0018] In the present application, in formula 3, R4 is C1-C4 alkyl, and R5 is vinyl or propynyl alkoxy. The present application studies that the preferred formula 3 can further synergize with other components, can further help to reduce the coordination limitation of Na + , and improve the stability of PF6 - , and can further strengthen the high-temperature long-term stability and fast charging stability of the ester-based electrolyte.

[0019] In the present application, the volume ratio of formula 1, formula 2 and formula 3 is 1~0.5:0.5~1:0.01~0.05; further can be 0.8~1:1:0.02~0.03; further preferably 0.95~1:1:0.02~0.03. Studies have shown that under this preferred ratio, it is helpful to further weaken the weak coordination restriction of Na + , improve the conduction of Na + , and stabilize PF6 - . It can effectively improve the high-temperature long-term stability and fast-charging stability of the ester-based electrolyte.

[0020] In the present application, the concentration of NaPF6 is 0.5~2M, preferably 0.8~1.2M, and further preferably 0.95~1.05M. Studies have shown that under this preferred concentration, it is helpful to further combine and synergize with the ingredients, to further weaken the weak coordination restriction of Na + , improve the conduction of Na + , and stabilize PF6 - . It can effectively improve the high-temperature long-term stability and fast-charging stability of the ester-based electrolyte.

[0021] The present application also provides a sodium ion battery, which comprises a cell and an ester-based electrolyte for soaking the cell, wherein the cell comprises a positive electrode, a separator and a negative electrode which are sequentially compounded, and the ester-based electrolyte is the ester-based electrolyte of the present application.

[0022] The sodium ion battery of the present application can be known in other components and structural relationships except for the ester-based electrolyte of the present application.

[0023] For example, the negative active material in the negative electrode can be one of hard carbon and sodium metal.

[0024] The positive active material of the positive electrode is one of sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium iron phosphate, sodium iron pyrophosphate, sodium nickel iron manganese acid, sodium manganate, sodium iron manganate, sodium nickel manganate, sodium chromate and sodium iron sulfate.

[0025] The separator is one of glass fiber, PP, PE, PP / PE, non-woven fabric composite separator.

[0026] Advantages

[0027] The combination of formula 1, formula 2 and formula 3, the joint control based on the ratio of the three, and the joint adaptation of NaPF6 can unexpectedly realize synergy, can obtain ideal interface stability without fluorinated solvent and fluorinated additive, and can also take into account excellent electrochemical performance, for example, the electrolyte has excellent ionic conductivity, rate, high-temperature and large-current cycle stability under the premise of taking into account high interface stability.

[0028] The special combined ester-based electrolyte has high electronic state and oxidation activity, can enhance the electrolyte moisture resistance, and can stabilize PF6 - , achieves the purpose of clearing acid; in addition, it is also beneficial to derive an inorganic-rich and more stable electrode-electrolyte interface layer on the electrode surface, significantly enhances the ion transport kinetics of the battery, and improves the high-temperature rate and cycle performance thereof. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is the constant current charge-discharge curve of the HC half-cell when the electrolyte obtained in Example 1 is applied for testing at room temperature;

[0030] Figure 2 It is the cycle performance of the HC half-cell when the electrolyte obtained in Example 1 is applied for testing at room temperature;

[0031] Figure 3 It is the rate performance of the HC half-cell when the electrolyte obtained in Example 1 is applied for testing at room temperature;

[0032] Figure 4 It is the rate performance of the HC half-cell when the electrolyte obtained in Example 1 is applied for testing at high temperature 60 DEG C;

[0033] Figure 5 It is the cycle performance of the HC half-cell when the electrolyte obtained in Example 1 is applied for testing at high temperature 60 DEG C;

[0034] Figure 6 It is the constant current charge-discharge curve of the HC / NVP full cell when the electrolyte obtained in Example 1 is applied for testing at room temperature;

[0035] Figure 7 It is the rate performance of the HC / NVP full cell when the electrolyte obtained in Example 1 is applied for testing at room temperature;

[0036] Figure 8 It is the cycle performance of the HC / NVP full cell when the electrolyte obtained in Example 1 is applied for testing at room temperature; DETAILED DESCRIPTION

[0037] Unless otherwise specified, all the raw materials, reagents, instruments and equipment used in the present application can be purchased in the market or prepared by the existing methods.

[0038] Example 1

[0039] The ester-based electrolyte is composed of NaPF6, Formula 1 (in this case, Formula 1A, which is a Formula 1 compound with R1 being H), Formula 2 (in this case, Formula 2A, which is a Formula 2 compound with R2 and R3 being methyl), and Formula 3 (in this case, Formula 3A, which has the structure of: ); wherein the volume ratio of Formula 1, Formula 2 and Formula 3 is 1:1:0.02; the concentration of NaPF6 is 1M.

[0040] The electrolyte provided in Example 1 is applied to a sodium-ion battery.

[0041] Sodium-ion button half-cell rate and cycle test:

[0042] The positive electrode side is a hard carbon positive electrode (including a positive electrode current collector (Cu foil) and a positive electrode material compounded on the surface thereof, the positive electrode material including hard carbon, acetylene black and PVDF in a weight ratio of 8:1:1), the counter electrode is a metal sodium, and the test voltage range is 0.01-3V.

[0043] Sodium-ion button full-cell rate and cycle test:

[0044] The positive electrode side is a sodium vanadium phosphate (Na3V2(PO4)3) positive electrode (including a positive electrode current collector (Al foil) and a positive electrode material compounded on the surface thereof, the positive electrode material including Na3V2(PO4)3, Super P and PVDF in a weight ratio of 7:2:1), the negative electrode side is a hard carbon negative electrode (including a negative electrode current collector (Cu foil) and a negative electrode material compounded on the surface thereof, the negative electrode material including hard carbon, acetylene black and PVDF in a weight ratio of 8:1:1), and the test voltage range is 2.2-3.7 V.

[0045] The button half-cell or full-cell is assembled in a glove box filled with high-purity argon (O2<0.1ppm, H20<0.1ppm, ). The battery test environment is normal temperature (25℃) or high temperature 60℃, and the half-cell rate test current density is 0.03-0.05-0.1-0.2-0.4-0.8-1.0-2.0-0.03 Ag -1 (the results are shown in Table 1).

[0046] The electrolyte ion conductivity test is carried out using a stainless steel / stainless steel battery, the AC impedance disturbance voltage is 5mV, and the frequency range is 0.01HZ~100KHZ (the results are shown in Table 1).

[0047] The results are as follows: as Figure 1As shown, in the first discharge, the hard carbon material provided a high discharge capacity of 426.29 mAh g -1 in the constructed electrolyte, and the first coulombic efficiency (ICE) was 71.24%. At the same time, the electrolyte had a high ionic conductivity of 5.12 mS cm -1 (Table 1). When matched with the hard carbon material, the battery had ultra-stable cycle performance Figure 2 and excellent rate performance Figure 3 . More importantly, this excellent rate performance and ultra-stable cycle performance could be well maintained even at a high temperature of 60°C Figure 4 , Figure 5 , reflecting the successful application of the ester electrolyte in sodium-ion batteries in Example 1. The combined control of NaPF6 with Formula 1A, Formula 2A, and Formula 3A not only improved the electrolyte ion transport kinetics, but also more effectively strengthened the battery interface stability, enabling it to have good cycle performance even in a high-temperature environment. A full battery was assembled using the polyanion NVP material as the positive electrode and the hard carbon material as the negative electrode, and as shown in Figure 6 and Figure 7 , the full battery provided excellent rate performance, and even after 500 cycles at a high rate of 1C, it still had a high specific capacity of 72.68 mAh g -1 ( Figure 8 ), with a capacity retention rate of 72% (the first 6 cycles were an activation process at 0.1C and 0.3C), indicating that the electrolyte obtained in Example 1 has good practical application prospects.

[0048] Example 2

[0049] Compared with Example 1, the only difference is that the type of Formula 3 is changed, and the experimental groups are as follows:

[0050] Group A: Formula 3 is Formula 3B (the structure is )

[0051] Group B: Formula 3 is Formula 3C (the structure is )

[0052] Other operations, parameters, and tests are the same as in Example 1.

[0053] Example 3

[0054] Compared with Example 1, the only difference is that the ratio between the components is changed, and the experimental groups are as follows:

[0055] Group A: the ratio of Formula 1, Formula 2, and Formula 3 is 1:1:0.01;

[0056] Group B: the ratio of Formula 1, Formula 2, and Formula 3 is 1:1:0.04;

[0057] Group C: the ratio of Formula 1, Formula 2 and Formula 3 is 0.8:1:0.02;

[0058] Group D: the concentration of NaPF6 is 0.8M.

[0059] Group E: the concentration of NaPF6 is 1.2M.

[0060] Other operations, parameters and tests are the same as Example 1.

[0061] Comparative Example 1

[0062] Compared with Example 1, the only difference is that Formula 3 is not added, and the ratio of Formula 1 and Formula 2 and the concentration of NaPF6 are the same as Example 1.

[0063] Comparative Example 2

[0064] Compared with Example 1, the only difference is that Formula 1 is missing, and the missing Formula 1 is supplemented by an equal volume of Formula 2, and other operations and parameters are the same as Example 1.

[0065] Comparative Example 3

[0066] Compared with Example 1, the only difference is that Formula 2 is missing, and the missing Formula 2 is supplemented by an equal volume of Formula 1, and other operations and parameters are the same as Example 1.

[0067] Comparative Example 4

[0068] Compared with Example 1, the only difference is that the ratio of the components is changed, and the experimental groups are respectively:

[0069] Group A: Compared with Example 1, the only difference is that Comparative Formula A (Comparative Formula A) with the same volume ratio as Formula 2A is additionally added, ), and other operations and parameters are the same as Example 1.

[0070] Group B: Compared with Example 1, the only difference is that Comparative Formula B (Comparative Formula B) with the same volume ratio as Formula 3A is additionally added, ), and other operations and parameters are the same as Example 1.

[0071] Comparative Example 5

[0072] Compared with Example 1, the only difference is that the ratio of the components is changed, and the experimental groups are respectively:

[0073] Group A: Compared with Example 1, the only difference is that the sodium salt is replaced by NaTFSI with the same molar content, and other operations and parameters are the same as Example 1.

[0074] Group B: Compared with Example 1, the only difference is that the sodium salt is replaced by NaFSI with the same molar content, and other operations and parameters are the same as Example 1.

[0075] Comparative Example 6

[0076] Compared with Example 1, the only difference is that the proportion of the components is changed, and the experimental groups are respectively:

[0077] Group A: Compared with Example 1, the only difference is that Formula 3A is replaced by Comparative Formula C with the same volume ratio ), and other operations and parameters are the same as Example 1.

[0078] Group B: Compared with Example 1, the only difference is that Formula 3A is replaced by Comparative Formula D with the same volume ratio ), and other operations and parameters are the same as Example 1.

[0079] Group C: Compared with Example 1, the only difference is that Formula 3A is replaced by Comparative Formula E with the same volume ratio ), and other operations and parameters are the same as Example 1.

[0080] The test results of each case are shown in Tables 1-6:

[0081]

[0082]

[0083]

[0084]

[0085]

[0086]

[0087] In summary, through the examples and comparative examples, it is known that the components of NaPF6, Formula 1, Formula 2 and Formula 3 are combined innovatively, based on the physicochemical characteristics between the components, the synergy can be achieved, and the conduction of Na + can be improved based on the weak coordination limiting mechanism of Na + , and the stability of PF6 - can be stabilized. The ester-based electrolyte described in the application can effectively improve the high-temperature long-term stability and fast-charging stability of the ester-based electrolyte.

[0088] Through Examples 1 and 2, in Formula 3, R4 is C1-C4 alkyl, and R5 is vinyl or propargyloxy. It can further synergize with other components, further reduce the coordination limitation of Na + , improve the stability of PF6 - , and further strengthen the high-temperature long-term stability and fast-charging stability of the ester-based electrolyte.

[0089] From Examples 1 and 3, the volume ratio of Formula 1, Formula 2 and Formula 3 is 1-0.5:0.5-1:0.01-0.05; further can be 0.8-1:1:0.02-0.03; further preferably 0.95-1:1:0.02-0.03. The concentration of NaPF6 is 0.5-2M, preferably 0.8-1.2M, further preferably 0.95-1.05M. Under the preferred conditions, it is helpful and the ingredients are further combined synergistically, which helps to further weaken the weak coordination of Na + , improves the conduction of Na + , and can stabilize PF6 - . It can effectively improve the high-temperature long-term stability and fast-charging stability of the ester-based electrolyte.

Claims

1. An ester-based electrolyte for a sodium-ion battery, characterized by, consisting of NaPF6, formula 1, formula 2 and formula 3; Formula 1; Formula 2; Formula 3; R1 is H or C1-C4 alkyl; R2, R3 are C1-C4 alkyl; R4 is C1-C4 alkyl or C1-C4 alkoxy; R5 is vinyl, ethynyl, vinyl substituted alkyl, vinyl substituted alkoxy or propynyl substituted alkoxy.

2. The ester-based electrolyte for sodium-ion batteries according to claim 1, wherein In the formula 1, R1 is H.

3. The ester-based electrolyte for sodium-ion batteries according to claim 1, wherein In the formula 2, R2, R3 are both methyl or ethyl.

4. The ester-based electrolyte for sodium-ion batteries according to claim 1, wherein In the formula 3, R4 is C1-C4 alkyl; R5 is vinyl or propynyl alkoxy.

5. The ester-based electrolyte for sodium-ion batteries according to any one of claims 1 to 4, wherein The volume ratio of formula 1, formula 2 and formula 3 is 1-0.5:0.5-1:0.01-0.05; preferably 0.8-1:1:0.02-0.03; further preferably 0.95-1:1:0.02-0.

03. 6.The ester-based electrolyte for sodium-ion batteries according to any one of claims 1-4, wherein, The concentration of NaPF6 is 0.5-2M, preferably 0.8-1.2M, further preferably 0.95-1.05M.

7. A sodium-ion battery comprising an electrode core and an ester-based electrolyte soaking the electrode core, the electrode core comprising a positive electrode, a separator and a negative electrode which are sequentially compounded, characterized in that, The ester-based electrolyte is the ester-based electrolyte according to any one of claims 1-6.

8. The sodium-ion battery of claim 7, wherein, The active material in the negative electrode is one of hard carbon, sodium metal.

9. The sodium-ion battery of claim 7, wherein, The active material in the positive electrode is one of sodium vanadium phosphate, sodium vanadium fluorophosphate, sodium iron phosphate, sodium iron pyrophosphate, sodium nickel iron manganese acid, sodium manganese acid, sodium iron manganese acid, sodium nickel manganese acid, sodium chromate, sodium iron sulfate.

10. The sodium-ion battery of claim 7, wherein, The separator is one of glass fiber, PP, PE, PP / PE, non-woven composite separator.

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