High-voltage-resistant sodium-ion battery electrolyte

Abstract

The invention relates to a high-voltage-resistant sodium-ion battery electrolyte which comprises a solvent, sodium salt and an additive. The additive is an additive with a special structure, the structure of the additive comprises at least two-C = N functional groups, and the electrolyte contains at least one of the additives. One-C = N in the additive is coordinated with Na < + > through N-Na < + > so as to participate in solvation structure modification of a Na < + > solvation structure, the coordination number of a solvent and Na < + > is reduced, and Na < + > in the electrolyte shuttles between the surfaces of a positive electrode and a negative electrode in a solvation structure form under the driving of voltage in the charging and discharging process, so that the electrolyte is formed. Therefore, due to the reduced solvent coordination number, the occurrence frequency and probability of the solvent on the surface of the high-voltage (greater than 4.0 V Na / Na < + >) positive electrode are reduced, so that the oxygenolysis of the electrolyte on the surface of the high-voltage positive electrode can be inhibited. According to the electrolyte designed after the additive with the special structure is added, the irreversible capacity loss of the battery can be obviously reduced, and the cycle life of the battery can be obviously prolonged.

Description

Technical Field

[0001] The invention relates to the field of batteries, and in particular to a high-voltage sodium ion battery electrolyte. Background Art

[0002] The high working voltage and high energy density of cathode materials make sodium-ion batteries likely to partially replace or supplement lithium-ion batteries in low- and medium-speed electric vehicles and large-scale energy storage, while taking advantage of their abundant reserves and low cost. However, the oxidative decomposition of the electrolyte on the surface of the high-voltage cathode, especially the oxidative decomposition of the solvent, consumes bulk sodium ions to generate an unstable cathode-electrolyte interface (CEI) rich in a series of organic substances, causing continuous and irreversible loss of bulk sodium ions, resulting in a continuous and rapid attenuation of the battery capacity and a poor battery cycle life. Summary of the invention

[0003] In order to solve the above problems, the present invention designs a high-voltage sodium ion battery electrolyte by introducing a special structural functional additive. The carbon chain ends of the additive each contain at least one -C≡N functional group, under the premise that one -C≡N functional group participates in the sodium ion solvation structure (the modified solvation structure reduces the solvent and Na + The coordination number of the electrolyte is Na + Solvated structure "Additive-Na + -Solvent-anion" shuttles between the positive and negative electrode surfaces, and the reduction of the solvent coordination number makes it possible to + )The frequency and probability of its appearance on the positive electrode surface are reduced, thereby weakening the oxidative decomposition of the electrolyte solvent on the high-voltage positive electrode surface. ), the other one preferentially adsorbs and contacts the high-voltage positive electrode on the positive electrode surface, followed by preferential oxidative decomposition, thereby constructing a stable CEI rich in nitrides, which can effectively inhibit the oxidative decomposition of the electrolyte on the high-voltage positive electrode surface.

[0004] Preferably, the mass percentage of the functional additive in the electrolyte is 0.5-10%, preferably 1-5%, and more preferably 2%.

[0005] Preferably, the sodium salt of the electrolyte is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bis(trifluoromethanesulfonyl imide) and sodium bis(fluorosulfonyl imide); the sodium salt concentration is 0.2-3 mol L -1 , preferably 0.5-1.5 mol L -1 , more preferably 1 mol L -1 .

[0006] Preferably, the organic solvent comprises cyclic carbonate, chain carbonate and dimethyl ether; the cyclic carbonate is selected from one or both of ethylene carbonate and propylene carbonate; the chain carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate and methyl propyl carbonate; the dimethyl ether is selected from one or more of dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME) and tetraethylene glycol dimethyl ether (TEGDME);

[0007] It is particularly preferred that when two or more organic solvents are contained simultaneously, they are mixed in equal volumes.

[0008] Those skilled in the art can combine the above solutions to obtain a preferred embodiment of the electrolyte of the present invention.

[0009] Furthermore, the present invention also provides a battery containing the electrolyte.

[0010] Preferably, the positive electrode material of the battery is a polyanionic compound, including one or more of sodium vanadium trifluorophosphate (Na3V2(PO4)2F3), Na3V2(PO4)2O2F, Na3V2(PO4)3, Na4VMn(PO4)3, Na4FeMn(PO4)3, Na3TiMn(PO4)3, Na4MnCr(PO4)3, Na3Fe2(SO4)3, NaFePO4, Na2FeP2O7, Na4Fe3(PO4)2P2O7, Na3NiZr(PO4)3, Na2FePO4F, and Na2FeSiO4; the negative electrode material is a carbon-based material, including one or more of hard carbon and soft carbon; the diaphragm is selected from one or more of glass fiber membrane and celgard membrane.

[0011] Particularly preferably, the positive electrode material of the battery is Na3V2(PO4)2F3 or Na3V2(PO4)2O2F.

[0012] Particularly preferably, the negative electrode material of the battery is a hard carbon material.

[0013] Particularly preferably, the separator of the battery is celgard.

[0014] One of the additives of the present invention -C≡N via N-Na + with Na + Coordination occurs, thereby participating in Na + Solvation structure modification to reduce the solvent and Na + The coordination number (because the electrolyte is mainly composed of solvent and Na + Coordination occurs and occupies most of the coordination sites. When additives are added, they will occupy some of the coordination sites of the solvent. During the charge and discharge process, Na+ The solvent, additives, and anions are carried between the positive and negative electrode surfaces in the form of a solvated structure. Therefore, the reduced solvent coordination number makes the solvent more stable at high voltage (>4.0V Na / Na + ) The frequency and probability of the positive electrode surface are reduced, thereby suppressing the oxidative decomposition of the electrolyte on the high voltage positive electrode surface (see Example 2 Figure 6 On the other hand, under the premise that the additive participates in the solvation structure, compared with the -CH2 / -CH3 group in the solvent, another -C≡N is preferentially adsorbed on the positive electrode surface to contact the high-voltage positive electrode, followed by preferential oxidation and decomposition to construct a stable cathode-electrolyte interface (Cathode Electrolyte Interface, CEI) rich in nitride (see Example 2). Figure 4 ). After adding the special structural additive to the designed electrolyte, the irreversible capacity loss of the battery can be significantly reduced and the cycle life of the battery can be significantly improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 a, structure of special structural additive; 1b, succinonitrile (SN);

[0016] Figure 2 |*1 and #5 have a constant potential of 4.2V (vs.Na / Na + ) electrolysis 1800s;

[0017] Figure 3 |*1 and &1 Linear sweep voltammetry(LSV)(2~6V vs.Na / Na + );

[0018] Figure 4 |XPS characterization of cathode (Na3V2(PO4)2F3)-electrolyte interface components formed by *1 and #2: a) C 1s, b) N1s;

[0019] Figure 5 |*1C cycle performance of #1 and #2 (Na3V2(PO4)2F3 cathode system);

[0020] Figure 6 |#2 Reduced solvent coordination number (obtained by fitting the Raman data). DETAILED DESCRIPTION

[0021] Ethylene carbonate / diethyl carbonate (1 / 1, volume ratio) solvent system:

[0022] Example 1 (#1)

[0023] In this example, 1 mol L -1NaPF6 electrolyte, the solvent is: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and malononitrile (MN) is added with a final mass percentage of 2%.

[0024] Example 2 (#2)

[0025] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and succinonitrile (SN) is added with a final mass percentage of 2%.

[0026] Example 3 (#3)

[0027] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and adiponitrile (DNB) is added with a final mass percentage of 2%.

[0028] Example 4 (#4)

[0029] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and 2% of pimelonitrile (DNP) is added.

[0030] Example 5 (#5)

[0031] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and 2% of suberonitrile (ON) is added.

[0032] DEGDME solvent system:

[0033] Example 6 (#6)

[0034] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is DEGDME, and malononitrile (MN) is added with a final mass percentage of 2%.

[0035] Example 7 (#7)

[0036] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is DEGDME, and succinonitrile (SN) is added with a final mass percentage of 2%.

[0037] Example 8 (#8)

[0038] In this example, 1 mol L -1NaPF6 electrolyte, the solvent is DEGDME, and adiponitrile (DNB) is added with a final mass percentage of 2%.

[0039] Example 9 (#9)

[0040] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is DEGDME, and DNP is added with a final mass percentage of 2%.

[0041] Example 10 (#10)

[0042] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is DEGDME, and suberonitrile (ON) is added with a final mass percentage of 2%.

[0043] Propylene carbonate / diethyl carbonate (1 / 1, volume ratio) solvent system:

[0044] Example 11 (#11)

[0045] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and malononitrile (MN) is added with a final mass percentage of 2%.

[0046] Example 12 (#12)

[0047] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and succinonitrile (SN) is added with a final mass percentage of 2%.

[0048] Example 13 (#13)

[0049] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and adiponitrile (DNB) is added with a final mass percentage of 2%.

[0050] Example 14 (#14)

[0051] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and 2% of pimelonitrile (DNP) is added.

[0052] Example 15 (#15)

[0053] In this example, 1 mol L -1NaPF6 electrolyte, the solvent is: propylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and 2% of suberonitrile (ON) is added.

[0054] Propylene carbonate / dimethyl carbonate (1 / 1, volume ratio) solvent system:

[0055] Example 16 (#16)

[0056] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio), and malononitrile (MN) is added with a final mass percentage of 2%.

[0057] Example 17 (#17)

[0058] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio), and succinonitrile (SN) is added with a final mass percentage of 2%.

[0059] Example 18 (#18)

[0060] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio), and adiponitrile (DNB) is added with a final mass percentage of 2%.

[0061] Example 19 (#19)

[0062] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio), and 2% of pimelonitrile (DNP) is added.

[0063] Example 20 (#20)

[0064] In this example, 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio), and suberonitrile (ON) is added with a final mass percentage of 2%.

[0065] Comparative ratio of blank samples of different solvent systems:

[0066] Comparative Example 1 (*1)

[0067] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, solvent: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio).

[0068] Comparative Example 2 (*2)

[0069] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, solvent is DEGDME.

[0070] Comparative Example 3 (*3)

[0071] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, solvent: propylene carbonate / diethyl carbonate = 1 / 1 (volume ratio).

[0072] Comparative Example 4 (*4)

[0073] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, solvent: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio).

[0074] Comparative example of single nitrile additive:

[0075] Comparative Example 5 (*5)

[0076] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, the solvent is: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and acrylonitrile (ANN) is added with a final mass percentage of 2%.

[0077] Comparative Example 6 (*6)

[0078] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, the solvent is DEGDME, and acrylonitrile (ANN) is added with a final mass percentage of 2%.

[0079] Comparative Example 7 (*7)

[0080] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and acrylonitrile (ANN) is added with a final mass percentage of 2%.

[0081] Comparative Example 8 (*8)

[0082] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, the solvent is: propylene carbonate / dimethyl carbonate = 1 / 1 (volume ratio), and acrylonitrile (ANN) is added with a final mass percentage of 2%.

[0083] Comparative ratio of different additive contents:

[0084] Comparative Example 9 (*9)

[0085] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, solvent: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), added with a final mass percentage of 0.2% succinonitrile (SN).

[0086] Comparative Example 10 (*10)

[0087] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, the solvent is: ethylene carbonate / diethyl carbonate = 1 / 1 (volume ratio), and succinonitrile (SN) is added with a final mass percentage of 12%.

[0088] Experimental example

[0089] Experimental Example 1(&1)

[0090] This comparative example prepared 1 mol L -1 NaPF6 electrolyte, the solvent is succinonitrile (SN).

[0091] Specific experimental process:

[0092] Since the solvent in the electrolyte has a lower potential at the negative electrode (<1.0V Na / Na + ) is very likely to undergo reduction decomposition, which makes it impossible to explain the effect of the additives in the electrolyte of the present invention on the positive electrode side. Therefore, Na3V2(PO4)3(NVP) with a potential of 1.6V was selected as the negative electrode in the battery performance test.

[0093] Constant Potential Electrolysis

[0094] The above electrolytes #2 and *1 were injected into the electrolytic cell (with a Pt sheet of length * width * thickness of 10 * 10 * 0.1 mm as the working electrode, Cu of the same shape and area as the working electrode, and metal Na of the same shape and area as the reference electrode) at 1 mVs -1 The voltage was increased to 4.2 V (vs. Na / Na + ), and then conduct a constant potential electrolysis test at 4.2V for 1800s. The results are as follows Figure 2 As shown, after adding the special structural functional additive of the invention, the peak oxidation current and the stabilized oxidation current of the electrolyte (#2) were weakened to 1 / 6 and 1 / 3 of *1 respectively, indicating that the additive can effectively inhibit the oxidative decomposition of the electrolyte under high voltage.

[0095] Linear Scan Voltammetry Test (LSV)

[0096] In order to prove the preferential oxidative decomposition of the additives, the same apparatus as the constant potential electrolysis was used to inject the *1 and &1 electrolytes at 1 mV s -1The scanning rate is between 2 and 6 V (vs. Na / Na + ) voltage range, and the Linear Scan Voltammetry test (LSV for short) is obtained. Figure 3 The results show that the oxidation potential of the additive of the present invention (initial oxidation potential is 3.3V, oxidation peak appears at 3.7V) is lower than that of the solvent (4.0V), so the additive undergoes preferential oxidation to construct a nitride-rich CEI (such as Figure 4 shown).

[0097] Battery performance test

[0098] 120 μL of the electrolytes of the above embodiments and comparative examples were injected into the sodium ion battery cell (the positive electrode was Na3V2(PO4)2F3 and Na3V2(PO4)2O2F, respectively, wherein the electrode components included electrode active material, conductive agent carbon black, and binder PVDF, which were fully mixed at a mass ratio of 94:3:3 and then coated on aluminum foil. The mixture was placed in a vacuum oven at 85°C for 24 hours, and the final loading on the aluminum foil was 3.44 mg cm -2 , cut into a circular electrode sheet with a diameter of 14 mm; the negative electrode is Na3V2(PO4)3, prepared in the same way as the positive electrode, with a loading of 11.29 mg / cm on aluminum foil -2 , cut into 16mm diameter circular electrode sheets; the membrane is a 16mm diameter glass fiber membrane. ), assemble a CR2032 type buckle battery, and charge at 0.2C at 1.5~2.8V (2~4.3V vs.Na / Na + ) for activation (0.2C charge to 2.8V, 0.2C discharge to 1.5V), and then 1C cycle performance test within 1.5~2.8V, the results are shown in Figure 5 , Table 1 and Table 2.

[0099] Table 1 1C cycle test results of Na3V2(PO4)2F3 cathode at room temperature

[0100]

[0101]

[0102] Table 2 Na3V2(PO4)2O2F 1C cycle test results at room temperature

[0103]

[0104] The present invention finds that after applying the special structural functional additive in the electrolyte, the amount of sodium ions consumed in the positive electrode bulk phase is reduced due to the reduction in oxidative decomposition of the solvent, which is reflected in the battery performance as a reduction in the irreversible capacity loss of the battery, that is, the reversible cycle capacity of the battery is improved, and at the same time the cycle life of the battery can be significantly improved.

[0105] Although the present invention has been described in detail above with general descriptions and specific embodiments, it is obvious to those skilled in the art that some modifications or improvements may be made thereto based on the present invention. Therefore, these modifications or improvements made without departing from the spirit of the present invention all fall within the scope of protection claimed by the present invention.

[0106] From the results, it can be seen that the irreversible capacity loss of the battery using the electrolyte of the present invention is reduced and the cycle life of the battery can be significantly improved.

Claims

1. An additive for sodium ion battery electrolyte, characterized in that: Including one or more of the structural compounds represented by Formula 1a or Formula 1b; Formula 1a, special structure additive structure; 1b, succinonitrile (SN) Where R1 is C 1-10 alkyl.

2. A sodium ion battery electrolyte, characterized in that: Contains one or more of the additives described in claim 1.

3. The electrolyte according to claim 2, characterized in that: The mass percentage of the additive in the electrolyte is 0.5-10%, preferably 1-5%, more preferably 2-3%.

4. The electrolyte according to claim 2 or 3, characterized in that: It also contains organic solvents and sodium salts; The organic solvent includes one or more of cyclic carbonate, chain carbonate, and dimethyl ether; The cyclic carbonate is selected from one or both of ethylene carbonate and propylene carbonate; The linear carbonate is selected from one or more of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, dipropyl carbonate, and methyl propyl carbonate; The dimethyl ether is selected from one or more of dimethyl ether (DME), diethylene glycol dimethyl ether (DEGDME), and tetraethylene glycol dimethyl ether (TEGDME); When two or more solvents are contained, it is preferred that the solvents are mixed in an equal volume ratio; The sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate, sodium trifluoromethanesulfonate, sodium bistrifluoromethanesulfonimide and sodium bis(trifluoromethanesulfonyl)imide; The sodium salt concentration in the electrolyte is 0.2-3 mol L -1 , preferably 0.5-1.5 mol L -1 , more preferably 1 mol L -1 .

5. A sodium ion battery, characterized in that: The electrolyte used is the electrolyte described in any one of claims 2 to 4.

6. The battery according to claim 5, characterized in that: The sodium ion battery is composed of a negative electrode, a separator and a polyanion positive electrode, which are arranged in sequence in an electrolyte; The positive electrode active material of the sodium ion battery is a polyanionic compound, which includes one or more of Na3V2(PO4)2F3, Na3V2(PO4)2O2F, Na3V2(PO4)3, Na4VMn(PO4)3, Na4FeMn(PO4)3, Na3TiMn(PO4)3, Na4MnCr(PO4)3, Na3Fe2(SO4)3, NaFePO4, Na2FeP2O7, Na4Fe3(PO4)2P2O7, Na3NiZr(PO4)3, Na2FePO4F, and Na2FeSiO4.

7. The battery according to claim 6, characterized in that: The negative electrode material of the sodium ion battery is a carbon-based material, including one or more of hard carbon, soft carbon, or Na3V2(PO4)3; the diaphragm is selected from one or more of glass fiber membrane and celgard membrane, preferably celgard membrane.

8. The battery according to claim 5, 6 or 7, characterized in that: The negative electrode and the polyanion positive electrode of the sodium ion battery are separated by a diaphragm and sequentially arranged in the electrolyte.

9. The battery according to claim 5, 6 or 7, characterized in that: The positive electrode voltage during charge and discharge is 2-4.7V, preferably 2-4.3V, and can withstand high voltage (>4.0V vs.Na / Na + ).

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