Sodium ion battery electrolyte and sodium ion battery

Abstract

The present invention belongs to the field of sodium ion batteries, and discloses a sodium ion battery electrolyte, including a sodium salt and a solvent, and also including an additive, wherein the additive has the following general formula I; wherein at least two of the three substituents R are amino groups and nitrile groups. Since the thiazolyl group and the amino group have weak alkalinity, they have the effect of reducing the HF content under high voltage, reducing the precipitation of metal ions in the positive electrode, and enhancing the stability of the interface film between the positive electrode and the electrolyte. The nitrile group can complex the ions of the positive electrode of the sodium ion battery to form an interface film on the surface of the positive electrode. The interface film can effectively inhibit the decomposition of the electrolyte and reduce the precipitation of metal ions, thereby improving the cycle performance of the high voltage system. In addition, the present invention also discloses a sodium ion battery.

Description

Technical Field

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

[0002] In recent years, sodium-ion battery technology has regained the favor of researchers due to its advantages such as abundant global sodium resources, low cost, and similar energy storage principles and process technologies as sodium-ion batteries, and has developed into an energy storage technology with great application potential. Although sodium-ion batteries have the potential advantage of low cost, their cycle life and rate performance still cannot meet the needs of today's large-scale energy storage technology. There is still a lack of in-depth understanding and regulation of the interface reaction, formation and properties of the interface film of sodium-ion battery electrode materials, which to a large extent hinders the improvement of the rate, cyclability, energy density, safety, and storage life of sodium-ion battery electrode materials. Increasing the working voltage of the battery is one of the effective ways to improve the energy density of sodium-ion batteries, but increasing the voltage can easily lead to the dissolution of transition metals in the positive electrode materials of sodium-ion batteries and the decomposition of commercial carbonate-based electrolytes. It can be seen that improving the stability of the battery's electrode / electrolyte (especially the positive electrode / electrolyte) interface is the basic prerequisite for the development of high-voltage sodium-ion batteries.

[0003] 202111144326.8 proposes an electrolyte additive in which a first additive (a silicon-containing additive) and a second additive (a boron-containing additive) cooperate with each other. The first additive can spontaneously react with trace water and hydrofluoric acid in the electrolyte to inhibit the hydrolysis of sodium hexafluorophosphate; the second additive can form a stable interface film on the surface of the positive and negative electrodes.

[0004] 202110729612.4 A sodium ion battery electrolyte additive is proposed, which is used in combination with additive a and additive b (nitrile-containing phosphate ester), which can form a stable and dense interface film on the surface of the positive and negative electrodes, reducing side reactions with the electrolyte.

[0005] The problem that this solution needs to solve is: How to develop a new additive to inhibit hydrofluoric acid in the electrolyte and form a stable interface film on the positive electrode surface. Summary of the invention

[0006] The purpose of the present invention is to provide a sodium ion battery electrolyte and a sodium ion battery, wherein the additive contains three effective groups, namely, an imidazole group, an amino group and a nitrile group. The thiazole group and the amino group are both weakly alkaline, so they can effectively reduce HF in the electrolyte, thereby reducing the precipitation of ions in the positive electrode of the battery and enhancing the stability of the interface film between the positive electrode and the electrolyte; the cyano group can complex the metal of the positive electrode of the sodium ion battery and form a film on the surface of the positive electrode, and the interface film can effectively inhibit the decomposition of the electrolyte and reduce the precipitation of positive electrode ions.

[0007] Unless otherwise specified in the present invention: nM represents nanomole / liter, μM represents micromole / liter, mM represents millimole / liter, and M represents mole / liter;

[0008] A sodium ion battery electrolyte comprises a sodium salt and a solvent, and also comprises an additive, wherein the additive has the following general formula I:

[0009]

[0010] Among them, at least two of the three substituents R are amino groups and nitrile groups.

[0011] Preferably, the additive is at least one of the following compounds:

[0012]

[0013]

[0014] Preferably, it also includes auxiliary additives, and the auxiliary additives have the following structural formula I:

[0015]

[0016] The mass ratio of the auxiliary additive to the additive is 1:2-4, preferably 1:3.

[0017] Preferably, the sodium salt is sodium hexafluorophosphate; the sodium salt may also be a combination of any proportion of sodium hexafluorophosphate and one or more of sodium nitrate, sodium perchlorate, sodium difluorophosphate, sodium bisoxalatoborate, sodium difluorooxalatoborate, sodium bistrifluoromethylsulfonyl imide and sodium bisfluorosulfonyl imide.

[0018] The solvent is selected from one or more of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate.

[0019] Preferably, the mass of the additive accounts for 0.1% to 5.0% of the total mass of the sodium salt and the solvent.

[0020] Preferably, the concentration of the sodium salt in the electrolyte is 0.5M to 1.5M.

[0021] In addition, the present invention also provides a sodium ion battery, comprising a positive electrode, a negative electrode, a separator and the sodium ion battery electrolyte as described above.

[0022] Preferably, the positive electrode material is sodium phosphovanadate. In addition, the positive electrode material can also be selected from one or more of Nax CoO2, Nax MnO2, NaNi0.33Fe0.33Mn0.33O2, NaFePO4, NaCoPO4, Na3V2(PO4)3; the negative electrode material is selected from one or more of soft carbon, hard carbon, sodium titanate and metals that can form alloys with sodium.

[0023] The beneficial effects of the present invention are:

[0024] The present invention provides a sodium ion battery electrolyte and a sodium ion battery. The additive contains three effective groups, namely, an imidazole group, an amino group and a nitrile group. The thiazole group and the amino group are both weakly alkaline, so they can effectively reduce HF in the electrolyte, thereby reducing the precipitation of ions in the positive electrode of the battery and enhancing the stability of the interface film between the positive electrode and the electrolyte; the cyano group can complex the metal of the positive electrode of the sodium ion battery and form a film on the surface of the positive electrode. The interface film can effectively inhibit the decomposition of the electrolyte and reduce the precipitation of positive electrode ions.

[0025] The present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than 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. DETAILED DESCRIPTION

[0026] In the description of the present invention, it should be noted that, if the specific conditions are not specified in the examples, the experiments were carried out according to conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used, if the manufacturer is not specified, are all conventional products that can be purchased commercially.

[0027] Example 1

[0028] Preparation of electrolyte: Ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC) are mixed in a mass ratio of EC:DEC:EMC=1:1:1, and then 1 mol of sodium hexafluorophosphate (NaPF6) is added to make the sodium salt concentration in the electrolyte reach 1M. After the sodium salt is completely dissolved, 0.5% of compound 1 additive is added.

[0029] 2. Preparation of positive electrode sheet: Sodium vanadium phosphate Na3V2(PO4)3, conductive agent SuperP, adhesive PVDF and carbon nanotubes (CNT) are mixed evenly in a mass ratio of 95:2.3:2:0.7 to form a sodium ion battery positive electrode slurry with a certain viscosity, and coated on the aluminum foil for current collector, with a coating amount of 30g / m 2, dried at 85°C and then cold pressed; then trimmed, cut into pieces, and slit, and after slitting, dried at 85°C under vacuum conditions for 4 hours, and the tabs were welded to make a sodium ion battery positive electrode that meets the requirements.

[0030] 3. Preparation of negative electrode sheet: hard carbon, conductive agent SuperP, thickener CMC, and adhesive SBR (styrene-butadiene rubber latex) are made into slurry in a mass ratio of 95:1.5:1.0:2.5, mixed evenly, and the mixed slurry is coated on both sides of the copper foil, and then dried and rolled to obtain the negative electrode sheet, thereby making a sodium ion battery negative electrode sheet that meets the requirements.

[0031] 4. Preparation of sodium ion battery: The positive electrode sheet, negative electrode sheet and separator prepared according to the above process are laminated to form a sodium ion battery with a thickness of 4.7mm, a width of 55mm and a length of 60mm. They are vacuum baked at 75°C for 10 hours and the above electrolyte is injected. After standing for 24 hours, they are charged to 4.5V with a constant current of 0.1C (180mA), and then charged with a constant voltage of 4.5V until the current drops to 0.05C (90mA); then discharged to 3.0V with 0.2C (180mA), and the charge and discharge are repeated twice. Finally, the battery is charged to 3.8V with 0.2C (180mA) to complete the battery production.

[0032] Examples 2 to 4

[0033] The steps are basically the same as those in Example 1, except that the addition amounts of Compound 1 are 1.0%, 2.0% and 5.0% respectively.

[0034] Example 5

[0035] The steps are basically the same as those in Example 1, except that the additive is a composite additive of Compound 1, Compound 2, and Compound 3, the total amount of the additive is 1%, and the mass ratio of Compound 1: Compound 2: Compound 3 is 1:1:1.

[0036] Example 6

[0037] The steps are basically the same as those in Example 1, except that the additive is a composite additive of Compound 2, Compound 3, and Compound 5, the total amount of the additive is 1%, and the mass ratio of Compound 2: Compound 3: Compound 5 is 1:1:1.

[0038] Example 7

[0039] The steps are basically the same as those in Example 1, except that the additive is a composite additive of Compound 2, Compound 3, and Compound 6, the total amount of the additive is 1%, and the mass ratio of Compound 2: Compound 3: Compound 6 is 1:1:1.

[0040] Example 8

[0041] The steps are basically the same as those in Example 1, except that the additive is a composite additive of compound 2, compound 3, compound 5 and an auxiliary additive having structural formula I, the total amount of the additive is 1%, and the mass ratio of compound 2: compound 3: compound 5: auxiliary additive is 1:1:1:1.

[0042] Example 9

[0043] The steps are basically the same as those in Example 1, except that propylene carbonate PC, diethyl carbonate DEC, and ethyl methyl carbonate EMC are selected as organic solvents, wherein the mass ratio of PC:DEC:EMC is 1:1:1, and the concentration of sodium hexafluorophosphate (NaPF6) is 0.8 mol / L.

[0044] Example 10

[0045] The steps are basically the same as those in Example 1, except that propylene carbonate PC, diethyl carbonate DEC, and ethyl methyl carbonate EMC are selected as organic solvents, wherein the mass ratio of PC:DEC:EMC is 1:1:1, and the concentration of sodium hexafluorophosphate (NaPF6) is 1.2 mol / L.

[0046] Comparative Examples 1 to 4

[0047] The electrolyte preparation method and battery preparation method refer to Example 1;

[0048] Comparative Example 1 does not add additives;

[0049] The additive used in Comparative Example 2 is Comparative Compound 1;

[0050] The additive used in Comparative Example 3 is Comparative Compound 2;

[0051] The additive used in Comparative Example 3 is Comparative Compound 3;

[0052] The additive amounts used in Comparative Examples 2 to 4 were all 1.0%.

[0053] Comparative Example 5

[0054] Comparative compounds 1 to 3 were added, each at 1.0% and the total amount was 3%.

[0055] Comparative compounds 1 to 3 are as follows:

[0056]

[0057] Comparative Examples 6 to 9

[0058] The electrolyte preparation method and battery preparation method refer to Example 1, the additives are comparative compounds 4 to 7, and the addition amount of the additives is 1.0%.

[0059] Comparative compounds 4 to 7 are as follows:

[0060]

[0061] The electrolyte components and battery systems of the above examples and comparative examples are shown in Table 1.

[0062] Table 1: Electrolyte compositions and battery systems of the embodiments and comparative examples.

[0063]

[0064]

[0065] Performance tests of embodiments and comparative examples:

[0066] 25℃1.0C / 1.0C normal temperature cycle test: Charge to 4.5V at 1.0C constant current at 25℃, charge to 4.5V at constant voltage of 4.5V to cut-off current of 0.05C, and then discharge the battery at 1.0C constant current. The discharge capacity is recorded as C0. Repeat the charge and discharge steps for 1000 cycles to obtain the 1000th cycle discharge capacity C1000. The capacity retention rate = C1000 / C0*100%.

[0067] Capacity retention rate test after 14-day storage at 60°C: After the battery is cycled 3 times at a charge and discharge rate of 1C, it is stored at 60°C for 14 days under full charge and then discharged. The obtained discharge capacity is divided by the discharge capacity of the first cycle to obtain the capacity retention rate after high-temperature storage.

[0068] -20℃ low temperature discharge test: charge at 25℃ with 1.0C constant current to 4.5V, charge at 4.5V constant voltage to cut-off current

[0069] 0.05C, then discharge the battery at 0.5C constant current, the discharge capacity is recorded as C0. At 25℃, charge to 4.5V at 1.0C constant current, charge to 0.05C at 4.5V constant voltage, then transfer the battery to -20℃ for 240min, then discharge the battery at 0.5C constant current, the discharge capacity is recorded as C1, -20℃ discharge rate = C1 / C0*100%.

[0070] After the electrolytes in the above embodiments and comparative examples were made into sodium ion batteries, the room temperature cycle energy absorption, high temperature cycle performance, high temperature storage performance, and low temperature discharge performance of the sodium ion batteries were tested. The results are shown in Table 2:

[0071] Table 2: Sodium ion battery performance test results

[0072]

[0073] analyze:

[0074] 1. It can be seen from Examples 1-4 that the compound of the present invention has the best performance when the addition amount is controlled at 1-2%.

[0075] 2. It can be seen from Examples 5-7 that the compounding of the compounds of the present invention has no obvious optimization effect on the product performance;

[0076] 3. It can be seen from Examples 2 and 8 of the present invention that the addition of auxiliary additives has a promoting effect on the additives of the present invention in terms of high-temperature storage and low-temperature discharge;

[0077] 4. It can be seen from Examples 2 and 9-10 of the present invention that the solvent is preferably ethylene carbonate (EC), diethyl carbonate (DEC) and ethyl methyl carbonate (EMC).

[0078] 5. It can be seen from Example 2 of the present invention and Comparative Examples 1-5 that the additive of the present invention is superior to Comparative Compounds 1-3;

[0079] 6. It can be seen from Example 2 of the present invention and Comparative Examples 6-9 that the additive of the present invention must contain an imidazole group, an amino group and a nitrile group, and the combination of these three has a synergistic effect on improving the overall comprehensive performance.

Claims

1. A sodium ion battery electrolyte, comprising a sodium salt and a solvent, characterized in that: Also included are additives having the following general formula I: Among them, at least two of the three substituents R are amino groups or nitrile groups; It also includes auxiliary additives, which have the following structural formula I: The mass ratio of the auxiliary additive to the additive is 1:2-4.

2. The sodium ion battery electrolyte according to claim 1, characterized in that The additive is at least one of the following compounds:

3. The sodium ion battery electrolyte according to claim 1, characterized in that The sodium salt is sodium hexafluorophosphate; The solvent is selected from one or more of ethylene carbonate EC, propylene carbonate PC, dimethyl carbonate DMC, diethyl carbonate DEC, and ethyl methyl carbonate EMC.

4. The sodium ion battery electrolyte according to claim 1, characterized in that The mass of the additive accounts for 0.1% to 5.0% of the total mass of the sodium salt and the solvent.

5. The sodium ion battery electrolyte according to claim 1, characterized in that The concentration of the sodium salt in the electrolyte is 0.5M to 1.5M.

6. A sodium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and a sodium ion battery electrolyte as claimed in any one of claims 1 to 5.

7. The sodium ion battery according to claim 6, characterized in that: The material of the positive electrode is sodium phosphovanadate.

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