Battery electrolyte with excellent cycle performance, preparation method and sodium ion battery

Abstract

The invention discloses a battery electrolyte with excellent cycle performance, a preparation method and a sodium ion battery, and belongs to the technical field of sodium ion batteries. The electrolyte comprises sodium salt, a solvent and an additive, the sodium salt is one or more of sodium hexafluorophosphate, sodium perchlorate and bis (trifluoromethylsulfonyl) imide sodium, the solvent is composed of cyclic carbonate and a linear carbonate solvent, and the additive is phosphorus / silicon ion-containing liquid. A phosphite ester compound containing a siloxy group and a phosphorus oxy group is used as an additive, the additive can participate in film formation in the system, one end of the siloxy group reacts with an inorganic matter to form a low-solubility phosphate component, and the other end of the siloxy group is compatible with an organic matter; therefore, the solid electrode / electrolyte interfacial film which is compact, high in polymerization degree and low in solubility and is composed of organic, silica and inorganic is formed. The existence of the phosphorus-oxygen group can play a role in removing water and inhibiting acid, so that the phenomenon of producing gas and acid in the battery is effectively inhibited, and the cycle performance and the rate capability of the battery are greatly improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion batteries, and in particular relates to a battery electrolyte with excellent cycle performance, a preparation method thereof, and a sodium ion battery. Background Art

[0002] Compared with lithium-ion batteries, sodium-ion batteries have the characteristics of low cost, high natural abundance, high energy density, and excellent safety performance. As an emerging energy storage technology, sodium-ion batteries have shown broad application prospects in the power field, especially in the low-speed electric vehicles and two-wheeled vehicle markets; in addition, sodium-ion batteries can also be used in the energy storage field, such as renewable energy access, industrial energy storage, etc. Therefore, sodium-ion batteries are regarded as a promising energy storage supplement technology in the field of electric vehicles and fixed energy storage.

[0003] As one of the important components of sodium-ion batteries, the electrolyte plays the role of transporting ions between the positive and negative electrodes through the battery. It has an important impact on the battery's capacity, operating temperature range, cycle performance and safety performance. When the battery is working, the electrolyte decomposes on the surface of the negative electrode to form a solid electrode / electrolyte interface film (SEI) with more organic components and less inorganic components. However, the SEI film of the sodium-ion battery is unstable during the charge and discharge process, and it constantly dissolves and regenerates, resulting in continuous decomposition of the electrolyte, thereby affecting the coulombic efficiency and cycle performance of the sodium-ion battery. Since Younesi et al. invented a method for constructing a low-solubility SEI film rich in inorganic substances through additives in 2016, the process of constructing a low-solubility SEI film through electrolyte design has been continuously optimized.

[0004] Zhang et al. designed a local high-concentration electrolyte, namely 1M sodium bis(fluorosulfonyl)imide dissolved in a mixed solvent system of triethyl phosphate and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether, to form an inorganic SEI film on the surface of hard carbon (HC). In addition, Fei et al. prepared an insoluble SEI film by designing a high-concentration electrolyte and applied it in a commercial electrolyte. Although the high-concentration and local high-concentration electrolyte methods can effectively inhibit the dissolution of the SEI film and improve the battery cycle life, there are problems such as complex preparation process, high cost, low ionic conductivity, and it is not suitable for large-scale production. Zhang et al. proposed a low-solvation electrolyte. The introduction of a low-polarity fluorinated phosphate solvent can not only construct an anion-rich solvation structure and form an inorganic-rich SEI film, but also reduce the ability of the solvent to dissolve the SEI on the hard carbon anode. The SEI film derived from this electrolyte has low solubility and good cycle stability of sodium ion batteries, but the introduction of low-polarity solvents leads to low ionic conductivity of the electrolyte. At the same time, the selected sulfur-containing sodium salt causes the battery to produce gas and the current collector to corrode. Patent publication number CN118825415A discloses an electrolyte in which sodium hexafluorophosphate and sodium bis(fluorosulfonyl)imide are mixed and dissolved in an ether solvent, and a certain proportion of phosphorus-containing or boron-containing solvents are added. This electrolyte system has good conductivity and stability, constructs an inorganic-rich SEI film, and improves the high and low temperature cycle stability of sodium ion batteries, but ether solvents are flammable and easy to decompose under high voltage, which is difficult to meet the application under extreme conditions. In addition, the excessive introduction of boron-containing solvents will lead to increased battery polarization, severe attenuation of the positive electrode voltage, and increased production costs. Summary of the invention

[0005] In view of the problem that the current sodium ion battery has a decreased cycle performance due to the dissolution of the SEI film, and at the same time overcoming the technical defects of the existing high-concentration / low-solvation electrolyte such as complex preparation, high cost, low ion conductivity and corrosion side reactions, the present invention proposes a sodium ion battery electrolyte that can form an inorganic-rich SEI film, inhibit the dissolution of the SEI film, and improve the cycle performance of the sodium ion battery, while not affecting other battery properties.

[0006] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0007] A method for preparing a battery electrolyte with excellent cycle performance comprises the following steps:

[0008] Step 1, using a carbonate solvent as a solvent, melting a cyclic carbonate, then mixing it with a linear carbonate, and cooling it to room temperature to obtain a binary solvent;

[0009] Step 2, mixing the binary solvent and the electrolyte salt, stirring evenly, to obtain a basic electrolyte;

[0010] Step 3, mixing the dehydrated and dried phosphorus / silicon-containing additive and the basic electrolyte at a certain mass ratio, at a constant temperature, and stirring evenly to obtain a phosphorus / silicon-containing electrolyte;

[0011] The above preparation process needs to be carried out under argon atmosphere, and the content of H2O and O2 should be less than 0.1ppm.

[0012] Furthermore, the cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate, and the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

[0013] Furthermore, the cyclic carbonate melts at 40 to 65° C.; and the volume ratio of the cyclic carbonate to the linear carbonate is 0.5 to 1:1.

[0014] Furthermore, the cooling temperature in step 1 is cooled to 25°C.

[0015] Furthermore, the electrolyte salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium bis(trifluoromethylsulfonyl)imide; and the molar concentration of the electrolyte salt is 0.7 to 1.5 mol / L.

[0016] Furthermore, the phosphorus / silicon-containing additive includes one or more of tris(trimethylsilyl)phosphite and tris(trimethylsilane)phosphate.

[0017] Furthermore, the amount of the phosphorus / silicon additive added to the phosphorus / silicon-containing electrolyte is 0.5 to 10 wt.%.

[0018] Furthermore, the stirring in step 2 is carried out at a speed of 100 to 300 r / min for 2 to 5 hours; and the stirring in step 3 is carried out at a speed of 100 to 300 r / min for 12 to 36 hours.

[0019] Furthermore, the mixing temperature in step 3 is 25°C.

[0020] Furthermore, the phosphorus / silicon additive is Molecular sieve drying to remove water.

[0021] A battery electrolyte with excellent cycle performance prepared by the above preparation method.

[0022] A sodium ion battery containing a battery electrolyte with excellent cycle performance. The negative electrode material of the sodium ion battery is hard carbon.

[0023] Compared with the prior art, the present invention has the following advantages:

[0024] (1) The present invention uses phosphite compounds containing silicon oxygen groups and phosphorus oxygen groups as additives. In this system, the additives can participate in film formation. One end of the silicon oxygen group reacts with inorganic matter to form a low-solubility phosphate component, and the other end is compatible with organic matter, thereby forming a dense, highly polymerized, and low-solubility organic-silicon oxygen-inorganic solid electrode / electrolyte interface film (SEI), which can effectively improve the cycle performance of sodium ion batteries.

[0025] (2) In the present invention, the introduction of phosphorus / silicon-containing additives after dehydration and drying can effectively avoid the influence of water on battery performance. At the same time, the presence of phosphorus oxygen groups can be beneficial to the capture of HF and PF5, thereby inhibiting the gas and acid production in the battery.

[0026] The phosphorus / silicon electrolyte provided by the present invention has the advantages of high ion conductivity, high thermal stability, and good compatibility with other parts of the battery. It is used in sodium ion battery electrolytes to effectively improve the battery's cycle performance, rate performance, and safety performance. In addition, the preparation method of the functional electrolyte is simple, low-cost, and easy to scale. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings required for use in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0028] Figure 1 This is the SEI solubility diagram of the electrolyte obtained in Experimental Example 1 of the present invention.

[0029] Figure 2 This is a cycle performance diagram of the electrolyte obtained in Test Example 2 of the present invention.

[0030] Figure 3 This is a rate performance diagram of the electrolyte obtained in Experimental Example 3 of the present invention. DETAILED DESCRIPTION

[0031] In order to gain a deeper understanding of the present invention, we will provide a comprehensive and detailed description of the present invention. However, the present invention has multiple implementations and is not limited to the specific examples listed herein. The presentation of these examples is intended to deepen the comprehensive understanding of the disclosure of the present invention.

[0032] Example 1

[0033] (1) Using a carbonate solvent as a solvent, first, ethylene carbonate is melted at 45° C., then mixed evenly with diethyl carbonate at a volume ratio of 1:1, and cooled to 25° C. to obtain a binary solvent.

[0034] (2) 167.95 g / mol of sodium hexafluorophosphate (NaPF6) was used as an electrolyte salt. NaPF6 and a binary solvent were mixed at a molar ratio of 1 mol / L at a constant temperature of 25° C. and stirred at a speed of 300 r / min for 2 h to obtain a basic electrolyte.

[0035] (3) Additive tris(trimethylsilyl)phosphite (TMSPi) is used The molecular sieve is dried to remove water. Then the additive and the basic electrolyte are mixed at a mass ratio of 1:49 at a constant temperature of 25°C and stirred at a speed of 300 r / min for 24 hours to obtain a phosphorus / silicon electrolyte.

[0036] (4) The above process must be carried out in a glove box filled with argon, where the content of H2O and O2 must be less than 0.1 ppm.

[0037] Example 2

[0038] (1) Using a carbonate solvent as a solvent, first, ethylene carbonate is melted at 60° C., then mixed evenly with ethyl methyl carbonate at a volume ratio of 1:1, and cooled to 25° C. to obtain a binary solvent.

[0039] (2) 167.95 g / mol of sodium hexafluorophosphate (NaPF6) was used as an electrolyte salt. NaPF6 and a binary solvent were mixed at a molar ratio of 1 mol / L at a constant temperature of 25° C. and stirred at a speed of 300 r / min for 2 h to obtain a basic electrolyte.

[0040] (3) Additive tris(trimethylsilyl) phosphate (TMSP) is used Molecular sieve drying to remove water. Then the additive and the basic electrolyte are mixed at a mass ratio of 1:99 at a constant temperature of 25°C and stirred at a speed of 300r / min for 12h to obtain a phosphorus / silicon electrolyte.

[0041] (4) The above process must be carried out in a glove box filled with argon, where the content of H2O and O2 must be less than 0.1 ppm.

[0042] Example 3

[0043] (1) A carbonate solvent is used as a solvent. First, ethylene carbonate is melted at 50° C., then mixed evenly with diethyl carbonate at a volume ratio of 3:7, and cooled to 25° C. to obtain a binary solvent.

[0044] (2) 167.95 g / mol of sodium hexafluorophosphate (NaPF6) was used as an electrolyte salt. NaPF6 and a binary solvent were mixed at a molar ratio of 1 mol / L at a constant temperature of 25° C. and stirred at a speed of 300 r / min for 4 h to obtain a basic electrolyte.

[0045] (3) Additive tris(trimethylsilyl)phosphite (TMSPi) is used Molecular sieve drying to remove water. Then the additive and the basic electrolyte are mixed at a mass ratio of 1:99 at a constant temperature of 25°C and stirred at a speed of 300r / min for 24h to obtain a phosphorus / silicon electrolyte.

[0046] (4) The above process must be carried out in a glove box filled with argon, where the content of H2O and O2 must be less than 0.1 ppm.

[0047] Example 4

[0048] (1) A carbonate solvent is used as a solvent. First, ethylene carbonate is melted at 50° C., then mixed evenly with ethyl methyl carbonate at a volume ratio of 1:1, and cooled to 25° C. to obtain a binary solvent.

[0049] (2) 167.95 g / mol of sodium hexafluorophosphate (NaPF6) was used as an electrolyte salt. NaPF6 and a binary solvent were mixed at a molar ratio of 1 mol / L at a constant temperature of 25° C. and stirred at a speed of 300 r / min for 4 h to obtain a basic electrolyte.

[0050] (3) Additive tris(trimethylsilyl)phosphite (TMSPi) is used Molecular sieve drying to remove water. Then the additive and the basic electrolyte are mixed at a mass ratio of 1:199 at a constant temperature of 25°C and stirred at a speed of 300r / min for 24h to obtain a phosphorus / silicon electrolyte.

[0051] (4) The above process must be carried out in a glove box filled with argon, where the content of H2O and O2 must be less than 0.1 ppm.

[0052] Comparative Example 1

[0053] (1) Using a carbonate solvent as a solvent, first, ethylene carbonate is melted at 60° C., then mixed evenly with ethyl methyl carbonate at a volume ratio of 1:1, and cooled to 25° C. to obtain a binary solvent.

[0054] (2) 167.95 g / mol of sodium hexafluorophosphate (NaPF6) was used as an electrolyte salt. NaPF6 and a binary solvent were mixed at a molar ratio of 1 mol / L at a constant temperature of 25° C. and stirred at a speed of 300 r / min for 2 h to obtain a basic electrolyte.

[0055] (3) The above process must be carried out in a glove box filled with argon, where the content of H2O and O2 must be less than 0.1 ppm.

[0056] Test Example 1

[0057] The electrolytes of Example 1 and Comparative Example 1 were used to assemble Cu||Na batteries, and Cu foil was used as the working electrode. The batteries were assembled in a glove box filled with argon. The two groups of batteries obtained in Example 1 and Comparative Example 1 were subjected to SEI solubility measurement. The test method was to cycle at a constant current density within a voltage range of 0.005-2V, and after every 5 cycles, stand for 50, 30, 15, and 5 hours, respectively. The discharge capacity increment before and after each standing indicated the electrolyte reduction reaction of the anode, which was used to indicate the dissolution of the SEI film during the standing period.

[0058] The solubility measurement results are as follows Figure 1 As shown, the SEI solubility of the Cu||Na half-cell using the electrolyte of Comparative Example 1 is the highest, and the capacity loss after standing for 50 hours is 3.20μAh, and the SEI film solubility is proportional to the increase in the standing time. The SEI film solubility formed by the battery using the electrolyte of Example 1 is low, and the capacity loss after standing for 50 hours is 1.20μAh, and the SEI film solubility is significantly improved, which shows that the use of the electrolyte of Example 1 can effectively construct a low-solubility SEI film.

[0059] Test Example 2

[0060] The electrolytes of Example 1, Example 2, Example 4 and Comparative Example 1 were used to assemble Na||HC half-cells, with Na used as the negative electrode and hard carbon used as the positive electrode, and the cells were assembled in a glove box filled with argon. The four groups of Na||HC half-cells obtained in Example 1, Example 2, Example 4 and Comparative Example 1 were subjected to cycle tests, and the test method was to charge and discharge 5 times at a rate of 0.1C to form a stable SEI film on the surface of the hard carbon negative electrode, and then cycle at 0.33C.

[0061] The cycle test results are as follows Figure 2 As shown, the capacity of the Na||HC half-cell using comparative example 1 decays rapidly, and the capacity retention rate after 110 cycles is only 70.64%, which is poor in cycle performance, while the half-cells using examples 1, 2 and 4 have good cycle stability, and the capacity retention rates after 110 cycles are 92.40%, 85.48% and 89.26%, respectively. This shows that the electrolyte of comparative example 1 forms a poor film on the hard carbon surface, and during the cycle, the SEI film dissolves and regenerates, the electrolyte continues to decompose, and the capacity rapidly depletes, while the electrolyte of the present invention can form a stable SEI film on the hard carbon negative electrode, thereby improving the cycle stability of the battery.

[0062] Test Example 3

[0063] The Na||HC half-cells were assembled using the electrolytes of Example 3 and Comparative Example 1, with Na being used as the negative electrode and hard carbon being used as the positive electrode, and the cells were assembled in a glove box filled with argon. The two groups of Na||HC half-cells obtained in Example 3 and Comparative Example 1 were subjected to rate tests, and the test method was to charge and discharge 5 times at a rate of 0.1C to form a stable SEI film on the surface of the hard carbon negative electrode, and then charge and discharge at different rates.

[0064] The rate performance test results are as follows: Figure 3 As shown, the half-cell using Example 3 has good rate performance. This is because the introduction of tris(trimethylsilyl)phosphite can form a uniform and thin SEI with low impedance, low desolvation energy barrier and good rate performance.

[0065] The contents not described in detail in the specification of the present invention belong to the prior art known to the professional and technical personnel in the field. Although the illustrative specific embodiments of the present invention are described above to facilitate the understanding of the present invention by the technical personnel in the field, it should be clear that the present invention is not limited to the scope of the specific embodiments. For the ordinary technical personnel in the field, as long as various changes are within the spirit and scope of the present invention defined and determined by the attached claims, these changes are obvious, and all inventions and creations using the concept of the present invention are protected.

Claims

1. A method for preparing a battery electrolyte with excellent cycle performance, characterized in that: The following steps are involved: Step 1, melting a cyclic carbonate, then mixing it with a linear carbonate, and cooling it to room temperature to obtain a binary solvent; Step 2, mixing the binary solvent and the electrolyte salt, stirring evenly, to obtain a basic electrolyte; Step 3, mixing the dehydrated and dried phosphorus / silicon-containing additive and the basic electrolyte at a certain mass ratio at a constant temperature, stirring evenly, to obtain a phosphorus / silicon-containing electrolyte; The above preparation process needs to be carried out under argon atmosphere, and the content of H2O and O2 should be less than 0.1ppm.

2. A battery electrolyte and sodium ion battery with excellent cycle performance according to claim 1, characterized in that: The cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate, and the linear carbonate includes one or more of dimethyl carbonate, diethyl carbonate and ethyl methyl carbonate.

3. The method for preparing a battery electrolyte with excellent cycle performance according to claim 1, characterized in that: The cyclic carbonate melts at 40-65° C.; the volume ratio of the cyclic carbonate to the linear carbonate is 0.5-1:

1.

4. The method for preparing a battery electrolyte with excellent cycle performance according to claim 1, characterized in that: The electrolyte salt includes one or more of sodium hexafluorophosphate, sodium perchlorate, and sodium bis(trifluoromethylsulfonyl)imide; the molar concentration of the electrolyte salt is 0.7-1.5 mol / L.

5. The method for preparing a battery electrolyte with excellent cycle performance according to claim 1, characterized in that: The phosphorus / silicon-containing additive includes one or more of tris(trimethylsilyl)phosphite and tris(trimethylsilane)phosphate.

6. The method for preparing a battery electrolyte with excellent cycle performance according to claim 1, characterized in that: The amount of the phosphorus / silicon additive added to the phosphorus / silicon-containing electrolyte is 0.5 to 10 wt.%.

7. The method for preparing a battery electrolyte with excellent cycle performance according to claim 1, characterized in that: The stirring in step 2 is performed at a speed of 100 to 300 r / min for 2 to 5 hours; the stirring in step 3 is performed at a speed of 100 to 300 r / min for 12 to 36 hours.

8. The method for preparing a battery electrolyte with excellent cycle performance according to claim 1, characterized in that: The phosphorus / silicon additive is Molecular sieve drying to remove water.

9. A battery electrolyte having excellent cycle performance obtained by the preparation method according to any one of claims 1 to 8.

10. A sodium ion battery containing a battery electrolyte having excellent cycle performance prepared by the preparation method according to any one of claims 1 to 8.

Images