Electrolyte of negative-electrode-free sodium ion battery, application of electrolyte and negative-electrode-free sodium ion battery

Abstract

The invention provides an electrolyte of a negative-electrode-free sodium-ion battery, an application of the electrolyte and the negative-electrode-free sodium-ion battery, and relates to the technical field of batteries. The electrolyte of the negative-electrode-free sodium ion battery provided by the invention comprises the following components in percentage by mass: 1%-3% of trifluoromethanesulfonic acid metal salt, 14%-20% of NaPF6, 10%-20% of a cosolvent and the balance of a solvent. According to the electrolyte, the potential barrier of sodium nucleation is reduced, the deposition of sodium on the negative electrode side is promoted, the uniformity of sodium deposition is improved, the contact and reaction between sodium and the electrolyte are reduced, and the battery performance is improved; the trifluoromethanesulfonate ions have relatively high transference number and conductivity and can promote rapid transmission of sodium ions in an electrolyte, so that the charge-discharge efficiency and the rate capability of the battery are improved, meanwhile, the trifluoromethanesulfonate ions are easy to form a film at a negative electrode, a stable SEI film rich in F / S can be constructed, generation of dendritic crystals is inhibited, and the safety performance of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to an electrolyte for a negative electrode-free sodium ion battery and applications thereof, and a negative electrode-free sodium ion battery. Background Art

[0002] Sodium metal batteries are considered to be a potential solution for high-energy storage due to their high specific capacity (1165mAh / g), abundant sodium resources and controllable cost-effectiveness. However, metallic sodium anodes have significant limitations in practical applications. For example, sodium metal easily forms dendrites during the cycle, causing battery short circuits and even safety issues (such as thermal runaway and explosion). In addition, the metallic sodium anode has side reactions when in contact with the electrolyte, which will further reduce the coulombic efficiency and cycle life of the battery. In view of this, the concept of anode-free sodium-ion battery was proposed. The core idea is to eliminate the metallic sodium anode and directly derive sodium ions from the positive electrode material or sodium salt in the electrolyte, thereby avoiding the instability of the sodium metal anode. This design can theoretically improve the safety and cycle performance of the battery while reducing material costs.

[0003] However, existing anode-free sodium-ion battery technology still faces several key challenges: for example, the lack of active sodium storage materials on the anode side leads to uneven sodium ion deposition, which easily forms an unstable interface structure and further affects the battery's cycling performance and coulombic efficiency. Among them, the influence of the electrolyte is crucial. Anode-free batteries produce a lot of gas and have poor high-temperature cycling and storage performance. This is mainly due to the high activity of metallic sodium on the anode side, which is prone to electrolyte reactions, resulting in an unstable and easily ruptured SEI film.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The first object of the present invention is to provide a negative electrode-free sodium ion battery current collector to solve the above technical problems.

[0006] The second object of the present invention is to provide an application of the above-mentioned negative electrode-free sodium ion battery current collector in a negative electrode-free sodium ion battery.

[0007] A third object of the present invention is to provide a negative electrode-free sodium ion battery.

[0008] In order to achieve the above objectives, the following technical solutions are adopted:

[0009] In a first aspect, the present invention provides an electrolyte for a negative electrode-free sodium ion battery, comprising, by mass percentage: 1%-3% of a metal trifluoromethanesulfonate, 14%-20% of NaPF6, 10%-20% of a co-solvent, and the balance being a solvent;

[0010] The co-solvent includes at least one of tetrahydrofuran, 2-methyltetrahydrofuran or 1,3-dioxolane;

[0011] The solvent includes at least one of diethylene glycol dimethyl ether (G2) or tetraethylene glycol dimethyl ether (G4).

[0012] As a further technical solution, the electrolyte comprises, by mass percentage, 2% of trifluoromethanesulfonic acid metal salt, 20% of NaPF6, 20% of co-solvent, and the balance is solvent.

[0013] As a further technical solution, the trifluoromethanesulfonate metal salt includes zinc trifluoromethanesulfonate or tin trifluoromethanesulfonate.

[0014] As a further technical solution, the trifluoromethanesulfonic acid metal salt is zinc trifluoromethanesulfonate.

[0015] As a further technical solution, the electrolyte also includes an electrolyte additive.

[0016] As a further technical solution, the electrolyte additive includes at least one of vinylene carbonate (VC), fluoroethylene carbonate (FEC) or diethylene sulfate (DTD).

[0017] As a further technical solution, in the electrolyte, the mass proportion of the electrolyte additive is 0.2%-0.5%.

[0018] As a further technical solution, the electrolyte comprises, by mass percentage, 2% zinc trifluoromethanesulfonate, 20% NaPF6, 20% tetrahydrofuran, 0.5% vinylene carbonate, and the remainder is diethylene glycol dimethyl ether.

[0019] In a second aspect, the present invention provides the use of the above-mentioned electrolyte in a negative electrode-free sodium ion battery.

[0020] In a third aspect, the present invention provides the above-mentioned negative electrode-free sodium ion battery, comprising the above-mentioned electrolyte.

[0021] Compared with the prior art, the electrolyte of the negative electrode-free sodium ion battery provided by the present invention has the following beneficial effects:

[0022] In the present invention, a sodium-philic metal trifluoromethanesulfonate is added to the electrolyte, wherein the sodium-philic metal is reduced to a sodium-philic metal element before sodium ions on the negative electrode side during the first charging process, thereby reducing the potential barrier for sodium nucleation, promoting the deposition of sodium on the negative electrode side, and improving the uniformity of sodium deposition. At the same time, sodium and the sodium-philic metal can form a Na-X (sodium-philic metal) alloy in situ during the first charging process, reducing the contact and reaction of sodium with the electrolyte, and improving battery performance.

[0023] Trifluoromethanesulfonate ions have a high migration number and conductivity, which can promote the rapid transport of sodium ions in the electrolyte, thereby improving the charge and discharge efficiency and rate performance of the battery. At the same time, they are easy to form a film on the negative electrode, can construct a stable F / S-rich SEI film, inhibit the formation of dendrites, and improve the safety performance of the battery. DETAILED DESCRIPTION

[0024] Below in conjunction with embodiment and example, embodiment of the present invention is described in detail, but those skilled in the art will appreciate that the following embodiment and example are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiment in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the scope of protection of the present invention. Unspecified conditions are carried out according to the conditions of normal conditions or manufacturer's recommendations. Reagents used or instruments not specified by the manufacturer are conventional products that can be purchased commercially.

[0025] In a first aspect, the present invention provides an electrolyte for a negative electrode-free sodium ion battery, comprising, by mass percentage: 1%-3% of a metal trifluoromethanesulfonate, 14%-20% of NaPF6, 10%-20% of a co-solvent, and the balance being a solvent;

[0026] The co-solvent is, but is not limited to, at least one of tetrahydrofuran, 2-methyltetrahydrofuran, or 1,3-dioxolane;

[0027] The solvent includes but is not limited to at least one of diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

[0028] In the present invention, a sodium-philic metal trifluoromethanesulfonate is added to the electrolyte, wherein the sodium-philic metal is reduced to a sodium-philic metal element before sodium ions on the negative electrode side during the first charging process, thereby reducing the potential barrier for sodium nucleation, promoting the deposition of sodium on the negative electrode side, and improving the uniformity of sodium deposition. At the same time, sodium and the sodium-philic metal can form a Na-X alloy in situ during the first charging process, reducing the contact and reaction between sodium and the electrolyte, and improving battery performance.

[0029] Trifluoromethanesulfonate ions have a high migration number and conductivity, which can promote the rapid transport of sodium ions in the electrolyte, thereby improving the charge and discharge efficiency and rate performance of the battery. At the same time, they are easy to form a film on the negative electrode, can construct a stable F / S-rich SEI film, inhibit the formation of dendrites, and improve the safety performance of the battery.

[0030] In some optional embodiments, the electrolyte comprises, by mass percentage, 2% of metal trifluoromethanesulfonate, 20% of NaPF6, 20% of co-solvent, and the balance being solvent.

[0031] In some optional embodiments, the metal trifluoromethanesulfonate includes zinc trifluoromethanesulfonate or tin trifluoromethanesulfonate, preferably zinc trifluoromethanesulfonate.

[0032] In some optional embodiments, the electrolyte further includes an electrolyte additive.

[0033] In some optional embodiments, the electrolyte additive includes but is not limited to at least one of vinylene carbonate, fluoroethylene carbonate or vinyl sulfate.

[0034] In some optional embodiments, the mass proportion of the electrolyte additive in the electrolyte may be, for example, but not limited to, 0.2%, 0.3% or 0.5%.

[0035] In some optional embodiments, the electrolyte comprises, by mass percentage, 2% zinc trifluoromethanesulfonate, 20% NaPF6, 20% tetrahydrofuran, 0.5% vinylene carbonate, and the balance diethylene glycol dimethyl ether.

[0036] By further optimizing and adjusting the proportions of the various components, the electrolyte of the present invention can achieve better effects.

[0037] In a second aspect, the present invention provides the use of the above-mentioned electrolyte in a negative electrode-free sodium ion battery.

[0038] In a third aspect, the present invention provides the above-mentioned negative electrode-free sodium ion battery, comprising the above-mentioned electrolyte.

[0039] The battery has good safety, good charge and discharge efficiency and rate performance.

[0040] The present invention is further described below by means of specific examples and comparative examples. However, it should be understood that these examples are merely provided for more detailed description and are not to be construed as limiting the present invention in any form.

[0041] Example 1

[0042] An electrolyte comprises, by mass percentage, 16% NaPF6, 1% tin trifluoromethanesulfonate, 62.8% diethylene glycol dimethyl ether (DEGDME), 20% 2-methyltetrahydrofuran and 0.2% FEC.

[0043] Example 2

[0044] An electrolyte comprises, by mass percentage, 20% NaPF6, 2% tin trifluoromethanesulfonate, 57.5% diethylene glycol dimethyl ether (DEGDME), 20% tetrahydrofuran (THF) and 0.5% VC.

[0045] Example 3

[0046] An electrolyte comprises, by mass percentage, 18% NaPF6, 2% tin trifluoromethanesulfonate, 64.7% tetraethylene glycol dimethyl ether (DEGDME), 15% 1,3-dioxolane and 0.3% DTD.

[0047] Example 4

[0048] An electrolyte comprises, by mass percentage, 20% NaPF6, 2% zinc trifluoromethanesulfonate, 57.5% diethylene glycol dimethyl ether (DEGDME), 20% tetrahydrofuran (THF) and 0.5% VC.

[0049] Example 5

[0050] An electrolyte comprises, by mass percentage, 16% NaPF6, 1% zinc trifluoromethanesulfonate, 1% tin trifluoromethanesulfonate, 61.8% diethylene glycol dimethyl ether (DEGDME), 20% tetrahydrofuran (THF), and 0.2% VC.

[0051] Comparative Example 1

[0052] An electrolyte comprises, by mass percentage, 16% NaPF6, 63.8% diethylene glycol dimethyl ether (DEGDME), 20% 2-methyltetrahydrofuran and 0.2% FEC.

[0053] Comparative Example 2

[0054] An electrolyte comprises, by mass percentage, 16% NaPF6, 1% iron trifluoromethanesulfonate, 62.8% diethylene glycol dimethyl ether (DEGDME), 20% 2-methyltetrahydrofuran and 0.2% FEC.

[0055] Comparative Example 3

[0056] An electrolyte comprises, by mass percentage, 16% NaPF6, 1% stannous isooctanoate, 62.8% diethylene glycol dimethyl ether (DEGDME), 20% 2-methyltetrahydrofuran and 0.2% FEC.

[0057] Test Example 1

[0058] The current collectors provided in the above examples and comparative examples were used as negative electrodes to prepare negative electrode-free sodium ion batteries, wherein the positive electrode sheet was composed of sodium iron pyrophosphate, PVDF, conductive carbon black, and a dispersant in a mass ratio of 95.1:2.0:2.4:0.5;

[0059] The electrolyte was: diethylene glycol dimethyl ether containing 1 M NaPF6;

[0060] Diaphragm: PP diaphragm.

[0061] The negative electrode-free sodium ion battery was assembled in an inert atmosphere glove box according to the same preparation method.

[0062] The first coulombic efficiency and cycle performance of the negative electrode-free sodium metal batteries prepared in each embodiment and comparative example were tested. The specific testing methods are as follows:

[0063] First coulombic efficiency test of the battery: After the assembled battery is set aside for 10 hours, it is charged to 3.5V at a constant current and constant voltage of 0.2C. After another 0.5 hour, it is discharged to 2.0V at a constant current of 0.5C. The ratio of the battery discharge capacity to the charge capacity is calculated as CE.

[0064] Cycle life test: After the assembled battery was left for 10 hours, it was charged at a constant current and constant voltage of 0.5C to 3.5V at room temperature (25°C). After 0.5 hours, it was discharged at a constant current of 1C to 2.0V. This cycle was repeated 100 times, and the capacity retention rate was recorded. The test results are shown in Table 1.

[0065] Group First coulombic efficiency (%) 100-cycle capacity retention rate (%) Example 1 95.2 92.5 Example 2 97.6 96.4 Example 3 95.8 93.5 Example 4 98.1 97.2 Example 5 96.7 95.7 Comparative Example 1 91.3 84.5 Comparative Example 2 88.6 78.6 Comparative Example 3 93.4 88.3

[0066] As can be seen from Table 1, the current collectors prepared in various embodiments of the present invention have better performance after being assembled into a negative electrode-free sodium metal battery. Comparing each embodiment with Comparative Example 1, the performance of the embodiment is significantly better, indicating that adding zinc trifluoromethanesulfonate and tin salt to the electrolyte can effectively improve the performance of the battery.

[0067] Comparing Example 2 with Example 4, the various properties of Example 4 are significantly better, indicating that if zinc salt is added to the electrolyte, its sodium affinity is better and the performance of the battery can be improved to a greater extent;

[0068] Comparing Comparative Example 2 with Example 1, the various properties of Comparative Example 2 are significantly worse, indicating that the added iron salt fails to effectively form sodium-philic metal sites on the negative electrode side, resulting in poor battery performance;

[0069] Comparing Comparative Example 3 with Example 1, the various properties of Comparative Example 3 are significantly worse, indicating that the addition of trifluoromethanesulfonate ions can effectively improve the performance of the battery.

[0070] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An electrolyte for a negative electrode-free sodium ion battery, characterized in that: Calculated by mass percentage, it includes: 1%-3% of trifluoromethanesulfonic acid metal salt, 14%-20% of NaPF6, 10%-20% of co-solvent, and the balance is solvent; The co-solvent includes at least one of tetrahydrofuran, 2-methyltetrahydrofuran or 1,3-dioxolane; The solvent includes at least one of diethylene glycol dimethyl ether or tetraethylene glycol dimethyl ether.

2. The electrolyte of the negative electrode-free sodium ion battery according to claim 1, characterized in that The electrolyte comprises, by mass percentage, 2% of trifluoromethanesulfonic acid metal salt, 20% of NaPF6, 20% of co-solvent, and the balance being solvent.

3. The electrolyte of the negative electrode-free sodium ion battery according to claim 1, characterized in that The metal trifluoromethanesulfonate includes zinc trifluoromethanesulfonate or tin trifluoromethanesulfonate.

4. The electrolyte of the negative electrode-free sodium ion battery according to claim 1, characterized in that The trifluoromethanesulfonic acid metal salt is zinc trifluoromethanesulfonate.

5. The electrolyte of the negative electrode-free sodium ion battery according to claim 1, characterized in that The electrolyte further includes an electrolyte additive.

6. The electrolyte of the negative electrode-free sodium ion battery according to claim 5, characterized in that The electrolyte additive includes at least one of vinylene carbonate, fluoroethylene carbonate or vinyl sulfate.

7. The electrolyte of the negative electrode-free sodium ion battery according to claim 5, characterized in that In the electrolyte, the mass proportion of the electrolyte additive is 0.2%-0.5%.

8. The electrolyte of the negative electrode-free sodium ion battery according to claim 1, characterized in that The electrolyte comprises, by mass percentage, 2% zinc trifluoromethanesulfonate, 20% NaPF6, 20% tetrahydrofuran, 0.5% vinylene carbonate, and the balance diethylene glycol dimethyl ether.

9. Use of the electrolyte according to any one of claims 1 to 8 in a negative electrode-free sodium ion battery.

10. A negative electrode-free sodium ion battery, characterized in that: The electrolyte comprises the electrolyte according to any one of claims 1 to 8.