Sodium-ion battery electrolyte, preparation method thereof and sodium-ion battery

Abstract

The invention relates to the technical field of energy storage batteries, in particular to a sodium-ion battery electrolyte, a preparation method thereof and a sodium-ion battery. The electrolyte comprises sodium salt, a solvent and an additive; the additive comprises a sodium salt additive; the sodium salt additive is at least one of sodium naphthyl or sodium biphenyl. According to the invention, the specific sodium-containing additive (such as sodium naphthyl or sodium biphenyl) is added into the electrolyte to cooperate with the solvent and the sodium salt according to the type and the ratio, so that the irreversible active sodium loss in a stable SEI film constructed on an electrode-electrolyte interface is reduced, and the first charge-discharge efficiency and the cycle performance of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage batteries, in particular to a sodium ion battery electrolyte, a preparation method thereof and a sodium ion battery. BACKGROUND

[0002] Sodium ion batteries (SIBs) are considered as a promising alternative to lithium ion batteries (LIBs) due to their high elemental abundance. However, its large-scale commercial application is limited by the low initial coulombic efficiency (ICE), mainly due to the inevitable formation of a solid electrolyte interface phase (SEI) on the anode side and anode structure defects (such as irreversible volume change) caused by sodium ion intercalation during the first charge-discharge process, resulting in permanent loss of active sodium ions.

[0003] Sodium ion batteries are another promising battery system after lithium ion batteries, with the characteristics of low cost and high safety, which is expected to partially replace lithium ion batteries and become the main force for the application of new generation new energy power systems. However, the low initial coulombic efficiency ICE seriously hinders the development of sodium ion batteries, and the pre-sodium technology can provide additional active sodium ions to compensate for the loss of irreversible active sodium ions. At present, the sodium supplement effect of sodium battery negative electrode is good, and the material prepared is sodium-containing, but the material after processing is easy to oxidize or deactivate in subsequent processing and storage, and has high requirements for production environment. In terms of positive electrode pre-sodium, the sodium-rich positive electrode prepared by self-sacrificing additive is simple and easy to operate, but the gas and by-products generated by it have a certain influence on the electrochemical performance. Therefore, the design of the sodium supplement agent for practical application should have a pre-sodium strategy with high chemical stability and excellent sodium supplement performance, which is crucial to improve the ICE and energy density of sodium ion batteries. SUMMARY

[0004] The purpose of the present application is to overcome the deficiencies and shortcomings of the prior art, and to provide a sodium ion battery electrolyte, a preparation method thereof and a sodium ion battery.

[0005] In order to achieve the above-mentioned purpose, the following solutions are adopted in the present application:

[0006] A sodium ion battery electrolyte, comprising a sodium salt, a solvent and an additive; the additive comprises a sodium salt additive; the sodium salt additive is at least one of naphthyl sodium or diphenyl sodium.

[0007] The mass fraction of the sodium salt additive is 0.5-2%, preferably 0.6%, and specifically can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%.

[0008] The sodium salt is at least one of NaPF6, NaFSI, NaDFOB, NaPO2F2, NaBF4; preferably, the mass concentration of the sodium salt is 10-20%; preferably, 15%.

[0009] The sodium salt is a mixture of at least two of NaPF6, NaFSI, NaDFOB, NaPO2F2, NaBF4;

[0010] Preferably, the sodium salt is a mixture of NaBF4 and NaFP6; the mass ratio of the two is 2:13.

[0011] The solvent includes at least one of a carbonate solvent or an ether solvent; preferably, an ether solvent.

[0012] The carbonate solvent includes at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate.

[0013] The ether solvent includes at least one of diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0014] The additive further includes a film-forming additive, and the film-forming additive is fluoroethylene carbonate.

[0015] The content of FEC, vinyl sulfate DTD, fluoroethylene carbonate FEC, and vinyl sulfate DTD is independently 0.5%-2%; preferably, the mass content of fluoroethylene carbonate FEC is 1.5%, and the mass content of vinyl sulfate DTD is 1%.

[0016] The application further includes a preparation method of the electrolyte, including the following steps: dissolving the sodium salt and the sodium salt additive in the solvent and stirring uniformly, adding the film-forming additive optionally after the sodium salt is completely dissolved, and stirring uniformly to obtain the electrolyte.

[0017] The application further includes a sodium ion battery including the electrolyte.

[0018] Compared with the prior art, the application has the following beneficial effects:

[0019] The application is achieved by adding specific sodium-containing additives (such as naphthyl sodium or diphenyl sodium) in the electrolyte, cooperating with the type and ratio of the solvent and the sodium salt, reducing the irreversible active sodium loss in the construction of a stable SEI film at the electrode-electrolyte interface, and improving the first charge-discharge efficiency and the cycle performance of the battery. DETAILED DESCRIPTION

[0020] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. Unless otherwise specified, all percentages in this application are mass percentages.

[0021] Example 1:

[0022] 1. Preparation of electrolyte: In an argon-filled glove box (moisture <0.1ppm, oxygen <0.1ppm), NaBF4 and NaFP6 in a ratio of 2wt%:13wt% in the electrolyte, and sodium additive Na-Naph (sodium naphthalene) in a ratio of 0.6% in the electrolyte, are dissolved in diethylene glycol dimethyl ether in a solvent in a ratio of 85wt% in the electrolyte and stirred evenly. After the sodium salts are completely dissolved, film-forming additives FEC (fluoroethylene carbonate) and DTD (ethylene sulfate) are added, with the contents of each component in the electrolyte being 1.5% and 1%, respectively. After stirring evenly, a high-efficiency sodium-ion battery electrolyte is obtained.

[0023] 2. Preparation of sodium-ion batteries:

[0024] (1) Sodium-based non-metallic oxide cathode material (NFM), conductive carbon black (SP), carbon nanotubes (CNT), and polyvinylidene fluoride (PVDF) are mixed in a mass ratio of 95%:1.5%:0.5%:3% and dispersed in the organic solvent NMP (N-methylpyrrolidone). The mixture is stirred until stable and homogeneous to form a cathode slurry. The cathode slurry is then coated onto an aluminum current collector using a transfer coating machine, and subsequently rolled and cut to obtain the cathode sheet.

[0025] (2) Hard carbon anode material, conductive carbon black (SP), carbon nanotubes (CNT), CMC (sodium carboxymethyl cellulose), and SBR (styrene-butadiene rubber) are mixed in a ratio of 93.7%:2%:0.5%:1%:1.8%, dispersed in pure water, and stirred until stable and homogeneous to form a negative electrode slurry. The negative electrode slurry is coated onto an aluminum current collector using a transfer coating machine, and then rolled and cut to obtain the negative electrode sheet.

[0026] (3) The positive and negative electrode sheets are made into a full cell through sheet fabrication and assembly, and its performance is tested.

[0027] Example 2:

[0028] The difference between this embodiment and Example 1 is that the type of solvent is changed, that is, diethylene glycol dimethyl ether is replaced with tetraethylene glycol dimethyl ether. The other steps and parameters are the same as in Example 1.

[0029] Example 3:

[0030] The difference between this embodiment and Example 1 is that the type of solvent is increased, namely, diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether are added to the electrolyte in a ratio of 65wt%:20wt%. The other steps and parameters are the same as in Example 1.

[0031] Example 4:

[0032] The difference between this embodiment and Embodiment 1 is that the type of sodium supplement is changed to sodium biphenyl; the other steps and parameters are the same as in Embodiment 1.

[0033] Example 5:

[0034] The difference between this embodiment and Embodiment 2 is that the type of sodium supplement is changed to sodium biphenyl, while the other steps and parameters are the same as in Embodiment 2.

[0035] Example 6:

[0036] The difference between this embodiment and Embodiment 3 is that the type of sodium supplement is changed to sodium biphenyl; the other steps and parameters are the same as in Embodiment 3.

[0037] Example 7:

[0038] The difference between this embodiment and Example 6 is that the solvent is changed, and diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether are replaced with ester solvents (propylene carbonate and dimethyl carbonate in a volume ratio of 1:1). The other steps and parameters are the same as in Example 1.

[0039] Example 8:

[0040] The difference between this embodiment and Embodiment 7 is that the salt types are changed, with NaBF4 replaced by NaODFB and NaPO2F2 at a ratio of 0.3wt%:0.24wt%, and NaPF6 at 13.46wt%. Other steps and parameters are the same as in Embodiment 1.

[0041] Comparative Example 1:

[0042] The difference between this comparative example and Example 6 is that no sodium supplement was added, while the other steps and parameters are the same as in Example 6.

[0043] Comparative Example 2:

[0044] The difference between this comparative example and Example 8 is that no sodium supplement was added, while the other steps and parameters are the same as in Example 8.

[0045] Table 2 Comparison of Performance Test Results

[0046] Based on the test results, within the same system:

[0047] Based on Examples 1 / 2 / 3 and Examples 4 / 5 / 6, it is known that sodium biphenyl, a sodium-containing additive, significantly improves the first charge-discharge efficiency of the battery, indicating that sodium biphenyl has good solubility and high stability of its biphenyl radicals, resulting in reduced gas production.

[0048] Example 6 shows that the mixed ether solvent exhibits the best first-cycle discharge specific capacity, first-cycle efficiency, and 50-cycle capacity retention. This indicates that the biphenyl radical in the mixed ether solvent electrolyte has high stability, and the ether solvent has a weaker binding force on Na+, which is beneficial for forming a thinner and denser SEI film. The introduction of sodium salt additives "sacrifices" itself to generate a superior protective film, indirectly improving the stability of the entire electrolyte system. Reduced gas production can decrease irreversible active sodium loss in building a stable SEI film at the electrode-electrolyte interface, thereby improving the battery's first charge-discharge efficiency and cycle performance.

[0049] By combining two or more sodium salts, leveraging their respective strengths, a more stable and efficient solid electrolyte interphase (SEI) membrane and CEI membrane can be constructed on the electrode (especially the positive and negative electrodes) surfaces. This overcomes the inherent defects of single-salt systems, such as the different sizes and association abilities of cations and anions in different sodium salts. In complex salt systems, the transport number of ions and the overall ionic conductivity in the electrolyte can be optimized, thereby improving the rate performance of the battery.

[0050] Comparing Examples 6, 7, and 8, it is evident that sodium biphenyl additive cannot construct a stable SEI film in ester solvents. Both the initial charge-discharge efficiency and cycle stability are reduced, indicating poor compatibility between sodium biphenyl additive and ester solvents. Ester solvents compete with sodium biphenyl additive for reduction and preferentially form a suboptimal primary SEI film with excessive organic components on the negative electrode surface. This film hinders sodium biphenyl from effectively approaching the electrode surface and undergoing efficient electrochemical polymerization, resulting in poor performance.

[0051] Comparing Example 6 with Comparative Example 1, it is known that adding sodium-containing additives can improve the first charge and discharge efficiency of the battery, and generate organic matter containing biphenyl fragments, thereby improving SEI flexibility and enhancing battery cycle stability and safety.

[0052] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention.

[0053] Therefore, the embodiments should be regarded as exemplary and non-limiting in all respects, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of the equivalents of the claims be included within the invention.

[0054] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A sodium-ion battery electrolyte, characterized in that, It includes sodium salt, solvent, and additives; the additives include sodium salt additives; the sodium salt additives are at least one of sodium naphthyl or sodium biphenyl.

2. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt additive has a mass fraction of 0.5-2%; preferably 0.6%.

3. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt is at least one selected from NaPF6, NaFSI, NaDFOB, NaPO2F2, and NaBF4; preferably, the mass concentration of the sodium salt is 10-20%; more preferably, it is 15%.

4. The sodium-ion battery electrolyte according to claim 1, characterized in that, The sodium salt is a mixture of at least two of NaPF6, NaFSI, NaDFOB, NaPO2F2, and NaBF4; Preferably, the sodium salt is a mixture of NaBF4 and NaFP6, with a mass ratio of 2:

13.

5. The sodium-ion battery electrolyte according to claim 1, characterized in that, The solvent includes at least one of carbonate solvents or ether solvents; preferably, an ether solvent.

6. The sodium-ion battery electrolyte according to claim 4, characterized in that, The carbonate solvents include at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, and diethyl carbonate.

7. The sodium-ion battery electrolyte according to claim 4, characterized in that, The ether solvent includes at least one of diethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

8. The sodium-ion battery electrolyte according to claim 4, characterized in that, The additives also include film-forming additives, which are fluoroethylene carbonate (FEC) and vinyl sulfate (DTD), with the content of FEC and DTD being 0.5%-2% independently; preferably, the mass content of FEC is 1.5% and the mass content of DTD is 1%.

9. A method for preparing the electrolyte according to any one of claims 1-8, characterized in that, The process includes the following steps: dissolving sodium salt and sodium salt additive in a solvent and stirring until the sodium salt is completely dissolved; optionally, adding a film-forming additive and stirring until the electrolyte is obtained.

10. A sodium-ion battery, characterized in that, Includes the electrolyte according to any one of claims 1-8.

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