Carbon-based anode material for sodium secondary battery, using pre-sodiation and reduction method

Abstract

A carbon-based anode material for a sodium secondary battery, using pre-sodiation and reduction method is disclosed. The carbon-based anode material for a sodium secondary battery, according to one embodiment may comprise a solid electrolyte interface (SEI) layer. Here, the SEI layer is pre-formed by the sodium, which was loaded through pre-sodiation, before charging / discharging of a sodium secondary battery.

Description

Carbon-based cathode material for sodium secondary batteries using pre-sodium insertion and reduction method

[0001] The following description relates to a carbon-based negative electrode material for a sodium secondary battery using a pre-sodium insertion and reduction method.

[0002] As the secondary battery market rapidly grows, the scarcity and price of lithium resources are becoming serious issues. To address this, active research is underway to develop next-generation batteries utilizing sodium, a potential lithium substitute.

[0003] Existing lithium secondary batteries primarily use carbon-based graphite anode materials. However, graphite anode materials suffer from thermodynamic instability and the large size of sodium ions, which hinder intercalation of sodium ions between layers, making them unsuitable for use in sodium-ion batteries. Therefore, with the advancement of the electrochemical industry, research on carbon-based anode materials applicable to low-cost sodium-ion batteries is increasing. While various studies are underway on hard carbon anode materials as suitable materials for sodium-ion batteries, they suffer from very low initial Coulombic efficiency. For example, during the first charge process, some of the sodium source in the anode is used to form the solid-electrolyte interface (SEI) layer on the anode. This results in a loss of sodium that could otherwise contribute to capacity, resulting in a very low initial Coulombic efficiency.

[0004] A carbon-based negative electrode material for a sodium secondary battery is provided using a prior sodium insertion and reduction method.

[0005] A carbon-based negative electrode material for a sodium secondary battery is provided, which includes a SEI (Solid-Electrolyte Interface) layer, and wherein the SEI layer is formed in advance before charging and discharging of a sodium secondary battery through sodium loaded through a pre-sodiumization process.

[0006] According to one aspect, the pre-sodiumization process may be characterized by including a process of pre-loading sodium onto the negative electrode material by immersing the negative electrode material in a pre-sodiumization solution prepared by mixing triphenylethylene and sodium metal in a solvent, and pre-forming the SEI layer through the pre-loaded sodium.

[0007] According to another aspect, it may be characterized in that in the pre-sodiumization process, the triphenylethylene is combined with the sodium contained in the sodium metal, and then sodium is reduced to the cathode material, thereby pre-loading the cathode material with sodium.

[0008] According to another aspect, the time for immersing the cathode material in the pre-sodium solution may be characterized as being less than 20 minutes.

[0009] According to another aspect, the solvent may be characterized as containing DME (Dimethoxy ethane).

[0010] A sodium secondary battery is provided, comprising: a cathode; an anode including a cathode material having a pre-formed SEI (Solid-Electrolyte Interface) layer; and an electrolyte for transferring lithium ions between the cathode and the anode, wherein the SEI layer is pre-formed before charge / discharge of the sodium secondary battery through sodium loaded on the cathode material through a pre-sodiumization process.

[0011] A method for producing a carbon-based negative electrode material for a sodium secondary battery is provided, comprising: a step of producing a pre-sodium solution by mixing triphenylethylene and sodium metal in a solvent; and a step of pre-loading sodium onto the negative electrode material by immersing the negative electrode material in the pre-sodium solution, wherein a solid-electrolyte interface (SEI) layer is formed in advance on the negative electrode material through the pre-loaded sodium before charge and discharge of the sodium secondary battery.

[0012] A carbon-based negative electrode material for a sodium secondary battery can be provided using a prior sodium insertion and reduction method.

[0013] Figure 1 is a drawing showing an example of charging and discharging a sodium secondary battery when pre-sodiumization is not performed.

[0014] FIG. 2 is a drawing showing an example of charging and discharging a sodium secondary battery in a case where pre-sodiumization is performed in one embodiment of the present invention.

[0015] FIG. 3 is a drawing showing an example of a process for preparing a pre-sodium solution for a pre-sodium process according to one embodiment of the present invention.

[0016] FIG. 4 is a drawing showing an example of a pre-sodiumization process in one embodiment of the present invention.

[0017] FIG. 5 is a drawing showing an example of the electrochemical performance of a pre-sodiumized negative electrode material according to one embodiment of the present invention.

[0018] FIG. 6 is a diagram showing an example of the resistance value of a pre-sodiumized cathode material according to one embodiment of the present invention.

[0019] FIG. 7 is a drawing showing an example of the cycling safety of a sodium secondary battery using a pre-sodiumized negative electrode material according to one embodiment of the present invention.

[0020] FIG. 8 is a drawing showing an example of changes in the formation of an SEI layer according to immersion time in one embodiment of the present invention.

[0021] FIG. 9 is a drawing showing an example of XPS (X-ray Photoelectron Spectroscopy) measurement results in one embodiment of the present invention.

[0022] The present invention can be modified in various ways and has various embodiments. Hereinafter, specific embodiments will be described in detail based on the attached drawings.

[0023] In describing the present invention, if it is determined that a detailed description of a related known technology may obscure the gist of the present invention, the detailed description is omitted.

[0024] Hard carbon anodes for sodium secondary batteries have a critical drawback: during the first charge process, they consume some of the sodium source in the anode, forming a solid-electrolyte interface (SEI) layer at the cathode interface. This, in turn, reduces the initial Coulombic efficiency. Therefore, resolving the low initial Coulombic efficiency of hard carbon anodes is essential for the development of next-generation sodium secondary batteries.

[0025] Embodiments of the present invention can provide a carbon-based negative electrode material for a sodium secondary battery capable of achieving an initial coulombic efficiency of 100% and electrochemical stabilization through a process of performing chemical pre-sodiation of a hardcarbon negative electrode using a triphenylethylene material.

[0026] FIG. 1 is a drawing showing an example of charge / discharge of a sodium secondary battery when pre-sodiumization is not performed, and FIG. 2 is a drawing showing an example of charge / discharge of a sodium secondary battery when pre-sodiumization is performed in one embodiment of the present invention.

[0027] Figure 1 shows that when a sodium secondary battery is charged and discharged without prior sodiumization, some of the Na is used to form an SEI layer at the negative electrode interface, resulting in Na loss from the positive electrode. This initial Na loss, as previously explained, causes a decrease in the initial Coulombic efficiency.

[0028] Figure 2 illustrates that the extra Na in the pre-sodiumed cathode material is utilized to form an SEI layer in advance, thereby preventing the loss of Na transferred from the initial cathode during charging and discharging of the sodium secondary battery. Therefore, it becomes possible to achieve an initial Coulombic efficiency of 100%.

[0029] FIGS. 3 and 4 are drawings illustrating examples of a pre-sodium process in one embodiment of the present invention. FIG. 3 shows an example of a process in which triphenylethylene and Na metal are mixed in a solvent DME (Dimethoxyethane), stirred for 12 hours, and then a 0.5 M TriPE (triphenylethylene)-Na DME solution (pre-sodium solution) is obtained, and FIG. 4 shows an example of a pre-sodium process in which a cathode material is added to the pre-sodium solution and sodium is pre-loaded onto the cathode material. Triphenylethylene has many benzene rings and, accordingly, many electrons, which can be of great help in reduction, and can be helpful in pre-sodiuming the cathode material by combining with Na in DME and then reducing Na with the cathode material.

[0030] As previously explained in Fig. 2, the pre-sodiumed cathode material can prevent initial Na loss by forming an SEI layer in advance using extra Na.

[0031] FIGS. 5 and 6 are drawings showing examples of the performance of a pre-sodiumized cathode material according to one embodiment of the present invention.

[0032] The graph in Fig. 5 shows an example of the electrochemical performance of a pre-sodium-treated anode material. When a cathode material (Pristine) that was not pre-sodium-treated was used, a capacity loss of 15.58% occurred, whereas when the pre-sodium-treated process was performed for 5 minutes (soaking time of 5 minutes for placing the cathode material in the pre-sodium-treated solution), a capacity loss of 3.55% occurred, when the pre-sodium-treated process was performed for 10 minutes, a capacity loss of 0% occurred, and when the pre-sodium-treated process was performed for 20 minutes, an example of a capacity increase of 6.81% was shown.

[0033] FIG. 6 is a diagram showing an example of the resistance value of a pre-sodium-treated negative electrode material according to an embodiment of the present invention. The upper graph of FIG. 6 shows the results of EIS (Electrochemical Impedance Spectroscopy) analysis performed to investigate the resistance of a pre-formed SEI layer, and the lower graph of FIG. 6 shows the relationship between the time of the pre-sodium-treated process and the resistance. The results of FIG. 6 show that the resistance is the lowest when the pre-sodium-treated process is performed for 10 minutes, and that the resistance actually increases significantly when the pre-sodium-treated process is performed for 20 minutes. This shows the importance of an appropriate soaking time.

[0034] FIG. 7 is a diagram illustrating an example of the cycling safety of a sodium secondary battery using a pre-sodium-treated negative electrode material according to an embodiment of the present invention. The graph of FIG. 7 shows the charge capacity as the charge / discharge cycle progresses for a sodium secondary battery using a pre-sodium-treated negative electrode material. In the case of Pristine, a decrease in capacity is observed after 70 cycles, whereas when the pre-sodium treatment is performed for 5 or 10 minutes, the cycling stability is high due to the stability of the pre-formed SEI layer. On the other hand, when the pre-sodium treatment is performed for 20 minutes, poor cycle characteristics are observed due to Na dissolution caused by over-sodium treatment.

[0035] FIG. 8 is a diagram illustrating an example of a change in the formation of an SEI layer according to the immersion time in one embodiment of the present invention. FIG. 8 shows SEM (Scanning Electron Microscopy) images and TEM (Transmission Electron Microscopy) images of the surface of a cathode material as the immersion time increases from 0 minutes to 5 minutes, 10 minutes, and 20 minutes. The images in FIG. 8 show that the thickness of the SEI layer is 0.9 nm for pristine, but increases to 1.8 nm, 3 nm, and 7 nm as the immersion time increases to 5 minutes, 10 minutes, and 20 minutes. The results in FIG. 8 also show the importance of an appropriate immersion time.

[0036] FIG. 9 is a diagram showing examples of XPS (X-ray Photoelectron Spectroscopy) measurement results according to an embodiment of the present invention. The XPS measurement results of FIG. 9 indicate components of the surface of a cathode material, and the sodium peaks due to pre-sodiumization indicate that an SEI layer was formed in advance through pre-sodiumization.

[0037] The above description is merely an illustrative illustration of the technical idea of ​​the present invention, and those skilled in the art will appreciate that various modifications and variations can be made without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are intended to illustrate, rather than limit, the technical idea of ​​the present invention, and the present invention is not limited to these embodiments. The scope of protection of the present invention should be interpreted by the following claims, and all technical ideas within a scope equivalent thereto should be interpreted as being included within the scope of the rights of the present invention.

Claims

1. Contains a SEI (Solid-Electrolyte Interface) layer, The above SEI layer is formed in advance before charging and discharging of a sodium secondary battery through sodium loaded through a pre-sodiumization process. Carbon-based negative electrode material for sodium secondary batteries characterized by .

2. In paragraph 1, A carbon-based negative electrode material for a sodium secondary battery, characterized in that the above pre-sodiumization process includes a process of pre-loading sodium onto the negative electrode material by immersing the negative electrode material in a pre-sodiumization solution prepared by mixing triphenylethylene and sodium metal in a solvent, and pre-forming the SEI layer through the pre-loaded sodium.

3. In paragraph 2, A carbon-based negative electrode material for a sodium secondary battery, characterized in that sodium is pre-loaded into the negative electrode material by reducing sodium with the negative electrode material after the triphenylethylene is combined with the sodium contained in the sodium metal in the above pre-sodiumization process.

4. In paragraph 2, A carbon-based negative electrode material for a sodium secondary battery, characterized in that the time for immersing the negative electrode material in the above pre-sodium solution is less than 20 minutes.

5. In paragraph 2, A carbon-based negative electrode material for a sodium secondary battery, characterized in that the solvent comprises DME (Dimethoxy ethane).

6. Bipolar; A cathode comprising a cathode material having a pre-formed SEI (Solid-Electrolyte Interface) layer; and An electrolyte that transfers lithium ions between the positive electrode and the negative electrode Including, The above SEI layer is formed in advance before charging and discharging of a sodium secondary battery through sodium loaded on the negative electrode material through a pre-sodiumization process. Sodium secondary battery characterized by .

7. In paragraph 6, The above pre-sodiumization process includes a process of pre-loading sodium on the negative electrode material by immersing the negative electrode material in a pre-sodiumization solution prepared by mixing triphenylethylene and sodium metal in a solvent, and pre-forming the SEI layer through the pre-loaded sodium. Sodium secondary battery characterized by .

8. In paragraph 7, In the above pre-sodiumization process, the triphenylethylene is combined with the sodium contained in the sodium metal, and then sodium is reduced to the negative electrode material, thereby pre-loading the negative electrode material with sodium. Sodium secondary battery characterized by .

9. In paragraph 7, The time for immersing the cathode material in the above pre-sodium solution is less than 20 minutes. Sodium secondary battery characterized by .

10. In a method for manufacturing a carbon-based negative electrode material for a sodium secondary battery, A step of preparing a pre-sodium solution by mixing triphenylethylene and sodium metal in a solvent; and A step of pre-loading sodium onto the cathode material by immersing the cathode material in the above pre-sodium solution. Including, A solid-electrolyte interface (SEI) layer is formed in advance on the negative electrode material through the above-mentioned pre-loaded sodium before charging and discharging of the sodium secondary battery. A method for manufacturing a carbon-based negative electrode material for a sodium secondary battery characterized by the following.

11. In paragraph 10, In the above pre-sodiumization process, the triphenylethylene is combined with the sodium contained in the sodium metal, and then sodium is reduced to the negative electrode material, thereby pre-loading the negative electrode material with sodium. A method for manufacturing a carbon-based negative electrode material for a sodium secondary battery characterized by the following.

12. In paragraph 10, In the above pre-loading step, The time for immersing the cathode material in the above pre-sodium solution is less than 20 minutes. A method for manufacturing a carbon-based negative electrode material for a sodium secondary battery characterized by the following.

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