Cobalt oxide artificial SEI membrane, preparation method and application in sodium ion battery

Abstract

The invention discloses a cobalt oxide artificial SEI (solid electrolyte interface) film, a preparation method and application of the cobalt oxide artificial SEI film in a sodium-ion battery. According to the method, cobaltocene and oxygen plasmas are alternately introduced into a reaction cavity by utilizing an atomic layer deposition method to serve as precursor sources; the cobalt oxide artificial SEI is constructed on the surface of the uniformly coated hard carbon negative electrode through sequential reaction self-limiting and chemical adsorption self-limiting characteristics of ALD (Atomic Layer Deposition). According to the invention, the cobalt oxide SEI effectively inhibits the side reaction on the surface of the electrode and improves the first coulombic efficiency; the ion transmission rate is increased, and the rate capability is improved; the electrode interface is stabilized, the corrosion of electrolyte is resisted, and the cycling stability and safety are enhanced.

Description

Technical Field

[0001] The present invention belongs to the technical field of preparation of sodium ion batteries, and in particular relates to the preparation and application of an artificial SEI film. Background Art

[0002] Since sodium resources are abundant worldwide and show excellent performance improvement potential in low-temperature performance, over-discharge resistance, safety and environmental protection, it is considered to be one of the potential alternatives to lithium-ion batteries and has broad application prospects.

[0003] Anode materials for sodium-ion batteries include carbon-based materials, alloys, metal oxides or sulfides, Prussian blue, and organic compounds. Carbon-based materials include hard carbon and soft carbon. Hard carbon has a high theoretical specific capacity, typically around 300–400 mAh / g. Its structure contains numerous micropores and disordered carbon layers, which provide abundant sodium storage sites. However, the surface of hard carbon materials is rich in defects and polar functional groups. During the first charge, the electrolyte easily undergoes irreversible decomposition on these surfaces, forming a solid electrolyte interface (SEI), which consumes a large amount of sodium ions and electrolyte, resulting in low initial Coulombic efficiency and capacity. Furthermore, the disordered microporous structure of hard carbon leads to complex and high resistance sodium ion diffusion pathways. This makes it difficult for sodium ions to quickly intercalate and deintercalate, especially during high-rate charge and discharge. These disordered microporous structures may collapse during charge and discharge, affecting the battery's rate and cycling performance. Current research on hard carbon materials includes the design of high-carbon-content, low-heteroatom precursors, pore structure optimization, surface modification, and electrolyte matching. Presetting an artificial SEI film is also an aspect of surface modification. A large number of studies have shown that presetting an artificial SEI film can inhibit the occurrence of side reactions on the electrode surface, improve ionic conductivity, stabilize the electrode interface, effectively improve the above problems, and enhance battery performance. For example, in order to alleviate the volume expansion of the lithium metal negative electrode and the problem of unstable SEI film, patent CN 115881896 A uses plasma-assisted chemical vapor deposition technology (PECVD) / magnetron sputtering / electrodeposition and other methods to first synthesize graphene nanosheets on a carbon substrate and then continue to deposit lithium-philic substances and then composite with lithium metal to finally obtain a composite electrode. The formation process of its surface artificial SEI film is to use PECVD to introduce nitrogen trifluoride to form Li3N and LiF artificial SEI films on the surface of the composite electrode. This method is cumbersome and complicated, and the PECVD process is complex and the film thickness cannot be accurately controlled. Summary of the Invention

[0004] To address the existing problems of sodium-ion batteries, such as low initial efficiency, poor rate performance, and poor stability, caused by electrolyte consumption during SEI film formation, uneven and continuously thickening thickness, and low ion transport efficiency, the present invention provides a method for preparing a cobalt oxide artificial SEI film and its application in sodium-ion batteries. The present invention employs a surface modification method, using cobaltocene and oxygen plasma as precursor sources, and a plasma-enhanced atomic layer deposition (PEALD) apparatus to deposit a cobalt oxide artificial SEI film of controllable thickness onto the surface of hard carbon-coated aluminum foil. This negative electrode exhibits excellent battery performance.

[0005] The present invention adopts the following technical solutions to solve the above problems:

[0006] A method for preparing a cobalt oxide artificial SEI film comprises the following steps:

[0007] Step S1: slurrying the hard carbon material, sodium carboxymethyl cellulose colloid (CMC) and Super P, and adding water to adjust the viscosity to obtain a hard carbon slurry;

[0008] Step S2: evenly coating the hard carbon slurry obtained in step S1 on aluminum foil and drying it in a forced air drying oven;

[0009] Step S3: Place the electrode dried in step S2 in a PEALD reaction chamber and alternately introduce cobalt cyclopentadienyl and oxygen plasma to perform a deposition process. After the reaction chamber temperature cools naturally, take out the electrode to obtain the target product, a cobalt oxide artificial SEI film.

[0010] As a preferred technical solution of the present invention, according to the battery performance requirements and raw material characteristics, the proportion of each component in the slurry production process needs to be strictly controlled, and the feeding ratio of the hard carbon material, CMC and Super P in step S1 is further limited to a mass ratio of (7~9):(1~2):(1~2).

[0011] As a preferred technical solution of the present invention, the electrode slurry needs to have a stable and appropriate viscosity, which has a crucial impact on the electrode coating process. It is further defined that the slurry viscosity in step S1 is 1000 to 9000 mPa·s.

[0012] As a preferred technical solution of the present invention, the pulping operation in step S1 is performed in equipment including but not limited to a ball mill, a deaerator, and the like.

[0013] As a preferred technical solution of the present invention, the coating thickness has an important influence on battery capacity, internal resistance and other properties. Ensuring uniform thickness of the electrode contributes to the performance of the battery. The coating thickness in step S2 is further limited to 100 to 400 μm.

[0014] As a preferred technical solution of the present invention, atomic layer deposition controls the film thickness by controlling the number of cycles, and further limits the number of cycles of the deposition process in step S3 to a range of 10 to 100.

[0015] As a preferred technical solution of the present invention, the flow rate of the carrier gas in the atomic layer deposition equipment can control the amount of reaction source entering the reaction chamber, thereby controlling the film deposition rate and quality, and further limiting the reaction source carrier gas flow range in step S3 to 50 sccm to 200 sccm.

[0016] As a preferred technical solution of the present invention, the carrier gas in step S3 is one or both of argon and nitrogen.

[0017] As a preferred technical solution of the present invention, in the atomic layer deposition equipment, the pulse time can be used to control the amount of reaction source carried by the carrier gas into the reaction chamber, thereby controlling the film deposition rate and quality. The reaction source pulse time in step S3 is further limited to 0.1s to 20s.

[0018] As a preferred technical solution of the present invention, whether the reaction occurs and the film deposition rate can be controlled by the reaction chamber temperature in the atomic layer deposition equipment, and the reaction chamber temperature in step S3 is further limited to 100-300°C.

[0019] As a preferred technical solution of the present invention, the oxygen plasma generation power in the atomic layer deposition equipment can control whether oxygen plasma is generated and also affect the concentration of oxygen plasma, thereby affecting the thin film deposition rate. The oxygen plasma generation power in step S3 is further limited to 200W~800W.

[0020] The present invention uses PEALD to uniformly deposit cobalt oxide as an artificial SEI film on the surface of hard carbon-coated aluminum foil, and utilizes the conformality and thickness controllability of PEALD to synthesize a uniform and dense cobalt oxide film. The cobalt oxide artificial SEI film can effectively inhibit side reactions on the electrode surface, improve the initial coulombic efficiency, enhance the electrode surface reaction kinetics, promote the insertion and extraction of sodium ions, improve rate performance, and still have good charge and discharge performance under faster charging conditions. At the same time, because the cobalt oxide artificial SEI film isolates the electrode material from the electrolyte, it avoids the continuous consumption of the electrode material and the decomposition of the electrolyte, and effectively inhibits the phenomenon of sodium precipitation, thereby effectively improving the cycle stability of the battery.

[0021] Compared with the prior art, the present invention has the following advantages and beneficial effects:

[0022] 1. The present invention utilizes a surface modification strategy to achieve the construction of a cobalt oxide artificial SEI film on the surface of a hard carbon negative electrode for the first time through PEALD. The uniform and dense cobalt oxide artificial SEI film effectively inhibits the occurrence of side reactions on the electrode surface and provides additional sodium adsorption sites, effectively improving the initial coulombic efficiency and specific capacity.

[0023] 2. The cobalt oxide artificial SEI film prepared by the present invention accelerates the ion transfer rate and improves the electrode surface reaction kinetics, so that the battery still has excellent discharge performance under high rate conditions of 10C, thereby improving the battery's rate performance.

[0024] 3. The construction of the artificial SEI film of cobalt oxide in the present invention stabilizes the electrode interface, inhibits the occurrence of reactions such as electrolyte decomposition, electrode material dissolution, and sodium precipitation. The assembled sodium ion battery still has a capacity retention rate of 95% after 500 cycles at 0.5C, effectively improving the battery's cycle stability. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0026] Figure 1 0.1C first cycle charging curves of cobalt oxide artificial SEI films C1-C7 prepared in Comparative Example 1 and Examples 2-7;

[0027] Figure 2 0.1C first cycle discharge curves of cobalt oxide artificial SEI films C1-C7 prepared in Comparative Example 1 and Examples 2-7;

[0028] Figure 3 Rate curves of cobalt oxide artificial SEI films C1 to C7 prepared in Comparative Example 1 and Examples 2 to 7;

[0029] Figure 4 Impedance test curves of cobalt oxide artificial SEI films C1 to C7 prepared in Comparative Example 1 and Examples 2 to 7;

[0030] Figure 5 Linear voltammetric curves of cobalt oxide artificial SEI films C1 to C7 prepared in Comparative Example 1 and Examples 2 to 7;

[0031] Figure 6 Tafel slope curves of cobalt oxide artificial SEI films C1-C7 prepared in Comparative Example 1 and Examples 2-7;

[0032] Figure 7 This is the cycle curve of the cobalt oxide artificial SEI film prepared in Example 4. DETAILED DESCRIPTION

[0033] The above contents of the present invention are further described in detail below through examples, but this should not be understood as limiting the scope of the above subject matter of the present invention to the following examples. All technologies implemented based on the above contents of the present invention fall within the scope of the present invention.

[0034] Comparative Example 1

[0035] Step S1: 4 g of hard carbon material, 20 g of CMC, and 0.5 g of Super P were slurried, and water was added to adjust the viscosity to obtain a hard carbon slurry with a viscosity of 6000 mPa·s;

[0036] Step S2: The hard carbon slurry obtained in step S1 was evenly coated on an aluminum foil in a thickness of 200 μm, and dried in a forced air drying oven at 60° C. for 12 h to obtain C1.

[0037] Example 2

[0038] The preparation method of the cobalt oxide artificial SEI film in this embodiment is as follows:

[0039] Step S1: 4 g of hard carbon material, 20 g of CMC, and 0.5 g of Super P were slurried, and water was added to adjust the viscosity to obtain a hard carbon slurry with a viscosity of 6000 mPa·s;

[0040] Step S2: The hard carbon slurry obtained in step S1 is evenly coated on an aluminum foil with a thickness of 200 μm, and dried in a forced air drying oven at 60° C. for 12 h;

[0041] Step S3: Place the electrode dried in step S2 in a PEALD (PICOSUN, R-200AdV) reaction chamber, and use carrier gas to alternately introduce cobalt cyclopentadienyl (pulse time: 1.5s, carrier gas flow rate: 100sccm) and oxygen plasma (pulse time: 10s, power: 400W, carrier gas flow rate: 80sccm) at 250°C. After the process cycle is repeated 10 times and the reaction chamber temperature is naturally cooled, the electrode is taken out to obtain C2.

[0042] Example 3

[0043] The preparation method of the cobalt oxide artificial SEI film in this embodiment is as follows:

[0044] Step S1: 4 g of hard carbon material, 20 g of CMC, and 0.5 g of Super P were slurried, and water was added to adjust the viscosity to obtain a hard carbon slurry with a viscosity of 6000 mPa·s;

[0045] Step S2: The hard carbon slurry obtained in step S1 is evenly coated on an aluminum foil with a thickness of 200 μm, and dried in a forced air drying oven at 60° C. for 12 h;

[0046] Step S3: Place the electrode dried in step S2 in a PEALD (PICOSUN, R-200AdV) reaction chamber, and use carrier gas to alternately introduce cobalt cyclopentadienyl (pulse time: 1.5s, carrier gas flow rate: 100sccm) and oxygen plasma (pulse time: 10s, power: 400W, carrier gas flow rate: 80sccm) at 250°C. After the process cycle is repeated 30 times and the reaction chamber temperature is naturally cooled, the electrode is taken out to obtain C3.

[0047] Example 4

[0048] The preparation method of the cobalt oxide artificial SEI film in this embodiment is as follows:

[0049] Step S1: 4 g of hard carbon material, 20 g of CMC, and 0.5 g of Super P were slurried, and water was added to adjust the viscosity to obtain a hard carbon slurry with a viscosity of 6000 mPa·s;

[0050] Step S2: The hard carbon slurry obtained in step S1 is evenly coated on an aluminum foil with a thickness of 200 μm, and dried in a forced air drying oven at 60° C. for 12 h;

[0051] Step S3: Place the electrode dried in step S2 in a PEALD (PICOSUN, R-200AdV) reaction chamber, and use carrier gas to alternately introduce cobalt cyclopentadienyl (pulse time: 1.5s, carrier gas flow rate: 100sccm) and oxygen plasma (pulse time: 10s, power: 400W, carrier gas flow rate: 80sccm) at 250°C. After the process cycle is repeated 50 times and the reaction chamber temperature is naturally cooled, the electrode is taken out to obtain C4.

[0052] Example 5

[0053] The preparation method of the cobalt oxide artificial SEI film in this embodiment is as follows:

[0054] Step S1: 4 g of hard carbon material, 20 g of CMC, and 0.5 g of Super P were slurried, and water was added to adjust the viscosity to obtain a hard carbon slurry with a viscosity of 6000 mPa·s;

[0055] Step S2: The hard carbon slurry obtained in step S1 is evenly coated on an aluminum foil with a thickness of 200 μm, and dried in a forced air drying oven at 60° C. for 12 h;

[0056] Step S3: Place the electrode dried in step S2 in a PEALD (PICOSUN, R-200AdV) reaction chamber, and use carrier gas to alternately introduce cobalt cyclopentadienyl (pulse time: 1.5s, carrier gas flow rate: 100sccm) and oxygen plasma (pulse time: 10s, power: 400W, carrier gas flow rate: 80sccm) at 250°C. The process cycle is repeated 70 times and the reaction chamber temperature is naturally cooled before taking out the electrode to obtain C5.

[0057] Example 6

[0058] The preparation method of the cobalt oxide artificial SEI film in this embodiment is as follows:

[0059] Step S1: 4 g of hard carbon material, 20 g of CMC, and 0.5 g of Super P were slurried, and water was added to adjust the viscosity to obtain a hard carbon slurry with a viscosity of 6000 mPa·s;

[0060] Step S2: The hard carbon slurry obtained in step S1 is evenly coated on an aluminum foil with a thickness of 200 μm, and dried in a forced air drying oven at 60° C. for 12 h;

[0061] Step S3: Place the electrode dried in step S2 in a PEALD (PICOSUN, R-200AdV) reaction chamber, and use carrier gas to alternately introduce cobalt cyclopentadienyl (pulse time: 1.5s, carrier gas flow rate: 100sccm) and oxygen plasma (pulse time: 10s, power: 400W, carrier gas flow rate: 80sccm) at 250°C. The process cycle is repeated 90 times and the reaction chamber temperature is naturally cooled before taking out the electrode to obtain C6.

[0062] Example 7

[0063] The preparation method of the cobalt oxide artificial SEI film in this embodiment is as follows:

[0064] Step S1: 4 g of hard carbon material, 20 g of CMC, and 0.5 g of Super P were slurried, and water was added to adjust the viscosity to obtain a hard carbon slurry with a viscosity of 6000 mPa·s;

[0065] Step S2: The hard carbon slurry obtained in step S1 is evenly coated on an aluminum foil with a thickness of 200 μm, and dried in a forced air drying oven at 60° C. for 12 h;

[0066] Step S3: Place the electrode dried in step S2 in a PEALD (PICOSUN, R-200AdV) reaction chamber, and use carrier gas to alternately introduce cobalt cyclopentadienyl (pulse time: 1.5s, carrier gas flow rate: 100sccm) and oxygen plasma (pulse time: 10s, power: 400W, carrier gas flow rate: 80sccm) at 250°C. After the process cycle is repeated 100 times and the reaction chamber temperature is naturally cooled, the electrode is taken out to obtain C7.

[0067] The negative electrode sheets prepared in Examples 2 to 7 and Comparative Example 1 were assembled into button-type batteries for performance testing. Sodium sheets were used as counter electrodes. Some of the test results are shown in Table 1.

[0068] Table 1 Power-off test data

[0069]

[0070]

[0071] According to the data in Table 1, in this experiment, the discharge capacities of Examples 2-7 were superior to those of Comparative Example 1, and their specific discharge capacities were comparable, demonstrating that the cobalt oxide film coating did not affect the capacity of the hard carbon anode and even enhanced it. In this experiment, Example 4 achieved the best initial coulombic efficiency of 87.48%, surpassing the 81.05% of the Comparative Example.

[0072] from Figure 1 and Figure 2 It can be seen that Example 4 has the best 0.1C first cycle discharge capacity of 0.701 mAh, which is better than other examples and comparative examples. Figure 3 ) shows that Example 4 has good performance at 10C, indicating that the cobalt oxide SEI film has good ionic conductivity, can help sodium ions migrate quickly, and reduce negative effects such as sodium precipitation. Figure 4 The impedance curve test shows that the presence of the cobalt oxide SEI film does not increase the internal impedance of the battery, and even reduces the battery impedance. Figure 6 The Tafel slope also proves that Example 4 has the best chemical reaction rate, further indicating that the cobalt oxide SEI has a beneficial effect on the battery. The above results show that the cobalt oxide SEI improves all aspects of battery performance.

[0073] It should be noted that when numerical ranges are mentioned in the present invention, it should be understood that both endpoints of each numerical range and any value between the two endpoints may be selected. Since the steps and methods used are the same as those in the embodiments, in order to avoid redundancy, the present invention describes preferred embodiments. Although preferred embodiments of the present invention have been described, those skilled in the art may make additional changes and modifications to these embodiments once they understand the basic inventive concepts. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments and all changes and modifications that fall within the scope of the present invention.

[0074] The above embodiments describe the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The above embodiments and the description only illustrate the principles of the present invention. Without departing from the scope of the principles of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of protection of the present invention.

Claims

1. A method for preparing an artificial SEI film of cobalt oxide, characterized in that The following steps are involved: Step S1: slurrying the hard carbon material, sodium carboxymethyl cellulose colloid (CMC) and Super P, and adding water to adjust the viscosity to obtain a hard carbon slurry; Step S2: evenly coating the hard carbon slurry obtained in step S1 on aluminum foil and drying it in a forced air drying oven; Step S3: Place the electrode dried in step S2 in the reaction chamber of a plasma-enhanced atomic layer deposition device, use carrier gas to alternately introduce cobalt cyclopentadienyl and oxygen plasma for a deposition process, and remove the electrode after the reaction chamber temperature is naturally cooled to obtain the target product, a cobalt oxide artificial SEI film.

2. The method for preparing a cobalt oxide artificial SEI film according to claim 1, wherein: The mass ratio of the hard carbon material, CMC and Super P in step S1 is (7~9):(1~2):(1~2).

3. The method for preparing a cobalt oxide artificial SEI film according to claim 1, wherein: The viscosity is adjusted in step S1 to a range of 1000 to 9000 mPa·s.

4. The method for preparing a cobalt oxide artificial SEI film according to claim 1, wherein: The coating thickness in step S2 is 100-400 μm.

5. The method for preparing a cobalt oxide artificial SEI film according to claim 1, wherein: In step S3, the carrier gas is one or both of argon and nitrogen, and the carrier gas flow rate ranges from 50 sccm to 200 sccm.

6. The method for preparing a cobalt oxide artificial SEI film according to claim 1, wherein: The pulse time of alternately introducing cobaltocene and oxygen plasma using carrier gas in step S3 is 0.1 s to 20 s.

7. The method for preparing a cobalt oxide artificial SEI film according to claim 1, wherein: In step S3, the reaction chamber temperature is 100-300° C., and the oxygen plasma generating power is 200 W-800 W.

8. The method for preparing a cobalt oxide artificial SEI film according to claim 1, wherein: The number of deposition process cycles in step S3 ranges from 10 to 100.

9. The cobalt oxide artificial SEI film obtained according to the preparation method according to any one of claims 1 to 8.

10. Use of the cobalt oxide artificial SEI film according to claim 9 in sodium ion batteries.

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