Method for modifying graphite current collector through LDHs and modified graphite current collector

Abstract

The invention discloses a method for modifying a graphite current collector through LDHs and a modified graphite current collector, a solution containing LDHs is uniformly dropwise added to the surface of a pretreated graphite current collector, spin coating is performed, vacuum drying is performed, a coating film with the thickness of 1-100 microns is formed on the surface of the graphite current collector, and the LDHs modified graphite current collector is obtained. And finally, the efficient operation of the liquid metal battery is realized.

Description

Technical Field

[0001] This invention belongs to the field of graphite current collector surface modification technology, specifically relating to a method for modifying graphite current collectors with LDHs and the modified graphite current collector. Background Technology

[0002] Energy storage devices that complete electrochemical reactions in a fully liquid system are called liquid metal batteries. Compared to traditional solid-state batteries, the liquid contact surface of these batteries can avoid the volume expansion and contraction phenomenon common in solid-state electrodes, making them naturally suitable for energy storage scenarios with high energy density and long cycle life. They show broad application potential in large-scale energy storage fields, such as grid peak shaving and renewable energy grid integration.

[0003] The actual reaction interface of liquid metal batteries is a liquid-liquid contact, a characteristic that allows them to avoid the dendrite problem common in most metal batteries, thus achieving better cycle life. However, the solid-liquid contact characteristic interface does not completely disappear, but rather shifts to the interface between the electrode and the current collector. Graphite is a commonly used current collector material in liquid metal batteries, and its high-temperature resistance matches the operational requirements of liquid metal batteries. However, graphite current collectors have significant drawbacks: they are prone to embrittlement and cracking failure at high temperatures; their low surface energy results in high interfacial contact resistance, which in turn continuously affects the battery's operating efficiency and energy utilization efficiency; at the same time, the battery's rate performance and cycle performance are also adversely affected by limitations in electronic conductivity. Therefore, exploring high-efficiency current collector-electrode interface treatment processes is of significant practical value for achieving efficient design and industrial application of liquid metal batteries.

[0004] Layered double hydroxides (LDHs, often simply referred to as layered hydroxides) are a class of anionic clays with a typical layered structure, and their chemical formula is [M 2+ 1-x M 3+ x (OH)2] x+ (A n- ) x / n •mH2O. Wherein, M 2+ Represents Ni 2+ Co 2+ Divalent metal cations, M 3+ Representing Al 3+ Fe 3+ Trivalent metal cations, A n- This represents NO3 2 CO3 2 ⁻Isolayer anions. Its unique structure gives it three major advantages: (1) Adjustability of interlayer structure: By introducing highly conductive metal cations (such as Ni)2+ Co²⁺ can significantly improve the electronic conductivity of materials; (2) Advantages in interfacial wettability: The surface of the plate contains a large number of -OH groups, which can coordinate with liquid metals (such as Na and Li), greatly reducing the contact angle and improving the interfacial wettability. (3) High-temperature stability: The composite oxide generated by low-temperature heat treatment of LDHs can maintain its layered structure and will not decompose below 500℃. Furthermore, it bonds tightly with the graphite substrate, enhancing the overall mechanical strength. Based on these characteristics, LDHs have significant potential for optimizing the current collector-electrode interface in liquid metal batteries. Currently, no LDH-based current collector modification schemes have been reported for the design of graphite current collector interface films in liquid metal batteries. Summary of the Invention

[0005] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0006] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0007] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for modifying graphite current collectors with LDHs.

[0008] To solve the above-mentioned technical problems, the present invention provides the following technical solution: including, The LDHs solution was uniformly added dropwise to the surface of the pretreated graphite current collector, then spin-coated and vacuum dried to form a film with a thickness of 1μm to 100μm on the surface of the graphite current collector, thus obtaining the LDHs modified graphite current collector.

[0009] As a preferred embodiment of the method for modifying graphite current collectors with LDHs according to the present invention, the solvent of the LDHs solution includes one of water, DMSO, and NVP.

[0010] As a preferred embodiment of the method for modifying graphite current collectors with LDHs according to the present invention, the concentration of LDHs in the LDHs solution is 8-12 wt%.

[0011] As a preferred embodiment of the method for modifying graphite current collectors with LDHs according to the present invention, the LDHs include one of NiAl-LDHs, NiFe-LDHs, NiCo-LDHs, CoMn-LDHs, and CoFe-LDHs.

[0012] As a preferred embodiment of the method for modifying graphite current collectors with LDHs according to the present invention, wherein the LDHs are synthesized by a nitrate brine thermal method.

[0013] As a preferred embodiment of the method for modifying graphite current collectors with LDHs according to the present invention, the pretreatment of the graphite current collector surface includes sequential ultrasonic cleaning with anhydrous ethanol and deionized water at 150-250W for 15-20 minutes, and drying in an oven at 60-70℃ for 25-35 minutes.

[0014] As a preferred embodiment of the method for modifying graphite current collectors with LDHs according to the present invention, the spin coating speed is 2500-3500 r / min and the time is 70-80 s.

[0015] As a preferred embodiment of the method for modifying graphite current collectors with LDHs according to the present invention, the vacuum drying temperature is 110-130℃, the vacuum degree is -0.095MPa, and the vacuum drying time is 2.5-3.5h.

[0016] The purpose of this invention is to overcome the shortcomings of the prior art and provide a graphite current collector modified by LDHs, which is suitable for liquid metal battery systems, including Li||Sb and Li||Bi.

[0017] Beneficial effects of this invention: (1) The present invention utilizes LDHs-modified graphite current collectors to form an LDHs coating on the surface of the graphite current collectors, which can significantly reduce the contact resistance at the graphite current collector-electrode interface, thereby increasing the efficiency of the liquid metal battery to 87% and greatly reducing ohmic losses during charging and discharging. The layered structure of LDHs can form a dense protective barrier on the graphite surface, inhibiting the corrosion reaction between the electrolyte and graphite, thus achieving a higher capacity retention rate.

[0018] (2) The present invention uses spin coating to prepare the coating. The process is simple and the equipment cost is low. It can be adapted to continuous production lines and can be compatible with graphite current collectors of different sizes and shapes without the need for complex molds.

[0019] (3) This invention synthesizes LDHs through a simple nitrate brine thermal method, and can be adapted to different liquid metal battery systems (such as Li||Sb, Li||Bi, etc.) by replacing metal ions, without the need to redesign the synthesis process, thus reducing the cost of technology promotion. (4) By adjusting parameters such as the concentration of the spin coating solution, the rotation speed, and the drying temperature, the coating thickness (1-100μm) and density of LDHs can be precisely controlled to meet the different requirements of interface performance for liquid metal batteries with different power requirements (such as energy storage type and power type). The processing time is short, and multiple current collectors can be processed at the same time, making it suitable for mass production. Attached Figure Description

[0020] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein: Figure 1 The X-ray diffraction test results are shown on the surface of the modified graphite current collector in Example 1.

[0021] Figure 2 The X-ray diffraction test results are for the surface of the unmodified graphite current collector in Comparative Example 1. Figure 3 The image shows the contact angle test result of the modified graphite current collector surface in Example 1.

[0022] Figure 4 The contact angle test diagram is shown for the surface of the unmodified graphite current collector in Comparative Example 1. Figure 5 This is a comparison chart of the efficiency of liquid metal batteries assembled using the current collectors in Example 1 and Comparative Example 1.

[0023] Figure 6 Cycle stability of the liquid metal battery assembled using the current collector in Example 1.

[0024] Figure 7 To assess the cycle stability of the liquid metal battery assembled using the current collector of Comparative Example 1.

[0025] Figure 8 This is a comparison of the improvement effects of the current collectors modified with different LDHs materials in Examples 1 to 5 of the present invention compared with the unmodified current collector in Comparative Example 1.

[0026] Figure 9 This illustrates the effect of adjusting the spin coating concentration on the surface wettability of the modified current collector in Example 6 of the present invention. Detailed Implementation

[0027] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0028] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0029] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments.

[0030] Unless otherwise specified, all raw materials used in this invention are commercially available in the field.

[0031] Example 1 This embodiment provides a method for modifying graphite current collectors with NiAl-LDHs, specifically: 1) Synthesis of NiAl-LDHs: Nickel nitrate and aluminum nitrate (n(Ni):n(Al)=3) were dissolved in 30 mL of deionized water and stirred with a glass rod until the solution was clear. Add 4.23 g of urea (n(CO(NH2)2):n(M) + )=3) Add to the mixed solution, stir with a glass rod until transparent, and transfer the mixed solution to a 150 mL hydrothermal reactor and react at 150℃ for 12 h. Cool to obtain a green precipitate; The precipitate was washed five times with deionized water and then dried in an oven at 80°C for 12 h to finally obtain NiAl-LDH.

[0032] 2) Take 2g of NiAl-LDHs powder, add 18g of mixed solvent (water / DMSO volume ratio 1:1), and ultrasonically treat with an ultrasonic cleaner (300W) for 45min to obtain a uniform LDHs spin-coating solution with no obvious agglomeration particles and a mass concentration of 10%. 3) The graphite current collector was ultrasonically cleaned with anhydrous ethanol and deionized water for 18 min (200W) in sequence, and dried in an oven at 65℃ for 30 min to obtain the pretreated graphite current collector. 4) Use a pipette to take 2 mL of LDHs spin-coating solution and evenly drop it onto the surface of the graphite current collector. Fix it on the suction cup of the spin coater, set the rotation speed to 3000 r / min and the spin coating time to 75 s to obtain a coating with a thickness of 50 μm.

[0033] 5) After spin coating, the current collector is placed in a vacuum drying oven at 120℃ (vacuum degree -0.095MPa) and dried for 3 hours to obtain the NiAl-LDHs@Gr modified current collector of this embodiment.

[0034] Comparative Example 1 This comparative example uses unmodified graphite current collectors as a control.

[0035] Figure 1 The results are X-ray diffraction test results of the modified graphite current collector surface in Example 1. Figure 2 The X-ray diffraction test results are for the surface of the unmodified graphite current collector in Comparative Example 1. Figure 1 , Figure 2 The XRD comparison results showed that the characteristic peaks of NiAl-LDHs appeared at 12°, 24°, 35°, 40° and 47° in Example 1, which proved the successful modification of Example 1.

[0036] Figure 3 This is a contact angle test diagram of the modified graphite current collector surface in Example 1. Figure 4 The image shows the contact angle test results of the unmodified graphite current collector surface in Comparative Example 1. The results show that the contact angle of the modified Example 1 is smaller than that of the unmodified stainless steel surface in Comparative Example 1, indicating a better wetting effect.

[0037] The surface-modified current collector obtained in Example 1 was assembled with the current collector in Comparative Example 1 to form a Li||Te liquid metal battery (positive electrode: Te, negative electrode: Li, electrolyte: LiCl-KCl). Electrochemical cycling was performed under the rated capacity of 0.1 C, and the efficiency and cycle capacity retention were calculated. The results are as follows: Figures 5-7 .

[0038] Figure 5 This is a comparison chart of the efficiency of liquid metal batteries assembled using the current collectors in Example 1 and Comparative Example 1. Figure 6 To assess the cycle stability of the liquid metal battery assembled using the current collector in Example 1, Figure 7 To assess the cycle stability of the liquid metal battery assembled using the current collector in Comparative Example 1, from... Figures 5-7 The results show that the operating efficiency of the liquid metal battery modified in Example 1 is significantly higher than that of the unmodified group, and the efficiency fluctuation is smaller. The battery modified with LDHs and graphite current collector exhibits slow capacity decay during charging / discharging and maintains a high capacity retention rate for a long time, which is significantly improved compared with the unmodified Comparative Example 1. This proves that LDHs modification simultaneously improves the operating efficiency and cycle life of the liquid metal battery, and completely solves the core performance shortcomings of the unmodified graphite current collector.

[0039] Example 2 The difference between this embodiment and Embodiment 1 is that the LDHs material is adjusted to NiFe-LDHs. Specifically, aluminum nitrate in step 1) is replaced with iron nitrate, and n(Ni):n(Fe) = 3:1 is controlled. The remaining steps are the same as in Embodiment 1, and finally NiFe-LDHs and NiFe-LDHs@Gr modified current collectors are obtained.

[0040] Example 3 The difference between this embodiment and Embodiment 1 is that the LDHs material is adjusted to NiCo-LDHs. Specifically, aluminum nitrate in step 1) is replaced with cobalt nitrate, and n(Ni):n(Fe) = 3:1 is controlled. The remaining steps are the same as in Embodiment 1, and finally NiCo-LDHs and NiCo-LDHs@Gr modified current collectors are obtained.

[0041] Example 4 The difference between this embodiment and Example 1 is that the LDHs material is adjusted to CoMn-LDHs. Specifically, nickel nitrate and aluminum nitrate in step 1) are replaced with cobalt nitrate nonahydrate and manganese nitrate nonahydrate, and the ratio of n(Mn):n(Co) is controlled to be 3:1. The remaining steps are the same as in Example 1, and CoMn-LDHs and CoMn-LDHs@Gr modified current collectors are finally obtained.

[0042] Example 5 The difference between this embodiment and Example 1 is that the LDHs material is adjusted to CoFe-LDHs. Specifically, nickel nitrate and aluminum nitrate in step 1) are replaced with cobalt nitrate nonahydrate and ferric nitrate nonahydrate, and the ratio of n(Fe):n(Co) is controlled to be 3:1. The remaining steps are the same as in Example 1, and finally CoFe-LDHs and CoFe-LDHs@Gr modified current collectors are obtained.

[0043] The improvement effects of the current collectors modified with different LDH materials in Examples 1-5 compared to the unmodified current collector in Comparative Example 1 are shown in Table 1 and 5. Figure 8 As shown.

[0044] Table 1

[0045] As can be seen from Table 1, the LDHs material of Example 1 has the best modification effect. This is because its adsorption properties are weaker and its activity is at a lower level compared to other LDHs materials, which can effectively suppress the occurrence of side reactions.

[0046] Example 6 The difference between this embodiment and Embodiment 1 is that the concentration of the LDHs spin-coating solution in step 2) was adjusted to 5%, 7%, 10%, 13%, and 15%, respectively. The remaining steps were the same as in Embodiment 1. This resulted in graphite current collectors modified with different LDHs spin-coating solution concentrations. The contact angle of the coating was measured to characterize the improvement effect of the coating on wettability. The results are shown in Table 2. Figure 9 As shown.

[0047] Table 2

[0048] The concentration of the LDH spin-coating solution determines the exposure of -OH groups on the LDH surface and the efficiency of interfacial interactions by controlling the dispersion stability of the suspension and the uniformity and density of the coating. Excessively high LDH concentrations can cause spontaneous sedimentation of the slurry during spin-coating. Therefore, the LDH concentration should be below 13%.

[0049] In summary, this invention, through the LDHs-modified graphite current collector, forms an LDHs coating on the graphite current collector surface, which significantly reduces the contact resistance at the graphite current collector-electrode interface, thereby increasing the efficiency of the liquid metal battery to 87% and greatly reducing ohmic losses during charge and discharge. The layered structure of LDHs can form a dense protective barrier on the graphite surface, inhibiting the corrosion reaction between the electrolyte and graphite, thus achieving a higher capacity retention rate.

[0050] This invention uses spin coating to prepare the coating, which is simple, has low equipment cost, can be adapted to continuous production lines, and is compatible with graphite current collectors of different sizes and shapes, without the need for complex molds.

[0051] This invention synthesizes LDHs via a simple nitrate-salt thermal method, and can be adapted to different liquid metal battery systems (such as Li||Sb, Li||Bi, etc.) by replacing metal ions, without requiring a redesign of the synthesis process, thus reducing the cost of technology promotion. By adjusting parameters such as the concentration of the spin coating solution, the rotation speed, and the drying temperature, the coating thickness (1-100μm) and density of LDHs can be precisely controlled, meeting the differentiated requirements of interface performance for liquid metal batteries with different power requirements (such as energy storage and power types). The processing time is short, and multiple current collectors can be processed simultaneously, making it suitable for mass production.

[0052] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A method for modifying graphite current collectors with LDHs, characterized in that: include, The LDHs solution was uniformly added dropwise to the surface of the pretreated graphite current collector, then spin-coated and vacuum dried to form a film with a thickness of 1μm to 100μm on the surface of the graphite current collector, thus obtaining the LDHs modified graphite current collector.

2. The method for modifying graphite current collectors with LDHs as described in claim 1, characterized in that: The solvent for the LDHs solution includes one of water, DMSO, and NVP.

3. The method for modifying graphite current collectors with LDHs as described in claim 2, characterized in that: The concentration of LDHs in the LDHs solution is 8-12 wt%.

4. The method for modifying graphite current collectors with LDHs as described in claim 3, characterized in that: The LDHs include one of NiAl-LDHs, NiFe-LDHs, NiCo-LDHs, CoMn-LDHs, and CoFe-LDHs.

5. The method for modifying graphite current collectors with LDHs as described in claim 4, characterized in that: The LDHs were synthesized via a nitrate saline thermal method.

6. The method for modifying graphite current collectors with LDHs as described in claim 1, characterized in that: The pretreatment of the graphite current collector surface includes sequential ultrasonic cleaning with anhydrous ethanol and deionized water at 150-250W for 15-20 minutes, followed by drying in an oven at 60-70℃ for 25-35 minutes.

7. The method for modifying graphite current collectors with LDHs as described in claim 1, characterized in that: The spin coating speed is 2500-3500 r / min, and the time is 70-80 s.

8. The method for modifying graphite current collectors with LDHs as described in claim 1, characterized in that: The vacuum drying temperature is 110-130℃, the vacuum degree is -0.095MPa, and the vacuum drying time is 2.5-3.5h.

9. The modified graphite current collector obtained by the method described in any one of claims 1 to 8, characterized in that: The modified graphite current collector is suitable for liquid metal battery systems, including Li||Sb and Li||Bi.

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