Preparation method of negative current collector with sodium-philic composite coating, negative current collector and negative-electrode-free all-solid-state battery

Abstract

The invention provides a preparation method of a negative electrode current collector with a sodium-philic composite coating, the negative electrode current collector and a negative-electrode-free all-solid-state battery, and relates to the technical field of sodium ion battery cells, and the preparation method comprises the following steps: S1, depositing a layer of MAX phase film on the surface of the negative electrode current collector; and step S2, removing the aluminum layer in the MAX phase film so as to form a sodium-philic composite coating coated with multiple layers of MXene on the surface of the negative electrode current collector. The preparation method has the beneficial effects that the sodium-philic composite coating coated with multiple layers of MXene can be formed on the surface of the negative electrode current collector through two-step operation, so that the MXene layer with ionic conduction and the metal layer with electronic conduction are mixed together, the effect of mixed conduction of ions and electrons is realized, and further by virtue of the two-dimensional structure and the sodium-philic characteristic of the MXene material, the performance of the negative electrode is improved. The deposition overpotential of sodium electricity can be reduced, and sodium ions are induced to be uniformly deposited on the surface of the current collector; in addition, high mechanical strength and good conductivity of MXene can effectively inhibit volume expansion of the electrode, so that the cycle life of the battery is prolonged, and the safety of the battery is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of sodium ion battery cells, and particularly to a preparation method of a negative current collector with a sodium-philic composite coating, a negative current collector, and a sodium-free all-solid-state battery. Background Art

[0002] Under the current background of global energy transformation, low-carbon travel modes such as new energy vehicles and electric two-wheelers are being popularized at an unprecedented speed and have become the key force to promote the sustainable development of society. Behind this trend, as the core driving force, the performance of battery technology is directly related to the market competitiveness of products and the user experience. Therefore, core indicators such as the use safety, driving range, cycle life, and cost-effectiveness of batteries have naturally become the focus of common concern in the industry and among consumers. Although significant progress has been made in liquid lithium-ion batteries in the past few decades, they still face bottleneck problems such as insufficient safety, limited room for improvement in energy density, and the increasingly tight lithium resources. These problems not only limit the driving range of electric vehicles, increase production costs, but also may cause long-term supply risks due to resource scarcity.

[0003] In view of this, the scientific research community and the industrial community have turned their attention to the all-solid-state sodium battery, a potential alternative solution. Compared with lithium-ion batteries, the greatest advantage of sodium batteries lies in the abundance of sodium resources, which are almost not restricted by geography, have a lower cost, and theoretically have a higher potential for energy density. More importantly, the all-solid-state battery structure can effectively solve the safety hazard of the flammable and explosive liquid electrolyte, bringing a qualitative leap to the battery safety performance. However, due to the soft texture and sticky characteristics of sodium metal, it is extremely easy to deform during the processing and forming process, making it difficult to meet the requirements of the ideal electrode structure. In addition, the instability of sodium in the air, which easily reacts with oxygen or water vapor, increases the difficulty of quality control during the production process and is very unfavorable for the future large-scale production of sodium metal batteries.

[0004] It is precisely in this context that the concept of sodium-based sodium-free batteries has emerged, opening up a new path for the development of sodium battery technology. The sodium-free battery design cleverly bypasses the direct use of sodium metal negative electrodes and instead optimizes the surface characteristics of the current collector to induce sodium ions to directly deposit on the current collector to form metallic sodium during charging. This process is called "bottom-up metallic sodium deposition". The key to this process lies in how to effectively regulate the initial nucleation behavior on the surface of the current collector to ensure the uniform deposition of sodium ions, thereby avoiding uneven deposition problems caused by uneven ion / electron distribution.

[0005] Early studies have shown that an unmodified aluminum foil current collector is not conducive to the uniform nucleation of sodium, which has prompted researchers to explore the possibility of forming sodium alloys on the surface of the negative electrode current collector. The formation of sodium alloys can, to a certain extent, alleviate the problem of uneven ion distribution and promote the uniform deposition of sodium ions. However, the volume distortion accompanying the alloying process, as well as the repeated volume changes brought about by the reversible alloying / dealloying reaction, pose a severe challenge to the formation of a stable solid electrolyte interface (SEI) film on the negative electrode surface.

[0006] Therefore, it is urgent to solve the technical problems of uneven deposition caused by uneven ion / electron distribution at the negative electrode interface of a sodium-free battery and the large volume expansion of the battery cell. Summary of the Invention

[0007] In view of the problems existing in the prior art, the present invention provides a method for preparing a negative electrode current collector with a sodium-philic composite coating, including:

[0008] Step S1, depositing a MAX-phase thin film on the surface of the negative electrode current collector;

[0009] Step S2, removing the aluminum layer in the MAX-phase thin film to form a multi-layer MXene-coated sodium-philic composite coating on the surface of the negative electrode current collector.

[0010] Preferably, in step S1, a magnetron sputtering method is used to deposit a MAX-phase thin film on the surface of the negative electrode current collector.

[0011] Preferably, in step S2, a metal molten salt etching method is used to selectively etch the MAX-phase thin film to remove the aluminum layer in the MAX-phase thin film.

[0012] Preferably, the negative electrode current collector is one or more of a planar metal current collector, a three-dimensional metal current collector, and a carbon-based current collector.

[0013] Preferably, the molten salt used in the metal molten salt etching method is one of ZnCl2 and SnCl2.

[0014] Preferably, the thickness of the sodium-philic composite coating is 50 nm to 500 nm.

[0015] Preferably, the MAX-phase thin film is a MAX-phase material of Ti4AlN3.

[0016] The present invention also provides a negative electrode current collector, on the surface of which a sodium-philic composite coating is formed, and the sodium-philic composite coating is prepared by the above preparation method.

[0017] The present invention also provides a sodium-free all-solid-state battery, including the above negative electrode current collector.

[0018] The above technical solution has the following advantages or beneficial effects: By performing two-step operations, a sodiumophilic composite coating coated with multiple layers of MXene can be formed on the surface of the negative electrode current collector, enabling the MXene layer with ionic conductivity and the metal layer with electronic conductivity to be mixed together, achieving the effect of mixed ionic and electronic conductivity. Furthermore, by virtue of the two-dimensional structure and sodiumophilic properties of the MXene material, the deposition overpotential of sodium batteries can be reduced, inducing uniform deposition of sodium ions on the surface of the current collector; in addition, the high mechanical strength and good conductivity of MXene can effectively inhibit the volume expansion of the electrode, thereby improving the cycle life and safety of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 In a preferred embodiment of the present invention, it is a schematic flow chart of a method for preparing a negative electrode current collector with a sodiumophilic composite coating. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0020] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. The present invention is not limited to this embodiment, and other embodiments may also fall within the scope of the present invention as long as they conform to the gist of the present invention.

[0021] In a preferred embodiment of the present invention, in view of the above problems existing in the prior art, a method for preparing a negative electrode current collector with a sodiumophilic composite coating is now provided, as Figure 1 shown, including:

[0022] Step S1, depositing a MAX phase thin film on the surface of the negative electrode current collector;

[0023] Step S2, removing the aluminum layer in the MAX phase thin film to form a sodiumophilic composite coating coated with multiple layers of MXene on the surface of the negative electrode current collector.

[0024] Specifically, in this embodiment, a uniform and dense Ti4AlN3 MAX phase thin film is deposited on the surface of the negative electrode current collector by using a magnetron sputtering method, and then a molten salt etching method for metals is adopted to selectively etch the Al layer in Ti4AlN3 through a high-temperature chemical reaction, and finally a multi-layer Ti4MN3T is formed X(M represents a metal element) MXene-coated sodiumophilic current collector. Taking ZnCl2 as the molten salt used in the molten salt etching method of metal, the specific etching mechanism is that the Cl- in ZnCl2 reacts with the Al element in Ti4AlN3 to form volatile AlCl3 (gaseous), removing the Al layer. As a result, a uniform distribution of -Cl on the surface of Ti4N3 is achieved, and the sodium halide formed with Na contributes to its efficient Na conduction, thereby reducing the generation of sodium dendrites. In addition, sodiumophilic metal atoms such as Zn and Sn introduced during the etching process serve as deposition sites for sodium ions, guiding the ions to preferentially deposit and grow uniformly at the sites.

[0025] It can be seen that by forming a multi-layer MXene-coated sodiumophilic composite coating on the surface of the current collector, the sodiumophilic property of MXene can reduce the deposition overpotential of sodium electricity and induce uniform deposition of sodium ions on the surface of the current collector. The high mechanical strength and good conductivity of MXene can effectively inhibit the volume expansion during the charge and discharge process of the electrode, thereby improving the cycle life and safety of the battery.

[0026] Furthermore, the preparation of the sodiumophilic composite coating can be achieved only by two steps of operation. The preparation method is simple and easy to operate, and is suitable for large-scale production and promotion. Among them, the multi-layer MXene-coated sodiumophilic composite coating realizes the mixing of the MXene layer with ionic conductivity and the metal layer with electronic conductivity, achieving the effect of mixed ionic and electronic conductivity.

[0027] In a preferred embodiment of the present invention, in step S1, a MAX phase thin film is deposited on the surface of the negative electrode current collector by a magnetron sputtering method.

[0028] In a preferred embodiment of the present invention, in step S2, the MAX phase thin film is selectively etched by a molten salt etching method of metal to remove the aluminum layer in the MAX phase thin film.

[0029] In a preferred embodiment of the present invention, the negative electrode current collector is one or more of a planar metal current collector, a three-dimensional metal current collector, and a carbon-based current collector. Among them, the planar metal current collector is preferably one of copper foil, aluminum foil, carbon cloth, stainless steel foil, nickel foil, and titanium foil.

[0030] In a preferred embodiment of the present invention, the molten salt used in the molten salt etching method of metal is one or more combinations of ZnCl2, SnCl2, NaCl, NaF, and KF.

[0031] In a preferred embodiment of the present invention, the thickness of the sodiumophilic composite coating is 50 nm to 500 nm.

[0032] In a preferred embodiment of the present invention, the MAX phase thin film is a MAX phase material of Ti4AlN3.

[0033] The present invention also provides a negative electrode current collector, on the surface of which a sodium-philic composite coating is formed, and the sodium-philic composite coating is prepared by the above-mentioned preparation method.

[0034] The present invention also provides a non-negative electrode all-solid-state battery, including the above-mentioned negative electrode current collector.

[0035] The following takes the type of molten salt / thickness of the composite layer as variables to discuss the embodiments:

[0036] Example 1

[0037] In this embodiment, Na3V2(PO4)3 is used as the positive electrode active material, and the positive electrode layer is prepared by a wet process.

[0038] For the negative electrode, a copper foil is used as the current collector. Using a Ti4AlN3 alloy target, in a mixed atmosphere of Ar:N = 4:1, the gas pressure is set to 0.5 Pa, the target power is set to 300 W, the substrate temperature is controlled at 650 °C, the target-substrate distance is maintained at 7 cm, and a -100 V bias voltage is applied to the substrate. The deposition rate is maintained at 10 nm / min for 10 minutes. After deposition, annealing is carried out at 600 °C to complete the preparation of the composite foil.

[0039] In order to etch the Ti4AlN3 thin film, a mixed solution containing 0.2 M ZnCl and 0.01 M HCl is used, the temperature is controlled at 600 °C, and the solution is stirred at a speed of 100 rpm by a magnetic stirrer. During the etching process, the sample is immersed in the solution 3 times, and each immersion time is 3 minutes. After the etching is completed, the sample is immediately taken out and rinsed with deionized water, then the sample is immersed in a 0.01 M NaHCO solution for neutralization treatment, rinsed thoroughly with water, and finally dried with nitrogen to obtain the target current collector.

[0040] Using the above Na3V2(PO4)3 as the positive electrode and the composite copper foil current collector, in combination with a Na3Zr2Si2PO 12 oxide solid electrolyte, a full cell is prepared.

[0041] Example 2:

[0042] Different from Example 1, in this embodiment, the magnetron sputtering deposition time is changed to 5 min, and the deposition thickness is 50 nm.

[0043] The remaining parameters are the same as those in Example 1 and will not be elaborated here.

[0044] Example 3:

[0045] Different from Example 1, in this embodiment, the magnetron sputtering deposition time is changed to 20 min, and the deposition thickness is 200 nm.

[0046] The remaining parameters are the same as those in Example 1 and will not be elaborated here.

[0047] Example 4:

[0048] Different from Example 1, in this example, SnCl2 is used as the etching material.

[0049] The remaining parameters are the same as those in Example 1 and will not be elaborated here.

[0050] Comparative Example 1:

[0051] Different from Example 1, in this comparative example, a composite copper foil without using molten salt etching is used as the current collector, the positive electrode and the solid electrolyte remain unchanged, and a full cell is assembled.

[0052] Comparative Example 2:

[0053] Different from Example 1, in this comparative example, an unmodified copper foil is used as the current collector, the positive electrode and the solid electrolyte remain unchanged, and a full cell is assembled.

[0054] The above batteries are subjected to rate and cycle tests:

[0055] Rate test scheme:

[0056] Charge at a current of 0.5C to the upper cut-off voltage; rest for 30 min; discharge at a current of 0.2C to the lower cut-off voltage, and record the capacity C0; rest for 30 min; charge at a current of 0.5C to the upper cut-off voltage; rest for 30 min; discharge at a current of 1C to the lower cut-off voltage, and record the capacity C1; calculate the rate retention rate: (C1 / C0 * 100%).

[0057] Cycle test scheme:

[0058] Charge at a current of 0.5C to the upper cut-off voltage; rest for 30 min; discharge at a current of 0.5C to the lower cut-off voltage; rest for 30 min; repeat the above steps 200 cycles; record the capacity C1 of the first cycle and the capacity C200 of the 200th cycle; calculate the cycle capacity retention rate: (C200 / C1 * 100%). The test results are shown in the following table:

[0059]

[0060]

[0061] As can be seen from the above table, by first depositing a MAX phase thin film on the surface of the negative electrode current collector and then removing the aluminum layer in the MAX phase thin film by molten salt etching to form a negative electrode current collector with a sodium-philic composite coating, the all-cell assembled with this negative electrode current collector has good rate retention and 200-cycle capacity retention. Moreover, compared with the composite copper foil without molten salt etching as the current collector and the unmodified copper foil as the current collector, the rate retention and 200-cycle capacity retention are significantly improved.

[0062] The above are only the preferred embodiments of the present invention, and thus do not limit the implementation manners and protection scope of the present invention. For those skilled in the art, it should be realized that all the equivalent replacements and obvious changes made by using the content of this specification and the drawings should be included in the protection scope of the present invention.

Claims

1. A method for preparing a negative electrode current collector with a sodium-philic composite coating, characterized in that, Including: Step S1: depositing a MAX phase thin film on the surface of the negative electrode current collector; Step S2: removing the aluminum layer in the MAX phase thin film to form a multi-layer MXene-coated sodium-philic composite coating on the surface of the negative electrode current collector.

2. The sodiumophilic negative electrode current collector according to claim 1, wherein In the step S1, a MAX phase thin film is deposited on the surface of the negative electrode current collector by magnetron sputtering.

3. The sodiumophilic negative electrode current collector according to claim 1, characterized in that, In the step S2, the MAX phase thin film is selectively etched by a molten metal salt etching method to remove the aluminum layer in the MAX phase thin film.

4. The sodiumophilic negative electrode current collector according to claim 1, wherein The negative electrode current collector is one or more of a planar metal current collector, a three-dimensional metal current collector, and a carbon-based current collector.

5. The sodiumophilic negative electrode current collector according to claim 3, wherein, The molten salt used in the molten metal salt etching method is one of ZnCl2 and SnCl2.

6. The sodiumophilic negative electrode current collector according to claim 1, characterized in that, The thickness of the sodium-philic composite coating is 50 nm to 500 nm.

7. The sodiumophilic negative electrode current collector according to claim 1, characterized in that, The MAX phase thin film is a MAX phase material of Ti4AlN3.

8. A negative electrode current collector, characterized in that, A sodium-philic composite coating is formed on the surface of the negative electrode current collector, and the sodium-philic composite coating is prepared by the preparation method described in any one of claims 1-7.

9. A non-negative electrode all-solid-state battery, characterized in that, Including the negative electrode current collector described in claim 8.

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