In-situ generated lithium-free negative electrode with gradient lithiated three-dimensional structure and preparation method of lithium-free negative electrode

Abstract

The invention relates to the technical field of lithium battery negative electrode materials, and particularly discloses an in-situ generated lithium-free negative electrode with a gradient lithiophilic three-dimensional structure and a preparation method thereof.The lithium-free negative electrode comprises a CuZn alloy layer, a graphene lithium-phobic layer located on one surface of the CuZn alloy layer and a Cu2O lithium-philic layer located on the other surface of the CuZn alloy layer, the graphene lithium phobic layer is located on the side, close to electrolyte, of the CuZn alloy layer, and the CuZn alloy layer is of a nano-scale or micron-scale porous structure. Through a two-step electrochemical treatment mode, the nano-scale even micron-scale porous three-dimensional Cu / CuZn skeleton is constructed, and the graphene lithium-phobic layer and the Cu2O lithium-loving layer are generated on the two surfaces of the three-dimensional Cu / CuZn skeleton in situ, so that the problems of negative electrode-electrolyte interface instability, dendritic crystal growth and the like are solved, and the cycle performance, the specific capacity and the like of the battery are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium battery negative electrode materials, in particular to a lithium-free negative electrode with gradient lithiumophilic three-dimensional structure generated in situ and a preparation method thereof BACKGROUND Lithium ion batteries have become an important research topic in recent years as the core energy storage method in the fields of consumer electronics, electric vehicles, and smart grids. With the increasing demand for high energy density in energy storage systems, lithium metal batteries with metal lithium as the negative electrode have stood out due to their high theoretical capacity. However, the high activity of metal lithium leads to issues such as dendrite growth, interface side reactions, and difficulty in preparing ultra-thin lithium foil, which severely restricts the practical application of lithium batteries. Based on the above situation, the existing technology proposes an anode-free lithium metal battery (AFLMBs), which completely eliminates the pre-embedded lithium negative electrode and becomes a new energy storage battery that balances high energy density, low manufacturing cost, and safety. However, the lithium source in AFLMBs completely depends on the release of the positive electrode, and issues such as electrode-electrolyte interface instability and dendrite growth during the cycling process result in poor cycle stability and low coulombic efficiency.

[0002] To address the above-mentioned problems of AFLMBs, a lithium-repellent-lithiumophilic 3D gradient current collector and its preparation and application are provided in Patent No. CN116053482A. The 3D conductive framework is made of porous conductive material, the upper layer is made of organic matter, and the lower layer is made of lithiumophilic metal. The upper layer is prepared by molecular layer deposition, and the lower layer is prepared by sputtering. The prepared lithium-repellent-lithiumophilic 3D gradient current collector has high surface area and large lithium storage space, which is beneficial to reduce the actual current density of lithium deposition and avoid lithium dendrite piercing the separator. On the other hand, the introduction of lithium-repellent material in the upper layer helps to inhibit the uneven deposition of lithium metal, and the introduction of lithiumophilic material in the lower layer can achieve directional deposition of lithium metal and enhance the uniformity of deposition. The 3D current collector is used for the negative electrode current collector of lithium metal batteries, which can greatly improve the cycle stability of lithium metal negative electrode and the safety performance of the battery through the synergistic effect of the above two aspects, and has important practical application value.

[0003] The existing lithium battery negative electrode materials have poor cycle performance in practical application. SUMMARY

[0004] The present application aims to solve the problem of poor cycle performance of existing anode-free lithium metal batteries.

[0005] The present application is achieved by the following technical solutions: The application provides a lithium-free negative electrode with a gradient lithiophilic three-dimensional structure generated in situ, comprising a CuZn alloy layer, a graphene lithium-averse layer on one surface of the CuZn alloy layer and a Cu2O lithiumophilic layer on the other surface of the CuZn alloy layer, wherein the graphene lithium-averse layer is on the side of the CuZn alloy layer close to the electrolyte, and the CuZn alloy layer has a nano-scale or micro-scale porous structure.

[0006] Preferably, the thickness of the CuZn alloy layer is 5-10 microns, the thickness of the graphene lithium-averse layer is 50-200 microns, and the thickness of the Cu2O lithiumophilic layer is 50-100 microns.

[0007] The application further provides a preparation method of the lithium-free negative electrode with the gradient lithiophilic three-dimensional structure generated in situ. S1 pretreatment: The CuZn alloy foil is taken, cleaned and activated in sequence, and then reserved; the graphene oxide is taken and prepared into a plating solution, and then reserved; S2 plating of graphene: The CuZn alloy foil is placed in the plating solution, and then plating is performed by power supply to obtain a graphene alloy foil; S3 dealloying treatment: The graphene alloy foil is placed in an acid solution, and then dealloying treatment is performed by power supply to obtain the lithium-free negative electrode.

[0008] Preferably, in step S1, the CuZn alloy foil is first placed in petroleum ether and ultrasonically cleaned for multiple times, and then placed in dilute sulfuric acid for surface activation treatment.

[0009] Preferably, in step S1, the concentration of the plating solution is 3-5 mg / mL.

[0010] Preferably, in step S2, the voltage is 5-15 V during plating, and the plating time is 5-10 min.

[0011] Preferably, in step S3, the voltage is 0.3-0.5 V during dealloying treatment, and the treatment time is 2-5 h.

[0012] The technical scheme of the application has the following beneficial effects: The present application has found that, through research and analysis, the existing lithium battery without lithium negative electrode material can make lithium deposit directionally through gradient design, but the existence of excess lithium reduces the energy density and safety of the electrode, the preparation process is complex, the cost is high, and the violent material volume change cannot be inhibited; although the 3D skeleton proposed in the prior art can alleviate the volume change, the introduction of the 3D skeleton material leads to an excessively thick electrode, thereby reducing the energy density, and the negative electrode without gradient design is prone to top deposition, lithium dendrite, volume expansion and other problems; at the same time, violent side reactions and dendrite growth also damage the SEI film.

[0013] Based on the above situation, the present application constructs a three-dimensional structure of a lithium-free negative electrode with a gradient lithiumophilic structure to overcome the problems of negative electrode-electrolyte interface instability and dendrite growth. Specifically, a two-step electrochemical method is used, first, the CuZn alloy base material is dealloyed by electrochemical treatment, and part of the Zn is dissolved to form a nano-scale or even micron-scale porous three-dimensional Cu / CuZn skeleton, which provides space for lithium deposition and improves the mechanical stability of the entire material structure. The pore size can be adjusted according to the current density and reaction time, and the rich pore structure makes the three-dimensional skeleton have a high specific surface area, which can reduce the current density of the negative electrode during battery charging and discharging, and reduce the generation of lithium dendrites. In this process, a Cu2O lithiumophilic layer can be directly covered on the surface of the three-dimensional skeleton material near the opposite electrode, the Cu2O formed on the surface has good lithiumophilic property and can induce directional and uniform deposition of lithium; a graphene lithiumophobe layer is deposited on the other side of the three-dimensional skeleton material, which has the ability to promote lithium ion diffusion. The graphene lithiumophobe layer is located near the electrolyte side, and its lithiumophobic property can further induce lithium ions to deposit away from the separator side, and the coating can reduce the contact between the three-dimensional skeleton material and the electrolyte, effectively reducing the occurrence of negative electrode / electrolyte interface side reactions, ultimately achieving long cycle and high specific capacity of the battery; and the graphene lithiumophobe layer has high Young's modulus and mechanical strength, which can effectively alleviate the damage of lithium dendrite growth to the SEI film, avoid the destruction and reconstruction of the SEI film caused by dendrite growth and continuous consumption, thereby prolonging the service life of the battery and improving the coulombic efficiency. BRIEF DESCRIPTION OF DRAWINGS

[0014] Figure 1 It is a structure schematic diagram of the lithium-free negative electrode in Example 1. Figure 2 It is a long cycle performance test diagram of the lithium-free negative electrode in Test Example 1. Figure 3 It is a long cycle performance test diagram of the lithium-free negative electrode in Test Example 2. Figure 4 It is a SEM diagram of the lithium-free negative electrode in Example 1 amplified 4500 times (Cu2O lithiumophilic layer side).

[0015] DETAILED DESCRIPTION In order to make the purposes, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below. Wherein, the specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions suggested by the manufacturer; the instruments, devices or reagents raw materials not mentioned by the manufacturer are all conventional products that can be obtained by market purchase.

[0016] The present application provides a lithium-free negative electrode with gradient lithiophilic three-dimensional structure generated in situ, which generates graphene lithium-averse layer and Cu2O lithiumophilic layer in situ through electrochemical dealloying while forming porous current collector, and prepares three-dimensional structure with lithiumophilic gradient by virtue of the difference in lithiophilicity, so as to realize the "bottom-up" lithium growth mode.

[0017] The lithium-free negative electrode with gradient lithiophilic three-dimensional structure generated in situ in the present application, as shown in the figure, includes a 5-10 μm thick CuZn alloy layer, a 50-200 μm thick graphene lithium-averse layer located on the top surface of the CuZn alloy layer, and a 50-100 μm thick Cu2O lithiumophilic layer located on the bottom surface of the CuZn alloy layer, the CuZn alloy layer is a porous copper framework after dealloying and mainly consists of Cu and Cu0.64Zn0.36 alloy, and the graphene lithium-averse layer and Cu2O lithiumophilic layer are generated in situ through electrochemical dealloying while forming the porous current collector, and the three-dimensional structure with lithiumophilic gradient is prepared by virtue of the difference in lithiophilicity. Figure 1

[0018] Wherein, the top layer is the graphene lithium-averse layer generated in situ by electroplating, the existence of the graphene lithium-averse layer can reduce the direct contact of the electrolyte with the negative electrode, and at the same time, the graphene lithium-averse layer itself has chemical inertness, so as to effectively reduce the occurrence of side reactions and has the function of stabilizing the solid electrolyte interface film (SEI film); the compound generated by the reaction of graphene with lithium has the function of optimizing the chemical performance of the SEI film, can homogenize the lithium ion flux and uniform current density; and the graphene layer has high Young's modulus and mechanical strength, can effectively alleviate the damage of the SEI film caused by the growth of lithium dendrites, and can avoid the destruction and reconstruction of the SEI film caused by the growth of dendrites and continuous consumption; the middle layer is a three-dimensional porous structure prepared by electrochemical dealloying of the CuZn alloy, the dense porous framework makes the current density more uniform so as to make the lithium deposition more uniform, the framework structure provides space for lithium deposition to relieve the volume change and at the same time improves the mechanical strength of the structure; the structure far from the separator side is the Cu2O lithiumophilic layer generated in situ on the framework by electrochemical dealloying, and the lithiophilicity of the Cu2O lithiumophilic layer can induce lithium ions to deposit at the bottom of the framework rather than on the surface, so as to realize the "bottom-up" lithium growth mode and greatly improve the cycle stability of the battery.

[0019] In the present application, the preparation method of the lithium-free negative electrode includes the following steps: ​(1) Pretreatment of CuZn alloy foil: Take a sheet-shaped CuZn alloy foil with a thickness of about 10 μm cut into a certain shape, use petroleum ether as a cleaning solution, and put it into an ultrasonic cleaner to clean it to remove surface grease, then wash it with ethanol to remove natural oxides, and then wash it with deionized water to remove surface organic reagents. The cleaned CuZn alloy foil is immersed in 5% dilute sulfuric acid at room temperature for 5 min to remove surface oxides and activate the surface, which can increase the adhesion of the subsequent plated layer. Then it is taken out and washed with deionized water to remove residual dilute sulfuric acid, and a pretreated CuZn alloy foil is obtained for standby use.

[0020] (2) Preparation of electroplating solution: Take graphene oxide powder, disperse it in deionized water, and prepare a graphene oxide dispersion solution with a concentration of 3-5 mg / mL, and ultrasonically treat it at room temperature for 4 h to obtain an electroplating solution.

[0021] (3) Preparation of graphene alloy foil: Put the pretreated CuZn alloy foil into the electroplating solution, use the CuZn alloy foil as the negative electrode and platinum sheet as the positive electrode, use a direct current power supply, and carry out electroplating treatment at a constant voltage of 5-15 V for 5-10 min to obtain a graphene alloy foil.

[0022] (4) Preparation of lithium-free negative electrode: Put the graphene alloy foil into a 5% dilute sulfuric acid solution, use a two-electrode system, use the graphene alloy foil as the working electrode and the nickel foam as the counter electrode, and use the constant voltage method of the electrochemical workstation to carry out electrochemical dealloying treatment at a voltage of 0.3-0.5 V for 2-5 h. Under acidic conditions, this voltage and treatment condition can make Cu more inclined to be oxidized to cuprous ions. Since there is a graphene lithium-averse layer near the separator side, only cuprous oxide is formed on the side far from the separator during the dealloying process. Cuprous oxide has a very low nucleation barrier to lithium, and lithium ions are more inclined to deposit on the substrate with a low nucleation energy. Therefore, the cuprous oxide layer has an induction effect on lithium deposition.

[0023] This electrochemical treatment condition can effectively remove Zn from the CuZn alloy, leaving a mixed porous framework composed of CuZn intermetallic compounds and copper single elements. Since cuprous ions are more stable in the acidic environment provided by sulfuric acid, copper is oxidized to cuprous ions, and a layer of cuprous oxide is generated in situ on the surface of the porous framework during the dealloying process. Due to the presence of the graphene layer, the current collector only forms cuprous oxide on one side, thereby forming a three-dimensional porous structure with a lithium-philic gradient.

[0024] Example 1 Take 10 μm thick 2 cm x 2 cm square CuZn alloy foil sheet, repeatedly washed with anhydrous ethanol and deionized water for 2 times, then placed in petroleum ether, and then put into an ultrasonic cleaner for 5 min, after the end, change the petroleum ether and wash again for 5 min, and then put the CuZn alloy foil into 5% dilute sulfuric acid for 5 min at room temperature, then take out and wash with deionized water to obtain the pretreated CuZn alloy foil for standby.

[0025] Take the graphene oxide, disperse in deionized water, ultrasonic treatment for 4 h at room temperature, and prepare a graphene oxide dispersion solution with a concentration of 4 mg / mL as an electroplating solution for standby.

[0026] The pretreated CuZn alloy foil is placed in the electroplating solution, with the CuZn alloy foil as the negative electrode and the platinum sheet as the positive electrode, and the electroplating is carried out by using a direct current power supply at a voltage of 10 V, and the electroplating time is 8 min; then the CuZn alloy foil after electroplating is placed in 5% dilute sulfuric acid solution, and the CuZn alloy foil is used as the working electrode and the nickel foam is used as the counter electrode, and the two electrode systems are connected to the electrochemical workstation, and the electrochemical dealloying treatment is carried out by using the constant voltage method at a voltage of 0.4 V, and the treatment time is 3 h, and the lithium-free negative electrode material is obtained.

[0027] Example 2 The difference between this example and Example 1 is that the electroplating time is 4 min.

[0028] Example 3 The difference between this example and Example 1 is that the CuZn alloy foil without dealloying is used as the raw material to prepare the negative electrode material.

[0029] Test Example 1 The lithium-free negative electrode of Example 1 is cut into an electrode sheet with a diameter of 14 mm as the positive electrode, 1M lithium bis-trifluoromethanesulfonimide solution (wherein the solvent is 1,3-dioxolane and ethylene glycol dimethyl ether in a volume ratio of 1:1, and 2wt% LiNO3 is added) is used as the electrolyte, Cellgard2000 is used as the separator, and lithium sheet is used as the negative electrode. A 2032 type button cell is assembled in a high-purity argon atmosphere glove box (wherein the contents of O2 and H2O are both less than 0.01 ppm). First, deposit 3 mAh of lithium on the positive electrode (lithium-free negative electrode), then assemble the symmetric battery, and test the cycle performance of the metal lithium negative electrode at a current density of 1 mA / cm 2 and 1 mAh / cm 2 The results are shown in Figure 2 .

[0030] Test Example 2 The test example is different from test example 1 in that the lithium-free negative electrode obtained in example 3 is cut into an electrode piece with a diameter of 14 mm by using a cutting machine to assemble a symmetrical battery, and the cycle performance of the lithium battery is tested at a current density of 1 mA / cm 2 2 mA / cm 2 2 and 1 mAh / cm Figure 3 2, and the results are shown in

[0031] As shown in Figures 2-4 , the lithium-free negative electrode prepared by the method of the application in example 1 has a cycle performance of 1800 h at a current density of 1 mA / cm 2 2 and 1 mAh / cm 2 2, and even at a high current density of 3 mA / cm 2 2, it still can reach 800 h, because the existence of the porous structure can effectively alleviate the growth of lithium dendrites, and the graphene lithium-averse layer near the separator side has the effect of optimizing the chemical properties of the SEI film and reducing the occurrence of side reactions, and the gradient structure formed by the graphene lithium-averse layer and the Cu2O lithiumophilic layer realizes the "bottom-up" lithium growth mode.

[0032] As can be seen from the above tests, the three-dimensional multi-level porous copper-containing composite with a lithiumophilic gradient is prepared by electrochemical plating and dealloying of a Cu-Zn alloy, which has a microporous structure composed of CuZn intermetallic compounds and elemental copper (as shown in Figure 4 ), a graphene lithium-averse layer near the separator side in-situ grown by electroplating has the effect of stabilizing the SEI film, and a Cu2O lithiumophilic layer far from the separator side is generated in-situ, which can increase the current density and induce lithium deposition. Near the separator side, the graphene lithium-averse layer is prepared by electroplating, and the existence of the graphene lithium-averse layer has the effects of mechanical isolation, optimizing the chemical properties of the SEI film, improving the mechanical strength of the SEI film, etc., and has the effect of stabilizing the SEI film; the middle layer is a porous Cu / CuZn composite skeleton prepared by electrochemical dealloying, which has the effects of improving the ion / electron conductivity, improving the mechanical strength, and providing deposition space; the Cu2O lithiumophilic layer far from the separator side has the effect of inducing lithium ions to deposit inside the skeleton, and due to the existence of the surface lithium-averse layer and the high ion / electron conductivity skeleton inside, the "bottom-up" lithium growth mode is realized.

[0033] The above is only a preferred embodiment of the application and is not intended to limit the application. For those skilled in the art, the application can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the application shall be included in the protection scope of the application.

Claims

1. A lithium-free anode in-situ generated with a gradient lithiophilic three-dimensional structure, characterized in that, The CuZn alloy layer, a graphene lithium-phobe layer on one surface of the CuZn alloy layer, and a Cu2O lithium-phile layer on the other surface of the CuZn alloy layer, wherein the graphene lithium-phobe layer is on the side of the CuZn alloy layer close to the electrolyte, and the CuZn alloy layer has a nano-scale or micro-scale porous structure.

2. The lithium-free anode in-situ generating a gradient lithiophilic three-dimensional structure according to claim 1, characterized in that, The CuZn alloy layer has a thickness of 5-10 μm, the graphene lithium-phobe layer has a thickness of 50-200 μm, and the Cu2O lithium-phile layer has a thickness of 50-100 μm.

3. A method for producing a lithium-free anode having a gradient lithiophilic three-dimensional structure generated in situ according to claim 1 or 2, characterized by, The method comprises the following steps: S1 pretreatment: Take CuZn alloy foil, sequentially clean and activate, and reserve; take graphene oxide, prepare plating solution, and reserve; S2 graphene plating: Place the CuZn alloy foil in the plating solution, and conduct plating by applying electricity to obtain graphene alloy foil; S3 dealloying treatment: Place the graphene alloy foil in acid solution, and conduct dealloying treatment by applying electricity to obtain the lithium-free negative electrode.

4. The method of claim 3, wherein the lithium-free anode having a gradient lithiophilic three-dimensional structure is prepared in situ. In step S1, the CuZn alloy foil is first placed in petroleum ether, and ultrasonic cleaning is performed for multiple times, and then the CuZn alloy foil is placed in dilute sulfuric acid for surface activation treatment.

5. The method of claim 3, wherein the lithium-free anode having a gradient lithiophilic three-dimensional structure is prepared in situ. In step S1, the concentration of the plating solution is 3-5 mg / mL.

6. The method of claim 3, wherein the lithium-free anode having a gradient lithiophilic three-dimensional structure is prepared in situ. In step S2, the voltage is 5-15 V during plating, and the plating time is 5-10 min.

7. The method of claim 3, wherein the lithium-free anode having a gradient lithiophilic three-dimensional structure is generated in situ. In step S3, the voltage is 0.3-0.5 V during dealloying treatment, and the treatment time is 2-5 h.

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