Framework material with lithium-loving gradient as well as preparation method and application thereof

Abstract

The invention discloses a framework material with lithium-loving gradient and a preparation method and application thereof. An upper half layer framework of a foam metal framework is modified with a moderate lithium-loving material Cu2Se, and a lower half layer framework of the foam metal framework is modified with a strong lithium-loving material Ag. Natural pore channels of the foam metal provide effective channels and deposition spaces for diffusion and migration of lithium ions, the pore sizes and the lithium affinity of the upper part and the lower part of the frame material are regulated and controlled by modifying the lithium affinity layer, and nucleation is preferentially performed at the bottom with relatively high lithium affinity; the modification layer with gradient lithium affinity induces the lithium ions to be uniformly deposited in gaps of the frame material from bottom to top, so that uniform and sufficient deposition of the lithium ions is realized; the rigid frame effectively inhibits lithium ion expansion and cooperates with the lithium-loving layer, so that the local current density of the lithium negative electrode is reduced, volume expansion is delayed, growth of dendritic lithium and formation of dead lithium are inhibited, and the rate capability and the cycle performance are good; and battery failure or thermal runaway or even explosion caused by stripping from the current collector and fragile or falling of the material in the repeated charging and discharging process is avoided.

Description

Technical Field

[0001] The invention relates to a negative electrode material for a lithium metal battery, and in particular to a framework material with a lithium affinity gradient, a preparation method and an application thereof. Background Art

[0002] Lithium metal has a very high theoretical specific capacity density of 3860 mAh / g, a low reduction potential of -3.04 V relative to the standard hydrogen electrode and a low weight density of 0.534 g / cm 3 , improving the overall energy density of the entire battery system, and is considered to be one of the most promising negative electrode materials to replace the existing graphite electrode. At present, lithium metal is restricted in its use as a negative electrode material: (1) Lithium ions are extremely active. During the first charging of the battery, the organic electrolyte is reduced and decomposed on the surface of the negative electrode material to form a solid electrolyte interface film (SEI), which consumes the lithium in the positive electrode material. This process is irreversible, resulting in a low coulombic efficiency in the first cycle, reducing the capacity, energy density and cycle life of the lithium metal battery; (2) During the battery cycle, continuous lithium plating or stripping will inevitably produce lithium dendrites. The continuous growth of dendrites can easily pierce the diaphragm, causing the battery to short-circuit, affecting its electrochemical performance and safety performance; (3) Lithium metal is an expanding ownerless anode. During the cycle, a large amount of metallic lithium is stripped / plated from the negative electrode, which can easily cause irregular volume changes, damage the structure, and cause battery failure or thermal runaway or even explosion. Foam metal conductive scaffolds have rich pore structures and high specific surface area, and are considered to be a feasible solution to this problem, and sufficient efforts have been made. Designing a scaffold with gradient conductivity or lithium affinity can effectively guide the uniform deposition of lithium, thereby eliminating dendrites in the early stage of lithium plating, which is more conducive to the stability of long-term cycles. By introducing lithium-affinity active substances into the three-dimensional skeleton and utilizing the differences in their lithium affinity, lithium ions can be guided to preferentially nucleate at the bottom, thereby achieving uniform deposition from bottom to top. Due to the preparation conditions and the interaction between each other, lithium-affinity modification layers of different materials are not easy to stably exist in the three-dimensional skeleton. Therefore, due to the stability of the lithium-affinity modification layer and the modification effect, the lithium-affinity modification of the three-dimensional skeleton is currently mostly modified with homogeneous materials. Homogeneous materials with different lithium-affinity properties are modified on the three-dimensional metal skeleton. As the number of battery cycles increases, there is a risk of material transformation, and the lithium-affinity properties tend to be consistent, losing the guiding effect on lithium ions during the charge and discharge process. Finally, lithium dendrites are inevitably generated as the battery is used. The continuous growth of dendrites easily pierces the diaphragm, causing the battery to short-circuit and affect its electrochemical performance and safety performance. Summary of the invention

[0003] Purpose of the invention: The purpose of the present invention is to improve the effectiveness and durability of the framework material against lithium ion deposition / stripping, and to provide a framework material with a lithium affinity gradient; another purpose of the present invention is to provide a method for preparing the above material; another purpose of the present invention is to provide the application of the above material in lithium metal battery negative electrode materials.

[0004] Technical solution: The framework material with a lithium affinity gradient of the present invention comprises a foam metal skeleton, wherein the upper half of the foam metal skeleton is modified with a moderately lithium affinity material Cu2Se, and the lower half of the skeleton is modified with a strongly lithium affinity material Ag.

[0005] Furthermore, the foam metal skeleton is foam nickel, foam steel, foam aluminum, foam titanium or foam zinc. The foam metal has a natural pore structure, which provides an effective channel and deposition space for the diffusion and migration of lithium ions, and improves the uniformity and deposition amount of lithium ions; at the same time, the pores of the foam metal frame have a certain rigidity, which can effectively inhibit the expansion of lithium ion electrodes.

[0006] Furthermore, by adjusting the copper electroplating time, the thickness of the copper plating of the upper and lower parts is adjusted, and then the thickness of the subsequent modified lithium-affinity layer is adjusted, so that the thickness of the upper half layer of moderate lithium-affinity material Cu2Se is controlled at 50-100 microns, and the thickness of the lower half layer of strong lithium-affinity material Ag is controlled at 100-150 microns. By controlling the selenization conditions, the Cu2Se particle size range is controlled to be 0.5-2 microns, and the Ag replacement Cu particle size range is controlled to be 0.5-1 micron. By modifying the lithium-affinity layer with different particle sizes and thicknesses to regulate the lithium-affinity of the upper and lower parts of the framework material, the lower half layer of the metal framework has stronger lithium-affinity and more lithium-affinity sites. Lithium ions come from the top of the framework and first deposit in the lower half layer with more lithium-affinity sites and then gradually deposit upward, preventing the lithium ions from depositing too quickly in the upper half layer to block the pores of the framework material. After the modification of the metal framework, lithium ions preferentially nucleate at the bottom with strong lithium affinity, and the modified layer with gradient lithium affinity induces lithium ions to spread and deposit evenly from bottom to top in the pores of the framework electrode material, achieving uniform and sufficient deposition of lithium ions and forming a lithium-affinity layer with low lithium nucleation points. At the same time, the rigid pores cooperate with the lithium-affinity layer with low lithium nucleation points to reduce the local current density of the lithium negative electrode and further delay the volume expansion effect, so that the material has high rate performance and stable cycle performance, while avoiding peeling from the current collector during repeated charge and discharge, and avoiding the material from being fragile and easy to fall off, causing battery failure or thermal runaway or even explosion.

[0007] The method for preparing the framework material having a lithium affinity gradient according to the present invention comprises the following steps:

[0008] (1) Cutting the foam metal into thin slices of a certain size, immersing them in a hydrochloric acid solution for ultrasonic treatment and cleaning them for later use;

[0009] (2) The foam metal is used as the working electrode, the copper sheet is used as the counter electrode, and the silver chloride is used as the reference electrode. In a CuSO4 solution, copper of different thicknesses is electroplated on the upper and lower parts of the foam metal respectively, and then dried.

[0010] (3) In an argon atmosphere, the upper half layer of the foam metal is selenized by vertical fumigation to modify a certain thickness of the moderately lithium-philic Cu2Se layer;

[0011] (4) The metal foam treated in step (3) is immersed in a silver nitrate solution containing sodium dodecyl sulfate, and the lower half layer of the copper plating layer that has not been selenized undergoes a replacement reaction with the silver nitrate, and the lower half layer of the metal foam is modified with a certain thickness of a strongly lithium-philic Ag layer to obtain a lithium-philic gradient framework material.

[0012] Furthermore, in the step (2), the copper plating time of the upper half layer is 50 to 150 seconds, and the copper plating time of the lower half layer is 150 to 350 seconds.

[0013] Furthermore, the concentration of the CuSO4 solution in step (2) is 3 to 7 M. The appropriate concentration is conducive to forming a uniform coating on the surface of the frame material, affecting the rate, uniformity and stability of subsequent selenization or Ag replacement, and further affecting the guiding effect of the lithium-philic gradient layer on lithium ion deposition.

[0014] Furthermore, during the selenization in step (3), the copper-plated foam metal is vertically fixed in a tube furnace, the selenization temperature is 250° C. to 400° C., the selenization time is 1 to 3 hours, and the selenization temperature and time are adjusted to control the thickness and particle size range of the upper half layer of moderately lithium-philic material Cu2Se.

[0015] Furthermore, in step (4), the concentration of AgNO3 in the replacement solution is 3-7 mM, and the replacement time is 200-400 s. The concentration of sodium dodecyl sulfate is 0.5-1 mM. Adding an appropriate amount of sodium dodecyl sulfate slows down the replacement rate, slows down the silver replacement speed, and makes it deposit evenly and slowly, thereby avoiding the growth of tree-like silver dendrites. During the replacement, the upper half layer after selenization does not require special protective measures, does not affect the structure of the upper half layer, and simplifies the preparation steps.

[0016] The framework material with a lithium affinity gradient described in the present invention can be applied to negative electrode materials of lithium metal batteries.

[0017] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages: 1. The foam metal is used as the basic framework material, and its natural pore structure provides an effective channel and deposition space for the diffusion and migration of lithium ions. The pore size and lithium affinity of the upper and lower parts of the framework material are regulated by modifying the lithium affinity layer, and nucleation is preferentially performed at the bottom with stronger lithium affinity. The modified layer with gradient lithium affinity induces lithium ions to deposit uniformly from bottom to top in the gaps of the framework electrode material, thereby achieving uniform and sufficient deposition of lithium ions; 2. The foam metal framework material has a certain rigidity that effectively inhibits the expansion of the lithium ion electrode, and cooperates with the lithium affinity layer with a lower lithium nucleation point, which reduces the local current density of the lithium negative electrode and further delays the volume expansion effect, so that the material has a higher rate performance and stable cycle performance, while avoiding peeling from the current collector during repeated charge and discharge, and avoiding the material from being fragile and easy to fall off, causing battery failure or thermal runaway or even explosion; 3. Reducing the consumption of active lithium and electrolyte can effectively inhibit the growth of dendrite lithium and the formation of dead lithium, thereby improving the cycle performance and rate performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a schematic diagram of the preparation process of the present invention;

[0019] Figure 2 This is the XRD pattern of the framework material prepared in Example 2;

[0020] Figure 3 This is the EDX spectrum of the cross section of the framework material prepared in Example 2;

[0021] Figure 4 This is a scanning electron microscope image of the frame material prepared in Example 1;

[0022] Figure 5 This is a scanning electron microscope image of the frame material prepared in Example 2;

[0023] Figure 6 This is a scanning electron microscope image of the frame material prepared in Example 3;

[0024] Figure 7 This is a scanning electron microscope image of the upper half layer of the frame material prepared in Example 4;

[0025] Figure 8 This is a scanning electron microscope image of the lower half layer of the frame material prepared in Comparative Example 1;

[0026] Fig. 9 The scanning electron microscope images of the lower layer of the frame prepared in Comparative Example 2 at different magnifications;

[0027] Fig.10 The scanning electron microscope images of lithium deposition of the framework material in different preparation degrees in Example 2;

[0028] Fig.11 Long cycle performance diagram of half-cells assembled from materials prepared in Examples 1 to 3;

[0029] Fig.12 This is a rate performance diagram of the framework material prepared in Example 2 as a negative electrode material for a lithium metal battery. DETAILED DESCRIPTION

[0030] The technical solution of the present invention is further described below in conjunction with the examples and drawings, and all reagents used are commercially available.

[0031] The framework material with a lithium affinity gradient comprises a foam metal skeleton, wherein the upper half of the skeleton of the foam metal skeleton is modified with a moderately lithium affinity material Cu2Se, and the lower half of the skeleton is modified with a strongly lithium affinity material Ag. The foam metal skeleton used in the present invention is nickel foam, and foam steel, aluminum foam, titanium foam or zinc foam can also be selected according to actual needs. The thickness of the copper plating of the upper and lower parts is adjusted by adjusting the time of copper electroplating, and then the thickness of the subsequent modified lithium affinity layer is adjusted, so that the thickness of the upper half layer of the moderately lithium affinity material Cu2Se is controlled to be 50 to 100 microns, and the thickness of the lower half layer of the strongly lithium affinity material Ag is controlled to be 100 to 150 microns. The particle size range of Cu2Se is controlled to be 0.5 to 2 μm by controlling the selenization conditions, and the particle size range of Ag is controlled to be 0.5 to 1 μm by controlling the regulation of Ag replacing Cu. For details of the specific preparation process, see Figure 1 .

[0032] Example 1

[0033] (1) Cut the commercial nickel foam into 3 cm × 3 cm slices, immerse them in a 4 M hydrochloric acid solution for ultrasonic treatment, and then wash them three times with acetone, deionized water, and ethanol for later use;

[0034] (2) Using nickel foam as the working electrode and copper sheet as the counter electrode, the material was electroplated in a 3M CuSO4 solution, the lower half layer was electroplated for 150 seconds, the upper half layer was electroplated for 50 seconds, and the electroplated sheet was dried;

[0035] (3) Add 10 mg of selenium powder to the crucible, place the crucible sideways in a tube furnace, ensure that the electrode sheet is vertically fixed in the tube furnace, and calcine at 250 ° C for 1 h in an argon atmosphere at a heating rate of 2 ° C / min to perform single-sided vertical selenization to modify the upper half layer of moderately lithium-philic material Cu2Se;

[0036] (4) The above-prepared material was placed in 50 mL of 3 mM AgNO3 solution, and 0.5 mM sodium dodecyl sulfate was added to replace the electroplated copper in the lower half layer. The replacement time was 200 s. The lower half layer of the foam metal was modified with a strong lithium-philic Ag layer of a certain thickness, and then vacuum dried at 60°C for 12 h to obtain a lithium-philic gradient framework material.

[0037] Example 2

[0038] (1) Cut the commercial nickel foam into 3 cm × 3 cm slices, immerse them in a 4 M hydrochloric acid solution for ultrasonic treatment, and then wash them three times with acetone, deionized water, and ethanol for later use;

[0039] (2) Using nickel foam as the working electrode and copper sheet as the counter electrode, the material was electroplated in a 5M CuSO4 solution, the lower half layer was electroplated for 200 seconds, the upper half layer was electroplated for 100 seconds, and the electroplated sheet was dried;

[0040] (3) Add 20 mg of selenium powder to the crucible, place the crucible sideways in a tube furnace, ensure that the electrode sheet is vertically fixed in the tube furnace, and calcine at 300 ° C for 2 h in an argon atmosphere with a heating rate of 2 ° C / min to perform single-sided vertical selenization to modify the upper half layer of moderately lithium-philic material Cu2Se;

[0041] (4) The above-prepared material was placed in 50 mL of 5 mM AgNO3 solution, and 0.7 mM sodium dodecyl sulfate was added to replace the electroplated copper in the lower half layer for 300 s. The lower half layer of the foam metal was modified with a strong lithium-philic Ag layer of a certain thickness, and then vacuum dried at 60°C for 12 h to obtain a lithium-philic gradient framework material.

[0042] Example 3

[0043] (1) Cut the commercial nickel foam into 3 cm × 3 cm slices, immerse them in a 4 M hydrochloric acid solution for ultrasonic treatment, and then wash them three times with acetone, deionized water, and ethanol for later use;

[0044] (2) Using nickel foam as the working electrode and copper sheet as the counter electrode, the material was electroplated in a 7M CuSO4 solution, the lower half layer was electroplated for 250 seconds, the upper half layer was electroplated for 150 seconds, and the electroplated sheet was dried;

[0045] (3) Add 20 mg of selenium powder to the crucible, place the crucible sideways in a tube furnace, ensure that the electrode sheet is vertically fixed in the tube furnace, and calcine at 350 ° C for 3 h in an argon atmosphere with a heating rate of 2 ° C / min to perform single-sided vertical selenization to modify the upper half layer of moderately lithium-philic material Cu2Se;

[0046] (4) The above-prepared material was placed in 50 mL of 5 mM AgNO3 solution, and 1 mM sodium dodecyl sulfate was added to replace the electroplated copper in the lower half layer. The replacement time was 300 s. The lower half layer of the foam metal was modified with a strong lithium-philic Ag layer of a certain thickness, and then vacuum dried at 60 ° C for 12 h to obtain a lithium-philic gradient framework material.

[0047] Example 4

[0048] (1) Cut the commercial nickel foam into 3 cm × 3 cm slices, immerse them in a 4 M hydrochloric acid solution for ultrasonic treatment, and then wash them three times with acetone, deionized water, and ethanol for later use;

[0049] (2) Using nickel foam as the working electrode and copper sheet as the counter electrode, the material was electroplated in a 5M CuSO4 solution, the lower half layer was electroplated for 200 seconds, the upper half layer was electroplated for 100 seconds, and the electroplated sheet was dried;

[0050] (3) Add 30 mg of selenium powder to the crucible, place the crucible sideways in a tube furnace, ensure that the electrode sheet is vertically fixed in the tube furnace, and calcine at 300 ° C for 2 h in an argon atmosphere with a heating rate of 2 ° C / min to perform single-sided vertical selenization to modify the upper half layer of the moderately lithium-philic material Cu2Se;

[0051] (4) The above-prepared material was placed in 50 mL of 7 mM AgNO3 solution, and 0.7 mM sodium dodecyl sulfate was added to replace the electroplated copper in the lower half layer. The replacement time was 400 s. The lower half layer of the foam metal was modified with a strong lithium-philic Ag layer of a certain thickness, and then vacuum dried at 60°C for 12 h to obtain a lithium-philic gradient framework material.

[0052] Comparative Example 1

[0053] (1) Cut the commercial nickel foam into 3 cm × 3 cm slices, immerse them in a 4 M hydrochloric acid solution for ultrasonic treatment, and then wash them three times with acetone, deionized water, and ethanol for later use;

[0054] (2) Using nickel foam as the working electrode and copper sheet as the counter electrode, the material was electroplated in a 5M CuSO4 solution, the lower half layer was electroplated for 200 seconds, the upper half layer was electroplated for 100 seconds, and the electroplated sheet was dried;

[0055] (3) Add 20 mg of selenium powder to the crucible, place the crucible sideways in a tube furnace, ensure that the electrode sheet is vertically fixed in the tube furnace, and calcine at 300 ° C for 2 h in an argon atmosphere with a heating rate of 2 ° C / min to perform single-sided vertical selenization to modify the upper half layer of moderately lithium-philic material Cu2Se;

[0056] (4) The material prepared above was placed in 50 mL of 5 mM AgNO3 solution to replace the electroplated copper in the lower layer for 300 s. The lower layer of the foam metal was modified with a strong lithium-philic Ag layer of a certain thickness, and then vacuum dried at 60°C for 12 h to obtain a lithium-philic gradient framework material.

[0057] Comparative Example 2

[0058] (1) Cut the commercial nickel foam into 3 cm × 3 cm slices, immerse them in a 4 M hydrochloric acid solution for ultrasonic treatment, and then wash them three times with acetone, deionized water, and ethanol for later use;

[0059] (2) Using nickel foam as the working electrode and copper sheet as the counter electrode, the material was electroplated in a 5M CuSO4 solution, the lower half layer was electroplated for 200 seconds, the upper half layer was electroplated for 100 seconds, and the electroplated sheet was dried;

[0060] (3) Add 20 mg of selenium powder to the crucible, place the crucible sideways in a tube furnace, ensure that the electrode sheet is vertically fixed in the tube furnace, and calcine at 300 ° C for 2 h in an argon atmosphere with a heating rate of 2 ° C / min to perform single-sided vertical selenization to modify the upper half layer of moderately lithium-philic material Cu2Se;

[0061] (4) The above-prepared material was placed in 50 mL of 10 mM AgNO3 solution, and 0.7 mM sodium dodecyl sulfate was added to replace the electroplated copper in the lower half layer for 300 s. The lower half layer of the foam metal was modified with a strong lithium-philic Ag layer of a certain thickness, and then vacuum dried at 60°C for 12 h to obtain a lithium-philic gradient framework material.

[0062] The performance of the framework materials with lithium affinity gradient prepared in the above examples and comparative examples was characterized.

[0063] Figure 2 The XRD patterns of the upper and lower layers of the framework material with a lithium affinity gradient are shown in Figure 2. Figure 2 From the XRD pattern of the upper layer on the left, we can see that the diffraction peaks at 26.41° and 43.80° correspond to Cu2Se (111) and (220) crystal planes (PDF#76-0136). Figure 2 From the XRD pattern of the lower half layer on the right, it can be seen that the peaks at 38.11°, 44.27°, and 64.42° correspond to the (111), (200), and (220) crystal planes of Ag, respectively, and there are no other impurity peaks, which proves that two substances with different lithium affinity, Cu2Se and Ag, are generated on this framework. Figure 3 This is the corresponding EDX energy spectrum of the cross section of the framework. It can be seen from the figure that the copper element is evenly distributed on both sides of the nickel foam, the upper layer contains a large amount of selenium, and the lower layer contains a large amount of silver, which proves that a lithium-philic gradient framework material is indeed formed.

[0064] Figures 4 to 9 It is the morphology of the upper layer under the conditions of Examples 1 to 4 and Comparative Examples 1 to 2. Figure 4 It can be seen that in Example 1, due to the small amount of selenium powder added to the upper layer, the generated cuprous selenide is sparsely distributed in the upper layer of the frame; while in the lower layer, due to the short replacement time of silver, partial replacement occurs, and silver is mainly distributed at the edge of the frame, and a distinctive lithium-philic layer cannot be formed to effectively guide lithium ions to spread and deposit evenly in the pores of the frame material. Figure 5It can be seen that the upper and lower parts of the frame material of Example 2 generate two completely different morphologies. The upper half of the frame material is evenly covered with Cu2Se, and the lower half is evenly covered with Ag. Figure 6 It was observed that the high temperature of the selenization reactants in Example 3 caused large cracks in the nickel foam frame, affecting the stability of the structure of the entire material and further affecting the effective guidance of lithium ion deposition. Figure 7 It is observed that in Example 4, if the amount of selenization or Ag substitution of the electroplating pattern of the frame material is further increased, excessive precipitation will be caused on the surface of the frame material, and the size of the pores of the frame material cannot be effectively distinguished, modified and changed, and the pores are easily blocked, thereby affecting the effective guidance of lithium ion deposition, and it is impossible to form a uniform and sufficient amount of lithium ion deposition. Figure 8 It was observed that compared with Example 2, Comparative Example 1 did not add the surfactant sodium dodecyl sulfate (SDS) to slowly release and regulate the replacement rate, which made the silver replacement rate fast and uneven, resulting in the growth of tree-like silver dendrites. Fig. 9 It was observed that compared with Example 2, Comparative Example 2 also resulted in a fast and uneven silver replacement rate due to the higher concentration of the silver nitrate solution, forming a large number of tree-like silver dendrites.

[0065] Fig.10 These are lithium deposition morphologies of the frame material obtained in different preparation processes of Example 2, where a1 and a2 are lithium ion deposition morphologies of the frame material after copper electroplating in steps (1) to (2), b1 and b2 are lithium ion deposition morphologies of the frame material after copper electroplating in steps (1) to (3) and selenization in the upper half layer, and c1 and c2 are lithium ion deposition morphologies of the frame material after copper electroplating in steps (1) to (4) and selenization in the upper half layer and replacement of Cu with Ag in the lower half layer. The top view and cross-sectional view of lithium ion deposition of the framework material formed at different stages clearly show the lithium deposition pattern. The upper layer of the single-sided modified framework has more lithium-affinity sites, which leads to the tendency of lithium ions to deposit on the upper layer of the framework. After copper plating of a1 and a2, lithium ions are deposited on the top of the framework material and the surface uniformity is very poor. After selenization of b1 and b2, the amount of lithium ions deposited inside the framework material increases, and the surface uniformity also improves. However, there is still undeposited space at the bottom of the framework material, and there are no channels at the bottom for lithium ions to pass through, resulting in insufficient lithium ion deposition and low utilization of the framework material. The lower layer of the double-sided modified lithium-affinity gradient framework has stronger lithium-affinity and sufficient lithium-affinity sites. Lithium is preferentially deposited in the lower layer, forming a lithium deposition pattern from bottom to top, which is conducive to deep lithium deposition. From c2, we can see that lithium ions are uniformly deposited from top to bottom in the framework material, and from c1, we can also see that there are channels at the bottom, indicating that the double-sided modified lithium-affinity gradient layer effectively guides the deposition of lithium ions and improves the uniformity and amount of lithium ion deposition.

[0066] The materials prepared in the above examples and lithium sheets were assembled into a half-cell to test its coulombic efficiency. Fig.11 As shown, the lithium-philic gradient framework prepared in Example 2 has the strongest affinity for lithium under the combined synergistic effect of the upper selenide layer and the lower silver layer, can provide sufficient lithium-philic sites to guide lithium deposition, and exhibits excellent electroplating / stripping behavior during long cycles.

[0067] The materials prepared in the above examples and comparative examples were deposited at a deposition rate of 5 mAh / cm 2 As the negative electrode, commercial LFP, acetylene black and PVDF were mixed in a mass ratio of 8:1:1 and evenly coated on aluminum foil as the positive electrode. CR2023 button cells were assembled in an argon-filled glove box and their rate performance was tested under different current density conditions. Fig.12 It can be seen that the full battery assembled from the materials prepared in Example 2 has the best rate performance. As the current density increases, its capacity decays slowly. When the current density returns to 0.5C, the capacity returns quickly, reflecting its good rate performance.

Claims

1. A framework material having a lithium affinity gradient, characterized in that: The invention comprises a foam metal skeleton, wherein the upper half layer of the foam metal skeleton is modified with a moderately lithium-affinity material Cu2Se, and the lower half layer of the foam metal skeleton is modified with a strongly lithium-affinity material Ag.

2. The framework material with a lithium affinity gradient according to claim 1, characterized in that The foam metal skeleton is foam nickel, foam steel, foam aluminum, foam titanium or foam zinc.

3. The framework material with a lithium affinity gradient according to claim 1, characterized in that The thickness of the moderately lithium-philic material Cu2Se is 50-100 microns, and the particle size of Cu2Se ranges from 0.5 to 2 μm.

4. The framework material with a lithium affinity gradient according to claim 1, characterized in that The thickness of the strong lithium-affinity material Ag is 100-150 micrometers, and the particle size of Ag is in the range of 0.5-1 micrometer.

5. A method for preparing a framework material having a lithium affinity gradient according to any one of claims 1 to 4, characterized in that: The steps include: (1) Cutting the foam metal into thin slices, immersing them in a hydrochloric acid solution for ultrasonic treatment and cleaning them for later use; (2) The foam metal is used as the working electrode, the copper sheet is used as the counter electrode, and the silver chloride is used as the reference electrode. In a CuSO4 solution, copper of different thicknesses is electroplated on the upper and lower parts of the foam metal respectively, and then dried. (3) In an argon atmosphere, the upper half layer of the foam metal is selenized by vertical fumigation to modify the Cu2Se layer, a moderately lithium-philic material; (4) The metal foam treated in step (3) is immersed in a silver nitrate solution containing sodium dodecyl sulfate, and the lower half layer of the copper plating layer that has not been selenized undergoes a replacement reaction with the silver nitrate, and the lower half layer of the metal foam is modified with a strongly lithium-philic Ag layer to obtain a lithium-philic gradient framework material.

6. The method for preparing a framework material having a lithium affinity gradient according to claim 5, characterized in that: In the step (2), the copper plating time for the upper half layer is 50 to 150 seconds, and the copper plating time for the lower half layer is 150 to 250 seconds.

7. The method for preparing a framework material having a lithium affinity gradient according to claim 5, characterized in that: The concentration of the CuSO4 solution in step (2) is 3-7M.

8. The method for preparing a framework material having a lithium affinity gradient according to claim 5, characterized in that: During the selenization in step (3), the copper-plated foam metal is vertically fixed in a tube furnace, the selenization temperature is 250° C. to 350° C., and the selenization time is 1 to 3 hours.

9. The method for preparing a framework material having a lithium affinity gradient according to claim 5, characterized in that: In the step (4), the concentration of AgNO3 in the replacement solution is 3-7 mM, and the replacement time is 200-400 s.

10. Use of the framework material with lithium affinity gradient according to any one of claims 1 to 9 in negative electrode materials for lithium metal batteries.

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