Nano-diamond / microstructure alloy composite material and preparation method and application thereof

Abstract

The invention belongs to the field of batteries, and particularly relates to a nano-diamond / microstructure alloy composite material and a preparation method and application thereof. The composite material comprises a substrate material, a porous metal layer and a carbon composite layer, wherein the porous metal layer and the carbon composite layer are sequentially stacked on the substrate material; the carbon composite layer comprises a carbon layer and nano diamond particles distributed in the carbon layer; the average pore size of one side, far away from the substrate material, of the porous metal layer is larger than that of one side, close to the substrate material, of the porous metal layer. According to the composite material disclosed by the invention, a buffer network is formed by the porous metal layer and the nano-diamond, so that the volume expansion of the composite material serving as a battery negative electrode in a charging and discharging process is relieved. Therefore, the composite material is stable in structure, volume expansion when the composite material is used as a battery negative electrode can be inhibited, the stability of an interfacial film is enhanced, the ion transmission rate is increased, and finally, the effects of improving the cycle performance and the rate performance of the battery are achieved.

Description

Technical Field

[0001] The present invention belongs to the field of batteries, and particularly relates to a nanodiamond / microstructure alloy composite material, a preparation method thereof, and an application thereof. Background Art

[0002] Sodium-ion batteries have become potential alternatives to lithium-ion batteries due to the abundant and evenly distributed sodium metal resources. However, because the sodium atomic radius is larger than the lithium atomic radius, many lithium-ion battery electrode materials are not suitable for sodium-ion batteries. Therefore, there is an urgent need to develop electrode materials suitable for sodium storage. The anode material plays a crucial role in sodium-ion batteries. Compared with carbon-based materials, organic materials, and titanium-based materials, alloy (Sn, Sb, Bi, etc.) materials have become one of the research hotspots due to their higher theoretical capacity. Sn metal has become one of the ideal candidates due to its ultra-high theoretical capacity (847 mAh / g), excellent electrical conductivity, and low cost. However, Sn metal faces serious volume expansion and interfacial side reaction problems, resulting in electrode pulverization and shedding of active substances, causing low Coulomb efficiency, capacity attenuation, and short cycle life in the first cycle of the battery. Therefore, developing new alloy composite materials to improve interfacial compatibility and inhibit volume expansion is an important path to break through the bottleneck of sodium-ion battery anodes.

[0003] Currently, a large number of studies focus on solving the volume expansion problem of alloy materials. The mainstream strategies include nanostructures, composite materials, and alloying, etc. Among them, (1) Nanostructures: Constructing nanostructured or porous structures to buffer volume expansion and at the same time increase the specific surface area. However, there is still a risk of structural collapse during long-term cycling. And nanostructured alloy particles are prone to agglomeration due to high surface energy during cycling, resulting in a reduction in active sites. (2) Composite materials: Composite with carbon materials (graphene, carbon fiber), and use the flexibility of carbon to inhibit alloy pulverization and improve cycling performance. However, the interfacial bonding force of carbon composites is weak: the interface between the alloy and the carbon matrix (such as graphene, carbon fiber) mostly relies on physical adsorption, and the interfacial bonding force of carbon composites is weak, resulting in easy peeling of the interface during cycling. (3) Alloying: Combine with active metals to form some specific structures to inhibit volume expansion, such as SnSb alloy; combine with inactive metals (such as Fe, Co) to enhance mechanical stability. However, all alloying materials face continuous rupture-reconstruction of the interfacial film, consuming the electrolyte and increasing the interfacial impedance.

[0004] In summary, although certain achievements have been obtained in the modification of alloy-type anode materials, there are still problems such as slow ion diffusion kinetics between the electrolyte and the electrode material, insufficient structural strength, structural collapse of the material, uneven Na deposition, limited inhibition of volume expansion, reduction of long-cycle performance, instability of the solid electrolyte interface film, etc., resulting in limited cycle life of sodium metal storage, etc. Some technologies also have problems such as complex preparation steps, huge costs, and difficulty in large-scale promotion. Summary of the Invention

[0005] In order to overcome at least one of the above-mentioned technical problems existing in the prior art, one of the objectives of the present invention is to provide a composite material. The composite material of the present invention contains a porous metal layer. When used as a battery negative electrode, it can relieve the swelling of the battery negative electrode, thereby avoiding the problem of structural pulverization failure caused by volume expansion during the charge and discharge process of the metal alloy electrode. At the same time, nano-diamond is introduced into the composite material of the present invention, which improves the strength of the composite material. When applied to the battery negative electrode, it can avoid the problem of repeated rupture of the interface film. The presence of the carbon layer can, on the one hand, stably load the nano-diamond on the surface of the carbon layer, and on the other hand, improve the conductivity of the composite material.

[0006] The second objective of the present invention is to provide a preparation method of the composite material.

[0007] The third objective of the present invention is to provide a battery negative electrode.

[0008] The fourth objective of the present invention is to provide a battery.

[0009] In order to achieve the above objectives, the technical solutions adopted by the present invention are as follows: The first aspect of the present invention provides a composite material, including a base material and a porous metal layer and a carbon composite layer sequentially stacked on the base material; the carbon composite layer includes a carbon layer and nano-diamond particles distributed in the carbon layer; the average pore size on the side of the porous metal layer away from the base material is larger than the average pore size on the side of the porous metal layer close to the base material.

[0010] In some embodiments of the present invention, the porous metal layer has a gradient pore structure. The gradient pore structure can, on the one hand, provide sufficient pores to adapt to the volume change of the battery negative electrode and reduce the internal stress, and on the other hand, maintain the overall mechanical strength and conductivity of the material, thereby helping to improve the cycle stability and rate performance of the battery.

[0011] In some embodiments of the present invention, the porosity of the porous metal layer on the side away from the base material is higher than the porosity of the porous metal layer on the side close to the base material.

[0012] In some embodiments of the present invention, the difference between the average pore size on the side of the porous metal layer away from the base material and the average pore size on the side of the porous metal layer close to the base material is 1-5 μm.

[0013] The porous metal layer in the present invention has a large number of pores, which can alleviate the volume expansion of the battery negative electrode using this composite material, increase the sodium deposition sites, and improve the wettability of the electrolyte. In addition, the porous metal layer has a gradient pore structure. The pore size of the porous metal layer near the substrate material side is larger than the pore size and porosity of the porous metal layer near the carbon composite layer side. The porous metal layer with this gradient pore structure can significantly improve the wettability of the electrolyte, provide more active sites, and have a better effect of alleviating volume expansion.

[0014] In some embodiments of the present invention, the porosity of the porous metal layer gradually increases in the direction away from the substrate material.

[0015] In some embodiments of the present invention, the average pore size of the porous metal layer gradually increases in the direction away from the substrate material.

[0016] Compared with the prior art, the porous metal layer in the present invention adopts a unique gradient pore structure, and its structure shows the characteristic of gradually increasing pores. It can guide sodium to deposit in the order from the inside (i.e., the side of the porous metal layer near the substrate material) to the outside (i.e., the side of the porous metal layer away from the substrate material), greatly increasing the deposition sites of sodium and the active metal in the porous metal layer. With the increase of porosity, the specific surface area of the porous metal layer increases significantly, which enhances its wettability with the electrolyte and creates favorable conditions for accelerating the ion transport rate. At the same time, the higher porosity plays a key role in alleviating the serious volume expansion problem generated during the alloying process of sodium and the active metal, effectively maintaining the stability of the material structure.

[0017] In some embodiments of the present invention, the particle size of the nanodiamond is 1 - 500 nm; in some specific embodiments of the present invention, the particle size of the nanodiamond is any value among 1 nm, 5 nm, 10 nm, 50 nm, 60 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or the range value formed by any two of them. In some preferred embodiments of the present invention, the particle size of the nanodiamond is 40 - 70 nm.

[0018] Nanodiamond has the characteristics of high hardness, high thermal conductivity and chemical stability. Adding nanodiamond and combining it with a porous alloy layer with a gradient pore structure to form a buffer network can improve the stability of the interface film, enhance the wettability of the electrolyte, evenly deposit sodium and relieve the pulverization of the electrode material structure during charge and discharge, making the structure of the composite material more stable, which can inhibit volume expansion, enhance the stability of the solid electrolyte interface film, improve the ion transport rate, and achieve high-rate and long-life sodium storage performance. In addition, nanodiamond can increase the hardness of the composite material, guide the uniform deposition of sodium, and relieve the pulverization of the electrode material structure during charge and discharge. Nanodiamond interacts with other components in the film to optimize the microstructure, enabling the interface film to maintain its structure and function in complex electrochemical reactions. And nanodiamond does not chemically react with sodium and can guide the alloying of sodium with the surrounding tin during sodium deposition. During charge and discharge, nanodiamond provides support for the electrode material with its compressive ability, disperses stress, inhibits structure pulverization, ensures the structure and performance of the electrode during long-term cycling, and improves the comprehensive performance and service life of the battery.

[0019] In some embodiments of the present invention, the thickness of the carbon composite layer is 1 - 500 nm; in some specific embodiments of the present invention, the thickness of the carbon composite layer is any value among 1 nm, 5 nm, 10 nm, 50 nm, 60 nm, 80 nm, 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm or the range value formed by any two of them. When the thickness of the carbon composite layer is within the above range, it can enhance the conductivity of the composite material and does not affect the alloying reaction between sodium and the porous metal layer.

[0020] In some embodiments of the present invention, the thickness of the porous metal layer is 2 - 6 μm; in some specific embodiments of the present invention, the thickness of the porous metal layer is any value among 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm or the range value formed by any two of them.

[0021] In some embodiments of the present invention, the material of the porous metal layer includes at least one of bismuth, antimony, tin, zinc, and copper. Copper is an inactive metal component, and the copper component in the porous metal layer can also play a role in relieving volume expansion.

[0022] In some embodiments of the present invention, the substrate material is a metal substrate.

[0023] In some embodiments of the present invention, the substrate material is selected from at least one of copper, aluminum, and tin.

[0024] In some embodiments of the present invention, the raw material for preparing the carbon layer is a carbon-containing polymer, and the carbon-containing polymer includes at least one of polystyrene sulfonic acid and polyacrylic acid.

[0025] In some embodiments of the present invention, the diameter of the pores in the porous metal layer is 2 - 10 μm; in some embodiments of the present invention, the diameter of the pores in the porous metal layer is any value among 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm or a range value formed by any two of them.

[0026] In some embodiments of the present invention, the porous metal layer is prepared by a preparation method including the following steps: First, magnetron sputter metal tin on a substrate material, then co-sputter aluminum and tin for the first time, and then co-sputter aluminum and tin for the second time to obtain a tin-aluminum composite layer; After annealing treatment, remove the metal aluminum in the tin-aluminum composite layer to obtain it; The sputtering power of the aluminum target during the second co-sputtering is greater than the sputtering power of the aluminum target during the first co-sputtering.

[0027] The porous metal layer in the present invention is prepared by magnetron sputtering and dealloying. The preparation process is mature and the operation is simple. The magnetron sputtering process can deposit metal at a lower temperature, effectively avoid heat damage to the substrate material, and at the same time achieve uniform deposition on large-area and complex substrate materials, ensuring precise control of the film composition and thickness, thereby preparing a tin-aluminum composite layer with high purity, density and strong adhesion, and then forming a gradient pore structure by the method of dealloying.

[0028] In some embodiments of the present invention, the power of the tin target when magnetron sputtering metal tin is 70 - 90 W.

[0029] In some embodiments of the present invention, the deposition time when magnetron sputtering metal tin is 8 - 12 min.

[0030] In some embodiments of the present invention, the atmosphere when magnetron sputtering metal tin is an inert atmosphere.

[0031] In some embodiments of the present invention, the flow rate of the inert atmosphere when magnetron sputtering metal tin is 30 - 50 sccm.

[0032] In some embodiments of the present invention, the flow rate of the inert atmosphere during the first co-sputtering is 30 - 50 sccm.

[0033] In some embodiments of the present invention, the flow rate of the inert atmosphere during the second co-sputtering is 30 - 50 sccm.

[0034] In some embodiments of the present invention, the bias voltage during magnetron sputtering of metallic tin is 35 - 45V.

[0035] In some embodiments of the present invention, the bias voltage during the first co - sputtering is 35 - 45V.

[0036] In some embodiments of the present invention, the bias voltage during the second co - sputtering is 35 - 45V.

[0037] In some embodiments of the present invention, the rotation rate of the substrate material during magnetron sputtering of metallic tin is 5 - 10 rpm.

[0038] In some embodiments of the present invention, the rotation rate of the substrate material during the first co - sputtering is 5 - 10 rpm.

[0039] In some embodiments of the present invention, the rotation rate of the substrate material during the second co - sputtering is 5 - 10 rpm.

[0040] In some embodiments of the present invention, the sputtering power of the Sn target during the first co - sputtering is 60 - 100W; in some specific embodiments of the present invention, the sputtering power of the Sn target during the first co - sputtering is any value among 60W, 65W, 70W, 75W, 80W, 85W, 90W, 95W, 100W or any range value formed by any two of them. In some preferred embodiments of the present invention, the sputtering power of the Sn target during the first co - sputtering is 65 - 95W.

[0041] In some embodiments of the present invention, the sputtering power of the Al target during the first co - sputtering is 0 - 50W and not 0; in some specific embodiments of the present invention, the sputtering power of the Al target during the first co - sputtering is any value among 0.001W, 1W, 5W, 10W, 15W, 20W, 25W, 30W, 35W, 40W, 45W, 50W or any range value formed by any two of them; in some preferred embodiments of the present invention, the sputtering power of the Al target during the first co - sputtering is 15 - 45W.

[0042] In some embodiments of the present invention, the time of the first co - sputtering is 0 - 60min and not 0; in some embodiments of the present invention, the time of the first co - sputtering is any value among 0.1min, 1min, 5min, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min or any range value formed by any two of them; in some preferred embodiments of the present invention, the time of the first co - sputtering is 25 - 45min.

[0043] In some embodiments of the present invention, the atmosphere for the first co-sputtering is an inert atmosphere.

[0044] In some embodiments of the present invention, the inert atmosphere is selected from at least one of nitrogen, argon, and xenon.

[0045] In some embodiments of the present invention, the sputtering power of the Sn target during the second co-sputtering is 60 - 100 W; in some specific embodiments of the present invention, the sputtering power of the Sn target during the second co-sputtering is any value among 60 W, 65 W, 70 W, 75 W, 80 W, 85 W, 90 W, 95 W, 100 W or the range value formed by any two of them. In some preferred embodiments of the present invention, the sputtering power of the Sn target during the second co-sputtering is 70 - 90 W.

[0046] In some embodiments of the present invention, the sputtering power of the Al target during the second co-sputtering is 25 - 80 W; in some specific embodiments of the present invention, the sputtering power of the Al target during the second co-sputtering is any value among 25 W, 30 W, 35 W, 40 W, 45 W, 50 W, 55 W, 60 W, 65 W, 70 W, 75 W, 80 W or the range value formed by any two of them; in some preferred embodiments of the present invention, the sputtering power of the Al target during the second co-sputtering is 40 - 65 W.

[0047] In some embodiments of the present invention, the time for the second co-sputtering is 0 - 60 min and not 0; in some specific embodiments of the present invention, the time for the second co-sputtering is any value among 0.01 min, 1 min, 5 min, 10 min, 15 min, 20 min, 25 min, 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, 60 min or the range value formed by any two of them; in some preferred embodiments of the present invention, the time for the second co-sputtering is 20 - 35 min.

[0048] In some embodiments of the present invention, the atmosphere for the second co-sputtering is an inert atmosphere.

[0049] In some embodiments of the present invention, in the method for preparing the porous metal layer, the heating rate in the annealing step is 5 - 20 °C / min; in some specific embodiments of the present invention, the heating rate in the annealing step is any value among 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, 12 °C / min, 14 °C / min, 16 °C / min, 18 °C / min, 20 °C / min or the range value formed by any two of them; in some preferred embodiments of the present invention, the heating rate in the annealing step is 5 - 10 °C / min.

[0050] In some embodiments of the present invention, in the method for preparing the porous metal layer, the annealing temperature is 100 - 350 °C; in some specific embodiments of the present invention, the annealing temperature is any value among 100 °C, 150 °C, 200 °C, 230 °C, 250 °C, 280 °C, 300 °C, 320 °C, 350 °C or the range value formed by any two of them; in some preferred embodiments of the present invention, the annealing temperature is 280 - 320 °C.

[0051] In some embodiments of the present invention, in the method for preparing the porous metal layer, the holding time of the annealing temperature is 0.2 - 3 h; in some specific embodiments of the present invention, the holding time of the annealing temperature is any value among 0.2 h, 0.5 h, 1 h, 1.5 h, 2 h, 2.5 h, 3 h or the range value formed by any two of them; in some preferred embodiments of the present invention, the holding time of the annealing temperature is 1.2 - 2.8 h.

[0052] In some embodiments of the present invention, in the method for preparing the porous metal layer, the atmosphere during annealing is an inert atmosphere.

[0053] In some embodiments of the present invention, in the method for preparing the porous metal layer, the flow rate of the inert atmosphere during annealing is 70 - 90 sccm.

[0054] The interfacial bonding force between the substrate material, the porous metal layer and the nanodiamond can be strengthened through the annealing process. The annealing process can effectively eliminate the residual stress generated by the porous metal layer film formed by sputtering during the preparation of the composite material, and promote the recombination and recrystallization of grains, making the microstructure inside the composite material more uniform and stable, thereby significantly improving the mechanical toughness, electrical conductivity, corrosion resistance, etc.

[0055] In some embodiments of the present invention, the removal of metallic aluminum in the tin-aluminum composite layer is carried out by using an alkali solution or by an electrochemical method.

[0056] In some embodiments of the present invention, the step of removing metallic aluminum in the tin-aluminum composite layer is: soaking the tin-aluminum composite layer in a sodium hydroxide solution with a mass percentage of 0.001% - 10% for 10 - 60 min. In some embodiments of the present invention, the step of removing metallic aluminum in the tin-aluminum composite layer is: soaking the tin-aluminum composite layer in a sodium hydroxide solution with a mass percentage of 0.001% - 10% for 10 - 60 min, and then cleaning.

[0057] In some embodiments of the present invention, the cleaning is performed using ethanol and / or deionized water.

[0058] In some embodiments of the present invention, the mass percentage of the sodium hydroxide solution is any value among 0.001%, 0.01%, 0.1%, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10% or any range value formed by any two of them; in some preferred embodiments of the present invention, the mass percentage of the sodium hydroxide solution is 0.05% - 1%.

[0059] In some embodiments of the present invention, the soaking time in the sodium hydroxide solution is any value among 10 min, 20 min, 30 min, 40 min, 50 min, 60 min or any range value formed by any two of them; in some preferred embodiments of the present invention, the soaking time in the sodium hydroxide solution is 50 - 60 min.

[0060] The second aspect of the present invention provides a method for preparing a composite material, comprising the following steps: First, form a porous metal layer on a substrate material; Load a mixture of a carbon-containing polymer and nanodiamonds on the porous metal layer, and perform annealing treatment to obtain the composite material as described in the first aspect of the present invention.

[0061] In some embodiments of the present invention, the method for preparing the composite material comprises the following steps: S1: First, magnetron sputter metallic tin on a substrate material, then co-sputter aluminum and tin for the first time, and then co-sputter aluminum and tin for the second time to obtain a tin-aluminum composite layer; after annealing treatment, remove metallic aluminum in the tin-aluminum composite layer to obtain a porous metal layer; S2: Soak the porous metal layer in a mixed solution of a carbon-containing polymer and nanodiamonds, dry it, and then perform annealing treatment to obtain the composite material as described in the first aspect of the present invention.

[0062] In steps S1 and S2 of the present invention, the annealing steps can strongly promote the recombination and recrystallization of grains, making the microstructure inside the composite material more uniform and stable, and can significantly reduce defects such as voids and dislocations inside the material, finally improving the mechanical toughness, electrical conductivity, and corrosion resistance. The annealing step in step S2 can enhance the interfacial bonding force between the substrate material, the porous metal layer, and the carbon composite layer, and can also convert the carbon-containing polymer into a carbon layer, further improving the electrical conductivity of the electrode material, promoting the formation of a uniform and stable solid electrolyte interface film, and ultimately greatly increasing the service life of the electrode.

[0063] In some embodiments of the present invention, the heating rate in the annealing step in step S2 is 5~20 °C / min; in some specific embodiments of the present invention, the heating rate in the annealing step is any value among 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min, 10 °C / min, 12 °C / min, 14 °C / min, 16 °C / min, 18 °C / min, 20 °C / min or the range value formed by any two of them; in some preferred embodiments of the present invention, the heating rate in the annealing step is 5~10 °C / min.

[0064] In some embodiments of the present invention, the annealing temperature in step S2 is 100~350 °C; in some specific embodiments of the present invention, the annealing temperature is any value among 100 °C, 150 °C, 200 °C, 230 °C, 250 °C, 280 °C, 300 °C, 320 °C, 350 °C or the range value formed by any two of them; in some preferred embodiments of the present invention, the annealing temperature is 280~320 °C.

[0065] In some embodiments of the present invention, the holding time of the annealing temperature in step S2 is 1~10 h; in some specific embodiments of the present invention, the holding time of the annealing temperature is any value among 1 h, 2 h, 3 h, 4 h, 5 h, 7 h, 9 h, 10 h or the range value formed by any two of them; in some preferred embodiments of the present invention, the holding time of the annealing temperature is 3~5 h.

[0066] In some embodiments of the present invention, the atmosphere during annealing in step S2 is an inert atmosphere.

[0067] In some embodiments of the present invention, the flow rate of the inert atmosphere during annealing in step S2 is 70~90 sccm.

[0068] The annealing treatment step in step S2 can convert a carbon-containing polymer such as polystyrenesulfonic acid into an amorphous carbon layer at high temperature, which can improve the electrical conductivity of the composite material and promote the formation of a uniform and stable solid electrolyte interface film.

[0069] The polymer chains of the carbon-containing polymer have a certain physical entanglement effect on the nanodiamonds, enabling the nanodiamonds to be evenly and firmly distributed in the carbon layer.

[0070] In some embodiments of the present invention, in the mixed solution of the carbon-containing polymer and the nanodiamonds, the mass percentage of the carbon-containing polymer is 8-15%.

[0071] In some embodiments of the present invention, the soaking time in the mixed solution of the carbon-containing polymer and the nanodiamonds is 0.5-20 min; in some specific embodiments of the present invention, the soaking time in the mixed solution of the carbon-containing polymer and the nanodiamonds is any value among 0.5 min, 1 min, 2 min, 5 min, 7 min, 10 min, 12 min, 15 min, 17 min, 20 min or the range value formed by any two of them; in some preferred embodiments of the present invention, the soaking time in the mixed solution of the carbon-containing polymer and the nanodiamonds is 2-8 min.

[0072] In some embodiments of the present invention, in the mixed solution of the carbon-containing polymer and the nanodiamonds, the mass percentage of the nanodiamonds is 0.05-0.5%.

[0073] The preparation method of the composite material in the present invention improves the electrolyte wettability and volume expansion problem of the composite material as the battery negative electrode with relatively low cost and a relatively simple preparation method, reduces the production cost, improves the conductivity of the composite material, and thus enables the battery containing the composite material to have excellent long-term cycling performance and rate performance.

[0074] The third aspect of the present invention provides a battery negative electrode, comprising the composite material described in the first aspect of the present invention. The battery negative electrode in the present invention is the composite material described in the first aspect of the present invention, and no additional conductive agent and binder need to be introduced during preparation, which improves the electrochemical performance and energy density of the battery containing it.

[0075] The fourth aspect of the present invention provides a battery, comprising the composite material described in the first aspect of the present invention, or, comprising the battery negative electrode described in the third aspect of the present invention.

[0076] In some embodiments of the present invention, the battery is a sodium ion battery, a lithium ion battery or a potassium ion battery.

[0077] The beneficial effects of the present invention are as follows: In the composite material of the present invention, a buffer network is formed by the porous metal layer and the nanodiamond, which alleviates the volume expansion of the composite material as the negative electrode of the battery during charge and discharge. The carbon layer can improve the electrode conductivity, promote the formation of a uniform and stable interfacial film, and enable the nanodiamond to stably adhere to the surface of the carbon layer. The nanodiamond can improve the stability of the interfacial film, uniformly deposit sodium, and alleviate the pulverization of the electrode material structure during charge and discharge. Therefore, the composite material in the present invention has a stable structure, can inhibit volume expansion when used as the negative electrode of the battery, enhance the stability of the interfacial film, and improve the ion transport rate, ultimately playing a role in improving the cycle and rate performance of the battery.

[0078] The maximum number of cycles with a battery capacity retention rate of not less than 80% prepared by using the negative electrode material of the present invention is 689 - 2404 cycles, and the discharge specific capacity is 56 - 96.7 mAh / g, both of which are higher than those of the pure tin negative electrode material. Brief Description of the Drawings

[0079] Figure 1 It is the SEM image of the nanodiamond / microstructure alloy composite material prepared in Example 1.

[0080] Figure 2 It is the contact angle test diagram of the nanodiamond / microstructure alloy composite material and the pure tin material with the electrolyte in Example 1.

[0081] Figure 3 It is the XRD diagram of the nanodiamond / microstructure alloy composite material in Example 1.

[0082] Figure 4 It is the EDS line scan diagram of the nanodiamond / microstructure alloy composite material in Example 1.

[0083] Figure 5 It is the first cycle charge and discharge curve diagram of the sodium ion batteries prepared in Example 1 and Comparative Example 1.

[0084] Figure 6 It is the long cycle performance test diagram of the sodium ion batteries prepared in Example 1 and Comparative Example 1. Specific Embodiments

[0085] The following further details the specific implementation of the present invention in conjunction with the drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that for the processes not specifically described in detail below, those skilled in the art can refer to the prior art to implement or understand them. The reagents or instruments used without indicating the manufacturer can be obtained as conventional products through commercial purchase.

[0086] Example 1 The nanodiamond / microstructured alloy composite material in this example includes a copper current collector and a porous alloy tin layer and a carbon composite layer sequentially arranged on the copper current collector. The carbon composite layer includes a carbon layer and nanodiamonds distributed in the carbon layer; the average pore size of the porous alloy tin layer near the copper current collector side is smaller than the average pore size of the porous alloy tin layer far from the copper current collector side.

[0087] This example provides a method for preparing a nanodiamond / microstructured alloy composite material, which specifically includes the following steps: 1. Preparation of porous alloy tin@Cu: (1) Take a copper foil with a purity ≥ 99.9% and a thickness of 20 μm, cut it into a suitable size, and then put it into hydrochloric acid with a mass percentage of 2% to remove the copper oxide on the surface. Then put the treated copper foil into an anhydrous ethanol solution for ultrasonic cleaning for 10 min, and ultrasonic cleaning in deionized water for 10 min, repeating three times. Finally, dry the cleaned copper foil.

[0088] (2) Use a DC magnetron sputtering device to sequentially sputter an Al target and an Sn target on the copper foil surface. The purity of all used targets is ≥ 99.99%. Put the copper foil on the substrate, and then turn on the device to pump the vacuum to below 10 -5 Pa. Then start sputtering, and the parameters are as follows: Ar gas flow rate: 40 sccm, bias power supply: 40 V, copper foil substrate rotation rate: 5 rpm. First, sputter the Sn target: power: 80W, deposition time: 10 min. Then co-sputter the Al and Sn targets in two times in total: in the first co-sputtering power, the power of the Sn target: 80W, the power of the Al target: 25 W, the first co-sputtering time: 30 min; in the second co-sputtering power, the power of the Sn target: 80 W, the power of the Al target: 50 W, the second co-sputtering time: 30 min, to obtain an AlSn@Cu composite material.

[0089] (3) Put the obtained AlSn@Cu composite material into a tube furnace for annealing. Open the Ar gas flow to remove the air in the tube furnace to form a pure Ar environment and then start annealing. The specific parameters are as follows: heating rate: 5℃ / min, Ar gas flow rate: 80 sccm, furnace temperature: 300 ℃, holding time: 1.5 h, and natural cooling.

[0090] (4) Immerse the annealed AlSn@Cu composite material in a NaOH solution with a mass percentage of 0.1% (i.e., the concentration of NaOH is 0.1%) for 1 h to remove Al to form porous alloy tin@Cu. Then put the porous alloy tin@Cu into an anhydrous ethanol solution for ultrasonic cleaning for 10 min, and ultrasonic cleaning in deionized water for 10 min, repeating three times. Finally, dry the cleaned porous alloy tin@Cu.

[0091] 2. Preparation of nanodiamond / microstructured alloy composite materials: (1) Prepare an aqueous mixed solution of 10 wt% polystyrenesulfonic acid and 0.1 wt% nanodiamonds with a particle size of 50 nm, and ultrasonicate for 30 min to uniformly disperse polystyrenesulfonic acid and nanodiamonds in deionized water. Subsequently, immerse the porous alloy Sn@Cu in the aqueous mixed solution of polystyrenesulfonic acid and nanodiamonds for 5 min, and then dry it to form a mixture of polystyrenesulfonic acid and nanodiamonds covering the surface of the porous alloy Sn@Cu, obtaining a porous alloy Sn-nanodiamond composite material.

[0092] (2) Place the obtained porous alloy Sn-nanodiamond composite material in a tube furnace for annealing. Open the Ar gas flow to remove the air in the tube furnace to form a pure Ar environment and then start annealing. The specific parameters are as follows: heating rate: 5 °C / min, Ar gas flow rate: 80 sccm, furnace temperature: 300 °C, holding time: 4 h, and natural cooling to obtain the nanodiamond / microstructured alloy composite material in this example.

[0093] This example also provides a method for preparing a sodium-ion battery, including the following steps: (1) Preparation of the graphite positive electrode of the battery: Weigh expanded graphite, conductive carbon black, and polytetrafluoroethylene in a mass ratio of 8:1:1 in a grinding device, and then add N-methylpyrrolidone solvent and grind thoroughly to obtain a uniform slurry; then uniformly coat the slurry on the surface of the aluminum foil, control the areal density of the electrode sheet to be 10 mg / cm 2 , vacuum dry at 80 °C for 12 h, cut the dried electrode sheet into electrode sheets of appropriate size, weigh them, and place them in a glove box for standby.

[0094] (2) Preparation of the separator: Cut the glass fiber paper into appropriate size, dry it in a drying oven, and place it in a glove box as a separator for standby.

[0095] (3) Preparation of the electrolyte: Weigh 10.08 g of NaPF6 in a glove box and add it to a mixed solvent of 10 mL of ethyl methyl carbonate (EMC), 10 mL of ethylene carbonate (EC), and 10 mL of dimethyl carbonate (DMC), and add 1.5 mL of fluoroethylene carbonate, and then heat and stir evenly until NaPF6 is completely dissolved.

[0096] (4) Preparation of the negative electrode: Cut the nanodiamond / microstructured alloy composite material prepared in this example into electrodes of appropriate size.

[0097] (5) Assembling the battery: In a glove box protected by argon, the materials prepared above were sequentially placed into the negative electrode case from bottom to top in order: negative electrode material, separator, electrolyte, positive electrode material, gasket, shrapnel, positive electrode case. Finally, the battery was encapsulated to obtain the sodium-ion battery in this example.

[0098] The surface morphology of the nano-diamond / microstructure alloy composite material prepared in this example was tested by scanning electron microscopy, as specifically shown in Figure 1 the figure. It can be seen from Figure 1 that the nano-diamond / microstructure alloy composite material prepared in this example has a gradient pore structure. The pore size on the side far from the copper current collector is larger, and the pore size on the side close to the copper current collector is smaller. The pore size slowly increases along the direction from the base material side to the carbon layer side, showing a morphology similar to an inverted conical pore, with an average pore size of 2 - 8 μm. It further shows that the porous alloy tin layer prepared in this example has a gradient pore structure, which weakens the expansion stress during the alloying process of sodium and metal (such as sodium) through the elastic deformation of internal pores, alleviates volume expansion, avoids electrode pulverization, and maintains the stability of the material structure. At the same time, the increase in porosity increases the specific surface area, which can enhance the wettability between the electrode and the electrolyte, increase the sodium deposition sites, and improve the mass transfer and charge transfer kinetics. The non-active metal in the porous alloy can appropriately alleviate volume expansion.

[0099] The electrolyte prepared in this example was respectively dropped on the surfaces of pure tin material and nano-diamond / microstructure alloy composite material, and the contact angle test diagrams are as shown in Figure 2 the figure. Among them, Figure 2 (a) in it is the contact angle test diagram of the electrolyte on the pure tin material, Figure 2 (b) in it is the contact angle test diagram of the electrolyte on the nano-diamond / microstructure alloy composite material. Then, a contact angle tester was used to measure the contact angle. Among them, the contact angle of pure tin is 15°, and the contact angle of the nano-diamond / microstructure alloy composite material is 0°. It can be seen that the nano-diamond / microstructure alloy composite material has better wettability to the electrolyte than pure tin.

[0100] The nano-diamond / microstructure alloy composite material was tested by an X-ray diffractometer, and the test diagram is as shown in Figure 3 the figure. It can be seen from Figure 3 that the appearance of the diamond peak indicates that the nano-diamond is well combined with the porous alloy tin, and at the same time, the Cu6Sn5 alloy phase appears. Cu is a non-active metal, which can also alleviate volume expansion. The EDS line scan diagram of the nano-diamond / microstructure alloy composite material in this example was tested, as specifically shown in Figure 4 the figure. The scanning was carried out from the carbon composite layer to the base material layer during the test. It can be seen from Figure 4It can be seen that the carbon content intensity gradually decreases from the carbon composite layer towards the substrate material layer, while the tin intensity first gradually increases and then gradually decreases. This proves that the outermost layer of the composite material in the present invention is a carbon layer. Combining with the XRD pattern, it can be seen that nanodiamonds are distributed on the surface of the carbon layer.

[0101] Comparative Example 1 This example provides a preparation method of a sodium-ion battery. The difference between its preparation method and that of Example 1 is only that: in step (4) for preparing the negative electrode, pure tin is cut into electrodes of appropriate size, and the pure tin electrode sheet is not treated with anything and does not have the gradient porous feature.

[0102] The assembled sodium-ion batteries of Example 1 and Comparative Example 1 are respectively installed on the battery channels of a Neware battery cabinet for electrochemical performance testing. Their cycling performance at a current density of 1000 mA / g is tested. First, they are cycled five times at 200 mA / g for battery activation, and then the cycling test starts at 1000 mA / g. The first-cycle charge-discharge curves at a current density of 1000 mA / g are as Figure 5 shown, where Figure 5 the left figure in Figure 6 is the test figure of Example 1, and the right figure is the test figure of Comparative Example 1. The long-cycle performance test figure is as Figure 5 shown. Then, the maximum number of cycles with a capacity retention rate of not less than 80% is recorded. It can be seen from Figure 6 that the initial discharge specific capacity of the sodium-ion battery prepared in Example 1 is 96.7 mAh / g. It can be seen from

[0103] Examples 2 - 9 The difference between the preparation methods of the nanodiamond / microstructure alloy composite materials in Examples 2 - 9 and that of Example 1 is only that: in step (2) for preparing the porous alloy tin, the sputtering power of Sn in the first co-sputtering power is different, as shown in Table 1 specifically.

[0104] Examples 10 - 19 The difference between the preparation methods of the nanodiamond / microstructure alloy composite materials in Examples 10 - 19 and that of Example 1 is only that: in step (2) for preparing the porous alloy tin, the sputtering power of Al in the first co-sputtering power is different, as shown in Table 1 specifically.

[0105] Examples 20 - 27 The preparation methods of the nanodiamond / microstructured alloy composites in Examples 20 to 27 are different from that in Example 1 only in that: in step (2) of preparing the porous alloy tin, the sputtering power of Sn in the second co-sputtering power is different, as shown in Table 1 specifically.

[0106] Examples 28 to 38 The preparation methods of the nanodiamond / microstructured alloy composites in Examples 28 to 38 are different from that in Example 1 only in that: in step (2) of preparing the porous alloy tin, the sputtering power of Al in the second co-sputtering power is different, as shown in Table 1 specifically.

[0107] The nanodiamond / microstructured alloy composites in Examples 2 to 38 are respectively assembled into sodium-ion batteries according to the preparation method of the sodium-ion battery recorded in Example 1, and then the cycle performance of the prepared batteries at a current density of 1000 mA / g is tested according to the testing method of Example 1, and the initial discharge specific capacity of the batteries and the maximum number of cycles with a capacity retention rate of not less than 80% are respectively recorded, as shown in Table 1 below specifically.

[0108] Table 1 Preparation parameters and battery performance data of the composites in Examples 1 to 38

[0109] As can be seen from Table 1, the sodium-ion batteries prepared in Examples 1 to 38 all have excellent long-term cycle performance, the number of cycles when the energy retention rate is not less than 80% is 1712 to 2404 cycles, and the initial discharge specific capacity is 73 to 96.7 mAh / g; compared with Examples 2 to 38, the performance of Example 1 is better, and both the number of cycles and the initial discharge specific capacity when the capacity retention rate is not less than 80% are larger. By comparing Examples 1 to 38, it can be seen that different sputtering powers of Al and Sn during the first co-sputtering and the second co-sputtering will both result in different porosities during subsequent chemical dealloying, which also indicates that appropriate porosity has a significant impact on improving the electrochemical performance of the electrode.

[0110] Examples 39 to 49 The preparation methods of the nanodiamond / microstructured alloy composites in Examples 39 to 49 are different from that in Example 1 only in that: in step (2) of preparing the porous alloy tin, the first co-sputtering time is different, as shown in Table 2 below specifically.

[0111] Examples 50 to 61 The preparation methods of the nanodiamond / microstructured alloy composites in Examples 50 to 61 are different from that in Example 1 only in that: in step (2) of preparing the porous alloy tin, the second co-sputtering time is different, as shown in Table 2 below specifically.

[0112] The nanodiamond / microstructured alloy composites in Examples 39 to 61 were respectively assembled into sodium-ion batteries according to the preparation method of the sodium-ion battery described in Example 1. Then, according to the test method of Example 1, the cycle performance of the prepared batteries at a current density of 1000 mA / g was tested, and the initial discharge specific capacity of the batteries and the maximum number of cycles with a capacity retention rate of not less than 80% were respectively recorded, as shown in Table 2 below.

[0113] Table 2 Preparation parameters and battery performance data of the composites in Examples 39 to 61

[0114] As can be seen from Table 2, the maximum number of cycles of the sodium-ion batteries prepared in Examples 39 to 61 with a capacity retention rate of not less than 80% was 1512 to 2245 cycles, and the discharge specific capacity was 78 to 93 mAh / g, which was lower than that of Example 1; further indicating that different sputtering times would result in different film thicknesses of the deposited films. Too thick a film would increase the ion transport path and the resistance of the electrode material, resulting in a decrease in the ion transport rate; too thin a film would reduce the strength of the electrode material and the amount of active metal, ultimately leading to a decrease in the discharge specific capacity and cycle performance of the battery.

[0115] Examples 62 to 64 The preparation method of the nanodiamond / microstructured alloy composites in Examples 62 to 64 is different from that of Example 1 only in that: in step (3) of preparing the porous alloy tin, the heating rate during annealing is different, as shown in Table 3 below.

[0116] Examples 65 to 70 The preparation method of the nanodiamond / microstructured alloy composites in Examples 65 to 70 is different from that of Example 1 only in that: in step (3) of preparing the porous alloy tin, the holding time during annealing is different, as shown in Table 3 below.

[0117] Examples 71 to 75 The preparation method of the nanodiamond / microstructured alloy composites in Examples 71 to 75 is different from that of Example 1 only in that: in step (3) of preparing the porous alloy tin, the furnace temperature during annealing is different, as shown in Table 3 below.

[0118] The nanodiamond / microstructured alloy composites in Examples 62 to 75 were respectively assembled into sodium-ion batteries according to the preparation method of the sodium-ion battery described in Example 1. Then, the cycle performance of the prepared batteries at a current density of 1000 mA / g was tested according to the testing method of Example 1, and the initial discharge specific capacity of the batteries and the maximum number of cycles with a capacity retention rate of not less than 80% were respectively recorded, as shown in Table 3 below.

[0119] Table 3 Preparation parameters and battery performance data of the composites in Examples 62 to 75

[0120] As can be seen from Table 3, the maximum number of cycles of the sodium-ion batteries prepared in Examples 62 to 75 with a capacity retention rate of not less than 80% was 862 to 2230 cycles, and the discharge specific capacity was 72 to 93 mAh / g, which was lower than that of Example 1; it further indicated that the heating rate would affect the stress of the deposited film, and rapid heating (such as 30 °C / min) might cause thermal stress concentration inside the film, leading to microcracks and uneven grain size distribution. The temperature in the furnace determined the recrystallization and phase transformation behavior of the material. Too high a temperature might cause other reactions in the material, while too low a temperature could not cause the recrystallization and phase transformation of the material. The holding time would affect the grain stability and stress release. Short-time annealing might not be sufficient to complete recrystallization, while too long might lead to excessive grain growth.

[0121] Examples 76 to 83 The preparation method of the nanodiamond / microstructured alloy composites in Examples 76 to 83 was only different from that of Example 1 in that: in step (4) of preparing the porous alloy tin, the concentration of NaOH used for dealloying was different, as shown in Table 4 below.

[0122] Examples 84 to 88 The preparation method of the nanodiamond / microstructured alloy composites in Examples 84 to 88 was only different from that of Example 1 in that: in step (4) of preparing the porous alloy tin, the soaking time in the sodium hydroxide solution during dealloying was different, as shown in Table 4 below.

[0123] The nanodiamond / microstructured alloy composites in Examples 76 to 88 were respectively assembled into sodium-ion batteries according to the preparation method of the sodium-ion battery described in Example 1. Then, the cycle performance of the prepared batteries at a current density of 1000 mA / g was tested according to the testing method of Example 1, and the initial discharge specific capacity of the batteries and the maximum number of cycles with a capacity retention rate of not less than 80% were respectively recorded, as shown in Table 4 below.

[0124] Table 4 Preparation parameters and battery performance data of the composites in Examples 76 to 88

[0125] As can be seen from Table 4, the maximum number of cycles of the sodium-ion batteries prepared in Examples 76 to 88 with a capacity retention rate of not less than 80% is 1245 to 2286 cycles, and the discharge specific capacity is 79 to 94 mAh / g, which is lower than that of Example 1; further indicating that too high a concentration of the NaOH solution will rapidly destroy Al and cause Sn to fall off, while too low a concentration of the NaOH solution cannot completely remove Al. Too short an immersion time also cannot completely remove aluminum, resulting in a decrease in the porosity of the porous alloy tin, thereby affecting the cycle performance of the battery, etc.

[0126] Examples 89 to 95 The difference between the preparation method of the nanodiamond / microstructured alloy composite materials in Examples 89 to 95 and that of Example 1 is only that: the immersion time in the mixed aqueous solution of polystyrene sulfonic acid and nanodiamond is different, as shown in Table 5 below.

[0127] Examples 96 to 101 The difference between the preparation method of the nanodiamond / microstructured alloy composite materials in Examples 96 to 101 and that of Example 1 is only that: the particle size of the nanodiamond is different, as shown in Table 5 below.

[0128] The nanodiamond / microstructured alloy composite materials in Examples 89 to 101 were respectively assembled into sodium-ion batteries according to the preparation method of the sodium-ion batteries described in Example 1, and then the cycle performance of the prepared batteries at a current density of 1000 mA / g was tested according to the test method of Example 1, and the initial discharge specific capacity of the batteries and the maximum number of cycles with a capacity retention rate of not less than 80% were respectively recorded, as shown in Table 5 below.

[0129] Table 5 Preparation parameters and battery performance data of the composite materials in Examples 89 to 101

[0130] As can be seen from Table 5, the maximum number of cycles of the sodium-ion batteries prepared in Examples 89 to 101 with a capacity retention rate of not less than 80% is 689 to 2102 cycles, and the discharge specific capacity is 56 to 94 mAh / g, which is lower than that of Example 1; further indicating that too long an immersion time in the mixed aqueous solution of polystyrene sulfonic acid and nanodiamond will result in too thick a carbon composite layer, affecting the deposition of sodium and the composite material, while too short a time will result in too thin a carbon composite layer, which cannot play an effective role. Too large a particle size of the nanodiamond may lead to a decrease in electrode activity, while a smaller particle size of the nanodiamond has less impact on electrode activity and can improve the stability of the electrode structure.

[0131] In summary, in the sodium-ion batteries prepared in the embodiments of the present invention, the maximum number of cycles with a capacity retention rate of not less than 80% is 689 to 2404 cycles, and the discharge specific capacity is 56 to 96.7 mAh / g, both of which are higher than those of the pure tin negative electrode material.

[0132] The above has described the embodiments of the present invention in detail. However, the present invention is not limited to the above embodiments. Within the scope of knowledge possessed by those of ordinary skill in the art, various changes can be made without departing from the gist of the present invention. In addition, without conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other.

Claims

1. A composite material, characterized in that: It includes a substrate material, a porous metal layer, and a carbon composite layer that are sequentially stacked on the substrate material; the carbon composite layer includes a carbon layer and nanodiamond particles distributed in the carbon layer; the average pore diameter on the side of the porous metal layer away from the substrate material is larger than the average pore diameter on the side of the porous metal layer close to the substrate material.

2. The composite material according to claim 1, characterized in that: The difference between the average pore diameter on the side of the porous metal layer away from the substrate material and the average pore diameter on the side of the porous metal layer close to the substrate material is 1 to 5 μm.

3. The composite material according to claim 1, characterized in that: The particle size of the nanodiamond is 1 to 500 nm; and / or, the thickness of the carbon composite layer is 1 - 500 nm; and / or, the thickness of the porous metal layer is 2 to 6 μm.

4. The composite material according to claim 1, characterized in that: The material of the porous metal layer includes at least one of bismuth, antimony, tin, zinc, and copper; and / or, the raw material for preparing the carbon layer is a carbon-containing polymer, and the carbon-containing polymer includes at least one of polystyrene sulfonic acid and polyacrylic acid.

5. The composite material according to claim 1, characterized in that: The diameter of the pores in the porous metal layer is 2 to 10 μm.

6. The composite material according to any one of claims 1 to 5, characterized in that: The porous metal layer is prepared by a preparation method including the following steps: First, magnetron sputter metal tin on the substrate material, then co-sputter aluminum and tin for the first time, and then co-sputter aluminum and tin for the second time to obtain a tin-aluminum composite layer; After annealing treatment, remove the metal aluminum in the tin-aluminum composite layer to obtain it; During the second co-sputtering, the sputtering power of the aluminum target is greater than the sputtering power of the aluminum target during the first co-sputtering.

7. The composite material according to claim 6, characterized in that: Removing the metal aluminum in the tin-aluminum composite layer is carried out by using an alkali solution or by an electrochemical method.

8. A method for preparing a composite material, characterized in that: It includes the following steps: First, form a porous metal layer on the substrate material; Load a mixture of a carbon-containing polymer and nanodiamonds on the porous metal layer, and perform annealing treatment to obtain the composite material according to any one of claims 1 to 7.

9. A battery negative electrode, characterized in that: It includes the composite material according to any one of claims 1 to 7.

10. A battery, characterized in that: It includes the composite material according to any one of claims 1 to 7, or includes the battery negative electrode according to claim 9.

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