Alkali metal battery and double-gradient 3D carbon current collector, alkali metal negative electrode, preparation method and application thereof

Abstract

The invention belongs to the field of battery materials, and particularly relates to an alkali metal battery and a double-gradient 3D carbon current collector, an alkali metal negative electrode, a preparation method and application thereof, the double-gradient 3D carbon current collector comprises a conductive substrate, a first carbon layer compounded on the conductive substrate, and a second carbon layer compounded on the surface of the first carbon layer, the material in the first carbon layer is microporous carbon a in which metal M sulfide is dispersed and distributed; the material in the second carbon layer is a carbon material b with a graded through hole structure, graded through holes comprise mesopores, macropores and super-macropores, and through hole structures exist among the holes. According to the double-gradient 3D carbon current collector prepared by the preparation method disclosed by the invention, the surface layer of the double-gradient 3D carbon current collector is provided with a continuous through macroporous / super-macroporous structure, so that an expressway is provided for electrolyte infiltration and ion transmission, and a battery has excellent high-rate performance. Under high current density, ions can be rapidly supplemented into the electrode, and dramatic polarization increase and rapid growth of dendritic crystals caused by ion deficiency are avoided.

Description

Technical Field

[0001] This invention belongs to the field of battery materials, specifically relating to the field of negative electrode technology for alkali metal batteries. Background Technology

[0002] Ion batteries are widely used in power batteries and energy storage batteries; however, the theoretical capacity of the graphite anodes used in them is relatively low, limiting the development of high-energy-density batteries. Therefore, there is an urgent need to develop anode materials with higher specific energy. Alkali metals, with their high theoretical specific capacity, low electrode potential, and low density, are excellent anode materials for next-generation high-energy-density batteries.

[0003] Alkali metal foil is commonly used as an alkali metal anode. By constructing an artificial interface layer (SEI) on the alkali metal surface, the interfacial reaction and dendrite growth caused by the SEI film formed between the alkali metal and the electrolyte during battery operation can be effectively mitigated. However, planar alkali metal anodes have two bottleneck problems. First, the planar alkali metal anode structure is difficult to adapt to the volume effect generated during alkali metal deposition / dissolution; the huge volume change brought about by the areal capacity can lead to damage to the interface layer. Second, the small specific surface area will result in excessively high current density on the electrode surface, causing uneven deposition of alkali metal and making dendrite formation more likely.

[0004] In existing technologies, three-dimensional carbon current collectors, with their high specific surface area and porous structure, can theoretically provide an ideal host space for alkali metal ion deposition. This structural design can effectively alleviate the volume expansion effect during alkali metal deposition and reduce local current density, thereby suppressing dendrite growth. However, in practical applications, this structure faces a severe challenge: because the electrode surface is in direct contact with the electrolyte, alkali metals tend to preferentially deposit in the pores of the electrode surface, leading to the following chain reaction:

[0005] 1. Pore blockage effect: Alkali metal deposits on the surface can hinder the electrolyte from penetrating into the current collector;

[0006] 2. Insufficient wetting: The bottom area of ​​the current collector is difficult to wet effectively due to the obstruction of electrolyte mass transfer;

[0007] 3. Imbalance in space utilization: While the surface pores are rapidly blocked, the internal pore structure is not fully utilized.

[0008] This non-uniform deposition phenomenon leads to two serious consequences: firstly, the alkali metals deposited on the surface are prone to dendrite formation, posing safety hazards; secondly, the unused internal pores result in low utilization of active materials. These two factors together accelerate the degradation of battery performance. The root cause lies in the fact that traditional homogeneous porous carbon current collectors cannot effectively guide the deposition behavior of alkali metals in space. Therefore, how to construct a host structure that can generate directional driving force in space through careful structural design, guiding alkali metals to preferentially nucleate at the bottom of the current collector and uniformly fill from bottom to top, has become a key technological bottleneck that urgently needs to be overcome in the current research and development of alkali metal anodes. Summary of the Invention

[0009] In view of the defects and shortcomings of the existing technology, the first objective of this invention is to provide a dual-gradient 3D carbon current collector for alkali metal batteries, which aims to prepare a current collector that is adapted to the charging and discharging principle of alkali metal batteries and facilitates the deposition and dissolution of alkali metals.

[0010] The second objective of this invention is to provide a method for preparing the aforementioned dual-gradient 3D carbon current collector.

[0011] A third objective of this invention is to provide a negative electrode for an alkali metal battery comprising the aforementioned dual-gradient 3D carbon current collector.

[0012] The fourth objective of this invention is to provide a method for preparing the negative electrode of the alkali metal battery.

[0013] The fifth objective of this invention is to provide an alkali metal battery comprising the negative electrode.

[0014] A dual-gradient 3D carbon current collector includes a conductive substrate, a first carbon layer composited on the conductive substrate, and a second carbon layer composited on the surface of the first carbon layer. The material in the first carbon layer is microporous carbon a dispersedly distributed with metal M sulfide. The material in the second carbon layer is carbon material b with a hierarchical through-pore structure, wherein the hierarchical through-pores include mesopores, macropores, and super-macropores, and there are through-pore structures between the pores.

[0015] This invention demonstrates an innovative approach: a first carbon layer is constructed using microporous carbon a with dispersed metal M sulfides, and a second carbon layer is constructed using a specially hierarchical porous material b. This hierarchical structure, with the first carbon layer as the bottom layer and the second carbon layer as the surface, achieves unexpected synergy, adapting to the charge-discharge characteristics of alkali metal batteries. It induces uniform deposition of alkali metals, reducing polarization issues. Furthermore, this hierarchical porous carbon material is lightweight and possesses ample internal space to accommodate alkali metals, effectively leveraging the high specific energy of alkali metal batteries and optimizing their electrochemical performance. The dual-gradient 3D carbon current collector prepared in this invention, with its continuously interconnected macropore / ultra-macropore structure on the surface, provides a "highway" for electrolyte wetting and ion transport, resulting in excellent high-rate performance. At high current densities, ions can rapidly replenish the electrode interior, preventing the dramatic increase in polarization and rapid dendrite growth caused by ion depletion.

[0016] In this invention, the conductive substrate includes at least one of conductive metal foil, flexible polymer substrate, oxide-coated conductive substrate, and conductive polymer film.

[0017] Preferably, in the first carbon layer, the M in the metal M sulfide includes at least one of Zn, Sn, or Ag.

[0018] Preferably, the content of metal sulfides in the microporous carbon with dispersed metal sulfides is 1.0% to 2.5%.

[0019] Preferably, the pore size of the microporous carbon a is 0.2 nm to 4 nm, and the porosity is 20% to 35%.

[0020] Preferably, the thickness of the first carbon layer is 35 μm to 110 μm; more preferably, it is 65 to 75 μm. This preferred thickness helps to further enhance stability.

[0021] Preferably, the electrical conductivity of the first carbon layer is 0.1~0.5Ω / m.

[0022] Preferably, the first carbon layer further includes a binder; wherein the binder content in the first carbon layer is 8-20%.

[0023] In this invention, the porosity of carbon material b is 40%~60%.

[0024] Preferably, the thickness of the second carbon layer is 5 μm to 55 μm; more preferably, it is 25 to 35 μm. This preferred thickness helps to further enhance stability.

[0025] Preferably, the electrical conductivity of the second carbon layer is 5~20 Ω / m.

[0026] Preferably, the second carbon layer further includes an adhesive; wherein the content of the adhesive in the first carbon layer is 3-5%.

[0027] The present invention also provides a method for preparing the dual-gradient 3D carbon current collector, wherein microporous carbon a and carbon material b are prepared in advance; the microporous carbon is composited on a conductive substrate to form a first carbon layer, and then carbon material b is composited on the surface of the first carbon layer to form a second carbon layer; subsequently, the dual-gradient 3D carbon current collector is obtained by hot pressing.

[0028] The preparation steps of the microporous carbon a include: subjecting carbon source a and microporous activator to a first-stage calcination treatment to obtain first-stage carbon; mixing the first-stage carbon with a sulfur-containing carbon source and subjecting it to a second-stage calcination treatment to obtain second-stage carbon; impregnating the second-stage carbon with a metal M source and then subjecting it to a third-stage calcination treatment to obtain the final product; wherein the temperature of the first-stage calcination is 700℃~1400℃, the temperature of the second-stage calcination is 400℃~800℃, and the temperature of the third-stage calcination is 500~1500℃;

[0029] The carbon material b is obtained by first-stage low-temperature sintering of carbon source b and composite template, followed by second-stage high-temperature sintering; wherein, the temperature of the first-stage low-temperature sintering is 300~800℃; and the temperature of the second-stage high-temperature sintering is 850~2000℃.

[0030] The composite template includes mesoporous template, macroporous template, and ultra-large pore template; wherein, the composite template contains at least zinc-based material; the weight ratio of mesoporous template, macroporous template, and ultra-large pore template in the composite template is 1:0.8~4:0.8~4; the weight ratio of carbon source b to composite template is 1:1.5~5.

[0031] This invention pre-prepares microporous carbon a and carbon material b using the special method described above, and then sequentially combines the two according to the hierarchical relationship described in this invention to form a material with a pore structure and active sites arranged in a dual gradient. This material is innovatively used in alkali metal batteries, which can induce uniform deposition of alkali metals, reduce polarization, and thus significantly improve the electrochemical performance of alkali metals.

[0032] In this invention, carbon source a and carbon source b are each at least one of small molecule organic carbon, natural polymers, and synthetic polymers; furthermore, they can be any one or more of petroleum coke, coal tar pitch, petroleum asphalt, paraffin wax, anthracite, lignite, graphite, carbon black, lignin, starch, phenolic resin, and carbon nanotube materials.

[0033] Preferably, the microporous activator includes KOH, NaOH, LiOH, Na2CO3, (NH4)2CO3, K2CO3, NaHCO3, KHCO3, NH4HCO3, H3PO4, ZnCl2, CO(NH2)2, NaNO3, C3H6N6, CO(NH2)2, C6H8O7, C7H5NS2, polyaniline (PANI), polypyrrole (PPy), and polyacrylonitrile (PAN, (C3H3N)). n ), polyethylene glycol (PEG, HO(CH2CH2O) n One or more of H);

[0034] Preferably, the microporous activator includes at least one selected from NaHCO3, KHCO3, and NH4HCO3. Studies have shown that this preferred microporous activator, when combined with the process, helps to synergistically enhance the interfacial stability of the prepared negative electrode.

[0035] Preferably, the weight ratio of carbon source a to microporous activator is 1:0.5~2.5, more preferably 1:1~2; even more preferably 1:1.4~1.6. Studies have shown that this preferred amount of microporous activator helps to work in conjunction with the process to further synergistically enhance the interfacial stability of the prepared negative electrode.

[0036] Preferably, the temperature of the first stage of calcination is 900~1100℃, more preferably 950~1050℃; studies have shown that at this preferred temperature, it is helpful to combine with the process to further synergistically enhance the interfacial stability of the prepared negative electrode.

[0037] Preferably, the roasting time for the first stage is 6 to 48 hours, and more preferably 7 to 12 hours.

[0038] Preferably, the sulfur-containing carbon source is at least one of sulfur-containing small molecule carbon sources, sulfur-containing natural polymers, and sulfur-containing synthetic polymers; further, it can be one of thiophene, thiourea, cysteine, thioacetamide, sulfonated polystyrene, and dibenzyl disulfide.

[0039] Preferably, the weight ratio of a carbon source to a sulfur-containing carbon source can be 1:0.5~3; more preferably, it can be 1:1~2.

[0040] Preferably, the temperature of the second stage of roasting is 500~600℃; more preferably, it can be 530~570℃.

[0041] Preferably, the second roasting time is 1-5 hours, and more preferably 2-3 hours.

[0042] In this invention, the metal M source is a water-soluble salt of metal M, and more specifically, a sulfate, nitrate, acetate, or other salt of metal M. Furthermore, metal M is zinc. Studies have shown that this preferred metal M helps to synergistically enhance the interfacial stability of the prepared anode in conjunction with the process.

[0043] During the impregnation process, the concentration of metal M can be 0.5~5M, and further can be 1~2M.

[0044] The liquid-to-solid ratio during the impregnation process can be 10~150ml / g; further, it can be 50~100ml / g.

[0045] Preferably, the temperature of the third stage of calcination is 550~850℃, more preferably 580~620℃; studies have shown that at this preferred temperature, it is helpful to combine with the process to further synergistically enhance the interfacial stability of the prepared negative electrode.

[0046] Preferably, the third roasting time is 1-5 hours, and more preferably 2-3 hours.

[0047] In this invention, the mesoporous template is zinc oxide.

[0048] Preferably, the particle size of the mesoporous template agent is 10 nm to 50 nm, and more preferably 25 to 35 nm;

[0049] Preferably, the macroporous template is selected from zinc oxide.

[0050] Preferably, the particle size of the macroporous template agent is 55 nm to 300 nm. More preferably, it can be 75 to 85 nm.

[0051] Preferably, the extra-large hole template is selected from zinc oxide.

[0052] Preferably, the particle size of the ultra-large pore template agent is 350 nm to 1000 nm; more preferably 450 nm to 550 nm; and even more preferably 480 nm to 520 nm.

[0053] Preferably, in the composite template, the weight ratio of the mesoporous template, macroporous template, and ultra-macroporous template is 1:0.9~3:0.9~3, more preferably 1:0.9~1.1:0.9~1.1. Studies have shown that this preferred template ratio helps to synergistically enhance the interfacial stability of the prepared anode by combining it with the process.

[0054] Preferably, the weight ratio of carbon source b to composite template is 1:2 to 3.5; more preferably, it is 1:2.4 to 2.6. Studies have shown that this preferred template dosage helps to synergistically enhance the interfacial stability of the prepared anode in conjunction with the process.

[0055] The first stage of low-temperature sintering is at a temperature of 550~750℃. The second stage of high-temperature sintering is at a temperature of 950~1200℃.

[0056] In this invention, the first stage of low-temperature calcination takes 1 to 5 hours, and can be further extended to 2 to 3 hours.

[0057] In this invention, the second stage of low-temperature calcination takes 1 to 5 hours, and can be further extended to 2 to 3 hours.

[0058] In this invention, microporous carbon a and binder are slurried with solvent, coated onto a conductive substrate, and dried to form a first carbon layer; carbon material b and binder are slurried with solvent, coated into the first carbon layer, and dried to form a second carbon layer.

[0059] The dual-gradient 3D carbon current collector is then obtained by hot pressing.

[0060] In this invention, the hot-pressing pressure is 3~10 MPa, more preferably 4~9 MPa, and even more preferably 7.5~8.5 MPa. The hot-pressing temperature is 50~110℃, preferably 60~100℃; more preferably 75~85℃. The hot-pressing time is 1~5 min, preferably 2~4 min, and even more preferably 2.5~3.5 min. Studies have shown that the preferred hot-pressing process helps to synergistically enhance the interfacial stability of the prepared negative electrode in conjunction with the process.

[0061] The present invention also provides a negative electrode for an alkali metal battery, comprising the aforementioned dual-gradient 3D carbon current collector and an alkali metal filled in a first carbon layer.

[0062] In this invention, the alkali metal can be, for example, at least one of lithium metal, sodium metal, and potassium metal.

[0063] The present invention also provides a method for preparing the negative electrode of the alkali metal battery, wherein the alkali metal is composited in a dual-gradient 3D carbon current collector by thermal melting and / or electrodeposition to obtain the negative electrode.

[0064] The present invention also provides an alkali metal battery comprising the negative electrode described herein.

[0065] Beneficial effects

[0066] The dual-gradient 3D carbon current collector described in this invention features a dual-gradient structure with decreasing active sites and increasing through-pores from bottom to top. Based on the combined control of composition and the hierarchical relationship between components, it can adapt to the charging and discharging characteristics of alkali metal batteries, resulting in superior performance. Specifically: Firstly, due to the effect of layered composite pores, it facilitates the diffusion and transport of electrolyte and can also serve as an ion buffer reservoir to improve ion transport efficiency, reduce alkali metal deposition on the negative electrode surface, thereby reducing surface dendrite formation and improving the safety of alkali metal batteries. Secondly, due to the modification of active sites, the overpotential of alkali metal ions deposited on the surface of active sites is greater than that of alkali metal ions directly deposited on the alkali metal surface. Alkali metal ions preferentially deposit in the three-dimensional structure inside the alkali metal negative electrode, effectively reducing the surface current density of the electrode, achieving uniform deposition of alkali metal, and controlling the volume expansion of alkali metal. Thirdly, due to the greater electric field strength near the copper foil side, as well as the effect of the gradient of pores and active sites, the electrolyte seeps to the bottom of the electrode and deposits on the side of the preferred active sites, increasing the space utilization rate inside the negative electrode and ultimately achieving "bottom-up" deposition. Attached Figure Description

[0067] Figure 1 The gradient composite pore structure and gradient active sites of Example 1 form a dual-gradient 3D carbon current collector with a loading capacity of 2 mAh / cm². 2 Scanning electron microscope image of the surface after alkali metal treatment.

[0068] Figure 2 The gradient composite pore structure and gradient active sites of Example 1 form a dual-gradient 3D carbon current collector with a loading capacity of 2 mAh / cm². 2 Cross-sectional scanning electron microscope image of alkali metal.

[0069] Figure 3 The graph shows the battery test performance of the dual-gradient 3D carbon current collector with gradient composite pore structure and gradient active sites in Example 1, and the carbon current collectors in Comparative Examples 1 to 5, after being assembled into half-cells.

[0070] Figure 4 The graph shows the battery test performance of the symmetrical battery assembled from the gradient composite pore structure and gradient active site dual-gradient 3D carbon current collector of Example 1, and the porous carbon current collectors of Comparative Example 2 and Comparative Example 5. Detailed Implementation

[0071] Unless otherwise defined, all technical terms used herein have the same meaning as commonly understood by those skilled in the art. The technical terms used herein are for the purpose of describing particular embodiments only and are not intended to limit the scope of the invention.

[0072] Unless otherwise specified, all raw materials, reagents, instruments and equipment used in this invention can be purchased from the market or prepared by existing methods.

[0073] Example 1

[0074] Step 1: Preparation of microporous carbon a;

[0075] Take 2g of asphalt and 3g of microporous activator (KHCO3), mix them evenly, and put them into a tube furnace filled with argon. The temperature is raised to 1000℃ (first stage calcination temperature T1) at a rate of 5℃ / min. Calcine for 8h. After cooling, wash the calcined material with water several times to obtain porous carbon material. Take 1g of porous carbon material and 2g of thiourea, mix them evenly, and put them into a tube furnace filled with argon. The temperature is raised to 550℃ (second stage calcination temperature T2) at a rate of 5℃ / min. Calcine for 2h. After cooling, immerse the calcined material in 100ml of 1mol / L metal source (ZnSO4) solution for 24h, filter and dry. Put the dried negative electrode material into a tube furnace filled with argon. The temperature is raised to 600℃ (third stage calcination temperature T3) at a rate of 5℃ / min. Calcine for 2h to obtain microporous carbon a.

[0076] Step 2: Preparation of composite porous carbon b:

[0077] Dissolve 2g of asphalt in 30ml of toluene, then place the asphalt-toluene solution in an oil bath and heat continuously at 110℃ with stirring. Slowly add 30nm ZnO template (mesopore template), 90nm ZnO template (macropore template), and 500nm ZnO template (ultra-macropore template) in a 1:1:1 ratio to the mixed solution (total template amount is 5g). After continuous heating, evaporate the toluene to dryness, collect the evaporated carbon material and place it in an argon-filled tube furnace. Heat the material to 600℃ at a rate of 5℃ / min and hold for two hours for the first stage of calcination. After cooling, acid wash the calcined material multiple times to remove the zinc oxide template. Then, heat the material to 1000℃ at a rate of 5℃ / min and hold for 2 hours in an argon-filled tube furnace for the second stage of calcination to obtain hierarchical porous carbon b.

[0078] Step 3: Preparation of the composite carbon layer of microporous carbon a and composite porous carbon b:

[0079] Microporous carbon a, acetylene black, and PVDF were added to an appropriate amount of NMP in a ratio of 90:5:5 to form a slurry. After stirring evenly, a microporous carbon a layer was uniformly coated on the surface of the conductive copper foil with a 170 μm blade. After the electrode was dried, the thickness of the microporous carbon a layer was measured to be 80 μm.

[0080] Composite porous carbon (b), acetylene black, and PVDF were added to an appropriate amount of NMP in a ratio of 80:5:15 to form a slurry. After thorough mixing, the composite carbon (b) layer was uniformly coated onto the surface of the microporous carbon (a) layer with a 160 μm diameter using a scraper. After coating, the electrode was hot-pressed at 80°C for 3 min under a pressure of 8 MPa. After the electrode dried, the total thickness of the composite carbon layer was measured to be 100 μm, resulting in a negative electrode with a composite carbon layer (a dual-gradient 3D carbon current collector with a gradient composite porous structure and gradient active sites). The thickness of the microporous carbon (a) layer (Ha) was approximately 70 μm, and the thickness of the composite carbon (b) layer (Hb) was approximately 30 μm.

[0081] Battery test:

[0082] The composite carbon layer anode and lithium sheet prepared in step 3 were used as the working electrode and counter electrode, respectively, to assemble a half-cell. The electrolyte was 1M LiTFSI in DOL∶DME=1∶1Vol%. CR2025 coin cells were assembled in a glove box filled with argon atmosphere. During battery charge-discharge testing, the current density was 1mA / cm³. 2 Area specific capacity 1mAh / cm 2 .

[0083] Example 2

[0084] Compared with Example 1, the only difference is that the type and proportion of microporous activator used in step 1 are different. The test results of the battery assembled from the microporous activator and the obtained negative electrode material are shown in Table 1. The battery assembly and testing process is the same as in Example 1.

[0085]

[0086] As demonstrated in Examples 1 and 2-1, using bicarbonate as an activator helps to further optimize the pore structure, enabling it to be combined with the hierarchical porous carbon b and the double-layer hot-pressing process described in this invention to further optimize the channel and interface structure, thereby further improving the material's performance. Furthermore, as demonstrated in Examples 1, 2-2, and 2-3, controlling the microporous activator to pitch ratio at a reasonable level, such as 1 to 2:1, can further synergistically optimize the channel and interface structure, facilitating further synergistic effects with other processes and enhancing the material's performance.

[0087] Example 3

[0088] Compared with Example 1, the only difference is that the type of metal source used in step 1 is adjusted. The amount of metal source and other operations are the same as in Example 1. The experimental results are shown in Table 2.

[0089]

[0090] As can be seen from Examples 1 and 3, using zinc as a metal source, combined with the preparation process of the present invention, helps to optimize the pore structure, interface, and exposure of active sites of the material, which helps to further induce the homogenized deposition of alkali metals such as lithium, optimize the interface structure, and obtain better electrochemical performance.

[0091] Example 4

[0092] Compared with Example 1, the only difference is that the amount of thiourea and metal source in step 1 is changed. All other operations and parameters are the same as in Example 1. The results are shown in Table 3.

[0093]

[0094] As demonstrated in Examples 1 and 4, the combination of sulfur source and metal source can synergistically form a sulfur- and zinc-rich composite layer in the inner layer and construct a layered gradient with the surface layer. Furthermore, by controlling the dosage ratio, it helps to further optimize the deposition behavior and effect of alkali metals and further improve the performance of the battery.

[0095] Example 5

[0096] Compared with Example 1, the only difference is that in step 1, the three-stage calcination temperature was changed. The test results of the battery assembled from the obtained negative electrode material are shown in Table 4. The battery assembly and testing process is the same as in Example 1.

[0097]

[0098] As can be seen from Examples 1 and 5, based on the three-stage calcination and the corresponding calcination temperature, it helps to optimize the pore and interface structure of the material, and helps to combine with the process to further synergistically improve the overpotential, coulombic efficiency and cycle stability of the material.

[0099] Example 6

[0100] Compared with Example 1, the only difference is that the proportion of template agent used in step 2 is different. The test results of the battery assembled from the obtained negative electrode material are shown in Table 5. The battery assembly and testing process is the same as that of Example 1.

[0101]

[0102] As can be seen from Example 6, controlling the proportion of the template helps to optimize the physicochemical structure of carbon b, and helps to further synergistically enhance the interface stability of the battery.

[0103] Example 7

[0104] Compared to Example 1, the only difference is the ratio of template mass to asphalt mass used in step 2 and the conditions:

[0105] Example 7-1: The amount of composite template used is 3g, which is the weight ratio of it to asphalt is 1.5:1;

[0106] Compared to group a: the amount of composite template used was 12g, which is a weight ratio of 6:1 with asphalt;

[0107] Compared to group B: the amount of composite template used was 1.5g, which is equivalent to a weight ratio of 0.75:1 with asphalt;

[0108] Example 7-2: The temperature of the first stage of roasting is 650℃ and the holding time is 3h; the temperature of the first stage of roasting is 1050℃ and the holding time is 3h.

[0109] Table 6 shows the test results of batteries assembled from negative electrode materials prepared using different template agent ratios in Example 7. The battery assembly and testing process was the same as in Example 1.

[0110]

[0111] Example 8

[0112] Compared with Example 1, the only difference is that the thickness of the microporous carbon a layer and the composite carbon b layer in step 3 is different. The test results of the battery assembled from the obtained negative electrode material are shown in Table 7. The battery assembly and testing process is the same as in Example 1.

[0113]

[0114] Example 9

[0115] Compared with Example 1, the only difference is that the hot pressing process parameters in step 3 are different. The test results of the battery assembled from the obtained negative electrode material are shown in Table 8. The battery assembly and testing process is the same as in Example 1.

[0116]

[0117] By employing the methods described in Examples 1 and 9, the stacking and hot-pressing processes help improve the interface, construct the dual-gradient structure, and further enhance the coulombic efficiency and cycle stability of the material.

[0118] Comparative Example 1

[0119] Compared with Example 1, the only difference is that the second stage (sulfur doping) and the third stage (zinc doping) calcination in step 1 are omitted. That is, after mixing 2g of asphalt with 3g of KHCO3 and calcining in the first stage (1000℃, 2h), microporous carbon a is directly obtained after washing with water and drying. Subsequent steps 2 and 3 are exactly the same as in Example 1.

[0120] Comparative Example 2

[0121] Compared with Example 1, the only difference is that in step 1, instead of the three-stage treatment, thiourea, metal source, asphalt, and activating additives are mixed together and subjected to a single-stage roasting treatment. The roasting temperature is the same as the first-stage roasting temperature of Example 1, the total roasting time is the same as the three-stage roasting of Example 1, and other operations and parameters are the same as in Example 1.

[0122] Comparative Example 3

[0123] Compared with Example 1, the only difference is that in step 2, the zinc oxide template is replaced with a template made of SiO2 material. All other operations and parameters are the same as in Example 1.

[0124] Comparative Example 4

[0125] Compared to Example 1, the only difference is that in step 3, after the second carbon layer is laminated, it is not hot-pressed, but directly dried and assembled into a battery. All other operations and parameters are the same as in Example 1.

[0126] Comparative Example 5

[0127] Compared to Example 1, the only difference is that in step 3, a carbon material layer b is pre-composite on a conductive substrate, followed by the formation of a microporous carbon layer a. The conditions for forming the carbon material layer b and the carbon layer a, as well as other operations and parameters, are the same as in Example 1.

[0128] The effect data for each comparative example are shown in Table 9:

[0129]

[0130] This invention pre-prepares microporous carbon a and carbon material b using the special method described above, and then sequentially combines the two according to the hierarchical relationship described in this invention to form a material with a pore structure and active sites arranged in a dual gradient. This material is innovatively used in alkali metal batteries, which can induce uniform deposition of alkali metals, reduce polarization, and thus significantly improve the electrochemical performance of alkali metals.

Claims

1. A dual-gradient 3D carbon current collector, characterized in that, The material comprises a conductive substrate, a first carbon layer composited on the conductive substrate, and a second carbon layer composited on the surface of the first carbon layer. The first carbon layer is composed of microporous carbon a with dispersed metal M sulfide. The second carbon layer is composed of carbon material b with a hierarchical through-pore structure, wherein the hierarchical through-pores include mesopores, macropores, and super-macropores, and there are through-pore structures between the pores.

2. The dual-gradient 3D carbon current collector as described in claim 1, characterized in that, The conductive substrate includes at least one of conductive metal foil, flexible polymer substrate, oxide-coated conductive substrate, and conductive polymer film; Preferably, in the first carbon layer, the M in the metal M sulfide includes at least one of Zn, Sn, or Ag; Preferably, in the microporous carbon with dispersed metal sulfides, the content of metal sulfides is 1.0~2.5%; Preferably, the pore size of the microporous carbon a is 0.2 nm to 4 nm; the porosity is 20% to 35%. Preferably, the thickness of the first carbon layer is 35 μm to 110 μm; Preferably, the resistivity of the first carbon layer is 0.1~0.5Ω / m; Preferably, the first carbon layer further includes a binder; wherein the binder content in the first carbon layer is 8-20%.

3. The dual-gradient 3D carbon current collector as described in claim 1, characterized in that, The ratio of mesopores, macropores, and supermacropores in carbon material b is 1:0.333~2.5:0.333~2.5; Preferably, the porosity of carbon material b is 40%~60%; Preferably, the thickness of the second carbon layer is 5 μm to 55 μm; Preferably, the electrical conductivity of the second carbon layer is 5~20 Ω / m; Preferably, the second carbon layer further includes an adhesive; wherein the content of the adhesive in the first carbon layer is 3-5%.

4. A method for preparing a dual-gradient 3D carbon current collector according to any one of claims 1 to 3, characterized in that, Microporous carbon a and carbon material b are prepared in advance; the microporous carbon is composited on a conductive substrate to form a first carbon layer, and then carbon material b is composited on the surface of the first carbon layer to form a second carbon layer; Subsequently, the dual-gradient 3D carbon current collector was obtained through hot pressing. The preparation steps of the microporous carbon a include: subjecting carbon source a and microporous activator to a first-stage calcination treatment to obtain first-stage carbon; mixing the first-stage carbon with a sulfur-containing carbon source and subjecting it to a second-stage calcination treatment to obtain second-stage carbon; impregnating the second-stage carbon with a metal M source and then subjecting it to a third-stage calcination treatment to obtain the final product; wherein the temperature of the first-stage calcination is 700℃~1400℃, the temperature of the second-stage calcination is 400℃~800℃, and the temperature of the third-stage calcination is 500~1500℃; The carbon material b is obtained by first-stage low-temperature sintering of carbon source b and composite template, followed by second-stage high-temperature sintering; wherein, the temperature of the first-stage low-temperature sintering is 300~800℃; and the temperature of the second-stage high-temperature sintering is 850~2000℃. The composite template includes mesoporous template, macroporous template, and ultra-large pore template; wherein, the composite template contains at least zinc-based material; the weight ratio of mesoporous template, macroporous template, and ultra-large pore template in the composite template is 1:0.8~4:0.8~4; the weight ratio of carbon source b to composite template is 1:1.5~5.

5. The method for preparing a dual-gradient 3D carbon current collector as described in claim 4, characterized in that, Carbon source a and carbon source b are each at least one of small molecule organic carbon, natural polymers, and synthetic polymers; furthermore, they can be any one or more of petroleum coke, coal tar pitch, petroleum asphalt, paraffin wax, anthracite, lignite, graphite, carbon black, lignin, starch, phenolic resin, and carbon nanotube materials. Preferably, the microporous activator includes one or more of the following: KOH, NaOH, LiOH, Na2CO3, (NH4)2CO3, K2CO3, NaHCO3, KHCO3, NH4HCO3, H3PO4, ZnCl2, CO(NH2)2, NaNO3, C3H6N6, CO(NH2)2, C6H8O7, C7H5NS2, polyaniline, polypyrrole, polyacrylonitrile, and polyethylene glycol. Preferably, the weight ratio of carbon source a to microporous activator is 1:0.5~2.5; Preferably, the temperature of the first stage of roasting is 900~1100℃, more preferably 950~1050℃; Preferably, the roasting time for the first stage is 6 to 48 hours; Preferably, the sulfur-containing carbon source is at least one of sulfur-containing small molecule carbon sources, sulfur-containing natural polymers, and sulfur-containing synthetic polymers; more preferably, it can be one of thiophene, thiourea, cysteine, thioacetamide, sulfonated polystyrene, and dibenzyl disulfide. Preferably, the weight ratio of a carbon source to a sulfur-containing carbon source can be 1:0.5~3; Preferably, the temperature of the second stage of roasting is 500~600℃; Preferably, the second stage of roasting takes 1 to 5 hours; Preferably, during the impregnation process, the concentration of metal M can be 0.5~5M; the liquid-to-solid ratio during the impregnation process can be 10~150ml / g; Preferably, the temperature of the third stage of roasting is 550~850℃, more preferably 580~620℃; Preferably, the third stage of roasting takes 1 to 5 hours.

6. The method for preparing a dual-gradient 3D carbon current collector as described in claim 4, characterized in that, The particle size of the mesoporous template agent is 10nm~50nm; Preferably, the particle size of the macroporous template agent is 55 nm to 300 nm; Preferably, the particle size of the ultra-large pore template agent is 350 nm to 1000 nm; more preferably 450 nm to 550 nm; and even more preferably 480 nm to 520 nm. Preferably, in the composite template, the weight ratio of the mesoporous template, the macroporous template, and the ultra-large-pore template is 1:0.9~3:0.9~3, and more preferably 1:0.9~1.1:0.9~1.1; Preferably, the weight ratio of carbon source b to composite template is 1:2 to 3.5; more preferably, it is 1:2.4 to 2.

6. Preferably, the temperature of the first stage of low-temperature sintering is 550~750℃; the temperature of the second stage of high-temperature sintering is 950~1200℃.

7. The method for preparing a dual-gradient 3D carbon current collector according to any one of claims 4 to 6, characterized in that, Microporous carbon a and binder are slurried with solvent, coated onto a conductive substrate, and dried to form a first carbon layer; carbon material b and binder are slurried with solvent, coated into the first carbon layer, and dried to form a second carbon layer; Subsequently, hot pressing was performed to obtain the dual-gradient 3D carbon current collector. Preferably, the hot pressing pressure is 3~10MPa, more preferably 4~9MPa, and even more preferably 7.5~8.5MPa; the hot pressing temperature is 50~110℃, preferably 60~100℃, and even more preferably 75~85℃; the hot pressing time is 1~5min, preferably 2~4min, and even more preferably 2.5~3.5min.

8. A negative electrode for an alkali metal battery, characterized in that, It includes the dual-gradient 3D carbon current collector as described in any one of claims 1 to 3 or the dual-gradient 3D carbon current collector prepared by the preparation method described in any one of claims 4 to 6, and the alkali metal filled in the first carbon layer.

9. A method for preparing the negative electrode of the alkali metal battery according to claim 8, characterized in that, The anode is prepared by composite alkali metals in a dual-gradient 3D carbon current collector using thermal melting and / or electrodeposition.

10. An alkali metal battery, characterized in that, It includes the negative electrode as described in claim 9.

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