A distributed cobalt-free high-entropy energy storage electrode and its preparation method and application

Abstract

The present invention relates to the field of new energy storage technology, and discloses a distributed cobalt-free high-entropy energy storage electrode, its preparation method, and application. The electrode includes an active material coating comprising an active material and carbon nanotubes. The active material comprises a solid solution of Fe, Ni, Mn, Al, and Ti, which is supported in the form of particles within and on the surface of the carbon nanotubes. The active material obtained by the present invention is a cobalt-free active material with high energy density and good cycle performance. In addition, it has a discharge efficiency of not less than 85% at low temperatures.

Description

Technical Field

[0001] The present invention relates to the field of new energy storage technology, and in particular to a distributed cobalt-free high-entropy energy storage electrode and a preparation method and application thereof. Background Art

[0002] With the rapid development of new energy vehicles and intelligent transportation systems, lithium-ion batteries, as core energy storage devices, are facing higher demands for energy density, cycle life, and environmental adaptability. Traditional cobalt-based ternary cathode materials (such as NCM and NCA) face scarce cobalt resources, poor thermal stability (thermal runaway temperature <200°C), and rapid phase transitions (lattice expansion >5%) at high voltages. This results in high battery costs, poor high-temperature performance, and limited cycle life (commercial NCM batteries have a capacity retention of <80% after 2000 cycles). Furthermore, the frequent vibration and shock experienced in traffic scenarios can cause structural pulverization of the electrode material due to repeated mechanical stress, leading to interfacial delamination from the active layer, resulting in capacity fading and shortened cycle life. Furthermore, extreme temperature fluctuations in traffic scenarios further exacerbate electrochemical performance degradation. Therefore, there is an urgent need to develop a cobalt-free electrode material that combines high energy density, wide temperature range adaptability, long cycle life, and excellent mechanical stability, along with efficient and low-cost preparation techniques. Summary of the Invention

[0003] In order to solve the above technical problems, the present invention provides a distributed cobalt-free high-entropy energy storage electrode and its preparation method and application. The electrode obtained by the present invention has high energy density, good cycle performance and adaptability to a wide temperature range; in addition, it has a discharge efficiency of not less than 85% at low temperatures.

[0004] The present invention provides a distributed cobalt-free high-entropy energy storage electrode, which includes an active material coating, which includes an active material and carbon nanotubes; the active material is a solid solution formed by Fe, Ni, Mn, Al and Ti, and the solid solution is loaded in the form of particles inside and on the surface of the carbon nanotubes.

[0005] Furthermore, the particle size of the solid solution is 20nm-50nm.

[0006] Furthermore, the coverage of the solid solution on the carbon nanotubes is 80%-95%.

[0007] Furthermore, in the solid solution, the atomic ratio of iron atoms, nickel atoms, manganese atoms, aluminum atoms and titanium atoms is 6:4:4:3:3.

[0008] Furthermore, the solid solution has a porous structure with a pore volume of not less than 0.25 cm 3 / g, with a specific surface area of ​​not less than 80m 2 / g.

[0009] Furthermore, the XRD of the solid solution has characteristic diffraction peaks at 15.1°, 17.5°, and 23.0° in an X-ray powder diffraction pattern represented by a diffraction angle 2θ.

[0010] Furthermore, the carbon nanotubes have a length of 1 μm-10 μm and a diameter of 10 nm-30 nm.

[0011] Furthermore, the active material coating has a porous structure, and in the thickness direction, the pore size inside the active material coating is larger than the pore size in the surface direction of the active material coating.

[0012] Furthermore, the pore size inside the active material coating is 100nm-500nm, and the pore size on the surface of the active material coating is 10nm-50nm.

[0013] Furthermore, the active material coating also includes a binder.

[0014] Furthermore, the binder includes PVDF.

[0015] Furthermore, the electrode further comprises a current collector, and the active material coating is loaded on the surface of the current collector.

[0016] Furthermore, the current collector includes metal.

[0017] Furthermore, the metal includes copper.

[0018] Furthermore, the current collector has a pore size of 150 μm-250 μm and a porosity of 85%-95%.

[0019] Furthermore, the thickness of the electrode is 150 μm-200 μm, the porosity is 60%-70%, and the surface density is 20 mg / cm 2 -25mg / cm 2 .

[0020] The present invention also provides a method for preparing the distributed cobalt-free high-entropy energy storage electrode, the preparation method comprising:

[0021] A chelating agent is added to a mixed solution containing an iron source, a nickel source, a manganese source, an aluminum source and a titanium source, the pH value is adjusted, and a hydrothermal reaction is carried out to obtain a precursor; the precursor and carbon nanotubes are ball-milled; the ball-milled product is subjected to a gradient heat treatment under an inert atmosphere to obtain an intermediate product; and the intermediate product is loaded on the surface of a current collector to obtain an electrode.

[0022] Furthermore, the iron source includes ferric nitrate.

[0023] Furthermore, the nickel source includes nickel nitrate.

[0024] Furthermore, the manganese source includes manganese acetate.

[0025] Furthermore, the aluminum source includes aluminum sulfate.

[0026] Furthermore, the titanium source includes tetrabutyl titanate.

[0027] Furthermore, the iron source is calculated as iron ions, the nickel source is calculated as nickel ions, the manganese source is calculated as manganese ions, the aluminum source is calculated as aluminum ions and the titanium source is calculated as titanium ions, and the molar ratio of iron ions, nickel ions, manganese ions, aluminum ions and titanium ions is 6:4:4:3:3.

[0028] Furthermore, the method for preparing the mixed solution containing the iron source, nickel source, manganese source, aluminum source and titanium source includes: dispersing the iron source, nickel source, manganese source, aluminum source and titanium source in deionized water.

[0029] Furthermore, the complexing agent includes citric acid.

[0030] Furthermore, the amount of the complexing agent is 1.2 to 1.8 times the total molar amount of the metal ions in the iron source, nickel source, manganese source, aluminum source and titanium source.

[0031] Furthermore, the pH value is adjusted to 3.8-4.2.

[0032] In the present invention, the reagent for adjusting pH includes nitric acid or ammonia water.

[0033] Furthermore, the temperature of the hydrothermal reaction is 160° C.-200° C., and the time of the hydrothermal reaction is 12 h-24 h.

[0034] Furthermore, the hydrothermal reaction further includes cooling, solid-liquid separation, washing, and drying.

[0035] Furthermore, the washing is performed with ethanol at least 3 times.

[0036] Furthermore, the drying is performed by vacuum drying, the drying temperature is 75° C.-85° C., and the drying time is 11 h-13 h.

[0037] Furthermore, based on mass, the ratio of the precursor to the carbon nanotubes is 7-9:3-1.

[0038] Furthermore, during the ball milling, the ball-to-material ratio is 8-12:1, the rotation speed is 200rpm-400rpm, and the ball milling time is 3h-5h.

[0039] Furthermore, the gradient heat treatment specifically includes:

[0040] The first stage: keep warm at 350℃-450℃ for 1h-3h, the second stage: keep warm at 700℃-800℃ for 3h-5h.

[0041] Those skilled in the art should understand that there are many ways to load the active material coating on the surface of the current collector, but based on the present invention, the active material coating needs to have a pore size inside the active material coating that is larger than the pore size in the direction of the active coating surface in the thickness direction. Therefore, the active material coating can be loaded on the surface of the current collector by electrostatic spraying.

[0042] Furthermore, the heating rate to reach the first stage temperature is 4°C / min-6°C / min, and the heating rate to reach the second stage temperature is 2°C / min-4°C / min.

[0043] Furthermore, the specific method of loading the intermediate product on the surface of the current collector includes:

[0044] The intermediate product is mixed with a binder and a solvent, and the mixed slurry is loaded on the surface of the current collector by an electrostatic spraying method.

[0045] Furthermore, the mixing method is ball milling, and the solid content of the slurry after ball milling is 44%-46%.

[0046] Furthermore, the solvent includes N-methylpyrrolidone.

[0047] Furthermore, based on mass, the ratio of the intermediate product, the binder and the solvent is 19:1:24.4.

[0048] Furthermore, the specific parameters of the electrostatic spraying method include:

[0049] Spray 20μm-30μm at a voltage of 29kV-31kV, a nozzle of 0.3mm, and a distance of 14cm-16cm;

[0050] Then spray 100μm-120μm at a voltage of 24kV-26kV, a nozzle of 0.5mm, and a distance of 19cm-21cm;

[0051] Finally, spray 20μm-30μm at a voltage of 29kV-31kV, a nozzle of 0.3mm, and a distance of 14cm-16cm.

[0052] Furthermore, after the intermediate product is loaded on the surface of the current collector, the electrode needs to be dried.

[0053] The present invention also provides the distributed cobalt-free high-entropy energy storage electrode in an electrochemical device, which can be used in terminal consumer products. The terminal consumer products applied for include but are not limited to mobile phones, laptops, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, and portable printers.

[0054] The present invention also provides an electrochemical device having the distributed cobalt-free high-entropy energy storage electrode. The electrochemical device can be used in electrical equipment, including large and small electrical equipment, wherein small electrical equipment includes end-consumer products, wearable electronic devices, or mobile electronic devices; large electrical equipment includes transportation electrical equipment. Transportation electrical equipment includes, but is not limited to, automobiles, motorcycles, power-assisted bicycles, buses, subways, high-speed trains, airplanes, and ships; wearable electronic devices or mobile electronic devices include, but are not limited to, stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, drones, motors, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors. The distributed cobalt-free high-entropy energy storage electrode of the present invention is applied to an electrochemical device, which can be housed in an electrical device in the form of an electrochemical device. Typically, the electrochemical device includes a battery pack or / multiple battery modules or / single battery module or / single battery cell and a management system for controlling them.

[0055] The embodiments of the present invention have the following technical effects:

[0056] 1. This invention achieves significant breakthroughs in cost, performance, environmental adaptability, and engineering applications through the collaborative innovation of a cobalt-free high-entropy alloy material system, a multi-scale gradient pore structure design, and an efficient preparation process. Compared to traditional cobalt-based ternary materials (such as NCM and NCA) and existing cobalt-free alternatives (such as LFP and lithium-rich manganese-based materials), the electrode material of this invention completely eliminates the cobalt element and utilizes a five-element high-entropy alloy system of Fe, Ni, Mn, Al, and Ti. This system combines a gradient pore distribution of surface nanopores and internal micropores, addressing the issues of traditional materials such as high cost, rapid cyclic decay, poor mechanical stability, and insufficient performance over a wide temperature range.

[0057] 2. In the present invention, based on the differences in atomic radius, five metal elements, Fe, Ni, Mn, Al, and Ti, were selected as active materials. The atomic ratio of these metal elements was further designed. It was found that at this ratio, the atoms of the metal elements can have the maximum lattice distortion energy (calculated value ≥1.8×10 9 J / m 3 ), this active material effectively suppresses lattice expansion caused by lithium insertion / extraction during cycling. This ratio also takes into account the technical issues of phase separation or localized stress concentration in the active material. The resulting active material exhibits a uniform distribution of metal elements, reducing localized stress and phase separation, thereby improving the cycling stability of the active material.

[0058] 3. The cobalt-free active material obtained by the present invention has a cobalt-free design that avoids the catalytic decomposition effect of cobalt at high temperatures (the thermal runaway temperature of traditional NCM materials is <200°C). The active material obtained by the present invention improves the thermal stability of the electrode to above 300°C. Combined with the multi-element solid solution structure of the high-entropy alloy, it significantly suppresses the risk of thermal runaway, meeting the stringent requirements for high safety in traffic scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0060] Figure 1 1 is an EIS diagram provided by the examples and comparative examples of the present invention.

[0061] Figure 2 1 is the XRD pattern provided by the examples and comparative examples of the present invention.

[0062] Figure 3 It is the SEM picture provided by the embodiment of the present invention and comparative example.

[0063] Figure 4 It is a comparison chart of energy density and life provided by the embodiments of the present invention and the comparative examples. DETAILED DESCRIPTION

[0064] To make the objectives, technical solutions, and advantages of the present invention more clear, the technical solutions of the present invention are described clearly and completely below. Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without inventive effort are also within the scope of protection of the present invention.

[0065] In a first aspect, some embodiments of the present invention provide a distributed cobalt-free high-entropy energy storage electrode, wherein the electrode includes an active material coating, and the active material coating includes an active material and carbon nanotubes; the active material is a solid solution formed by Fe, Ni, Mn, Al and Ti, and the solid solution is loaded in the form of particles in and on the surface of the carbon nanotubes.

[0066] In the present invention, carbon nanotubes can provide locations for loading active materials, thereby facilitating more uniform loading of active materials. In addition, carbon nanotubes can enhance the mechanical strength and electrical conductivity of the active material coating.

[0067] In the present invention, the active material is used to achieve lithium ion intercalation and deintercalation. Therefore, based on the inventive concept, the active material's structure must be stable. Solid solutions have good structural stability, but not all metals can form solid solutions. The formation of solid solutions depends on the crystal structure, atomic size, and electrochemical properties of the selected materials. Based on a comprehensive consideration, Fe, Ni, Mn, Al, and Ti were selected in the present invention.

[0068] In some embodiments, the particle size of the solid solution is 20 nm-50 nm.

[0069] In some embodiments, the coverage of the solid solution on the carbon nanotubes is 80%-95%.

[0070] In some embodiments, in the solid solution, the atomic ratio of iron atoms, nickel atoms, manganese atoms, aluminum atoms and titanium atoms is 6:4:4:3:3.

[0071] In the present invention, when selecting atoms that can form a solid solution, it is necessary to further consider how to control the ratio between these atoms to achieve structural stability and facilitate the deintercalation and extraction of lithium ions. When the selected ratio is not appropriate, it will cause phase separation or local stress concentration in the structure, thereby reducing the cycle performance of the electrode. The atomic ratio of the active material of the present invention has the maximum lattice distortion energy (≥1.8×10 9 J / m 3 ), which can effectively inhibit the lattice expansion caused by lithium insertion / extraction during the cycle, not only suppressing the risk of thermal runaway, but also improving the cycle performance of the electrode.

[0072] In some embodiments, the solid solution has a porous structure with a pore volume of not less than 0.25 cm 3 / g, with a specific surface area of ​​not less than 80m 2 / g.

[0073] In some embodiments, the XRD pattern of the solid solution, expressed as an X-ray powder diffraction pattern with a diffraction angle of 2θ, has characteristic diffraction peaks at 15.1°, 17.5°, and 23.0°.

[0074] In some embodiments, the carbon nanotubes have a length of 1 μm-10 μm and a diameter of 10 nm-30 nm.

[0075] In some embodiments, the active material coating has a porous structure, and in the thickness direction, the pore size inside the active material coating is larger than the pore size in the surface direction of the active material coating.

[0076] In the present invention, the electrode performance is optimized by the coordinated design of internal macropores and small pores on both sides of the active coating. The larger internal pores can accelerate the electrolyte infiltration and ion transport of the active coating, significantly reducing concentration polarization, thereby improving the high-rate discharge capability of the electrode, while the dense small pores on the surface of the coating fully expose the active sites by increasing the specific surface area, which not only enhances the contact efficiency between the material and the electrolyte, but also improves the contact efficiency between the coating and the current collector, can achieve improved reaction kinetics, and can form a gradient pore size with the macropores to improve the wetting effect of the coating. In addition, the loose internal porous structure can effectively buffer the volume expansion caused by lithium ion insertion / extraction, reduce the structural pulverization of the active material, and thus greatly improve the cycle stability.

[0077] The solid solution is loaded onto carbon nanotubes, where its hollow structure and high specific surface area provide an ideal carrier for the formation of gradient pore sizes. During the electrostatic spraying process, fine particles in the active coating slurry (such as binders and other non-agglomerated substances) preferentially adsorb to the CNT surface under the action of the electric field, forming a dense layer. By adjusting the electrostatic spraying parameters, coarse particles in the slurry (non-uniformly dispersed particles such as carbon nanotubes and solid solution) are deposited on the dense layer formed by gravity and airflow, forming a loose pore structure within the active coating. Finally, the electrostatic spraying parameters are adjusted to further deposit a dense layer on top. By adjusting the solid solution, carbon nanotubes, and electrostatic spraying parameters, an active coating with a loose internal pore structure and a dense surface pore distribution is obtained. At the same time, the chemical bonds (such as CO-Fe / Ni) formed between CNTs and solid solutions through gradient heat treatment enhance the interfacial bonding between CNTs and active particles, reduce the contact resistance during lithium ion insertion and extraction, thereby stabilizing the pore structure and preventing volume expansion or mechanical stress caused by lithium ion insertion / extraction during the cycle, leading to pore collapse and interface peeling.

[0078] In some embodiments, the pore size inside the active material coating is 100 nm-500 nm, and the pore size on the surface of the active material coating is 10 nm-50 nm.

[0079] In some embodiments, the active material coating further includes a binder.

[0080] In some embodiments, the binder comprises PVDF.

[0081] In some embodiments, the electrode further includes a current collector, and the active material coating is supported on the surface of the current collector.

[0082] In some embodiments, the current collector comprises metal.

[0083] In some embodiments, the metal includes copper.

[0084] In some embodiments, the current collector has a pore size of 150 μm-250 μm and a porosity of 85%-95%.

[0085] In some embodiments, the thickness of the electrode is 150 μm-200 μm, the porosity is 60%-70%, and the surface density is 20 mg / cm 2 -25mg / cm 2 .

[0086] In a second aspect, some embodiments of the present invention further provide a method for preparing the distributed cobalt-free high entropy energy storage electrode, the preparation method comprising:

[0087] A chelating agent is added to a mixed solution containing an iron source, a nickel source, a manganese source, an aluminum source and a titanium source, the pH value is adjusted, and a hydrothermal reaction is carried out to obtain a precursor; the precursor and carbon nanotubes are ball-milled; the ball-milled product is subjected to a gradient heat treatment under an inert atmosphere to obtain an intermediate product; and the intermediate product is loaded on the surface of a current collector to obtain an electrode.

[0088] In the method of the present invention, a chemical bond is formed between the active material and the carbon nanotubes through gradient heat treatment, and the interface contact resistance is reduced to 0.2Ω·cm 2 The following is beneficial to the transmission of electrons.

[0089] In some embodiments, the iron source includes ferric nitrate.

[0090] In some embodiments, the nickel source includes nickel nitrate.

[0091] In some embodiments, the manganese source includes manganese acetate.

[0092] In some embodiments, the aluminum source includes aluminum sulfate.

[0093] In some embodiments, the titanium source includes tetrabutyl titanate.

[0094] In some embodiments, the iron source is calculated as iron ions, the nickel source is calculated as nickel ions, the manganese source is calculated as manganese ions, the aluminum source is calculated as aluminum ions, and the titanium source is calculated as titanium ions, and the molar ratio of iron ions, nickel ions, manganese ions, aluminum ions and titanium ions is 6:4:4:3:3.

[0095] In some embodiments, the method for preparing the mixed solution containing the iron source, nickel source, manganese source, aluminum source and titanium source includes: dispersing the iron source, nickel source, manganese source, aluminum source and titanium source in deionized water.

[0096] In some embodiments, the complexing agent comprises citric acid.

[0097] In some embodiments, the amount of the complexing agent is 1.2 to 1.8 times the total molar amount of the metal ions in the iron source, nickel source, manganese source, aluminum source, and titanium source.

[0098] In some embodiments, the pH value is adjusted to 3.8-4.2.

[0099] In some embodiments, the temperature of the hydrothermal reaction is 160° C.-200° C., and the time of the hydrothermal reaction is 12 h-24 h.

[0100] In some embodiments, the ratio of the precursor to the carbon nanotubes is 7-9:3-1 by mass.

[0101] In some embodiments, during the ball milling, the ball-to-material ratio is 8-12:1, the rotation speed is 200 rpm-400 rpm, and the ball milling time is 3 h-5 h.

[0102] In some embodiments, the gradient heat treatment specifically includes:

[0103] The first stage: keep warm at 350℃-450℃ for 1h-3h, the second stage: keep warm at 700℃-800℃ for 3h-5h.

[0104] In some embodiments, the heating rate to reach the first stage temperature is 4° C. / min-6° C. / min, and the heating rate to reach the second stage temperature is 2° C. / min-4° C. / min.

[0105] Gradient heat treatment forms CO-Fe / Ni / Al / Ti bonds between the active particles and the carbon nanotubes, strengthening interfacial bonding and delaying high-temperature interfacial debonding. The high melting points of Fe, Ni, and Mn provide basic heat resistance, while Mn increases lattice distortion energy through solid solution strengthening and reduces thermal expansion.

[0106] In some embodiments, the specific method of loading the intermediate product on the surface of the current collector includes:

[0107] The intermediate product is mixed with a binder and a solvent, and the mixed slurry is loaded on the surface of the current collector by an electrostatic spraying method.

[0108] In some embodiments, the mixing method is ball milling, and the solid content of the slurry after ball milling is 44%-46%.

[0109] In some embodiments, the solvent includes N-methylpyrrolidone.

[0110] In some embodiments, the ratio of the intermediate product, the binder and the solvent is 19:1:24.4 by mass.

[0111] In some embodiments, the specific parameters of the electrostatic spraying method include:

[0112] Spray 20μm-30μm at a voltage of 29kV-31kV, a nozzle of 0.3mm, and a distance of 14cm-16cm;

[0113] Then spray 100μm-120μm at a voltage of 24kV-26kV, a nozzle of 0.5mm, and a distance of 19cm-21cm;

[0114] Finally, spray 20μm-30μm at a voltage of 29kV-31kV, a nozzle of 0.3mm, and a distance of 14cm-16cm.

[0115] The following is described in conjunction with specific examples and comparative examples:

[0116] Example 1:

[0117] Raw material preparation: weigh ferric nitrate (Fe(NO3)3·9H2O, 0.3 mol), nickel nitrate (Ni(NO3)2·6H2O, 0.2 mol), manganese acetate (Mn(CH3COO)2·4H2O, 0.2 mol), aluminum sulfate (Al2(SO4)3·18H2O, 0.075 mol), tetrabutyl titanate (C 16 H 36 O4Ti (0.075 mol) was dissolved in 1 L of deionized water and stirred until completely dissolved. Citric acid (C6H8O7, 1.5 times the total molar amount of the metal ions) was added as a complexing agent. The pH of the solution was adjusted to 4.0 ± 0.2 using nitric acid solution and ammonia water, forming a dark blue transparent sol.

[0118] Hydrothermal reaction: The sol was transferred to a polytetrafluoroethylene-lined autoclave, sealed, and placed in a forced air drying oven for 18 hours at 180°C. After the reaction, the mixture was cooled naturally, and the precipitate was collected by centrifugation, washed three times with ethanol, and dried under vacuum at 80°C for 12 hours to obtain a brown high-entropy hydroxide precursor.

[0119] The high-entropy hydroxide precursor was mixed with carbon nanotubes (CNTs, 20 nm in diameter and 5 μm in length) at a mass ratio of 8:2 and added to a zirconia ball mill (ball-to-material ratio of 10:1). The mixture was ball milled at 300 rpm for 4 hours under argon protection.

[0120] Gradient heat treatment: Place the mixed powder in a tube furnace, introduce argon (50 mL / min), and heat it up to 400°C at 5°C / min, and keep it at that temperature for 2 hours to remove organic matter. Continue to heat it up to 750°C at 3°C / min, and keep it at that temperature for 4 hours to reduce the metal oxide to high entropy alloy (Fe 30 Ni 20 Mn 20 Al15 Ti 15 ), while the CNTs and alloy particles form chemical bonds. The mixture is then cooled to room temperature, resulting in a black powder composite material.

[0121] The black powdered composite material was mixed with polyvinylidene fluoride (PVDF) binder in a mass ratio of 95:5, and N-methylpyrrolidone (NMP) solvent (122 mL) was added. The mixture was ball-milled for 6 h to form a uniform slurry with a solid content of 45%.

[0122] Electrostatic spraying:

[0123] Using a high-voltage electrostatic spraying device, the initial stage employed high voltage (30kV), a small nozzle (0.3mm), and a short spray distance (15cm) to fully atomize the slurry and preferentially deposit fine particles. The slurry was then sprayed onto the surface of a three-dimensional copper foam current collector (pore size 200μm, porosity 90%), forming a dense surface layer (pore size 10-50nm) with a spray depth of 30μm. In subsequent stages, the voltage was reduced (25kV), the nozzle was enlarged (0.5mm), and the spray distance was extended (20cm) to allow coarse particles to agglomerate and settle, creating a loose, porous internal layer (pore size 100-500nm) with a spray depth of 120μm. Finally, high voltage (30kV), a small nozzle (0.3mm), and a short spray distance (15cm) were used to spray a depth of 30μm. This layered spraying, through the effects of the electric field and other factors, created a gradient in the solids content of the slurry (45% on the surface, 55% in the interior), ultimately achieving a gradient structure with decreasing pore size from the inside out. By controlling the ambient humidity (<30% RH) and preheating the current collector (60°C), the sprayed slurry viscosity (200-300 mPa·s) is maintained, ensuring controllable solvent evaporation rate and particle accumulation morphology. This ultimately creates a gradient structure with decreasing pore size from the inside out across the thickness, meeting the synergistic requirements of high ion transport and mechanical stability. Finally, the electrode is dried at 60°C.

[0124] Comparative Example 1:

[0125] The high entropy alloy formed is Fe 50 Ni 30 Mn 20 , the rest is the same as Example 1.

[0126] Comparative Example 2:

[0127] The high entropy alloy formed is Fe 40 Ni 30 Mn 20 Al 10 , the rest is the same as Example 1.

[0128] Comparative Example 3:

[0129] The high entropy alloy formed is Fe 30Ni 20 Mn 20 Al 15 Ti 15 , and then electrostatic spraying was not used (the black powdered composite material and polyvinylidene fluoride (PVDF) binder were mixed in a mass ratio of 95:5, N-methylpyrrolidone (NMP) solvent (122 mL) was added, and ball milling was performed for 6 hours to form a uniform slurry with a solid content of 45%. The slurry was applied to the surface of a three-dimensional foam copper current collector (pore size 200 μm, porosity 90%) to form a coating layer with a thickness of 180 μm. Other aspects were the same as in Example 1.

[0130] Comparative Example 4:

[0131] Raw material preparation: weigh ferric nitrate (Fe(NO3)3·9H2O, 0.3 mol), nickel nitrate (Ni(NO3)2·6H2O, 0.2 mol), manganese acetate (Mn(CH3COO)2·4H2O, 0.2 mol), aluminum sulfate (Al2(SO4)3·18H2O, 0.075 mol), tetrabutyl titanate (C 16 H 36 O4Ti, 0.075 mol) and lithium carbonate (Li2CO3, 0.05 mol) as lithium sources, aiming to form lithium-doped active materials (Li 0.1 Fe 30 Ni 20 Mn 20 Al 15 Ti 15 ) was dissolved in 1 L of deionized water and stirred until completely dissolved. Citric acid (C6H8O7, 1.5 times the total molar amount of the metal ions) was added as a complexing agent. The pH of the solution was adjusted to 4.0 ± 0.2 using nitric acid solution and ammonia water, forming a dark blue transparent sol.

[0132] Hydrothermal reaction: The sol was transferred to a polytetrafluoroethylene-lined autoclave, sealed, and placed in a forced air drying oven for reaction at 180°C for 18 hours. After the reaction, the mixture was cooled naturally, and the precipitate was collected by centrifugation, washed three times with ethanol, and vacuum dried at 80°C for 12 hours to obtain a brown high-entropy hydroxide precursor. Other conditions were the same as in Example 1.

[0133] Comparative Example 5:

[0134] The high entropy alloy formed is Fe 50 Ni 50 Mn 30 Al 20 Ti 50 , the rest is the same as Example 1.

[0135] The other steps are the same as those in Example 1.

[0136] The electrodes obtained in the examples and comparative examples were applied to batteries for testing, and the testing method was as follows:

[0137] (1) Energy density test:

[0138] Equipment: Blue Electric Test System (CT-3008), Arbin BT-2000.

[0139] Conditions: Voltage range: 2.5V-4.2V (vs. Li / Li + ); Charge and discharge rate: 0.5C constant current charge and discharge; Temperature: 25±1℃.

[0140] (2) Cycle life test:

[0141] Equipment: Xinwei Battery Testing System (BTS-4000).

[0142] Conditions: Charge and discharge regime: 1C constant current charge to 4.2V, then switch to constant voltage until the current is ≤0.05C; 1C constant current discharge to 2.5V; Temperature: 25±1℃; Cycle termination condition: capacity retention rate drops to 80%.

[0143] (3) Low temperature discharge efficiency test:

[0144] Equipment: High and low temperature test chamber (GDW-100), blue electric test system.

[0145] Steps: Fully charge the battery at 25°C. Move it to -20°C and let it stand for 2 hours. Discharge it at 1C rate to 2.5V and record the discharge capacity ( C low ). Discharge under the same conditions at room temperature (25℃) and record the capacity ( C low ).

[0146] (4) Interface contact resistance test:

[0147] Equipment: four-probe resistance meter (RTS-9), electrochemical workstation (CHI760E).

[0148] Methods: Electrochemical impedance spectroscopy (EIS) was used with a frequency range of 100 kHz to 0.01 Hz and an amplitude of 5 mV. The interfacial contact resistance was extracted by equivalent circuit fitting.

[0149] (5) Thermal stability test:

[0150] Equipment: Differential Scanning Calorimeter (DSC 214 Polyma).

[0151] Conditions: Heating rate: 5°C / min, temperature range: 25°C-400°C. Nitrogen atmosphere (flow rate: 50 mL / min).

[0152] (6) Structural characterization:

[0153] XRD analysis:

[0154] Equipment: X-ray diffractometer (Bruker D8 Advance).

[0155] Parameters: Cu Kα radiation (λ = 1.5406 Å), scan range: 10°–90°, step size: 0.02°.

[0156] SEM / EDS analysis:

[0157] Equipment: Field emission scanning electron microscope (FEI Nova NanoSEM 450) with EDS detector.

[0158] Parameters: accelerating voltage 15 kV, working distance 10 mm.

[0159] (7) Vibration test (mechanical stability):

[0160] Equipment: Electromagnetic vibration test bench (LDS V955).

[0161] Conditions: Frequency range: 20Hz-2000Hz, Acceleration: 5g, Duration: 3 hours.

[0162] (8) Rate performance test:

[0163] Equipment: Arbin BT-2000.

[0164] Steps: Charge and discharge at rates of 0.1C, 0.5C, 1C, 3C, and 5C (voltage range 2.5V-4.2V).

[0165] Results and Analysis:

[0166] Table 1 Electrode test results obtained in Examples and Comparative Examples

[0167]

[0168] The electrodes obtained from Example 1 and Comparative Example 4 were tested, and the test results are shown in Table 1 and Figure 4As shown. From the results in Table 1, it can be found that the electrode with the solid solution obtained by the present invention has better electrical properties and higher thermal runaway temperature than that of Comparative Example 4. In the process of preparing the solid solution, the present invention does not add lithium when preparing the solid solution, but realizes lithium removal and lithium insertion in the solid solution during the charge and discharge process, so as to avoid the delithiation and insertion processes causing damage to the stability of the solid solution structure. The method for preparing the solid solution of the present invention can firstly avoid the formation of a heterogeneous phase (LiFeO2) between lithium and other atoms, thereby reducing the effective active material and leading to a reduction in energy density; secondly, it can avoid the removal of lithium from the solid solution structure during the cycle, the insertion / extraction of lithium ions causing lattice stress concentration, the expansion of cracks in the heterogeneous phase area, and a significant decrease in the cycle performance of the electrode; thirdly, lithium doping increases the interface impedance, thereby reducing the discharge efficiency; fourthly, Li and Fe / Ni generate thermally unstable LiFeO2 and LiNiO2 phases, the formation of which will cause the exothermic reaction to be triggered in advance, thereby reducing the temperature of thermal runaway.

[0169] First, the active material obtained in the present invention is used to realize lithium ion intercalation and deintercalation. Therefore, based on the invention point of the present invention, the active material should have structural stability. However, not all metals can form a solid solution. The formation of the solid solution is attributed to the crystal structure, atomic size and electrochemical properties of the selected substance. Based on comprehensive factors, Fe, Ni, Mn, Al and Ti were selected in the present invention. By comparing Example 1 with Comparative Example 1, it can be found in Table 1 that the cycle performance of Comparative Example 1 is significantly reduced, and its life is only 1200 times, which is significantly lower than that of Example 1. This is because the solid solution lacks Al and Ti. Figure 2 The unit cell parameters of Comparative Example 1 were calculated based on the XRD data, and the lattice distortion energy of the solid solution alloy of Comparative Example 1 was determined (calculated value ≤ 1.2×10 9 J / m 3 ) is insufficient, resulting in stress concentration at the grain boundaries, which accelerates the structural pulverization during the cycle and ultimately causes a decrease in cycle performance. This can also be verified by Comparative Example 2. Although Al is introduced in Comparative Example 2, its rate is significantly reduced due to the lack of Ti. This is because the lack of titanium causes the interface contact resistance between the carbon nanotubes to increase to 0.8Ω·cm 2 , Example 1 is 0.2Ω·cm 2 ,like Figure 1As shown, the rate performance is reduced (the 5C discharge capacity retention rate of Comparative Example 2 is only 65%, while that of Example 1 is 85%). It can be seen that the formation of a solid solution is not possible with any metal. When the selected metal is inappropriate, it cannot form a solid solution, and even if a solid solution is formed, its performance will be reduced. In summary, in the present invention, Fe, Ni, Mn, Al and Ti form a solid solution through the "cocktail" effect, and can form a stable connection with the carbon nanotubes, thereby reducing the interface contact resistance; in addition, the electrode obtained by the present invention also has a higher energy density.

[0170] When selecting atoms that can form a solid solution, it is necessary to further consider how to control the ratio between these atoms to achieve structural stability and facilitate the deintercalation of lithium ions. When the selected ratio is not appropriate, phase separation or local stress concentration may occur in the structure, thereby reducing the cycle performance of the electrode, as shown by the comparison between Example 1 and Comparative Example 5 in Table 1. The solid solution obtained in Example 1 has the largest lattice distortion energy (≥1.8×10 9 J / m 3 ), which can effectively inhibit the lattice expansion caused by lithium insertion / extraction during the cycle, not only suppressing the risk of thermal runaway, but also improving the cycle performance of the electrode.

[0171] Comparative Example 3 uses the same element ratio as Example 1, but does not adopt a gradient pore structure design. Therefore, the electrical performance of the electrode in Comparative Example 3 is significantly lower than that of Example 1. This is because the stepped pore structure of the present invention can improve the infiltration of the electrolyte into the electrode, and the infiltration is more uniform. Therefore, the electrical performance of Example 1 of the present invention is significantly better than that of Comparative Example 3.

[0172] Although the different element ratios in Comparative Example 5 lead to reduced lattice distortion energy, the retained gradient pore structure still improves the electrolyte wetting uniformity compared to Comparative Example 3, and the low-temperature discharge efficiency reaches 85%, close to that of Example 1. This demonstrates that the gradient pore design is beneficial for improving the electrical performance of the electrode of the present invention.

[0173] Figure 3 The SEM images of Example 1 and Comparative Example 1 show that the particles in Comparative Example 1 are unevenly distributed, with significant agglomeration, a uniform pore structure, and a chaotic pore size distribution. The uniform structure and gradient porosity of Example 1 can mitigate the volume expansion caused by lithium ion insertion and extraction, reducing crack formation.

[0174] In summary, Example 1 demonstrates unique advantages in energy density, cycle life, interface stability and wide temperature range adaptability through the precise proportion of the five-element high entropy alloy, gradient pore design and carbon nanotube bonding process.

[0175] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the technical solutions of the embodiments of the present invention.

Claims

1. A distributed cobalt-free high entropy energy storage electrode, characterized in that: The electrode includes an active material coating, which includes an active material and carbon nanotubes; the active material includes a solid solution formed by Fe, Ni, Mn, Al and Ti, and the solid solution is supported in the form of particles inside and on the surface of the carbon nanotubes; The solid solution adopts Fe, Ni, Mn, Al, and Ti to form a five-element high entropy alloy system. In the solid solution, the atomic ratio of iron atoms, nickel atoms, manganese atoms, aluminum atoms, and titanium atoms is 6:4:4:3:

3.

2. The electrode according to claim 1, characterized in that The particle size of the solid solution is 20nm-50nm; The coverage of the solid solution on the carbon nanotubes is 80%-95%; The solid solution has a porous structure with a pore volume of not less than 0.25 cm 3 / g, with a specific surface area of ​​not less than 80m 2 / g; The carbon nanotubes have a length of 1 μm-10 μm and a diameter of 10 nm-30 nm.

3. The electrode according to claim 1, characterized in that The XRD of the solid solution has characteristic diffraction peaks at 15.1°, 17.5° and 23.0° in an X-ray powder diffraction pattern represented by a diffraction angle 2θ.

4. The electrode according to claim 1, characterized in that The active material coating has a porous structure. In the thickness direction, the pore diameter inside the active material coating is larger than the pore diameter in the surface direction of the active material coating.

5. A method for preparing a distributed cobalt-free high entropy energy storage electrode, characterized in that: The preparation method is used to prepare the distributed cobalt-free high-entropy energy storage electrode according to any one of claims 1 to 4, and the preparation method comprises: A chelating agent is added to a mixed solution containing an iron source, a nickel source, a manganese source, an aluminum source and a titanium source, the pH value is adjusted, and a hydrothermal reaction is carried out to obtain a precursor; the precursor and carbon nanotubes are ball-milled; the ball-milled product is subjected to a gradient heat treatment under an inert atmosphere to obtain an intermediate product; and the intermediate product is loaded on the surface of a current collector to obtain an electrode.

6. The preparation method according to claim 5, characterized in that The iron source includes ferric nitrate; the nickel source includes nickel nitrate; the manganese source includes manganese acetate; the aluminum source includes aluminum sulfate; the titanium source includes tetrabutyl titanate; and the complexing agent includes citric acid; The iron source is calculated as iron ions, the nickel source is calculated as nickel ions, the manganese source is calculated as manganese ions, the aluminum source is calculated as aluminum ions, and the titanium source is calculated as titanium ions, and the molar ratio of iron ions, nickel ions, manganese ions, aluminum ions and titanium ions is 6:4:4:3:3; The amount of the complexing agent is 1.2 to 1.8 times the total molar amount of the metal ions in the iron source, nickel source, manganese source, aluminum source and titanium source; The ratio of the precursor to the carbon nanotubes is 7-9:3-1 by mass.

7. The preparation method according to claim 5, characterized in that The temperature of the hydrothermal reaction is 160°C-200°C, and the time of the hydrothermal reaction is 12h-24h; During the ball milling, the ball-to-material ratio is 8-12:1, the rotation speed is 200 rpm-400 rpm, and the ball milling time is 3 h-5 h.

8. The preparation method according to claim 5, characterized in that The gradient heat treatment specifically includes: The first stage: keep warm at 350℃-450℃ for 1h-3h, the second stage: keep warm at 700℃-800℃ for 3h-5h.

9. The preparation method according to claim 5, characterized in that The specific method of loading the intermediate product on the surface of the current collector includes: The intermediate product is mixed with a binder and a solvent, and the mixed slurry is loaded on the surface of the current collector by an electrostatic spraying method.

10. Use of the distributed cobalt-free high entropy energy storage electrode according to any one of claims 1 to 4 in a battery.

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