Modified positive electrode with multi-stage modification structure, preparation method and aqueous secondary battery

Abstract

The invention relates to a modified positive electrode with a multi-stage modification structure, a preparation method and an aqueous secondary battery, and belongs to the technical field of aqueous batteries. Comprising an aqueous secondary battery oxide positive electrode substrate, and an amorphous heterostructure modification layer, a metal-metal oxide composite modification layer and a metal oxide modification layer which are formed by a metal oxide-oxide positive electrode active material and are sequentially arranged from the surface of the substrate, the modified positive electrode is obtained by carrying out radio frequency magnetron sputtering on metal on the surface of an oxide positive electrode substrate and then carrying out natural oxidation. When the modified positive electrode is applied to the aqueous secondary battery, the conductivity of the electrode can be increased, the stability of the positive electrode structure in the circulation process is improved by regulating and controlling the embedding proportion of Zn < 2 + > / H < + >, and an oxide positive electrode and an electrolyte are isolated, so that the effect of inhibiting a positive electrode material from being dissolved in the electrolyte is achieved; and the rate capability and the long cycle stability of the water-based secondary battery are optimized.

Description

Technical Field

[0001] This invention relates to a modified cathode with a multi-level modified structure, its preparation method, and an aqueous secondary battery, belonging to the field of aqueous battery technology. Background Technology

[0002] Global warming and the depletion of fossil fuel resources have spurred global research into sustainable energy conversion and storage technologies to meet foreseeably rapid energy consumption growth. The intermittent nature of renewable energy sources limits energy conversion and transmission efficiency, creating an urgent need for highly efficient, clean, sustainable, and pollution-free energy storage systems. Electrochemical energy storage devices, which convert chemical energy into electrical energy, have significant applications in renewable energy integration, grid frequency regulation, and power quality improvement, and are crucial for achieving renewable energy utilization and dual-carbon goals. In recent years, the application scenarios for electrochemical energy storage devices have been continuously expanding, from small-scale microelectromechanical systems to large-scale energy storage power stations. Energy storage systems profoundly impact a nation's future energy structure and energy security.

[0003] Battery systems are the core of energy storage systems. Lithium-ion batteries have become the most commonly used battery type in current energy storage systems due to their high energy density, long lifespan, and environmental friendliness. However, the uneven distribution of lithium resources and the safety issues caused by thermal runaway of lithium-ion batteries have hindered their application in the field of energy storage. Aqueous secondary batteries are one of the new generation of safe energy storage technologies, which have the following advantages: (1) Abundant resources: The negative electrode metals aluminum, zinc, or calcium are abundant in the earth's crust, widely distributed, and inexpensive; (2) High safety: Aqueous secondary batteries use aqueous electrolytes, which are not flammable and have good safety; (3) Environmentally friendly: The production and recycling process of aqueous secondary batteries has a smaller impact on the environment; (4) High power density: Aqueous secondary batteries can provide high power density, and the high ionic conductivity of aqueous electrolytes can achieve high rate performance, which is suitable for fast charging applications.

[0004] The cathode material plays a decisive role in the operating voltage, capacity, and stability of a battery, and is key to the research of aqueous secondary batteries. Existing cathode materials include manganese-based oxide cathode materials, vanadium-based oxide cathode materials, Prussian blue analogues, and small organic molecule cathodes. Oxide cathode materials have become an ideal choice for aqueous secondary batteries due to their abundant resources, low cost, excellent electrochemical performance, and good compatibility with aqueous electrolytes. Even with these advantages, oxide cathode materials still face some challenges in practical applications, such as poor structural stability and low intrinsic conductivity, which limit their practical application in aqueous secondary batteries. Summary of the Invention

[0005] In view of this, the object of the present invention is to provide a modified cathode with a multi-level modified structure, a preparation method thereof, and an aqueous secondary battery. Applying this modified cathode to an aqueous secondary battery can increase the electrode conductivity by controlling the Zn content. 2+ / H + The embedding ratio improves the stability of the cathode structure during cycling, isolates the oxide cathode from the electrolyte, thereby suppressing the dissolution of cathode materials in the electrolyte and optimizing the rate performance and long-cycle stability of aqueous secondary batteries.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows.

[0007] A modified cathode with a multi-level modification structure includes an aqueous secondary battery oxide cathode substrate and an amorphous heterostructure modification layer, a metal-metal oxide composite modification layer, and a metal oxide modification layer formed by sequentially depositing metal oxide-oxide cathode active materials on the substrate surface. The modified cathode is obtained by radio frequency magnetron sputtering of metal on the surface of the oxide cathode substrate followed by natural oxidation. The metal oxide in the amorphous heterostructure modification layer is an oxide formed by the combination of the metal and oxygen atoms on the surface of the oxide cathode active material. The metal oxides in the metal-metal oxide composite modification layer and the metal oxide modification layer are oxides obtained by natural oxidation of the metal.

[0008] Preferably, the thickness of the oxide cathode substrate is 10–15 μm, the thickness of the amorphous heterostructure modification layer is 8–10 nm, the thickness of the composite modification layer is 10–40 nm, and the thickness of the metal oxide modification layer is 6–10 nm.

[0009] Preferably, the oxide cathode active material includes manganese-based oxides, vanadium-based oxides, and molybdenum-based oxides. More preferably, the oxide cathode matrix includes α-MnO2, β-MnO2, δ-MnO2, MnOOH, V2O5, NaV3O8, and NH4V4O. 10 MoO3.

[0010] Preferably, the metal is one or more of niobium (Nb), aluminum (Al), copper (Cu), molybdenum (Mo), tungsten (W), copper-nickel alloy (Cu-Ni), and gadolinium-iron alloy (Gd-Fe).

[0011] The method for preparing the modified cathode with a multi-level modified structure according to the present invention includes the following steps:

[0012] Under a protective gas atmosphere, metal was used as the target material to deposit on the oxide cathode substrate of an aqueous secondary battery using radio frequency magnetron sputtering. After deposition, the substrate was naturally oxidized to obtain a modified cathode with a multi-level modified structure.

[0013] During radio frequency magnetron sputtering, a vacuum of 1×10⁻⁶ is first applied. -4 The pressure is below Pa, then a protective gas is introduced until the sputtering chamber pressure is 1-5 Pa. The sputtering power is controlled at 30-200 W, the sputtering voltage at 200-300 V, and the coating time at 4-15 min.

[0014] Preferably, the protective gas is nitrogen or an inert gas (a gaseous element corresponding to all group 0 elements in the periodic table, such as argon).

[0015] Preferably, the sputtering chamber pressure is 1-2 Pa; the sputtering power is 50-100 W; the sputtering voltage is 220-250 V; and the coating time is 6-10 min.

[0016] Preferably, the deposition thickness of RF magnetron sputtering is 10–100 nm. More preferably, the deposition thickness of RF magnetron sputtering is 20–30 nm.

[0017] Preferably, the aqueous secondary battery oxide cathode substrate is prepared by the following method: mixing oxide cathode active material, conductive agent and binder to obtain cathode slurry, coating cathode slurry on current collector, and drying to obtain cathode substrate. More preferably, based on the total mass of the positive electrode slurry as 100%, the mass fraction of the oxide positive electrode active material is 70%–85%, the mass fraction of the conductive agent is 10%–20%, and the mass fraction of the binder is 5%–10%; the conductive agent is one or more of acetylene black, carbon fiber (VGCF), carbon nanotubes (CNTs), Ketjenblack, graphene, and conductive carbon black (Super-P); the binder is one or more of polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), and polyvinyl alcohol (PVA); the current collector is nickel foam, copper foam, titanium foam, iron foam, titanium mesh, stainless steel mesh, carbon paper, carbon fiber cloth, tantalum foil (Ta), niobium foil (Nb), or molybdenum foil (Mo); most preferably, the conductive agent is conductive carbon black, the binder is polyvinylidene fluoride, and the current collector is carbon paper (C) or titanium mesh.

[0018] Aqueous secondary battery, wherein the positive electrode of the battery adopts the modified positive electrode with multi-level modification structure described in this invention.

[0019] Preferably, the aqueous secondary battery includes an aqueous zinc metal battery, an aqueous aluminum metal battery, an aqueous iron-ion battery, an aqueous sodium-ion battery, and an aqueous ammonium-ion battery.

[0020] Preferably, the aqueous secondary battery includes a battery casing, a modified positive electrode with a multi-level modified structure as described in this invention, a metal negative electrode, an electrolyte, and a separator. More preferably, the metal negative electrode is a zinc negative electrode, an aluminum negative electrode, or a calcium negative electrode, with a thickness of 50–100 μm and a purity ≥99.99%; the electrolyte is a metal salt with a concentration of 2–3 mol / L, wherein the metal salt is zinc sulfate (ZnSO4), aluminum chloride (AlCl3), or calcium trifluoromethanesulfonate ((CF3SO3)2Ca); and the separator is a glass cellulose membrane (GF / D).

[0021] Beneficial effects

[0022] This invention constructs a multi-level modified interface on the surface of an oxide cathode substrate for aqueous secondary batteries. The outermost metal oxide layer significantly improves conductivity and corrosion resistance; the middle layer is a composite modification layer of metal and metal oxide, which can effectively regulate the metal ion concentration (Zn). 2+ Al 3+ Ca 2+ (etc.) and hydrogen ions (H) + The innermost layer is a modification layer that forms an amorphous heterostructure between the metal and the surface of the positive electrode oxide matrix, enhancing the electrode's reactivity and ion conductivity. This multi-level structure significantly improves the cycle stability of the positive electrode and effectively suppresses the growth of metal dendrites in the battery, thereby extending the battery's lifespan. This structural optimization of the positive electrode provides a new solution for improving the performance of aqueous secondary batteries and has promising application prospects. Attached Figure Description

[0023] Figure 1 The image shown is a scanning electron microscope (SEM) image of the modified cathode with a multi-level modified structure obtained in Example 1.

[0024] Figure 2 The X-ray diffraction (XRD) pattern of the modified cathode with a multi-level modified structure obtained in Example 1;

[0025] Figure 3 The energy spectrum of the modified cathode with multi-level modified structure obtained in Example 1 is shown in the surface energy spectrum scan.

[0026] Figure 4 The image shows a transmission electron microscope (TEM) image of the modified cathode with a multi-level modified structure obtained in Example 1.

[0027] Figure 5 The cyclic voltammetry (CV) curves of the modified positive electrode and the unmodified positive electrode obtained in Example 1 are shown.

[0028] Figure 6 The diagram shows the long-cycle performance of the modified and unmodified positive electrode sheets obtained in Example 1. Detailed Implementation

[0029] The present invention will be further described in detail below with reference to specific embodiments.

[0030] In the following embodiments, a positive electrode sheet is prepared by coating a positive electrode slurry formed from a metal oxide active material, a conductive agent, and a binder onto a positive electrode current collector. The resulting electrode sheet is then treated using radio frequency magnetron sputtering to deposit a thin film of metal atoms or compounds, resulting in a modified positive electrode with a multi-level modified structure. The outermost layer of the multi-level structure is a metal oxide (formed by the natural oxidation of the deposited metal), the middle layer is a composite modification layer of metal and metal oxide, and the innermost layer is a modification layer with an amorphous heterostructure between the metal oxide (formed by the innermost deposited metal and oxygen in the substrate) and the surface of the substrate metal oxide.

[0031] The specific steps of the radio frequency magnetron sputtering method include: attaching the positive electrode to the sample stage, placing it in the vacuum chamber of the sputtering equipment, and connecting it to the ground electrode; fixing the target material in the positive electrode position; starting the vacuum pump, turning on the radio frequency power supply, and applying radio frequency power to the target material; the sputtered metal atoms or molecules are deposited on the surface of the positive electrode to form a uniform thin film. When the desired film thickness is reached, the radio frequency power supply is turned off, the sputtering process is stopped, the deposited film is removed, and natural oxidation is performed to obtain the modified positive electrode.

[0032] In this invention, the oxide cathode includes manganese-based oxide cathodes (α-MnO2, β-MnO2, δ-MnO2, MnOOH) and vanadium-based oxide cathodes (V2O5, Na). x V3O8, NH4V4O 10 At least one of the following: molybdenum-based oxide cathode (MoO3).

[0033] In this invention, a radio frequency magnetron-controlled positive electrode target is provided as the initial component of the coating. The target is selected from at least one of niobium (Nb), aluminum (Al), copper (Cu), molybdenum (Mo), tungsten (W), copper-nickel alloy (Cu-Ni), and gadolinium-iron alloy (Gd-Fe). Preferably, the positive electrode target is an Nb target and an Al target.

[0034] In this invention, the specific reaction conditions for depositing a protective layer on the positive electrode surface using radio frequency magnetron sputtering can be as follows: the sputtering atmosphere is argon or nitrogen, the sputtering chamber pressure is 1–5 Pa, the sputtering power is 30–200 W, the sputtering voltage is 200–300 V, and the thickness of the deposited metal layer is 10–100 nm. Preferably, the specific reaction conditions for depositing a protective layer on the positive electrode surface using radio frequency magnetron sputtering are as follows: the sputtering atmosphere is argon, the sputtering chamber pressure is 1–2 Pa, the sputtering power is 50–100 W, the sputtering voltage is 220–250 V, and the thickness of the deposited metal layer is 20–30 nm.

[0035] In this invention, the positive electrode slurry comprises a positive electrode active material, a conductive agent, and a binder. Based on the total mass of the positive electrode slurry as 100%, the mass fraction of the positive electrode active material is 70% to 85%, the mass fraction of the conductive agent is 10% to 20%, and the mass fraction of the binder is 5% to 10%.

[0036] In this invention, the positive electrode current collector can be one of the following: nickel foam, copper foam, titanium foam, iron foam, stainless steel mesh, carbon paper, carbon fiber cloth, tantalum foil (Ta), niobium foil (Nb), or molybdenum foil (Mo). Preferably, the positive electrode current collector is carbon paper (C) or titanium mesh (Ti).

[0037] In this invention, the conductive agent is selected from at least one of acetylene black, carbon fiber (VGCF), carbon nanotubes (CNTs), Ketjenblack, graphene, and conductive carbon black (Super-P). Preferably, the conductive agent is conductive carbon black (Super-P).

[0038] In this invention, the adhesive is selected from at least one of polyvinylidene fluoride (PVDF), polyvinylpyrrolidone (PVP), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), polytetrafluoroethylene (PTFE), and polyvinyl alcohol (PVA). Preferably, the adhesive is polyvinylidene fluoride (PVDF).

[0039] The present invention also provides an aqueous secondary battery based on the above-mentioned electrode, the battery comprising a battery casing, a modified positive electrode, a zinc negative electrode, an electrolyte, and a separator.

[0040] In this invention, the metal anode includes one of zinc anode, aluminum anode, and calcium anode, preferably with a thickness of 50-100 μm and a purity of ≥99.99%.

[0041] In this invention, the electrolyte is a 2-3 mol / L metal salt, which is one of zinc sulfate (ZnSO4), aluminum chloride (AlCl3), calcium trifluoromethanesulfonate ((CF3SO3)2Ca), etc., and is specifically selected according to the battery type.

[0042] In this invention, the membrane material can be PE membrane (polyethylene), PP membrane (polypropylene), glass fiber membrane, non-woven membrane, etc., and preferably glass cellulose membrane (GF / D).

[0043] Example 1

[0044] First, 2 mmol of KMnO4 was completely dissolved in 55 mL of deionized water and magnetically stirred for 10 min. After complete dissolution, solution A was obtained. 0.83 mL of HCl was added dropwise, and the mixture was thoroughly mixed to obtain solution B. Solution B was transferred to a 100 mL polytetrafluoroethylene (PTFE) high-pressure reactor. The reactor was sealed, and the reaction was carried out hydrothermally at 140 °C for 12 h. After cooling to room temperature, the brown reaction product was collected using a centrifuge. Subsequently, the product was repeatedly washed several times with deionized water. Finally, it was dried at 80 °C for 12 h, and the dried material was collected to obtain α-MnO2-1.

[0045] The prepared α-MnO2-1, Super P, and PVDF were weighed at a mass ratio of 7:2:1 and placed in a 5 mL isotope bottle. An appropriate amount of NMP solvent was added, and the mixture was stirred with a magnetic stirrer for 24 h to prepare a homogeneous slurry. The homogeneous slurry was then drop-coated onto 11 mm diameter hydrophilic carbon paper using a pipette and dried in a vacuum oven at 80 °C for 12 h to prepare a positive electrode. The positive electrode was attached to the sample stage, placed in the vacuum chamber of the sputtering equipment, and connected to the ground electrode. The Nb target was fixed at the positive electrode position. The vacuum pump was started, the sputtering atmosphere was argon, the sputtering chamber pressure was 1 Pa, the sputtering power was 50 W, and the sputtering voltage was 220 V. The sputtered Nb atoms were deposited on the surface of the positive electrode, forming a uniform metal film. When the sputtering process reaches 20nm, the RF power supply is turned off, the metal film-coated positive electrode is removed, and it is naturally oxidized to obtain a modified positive electrode with a multi-level modified structure, denoted as Nb@MnO2-1.

[0046] The positive electrode used in this embodiment is Nb@MnO2-1, the negative electrode is zinc foil with a thickness of 100 μm, the separator is glass cellulose membrane (GF-D), and the electrolyte is 2 mol / L ZnSO4 + 0.1 mol / L MnSO4, with an electrolyte addition of 150 μL. This was used to assemble a CR2025 experimental button battery. The assembled aqueous zinc-ion battery was placed in a 30°C constant temperature chamber and allowed to stand for 12 hours before being subjected to constant current charge-discharge testing on a LAND CT2001A tester at a charge-discharge current density of 200 mA / g.

[0047] Example 2

[0048] First, 1 mmol of KMnO4 was completely dissolved in 55 mL of deionized water and magnetically stirred for 10 min. After complete dissolution, solution A was obtained. 0.83 mL of HCl was added dropwise, and the mixture was thoroughly mixed to obtain solution B. Solution B was transferred to a 100 mL polytetrafluoroethylene (PTFE) high-pressure reactor. The reactor was sealed, and the reaction was carried out hydrothermally at 140 °C for 12 h. After cooling to room temperature, the brown reaction product was collected using a centrifuge. Subsequently, the product was repeatedly washed several times with deionized water. Finally, it was dried at 80 °C for 12 h, and the dried material was collected to obtain α-MnO2-.

[0049] The prepared α-MnO2-2, Super P, and PVDF were weighed at a mass ratio of 7:2:1 and placed in a 5 mL isotope bottle. An appropriate amount of NMP solvent was added, and the mixture was stirred with a magnetic stirrer for 24 h to prepare a homogeneous slurry. The homogeneous slurry was then drop-coated onto 11 mm diameter hydrophilic carbon paper using a pipette and dried in a vacuum drying oven at 80 °C for 12 h to prepare a positive electrode. The positive electrode was attached to the sample stage, placed in the vacuum chamber of the sputtering equipment, and connected to the ground electrode. The Nb target was fixed at the positive electrode position. The vacuum pump was started, the sputtering atmosphere was argon, the sputtering chamber pressure was 1 Pa, the sputtering power was 50 W, and the sputtering voltage was 220 V. The sputtered Nb atoms were deposited on the surface of the positive electrode, forming a uniform metal film. When the sputtering process reaches 20nm, the RF power supply is turned off, the metal film-coated positive electrode is removed, and it is naturally oxidized to obtain a modified positive electrode with a multi-level modified structure, denoted as Nb@MnO2-2.

[0050] The positive electrode sheet used in this embodiment is Nb@MnO2-2, and the rest is the same as in Example 1. The CR2025 experimental button cell is then assembled.

[0051] Example 3

[0052] First, 4 mmol of KMnO4 was completely dissolved in 55 mL of deionized water and magnetically stirred for 10 min. After complete dissolution, solution A was obtained. 0.83 mL of HCl was added dropwise, and the mixture was thoroughly mixed to obtain solution B. Solution B was transferred to a 100 mL polytetrafluoroethylene (PTFE) high-pressure reactor. The reactor was sealed, and the reaction was carried out hydrothermally at 140 °C for 12 h. After cooling to room temperature, the brown reaction product was collected using a centrifuge. Subsequently, the product was repeatedly washed several times with deionized water. Finally, it was dried at 80 °C for 12 h, and the dried material was collected to obtain α-MnO2-3.

[0053] The prepared α-MnO2-3, Super P, and PVDF were weighed at a mass ratio of 7:2:1 and placed in a 5 mL isotope bottle. An appropriate amount of NMP solvent was added, and the mixture was stirred with a magnetic stirrer for 24 h to prepare a homogeneous slurry. The homogeneous slurry was then drop-coated onto 11 mm diameter hydrophilic carbon paper using a pipette and dried in a vacuum drying oven at 80 °C for 12 h to prepare a positive electrode. The positive electrode was attached to the sample stage, placed in the vacuum chamber of the sputtering equipment, and connected to the ground electrode. The Nb target was fixed at the positive electrode position. The vacuum pump was started, the sputtering atmosphere was argon, the sputtering chamber pressure was 1 Pa, the sputtering power was 50 W, and the sputtering voltage was 220 V. The sputtered Nb atoms were deposited on the surface of the positive electrode, forming a uniform metal film. When the sputtering process reaches 20nm, the RF power supply is turned off, the metal film-coated positive electrode is removed, and it is naturally oxidized to obtain a modified positive electrode with a multi-level modified structure, denoted as Nb@MnO2-3.

[0054] The positive electrode sheet used in this embodiment is Nb@MnO2-3, and the rest is the same as in Example 1. The CR2025 experimental button cell is then assembled.

[0055] Example 4

[0056] First, 2 mmol of KMnO4 was completely dissolved in 55 mL of deionized water and magnetically stirred for 10 min. After complete dissolution, solution A was obtained. 0.83 mL of HCl was added dropwise, and the mixture was thoroughly mixed to obtain solution B. Solution B was transferred to a 100 mL polytetrafluoroethylene (PTFE) high-pressure reactor. The reactor was sealed, and the reaction was carried out hydrothermally at 140 °C for 12 h. After cooling to room temperature, the brown reaction product was collected using a centrifuge. Subsequently, the product was repeatedly washed several times with deionized water. Finally, it was dried at 80 °C for 12 h, and the dried material was collected to obtain α-MnO2-1.

[0057] The prepared α-MnO2-6, Super P, and PVDF were weighed at a mass ratio of 7:2:1 and placed in a 5 mL isotope bottle. An appropriate amount of NMP solvent was added, and the mixture was stirred with a magnetic stirrer for 24 h to prepare a homogeneous slurry. The homogeneous slurry was then drop-coated onto 11 mm diameter hydrophilic carbon paper using a pipette and dried in a vacuum oven at 80 °C for 12 h to prepare a positive electrode. The positive electrode was attached to the sample stage, placed in the vacuum chamber of the sputtering equipment, and connected to the ground electrode. The Al metal target was fixed at the positive electrode position. The vacuum pump was started, the sputtering atmosphere was argon, the sputtering chamber pressure was 1 Pa, the sputtering power was 50 W, and the sputtering voltage was 220 V. The sputtered Al atoms were deposited on the surface of the positive electrode, forming a uniform metal film. When the sputtering process reaches 20nm, the RF power supply is turned off, the metal film-coated positive electrode is removed, and it is naturally oxidized to obtain a modified positive electrode with a multi-level modified structure, denoted as Al@MnO2-1.

[0058] The positive electrode sheet used in this embodiment is Al@MnO2-1, and the rest is the same as in Example 1. The CR2025 experimental button cell is then assembled.

[0059] Example 5

[0060] First, 2 mmol of KMnO4 was completely dissolved in 55 mL of deionized water and magnetically stirred for 10 min. After complete dissolution, solution A was obtained. 0.83 mL of HCl was added dropwise, and the mixture was thoroughly mixed to obtain solution B. Solution B was transferred to a 100 mL polytetrafluoroethylene (PTFE) high-pressure reactor. The reactor was sealed, and the reaction was carried out hydrothermally at 140 °C for 12 h. After cooling to room temperature, the brown reaction product was collected using a centrifuge. Subsequently, the product was repeatedly washed several times with deionized water. Finally, it was dried at 80 °C for 12 h, and the dried material was collected to obtain α-MnO2-1.

[0061] The prepared α-MnO2-1, Super P, and PVDF were weighed at a mass ratio of 7:2:1 and placed in a 5 mL isotope bottle. An appropriate amount of NMP solvent was added, and the mixture was stirred with a magnetic stirrer for 24 h to prepare a homogeneous slurry. The homogeneous slurry was then drop-coated onto 11 mm diameter hydrophilic carbon paper using a pipette and dried in a vacuum oven at 80 °C for 12 h to prepare a positive electrode. The positive electrode was attached to the sample stage, placed in the vacuum chamber of the sputtering equipment, and connected to the ground electrode. A W metal target was fixed at the positive electrode position. The vacuum pump was started, the sputtering atmosphere was argon, the sputtering chamber pressure was 1 Pa, the sputtering power was 50 W, and the sputtering voltage was 300 V. The sputtered W atoms were deposited on the surface of the positive electrode, forming a uniform metal film. When the sputtering process reaches 20nm, the RF power supply is turned off, the metal film-coated positive electrode is removed, and it is naturally oxidized to obtain a modified positive electrode with a multi-level modified structure, denoted as W@MnO2-1.

[0062] The positive electrode sheet used in this embodiment is W@MnO2-1, and the rest is the same as in Embodiment 1. The CR2025 experimental button cell is then assembled.

[0063] Example 6

[0064] First, 2 mmol of KMnO4 was completely dissolved in 55 mL of deionized water and magnetically stirred for 10 min. After complete dissolution, solution A was obtained. 0.83 mL of HCl was added dropwise, and the mixture was thoroughly mixed to obtain solution B. Solution B was transferred to a 100 mL polytetrafluoroethylene (PTFE) high-pressure reactor. The reactor was sealed, and the reaction was carried out hydrothermally at 140 °C for 12 h. After cooling to room temperature, the brown reaction product was collected using a centrifuge. Subsequently, the product was repeatedly washed several times with deionized water. Finally, it was dried at 80 °C for 12 h, and the dried material was collected to obtain α-MnO2-1.

[0065] The prepared α-MnO2-1, Super P, and PVDF were weighed at a mass ratio of 7:2:1 and placed in a 5 mL isotope bottle. An appropriate amount of NMP solvent was added, and the mixture was stirred with a magnetic stirrer for 24 h to prepare a homogeneous slurry. The homogeneous slurry was then drop-coated onto 11 mm diameter hydrophilic carbon paper using a pipette and dried in a vacuum oven at 80 °C for 12 h to prepare a positive electrode. The positive electrode was attached to the sample stage, placed in the vacuum chamber of the sputtering equipment, and connected to the ground electrode. The Nb target was fixed at the positive electrode position. The vacuum pump was started, the sputtering atmosphere was argon, the sputtering chamber pressure was 1 Pa, the sputtering power was 100 W, and the sputtering voltage was 220 V. The sputtered Nb atoms were deposited on the surface of the positive electrode, forming a uniform metal film. When the sputtering process reaches 20nm, the RF power supply is turned off, the metal film-coated positive electrode is removed, and it is naturally oxidized to obtain a modified positive electrode with a multi-level modified structure, denoted as Nb@MnO2-4.

[0066] The positive electrode sheet used in this embodiment is Nb@MnO2-4, and the rest is the same as in Example 1. The CR2025 experimental button cell is then assembled.

[0067] Example 7

[0068] In this embodiment, the electrolyte was selected as 2 mol / L ZnSO4 + 0.1 mol / L MnSO4, the electrolyte addition was 300 μL, and the rest was the same as in Example 1, and the CR2025 experimental button cell was assembled.

[0069] Example 8

[0070] In this embodiment, the electrolyte was selected as 2 mol / L ZnSO4 + 0.1 mol / L MnSO4, the electrolyte addition was 300 μL, and the rest was the same as in Example 6, and the CR2025 experimental button cell was assembled.

[0071] Comparative Example 1

[0072] In this comparative example, the positive electrode is α-MnO2-1 prepared in Example 1, and the rest is the same as in Example 1. The CR2025 experimental button cell was assembled.

[0073] The relevant performance tests of the batteries assembled in the above embodiments and comparative examples are shown in Table 1 below.

[0074] Table 1

[0075]

[0076] pass Figure 1The SEM results show that the modified positive electrode sheet with a multi-layer modified structure proposed in this invention has a more uniform surface. This indicates that the modification layer deposited by magnetron sputtering effectively covers the positive electrode sheet, potentially improving the overall contact of the electrode. The uniform surface structure helps to improve the conductivity and reactivity of the electrode, resulting in a more uniform current distribution during charging and discharging.

[0077] pass Figure 2 The XRD patterns show that the crystal structure of the modified cathode sheet did not change significantly, indicating that metal deposition may not have led to the formation of a new phase. The basic crystal structure of the manganese-based material remains stable, which is beneficial for maintaining its original electrochemical properties. Niobium deposition mainly enhances material performance by improving surface properties and interfacial contact, rather than changing its crystal phase. The modification layer improves battery performance by enhancing conductivity and reactivity.

[0078] pass Figure 3 The EDS results show a uniform distribution of metal elements, indicating that the modification layer deposited by magnetron sputtering successfully covered the surface of the manganese-based material. This uniformity is crucial for improving electrode performance. Its uniform distribution can improve electrode conductivity, promote uniform current flow, and enhance the efficiency of electrochemical reactions. The uniform modification layer optimizes the contact between the positive electrode and the electrolyte, which helps to improve the reaction rate during charge and discharge processes.

[0079] pass Figure 4 TEM images show that the modified layers exhibit a distinct multi-level structure (① represents the outermost naturally oxidized metal oxide modified layer, ② represents the metal-metal oxide composite modified layer, and ③ represents the amorphous heterostructure modified layer formed by the metal oxide-oxide cathode active material). This indicates a hierarchical distribution and morphology of the modified layers, which contributes to the electrochemical performance of the electrode. The outermost metal oxide layer isolates the cathode material from the electrolyte, preventing electrolyte corrosion of the cathode material and inhibiting manganese dissolution from the cathode material. The intermediate layers are composed of different phases or microstructures, affecting the migration rates of zinc ions and protons. Due to the different radii and charges of zinc ions and protons, their migration barriers within the material also differ. The innermost layer clearly exhibits an amorphous structure, and the interface with the manganese-based material promotes rapid electron conduction, reduces contact resistance, and thus improves the overall battery performance. The amorphous composition provides more active sites on the electrode surface, enabling rapid ion adsorption and desorption. By optimizing the interfacial chemistry and structural properties, the pseudocapacitive effect can be further enhanced.

[0080] pass Figure 5The CV curve results show that the peak intensities for zinc ion and proton intercalation are inconsistent, reflecting the difference in their behavior within the electrode material. The modified cathode with the addition of the modification layer exhibits a significantly enhanced proton intercalation electrochemical response. Zinc ion intercalation typically involves a larger ionic radius and higher charge, leading to a higher energy barrier. In contrast, proton migration within the structure is relatively rapid.

[0081] pass Figure 6 The medium-to-long-term cycling performance graph shows the performance changes of modified and unmodified positive electrode sheets during long-term cycling. The modified electrode sheet can still maintain high capacity and stable cycling after multiple cycles, indicating that the introduction of multi-level modification layers enhances the stability and cycle life of the electrode and reduces material degradation.

[0082] As shown in Table 1, the aqueous secondary battery of this invention exhibits high discharge specific capacity and good cycle stability. In the embodiments, by adjusting the magnetron sputtering power and sputtering time, the characteristics of the modified layer were improved, thereby enhancing the conductivity and ion conductivity of the electrode material. Compared with Comparative Example 1, which did not employ the technical solution of this invention, the manganese-based modified cathode proposed in this invention achieves significant progress in discharge specific capacity and cycle stability of the aqueous secondary battery by improving conductivity and ion migration. This design concept provides a strong reference for the future optimization of battery materials.

[0083] In summary, the invention includes, but is not limited to, the above embodiments. Any equivalent substitutions or partial improvements made under the spirit and principles of this invention shall be considered to be within the protection scope of this invention.

Claims

1. A modified cathode with a multi-level modified structure, characterized in that: The modified cathode comprises an oxide cathode substrate for an aqueous secondary battery and an amorphous heterostructure modification layer, a metal-metal oxide composite modification layer, and a metal oxide modification layer formed by sequentially depositing metal oxide-oxide cathode active materials on the surface of the substrate. The modified cathode is obtained by radio frequency magnetron sputtering of metal onto the surface of the oxide cathode substrate followed by natural oxidation. The metal oxide in the amorphous heterostructure modification layer is an oxide formed by the combination of the metal and oxygen atoms on the surface of the oxide cathode active material. The metal oxide in the metal-metal oxide composite modification layer and the metal oxide modification layer is an oxide obtained by natural oxidation of the metal.

2. The modified cathode with a multi-level modified structure as described in claim 1, characterized in that: The oxide cathode substrate has a thickness of 10–15 μm, the amorphous heterostructure modification layer has a thickness of 8–10 nm, the composite modification layer has a thickness of 10–40 nm, and the metal oxide modification layer has a thickness of 6–10 nm.

3. The modified cathode with a multi-level modified structure as described in claim 1 or 2, characterized in that: The oxide cathode active material includes manganese-based oxides, vanadium-based oxides, and molybdenum-based oxides; preferably, the oxide cathode matrix includes α-MnO2, β-MnO2, δ-MnO2, MnOOH, V2O5, NaV3O8, and NH4V4O. 10 MoO3.

4. The modified cathode with a multi-level modified structure as described in claim 1 or 2, characterized in that: The metal is one or more of niobium, aluminum, copper, molybdenum, tungsten, copper-nickel alloys, and gadolinium-iron alloys.

5. A method for preparing a modified cathode with a multi-level modified structure as described in any one of claims 1 to 4, characterized in that: The method steps include: Under a protective gas atmosphere, metal was used as the target material to deposit on the oxide cathode substrate of an aqueous secondary battery using radio frequency magnetron sputtering. After deposition, the substrate was naturally oxidized to obtain a modified cathode with a multi-level modified structure. During radio frequency magnetron sputtering, a vacuum of 1×10⁻⁶ is first applied. -4 The pressure is below Pa, then a protective gas is introduced until the sputtering chamber pressure is 1-5 Pa. The sputtering power is controlled at 30-200 W, the sputtering voltage at 200-300 V, and the coating time at 4-15 min.

6. The method for preparing a modified cathode with a multi-level modified structure as described in claim 5, characterized in that: The protective gas is nitrogen or an inert gas; The sputtering chamber pressure is 1–2 Pa; the sputtering power is 50–100 W; the sputtering voltage is 220–250 V; and the coating time is 6–10 min. The deposition thickness of radio frequency magnetron sputtering is 10–100 nm; preferably, the deposition thickness of radio frequency magnetron sputtering is 20–30 nm.

7. The method for preparing a modified cathode with a multi-level modified structure as described in claim 5, characterized in that: The aqueous secondary battery oxide cathode substrate is prepared by the following method: mixing oxide cathode active material, conductive agent, and binder to obtain cathode slurry; coating the cathode slurry onto a current collector; and drying to obtain the cathode substrate. Preferably, based on the total mass of the cathode slurry (100%), the mass fraction of oxide cathode active material is 70%–85%, the mass fraction of conductive agent is 10%–20%, and the mass fraction of binder is 5%–10%. The conductive agent is one or more of acetylene black, carbon fiber, carbon nanotubes, Ketjen black, graphene, and conductive carbon black. The binder is one or more of polyvinylidene fluoride, polyvinylpyrrolidone, sodium hydroxymethyl cellulose, styrene-butadiene rubber, polyacrylic acid, polytetrafluoroethylene, and polyvinyl alcohol. The current collector is nickel foam, copper foam, titanium foam, iron foam, titanium mesh, stainless steel mesh, carbon paper, carbon fiber cloth, tantalum foil, niobium foil, or molybdenum foil. Preferably, the conductive agent is conductive carbon black, the binder is polyvinylidene fluoride, and the current collector is carbon paper or titanium mesh.

8. An aqueous secondary battery, characterized in that: The positive electrode of the battery adopts the modified positive electrode with a multi-level modification structure as described in any one of claims 1 to 4.

9. The aqueous secondary battery as described in claim 8, characterized in that: The aqueous secondary batteries include aqueous zinc metal batteries, aqueous aluminum metal batteries, aqueous iron-ion batteries, aqueous sodium-ion batteries, and aqueous ammonium-ion batteries.

10. The aqueous secondary battery as described in claim 8, characterized in that: The aqueous secondary battery further includes a battery casing, a metal negative electrode, an electrolyte, and a separator; the metal negative electrode is a zinc metal negative electrode, an aluminum metal negative electrode, or a calcium metal negative electrode, with a thickness of 50-100 μm and a purity ≥99.99%; the electrolyte is a metal salt with a concentration of 2-3 mol / L, and the metal salt is zinc sulfate, aluminum chloride, or calcium trifluoromethanesulfonate; the separator is a glass cellulose separator.

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