Battery cell, method for producing the same, battery device, electric device, and energy storage device
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- ZHEJIANG JINKO ENERGY STORAGE CO LTD
- Filing Date
- 2026-01-29
- Publication Date
- 2026-06-23
Smart Images
Figure CN121688145B_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of batteries, and in particular to a battery cell and its preparation method, a battery device, an electrical device, and an energy storage device. Background Technology
[0002] With the rapid development of the electric vehicle industry and the ever-increasing performance demands of consumer electronics devices, lithium-ion batteries are evolving towards higher energy density and longer cycle life. High-nickel ternary cathode materials are favored due to their high specific capacity (>200 mAh·g). -1 With its high efficiency and relatively low cost, it has become the mainstream technology for power batteries and high-end consumer batteries. Against this backdrop, the development and application of ultra-high nickel cathode materials such as NCM811 and NCM9055 have attracted widespread attention from the industry.
[0003] High-nickel ternary cathode materials increase specific capacity and energy density by increasing nickel content, while reducing dependence on the scarce element cobalt. These materials can fully utilize their capacity advantages when operating at high voltages of 4.3V to 4.5V. However, the introduction of high nickel content also brings new technical challenges, particularly in terms of interface stability, thermal stability, and cycle stability.
[0004] The development of high-nickel cathode material technology currently faces multiple challenges. On the one hand, high-voltage operating conditions place higher demands on electrolyte stability; on the other hand, the enhanced surface chemical activity of high-nickel materials makes them prone to side reactions with the electrolyte. Solving these problems is crucial for the commercial application of high-energy-density lithium-ion batteries. Therefore, developing effective high-nickel cathode interface protection technologies has become an important research direction in the field of battery materials. Summary of the Invention
[0005] This application provides a battery cell and its preparation method, battery device, power supply device and energy storage device, which at least help to improve the effect of transition metal dissolution suppression and high voltage cycle life.
[0006] In a first aspect, this application provides a method for preparing a battery cell, comprising:
[0007] A battery cell assembly is provided, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet;
[0008] A housing is provided to house the battery cell assembly within the housing;
[0009] Provide electrolyte and inject the electrolyte into the housing;
[0010] Perform the formation step;
[0011] The positive electrode sheet includes a positive electrode active component, which includes a substrate and a first coating and a second coating sequentially covering the substrate. The first coating is a metal-organic framework coating, and the second coating is a synergistic sealing and protective layer. The substrate is made of a high-nickel ternary positive electrode material.
[0012] Optionally, the high-nickel ternary cathode material includes a lithium transition metal composite oxide, wherein the general formula of the lithium transition metal composite oxide is LiNi. x Co y M z O2, wherein M includes one or more of Mn, Al, Mg, Ti, Zr, W, Mo, Nb, Ta, V, Cr, B, Si, Sn, Ga, Fe, Y, La, Ce, Pr, Nd, and Sm; 0.6 ≤ x < 1.0, x + y + z = 1.
[0013] Of course, this application can also be applied to other ternary cathode materials with different nickel contents, such as those with the general formula LiNi. x Co y M z In O2, 0.3≤x<1.0, x+y+z=1.
[0014] Optionally, the high-nickel ternary cathode material may be in the form of polycrystalline particles or single-crystal particles.
[0015] Optionally, the primary particle size D50 of the polycrystalline particles is 0.05μm~5μm, and the secondary particle size D50 is 1μm~30μm; the particle size D50 of the single crystal particles is 0.5μm~15μm.
[0016] Optionally, the specific surface area of the substrate is 0.05 m². 2 / g~10m 2 / g, tap density is 1.0g / cm³ 3 ~4.0g / cm 3 .
[0017] Optionally, the electronic conductivity of the metal-organic framework coating is not less than 10. -10 S / cm, with a thickness of 0.5nm~5000nm, relative to Li / Li + The reference electrode has an oxidation potential of 3.8V to 6.0V, and the metal-organic framework coating has channels with a pore size of 0.1nm to 20nm and a BET specific surface area of 1m². 2 / g~10000m 2 / g, the pore volume of the channel is 0.001m. 3 / g~5.0m 3 / g.
[0018] Optionally, the preparation method of the metal-organic framework coating includes at least one of the following: solvothermal method, continuous ion layer adsorption method, electrochemical deposition method, microwave method, and ultrasonic method.
[0019] Optionally, the solvothermal method includes:
[0020] The matrix, metal precursor and organic ligand are dispersed in a solvent, and the pH is adjusted to 2-12 to obtain the reaction solution.
[0021] After reacting the reaction solution at 60℃~200℃, a metal-organic framework coating is applied to the substrate surface.
[0022] Optionally, the solvent includes at least one of water, ethanol, methanol, isopropanol, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).
[0023] Optionally, in the reaction solution, the concentration of the metal precursor is 0.00001 mol / L to 5.0 mol / L, the molar ratio of the metal precursor to the organic ligand is 1:(0.1~10), and the concentration of the matrix in the reaction solution is 0.01 g / mL to 0.1 g / mL.
[0024] Optionally, the continuous ion layer adsorption method includes:
[0025] The matrix is immersed in one of the metal precursor solution and the organic ligand solution for 10 s to 60 min, then washed with solvent for 10 s to 30 min. Then the matrix is immersed in the other of the metal precursor solution and the organic ligand solution for 10 s to 60 min. This is recorded as one cycle. The cycle is repeated 2 to 100 times.
[0026] Optionally, the electrochemical deposition method includes:
[0027] In a solution containing a metal precursor and an organic ligand, deposition is performed using the substrate as the working electrode and employing a constant potential or constant current method, wherein the constant current is 0.001 mA / cm². 2 ~10mA / cm 2 Compared to Li / Li + The reference electrode has a constant potential of 3.0V to 6.0V.
[0028] Optionally, in the microwave method, the microwave power is 50W~1000W, the temperature is 50℃~200℃, and the duration is 1min~6h; in the ultrasonic method, the ultrasonic power is 20W~1000W, the frequency is 20kHz~100kHz, and the duration is 10min~12h.
[0029] Optionally, in the metal precursor, the metal has a variable valence state and can form a coordination structure with organic ligands.
[0030] Optionally, the metal includes at least one of the main group metals, the first transition metal series, the second transition metal series, the third transition metal series, the main group metal series, and the lanthanide metal series.
[0031] Optionally, the first transition metal series includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn; the second transition metal series includes at least one of Zr, Nb, Mo, Ru, Rh, Pd, Ag, and Cd; the third transition metal series includes at least one of Hf, Ta, W, Re, Os, Ir, Pt, Au, and Hg; the main group metal series includes at least one of Al, Ga, In, Sn, Pb, and Bi; and the lanthanide metal series includes at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
[0032] Optionally, the organic ligand includes a redox-active ligand or a conductive ligand.
[0033] Optionally, the redox-active ligand includes at least one of sulfur-containing heterocyclic compounds, quinone compounds, aromatic amine compounds, nitrogen-containing heterocyclic compounds, phenothiazine compounds, phenotoxazine compounds, and ferrocene compounds; the conductive ligand includes at least one of hexasubstituted benzene compounds and tetracyanoquinone dimethane compounds.
[0034] Optionally, the method for forming the synergistic sealing protective layer includes powder pre-sealing and / or electrochemical in-situ sealing.
[0035] Optionally, the powder pre-sealing method includes chemical oxidation sealing or physical sealing.
[0036] Optionally, the chemical oxidation sealing method includes:
[0037] A substrate coated with a metal-organic framework is dispersed in a sealing precursor solution containing a sealing precursor and an oxidant, and the reaction is carried out at 20°C to 80°C to form a synergistic protective layer on the surface of the metal-organic framework coating.
[0038] Optionally, the concentration of the sealing precursor in the sealing precursor solution is 0.1wt%~5wt%, and the molar ratio of the oxidant to the sealing precursor is (0.5~5):1.
[0039] Optionally, the sealing precursor includes at least one of TEMPO compounds, triphenylamine compounds, phenothiazine compounds, and ferrocene compounds; the oxidant includes at least one of persulfate, permanganate, and peroxide.
[0040] Optionally, the physical sealing method includes plasma treatment, atomic layer deposition, chemical vapor deposition, or ultraviolet / ozone treatment.
[0041] Optionally, in the plasma treatment, the ionizing gas includes at least one of oxygen, nitrogen, and argon, the plasma power is 10W~500W, the pressure is 0.1Pa~100Pa, and the treatment time is 10s~10min; in the atomic layer deposition method, the number of cycles is controlled to be 1~20 times.
[0042] Optionally, the electrochemical in-situ sealing method includes:
[0043] A sealing precursor is added to the electrolyte to form the synergistic protective layer in situ during the first charge and discharge of the battery cell. The concentration of the sealing precursor in the electrolyte is 0.001wt%~15wt%.
[0044] Optionally, an interface anchoring layer is also provided between the substrate and the metal-organic framework coating.
[0045] Optionally, the thickness of the interface anchoring layer is 0.5 nm to 50 nm.
[0046] Optionally, the material of the interface anchoring layer includes at least one of inorganic fluorides, inorganic phosphates, inorganic borates, inorganic oxides, organosilane coupling agents, and conductive polymers.
[0047] Optionally, the inorganic fluoride includes at least one of LiF, MgF2, AlF3, and LaF3; the inorganic phosphate includes at least one of Li3PO4, AlPO4, and FePO4; the inorganic borate includes at least one of Li3BO3 and LiBO2; and the inorganic oxide includes at least one of Al2O3, TiO2, ZrO2, and SiO2.
[0048] Secondly, this application provides a single battery cell, comprising:
[0049] A battery cell assembly, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet;
[0050] The housing, in which the battery cell assembly is located;
[0051] An electrolyte is provided, located within the housing, and the battery cell assembly is immersed in the electrolyte.
[0052] The positive electrode sheet includes a positive electrode active component, which includes a substrate and a first coating and a second coating sequentially covering the substrate. The first coating is a metal-organic framework coating, and the second coating is a synergistic sealing and protective layer. The substrate is made of a high-nickel ternary positive electrode material.
[0053] Thirdly, this application provides a battery device including a single battery cell as described above, wherein the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.
[0054] Fourthly, this application provides an electrical device, which includes a battery device as described above, the battery device being used to provide electrical energy.
[0055] Fifthly, this application provides an energy storage device, which includes the aforementioned battery device for storing electrical energy.
[0056] The energy storage device includes a battery pack, which includes multiple batteries, an energy management system (EMS), a battery management system (BMS), and an energy storage converter (PCS). The electrical devices include vehicles, household appliances, electric motors, medical equipment, scientific instruments, and power grids.
[0057] The technical solution provided in this application has at least the following advantages:
[0058] Based on the concept of function-oriented molecular design, this application proposes a bifunctional metal-organic framework (MOF) coating technology that integrates "sacrificial oxidation buffering" and "transition metal ion capture". The core of this solution lies in utilizing the tunability and multifunctionality of metal-organic framework materials to construct an intelligent protection system that can actively respond to abnormal battery conditions and continuously purify the interface environment.
[0059] Compared to the passive protection approach of conventional technologies, this application adopts an innovative concept of active regulation, organically combining the redox activity, porous adsorption characteristics, and structural stability of MOF materials. This design makes the coating not only a static physical barrier, but also a "smart shield" that can actively respond to changes in the interfacial environment. When the battery is overcharged, the redox active centers of the MOF preferentially undergo oxidation reactions, consuming excess charge and preventing the large-scale decomposition of the electrolyte; at the same time, the porous structure and functional ligands of the MOF continuously capture harmful metal ions dissolved from the positive electrode, maintaining the purity of the electrolyte.
[0060] The key innovation of this technical solution lies in achieving a synergistic effect of electrochemical protection and chemical purification. By precisely controlling the redox potential of the MOF to a suitable window, it ensures stability under normal operating voltage and timely response under abnormally high voltage. Simultaneously, the introduction of conductive ligands not only provides redox activity but also guarantees the electronic conductivity of the coating, avoiding the problem of insufficient conductivity in traditional coatings.
[0061] Compared to traditional Al2O3 coatings, this application significantly improves the suppression of transition metal dissolution and high-voltage cycle life, substantially enhancing the cycle stability and safety performance of high-nickel cathodes, and providing effective technical support for the reliable application of high-energy-density lithium-ion batteries. It facilitates the realization of high-capacity battery cells and is suitable for long-term energy storage applications, such as energy storage systems that can operate continuously for 4 to 8 hours at rated power. Attached Figure Description
[0062] One or more embodiments are illustrated by way of example with reference to the accompanying drawings. These illustrations do not constitute a limitation on the embodiments. Unless otherwise stated, the drawings in the accompanying drawings do not constitute a limitation on scale. In order to more clearly illustrate the technical solutions in the embodiments of this application or in the conventional art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0063] Figure 1 The flowchart corresponds to the method for preparing a single battery cell provided in the embodiments of this application. Detailed Implementation
[0064] As the background technology indicates, current technical solutions for improving the interfacial stability of high-nickel cathodes mainly include surface coating, bulk doping, and electrolyte optimization. Surface coating is the most commonly used technical route, primarily employing metal oxide coatings to isolate the cathode from direct contact with the electrolyte. Typical coating materials include Al2O3, ZrO2, and TiO2, which are used to form a protective layer of several nanometers to tens of nanometers on the surface of cathode particles through sol-gel methods, atomic layer deposition (ALD), or co-precipitation methods.
[0065] The working principle of metal oxide coating is based on physical isolation and chemical stability. The coating layer acts as a physical barrier, reducing the contact area between the cathode and the electrolyte, and lowering the probability of interfacial side reactions. Simultaneously, these oxides exhibit good chemical stability under high voltage and are not easily oxidized or decomposed. The process typically includes steps such as precursor solution preparation, cathode powder dispersion, coating reaction, drying, and heat treatment.
[0066] Bulk doping technology stabilizes the layered structure of cathode materials by introducing heterogeneous ions into the crystal lattice. Commonly used doping elements include Al. 3+ Ti 4+ Zr 4+ These ions possess strong MO bonding capabilities, which can suppress structural phase transitions and oxygen release during high-voltage charging. Doping processes are typically carried out simultaneously during the synthesis of the cathode material, uniformly distributing the dopant elements within the material through co-precipitation or solid-state reactions.
[0067] Electrolyte optimization methods improve the positive electrode interface environment by adding functional additives. Typical additives include fluorocarbonates, sulfates, and nitrile compounds. These additives can preferentially decompose on the positive electrode surface to form a stable CEI film, or inhibit the dissolution of transition metal ions through complexation.
[0068] While the aforementioned existing technologies have achieved some success in improving the performance of high-nickel cathodes, they still have significant limitations in practical applications. Firstly, traditional metal oxide coatings face the fundamental problem of insufficient conductivity. Typical coating materials such as Al2O3 and ZrO2 are electronic insulators; when their thickness exceeds several nanometers, they significantly increase charge transfer impedance, affecting the battery's rate performance. Simultaneously, these rigid ceramic layers are prone to cracking and peeling due to stress during long-term cycling, losing their protective effect.
[0069] Secondly, existing technologies lack the ability to actively control the dissolution of transition metal ions. Although physical coating can slow down the dissolution of metal ions to some extent, it cannot completely prevent it, especially under extreme conditions such as high temperature or overcharge. The dissolved metal ions migrate in the electrolyte and eventually deposit on the surface of the negative electrode, damaging the integrity of the SEI film. This "cross-contamination" effect is an important reason for the rapid degradation of the battery.
[0070] Furthermore, while bulk doping can stabilize the cathode structure, it often comes at the cost of reduced material capacity. Dopant elements are typically electrochemically inert ions, and their introduction reduces the number of active lithium sites, leading to a decrease in specific capacity. Simultaneously, controlling the uniformity of doping is difficult, easily resulting in phase separation or compositional segregation, affecting the consistency of material performance.
[0071] While electrolyte additive methods offer simplicity, they suffer from drawbacks such as a narrow concentration optimization window and complex interactions among multiple additives. Some additives, while improving the positive electrode interface, may adversely affect the negative electrode SEI film, necessitating a complex balance among different interface requirements. More importantly, existing additives generally lack the ability to actively protect against abnormal operating conditions such as overcharging.
[0072] The root cause of these problems lies in the fact that existing technologies employ passive protection strategies, lacking the ability to actively regulate the positive electrode interface environment. Traditional methods either only provide physical isolation or focus only on solving single problems, failing to achieve a systematic improvement in interface stability. Therefore, there is an urgent need to develop new interface engineering technologies with multiple protection functions and active response capabilities.
[0073] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.
[0074] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.
[0075] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).
[0076] In the description of the embodiments of this application, when a component "includes" another component, other components are not excluded unless otherwise stated, and other components may be further included. Furthermore, when a component such as a layer, film, region, or plate is referred to as being "on / located" on another component, it can be "directly on" the other component (i.e., located on the surface of the other component with no other components between them), or another component may be present therein. Moreover, when a component such as a layer, film, region, or plate is "directly located" on another component, or when a component such as a layer, film, region, or plate is located on the surface of another component, it indicates that no other components are located therein.
[0077] The terminology used in the description of the various embodiments herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used in the description of the various embodiments and the appended claims, the term "part" is also intended to include the plural form unless the context clearly indicates otherwise. Components include layers, films, regions, or plates, etc.
[0078] The embodiments of this application will now be described in detail with reference to the accompanying drawings. However, those skilled in the art will understand that many technical details have been provided in the embodiments of this application to facilitate a better understanding of the application. However, the technical solutions claimed in this application can be implemented even without these technical details and various variations and modifications based on the following embodiments.
[0079] Firstly, this application provides a method for preparing a battery cell, such as... Figure 1 As shown, it includes:
[0080] S1. Provide a battery cell assembly, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet;
[0081] S2. Provide a housing and place the battery cell assembly inside the housing;
[0082] S3. Provide electrolyte and inject the electrolyte into the casing;
[0083] S4. Perform the formation step;
[0084] The positive electrode sheet includes a positive electrode active component, which includes a substrate and a first coating and a second coating sequentially covering the substrate. The first coating is a metal-organic framework coating, and the second coating is a synergistic sealing and protective layer. The substrate is made of a high-nickel ternary positive electrode material.
[0085] Compared to traditional Al2O3 coatings, this application can significantly improve the transition metal dissolution suppression effect and high voltage cycle life, substantially improve the cycle stability and safety performance of high-nickel cathodes, and provide effective technical support for the reliable application of high-energy-density lithium-ion batteries.
[0086] Existing high-nickel cathode protection technologies are mainly based on the concept of "passive protection," passively adapting to changes in the interfacial environment through physical isolation and chemical stabilization. Typical oxide coatings such as Al2O3 and ZrO2 can only provide static physical barriers. Bulk doping technology stabilizes the crystal structure by introducing inert ions, and electrolyte additives form a protective film through chemical reactions. These methods are essentially passive response strategies.
[0087] This application proposes for the first time the concept of "active regulation" protection, integrating the multiple functions of MOF materials, such as redox activity, selective adsorption, and porous transport, into a single coating system to construct an "intelligent protection system" capable of actively sensing and responding to the battery's operating state. When the battery is in normal operating condition, the MOF coating maintains electrochemical stability and provides ion transport channels; when the battery experiences abnormal states such as overcharging, the redox active centers of the MOF immediately respond, consuming excess charge through sacrificial oxidation reactions to actively protect the electrolyte and positive electrode interface. This shift from "passive protection" to "active regulation" represents the development direction of positive electrode protection technology.
[0088] Traditional protection technologies typically only address a single problem. For example, physical coating mainly blocks interfacial contact, bulk doping mainly stabilizes the structure, and electrolyte additives mainly improve interfacial film formation. These methods lack synergistic effects and often require a complex combination of multiple technologies to achieve comprehensive protection.
[0089] This application creatively achieves a dual synergistic mechanism of "electrochemical buffering protection" and "chemical purification and capture." The electrochemical buffering function preferentially consumes excess charge during overcharging through the redox activity of the MOF, reducing electrolyte decomposition and gas generation at the source. The chemical purification function continuously captures dissolved transition metal ions through the porous structure and functional ligands of the MOF, blocking the "cross-contamination" effect. The two mechanisms promote each other; electrochemical protection reduces the driving force for ion dissolution, while chemical purification promptly removes dissolved harmful ions, forming a closed-loop synergistic protection system.
[0090] Existing coating materials such as Al2O3, ZrO2, and TiO2 are all electrochemically inert materials, which do not undergo redox reactions within the battery's operating voltage range and can only provide passive physical isolation. These materials typically have extremely low electronic conductivity (e.g., Al2O3 has approximately 10⁻⁶). -11 When the thickness exceeds a few nanometers (S / cm), the charge transfer resistance increases significantly, affecting the rate performance of the battery.
[0091] This application is the first to use electrochemically active MOF materials as a positive electrode protective coating. Through precise potential window design, the redox potential of the MOF is positioned within a specific range between the positive electrode operating voltage and the electrolyte decomposition voltage. This design ensures that the MOF remains stable during normal charge and discharge, and oxidation only occurs under abnormal conditions such as overcharge. Simultaneously, MOF systems based on conductive ligands (such as Cu3(HITP)2) exhibit excellent intrinsic electronic conductivity (>10). -3 The conductivity (S / cm) is more than eight orders of magnitude higher than that of traditional oxide coatings, fundamentally solving the problem of insufficient conductivity of the coating.
[0092] Traditional coating technologies primarily rely on the macroscopic properties of materials, such as crystal structure, surface energy, and mechanical strength, making it difficult to achieve precise functional control at the molecular scale. Modification of these technologies typically involves macroscopic methods such as altering process parameters and doping elements, lacking the design flexibility required at the molecular level.
[0093] This application, based on the molecular engineering design concept of MOF materials, achieves precise control over key properties of coatings, such as electrochemical properties, pore structure, and surface chemistry, at the molecular scale through the precise selection and combination of metal nodes and organic ligands. Different metal nodes provide different redox potentials and coordination environments, while different organic ligands provide different electrical conductivities and pore characteristics. Molecular design allows for the "customization" of coating materials with specific functions. This degree of design freedom at the molecular scale is unparalleled by traditional inorganic coating materials.
[0094] Current technologies primarily employ passive defense strategies to address the dissolution of transition metal ions, reducing the dissolution rate by decreasing the interfacial contact area or by using electrolyte additives to complex dissolved ions. These methods cannot fundamentally prevent ion dissolution, and their effectiveness is limited, especially under extreme conditions such as high temperature and high voltage. Electrolyte additive methods also face challenges such as difficulty in concentration optimization and complex interactions among multiple components.
[0095] The MOF coating of this application has selective ion capture capabilities, capturing Ni through multiple mechanisms such as coordination complexation, electrostatic adsorption, and pore trapping. 2+ Co 2+ Mn 2+ Transition metal ions exhibit strong affinity and high capture capacity. The porous structure of MOF provides numerous adsorption sites, functional ligands provide specific binding sites, and the pore size allows for selective ion permeation. This active chemical purification function continuously maintains the purity of the electrolyte, effectively preventing the migration of transition metal ions to the negative electrode and their damage to the SEI membrane.
[0096] Traditional coatings are typically dense, continuous films, which, while providing some protection, can also hinder lithium-ion transport. To balance protection and ion transport, the coating thickness often needs to be controlled within a few nanometers, which limits the full potential of the protective function. Furthermore, defects formed during fabrication and mechanical damage during use can lead to localized failure of the protective effect.
[0097] This application develops a unique multi-level synergistic sealing technology, employing a dual strategy of powder-stage pre-sealing and electrochemical in-situ sealing to construct a complete protection system based on the porous structure of MOFs. Pre-sealing addresses macropores and defects in the MOF coating, maintaining necessary ion transport channels; in-situ sealing dynamically repairs potential micro-defects during battery use. This multi-level sealing strategy ensures both the integrity of the protective function and the high efficiency of ion transport, achieving an optimal balance between protection and transport.
[0098] While existing high-performance coating technologies such as atomic layer deposition (ALD) can produce high-quality coatings, they are complex, costly, and inefficient, making it difficult to meet the needs of large-scale industrialization. Although wet coating technology is less expensive, it is sensitive to process conditions such as pH and temperature, and is prone to problems such as uneven coating and poor adhesion to the substrate.
[0099] This application develops various MOF coating preparation processes, including solvothermal, microwave-assisted, ultrasonic-assisted, and electrochemical deposition methods, which possess good process adaptability and scalable production potential. While the solvothermal method has a longer reaction time, it can produce high-crystallinity coatings with strong adhesion to the substrate. Microwave and ultrasonic-assisted methods can significantly shorten reaction time and improve production efficiency. Electrochemical deposition allows for precise control of coating thickness and morphology. These multiple process routes provide flexible options for production at different scales and with varying quality requirements.
[0100] Traditional coating technologies have relatively limited functionality, mainly confined to specific protective mechanisms, with limited room for technological improvement. The performance differences between different coating materials are mainly reflected in basic properties such as chemical stability and mechanical strength, lacking functional designability and scalability.
[0101] The technical solution based on the MOF material platform in this application possesses excellent functional scalability. By changing the combination of metal nodes and organic ligands, a series of products with different redox potentials, pore structures, and selective adsorption characteristics can be designed to meet the specific needs of different cathode materials and application scenarios. The technology platform also has the potential to be extended to other battery systems, such as sodium-ion batteries and potassium-ion batteries. Simultaneously, the MOF coating can integrate other functions, such as flame retardancy, thermal conductivity, and antibacterial properties, achieving a multifunctional integrated design.
[0102] In some embodiments, the cathode material system is based on the coated high-nickel ternary material of this application, which can be optimized and matched with various battery components. The cathode formulation comprises 85wt%~95wt% coated cathode active material, 2wt%~8wt% conductive agent, and 2wt%~8wt% binder. The conductive agent can be selected from traditional carbon black, high-structure carbon black, acetylene black, carbon nanotubes, graphene, conductive graphite, etc., used alone or in combination to construct an efficient electron conduction network. The binder can be selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polytetrafluoroethylene (PTFE), polyimide (PI), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyacrylic acid (PAA), etc. The cathode current collector uses aluminum foil with a thickness of 10μm~25μm, and carbon-coated aluminum foil or other surface-modified aluminum foil can be selected to further improve conductivity and corrosion resistance.
[0103] Anode material systems can be selected from various materials such as graphite, silicon-based materials, and lithium titanate to suit different application requirements. Graphite anodes include natural graphite, artificial graphite, spheroidized graphite, and surface-modified graphite, which have mature processing technology and good cycle stability. Silicon-based anodes include silicon-carbon composites, silicon oxide, and silicon nanowires, which have high capacity advantages but require special binders and electrolyte optimization. Lithium titanate anodes have excellent safety and fast-charging performance, making them suitable for high-power applications. Anode formulations are optimized according to material characteristics, with active material content typically ranging from 90wt% to 98wt%, conductive agent from 1wt% to 8wt%, and binder from 1wt% to 10wt%.
[0104] Membrane materials can include polyolefin membranes, ceramic-coated membranes, and polymer membranes. Polyolefin membranes include polyethylene (PE), polypropylene (PP), and PP / PE / PP three-layer composite membranes, with a typical thickness of 12μm to 25μm. Ceramic-coated membranes have inorganic particles such as Al2O3, SiO2, and TiO2 coated on the surface of the polyolefin substrate to improve the membrane's heat resistance and safety; the coating thickness is 1μm to 5μm. Novel membranes such as nanofiber membranes and non-woven fabric membranes can also be selected according to application requirements.
[0105] The electrolyte system needs to be specifically matched and optimized for the MOF-coated cathode of this application. The basic electrolyte consists of an organic solvent, a lithium salt, and functional additives. The organic solvent is mainly a carbonate solvent, including a mixture of cyclic carbonates (ethylene carbonate EC, propylene carbonate PC, etc.) and chain carbonates (dimethyl carbonate DMC, diethyl carbonate DEC, methyl ethyl carbonate EMC, etc.), and a small amount of auxiliary solvents such as ethers, esters, and nitriles may also be added. The lithium salt is mainly LiPF6, with a concentration of 0.8M~1.5M, and can be used in conjunction with other lithium salts such as LiTFSI, LiFSI, and LiBF4.
[0106] The selection of functional additives needs to consider their compatibility and synergistic effects with the MOF coating. Film-forming additives, such as vinylene carbonate (VC), fluoroethylene carbonate (FEC), and 1,3-propanesulfonate lactone (PS), are used at a content of 0.1wt%~10wt% to improve the quality of the positive and negative electrode interface film. Flame retardant additives, such as trimethyl phosphate (TMP) and triethyl phosphate (TEP), are used at a content of 0.5wt%~20wt% to improve battery safety. High-voltage stabilizers, such as adiponitrile (ADN) and glutaronitrile (GLN), are used at a content of 0.1wt%~5wt% to improve the stability of the electrolyte under high voltage.
[0107] In particular, when using an electrochemical in-situ sealing strategy, a redox mediator, such as TEMPO, triphenylamine, or phenothiazine, needs to be added to the electrolyte as a sealing precursor, with a content of 0.001wt%~15wt%, 0.01wt%~10wt%, 0.1wt%~5wt%, or 0.5wt%~2wt%.
[0108] Optionally, the high-nickel ternary cathode material includes a lithium transition metal composite oxide, wherein the general formula of the lithium transition metal composite oxide is LiNi. x Co y M z O2, wherein M includes one or more of Mn, Al, Mg, Ti, Zr, W, Mo, Nb, Ta, V, Cr, B, Si, Sn, Ga, Fe, Y, La, Ce, Pr, Nd, and Sm; 0.6 ≤ x < 1.0, x + y + z = 1.
[0109] Of course, this application can also be applied to other ternary cathode materials with different nickel contents, such as those with the general formula LiNi. x Co y M z In O2, 0.3≤x<1.0, x+y+z=1.
[0110] Optionally, the high-nickel ternary cathode material may have a polycrystalline or monocrystalline morphology. Both polycrystalline and monocrystalline morphologies refer to the crystallization morphology of the aforementioned high-nickel ternary cathode material.
[0111] Optionally, the primary particle size D50 of the polycrystalline particles is 0.05μm to 5μm, specifically 0.05μm, 0.08μm, 0.1μm, 0.2μm, 0.5μm, 0.8μm, 1μm, 2μm, 3μm, 5μm; the secondary particle size D50 is 1μm to 30μm, specifically 1μm, 2μm, 3μm, 5μm, 7μm, 9μm, 10μm, 12μm, 15μm, 20μm, 25μm, 30μm; and the particle size D50 of the single crystal particles is 0.5μm to 15μm, specifically 0.5μm, 0.8μm, 1μm, 2μm, 3μm, 5μm, 6μm, 8μm, 10μm, 12μm, 15μm.
[0112] The primary particle size was measured statistically from SEM images, while the secondary particle size was measured using a laser particle size analyzer.
[0113] Optionally, the specific surface area of the substrate is 0.05 m². 2 / g~10m 2 / g, specifically 0.05m 2 / g, 0.08m 2 / g, 0.1m 2 / g, 0.2m 2 / g, 0.3m 2 / g、1m 2 / g, 1.5m 2 / g、3m 2 / g、5m 2 / g、8m 2 / g, 10m 2 / g; tap density is 1.0g / cm³ 3 ~4.0g / cm 3 Specifically, it can be 1.0 g / cm³. 3 1.5g / cm 3 2.0g / cm 3 2.5g / cm 3 3.0g / cm 3 3.5g / cm 3 4.0g / cm 3 To ensure high volumetric energy density of the electrodes.
[0114] Optionally, the electronic conductivity of the metal-organic framework coating (under standard conditions at 25°C) is not less than 10. -10 S / cm, specifically 10 -10 S / cm, 10 -8 S / cm, 10 -6 S / cm, 10 -3 S / cm, far exceeding the 10 of traditional Al2O3 coatings.-11 S / cm, thus ensuring that the charge transport kinetics of the electrode are not affected. The thickness of the metal-organic framework coating ranges from 0.5 nm to 5000 nm, specifically 0.5 nm, 1 nm, 5 nm, 10 nm, 20 nm, 50 nm, 100 nm, 200 nm, 500 nm, 1000 nm, 2000 nm, 3000 nm, and 5000 nm. The metal-organic framework coating, relative to Li / Li... + The oxidation potential of the reference electrode is 3.8V~6.0V, specifically 3.8V, 4.0V, 4.2V, 5.0V, 5.5V, and 6.0V. Relative to the charging cutoff voltage of the matched cathode material, the oxidation potential of the MOF should be 0.01V~1.0V higher, specifically 0.01V, 0.05V, 0.08V, 0.1V, 0.2V, 0.3V, 0.5V, 0.8V, and 1.0V. Precise control of the redox potential ensures that the MOF remains electrochemically stable under normal operating conditions, with oxidation occurring only under abnormal conditions such as overcharging. The metal-organic framework coating contains channels with pore sizes ranging from 0.1 nm to 20 nm, specifically 0.1 nm, 0.2 nm, 0.3 nm, 0.5 nm, 0.8 nm, 1 nm, 2 nm, 3 nm, 5 nm, 10 nm, 15 nm, and 20 nm. This pore size design ensures low-impedance transport of lithium ions (solvation radius approximately 0.4 nm to 0.6 nm) while simultaneously providing effective steric hindrance and chemisorption for dissolved transition metal hydrated ions. The BET specific surface area of the channels is 1 m². 2 / g~10000m 2 / g, specifically 1m 2 / g、5m 2 / g, 10m 2 / g、20m 2 / g, 50m 2 / g, 100m 2 / g、200m 2 / g、500m 2 / g, 1000m 2 / g, 1500m 2 / g、2000m 2 / g、3000m 2 / g、5000m 2 / g、8000m 2 / g、10000m 2 / g, the pore volume of the channel is 0.001m. 3 / g~5.0m 3 / g, specifically 0.001m 3 / g, 0.005m 3 / g, 0.01m3 / g, 0.05m 3 / g, 0.08m 3 / g, 0.1m 3 / g, 0.15m 3 / g, 0.2m 3 / g, 0.5m 3 / g, 0.8m 3 / g, 1.0m 3 / g, 1.5m 3 / g, 2.0m 3 / g, 3.0m 3 / g, 4.0m 3 / g, 5.0m 3 / g.
[0115] Optionally, the uniformity of the metal-organic framework coating thickness is characterized by a coefficient of variation of less than 50%, specifically 30%, 20%, or 10%, to ensure uniform protection across the entire particle surface. The loading of the metal-organic framework coating relative to the total mass of the cathode material is 0.001 wt% to 20 wt%, specifically 0.001 wt%, 0.005 wt%, 0.01 wt%, 0.05 wt%, 0.1 wt%, 0.5 wt%, 1 wt%, 3 wt%, 5 wt%, 10 wt%, 15 wt%, or 20 wt%.
[0116] The design of the pore structure needs to take into account the dual functional requirements of rapid lithium-ion transport and effective capture of transition metal ions.
[0117] The preparation process of metal-organic framework coatings is a key aspect of the implementation of the technology in this application, and it is necessary to ensure coating quality while taking into account production efficiency and cost control.
[0118] Optionally, the preparation method of the metal-organic framework coating includes at least one of the following: solvothermal method, continuous ion layer adsorption method, electrochemical deposition method, microwave method, and ultrasonic method. Among them, the solvothermal method can achieve the preparation of high-quality coatings by precisely controlling the nucleation and growth process of MOF.
[0119] The solvothermal process includes steps such as raw material preparation, reaction system preparation, solvothermal reaction, product separation and purification, drying and activation.
[0120] The raw material preparation stage requires pretreatment of the positive electrode substrate material, including sieving, impurity removal, and surface cleaning, to ensure uniform particle size distribution and surface cleanliness. Metal precursors should be selected from nitrates, sulfates, chlorides, acetates, etc., of the corresponding metals, with a purity ≥99%, and should be stored in a dry environment before use. Organic ligands need to be purified to remove impurities and moisture, with a purity ≥95%. High-purity reagents with a water content <50ppm should be selected as the reaction solvent.
[0121] Optionally, the solvothermal method includes:
[0122] The matrix, metal precursor and organic ligand are dispersed in a solvent, and the pH is adjusted to 2-12 to obtain the reaction solution.
[0123] After reacting the reaction solution at 60℃~200℃, a metal-organic framework coating is applied to the substrate surface. The specific reaction temperatures can be 60℃, 70℃, 80℃, 90℃, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, and 200℃.
[0124] The solvothermal reaction is carried out in a closed reactor. During the reaction, stirring, ultrasound and other methods can be used to promote mass transfer and uniform nucleation. After the reaction is completed, the reactor is allowed to cool naturally or cooled to room temperature by a programmed process.
[0125] The solid-phase product was separated by centrifugation and filtration. It was washed 2 to 10 times with the reaction solvent or other suitable solvent, with each wash lasting 10 minutes to 2 hours, to remove unreacted precursors and byproducts. The washed product was then dried under vacuum or an inert atmosphere at 40°C to 200°C for 2 to 48 hours.
[0126] Optionally, the solvent includes at least one of water, ethanol, methanol, isopropanol, N,N-dimethylformamide (DMF), N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP), and dimethyl sulfoxide (DMSO).
[0127] Optionally, in the reaction solution, the concentration of the metal precursor is 0.00001 mol / L to 5.0 mol / L, specifically 0.00001 mol / L, 0.00005 mol / L, 0.0001 mol / L, 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.1 mol / L, 1.0 mol / L, 2.0 mol / L, 3.0 mol / L, 4.0 mol / L, or 5.0 mol / L, and the concentration of the organic ligand is 0.00001 mol / L to 5.0 mol / L, specifically 0.00001 mol / L, 0.00005 mol / L, or 0.00005 mol / L. The concentrations of the metal precursor and organic ligand in the reaction solution are 0.01 g / mL to 0.0001 mol / L, 0.001 mol / L, 0.005 mol / L, 0.01 mol / L, 0.1 mol / L, 1.0 mol / L, 2.0 mol / L, 3.0 mol / L, 4.0 mol / L, and 5.0 mol / L, respectively. The molar ratio of the metal precursor to the organic ligand is 1:(0.1~10), specifically 1:0.5, 1:1, 1:2, 1:3, 1:5, and 1:10. The concentration of the matrix in the reaction solution is 0.01 g / mL to 0.1 g / mL, specifically 0.01 g / mL, 0.02 g / mL, 0.05 g / mL, and 0.1 g / mL.
[0128] Continuous Ion Layer Adsorption Reaction (SILAR) technology is suitable for precisely controlling the thickness and structure of ultrathin coatings. The process flow includes substrate pretreatment, cyclic immersion, intermediate washing, and final treatment. This method can achieve atomic-level thickness control.
[0129] Optionally, the continuous ion layer adsorption method includes:
[0130] The matrix is immersed in one of the metal precursor solution and the organic ligand solution for 10 s to 60 min, then washed with solvent for 10 s to 30 min. Then the matrix is immersed in the other of the metal precursor solution and the organic ligand solution for 10 s to 60 min. This is recorded as one cycle. The cycle is repeated 2 to 100 times.
[0131] Electrochemical deposition technology enables the directional growth and precise thickness control of MOFs through electric field-driven processes. This method is suitable for forming dense and uniform coatings.
[0132] Optionally, the electrochemical deposition method includes:
[0133] In a solution containing a metal precursor and an organic ligand, deposition is performed using the substrate as the working electrode and employing a constant potential or constant current method, wherein the constant current is 0.001 mA / cm². 2 ~10mA / cm 2 Compared to Li / Li+ The reference electrode has a constant potential of 3.0V to 6.0V.
[0134] Microwave-assisted synthesis and ultrasound-assisted synthesis processes can significantly shorten reaction time and improve product uniformity.
[0135] Optionally, in the microwave method, the microwave power is 50W~1000W, the temperature is 50℃~200℃, and the duration is 1min~6h; in the ultrasonic method, the ultrasonic power is 20W~1000W, the frequency is 20kHz~100kHz, and the duration is 10min~12h.
[0136] Optionally, in the metal precursor, the metal has a variable valence state and can form a coordination structure with organic ligands. This is based on a comprehensive consideration of electrochemical activity, structural stability, and cost-effectiveness.
[0137] Optionally, the metal includes at least one of the main group metals, the first transition metal series, the second transition metal series, the third transition metal series, the main group metal series, and the lanthanide metal series.
[0138] Optionally, the first transition metal series includes at least one of Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn; the second transition metal series includes at least one of Zr, Nb, Mo, Ru, Rh, Pd, Ag, and Cd; the third transition metal series includes at least one of Hf, Ta, W, Re, Os, Ir, Pt, Au, and Hg; the main group metal series includes at least one of Al, Ga, In, Sn, Pb, and Bi; and the lanthanide metal series includes at least one of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu.
[0139] Optionally, the organic ligand includes a redox-active ligand or a conductive ligand.
[0140] Organic ligands are key components for regulating the electrochemical properties and pore structure of MOFs, and must simultaneously possess coordination ability, redox activity, and good chemical stability.
[0141] Optionally, the redox-active ligand includes at least one of sulfur-containing heterocyclic compounds, quinone compounds, aromatic amine compounds, nitrogen-containing heterocyclic compounds, phenothiazine compounds, phenotoxazine compounds, and ferrocene compounds; the conductive ligand includes at least one of hexasubstituted benzene compounds, tetrathiofulvalene compounds, and tetracyanoquinone dimethane compounds.
[0142] Optionally, the sulfur-containing heterocyclic compounds include at least one of tetrathiofulvalene and its derivatives, and dithioene compounds; the quinone compounds include at least one of hydroquinone and its derivatives, anthraquinone and its derivatives, and naphthoquinone and its derivatives; the aromatic amine compounds include triphenylamine and its derivatives; the nitrogen-containing heterocyclic compounds include at least one of pyridine, phenanthroline, and bipyridine; and the hexasubstituted benzene compounds include at least one of hexamethylenetriphenylene, hexamethylenetriphenylene, and hexamethylenetriphenylene.
[0143] Optionally, when the metal is Cu and the organic ligand is HITP, the resulting Cu3(HITP)2 system exhibits excellent intrinsic electronic conductivity and a suitable redox potential window.
[0144] The redox-active metal-organic framework coating is the core element for achieving dual protection in this application. It constructs a three-dimensional network framework with specific pore structures and electrochemical activity through the precise coordination and assembly of metal nodes and organic ligands. This framework simultaneously possesses the dual functions of electrochemical buffering and ion trapping, representing a key innovation that distinguishes it from traditional inert coating materials.
[0145] Optionally, the method for forming the synergistic sealing protective layer includes powder pre-sealing and / or electrochemical in-situ sealing. During the reaction process, the precursor is oxidized and deposited within the MOF channels to form the sealing layer.
[0146] The two sealing methods are sequential: pre-sealing in the powder stage is completed during the material preparation stage, while electrochemical in-situ sealing is achieved during the battery formation stage. In practical applications, a combination strategy of pre-sealing followed by in-situ sealing can be chosen, but either method can be used individually as needed.
[0147] Optionally, the powder pre-sealing method includes chemical oxidation sealing or physical sealing.
[0148] Optionally, the chemical oxidation sealing method includes:
[0149] A substrate coated with a metal-organic framework is dispersed in a sealing precursor solution containing a sealing precursor and an oxidant, and the reaction is carried out at 20°C to 80°C to form a synergistic protective layer on the surface of the metal-organic framework coating.
[0150] Optionally, the concentration of the sealing precursor in the sealing precursor solution is 0.1wt%~5wt%, specifically 0.1wt%, 0.5wt%, 1wt%, 2wt%, 3wt%, 4wt%, or 5wt%, and the molar ratio of the oxidant to the sealing precursor is (0.5~5):1, specifically 0.5:1, 1:1, 2:1, 3:1, 4:1, or 5:1.
[0151] Optionally, the sealing precursor includes at least one of TEMPO compounds, triphenylamine compounds, phenothiazine compounds, and ferrocene compounds; the oxidant includes at least one of persulfate, permanganate, and peroxide.
[0152] Optionally, the physical sealing method includes plasma treatment, atomic layer deposition, chemical vapor deposition, or ultraviolet / ozone treatment.
[0153] Optionally, in the plasma treatment, the ionized gas includes at least one of oxygen, nitrogen, and argon; the plasma power is 10W~500W; the pressure is 0.1Pa~100Pa; and the treatment time is 10s~10min. In the atomic layer deposition method, the number of cycles is controlled to be 1~20. Ultrathin layers such as Al2O3 and TiO2 can be precisely deposited.
[0154] Optionally, the electrochemical in-situ sealing method includes:
[0155] A sealing precursor is added to the electrolyte to form the synergistic protective layer in situ during the first charge and discharge of the battery cell. The concentration of the sealing precursor in the electrolyte is 0.001wt%~15wt%.
[0156] Optionally, an interface anchoring layer is also provided between the substrate and the metal-organic framework coating.
[0157] Optionally, the thickness of the interface anchoring layer is 0.5nm~50nm, specifically 0.5nm, 0.8nm, 1nm, 5nm, 8nm, 10nm, 15nm, 20nm, 25nm, 30nm, 35nm, 40nm, 45nm, or 50nm.
[0158] Optionally, the material of the interface anchoring layer includes at least one of inorganic fluorides, inorganic phosphates, inorganic borates, inorganic oxides, organosilane coupling agents, and conductive polymers.
[0159] Optionally, the inorganic fluoride includes at least one of LiF, MgF2, AlF3, and LaF3; the inorganic phosphate includes at least one of Li3PO4, AlPO4, and FePO4; the inorganic borate includes at least one of Li3BO3 and LiBO2; and the inorganic oxide includes at least one of Al2O3, TiO2, ZrO2, and SiO2.
[0160] When assembling and matching lithium-ion batteries using the coated cathode material of this application, compatibility with the MOF coating needs to be considered. The batteries can be packaged in various forms, including pouch, cylindrical, and prismatic.
[0161] Electrode fabrication employs traditional coating processes, but requires optimization of the slurry formulation and process parameters. During positive electrode slurry preparation, mixing time and shear force need to be controlled to avoid damaging the MOF coating structure. The coating thickness is determined based on the designed capacity, typically with an areal density of 15 mg / cm³. 2 ~30mg / cm 2 The drying temperature is controlled between 80℃ and 120℃ to avoid damaging the MOF structure due to excessive heat. The compacted density after roller pressing is 2.8 g / cm³. 3 ~3.8g / cm 3 The pressure needs to be increased gradually to prevent the coating from peeling off.
[0162] Battery assembly is carried out in a dry environment with humidity <1%. After stacking or winding, the cells are installed into the battery casing, and electrolyte is injected, with the injection volume calculated to be 1.1 to 1.3 times the design capacity. Vacuum impregnation ensures that the electrolyte fully wets the electrodes and MOF coating.
[0163] The formation process employs a stepped charge-discharge method. The initial charging current is 0.05C~0.2C, charging to 4.1V~4.3V, followed by a resting period of 2h~12h, and then discharging to 2.8V~3.0V. This process is repeated 2 to 5 times before capacity testing. For batteries using electrochemical in-situ sealing, the upper voltage limit and charging rate need to be controlled during the initial charging process to ensure the sealing reaction proceeds fully.
[0164] Quality control of MOF coatings is crucial to ensuring product consistency and performance stability. Establishing a comprehensive testing system allows for the verification of coating thickness, structural characteristics, pore structure, and electrochemical performance using conventional characterization and electrochemical testing methods. Strict process control standards should be established, including requirements for raw material purity, reaction conditions, environmental control, and equipment maintenance.
[0165] Secondly, this application provides a single battery cell, comprising:
[0166] A battery cell assembly, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet;
[0167] The housing, in which the battery cell assembly is located;
[0168] An electrolyte is provided, located within the housing, and the battery cell assembly is immersed in the electrolyte.
[0169] The positive electrode sheet includes a positive electrode active component, which includes a substrate and a first coating and a second coating sequentially covering the substrate. The first coating is a metal-organic framework coating, and the second coating is a synergistic sealing and protective layer. The substrate is made of a high-nickel ternary positive electrode material.
[0170] Thirdly, this application provides a battery device including a single battery cell as described above, wherein the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.
[0171] Fourthly, this application provides an electrical device, which includes a battery device as described above, the battery device being used to provide electrical energy.
[0172] Fifthly, this application provides an energy storage device, which includes the aforementioned battery device for storing electrical energy.
[0173] To verify the performance improvement effect of the high-nickel ternary cathode interface synergistic protective coating based on redox active metal-organic framework proposed in this application, 13 samples, including Examples 1-7 and Comparative Examples 1-6, were designed for systematic comparative studies. Example 1 uses a Cu3(HITP)2 conductive MOF main coating reinforced with an anchoring layer and a dual sealing process to achieve a synergistic effect of electrochemical buffer protection and chemical purification and capture. Comparative Examples 1-6 represent uncoated, traditional oxide coating, non-redox active MOF, non-conductive MOF, unsealed MOF, and pre-sealed MOF, respectively, to systematically verify the necessity and synergistic effect of the key technical features of this application. Examples 2-5 examine the impact of key parameters on performance and verify the rationality of the preferred range by changing the MOF metal node type, coating thickness, and organic ligand structure. Examples 6 and 7 apply the technical solution of this application to ultra-high nickel NCM90 cathode and NCA cathode systems to verify the versatility and scalability of the technical solution. The specific formulations of each embodiment and comparative example are shown in Tables 1-1 and 1-2, and the correspondence between samples and test items is shown in Table 5.
[0174] The raw materials and their specifications used in each embodiment and comparative example are described below. The high-nickel ternary cathode matrix material includes polycrystalline NCM811 (nickel-cobalt-manganese molar ratio of approximately 8:1:1, average particle size D50 of 8μm~12μm, and tap density of 2.2g / cm³). 3 ~2.5g / cm 3 Its specific surface area is 0.3 m². 2 / g~0.6m 2The cathode substrate materials include: NCM90 (nickel-cobalt-manganese molar ratio approximately 9:0.5:0.5, single-crystal or polycrystalline structure, average particle size D50 of 3μm~8μm), and NCA (nickel-cobalt-aluminum ternary material, nickel-cobalt-aluminum molar ratio approximately 8.5:1.5:0.5, average particle size D50 of 10μm~15μm). Before use, the cathode substrate materials must be vacuum dried at 120℃~150℃ for 6h~12h to remove surface adsorbed moisture. The moisture content should be controlled below 200ppm, and the materials should be stored and handled in a dry environment with a dew point below -40℃.
[0175] The anchoring layer materials mainly include lithium phosphate (Li3PO4), aluminum phosphate (AlPO4), titanium phosphate (TiPO4), and their solutions. Lithium phosphate can be prepared by reacting triethyl phosphate with lithium hydroxide in anhydrous ethanol or tetrahydrofuran; aluminum phosphate can be obtained by reacting phosphoric acid with aluminum hydroxide or aluminum isopropoxide; and titanium phosphate can be prepared by reacting tetrabutyl titanate with phosphoric acid under controlled hydrolysis conditions. The selection of the anchoring layer material needs to consider its chemical compatibility with the positive electrode substrate and the MOF main coating. Materials with moderate lithium-ion conductivity (10⁻⁶ ppm) can be selected. -7 S / cm~10 -5 Phosphate compounds with good electrochemical stability (S / cm) and thickness controlled in the range of 1nm to 5nm to balance interfacial adhesion and ion transport.
[0176] The preparation of metal-organic framework coatings involves two core raw materials: metal precursors and organic ligands. Metal precursors include copper nitrate (Cu(NO3)2·3H2O), nickel nitrate (Ni(NO3)2·6H2O), and zinc acetate (Zn(CH3COO)2·2H2O), with a purity ≥99.0%. They must be stored in a desiccator before use to prevent deliquescence. Organic ligands include hexamethylenetriphenylene (HITP, 2,3,6,7,10,11-hexaiminotriphenylene), hexahydroxytriphenylene (HHTP, 2,3,6,7,10,11-hexahydroxytriphenylene), and benzene-1,4-dicarboxylicacid (BDC), with a purity ≥95%. They must be dried under vacuum at 80℃~120℃ for 4 hours before use to remove residual solvents and moisture. Conductive ligands such as HITP and HHTP can impart high electronic conductivity to MOFs due to their conjugated π-electron system, making them preferred ligands for constructing electrochemically active MOF coatings; while non-conductive ligands such as BDC are mainly used for the preparation of comparative samples.
[0177] The reaction solvent system is selected based on the MOF type and reaction conditions, mainly including anhydrous acetonitrile (water content <20ppm), anhydrous tetrahydrofuran (THF, water content <50ppm), anhydrous N,N-dimethylformamide (DMF, water content <50ppm), anhydrous dimethyl sulfoxide (DMSO), and their mixed solvents. Solvent selection must comprehensively consider factors such as the solubility of the metal precursor and ligands, reaction temperature, MOF growth rate, and crystal quality. For the Cu3(HITP)2 system, anhydrous acetonitrile or an acetonitrile-water (volume ratio 95:5~98:2) mixed solvent can be used, with the reaction temperature controlled at 60℃~80℃; for the Zn-BDC system, DMF or a DMF-ethanol mixed solvent can be used, with the reaction temperature at 80℃~120℃. The solvent must be dried using molecular sieves before use and stored and transferred under argon or nitrogen protection.
[0178] Precursors for pore sealing include 2,2,6,6-tetramethylpiperidine oxide (TEMPO, purity ≥98%) and its derivatives such as 4-hydroxy-TEMPO and 4-amino-TEMPO for powder pre-sealing, as well as redox mediator additives for electrochemical in-situ pore sealing. TEMPO, as a stable free radical compound, can be converted into nitrogen-oxygen cations under mild oxidation conditions. These cations react in situ with functional sites within the MOF pores or achieve pore sealing through electrostatic adsorption. Simultaneously, its oxidation products can co-deposit with the positive electrode electrolyte interface (CEI) components to form a dense protective layer. In the powder pre-sealing process, the amount of TEMPO is typically 0.1wt%~2.0wt% of the MOF mass, optionally 0.3wt%~1.0wt%. Electrochemical in-situ pore sealing is achieved by adding 0.01wt%~0.5wt% of a redox mediator to the electrolyte, which oxidizes and seals the MOF pores in situ on the positive electrode surface during the first charge.
[0179] The electrolyte system employs a combination of a high-voltage-stable organic carbonate solvent and a high-concentration lithium salt. The base solvent is a mixture of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), and methyl ethyl carbonate (EMC), with a typical ratio of EC:EMC:DEC = 1:1:1 (volume ratio) or EC:PC:DMC = 3:2:5. The primary lithium salt used is lithium hexafluorophosphate (LiPF6), at a concentration of 1.0M~1.2M, supplemented with a small amount of lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) or lithium bis(fluorosulfonyl)imide (LiFSI) to improve ionic conductivity and high-temperature stability. Functional additives include film-forming additives such as fluoroethylene carbonate (FEC, 1wt%~5wt%) and vinylene carbonate (VC, 0.5wt%~2wt%), high-voltage stabilizers such as adiponitrile (ADN, 0.5wt%~3wt%) and tris(trimethylsilane) phosphate (TMSP, 0.1wt%~1wt%), and optional electrochemical in-situ sealing redox mediators (0.01wt%~0.5wt%). Electrolyte preparation must be carried out in a drying room or glove box with a dew point <-40℃, and the water content must be strictly controlled below 10ppm.
[0180] The selection of anode materials, separators, and other battery components is as follows. For the anode, artificial graphite (average particle size D50 of 12μm~18μm, initial coulombic efficiency ≥92%) can be selected, or silicon-carbon composite anode (silicon content 5wt%~15wt%) or lithium titanate anode can be used to adapt to different application scenarios. The anode sheet is made by mixing anode active material (94wt%~97wt%), conductive agent (1wt%~3wt%, acetylene black or graphene), and binder (2wt%~3wt%, sodium carboxymethyl cellulose (CMC) mixed with styrene-butadiene rubber (SBR) or polyvinylidene fluoride (PVDF)) in deionized water or N-methylpyrrolidone (NMP) solvent to form a slurry, which is then coated onto a copper foil current collector (thickness 8μm~12μm), dried, and rolled to the designed density. The separator is made of polyolefin material, including single-layer polypropylene (PP), polyethylene (PE), or PP / PE / PP three-layer composite membrane, with a thickness of 16μm~25μm, porosity of 38%~45%, and a closure temperature of 130℃~135℃. For applications with high safety requirements, ceramic-coated separators or aramid-coated separators can be selected. The positive electrode sheet is made by mixing coated positive electrode active material (92wt%~95wt%), conductive agent (2wt%~5wt%, a mixture of carbon black SP and carbon nanotubes CNT), and binder (2wt%~4wt%, PVDF) in NMP solvent to form a slurry, which is then coated onto aluminum foil current collector (thickness 12μm~20μm, carbon-coated aluminum foil optional), dried, rolled, and punched into the required size.
[0181] The preparation of coated cathode materials in each embodiment and comparative example follows a similar overall process, but specific process parameters and coating composition are adjusted according to the sample design. The preparation process mainly includes cathode substrate pretreatment, anchoring layer preparation (if required), in-situ growth of MOF main coating, pore sealing (if required), and post-treatment and quality control steps. All operations involving moisture-sensitive materials are carried out in a dry room with a dew point below -40°C or in an argon-filled glove box to avoid the adverse effects of moisture on the MOF structure and cathode surface.
[0182] Pretreatment of the cathode substrate is a crucial preliminary step to ensure coating quality. First, the high-nickel ternary cathode powder is sieved to remove coarse particles larger than 30 μm and ultrafine powder smaller than 1 μm, obtaining powder with a relatively uniform particle size distribution. Then, it is dried in a vacuum oven at 120℃~150℃ for 8h~12h to reduce the moisture content to below 200ppm. For some samples, a light plasma surface treatment (argon plasma, power 50W~100W, treatment time 30s~60s) can be performed after drying to remove surface organic contaminants and increase surface active sites, improving the adhesion and uniformity of subsequent coatings. The treated cathode powder is immediately transferred to a glove box for storage.
[0183] For samples requiring an anchoring layer (Comparative Examples 3-6 and Examples 1-7), the anchoring layer was formed in situ on the surface of the cathode particles using a liquid-phase impregnation-heat treatment process. Taking a lithium phosphate anchoring layer as an example, triethyl phosphate and lithium hydroxide were dissolved in anhydrous ethanol at a molar ratio of 1:1, with the lithium ion concentration controlled at 0.001M~0.01M. The mixture was stirred at 60°C for 2-4 hours until the solution became clear. Subsequently, the pretreated cathode powder was added to the above solution at a solid-liquid ratio of 1:50 g / mL~1:100 g / mL, and gently stirred at room temperature for 30-60 minutes to allow the anchoring layer precursor to be uniformly adsorbed onto the cathode surface. Care was taken to avoid vigorous stirring that could cause particle breakage. After adsorption, the powder was collected by vacuum filtration or centrifugation, and slowly dried in a vacuum environment at 60°C~80°C for 2-4 hours to remove most of the solvent. Then, it was heat-treated in an argon atmosphere at 300°C~400°C for 1-3 hours to convert the anchoring layer precursor into a dense lithium phosphate anchoring layer. During heat treatment, the heating rate is controlled at 2℃ / min to 5℃ / min to avoid gas release and uneven coating caused by rapid heating. The thickness of the anchoring layer is controlled by the concentration of the anchoring layer precursor solution and the immersion time, with a target thickness of 1nm to 5nm, corresponding to a mass increase of approximately 0.1wt% to 0.5wt%. For aluminum phosphate or titanium phosphate anchoring layers, corresponding anchoring layer precursors and similar processes are used, and the heat treatment temperature is adjusted appropriately according to the material properties.
[0184] MOF coatings are grown in situ on the surface of cathode particles using a solvothermal synthesis method. Taking the Cu3(HITP)2 coating of Example 1 as an example, the preparation process is as follows: First, a metal precursor solution is prepared by dissolving copper nitrate in anhydrous acetonitrile, with a copper ion concentration of 0.5 mM to 5 mM, and stirring under argon protection until completely dissolved. An organic ligand solution is prepared separately by dissolving HITP in anhydrous acetonitrile or an acetonitrile-dimethyl sulfoxide mixed solvent, with a ligand concentration of 0.3 mM to 3 mM. Due to the low solubility of HITP, ultrasonic-assisted dissolution can be performed at 60℃ to 80℃. The cathode powder treated with the anchoring layer is dispersed in the metal precursor solution at a solid-liquid ratio of 1:30 g / mL to 1:80 g / mL, and stirred evenly under argon protection. Then, the ligand solution is quickly added and thoroughly mixed. The molar ratio of metal precursor to ligand is controlled at 1:0.5 to 1:1.5, and 1:0.67 can be selected to match the stoichiometric ratio of Cu3(HITP)2. The reaction system was transferred to a three-necked flask equipped with a reflux condenser and refluxed in an oil bath at 60℃~80℃ for 2h~8h. During the reaction, a dark MOF coating gradually grew on the surface of the cathode particles. The reaction time and temperature need to be adjusted according to the target coating thickness. A coating of about 20nm can be obtained after 2h of reaction, a coating of about 50nm can be obtained after 6h of reaction, and a coating of more than 100nm can be obtained after 12h or more of reaction.
[0185] For different types of MOF coatings, the process parameters need to be adjusted accordingly. In Example 2, the Ni3(HITP)2 coating uses nickel nitrate instead of copper nitrate. Other conditions are similar to those in Example 1, but due to differences in nickel-ligand coordination kinetics, the reaction temperature can be increased to 80℃~100℃, and the reaction time extended to 10h~15h to obtain a coating of the same thickness. In Comparative Example 2, the conductive but non-redox active MOF coating uses a specific combination of ligands and metal nodes to maintain high conductivity while keeping its redox potential far from the operating window (e.g., no obvious redox peak in the 4.2V~4.6V range). The specific formulation can be selected based on conductive MOF systems reported in the literature, such as partially nickel-based or copper-based conjugated ligand frameworks. Comparative Example 3: The Zn-BDC non-conductive MOF coating was prepared by dissolving zinc acetate and terephthalic acid in DMF at a molar ratio of 1:1 and reacting under solvothermal conditions at 100℃~120℃ for 8h~12h. Due to the lack of conductivity of this system and the non-conjugated structure of the ligands, the electronic conductivity of the resulting coating was below 10. -9 S / cm~10 -11 The order of magnitude is in the S / cm range.
[0186] After the MOF coating is grown, the coated powder is collected by filtration or centrifugation. It is then washed 3-5 times with anhydrous acetonitrile or other low-boiling-point solvents to remove unreacted precursors and loosely adsorbed MOF particles. Next, it is dried under vacuum at 60℃-80℃ for 4-8 hours to ensure complete removal of residual solvent (residual solvent <100ppm). The dried coated powder is then subjected to a mild thermal activation treatment at 80℃-120℃ for 1-2 hours under argon protection to improve MOF crystal quality and coating structural stability. However, the temperature should not be too high to avoid MOF structure decomposition or adverse reactions with the cathode substrate.
[0187] For samples requiring pore sealing (Comparative Example 6 and Examples 1-7), pre-sealing with powder was first performed. The MOF coating powder prepared above was dispersed in a dilute solution of TEMPO (TEMPO concentration in acetonitrile or toluene was 0.5 mg / mL to 5 mg / mL), with a solid-liquid ratio of 1:20 g / mL to 1:50 g / mL. The mixture was gently stirred at room temperature for 2-4 hours to allow TEMPO molecules to diffuse into the MOF pores and partially adsorb onto the pore walls. Alternatively, a mild oxidant such as a dilute solution of ammonium persulfate (concentration 0.1 mM to 1 mM) could be used to assist in the oxidation of TEMPO and promote its chemical bonding with the functional sites of the MOF. However, the concentration of the oxidant must be strictly controlled to avoid excessive oxidation and damage to the cathode surface. After treatment, the powder was collected by filtration, quickly washed with anhydrous solvent to remove residual TEMPO from the surface, and dried under vacuum at 60°C for 2-4 hours. The TEMPO content in the pre-sealed coating powder was confirmed by thermogravimetric analysis or elemental analysis, with a target loading of 0.3 wt% to 1.0 wt% of the MOF mass. Electrochemical in-situ sealing is achieved after battery assembly through a specific formation process, as detailed in the battery assembly section.
[0188] For the Al2O3 coating of Comparative Example 1, the traditional sol-gel method was used for preparation. Aluminum isopropoxide was dissolved in isopropanol at an aluminum concentration of 0.01 M–0.1 M. A small amount of deionized water (molar ratio of water to aluminum 1:1–3:1) was added to initiate hydrolysis, and the mixture was stirred at 60 °C for 2–4 h to form a sol. Pretreated cathode powder was added to the sol at a solid-liquid ratio of 1:30 g / mL, stirred until homogeneous, and then the solvent was slowly removed by rotary evaporation to obtain powder coated with the aluminum hydroxide precursor. The precursor was calcined in air at 300 °C–500 °C for 2–4 h to convert it into an Al2O3 coating. The coating thickness was controlled by the sol concentration and the number of coating cycles, with a target thickness of 5 nm–10 nm and a mass increase of approximately 1 wt%–2 wt%.
[0189] Lithium-ion batteries using the coated cathode material of this application were assembled in a dry room or argon glove box with a dew point below -40°C (H2O and O2 content both <0.1ppm). Battery types included CR2032 coin cells (for rapid screening and basic performance evaluation), pouch cells (for capacity, rate, and cycle performance testing), and cylindrical or prismatic cells (for simulating real-world application conditions). The assembly processes for different battery types were similar; the following description uses coin cell half-cells and pouch cell full-cells as examples.
[0190] The assembly of coin cell half-cells uses a coated positive electrode and a lithium metal sheet as the counter electrode, primarily for evaluating the intrinsic electrochemical performance of the positive electrode material. During positive electrode preparation, coated positive electrode powder, a conductive agent (a mixture of carbon black SuperP and carbon nanotubes at a mass ratio of 2:1), and a binder, polyvinylidene fluoride, are mixed in an N-methylpyrrolidone solvent at a mass ratio of 92:5:3 to form a uniform slurry with a solid content controlled between 65wt% and 75wt%. The slurry is coated onto a carbon-coated aluminum foil current collector using a doctor blade coating method. The coating thickness is adjusted according to the target areal capacity, typically 50μm to 80μm on one side. The coated electrode is then initially dried at 80℃ and atmospheric pressure for 30 minutes to remove most of the solvent, and then transferred to a 120℃ vacuum oven for thorough drying for 8 hours. The dried electrode is then rolled to a compaction density of 2.8 g / cm³. 3 ~3.2g / cm 3 The electrodes are cut into circular sheets with a diameter of 12 mm or 14 mm, dried again under vacuum at 120℃ for 4 hours, and then transferred to a glove box for later use. The active material loading of the electrodes is 8 mg / cm³. 2 ~12mg / cm 2 The corresponding theoretical surface capacity is approximately 1.6 mAh / cm². 2 ~2.4mAh / cm 2 .
[0191] The coin cell assembly is performed in the following order: Place a stainless steel gasket, positive electrode plate (coating side up), and separator (polypropylene or polyethylene, 19 mm in diameter) at the bottom of the positive electrode casing. Add 60 μL to 80 μL of electrolyte to fully wet the separator without significant liquid accumulation. Place a lithium metal sheet (15 mm in diameter, 0.45 mm thick; scrape off the surface oxide layer with a blade before use) as the counter electrode. Then, stack the stainless steel gasket, spring sheet, and negative electrode casing in sequence. Seal the battery using a sealing machine under approximately 1 MPa pressure. Allow the assembled coin cell to stand at room temperature for 6 to 12 hours to allow the electrolyte to fully wet the electrodes and separator, then perform electrochemical testing.
[0192] The assembly of the pouch cell uses a coated positive electrode and a graphite negative electrode configuration, which is closer to practical application scenarios. The positive electrode preparation is the same as that of the coin cell, but the size is determined according to the design capacity, with a typical size of 50mm × 70mm, double-sided coating, and a single-sided active material loading of 10mg / cm³. 2 ~15mg / cm 2 The negative electrode uses artificial graphite as the active material, which is mixed with carbon black, sodium carboxymethyl cellulose, and styrene-butadiene rubber in a mass ratio of 96:1:2:1 in deionized water to form a slurry. This slurry is then coated onto a copper foil current collector, and after drying and rolling, the loading capacity is 8 mg / cm². 2 ~12mg / cm 2 The electrode size is slightly larger than the positive electrode (e.g., 55mm × 75mm) to avoid lithium deposition at the edge of the positive electrode. The positive and negative electrode capacity ratio (N / P ratio) is designed to be 1.05~1.15.
[0193] The pouch battery adopts a stacked structure and is assembled in a drying room or glove box according to the following steps: The negative electrode is laid flat, covered with a separator (60mm × 80mm), and then the positive electrode is stacked, with the positive and negative electrode tabs staggered for welding. Depending on the design capacity, a single-layer or multi-layer stacked structure can be used, with separators separating the layers. After stacking, the entire cell is placed in an aluminum-plastic film packaging bag, heat-sealed on three sides, leaving an injection port. Electrolyte is injected through the injection port; the injection volume is calculated based on the cell capacity and pore volume, generally 1.5g / Ah to 2.5g / Ah. After injection, the battery is left to stand in a vacuum environment for 0.5h to 1h to promote electrolyte penetration, then pre-pressurized (approximately 0.1MPa) before sealing to remove air bubbles, and finally heat-sealed to complete the assembly. The assembled pouch battery is left to stand at room temperature for 12h to 24h to allow the electrolyte to fully impregnate it before proceeding to the formation process.
[0194] For samples using electrochemical in-situ sealing (Comparative Example 6 and Examples 1-7), the formation process needs to be specially designed to achieve in-situ sealing of MOF channels. The initial charge uses a low current (0.05C~0.1C) and multiple stepped voltage plateaus. The specific procedure is as follows: charge at a constant current of 0.05C from the open-circuit voltage to 3.8V, rest for 30 minutes; then charge at 0.05C to 4.2V, rest for 30 minutes; continue charging at 0.05C to 4.4V or 4.5V (adjusted according to the cathode system and MOF oxidation potential), and maintain constant voltage for 1-2 hours. This allows the redox mediators in the electrolyte to be oxidized at the high cathode potential, and their oxidation products react chemically with the functional sites within the MOF channels or achieve channel sealing through electrostatic interaction. After the constant voltage period, discharge at 0.1C to 2.8V to complete the initial formation. Repeat the above charge-discharge cycle 2 to 3 times, then perform a standard 0.5C charge-discharge capacity test to determine the actual capacity and first-cycle coulombic efficiency of the battery. For samples without in-situ sealing, the formation process uses a conventional stepped charge-discharge method, initially charging to 4.3V and discharging to 2.8V, repeating this 3 times before capacity testing.
[0195] Table 1-1
[0196]
[0197] In Tables 1-1 and 1-2, the verification purpose of Comparative Example 1 is to demonstrate the necessity of the coating (interfacial side reactions, TM dissolution, gas production baseline); the verification purpose of Comparative Example 2 is to demonstrate the traditional inert coating benchmark (poor conductivity, no active protection, no ion capture); the verification purpose of Comparative Example 3 is to demonstrate the necessity of redox activity (conductive + pores but no sacrificial oxidation leading to poor overcharge protection); the verification purpose of Comparative Example 4 is to demonstrate the necessity of conductivity (pores but no conductivity leading to poor rate capability and high impedance); the verification purpose of Comparative Example 5 is to demonstrate the necessity of pore sealing (gradual MOF degradation, poor high-temperature stability); and the verification purpose of Comparative Example 6 is to demonstrate in-situ... The verification objectives of Example 1 are: comprehensive optimization (dual synergistic protection + complete sealing), the verification objectives of Example 2 are: verification of the replaceability of MOF metal nodes, the verification objectives of Example 3 are: thickness optimization lower limit (protection capability vs. transmission impedance), the verification objectives of Example 4 are: thickness optimization upper limit (enhanced protection but increased impedance), the verification objectives of Example 5 are: oxidation potential window control (verification of potential design rationality), the verification objectives of Example 6 are: applicable to ultra-high nickel cathode (Ni≥0.90), and the verification objectives of Example 7 are: applicable to NCA cathode systems.
[0198] Table 1-2
[0199]
[0200] To comprehensively evaluate the performance of the coated cathode material and its assembled battery, nine systematic tests covering electrochemical performance, interface characteristics, safety performance, and material characterization were designed (as shown in Table 2). All electrochemical tests were conducted in a constant temperature chamber or constant temperature water bath environment, with temperature fluctuations controlled within ±1℃. The testing equipment included a battery testing system (current accuracy 0.05%FS, voltage accuracy 0.02%FS), an electrochemical workstation (frequency range 10μHz~1MHz, current resolution 1pA), and a dedicated safety performance testing device. The specific test methods and conditions are as follows.
[0201] The ambient temperature cycling performance test was conducted in a constant temperature environment of 25℃. The test samples were pouch cells or coin cells. After three cycles of activation at 0.5C, the batteries underwent long-term charge-discharge cycles at 1C. The charging cutoff voltage was 4.3V (NCM811 and NCM90 systems) or 4.35V (NCA system). Constant current charging was performed until the cutoff voltage, followed by constant voltage charging until the current dropped to 0.05C. The discharge cutoff voltage was 2.8V, and constant current discharge was performed throughout the cycle. The charging capacity, discharging capacity, and coulombic efficiency were recorded for each cycle, and the capacity retention rate was calculated based on the first discharge capacity. The test period was set to 500 cycles, with capacity retention rate data recorded at the critical nodes of cycle 100, 200, and 500. The first discharge capacity C1 was defined as the discharge specific capacity of the first 1C cycle after activation, and the capacity retention rate C... 100 / C1、C 200 / C1、C 500 / C1 represents the percentage of discharge capacity relative to C1 at weeks 100, 200, and 500, respectively. Average coulombic efficiency CE avg The calculation is the arithmetic mean of the coulombic efficiency for all cycles from week 5 to week 500. The irreversible capacity in the first week is defined as the difference between the capacity during the first charge and the capacity during the first discharge.
[0202] High-temperature cycling performance testing was conducted at a constant temperature of 45℃, using the same battery type and test rate as the room-temperature cycling test. The batteries were first activated at 25℃ with a 0.5C rate for 3 weeks, then transferred to a 45℃ constant-temperature chamber and left to stand for 2 hours to allow for full thermal equilibrium before cycling began. The charge and discharge conditions were the same as the room-temperature cycling test, with a test cycle of 200 cycles. The initial discharge capacity C was recorded. 1, HT and capacity retention C at weeks 100 and 200 100 / C 1, HT and C 200 / C 1, HT. High-temperature average coulombic efficiency (CE) avg,HTThe calculation represents the average coulombic efficiency from week 5 to week 200. For some samples, the calculation can be extended to higher temperatures, such as 60°C, or longer cycles to examine stability under extreme conditions, but standard comparisons are based on 45°C and 200 weeks.
[0203] Rate performance testing was conducted at 25℃, using a stepped variable rate charge-discharge method to evaluate the capacity utilization of the electrodes at different current densities. The battery was first activated by charging and discharging at a 0.2C rate for 3 weeks to establish a 0.2C capacity baseline. Then, it was cycled sequentially at 0.2C, 0.5C, 1C, 2C, 3C, and 5C rates for 3 weeks each. The discharge capacity of the third week in each rate cycle was taken as the stable capacity at that rate. The charging process consistently used a 0.5C constant current charge to the cutoff voltage, followed by a 0.05C constant voltage charge. The discharging process used a constant current discharge at the corresponding test rate until 2.8V. The 0.2C discharge capacity C... 0.2 Using C as the baseline, calculate the capacity retention rate R at each rate. 0.5 C=C 0.5 C / C 0.2 C, R1C = C1C / C 0.2 C, R2C = C2C / C 0.2 C, R3C = C3C / C 0.2 C and R5C = C5C / C 0.2 C represents a percentage. After the rate test, the battery was cycled at 0.2C for 3 weeks to confirm that the capacity could be restored to more than 95% of the initial value, verifying that the rate test process did not cause irreversible damage to the electrodes.
[0204] Electrochemical impedance spectroscopy (EIS) was performed using a three-electrode or quasi-three-electrode system at 25°C. An electrochemical workstation was used to record the AC impedance response of the battery under specific states of charge. Before testing, the battery was charged to 50% SOC at 0.5C and allowed to rest for 2 hours to reach equilibrium. The impedance measurement frequency range was 10 mHz to 100 kHz, with an AC excitation signal amplitude of 5 mV. Stable data was collected at each frequency point before moving to the next. Impedance spectra were measured before cycling, after 100 cycles, and after 200 cycles. Before each measurement, the battery was charged to 50% SOC and allowed to rest for 2 hours. The charge transfer resistance R was extracted by fitting the semicircular arc of the Nyquist plot. ct The initial charge transfer resistance is denoted as R. ct,0 After 100 cycles, it is denoted as R. ct,10 After 200 cycles, it is denoted as R. ct,200 Calculate the increase in charge transfer resistance ΔR. ct =R ct,200 R ct,0 and the impedance growth rate ΔR ct / ΔN=(R ct,200 R ct,0 ) / 200, in Ω·cm 2 / cycle. The solution resistance R of some samples can be measured. s,0 The evaluation focuses on electrolyte conductivity and ohmic polarization, but the primary comparison parameter is R. ct Relevant data.
[0205] The coating conductivity test is performed on MOF coated powder or thin film samples, using the four-probe method or the pellet method to measure the electronic conductivity at room temperature. For powder samples, an appropriate amount of coating powder is cold-pressed into a disc with a diameter of 13 mm and a thickness of approximately 1 mm in a mold, under a pressure of 10 MPa to 15 MPa. The resistance at both ends of the disc is measured, and the volume conductivity σ is calculated based on the geometric dimensions. MOF For coated films, a thicker MOF coating (thickness > 500 nm) can be prepared on the substrate, and then peeled off to form a self-supporting film for testing. In the four-probe test, the probe spacing is fixed at 1 mm to 2 mm, a constant current I (typically 1 mA to 10 mA) is applied, and the voltage between the two middle probes is measured. The conductivity is calculated based on the wafer geometry and probe configuration. The test environment is a dry nitrogen atmosphere at 25°C and relative humidity <10% to avoid the influence of moisture on the MOF conductivity. The Al2O3 coating in Comparative Example 1 exhibits extremely low conductivity (approximately 10 nm). -11 The conductivity (S / cm) is close to the lower limit of measurement and can be labeled as "insulator" or given as an estimated value. Conductive MOF coatings such as Cu3(HITP)2 typically have a conductivity in the range of 10. -4 S / cm to 10 -2 The S / cm range, and the specific value, are related to factors such as the crystal quality of MOF and the lithium ion content in the pores.
[0206] Transition metal ion dissolution was tested by analyzing the concentrations of nickel, cobalt, and manganese ions in the electrolyte after cycling using inductively coupled plasma mass spectrometry (ICP-MS) to quantitatively evaluate the inhibitory effect of the coating on transition metal dissolution. The test sample was a pouch cell full battery, which was disassembled after 200 cycles at 1C at 25°C. Disassembly was performed in a glove box. The battery was first discharged to 2.8V, allowed to stand for 4 hours, and then the aluminum-plastic film was cut along the sealing edge. Approximately 1-2 mL of electrolyte was drawn using a syringe and immediately transferred to pre-cleaned and dried polypropylene centrifuge tubes for sealing and storage. The electrolyte sample was diluted 10-100 times with dilute nitric acid (1-5 wt%) to reduce the organic solvent concentration and acidify it. After filtration through a 0.22 μm filter membrane, ICP-MS analysis was performed. The concentrations of nickel (…) were measured. 58 Ni), cobalt ( 59 Co), manganese ( 55 The mass concentration of Mn was expressed in ppm (mg / L) and denoted as [Ni]. 2+ ]、[Co2+ ]、[Mn 2+ Calculate the total transition metal ion concentration ΣTM total =[Ni 2+ ]+[Co 2+ ]+[Mn 2+ To ensure data accuracy, three parallel cells were prepared for each sample, and the average value and standard deviation were recorded. The ICP-MS instrument used the standard curve method for quantification, with a detection limit of approximately 0.1 ppb and a relative standard deviation of <5%.
[0207] Overcharge safety performance testing simulates overcharge conditions caused by battery management system failure, evaluating the coating's inhibitory effect on electrolyte decomposition, gas generation, and thermal runaway. The test samples were pouch cells, activated at 0.5C for 3 weeks at 25℃. Cells with capacities close to the average and internal resistance differences <5% were selected for overcharge testing. Batteries were charged at a constant current of 0.5C, with a normal cutoff voltage of 4.3V. During the overcharge test, charging continued to 4.6V, 4.8V, or 150% SOC (charging capacity of 1.5 times the rated capacity). Battery voltage, current, and surface temperature were monitored in real-time during charging (measured by thermocouples attached to the battery surface). The time t to reach the target overcharge voltage was recorded. 4.8V The maximum temperature rise ΔT during overcharging max (Temperature increment relative to room temperature 25°C), and changes in battery appearance after overcharging. For pouch batteries, the degree of gas production can be quantitatively evaluated by measuring changes in battery thickness; the percentage of the thickness increment Δh before and after overcharging relative to the initial thickness h0, Δh / h0, reflects the degree of gas production and bulging. Some samples are equipped with pressure sensors to measure the internal pressure rise ΔP. After overcharging, the batteries are left at room temperature for 2 hours, then discharged at 0.2C to 2.8V, and the initial discharge capacity C after overcharging is measured. after,OC The normal discharge capacity C before overcharging before,OC Compared to calculating capacity retention C after,OC / C before,OC Overcharge testing is inherently dangerous and must be conducted in an explosion-proof enclosure or a dedicated safety testing cabinet equipped with smoke alarms, temperature monitoring, and automatic power-off protection.
[0208] The self-discharge and high-temperature storage performance test evaluates the capacity loss and reversibility of a battery during long-term storage under high charge and high temperature conditions, reflecting interfacial side reactions, electrolyte decomposition, and self-discharge rate. The test sample is a pouch cell full battery, which is first activated at 25°C with 0.5C cycling for 3 weeks, then charged at 0.5C to 4.3V and then constant-voltage charged at 0.05C until the current <0.02C, at which point the battery's SOC is approximately 100%. The open-circuit voltage OCV0 (typically 4.30V~4.35V) and discharge capacity C after full charge are recorded. beforeAs a baseline, the batteries were immediately transferred to a 60°C constant temperature chamber for static storage, maintaining an open circuit state without any charging or discharging during storage. On the 7th and 30th days of storage, portions of the batteries were removed, cooled to 25°C, and then left to rest for 2 hours to allow temperature equilibration. The open circuit voltage (OCV) was then measured. after The remaining capacity C was measured by discharging at 0.5C to 2.8V. after Capacity retention rate R storage Calculated as R storage,7d =C after,7d / C before Or R storage,30d =C after,30d / C before This reflects the total capacity loss during storage. The open-circuit voltage change ΔOCV = OCV0 OCV after This reflects the battery's self-discharge level. After discharge, the battery is recharged and discharged at 0.5C for 3-5 weeks. The discharge capacity C in the 5th week is... recover Compared to C before The percentage is defined as the capacity recovery rate R. recover =C recover / C before This reflects the reversible and irreversible capacity loss caused by storage. Since the self-discharge test cycle is long and consumes a large number of batteries, it is only performed on a portion of representative samples, typically including key comparative samples such as uncoated, conventionally coated, MOF coating without pores, and fully coated MOF.
[0209] Oxidation potential characterization was performed by cyclic voltammetry (CV) to determine the redox peak positions and reversibility of the MOF coating, directly verifying whether the electrochemical activity window of the MOF met the design requirements. A coin-type three-electrode half-cell was used for testing, with a coated positive electrode as the working electrode and lithium metal sheets as the counter and reference electrodes. CV scans were performed at 25°C at a scan rate of 0.1 mV / s, with a voltage window of 2.8 V–4.8 V (vsLi / Li). + Scan for 3-5 cycles until the curve reproducibility is good. Extract the characteristic oxidation peak potential E of MOF from the CV curve. MOF,ox and reduction peak potential E MOF,red Interpeak potential difference ΔE MOF =E MOF,ox E MOF,red Reflecting the reversibility of redox reactions, a smaller ΔE indicates better reversibility. Oxidation peak current density i ox The value is obtained by dividing the peak current by the electrode area, with the unit being mA / cm². 2 For comparative samples such as CE1 (Al2O3 coating) and CE2 (non-redox active MOF), the CV curves show the main redox peaks at the cathode (approximately 3.8V and 4.2V corresponding to Ni). 2+ / Ni 3+ and Ni 3+ / Ni 4+ No additional redox peaks should appear besides those indicating oxidation, confirming no significant electrochemical activity within the 4.2V~4.6V window. For the example samples, a reversible redox peak attributable to the MOF should be observed in the 4.4V~4.6V range, with the peak position approximately 0.1V~0.3V above the positive electrode cutoff voltage (4.3V), meeting the design requirements of a "sacrificial oxidation buffer." CV test data and overcharge safety performance test results corroborate each other, jointly supporting the contribution of MOF redox activity to overcharge protection.
[0210] To ensure the comparability and data quality of the test results for each embodiment and comparative example, the following unified regulations are made regarding test conditions, data acquisition, and processing methods. All electrochemical tests are performed on a calibrated battery testing system, with current and voltage measurement accuracies of no less than 0.1% and 0.05%, respectively, and a data sampling frequency of no less than 1Hz. A constant temperature environment is provided by a constant temperature chamber or water bath with PID temperature control, with temperature fluctuations controlled within ±1℃ of the set value. Temperature sensors are calibrated regularly to ensure accuracy. At least three parallel batteries are prepared for each sample group. The test data are averaged, and the standard deviation is calculated. A standard deviation exceeding 10% of the average is considered abnormal, requiring an increase in the number of samples or investigation of consistency issues in the preparation process.
[0211] Capacity-related indicators such as C1, C 100 / C1、C 500 / C1, etc., are all calculated based on discharge specific capacity, with units of mAh / g (relative active material mass) or mAh / cm³. 2 (Relative electrode area), the specific unit is selected according to the battery type and data application. Coulombic efficiency CE is defined as the ratio of single-cycle discharge capacity to charge capacity, and average coulombic efficiency CE... avg This is the arithmetic mean of the coulombic efficiency over multiple cycles, after removing the first three activation cycles and obviously outlier data points. Capacity retention R in rate performance. xC The 0.2C capacity is used as the benchmark. The discharge capacity at the third cycle is taken for each rate to ensure that the data reflects steady-state performance rather than transient response.
[0212] Electrochemical impedance spectroscopy (EIS) was fitted using an equivalent circuit model, typically Rs(Rf‖CPEf)(Rct‖CPEdl)Zw, where Rs is the solution resistance, Rf is the SEI or CEI film resistance, Rct is the charge transfer resistance, CPE is a constant phase angle element, and Zw is the Warburg diffusion impedance. ZView or EISSpectrumAnalyser was used for fitting, and the fitting error χ² was [not specified]. 2 A result is considered reliable if the value is less than 0.01. Charge transfer resistance Rct Reading from the diameter of the semicircular arc in the mid-frequency region, for complex impedance spectra with two overlapping semicircles, the high-frequency and mid-frequency contributions are separated by deconvolution or multi-peak fitting to ensure R0. ct The accuracy and consistency of the numerical values are crucial. The resting time before impedance testing is uniformly set at 2 hours. Ensure the battery open-circuit voltage change is <5mV / h, reaching a quasi-equilibrium state.
[0213] In transition metal ion dissolution testing, the dilution factor of the electrolyte sample is adjusted according to the expected concentration range to ensure that the measured values fall within the linear range of the ICP-MS standard curve (typically 0.1 ppb to 1000 ppb). Blank samples (electrolyte from uncycled batteries) and standard addition samples are used for quality control and matrix effect correction. Measurement results are expressed as mass concentration (ppm), and the metal dissolution per unit of active material (μmol / g) can also be calculated based on the total electrolyte volume and the mass of the positive electrode active material for more in-depth mechanistic analysis.
[0214] In the overcharge safety performance test, the temperature rise ΔT max Measurements must ensure the thermocouple is in close contact with the battery surface and located in the area with the highest expected temperature (usually the center of the cell). Thermally conductive adhesive or high-temperature tape can be used for fixation. For repeated tests, different batches of batteries should be used to evaluate the reproducibility of results. For three batteries overcharged under the same conditions, the relative deviation in temperature rise and capacity retention should be <15%. If the battery exhibits significant swelling, leakage, or smoke after overcharging, this should be described in detail in the test record. Such batteries should not be subjected to further discharge tests to avoid safety risks.
[0215] The ambient humidity for self-discharge testing should be controlled at a relative humidity of <30% to prevent moisture from entering the battery and affecting the test results. During storage, the temperature profile of the constant temperature chamber should be recorded regularly (e.g., every 3 days) to confirm the stability of temperature control. The cooling and resting steps before capacity testing are essential; directly removing the battery from 60℃ for discharge will result in an inflated capacity reading due to temperature effects, affecting data accuracy.
[0216] In CV testing for characterizing oxidation potential, the initial scan curve often differs from subsequent scans due to the formation of the interfacial film and the evolution of the electrode surface state. Therefore, peak position analysis is typically performed on the 3rd or 5th CV scan. Peak potential is extracted using the peak-top method or the differential curve method. The calculation of peak current density requires subtracting the background current (by fitting a baseline or taking the current value from adjacent peakless regions). For complex systems with multiple overlapping oxidation peaks, Gaussian or Lorentz multi-peak fitting can be used to separate the position and intensity of each peak.
[0217] Test data should be summarized and plotted using software tools such as Origin, Excel, or Python. When smoothing curves, care should be taken to preserve the original characteristics of the data and avoid over-smoothing to mask the true trend. Individual outliers in the cyclic performance curves (such as sudden capacity jumps or drops >5%), if confirmed to be caused by test equipment malfunction or operational error, can be marked and removed during analysis, but the reason must be explained in the remarks column of the data table. All quantitative data should be retained to 2-3 significant figures, and percentage data should be retained to 1 decimal place to avoid false precision. Untested items in the experimental data tables should be marked with "—" or "Not Tested," clearly distinguishing between "Not Tested" and "Test Failed" or "Value Zero."
[0218] Table 2
[0219]
[0220] This application verifies the technical advantages of a high-nickel ternary cathode interface synergistic protective coating based on a redox active metal-organic framework through systematic experimental design. Experimental results show that the synergistic design of a conductive MOF main coating, an anchoring layer to strengthen the interface, and a dual-sealing process can achieve both electrochemical buffering protection and chemical purification and capture while maintaining high conductivity, significantly improving the cycle stability, safety performance, and rate characteristics of the high-nickel cathode under extreme conditions such as high voltage, high temperature, and overcharge. The following systematically analyzes the performance differences and underlying mechanisms of various embodiments and comparative examples from multiple dimensions, including room temperature cycling performance, high temperature stability, rate performance, interface impedance evolution, transition metal ion dissolution, overcharge safety performance, coating conductivity, self-discharge characteristics, oxidation potential characterization, parameter optimization, and application expansion (as shown in Tables 3-1, 3-2, 4-1, and 4-2).
[0221] 1) Comparison of room temperature cycling performance and analysis of coating protection mechanism
[0222] The room-temperature cycling performance test results clearly demonstrate the significant improvement effect of the proposed technical solution on the long-term cycling stability of high-nickel cathodes. Comparative Example 1, without coating, maintained a capacity retention of only 68.0% after 100 cycles at 25°C and 1C rate, further decreasing to 52.0% after 200 cycles. Battery failure was then triggered around 250 cycles, manifested as a sharp increase in internal resistance and a precipitous drop in capacity, typically reflecting the runaway interfacial side reactions of high-nickel cathodes under unprotected conditions. Comparative Example 2, using a traditional Al2O3 coating, showed significantly improved cycling performance, achieving a capacity retention of 72.0% after 500 cycles; however, this level still cannot meet the application requirements of long-life power batteries.
[0223] The conductive MOF coating system of this application exhibits a systematic advantage in cycling stability. Comparative Example 3 uses a conductive MOF coating without redox activity. Although its electronic conductivity is significantly higher than that of Al2O3, its 500-cycle capacity retention is only 76.0%, slightly better than the traditional coating but failing to reach the expected level. Comparative Example 4 uses a non-conductive MOF coating, with a 500-cycle capacity retention of 71.0%, close to that of Al2O3. This indicates that the protective effect of a MOF coating that simply provides a porous structure and ion trapping sites without high electronic conductivity is limited by charge transport impedance. Both sets of comparative examples demonstrate that both redox activity and electronic conductivity of the coating are necessary conditions for achieving long-term cycling stability, and neither can be lacking.
[0224] The effect of sealing treatment on cycling performance was verified through a gradient comparison of Comparative Examples 5, 6, and 1. Comparative Example 5 used a Cu3(HITP)2 conductive red oxygen active MOF coating without sealing treatment, achieving a 500-cycle capacity retention of 79.0%, indicating that the active MOF coating itself provides a certain degree of protection. Comparative Example 6, by adding powder pre-sealing treatment, improved the capacity retention to 83.0%, demonstrating the positive effect of sealing in inhibiting electrolyte penetration and reducing side reactions. Example 1 further employed an electrochemical in-situ sealing process on top of pre-sealing, achieving a 500-cycle capacity retention of 89.0%, an improvement of 10 percentage points compared to Comparative Example 4 and 37 percentage points compared to Comparative Example 1. This stepwise improvement clearly demonstrates the key contribution of the dual sealing process to the long-term stability of the MOF coating.
[0225] From the perspective of average coulombic efficiency, Comparative Example 1 has an average coulombic efficiency of 97.8%, which means that there is an irreversible capacity loss of about 2.2% per cycle, which accumulates and leads to rapid decay. The traditional Al2O3 coating improves the average coulombic efficiency to 98.9%, but there are still obvious side reactions. The average coulombic efficiency of the conductive MOF coating samples generally reaches above 99.2%, and Example 1 even reaches 99.5%, indicating that the irreversible loss per cycle is controlled below 0.5%. This improvement comes from the dual protection mechanism of the MOF coating: on the one hand, the redox active centers preferentially oxidize under overcharge or local high potential conditions, consuming excess charge and releasing a small amount of gas or forming a passivation layer, playing a "sacrificial buffer" role and preventing the electrolyte from undergoing violent oxidation and decomposition directly on the positive electrode surface; on the other hand, the porous structure and functional ligands of MOF continuously capture transition metal ions dissolved from the positive electrode, preventing them from migrating to the negative electrode and destroying the SEI film, thereby maintaining the stability of the negative electrode.
[0226] The first-cycle coulombic efficiency data further support the above mechanism. The first-cycle coulombic efficiency (first-cycle CE) of Comparative Example 1 was 78.5%, corresponding to approximately 21.5% irreversible capacity loss, mainly due to the initial formation of the CEI film and side reactions at surface defects. The conventional Al2O3 coating improved the first-cycle coulombic efficiency to 85.0%, while MOF-coated samples generally reached over 87.0%. Example 1 achieved the highest first-cycle coulombic efficiency of 91.0% among all samples. This indicates that the anchoring layer-enhanced MOF coating can effectively suppress irreversible side reactions and reduce the consumption of active lithium during the formation stage, establishing a good interfacial foundation for subsequent cycling.
[0227] 2) High-temperature cycling performance and thermal stability evaluation
[0228] High-temperature environments pose a severe challenge to the interfacial stability of high-nickel cathodes, accelerating various degradation mechanisms such as transition metal dissolution, electrolyte decomposition, and structural degradation. Cyclic testing at 45°C showed that the uncoated Comparative Example 1 retained only 46.0% capacity after 100 cycles, subsequently failing rapidly, demonstrating that the interfacial side reaction rate of high-nickel cathodes is significantly accelerated at high temperatures. The traditional Al2O3 coating improved the capacity retention to 72.0% after 100 cycles and 66.0% after 200 cycles, demonstrating the role of the physical barrier in suppressing high-temperature side reactions, but the improvement was limited.
[0229] The advantages of conductive MOF coating systems are more pronounced at high temperatures. Comparative Example 3 uses a conductive inactive MOF coating, achieving capacity retention rates of 75.0% and 68.0% after 100 and 200 cycles at 45°C, respectively. These are slightly better than Al2O3, but the difference is not significant, indicating that simply increasing electronic conductivity has limited contribution to high-temperature stability. Comparative Example 5 uses an active MOF but without pore sealing, achieving capacity retention rates of 78.0% and 73.0% after 100 and 200 cycles, respectively, demonstrating the inhibitory effect of active MOFs on high-temperature side reactions. Example 1, through a dual-pore sealing process, pushes high-temperature cycling performance to a new level, achieving capacity retention rates of 88.0% and 86.0% after 100 and 200 cycles, respectively, representing improvements of 42 and 86 percentage points compared to Comparative Example 1, and 16 and 20 percentage points compared to Comparative Example 2.
[0230] The average coulombic efficiency data at high temperatures provides a quantitative assessment of the side reaction rate. Comparative Example 1 showed a significant decrease in coulombic efficiency at high temperatures (data not detailed but inferred from rapid decay), Comparative Example 2 was around 98.5%, while Example 1 maintained an average coulombic efficiency of over 99.3% at high temperatures. This indicates that the MOF coating after sealing effectively suppresses the interfacial reaction between the electrolyte and the cathode at high temperatures. This advantage stems from the stability of the sealing layer at high temperatures: pre-sealing, through TEMPO modification, blocks most of the open pores of the MOF, reducing the channels for electrolyte penetration; the dense passivation layer formed inside the pores and on the coating surface during the first charge of in-situ sealing further reduces interfacial activity at high temperatures.
[0231] Example 6, showcasing the ultra-high nickel system on an NCM90 cathode, verifies the high-temperature applicability of the technology. Due to its high nickel content (90%), NCM90 exhibits a more fragile surface structure and chemical stability compared to NCM811, typically facing greater challenges during high-temperature cycling. Example 6 achieved capacity retention of 86.0% and 83.0% at 45°C for 100 and 200 cycles, respectively. While slightly lower than Example 1's performance on NCM811, this is still significantly better than all comparative examples, demonstrating that the MOF coating technology of this application is equally effective for ultra-high nickel cathode systems.
[0232] 3) Rate performance and charge transport capability analysis
[0233] Rate performance is a core indicator for evaluating the charge transport capability of electrode materials, directly impacting the feasibility of fast charging and high-power applications. The test results clearly demonstrate the decisive influence of coating electronic conductivity on rate performance. Comparative Example 4, employing a non-conductive MOF coating, while possessing a porous structure and ion trapping capabilities, exhibited the worst capacity retention at 3C rate at only 52.0%, directly proving that insufficient electronic conductivity severely limits electrochemical reaction kinetics at high rates.
[0234] Comparative Example 2, with its traditional Al2O3 coating, exhibited a capacity retention of 63.0% at 3C, which is superior to non-conductive MOFs but still relatively low. This is because Al2O3 acts as an electronic insulator (with an electrical conductivity of approximately 10). -11 Even with a thickness of only 5nm to 10nm, a 5nm-10nm layer can introduce significant electron transport impedance on the electrode surface, leading to uneven reaction distribution and increased polarization on the surface of the cathode particles at high rates. In contrast, Comparative Example 3, using a conductive MOF coating, significantly improved the 3C capacity retention to 70.0%, a 7 percentage point increase compared to Al2O3, demonstrating the advantage of conductive MOFs in reducing interfacial electron transport impedance.
[0235] Example 1 achieved an 80.0% 3C capacity retention rate, the best among all samples, through the synergistic design of an anchoring layer-enhanced conductive MOF coating and a dual-sealing process. This performance is attributed to the synergistic effect of three factors: First, the electronic conductivity of Cu3(HITP)2 reaches 3.2 × 10⁻⁶. -3 The S / cm ratio is eight orders of magnitude higher than that of Al2O3, providing a low-resistance channel for rapid electron transport. Secondly, the anchoring layer improves the interfacial contact between the coating and the cathode substrate, reducing the interfacial charge transfer impedance. Finally, although the sealing treatment slightly reduces the ion diffusion rate of the MOF, by optimizing the degree of sealing (retaining some open channels or forming a thin passivation layer that allows ions to penetrate), sufficient lithium-ion transport capacity is maintained while ensuring stability.
[0236] Analysis of the capacity retention gradient at different current densities shows that Comparative Example 1 exhibits capacity retention rates of 82.0%, 75.0%, 58.0%, and 43.0% at 0.5C, 1C, 2C, and 3C, respectively, demonstrating typical exponential decay characteristics. This indicates that interfacial impedance and polarization deteriorate sharply with increasing current density. The corresponding values for Example 1 are 96.0%, 95.0%, 87.0%, and 80.0%, which are not only higher in absolute value but also show a slower decay rate, indicating that the conductive MOF coating can maintain stable electrochemical reaction kinetics over a wide current density range.
[0237] The thickness effect in the parameter optimization examples is particularly evident in rate performance. Example 3, using a 20nm thin coating, achieved a 3C capacity retention of 81.0%, slightly better than Example 1's 80.0%, indicating that thin coatings have an advantage in reducing transmission path length. Example 4, using a 100nm thick coating, saw the 3C capacity retention drop to 77.0%, demonstrating that even with high electronic conductivity, excessively thick coatings still increase overall impedance due to the longer transmission path. The 50nm thickness design in Example 1 achieved the optimal balance between rate performance and cycle stability, taking into account both charge transport efficiency and interface protection.
[0238] 4) Interfacial impedance evolution and charge transfer dynamics
[0239] Electrochemical impedance spectroscopy (EIS) provides quantitative information on the evolution of interfacial charge transfer impedance over cycling, and is a key tool for understanding the impact of coatings on interfacial stability. Initial charge transfer impedance R ct,0 The data reveals the immediate effect of the coating on interfacial electron transport. Comparative Example 1's R... ct,0 165Ω·cm 2 Although Comparative Example 2 has the physical isolation effect of the Al2O3 coating, due to its insulating properties, R ct,0 Instead, it dropped to 78Ω·cm 2This is because the Al2O3 coating stabilizes the positive electrode surface to a certain extent and reduces the local high impedance at defect sites, but its absolute impedance value is still significantly higher than that of the conductive MOF coating sample.
[0240] The initial impedance of the conductive MOF-coated sample is significantly lower. (Comparative Example 3, R...) ct,0 52Ω·cm 2 Comparative Example 5 has an Ω·cm value of 45 Ω·cm. 2 Example 1 is 35Ω·cm 2 The initial impedance of Example 1 is significantly lower than that of traditional coated samples. The lowest initial impedance is due to the synergistic effect of the optimized interfacial contact of the anchoring layer and the highly conductive MOF coating: the anchoring layer improves the bonding force and charge transport path between the cathode particles and the coating, while the conductive framework of the MOF provides a low-resistance electron transport channel.
[0241] The rate of impedance increase during cycling is a more sensitive indicator for evaluating interface stability. Comparative Example 1 shows the impedance increase rate ΔR. ct / ΔN is greater than 1.5Ω·cm 2 / cycle, after 200 cycles R ct Over 500Ω·cm 2 This reflects severe interfacial side reactions and continuous thickening of the CEI film. The impedance growth rate of Comparative Example 2 was 0.54 Ω·cm. 2 / cycle, R after 200 weeks ct Reaching 185Ω·cm 2 Although the growth rate has decreased, the absolute value remains high. Comparative Example 4 exhibits the highest impedance growth rate, reaching 0.80 Ω·cm. 2 / cycle, R after 200 weeks ct Soaring to 285Ω·cm 2 This demonstrates that although the non-conductive MOF coating has a porous structure, the obstructed electron transport leads to uneven interfacial electrochemical reactions, which exacerbates local side reactions and impedance accumulation.
[0242] The impedance growth rate in Example 1 was only 0.17 Ω·cm. 2 / cycle, R after 200 weeks ct 68Ω·cm 2 The impedance growth rate was the slowest and lowest among all samples. This excellent performance stems from the synergistic protection of dual sealing and redox activity: the sealing layer effectively prevents direct contact between the electrolyte and the positive electrode, slowing down the growth of the CEI film and the accumulation of byproducts; the red oxygen-active MOF preferentially undergoes oxidation at local high potentials, consuming active species and forming a stable passivation layer, further suppressing interfacial side reactions. The impedance growth rates of Comparative Examples 5 and 6 were 0.34 Ω·cm. 2 / cycle and 0.33Ω·cm 2 / cycle, falling between Comparative Example 2 and Example 1, clearly demonstrates the contribution of the sealing treatment to mitigating impedance growth.
[0243] Example 2 uses a Ni3(HITP)2 metal node instead of Cu3(HITP)2, and the impedance growth rate is 0.19 Ω·cm. 2 The impedance growth rate is similar to that of Example 1, indicating the replaceability of the metal node. The impedance growth rates of Examples 3 and 4 are 0.23 Ω·cm, respectively. 2 / cycle and 0.24Ω·cm 2 / cycle, slightly higher than Example 1, reflects the effect of coating thickness on impedance evolution: the protection capability of the thinner coating (20nm) is slightly insufficient, and the interface side reaction still occurs to a certain extent; although the protection is better for the thicker coating (100nm), the longer transmission path leads to a higher impedance baseline.
[0244] 5) Transition metal ion dissolution and chemical purification and capture mechanisms
[0245] Transition metal ion dissolution is one of the core issues affecting the degradation of high-nickel cathodes. Dissolved nickel, cobalt, and manganese ions migrate to the anode surface, damaging the SEI film and triggering side reactions, leading to increased impedance and rapid capacity decay. ICPMS testing quantitatively revealed the significant inhibitory effect of the MOF coating in this application on transition metal dissolution. In Comparative Example 1, after 200 cycles, the total transition metal ion concentration in the electrolyte reached 605 ppm, with nickel ions dominating (485 ppm), significantly higher than cobalt (68 ppm) and manganese (52 ppm), consistent with the characteristics of high-nickel cathodes, which have high nickel content and relatively poor chemical stability.
[0246] Traditional Al₂O₃ coatings reduced the total metal ion concentration to 291 ppm, a decrease of approximately 52%, demonstrating that the physical barrier plays a role in inhibiting metal dissolution. However, as an inert oxide, Al₂O₃'s protective mechanism is limited to slowing down the contact between the electrolyte and the positive electrode, and it cannot actively capture dissolved metal ions. Comparative Examples 3 and 4, after employing MOF coatings, further reduced the total metal ion concentration to 234 ppm and 256 ppm, respectively, indicating that the porous structure and functional ligands of MOFs possess a certain adsorption and coordination capacity for metal ions. Even without redox activity, they can reduce the migration of metal ions to the negative electrode through a chemical capture mechanism.
[0247] The core innovation of this application lies in combining redox activity with ion trapping function, achieving dual inhibition of metal dissolution. Comparative Example 5 uses an active MOF but without pore sealing, reducing the total metal ion concentration to 124 ppm, a further reduction of approximately 47% compared to 234 ppm in Comparative Example 3, demonstrating the significant contribution of redox activity to inhibiting metal dissolution. The mechanism of this effect is that the red oxygen-active MOF undergoes a reversible oxidation reaction at high potential at the cathode, locally consuming protons or other acidic species, thus inhibiting the Ni on the cathode surface. 2+ The dissolution reaction of metal ions (which is usually accelerated in an acidic environment) is enhanced; at the same time, the coordination ability of the oxidized MOF center to transition metal ions is enhanced, further improving the capture efficiency.
[0248] Comparative Example 6 and Example 1 further reduced the total metal ion concentration to 87 ppm and 52 ppm respectively through pore sealing treatment. The value of Example 1 was only 8.6% of that of Comparative Example 1, achieving deep inhibition of metal dissolution. The role of the pore sealing layer is reflected in two aspects: pre-sealing blocks the external pores of MOF through TEMPO modification, preventing the dissolved metal ions from diffusing into the electrolyte body through the pores, confining them inside the coating and gradually capturing them by the functional sites of MOF; the dense passivation layer formed by in-situ pore sealing on the coating surface further reduces the penetration rate of electrolyte to the positive electrode surface, reducing the driving force of metal dissolution from the source.
[0249] Elemental analysis provided deeper mechanistic insights. The inhibition effect on nickel ions was the most significant, with a nickel ion concentration of only 38 ppm in Example 1, a 92.2% reduction compared to 485 ppm in Comparative Example 1. The concentrations of cobalt and manganese ions also decreased to 8 ppm and 6 ppm, respectively, representing reductions of 88.2% and 88.5%. This consistent inhibition effect on different metal ions indicates that the protective mechanism of the MOF coating is not dependent on the specific type of metal ion, but rather achieved through a general mechanism of interfacial stabilization and chemical trapping. Notably, the total metal ion concentration in the ultra-high nickel NCM90 system in Example 6 was 93 ppm, slightly higher than in Example 1, but still significantly lower than all comparative examples, proving that the technical solution of this application remains effective even in extreme systems with nickel content as high as 90%.
[0250] 6) Overcharge safety performance and sacrificial oxidation buffer mechanism
[0251] Overcharging is one of the most dangerous operating conditions that lithium-ion batteries may encounter during use. During overcharging, the positive electrode potential exceeds the safety window, causing severe oxidative decomposition of the electrolyte, massive gas production, and a rapid temperature rise, potentially leading to thermal runaway. The overcharge safety performance test results fully demonstrate the "sacrificial oxidation buffer" mechanism of the redox active MOF coating in this application and its significant role in overcharge protection. Comparative Example 1, when charged to 150% SOC (corresponding to approximately 4.82V), experienced a temperature rise of 88.0℃, gas production of 4.8mL / g, and significant battery swelling, posing a serious safety hazard.
[0252] Traditional Al2O3 coatings improve overcharge safety to some extent; in Comparative Example 2, the temperature rise was 68.0℃ and the gas production was 2.8 mL / g, but the improvement was limited. This is because Al2O3, as an inert coating, can slow down the contact between the electrolyte and the positive electrode, but it cannot actively participate in the electrochemical reaction to consume excess charge during overcharging. As the voltage continues to rise, the oxidative decomposition of the electrolyte on the positive electrode surface is still inevitable. Comparative Example 3 used a conductive MOF coating but lacked redox activity; the temperature rise was 63.0℃ and the gas production was 2.2 mL / g, slightly better than Al2O3, but the difference was not significant, demonstrating that simply increasing conductivity and providing a porous structure have limited contributions to overcharge protection.
[0253] The key breakthrough of this application lies in the introduction of a red oxygen-active MOF coating with precisely regulated oxidation potential. Comparative Example 5 used Cu3(HITP)2 without sealing the pores; its MOF oxidation peak potential was 4.48V (see CV test results), slightly higher than the normal operating cutoff voltage of 4.3V for the positive electrode. When overcharged to approximately 4.70V, the MOF coating began to oxidize, preferentially consuming charge and releasing a small amount of gas or forming an oxidized passivation layer, thereby delaying the direct oxidative decomposition of the electrolyte. When the temperature of Comparative Example 5 rose to 42.0℃, the gas production decreased to 1.2 mL / g, a reduction of 52% and 75% compared to Comparative Example 1, directly demonstrating the significant effect of red oxygen activity on overcharge protection.
[0254] Comparative Example 6 and Example 1 further improved overcharge safety through pore sealing treatment. The temperature rise of Comparative Example 6 (pre-sealed only) was 38.0°C, and the gas production was 0.85 mL / g. Example 1 (double-sealed) had a temperature rise of only 32.0°C and a gas production as low as 0.45 mL / g, representing reductions of 64% and 91% respectively compared to Comparative Example 1. The contribution of the pore sealing layer lies in: pre-sealing blocks the MOF pores, reducing electrolyte penetration into the coating interior and lowering side reactions within the coating during overcharging; the dense layer formed by in-situ pore sealing on the coating surface further enhances the chemical stability of the interface, making the MOF oxidation reaction more controllable and preventing structural collapse and excessive gas production caused by excessive oxidation.
[0255] Analysis of the overcharge voltage plateau shows that Comparative Example 1 reached an overcharge voltage of 4.82V at 150% SOC, indicating high internal impedance and severe polarization and side reactions during charging. The overcharge voltage of the conventionally coated sample decreased slightly but remained around 4.80V. Example 1 exhibited an overcharge voltage plateau of only 4.66V, the lowest among all samples. This low voltage plateau reflects the effective consumption of overcharge by the MOF oxidation reaction: when the battery is continuously charged, some charge is converted through the MOF oxidation reaction, rather than being entirely used for the oxidative decomposition of the electrolyte. Therefore, the voltage rise rate slows down, eventually stabilizing at a lower plateau.
[0256] Example 5 uses a ligand-controlled Cu3(HHTP)2 system, whose oxidation peak potential shifts upward to 4.55V. In the overcharge test, the temperature rise is 36.0℃, and the gas production is 0.52 mL / g, slightly higher than Example 1 but still significantly better than all comparative examples. This indicates that precise control of the oxidation potential is an important means to optimize the overcharge protection effect: too low an oxidation potential will cause the MOF to be oxidized prematurely during normal cycling, reducing energy efficiency; too high an oxidation potential will fail to respond promptly in the early stages of overcharge, weakening the protection effect. The Cu3(HITP)2 system of Example 1 (oxidation potential 4.50V) achieves the optimal balance, providing a fast and effective overcharge response while ensuring normal cycling efficiency.
[0257] 7) Comparison of coating conductivity and electron transport mechanism
[0258] The electrical conductivity of the coating is a key parameter determining the rate performance and interfacial polarization of electrode materials. The four-probe method test results clearly demonstrate the significant differences in electronic conductivity among different coating systems. The conductivity of the traditional Al₂O₃ coating is approximately 10⁻⁶. -11 With a conductivity of S / cm, on the order of typical insulators, this extremely low conductivity is the fundamental reason limiting the thickness of the Al2O3 coating—even a thickness of only 5nm to 10nm introduces significant electron transport impedance at the interface. Comparative Example 4 uses a non-conductive MOF coating with a conductivity of 8.5 × 10⁻⁶. -9 Although its S / cm is two orders of magnitude higher than that of Al2O3, it is still far below the standard for good conductive materials. This low conductivity directly leads to its poor performance in rate performance tests.
[0259] The conductive MOF system used in this application achieves a qualitative leap in conductivity. The coating conductivity of Comparative Example 3, Comparative Example 5, Example 1, Example 2, and Example 5 is 1.2 × 10⁻⁶. -3 2.8×10 -3 3.2×10 -3 2.8×10 -3 and 3.0×10 -3 S / cm, all within 10-3 The efficiency is on the order of S / cm, approximately eight orders of magnitude higher than that of Al2O3. This significant improvement stems from the π-electron delocalization of conjugated ligands (such as HITP and HHTP) and the charge transport channels between metal ligands. In the Cu3(HITP)2 structure, copper ions are connected to HITP ligands via coordinate bonds. The conjugated triazine rings and imino groups on the ligands provide extended π-electron clouds, allowing electrons to rapidly transition between the ligand backbone and the metal center, forming a highly efficient electron transport network.
[0260] The correlation between coating conductivity and electrochemical performance further validates the importance of conductivity. Comparative Example 4 exhibits low conductivity (8.5 × 10⁻⁶). -9 The S / cm corresponds to the highest initial charge transfer impedance (125 Ω·cm). 2 The worst 3C rate capacity retention (52.0%) was observed, while Example 1 exhibited high conductivity (3.2 × 10⁻⁶). -3 The S / cm corresponds to the lowest initial impedance (35Ω·cm). 2 The coating conductivity not only affects the electron transport of the coating itself, but more importantly, it affects the uniformity of the electrochemical reaction at the entire electrode interface: a highly conductive coating can quickly disperse electrons, avoiding uneven reactions and "hot spots" caused by excessively high local current density, thereby improving the overall electrochemical performance.
[0261] It is worth noting that the conductivity of Comparative Example 3 is 1.2 × 10⁻⁶. -3 S / cm, lower than 3.2 × 10 in Example 1. -3 The difference in conductivity (S / cm) stems from the influence of MOF structure and redox activity. Cu3(HITP)2 in Example 1 not only possesses a conductive framework, but its redox active centers undergo valence state changes during cycling. This redox process, accompanied by electron injection and extraction, dynamically modulates the electronic structure of the MOF, further optimizing charge transport characteristics. Comparative Example 3, although also employing conjugated ligands, lacks redox active centers, resulting in a relatively simple electron transport path and thus a slightly lower conductivity.
[0262] The effect of the metal node on conductivity was verified in Example 2. The conductivity of Ni3(HITP)2 was 2.8 × 10⁻⁶. -3 S / cm, slightly lower than Cu3(HITP)2's 3.2×10 -3 The difference in S / cm reflects a subtle difference in the coupling strength between the metal d-orbital energy levels and the metal ligand orbitals. Nevertheless, both exhibit electrical conductivities on the same order of magnitude and are significantly superior to non-conductive MOFs and conventional coatings, demonstrating the replaceability of metal nodes and the universality of conductive MOF systems.
[0263] 8) Self-discharge and high-temperature storage performance analysis
[0264] High-temperature storage tests simulate the extreme conditions of batteries being idle for extended periods under high charge and high temperature environments, providing a rigorous test for evaluating interface stability and electrolyte-electrode compatibility. Capacity retention data after 30 days of storage at 60℃ and 100% SOC reveals the crucial role of sealing treatment in suppressing interfacial side reactions. Comparative Example 1 showed a 30-day capacity retention of only 78.0%, corresponding to a 22% capacity loss, along with a 185mV drop in open-circuit voltage. This indicates that severe side reactions occurred at the cathode electrolyte interface under high temperature and high SOC conditions, including the coupled effects of multiple degradation mechanisms such as electrolyte oxidative decomposition, cathode surface structure degradation, and accelerated transition metal dissolution.
[0265] Traditional Al2O3 coatings improved capacity retention to 84.0% and reduced open-circuit voltage to 128 mV, demonstrating the role of physical isolation in mitigating side reactions. However, Al2O3 coatings contain defect channels such as microcracks and grain boundaries. During long-term high-temperature storage, electrolyte may still penetrate to the cathode surface through these channels, triggering localized side reactions. Comparative Example 5 used an active MOF without sealing, achieving a capacity retention of 83.0% and an open-circuit voltage reduction to 95 mV. This was a significant improvement over Comparative Example 1 but still not ideal, indicating that the open-pore MOF coating would gradually be wetted by electrolyte during long-term storage. Although the ion-trapping function of MOFs can mitigate the impact of some side reaction products, it cannot completely prevent electrolyte penetration to the cathode surface.
[0266] Example 1 improved the 30-day capacity retention to 91.0% and the open-circuit voltage drop to only 52mV through a dual-sealing process, representing improvements of 13 percentage points and 133 percentage points, respectively, compared to Comparative Example 1. Capacity recovery testing further revealed the reversibility of the side reactions: Comparative Example 1 showed a capacity recovery rate of 85.0% after storage and recharging, meaning that 7% of the 22% capacity loss was irreversible, stemming from permanent degradation of the cathode structure or loss of active material; Example 1 achieved a capacity recovery rate as high as 97.0%, indicating that the capacity loss caused by storage was almost completely reversible, mainly due to self-discharge and reversible interfacial film thickening, rather than irreversible structural damage.
[0267] The protective mechanism of the sealing layer during high-temperature storage can be understood from both microscopic and macroscopic levels. Microscopically, pre-sealing, through TEMPO modification, forms a molecular-level barrier within the MOF channels, blocking the diffusion channels of electrolyte molecules. In-situ sealing creates a dense passivation layer on the coating surface and at the channel entrances, further reducing the electrolyte permeation rate. Macroscopically, the sealed coating maintains its structural integrity and chemical stability at high temperatures, preventing degradation of the MOF framework and collapse of the channels, ensuring long-term protection. In contrast, Comparative Example 5, without sealing, shows that the MOF may undergo slow solvation or coordination bond hydrolysis at high temperatures, leading to gradual deterioration of the coating performance, as evidenced by its higher open-circuit voltage drop and lower capacity recovery rate.
[0268] The rate of change of open-circuit voltage provides further insight into the self-discharge mechanism. The voltage drop rate was approximately 6.2 mV / day in Comparative Example 1, 4.3 mV / day in Comparative Example 2, and only 1.7 mV / day in Example 1. The voltage drop mainly comes from two contributions: the decrease in the state of charge caused by oxidation side reactions on the positive electrode side, and the potential drift caused by the continuous growth of the SEI film on the negative electrode side. The low voltage drop rate of Example 1 indicates that the suppression of side reactions on the positive electrode side by the MOF coating not only reduces the capacity loss of the positive electrode itself, but also indirectly alleviates the burden on the negative electrode—because the reduction of metal ions dissolved from the positive electrode suppresses the destruction and reconstruction process of the SEI film on the negative electrode, thereby reducing the overall self-discharge rate.
[0269] 9) Characterization of oxidation potential and verification of redox activity
[0270] Cyclic voltammetry provides direct electrochemical evidence of the redox properties of the MOF coating, and is a key experiment for verifying the "precise control of oxidation potential" design concept of this application. The CV curve of Comparative Example 2 (Al2O3 coating) only shows the characteristic peaks of the cathode material itself within the 2.8-4.8V scan window (approximately 3.75V and 4.15V corresponding to Ni). 2+ / Ni 3+ and Ni 3+ / Ni 4+ The oxidation-reduction (OR) curve showed no additional redox peaks in the 4.2V–4.6V range, confirming that Al₂O₃, as an inert coating, does not participate in the electrochemical reaction. Comparative Example 4 used a conductive but inactive MOF coating; its CV curve also showed no significant additional peaks within the target potential window, demonstrating that while this MOF system possesses electronic conductivity and a porous structure, it lacks redox activity in the 4.2V–4.6V range.
[0271] The CV curve of Example 1 shows a distinct oxidation peak at 4.50 V, with a peak current density of 1.35 mA / cm². 2The corresponding reduction peak appears at approximately 4.38V (data not detailed in the table, but can be estimated from the inter-peak potential difference), with an inter-peak potential difference of approximately 120mV, indicating that the redox reaction of MOF has good reversibility. The position of this oxidation peak is about 0.20V higher than the normal cutoff voltage of the positive electrode (4.3V), which fully meets the design requirements of this application: during normal charge and discharge, MOF remains in a reduced state and does not participate in the reaction, avoiding energy efficiency loss; when the battery is overcharged or the local potential rises abnormally, MOF begins to oxidize near 4.50V, preferentially consuming excess charge and playing a "sacrificial buffer" role.
[0272] The oxidation peak potentials of Comparative Examples 5, 6, and 1 were all in the range of 4.48V to 4.50V, with similar peak shapes and peak current densities. This demonstrates that the sealing treatment does not alter the intrinsic redox properties of the MOF, and the thickness and density of the sealing layer were precisely controlled within the range allowing electron transport and lithium-ion diffusion. The peak current density of Comparative Example 6 was 1.18 mA / cm². 2 Slightly lower than Example 1 (1.35 mA / cm) 2 This may reflect that when only the pores are pre-sealed, some pores remain open, resulting in a slightly larger effective reaction area for the MOF. However, incomplete pore sealing leads to the gradual deactivation of some MOFs during cycling, thus reducing the peak current.
[0273] Example 2 uses the Ni3(HITP)2 system, with an oxidation peak potential of 4.46V, slightly lower than the 4.50V of Cu3(HITP)2, and a peak current density of 1.28mA / cm. 2 This difference reflects the influence of the metal center on the redox potential: the electronegativity and d-orbital energy levels of nickel differ slightly from those of copper, leading to a minor adjustment in the redox potential of the Ni ligand coordination field. Nevertheless, the difference between 4.46V and 4.50V is only 40mV, which has little impact in practical applications, and both provide effective protection against overcharge. Example 5 uses a ligand-controlled Cu3(HHTP)2 system, shifting the oxidation peak potential to 4.55V with a peak current density of 1.22mA / cm². 2 Compared to HITP ligands, HHTP ligands replace imino groups with hydroxyl groups, altering electron cloud density and coordination ability, leading to an upward shift in the oxidation potential of MOFs. This result validates the feasibility of controlling the oxidation potential through ligand design, providing design flexibility for customizing MOF coatings for different cathode systems and operating voltage windows in the future.
[0274] The oxidation peak current density is related to the MOF loading, crystal quality, and electrochemical active site density. The peak current density in Example 1 was 1.35 mA / cm². 2The peak current density is the highest among all samples, reflecting optimal coating quality and the most effective reaction sites. This peak current indicates that the MOF can respond quickly and consume a large amount of charge during overcharging, providing a strong buffering effect. The peak current density of Comparative Example 5 is 1.25 mA / cm². 2 The result was slightly lower than in Example 1, possibly because the unsealed MOF underwent partial degradation during the activation cycle before testing, resulting in a slight loss of active sites.
[0275] The CV test results are highly consistent with the overcharge safety performance test data. The oxidation peak potential (4.50V) and peak current density (1.35mA / cm²) of Example 1 are also consistent. 2 The lowest overcharge temperature rise (32.0 °C) and gas production (0.45 mL / g) were observed in Example 3; the lack of an oxidation peak in Example 3 corresponded to a higher temperature rise (63.0 °C) and gas production (2.2 mL / g); the high oxidation potential (4.55 V) in Example 5 corresponded to a slightly higher temperature rise (36.0 °C) because the oxidation reaction had a higher initiation voltage and a slightly slower response. This consistency verifies the scientific validity and effectiveness of the "active protection mechanism of redox-active MOF coating" in this application from both electrochemical and safety performance perspectives.
[0276] 10) Parameter optimization and application expansion verification
[0277] Coating thickness is a key parameter affecting protective effectiveness and electrochemical performance. Examples 3, 1, and 4 used Cu3(HITP)2 coating thicknesses of 20 nm, 50 nm, and 100 nm, respectively, to systematically investigate the effects of thickness on cycle performance, rate performance, and impedance evolution. Example 3 showed a 500-cycle capacity retention of 84.0%, lower than Example 1's 89.0%, indicating that the excessively thin coating (20 nm) lacked sufficient protective capability during long-term cycling, leaving some cathode surface exposed or with insufficient coating density, leading to incomplete suppression of side reactions. However, Example 3 exhibited the best rate performance, achieving a 3C capacity retention of 81.0% and an initial impedance of only 32 Ω·cm. 2 This demonstrates the advantages of thin coatings in reducing transmission impedance.
[0278] Example 4 exhibited a 500-week capacity retention of 87.0%, higher than Example 3 but slightly lower than Example 1, indicating that the thick coating (100 nm) provided a stronger physical barrier and more ion trapping sites. However, its 3C capacity retention decreased to 77.0%, and its initial impedance increased to 48 Ω·cm. 2 This indicates that an excessively thick coating increases the charge transport path length, leading to a deterioration in rate performance and impedance. The 50nm thickness design in Example 1 achieved an optimal balance: 89.0% capacity retention over 500 cycles, 80.0% 3C capacity retention, and an initial impedance of 35 Ω·cm. 2It achieves the best compromise in terms of protection effect, rate performance and impedance control, and verifies the rationality of the preferred thickness range (20nm~100nm, more preferably 40nm~80nm) of this application.
[0279] The replaceability of the metal nodes was verified in Example 2. The Ni3(HITP)2 system exhibited good capacitance retention (86.0%), rate performance (78.0% capacitance retention at 3C), and impedance growth rate (0.19 Ω·cm) at 500 cycles. 2 Key performance indicators such as per cycle are close to those of Example 1, demonstrating the similarity in performance between Cu and Ni metal centers. The minor differences mainly stem from the coupling strength between the metal d orbitals and the ligand π orbitals, and the fine-tuning of the redox potential (4.46V for Ni3(HITP)2 and 4.50V for Cu3(HITP)2), but these differences have little impact on practical applications. This result provides flexibility for the large-scale preparation of MOF coatings: suitable metal nodes can be selected based on raw material costs, supply stability, and specific application requirements, without being confined to a single system.
[0280] The effect of ligand structure on oxidation potential and overcharge protection was verified in Example 5. The oxidation peak potential of the Cu3(HHTP)2 system shifted upward to 4.55V, which is 50mV higher than that of Cu3(HITP)2 (4.50V) in Example 1. In the overcharge test, the temperature rise was 36.0℃ and the gas production was 0.52mL / g, slightly higher than the 32.0℃ and 0.45mL / g of Example 1. This difference indicates that an excessively high oxidation potential delays the MOF response time: when the battery voltage rises from the normal cutoff of 4.3V to the overcharge range, an oxidation potential of 4.50V initiates the buffer reaction earlier, while an oxidation potential of 4.55V initiates it slightly later, allowing more electrolyte decomposition to occur. However, the 500-cycle capacity retention rate of Example 5 was 88.0%, which is essentially equivalent to 89.0% of Example 1, indicating that the ligand difference has a relatively small impact on long-term stability during normal cycling. Taking all factors into consideration, HITP ligands are the preferred ligands for this application due to their moderate oxidation potential and good structural stability.
[0281] The extended application examples verify the universality of the technical solution of this application for different high-nickel cathode systems. Example 6 applies a Cu3(HITP)2 coating to an NCM90 ultra-high-nickel cathode with a nickel content as high as 90%, achieving a capacity retention of 85.0% after 500 cycles, 83.0% after 200 cycles of high-temperature cycling, and a total metal ion dissolution of 93 ppm, all significantly better than all comparative examples. Although these values are slightly lower than those of Example 1 on NCM811, considering the inherent high activity and low stability of the NCM90 system, this result is already excellent, demonstrating the effective protection of the MOF coating for ultra-high-nickel systems. Example 7 applies the technical solution to an NCA cathode system, achieving a capacity retention of 87.0% after 500 cycles, close to the 89.0% of Example 1, verifying the applicability of this application to nickel-cobalt-aluminum systems. These two extended application examples together support the claims in this application regarding its applicability to LiNi... x Co y M z The relevant formulations of O2 (x≥0.5, y+z=1-x, M is Mn, Al or a combination thereof) lay the foundation for the commercial application of the technical solution.
[0282] In summary, the high-nickel ternary cathode interface synergistic protective coating technology based on a redox-active metal-organic framework (MOF) proposed in this application achieves dual functions of electrochemical buffering protection and chemical purification and capture through the synergistic design of a conductive MOF main coating, an anchoring layer to strengthen the interface, and a dual sealing process. This significantly improves the performance of the high-nickel cathode in multiple dimensions, including cycle life, rate capability, high temperature, and overcharge. The comparative design of the system clearly verifies the individual contributions and synergistic effects of redox activity, electronic conductivity, ion capture function, and sealing treatment. Parameter optimization and application expansion examples further demonstrate the controllability and universality of the technical solution. This application provides a novel design approach for interface engineering of high-nickel cathodes, possessing significant scientific and application value.
[0283] Table 3-1
[0284]
[0285] Table 3-2
[0286]
[0287] Table 4-1
[0288]
[0289] Table 4-2
[0290]
[0291] Table 5
[0292]
[0293] Those skilled in the art will understand that the above embodiments are specific examples of implementing this application, and in practical applications, various changes in form and detail can be made without departing from the spirit and scope of this application. Any person skilled in the art can make various alterations and modifications without departing from the spirit and scope of this application; therefore, the scope of protection of this application should be determined by the scope defined in the claims.
Claims
1. A method for preparing a single battery cell, characterized in that, include: A battery cell assembly is provided, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet; A housing is provided to house the battery cell assembly within the housing; Provide electrolyte and inject the electrolyte into the housing; Perform the formation step; The positive electrode sheet includes a positive electrode active component, which includes a substrate and a first coating and a second coating sequentially covering the substrate. The first coating is a metal-organic framework coating with redox activity, and the second coating is a synergistic sealing and protective layer. The substrate is made of a high-nickel ternary positive electrode material. The method for forming the synergistic sealing protective layer includes powder pre-sealing and electrochemical in-situ sealing; The powder pre-sealing method includes chemical oxidation sealing or physical sealing; The chemical oxidation sealing method includes: A substrate coated with a metal-organic framework is dispersed in a sealing precursor solution containing a sealing precursor and an oxidant, and the reaction is carried out at 20°C to 80°C to form a synergistic protective layer on the surface of the metal-organic framework coating. The electrochemical in-situ sealing method includes: A sealing precursor is added to the electrolyte to form the synergistic protective layer in situ during the first charge and discharge of the battery cell. The sealing precursor includes at least one of TEMPO compounds, triphenylamine compounds, phenothiazine compounds, and ferrocene compounds; The physical sealing method includes plasma treatment, atomic layer deposition, chemical vapor deposition, or ultraviolet / ozone treatment.
2. The method for preparing a single battery cell according to claim 1, characterized in that, The electronic conductivity of the metal-organic framework coating is not less than 10. -10 S / cm, with a thickness of 0.5nm~5000nm, relative to Li / Li + The reference electrode has an oxidation potential of 3.8V to 6.0V, and the metal-organic framework coating has channels with a pore size of 0.1nm to 20nm and a BET specific surface area of 1m². 2 / g~10000m 2 / g, the pore volume of the channel is 0.001m. 3 / g~5.0m 3 / g.
3. The method for preparing a battery cell according to claim 1 or 2, characterized in that, The preparation methods of the metal-organic framework coating include at least one of the following: solvothermal method, continuous ion layer adsorption method, electrochemical deposition method, microwave method, and ultrasonic method.
4. The method for preparing a single battery cell according to claim 3, characterized in that, The solvothermal method includes: The matrix, metal precursor and organic ligand are dispersed in a solvent, and the pH is adjusted to 2-12 to obtain the reaction solution. After reacting the reaction solution at 60℃~200℃, a metal-organic framework coating is applied to the substrate surface.
5. The method for preparing a single battery cell according to claim 4, characterized in that, In the reaction solution, the concentration of the metal precursor is 0.00001 mol / L to 5.0 mol / L, the molar ratio of the metal precursor to the organic ligand is 1:(0.1~10), and the concentration of the matrix in the reaction solution is 0.01 g / mL to 0.1 g / mL.
6. The method for preparing a battery cell according to claim 4 or 5, characterized in that, In the metal precursor, the metal has a variable valence state and can form a coordination structure with organic ligands.
7. The method for preparing a battery cell according to claim 6, characterized in that, The metal includes at least one of the main group metals, the first transition metal series, the second transition metal series, the third transition metal series, and the lanthanide series.
8. The method for preparing a battery cell according to claim 4 or 5, characterized in that, The organic ligands include redox-active ligands or conductive ligands.
9. The method for preparing a battery cell according to claim 1, characterized in that, An interface anchoring layer is also provided between the substrate and the metal-organic framework coating.
10. A single battery cell, characterized in that, include: A battery cell assembly, wherein the battery cell assembly is formed by stacking or winding a positive electrode sheet, a separator and a negative electrode sheet; The housing, in which the battery cell assembly is located; An electrolyte is provided, located within the housing, and the battery cell assembly is immersed in the electrolyte. The positive electrode sheet includes a positive electrode active component, which includes a substrate and a first coating and a second coating sequentially covering the substrate. The first coating is a metal-organic framework coating with redox activity, and the second coating is a synergistic sealing and protective layer. The substrate is made of a high-nickel ternary positive electrode material. The method for forming the synergistic sealing protective layer includes powder pre-sealing and electrochemical in-situ sealing; The powder pre-sealing method includes chemical oxidation sealing or physical sealing; The chemical oxidation sealing method includes: A substrate coated with a metal-organic framework is dispersed in a sealing precursor solution containing a sealing precursor and an oxidant, and the reaction is carried out at 20°C to 80°C to form a synergistic protective layer on the surface of the metal-organic framework coating. The electrochemical in-situ sealing method includes: A sealing precursor is added to the electrolyte to form the synergistic protective layer in situ during the first charge and discharge of the battery cell. The sealing precursor includes at least one of TEMPO compounds, triphenylamine compounds, phenothiazine compounds, and ferrocene compounds; The physical sealing method includes plasma treatment, atomic layer deposition, chemical vapor deposition, or ultraviolet / ozone treatment.
11. A battery device, characterized in that, The battery device includes a battery cell obtained by the preparation method as described in any one of claims 1 to 9, or a battery cell as described in claim 10, and the battery device includes one or more of a battery module, a battery pack, and an energy storage battery.
12. An electrical appliance, characterized in that, The electrical device includes the battery device as described in claim 11, the battery device being used to provide electrical energy.
13. An energy storage device, characterized in that, The energy storage device includes the battery device as described in claim 11, the battery device being used to store electrical energy.