Manganese-based positive electrode tab, method for manufacturing the same, secondary battery, and electric device

Abstract

The application relates to the secondary battery technical field, and discloses a manganese-based positive pole piece, a preparation method thereof, a secondary battery and an electric equipment. The positive pole piece comprises, in sequence from the thickness direction of the pole piece, a current collector, a manganese-based positive active material layer, an oxide layer and a phosphorus-containing oxygen acid covalent modification layer; the oxide layer and the phosphorus-containing oxygen acid covalent modification layer are connected through P-O bonds. The application proposes that the application constructs a stable multilayer interface modification structure by covalently combining the oxide layer and the phosphorus-containing oxygen acid covalent modification layer through sequentially stacking a multilayer structure, can cover the entire pole piece macroscopic interface, has strong binding force, can strengthen the adsorption capacity of manganese ions, block the interface side reaction chain, avoids the problems that the traditional particle-level coating is easy to break and fail, the binding force of the conventional protective film is weak and the distribution is uneven, and therefore can effectively inhibit the manganese ion elution and electrolyte decomposition, has the advantages of improving the battery capacity retention rate, the cycle stability and the thermal safety.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a manganese-based positive electrode sheet and its preparation method, a secondary battery, and an electrical device. Background Technology

[0002] In the widespread application of high-voltage, high-energy-density lithium batteries, manganese-based cathode materials have become a research hotspot due to their abundant resources and cost advantages. However, under cycling and high-temperature operating conditions, the surface of manganese-based cathode materials is prone to severe interfacial side reactions, leading to the dissolution of large amounts of transition metal ions such as manganese. These dissolved ions not only catalyze the continuous decomposition of the electrolyte, producing gases and harmful byproducts, but also migrate to the negative electrode to form an insulating deposition layer, severely impairing the battery's capacity retention, cycle stability, and thermal safety.

[0003] To alleviate this problem, existing technologies generally employ oxide coating strategies to modify the cathode. For example, some methods deposit an alumina film on the outer layer of the cathode active material particles. However, this method only provides particle-level protection and cannot cover the entire macroscopic interface of the electrode sheet. Furthermore, the fragile coating layer is prone to breakage and failure during the slurry mixing and rolling processes in electrode preparation. Another approach attempts to introduce phosphate ester additives to form a protective film on the cathode surface. However, this film often suffers from uneven distribution and weak adhesion to the substrate, making it difficult to maintain effective capture of manganese ions during long-term cycling, resulting in a rapid decay in the effect of inhibiting metal dissolution. Therefore, there is an urgent need to construct a novel electrode structure system that significantly enhances the adsorption capacity of manganese ions, fundamentally blocking the interfacial side reaction chain to improve the overall performance of the battery. Summary of the Invention

[0004] In view of this, the purpose of this application is to provide a manganese-based positive electrode sheet and its preparation method, which enables the positive electrode sheet to effectively suppress manganese-based positive electrode interface side reactions, reduce manganese ion dissolution, and improve the battery capacity retention rate, cycle stability and thermal safety.

[0005] Another objective of this application is to provide a secondary battery and electrical device based on the positive electrode sheet described in this application.

[0006] To achieve all or part of the above objectives, as a first aspect of this application, a manganese-based positive electrode sheet is provided, comprising a current collector, a manganese-based positive electrode active material layer, an oxide layer, and a phosphorus oxyacid covalent modification layer; the current collector, the manganese-based positive electrode active material layer, the oxide layer, and the phosphorus oxyacid covalent modification layer are sequentially stacked along the thickness direction of the electrode sheet; the oxide layer and the phosphorus oxyacid covalent modification layer are connected by PO bonds.

[0007] Optionally, the oxide layer includes one or more of Al2O3, TiO2, ZrO2, SiO2, MgO, CeO2, LLZO, and LATP; the phosphorus oxyacid surface graft layer includes one or more of organic phosphonic acid and inorganic phosphoric acid. Further optionally, the inorganic phosphoric acid includes one or more of orthophosphoric acid, pyrophosphoric acid, and phosphorous acid; the organic phosphonic acid includes one or more of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, phenylphosphonic acid, vinylphosphonic acid, methylphosphonic acid, ethylphosphonic acid, benzylphosphonic acid, and aminopropylphosphonic acid.

[0008] Further optionally, the hydroxyl density of the oxide layer is 3 OH / nm. 2 above.

[0009] Alternatively, the oxide layer may further include an adhesive.

[0010] Optionally, the manganese-based positive electrode active material layer includes one or more of lithium manganese oxide, lithium manganese iron phosphate, nickel-cobalt-manganese ternary materials, and lithium-rich manganese-based materials.

[0011] As a second aspect of this application, a method for preparing a manganese-based positive electrode sheet as described in this application is provided, comprising: A manganese-based positive electrode active material is disposed on at least one surface of the current collector to form a manganese-based positive electrode active material layer. An oxide layer is formed by depositing an oxide layer on the surface of the manganese-based positive electrode active material layer. A phosphorus-oxyacid solution is applied to the surface of the oxide layer to react and form a phosphorus-oxyacid covalent modification layer, thereby obtaining the manganese-based positive electrode sheet.

[0012] Optionally, the reaction temperature is 80-170°C.

[0013] Optionally, the manganese-based positive electrode active material includes a manganese-based positive electrode active material, a binder, and a conductive agent. The manganese-based positive electrode active material includes one or more of lithium manganese oxide, lithium manganese iron phosphate, nickel-cobalt-manganese ternary materials, and lithium-rich manganese-based materials.

[0014] Optionally, the manganese-based positive electrode active material is lithium manganese oxide and lithium iron manganese phosphate, and the mass ratio of lithium manganese oxide to lithium iron manganese phosphate is (2-4):(8-6).

[0015] As a third aspect of this application, a secondary battery is provided, including a negative electrode, a positive electrode as described in this application, and an electrolyte.

[0016] As a fourth aspect of this application, an electrical device is provided, including the secondary battery described in this application, wherein the secondary battery provides electrical energy to the electrical device or serves as an energy storage unit for the electrical device.

[0017] This application constructs a stable multi-layer interface modification structure by sequentially stacking multiple layers and utilizing the covalent bonding between the oxide layer and the phosphorus oxyacid covalent modification layer. This structure can cover the entire macroscopic interface of the electrode, exhibiting strong bonding and enhancing the adsorption capacity for manganese ions. It also blocks the interfacial side reaction chain, avoiding the problems of easy breakage and failure of traditional particle-level coatings, weak bonding and uneven distribution of conventional protective films. Therefore, it can effectively inhibit the dissolution of manganese ions and the decomposition of electrolyte, and has the advantages of improving battery capacity retention, cycle stability and thermal safety. Attached Figure Description

[0018] The accompanying drawings, which form part of this application, are used to provide a further understanding of this application. The illustrative embodiments of this application and their descriptions are used to explain this application and do not constitute an undue limitation of this application. Figure 1 The diagram shown is a schematic representation of the structure of the manganese-based positive electrode sheet of this application; 1: Phosphorus oxyacid covalent modification layer; 2: Oxide layer; 3: Manganese-based positive electrode active material layer; 4: Current collector; Figure 2 The diagram shows the phosphonic acid / phosphoric acid reaction process on the oxide surface. Figure 3 The figures show the 1C / 1C cycle test results of the secondary batteries assembled with positive electrode sheets in the examples and comparative examples; the curves from top to bottom represent the results of Example 1, Example 2, Example 3, Example 5, Example 4, Comparative Example 2, Comparative Example 3, Comparative Example 4, and Comparative Example 1, respectively. Detailed Implementation

[0019] This application discloses a manganese-based positive electrode sheet and its preparation method, a secondary battery, and electrical equipment. Those skilled in the art can refer to the content of this application and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this application. The products and processes described in this application have been described through preferred embodiments. Those skilled in the art can obviously modify or appropriately change and combine the products and processes described herein without departing from the content, spirit, and scope of this application to realize and apply the technology of this application. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0020] It should be noted that, in this document, relational terms such as "first" and "second," "step 1" and "step 2," and "(1)" and "(2)" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element. Moreover, the embodiments and features described in this application can be combined with each other without conflict.

[0021] In traditional high-voltage, high-energy-density lithium batteries, manganese-based cathode materials are prone to interfacial side reactions under cycling and high-temperature conditions, leading to the dissolution of transition metal ions and electrolyte decomposition, thus affecting the battery's cycle life and safety. Current mainstream oxide coating technologies have insufficient surface active sites and limited ability to capture manganese ions, making it difficult to fundamentally suppress interfacial side reactions and metal dissolution. Furthermore, the coating layer is easily damaged during slurry stirring and rolling. Using phosphate ester additives alone may result in uneven film formation and poor adhesion on the cathode surface, making it difficult to stably suppress manganese dissolution in the long term.

[0022] Based on this, in the first aspect of this application, a manganese-based positive electrode sheet is proposed, comprising a current collector, a manganese-based positive electrode active material layer, an oxide layer, and a phosphorus oxyacid covalent modification layer. The current collector, manganese-based positive electrode active material layer, oxide layer, and phosphorus oxyacid covalent modification layer are sequentially stacked along the thickness direction of the electrode sheet, wherein the oxide layer and the phosphorus oxyacid covalent modification layer are connected by PO bonds. This structure aims to improve the manganese ion adsorption capacity and suppress interfacial side reactions and metal dissolution through multi-layer synergistic protection, thereby improving the cycle life and safety of the battery. A schematic diagram of the structure is shown below. Figure 1 .

[0023] The current collector can be made of conductive materials, such as metal foil (aluminum foil, copper foil, etc.), composite current collectors, etc. As the carrier for collecting and conducting current, the current collector provides support for subsequent layers.

[0024] The manganese-based positive electrode active material layer can be disposed on one or both surfaces along the thickness direction of the current collector, as needed. This layer is formed by mixing the manganese-based positive electrode active material with solvents, conductive agents, binders, etc., to prepare a slurry, then coating it onto the current collector and performing processes such as drying and rolling. The manganese-based positive electrode active material can be a single manganese-based compound, such as lithium manganese oxide, or a combination of multiple manganese-based compounds.

[0025] An oxide layer is deposited on the surface of the manganese-based cathode active material layer. This layer can be formed in various ways, such as physical vapor deposition, chemical vapor deposition, atomic layer deposition, or solution coating, to uniformly deposit or coat the oxide material onto the surface of the manganese-based cathode active material layer. The oxide material can be a metal oxide, such as aluminum oxide. Oxygen vacancies and metal coordination bonds present on the oxide surface will undergo a dissociation reaction with water molecules in the air, resulting in the formation of hydroxyl groups on the oxide surface.

[0026] A phosphorus oxyacid covalent modification layer is deposited on the surface of an oxide layer. This layer is formed by coating the oxide layer surface with a phosphorus oxyacid solution and then reacting the solution. The phosphorus oxyacid can be a phosphoric acid compound, such as orthophosphoric acid, or a combination of multiple phosphoric acid compounds.

[0027] The current collector, manganese-based positive electrode active material layer, oxide layer, and phosphorus oxyacid covalent modification layer are sequentially stacked along the electrode thickness direction. This stacked structure ensures that the functional layers can work synergistically, providing multiple layers of protection for the manganese-based positive electrode active material layer. The oxide layer and the phosphorus oxyacid covalent modification layer are connected by PO bonds. This covalent connection can be formed by a chemical reaction between the phosphorus oxyacid and the hydroxyl or oxygen atoms on the surface of the oxide layer. For example, under certain temperature and atmosphere conditions, the hydroxyl groups in the phosphorus oxyacid molecules undergo a condensation reaction with the hydroxyl groups or metal atoms on the oxide surface to form POM bonds (where M is a metal atom in the oxide, such as Al, Ti, Zr, Si, Mg, Ce, etc.), thereby fixing the phosphorus oxyacid molecules on the oxide layer surface. This multi-interface protection system can effectively block direct contact between the manganese-based positive electrode active material and the electrolyte, while enhancing the capture ability of dissolved manganese ions. This effectively suppresses the interfacial side reactions and transition metal ion dissolution problems that easily occur in manganese-based positive electrodes under cycling and high-temperature conditions, thereby improving the cycle life and safety of the battery.

[0028] In some embodiments of this application, the oxide layer includes one or more of Al2O3, TiO2, ZrO2, SiO2, MgO, CeO2, LLZO, and LATP. This oxide layer serves as an intermediate layer between the manganese-based positive electrode active material layer and the phosphorus oxyacid covalent modification layer. Its core function is to provide a stable chemical environment, physical isolation, and sufficient reaction sites for subsequent covalent grafting of the phosphorus oxyacid. Al2O3 (alumina) is known for its excellent chemical stability and insulation properties, and its surface readily forms hydroxyl groups, providing an ideal substrate for the covalent grafting of phosphorus oxyacids. TiO2 (titanium dioxide) not only possesses good chemical inertness and semiconductor properties, but its surface is also rich in hydroxyl groups, which is beneficial for subsequent surface modification reactions. Furthermore, ZrO2 (zirconia), with its high melting point, high hardness, and corrosion resistance, can effectively block the migration of transition metal ions, while SiO2 (silicon dioxide), with its good insulation and chemical stability, as well as abundant surface hydroxyl groups, is easily functionalized. MgO (magnesium oxide) provides an alkaline environment, neutralizing any acidic substances that may be generated, thereby improving interfacial stability. CeO2 (cerium dioxide), due to its unique oxygen vacancy structure, can capture free radicals, further enhancing electrolyte stability. LLZO (garnet oxide) and LATP (lithium aluminum titanium phosphate), as solid-state electrolyte materials, can provide additional ion transport channels in specific applications, and their surfaces also possess active sites for reaction with phosphorus oxyacids. By selecting these materials, it can be ensured that the oxide layer effectively isolates the manganese-based positive electrode active material layer while providing the necessary chemical basis for the stable formation of the phosphorus oxyacid covalent modification layer.

[0029] In some embodiments of this application, the phosphorus oxyacid surface graft layer comprises one or more of organophosphonic acids and inorganic phosphoric acids. The organophosphonic acid contains organic groups and phosphonic acid groups. The organic groups can provide additional functionality, such as adjusting the hydrophobicity of the interface or providing steric hindrance, while the phosphonic acid groups are responsible for reacting with the hydroxyl groups on the oxide layer surface to form stable PO bonds and efficiently capturing dissolved manganese ions. Examples include aminotrimethylenephosphonic acid and ethylenediaminetetramethylenephosphonic acid. Inorganic phosphoric acid, such as orthophosphoric acid, pyrophosphoric acid, and phosphorous acid, contains multiple phosphate groups, enabling it to form multi-point connections with the oxide layer surface, thereby significantly enhancing the adhesion of the modified layer and providing abundant active sites for capturing manganese ions. The selection of these phosphorus oxyacid materials ensures that the modified layer can firmly adhere to the oxide layer surface and possesses a strong manganese ion capture capability.

[0030] In some other embodiments of this application, the inorganic phosphoric acid includes one or more of orthophosphoric acid, pyrophosphoric acid, and phosphorous acid. The molecular structure of inorganic phosphoric acid typically contains phosphorohydroxyl groups (P-OH), which have high reactivity and can undergo condensation reactions with hydroxyl groups on the oxide layer surface to form stable PO covalent bonds. Furthermore, the phosphorohydroxyl groups in the inorganic phosphoric acid molecule also provide abundant active sites for capturing and adsorbing dissolved transition metal manganese ions. Besides orthophosphoric acid, pyrophosphoric acid, and phosphorous acid, those skilled in the art can select other inorganic phosphoric acid derivatives with similar reactivity, such as polyphosphoric acid or hypophosphoric acid, according to specific needs, to achieve covalent bonding with the oxide layer and manganese ion capture. Orthophosphoric acid (H3PO4) is the most common type of phosphoric acid, containing three phosphorohydroxyl groups in its molecule. These hydroxyl groups can efficiently react with the oxide layer surface to form PO covalent bonds, ensuring the firm adhesion of the modified layer. Simultaneously, its multiple hydroxyl groups also provide sufficient sites for chelating or adsorbing manganese ions. Pyrophosphoric acid (H4P2O7) is formed by the dehydration of two orthophosphoric acid molecules and contains four phosphorohydroxyl groups. Compared to orthophosphoric acid, pyrophosphoric acid has more active sites, enabling it to form a denser covalently modified layer and providing stronger manganese ion capture capability. Phosphorous acid (H3PO3) is a reducing phosphoric acid containing two phosphorus oxyhydroxyl groups and a pH bond in its molecule. Although it has fewer hydroxyl groups than orthophosphoric acid and pyrophosphoric acid, its phosphorus oxyhydroxyl groups still possess sufficient activity to form PO covalent bonds with the oxide layer and can effectively adsorb manganese ions.

[0031] In other embodiments of this application, the organophosphonic acid includes one or more of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, phenylphosphonic acid, vinylphosphonic acid, methylphosphonic acid, ethylphosphonic acid, benzylphosphonic acid, and aminopropylphosphonic acid. Organophosphonic acids are organic compounds containing a carbon-phosphorus bond and at least one phosphonic acid group (-PO(OH)2) in their molecules. The phosphonic acid group exhibits similar reactivity to inorganic phosphoric acid, capable of forming stable PO covalent bonds with the oxide layer surface. The unique feature of organophosphonic acids lies in the diversity of their organic side chains. These side chains can be used to adjust the hydrophilicity / hydrophobicity, steric hindrance, and compatibility with the electrolyte of the modified layer as needed, thereby achieving precise control over the electrode interface performance. Besides aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, phenylphosphonic acid, vinylphosphonic acid, methylphosphonic acid, ethylphosphonic acid, benzylphosphonic acid, and aminopropylphosphonic acid, those skilled in the art can also select other phosphonic acid derivatives with different organic side chains, such as phosphonic acids with long-chain alkyl groups, to meet specific application requirements. Aminotrimethylenephosphonic acid (ATMP) is a polyphosphonic acid containing three phosphonic acid groups and one amino group. Its polyphosphonic acid groups provide multiple covalent bonding sites and strong manganese ion chelation ability, while the amino group may further enhance its interaction with the oxide layer or manganese ions. Ethylenediaminetetramethylenephosphonic acid (EDTMP) is another polyphosphonic acid containing four phosphonic acid groups and two amino groups. Its structure provides an extremely rich number of active sites, enabling the formation of a very stable and efficient covalently modified layer with excellent manganese ion capture ability. Phenylphosphonic acid contains phenyl and phosphonic acid groups; the presence of the phenyl group increases the thermal and chemical stability of the modified layer, while the phosphonic acid group ensures covalent bonding with the oxide layer and manganese ion adsorption function. Vinylphosphonic acid contains vinyl and phosphonic acid groups; the vinyl group has unsaturated bonds and can participate in polymerization reactions under specific conditions, potentially forming a more robust and continuous modified layer, further enhancing the protective effect. Methylphosphonic acid contains methyl and phosphonic acid groups; as a relatively simple organophosphonic acid, it provides basic phosphonic acid functionality, effectively forming PO covalent bonds and adsorbing manganese ions, while its small molecular weight facilitates uniform coverage. Ethylphosphonic acid contains ethyl and phosphonic acid groups; similar to methylphosphonic acid, it provides basic phosphonic acid functionality, but the slightly longer ethyl chain may fine-tune the physicochemical properties of the modified layer. Benzylphosphonic acid contains benzyl (benzyl) and phosphonic acid groups; combining the stability of aromatic rings with the flexibility of alkyl chains, its phosphonic acid groups can effectively connect to the oxide layer and capture manganese ions. Aminopropylphosphonic acid contains aminopropyl and phosphonic acid groups; the presence of the amino group can provide additional coordination sites, enhancing the adsorption capacity for manganese ions and potentially improving the interfacial compatibility between the modified layer and the electrolyte.

[0032] In some embodiments of this application, the hydroxyl density of the oxide layer is 3 OH / nm. 2 The above, for example, 3-20OH / nm2 3 OH / nm 2 4 OH / nm 2 5 OH / nm 2 6 OH / nm 2 7 OH / nm 2 8 OH / nm 2 9 OH / nm 2 10 OH / nm 2 11 OH / nm 2 12 OH / nm 2 13 OH / nm 2 14 OH / nm 2 15 OH / nm 2 16 OH / nm 2 17 OH / nm 2 18 OH / nm 2 19 OH / nm 2 20 OH / nm 2 The hydroxyl density of an oxide layer refers to the number of hydroxyl groups (-OH) per unit area on the oxide layer surface. Hydroxyl groups, as active sites, are crucial for the covalent bonding reaction between the oxide layer and phosphorus oxyacids. To achieve a surface density of 3 OH / nm... 2 The hydroxyl density mentioned above can be achieved using various techniques. For example, the number of hydroxyl groups on the surface of the oxide layer can be increased by performing specific surface treatments, such as heat treatment in a humid and hot environment or immersion in a weak acid solution. Furthermore, when preparing the oxide layer, selecting suitable oxide materials, such as the aforementioned Al₂O₃, TiO₂, ZrO₂, SiO₂, MgO, CeO₂, LLZO, LATP, etc., typically results in a high hydroxyl density on their surface. The hydroxyl density can be quantitatively analyzed using surface analysis techniques such as X-ray photoelectron spectroscopy (XPS) or Fourier transform infrared spectroscopy (FTIR). By controlling the hydroxyl density of the oxide layer to 3 OH / nm... 2In summary, this application provides sufficient reaction sites for the formation of PO bonds between the phosphorus oxyacid covalent modification layer and the oxide layer. This significantly enhances the bonding strength between the phosphorus oxyacid covalent modification layer and the oxide layer, effectively preventing the phosphorus oxyacid covalent modification layer from detaching due to insufficient bonding force under long-term battery cycling or high-temperature conditions, thus maintaining the long-term stability of the positive electrode structure. Simultaneously, the high density of hydroxyl sites allows the oxide layer to load more phosphorus oxyacid, thereby significantly increasing the number of active sites for capturing manganese ions in the phosphorus oxyacid covalent modification layer. This enables the manganese-based positive electrode to more efficiently and persistently suppress manganese ion dissolution and interfacial side reactions, fundamentally solving the problems of electrolyte decomposition and battery performance degradation caused by manganese ion dissolution, and significantly improving the cycle life and safety of the secondary battery.

[0033] In some embodiments of this application, the oxide layer further includes a binder. Introducing a binder into the oxide layer enhances its structural stability and integrity. The binder tightly bonds the individual oxide particles within the oxide layer into a cohesive whole, effectively preventing the oxide particles from scattering or detaching under external stress. Simultaneously, the binder significantly strengthens the adhesion between the oxide layer and the underlying manganese-based positive electrode active material layer, ensuring the oxide layer firmly adheres to the surface of the manganese-based positive electrode active material layer. This effectively prevents the oxide layer from cracking or detaching during long-term battery cycling. Furthermore, the binder, added to the existing oxide layer, does not damage the structure of the original manganese-based positive electrode active material layer, nor does it negatively impact the overall electrochemical performance of the electrode, thus guaranteeing the excellent performance of the manganese-based positive electrode in terms of cycle life and safety. In other embodiments of this application, the mass percentage of the binder in the oxide layer is 0.5-10%, for example, 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, or any value between the two. A suitable binder percentage not only ensures the structural stability and integrity of the oxide layer but also provides sufficient hydroxyl reaction sites for covalent bonding with phosphorus oxyacids. The binder can be a conventional binder used in the secondary battery field, such as PVDF (polyvinylidene fluoride), CMC (sodium carboxymethyl cellulose), SBR (styrene-butadiene rubber), PAA (polyacrylic acid), and PTFE (polytetrafluoroethylene), or a suitable combination thereof.

[0034] In some embodiments of this application, the manganese-based cathode active material layer includes one or more of lithium manganese oxide, lithium manganese iron phosphate, nickel-cobalt-manganese ternary materials, and lithium-rich manganese-based materials. Lithium manganese oxide, as a typical manganese-based cathode active material, is characterized by excellent rate performance and high safety. Its stable crystal structure helps maintain structural integrity during lithium-ion insertion and extraction, thereby improving the cycle stability of the electrode. Lithium manganese iron phosphate is another important manganese-based cathode active material, with advantages including high specific capacity and a stable voltage platform, while exhibiting excellent thermal stability. Its unique olivine structure effectively suppresses lattice collapse during charge and discharge, further enhancing the cycle life of the material. Nickel-cobalt-manganese ternary materials are a type of cathode material whose performance is optimized by precisely controlling the ratio of nickel, cobalt, and manganese. These materials typically have high energy density and good cycle performance, and their diverse composition allows them to be customized according to specific application requirements to achieve the best balance between energy density, power output, and cost. Lithium-rich manganese-based materials have attracted significant attention due to their significantly higher specific capacity, making them an ideal choice for developing high-energy-density lithium batteries. Their unique layered structure allows for the storage of more lithium ions, thereby greatly improving the battery's energy storage capacity and driving range. By selecting one or more of these materials in combination, the performance of the active material layer can be flexibly adjusted according to the performance requirements of the actual application, allowing the active material layer to better adapt to the protective structure composed of the outer oxide layer and the phosphorus oxyacid covalent modification layer. This adaptability ensures that the outer protective structure can fully exert its role in suppressing interfacial side reactions and transition metal dissolution, thus effectively solving the problems of interfacial side reactions and transition metal ion dissolution that easily occur in manganese-based cathode materials under cycling and high-temperature conditions. This significantly improves the battery's cycle life and safety, and meets the application requirements of high-voltage, high-energy-density lithium batteries.

[0035] In a second aspect of this application, a method for preparing a manganese-based positive electrode sheet as described in this application is provided, comprising the following steps: A manganese-based positive electrode active material is disposed on at least one surface of the current collector to form a manganese-based positive electrode active material layer. An oxide layer is formed by depositing an oxide layer on the surface of the manganese-based positive electrode active material layer. A phosphorus-oxyacid solution is applied to the surface of the oxide layer to react and form a phosphorus-oxyacid covalent modification layer, thereby obtaining the manganese-based positive electrode sheet.

[0036] In this process, a manganese-based positive electrode active material is deposited on at least one surface of the current collector to form a manganese-based positive electrode active material layer. This step aims to construct the core energy storage structure of the electrode and provide a smooth and stable substrate for the subsequent construction of the protective layer. The implementation methods may include, but are not limited to: mixing the manganese-based positive electrode active material, binder, conductive agent, and other components with a solvent to prepare a uniform slurry, and then uniformly coating the slurry onto the surface of the current collector using methods such as scraping, rolling, or slot coating, followed by drying and rolling to form a dense active material layer; or, uniformly spraying a suspension containing the manganese-based positive electrode active material onto the surface of the current collector using a spraying method, followed by drying and curing to form the active material layer.

[0037] An oxide layer is formed on the surface of the manganese-based positive electrode active material layer. This step aims to provide overall interfacial protection for the electrode and provide sufficient connection reaction sites for subsequent covalent modification with phosphorus oxyacids. The implementation methods may include, but are not limited to: using a solution immersion-heat treatment method, immersing the electrode with the formed manganese-based positive electrode active material layer in a solution containing an oxide precursor (such as a metal salt solution), and after the precursor is adsorbed or permeated, performing appropriate heat treatment to decompose or transform the precursor into an oxide layer; or using physical vapor deposition (PVD) or chemical vapor deposition (CVD) techniques to deposit a uniform oxide film layer on the surface of the active material layer through evaporation, sputtering, or chemical reaction; or using a spraying method to uniformly spray an oxide nanoparticle dispersion onto the surface of the active material layer, followed by drying or sintering.

[0038] In some embodiments of this application, the oxide layer thickness is between 1 and 20 μm, for example, 1 μm, 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, 10 μm, 11 μm, 12 μm, 13 μm, 14 μm, 15 μm, 16 μm, 17 μm, 18 μm, 19 μm, 20 μm, or any value between the two. If the coating is too thin, the number of functional groups on the surface oxide will be insufficient, reducing the effectiveness of the coating's adsorption. Furthermore, a thin coating cannot guarantee effective protection of the entire electrode surface, and the manufacturing process becomes more difficult. If the coating is too thick, it will severely affect the cell's energy density. The coating itself does not provide capacity, and excessive thickness will lead to a significant decrease in the overall energy density of the cell. Simultaneously, excessive thickness will lengthen the path of oxide lithium ions from the negative electrode to the positive electrode, significantly increasing charge-discharge polarization and degrading the cell's charge-discharge performance.

[0039] A phosphorus oxyacid solution is applied to the surface of the oxide layer to react and form a phosphorus oxyacid covalent modification layer. This step aims to form a stable and uniform phosphorus oxyacid covalent modification layer on the oxide layer surface through a chemical reaction, thereby enhancing the capture ability of manganese ions. The implementation methods may include, but are not limited to: immersing the electrode with the oxide layer in a pre-prepared organic solvent or aqueous solution of phosphorus oxyacid, and reacting it at a specific temperature and time, causing the phosphorus oxyacid molecules to undergo esterification or condensation reactions with the hydroxyl functional groups on the oxide layer surface, forming stable PO covalent bonds; or applying the phosphorus oxyacid solution to the oxide layer surface by spraying or dripping, followed by heating or curing to promote the formation of covalent bonds and stable adhesion of the modification layer; for example, atomizing and spraying an inorganic phosphoric acid or organic phosphonic acid solution onto the oxide layer surface, with an inorganic phosphoric acid or organic phosphonic acid spraying concentration of approximately 3-300 mg / m³. 2 For example, 3 mg / m 2 10 mg / m 2 30 mg / m 2 60mg / m 2 80 mg / m 2 100 mg / m 2 120 mg / m 2 150 mg / m 2 180 mg / m 2 200 mg / m 2 240 mg / m 2 280mg / m 2 300 mg / m 2 The concentration of the inorganic phosphoric acid or organophosphonic acid solution is 0.1-100 mmol / L, for example, 0.1 mmol / L, 1 mmol / L, 2 mmol / L, 5 mmol / L, 10 mmol / L, 15 mmol / L, 20 mmol / L, 25 mmol / L, 30 mmol / L, 35 mmol / L, 40 mmol / L, 45 mmol / L, 50 mmol / L, 55 mmol / L, 60 mmol / L, 65 mmol / L, 70 mmol / L, 75 mmol / L, 80 mmol / L, 85 mmol / L, 90 mmol / L, 95 mmol / L, 100 mmol / L, or any value between any two.

[0040] In some embodiments of this application, the reaction temperature is 80-170°C, for example, 80°C, 90°C, 100°C, 110°C, 120°C, 130°C, 140°C, 150°C, 160°C, 170°C, or any value between two of these, and the reaction time is 10-180 min, for example, 10 min, 20 min, 30 min, 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min, 110 min, 120 min, 130 min, 140 min, 150 min, 160 min, 170°C. The optimal reaction temperature and time, whether 180 min or any value between these two values, provide sufficient activation energy for the dehydration grafting reaction of the phosphorus oxyacid with the hydroxyl groups on the oxide layer surface. This ensures the reaction proceeds fully, promotes the formation of more stable PO bonds, and allows the phosphorus oxyacid to be uniformly and firmly grafted onto the oxide layer surface. This avoids problems such as insufficient adhesion and uneven film formation, ensuring the modified layer can stably capture manganese ions and suppress interfacial side reactions over a long period. Furthermore, it does not damage the original structure of the prepared current collector, manganese-based cathode active material layer, and oxide layer, nor does it generate excessive unnecessary byproducts during the reaction. This guarantees the overall structural integrity and electrochemical performance of the manganese-based cathode sheet.

[0041] In some embodiments of this application, after the reaction is completed, an organic solvent may be used for cleaning, such as anhydrous ethanol, and then the organic solvent may be evaporated with a protective gas, such as nitrogen or a commonly used inert gas.

[0042] In some embodiments of this application, the manganese-based positive electrode active material includes a manganese-based positive electrode active material, a binder, and a conductive agent. The manganese-based positive electrode active material includes one or more of lithium manganese oxide, lithium manganese iron phosphate, nickel-cobalt-manganese ternary materials, and lithium-rich manganese-based materials. The manganese-based positive electrode active material is the core component providing electrochemical capacity in the manganese-based positive electrode active material. It refers to a compound containing manganese that can undergo reversible lithium-ion intercalation / deintercalation reactions. Its role is to act as a lithium-ion carrier and reaction center, determining the battery's energy density and cycle performance. The binder plays a role in firmly binding the active material particles, conductive agent, and current collector together in the manganese-based positive electrode active material. It is defined as a high-molecular polymer that provides mechanical strength and flexibility, ensuring that the active material layer does not detach or pulverize during preparation and battery cycling. Common binders may include polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), sodium carboxymethyl cellulose (CMC), etc. Conductive agents in manganese-based cathode active materials are used to improve the overall conductivity of the active material layer, reduce the internal resistance of the electrode, and ensure efficient electron transport between active material particles and between the active material and the current collector. They refer to carbon-based or metal-based materials with high conductivity. Common conductive agents can include carbon black (such as acetylene black and Ketjen black), graphite (such as natural graphite and artificial graphite), carbon nanotubes, graphene, and conductive carbon fibers.

[0043] In some other embodiments of this application, the manganese-based cathode active material is a combination of lithium manganese oxide and lithium iron manganese phosphate. Lithium manganese oxide, a common manganese-based cathode material, is characterized by low cost and excellent rate performance, providing good power output for the battery. Its crystal structure is typically spinel-type, such as LiMn₂O₄. Lithium iron manganese phosphate, an olivine-type cathode material, has high specific capacity and excellent structural stability, contributing to improved battery energy density and cycle life. For example, LiMnFePO₄. The combination of these two materials aims to compensate for the shortcomings of a single material through synergistic effects, such as the cycle stability problem of lithium manganese oxide at high temperatures and the conductivity challenges of lithium iron manganese phosphate. The mass ratio of lithium manganese oxide to lithium iron manganese phosphate is (2-4):(8-6), for example, 2:8, 3:7, 4:6, or any value between the two. A suitable combination and ratio can fully leverage the excellent rate performance and cost advantages of lithium manganese oxide, while utilizing the high specific capacity and structural stability of lithium iron manganese phosphate to achieve a synergistic effect. In the preparation of manganese-based cathode sheets, this formulation ensures a more balanced electrochemical performance of the active material layer, meeting the requirements of high energy density while effectively improving the structural stability of the cathode. Combined with the overall protection of the cathode sheet by the oxide layer and the phosphorus oxyacid covalent modification layer, this optimized active material formulation can more effectively suppress manganese ion dissolution and reduce interfacial side reactions, thereby significantly improving the cycle life and safety of the battery. This overcomes the problems of interfacial side reactions and transition metal ion dissolution that easily occur in existing manganese-based cathode materials under cycling and high-temperature conditions.

[0044] In a third aspect of this application, a secondary battery is provided, comprising a negative electrode, a positive electrode as described in this application, and an electrolyte.

[0045] The negative electrode is the core component in a secondary battery that facilitates the lithium insertion and extraction reactions. It typically consists of a current collector (e.g., copper foil) coated with a negative electrode active material, a binder, and optionally a conductive agent. The negative electrode active material can be selected from various lithium storage materials such as graphite (natural or artificial), silicon-carbon composites, lithium titanate, hard carbon, and soft carbon. The binder can be selected from polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), carboxymethyl cellulose (CMC), and polyacrylic acid (PAA). The conductive agent can be selected from carbon black, acetylene black, carbon nanotubes, and graphene.

[0046] The positive electrode sheet of this application is a manganese-based positive electrode sheet with special interface modification. It has a multi-layer protective structure that can effectively suppress interfacial side reactions and manganese ion dissolution of the manganese-based positive electrode.

[0047] The electrolyte is the medium for lithium-ion transport within a secondary battery, connecting the electrochemical reaction interface between the positive and negative electrodes. Electrolytes are typically composed of lithium salts dissolved in organic solvents, and various additives can be added to improve performance and safety. Commonly used lithium salts include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium bis(fluorosulfonyl)imide (LiTFSI), and lithium bis(oxalato)borate (LiBOB). Suitable organic solvents include ethylene carbonate (EC), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), and propylene carbonate (PC). The electrolyte ensures the normal migration of lithium ions within the battery, enabling the secondary battery to continuously and stably complete the charge-discharge process.

[0048] In a fourth aspect of this application, an electrical device is provided, including the secondary battery described in this application, the secondary battery providing electrical energy to the electrical device or serving as an energy storage unit for the electrical device.

[0049] The secondary battery provides electrical energy to electrical devices by converting stored chemical energy into electrical energy through a discharge process and supplying it to the devices to power their normal operation. For example, in electric vehicles, the secondary battery powers the drive motor; in portable electronic devices, the secondary battery directly supplies power to the internal circuitry.

[0050] The secondary battery, used as an energy storage unit in electrical equipment, refers to a battery that not only provides electrical energy but also acts as an energy buffer and storage medium. It can be charged when powered by an external power source and released when needed. For example, in smart grids or home energy storage systems, secondary batteries can be charged during off-peak electricity periods and discharged during peak periods, achieving peak shaving and valley filling, thus optimizing energy utilization. In hybrid vehicles, secondary batteries can recover and store braking energy, providing auxiliary power during acceleration and improving fuel efficiency.

[0051] The electrical equipment may include, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0052] In the comparative experiments provided in this application, unless otherwise specified, all experimental conditions and materials remain consistent to ensure comparability. Furthermore, all materials used in this application are commercially available.

[0053] The following provides a further description of a manganese-based positive electrode sheet, its preparation method, a secondary battery, and an electrical device provided in this application.

[0054] Example 1: A positive electrode sheet was prepared using lithium manganese oxide and lithium manganese iron phosphate as active materials, with a mass ratio of lithium manganese oxide: lithium manganese iron phosphate = 3:7 and a mass ratio of active material: conductive agent SP: PVDF = 96.7: 1.5: 1.8. Then, an aluminum oxide coating with a thickness of 4 μm was applied to its surface.

[0055] The positive electrode plate coated with aluminum oxide is placed in the reaction chamber and heated to 150°C.

[0056] Using an aminotrimethylenephosphonic acid ethanol solution as a liquid-phase precursor, with a concentration of 1.67 mmol / L, the aminotrimethylenephosphonic acid ethanol solution was sprayed onto the surface of the positive electrode using ultrasonic atomization. The spraying time was 60 s, the spraying flow rate was 2 mL / s, and the spraying amount was 60 mg / m³. 2 .

[0057] The reaction temperature was controlled at 150℃ and the reaction time was 30 min. Aminotrimethylenephosphonic acid molecules underwent a liquid-solid interface dehydration condensation reaction with the hydroxyl groups on the surface of the alumina coating. Aminotrimethylenephosphonic acid functional groups were covalently grafted in situ onto the oxide coating surface. A schematic diagram of the phosphonic acid / phosphoric acid reaction process on the oxide surface is shown below. Figure 2 .

[0058] After the reaction is complete, anhydrous ethanol is sprayed onto the surface of the electrode for cleaning, and then nitrogen is purged for 10-30 minutes. The electrode is then cooled to room temperature to obtain a surface-functionalized modified positive electrode.

[0059] Example 2: The method is the same as in Example 1, except that the aminotrimethylenephosphonic acid ethanol solution in Example 1 is replaced with ethylenediaminetetramethylenephosphonic acid ethanol solution, while keeping the phosphorus stoichiometry consistent with that in Example 1, that is, the ethylenediaminetetramethylenephosphonic acid ethanol solution is 1.25 mmol / L.

[0060] Example 3: The method is the same as in Example 1, except that the alumina coating of Example 1 is replaced with a titanium oxide coating.

[0061] Example 4: The method is the same as in Example 1, except that the alumina coating of Example 1 is replaced with an LLZO coating.

[0062] Example 5: The method is the same as in Example 1, except that the aminotrimethylenephosphonic acid ethanol solution in Example 1 is replaced with an aqueous solution of orthophosphoric acid, while keeping the phosphorus stoichiometry consistent with that in Example 1, i.e., the aqueous solution of orthophosphoric acid is 5 mmol / L.

[0063] Comparative Example 1: The method is the same as in Example 1, except that there is no oxide layer and a phosphate covalently modified layer.

[0064] Comparative Example 2: The method is the same as in Example 1, except that there is only an alumina coating and no phosphate covalent modification layer.

[0065] Comparative Example 3: The method is the same as in Example 3, except that only a titanium oxide coating is used, without a phosphate covalent modification layer.

[0066] Comparative Example 4: The method is the same as in Example 4, except that there is only an LLZO coating and no phosphate covalent modification layer.

[0067] Experimental example: The positive electrode sheets prepared using the various embodiments and comparative examples were assembled into test batteries. First, a 0.33C charge-discharge calibration was performed, followed by a 1C / 1C cycle test at 45°C. The results are shown in Table 1 below. Figure 3 ; Table 1

[0068] Combining Table 1 and Figure 3 The results clearly show that the oxide coating of this application produces a strong synergistic effect after chemical reaction with phosphoric acid / organophosphonic acid, which significantly improves the adsorption and fixation effect of manganese ions, significantly reduces the amount of manganese ions deposited on the negative electrode, has a significant effect on improving the stability of the negative electrode SEI film, and significantly improves the cycle performance of the battery cell.

[0069] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed herein.

Claims

1. A manganese-based positive electrode sheet, characterized in that, It includes a current collector, a manganese-based positive electrode active material layer, an oxide layer, and a phosphorus oxyacid covalent modification layer; the current collector, the manganese-based positive electrode active material layer, the oxide layer, and the phosphorus oxyacid covalent modification layer are stacked sequentially along the thickness direction of the electrode; the oxide layer and the phosphorus oxyacid covalent modification layer are connected by PO bonds.

2. The manganese-based positive electrode sheet according to claim 1, characterized in that, The oxide layer includes one or more of Al2O3, TiO2, ZrO2, SiO2, MgO, CeO2, LLZO, and LATP; the phosphorus oxyacid surface graft layer includes one or more of organic phosphonic acid and inorganic phosphoric acid.

3. The manganese-based positive electrode sheet according to claim 2, characterized in that, The inorganic phosphoric acid includes one or more of orthophosphoric acid, pyrophosphoric acid, and phosphorous acid; the organic phosphonic acid includes one or more of aminotrimethylenephosphonic acid, ethylenediaminetetramethylenephosphonic acid, phenylphosphonic acid, vinylphosphonic acid, methylphosphonic acid, ethylphosphonic acid, benzylphosphonic acid, and aminopropylphosphonic acid.

4. The manganese-based positive electrode sheet according to claim 2, characterized in that, The hydroxyl density of the oxide layer is 3OH / nm. 2 above.

5. The manganese-based positive electrode sheet according to claims 1, 2, and 4, characterized in that, The oxide layer also includes an adhesive.

6. The manganese-based positive electrode sheet according to claim 1, characterized in that, The manganese-based positive electrode active material layer includes one or more of lithium manganese oxide, lithium manganese iron phosphate, nickel-cobalt-manganese ternary materials, and lithium-rich manganese-based materials.

7. A method for preparing a manganese-based positive electrode sheet as described in claim 1, characterized in that, include: A manganese-based positive electrode active material is disposed on at least one surface of the current collector to form a manganese-based positive electrode active material layer. An oxide layer is formed by depositing an oxide layer on the surface of the manganese-based positive electrode active material layer. A phosphorus-oxyacid solution is applied to the surface of the oxide layer to react and form a phosphorus-oxyacid covalent modification layer, thereby obtaining the manganese-based positive electrode sheet.

8. The preparation method according to claim 7, characterized in that, The reaction temperature is 80-170℃.

9. The preparation method according to claim 7, characterized in that, The manganese-based positive electrode active material includes a manganese-based positive electrode active material, a binder, and a conductive agent. The manganese-based positive electrode active material includes one or more of lithium manganese oxide, lithium manganese iron phosphate, nickel-cobalt-manganese ternary materials, and lithium-rich manganese-based materials.

10. The preparation method according to claim 9, characterized in that, The manganese-based positive electrode active material is lithium manganese oxide and lithium iron manganese phosphate, and the mass ratio of lithium manganese oxide to lithium iron manganese phosphate is (2-4):(8-6).

11. A secondary battery, characterized in that, It includes a negative electrode, a positive electrode as described in any one of claims 1-6, and an electrolyte.

12. An electrical appliance, characterized in that, Includes the secondary battery of claim 11, wherein the secondary battery provides electrical energy to the electrical device or serves as an energy storage unit for the electrical device.

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