Positive electrode active material, preparation method, positive plate, battery, battery pack and electric equipment

Abstract

The embodiment of the invention provides a positive active material, a preparation method, a positive plate, a battery, a battery pack and electric equipment. The positive electrode active material comprises a LixMayPO4 inner core and a coating layer covering at least part of the surface of the lithium iron phosphate inner core, the coating layer comprises a carbon matrix and an M-N4 coordination structure distributed in the carbon matrix, M is a metal element, Ma comprises at least one of Fe, Mn, Ni and Co, a is greater than or equal to 0.9 and less than or equal to 1.1, and y is greater than or equal to 0.9 and less than or equal to 1.05. The positive electrode active material not only is beneficial to improving the cycle performance of the battery, but also improves the safety performance and the rate capability of the battery to a certain extent.

Description

Technical Field

[0001] This application relates to the field of batteries, and more particularly to a positive electrode active material, a preparation method, a positive electrode sheet, a battery, a battery pack, and an electrical device. Background Technology

[0002] Rechargeable batteries, also known as secondary batteries, are widely used in modern society. In consumer electronics, they serve as the "power heart" of devices such as mobile phones, tablets, and laptops, enabling people to maintain communication, entertainment, and work anytime, anywhere. In transportation, the rechargeable batteries in electric vehicles have driven a green travel revolution, reducing reliance on traditional fuels and lowering carbon emissions. Furthermore, rechargeable batteries play an indispensable role in specialized fields such as aerospace, medical devices, and energy storage systems, ensuring the normal operation of equipment. The efficient and stable performance of rechargeable batteries depends on the coordinated operation of their various key components. Among these, the positive electrode active material, as one of the core components of a rechargeable battery, directly determines key indicators such as energy density, cycle life, and safety performance.

[0003] Among numerous cathode materials, phosphate systems, represented by olivine-structured lithium iron phosphate (LiFePO4), offer significant advantages. Intrinsic safety is a key highlight of lithium iron phosphate. Its strong covalent P-O bonds are stable at high temperatures, effectively suppressing oxygen release. Its thermal runaway temperature is significantly higher than that of layered oxides, greatly reducing the risk of accidents caused by thermal runaway under extreme operating conditions. Simultaneously, iron resources are abundant and non-toxic, significantly reducing raw material costs and environmental risks, aligning with companies' requirements for cost control and environmental protection.

[0004] However, the problems of rapid capacity decay, excessive gas production, and low capacity at high rates during the cycling process of lithium iron phosphate batteries cannot be ignored. How to effectively improve the cycle performance, safety performance, and rate performance of lithium iron phosphate batteries is a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] This application provides a positive electrode active material whose special chemical composition helps to reduce the water content in the battery system, which not only improves the cycle performance of the battery, but also improves the safety performance and rate performance of the battery to a certain extent.

[0006] This application provides a preparation method that can prepare the above-mentioned positive electrode active material.

[0007] This application provides a positive electrode sheet comprising the aforementioned positive electrode active material, which helps improve the battery's performance in terms of cycle performance, rate performance, and safety performance.

[0008] This application also provides a battery including the above-mentioned positive electrode, which exhibits excellent cycle performance, rate performance and safety performance.

[0009] This application also provides a battery pack including the above-mentioned battery, which exhibits excellent cycle performance, rate performance, and safety performance.

[0010] This application also provides an electrical device including the above-mentioned battery or battery pack, which not only has a longer standby time and service life, but also takes into account the advantages of high safety and fast charging.

[0011] This application provides a positive electrode active material, including Li x Ma y PO4 kernel and overlaid on the Li x Ma y A coating layer on at least part of the surface of the PO4 core; the coating layer includes a carbon matrix and an M-N4 coordination structure distributed in the carbon matrix, wherein M is a metal element, Ma includes at least one of Fe, Mn, Ni, and Co, 0.9≤a≤1.1, and 0.9≤y≤1.05.

[0012] In the positive electrode active material described above, the bond length of the MN bond in the M-N4 coordination structure is 1.3~3 Å.

[0013] The positive electrode active material as described above, wherein the coating layer includes a metallic material, which includes at least one of elemental metal and metal compound; the metallic element in the metallic material is the same as M.

[0014] The positive electrode active material as described above, wherein the elemental metal includes at least one of Fe, Co, Ni, Ru, Ir, Pt, Pd, Mn, Zn, Cu, Al, Mo, Ag, and Au; and / or, the metal compound includes at least one of oxides, sulfides, phosphides, and fluorides of Fe, Co, Ni, Ru, Ir, Pt, Pd, Mn, Zn, Cu, Al, Mo, Ag, and Au.

[0015] The positive electrode active material as described above, wherein the particle size of the metallic material is in the nanometer range.

[0016] In the above-described positive electrode active material, the particle size of the metallic material is 0.5 nm to 5 nm; and / or,

[0017] The metallic material has a mass percentage content of 0.2% to 1.5% in the positive electrode active material.

[0018] In the positive electrode active material described above, the mass percentage of nitrogen element in the coating layer is 5-30%.

[0019] In the above-described positive electrode active material, the thickness of the coating layer is 5-20 nm; and / or, the mass percentage of the carbon matrix in the positive electrode active material is 1-2.5%; and / or, the carbon matrix comprises amorphous carbon.

[0020] The positive electrode active material as described above, wherein the specific surface area of ​​the positive electrode active material is 10-20 m² / g; and / or, the Li x Ma y The PO4 kernel is Li x Mn n Fe m PO4, n+m=y, n>0, m>0.

[0021] This application provides a method for preparing the positive electrode active material according to any one of the above claims, comprising the following steps:

[0022] The nitrogen-macrocyclic compound-M complex with Li x Ma y After the reaction with PO4, the solid product is calcined to obtain the positive electrode active material.

[0023] In the preparation method described above, the aza-macrocyclic compound-M complex includes at least one of porphyrin compounds, phthalocyanine compounds, and carboxylic acid compounds.

[0024] In the preparation method described above, the aza-macrocyclic compound-M complex is obtained by reacting the aza-macrocyclic compound with an M salt.

[0025] This application provides a positive electrode sheet, which includes the positive electrode active material described in any of the above claims, or the positive electrode active material prepared by any of the above preparation methods.

[0026] This application provides a battery including the positive electrode described above.

[0027] This application provides a battery pack comprising at least two batteries as described above.

[0028] This application provides an electrical device, including the battery or battery pack described above.

[0029] The positive electrode active material provided in this application embodiment is in Li x Ma yThe PO4 core is at least partially coated with a carbon matrix coating layer comprising an M-N4 coordination structure. This coating layer acts as a catalyst to remove moisture from the battery, preventing side reactions with the electrolyte during cycling that could lead to the consumption of active lithium, gas expansion, and collapse of the positive electrode active material. Furthermore, it increases the lithium-ion and electron transport rates of the positive electrode active material. Therefore, the positive electrode active material of this application not only possesses the inherent safety advantages of phosphate materials but also further enhances the battery's stability, safety, and rate performance during cycling. Attached Figure Description

[0030] Figure 1 This is a schematic diagram of an embodiment of the positive electrode active material of this application. Detailed Implementation

[0031] To enable those skilled in the art to better understand the solutions of this application, a further detailed description of this application is provided below. The specific embodiments listed below are merely descriptions of the principles and features of this application; the examples are only for explaining this application and are not intended to limit its scope. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without inventive effort are within the scope of protection of this application. When the following description relates to the accompanying drawings, unless otherwise indicated, the same numbers in different drawings represent the same or similar elements.

[0032] To suppress the rapid capacity decay of phosphate-based cathode active materials during cycling, the inventors studied the material changes of phosphate-based cathode active materials during charge and discharge processes. They discovered that phosphate-based cathode active materials, due to their large specific surface area, absorb water during battery fabrication. The water reacts with the electrolyte to produce a large amount of HF, which not only consumes the active lithium in the system during battery cycling but also causes the dissolution of transition metals in the cathode active material, leading to rapid capacity decay. Simultaneously, hydrogen ions are reduced to H2 at the negative electrode, causing significant gas production in the battery and posing a safety risk.

[0033] Therefore, in order to reduce the water content in the battery, the inventors attempted to bake the battery after formation to remove water. However, the water removal effect was not significant, and the water content in the positive electrode remained above 1000 ppm. The inventors analyzed that baking could only remove water by heating it to the boiling point of water at high temperatures, causing it to vaporize. However, due to the high tortuosity of the electrodes and the high porosity of the electrode material, the capillary adsorption of water by the electrode pores was strong, making it difficult to remove the water even through long-term baking at high temperatures.

[0034] Based on this, embodiments of this application provide a positive electrode active material, including Li x May PO4 kernel and overlaid on the Li x Ma y A coating layer on at least part of the surface of the PO4 core; the coating layer includes a carbon matrix and an M-N4 coordination structure distributed in the carbon matrix, wherein M is a metal element, Ma includes at least one of Fe, Mn, Ni, and Co, 0.9≤a≤1.1, and 0.9≤y≤1.05.

[0035] Specifically, the positive electrode active material in this application embodiment has a core-shell coated structure, wherein Li x Ma y PO4 forms the core of the positive electrode active material. The coating layer on at least a portion of the outer surface of this core includes a carbon matrix formed of carbon material and M-N4 coordination structures dispersed within the carbon matrix. This application does not limit the number of M-N4 coordination structures in the carbon matrix. Each M-N4 coordination structure includes four nitrogen atoms and one M atom (where M is a metal element) bonded to each nitrogen atom. The choice of M is not specifically limited in this application.

[0036] The positive electrode active material of this application embodiment helps to reduce the water content in the battery. Specifically, by subjecting the battery including the positive electrode active material of this application embodiment to high-pressure dehydration after formation, due to the catalytic effect of the M-N4 coordination structure, most of the water in the battery will undergo electrocatalytic oxidation under high voltage and decompose into gas. The decomposed gas enters the gas bag and is collected and discharged from the battery system, thereby significantly reducing the water content in the battery, effectively suppressing the consumption of active lithium and the dissolution of transition metals, and giving the battery superior electrical performance, including cycle performance.

[0037] The excellent water removal performance of the positive electrode active material in this application embodiment is mainly due to the coordination structure in the coating layer. In the M-N4 coordination structure, the central metal M typically exists in a +2 or +3 valence state and can undergo reversible valence state changes during electrochemical reactions. This reversible valence state change characteristic enables the central metal M to act as an electron transfer medium, promoting the oxidation reaction of water molecules at the positive electrode. During this reaction process, oxygen-oxygen bonds are gradually formed, eventually generating oxygen. This series of reaction mechanisms allows water molecules to be removed from the battery system, helping to maintain the stability of the internal chemical reaction environment of the battery and reducing the adverse effects that may be caused by the presence of moisture.

[0038] Furthermore, when water molecules undergo oxidation, oxygen and peroxide intermediates are produced. The planar four-coordinate structure M-N4, formed by the lone pair electrons of four nitrogen atoms coordinating with metal M, stabilizes these intermediates. This coordination structure, through specific chemical interactions, keeps the oxygen and peroxide intermediates in a relatively stable state, preventing unnecessary side reactions or decomposition and ensuring the controllability of the reaction process. Simultaneously, the M-N4 coordination structure causes some orbitals of metal M to overlap with those of the oxygen and peroxide intermediates. This orbital overlap lowers the energy barrier of the oxidation reaction, allowing it to proceed more smoothly towards the forward reaction direction.

[0039] Based on the above-described mechanism, the battery containing the positive electrode active material of this application embodiment can perform a highly efficient electrocatalytic water splitting reaction. Through this reaction, the water content in the battery is effectively reduced, thereby suppressing the occurrence of side reactions. The reduction of side reactions not only increases the active lithium content in the battery system and enhances the structural stability of the positive electrode active material, but also reduces the gas production of the system. These positive effects work together to make the battery perform excellently in terms of cycle performance and safety performance, providing strong support for its stability and reliability in practical applications.

[0040] It is worth mentioning that the aforementioned coordination structure M-N4 in the coating layer further enriches the connection pathways of the conductive network within the coating layer, making electron transport smoother and more efficient. Simultaneously, it can also efficiently induce polarization in the coating layer. The polarized coating layer exhibits stronger adsorption and guidance capabilities for lithium ions. This change significantly lowers the diffusion barrier of lithium ions, reducing the resistance encountered by lithium ions during migration within the battery, enabling them to travel more quickly between the positive and negative electrodes. This results in batteries containing this positive electrode active material exhibiting excellent rate performance, with particularly outstanding fast charging capabilities. Whether in fast charging or high-current discharge scenarios, the battery can operate stably and efficiently, meeting users' needs for rapid battery replenishment and efficient output.

[0041] As mentioned earlier, during the formation and capacity testing of a battery including the positive electrode active material of this application, the battery is charged to induce an electrocatalytic oxidation reaction of water in the battery. Oxygen is oxidized to oxygen at the positive electrode, and hydrogen diffuses to the negative electrode and is reduced to hydrogen. Both oxygen and hydrogen are then discharged from the battery system. This application does not limit the specific charge-discharge regime for water removal, but it should be noted that the theoretical potential for water oxidation is 1.23V vs. RHE, and the potential of lithium to hydrogen is -3.04V. Therefore, the theoretical potential for water oxidation at the positive electrode is 4.27V vs. Li. Due to the large reaction energy barrier, the actual charging cutoff voltage needs to be controlled to be higher than the theoretical voltage during the water removal process. Generally, the water removal process voltage is set to 4.5V. Specifically, this water removal process needs to be carried out before capacity testing to ensure that the generated gas can be discharged during the capacity testing process. The water removal process can be completed together with the formation process at the water removal process voltage; the formation process can be performed first, followed by water removal according to the water removal process voltage.

[0042] In one specific embodiment, the bond length of each MN bond in the M-N4 coordination structure is 1.3~3 Å. At this bond length, the M-N4 coordination structure has higher efficiency for the electrocatalytic oxidation of water in the battery, which facilitates further reduction of the residual water content in the battery.

[0043] Figure 1 This is a cross-sectional schematic diagram of an embodiment of the positive electrode active material of this application. In one specific embodiment, in the positive electrode active material of this application, the coating layer 1 covers the Li... x Ma y At least a portion of the surface of the PO4 core 2, and the coating layer 1, in addition to comprising a carbon matrix, also includes a metallic material 1a, which includes at least one of an elemental metal and a metal compound; the metal element in the metallic material 1a is the same as M. Specifically, M in the M-N4 coordination structure originates from the metallic material 1a. For example, when the metallic material is an elemental metal, one M atom of the elemental metal forms the aforementioned M-N4 coordination structure with four nitrogen atoms in the coating layer; when the metallic material is a metal compound, one M atom of the metal compound forms the M-N4 coordination structure with four nitrogen atoms in the coating layer.

[0044] The embodiments of this application do not limit the types of metal compounds. Any compound formed by the chemical bonding of a metal element M with other non-metal elements is considered a metal compound in the embodiments of this application.

[0045] In one specific embodiment, the metallic element includes at least one selected from Fe, Co, Ni, Ru, Ir, Pt, Pd, Mn, Zn, Cu, Al, Mo, Ag, and Au. In another specific embodiment, the metallic compound includes at least one selected from oxides, sulfides, phosphides, and fluorides of Fe, Co, Ni, Ru, Ir, Pt, Pd, Mn, Zn, Cu, Al, Mo, Ag, and Au. Exemplarily, the metallic material can be a mixture of Pt / Ni, a mixture of Pt / Co, a mixture of Fe / Fe₂O₃, etc. In specific implementations, when M is Pt, the electrocatalytic water removal performance of the battery including the positive electrode active material of this application is better.

[0046] To enhance the electrocatalytic activity of the positive electrode active material for water in the embodiments of this application, the particle size of the metal-based material can be controlled to be at the nanometer scale. Specifically, the metal-based material is distributed in a carbon matrix, and the particle size of each metal-based material is independently in the range of 1-100 nm. Since the particle size of the metal-based material is at the nanometer scale, the resulting M-N4 coordination structure is also more dispersed, which facilitates increasing the contact area with water, thereby improving the electrocatalytic oxidation activity for water.

[0047] In the specific implementation of the embodiments of this application, reasonably controlling the particle size of metallic materials is beneficial to further improving the cycle performance of lithium-ion batteries. Therefore, the particle size of metallic materials can be controlled within 5 nm. The inventors have found that as the particle size of metallic materials decreases within a certain range, the cycle performance of the battery first shows an increasing trend, and then remains basically unchanged. Therefore, for economic reasons, the particle size of metallic materials is generally controlled between 0.5 nm and 5 nm.

[0048] Furthermore, to reduce the impact of metallic materials on battery energy density, the mass percentage of metallic materials in the positive electrode active material can be controlled between 0.2% and 1.5%. Within this range, not only can the water content in the battery be minimized, but it will also not negatively affect the battery's energy density. Further, the mass percentage of metallic materials in the positive electrode active material can be controlled between 0.5% and 1.5%, and even further, between 0.7% and 1.2%.

[0049] Furthermore, the mass percentage of nitrogen in the coating layer is 5-30%. On the one hand, controlling the nitrogen content within this range helps to form sufficient M-N4 coordination structures, thereby meeting the water removal requirements of the battery. On the other hand, the appropriate amount of nitrogen doped into the carbon matrix can not only induce some defects in the coating layer, thereby further improving the electronic conductivity and lithium-ion diffusion rate of the positive electrode active material, but also improve the interfacial wetting performance between the positive electrode active material and the electrolyte, promoting the penetration of the electrolyte into the positive electrode sheet.

[0050] In one specific embodiment, the thickness of the coating layer is 5~20 nm. As Li x Ma y The thickness of the coating layer, which acts as a barrier outside the PO4 core, is also a crucial factor affecting battery performance. In this application, the coating layer thickness is controlled to be 5-20 nm, maximizing the rate performance of the positive electrode active material while ensuring normal lithium-ion diffusion.

[0051] Furthermore, in this application embodiment, the carbon matrix is ​​mainly used to improve the conductivity of the positive electrode active material. In this application embodiment, when the mass percentage of the carbon matrix in the positive electrode active material is controlled to be 1~2.5%, rapid electron conduction and smooth ion migration are ensured while maximizing Li... x Ma y The PO4 core provides capacity utilization efficiency, achieving an optimal balance between energy density and rate performance of the cathode active material.

[0052] Furthermore, when the carbon matrix in the coating layer includes amorphous carbon, the amorphous carbon is beneficial to further increase the dispersion performance of the metallic materials and avoid the agglomeration of the metallic materials, which would affect the electrocatalytic activity of the positive electrode active material for water in the embodiments of this application.

[0053] To further improve the cycle performance of the battery, the specific surface area of ​​the positive electrode active material is limited in this application embodiment. Specifically, when the specific surface area of ​​the positive electrode active material is 10-20 m² / g, the positive electrode active material provides more active sites for lithium ion insertion / extraction while maximally suppressing electrolyte side reactions.

[0054] Furthermore, the inventors discovered that the Li of the positive electrode active material in the embodiments of this application... x Ma y The PO4 core is made of lithium manganese iron phosphate, i.e., Li x Ma y The PO4 kernel is Li x Mn n Fe m When PO4 (n+m=y, n>0, m>0) is present, the electrocatalytic water removal effect of the battery is more significant, which helps to make the positive electrode active material exhibit better structural stability and extend the cycle life of the battery.

[0055] The methods used in this application to detect the composition of the positive electrode active material include those commonly used in the field of chemistry. For example, the chemical composition of the core is detected by ICP-OES; the nitrogen content in the coating layer is detected by XPS; the coordination structure and bond length of the coordination bonds in the coating layer are detected by a combination of XANES and EXAFS; the size of the metal material and the thickness of the coating layer are detected by high-angle annular dark-field spherical aberration electron microscopy; the carbon content in the positive electrode active material is detected by carbon-sulfur analysis; and the chemical composition of the metal material is determined by SEM-EDS and XRD.

[0056] For example, when testing the positive electrode active material in a battery, the discharged battery is disassembled and the positive electrode sheet is removed. The positive electrode sheet is soaked in water to deactivate the binder, thus separating the positive electrode active layer from the positive electrode current collector. The positive electrode active layer is ground and dissolved in NMP, heated at 120°C and stirred at 1200 rpm for 2 hours to fully dissolve the binder. The mixture is filtered to obtain a solid material, washed three times with NMP, and then filtered again to completely remove residual binder. The remaining system is then added to water. Because the density of the positive electrode active material is greater than that of the conductive agent, the denser positive electrode active material sinks to the bottom, while the less dense conductive agent floats in the supernatant. By centrifuging the system at different speeds (5000-8000-10000-15000 rpm), the supernatant is continuously removed until no positive electrode active material is visible in the SEM of the supernatant and no conductive agent is present in the lower layer, indicating that the conductive agent has been completely removed. The remaining solid material is mixed, washed three times with deionized water, and dried to obtain pure positive electrode active material. Subsequently, the relevant parameters of the positive electrode active material were tested according to the aforementioned testing method.

[0057] A second aspect of this application provides a method for preparing the aforementioned positive electrode active material, comprising the following steps:

[0058] The nitrogen-macrocyclic compound-M complex with Li x Ma y After the reaction with PO4, the solid product is calcined to obtain the positive electrode active material.

[0059] In the embodiments of this application, the nitrogen-macrocyclic compound-M complex refers to a compound formed by the coordination bond between a nitrogen-containing macrocyclic organic ligand and a metal element M. The nitrogen-macrocyclic ligand refers to a cyclic organic molecule (usually composed of 12-16 atoms) whose ring skeleton contains multiple nitrogen atoms (such as tetraaza-macrocycles, hexaaza-macrocycles, etc.), and these nitrogen atoms provide lone pairs of electrons to coordinate with the metal M.

[0060] By combining the nitrogen-macrocyclic compound-M complex with Li x Ma y After the reaction of PO4, it forms on Li xMa y Solid-phase products containing aza-macrocyclic compound-M complexes are adsorbed and aggregated on the PO4 surface. During subsequent calcination of these solid-phase products, the M-N4 coordination structure within the aza-macrocyclic compound-M complex remains intact, while the carbon skeleton forms a carbon matrix, resulting in the positive electrode active material of this embodiment. Simultaneously, M atoms and derivative atoms (atoms other than carbon, N, and M atoms in the aza-macrocyclic compound-M complex) aggregate to form metallic elements or metallic compounds, or other metallic materials.

[0061] In one specific embodiment, a complex comprising a nitrogen-based macrocyclic compound-M and Li x Ma y After the PO4 reaction solution reacts at 80-120°C for 12-24 hours, the reaction system is subjected to solid-liquid separation and the solid product is washed. Subsequently, the washed solid product is calcined at 600-750°C for 3-5 hours to obtain the positive electrode active material of this embodiment. Exemplarily, the solvent in the reaction solution can be at least one of DMF, DMSO, DMAc, DMPU, and NMP.

[0062] In one specific embodiment, the aza-macrocyclic compound includes at least one of porphyrin compounds, phthalocyanine compounds, porphyrin compounds, and carboxylic acid compounds.

[0063] In detail, porphyrin compounds include porphyrins and their derivatives, phthalocyanine compounds include phthalocyanines and their derivatives, porphyrin compounds include porphyrins and their derivatives, and carboxylic acid compounds include carboxylic acid and its derivatives.

[0064] Taking phthalocyanine (Formula a), porphyrin (Formula b), porphyrin (Formula c), and porphyrin derivative (Formula d) as examples, the phthalocyanine macrocyclic compounds in the embodiments of this application have a special conjugated structure. The four nitrogen atoms at the center have lone pairs of electrons, which readily form phthalocyanine macrocyclic compound-M complexes with metal element M, including M-N4 coordination structures, namely phthalocyanine-M complex (Formula A), porphyrin-M complex (Formula B), porphyrin-M complex (Formula C), and porphyrin derivative-M complex (Formula D).

[0065] Formula a Formula A

[0066] Formula b Formula B

[0067] Formula c Formula C

[0068] Formula d Formula D

[0069] This application does not limit the preparation method of the above-mentioned aza-macrocyclic compound-M complex. In one specific embodiment, the aza-macrocyclic compound-M complex is obtained by reacting the aza-macrocyclic compound with an M salt. Specifically, the aza-macrocyclic compound and the M salt are dissolved in a solvent, and then heated to induce a coordination reaction. After post-treatment of the reaction system, including precipitation and washing, the aza-macrocyclic compound-M complex is obtained. The anion in the M salt can be, for example, chloride, sulfate, nitrate, acetate, etc. Generally, the molar ratio of the aza-macrocyclic compound to the M salt can be 1:(0.8-1.5); the solvent can be at least one of DMF, DMSO, DMAc, DMPU, NMP, etc.; the heating temperature for inducing the coordination reaction can be, for example, 80℃-120℃, and the heating reaction time can be, for example, 12h-48h.

[0070] Furthermore, the embodiments of this application address Li x Ma y The preparation method of PO4 is not specifically limited, and commonly used methods in the field can be employed. For example, a Ma source and a phosphorus source are added to a deionizer in a certain proportion, and the pH is adjusted to generate a precursor precipitate. Subsequently, the precursor precipitate and a lithium source are ball-milled and calcined at a certain temperature, then dispersed and sieved to obtain Li. x Ma y PO4.

[0071] A third aspect of this application provides a positive electrode sheet, which includes the positive electrode active material described in the first aspect or the positive electrode active material prepared in the second aspect. Therefore, the positive electrode sheet of this application provides a certain degree of improvement in the cycle performance, rate performance, and safety performance of the battery.

[0072] The positive electrode sheet of this application specifically includes a positive current collector and a positive active layer comprising a positive active material disposed on at least one surface of the positive current collector.

[0073] In the specific preparation of the positive electrode sheet, for example, the positive electrode active material, conductive agent, and binder of the embodiments of this application can be dispersed in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred and mixed to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder, and further comprises 80-98 wt% of positive electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0074] The positive current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0075] A fourth aspect of this application also provides a battery, including the aforementioned positive electrode sheet. The battery provided by this application has excellent cycle performance, rate performance, and safety performance.

[0076] In the embodiments of this application, unless otherwise specified, the coating, drying, rolling and other processes involved are all conventional operations in the art, and the equipment used can be conventional equipment in the art, and there are no special restrictions on them.

[0077] Generally, a battery includes an electrolyte, a battery cell, and a casing that encapsulates the battery cell. The electrolyte is injected into the battery cell inside the casing. The battery cell includes a positive electrode, a negative electrode, and a separator located between the positive and negative electrode. The battery cell can be a stacked cell, meaning it is composed of alternating layers of positive electrode, separator, and negative electrode; or it can be a wound cell, meaning it is composed of stacked positive electrode, separator, and negative electrode, which are then wound together.

[0078] Specifically, the negative electrode sheet includes a negative current collector and a negative active layer located on at least one side surface of the negative current collector. Specifically, the negative active layer can be provided on one side surface of the negative current collector, or negative active layers can be provided on both opposite sides of the negative current collector in the thickness direction.

[0079] Specifically, the negative electrode active layer may include a negative electrode active material, a conductive agent, and a binder, all of which can be conventional materials in the art. For example, the negative electrode active material may include one or more of natural graphite, artificial graphite, petroleum coke, and silicon carbide materials; the conductive agent may include one or more of conductive carbon black, carbon nanotubes (CNT), acetylene black, graphene, Ketjen black, and carbon fiber; and the binder may include one or more of sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate.

[0080] The embodiments of this application may employ conventional negative electrode current collectors in the art, for example, negative electrode current collectors may include copper foil.

[0081] In this embodiment, the negative electrode sheet can be prepared by conventional methods in the art, such as by coating. Specifically, the components used to form the negative electrode active layer, such as the negative electrode active material, conductive agent, and binder, can be dispersed in a solvent, such as water, to prepare a negative electrode slurry. This slurry is then coated onto the surface of the negative electrode current collector, and after drying, rolling, and other processes, the negative electrode sheet is obtained. The coating, drying, and rolling processes involved are conventional operations for preparing negative electrode sheets using the coating method, and are not particularly limited thereto.

[0082] The electrolyte in this application embodiment can be a conventional electrolyte in the art. For example, the electrolyte is a non-aqueous electrolyte, which may specifically include organic solvents, additives and electrolyte salts. Organic solvents include one or more of ethylene carbonate (EC), diethyl carbonate (DEC) and propylene carbonate (PC). Additives include, for example, fluoroethylene carbonate (FEC) and vinylene carbonate (VC). Electrolyte salts may include lithium salts, such as lithium hexafluorophosphate (LiPF6), but are not limited thereto.

[0083] In this embodiment, the separator is used to separate the positive and negative electrode plates, preventing short circuits caused by contact between them. Conventional separators in the art can be used in this embodiment, and there are no particular limitations. For example, the separator material can be one or more of the following: high-density polyethylene, ultra-high-density polyethylene, low-density polyethylene, linear low-density polyethylene, high-density polypropylene, ultra-high-density polypropylene, polyimide, and polyvinylidene fluoride.

[0084] In this embodiment, the battery cell can be packaged using conventional housing materials in the art, such as flexible packaging materials like aluminum-plastic film, but is not limited to these.

[0085] The embodiments of this application can assemble components such as positive electrode, separator and negative electrode into a battery using conventional methods in the art. For example, positive electrode, separator and negative electrode can be stacked in an alternating manner to obtain a stacked cell (or wound into a wound cell); then the cell is placed in a casing (outer packaging) and after conventional processes such as electrolyte injection (i.e., injection of electrolyte) and encapsulation, a battery is obtained.

[0086] The fifth aspect of this application also provides a battery pack including at least two of the above-described batteries, which has advantages corresponding to the above-described batteries, and will not be described in detail hereafter.

[0087] Generally, a battery pack includes multiple batteries as individual cells, which are connected to form the battery pack. These batteries can be electrically connected using methods conventional in the art, such as series connection, parallel connection, or a combination of these connection methods, without any particular limitation.

[0088] This application also provides an electrical device, including the battery or battery pack described above, which has the advantages of long standby time, long service life, and safe fast charging.

[0089] The electrical equipment used in the embodiments of this application can be conventional electrical equipment in the art, such as power equipment (e.g., electric vehicles, electric cars), electronic equipment (e.g., mobile phones, tablets, laptops, digital cameras, etc.), wearable devices (e.g., watches, bracelets, VR glasses, etc.), energy storage power stations, etc., and there are no special limitations on this.

[0090] The positive electrode active material of this application will be described in detail below through specific embodiments.

[0091] Example 1

[0092] The preparation method of the positive electrode active material in this embodiment includes the following steps:

[0093] 1) Dissolve MnSO4 and FeSO4 in deionized water at a ratio of 6:4, add phosphoric acid at a molar ratio of (Fe+Mn) / P = 1.05, and adjust the pH to 9 by adding ammonia solution dropwise to generate the coprecipitate precursor Mn. x Fe 1-x PO4 was ball-milled with lithium source Li2CO3 at a ratio of 1:1.05 and then sintered at 700℃, followed by gas-powdering to form LiMn. 0.6 Fe 0.4 PO4 particles;

[0094] 2) PtCl2 and the porphyrin shown in formula c were dissolved in DMF solution at a molar ratio of 1:1. The mixture was reacted in an oil bath at 80°C for 12 h. After centrifugation, washing and drying of the precipitate, the nitrogen-macrocyclic compound-M complex, i.e., Pt-TPP powder, was obtained.

[0095] 3) LiMn 0.6 Fe 0.4 PO4 particles and Pt-TPP powder from step 2) were dispersed in DMF solution at a mass ratio of 100:10. The mixture was reacted in an oil bath at 120°C for 24 hours. After centrifugation and washing three times in DMF, the mixture was baked and dried. It was then calcined at 700°C for 4 hours in an Ar atmosphere to obtain the positive electrode active material of this embodiment.

[0096] Example 2

[0097] The preparation method of this embodiment is basically the same as that of Example 1, except that in step 2), FeCl2 is used to replace PtCl2 to obtain Fe-TPP powder.

[0098] Example 3

[0099] The preparation method of this embodiment is basically the same as that of Example 1, except that in step 2), Co(NO3)2 is used to replace PtCl2 to obtain Co-TPP powder.

[0100] Example 4

[0101] The preparation method of this embodiment is basically the same as that of Example 1, except that in step 2), MnSO4 is used to replace PtCl2 to obtain Mn-TPP powder.

[0102] Example 5

[0103] The preparation method of this embodiment is basically the same as that of Example 2, except that in step 2), the porphyrin derivative shown in formula d is used to replace the porphyrin to obtain Fe-TCPP powder.

[0104] Example 6

[0105] The preparation method of this embodiment is basically the same as that of Example 1. The difference is that in step 2), Ni(NO3)2 is used to replace part of PtCl2 so that the molar ratio of Ni to Pt is 1:1, and a mixture of Pt-TPP powder and Ni-TPP powder is obtained.

[0106] Example 7

[0107] The preparation method of this embodiment is basically the same as that of Example 2, except that step 2) includes steps 2a) and 2b), wherein step 2a) is the same as step 2) of Example 2, and step 2b) is the same as step 2) of Example 5, to obtain a mixture of Fe-TPP powder and Fe-TCPP powder. The molar ratio of Fe-TPP powder to Fe-TCPP powder is 1:1.

[0108] Example 8

[0109] The preparation method of this embodiment is basically the same as that of Example 1, except that in step 2), phthalocyanine as shown in formula a is used to replace porphyrin to obtain Pt-Pc powder.

[0110] Example 9

[0111] The preparation method in this embodiment is basically the same as that in Example 1, except that in step 3), LiMn 0.6 Fe 0.4 The mass ratio of PO4 particles to Pt-TPP powder in step 2) is 100:5.

[0112] Example 10

[0113] The preparation method in this embodiment is basically the same as that in Example 1, except that in step 3), LiMn 0.6 Fe 0.4The mass ratio of PO4 particles to Pt-TPP powder in step 2) is 100:15.

[0114] Example 11

[0115] The preparation method in this embodiment is basically the same as that in Example 1, except that in step 3), LiMn 0.6 Fe 0.4 The mass ratio of PO4 particles to Pt-TPP powder in step 2) is 100:20.

[0116] Example 12

[0117] The preparation method of this embodiment is basically the same as that of Example 1, except that in step 2), PtCl2 and porphyrin are dissolved in DMF at a molar ratio of 1.5:1.

[0118] Example 13

[0119] The preparation method in this embodiment is basically the same as that in Example 1. The difference is that in step 1), no Mn source MnSO4 is added, and the coprecipitated precursor FePO4 is generated.

[0120] Comparative Example 1

[0121] The preparation method of this comparative example includes the following steps:

[0122] The LiMn in Example 1 0.6 Fe 0.4 PO4 and the porphyrin shown in formula c were dispersed in DMF solution at a mass ratio of 100:10. The mixture was reacted in an oil bath at 120°C for 24 hours. After centrifugation and washing three times in DMF, the mixture was baked and dried. It was then calcined at 700°C for 4 hours in an Ar atmosphere to obtain the positive electrode active material of this comparative example.

[0123] Experimental Example 1

[0124] The following parameters of the positive electrode active materials in the examples and comparative examples were tested, and the results are shown in Tables 1 and 2.

[0125] 1) Chemical composition of the core: The positive electrode active material is dissolved in aqua regia and filtered to remove the coating layer. The filtrate is then subjected to ICP-OES testing.

[0126] 2) Specific surface area (BET) of the positive electrode active material: detected by gas adsorption method.

[0127] 3) Mass percentage of N element in the coating layer w1: XPS was used to detect the positive electrode active material, and the sputtering range was controlled to be <5nm to avoid the coating layer being penetrated. The mass percentage of N element in the coating layer can be obtained by the total spectrum.

[0128] 4) Coordination Structure and Coordination Bond Lengths: Synchrotron radiation XANES and EXAFS are used to analyze the coordination environment around metals. By fitting the R-space data after Fourier transform, the bond length and coordination number between metal M and nitrogen can be accurately determined. The sample to be tested is dispersed in an alcohol solution and then uniformly coated on a carbon film. The light source is set to absorb energy at the K-edge (e.g., Fe K-edge ≈ 7112 eV, Co K-edge ≈ 7709 eV). The scanning range is set as follows: XANES region: -50 eV before absorption edge to +100 eV after absorption edge (e.g., Fe: 7060-7212 eV). EXAFS region: +50 eV after absorption edge to +1000 eV (e.g., Fe: 7162-8112 eV). The test data are calibrated for energy, background subtracted, and normalized. Fourier transform (FT) processing: The k-space χ(k) function is converted to the R-space χ(R) function to display the composition (elements and coordination number) of the coordination structure in the coating layer, as well as the coordination bond lengths.

[0129] 5) Particle size d and coating thickness H of metallic materials: These were measured using a high-angle annular dark-field spherical aberration electron microscope. Under dark field conditions, metallic materials exist as light spots, and the size of these light spots is the particle size d. The coating thickness H was measured using a conventional high-resolution transmission electron microscope (HRTEM). The sample was dispersed in an ethanol solution and dropped onto a copper grid, followed by HRTEM measurement.

[0130] 6) Mass percentage of carbon matrix in positive electrode active material w2: Tested by carbon-sulfur analysis, and calculated by the mass difference after combustion using the combustibility of carbon.

[0131] 7) Metallic Material Composition: The core and cross-section of the positive electrode active material are exposed through FIB cutting and argon ion polishing. The cut and polished positive electrode active material is then ultrasonically dispersed onto a silicon nitride microgrid film. HRTEM is used to locate the scanning range within the coating layer region. SAED (Selected Area Electron Diffraction) is then used to test the composition of the metallic materials in the coating layer. By measuring the SAED diffraction dot spacing and comparing it to a standard card, the composition of the metallic materials can be obtained.

[0132] 8) Mass percentage of metallic materials in positive electrode active material w3: The catalyst can be separated by mass difference. After removing the carbon matrix by utilizing the combustibility of carbon, the remaining solids are dispersed in water and centrifuged at a high speed of 15000 rpm. The core settles to the bottom, while the metallic materials, due to their small mass, are in the supernatant. w3 can be calculated by collecting the metallic materials in the supernatant.

[0133] Table 1

[0134]

[0135] Table 2

[0136]

[0137] Experimental Example 2

[0138] 1. The positive electrode active materials of the examples and comparative examples were used to prepare a positive electrode slurry with a mass ratio of positive electrode active material: carbon nanotubes: carbon black: PVDF: NMP = 100: 1: 1: 3: 70. The slurry was then coated on the surface of the positive electrode current collector (aluminum foil) and dried to obtain an areal density of 400 g / m³. 2 The double-sided positive electrode sheet was used. The positive electrode sheet and graphite negative electrode sheet were stacked to form a soft-pack full cell, which was then baked and filled with electrolyte. The comparative examples were divided into Comparative Example 1-1 and Comparative Example 1-2. After each cell was immersed at 45°C for 24 hours, the cells of the examples and Comparative Example 1-2 were subjected to formation-dehydration-capacity testing according to the following method. The cell of Comparative Example 1-1 was subjected to formation-capacity testing according to the following method (i.e., directly capacity testing after formation, without dehydration).

[0139] (1) Formation: Charge at 0.05C for 2 hours, then charge at 0.1C constant current and constant voltage until 4.3V is cut off at 0.05C. Aging at 45℃ for 24 hours further stabilizes the negative electrode SEI.

[0140] (2) Dehydration: First, charge at a constant current of 0.1C to 4.3V, then charge at a constant voltage of 4.3V until the current is less than 0.05C (this step ensures that all lithium in the positive electrode active material is removed, and the positive electrode active material does not participate in the current distribution in the subsequent dehydration process), then charge at a constant current of 0.01C to 4.5V, then charge at a constant voltage of 4.5V until the current is less than 0.005C (this step is the dehydration process).

[0141] Meanwhile, based on Archimedes' principle, the battery volume was tested by placing the cells before and after water removal in water to test V. 除水后 and V 除水前 Gas production per unit area (excluding water) = V 除水后 -V 除水前 The results are shown in Table 3.

[0142] (3) Capacity testing: Charge at 0.33C constant current and constant voltage to 4.3V, cut off at 0.05C, let stand for 10 minutes, and discharge at 0.33C to 2.5V. The above charge and discharge test is repeated three times, and the discharge capacity C0 of the last cycle is used as the nominal capacity of the battery for subsequent tests.

[0143] 2. The cycle performance, cycle gas production, cathode metal dissolution, and 5C rate performance of the above batteries were tested, and the results are shown in Table 3.

[0144] Cycling performance: At 45±2℃, charge at a constant current of 1C to 4.3V, then charge at a constant voltage to 0.05C (cutoff); rest for 10 minutes; discharge at a constant current of 1C to 2.5V, which constitutes one cycle. Repeat this process to test the battery discharge capacity C1 after one cycle and the battery discharge capacity C after 1000 cycles. 1000 .

[0145] Capacity retention rate Q=C 1000 / C1×100%.

[0146] Cyclic gas production test: Based on Archimedes' principle, the battery volume is tested by placing the battery cells before and after cycling according to the above cycle performance in water to test V. 循环后 and V 循环前 Volume, Gas Production in Cycle = V 循环后 -V 循环前 .

[0147] Positive electrode metal leaching: After the cycled battery is discharged to empty capacity, the negative electrode is removed from the battery. The negative electrode powder is scraped off with a scraper, ground into powder, dissolved in aqua regia, filtered, and the Fe and Mn content in the filtrate is tested by ICP.

[0148] 5C rate: At 25±2℃, charge at a constant current of 0.33C to 4.3V, then charge at a constant voltage to 0.05C (cutoff); rest for 10 minutes; then discharge at a constant current of 5C to 2V. Based on the battery's 5C discharge capacity C, calculate the battery's 5C discharge retention rate = C / C0 × 100%.

[0149] Table 3

[0150]

[0151] As shown in Table 3, the positive electrode active material in this embodiment helps to reduce the water content of the positive electrode active material and the amount of dissolution during the sub-cycle process, thus significantly improving the cycle performance of the battery. Simultaneously, it also has a certain degree of improvement effect on the rate performance of the battery.

[0152] Finally, it should be noted that other embodiments of this application will readily conceive of by those skilled in the art upon consideration of the specification and practice of the application disclosed herein. This application is intended to cover any variations, uses, or adaptations of this application that follow the general principles of this application and include common knowledge or customary techniques in the art not disclosed herein, and is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and alterations may be made without departing from its scope. The scope of this application is limited only by the appended claims.

Claims

1. A positive electrode active material, characterized in that, Including Li x Ma y PO4 kernel and overlaid on the Li x Ma y A coating layer on at least part of the surface of the PO4 core; the coating layer includes a carbon matrix and an M-N4 coordination structure distributed in the carbon matrix, wherein M is a metal element, Ma includes at least one of Fe, Mn, Ni, and Co, 0.9≤a≤1.1, and 0.9≤y≤1.

05.

2. The positive electrode active material according to claim 1, characterized in that, In the M-N4 coordination structure, the bond length of the MN bond is 1.3~3 Å.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The coating layer includes a metallic material, which includes at least one of elemental metals and metal compounds; the metallic element in the metallic material is the same as M.

4. The positive electrode active material according to claim 3, characterized in that, The metallic element includes at least one of Fe, Co, Ni, Ru, Ir, Pt, Pd, Mn, Zn, Cu, Al, Mo, Ag, and Au; and / or, the metallic compound includes at least one of oxides, sulfides, phosphides, and fluorides of Fe, Co, Ni, Ru, Ir, Pt, Pd, Mn, Zn, Cu, Al, Mo, Ag, and Au.

5. The positive electrode active material according to claim 3 or 4, characterized in that, The particle size of the metallic material is in the nanometer range.

6. The positive electrode active material according to any one of claims 3-5, characterized in that, The particle size of the metallic material is 0.5 nm to 5 nm; and / or, The metallic material has a mass percentage content of 0.2% to 1.5% in the positive electrode active material.

7. The positive electrode active material according to any one of claims 1-6, characterized in that, The mass percentage of nitrogen in the coating layer is 5-30%.

8. The positive electrode active material according to any one of claims 1-7, characterized in that, The thickness of the coating layer is 5~20 nm; and / or, the carbon matrix in the positive electrode active material has a mass percentage of 1~2.5%; and / or, the carbon matrix includes amorphous carbon.

9. The positive electrode active material according to any one of claims 1-8, characterized in that, The specific surface area of ​​the positive electrode active material is 10-20 m² / g; and / or, the Li... x Ma y The PO4 kernel is Li x Mn n Fe m PO4, n+m=y, n>0, m>0.

10. A method for preparing a positive electrode active material according to any one of claims 1-9, characterized in that, Includes the following steps: The nitrogen-macrocyclic compound-M complex with Li x Ma y After the reaction with PO4, the solid product is calcined to obtain the positive electrode active material.

11. The preparation method according to claim 10, characterized in that, The aza-macrocyclic compound-M complex includes at least one of porphyrin compounds, phthalocyanine compounds, and carboxylic acid compounds.

12. The preparation method according to claim 10 or 11, characterized in that, The aza-macrocyclic compound-M complex is obtained by reacting the aza-macrocyclic compound with an M salt.

13. A positive electrode plate, characterized in that, The positive electrode sheet comprises the positive electrode active material according to any one of claims 1-9, or the positive electrode active material prepared by the preparation method according to any one of claims 10-12.

14. A battery, characterized in that, Includes the positive electrode sheet as described in claim 13.

15. A battery pack, characterized in that, It includes at least two batteries as described in claim 13.

16. An electrical appliance, characterized in that, Includes the battery of claim 14 or the battery pack of claim 15.

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