Positive electrode sheet, battery, energy storage device, and electric device

Abstract

The application provides a positive electrode sheet, a battery, an energy storage device and an electric device. The positive electrode sheet comprises a positive electrode current collector. At least one side of the positive electrode current collector has a positive electrode material layer. The positive electrode material layer comprises a positive electrode material. The positive electrode material comprises first lithium iron phosphate particles and second lithium iron phosphate particles. The Dv50 of the second lithium iron phosphate particles is greater than the Dv50 of the first lithium iron phosphate particles. The second lithium iron phosphate particles are formed by fusion of a plurality of primary particles. The primary particles contain a fusion-assisting element and a doping element. The primary particles have tortuous gaps between them. The fusion-assisting element comprises at least one of tungsten, scandium, yttrium, a lanthanide series element, an actinide series element and boron. The doping element comprises at least one of titanium and vanadium.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and in particular to a positive electrode sheet, a battery, an energy storage device, and an electrical device. Background Technology

[0002] Secondary batteries (such as lithium-ion batteries) have the characteristics of high specific energy, high operating voltage, low self-discharge rate, small size and light weight, and are therefore widely used in energy storage equipment and other fields.

[0003] Lithium iron phosphate (LFP) is currently the preferred cathode material for lithium-ion battery energy storage cells due to its long cycle life and high safety. However, achieving high-density cathode materials often requires large-particle materials. Large-particle materials, due to their longer lithium-ion transport paths and poorer kinetic performance, result in lower capacity utilization, and the energy efficiency and cycle life of secondary batteries need improvement. Summary of the Invention

[0004] To address the aforementioned technical problems, this application discloses a positive electrode sheet, a battery, an energy storage device, and an electrical appliance to improve the energy efficiency and cycle life of secondary batteries.

[0005] In one aspect, this application provides a positive electrode sheet, comprising: a positive current collector, wherein at least one side of the positive current collector has a positive electrode material layer, the positive electrode material layer comprises a positive electrode material, wherein the positive electrode material comprises a first lithium iron phosphate particle and a second lithium iron phosphate particle, wherein the Dv50 of the second lithium iron phosphate particle is greater than the Dv50 of the first lithium iron phosphate particle;

[0006] The second lithium iron phosphate particle is formed by fusing multiple primary particles, wherein the primary particles contain fluxing elements and doping elements, and the primary particles have tortuous gaps between them;

[0007] The fusion-enhancing element includes at least one of tungsten, scandium, yttrium, lanthanides, actinides, and boron.

[0008] The doping element includes at least one of titanium and vanadium.

[0009] In some embodiments of this application, the number of the second lithium iron phosphate particles with a particle size greater than 1 μm accounts for 90% to 95% of the total number of the second lithium iron phosphate particles, and the number of the second lithium iron phosphate particles with a particle size less than or equal to 1 μm accounts for 5% to 10% of the total number of the second lithium iron phosphate particles.

[0010] In some embodiments of this application, a second lithium iron phosphate particle with a particle size greater than 1 μm comprises at least three primary particles with a particle size less than 1 μm, and the maximum width of the gap is less than or equal to 100 nm.

[0011] And / or, in the second lithium iron phosphate particles with a particle size of less than or equal to 1 μm, the maximum width of the gap is less than or equal to 20 nm.

[0012] In some embodiments of this application, the surface of the primary particle has a fusion layer with a thickness of 3nm to 30nm, and the fusion aid element and the dopant element are distributed within the fusion layer.

[0013] In some embodiments of this application, the mass fraction of the fluxing element in the second lithium iron phosphate particle is a, where 0.05% ≤ a ≤ 0.5%;

[0014] And / or, the mass fraction of the doping element in the second lithium iron phosphate particle is b, 0.1%≤b≤0.5%.

[0015] In some embodiments of this application, the mass fraction of the first lithium iron phosphate particles in the cathode material is 10% to 50%, and the mass fraction of the second lithium iron phosphate particles in the cathode material is 50% to 90%.

[0016] In some embodiments of this application, the Dv50 of the second lithium iron phosphate particle is 1.6 μm to 2.2 μm, and the Dv50 of the first lithium iron phosphate particle is 0.4 μm to 0.7 μm.

[0017] Secondly, this application provides a battery including the positive electrode sheet described in the first aspect.

[0018] Thirdly, this application provides an energy storage device, including a housing and at least one battery as described in the second aspect, the battery being housed within the housing.

[0019] Fourthly, this application provides an electrical device including the energy storage device described in the third aspect, wherein the energy storage device supplies power to the electrical device.

[0020] Compared with the prior art, this application has at least the following beneficial effects:

[0021] This application provides a positive electrode sheet, a battery, an energy storage device, and an electrical device. The positive electrode sheet includes a positive current collector, at least one side of which has a positive electrode material layer. The positive electrode material layer includes a positive electrode material, which comprises first lithium iron phosphate particles and second lithium iron phosphate particles. The Dv50 of the second lithium iron phosphate particles is greater than that of the first lithium iron phosphate particles, achieving particle size distribution of the positive electrode material. The second lithium iron phosphate particles are formed by fusing multiple primary particles. The primary particles contain a fluxing element and a dopant element. The fluxing element includes at least one of tungsten, scandium, yttrium, lanthanides, actinides, and boron. The dopant element includes at least one of titanium and vanadium. The fluxing element can form more microcrystalline regions inside the second lithium iron phosphate particles, resulting in improved kinetics during the lithium insertion / extraction process, increasing the cycle energy efficiency of the positive electrode material. Furthermore, the bonding effect of the fluxing element at the grain boundaries reduces cracks that occur during the cycling of the second lithium iron phosphate particles, improving the cycle life of the positive electrode material. The dopant element can improve the capacity utilization of the second lithium iron phosphate particles. Through the synergistic effect of fluxing and doping elements, combined with particle size distribution, the capacity utilization performance of the cathode material is improved while maintaining high compaction density, thereby enhancing the energy efficiency and cycle life of the secondary battery. When the secondary battery of this application is applied to energy storage devices, it improves the energy storage efficiency and lifespan of the energy storage devices. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of this application, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of an energy storage system according to one embodiment of this application;

[0024] Figure 2 This is a schematic diagram of the energy storage system according to another embodiment of this application;

[0025] Figure 3 This is a schematic diagram of the energy storage system according to another embodiment of this application;

[0026] Figure 4 This is a scanning electron microscope (SEM) image of the second lithium iron phosphate particles prepared in Example 1 of this application;

[0027] Figure 5 This is a cross-sectional view of the second lithium iron phosphate particles prepared in Example 1 of this application;

[0028] Figure 6This is a backscattered mode view of the second lithium iron phosphate particle prepared in Example 1 of this application;

[0029] Figure 7 SEM image of the large lithium iron phosphate particles in Comparative Example 1.

[0030] Figure 8 This is a cross-sectional view of the second lithium iron phosphate particles prepared in Comparative Example 1.

[0031] Figure 9 This is a backscattered mode view of the second lithium iron phosphate particles prepared in Comparative Example 1.

[0032] Explanation of reference numerals in the attached drawings: 400-Energy storage system, 410-First power conversion device, 420-First user load, 430-Second user load, 440-Energy storage device, 450-High voltage cable, 460-Second power conversion device, 470-Vehicle, 480-Photovoltaic-energy storage-charging station. Detailed Implementation

[0033] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0034] Furthermore, in addition to indicating location or positional relationship, some of the aforementioned terms may also have other meanings. For example, the term "above" may also be used in some cases to indicate a certain dependency or connection relationship. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0035] Furthermore, the terms "installation," "setup," "equipped with," "connection," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral structure; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium, or an internal connection between two devices, components, or parts. Those skilled in the art can understand the specific meaning of these terms in this application based on the specific circumstances.

[0036] Furthermore, the terms "first," "second," etc., are primarily used to distinguish different devices, components, or parts (which may be the same or different in specific type and construction), and are not intended to indicate or imply the relative importance or quantity of the indicated devices, components, or parts. Unless otherwise stated, "a plurality of" means two or more.

[0037] It should be noted that this application uses lithium-ion batteries as an example of secondary batteries to explain the application, but the secondary batteries in this application are not limited to lithium-ion batteries.

[0038] This application provides a positive electrode sheet, which includes a positive current collector. At least one side of the positive current collector has a positive electrode material layer, which includes a positive electrode material. The positive electrode material includes first lithium iron phosphate particles and second lithium iron phosphate particles. The Dv50 of the second lithium iron phosphate particles is greater than that of the first lithium iron phosphate particles, thereby achieving particle size distribution of the positive electrode material. The second lithium iron phosphate particles are formed by fusing multiple primary particles, and are fused particles with a relatively large particle size. The primary particles contain a fluxing element and a dopant element, and there are tortuous gaps between the primary particles. The fluxing element includes at least one of tungsten (W), scandium (Sc), yttrium (Y), lanthanides (La~Lu), and actinides (Ac~Lr). The dopant element includes at least one of titanium (Ti) and vanadium (V).

[0039] The positive electrode sheet of this application contains the aforementioned positive electrode material. The fluxing element therein can form more microcrystalline regions within the lithium iron phosphate particles, leading to improved kinetics during the lithium insertion / extraction process, increasing the cycle energy efficiency of the positive electrode material, and reducing cracks that occur during cycling, thus improving the cycle life of the positive electrode material. The doping element therein can enhance the capacity utilization of the lithium iron phosphate particles. Through the synergistic effect of the fluxing element and the doping element, combined with particle size distribution, the capacity utilization performance of the positive electrode material is improved while maintaining high compaction density, thereby improving the energy efficiency and cycle life of the lithium-ion battery. When the lithium-ion battery of this application is applied to energy storage devices, it improves the energy storage efficiency and lifespan of the energy storage device.

[0040] In this application, Dv50 represents the particle size that, in the volumetric particle size distribution, reaches 50% of the total volumetric size, starting from the smallest particle size.

[0041] In one optional embodiment, the number of lithium iron phosphate particles with a particle size greater than 1 μm accounts for 90% to 95% of the total number of lithium iron phosphate particles, while the number of lithium iron phosphate particles with a particle size less than or equal to 1 μm accounts for 5% to 10% of the total number of lithium iron phosphate particles. This results in a higher proportion of large particles in the lithium iron phosphate particles, leading to a higher compaction density. The particle size of the lithium iron phosphate particles with a particle size greater than 1 μm is defined as D, where 1 μm < D ≤ 8 μm.

[0042] In this application, the particle size refers to the equivalent sphere diameter of the cathode material particles.

[0043] In one optional embodiment, a second lithium iron phosphate particle with a particle size greater than 1 μm comprises at least three primary particles with a particle size less than 1 μm. The gaps are formed during the fusion process of the primary particles, and the maximum width of the gaps is less than or equal to 100 nm, for example, the maximum width of the gaps is 70 nm, 80 nm, 90 nm, or 100 nm. The number of gaps is greater than or equal to three, for example, three, four, five, or six gaps. In this way, the particles inside the second lithium iron phosphate particle are in close contact with each other and have few pores, which is beneficial to further improving the compaction density. Moreover, each primary particle can uniformly insert and extract lithium during charge, discharge, and overcharge, thus improving the kinetic performance of the fused large particles.

[0044] In one optional embodiment, within the second lithium iron phosphate particles with a particle size of 1 μm or less, the gaps are gaps generated during a single particle fusion process. The maximum width of the gap is 20 nm or less, and the number of gaps is 1 to 3. For example, the maximum width of the gap is 50 nm, 10 nm, 15 nm, or 20 nm, and the number of gaps is 1, 2, or 3. Thus, by combining cathode materials with different particle sizes, a cathode sheet with a high compaction density can be achieved.

[0045] In one optional embodiment, the surface of the primary particle has a fusion layer with a thickness of 3 nm to 30 nm, and the fluxing element and dopant element are distributed within the fusion layer. For example, the thickness of the fusion layer is 3 nm, 10 nm, 20 nm, or 30 nm. In this way, multiple small particle regions are formed inside a single second lithium iron phosphate particle, increasing the lithium insertion / extraction rate during the charge / discharge process.

[0046] In one optional embodiment, the mass fraction of the fluxing element in the second lithium iron phosphate particle is 'a', where 0.05% ≤ a ≤ 0.5%. For example, 'a' can be 0.05%, 0.1%, 0.2%, or 0.5%. This facilitates the effective functioning of the fluxing element in the second lithium iron phosphate particle.

[0047] In one optional embodiment, the mass fraction of the dopant element in the second lithium iron phosphate particle is b, where 0.1% ≤ b ≤ 0.5%. For example, b can be 0.1%, 0.2%, 0.3%, or 0.5%. This facilitates the effective functioning of the dopant element in the second lithium iron phosphate particle.

[0048] In one optional embodiment, the first lithium iron phosphate particles have a mass fraction of 10% to 50% in the cathode material, for example, 10%, 30%, 40%, or 50% by mass; the second lithium iron phosphate particles have a mass fraction of 50% to 90% in the cathode material, for example, 50%, 70%, 80%, or 90% by mass. This allows for better particle size distribution, improving the capacity utilization and compaction density of the cathode material.

[0049] In one optional embodiment, the Dv50 of the second lithium iron phosphate particle is 1.6 μm to 2.2 μm, and the Dv50 of the first lithium iron phosphate particle is 0.4 μm to 0.7 μm. This allows for better particle size distribution, improving the capacity utilization and compaction density of the cathode material.

[0050] This application does not impose any particular limitation on the preparation method of the cathode material, as long as it achieves the purpose of this application. In one example, the preparation method of the cathode material includes the following steps:

[0051] Step A: Mix iron phosphate, lithium source, flux, dopant source and carbon source, grind and spray dry, and then perform pre-sintering treatment. The pre-sintering temperature is 400℃~600℃ and the pre-sintering time is 1h~3h to obtain the pre-sintered product.

[0052] Step B: The pre-sintered product is sintered at a temperature of 700℃~800℃ for 12h~18h, and then crushed to obtain lithium iron phosphate particles.

[0053] Step C: Mix the first lithium iron phosphate particles with a Dv50 of 0.4μm~0.7μm and the second lithium iron phosphate particles according to the designed mass ratio to obtain the cathode material.

[0054] In step A, the pre-sintering treatment causes partial carbonization of the carbon source in the raw material, which adheres to the particle surface. This results in each primary particle surface in the second lithium iron phosphate particles formed after subsequent high-temperature sintering having an independent carbon coating layer, thereby improving the overall electronic conductivity of the second lithium iron phosphate particles. The flux is selected from compounds containing elements such as tungsten (W), scandium (Sc), yttrium (Y), lanthanides (La~Lu), and actinides (Ac~Lr) (e.g., carbonates, phosphates, oxides, organic salts, etc.) and salts containing polyanionic groups (e.g., phosphate, borate). The metal atoms and anionic groups in the above flux are less likely to enter lattice sites during the lithium iron phosphate sintering process, forming lattice doping and causing crystal structure defects. This improves the intrinsic crystal structure stability of the lithium iron phosphate material and extends its cycle life. The lithium source includes, but is not limited to, lithium carbonate; the doping element source includes, but is not limited to, at least one of titanium dioxide, titanium oxysulfate, and ammonium metavanadate; and the carbon source includes, but is not limited to, glucose. The iron phosphate and lithium sources can be mixed according to the stoichiometric ratio of lithium iron phosphate; the amount of flux and dopant added can be adjusted by technicians according to the designed content of flux and dopant; the amount of carbon source added can be adjusted by technicians according to the designed carbon content.

[0055] In step B, according to Oswald's ripening theory, small particles easily melt during sintering and deposit on the surface of large particles, leading to grain boundary fusion and further particle growth. Fluxing elements such as W, Ce, Y, Sc, and La have high melting points, which inhibit the growth of small particles and refine the grains during sintering. They also hinder grain boundary fusion, reducing the interfacial energy that small particles need to overcome during melting, thus accelerating the melting of small particles and forming more microcrystalline regions inside the large particles, resulting in fused large particles. Polyanionic fluxes containing B and P elements have low melting points and preferentially form a fluid liquid phase during sintering, accelerating diffusion and mass transfer, and forming a continuous interphase network between particles, connecting different particles to form fused large particles. Because the fused large particles contain more microparticles and crystalline regions, more small particles and crystalline regions simultaneously undergo lithium-ion migration during charging and discharging, resulting in faster lithium insertion / extraction kinetics compared to traditional large single-crystal particles, thereby improving energy efficiency and capacity utilization. Besides the improved kinetics, the fused large particles, due to the carbon coating formed by the internal small particles during sintering, have a carbon-protected interface exposed after cracking during cycling, preventing side reactions with the electrolyte and reducing iron dissolution in the bulk phase, thus effectively improving cycle life. Conversely, in the cycling process of traditional large single-crystal particles, particle cracks caused by internal stress accumulation expose pure lithium iron phosphate interfaces without carbon coating, which continuously react with the electrolyte, causing iron dissolution and structural damage, resulting in loss of active materials and hindering improved cycle performance. Furthermore, the second lithium iron phosphate particles in this application retain their fused morphology after crushing, with the flux acting as a connector between the internal particles.

[0056] In step C, the first lithium iron phosphate particles are conventional lithium iron phosphate particles without doping or fluxing elements. The first lithium iron phosphate particles can be obtained through commercial channels, and technicians can select first lithium iron phosphate particles with a suitable particle size distribution as needed.

[0057] This application also provides a battery including the positive electrode sheet described in any of the above embodiments.

[0058] In this application, the positive electrode material layer can be disposed on one surface or on two surfaces along the thickness direction of the positive electrode current collector. Specifically, the positive electrode material layer can be disposed on a portion or the entire surface of the positive electrode current collector. The positive electrode current collector is not particularly limited in this application, as long as it achieves the purpose of this application; for example, it can be, but is not limited to, aluminum foil, aluminum alloy foil, or composite current collectors. The thickness of the positive electrode current collector is not particularly limited in this application, as long as it achieves the purpose of this application; for example, a thickness of 4 μm to 15 μm is acceptable. The single-sided thickness of the positive electrode material layer in this application can be 60 μm to 140 μm.

[0059] The lithium-ion battery of this application also includes a negative electrode sheet. This application does not impose any particular limitation on the negative electrode sheet, as long as it achieves the purpose of this application. For example, the negative electrode sheet typically includes a negative current collector and a negative electrode material layer. The negative electrode material layer can be disposed on one or both surfaces along the thickness direction of the negative current collector. In this application, the negative electrode material layer is disposed on the surface of the negative current collector; that is, the negative electrode material layer can be disposed on a portion of one surface of the negative current collector, or it can be disposed on the entire surface of one surface of the negative current collector. This application does not impose any particular limitation on the negative current collector, as long as it achieves the purpose of this application. For example, it can include, but is not limited to, copper foil, copper alloy foil, nickel foil, or composite current collectors. In this application, there is no particular limitation on the thickness of the negative current collector, as long as it achieves the purpose of this application, for example, a thickness of 4μm to 12μm. The single-sided thickness of the negative electrode material layer in this application can be 70μm to 200μm.

[0060] In this application, the negative electrode material layer includes a negative electrode material. The negative electrode material is not particularly limited, as long as it can achieve the purpose of this application. For example, it may include at least one of artificial graphite, natural graphite, mesophase carbon microspheres, soft carbon, hard carbon, silicon, and silicon-carbon.

[0061] In this application, the negative electrode material layer may also include a negative electrode binder. This application does not impose any particular limitation on the negative electrode binder, as long as it can achieve the purpose of this application. For example, it may include, but is not limited to, at least one of acrylate, polyamide, polyimide, polyamide-imide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

[0062] The lithium-ion battery of this application also includes a separator. This application does not impose any particular limitation on the separator; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane can be selected.

[0063] The battery of this application also includes an electrolyte. This application does not impose any particular limitations on the electrolyte; those skilled in the art can choose according to actual needs, as long as the purpose of this application is achieved. For example, at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), vinylene carbonate (VC), ethylene ethylene carbonate (VEC), or fluoroethylene carbonate (FEC) can be mixed in a certain mass or volume ratio to obtain a non-aqueous organic solvent, and then a lithium salt can be added to dissolve and mix evenly. This application does not limit the type of lithium salt, as long as the purpose of this application is achieved. For example, lithium salts may include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, lithium bis(fluorosulfonyl)imide (LIFSI), lithium dioxalatoborate (LiBOB), or lithium difluoroborate.

[0064] This application does not impose any particular limitation on the concentration of lithium salt in the electrolyte, as long as the purpose of this application can be achieved. For example, the concentration of lithium salt can be 1.0 mol / L to 2.0 mol / L.

[0065] The battery of this application also includes a casing. This application does not impose any particular restrictions on the casing, and those skilled in the art can choose one according to actual needs, as long as it can achieve the purpose of this application. For example, the casing may include an aluminum-plastic film.

[0066] This application does not impose any particular limitation on the battery preparation method; any preparation method known in the art can be used, as long as it can achieve the purpose of this application. For example, the battery preparation method includes, but is not limited to, the following steps: stacking the positive electrode sheet, separator, and negative electrode sheet in sequence, and performing operations such as winding and folding as needed to obtain a bare cell with a wound structure; placing the bare cell in a packaging bag; injecting electrolyte into the packaging bag and sealing it to obtain the battery.

[0067] This application also provides an energy storage device, including a housing and at least one battery as described in any of the above embodiments, the battery being housed within the housing. The energy storage device with this battery exhibits excellent performance, which is beneficial for its use. Housing the battery within the housing increases its stability and protection, thereby extending the lifespan of the energy storage device. It is understood that the energy storage device may contain one or more batteries, and when the energy storage device contains multiple batteries, the multiple batteries can be connected in at least one manner, such as parallel or series connection.

[0068] This application also provides an electrical device including the energy storage device described in the above embodiments, which is beneficial for improving the product competitiveness and performance of the electrical device. In an optional embodiment, the electrical device includes an electrical device body, and the energy storage device is used to supply power to the electrical device body. In an optional embodiment, the electrical device body includes a positive terminal and a negative terminal, the positive electrode of the battery in the energy storage device is used to electrically connect to the positive terminal of the electrical device body, and the negative electrode of the battery in the energy storage device is used to electrically connect to the negative terminal of the electrical device body, so as to supply power to the electrical device.

[0069] The electrical equipment in this application may include, but is not limited to: containers, electric vehicles, electric cars, ships, spacecraft, electric toys, and power tools, etc. Among them, spacecraft include, for example, airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include, for example, stationary or mobile electric toys, specifically, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include, for example, metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, specifically, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0070] Because the energy we need is highly time- and space-dependent, in order to utilize energy rationally and improve energy efficiency, it is necessary to store one form of energy in the same way or by converting it into another, and then release it in a specific energy form for future applications. Currently, the main way to generate green electricity is to develop green energy sources such as photovoltaics and wind power to replace fossil fuels.

[0071] Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0072] Taking electrochemical energy storage as an example, this solution provides an energy storage device 440, which is applied to an energy storage system 400. The energy storage device 440 is equipped with a set of chemical batteries, which mainly use the chemical elements in the batteries as energy storage medium. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage medium. Simply put, the electrical energy generated by wind and solar energy is stored in the chemical batteries. When the use of external electrical energy reaches its peak, the stored electrical energy is released for use, or transferred to places with a shortage of electricity for use.

[0073] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding types of energy storage devices include:

[0074] (1) Large-scale energy storage power stations (composed of multiple prefabricated energy storage modules) applied to wind power and photovoltaic power stations can help renewable energy power generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power regulation power source on the power supply side, the energy storage power station realizes the load matching of power in time and space, enhances the renewable energy absorption capacity, reduces instantaneous power changes, reduces the impact on the power grid, improves the problem of new energy power generation absorption, and is of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation.

[0075] (2) The energy storage prefabricated cabin applied on the grid side mainly functions as peak regulation, frequency regulation and grid congestion relief. In terms of peak regulation, it can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption.

[0076] (3) Small energy storage cabinets applied to the electricity consumption side mainly function as self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improvement of power supply reliability. Depending on the application scenario, electricity consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices, energy storage charging piles, etc., which are generally used in conjunction with distributed photovoltaics. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley pricing, by charging the energy storage system when the electricity price is low and discharging the energy storage system when the electricity price is high, peak-valley price arbitrage can be achieved, reducing electricity costs. In addition, industrial enterprises subject to two-part tariffs can use energy storage systems to store energy during off-peak hours and discharge during peak loads, thereby reducing peak power and the maximum demand declared, achieving the goal of reducing capacity costs. Household photovoltaics with energy storage can improve the level of self-consumption of electricity. Due to high electricity prices and poor power supply stability, the demand for household photovoltaic installations is driven. Given that photovoltaic power generation occurs during the day while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0077] In some embodiments, see Figure 1 , Figure 1 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application. Figure 1 This application Figure 1 The embodiments are illustrated using a home energy storage scenario in user-side energy storage as an example. The energy storage device 440 of this application is not limited to the home energy storage scenario.

[0078] This application provides an energy storage system 400, which includes a first power conversion device 410 (photovoltaic panel), a first user load 420 (household lighting fixture), a second user load 430 (e.g., household appliances such as air conditioners), and an energy storage device 440. The energy storage device 440 is a small energy storage box that can be wall-mounted on an outdoor wall. However, the energy storage device 440 is not limited to wall mounting and can also be placed in a user's residence in other ways. Specifically, the photovoltaic panel can convert solar energy into electrical energy during periods of low electricity prices, and the energy storage device 440 stores this electrical energy and supplies it to lighting fixtures and household appliances during peak electricity prices, or provides power during power outages / power interruptions.

[0079] In some embodiments, see Figure 2 , Figure 2 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application. Figure 1 And this application Figure 2 The embodiments are illustrated using a shared energy storage scenario on the generation / distribution side as an example. The energy storage device 440 of this application is not limited to the energy storage scenario on the generation / distribution side.

[0080] This application provides an energy storage system 400, which includes: a high-voltage cable 450, a first power conversion device 410, a second power conversion device 460, and an energy storage device 440 provided in this application. In some embodiments of the power generation scenario, the second power conversion device 460 can be a wind power conversion device. Since the electricity generated by wind power conversion is volatile, random, and intermittent, the unstable electricity output by the wind power conversion device can be stored in the energy storage device 440 through grid connection. The energy storage device 440 is connected to the high-voltage cable and outputs smooth electricity to the power consumption side of the distribution network, realizing peak shaving and frequency regulation, and stable grid operation; or, wind power... The conversion device is always connected to the high-voltage cable. Under normal power generation conditions, the power output of the wind power conversion device is supplied to the power consumption side of the distribution network through the high-voltage cable. When the current power load is low and the wind power conversion device generates excess power, the excess power is first stored in the energy storage device 440 to reduce wind and solar curtailment rates and improve the problem of new energy power generation consumption. When the power load is high, the power grid issues an instruction to transmit the power stored in the energy storage device 440 together with the high-voltage cable 450 in grid-connected mode to supply power to the power consumption side. This provides the power grid with various services such as peak shaving, frequency regulation, and backup, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure of the power grid.

[0081] In some embodiments on the distribution network side, the first power conversion device 410 can be a photovoltaic panel, and the energy storage device 440 is connected to the high-voltage cable 450 and installed downstream of the high-voltage cable 450 and between the user load. The electrical energy output by the photovoltaic power conversion device is stored in the energy storage device 440, which can respond in a timely manner to act as a backup power source when the power grid / distribution network fails; or, it can provide power supply support to alleviate line congestion when the high-voltage cable 450 transmission line is blocked, and to delay the economic pressure caused by the expansion of the power grid / distribution capacity when the power grid is planned to be expanded.

[0082] In some embodiments, see Figure 3 , Figure 3 This is a schematic diagram of the structure of an energy storage system 400 according to an embodiment of this application. Figure 3 And this application Figure 3 The embodiments are illustrated using an industrial and commercial energy storage scenario as an example. The energy storage device 440 of this application is not limited to industrial and commercial energy storage scenarios.

[0083] This application provides an energy storage system 400, which includes: an energy storage device 440, a high-voltage cable 450, a factory equipped with a first power conversion device 410, a photovoltaic-energy storage-charging station 480, and a vehicle 470. In some embodiments of industrial and commercial scenarios, the first power conversion device 410 can be a photovoltaic panel, which converts solar energy into electrical energy and stores it in the energy storage device 440 in the factory. In the event of a power grid failure, the energy storage device 440 provides power to ensure the safe and stable operation of the factory without interruption. Alternatively, when the factory's power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 440 in conjunction with the high-voltage cable 450 in a grid-connected mode to supply the factory with electricity, providing various services such as peak shaving / frequency regulation and backup for the power grid operation. In addition, the first power conversion device 410 can also convert solar energy into electrical energy and store it in the energy storage device 440 of the photovoltaic-energy storage-charging station 480, which can then directly charge the vehicle 470, making it fast and convenient.

[0084] Optionally, the first power conversion device 410 may include, but is not limited to, a photovoltaic panel, and the second power conversion device 460 may include, but is not limited to, a wind power conversion device. The first power conversion device 410 and the second power conversion device 460 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electrical energy.

[0085] Optionally, the energy storage device 440 may include, but is not limited to, energy storage applications such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and may also be applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0086] Optionally, the energy storage device 440 may include, but is not limited to, individual batteries, or battery modules, battery packs, battery clusters, power banks, energy storage cabinets / prefabricated energy storage compartments, and other battery integrated systems composed of individual batteries. The actual application form of the energy storage device 440 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 440.

[0087] Optionally, the individual cell can be, but is not limited to, at least one of cylindrical, prismatic, prismatic, or other shaped cells.

[0088] Optionally, the single cell can be a rechargeable battery, which refers to a single cell that can be recharged after discharge to activate the active materials and continue to be used. The single cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application does not specifically limit it.

[0089] Example

[0090] The embodiments and comparative examples provided below illustrate the implementation of this application in more detail. Various tests and evaluations were conducted according to the methods described below.

[0091] Example 1

[0092] <Preparation of cathode materials>

[0093] A mixture of iron phosphate (FePO4), lithium carbonate (lithium source), cerium oxide (CeO2) (fluxant), titanium dioxide (dopant source), and glucose (carbon source) was prepared. This mixture was then ground, spray-dried, and pre-sintered at 500℃ for 2 hours to obtain a pre-sintered product. The pre-sintered product was then sintered at 750℃ for 16 hours, and the resulting product was crushed to obtain second lithium iron phosphate particles. These second lithium iron phosphate particles were then mixed with first lithium iron phosphate particles (conventional lithium iron phosphate particles with a Dv50 of 0.6 μm) at a mass ratio of 70:30 to obtain the cathode material. The content of the fluxing element and dopant element in the second lithium iron phosphate particles is shown in Table 1. The carbon source was added at 10% of the total mass of the mixture. In the secondary lithium iron phosphate particles, the proportion of secondary lithium iron phosphate particles with a particle size of less than or equal to 1 μm is 6%, the number of gaps between primary particles is 1 to 3, and the maximum width of the gap is less than or equal to 20 nm; in the secondary lithium iron phosphate particles, the proportion of secondary lithium iron phosphate particles with a particle size of greater than 1 μm is 94%, the number of gaps in primary particles is greater than 3, and the maximum width of the gap is less than or equal to 100 nm.

[0094] <Preparation of the positive electrode>

[0095] The prepared positive electrode material, conductive carbon black (Super-P), and binder PVDF were mixed at a mass ratio of 98:0.4:1.6. N-methylpyrrolidone (NMP) was then added as a solvent to prepare a positive electrode slurry with a solid content of 65 wt%. The mixture was stirred until homogeneous. The positive electrode slurry was then uniformly coated onto one surface of a 13 μm thick aluminum foil used as a positive electrode current collector. After drying, cold pressing, slitting, and cutting, the positive electrode sheet was obtained. The single-sided thickness of the positive electrode material layer was 90 μm, and the compaction density was 2.45 g / cm³. 3 .

[0096] <Preparation of Negative Electrode Sheets>

[0097] Artificial graphite (anode material), sodium carboxymethyl cellulose (CMC) thickener, Super-P conductive carbon black, and styrene-butadiene rubber latex (SBR) binder were mixed in a mass ratio of 96:2:1:1. Deionized water was added to prepare a negative electrode slurry with a solid content of 50 wt%, and the mixture was stirred evenly. The negative electrode slurry was uniformly coated onto one surface of an 8 μm thick copper foil current collector. After drying, cold pressing, slitting, and cutting, the negative electrode sheet was obtained. The single-sided thickness of the negative electrode material layer was 110 μm.

[0098] <Preparation of Electrolyte>

[0099] In an argon-atmosphere glove box with a moisture content ≤1ppm, ethylene carbonate (EC), diethyl carbonate (DEC), and dimethyl carbonate (DMC) were mixed in a mass ratio of 1:1:1. The dried solute was then dissolved in the solvent and stirred until completely dissolved and homogeneous to obtain the electrolyte. The solute in the electrolyte was lithium hexafluorophosphate, with a molar concentration of 1.0 mol / L.

[0100] <Preparation of the diaphragm>

[0101] A 16 μm thick porous polypropylene polymer film was used as the separator.

[0102] <Lithium-ion battery assembly>

[0103] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrode. Then, they are wound into a bare cell. After welding the tabs, the bare battery is placed in an outer packaging shell, dried, and then injected with the electrolyte. After vacuum sealing, settling, formation, and shaping, a lithium-ion battery with a rated capacity of 3Ah is obtained.

[0104] Examples 2 to 12

[0105] Except for adjusting the relevant preparation parameters according to Table 1 in the section on "Preparation of Cathode Materials", the rest is the same as in Example 1.

[0106] Example 13

[0107] Except for replacing titanium dioxide with amine metavanadate in the <Preparation of Cathode Material> section, the rest is the same as in Example 1.

[0108] Examples 14-15

[0109] Except for adjusting the amount of dopant source added in the <Preparation of Cathode Material> section to adjust the dopant content according to Table 1, the rest is the same as in Example 1.

[0110] Examples 16-18

[0111] Except for adjusting the mass ratio of the second lithium iron phosphate particles to the first lithium iron phosphate particles according to Table 1 in the <Preparation of Cathode Material>, the rest is the same as in Example 1.

[0112] Comparative Example 1

[0113] Except for the preparation of the cathode material, in which large conventional lithium iron phosphate particles (Dv50 of 1.6 μm) and small conventional lithium iron phosphate particles (Dv50 of 0.6 μm) are mixed at a mass ratio of 90:10, the rest is the same as in Example 1.

[0114] Comparative Examples 2 to 3

[0115] Except for adjusting the mass ratio of large particles to small particles according to Table 1 in the section on "Preparation of Cathode Materials", the rest is the same as in Comparative Example 1.

[0116] Table 1: Preparation parameters for each example and comparative example

[0117]

[0118] In Table 1, " / " indicates that no relevant preparation parameters exist.

[0119] Test methods and equipment:

[0120] Testing of fluxing elements in cathode materials:

[0121] The content of fluxing elements was tested using inductively coupled plasma (ICP). The specific steps were as follows: S1 The positive electrode material powder sample was digested with a strong acid (aqua regia, concentrated hydrochloric acid: concentrated nitric acid = 1:3, volume ratio), with a concentration of 37% and 65% of concentrated hydrochloric acid, until the sample was completely dissolved; S2 Standard solutions of different concentrations were prepared using diluents according to the elements to be detected; S3 The instrument measured the signal intensity of the standard solutions and plotted a standard curve; S4 The sample solution was tested using the same method, steps, and parameters as the standard solutions; S5 The sample data was compared with the standard solution data, and the test results were output.

[0122] Test on the percentage of lithium iron phosphate particles with a diameter greater than 1 μm / particles with a diameter less than or equal to 1 μm:

[0123] The positive electrode sheet was prepared by SEM-CP. The cross-section of the electrode sheet was cut by ion beam cutting to prepare a cross-section polished (CP) sample. Twenty cross-sectional images of the electrode sheet were taken at 5K magnification and 20K magnification respectively using high-resolution SEM. The particle size of the particles in the cross-sectional images was statistically analyzed using image recognition software. The number and proportion of particles with a diameter >1μm were counted at 5K magnification, and the number and proportion of particles with a diameter <1μm were counted at 20K magnification.

[0124] Test of the gap width between primary particles in the second lithium iron phosphate granules:

[0125] Similarly, by testing the cross-sectional images of the positive electrode (the electrode preparation and SEM sample pretreatment methods were consistent with the particle size statistics methods), cross-sectional SEM backscattering mode images of the lithium iron phosphate particles were taken, and referenced. Figure 6 The gap width between primary particles inside the second lithium iron phosphate particle was measured by the difference in brightness contrast inside the particle in backscatter mode.

[0126] Fusion layer thickness test:

[0127] The thickness of the fusion layer was measured by X-ray photoelectron spectroscopy (XPS). The lithium iron phosphate particles were subjected to gradient argon ion etching with a single etching thickness of 10 nm. XPS elemental analysis was performed before and after each etching. The thickness of the fusion layer was determined by comparing the differences in the content of fluxing elements (such as Ce).

[0128] Cathode material particle Dv50 test:

[0129] The Dv50 of the first and second lithium iron phosphate particles was tested using a laser particle size analyzer.

[0130] Determination of the equivalent sphere diameter of the cathode material particles:

[0131] The morphology of the cathode material particles was obtained by taking SEM images, and the equivalent sphere diameter of the cathode material particles was determined by the ImageJ particle size statistics function in the simulation software.

[0132] Charge-discharge cycle test:

[0133] The lithium-ion battery was subjected to constant power charge-discharge cycle testing on a charge-discharge tester (model Landt CT2001A). The test temperature was 25℃, the charge-discharge power was 0.5P (charge-discharge power = battery voltage plateau × battery rated capacity), and the charge-discharge voltage window was 2.5V~3.65V (i.e., the battery charging cut-off voltage was 3.65V, and the battery discharging cut-off voltage was 2.5V; it is generally considered that when the charging cut-off voltage is ≥3.65V, the battery charging cut-off voltage is relatively high). The capacity retention rate after 300 cycles was calculated using the following formula: Capacity retention rate after the nth cycle = (discharge capacity after the nth cycle / discharge capacity of the first cycle) × 100%.

[0134] Energy efficiency test:

[0135] At 25°C, under constant power of 0.5P, and within a voltage window of 2.5V~3.65V, the battery is cycled for 3 times. The ratio of discharge energy to charge energy in each cycle is recorded as the energy efficiency of that cycle. The average energy efficiency of the first 3 cycles is recorded as the initial energy efficiency of the lithium-ion battery (i.e., 0.5P energy efficiency). The energy efficiency of the 300th cycle is recorded as the energy efficiency of the 300th cycle.

[0136] Table 2: Performance data of each embodiment and comparative example

[0137]

[0138] As can be seen from Examples 1 to 8 and Comparative Examples 1 to 3, using ordinary lithium iron phosphate material with particle size distribution results in low 0.5P discharge capacity, 0.5P energy efficiency, 300-cycle capacity retention rate, and 300-cycle energy efficiency; while the lithium-ion battery of this application has high 0.5P discharge capacity, 0.5P energy efficiency, 300-cycle capacity retention rate, and 300-cycle energy efficiency, exhibiting good discharge performance, energy efficiency, and cycle life.

[0139] The type and content of fluxing elements, the content of doping elements, and the ratio of second lithium iron phosphate particles to first lithium iron phosphate particles also typically affect the performance of the cathode material. As can be seen from Examples 1 to 18, by adjusting the above parameters within the scope of this application, based on the cathode material possessing the features of this application, it is beneficial to improve the cycle life of the cathode material, thereby improving the energy efficiency and cycle life of the lithium-ion battery.

[0140] Figure 4 This is a SEM image of the second lithium iron phosphate particles prepared in Example 1 of this application. Figure 4 It can be seen that there are lithium iron phosphate particles larger than 3μm that help to fuse, and the particle surface is not uniform and flat, and is formed by the fusion of multiple primary particles; Figure 5This is a cross-sectional view of the second lithium iron phosphate particles prepared in Example 1 of this application. Figure 5 It can be seen that a single lithium iron phosphate particle contains more than three primary particles, and the gaps between the multiple primary particles are very small. Figure 6 This is a backscattered mode view of the second lithium iron phosphate particle prepared in Example 1 of this application. Figure 6 It can be seen that the gap width between multiple primary particles inside the second lithium iron phosphate particle is <20nm, and the marked particles numbered ①~⑩ are the primary particles that form the second lithium iron phosphate particle.

[0141] Figure 7 The image shows a SEM image of the large lithium iron phosphate particles in Comparative Example 1. Figure 7 It can be seen that, among the conventional large particles prepared by strategies other than those proposed in this application, the particle surfaces are smooth and flat, with no obvious signs of fusion. Figure 8 and Figure 9 The images show cross-sectional views and backscattered mode views of the large lithium iron phosphate particles prepared in Comparative Example 1, respectively. Figure 8 and Figure 9 It can be seen that the number of primary particles inside the large lithium iron phosphate particles is less than or equal to 3, and the marked particles numbered ① to ③ are the primary particles that form the large lithium iron phosphate particles.

[0142] The above provides a detailed description of a positive electrode sheet, battery, energy storage device, and electrical equipment disclosed in this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core inventive points of the embodiments of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A positive electrode plate, characterized in that, include: A positive electrode current collector, wherein at least one side of the positive electrode current collector has a positive electrode material layer, the positive electrode material layer includes a positive electrode material, the positive electrode material includes a first lithium iron phosphate particle and a second lithium iron phosphate particle, wherein the Dv50 of the second lithium iron phosphate particle is greater than the Dv50 of the first lithium iron phosphate particle. The second lithium iron phosphate particle is formed by fusing multiple primary particles, wherein the primary particles contain fluxing elements and doping elements, and the primary particles have tortuous gaps between them; The fluxing element includes at least one of tungsten, scandium, yttrium, and lanthanides, and the fluxing element forms more microcrystalline regions inside the second lithium iron phosphate particle; The doping element includes at least one of titanium and vanadium.

2. The positive electrode sheet according to claim 1, characterized in that, The number of second lithium iron phosphate particles with a particle size greater than 1 μm accounts for 90% to 95% of the total number of second lithium iron phosphate particles, and the number of second lithium iron phosphate particles with a particle size less than or equal to 1 μm accounts for 5% to 10% of the total number of second lithium iron phosphate particles.

3. The positive electrode sheet according to claim 2, characterized in that, A second lithium iron phosphate particle with a particle size greater than 1 μm comprises at least three primary particles with a particle size less than 1 μm, and the maximum width of the gap is less than or equal to 100 nm. And / or, in the second lithium iron phosphate particles with a particle size of less than or equal to 1 μm, the maximum width of the gap is less than or equal to 20 nm.

4. The positive electrode sheet according to claim 1, characterized in that, The surface of the primary particle has a fusion layer with a thickness of 3nm to 30nm, and the fusion aid element and the dopant element are distributed within the fusion layer.

5. The positive electrode sheet according to claim 1, characterized in that, The mass fraction of the fluxing element in the second lithium iron phosphate particle is a, where 0.05% ≤ a ≤ 0.5%; And / or, the mass fraction of the doping element in the second lithium iron phosphate particle is b, 0.1%≤b≤0.5%.

6. The positive electrode sheet according to claim 1, characterized in that, The first lithium iron phosphate particles have a mass fraction of 10% to 50% in the cathode material, and the second lithium iron phosphate particles have a mass fraction of 50% to 90% in the cathode material.

7. The positive electrode sheet according to claim 1, characterized in that, The Dv50 of the second lithium iron phosphate particle is 1.6 μm ~ 2.2 μm, and the Dv50 of the first lithium iron phosphate particle is 0.4 μm ~ 0.7 μm.

8. A battery, characterized in that, Includes the positive electrode sheet as described in any one of claims 1 to 7.

9. An energy storage device, characterized in that, It includes a housing and at least one battery as described in claim 8, the battery being housed within the housing.

10. An electrical appliance, characterized in that, The device includes the energy storage device of claim 9, wherein the energy storage device supplies power to the electrical equipment.

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