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 equipment, wherein the positive electrode sheet comprises a positive electrode current collector, at least one side of the positive electrode current collector is provided with a positive electrode material layer, the positive electrode material layer comprises a positive electrode material, the positive electrode material comprises first particles and second particles, the second particles are secondary particles formed by third particles, and the first particles and the third particles are primary particles; along the direction of the longest diameter of the second particle and away from the center of the second particle, the third particles on the surface of the second particle form a plurality of stepped structures with a decreasing height trend, and the plurality of stepped structures have gaps; and the ratio of the surface area of the second particle to the area of the maximum cross section of the second particle is A, 3<=A<=10.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of energy storage, in particular to a positive electrode sheet, a battery, an energy storage device and an electric equipment. BACKGROUND

[0002] Secondary batteries (for example, lithium ion batteries) have the characteristics of high specific energy, high working voltage, low self-discharge rate, small volume, light weight, etc., and are widely used in various fields such as electric energy storage, portable electronic devices and electric vehicles.

[0003] Lithium ion batteries based on lithium iron phosphate positive electrode materials have the advantage of high safety stability. With the increasing requirement of high capacity of batteries in energy storage scenarios, smaller particle size lithium iron phosphate materials are currently used, but the problem of high elongation of the positive electrode sheet during the rolling process arises. SUMMARY

[0004] In order to solve the above technical problems, the present application discloses a positive electrode sheet, a battery, an energy storage device and an electric equipment, which reduce the elongation of the positive electrode sheet while improving the capacity performance of the secondary battery.

[0005] In a first aspect, the present application provides a positive electrode sheet, comprising a positive electrode current collector, at least one side of the positive electrode current collector having a positive electrode material layer, the positive electrode material layer comprising a positive electrode material, the positive electrode material comprising first particles and second particles, the second particles being secondary particles formed by third particles, the first particles and the third particles being primary particles;

[0006] Wherein, along the direction of the longest diameter of the second particle and away from the center of the second particle, the third particles located on the surface of the second particle form a plurality of stepped structures with a decreasing height trend, and the plurality of stepped structures have gaps;

[0007] The ratio of the surface area of the second particle to the area of the maximum cross section of the second particle is A, 3≤A≤10.

[0008] In some embodiments of the present application, the average particle size of the third particles located on the surface of the second particle is d1, 1μm≤d1≤3μm.

[0009] In some embodiments of the present application, the Dv50 of the positive electrode material is 1μm~3μm.

[0010] In some embodiments of the present application, one of the stepped structures is formed by fusion of a plurality of third particles, and the gap is located at the fusion interface.

[0011] In some embodiments of the present application, the gap is located at the junction of adjacent stepped structures.

[0012] In some embodiments of the present application, the positive electrode material has a chemical formula of LiFe x Ti y PO4 / C, x+y=1, and 0<y≤0.05.

[0013] In some embodiments of the present application, the positive electrode tab has an elongation of 0.5%-2.3%.

[0014] In a second aspect, the present application provides a battery comprising the positive electrode tab of the first aspect.

[0015] In a third aspect, the present application provides an energy storage device comprising a box body and at least one battery of the second aspect, wherein the battery is accommodated in the box body.

[0016] In a fourth aspect, the present application provides an electrical equipment comprising the energy storage device of the third aspect, wherein the energy storage device supplies power for the electrical equipment.

[0017] Compared with the prior art, the present application has at least the following beneficial effects:

[0018] The present application provides a positive electrode tab, a battery, an energy storage device and electrical equipment, wherein the positive electrode tab 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 particles and second particles, the second particles are secondary particles formed by third particles, wherein along the direction of the longest diameter of the second particle and away from the center of the second particle, the third particles located on the surface of the second particle form a plurality of stepped structures with a decreasing height trend, so that the surface of the second particle is much rougher than that of ordinary lithium iron phosphate material particles; the ratio of the surface area of the second particle to the area of the maximum cross section of the second particle is A, 3≤A≤10, which is conducive to hindering the deformation and sliding of the particles under pressure and reducing the elongation of the positive electrode tab; and the plurality of stepped structures have gaps, which can promote the rapid infiltration of the electrolyte into the interior of the second particles, thereby improving the Li + diffusion capacity and promoting the capacity of the positive electrode material. In summary, the present application can reduce the elongation of the positive electrode tab while improving the capacity performance of the secondary battery, which is conducive to improving the capacity and service life of the energy storage device. BRIEF DESCRIPTION OF DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0020] Figure 1 Schematic diagram of the second particle of one embodiment of the present application;

[0021] Figure 2 Schematic diagram of the stepped structure in the second particle of one embodiment of the present application;

[0022] Figure 3 Schematic diagram of the structure of the household energy storage system of one embodiment of the present application;

[0023] Figure 4 Schematic diagram of the structure of the commercial energy storage system of one embodiment of the present application;

[0024] Figure 5 Schematic diagram of the positive electrode sheet elongation test of the present application;

[0025] Figure 6 Scanning electron microscope (SEM) image of the positive electrode material of Example 1 (magnification: 10,000 times);

[0026] Figure 7 SEM image of the positive electrode material of Example 1 (magnification: 30,000 times);

[0027] Figure 8 SEM image of the positive electrode material of Comparative Example 1 (magnification: 10,000 times);

[0028] Figure 9 SEM image of the positive electrode material of Comparative Example 1 (magnification: 30,000 times).

[0029] BRIEF DESCRIPTION OF DRAWINGS 1-energy storage device, 2-electric energy conversion device, 3-first user load, 4-second user load, 10-stepped structure, 40-roller, 101-first stepped structure, 102-second stepped structure, 103-third stepped structure, 1021-third particle, 400-commercial energy storage system, 410-high voltage cable, 420-first electric energy conversion device, 430-second electric energy conversion device. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0031] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are mainly used to better describe the present application and its embodiments, and are not intended to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0032] In addition, in addition to indicating the orientation or positional relationship, the above-mentioned partial terms can also be used to indicate other meanings, for example, the term "upper" can also be used to indicate a certain dependent relationship or connection relationship in some cases. For those skilled in the art, the specific meaning of these terms in the present application can be understood according to the specific circumstances.

[0033] In addition, the terms "mount", "set", "provided with", "connected", "connected" should be broadly understood. For example, it can be fixedly connected, detachably connected, or integrally constructed; it can be mechanically connected, or electrically connected; it can be directly connected, or indirectly connected through an intermediate medium, or internal communication between two devices, elements or components. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0034] In addition, the terms "first", "second" and the like are mainly used to distinguish different devices, elements or components (the specific types and structures may be the same or different), and are not intended to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise stated, the meaning of "multiple" is two or more.

[0035] It should be noted that in the content of the present application, the lithium ion battery is taken as an example of the secondary battery to explain the present application, but the secondary battery of the present application is not limited to the lithium ion battery.

[0036] The present application provides a positive electrode tab, which 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 particles and second particles, the second particles are secondary particles formed by third particles, and the first particles and the third particles are primary particles. The material types of the first particles and the second particles can be the same, for example, both are lithium iron phosphate materials. Referring to Figure 1, the third particles on the surface of the second particle form a plurality of stepped structures 10 with a height-decreasing trend in a direction along the longest diameter D of the second particle and away from the center O of the second particle (the direction of the arrow shown in the figure), and the plurality of stepped structures have gaps; a ratio of a surface area of the second particle to an area of the largest cross section of the second particle is A, 3≤A≤10. For example, A=3, A=6, A=7, A=9, or A=10.

[0037] The positive electrode tab of the present application comprises the above-mentioned positive electrode material, wherein the plurality of stepped structures with a height-decreasing trend can make the surface of the second particle much rougher than that of the ordinary lithium iron phosphate material particles, so that the positive electrode material is less likely to deform and slip under pressure; the inventors have found that when the value of A is too small (for example, less than 3), the shape of the second particle tends to be a spherical structure, which is more likely to displace and deform under rolling, which is not conducive to reducing the ductility of the positive electrode tab; when the value of A is too large (for example, greater than 10), the roughness of the second particle is too high, the positive electrode material is less likely to deform and slip under pressure, and the ductility of the positive electrode tab is significantly reduced, but the capacity of the energy storage device is reduced due to the increase of the gap between the particles, thereby reducing the compaction of the positive electrode tab. By adjusting the value of A within the above range, the deformation and slip of the particles under pressure are hindered, and the ductility of the positive electrode tab is reduced. Moreover, the plurality of stepped structures in the second particle have gaps, which can promote the rapid infiltration of the electrolyte into the interior of the second particle, thereby improving the Li + diffusion capacity and promoting the capacity performance of the positive electrode material. In summary, the present application can reduce the ductility of the positive electrode tab while improving the capacity performance of the lithium ion battery, thereby improving the capacity and service life of the energy storage device.

[0038] In the present application, the area of the largest cross section of the second particle refers to that 50 second particles are randomly selected, the area of the cross section of each particle is calculated, and the area of the largest cross section is taken as the record value.

[0039] In an optional embodiment, the average particle size of the third particles on the surface of the second particle is d1, 1μm≤d1≤3μm. For example, d1=1μm, d1=1.5μm, d1=2μm, or d1=3μm. By adjusting d1 within the above range, the plurality of stepped structures with a height-decreasing trend of the concave-convex structure are formed, thereby improving the roughness of the surface of the second particle.

[0040] In an optional embodiment, the Dv50 of the positive electrode material is 1μm~3μm. For example, the Dv50 of the positive electrode material is 1μm, 2μm, or 3μm. By adjusting the Dv50 of the positive electrode material within the above range, the positive electrode material has a higher compaction density, thereby improving the capacity performance of the positive electrode material.

[0041] In the present application, Dv50 represents the particle size at which 50% of the volume is accumulated from the small particle size side in the particle size distribution on a volume basis.

[0042] In an alternative embodiment, a step-like structure is formed by fusing a plurality of third particles, and the gap is located at the fusion interface, so as to facilitate the electrolyte to enter the second particle through the gap, improve the electrolyte wettability of the second particle, and thus improve the capacity performance of the positive electrode material. Figure 2 , shows three step-like structures of first step-like structure 101, second step-like structure 102, and third step-like structure 103, which have heights decreasing in stages. Taking the second step-like structure 102 as an example, four fused third particles 1021 are shown in the second step-like structure 102, and the gap can be located at the fusion interface of the third particles 1021, and the third particles 1021 belong to a primary particle.

[0043] In an alternative embodiment, the gap is located at the interface of adjacent step-like structures, so as to facilitate the electrolyte to enter the second particle through the gap, improve the electrolyte wettability of the second particle, and thus improve the capacity performance of the positive electrode material. Figure 2 , for example, the gap can be located at the interface of the first step-like structure 101 and the second step-like structure 102, and / or the gap can be located at the interface of the second step-like structure 102 and the third step-like structure 103.

[0044] In an alternative embodiment, the positive electrode material has a chemical formula of LiFe x Ti y PO4 / C, x+y = 1, and 0 < y ≤ 0.05. For example, y = 0.01, 0.02, 0.03, 0.04, or 0.05. The positive electrode material with the above chemical formula contains the doping element titanium (Ti), which can provide more capacity and is beneficial to the improvement of the capacity performance of the lithium ion battery.

[0045] In an alternative embodiment, the elongation of the positive electrode tab is 0.5% to 2.3%; in another alternative embodiment, the elongation of the positive electrode tab is 0.5% to 1.6%. For example, the elongation of the positive electrode tab is 0.5%, 0.8%, 1.0%, 1.3%, 1.6%, or 2.3%, which has a lower elongation, is beneficial to the reduction of the risk of edge cracking of the positive electrode tab, and improves the yield of the lithium ion battery.

[0046] In an alternative embodiment, the preparation method of the positive electrode material comprises the following steps:

[0047] Step A, preparation of the first precursor material:

[0048] Step a, preparing LiFex Ti y The stoichiometric ratio of the required iron source, phosphorus source, lithium source, titanium source and carbon source in PO4 / C (x+y=1, and 0

[0049] Step b, the high-energy ball-milled material is spray dried to form a granular powder;

[0050] Step c, the granular powder is placed into a vacuum atmosphere sintering furnace for first sintering treatment, and after crushing treatment, a first precursor material is obtained.

[0051] In step a, the iron source can be selected from ferrous oxalate, iron phosphate or iron oxide, the phosphorus source can be selected from lithium dihydrogen phosphate or ammonium dihydrogen phosphate, the lithium source can be selected from lithium carbonate or lithium hydroxide, the titanium source is selected from titanium dioxide, and the carbon source can be selected from glucose, sucrose or citric acid; the ball-to-material ratio of high-energy ball milling is 3-5:1, the rotation speed is 1000 r / min-2000 r / min, and the ball milling time is 15 h-20 h.

[0052] In step b, the pump speed of spray drying is 8 mL / min-12 mL / min, the drying temperature is 180°C-220°C, and the formed powder is granular.

[0053] In step c, the protective atmosphere is nitrogen, the temperature of first sintering treatment is 380°C-420°C, and the sintering time is 5 h-10 h.

[0054] Step B, preparation of a second precursor material:

[0055] Step a', according to LiFe x Ti y The stoichiometric ratio of the required iron source, phosphorus source, lithium source, titanium source and carbon source in PO4 / C (x+y=1, and 0

[0056] Step b', the mixed metal salt solution, the complexing agent solution and the precipitant solution prepared above are placed in a reaction kettle, and stirring is continuously carried out, the pH value of the reaction liquid is maintained at 9±0.5, the reaction temperature is 180°C-200°C, the reaction time is 8 h-10 h, and the second precursor material is prepared by using a precipitation reaction synthesis, followed by solid-liquid separation, washing and drying.

[0057] In step a', the iron source can be selected from ferrous oxalate, ferric sulfate or ferric chloride, the phosphorus source can be selected from phosphoric acid or ammonium dihydrogen phosphate, the lithium source can be selected from lithium carbonate or lithium hydroxide, the titanium source is selected from titanium tetrachloride, and the carbon source can be selected from glucose, sucrose or citric acid; each of the above raw materials can be first prepared into a corresponding solution, and then the solution containing each of the above raw materials is mixed to obtain a mixed metal salt solution, wherein the molar concentration of titanium in the mixed metal salt solution is 0.3 mol / L to 0.7 mol / L; the strong alkali solution can be a sodium hydroxide solution with a molar concentration of 0.5 mol / L to 1 mol / L, and the molar concentration of ammonia water is 0.5 mol / L to 1.5 mol / L. The solvent in the mixed metal salt solution in the present application can include water.

[0058] In step b', the complexing agent can be first added to the mixed metal salt solution, the pH value is adjusted to 9±0.5, then the precipitant solution is added, and the complexing agent is continuously added to adjust the pH value to 9±0.5 as the precipitate is generated. This process is a precipitation reaction process.

[0059] Step C, preparation of the positive electrode material:

[0060] The first precursor material and the second precursor material are mixed to obtain a pre-sintering material, the mass percentage of the second precursor material in the pre-sintering material is 10% to 50%, and preferably 20% to 50%; then the pre-sintering material is placed into a vacuum atmosphere sintering furnace for a second sintering treatment, and then a crushing treatment is performed to obtain the positive electrode material, wherein the protective atmosphere is nitrogen, the temperature of the second sintering treatment is 700°C to 800°C, and preferably 700°C to 780°C; and the sintering time is 10h to 20h, and preferably 10h to 18h.

[0061] The present application does not have a particular limitation on the way of regulating the ratio of the surface area of the second particles to the area of the maximum cross section of the second particles (A value), as long as the purpose of the present application can be achieved. For example, the A value is generally reduced as the content of the second precursor material in the pre-sintering material increases, based on which the present application can regulate the A value by regulating the content of the second precursor material in the pre-sintering material; for another example, the A value is generally reduced as the sintering temperature of the second sintering treatment increases, based on which the present application can regulate the A value by regulating the sintering temperature of the second sintering treatment; for another example, the A value is generally reduced as the sintering time of the second sintering treatment increases, based on which the present application can regulate the A value by regulating the sintering time of the second sintering treatment.

[0062] The present application does not have a particular limitation on the way of regulating d1, as long as the purpose of the present application can be achieved. For example, d1 is generally increased as the content of the second precursor material in the pre-sintering material increases, based on which the present application can regulate d1 by regulating the content of the second precursor material in the pre-sintering material.

[0063] The application does not have special restrictions on the way of regulating the Dv50 of the positive electrode material, as long as the purpose of the application can be achieved. For example, the Dv50 of the positive electrode material generally increases with the increase of the content of the second precursor material in the pre-burning material, and based on this, the application can regulate the Dv50 of the positive electrode material by regulating the content of the second precursor material in the pre-burning material.

[0064] The application also provides a battery comprising the positive electrode sheet according to any one of the above embodiments.

[0065] In the application, the positive electrode material layer can be arranged on one surface in the thickness direction of the positive electrode current collector, or on both surfaces in the thickness direction of the positive electrode current collector. In the application, the positive electrode material layer is arranged on the surface of the positive electrode current collector, that is, the positive electrode material layer can be arranged in part of the area of one surface of the positive electrode current collector, or in the entire area of one surface of the positive electrode current collector. In the application, the positive electrode current collector is not particularly limited, as long as the purpose of the application can be achieved, for example, it can include but is not limited to aluminum foil, aluminum alloy foil or composite current collector, etc. In the application, the thickness of the positive electrode current collector is not particularly limited, as long as the purpose of the application can be achieved, for example, the thickness is 4 μm to 12 μm. The single-sided thickness of the positive electrode material layer of the application can be 8 μm to 15 μm.

[0066] The lithium ion battery of the application also comprises a negative electrode sheet. The negative electrode sheet is not particularly limited in the application, as long as the purpose of the application can be achieved, for example, the negative electrode sheet generally comprises a negative electrode current collector and a negative electrode material layer. The negative electrode material layer can be arranged on one surface or both surfaces in the thickness direction of the negative electrode current collector. In the application, the negative electrode material layer is arranged on the surface of the negative electrode current collector, that is, the negative electrode material layer can be arranged in part of the area of one surface of the negative electrode current collector, or in the entire area of one surface of the negative electrode current collector. The negative electrode current collector is not particularly limited in the application, as long as the purpose of the application can be achieved, for example, it can include but is not limited to copper foil, copper alloy foil, nickel foil or composite current collector, etc. In the application, the thickness of the negative electrode current collector is not particularly limited, as long as the purpose of the application can be achieved, for example, the thickness is 4 μm to 12 μm. The single-sided thickness of the negative electrode material layer of the application can be 70 μm to 200 μm.

[0067] In the application, the negative electrode material layer comprises a negative electrode material, wherein the negative electrode material is not particularly limited, as long as the purpose of the application can be achieved, for example, it can include at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon, silicon-carbon.

[0068] In the present application, the negative electrode material layer can further include a negative electrode binder. The present application does not have a particular limitation on the negative electrode binder, as long as the purpose of the present application can be achieved, for example, can 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.

[0069] The lithium ion battery of the present application further includes a separator. The present application does not have a particular limitation on the separator, which can be selected by a person skilled in the art according to actual needs, as long as the purpose of the present application can be achieved. For example, the separator can include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a composite film 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 film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film can be selected.

[0070] The battery of the present application further includes an electrolyte. The present application does not have a particular limitation on the electrolyte, which can be selected by a person skilled in the art according to actual needs, as long as the purpose of the present application can be 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) or fluoroethylene carbonate (FEC) is mixed in a certain mass ratio or volume ratio to obtain a non-aqueous organic solvent, and then a lithium salt is added and uniformly mixed. The present application does not limit the type of lithium salt, as long as the purpose of the present application can be achieved. For example, the lithium salt can include at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, LiSiF6, lithium bis(oxalato)borate (LiBOB) or lithium difluoroborate.

[0071] The present application does not have a particular limitation on the concentration of lithium salt in the electrolyte, as long as the purpose of the present application can be achieved. Taking LiPF6 as an example, the concentration of LiPF6 in the electrolyte is 5wt% to 25wt%, for example, the concentration of LiPF6 is 5wt%, 10wt%, 11wt%, 12wt%, 12.5wt%, 15wt%, 20wt% or 25wt%.

[0072] The battery of the present application further includes a shell, which does not have a particular limitation, and a person skilled in the art can select according to actual needs, as long as the purpose of the present application can be achieved. For example, the shell can include an aluminum plastic film.

[0073] The preparation method of the battery is not particularly limited in the present application, and a preparation method known in the art can be selected as long as the purpose of the present application can be achieved. For example, the preparation method of the battery includes but is not limited to the following steps: stacking the positive electrode sheet, the separator and the negative electrode sheet in order, and winding, folding or other operations as needed to obtain a bare cell with a winding structure, placing the bare cell into a packaging bag, injecting electrolyte into the packaging bag and sealing the packaging bag to obtain the battery.

[0074] The present application also provides an energy storage device, which comprises a box body and at least one battery according to any one of the above embodiments, and the battery is accommodated in the box body. The energy storage device with the battery has excellent performance, which is beneficial to the use of the energy storage device. By accommodating the battery in the box body, the fixing and protection of the battery can be increased, and the service life of the energy storage device can be improved. It can be understood that the energy storage device can have one or more batteries, and when the energy storage device contains multiple batteries, the multiple batteries can be connected in at least one of parallel and series.

[0075] The present application also provides an electrical equipment, which comprises the energy storage device according to the above embodiments, which is beneficial to improve the product competitiveness and use performance of the electrical equipment. In an alternative embodiment, the electrical equipment comprises an electrical equipment body, and the energy storage device is used to supply power to the electrical equipment body. In an alternative embodiment, the electrical equipment body comprises a device positive electrode and a device negative electrode, and the positive electrode sheet of the battery in the energy storage device is used to electrically connect the device positive electrode of the electrical equipment body, and the negative electrode sheet of the battery in the energy storage device is used to electrically connect the device negative electrode of the electrical equipment body, so as to supply power to the electrical equipment.

[0076] The electrical equipment of the present application can include but is not limited to a container, an electric car, an electric vehicle, a ship, a spacecraft, an electric toy and an electric tool, etc., wherein the spacecraft is, for example, an airplane, a rocket, a space shuttle and a spaceship, etc., the electric toy includes, for example, a fixed or mobile electric toy, and specifically includes, for example, an electric vehicle toy, an electric ship toy and an electric airplane toy, etc., and the electric tool includes, for example, a metal cutting electric tool, a grinding electric tool, an assembling electric tool and a railway electric tool, and specifically includes, for example, a power drill, a power grinder, a power wrench, a power screwdriver, a power hammer, an impact power drill, a concrete vibrator and a power planer.

[0077] Please refer to Figure 3 , Figure 3 for the structural schematic diagram of a household energy storage system according to an embodiment of the present application, and the present application Figure 3 The present application is not limited to the household energy storage scene in the user side energy storage.

[0078] The application provides a household energy storage system, which comprises an electric energy conversion device 2 (a photovoltaic panel), a first user load 3 (a street lamp), a second user load 4 (for example, a household appliance such as an air conditioner), and an energy storage device 1. The energy storage device 1 is a small energy storage box, which can be installed on an outdoor wall in a wall-mounted manner. Specifically, the photovoltaic panel can convert solar energy into electric energy during a low electricity price period, and the energy storage device 1 is used for storing the electric energy and supplying the street lamp and the household appliance for use during a high electricity price period or supplying power when the power grid is disconnected.

[0079] Please refer to Figure 4 , Figure 4 The application provides a commercial energy storage system 400, and the application Figure 4 The application provides a commercial energy storage system 400, and the application

[0080] The application provides a commercial energy storage system 400, and the application

[0081] The application provides a commercial energy storage system 400, and the application

[0082] The application provides a commercial energy storage system 400, and the application

[0083] Optionally, the energy storage device 1 can include, but is not limited to, a battery module, a battery pack, a battery system, etc. Among them, the battery module can be a battery module formed by a plurality of batteries of the present application in series / parallel connection, the battery pack can include a plurality of batteries of the present application, and the battery system can be a charging and discharging system including the batteries or the battery pack of the present application.

[0084] The actual application form of the energy storage device 1 provided by the embodiments of the present application can be, but is not limited to, the listed products, and can also be other application forms. The embodiments of the present application do not strictly limit the application form of the energy storage device 1. The embodiments of the present application only take the energy storage device 1 as an example of a multi-core battery. When the energy storage device 1 includes a single battery, the single battery therein can be at least one of a cylindrical battery, a square battery, etc.

[0085] Embodiments

[0086] Hereinafter, preparation examples, examples and comparative examples are given to more specifically explain the embodiments of the present application. Various tests and evaluations are carried out according to the following methods.

[0087] Example 1

[0088] <Preparation of positive electrode sheet>

[0089] <Preparation of first precursor material>

[0090] According to LiFe 0.99 Ti 0.01 The stoichiometric ratio required in the TiPO4 / C was weighed with ferrous oxalate as an iron source, ammonium dihydrogen phosphate as a phosphorus source, lithium carbonate as a lithium source, titanium dioxide as a titanium source, and glucose as a carbon source. The mixture was uniformly mixed in a ball mill, and then a proper amount of pure water was added as a dispersant. High-energy ball milling was then performed with a ball-to-material ratio of 4:1 and a rotation speed of 2000 r / min for 20 h. The high-energy ball-milled material was then spray dried at a pump speed of 10 mL / min and a drying temperature of 200°C to form a granular powder. The granular powder was placed in a vacuum atmosphere sintering furnace for first sintering treatment, with nitrogen as the protective atmosphere, a sintering temperature of 400°C, and a sintering time of 8 h. After ball milling and crushing, the first precursor material was obtained.

[0091] <Preparation of second precursor material>

[0092] According to LiFe 0.99 Ti 0.01The stoichiometric ratio required in the PO4 / C is weighed with ferrous oxalate as the iron source, lithium dihydrogen phosphate as the phosphorus source, lithium carbonate as the lithium source, titanium tetrachloride as the titanium source, and glucose as the carbon source, and a mixed metal salt solution is obtained after mixing; a strong alkali solution is prepared as a precipitant solution, and ammonia water is prepared as a complexing agent solution; the molar concentration of titanium in the mixed metal salt solution is 0.5 mol / L, the strong alkali solution is a sodium hydroxide solution with a molar concentration of 1 mol / L, and the molar concentration of the ammonia water is 1 mol / L; the mixed metal salt solution, the complexing agent solution, and the precipitant solution prepared above are placed in a reaction kettle, and stirring is continuously performed, the pH value of the reaction liquid is maintained at 9, the reaction temperature is 200℃, and the reaction time is 10 h, and a second precursor material is synthesized by a precipitation reaction, and is obtained after solid-liquid separation, washing, and drying.

[0093] <Preparation of the positive electrode material>

[0094] The first precursor material and the second precursor material are mixed to obtain pre-fired material, and the content of the second precursor material in the pre-fired material is 10wt%; then the pre-fired material is placed in a vacuum atmosphere sintering furnace for second sintering treatment, and the positive electrode material is obtained after crushing treatment, wherein the protective atmosphere is nitrogen, the sintering temperature of the second sintering treatment is 700℃, and the sintering time is 10 h.

[0095] <Preparation of the positive electrode material layer>

[0096] The positive electrode material, the binder PVDF, and the conductive carbon black (Super-P) are mixed in a mass ratio of 95:3:2, then N-methyl pyrrolidone (NMP) is added as a solvent, and the positive electrode slurry with a solid content of 50wt% is prepared by mixing and stirring uniformly, then the positive electrode slurry is uniformly coated on one surface of the positive electrode current collector with a thickness of 10μm, and is dried at 85℃, then the above steps are repeated on the other surface of the positive electrode sheet, and the positive electrode sheet with the positive electrode material layer coated on both sides is obtained after rolling, and the single-sided thickness of the positive electrode material layer is 100μm.

[0097] <Preparation of the negative electrode sheet>

[0098] The negative electrode material artificial graphite, the conductive carbon black (Super-P), and the sodium carboxymethyl cellulose (CMC-Na) are mixed in a mass ratio of 95:2.5:2.5, deionized water is added, and the negative electrode slurry with a solid content of 60wt% is prepared by mixing and stirring uniformly. The negative electrode slurry is uniformly coated on one surface of the negative electrode current collector copper foil with a thickness of 10μm, and is dried at 150℃, then the above steps are repeated on the other surface of the negative electrode sheet, and the negative electrode sheet with the negative electrode material layer coated on both sides is obtained after rolling, and the single-sided thickness of the negative electrode material layer is 70μm.

[0099] <Preparation of the electrolyte>

[0100] Ethylene carbonate (EC) and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1, dissolved and stirred thoroughly, then lithium salt LiPF6 was added, and the electrolyte was obtained after mixing uniformly. The concentration of LiPF6 in the electrolyte was 12.5 wt%.

[0101] <Preparation of the separator>

[0102] A polyethylene (PE) porous polymer film with a thickness of 16 μm was used as the separator.

[0103] <Assembly of the lithium ion battery>

[0104] The prepared positive electrode sheet and negative electrode sheet were respectively put into a press for pressing, then a puncher was used to cut a circular positive electrode sheet with a diameter of 15 mm and a circular negative electrode sheet with a diameter of 18 mm; then the circular positive electrode sheet, the separator and the circular negative electrode sheet were stacked in order with the separator in the middle of the circular positive electrode sheet and the circular negative electrode sheet to play a role of isolation, then the prepared electrolyte was injected to assemble a lithium ion battery.

[0105] Examples 2-5

[0106] Except that the content of the second precursor material in the pre-sintered material was adjusted according to Table 1 in the <Preparation of the positive electrode material>, the rest was the same as Example 1.

[0107] Examples 6-10

[0108] Except that the sintering temperature of the second sintering treatment was adjusted according to Table 1 in the <Preparation of the positive electrode material>, the rest was the same as Example 1.

[0109] Examples 11-15

[0110] Except that the sintering time of the second sintering treatment was adjusted according to Table 1 in the <Preparation of the positive electrode material>, the rest was the same as Example 1.

[0111] Example 16

[0112] Except that the content of the second precursor material in the pre-sintered material was adjusted according to Table 1 in the <Preparation of the positive electrode material>, the rest was the same as Example 1. 0.98 Ti 0.02 PO4 / C except that the stoichiometric ratio of each raw material required was weighed, and the rest was the same as Example 1.

[0113] Example 17

[0114] Except that the content of the second precursor material in the pre-sintered material was adjusted according to Table 1 in the <Preparation of the positive electrode material>, the rest was the same as Example 1. 0.97 Ti 0.03The stoichiometric ratio required in PO4 / C was weighed for each raw material, and the rest was the same as Example 1.

[0115] Example 18

[0116] In addition to <preparation of the first precursor material>, <preparation of the second precursor material>, LiFe 0.96 Ti 0.04 The stoichiometric ratio required in PO4 / C was weighed for each raw material, and the rest was the same as Example 1.

[0117] Example 19

[0118] In addition to <preparation of the first precursor material>, <preparation of the second precursor material>, LiFe 0.95 Ti 0.05 The stoichiometric ratio required in PO4 / C was weighed for each raw material, and the rest was the same as Example 1.

[0119] Comparative Example 1

[0120] In addition to <preparation of the positive electrode material>, the pre-burning material only contains the first precursor material without the second precursor material, and the rest is the same as Example 1.

[0121] Table 1: Related preparation parameters of each example and comparative example

[0122]

[0123]

[0124] In Table 1, " / " indicates that the relevant preparation parameter does not exist.

[0125] Test method and equipment:

[0126] Test of the ratio of the surface area of the second particle to the area of the maximum cross section:

[0127] The three-dimensional surface topography of 100 second particles in the positive electrode material was accurately measured by an optical 3D surface profiler (model VR-6000, resolution 0.1 μm), and the surface area and the area of the maximum cross section of each second particle were calculated synchronously. Then the total surface area and the total area of the maximum cross section of 100 second particles were calculated, and were recorded as S 1总 and S 2总 , then the ratio A of the surface area of the second particle to the area of the maximum cross section of the second particle = S 1总 / S 2总 .

[0128] Test of the average particle size of the third particle on the surface of the second particle:

[0129] In a scanning electron microscope (SEM), a 3k times area was photographed, 100 second particles were randomly selected, the third particles attached to the surface of the particles were calculated, the particle size of the third particles was tested by using ImageJ graphics testing software, and then the average value was obtained.

[0130] Positive electrode material particle size distribution test:

[0131] A laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000) was used to measure the particle size distribution of the positive electrode material according to the particle size distribution laser diffraction method (GB / T19077-2016), so as to measure the Dv50 of the positive electrode material.

[0132] Positive electrode sheet elongation rate test:

[0133] As shown in Figure 5 , for example, the positive electrode sheet includes a positive electrode current collector 11, a first positive electrode material layer 12 and a second positive electrode material layer 13. Mark two points A and B on the surface of the first positive electrode material layer 12 or the surface of the second positive electrode material layer 13 before rolling. L1 is the distance between points A and B of the positive electrode sheet before rolling. After rolling through the roller 40, the positive electrode sheet will be elongated along its length direction, so the distance between points A and B will be lengthened, that is, the distance between A' and B' is recorded as L2. The sheet elongation rate is calculated as: (L2-L1) / L1 x 100%.

[0134] Rate performance test:

[0135] The test temperature was 25°C, the lithium ion battery was charged to 3.65V at 0.1C rate (C), then discharged to 2.5V at 0.1C rate, and the 0.1C discharge capacity at this time was recorded, with unit of mAh / g.

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

[0137]

[0138]

[0139] From Examples 1-19 and Comparative Example 1, it can be seen that the elongation rate of the positive electrode sheet of Comparative Example 1 is high, and the 0.1C discharge capacity is low, which may be due to the fact that the positive electrode material of Comparative Example 1 does not have the morphology structure of the positive electrode material of the present application, making it difficult to use the second particles with stepped structure to hinder the displacement deformation of the positive electrode material particles when the positive electrode sheet is under pressure, and the electrolyte is difficult to effectively infiltrate into the interior of the positive electrode material particles, affecting the capacity of the positive electrode material. The positive electrode sheet of the present application exhibits low elongation rate, and the lithium ion battery exhibits excellent capacity performance.

[0140] The content of the second precursor material in the pre-burning material, the sintering temperature of the second sintering treatment, the sintering time, and the content of the doping element (e.g., Ti) in the positive electrode material also generally affect the performance of the positive electrode sheet. It can also be seen from Examples 1-19 that, on the basis of the positive electrode material having the structural features of the present application, by adjusting the above preparation parameters within the scope of the present application, it is beneficial to obtain a lithium ion battery with low ductility and high capacity performance.

[0141] Figure 6 SEM image of the positive electrode material of Example 1 (magnification of 10,000 times), Figure 7 SEM image of the positive electrode material of Example 1 (magnification of 30,000 times). From Figure 6 and Figure 7 It can be seen that the second particles (i.e., the secondary particles with darker color and larger size in the figure) include multiple step-like structures with a highly decreasing trend, and the step-like structures have gaps, some of which are located at the fusion interfaces of the primary particles, and some of which are located at the junctions of adjacent step-like structures; and the surface of the second particles also adheres to the first particles (i.e., the small particles with brighter color in the figure) with relatively small particle size, which belong to the primary particles.

[0142] Figure 8 SEM image of the positive electrode material of Comparative Example 1 (magnification of 10,000 times), Figure 9 SEM image of the positive electrode material of Comparative Example 1 (magnification of 30,000 times). From Figure 8 and Figure 9 It can be seen that the positive electrode material particles have an ellipsoidal structure and do not have step-like structures with a highly decreasing trend.

[0143] The above has introduced in detail a positive electrode sheet, a battery, an energy storage device, and an electrical equipment disclosed by the present application. The principles and implementation manners of the present application are described by applying specific examples in this paper. The above example descriptions are only used to help understand the technical solutions and core invention points of the embodiments of the present application; at the same time, for those skilled in the art, according to the idea of the present application, the specific implementation manners and application ranges will be changed; in summary, the content of the specification should not be understood as a limitation of the present application.

Claims

1. A positive electrode plate, characterized in that, The device 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 includes a first particle and a second particle. The second particle is a secondary particle formed from a third particle. The first particle and the third particle are primary particles. Both the first particle and the second particle are lithium iron phosphate materials. Among them, along the longest diameter of the second particle and away from the center of the second particle, the third particle located on the surface of the second particle forms a plurality of stepped structures with a decreasing height, and the plurality of stepped structures have gaps. The ratio of the surface area of ​​the second particle to the area of ​​the maximum cross-section of the second particle is A, where 3 ≤ A ≤ 10.

2. The positive electrode sheet according to claim 1, characterized in that, The average particle size of the third particle located on the surface of the second particle is d1, where 1μm≤d1≤3μm.

3. The positive electrode sheet according to claim 1, characterized in that, The Dv50 of the cathode material is 1μm~3μm.

4. The positive electrode sheet according to claim 1, characterized in that, One of the stepped structures is formed by the fusion of multiple third particles, with the gap located at the fusion interface.

5. The positive electrode sheet according to claim 1, characterized in that, The gap is located at the junction of adjacent stepped structures.

6. The positive electrode sheet according to claim 1, characterized in that, The cathode material has the chemical formula LiFe. x Ti y PO4 / C, x+y=1, and 0<y≤0.

05.

7. The positive electrode sheet according to claim 1, characterized in that, The elongation of the positive electrode sheet is 0.5% to 2.3%.

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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