Positive pole piece, battery, energy storage device and electric equipment

Abstract

The invention provides a positive pole piece, a battery, an energy storage device and electric equipment, the positive pole piece comprises a positive current collector, at least one surface of the positive current collector is provided with a positive material layer, and the positive material layer comprises a positive material; the positive electrode material comprises a positive electrode material core, and a first coating layer and a second coating layer which are sequentially arranged on the surface of the positive electrode material core; the material of the first coating layer comprises a carbon material; and the material of the second coating layer comprises a carbonate material.

Description

Technical Field

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

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

[0003] With the improvement of the performance requirements for secondary batteries, for example, the improvement of the performance requirements for secondary batteries in energy storage scenarios, it is not only required that secondary batteries have good cycle performance, but also required that secondary batteries have good overcharge safety performance, capacity utilization performance, and low impedance. However, after overcharging, the potential on the positive electrode sheet side of the secondary battery is relatively high, and the positive electrode sheet is immersed in the electrolyte, which easily causes side reactions of the components in the electrolyte to generate a large amount of heat and consume the effective components of the electrolyte, affecting the safety, cycle performance, and other performances of the secondary battery. Summary of the Invention

[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 electrical equipment to improve the performance of secondary batteries.

[0005] In a first aspect, the present application provides a positive electrode sheet, including a positive electrode current collector, at least one surface of the positive electrode current collector having a positive electrode material layer, the positive electrode material layer including a positive electrode material, wherein the positive electrode material includes a positive electrode material core and a first coating layer and a second coating layer sequentially provided on the surface of the positive electrode material core; the material of the first coating layer includes a carbon material; the material of the second coating layer includes a carbonate material.

[0006] In some embodiments of the present application, based on the mass of the positive electrode material, the mass percentage content of the carbon material is a, 0.8% ≤ a ≤ 1.8%, and the mass percentage content of the carbonate material is b, 1% ≤ b ≤ 5%.

[0007] In some embodiments of the present application, the Dv50 of the positive electrode material is D, 0.8 μm ≤ D ≤ 1.4 μm.

[0008] In some embodiments of the present application, 1% ≤ a ≤ 1.4%, 1.7% ≤ b ≤ 2.5%.

[0009] In some embodiments of the present application, 0.9 μm ≤ D ≤ 1.3 μm.

[0010] In some embodiments of the present application, the decomposition potential of the carbonate material is U1, 3.75 V ≤ U1 ≤ 5.475 V.

[0011] In some embodiments of the present application, a bottom coating is further provided between the positive current collector and the positive electrode material layer.

[0012] In some embodiments of the present application, the carbonate material includes carbonates of alkali metal elements.

[0013] In some embodiments of the present application, the carbonate material includes at least one of lithium carbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate.

[0014] In some embodiments of the present application, the carbon material includes at least one of conductive carbon black, carbon nanotubes, and graphene; alternatively, the carbon material is formed by carbonizing a carbon source material.

[0015] In some embodiments of the present application, the average roughness of the positive electrode sheet is Ra, and 0.1 μm ≤ Ra ≤ 1.5 μm.

[0016] In a second aspect, the present application provides a battery, including the positive electrode sheet described in the first aspect.

[0017] In a third aspect, the present application provides an energy storage device, including a box body and at least one battery described in the second aspect, and the battery is housed in the box body.

[0018] In a fourth aspect, the present application provides an electrical device, including the energy storage device described in the third aspect, and the energy storage device supplies power to the electrical device.

[0019] Compared with the prior art, the present application has at least the following beneficial effects:

[0020] The present application provides a positive electrode plate, a battery, an energy storage device, and an electrical device. The positive electrode plate includes a positive electrode current collector, and at least one surface of the positive electrode current collector has a positive electrode material layer. The positive electrode material layer includes a positive electrode material, and the positive electrode material includes a positive electrode material core and a first coating layer and a second coating layer sequentially disposed on the surface of the positive electrode material core. The material of the first coating layer includes a carbon material, and the material of the second coating layer includes a carbonate material. In the present application, the carbonate material in the second coating layer can decompose during overcharging of the secondary battery to generate inert gases such as CO2, increasing the contact impedance between the particles of the positive electrode material, thereby rapidly increasing the battery voltage to reach the overcharge cut-off voltage. Moreover, the generated inert gases such as CO2 can also cause the positive electrode plate to separate from the separator, resulting in an internal open circuit of the battery, which also has the effect of rapidly increasing the battery voltage to reach the overcharge cut-off voltage, preventing subsequent side reactions from occurring, reducing the heat generated by the decomposition of side reactions, and improving the overcharge safety performance of the battery. Additionally, the second coating layer can also protect the positive electrode material core from being eroded by the electrolyte, reducing the formation of the CEI (Chemical-Electrochemical Interface) film on the positive electrode side, reducing the consumption of lithium salts in the electrolyte and the consumption of active lithium in the battery system, which is beneficial to improving the cycle performance of the lithium-ion battery. Furthermore, the first coating layer containing a carbon material connects the positive electrode material core and the second coating layer, which can improve the conductivity of the positive electrode material core, promote the capacity utilization of the positive electrode material, thereby improving the capacity performance of the secondary battery, reduce the EIS impedance of the lithium-ion battery, and is also beneficial to improving the cycle performance of the secondary battery. In summary, through the combined action of the first coating layer and the second coating layer of the present application, the safety of the secondary battery is improved while still having good cycle performance, and the secondary battery has a high capacity and a low impedance, thereby improving the operation safety and service life of the energy storage device. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for use in the embodiments. Obviously, the drawings described below are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0022] Figure 1 Schematic structural diagram of a positive electrode plate according to an embodiment of the present application;

[0023] Figure 2 Schematic structural diagram of particles of a positive electrode material according to an embodiment of the present application;

[0024] Figure 3 Schematic structural diagram of a household energy storage system according to an embodiment of the present application;

[0025] Figure 4 Schematic structural diagram of a commercial energy storage system according to an embodiment of the present application;

[0026] Figure 5 SEM image of the positive electrode material of Comparative Example 1;

[0027] Figure 6 SEM image of the positive electrode material of Example 1.

[0028] Description of reference numerals: 1 - energy storage device, 2 - power conversion device, 3 - first user load, 4 - second user load, 10 - positive current collector, 20 - positive electrode material layer, 21 - positive electrode material core, 22 - first coating layer, 23 - second coating layer, 30 - bottom coating layer, 400 - commercial energy storage system, 410 - high - voltage cable, 420 - first power conversion device, 430 - second power conversion device. Detailed implementation manners

[0029] Next, the technical solutions in the embodiments of the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a 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 of ordinary skill in the art without creative efforts shall fall within the protection scope of the present application.

[0030] In the present application, the orientation or positional relationships indicated by the terms "upper", "lower", "left", "right", "front", "rear", "top", "bottom", "inner", "outer", "vertical", "horizontal", "lateral", "longitudinal", etc. are based on the orientation or positional relationships shown in the accompanying drawings. These terms are mainly used to better describe the present application and its embodiments, and are not used to limit that the indicated devices, elements or components must have a specific orientation or be constructed and operated in a specific orientation.

[0031] Moreover, in addition to being able to represent orientation or positional relationships, some of the above - mentioned terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the present application can be understood according to specific situations.

[0032] In addition, the terms "installed", "set up", "provided with", "connected", and "linked" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there can be internal communication between two devices, components, or parts. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0033] In addition, the terms "first", "second", etc. are mainly used to distinguish different devices, components, or parts (the specific types and structures may be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, components, or parts. Unless otherwise specified, the meaning of "a plurality" is two or more.

[0034] It should be noted that in the content of this application, a lithium-ion battery is used as an example of a secondary battery to explain this application, but the secondary battery of this application is not limited to lithium-ion batteries.

[0035] After the lithium-ion battery is overcharged, the potential on the positive electrode tab side is relatively high, exceeding the electrochemical window of the electrolyte additive or solvent in the electrolyte, resulting in the decomposition reaction of some components in the electrolyte to generate a large amount of heat. Moreover, the longer the overcharge time, the more side reactions occur until the components that have decomposed in the electrolyte react completely, increasing the safety risk of the lithium-ion battery and consuming the electrolyte, which affects the cycle performance of the lithium-ion battery.

[0036] In view of this, this application provides a positive electrode tab, referring to Figure 1 , the positive electrode tab includes a positive electrode current collector 10, and at least one side of the positive electrode current collector 10 has a positive electrode material layer 20, and the positive electrode material layer 20 includes a positive electrode material. Referring to Figure 2 , the positive electrode material includes a positive electrode material core 21 and a first coating layer 22 and a second coating layer 23 sequentially arranged on the surface of the positive electrode material core 21. The material of the first coating layer 22 includes a carbon material, and the material of the second coating layer 23 includes a carbonate material.

[0037] For the positive electrode plate of the present application, the carbonate material in the second coating layer of the positive electrode material can decompose during overcharging of the lithium-ion battery to generate inert gases such as CO2, increasing the contact impedance between the particles of the positive electrode material, thereby rapidly increasing the battery voltage to reach the overcharge cut-off voltage; moreover, the generated inert gases such as CO2 can also cause the separation of the positive electrode plate from the separator, resulting in an internal open circuit of the battery, which also has the effect of rapidly increasing the battery voltage to reach the overcharge cut-off voltage. The above two factors can jointly prevent the occurrence of side reactions of the electrolyte, reduce the heat generation caused by the decomposition of side reactions, and improve the overcharge safety performance of the battery; moreover, the second coating layer can also protect the core of the positive electrode material from the erosion of the electrolyte, reduce the formation of the CEI film on the positive electrode side, reduce the consumption of lithium salt in the electrolyte and the consumption of active lithium in the battery system, which is beneficial to the improvement of the cycle performance of the lithium-ion battery; moreover, the first coating layer containing carbon material is located between the core of the positive electrode material and the second coating layer, playing a role in connecting the core of the positive electrode material and the second coating layer, which can improve the conductivity of the core of the positive electrode material, promote the capacity utilization of the positive electrode material, thereby improving the capacity of the lithium-ion battery, reduce the impedance of the lithium-ion battery, and is also beneficial to the improvement of the cycle performance of the lithium-ion battery. In summary, through the combined action of the first coating layer and the second coating layer of the present application, when the positive electrode plate containing the positive electrode material is applied to a lithium-ion battery, the safety of the lithium-ion battery is improved while still having good cycle performance, and the lithium-ion battery has a high capacity and a low impedance, thereby improving the operation safety and service life of the energy storage device.

[0038] In an alternative embodiment, based on the mass of the cathode material, the mass percentage content of the carbon material is a, where 0.8% ≤ a ≤ 1.8%, and the mass percentage content of the carbonate material is b, where 1% ≤ b ≤ 5%. In another alternative embodiment, 1% ≤ a ≤ 1.4% and 1.7% ≤ b ≤ 2.5%. For example, a is 0.8%, 1%, 1.2%, 1.5%, 1.7% or 1.8%, and b is 1%, 1.5%, 2%, 3% or 5%. When the value of a is too small (e.g., less than 0.8%), the conductivity of the first coating layer becomes weak, making it difficult to improve the conductivity of the cathode material core. When the value of a is too large (e.g., greater than 1.8%), the excessive carbon will provide more surface active sites, and the excessive carbon will lead to an increase in free carbon, increasing the possibility of contact between the cathode material and the electrolyte, resulting in an increase in side reactions of the electrolyte, thereby causing a decrease in the capacity and safety performance of the lithium-ion battery. When the value of b is too small (e.g., less than 1%), it is difficult to decompose enough CO2 gas during overcharging of the lithium-ion battery, making it difficult to rapidly increase the battery voltage to the overcharge cut-off voltage. When the value of b is too large (e.g., greater than 5%), it will cause too much hindrance to electrons and lithium ions, resulting in a decrease in the specific capacity of the cathode material, which is not conducive to the performance of the lithium-ion battery capacity. By regulating the contents of the carbon material and the carbonate material within the above ranges, the battery voltage can be rapidly increased to the overcharge cut-off voltage, thereby improving the safety of the lithium-ion battery and also being conducive to the performance of the lithium-ion battery capacity.

[0039] In an alternative embodiment, the Dv50 of the cathode material is D, where 0.8 μm ≤ D ≤ 1.4 μm. In an alternative embodiment, 0.9 μm ≤ D ≤ 1.3 μm. For example, D is 0.8 μm, 0.9 μm, 1.0 μm, 1.2 μm, 1.3 μm or 1.4 μm. By regulating the Dv50 of the cathode material within the above ranges, it is beneficial for the lithium-ion battery to have a lower impedance in the electrochemical impedance spectrum (EIS), and at the same time, the lithium-ion battery has good safety performance and cycling performance.

[0040] In this application, Dv50 represents the particle size at which, in the particle size distribution based on volume, starting from the small particle size side, the cumulative volume reaches 50%.

[0041] In an alternative embodiment, the decomposition potential of the carbonate material is U1, where 3.75 V ≤ U1 ≤ 5.475 V. For example, U1 is 3.75 V, 4 V, 5 V or 5.475 V. By selecting a carbonate material with the above decomposition potential, it can undergo electrochemical decomposition during overcharging to generate CO2, which plays a role in promoting internal circuit breakage of the battery and rapidly increasing the battery voltage to the overcharge cut-off voltage, thereby improving the safety performance of the lithium-ion battery. The decomposition potential in this application refers to the potential of the carbonate material during decomposition relative to metallic lithium, denoted as vs.Li / Li + 。

[0042] In an alternative embodiment, with reference to Figure 1 , there is also an undercoat layer 30 between the positive current collector 10 and the positive electrode material layer 20. In this way, the CO2 gas generated by decomposition during overcharging of the lithium-ion battery can enter the interface between the undercoat layer and the positive current collector, separating the undercoat layer from the positive current collector to open the circuit inside the battery, and also having the effect of rapidly increasing the battery voltage to reach the overcharge cut-off voltage, further improving the overcharge safety performance of the battery.

[0043] In an alternative embodiment, the carbonate material includes carbonates of alkali metal elements. Exemplarily, when the alkali metal element is the M element, its carbonate is selected from at least one of M2CO3 and MHCO3.

[0044] In an alternative embodiment, the carbonate material includes at least one of lithium carbonate, sodium carbonate, sodium bicarbonate, potassium carbonate, and potassium bicarbonate.

[0045] In an alternative embodiment, the carbon material includes at least one of conductive carbon black, carbon nanotubes, and graphene; or, the carbon material is formed by carbonizing a carbon source material, and the carbon source material is selected from at least one of glucose, sucrose, polyvinyl alcohol, polytetrafluoroethylene, starch, citric acid, phenolic resin, and ascorbic acid.

[0046] In an alternative embodiment, the average roughness of the positive electrode plate is Ra, and 0.1 μm ≤ Ra ≤ 1.5 μm. For example, Ra is 0.1 μm, 0.5 μm, 1 μm, or 1.5 μm. In this way, the interaction force between the positive electrode material and the binder in the positive electrode material layer can be improved, promoting the branched dispersion of the binder therein, facilitating the increase of the solid content of the positive electrode slurry, and thus facilitating the improvement of the processing performance.

[0047] In an alternative embodiment, the preparation method of the positive electrode material includes the following steps:

[0048] Step A, preparation of the first coating layer:

[0049] Step a, mixing the positive electrode material core with a carbon source, uniformly mixing on a ball mill, then adding an appropriate amount of water as a dispersant, and then performing ball milling;

[0050] Step b, spray-drying the ball-milled material to form granular powder;

[0051] Step c, putting the granular powder into a vacuum atmosphere sintering furnace for sintering treatment, and then obtaining the initial positive electrode material with the first coating layer after crushing treatment.

[0052] In step a, the carbon source material can be selected from glucose or sucrose; the ball-to-material ratio of ball milling is 3-5:1, the rotation speed is 1000 r / min - 2000 r / min, and the ball milling time is 10 h - 20 h.

[0053] 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.

[0054] In step c, the protective atmosphere is nitrogen, the sintering temperature is 500 °C - 800 °C, and the sintering time is 5 h - 10 h.

[0055] Step B: Preparation of the second coating layer:

[0056] Mix the prepared initial cathode material with the carbonate material and add them to water to form a mixed solution. The solid-liquid ratio in this mixed solution is 1:(5 - 20), preferably 1:(8 - 13), which is beneficial to the uniform dispersion of solid particles in the mixed solution. Then stir the mixed solution for 12 h - 24 h, and then place it in an oven at 60 °C - 80 °C for drying to obtain the cathode material with the second coating layer.

[0057] In the above preparation steps, the water is selected from deionized water, distilled water or pure water.

[0058] This application does not particularly limit the method of regulating Dv50 of the cathode material, as long as the purpose of this application can be achieved. For example, Dv50 of the cathode material generally increases with the increase of the particle size of the cathode material core. Based on this, this application can regulate Dv50 of the cathode material by regulating the particle size of the cathode material core. In addition, the cathode material core with the required particle size range can be obtained through a ball mill, a particle size screening tool, etc.

[0059] This application does not particularly limit the thicknesses of the first coating layer and the second coating layer, as long as the purpose of this application can be achieved, and their thicknesses can be at the nanometer level. Exemplarily, the thickness of the first coating layer is 5 nm - 20 nm, and the thickness of the second coating layer is 2 nm - 20 nm.

[0060] In this application, the content of the carbon material in the cathode material increases with the increase of the addition amount of the carbon source material. Based on this, the content of the carbon material in the cathode material can be regulated by regulating the addition amount of the carbon source material.

[0061] In this application, the first coating layer can cover the entire surface of the cathode material core, and the second coating layer can cover the entire surface of the first coating layer to form a fully coated core-shell structure; or, the first coating layer can cover a part of the surface of the cathode material core, and the second coating layer can cover a part of the surface of the first coating layer to form a partially coated core-shell structure.

[0062] There is no particular limitation on the type of the cathode material core in this application, as long as the purpose of this application can be achieved. For example, the cathode material core includes but is not limited to lithium iron phosphate-based, lithium manganese iron phosphate-based, or ternary material-based. Exemplarily, the cathode material includes but is not limited to LiFePO4, LiMn 0.6 Fe 0.4 PO4 / C, LiNi 0.6 Co 0.2 Mn 0.2 O2, etc.

[0063] There is no particular limitation on the materials in the bottom coating and the thickness of the bottom coating in this application. For example, the bottom coating includes materials such as binders and conductive agents, and the thickness of the bottom coating is 0.5 μm to 2 μm. The bottom coating can improve the adhesion strength between the cathode material layer and the cathode current collector.

[0064] This application also provides a battery, including the cathode electrode sheet described in any of the above embodiments.

[0065] In this application, the cathode material layer can be disposed on one surface in the thickness direction of the cathode current collector, or can be disposed on both surfaces in the thickness direction of the cathode current collector. In this application, the cathode material layer is disposed on the surface of the cathode current collector, that is, the cathode material layer can be disposed on a partial area of one surface of the cathode current collector, or can be disposed on the entire area of one surface of the cathode current collector. In this application, there is no particular limitation on the cathode current collector, as long as the purpose of this 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 this application, there is no particular limitation on the thickness of the cathode current collector, as long as the purpose of this application can be achieved. For example, the thickness is 4 μm to 12 μm. The single-sided thickness of the cathode material layer in this application can be 8 μm to 15 μm.

[0066] The lithium-ion battery of this application further includes a negative electrode sheet. There is no particular limitation on the negative electrode sheet in this application, as long as the purpose of this application can be achieved. For example, the negative electrode sheet generally includes a negative current collector and a negative material layer. The negative material layer can be disposed on one surface or both surfaces along the thickness direction of the negative current collector. In this application, the negative material layer is disposed on the surface of the negative current collector, that is, the negative material layer can be disposed on a partial area of one surface of the negative current collector, or can be disposed on the entire area of one surface of the negative current collector. There is no particular limitation on the negative current collector in this application, as long as the purpose of this 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 this application, there is no particular limitation on the thickness of the negative current collector, as long as the purpose of this application can be achieved. For example, the thickness is 4 μm to 12 μm. The single-sided thickness of the negative material layer in this application can be 70 μm to 200 μm.

[0067] In this application, the negative electrode material layer includes a negative electrode material. The negative electrode material is not particularly limited as long as the purpose of this application can be achieved. For example, it may include at least one of artificial graphite, natural graphite, mesocarbon microbeads, soft carbon, hard carbon, silicon, and silicon carbide.

[0068] In this application, the negative electrode material layer may also include a negative electrode binder. The negative electrode binder in this application is not particularly limited as long as the purpose of this application can be achieved. For example, it may include, but is not limited to, at least one of acrylate, polyamide, polyimide, polyamideimide, polyvinylidene fluoride, styrene-butadiene rubber, sodium alginate, polyvinyl alcohol, polytetrafluoroethylene, polyacrylonitrile, sodium carboxymethyl cellulose, and potassium carboxymethyl cellulose.

[0069] The lithium-ion battery of this application also includes a separator. The separator in this application is not particularly limited, and those skilled in the art can select it according to actual needs as long as the purpose of this application can be achieved. For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or 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 this application also includes an electrolyte. The electrolyte in this application is not particularly limited, and those skilled in the art can select it according to actual needs as long as the purpose of this application can be achieved. For example, after mixing at least one of ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), propyl propionate (PP), ethylene methyl carbonate (EMC), dimethyl carbonate (DMC), vinylene carbonate (VC), or fluoroethylene carbonate (FEC) in a certain mass ratio or volume ratio to obtain a non-aqueous organic solvent, a lithium salt is added and dissolved and mixed evenly. The type of lithium salt in this application is not limited as long as the purpose of this application can be achieved. For example, the lithium salt may 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 concentration of the lithium salt in the electrolyte in this application is not particularly limited as long as the purpose of this application can be achieved. Taking LiPF6 as an example, the concentration of LiPF6 in the electrolyte is 1 mol / L to 2 mol / L. For example, the concentration of LiPF6 is 1 mol / L, 1.3 mol / L, 1.5 mol / L, 1.8 mol / L, or 2 mol / L.

[0072] The battery of the present application further includes a housing, and the present application places no particular limitation on the housing. Those skilled in the art can select it according to actual needs as long as the purpose of the present application can be achieved. For example, the housing may include an aluminum-plastic film.

[0073] The present application places no particular limitation on the preparation method of the battery, and a preparation method well-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 sequence, and performing operations such as winding and folding them as needed to obtain a wound bare battery cell. Then, the bare battery cell is placed in a packaging bag, and the electrolyte is injected into the packaging bag and sealed to obtain the battery.

[0074] The present application also provides an energy storage device, which includes a box body and at least one battery in any of the above embodiments. The battery is housed in the box body. The energy storage device with this battery has excellent performance, which is beneficial to the use of the energy storage device. By housing the battery in the box body, the fixing and protection of the battery can be enhanced, and the service life of the energy storage device can be improved. It can be understood that one or more batteries can be included in the energy storage device. When the energy storage device contains multiple batteries, the multiple batteries can be connected in at least one of the parallel and series manners.

[0075] The present application also provides an electrical device, which includes the energy storage device in the above embodiments, which is beneficial to improving the product competitiveness and service 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 device positive electrode and a device negative electrode. The positive electrode sheet of the battery in the energy storage device is used to electrically connect to the device positive electrode of the electrical device body, and the negative electrode sheet of the battery in the energy storage device is used to electrically connect to the device negative electrode of the electrical device body to supply power to the electrical device.

[0076] The electrical devices of the present application may include but are not limited to: containers, battery cars, electric vehicles, ships, spacecrafts, electric toys, and electric tools, etc. Among them, spacecrafts such as airplanes, rockets, space shuttles, and spaceships, etc., electric toys include fixed or mobile electric toys, specifically, for example, electric vehicle toys, electric ship toys, and electric airplane toys, etc., and electric tools include metal cutting electric tools, grinding electric tools, assembly electric tools, and railway electric tools, specifically, for example, electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact electric drills, concrete vibrators, and electric planers.

[0077] Please refer to Figure 3 , Figure 3 which is a schematic structural diagram of a household energy storage system according to an embodiment of the present application, and the present application Figure 3The embodiments are described by taking the household energy storage scenario in user-side energy storage as an example. The energy storage device of the present application is not limited to the household energy storage scenario.

[0078] The present application provides a household energy storage system, which includes an electric energy conversion device 2 (photovoltaic panel), a first user load 3 (street lamp), a second user load 4 (such as household appliances like air conditioners), etc., and an energy storage device 1. The energy storage device 1 is a small energy storage box and can be installed on an outdoor wall in a wall-mounted manner. Specifically, the photovoltaic panel can convert solar energy into electric energy during the low electricity price period. The energy storage device 1 is used to store the electric energy and supply it to the street lamp and household appliances for use during the high electricity price period, or supply power when the power grid is powered off / out of power.

[0079] Please refer to Figure 4 , Figure 4 which is a schematic structural diagram of a commercial energy storage system 400 according to an embodiment of the present application, and the present application Figure 4 The embodiments are described by taking the shared energy storage scenario on the power generation / distribution side as an example. The energy storage device 1 of the present application is not limited to its energy storage scenario on the power generation / distribution side.

[0080] The present application provides a commercial energy storage system 400, which includes: a high-voltage cable 410, a first electric energy conversion device 420, a second electric energy conversion device 430, and the energy storage device 1 provided by the present application. In the case of power generation, the first electric energy conversion device 420 and the second electric energy conversion device 430 are used to convert other forms of energy into electric energy, connect with the high-voltage cable 410 and supply it for use on the power distribution network side. When the power consumption load is low and the first electric energy conversion device 420 and the second electric energy conversion device 430 generate excess power, the excess power is stored in the energy storage device 1 to reduce the wind curtailment and light curtailment rates and improve the problem of new energy power generation accommodation; when the power consumption load is high, the power grid issues an instruction, and the electric energy stored in the energy storage device 1 is transmitted to the power consumption side for use in a grid-connected mode in cooperation with the high-voltage cable 410, providing various services such as peak shaving, frequency modulation, and standby for the power grid operation, giving full play to the role of the power grid peak shaving, promoting the power grid to cut peaks and fill valleys, and alleviating the power supply pressure of the power grid.

[0081] Optionally, the first electric energy conversion device 420 and the second electric energy conversion device 430 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy, and mechanical energy into electric energy.

[0082] The number of the energy storage devices 1 can be multiple. The multiple energy storage devices 1 are connected in series or in parallel with each other, and the multiple energy storage devices 1 are supported and electrically connected by a separator (not shown in the figure). In this embodiment, "multiple" means two or more. An energy storage box can also be provided outside the energy storage device 1 for accommodating the energy storage device 1.

[0083] Optionally, the energy storage device 1 may include, but is not limited to, battery modules, battery packs, battery systems, etc. Among them, the battery module may be a battery module formed by connecting multiple batteries of the present application in series / parallel, the battery pack may include multiple batteries of the present application, and the battery system may be a charge-discharge system including the batteries or battery packs of the present application.

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

[0085] Embodiment

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

[0087] Example 1

[0088] <Preparation of the positive electrode sheet>

[0089] <Preparation of the positive electrode material>

[0090] Mix the positive electrode material core (LFP core) with the carbon source material glucose, perform uniform mixing on a ball mill, then add an appropriate amount of water as a dispersant, and then perform ball milling. The ball-to-material ratio of the ball milling is 4:1, the rotation speed is 1500 r / min, and the ball milling time is 15 h; spray-dry the ball-milled material. The pump speed of the spray drying is 10 mL / min, and the drying temperature is 200 °C to form granular powder; put the granular powder into a vacuum atmosphere sintering furnace for sintering treatment. The protective atmosphere is nitrogen, and the sintering temperature is 700 °C. After ball milling and crushing treatment, the initial positive electrode material with the first coating layer is obtained; then the prepared initial positive electrode material is mixed with the carbonate material Li2CO3 and added to water to form a mixed solution. The solid-liquid ratio in the mixed solution is 1:10. Stir the mixed solution for 24 h, and then dry it in an oven at 70 °C to obtain the positive electrode material with the second coating layer.

[0091] <Preparation of the positive electrode material layer>

[0092] Mix the prepared positive electrode material, binder PVDF, and conductive carbon black (Super-P) in a mass ratio of 97:2.5:0.5, then add N-methylpyrrolidone (NMP) as a solvent to prepare a positive electrode slurry with a solid content of 70 wt%, and stir it evenly. Then, uniformly coat the positive electrode slurry on one surface of an aluminum foil with a thickness of 13 μm, and the coating loading is 20 mg / cm2 It was dried at 85 °C and then a positive electrode sheet was obtained after roll pressing. After measurement, the average roughness Ra of the positive electrode sheet was 0.60 μm.

[0093] <Preparation of negative electrode sheet>

[0094] The negative electrode materials artificial graphite, carboxymethyl cellulose (CMC), conductive carbon black (Super-P), and styrene-butadiene rubber (SBR) were mixed according to a mass ratio of 96:2:1:1, deionized water was added, and a negative electrode slurry with a solid content of 60 wt% was formulated and stirred evenly. The negative electrode slurry was evenly coated on one surface of a copper foil with a thickness of 8 μm, and the coating loading was 11.5 mg / cm 2 It was dried at 80 °C and then a negative electrode sheet was obtained after roll pressing.

[0095] <Preparation of electrolyte>

[0096] Ethylene carbonate (EC), dimethyl carbonate (DMC), and ethyl methyl carbonate (EMC) were mixed according to a volume ratio of 1:1:1, dissolved and stirred thoroughly, and then the lithium salt LiPF6 was added. After mixing evenly, an electrolyte was obtained. Among them, the concentration of LiPF6 in the electrolyte was 1 mol / L.

[0097] <Preparation of separator>

[0098] A polypropylene (PP) porous polymer film with a thickness of 16 μm was used as the separator.

[0099] <Assembly of lithium-ion battery>

[0100] The prepared positive electrode sheet and negative electrode sheet were respectively placed in a press for pressing, and then a circular positive electrode sheet with a diameter of 12 mm and a circular negative electrode sheet with a diameter of 16 mm were respectively cut with a punch; then the circular positive electrode sheet, the separator, and the circular negative electrode sheet were stacked in sequence, with the separator placed in the middle between the circular positive electrode sheet and the circular negative electrode sheet to play a role in isolation, and then the prepared electrolyte was injected to assemble a lithium-ion battery.

[0101] Examples 2 to 8

[0102] Except that in <Preparation of positive electrode material>, the addition amount of the carbonate material was adjusted to adjust the value of b according to Table 1, the rest was the same as in Example 1.

[0103] Examples 9 to 12

[0104] Except that in <Preparation of positive electrode material>, the addition amount of the carbon source material was adjusted to adjust the value of a according to Table 1, the rest was the same as in Example 1.

[0105] Examples 13 to 18

[0106] Except in the <Preparation of Cathode Material>, where the particle size of the cathode material core was adjusted to adjust the Dv50 of the cathode material according to Table 1, the rest was the same as in Example 1.

[0107] Examples 19 to 22

[0108] Except in the <Preparation of Cathode Material>, where the type of carbonate material was adjusted according to Table 1, the rest was the same as in Example 1.

[0109] Comparative Example 1

[0110] Except in the <Preparation of Cathode Material>, where only the carbon material coating layer was prepared without preparing the lithium carbonate coating layer, the rest was the same as in Example 1.

[0111] Comparative Example 2

[0112] Except in the <Preparation of Cathode Material>, where only the lithium carbonate coating layer was prepared without preparing the carbon material coating layer, the rest was the same as in Example 1.

[0113] The preparation steps of the cathode material are as follows:

[0114] The cathode material core (LFP) was mixed with the carbonate material Li2CO3 and then added to water to form a mixed solution with a solid-liquid ratio of 1:10 in the mixed solution. Then the mixed solution was stirred for 24 h and then dried in an oven at 70 °C to obtain the cathode material with a second coating layer.

[0115] Table 1: Relevant preparation parameters of each example and comparative example

[0116]

[0117]

[0118] Note: In Table 1, " / " indicates the absence of relevant preparation parameters.

[0119] Testing methods and equipment:

[0120] Testing the carbon material content in the cathode material:

[0121] The content of the carbon material in the prepared cathode material was tested using an infrared absorption method carbon-sulfur analyzer (model: SCIENCE HCS-801): The cathode material was heated to 2000 °C under oxygen conditions to oxidize the carbon in it into carbon dioxide gas. Then the carbon dioxide gas was dried and the tail gas was treated and all discharged into the absorption cell to absorb the corresponding infrared radiation, which was forwarded by the detector as a signal and output the carbon content test result after being processed by the computer, that is, the content of the carbon material.

[0122] Positive electrode material particle size distribution test:

[0123] Use a laser diffraction particle size distribution analyzer (model: Malvern Mastersizer 3000) to test the positive electrode material sample dispersed in deionized water. By adjusting the instrument parameters to make the laser beam diameter less than or equal to 1 μm to adapt to the sample characteristics, the Dv50 of the positive electrode material can be measured.

[0124] Carbonate material decomposition potential test:

[0125] Place the coin cell on an electrochemical workstation (model: CHI600F) to perform cyclic voltammetry testing (CV). The test conditions are: 2V - 5.5V, scan rate of 0.1 mV / s. The starting position of the peak in the obtained CV curve is the decomposition potential of the carbonate material.

[0126] The preparation method of the coin cell is as follows:

[0127] Press the carbonate material into a disc with a diameter of 12 mm. Use a circular lithium sheet with a diameter of 16 mm as the counter electrode. Stack the circular positive electrode sheet, separator, and circular negative electrode sheet in sequence, with the separator in the middle between the circular positive electrode sheet and the circular negative electrode sheet to play an isolation role. Then inject the prepared electrolyte to assemble a lithium-ion battery. The electrolyte and separator are the same as those in Example 1.

[0128] First-cycle discharge capacity test:

[0129] The test temperature is 25°C. Charge the lithium-ion battery at a constant current of 0.1 C (C) to 3.75 V (vs. Li / Li + ), this is the charging stage; let it stand for 10 min, then discharge it at a constant current of 0.1 C to 2.5 V and let it stand for 10 min, this is the discharging stage. Record the discharge capacity in the first discharging stage as the first-cycle discharge capacity, with the unit mAh / g.

[0130] EIS impedance test:

[0131] Use an electrochemical workstation (model: CHI600F) to perform electrochemical impedance spectroscopy (EIS) on the prepared coin cell. The test conditions are: 0.1 Hz - 10 MHz.

[0132] Cycling performance test:

[0133] The lithium-ion battery was subjected to charge-discharge cycle tests on a charge-discharge instrument (model: BAT-NEEFLCT-05300-V010). The test temperature was 25 °C, the cycle rate was 0.1C (i.e., both the charge rate and the discharge rate were 0.1C), the charge voltage was from 2.5V to 3.65V, and the capacity retention rate after cycling was calculated. The formula for the capacity retention rate is: Capacity retention rate after 100 cycles (cls) = (Discharge capacity after the 100th cycle / Discharge capacity in the first cycle) × 100%.

[0134] Overcharge performance test:

[0135] The lithium-ion battery was placed on a charge-discharge instrument (model: Nebula Charge-Discharge Test System - 10V / 500A). Under the condition of a charging temperature of 25 °C, it was charged at a charging rate of 0.5C until the rated overcharge cut-off voltage was reached. Then, it was continuously charged at a rated current of 0.5C until the battery voltage reached 1.5 times the battery overcharge cut-off voltage, at which point charging was stopped. The temperature change of the lithium-ion battery during overcharge was recorded, and the overcharge charging time was recorded. Among them, the overcharge charging time refers to the time required for the lithium-ion battery to reach the overcharge cut-off voltage from the start of charging. The overcharge cut-off voltage refers to 1.5 times the working platform voltage of the lithium-ion battery. For example, for a lithium iron phosphate-graphite lithium-ion battery, its overcharge cut-off voltage is 3.65V × 1.5 = 5.475V.

[0136] Average roughness test of the positive electrode plate

[0137] Three electrode plate samples with a size of 40mm × 40mm were cut from the obtained positive electrode plate and fixed on the sample stage of an atomic force microscope (Bruker Dimension ICON). The atomic force microscope probe was used to contact the surface of the electrode plate sample and automatically scan and calculate. The "image Ra" value in the software is the roughness of the electrode plate. Three different positions on the same electrode plate were tested, and the average value of the nine data from the three electrode plates was taken as the average roughness of the positive electrode plate.

[0138] Table 2: Performance data of each example and comparative example

[0139]

[0140]

[0141] It can be seen from Examples 1 to 18 and Comparative Examples 1 to 2 that the overcharge time of Comparative Example 1 is too long, and the capacity retention rate is low after 100 cycles. This may be because the positive electrode material of Comparative Example 1 does not have the double-layer coating structure of the positive electrode material of the present application, resulting in difficulty in rapidly increasing the battery voltage to reach the overcharge cut-off voltage during overcharge, and the occurrence of side reactions in the electrolyte continuously consumes the lithium salt in the electrolyte and the active lithium in the battery system, affecting the cycle performance of the lithium-ion battery; the overcharge time of Comparative Example 2 is shorter, which may be because its positive electrode material does not have the first coating layer, resulting in increased polarization. Although it can quickly reach the overcharge cut-off voltage, its specific capacity is low and the EIS impedance is large. Moreover, due to the lack of the first coating layer, the impedance will increase significantly, resulting in low capacity utilization, and due to the lack of protection of the double-layer coating structure, the active lithium is consumed quickly, resulting in a lower capacity retention rate compared to Example 1; while the lithium-ion battery with the positive electrode sheet of the present application exhibits excellent overcharge safety performance and cycle performance, and the positive electrode material has a high specific capacity and a low EIS impedance.

[0142] The content of the carbonate material, the content of the carbon material, the Dv50 of the positive electrode material, and the type of the carbonate material usually also affect the performance of the positive electrode sheet, thereby affecting the performance of the lithium-ion battery. It can also be seen from Examples 1 to 22 that on the basis that the positive electrode material has the structure 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 excellent overcharge safety performance, cycle performance, capacity utilization, and low impedance.

[0143] Figure 5 SEM image of the positive electrode material of Comparative Example 1; Figure 6 SEM image of the positive electrode material of Example 1. From Figure 5 and Figure 6 it can be seen that the surface of the particles of the positive electrode material of Comparative Example 1 without the second coating layer is smooth; the surface of the particles of the positive electrode material of Example 1 with the second coating layer becomes rough, and the thickness of the second coating layer is nanoscale, which has basically no effect on the particle size of the positive electrode material.

[0144] The above has introduced in detail a positive electrode sheet, a battery, an energy storage device, and an electrical equipment disclosed in the present application. Specific examples are used in this article to elaborate on the principle and implementation manner of the present application. The description of the above examples is only used to help understand the technical solution and the core invention point of the embodiments of the present application; at the same time, for those of ordinary skill in the art, according to the idea of the present application, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present application.

Claims

1. A positive electrode sheet, characterized in that: It comprises a positive electrode current collector, at least one side of which has a positive electrode material layer, and the positive electrode material layer comprises a positive electrode material, wherein: The positive electrode material comprises a positive electrode material core and a first coating layer and a second coating layer sequentially arranged on the surface of the positive electrode material core; The material of the first coating layer includes a carbon material; The material of the second coating layer includes a carbonate material.

2. The positive electrode sheet according to claim 1, characterized in that: Based on the mass of the positive electrode material, the mass percentage of the carbon material is a, 0.8%≤a≤1.8%, and the mass percentage of the carbonate material is b, 1%≤b≤5%.

3. The positive electrode sheet according to claim 1, characterized in that: The Dv50 of the positive electrode material is D, 0.8 μm≤D≤1.4 μm.

4. The positive electrode sheet according to claim 2, characterized in that: 1%≤a≤1.4%, 1.7%≤b≤2.5%.

5. The positive electrode sheet according to claim 3, characterized in that: 0.9μm≤D≤1.3μm.

6. The positive electrode sheet according to claim 1, characterized in that: The decomposition potential of the carbonate material is U1, 3.75V≤U1≤5.475V.

7. The positive electrode sheet according to claim 1, characterized in that: A primer layer is provided between the positive electrode current collector and the positive electrode material layer.

8. The positive electrode sheet according to claim 1, characterized in that: The carbonate material includes carbonates of alkali metal elements.

9. The positive electrode sheet according to claim 8, characterized in that: The carbonate material includes at least one of lithium carbonate, sodium carbonate, sodium bicarbonate, potassium carbonate and potassium bicarbonate.

10. The positive electrode sheet according to claim 1, characterized in that: The carbon material includes at least one of conductive carbon black, carbon nanotubes and graphene; Alternatively, the carbon material is formed by carbonizing a carbon source material.

11. The positive electrode sheet according to claim 1, characterized in that: The average roughness of the positive electrode plate is Ra, 0.1 μm≤Ra≤1.5 μm.

12. A battery, characterized in that: The invention comprises the positive electrode sheet as described in any one of claims 1 to 11.

13. An energy storage device, characterized in that: The invention comprises a casing and at least one battery according to claim 12, wherein the battery is accommodated in the casing.

14. An electrical device, characterized in that: It includes the energy storage device as described in claim 13, and the energy storage device supplies power to the electrical equipment.

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