Electrode assembly, battery monomer, battery, electric equipment, positive pole piece and preparation method of positive pole piece

Abstract

The invention discloses an electrode assembly, a battery monomer, a battery, electric equipment, a positive pole piece and a preparation method thereof. The positive pole piece (31) comprises: a positive current collector (10); the positive electrode active material layer (20) is arranged on at least part of the surface of the positive electrode current collector (10); wherein the positive electrode active material layer (20) comprises at least two positive electrode active material sections which are arranged along the length direction (dL) of the positive electrode current collector (10); the specific surface area of the positive electrode active material contained in one part of the at least two positive electrode active material sections is larger than that of the positive electrode active material contained in the other part of the positive electrode active material sections.

Description

Electrode assembly, battery cell, battery, electrical equipment, positive electrode sheet and preparation method thereof Technical Field

[0001] The present disclosure relates to the field of battery technology, and in particular to an electrode assembly, a battery cell, a battery, an electrical device, a positive electrode sheet, and a preparation method thereof. Background Art

[0002] Secondary batteries, especially lithium-ion batteries, offer advantages such as high voltage, high specific energy, long cycle life, environmental friendliness, a wide operating temperature range, and low self-discharge. They are widely used in portable electronic devices and powering large-scale new energy electric vehicles, playing a significant role in addressing environmental pollution and the energy crisis. With the widespread use of secondary batteries, battery cycle performance and safety have become issues of close concern to users.

[0003] Summary of the Invention

[0004] In one aspect of the present disclosure, a positive electrode plate is provided, comprising: a positive electrode current collector; and a positive electrode active material layer, disposed on at least a portion of the surface of the positive electrode current collector; wherein the positive electrode active material layer comprises at least two positive electrode active material segments arranged along the length direction of the positive electrode current collector, and the specific surface area of ​​the positive electrode active material contained in one portion of the at least two positive electrode active material segments is greater than the specific surface area of ​​the positive electrode active material contained in another portion of the positive electrode active material segments.

[0005] According to the expansion and compression of different parts of the positive electrode plate during the operation of the battery cell, the specific surface area of ​​the positive electrode active material contained in a part of the positive electrode active material segment of the positive electrode active material layer is made larger, so as to improve the electrolyte infiltration ability of the positive electrode active material area with a higher degree of compression, reduce the risk of lithium precipitation caused by the electrolyte being squeezed out, and enable the electrolyte to fully react with the positive electrode active material on the positive electrode plate during the battery charging and discharging process, optimize the battery cycle performance, and improve the battery safety.

[0006] In some embodiments, the at least two positive electrode active material segments include a first positive electrode active material segment and a second positive electrode active material segment, the specific surface area BET1 of the first positive electrode active material contained in the first positive electrode active material segment is greater than the specific surface area BET2 of the second positive electrode active material contained in the second positive electrode active material segment, and the first positive electrode active material segment is closer to the winding starting end of the positive electrode sheet than the second positive electrode active material segment.

[0007] Taking into account that when the positive electrode plate is used in a wound electrode assembly, the plate layer closer to the winding center expands and is squeezed to a higher degree when the battery cell is working, the first positive electrode active material contained in the first positive electrode active material segment closer to the starting end of the winding is larger in specific surface area, so that it has a stronger electrolyte infiltration ability, so that it can still maintain a certain amount of electrolyte under a high degree of squeezing, reducing the risk of lithium precipitation due to lack of electrolyte, optimizing the battery's cycle performance, and improving the battery's safety.

[0008] In some embodiments, an end portion of the first positive active material segment adjacent to the winding start end of the positive electrode sheet is flush with the winding start end of the positive electrode sheet.

[0009] By making the end of the first positive electrode active material segment flush with the winding starting end, there is no need to precisely set the coating position of the first positive electrode active material segment on the side adjacent to the winding starting end, which helps to reduce the difficulty of coating the first positive electrode active material segment on the positive electrode current collector.

[0010] In some embodiments, the at least two positive electrode active material segments further include a third positive electrode active material segment, wherein the third positive electrode active material segment is located on a side of the first positive electrode active material segment away from the second positive electrode active material segment, and the specific surface area BET1 of the first positive electrode active material contained in the first positive electrode active material segment is greater than the specific surface area BET3 of the third positive electrode active material contained in the third positive electrode active material segment.

[0011] Taking into account that the positive electrode sheets of some wound electrode assemblies have a hollow structure, the electrode segments near the center position are relatively less expanded and squeezed when the battery cell is working. Therefore, by arranging a first positive electrode active material with a smaller specific surface area on the side of the first positive electrode active material segment close to the starting end of the winding, it is beneficial to reduce costs by reducing the use of the first positive electrode active material.

[0012] In some embodiments, the third positive electrode active material included in the third positive electrode active material segment is the same as the second positive electrode active material included in the second positive electrode active material segment.

[0013] Using the same positive electrode active material for the second positive electrode active material segment and the third positive electrode active material segment can simplify the electrode sheet processing process.

[0014] In some embodiments, the specific surface area BET1 of the first positive electrode active material satisfies: BET1 ≥ 12 m 2 / g.

[0015] By making the specific surface area BET1 of the first positive electrode active material greater than or equal to 12 m 2 / g, the material pores of the first positive electrode active material with a higher specific surface area can accommodate more electrolyte during the cycle, which is beneficial to alleviate the difficulty of insufficient wetting, reduce the risk of lithium plating, and improve the cycle life of the battery.

[0016] In some embodiments, the specific surface area BET1 of the first positive electrode active material satisfies: 14 m 2 / g≤BET1≤23m 2 / g.

[0017] By making the specific surface area BET1 of the first positive electrode active material satisfy 14 m 2 / g≤BET1≤23m 2 A further preferred range of 1:1 / g can improve the cycle life of the battery while increasing the stability of the positive electrode active material and improving the safety performance of the battery.

[0018] In some embodiments, the specific surface area BET2 of the second positive electrode active material satisfies: BET2<12m 2 / g.

[0019] By making the specific surface area BET2 of the second positive electrode active material less than 12 m 2 / g, which is conducive to using a positive electrode active material with a smaller specific surface area and lower cost to form the second positive electrode active material segment, thereby reducing the overall cost of the positive electrode sheet.

[0020] In some embodiments, the specific surface area BET2 of the second positive electrode active material satisfies: 2m 2 g≤BET2≤10m 2 / g.

[0021] By making the specific surface area BET2 of the second positive electrode active material satisfy 2m 2 / g≤BET2≤10m 2 A further preferred range of 100 μg / g can effectively reduce the overall cost of the positive electrode sheet.

[0022] In some embodiments, the median particle size Dv501 of the first positive electrode active material is smaller than the median particle size Dv502 of the second positive electrode active material.

[0023] Taking into account that when the positive electrode plate is used in a wound electrode assembly, the plate layer closer to the winding center expands and is squeezed to a higher degree when the battery cell is working, the median particle size of the first positive electrode active material contained in the first positive electrode active material segment closer to the starting end of the winding is larger, so that it has a stronger electrolyte infiltration ability, so that it can still maintain a certain amount of electrolyte even when it is squeezed to a high degree, reducing the risk of lithium precipitation due to lack of electrolyte and optimizing the battery cycle performance.

[0024] In some embodiments, the median particle size Dv501 of the first positive electrode active material satisfies: Dv501≤800 nm.

[0025] By making the median particle size Dv501 of the first positive electrode active material less than or equal to 800 nm, the material pores of the first positive electrode active material with a lower median particle size can accommodate more electrolyte during the cycle, which is conducive to alleviating the difficulty of insufficient wetting, reducing the risk of lithium plating, and improving the cycle life of the battery.

[0026] In some embodiments, the median particle size Dv501 of the first positive electrode active material satisfies: 100 nm ≤ Dv501 ≤ 400 nm.

[0027] By making the median particle size Dv501 of the first positive electrode active material meet the further preferred range of 100nm≤Dv501≤400nm, it is possible to improve local lithium precipitation, increase the cycle life of the battery, improve the electrochemical kinetics performance during battery charging and discharging, and reduce polarization.

[0028] In some embodiments, the median particle size Dv502 of the second positive active material satisfies: Dv502>800 nm.

[0029] By making the median particle size Dv502 of the second positive electrode active material greater than 800 nm, it is advantageous to use a positive electrode active material with a larger median particle size and lower cost to form the second positive electrode active material segment, thereby reducing the overall cost of the positive electrode sheet.

[0030] In some embodiments, the median particle size Dv502 of the second positive active material satisfies: 900 nm ≤ Dv502 ≤ 1500 nm.

[0031] By making the median particle size Dv502 of the second positive electrode active material satisfy the further preferred range of 900 nm ≤ Dv502 ≤ 1500 nm, the overall cost of the positive electrode sheet can be effectively reduced.

[0032] In some embodiments, the carbon content ωC1 of the first positive electrode active material is greater than the carbon content ωC2 of the second positive electrode active material.

[0033] Taking into account that when the positive electrode plate is used in a wound electrode assembly, the plate layer closer to the winding center expands and is squeezed to a higher degree when the battery cell is working, which makes it easy for lithium deposition to occur. By making the carbon content of the first positive electrode active material contained in the first positive electrode active material segment closer to the starting end of the winding larger, the conductivity of the plate is improved, the risk of lithium deposition is reduced, and the battery charging and discharging performance is optimized.

[0034] In some embodiments, the carbon content ωC1 of the first positive electrode active material satisfies: ωC1 ≥ 2.5%.

[0035] By making the carbon content ωC1 of the first positive electrode active material greater than or equal to 2.5%, the first positive electrode active material with a higher carbon content can achieve higher conductivity, which is beneficial to reducing the risk of lithium plating, improving the cycle life of the battery, reducing the internal resistance of the battery, and improving the cycle performance of the battery.

[0036] In some embodiments, the carbon content ωC1 of the first positive electrode active material satisfies: ωC1 ≥ 2.8%.

[0037] By making the carbon content ωC1 of the first positive electrode active material satisfy the further preferred range of ωC1 ≥ 2.8%, the conductivity of the electrode sheet can be effectively further improved, the internal resistance of the battery can be reduced, and the cycle life of the battery can be improved.

[0038] In some embodiments, the carbon content ωC2 of the second positive electrode active material satisfies: ωC2 ≤ 1.5%.

[0039] By making the carbon content ωC2 of the second positive electrode active material less than or equal to 1.5%, the proportion of the positive electrode active substance can be increased, and the energy density can be improved.

[0040] In some embodiments, the carbon content ωC2 of the second positive electrode active material satisfies: ωC2 ≤ 1.2%.

[0041] By making the carbon content ωC2 of the second positive electrode active material further satisfy ωC2 ≤ 1.2%, the proportion of the positive electrode active substance can be effectively increased, and the energy density can be improved.

[0042] In some embodiments, in the length direction of the positive electrode current collector, the ratio L1 / L of the length L1 of the first positive electrode active material segment to the length L of the positive electrode current collector satisfies: 0 < L1 / L ≤ 0.5.

[0043] The ratio L1 / L corresponds to the coverage ratio of the positive electrode active material in the length direction of the entire positive electrode current collector. If this ratio is too low, the improvement degree of the electrolyte infiltration ability is limited, and the risk of lithium plating caused by the extrusion of the electrolyte cannot be effectively reduced. If this ratio is too high, more first positive electrode active materials are required, which is likely to cause too high costs. By making L1 / L satisfy 0 < L1 / L ≤ 0.5, while reducing the risk of lithium plating on the electrode sheet and optimizing the cycle performance of the battery, the overall cost is reduced.

[0044] In some embodiments, the ratio L1 / L satisfies: 0.3 ≤ L1 / L ≤ 0.5.

[0045] By making L1 / L further satisfy 0.3 ≤ L1 / L ≤ 0.5, the risk of lithium plating on the electrode sheet can be more effectively reduced, the cycle performance of the battery can be optimized, and the overall cost can be reduced.

[0046] In some embodiments, the first positive electrode active material includes nano-lithium iron phosphate, and the second positive electrode active material includes lithium iron phosphate.

[0047] Here, the first positive electrode active material includes nano-lithium iron phosphate, and the second positive electrode active material includes lithium iron phosphate, so as to avoid excessive difference in performance between the first positive electrode active material segment and the second positive electrode active material segment of the positive electrode sheet.

[0048] In one aspect of the present disclosure, an electrode assembly is provided, comprising: a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the separator, and the negative electrode sheet are wound along a winding direction to form a wound structure, and the positive electrode sheet is the aforementioned positive electrode sheet. An electrode assembly using the aforementioned positive electrode sheet has improved cycle performance and safety.

[0049] In some embodiments, the coiled structure is a cylindrical structure.

[0050] For cylindrical electrode assemblies, the aforementioned positive electrode sheet can improve the electrolyte infiltration effect at the location where the expansion force is concentrated, thereby improving the cycle performance and safety of the electrode assembly.

[0051] In one aspect of the present disclosure, a battery cell is provided, comprising: the aforementioned electrode assembly. The battery cell using the aforementioned electrode assembly has better cycle performance and safety.

[0052] In one aspect of the present disclosure, a battery is provided, comprising the aforementioned battery cell. The battery using the aforementioned battery cell has better cycle performance and safety.

[0053] In one aspect of the present disclosure, an electrical device is provided, comprising the aforementioned battery. The electrical device using the aforementioned battery can achieve better safety and also help save battery consumption.

[0054] In one aspect of the present disclosure, a method for preparing a positive electrode sheet is provided, comprising:

[0055] Providing a positive electrode current collector, a first positive electrode slurry containing a first positive electrode active material, and a second positive electrode slurry containing a second positive electrode active material, wherein the specific surface area of ​​the first positive electrode active material is greater than the specific surface area of ​​the second positive electrode active material;

[0056] The first positive electrode slurry is coated on the surface of a portion of the at least two segments distributed along the length direction of the positive electrode collector, and the second positive electrode slurry is coated on the surface of another portion of the at least two segments distributed along the length direction of the positive electrode collector.

[0057] By respectively coating the first positive electrode slurry containing the first positive electrode active material and the second positive electrode slurry containing the second positive electrode active material onto the surface of different segments in the length direction of the positive electrode current collector, the obtained positive electrode sheet can improve the electrolyte wetting ability of the positive electrode active material area that is subjected to a higher degree of compression, reduce the risk of lithium precipitation caused by the electrolyte being squeezed out, and allow the electrolyte to fully react with the positive electrode active material on the positive electrode sheet during the battery charging and discharging process, thereby optimizing the battery cycle performance and improving the battery safety. BRIEF DESCRIPTION OF THE DRAWINGS

[0058] In order to more clearly illustrate the technical solutions of the embodiments of the present disclosure, the following briefly introduces the drawings required for use in the embodiments of the present disclosure. Obviously, the drawings described below are only some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on the drawings without any creative work.

[0059] The present disclosure can be more clearly understood from the following detailed description with reference to the accompanying drawings, in which:

[0060] FIG1 is a schematic structural diagram of some embodiments of an electric device according to the present disclosure;

[0061] FIG2 is an exploded schematic diagram of some embodiments of batteries according to the present disclosure;

[0062] FIG3 is an exploded schematic diagram of some embodiments of a battery cell according to the present disclosure;

[0063] FIG4 is a schematic diagram of a winding structure of an electrode assembly according to some embodiments of the present disclosure;

[0064] FIG5 is a schematic structural diagram of some embodiments of the positive electrode sheet according to the present disclosure in an unfolded state;

[0065] FIG6 is a schematic cross-sectional view taken along line AA of FIG5 ;

[0066] FIG7 is a schematic diagram of the dimensions of FIG5 ;

[0067] FIG8 is a schematic structural diagram of other embodiments of the positive electrode sheet according to the present disclosure in an unfolded state;

[0068] FIG9 is a schematic cross-sectional view taken along line AA of FIG8 ;

[0069] FIG10 is a schematic diagram of the dimensions of FIG8 ;

[0070] FIG11 is a schematic flow chart of some embodiments of a method for preparing a positive electrode sheet according to the present disclosure.

[0071] It should be understood that the size of each part shown in the drawings is not drawn according to the actual proportional relationship.In addition, the same or similar reference numerals represent the same or similar components.

[0072] Explanation of the accompanying figures: 10-positive electrode current collector; 20-positive electrode active material layer; 21-first positive electrode active material segment; 22-second positive electrode active material segment; 23-third positive electrode active material segment; 30-electrode assembly; 31-positive electrode sheet; 32-negative electrode sheet; 33-diaphragm; 34-housing; 35-end cover; 36-current collecting plate; 300-battery cell; 40-battery; 41-casing; 42-end cover; 50-vehicle. DETAILED DESCRIPTION

[0073] The following detailed description of the embodiments of the present disclosure is provided in conjunction with the accompanying drawings and examples. The detailed description of the following embodiments and the accompanying drawings are used to illustrate the principles of the present disclosure, but are not intended to limit the scope of the present disclosure, that is, the present disclosure is not limited to the described embodiments.

[0074] In the description of the present disclosure, it should be noted that, unless otherwise specified, "multiple" means more than two; the terms "upper", "lower", "left", "right", "inside", "outside", etc., indicating directions or positional relationships, are only for the convenience of describing the present disclosure and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as limiting the present disclosure. In addition, the terms "first", "second", "third", etc. are only used for descriptive purposes and cannot be understood as indicating or implying relative importance. "Vertical" is not strictly perpendicular, but is within the allowable error range. "Parallel" is not strictly parallel, but is within the allowable error range.

[0075] The directional words appearing in the following description are all directions shown in the figures and do not limit the specific structure of the present disclosure. In the description of the present disclosure, it should also be noted that, unless otherwise clearly specified and limited, the terms "installed", "connected", and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the present disclosure can be understood according to the specific circumstances.

[0076] The following describes some embodiments of the present invention in detail with reference to the accompanying drawings. In the absence of conflict, the features of the following embodiments can be combined with each other.

[0077] In the related art, the positive electrode sheet is prepared by coating the surface of the positive electrode collector with a single or double layer of positive electrode active material. The positive electrode sheet obtained by this preparation method can be used for the wound electrode assembly of the cylindrical battery. When the cylindrical battery is in a working cycle, due to the expansion pressure of the negative electrode sheet and the stress on the sheet, the expansion force of the winding layer closer to the center of the cylindrical battery is greater, which easily causes the electrolyte soaked in this part of the winding layer to be squeezed out. In addition, because the end tabs of the electrode assembly are overlapped and bent and are relatively tight to each other, the electrolyte cannot quickly enter the interior of the electrode assembly for replenishment, resulting in insufficient electrolyte infiltration and failure to embed in time at the locations with greater expansion force inside the electrode assembly, causing local lithium deposition, affecting the battery's cycle performance and safety.

[0078] In view of this, embodiments of the present disclosure provide an electrode assembly, a battery cell, a battery, an electrical device, a positive electrode sheet, and a method for preparing the same, which can improve battery performance.

[0079] The positive electrode plate of the embodiment of the present disclosure can be applied to various types of electrode assemblies, including electrode assemblies with a wound structure and electrode assemblies with a stacked structure, and the embodiment of the present application is not limited to this.

[0080] The electrode assembly of the embodiments of the present disclosure can be applied to various types of battery cells. Battery cells can include lithium-ion secondary batteries, lithium-ion primary batteries, lithium-sulfur batteries, sodium-lithium-ion batteries, sodium-ion batteries, or magnesium-ion batteries, etc., which are not limited in the embodiments of the present disclosure. Battery cells can be cylindrical, flat, rectangular, or other shapes, etc., which are not limited in the embodiments of the present application. Battery cells are generally divided into cylindrical battery cells, square battery cells, and soft-pack battery cells according to the packaging method, which are not limited in the embodiments of the present application.

[0081] The battery cells of the embodiments of the present disclosure are applicable to various types of batteries. The battery can be used to power electrical equipment such as vehicles, for example, to provide power for vehicle operation or driving. The battery may include a housing and a battery module. The housing is used to provide a storage space for the battery module, and the battery module is installed in the housing. The housing can be made of metal. The battery module may include multiple battery cells connected in series, parallel, or mixed. A battery cell is the smallest unit that makes up a battery. A battery cell includes an electrode assembly that can undergo an electrochemical reaction.

[0082] The battery of the embodiment of the present disclosure can be applied to various types of battery-using electrical equipment. Electrical equipment can be mobile phones, portable devices, laptop computers, battery cars, electric cars, ships, spacecraft, electric toys and electric tools, etc. For example, spacecraft include airplanes, rockets, space shuttles and spacecrafts, etc. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys and electric airplane toys, etc. Electric tools include metal cutting power tools, grinding power tools, assembly power tools and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators and electric planers. The embodiment of the present invention does not impose any special restrictions on the above-mentioned electrical equipment.

[0083] Figure 1 is a schematic diagram of the structure of some embodiments of electrical devices according to the present disclosure. For convenience, the electrical device is described using a vehicle as an example. Vehicle 50 can be a fuel-powered vehicle, a gas-powered vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle or a hybrid vehicle. A battery 40 can be installed at the bottom, front, or rear of vehicle 50.

[0084] The battery 40 can be used to power the vehicle 50. For example, the battery 40 can serve as the operating power source of the vehicle 50 and be used for the circuit system of the vehicle 50, such as the power requirements for starting, navigating, and operating the vehicle 50. The battery 40 can not only serve as the operating power source of the vehicle 50, but also as the driving power source of the vehicle 50, replacing or partially replacing fuel or natural gas to provide driving force for the vehicle 50.

[0085] Vehicle 50 may also be equipped with axles, wheels, a motor, and a controller. The controller controls the power supplied by battery 40 to the motor. For example, when vehicle 50 is powered by battery 40, the controller can provide the motor with the power required for constant speed and acceleration. The motor drives the axles to rotate, thereby driving the wheels.

[0086] Figure 2 is an exploded schematic diagram of some embodiments of batteries according to the present disclosure. Referring to Figure 2, in some embodiments, a battery 40 includes a housing 41 and one or more battery cells 300 disposed within the housing 41. The housing 41 provides cooling, sealing, and impact protection for the battery cells 300, while also preventing liquids or other foreign matter from adversely affecting the charging, discharging, and safety of the battery cells.

[0087] 2 , the battery cells 300 are electrically connected, such as in series, parallel, or hybrid, to achieve the required electrical performance parameters of the battery 40. Multiple battery cells 300 are arranged in rows, and one or more rows of battery cells 300 can be arranged in the box as needed.

[0088] In some embodiments, the battery cells 300 of the battery 40 can be arranged along at least one of the length and width of the housing. Depending on actual needs, at least one row or column of battery cells 40 can be provided. Alternatively, one or more layers of battery cells 300 can be arranged along the height of the battery 40 as needed.

[0089] In some embodiments, multiple battery cells 300 may be connected in series, parallel, or hybrid to form a battery module, and then the multiple battery modules may be connected in series, parallel, or hybrid to form a whole unit, which is then housed in the housing 41. In other embodiments, all battery cells 300 may be directly connected in series, parallel, or hybrid to form a whole unit, and then housed in the housing.

[0090] A battery cell 300 may include a housing, end caps, and an electrode assembly. The housing has a cavity for accommodating the electrode assembly, and the ends of the housing may be open to accommodate the end cap assembly. The electrode assembly is mounted in the housing cavity. In addition to the electrode assembly, end caps, and housing, the battery cell 300 also includes an electrolyte.

[0091] FIG3 is a schematic diagram of an exploded view of some embodiments of a battery cell according to the present disclosure. Referring to FIG3 , in some embodiments, a battery cell 300 may include a shell 34, an end cover 35, and an electrode assembly 30. The shell 34 has a cavity for accommodating the electrode assembly, and at least one end of the shell 34 may be configured to be open for providing the end cover 35. In addition to the electrode assembly 30, the end cover 35, and the shell 34, the battery cell 300 also includes an electrolyte. The battery cell 300 may further include a current collecting plate 36. The current collecting plate 36 is located between the tab of the electrode assembly 30 and the electrode post on the end cover 35, and may be fixedly connected to the smoothed tab by welding.

[0092] The cavity of the housing 34 can be used to accommodate the electrode assembly 30 and the electrolyte. The end opening of the housing 34 allows the electrode assembly 30 to enter the cavity through this end opening when the battery cell 300 is installed. The shape of the housing 34 can be determined according to the shape of the one or more electrode assemblies 30 accommodated in the cavity. For example, the housing 34 can be shaped as a hollow rectangular parallelepiped, a hollow cube, or a hollow cylinder. The housing 34 can be made of a metal (such as aluminum, an aluminum alloy, etc.) or a non-metallic material (plastic) with a certain hardness and strength.

[0093] The end cap 35 is provided at the end opening of the housing 34 to close the end opening and form a sealed cavity with the housing 34 to accommodate the electrode assembly 30. The end cap 35 can be made of a metal (such as aluminum, aluminum alloy, etc.) or a non-metallic material (plastic) with a certain hardness and strength. The end cap 35 and the housing 34 can be fixedly connected by welding, bonding, or connecting with a connector. Some functional components can be provided on the end cap 35, such as a pole for electrical connection to the electrode assembly 30, a liquid injection mechanism, a pressure relief mechanism, etc.

[0094] FIG4 is a schematic diagram of a winding structure according to some embodiments of an electrode assembly of the present disclosure. Referring to FIG4 , in some embodiments, the electrode assembly includes: a positive electrode sheet 31, a negative electrode sheet 32, and a separator 33 disposed between the positive electrode sheet 31 and the negative electrode sheet 32. The positive electrode sheet 31, the separator 33, and the negative electrode sheet 32 ​​are wound along a winding direction r to form a winding structure. The winding structure shown in FIG3 forms a cylindrical structure (e.g., a hollow cylindrical structure) after winding. Accordingly, the shell used by the battery cell including the electrode assembly is a cylindrical shell.

[0095] The operation of the electrode assembly 30 is achieved by the movement of metal ions between the positive and negative electrodes. The separator 33 can be made of materials such as PP (polypropylene) or PE (polyethylene). The electrolyte includes electrolytes and solvents. The electrolytes can be organic metal salts, inorganic salts, etc., which provide the metal ions that shuttle between the positive and negative electrodes.

[0096] The negative electrode sheet 32 ​​comprises a negative current collector substrate and a negative active material layer. The negative electrode tab is attached to the negative current collector substrate. For lithium-ion batteries, for example, the negative current collector substrate can be made of copper, and the negative active material can be materials capable of storing lithium ions, such as graphite, silicon, or lithium titanate. When a bonding material is used to bond the negative current collector substrate and the negative active material layer, the bonding material can be carboxymethyl cellulose, epoxy resin, or styrene-butadiene rubber.

[0097] FIG5 is a schematic diagram of the structure of some embodiments of the positive electrode sheet according to the present disclosure in an unfolded state. FIG6 is a schematic diagram of the AA section of FIG5 . FIG7 is a schematic diagram of the dimensions of FIG5 . Referring to FIG5 and FIG6 , in some embodiments, the positive electrode sheet 31 includes a positive electrode current collector 10 and a positive electrode active material layer 20. Taking a lithium-ion battery as an example, the material of the positive electrode current collector 10 can be aluminum, and the positive electrode active material contained in the positive electrode active material layer 20 can be a lithiated substance that can provide lithium ions, such as lithium cobalt oxide, lithium iron phosphate, ternary lithium, or lithium manganese oxide.

[0098] The positive electrode active material layer 20 is disposed on at least a portion of the surface of the positive electrode current collector 10. For example, the positive electrode active material layer 20 can be bonded to the surface of the positive electrode current collector 10 using PVDF (Polyvinylidene Fluoride). The positive electrode tab can be connected to or formed on the positive electrode current collector.

[0099] The positive electrode active material layer 20 includes a positive electrode current collector 10 along the length direction d L At least two positive electrode active material segments are arranged, wherein the specific surface area of ​​the positive electrode active material contained in one portion of the at least two positive electrode active material segments is greater than the specific surface area of ​​the positive electrode active material contained in another portion of the positive electrode active material segments.

[0100] According to the compression conditions of different parts of the positive electrode plate 31 when the battery cell is working, the specific surface area of ​​the positive electrode active material contained in a part of the positive electrode active material segment of the positive electrode active material layer 20 is made larger, so as to improve the electrolyte infiltration ability of the positive electrode active material area with a higher degree of compression, reduce the risk of lithium precipitation caused by the electrolyte being squeezed out, and enable the electrolyte to fully react with the positive electrode active material on the positive electrode plate 31 during the battery charging and discharging process, optimize the battery cycle performance, and improve the battery safety.

[0101] Here, at least two positive electrode active material segments may be arranged along the length direction d of the positive electrode current collector 10. L The part and the other part of the positive electrode active material segments mentioned here may be all the positive electrode active material segments or may not be all the positive electrode active material segments.

[0102] The specific surface area of ​​the positive electrode active material in the embodiments of the present disclosure has a well-known meaning in the art and can be measured using instruments and methods well-known in the art. For example, it can be measured with reference to GB / T 19587-2017 gas adsorption BET method for determining the specific surface area of ​​solid substances, using a nitrogen adsorption specific surface area analysis test method and calculating it using the BET (Brunauer Emmett Teller) method. The nitrogen adsorption specific surface area analysis test can be performed using a Tri Star II 3020 specific surface and pore analyzer from Micromeritics, USA.

[0103] 5 and 6 , in some embodiments, the at least two positive electrode active material segments include a first positive electrode active material segment 21 and a second positive electrode active material segment 22 , the specific surface area BET1 of the first positive electrode active material contained in the first positive electrode active material segment 21 being greater than the specific surface area BET2 of the second positive electrode active material contained in the second positive electrode active material segment 22 , and the first positive electrode active material segment 21 is closer to the winding starting end WS of the positive electrode sheet 31 than the second positive electrode active material segment 22 .

[0104] In Figure 5, the winding starting end WS of the positive electrode sheet 31 is the inner end of the positive electrode sheet 31 after being wound along the winding direction r in the electrode assembly 30 in Figure 4, and the winding ending end WE is the outer end of the positive electrode sheet 31 after being wound along the winding direction r in the electrode assembly 30 in Figure 4.

[0105] Considering that when the positive electrode plate 31 is applied to a wound electrode assembly, the plate layer closer to the winding center expands and is squeezed to a higher degree when the battery cell is working, the first positive electrode active material segment 21 closer to the winding starting end WS contains a larger specific surface area of ​​the first positive electrode active material, so that it has a stronger electrolyte infiltration ability, so that it can still maintain a certain amount of electrolyte under a high degree of squeezing, reducing the risk of lithium precipitation due to lack of electrolyte, optimizing the battery cycle performance, and improving the battery safety.

[0106] In Figures 5 and 6 , the end of the first positive active material segment 21 adjacent to the winding start end WS of the positive electrode sheet 31 can be flush with the winding start end WS of the positive electrode sheet 31. In other words, the first positive active material segment 21 begins to adhere to and cover the positive electrode current collector 10 from the winding start end WS of the positive electrode sheet 31. This eliminates the need to precisely position the first positive active material segment 21 on the side adjacent to the winding start end WS, which helps reduce the difficulty of coating the first positive active material segment 21 on the positive electrode current collector 10.

[0107] Figure 8 is a schematic diagram of the structure of other embodiments of the positive electrode sheet according to the present disclosure in an unfolded state. Figure 9 is a schematic diagram of the AA section of Figure 8. Figure 10 is a schematic diagram of the dimensions of Figure 8. Referring to Figures 8 and 9, in some embodiments, the at least two positive electrode active material segments further include a third positive electrode active material segment 23. The third positive electrode active material segment 23 is located on a side of the first positive electrode active material segment 21 away from the second positive electrode active material segment 22. The specific surface area BET1 of the first positive electrode active material contained in the first positive electrode active material segment 21 is greater than the specific surface area BET3 of the third positive electrode active material contained in the third positive electrode active material segment 23.

[0108] Considering that the positive electrode sheet 31 of some wound electrode assemblies has a hollow structure, the electrode sheet portion near the central position is relatively less squeezed during the operation of the battery cell. Therefore, by providing the first positive electrode active material with a relatively small specific surface area on one side of the first positive electrode active material segment 21 close to the winding starting end WS, it is beneficial to reduce costs by reducing the amount of the first positive electrode active material used.

[0109] In FIGS. 8 and 9, the third positive electrode active material included in the third positive electrode active material segment 23 may be the same as the second positive electrode active material included in the second positive electrode active material segment 22. This is equivalent to using the same positive electrode active material with a larger specific surface area to form the second positive electrode active material segment 22 and the third positive electrode active material segment 23 on both sides of the first positive electrode active material segment 22 along the length direction d L of the positive electrode sheet 31, which is beneficial to simplify the electrode sheet processing process.

[0110] Referring to FIGS. 7 and 10, in some embodiments, along the length direction d L of the positive electrode current collector 10, the ratio L1 / L of the length L1 of the first positive electrode active material segment 21 to the length L of the positive electrode current collector 10 satisfies: 0 < L1 / L ≤ 0.5.

[0111] The ratio L1 / L correspondsEND correspondsEND]] L corresponds to the coverage ratio of the positive electrode active material in the entire length direction d of the positive electrode current collector 10. If this ratio is too low, the improvement degree of the electrolyte wetting ability is limited, and the risk of lithium deposition caused by the extrusion of the electrolyte cannot be effectively reduced. If this ratio is too high, more first positive electrode active material is required, which is likely to cause too high costs. By making L1 / L satisfy 0 < L1 / L ≤ 0.5, the risk of lithium deposition on the electrode sheet can be reduced, the cycle performance of the battery can be optimized, and the overall cost can be reduced at the same time.

[0112] Furthermore, the ratio L1 / L may satisfy: 0.3 ≤ L1 / L ≤ 0.5. For example, the value of L1 / L is taken as 0.3, 1 / 3, 0.35, 0.4, 0.45, etc. By making L1 / L further satisfy 0.3 ≤ L1 / L ≤ 0.5, the risk of lithium deposition on the electrode sheet can be more effectively reduced, the cycle performance of the battery can be optimized, and the overall cost can be reduced.

[0113] The first positive electrode active material and the second positive electrode active material can be the same active material or different active materials. In some embodiments, the first positive electrode active material includes nano-lithium iron phosphate, and the second positive electrode active material includes lithium iron phosphate. Because nano-lithium iron phosphate and lithium iron phosphate differ in aspects such as specific surface area and particle size but are the same active material, the performance difference between the first positive electrode active material segment 21 and the second positive electrode active material segment 22 of the positive electrode sheet 31 can be avoided, thereby preventing the overall performance of the electrode assembly from being affected.

[0114] In other embodiments, the second positive electrode active material is lithium iron phosphate, and the first positive electrode active material may be ternary lithium, lithium-rich manganese-based materials, or M3P materials. Alternatively, both the second positive electrode active material and the first positive electrode active material are lithium iron phosphate, and the specific surface area of ​​the lithium iron phosphate used in the first positive electrode active material is greater than the specific surface area of ​​the lithium iron phosphate used in the second positive electrode active material. Alternatively, both the second positive electrode active material and the first positive electrode active material are nano-lithium iron phosphate, and the specific surface area of ​​the nano-lithium iron phosphate used in the first positive electrode active material is greater than the specific surface area of ​​the nano-lithium iron phosphate used in the second positive electrode active material.

[0115] In the above embodiments, the specific surface area BET1 of the first positive electrode active material may satisfy: BET1 ≥ 12 m 2 / g. By making the specific surface area BET1 of the first positive electrode active material greater than or equal to 12m 2 / g, the material pores of the first positive electrode active material with a higher specific surface area can accommodate more electrolyte during the cycle, which is beneficial to alleviate the difficulty of insufficient wetting, reduce the risk of lithium plating, and improve the cycle life of the battery.

[0116] Furthermore, the specific surface area BET1 of the first positive electrode active material may satisfy: 14m 2 / g≤BET1≤23m 2 / g, for example, let BET1 be 14m 2 / g、16m 2 / g、19m 2 / g、21m 2 / g or 23m 2 / g. By making the specific surface area BET1 of the first positive electrode active material satisfy 14m 2 / g≤BET1≤23m 2 A further preferred range of 1:1 / g can improve the cycle life of the battery while increasing the stability of the positive electrode active material and improving the safety performance of the battery.

[0117] In some embodiments, the specific surface area BET2 of the second positive electrode active material satisfies: BET2<12m 2 / g. By making the specific surface area BET2 of the second positive electrode active material less than 12m 2 / g, which is conducive to using a positive electrode active material with a smaller specific surface area and lower cost to form the second positive electrode active material segment 22, thereby reducing the overall cost of the positive electrode sheet 31.

[0118] Furthermore, the specific surface area BET2 of the second positive electrode active material satisfies: 2m 2 g≤BET2≤10m 2 / g, for example, let BET2 be 2m 2 g, 4m 2 / g、6m 2 / g、8m 2 / g or 10m 2 / g. By making the specific surface area BET2 of the second positive electrode active material satisfy 2m 2 / g≤BET2≤10m 2 A further preferred range of 1000 nm / g can effectively reduce the overall cost of the positive electrode sheet 31 .

[0119] In some other embodiments, on the basis of satisfying that the specific surface area BET1 of the first positive electrode active material is greater than the specific surface area BET2 of the second positive electrode active material, the specific surface area BET1 of the first positive electrode active material may also be less than 12 m 2 / g, or the specific surface area BET2 of the second positive electrode active material can also be greater than 12m 2 / g.

[0120] In each of the above embodiments, the median particle size Dv501 of the first positive electrode active material may be smaller than the median particle size Dv502 of the second positive electrode active material. Considering that when the positive electrode sheet 31 is used in a wound electrode assembly, the sheet layer closer to the winding center expands and is squeezed more during battery cell operation, the median particle size of the first positive electrode active material contained in the first positive electrode active material segment 21 closer to the winding starting end WS is increased to provide it with stronger electrolyte wetting ability. Thus, even under a high degree of squeezing, a certain amount of electrolyte can still be retained, reducing the risk of lithium precipitation due to lack of electrolyte and optimizing the battery's cycle performance.

[0121] The median particle size Dv50 of the positive electrode active material in the embodiments of the present disclosure is well known in the art and can be measured using instruments and methods known in the art. For example, it can be conveniently measured using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer from Malvern Instruments Ltd., UK, in accordance with GB / T 19077-2016 Particle Size Distribution Laser Diffraction Method.

[0122] In some embodiments, the median particle size Dv501 of the first positive electrode active material satisfies the following condition: Dv501 ≤ 800 nm. By setting the median particle size Dv501 of the first positive electrode active material to be less than or equal to 800 nm, the pores of the first positive electrode active material with a lower median particle size can accommodate more electrolyte during cycling, thereby alleviating the difficulty of insufficient infiltration, reducing the risk of lithium plating, and improving the cycle life of the battery.

[0123] Furthermore, the median particle size Dv501 of the first positive electrode active material may satisfy the following range: 100 nm ≤ Dv501 ≤ 400 nm. For example, Dv501 may be 100 nm, 160 nm, 210 nm, 280 nm, 340 nm, or 400 nm. By ensuring that the median particle size Dv501 of the first positive electrode active material satisfies the further preferred range of 100 nm ≤ Dv501 ≤ 400 nm, local lithium deposition can be improved, thereby increasing the cycle life of the battery, while also improving the electrochemical kinetics of the battery during charge and discharge and reducing polarization.

[0124] In some embodiments, the median particle size Dv502 of the second positive electrode active material satisfies: Dv502>800 nm. By setting the median particle size Dv502 of the second positive electrode active material to be greater than 800 nm, it is advantageous to use a positive electrode active material with a larger median particle size and lower cost to form the second positive electrode active material segment 22, thereby reducing the overall cost of the positive electrode sheet 31.

[0125] Furthermore, the median particle size Dv502 of the second positive electrode active material satisfies the following range: 900 nm ≤ Dv502 ≤ 1500 nm. For example, Dv502 is 900 nm, 1000 nm, 1150 nm, 1280 nm, 1360 nm, or 1500 nm. By ensuring that the median particle size Dv502 of the second positive electrode active material satisfies the further preferred range of 900 nm ≤ Dv502 ≤ 1500 nm, the overall cost of the positive electrode sheet 31 can be effectively reduced.

[0126] In other embodiments, on the basis of satisfying the requirement that the median particle size Dv501 of the first positive electrode active material is smaller than the median particle size Dv502 of the second positive electrode active material, the median particle size Dv501 of the first positive electrode active material may also be greater than 800 nm, or the median particle size Dv502 of the second positive electrode active material may also be less than 800 nm.

[0127] In the above embodiment, the carbon content ωC1 of the first positive electrode active material may be greater than the carbon content ωC2 of the second positive electrode active material. Considering that when the positive electrode sheet 31 is used in a wound electrode assembly, the sheet layer closer to the winding center expands and is squeezed more during battery cell operation, which can easily lead to lithium deposition, by increasing the carbon content of the first positive electrode active material contained in the first positive electrode active material segment 21 closer to the winding starting end WS, the conductivity of the sheet is improved, the risk of lithium deposition is reduced, and the battery charge and discharge performance is optimized.

[0128] The carbon content in the positive electrode active material of the disclosed embodiments can be measured using instruments and methods known in the art. For example, a high-frequency carbon-sulfur analyzer can be used for testing using infrared absorption. High temperatures are used to oxidize the carbon and sulfur in the positive electrode active material into carbon dioxide and sulfur dioxide gases. The gases, after treatment, enter a corresponding absorption cell, absorb infrared radiation, and, after signal conversion, output the carbon content test result.

[0129] In some embodiments, the carbon content ωC1 of the first positive electrode active material may satisfy the following condition: ωC1 ≥ 2.5%. By ensuring that the carbon content ωC1 of the first positive electrode active material is greater than or equal to 2.5%, the first positive electrode active material with a higher carbon content can achieve higher conductivity, which is beneficial for reducing the risk of lithium plating, increasing the cycle life of the battery, reducing the internal resistance of the battery, and improving the cycle performance of the battery.

[0130] Furthermore, the carbon content ωC1 of the first positive electrode active material satisfies: ωC1 ≥ 2.8%, for example, ωC1 is set to 2.8%, 2.9%, 3.2%, or 4.0%. By ensuring that the carbon content ωC1 of the first positive electrode active material satisfies the further preferred range of ωC1 ≥ 2.8%, the electrode sheet conductivity can be effectively further improved, the battery internal resistance can be reduced, and the battery cycle life can be increased.

[0131] In some embodiments, the carbon content ωC2 of the second positive electrode active material satisfies: ωC2≤1.5%. By making the carbon content ωC2 of the second positive electrode active material less than or equal to 1.5%, the proportion of positive electrode active material can be increased, thereby improving energy density.

[0132] Furthermore, the carbon content ωC2 of the second positive electrode active material can satisfy: ωC2 ≤ 1.2%. For example, ωC2 can be 1.2%, 1%, 0.8%, or 0.5%. By further ensuring that the carbon content ωC2 of the second positive electrode active material satisfies ωC2 ≤ 1.2%, the proportion of positive electrode active material can be effectively increased, thereby improving energy density.

[0133] In other embodiments, on the basis of satisfying that the median particle size carbon content ωC1 of the first positive electrode active material is greater than the carbon content ωC2 of the second positive electrode active material, the carbon content ωC1 of the first positive electrode active material may also be less than 2.5%, or the carbon content ωC2 of the second positive electrode active material may also be greater than 1.5%.

[0134] In the aforementioned embodiments, for the positive electrode sheet embodiment including the third positive electrode active material segment, the type and parameters of the third positive electrode active material of the third positive electrode active material segment can refer to the first positive electrode active material, and will not be repeated here.

[0135] The test results of multiple positive electrode plate embodiments and comparative examples are described with reference to the table below. The process of the Direct Current Resistance (DCR) test here includes: after the battery is fully charged at 1C at room temperature, it is discharged to 50% SOC at 1C, the battery ambient temperature is adjusted to -10°C, left for 2 hours, and then discharged at a rate of 3C for 10 seconds, and the DC internal resistance of the battery is obtained by calculating the ratio of (voltage before discharge - voltage after discharge) to current. The process of the inner ring lithium plating test includes: at room temperature, the battery is charged and discharged at 1C / 1C, and when the number of cycles is 2000, the battery is disassembled to observe whether there is lithium plating on the surface of the inner ring electrode of the battery. The cycle life test here includes: under normal temperature conditions, the battery is charged and discharged at 1C / 1C until the battery capacity decays to 80% SOH. At this time, the number of cycles is the cycle life of the battery.

[0136] From the above table, it can be seen that in Examples 1 to 3, the specific surface area is greater than 10m 2 / g of nano-lithium iron phosphate as the first positive electrode active material, and a specific surface area of ​​less than 10m 2 When lithium iron phosphate with a specific surface area greater than 10m2 is used as the second positive electrode active material to form the first positive electrode active material segment and the second positive electrode active material segment of the positive electrode sheet, a smaller DC internal resistance can be obtained, and there is only slight or no lithium deposition after 2000 cycles. The cycle life obtained by the cycle test can reach more than 3700 times. 2 When lithium iron phosphate (LiFePO4) with a concentration of 1000 t / g was used as the first and second cathode active materials to form the first and second cathode active material segments of the cathode sheet, respectively, the resulting DC internal resistance was high, and severe lithium deposition occurred in the inner ring after 2000 cycles, resulting in a cycle life of only 3000 cycles. Furthermore, compared to Example 1, the first cathode active materials of Examples 2 and 3 had a larger specific surface area BET1, correspondingly lower internal resistance, improved lithium deposition, and a cycle life of over 4200 cycles.

[0137] As can be seen from the above table, when using lithium iron phosphate nanoparticles with a median particle size less than 800 nm as the first positive electrode active material and lithium iron phosphate with a median particle size greater than 800 nm as the second positive electrode active material to form the first positive electrode active material segment and the second positive electrode active material segment of the positive electrode sheet respectively in Examples 3 to 5, a smaller DC internal resistance can be obtained, and there is no lithium deposition in the inner loop after 2000 cycles, and the cycle life obtained from the cycle test can be more than 3800 times. In the comparative examples, when using lithium iron phosphate with a median particle size greater than 800 nm as the first positive electrode active material and the second positive electrode active material to form the first positive electrode active material segment and the second positive electrode active material segment of the positive electrode sheet respectively, the obtained DC internal resistance is relatively high, and there is serious lithium deposition in the inner loop after 2000 cycles, and the cycle life obtained from the cycle test is only 3000 times. Compared with Example 5, the median particle size Dv501 of the first positive electrode active material in Examples 3 and 4 is in the range of 100 to 400 nm, and accordingly the internal resistance is smaller, and the cycle life reaches more than 5400 times.

[0138] As can be seen from the above table, when using lithium iron phosphate nanoparticles with a carbon content greater than 2.5% as the first positive electrode active material and lithium iron phosphate with a carbon content less than or equal to 1.5% as the second positive electrode active material to form the first positive electrode active material segment and the second positive electrode active material segment of the positive electrode sheet respectively in Examples 3 and 6, a smaller DC internal resistance can be obtained, and there is no lithium deposition in the inner loop after 2000 cycles, and the cycle life obtained from the cycle test can reach more than 5000 times. In the comparative examples, when using lithium iron phosphate with a carbon content less than or equal to 1.5% as the first positive electrode active material and the second positive electrode active material to form the first positive electrode active material segment and the second positive electrode active material segment of the positive electrode sheet respectively, the obtained DC internal resistance is relatively high, and there is serious lithium deposition in the inner loop after 2000 cycles, and the cycle life obtained from the cycle test is only 3000 times.

[0139] As can be seen from the above table, in Examples 3, 7 and 8, the ratio L1 / L of the length L1 of the first positive electrode active material segment to the length L of the positive electrode current collector satisfies the range of 0 < L1 / L ≤ 0.5, a smaller DC internal resistance can be obtained, and there is only slight lithium deposition or no lithium deposition after 2000 cycles, and the cycle life obtained from the cycle test can reach more than 3800 times. In the comparative example, both the first positive electrode active material segment and the second positive electrode active material segment are lithium iron phosphate and do not contain lithium iron phosphate nanoparticles. Therefore, L1 / L is equivalent to 0 at this time. The obtained DC internal resistance is relatively high, and there is serious lithium deposition in the inner loop after 2000 cycles, and the cycle life obtained from the cycle test is only 3000 times. In addition, compared with Example 7, the value of L1 / L in Examples 3 and 8 is in the range of 0.3 to 0.5, and accordingly the internal resistance is smaller, the lithium deposition is improved more, and the cycle life reaches more than 5200 times.

[0140] From the above table, it can be seen that in Examples 3, 9, 10 and 11, the specific surface area BET1 is greater than 10m 2 / g, median particle size Dv501 less than 800nm, and carbon content ωC1 greater than 2.5% of nano-lithium iron phosphate as the first positive electrode active material. Compared with Example 3, Examples 9, 10 and 11 respectively take different values ​​of the specific surface area BET2, median particle size Dv502 and carbon content ωC2 of the second positive electrode active material. It can be seen that by making the specific surface area BET2 less than 12m 2 / g, median particle size Dv502 greater than 800nm, carbon content ωC2 less than or equal to 1.2%, can obtain a smaller DC internal resistance, and there is no lithium deposition in the inner circle when circulating 2000 times. The cycle life obtained by the cycle test can reach more than 4400 times.

[0141] Figure 11 is a schematic flow diagram of some embodiments of a method for preparing a positive electrode sheet according to the present disclosure. Referring to Figure 1 , in some embodiments, the method for preparing a positive electrode sheet includes steps S1 and S2. In step S1, a positive electrode current collector, a first positive electrode slurry containing a first positive electrode active material, and a second positive electrode slurry containing a second positive electrode active material are provided, wherein the specific surface area of ​​the first positive electrode active material is greater than the specific surface area of ​​the second positive electrode active material.

[0142] In step S2, the first positive electrode slurry is coated on the surface of a portion of the at least two segments distributed along the length direction of the positive electrode collector, and the second positive electrode slurry is coated on the surface of another portion of the at least two segments distributed along the length direction of the positive electrode collector.

[0143] By respectively coating the first positive electrode slurry containing the first positive electrode active material and the second positive electrode slurry containing the second positive electrode active material onto the surfaces of different segments in the length direction of the positive electrode current collector, the obtained positive electrode sheet can improve the electrolyte wetting ability of the positive electrode active material area that is subjected to a higher degree of compression, reduce the risk of lithium precipitation caused by the electrolyte being squeezed out, and allow the electrolyte to fully react with the positive electrode active material on the positive electrode sheet during the battery charging and discharging process, thereby optimizing the battery's cycle performance and improving the battery's safety.

[0144] Here, at least two segments may be arranged continuously or at intervals along the length direction of the positive electrode current collector. The part and the other part of the segments mentioned here may be all segments or not all segments.

[0145] For example, when preparing the positive electrode sheet, the median particle size is 780nm and the specific surface area is 14.4m 2 / g of nano-lithium iron phosphate as the first positive electrode active material is dissolved in a solvent N-methylpyrrolidone (NMP) with a mass ratio of 97:0.8:2.2 together with a conductive agent (acetylene black) and a binder (polyvinylidene fluoride PVDF). The mixture is thoroughly stirred and mixed to obtain a first positive electrode slurry.

[0146] The median particle size is 1050 nm and the specific surface area is 9.8 m 2 / g of lithium iron phosphate as the second positive electrode active material is dissolved in a solvent N-methylpyrrolidone (NMP) with a conductive agent (acetylene black) and a binder (polyvinylidene fluoride PVDF) in a mass ratio of 97:0.8:2.2, and the mixture is thoroughly stirred and mixed to obtain a second positive electrode slurry.

[0147] Then, referring to Figure 5, the first positive electrode slurry is evenly coated on the surface of the positive electrode collector (aluminum foil) from the winding starting end WS along the length direction dL, so that the coating length is 1 / 3 of the length of the entire electrode sheet, and the second positive electrode slurry is evenly coated on the surface of the positive electrode collector (aluminum foil) so that the coating length is 2 / 3 of the length of the entire electrode sheet. The positive electrode sheets are then dried, cold pressed, and cut.

[0148] Based on the various embodiments of the positive electrode sheets described above, embodiments of the present disclosure further provide an electrode assembly, comprising the positive electrode sheet of any of the aforementioned embodiments, and further comprising a negative electrode sheet and a separator disposed between the positive electrode sheet and the negative electrode sheet, wherein the positive electrode sheet, the separator, and the negative electrode sheet are wound along a winding direction to form a wound structure. The electrode assembly using the aforementioned positive electrode sheet has improved cycle performance and safety.

[0149] In some embodiments, the wound structure is a cylindrical structure. For a cylindrical electrode assembly, the positive electrode sheet can improve the electrolyte infiltration effect at the location where the expansion force is concentrated, thereby improving the cycle performance and safety of the electrode assembly.

[0150] In one aspect of the present disclosure, a battery cell is provided, comprising the electrode assembly of any one of the aforementioned embodiments. The battery cell using the aforementioned electrode assembly has better cycle performance and safety.

[0151] In one aspect of the present disclosure, a battery is provided, comprising the battery cell of any one of the aforementioned embodiments. The battery using the aforementioned battery cell has better cycle performance and safety.

[0152] In one aspect of the present disclosure, an electrical device is provided, comprising a battery according to any one of the aforementioned embodiments. The electrical device using the aforementioned battery can achieve better safety and save battery consumption.

[0153] While the present disclosure has been described with reference to preferred embodiments, various modifications may be made thereto and equivalent components may be substituted without departing from the scope of the present disclosure. In particular, the various technical features described in the various embodiments may be combined in any manner, provided no structural conflicts exist. The present disclosure is not limited to the specific embodiments disclosed herein, but encompasses all technical solutions within the scope of the claims.

Claims

1. A positive electrode sheet (31), comprising: A positive electrode current collector (10); and A positive electrode active material layer (20) is arranged on the surface of the positive electrode current collector (10); The positive electrode active material layer (20) includes a positive electrode current collector (10) along the length direction (d L ) are arranged in a manner that the specific surface area of ​​the positive electrode active material contained in one part of the at least two positive electrode active material segments is greater than the specific surface area of ​​the positive electrode active material contained in another part of the at least two positive electrode active material segments.

2. The positive electrode sheet (31) according to claim 1, wherein the at least two positive active material segments include a first positive active material segment (21) and a second positive active material segment (22), the specific surface area BET1 of the first positive active material contained in the first positive active material segment (21) is greater than the specific surface area BET2 of the second positive active material contained in the second positive active material segment (22), and the first positive active material segment (21) is closer to the winding starting end (WS) of the positive electrode sheet (31) than the second positive active material segment (22).

3. The positive electrode sheet (31) according to claim 2, wherein the end of the first positive active material segment (21) adjacent to the winding start end (WS) of the positive electrode sheet (31) is flush with the winding start end (WS) of the positive electrode sheet (31).

4. The positive electrode sheet (31) according to claim 2, wherein the at least two positive electrode active material segments further include a third positive electrode active material segment (23), the third positive electrode active material segment (23) is located on a side of the first positive electrode active material segment (21) away from the second positive electrode active material segment (22), and the specific surface area BET1 of the first positive electrode active material contained in the first positive electrode active material segment (21) is greater than the specific surface area BET3 of the third positive electrode active material contained in the third positive electrode active material segment (23).

5. The positive electrode sheet (31) according to claim 4, wherein the third positive electrode active material contained in the third positive electrode active material segment (23) is the same as the second positive electrode active material contained in the second positive electrode active material segment (22).

6. The positive electrode sheet (31) according to any one of claims 2 to 5, wherein the specific surface area BET1 of the first positive electrode active material satisfies: BET1 ≥ 12 m 2 / g.

7. The positive electrode sheet (31) according to claim 6, wherein the specific surface area BET1 of the first positive electrode active material satisfies: 14 m 2 / g≤BET1≤23m 2 / g.

8. The positive electrode sheet (31) according to any one of claims 2 to 7, wherein the specific surface area BET2 of the second positive electrode active material satisfies: BET2<12 m 2 / g.

9. The positive electrode sheet (31) according to any one of claims 2 to 7, wherein the specific surface area BET2 of the second positive electrode active material satisfies: 2 m 2 g≤BET2≤10m 2 / g.

10. The positive electrode sheet (31) according to any one of claims 2 to 9, wherein the median particle size Dv501 of the first positive electrode active material is smaller than the median particle size Dv502 of the second positive electrode active material.

11. The positive electrode sheet (31) according to claim 10, wherein the median particle size Dv501 of the first positive electrode active material satisfies: Dv501≤800nm.

12. The positive electrode sheet (31) according to claim 11, wherein the median particle size Dv501 of the first positive electrode active material satisfies: 100 nm ≤ Dv501 ≤ 400 nm.

13. The positive electrode sheet (31) according to any one of claims 10 to 12, wherein the median particle size Dv502 of the second positive electrode active material satisfies: Dv502>800nm.

14. The positive electrode sheet (31) according to claim 13, wherein the median particle size Dv502 of the second positive electrode active material satisfies: 900nm≤Dv502≤1500nm.

15. The positive electrode sheet (31) according to any one of claims 2 to 13, wherein the carbon content ωC1 of the first positive electrode active material is greater than the carbon content ωC2 of the second positive electrode active material.

16. The positive electrode sheet (31) according to claim 15, wherein the carbon content ωC1 of the first positive electrode active material satisfies: ωC1 ≥ 2.5%.

17. The positive electrode sheet (31) according to claim 16, wherein the carbon content ωC1 of the first positive electrode active material satisfies: ωC1 ≥ 2.8%.

18. The positive electrode sheet (31) according to claim 15, wherein the carbon content ωC2 of the second positive electrode active material satisfies: ωC2≤1.5%.

19. The positive electrode sheet (31) according to claim 18, wherein the carbon content ωC2 of the second positive electrode active material satisfies: ωC2≤1.2%.

20. The positive electrode sheet (31) according to any one of claims 2 to 19, wherein in the length direction (d L ), the ratio L1 / L of the length L1 of the first positive electrode active material segment (21) to the length L of the positive electrode current collector (10) satisfies: <L1 / L≤0.5。 21. The positive electrode plate (31) according to claim 20, wherein the ratio L1 / L satisfies: 0.3≤L1 / L≤0.

5.

22. The positive electrode plate (31) according to any one of claims 1 to 21, wherein the first positive electrode active material comprises nano-lithium iron phosphate, and the second positive electrode active material comprises lithium iron phosphate.

23. An electrode assembly (30), comprising: A positive electrode sheet (31), a negative electrode sheet (32) and a separator (33) arranged between the positive electrode sheet (31) and the negative electrode sheet (32), wherein the positive electrode sheet (31), the separator (33) and the negative electrode sheet (32) are wound along a winding direction (r) to form a winding structure, and the positive electrode sheet (31) is the positive electrode sheet (31) according to any one of claims 1 to 22.

24. The electrode assembly (30) according to claim 23, wherein the wound structure is a cylindrical structure.

25. A battery cell (300), comprising: The electrode assembly (30) as claimed in claim 23 or 24.

26. A battery (40) comprising the battery cell (300) according to claim 25.

27. An electrical device comprising the battery (40) according to claim 26.

28. A method for preparing a positive electrode sheet, comprising: Providing a positive electrode current collector, a first positive electrode slurry containing a first positive electrode active material, and a second positive electrode slurry containing a second positive electrode active material, wherein the specific surface area of ​​the first positive electrode active material is greater than the specific surface area of ​​the second positive electrode active material; The first positive electrode slurry is coated on the surface of a part of at least two sections distributed along the length direction of the positive electrode collector, and the second positive electrode slurry is coated on the surface of another part of the at least two sections.

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