Positive pole piece, battery and electric equipment

Abstract

The invention relates to a positive pole piece, a battery and electric equipment, and belongs to the technical field of secondary batteries. The positive pole piece comprises a positive current collector, and a first positive active layer and a second positive active layer which are sequentially arranged on at least one side of the positive current collector; the first positive electrode active layer comprises a first lithium-containing positive electrode active material, the ionic conductivity of the first lithium-containing positive electrode active material is a, and the electronic conductivity of the first lithium-containing positive electrode active material is b, the second positive electrode active layer comprises a second lithium-containing active material, the ionic conductivity of the second lithium-containing active material is a ', and the electronic conductivity of the second lithium-containing active material is b'; wherein a is smaller than a ', and b is larger than b'. In the positive pole piece, the electronic conductivity of the active material close to the current collector is high, the ionic conductivity of the active material close to the current collector is low, the ionic conductivity of the active material far away from the current collector is high, and the electronic conductivity of the active material far away from the current collector is low, so that the positive pole piece is beneficial to lithium ion transmission and electron transmission, and the rate capability of the battery is improved.

Description

Technical Field

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

[0002] In existing lithium-ion batteries, in order to take into account the comprehensive performance of the positive electrode sheet, positive electrode active materials with different properties are usually mixed to form a positive electrode active layer. If the ion conductivity of the two mixed positive electrode active materials is very different, the kinetic performance of the entire battery will be poor. Therefore, two positive electrode active materials with large differences in ion conductivity are usually arranged in layers to form two different positive electrode active layers. However, simply arranging two positive electrode active materials with large differences in ion conductivity in layers cannot effectively improve the rate performance of the battery. Summary of the invention

[0003] In view of the deficiencies in the prior art, the present application provides a positive electrode plate, a battery and an electrical device to improve the rate performance of the battery.

[0004] In a first aspect, an embodiment of the present application provides a positive electrode plate, comprising a positive electrode current collector and a first positive electrode active layer and a second positive electrode active layer sequentially arranged on at least one side of the positive electrode current collector; the first positive electrode active layer comprises a first lithium-containing active material, the ion conductivity of the first lithium-containing active material is a, and the electronic conductivity is b; the second positive electrode active layer comprises a second lithium-containing active material, the ion conductivity of the second lithium-containing active material is a', and the electronic conductivity is b'; wherein, a<a', b>b'.

[0005] In the technical solution of the embodiment of the present application, two lithium-containing active materials with large differences in ionic conductivity and electronic conductivity are arranged in layers, which can avoid the mutual influence of the performance between the materials and make the performance of each material better. In addition, the second lithium-containing active material with higher ionic conductivity and lower electronic conductivity is concentrated on the surface of the positive electrode plate, which can be beneficial to the transmission of lithium ions, and the first lithium-containing active material with lower ionic conductivity and higher electronic conductivity is concentrated on the bottom layer of the positive electrode plate, which can make the electron transmission effect better, thereby improving the rate performance of the battery.

[0006] In some embodiments, the relationship between a and a' is: a'-a≥9×10 -10 The difference in ionic conductivity between the first lithium-containing active material and the second lithium-containing active material within this range can improve the lithium ion transmission effect of the entire positive electrode sheet, thereby further improving the rate performance of the battery.

[0007] In some embodiments, 9×10 -10 S / cm≤a'-a≤8×10 -9 S / cm.

[0008] In some embodiments, 1×10 -11 S / cm≤a≤9×10 -11 S / cm; 1×10 -9 S / cm≤a'≤1×10 -8 The ionic conductivity of the first lithium-containing active material and the second lithium-containing active material are respectively within the aforementioned ranges, which can make the rate performance of the battery better.

[0009] In some embodiments, the relationship between b and b' is: b-b'≥9×10 -10 The difference between the electronic conductivity of the first lithium-containing active material and the second lithium-containing active material within this range can improve the electron transmission effect of the entire positive electrode sheet, so that the rate performance of the battery is better.

[0010] In some embodiments, 9×10 -10 S / cm≤b-b'≤8×10 -9 S / cm.

[0011] In some embodiments, b' is 1×10 -10 S / cm~8×10 -9 S / cm, b is 1×10 -8 S / cm~4×10 -8 The electronic conductivity of the first lithium-containing active material and the second lithium-containing active material are respectively within the aforementioned ranges, which can make the rate performance of the battery better.

[0012] In some embodiments, the first lithium-containing positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese aluminum oxide. The positive electrode active material has high electronic conductivity and low ionic conductivity.

[0013] In some embodiments, the second lithium-containing active material includes a phosphate system material and / or a vanadate system material. The positive electrode active material has a low ion conductivity and a high electronic conductivity.

[0014] In some embodiments, the phosphate system material includes LiMPO4, wherein M includes Mn and non-Mn elements, and the non-Mn elements include manganese-site doping elements.

[0015] In some embodiments, the non-Mn element further includes a phosphorus-site doping element.

[0016] In some embodiments, the manganese-site doping element includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge.

[0017] In some embodiments, the manganese-site doping element includes at least two of Fe, Ti, V, Ni, Co, and Mg.

[0018] In some embodiments, the phosphorus-site doping element includes one or more elements of B, S, Si, and N.

[0019] In some embodiments, the second lithium-containing active material includes a chemical formula of Li a Mn 1-b A b P 1-c R c O4 compound, a is selected from the range of 0.9 to 1.1, b is selected from the range of 0.001 to 0.500, c is selected from the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge; R includes one or more elements selected from B, S, Si and N.

[0020] In some embodiments, the second lithium-containing active material includes a chemical formula of Li d A x Mn 1-y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B, S, Si and N, and D includes one or more elements selected from S, F, Cl and Br.

[0021] In some embodiments, the phosphate system material further comprises lithium iron phosphate.

[0022] In some embodiments, the vanadate system material includes Li3VO4 and / or Li2VO3.

[0023] In some embodiments, the first lithium-containing active material includes a lithium nickel cobalt manganese oxide material; and the second lithium-containing active material includes a lithium iron phosphate material.

[0024] In some embodiments, the first lithium-containing active material comprises a lithium nickel cobalt manganese oxide material; the second lithium-containing active material comprises Li d Ax Mn 1-y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B, S, Si and N, and D includes one or more elements selected from S, F, Cl and Br.

[0025] In some embodiments, the first lithium-containing active material includes a lithium iron phosphate material, and the second lithium-containing active material includes Li d A x Mn 1-y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B, S, Si and N, and D includes one or more elements selected from S, F, Cl and Br.

[0026] In some embodiments, the thickness of the second positive electrode active layer is greater than the thickness of the first positive electrode active layer, which can further improve the rate performance of the battery.

[0027] In some embodiments, the ratio of the thickness of the second positive electrode active layer to the thickness of the first positive electrode active layer is 1.2 to 1.6.

[0028] In some embodiments, the amount of the second lithium-containing active material added is greater than the amount of the first lithium-containing active material added, which can further improve the rate performance of the battery.

[0029] In some embodiments, the ratio of the amount of the second lithium-containing active material added to the amount of the first lithium-containing active material added is 1.2 to 1.6.

[0030] In a second aspect, the present application provides a battery, comprising the positive electrode plate provided in any one of the first aspects.

[0031] In a third aspect, the present application provides an electrical device, comprising the battery provided in the second aspect.

[0032] The above description is only an overview of the technical solution of the present application. In order to more clearly understand the technical means of the present application, it can be implemented in accordance with the contents of the specification. In order to make the above and other purposes, features and advantages of the present application more obvious and easy to understand, the specific implementation methods of the present application are listed below. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0034] Figure 1 A schematic diagram of the structure of a vehicle provided in some embodiments of the present application;

[0035] Figure 2 A schematic diagram of the exploded structure of a battery provided in some embodiments of the present application;

[0036] Figure 3 A schematic diagram of the structure of a battery cell provided in some embodiments of the present application;

[0037] Figure 4 An exploded view of a battery cell provided for some embodiments of the present application;

[0038] Figure 5 A schematic diagram of the first layer structure of a positive electrode sheet provided in some embodiments of the present application;

[0039] Figure 6 Schematic diagram of the second layer structure of the positive electrode plate provided in some embodiments of the present application.

[0040] Icons: 1000-vehicle; 100-battery; 10-casing; 11-accommodating space; 12-first part; 13-second part; 20-battery cell; 21-casing; 211-opening; 22-end cover assembly; 221-end cover; 222-electrode terminal; 23-electrode assembly; 231-positive electrode plate; 2311-positive current collector; 2312a-first positive active layer; 2312b-second positive active layer; 2312c-third positive active layer; 24-current collecting member; 25-insulating protection member; 200-controller; 300-motor. DETAILED DESCRIPTION

[0041] The following embodiments of the technical solution of the present application are described in detail in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0043] In the description of the embodiments of the present application, the technical terms "first", "second", etc. are only used to distinguish different objects, and cannot be understood as indicating or implying relative importance or implicitly indicating the number, specific order or primary and secondary relationship of the indicated technical features. In the description of the embodiments of the present application, the meaning of "multiple" is more than two, unless otherwise clearly and specifically defined.

[0044] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0045] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0046] In the description of the embodiments of the present application, the term "multiple" refers to more than two (including two). Similarly, "multiple groups" refers to more than two groups (including two groups), and "multiple pieces" refers to more than two pieces (including two pieces).

[0047] In the description of the embodiments of the present application, the technical terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings. They are only for the convenience of describing the embodiments of the present application and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the embodiments of the present application.

[0048] In the description of the embodiments of the present application, unless otherwise clearly specified and limited, technical terms such as "installed", "connected", "connected", "fixed" and the like 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 a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of two elements or the interaction relationship between two elements. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present application can be understood according to the specific circumstances.

[0049] At present, from the perspective of market development, the application of power batteries is becoming more and more extensive. Power batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of the application field of power batteries, the market demand is also constantly expanding.

[0050] The power battery can be a lithium-ion battery. During the charging process of the lithium-ion battery, lithium ions are released from the positive electrode active material, transmitted through the electrolyte, passed through the isolation membrane, and embedded in the negative electrode active material. In order to take into account the comprehensive performance of the positive electrode plate, positive electrode active materials with different properties are usually mixed to form a positive electrode active layer. If the ionic conductivity of the two mixed positive electrode active materials is very different, the kinetic performance of the entire battery will be poor. Therefore, two positive electrode active materials with large differences in ionic conductivity are usually arranged in layers to form two different positive electrode active layers. However, it is difficult to improve the rate performance of the battery by simply arranging two positive electrode active materials with large differences in ionic conductivity in layers.

[0051] Based on the above considerations, in order to improve the rate performance of the battery to a certain extent, after in-depth research, a positive electrode plate was designed, including a positive electrode collector and a first positive electrode active layer and a second positive electrode active layer sequentially arranged on at least one side of the positive electrode collector; the first positive electrode active layer includes a first lithium-containing active material, the ion conductivity of the first lithium-containing active material is a, and the electronic conductivity is b; the second positive electrode active layer includes a second lithium-containing active material, the ion conductivity of the second lithium-containing active material is a', and the electronic conductivity is b'; wherein, a<a', b>b'.

[0052] In such a positive electrode sheet, two lithium-containing active materials with large differences in ion conductivity and electronic conductivity are arranged in layers, which can avoid the mutual influence of the performance of the materials and make the performance of each material better. In addition, the second lithium-containing active material with higher ion conductivity and lower electronic conductivity is concentrated on the surface of the positive electrode sheet, which can be beneficial to the transmission of lithium ions, and the first lithium-containing active material with lower ion conductivity and higher electronic conductivity is concentrated on the bottom layer of the positive electrode sheet, which can make the electron transmission effect better, thereby improving the rate performance of the battery.

[0053] The positive electrode sheet can be used to prepare an electrode assembly, which can be assembled into a battery. The battery can be a battery cell, a module, a battery pack, etc. The battery can be used in, but not limited to, electrical equipment such as vehicles, ships, or aircraft. The battery disclosed in this application can be used to form a power supply system for the electrical equipment, which is conducive to improving the rate performance of the battery.

[0054] The embodiment of the present application provides an electric device that uses a battery as a power source. The electric device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle, and the like; the spacecraft includes an airplane, a rocket, a space shuttle, and a spacecraft, and the like; the electric toy includes a fixed or mobile electric toy, such as a game console, an electric car toy, an electric ship toy, and an electric airplane toy, and the like; the electric tool includes a metal cutting electric tool, a grinding electric tool, an assembly electric tool, and an electric tool for railways, such as an electric drill, an electric grinder, an electric wrench, an electric screwdriver, an electric hammer, an impact drill, a concrete vibrator, and an electric planer, and the like. The embodiment of the present application does not impose any special restrictions on the above-mentioned electric devices.

[0055] For the convenience of description, the following embodiments are described by taking the electric device as a vehicle as an example.

[0056] Please refer to Figure 1 , Figure 1The schematic diagram of the structure of the vehicle 1000 provided in some embodiments of the present application. The vehicle 1000 is provided with a battery 100 inside, and the battery 100 can be provided at the bottom, head or tail of the vehicle 1000. The battery 100 can be used to power the vehicle 1000, for example, the battery 100 can be used as an operating power source of the vehicle 1000.

[0057] The vehicle 1000 may further include a controller 200 and a motor 300 , wherein the controller 200 is used to control the battery 100 to supply power to the motor 300 , for example, to meet the power requirements of starting, navigating, and driving the vehicle 1000 .

[0058] In some embodiments of the present application, the battery 100 can not only serve as an operating power source for the vehicle 1000, but also serve as a driving power source for the vehicle 1000, replacing or partially replacing fuel or natural gas to provide driving power for the vehicle 1000.

[0059] Figure 2 This is a schematic diagram of the exploded structure of the battery 100 provided in some embodiments of the present application. Figure 2 The battery 100 includes a housing 10 and a battery cell 20 , and the battery cell 20 is accommodated in the housing 10 .

[0060] The box body 10 is used to provide a storage space 11 for the battery cell 20. In some embodiments, the box body 10 may include a first portion 12 and a second portion 13, and the first portion 12 and the second portion 13 cover each other to define the storage space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 can be sealed by a sealing member (not shown in the figure), and the sealing member can be a sealing ring, a sealant, etc.

[0061] The first part 12 and the second part 13 can be in various shapes, such as a cuboid, a cylinder, etc. The first part 12 can be a hollow structure with one side open to form a receiving cavity for receiving the battery cell 20, and the second part 13 can also be a hollow structure with one side open to form a receiving cavity for receiving the battery cell 20. The opening side of the second part 13 covers the opening side of the first part 12, thereby forming a box body 10 with a receiving space 11. Of course, if Figure 2 As shown, the first part 12 may be a hollow structure with one side open, and the second part 13 may be a plate-like structure. The second part 13 covers the open side of the first part 12 to form a box body 10 with an accommodating space 11.

[0062] In the battery 100, there can be one or more battery cells 20. If there are more than one battery cell 20, the battery cells 20 can be connected in series, in parallel or in a mixed connection. A mixed connection means that the battery cells 20 are connected in series and in parallel. The battery cells 20 can be directly connected in series, in parallel or in a mixed connection, and then the whole formed by the battery cells 20 can be accommodated in the box 10; of course, the battery cells 20 can be connected in series, in parallel or in a mixed connection to form a battery module, and then the battery modules can be connected in series, in parallel or in a mixed connection to form a whole, and then accommodated in the box 10. The battery cell 20 can be cylindrical, flat, rectangular or in other shapes. Figure 2 The example shows that the battery cell 20 is in a square shape.

[0063] In some embodiments, the battery 100 may further include a busbar component (not shown), and the multiple battery cells 20 may be electrically connected via the busbar component to achieve series connection, parallel connection, or mixed connection of the multiple battery cells 20 .

[0064] Figure 3 This is a schematic diagram of the structure of a battery cell 20 provided in some embodiments of the present application. Figure 4 This is an exploded view of a battery cell 20 provided in some embodiments of the present application. Figure 3 and Figure 4 The battery cell 20 may include a housing 21 , an end cap assembly 22 and an electrode assembly 23 . The housing 21 has an opening 211 , the electrode assembly 23 is accommodated in the housing 21 , and the end cap assembly 22 is used to cover the opening 211 .

[0065] The shape of the housing 21 can be determined according to the specific shape of the electrode assembly 23. For example, if the electrode assembly 23 is a rectangular parallelepiped structure, the housing 21 can be a rectangular parallelepiped structure. Figure 3 and Figure 4 The case where the housing 21 and the electrode assembly 23 are square is exemplarily shown.

[0066] The shell 21 may also be made of a variety of materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc., and the embodiment of the present application does not impose any special restrictions on this.

[0067] The end cap assembly 22 includes an end cap 221 and an electrode terminal 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a closed installation space (not shown), and the installation space is used to accommodate the electrode assembly 23. The installation space is also used to accommodate an electrolyte, such as an electrolyte. The end cap assembly 22 is a component for outputting the electrical energy of the electrode assembly 23. The electrode terminal 222 in the end cap assembly 22 is used to be electrically connected to the electrode assembly 23, that is, the electrode terminal 222 is electrically connected to the tab of the electrode assembly 23. For example, the electrode terminal 222 is connected to the tab through the current collecting member 24 to achieve electrical connection between the electrode terminal 222 and the tab.

[0068] It should be noted that the opening 211 of the shell 21 can be one or two. If the opening 211 of the shell 21 is one, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22, and the two electrode terminals 222 are respectively used to electrically connect to the positive pole ear and the negative pole ear of the electrode assembly 23. If the opening 211 of the shell 21 is two, for example, the two openings 211 are provided on opposite sides of the shell 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 are respectively covered at the two openings 211 of the shell 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, which is used to electrically connect to the positive pole ear of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, which is used to electrically connect to the negative pole piece of the electrode assembly 23.

[0069] In some embodiments, Figure 4 As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the periphery of the electrode assembly 23, and the insulating protective member 25 is used to insulate and isolate the electrode assembly 23 from the housing 21. Exemplarily, the insulating protective member 25 is a tape bonded to the periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 is arranged around the periphery of the multiple electrode assemblies 23, and the multiple electrode assemblies 23 are formed into an integral structure to maintain the stability of the electrode assembly 23 structure. Among them, the electrode assembly 23 can be a wound electrode assembly or a laminated electrode assembly, and the embodiments of the present application are not limited thereto.

[0070] The electrode assembly 23 includes a positive electrode sheet, a negative electrode sheet and a separator. The separator may be made of PP (polypropylene) or PE (polyethylene).

[0071] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer, wherein the negative electrode active material layer is disposed on the surface of the negative electrode current collector, and the negative electrode current collector not coated with the negative electrode active material layer protrudes from the negative electrode current collector coated with the negative electrode active material layer, and the negative electrode current collector not coated with the negative electrode active material layer serves as a negative electrode tab. Among them, the material of the negative electrode current collector may be one or more of copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, and the negative electrode active material may be a carbon material, a silicon material, a silicon-carbon composite material, etc.

[0072] Figure 5 For a schematic diagram of the first layer structure of the positive electrode sheet 231 provided in some embodiments of the present application, please refer to Figure 5The positive electrode plate 231 includes a positive electrode collector 2311, a first positive electrode active layer 2312a and a second positive electrode active layer 2312b sequentially arranged on the positive electrode collector 2311, the first positive electrode active layer 2312a includes a first lithium-containing active material, the ion conductivity of the first lithium-containing active material is a, and the electronic conductivity is b, the second positive electrode active layer 2312b includes a second lithium-containing active material, the ion conductivity of the second lithium-containing active material is a', and the electronic conductivity is b'; wherein, a<a', b>b'.

[0073] The material of the positive electrode current collector 2311 can be one or more of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy. The first lithium-containing active material and the second lithium-containing active material indicate that the present application is mainly based on the improvement of lithium-ion batteries. The positive electrode sheet 231 in the present application is the positive electrode sheet 231 of a lithium-ion battery.

[0074] The test method for the electronic conductivity b' of the second lithium-containing active material is: scrape a portion of the second positive electrode active layer 2312b, soak it in the solvent NMP, wash out the binder in the second positive electrode active layer 2312b, obtain a powder material, and test the electronic conductivity b' of the powder material.

[0075] The test method for the electronic conductivity b of the first lithium-containing active material is: slice the positive electrode sheet 231, the interface between the first positive electrode active layer 2312a and the second positive electrode active layer 2312b can be observed, the second positive electrode active layer 2312b is completely scraped off, and then a portion of the first positive electrode active layer 2312a is scraped off, and it is immersed in the solvent NMP to wash out the binder in the first positive electrode active layer 2312a to obtain a powder material, and the electronic conductivity of the powder material is tested to be b.

[0076] The test method for the ionic conductivity a' of the second lithium-containing active material is as follows: scrape a portion of the second positive electrode active layer 2312b, prepare it into a symmetrical battery to test the alternating current impedance EIS, take the impedance R of 10-15KHz, and calculate the ionic conductivity σ according to σ=L / (R×S), where S is the area of ​​the symmetrical battery electrode and L is the thickness of the positive electrode active layer of the symmetrical battery.

[0077] The testing method for the ionic conductivity a of the first lithium-containing active material is as follows: the positive electrode plate 231 is sliced, the interface between the first positive electrode active layer 2312a and the second positive electrode active layer 2312b can be observed, the second positive electrode active layer 2312b is completely scraped off, and then a portion of the first positive electrode active layer 2312a is scraped off to prepare a symmetrical battery to test the alternating current impedance EIS, and an impedance R of 10-15KHz is taken, and the ionic conductivity σ is calculated according to σ=L / (R×S), where S is the area of ​​the symmetrical battery plate and L is the thickness of the positive electrode active layer of the symmetrical battery.

[0078] In the technical solution of the embodiment of the present application, two lithium-containing active materials with large differences in ionic conductivity and electronic conductivity are arranged in layers, which can avoid the mutual influence of the performance between the materials and make the performance of each material better. In addition, the second lithium-containing active material with higher ionic conductivity and lower electronic conductivity is concentrated on the surface of the positive electrode plate 231, which can be beneficial to the transmission of lithium ions, and the first lithium-containing active material with lower ionic conductivity and higher electronic conductivity is concentrated on the bottom layer of the positive electrode plate, which can make the electron transmission effect better, thereby improving the rate performance of the battery.

[0079] In some embodiments, the relationship between the ionic conductivity a of the first lithium-containing active material and the ionic conductivity a' of the second lithium-containing active material is: a'-a≥9×10 -10 When the difference in ionic conductivity between the first lithium-containing active material and the second lithium-containing active material is within this range, the lithium ion transmission effect of the entire positive electrode sheet 231 can be improved, so that the rate performance of the battery 100 is improved.

[0080] As an example, the difference between the ionic conductivity a' of the second lithium-containing active material and the ionic conductivity a of the first lithium-containing active material is 9×10 -10 S / cm, 1×10 -9 S / cm, 2×10 -9 S / cm, 3×10 -9 S / cm, 4×10 -9 S / cm, 5×10 -9 S / cm, 6×10 -9 S / cm, 7×10 -9 S / cm, 8×10 -9 S / cm, 9×10 -9 S / cm, 1×10 -8 S / cm, 2×10 -8 S / cm, 3×10 -8 S / cm, 4×10 -8 S / cm or 5×10 -8 S / cm, etc., and of course other values ​​within the above range are also possible. Optionally, 9×10 -10 S / cm≤a'-a≤8×10 -9 S / cm.

[0081] In some embodiments, 1×10 -11 S / cm≤a≤9×10 -11 S / cm; 1×10 -9 S / cm≤a'≤1×10 -8S / cm. The ionic conductivities of the first lithium-containing active material and the second lithium-containing active material are respectively within the aforementioned ranges, which can make the rate performance of the battery 100 better.

[0082] As an example, the ionic conductivity a of the first lithium-containing active material is 1×10 -11 S / cm, 2×10 -11 S / cm, 3×10 -11 S / cm, 4×10 -11 S / cm, 5×10 -11 S / cm, 6×10 -11 S / cm, 7×10 -11 S / cm, 8×10 -11 S / cm or 9×10 -11 S / cm, etc., and of course other values ​​within the above range are also possible. The ionic conductivity a' of the second lithium-containing active material is 1×10 -9 S / cm, 2×10 -9 S / cm, 3×10 -9 S / cm, 4×10 -9 S / cm, 5×10 -9 S / cm, 6×10 -9 S / cm, 7×10 -9 S / cm, 8×10 -9 S / cm, 9×10 -9 S / cm or 1×10 -8 S / cm, etc., and may of course also be other values ​​within the above range.

[0083] In some embodiments, the electronic conductivity b of the first lithium-containing active material and the electronic conductivity b' of the second lithium-containing active material are related by: b-b'≥9×10 -10 When the difference in the electronic conductivity of the first lithium-containing active material and the second lithium-containing active material is within this range, the electron transmission effect of the entire positive electrode plate 231 can be improved, so that the rate performance of the battery 100 can be improved.

[0084] As an example, the difference between the electronic conductivity b of the first lithium-containing active material and the electronic conductivity b' of the second lithium-containing active material is 9×10 -10 S / cm, 1×10 -9 S / cm, 2×10 -9 S / cm, 3×10 -9 S / cm, 4×10 -9 S / cm, 5×10 -9 S / cm, 6×10 -9 S / cm, 7×10 -9 S / cm, 8×10-9 S / cm, 9×10 -9 S / cm, 1×10 -8 S / cm, 2×10 -8 S / cm, 3×10 -8 S / cm, 4×10 -8 S / cm or 5×10 -8 S / cm, etc., and of course other values ​​within the above range are also possible. Optionally, 9×10 -10 S / cm≤b-b'≤8×10 -9 S / cm.

[0085] In some embodiments, b' is 1×10 -10 S / cm~8×10 -9 S / cm, b is 1×10 -8 S / cm~4×10 -8 The electronic conductivities of the first lithium-containing active material and the second lithium-containing active material are respectively within the aforementioned ranges, which can make the rate performance of the battery 100 better.

[0086] As an example, the electronic conductivity b' of the second lithium-containing active material is 1×10 -10 S / cm, 2×10 - 10 S / cm, 3×10 -10 S / cm, 4×10 -10 S / cm, 5×10 -10 S / cm, 6×10 -10 S / cm, 7×10 -10 S / cm, 8×10 -10 S / cm, 9×10 -10 S / cm, 1×10 -9 S / cm, 2×10 -9 S / cm, 3×10 -9 S / cm, 4×10 -9 S / cm, 5×10 -9 S / cm, 6×10 -9 S / cm, 7×10 -9 S / cm or 8×10 -9 S / cm, etc., and of course other values ​​within the above range are also possible. The electronic conductivity b of the first lithium-containing active material is 1×10 -8 S / cm, 2×10 -8 S / cm, 3×10 -8 S / cm or 4×10 -8 S / cm, etc., and may of course also be other values ​​within the above range.

[0087] In some embodiments, the first lithium-containing positive electrode active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and lithium nickel cobalt manganese aluminum oxide. The positive electrode active material has high electronic conductivity and low ionic conductivity.

[0088] Optionally, the lithium nickel cobalt manganese oxide includes a chemical formula of LiNi x Co y Mn 1-x-y O2 compound, wherein 0<x<1, 0<y<1. As an example, lithium nickel cobalt manganese oxide includes a chemical formula of LiNi 0.4 Co 0.2 Mn 0.4 O2 compound, chemical formula is LiNi 0.5 Co 0.1 Mn 0.4 O2 compound, chemical formula is LiNi 0.4 Co 0.1 Mn 0.5 The compound and chemical formula of O2 is LiNi 0.8 Co 0.1 Mn 0.1 At least one of the compounds of O2.

[0089] Optionally, the lithium nickel cobalt aluminum oxide comprises a chemical formula of LiNi x Co y Al 1-x-y O2 compound, wherein 0<x<1, 0<y<1. As an example, lithium nickel cobalt aluminum oxide includes a chemical formula of LiNi 0.4 Co 0.2 Al 0.4 O2 compound, chemical formula is LiNi 0.5 Co 0.1 Al 0.4 O2 compound, chemical formula is LiNi 0.4 Co 0.1 Al 0.5 The compound and chemical formula of O2 is LiNi 0.8 Co 0.1 Al 0.1 At least one of the compounds of O2.

[0090] Optionally, the lithium nickel cobalt manganese aluminum oxide comprises a chemical formula of LiNi x Co y Mn z Al 1-x-y-z O2 compound, wherein 0<x<1, 0<y<1, 0<z<1. As an example, lithium nickel cobalt manganese aluminum oxide includes a chemical formula of LiNi 0.4 Co 0.2 Mn 0.2 Al0.2 O2 compound, chemical formula is LiNi 0.5 Co 0.1 Mn 0.2 Al 0.2 O2 compound, chemical formula is LiNi 0.4 Co 0.1 Mn 0.3 Al 0.2 The compound and chemical formula of O2 is LiNi 0.8 Co 0.1 Mn 0.05 Al 0.05 At least one of the compounds of O2. In some embodiments, the second lithium-containing active material includes a phosphate system material and / or a vanadate system material. The positive electrode active material has a low ion conductivity and a high electronic conductivity.

[0091] In some embodiments, the phosphate system material includes LiMPO4, wherein M includes Mn and non-Mn elements, and the non-Mn elements include manganese-site doping elements.

[0092] In some embodiments, the non-Mn element further includes a phosphorus-site doping element.

[0093] In some embodiments, the manganese-site doping element includes one or more elements of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge.

[0094] In some embodiments, the manganese-site doping element includes at least two of Fe, Ti, V, Ni, Co, and Mg.

[0095] In some embodiments, the phosphorus-site doping element includes one or more elements of B, S, Si, and N.

[0096] In some embodiments, the second lithium-containing active material includes a chemical formula of Li a Mn 1-b A b P 1-c R c O4 compound, a is selected from the range of 0.9 to 1.1, b is selected from the range of 0.001 to 0.500, c is selected from the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge; R includes one or more elements selected from B, S, Si and N.

[0097] As an example, the second lithium-containing active material includes a LiMn 0.9 Al 0.1 P0.9 S 0.1 O4 compound, chemical formula is Li 1.1 Mn 0.95 Ti 0.05 P 0.9 B 0.1 The compound and chemical formula of O4 is Li 0.9 Mn 0.9 Ni 0.1 P 0.95 Si 0.05 At least one of the compounds of O4.

[0098] In some embodiments, the second lithium-containing active material includes a chemical formula of Li d A x Mn 1-y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B, S, Si and N, and D includes one or more elements selected from S, F, Cl and Br.

[0099] As an example, the second lithium-containing active material includes a chemical formula of LiK 0.1 Mn 0.9 Ni 0.1 P 0.9 S 0.1 O 3.95 F 0.05 The compound with the chemical formula Li 0.95 Na 0.05 Mn 0.95 Ti 0.05 P 0.9 B 0.1 O 3.95 Cl 0.05 Compounds with the chemical formula Li 1.05 Mg 0.001 Mn 0. 9V 0.1 P 0.95 N 0.05 O 3.95 Br 0.05 The compound and chemical formula is Li1.001 Mn 0.999 Fe 0.001 P 0.999 Si 0.001 At least one of the compounds of O4. Among them, the compound Li 1.001 Mn 0.999 Fe 0.001 P 0.999 Si 0.001 The preparation method of O4 includes:

[0100] Step S1: Preparation of Fe-doped manganese oxalate:

[0101] 1148.2g of manganese carbonate and 1.2g of ferrous carbonate were added to a mixer and mixed thoroughly for 6h. The obtained mixture was then transferred to a reactor, and 5L of deionized water and 1260.6g of dihydrated oxalic acid were added, heated to 80°C, and stirred at a speed of 500rpm for 6h, mixed evenly until the reaction was terminated and no bubbles were generated, to obtain an Fe-doped manganese oxalate suspension. The suspension was then filtered, dried at 120°C, and sand-milled to obtain manganese oxalate iron particles with a particle size of 100nm.

[0102] Step S2: Preparation of Li 1.001 Mn 0.999 Fe 0.001 P 0.999 Si 0.001 O4:

[0103] Take the ferromanganese oxalate (C2O4Mn 0.999 Fe 0.001 ·2H2O) 1789.6g and 369.8g lithium carbonate, 1148.9g diammonium phosphate and 0.8g silicic acid were added to 20L deionized water, fully stirred, and uniformly mixed and reacted at 80°C for 10h to obtain slurry. The slurry was transferred to a spray drying device for spray drying and granulation, and dried at a temperature of 250°C to obtain a powder. The powder was sintered in a roller kiln at 700°C for 4h in a protective atmosphere (90% nitrogen and 10% hydrogen).

[0104] The preparation steps of lithium manganese iron phosphate material doped with other elements (such as Ti) are the same as the preparation steps of the aforementioned compounds, except that silicic acid is replaced as the source of the corresponding element (such as titanium tetrachloride) and the raw material ratio is adjusted to satisfy the molar ratio in the chemical formula of the corresponding compound.

[0105] In some embodiments, the phosphate system material further comprises lithium iron phosphate. Optionally, the chemical formula of lithium iron phosphate is LiFe x M 1-xPO4, wherein 0.5<x≤1 (equal to 1, representing no doping element M), M includes one or more elements selected from the group consisting of Mn, Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge.

[0106] In some embodiments, the vanadate system material includes Li3VO4 and / or Li2VO3.

[0107] In some embodiments, the first lithium-containing active material includes a lithium nickel cobalt manganese oxide material; and the second lithium-containing active material includes a lithium iron manganese phosphate material.

[0108] In some embodiments, the first lithium-containing active material comprises a lithium nickel cobalt manganese oxide material; the second lithium-containing active material comprises Li d A x Mn 1-y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B, S, Si and N, and D includes one or more elements selected from S, F, Cl and Br.

[0109] In some embodiments, the first lithium-containing active material includes a lithium iron phosphate material, and the second lithium-containing active material includes Li d A x Mn 1-y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B, S, Si and N, and D includes one or more elements selected from S, F, Cl and Br.

[0110] It should be noted that once the chemical formula composition of the first lithium-containing active material is determined, it does not mean that the unique ionic conductivity and electronic conductivity of the material can be known. In fact, the ionic conductivity and electronic conductivity of the first lithium-containing active material are not only related to the chemical formula composition of the first lithium-containing active material, but also to its preparation method, the particle size distribution of the material, the impurity content in the material and the type of impurities. The ionic conductivity and electronic conductivity of first lithium-containing active materials of the same composition but different models from the same manufacturer are different. The ionic conductivity and electronic conductivity of first lithium-containing active materials of the same composition from different manufacturers may also be different. The present application is to confirm the selection of the first positive electrode active material through the composition, ionic conductivity and electronic conductivity of the first lithium-containing active material. Once the chemical formula composition of the second lithium-containing active material is determined, it is not possible to know the unique ionic conductivity and electronic conductivity of the material. In fact, the ionic conductivity and electronic conductivity of the second lithium-containing active material are not only related to the chemical formula composition of the second lithium-containing active material, but also to its preparation method, the particle size distribution of the material, the impurity content in the material and the type of impurities. The ionic conductivity and electronic conductivity of second lithium-containing active materials of the same composition but different models from the same manufacturer are different. The ionic conductivity and electronic conductivity of second lithium-containing active materials of the same composition from different manufacturers may also be different. The present application is to confirm the selection of the second positive electrode active material through the composition, ionic conductivity and electronic conductivity of the second lithium-containing active material.

[0111] The battery will be accompanied by Li deintercalation and consumption during the charging and discharging process, and the molar content of Li is different when the battery is discharged to different states. In the list of positive electrode active materials in this application, the molar content of Li is the initial state of the material, that is, the state before feeding. The positive electrode active material is used in the battery system, and the molar content of Li will change after the charge and discharge cycle. In the list of positive electrode active materials in this application, the molar content of O is only a theoretical state value. The release of oxygen from the lattice will cause the molar content of oxygen to change, and the actual molar content of O will fluctuate.

[0112] In some embodiments, the thickness of the second positive electrode active layer 2312b is greater than the thickness of the first positive electrode active layer 2312a, which can further improve the battery rate performance.

[0113] In some embodiments, the ratio of the thickness of the second positive electrode active layer 2312b to the thickness of the first positive electrode active layer 2312a is 1.2 to 1.6. As an example, the ratio of the thickness of the second positive electrode active layer 2312b to the thickness of the first positive electrode active layer 2312a is 1.2, 1.3, 1.4, 1.5 or 1.6.

[0114] In some embodiments, the amount of the second lithium-containing active material added is greater than the amount of the first lithium-containing active material added, which can further improve the rate performance of the battery.

[0115] In some embodiments, the ratio of the amount of the second lithium-containing active material added to the amount of the first lithium-containing active material added is 1.2 to 1.6. As an example, the ratio of the amount of the second lithium-containing active material added to the amount of the first lithium-containing active material added is 1.2, 1.3, 1.4, 1.5 or 1.6.

[0116] Figure 6 For a schematic diagram of the second layer structure of the positive electrode sheet provided in some embodiments of the present application, please refer to Figure 6 , see Figure 6 The positive electrode plate 231 includes a positive electrode collector 2311, a first positive electrode active layer 2312a, a second positive electrode active layer 2312b and a third positive electrode active layer 2312c sequentially arranged on the positive electrode collector 2311, the first positive electrode active layer 2312a includes a first lithium-containing active material, the ion conductivity of the first lithium-containing active material is X, and the electronic conductivity is x, the second positive electrode active layer 2312b includes a second lithium-containing active material, the ion conductivity of the second lithium-containing active material is Y, and the electronic conductivity is y, the third positive electrode active layer 2312c includes a third lithium-containing active material, the ion conductivity of the third lithium-containing active material is Z, and the electronic conductivity is z; wherein, X<Y<Z, x>y>z.

[0117] The testing method for the electronic conductivity z of the third lithium-containing active material is: scrape a portion of the third positive electrode active layer 2312c, soak it in the solvent NMP, wash out the binder in the third positive electrode active layer 2312c, obtain a powder material, and test the electronic conductivity z of the powder material.

[0118] The testing method for the electronic conductivity y of the second lithium-containing active material is as follows: the positive electrode sheet 231 is sliced, the interface between the second positive electrode active layer 2312b and the third positive electrode active layer 2312c can be observed, the third positive electrode active layer 2312c is completely scraped off, and then a portion of the second positive electrode active layer 2312b is scraped off, and it is soaked in the solvent NMP, the binder in the second positive electrode active layer 2312b is washed out, and a powder material is obtained. The electronic conductivity of the powder material is tested to be y.

[0119] The testing method for the electronic conductivity x of the first lithium-containing active material is as follows: the positive electrode sheet 231 is sliced, the interface between the first positive electrode active layer 2312a and the second positive electrode active layer 2312b can be observed, the second positive electrode active layer 2312b and the third positive electrode active layer 2312c are completely scraped off, and then a portion of the first positive electrode active layer 2312a is scraped off and immersed in the solvent NMP to wash out the binder in the first positive electrode active layer 2312a to obtain a powder material, and the electronic conductivity of the powder material is tested to be x.

[0120] The testing method for the ionic conductivity Z of the third lithium-containing active material is as follows: scrape a portion of the third positive electrode active layer 2312c, prepare it into a symmetrical battery to test the AC impedance EIS, take the impedance R of 10-15KHz, and calculate the ionic conductivity σ according to σ=L / (R×S), where S is the area of ​​the symmetrical battery electrode and L is the thickness of the positive electrode active layer of the symmetrical battery.

[0121] The testing method for the ionic conductivity Y of the second lithium-containing active material is as follows: the positive electrode plate 231 is sliced, the interface between the second positive electrode active layer 2312b and the third positive electrode active layer 2312c can be observed, the third positive electrode active layer 2312c is completely scraped off, and then a portion of the second positive electrode active layer 2312b is scraped off to prepare a symmetrical battery to test the AC impedance EIS, and the impedance R of 10-15KHz is taken, and the ionic conductivity σ is calculated according to σ=L / (R×S), where S is the area of ​​the symmetrical battery plate and L is the thickness of the positive electrode active layer of the symmetrical battery.

[0122] The testing method for the ionic conductivity X of the first lithium-containing active material is as follows: the positive electrode plate 231 is sliced, and the interface between the first positive electrode active layer 2312a and the second positive electrode active layer 2312b can be observed. The second positive electrode active layer 2312b and the third positive electrode active layer 2312c are completely scraped off, and then a portion of the first positive electrode active layer 2312a is scraped off to prepare a symmetrical battery to test the alternating current impedance EIS, and an impedance R of 10-15KHz is taken. According to σ=L / (R×S), the ionic conductivity σ is calculated, where S is the area of ​​the symmetrical battery plate and L is the thickness of the positive electrode active layer of the symmetrical battery.

[0123] In the technical solution of the embodiment of the present application, the ionic conductivity of the lithium-containing active material gradually increases and the electronic conductivity gradually decreases along the direction from close to the positive electrode current collector 2311 to away from the positive electrode current collector 2311, so that the electron transmission and lithium ion transmission effects of the positive electrode plate 231 can be better, so that the battery's rate performance is better.

[0124] After the structure of the positive electrode plate 231 is introduced above, the preparation method of the positive electrode plate 231 is specifically introduced below.

[0125] In some embodiments, the positive electrode active layer of the positive electrode sheet 231 is a double-layer structure, and the preparation method of the positive electrode sheet 231 includes:

[0126] S110 , dispersing a first active material, a first conductive agent, and a first binder in a solvent to form a first active slurry.

[0127] S120, dispersing the second active material, the second conductive agent and the second binder in a solvent to form a second active slurry.

[0128] S130, coating the first active slurry on the surface of the positive electrode current collector 2311, and forming a first positive electrode active layer 2312a after drying; coating the second active slurry on the surface of the first positive electrode active layer 2312a, and forming a second positive electrode active layer 2312b after drying, to obtain the positive electrode sheet 231.

[0129] In some other embodiments, the positive electrode active layer of the positive electrode plate 231 is a three-layer structure, and the preparation method of the positive electrode plate 231 includes:

[0130] S210 , dispersing a first active material, a first conductive agent, and a first binder in a solvent to form a first active slurry.

[0131] S220 , dispersing a second active material, a second conductive agent, and a second binder in a solvent to form a second active slurry.

[0132] S230 , dispersing a third active material, a third conductive agent, and a third binder in a solvent to form a third active slurry.

[0133] S240, coating the first active slurry on the surface of the positive electrode collector 2311, and forming a first positive electrode active layer 2312a after drying; coating the second active slurry on the surface of the first positive electrode active layer 2312a, and forming a second positive electrode active layer 2312b after drying; coating the third active slurry on the surface of the second positive electrode active layer 2312b, and forming a third positive electrode active layer 2312c after drying, to obtain the positive electrode sheet 231.

[0134] After the positive electrode sheet 231 is prepared, the first isolation membrane, the positive electrode sheet 231, the second isolation membrane and the negative electrode sheet are stacked in sequence, wound to form a wound flat structure, and then hot pressed to obtain a wound electrode assembly 23; or, after the positive electrode sheet 231 is prepared, the positive electrode sheet 231, the isolation membrane, the negative electrode sheet, the isolation membrane, and so on are stacked in sequence to form a stacked electrode assembly 23.

[0135] The electrode assembly 23 can be used to prepare a battery cell 20 , and the battery cell 20 can be used to prepare a battery 100 and provide electrical energy to electrical devices.

[0136] Next, one or more embodiments are described in more detail with reference to the following examples. Of course, these examples do not limit the scope of one or more embodiments.

[0137] Experimental Example 1

[0138] (1) Preparation of positive electrode sheet:

[0139] A first lithium-containing active material, a conductive agent Super P, and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1.5:1.5 were mixed in a solvent N-methylpyrrolidone (NMP) to prepare a first active slurry with a solid content of 50 wt %.

[0140] A second lithium-containing active material, a conductive agent Super P, and a binder polyvinylidene fluoride (PVDF) in a mass ratio of 97:1.5:1.5 were mixed in a solvent N-methylpyrrolidone (NMP) to prepare a second active slurry with a solid content of 50 wt %.

[0141] The first active slurry was coated on the current collector aluminum foil (thickness of 6 μm) and dried at 85°C for 4 hours and then cold pressed to obtain the first positive electrode active layer; the second active slurry was coated on the first positive electrode active layer and dried at 85°C for 4 hours and then cold pressed to obtain the second positive electrode active layer; then the edges were trimmed and cut into pieces, and dried at 85°C under vacuum conditions for 4 hours to obtain the positive electrode sheet. Among them, the thickness of the single-side positive electrode active layer is 160 μm, and the specific parameters of the positive electrode sheet are shown in Tables 1 and 2.

[0142] (2) Preparation of negative electrode sheet:

[0143] Graphite, conductive agent Super P and binder polytetrafluoroethylene (PTFE) in a mass ratio of 95:2:3 were mixed in a solvent N-methylpyrrolidone (NMP) to prepare a negative electrode active slurry with a solid content of 50 wt%.

[0144] The negative electrode active slurry was coated on the current collector copper foil (thickness of 9 μm) and dried at 85°C for 4 hours, then cold pressed, and then trimmed and cut into pieces, and dried at 85°C under vacuum conditions for 4 hours to obtain a negative electrode sheet; wherein the thickness of the single-side negative electrode active layer was 150 μm.

[0145] (3) Preparation of electrode assembly:

[0146] The separator is made of PP (polypropylene) and has a thickness of 16 μm. The negative electrode sheet, the first separator, the positive electrode sheet and the second separator are stacked and then wound to form an electrode assembly.

[0147] (4) Preparation of battery cells:

[0148] The electrode lugs are welded, the electrode assembly is placed in the shell, and the electrolyte is injected (the electrolyte is 1M lithium hexafluorophosphate EC / DMC (1:1 vol%) solution), and then the battery cell is obtained through vacuum packaging, standing, forming, shaping and other processes.

[0149] Table 1 Some parameters of the positive electrode

[0150]

[0151] The performance of the battery cells prepared in the examples and comparative examples was tested:

[0152] (1) Ionic conductivity of the first lithium-containing active material and ionic conductivity of the second lithium-containing active material / S / cm:

[0153] Ionic conductivity of the second lithium-containing active material: scrape a portion of the second positive electrode active layer, prepare it into a symmetrical battery to test the alternating current impedance EIS, take the impedance R of 10-15KHz, and calculate the ionic conductivity σ according to σ=L / (R×S), where S is the area of ​​the symmetrical battery electrode and L is the thickness of the positive electrode active layer of the symmetrical battery.

[0154] Ionic conductivity of the first lithium-containing active material: The positive electrode sheet is sliced, and the interface between the first positive electrode active layer and the second positive electrode active layer can be observed. The second positive electrode active layer is completely scraped off, and then a portion of the first positive electrode active layer is scraped off to prepare a symmetrical battery to test the alternating current impedance EIS. The impedance R of 10-15KHz is taken, and the ionic conductivity σ is calculated according to σ=L / (R×S), where S is the area of ​​the symmetrical battery sheet and L is the thickness of the positive electrode active layer of the symmetrical battery.

[0155] (2) Ionic conductivity of the first lithium-containing active material and electronic conductivity of the second lithium-containing active material / S / cm:

[0156] Electronic conductivity of the second lithium-containing active material: Scrape a portion of the second positive electrode active layer, soak it in the solvent NMP, wash out the binder in the second positive electrode active layer to obtain a powder material, and test the electronic conductivity b' of the powder material.

[0157] Electronic conductivity of the first lithium-containing active material: Slice the positive electrode sheet, and the interface between the first positive electrode active layer and the second positive electrode active layer can be observed. Scrape off all the second positive electrode active layer, and then scrape off a portion of the first positive electrode active layer, soak it in the solvent NMP, wash out the binder in the first positive electrode active layer, and obtain a powder material. Test the electronic conductivity b of the powder material.

[0158] (3) Rate performance of battery cells / mAh / g:

[0159] Test method example: At 25°C, after the battery has been fully charged, let it stand for 30 minutes, then discharge it to 2.5V at a constant current of 0.1C. After standing for 1 hour, charge it to 4.25V at a constant current of 0.1C. Then, let it stand for 30 minutes, discharge it to 2.5V at a constant current of 0.1C. Let it stand for 1 hour, charge it to 4.25V at a constant current of 0.1C, charge it to 0.02C at a constant voltage, and record its actual capacity as C0. Next, discharge it to 2.0V at a constant current of 0.2C, let it stand for 1 hour, charge it to 4.25V at a constant current of 0.1C, charge it to 0.02C at a constant voltage, let it stand for 30 minutes, discharge it to 2.5V at a constant current of 1C, and record its actual capacity as C1. C1 / C0 is used as the rate characteristic at 1C. Next, let it stand for 1 hour, charge to 4.25V at 0.1C constant current, charge to 0.02C at constant voltage, let it stand for 30 minutes, discharge to 2.5V at 0.5C constant current, and let it stand for 1 hour. Then, charge to 4.25V at 0.1C constant current, charge to 0.02C at constant voltage, let it stand for 30 minutes, discharge to 2.5V at 1C constant current, let it stand for 1 hour, charge to 4.25V at 0.1C constant current, charge to 0.02C at constant voltage, let it stand for 30 minutes, discharge to 2.5V at 2C constant current, let it stand for 1 hour, record the actual capacity C2 at this time, and use C2 / C0 as the rate characteristic at 2C.

[0160] Among them, the performance of the battery monomer is shown in Table 2:

[0161] Table 2 Parameters of positive electrode and performance of battery cells

[0162]

[0163] Combining the contents recorded in Table 1 and Table 2, it can be seen that the rate performance of the battery provided in the embodiment of the present application is better than the rate performance of the battery provided in the comparative example, indicating that the ionic conductivity of the second lithium-containing active material in the second positive electrode active layer of the positive electrode sheet is higher than the ionic conductivity of the first lithium-containing active material in the first positive electrode active layer, and the electronic conductivity of the first lithium-containing active material in the first positive electrode active layer is higher than the electronic conductivity of the second lithium-containing active material in the second positive electrode active layer, which can improve the rate performance of the battery.

[0164] By comparing Examples 1 to 9, it can be seen that when 9.9×10 -10 S / cm≤a'-a≤8×10 -9 S / cm,9.9×10 - 10 S / cm≤b-b'≤8×10 -9By comparing Example 1 with Examples 10 to 13, it can be seen that when the values ​​of a'-a and b-b' are the same, the ratio of the thickness of the second positive electrode active layer to the thickness of the first positive electrode active layer is 1.2 to 1.6, which can further improve the rate performance of the battery.

[0165] The embodiments described above are part of the embodiments of the present application, rather than all of the embodiments. The detailed description of the embodiments of the present application is not intended to limit the scope of the present application for protection, but merely represents the selected embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present application.

Claims

1. A positive electrode sheet, characterized in that: It includes a positive electrode current collector and a first positive electrode active layer and a second positive electrode active layer sequentially arranged on at least one side of the positive electrode current collector; the first positive electrode active layer includes a first lithium-containing active material, the ion conductivity of the first lithium-containing active material is a, and the electronic conductivity is b; the second positive electrode active layer includes a second lithium-containing active material, the ion conductivity of the second lithium-containing active material is a', and the electronic conductivity is b'; wherein a<a', b>b'.

2. The positive electrode sheet according to claim 1, characterized in that: The relationship between a and a' is: a'-a≥9×10 -10 S / cm; Optionally, 9×10 -10 S / cm≤a'-a≤8×10 -9 S / cm.

3. The positive electrode sheet according to claim 2, characterized in that: 1×10 -11 S / cm≤a≤9×10 -11 S / cm;1×10 -9 S / cm≤a’≤1×10 -8 S / cm。 4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The relationship between b and b' is: b-b’≥9×10 -10 S / cm; Optionally, 9×10 -10 S / cm≤b-b'≤8×10 -9 S / cm.

5. The positive electrode sheet according to claim 4, characterized in that: b' is 1×10 -10 S / cm~8×10 -9 S / cm, b is 1×10 -8 S / cm~4×10 -8 S / cm.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The first lithium-containing active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide and lithium nickel cobalt manganese aluminum oxide.

7. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The second lithium-containing active material includes a phosphate system material and / or a vanadate system material.

8. The positive electrode sheet according to claim 7, characterized in that: The phosphate system material includes LiMPO4, wherein M includes Mn and non-Mn elements, and the non-Mn elements include manganese-doped elements; Optionally, the non-Mn element further includes a phosphorus-site doping element; Optionally, the manganese-site doping element includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge; Optionally, the manganese-site doping elements include at least two of Fe, Ti, V, Ni, Co and Mg; Optionally, the phosphorus-site doping element includes one or more elements selected from the group consisting of B, S, Si and N; Optionally, the second lithium-containing active material comprises a chemical formula of Li a Mn 1-b A b P 1-c R c O4 compound, a is selected from the range of 0.9 to 1.1, b is selected from the range of 0.001 to 0.500, c is selected from the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb and Ge; R includes one or more elements selected from B, S, Si and N; Optionally, the second lithium-containing active material comprises a chemical formula of Li d A x Mn 1-y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B, S, Si and N, and D includes one or more elements selected from S, F, Cl and Br.

9. The positive electrode sheet according to claim 8, characterized in that: The phosphate system material also includes lithium iron phosphate; Optionally, the vanadate system material includes Li3VO4 and / or Li2VO3.

10. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The first lithium-containing active material comprises a lithium nickel cobalt manganese oxide material; the second lithium-containing active material comprises a lithium iron phosphate material; Or, the first lithium-containing active material comprises a nickel-cobalt-manganese-based lithium material; the second lithium-containing active material comprises Li d A x Mn 1-y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements of Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements of B, S, Si and N, and D includes one or more elements of S, F, Cl and Br; Or, the first lithium-containing active material comprises a lithium iron phosphate material, and the second lithium-containing active material comprises Li d A x Mn 1- y B y P 1-z C z O 4-n D n A compound, d is selected from the range of 0.9 to 1.1, x is selected from the range of 0.001 to 0.100, y is selected from the range of 0.001 to 0.500, z is selected from the range of 0.001 to 0.100, and n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo and W, B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb and Ge, C includes one or more elements selected from B, S, Si and N, and D includes one or more elements selected from S, F, Cl and Br.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The thickness of the second positive electrode active layer is greater than the thickness of the first positive electrode active layer; Optionally, a ratio of a thickness of the second positive electrode active layer to a thickness of the first positive electrode active layer is 1.2 to 1.

6.

12. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The amount of the second lithium-containing active material added is greater than the amount of the first lithium-containing active material added; Optionally, the ratio of the amount of the second lithium-containing active material added to the amount of the first lithium-containing active material added is 1.2 to 1.

6.

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

14. An electrical device, characterized in that: Comprising the battery of claim 13.

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