Positive electrode sheet, battery, and electric device

Abstract

This application relates to a positive electrode sheet, a battery, and an electrical device, belonging to the field of secondary battery technology. The positive electrode sheet includes a positive current collector and a first positive active layer and a second positive active layer sequentially disposed on at least one side of the positive current collector. The first positive active layer includes a first lithium-containing positive active material with ionic conductivity *a* and electronic conductivity *b*. The second positive active layer includes a second lithium-containing active material with ionic conductivity *a'* and electronic conductivity *b'*, wherein *a* < *a'* and *b* > *b'*. In this positive electrode sheet, the active material closer to the current collector has high electronic conductivity and low ionic conductivity, while the active material farther from the current collector has high ionic conductivity and low electronic conductivity. This design facilitates lithium-ion and electron transport, thereby improving the rate performance of the battery.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and particularly to a positive electrode, a battery, and an electrical device. Background Technology

[0002] In existing lithium-ion batteries, to balance the overall performance of the positive electrode, positive electrode active materials with different properties are usually mixed to form the positive electrode active layer. If the two positive electrode active materials have significantly different ionic conductivities, the overall kinetic performance of the battery will be poor. Therefore, two positive electrode active materials with significantly different ionic conductivities are usually layered to form two different positive electrode active layers. However, simply layering two positive electrode active materials with significantly different ionic conductivities cannot effectively improve the rate performance of the battery. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this application provides a positive electrode, a battery, and an electrical device to improve the rate performance of the battery.

[0004] In a first aspect, embodiments of this application provide a positive electrode sheet, including a positive current collector and a first positive active layer and a second positive active layer sequentially disposed on at least one side of the positive current collector; the first positive active layer includes a first lithium-containing active material, the first lithium-containing active material having an ionic conductivity of a and an electronic conductivity of b; the second positive active layer includes a second lithium-containing active material, the second lithium-containing active material having an ionic conductivity of a' and an electronic conductivity of b'; wherein, a < a', b > b'.

[0005] In the technical solution of this application embodiment, two lithium-containing active materials with significant differences in ionic and electronic conductivity are layered, which avoids mutual interference between the properties of the materials and allows each material to perform better. Furthermore, the second lithium-containing active material with higher ionic conductivity and lower electronic conductivity is concentrated on the surface of the positive electrode, which is beneficial for lithium-ion transport. The first lithium-containing active material with lower ionic conductivity and higher electronic conductivity is concentrated on the bottom layer of the positive electrode, which improves electron transport, thereby increasing the rate performance of the battery.

[0006] In some embodiments, the relationship between a and a' is: a'-a≥9×10 -10 S / cm. The difference in ionic conductivity between the first and second lithium-containing active materials is within this range, which can improve the lithium-ion transport 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 S / cm. The ionic conductivity of the first and second lithium-containing active materials are within the aforementioned range, which can improve the rate performance of the battery.

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

[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 S / cm. The electronic conductivity of the first lithium-containing active material and the second lithium-containing active material are respectively within the aforementioned range, which can improve the rate performance of the battery.

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

[0013] In some embodiments, the second lithium-containing active material comprises a phosphate-based material and / or a vanadate-based material. This positive electrode active material has low ionic conductivity and 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-doped elements.

[0015] In some embodiments, the non-Mn elements also include phosphorus site doping elements.

[0016] In some embodiments, the manganese site doping element 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.

[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 doping element includes one or more elements selected from B, S, Si, and N.

[0019] In some embodiments, the second lithium-containing active material comprises Li a Mn 1-b A b P 1-c R c The compound of O4, wherein 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; and R includes one or more elements selected from B, S, Si and N.

[0020] In some embodiments, 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 The compounds are selected from the range of 0.9 to 1.1, x from the range of 0.001 to 0.100, y from the range of 0.001 to 0.500, z from the range of 0.001 to 0.100, and n 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 also includes 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 lithium nickel cobalt manganese oxide; the second lithium-containing active material includes lithium iron phosphate.

[0024] In some embodiments, the first lithium-containing active material includes lithium nickel cobalt manganese oxide; the second lithium-containing active material includes Li d Ax Mn 1-y B y P 1-z C z O 4-n D n The compounds are selected from the range of 0.9 to 1.1, x from the range of 0.001 to 0.100, y from the range of 0.001 to 0.500, z from the range of 0.001 to 0.100, and n 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 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 The compounds are selected from the range of 0.9 to 1.1, x from the range of 0.001 to 0.100, y from the range of 0.001 to 0.500, z from the range of 0.001 to 0.100, and n 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. This 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. This 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] Secondly, this application provides a battery including the positive electrode provided in any of the first aspects.

[0031] Thirdly, this application provides an electrical device including the battery provided in the second aspect.

[0032] The above description is only an overview of the technical solution of this application. In order to better understand the technical means of this application and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of this application more obvious and understandable, the following are specific embodiments of this application. Attached Figure Description

[0033] Various other advantages and benefits will become apparent to those skilled in the art upon reading the detailed description of the preferred embodiments below. The accompanying drawings are for illustrative purposes only and are not intended to limit the scope of this application. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0034] Figure 1 This application provides structural schematic diagrams of vehicles for some embodiments;

[0035] Figure 2 This is an exploded structural diagram of a battery provided in some embodiments of this application;

[0036] Figure 3 This is a schematic diagram of the structure of a battery cell provided in some embodiments of this application;

[0037] Figure 4 Exploded views of a single battery cell provided in some embodiments of this application;

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

[0039] Figure 6 This is a schematic diagram of the second layer structure of the positive electrode sheet provided in some embodiments of this application.

[0040] Icons: 1000 - Vehicle; 100 - Battery; 10 - Housing; 11 - Storage space; 12 - First part; 13 - Second part; 20 - Battery cell; 21 - Casing; 211 - Opening; 22 - End cap assembly; 221 - End cap; 222 - Electrode terminal; 23 - Electrode assembly; 231 - Positive electrode; 2311 - Positive current collector; 2312a - First positive active layer; 2312b - Second positive active layer; 2312c - Third positive active layer; 24 - Current collector component; 25 - Insulation protection component; 200 - Controller; 300 - Motor. Detailed Implementation

[0041] The embodiments of the technical solution of this application will now be described in detail with reference to the accompanying drawings. These embodiments are only used to more clearly illustrate the technical solution of this application and are therefore merely examples, and should not be used to limit the scope of protection of this application.

[0042] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the application; the terms “comprising” and “having”, and any variations thereof, in the specification, claims, and foregoing description of the drawings are intended to cover non-exclusive inclusion.

[0043] In the description of the embodiments of this application, technical terms such as "first" and "second" are used only to distinguish different objects and should not be construed as indicating or implying relative importance or implicitly specifying the number, specific order, or primary and secondary relationship of the indicated technical features. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly defined.

[0044] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments.

[0045] In the description of the embodiments in this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0046] In the description of the embodiments of this application, the term "multiple" refers to two or more (including two), similarly, "multiple sets" refers to two or more (including two sets), and "multiple pieces" refers to two or more (including two pieces).

[0047] In the description of the embodiments of this application, the technical terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," and "circumferential" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing the embodiments of this application and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the embodiments of this application.

[0048] In the description of the embodiments of this application, unless otherwise expressly specified and limited, technical terms such as "installation," "connection," "joining," and "fixing" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. For those skilled in the art, the specific meaning of the above terms in the embodiments of this application can be understood according to the specific circumstances.

[0049] Currently, judging from market trends, the application of power batteries is becoming increasingly widespread. Power batteries are not only used in energy storage systems such as hydropower, thermal power, wind power, and solar power plants, but also extensively used in electric vehicles such as electric bicycles, electric motorcycles, and electric cars, as well as in military equipment and aerospace. With the continuous expansion of power battery applications, market demand is also constantly increasing.

[0050] Power batteries can be lithium-ion batteries. During charging, lithium ions are released from the positive electrode active material, transported through the electrolyte, passed through the separator, and embedded in the negative electrode active material. To balance the overall performance of the positive electrode, 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 differs significantly, the overall kinetic performance of the battery will be poor. Therefore, two positive electrode active materials with significantly different ionic conductivity are usually layered to form two different positive electrode active layers. However, simply layering two positive electrode active materials with significantly different ionic conductivity is unlikely to improve the battery's rate performance.

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

[0052] In this type of positive electrode, layering two lithium-containing active materials with significantly different ionic and electronic conductivity avoids mutual interference between their performances, allowing each material to perform optimally. Furthermore, the second lithium-containing active material, with higher ionic conductivity and lower electronic conductivity, is concentrated on the surface of the positive electrode, facilitating lithium-ion transport. Conversely, the first lithium-containing active material, with lower ionic conductivity and higher electronic conductivity, is concentrated at the bottom layer, improving electron transport and thus enhancing the battery's rate performance.

[0053] The positive electrode sheet can be used to prepare electrode assemblies, which can be assembled into batteries. These batteries can be individual cells, modules, battery packs, etc., and can be used, but are not limited to, in electrical equipment such as vehicles, ships, or aircraft. The power system of such electrical equipment can be composed using batteries equipped with the specifications disclosed in this application, which is beneficial for improving the rate performance of the batteries.

[0054] This application provides an electrical device that uses a battery as its power source. The electrical device can be a vehicle, mobile phone, portable device, laptop, ship, spacecraft, electric toy, or power tool, etc. Vehicles can be gasoline-powered cars, natural gas-powered cars, or new energy vehicles; new energy vehicles can be pure electric vehicles, hybrid electric vehicles, or range-extended electric vehicles, etc.; spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc.; electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc.; power 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, etc. This application does not impose any special limitations on the above-mentioned electrical device.

[0055] For ease of explanation, the following embodiments use a vehicle as an example of electrical equipment.

[0056] Please refer to Figure 1 , Figure 1This is a schematic diagram of the structure of a vehicle 1000 provided in some embodiments of this application. A battery 100 is disposed inside the vehicle 1000, and the battery 100 may be located at the bottom, front, or rear of the vehicle 1000. The battery 100 can be used to power the vehicle 1000; for example, the battery 100 can serve as the operating power source for the vehicle 1000.

[0057] The vehicle 1000 may also include a controller 200 and a motor 300. The controller 200 is used to control the battery 100 to supply power to the motor 300, for example, for the power needs of the vehicle 1000 during startup, navigation and driving.

[0058] In some embodiments of this application, the battery 100 can not only serve as the operating power source for the vehicle 1000, but also as the 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 an exploded structural diagram of the battery 100 provided in some embodiments of this application. Please refer to... Figure 2 The battery 100 includes a housing 10 and a battery cell 20, with the battery cell 20 housed within the housing 10.

[0060] The housing 10 provides a receiving space 11 for the battery cell 20. In some embodiments, the housing 10 may include a first portion 12 and a second portion 13, which overlap each other to define the receiving space 11 for accommodating the battery cell 20. Of course, the connection between the first portion 12 and the second portion 13 may be sealed by a sealant (not shown), such as a sealing ring, sealant, etc.

[0061] The first part 12 and the second part 13 can be of various shapes, such as cuboids, cylinders, etc. The first part 12 can be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20, and the second part 13 can also be a hollow structure with an opening on one side to form a cavity for accommodating the battery cell 20. When the opening side of the second part 13 covers the opening side of the first part 12, a housing 10 with an accommodating space 11 is formed. Of course, as... Figure 2 As shown, the first part 12 can also be a hollow structure with an opening on one side, and the second part 13 can be a plate-like structure. The second part 13 covers the opening side of the first part 12, thus forming a box 10 with a accommodating space 11.

[0062] In battery 100, there can be one or more battery cells 20. If there are multiple battery cells 20, they can be connected in series, parallel, or in a mixed manner. A mixed connection means that multiple battery cells 20 are connected in both series and parallel. Multiple battery cells 20 can be directly connected in series, parallel, or in a mixed manner, and then the whole assembly of multiple battery cells 20 is housed in the housing 10. Alternatively, multiple battery cells 20 can first be connected in series, parallel, or in a mixed manner to form a battery module, and then multiple battery modules can be connected in series, parallel, or in a mixed manner to form a whole, which is then housed in the housing 10. Battery cells 20 can be cylindrical, flat, cuboid, or other shapes. Figure 2 An example is shown where the battery cell 20 is square.

[0063] In some embodiments, the battery 100 may also include a busbar (not shown), through which multiple battery cells 20 can be electrically connected to each other to achieve series, parallel, or mixed connection of 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 this application. Figure 4 Exploded views of a battery cell 20 provided for some embodiments of this application. Please refer to... 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 housed within the housing 21, and the end cap assembly 22 is used to seal the opening 211.

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

[0066] The outer shell 21 can also be made of various materials, such as copper, iron, aluminum, stainless steel, aluminum alloy, etc. This application embodiment does not impose any special restrictions on this.

[0067] The end cap assembly 22 includes an end cap 221 and electrode terminals 222. The end cap assembly 22 is used to seal the opening 211 of the housing 21 to form a sealed mounting space (not shown) for accommodating the electrode assembly 23. The mounting space also accommodates an electrolyte, such as an electrolyte solution. As a component that outputs electrical energy to the electrode assembly 23, the end cap assembly 22 has electrode terminals 222 for electrical connection to the electrode assembly 23, specifically, the electrode terminals 222 are electrically connected to the tabs of the electrode assembly 23. For example, the electrode terminals 222 and the tabs are connected via a current collector 24 to achieve the electrical connection between the electrode terminals 222 and the tabs.

[0068] It should be noted that the opening 211 of the outer casing 21 can be one or two. If the outer casing 21 has one opening 211, the end cap assembly 22 can also be one, and two electrode terminals 222 can be provided in the end cap assembly 22. The two electrode terminals 222 are used to electrically connect to the positive electrode tab and the negative electrode tab of the electrode assembly 23, respectively. If the outer casing 21 has two openings 211, for example, the two openings 211 are located on opposite sides of the outer casing 21, the end cap assembly 22 can also be two, and the two end cap assemblies 22 respectively cover the two openings 211 of the outer casing 21. In this case, the electrode terminal 222 in one end cap assembly 22 can be a positive electrode terminal, used to electrically connect to the positive electrode tab of the electrode assembly 23; the electrode terminal 222 in the other end cap assembly 22 can be a negative electrode terminal, used to electrically connect to the negative electrode plate of the electrode assembly 23.

[0069] In some embodiments, such as Figure 4 As shown, the battery cell 20 may further include an insulating protective member 25 fixed to the outer periphery of the electrode assembly 23. 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 adhesive tape bonded to the outer periphery of the electrode assembly 23. In some embodiments, there are multiple electrode assemblies 23, and the insulating protective member 25 surrounds the outer periphery of multiple electrode assemblies 23, forming a single integral structure to maintain the structural stability of the electrode assembly 23. The electrode assembly 23 may be a wound electrode assembly or a stacked electrode assembly; the embodiments of this application are not limited to these.

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

[0071] The negative electrode includes a negative current collector and a negative active material layer. The negative active material layer is disposed on the surface of the negative current collector. The negative current collector without the negative active material layer protrudes from the negative current collector with the negative active material layer, and the negative current collector without the negative active material layer serves as the negative electrode tab. The material of the negative current collector can be one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. The negative active material can be carbon material, silicon material, silicon-carbon composite material, etc.

[0072] Figure 5 For a schematic diagram of the first layer structure of the positive electrode 231 provided in some embodiments of this application, please refer to... Figure 5The positive electrode 231 includes a positive current collector 2311, and a first positive active layer 2312a and a second positive active layer 2312b are sequentially disposed on the positive current collector 2311. The first positive active layer 2312a includes a first lithium-containing active material with ionic conductivity a and electronic conductivity b. The second positive active layer 2312b includes a second lithium-containing active material with ionic conductivity a' and electronic conductivity 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 this application is mainly based on improvements to lithium-ion batteries, and the positive electrode 231 in this application is the positive electrode 231 of a lithium-ion battery.

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

[0075] The method for testing the electronic conductivity b of the first lithium-containing active material is as follows: slice the positive electrode 231 to observe the interface between the first positive electrode active layer 2312a and the second positive electrode active layer 2312b. scrape off all of the second positive electrode active layer 2312b, then scrape off a portion of the first positive electrode active layer 2312a and immerse it in the solvent NMP to wash out the binder in the first positive electrode active layer 2312a, thus obtaining the powder material. Test the electronic conductivity b of the powder material.

[0076] The test method for the ionic conductivity a' of the second lithium-containing active material is as follows: scrape off a portion of the second positive electrode active layer 2312b, prepare it into a symmetrical battery, 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.

[0077] The method for testing the ionic conductivity α of the first lithium-containing active material is as follows: slice the positive electrode 231 to observe the interface between the first positive electrode active layer 2312a and the second positive electrode active layer 2312b. scrape off all of the second positive electrode active layer 2312b and then scrape off a portion of the first positive electrode active layer 2312a to prepare a symmetrical battery. Test the AC impedance EIS and take the impedance R of 10-15KHz. 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.

[0078] In the technical solution of this application embodiment, two lithium-containing active materials with significant differences in ionic conductivity and electronic conductivity are layered, which can avoid mutual interference between the properties of the materials and allow each material to perform better. Furthermore, the second lithium-containing active material with higher ionic conductivity and lower electronic conductivity is concentrated on the surface layer of the positive electrode 231, which is beneficial for lithium-ion transport. The first lithium-containing active material with lower ionic conductivity and higher electronic conductivity is concentrated on the bottom layer of the positive electrode, which can improve electron transport, 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 S / cm. The difference in ionic conductivity between the first lithium-containing active material and the second lithium-containing active material is within this range, which can improve the lithium-ion transport effect of the entire positive electrode 231, thereby improving the rate performance of the battery 100.

[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 × 10⁻⁶. -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., can also be other values ​​within the above range. 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 conductivity of the first lithium-containing active material and the second lithium-containing active material are within the aforementioned range, which can improve the rate performance of the battery by 100%.

[0082] As an example, the ionic conductivity α of the first lithium-containing active material is 1 × 10⁻⁶. -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 1×10⁻⁶. -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., can 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 as follows: b - b' ≥ 9 × 10⁻⁶ -10 S / cm. The difference in electronic conductivity between the first lithium-containing active material and the second lithium-containing active material is within this range, which can improve the electron transport effect of the entire positive electrode 231 and make the rate performance of the battery 100 better.

[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 × 10⁻⁶. -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., can also be other values ​​within the above range. 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 S / cm. The electronic conductivity of the first lithium-containing active material and the second lithium-containing active material are respectively within the aforementioned range, 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 × 10⁻⁶. -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 1×10⁻⁶. -8 S / cm, 2×10 -8 S / cm, 3×10 -8 S / cm or 4×10 -8 S / cm, etc., can also be other values ​​within the above range.

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

[0088] Optionally, lithium nickel cobalt manganese oxide includes lithium nickel oxide with the chemical formula LiNi. x Co y Mn 1-x-y Compounds of O2, wherein 0 < x < 1, 0 < y < 1. As an example, lithium nickel cobalt manganese oxide comprises compounds with the chemical formula LiNi. 0.4 Co 0.2 Mn 0.4 O2 compounds with the chemical formula LiNi 0.5 Co 0.1 Mn 0.4 O2 compounds with the chemical formula 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 containing O2.

[0089] Optionally, lithium nickel cobalt aluminum oxide includes those with the chemical formula LiNi x Co y Al 1-x-y Compounds of O2, wherein 0 < x < 1, 0 < y < 1. As an example, lithium nickel cobalt aluminum oxide comprises compounds with the chemical formula LiNi. 0.4 Co 0.2 Al 0.4 O2 compounds with the chemical formula LiNi 0.5 Co 0.1 Al 0.4 O2 compounds with the chemical formula 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 containing O2.

[0090] Optionally, lithium nickel cobalt manganese aluminum oxide includes those with the chemical formula LiNi x Co y Mn z Al 1-x-y-z Compounds of O2, wherein 0 < x < 1, 0 < y < 1, 0 < z < 1. As an example, lithium nickel cobalt manganese aluminum oxide comprises compounds with the chemical formula LiNi. 0.4 Co 0.2 Mn 0.2 Al0.2 O2 compounds with the chemical formula LiNi 0.5 Co 0.1 Mn 0.2 Al 0.2 O2 compounds with the chemical formula 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 containing O2. In some embodiments, the second lithium-containing active material comprises a phosphate system material and / or a vanadate system material. This positive electrode active material has low ionic conductivity and 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-doped elements.

[0092] In some embodiments, the non-Mn elements also include phosphorus site doping elements.

[0093] In some embodiments, the manganese site doping element 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.

[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 doping element includes one or more elements selected from B, S, Si, and N.

[0096] In some embodiments, the second lithium-containing active material comprises Li a Mn 1-b A b P 1-c R c The compound of O4, wherein 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; and R includes one or more elements selected from B, S, Si and N.

[0097] As an example, the second lithium-containing active material includes materials with the chemical formula LiMn. 0.9 Al 0.1 P0.9 S 0.1 O4 compounds with the chemical formula 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 containing O4.

[0098] In some embodiments, 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 The compounds are selected from the range of 0.9 to 1.1, x from the range of 0.001 to 0.100, y from the range of 0.001 to 0.500, z from the range of 0.001 to 0.100, and n 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 materials with the chemical formula 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, 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 its chemical formula is Li1.001 Mn 0.999 Fe 0.001 P 0.999 Si 0.001 At least one of the compounds containing O4. Among them, compound Li 1.001 Mn 0.999 Fe 0.001 P 0.999 Si 0.001 Methods for preparing O4 include:

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

[0101] 1148.2 g of manganese carbonate and 1.2 g of ferrous carbonate were added to a mixer and mixed thoroughly for 6 hours. The resulting mixture was then transferred to a reaction vessel, and 5 L of deionized water and 1260.6 g of oxalic acid dihydrate were added. The mixture was heated to 80°C and stirred thoroughly at 500 rpm for 6 hours until homogeneous mixing and the reaction was terminated without bubble formation, yielding an Fe-doped manganese oxalate suspension. The suspension was then filtered, dried at 120°C, and milled to obtain ferromanganese oxalate particles with a particle size of 100 nm.

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

[0103] Take the manganese iron oxalate (in C2O4Mn) prepared in step S1 0.999 Fe 0.001 1789.6 g of lithium carbonate (based on 2H₂O), 369.8 g of lithium carbonate, 1148.9 g of ammonium dihydrogen phosphate, and 0.8 g of silicic acid were added to 20 L of deionized water and stirred thoroughly. The mixture was then uniformly mixed and reacted at 80 °C for 10 h to obtain a slurry. The slurry was transferred to a spray drying equipment for spray drying and granulation, and dried at 250 °C to obtain a powder. The powder was then sintered in a roller kiln at 700 °C for 4 h under a protective atmosphere (90% nitrogen and 10% hydrogen).

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

[0105] In some embodiments, the phosphate system material further includes 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), and M includes one or more elements selected from 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 lithium nickel cobalt manganese oxide; the second lithium-containing active material includes lithium manganese iron phosphate.

[0108] In some embodiments, the first lithium-containing active material includes lithium nickel cobalt manganese oxide; 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 The compounds are selected from the range of 0.9 to 1.1, x from the range of 0.001 to 0.100, y from the range of 0.001 to 0.500, z from the range of 0.001 to 0.100, and n 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 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 The compounds are selected from the range of 0.9 to 1.1, x from the range of 0.001 to 0.100, y from the range of 0.001 to 0.500, z from the range of 0.001 to 0.100, and n 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 determining the chemical formula of the first lithium-containing active material does not automatically reveal its unique ionic and electronic conductivity. In fact, the ionic and electronic conductivity of the first lithium-containing active material are related not only to its chemical formula but also to its preparation method, particle size distribution, impurity content, and impurity types. Even different models of the same lithium-containing active material from the same manufacturer will have different ionic and electronic conductivity, and similarly, different manufacturers may also have different ionic and electronic conductivity for the same lithium-containing active material. This application uses the composition, ionic conductivity, and electronic conductivity of the first lithium-containing active material to jointly determine the selection of the first lithium-containing cathode active material. Determining the chemical formula of the second lithium-containing active material does not guarantee its unique ionic and electronic conductivity. In fact, the ionic and electronic conductivity of the second lithium-containing active material are related not only to its chemical formula but also to its preparation method, particle size distribution, impurity content, and impurity types. Even different models of the same lithium-containing active material from the same manufacturer will have different ionic and electronic conductivity, and similarly, different manufacturers may produce materials with the same composition. This application uses the composition, ionic conductivity, and electronic conductivity of the second lithium-containing active material to jointly determine the selection of the second lithium-containing cathode active material.

[0111] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying Li molar content at different discharge states. In the examples of positive electrode active materials listed in this application, the Li molar content represents the initial state of the material, i.e., the state before material addition. As the positive electrode active material is applied to the battery system, the Li molar content changes after charge-discharge cycles. Similarly, in the examples of positive electrode active materials listed in this application, the O molar content is only a theoretical value. Lattice oxygen release causes changes in the oxygen molar content, leading to fluctuations in the actual O molar content.

[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. This 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. This 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 this application, please refer to [link / reference]. Figure 6 Please see Figure 6 The positive electrode 231 includes a positive current collector 2311, and a first positive active layer 2312a, a second positive active layer 2312b, and a third positive active layer 2312c are sequentially disposed on the positive current collector 2311. The first positive active layer 2312a includes a first lithium-containing active material with ionic conductivity X and electronic conductivity x. The second positive active layer 2312b includes a second lithium-containing active material with ionic conductivity Y and electronic conductivity y. The third positive active layer 2312c includes a third lithium-containing active material with ionic conductivity Z and electronic conductivity z. Wherein, X < Y < Z, x > y > z.

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

[0118] The method for testing the electronic conductivity y of the second lithium-containing active material is as follows: slice the positive electrode 231 to observe the interface between the second positive electrode active layer 2312b and the third positive electrode active layer 2312c. scrape off all of the third positive electrode active layer 2312c, then scrape off a portion of the second positive electrode active layer 2312b and immerse it in the solvent NMP to wash out the binder in the second positive electrode active layer 2312b, thus obtaining the powder material. Test the electronic conductivity y of the powder material.

[0119] The method for testing the electronic conductivity x of the first lithium-containing active material is as follows: slice the positive electrode 231 to observe the interface between the first positive electrode active layer 2312a and the second positive electrode active layer 2312b. scrape off all the second positive electrode active layer 2312b and the third positive electrode active layer 2312c, then scrape off a portion of the first positive electrode active layer 2312a and immerse it in the solvent NMP to wash out the binder in the first positive electrode active layer 2312a, thus obtaining the powder material. Test the electronic conductivity x of the powder material.

[0120] The test method for the ionic conductivity Z of the third lithium-containing active material is as follows: scrape off a portion of the third positive electrode active layer 2312c, prepare it into a symmetrical battery, 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 test method for the ionic conductivity Y of the second lithium-containing active material is as follows: slice the positive electrode 231 to observe the interface between the second positive electrode active layer 2312b and the third positive electrode active layer 2312c. scrape off all of the third positive electrode active layer 2312c, and then scrape off a portion of the second positive electrode active layer 2312b to prepare a symmetrical battery. Test the AC impedance EIS and take the impedance R of 10-15KHz. 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.

[0122] The method for testing the ionic conductivity X of the first lithium-containing active material is as follows: slice the positive electrode 231 to observe the interface between the first positive electrode active layer 2312a and the second positive electrode active layer 2312b. scrape off all the second positive electrode active layer 2312b and the third positive electrode active layer 2312c, and then scrape off a portion of the first positive electrode active layer 2312a to prepare a symmetrical battery. Test the AC impedance EIS and take the impedance R of 10-15KHz. 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.

[0123] In the technical solution of this application embodiment, along the direction from near the positive electrode current collector 2311 to away from the positive electrode current collector 2311, the ionic conductivity of the lithium-containing active material gradually increases and the electronic conductivity gradually decreases, which can make the electron transport and lithium-ion transport effects of the positive electrode 231 better, so as to make the rate performance of the battery better.

[0124] Having described the structure of the positive electrode 231 above, the preparation method of the positive electrode 231 will be described in detail below.

[0125] In some embodiments, the positive electrode active layer of the positive electrode 231 has a double-layer structure, and the method for preparing the positive electrode 231 includes:

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

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

[0128] S130, the first active slurry is coated on the surface of the positive electrode current collector 2311 and dried to form the first positive electrode active layer 2312a; the second active slurry is coated on the surface of the first positive electrode active layer 2312a and dried to form the second positive electrode active layer 2312b, thus obtaining the positive electrode sheet 231.

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

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

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

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

[0133] S240, the first active slurry is coated on the surface of the positive electrode current collector 2311 and dried to form the first positive electrode active layer 2312a; the second active slurry is coated on the surface of the first positive electrode active layer 2312a and dried to form the second positive electrode active layer 2312b; the third active slurry is coated on the surface of the second positive electrode active layer 2312b and dried to form the third positive electrode active layer 2312c, thus obtaining the positive electrode sheet 231.

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

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

[0136] The following examples will describe one or more embodiments in more detail. Of course, these examples do not limit the scope of the one or more embodiments.

[0137] Experimental Example 1

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

[0139] A first active slurry with a solid content of 50 wt% was prepared by mixing 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 in a solvent N-methylpyrrolidone (NMP).

[0140] A second active slurry with a solid content of 50 wt% was prepared by mixing 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 in a solvent N-methylpyrrolidone (NMP).

[0141] The first active slurry was coated onto a current collector aluminum foil (6 μm thick) and dried at 85°C for 4 hours, followed by cold pressing to obtain the first positive electrode active layer. The second active slurry was coated onto the first positive electrode active layer and dried at 85°C for 4 hours, followed by cold pressing to obtain the second positive electrode active layer. Then, the layers were trimmed, cut into sheets, and dried under vacuum at 85°C for 4 hours to obtain the positive electrode sheet. The thickness of the positive electrode active layer on one side is 160 μm. Specific parameters of the positive electrode sheet are shown in Tables 1 and 2.

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

[0143] A negative electrode active slurry with a solid content of 50 wt% was prepared by mixing graphite, conductive agent Super P and binder polytetrafluoroethylene (PTFE) in a mass ratio of 95:2:3 in the solvent N-methylpyrrolidone (NMP).

[0144] The negative electrode active slurry was coated onto the current collector copper foil (9 μm thick) and dried at 85°C for 4 h, then cold-pressed, trimmed, and cut into sheets. The sheets were then dried under vacuum at 85°C for 4 h to obtain the negative electrode sheet. The thickness of the single-sided 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 16μm. The negative electrode, the first separator, the positive electrode, and the second separator are stacked and then wound to form an electrode assembly.

[0147] (4) Preparation of battery cells:

[0148] The electrode assembly is welded to the tabs, the electrode assembly is placed into the housing, and an electrolyte (1M lithium hexafluorophosphate EC / DMC (1:1 vol%) solution) is injected. Then, the battery cell is obtained through vacuum sealing, settling, formation, and shaping processes.

[0149] Table 1. Some parameters of the positive electrode sheet

[0150]

[0151] Performance of the battery cells prepared in the test examples and comparative examples:

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

[0153] The ionic conductivity of the second lithium-containing active material: A portion of the second positive electrode active layer is scraped off and a symmetrical battery is prepared. The AC impedance EIS is tested. The impedance R is taken as 10-15KHz. The ionic conductivity σ is calculated 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] The ionic conductivity of the first lithium-containing active material: By slicing the positive electrode sheet, 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. The AC impedance EIS is tested, and the 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 electrode 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: A portion of the second positive electrode active layer was scraped off, immersed in the solvent NMP, and the binder in the second positive electrode active layer was washed out to obtain a powder material. The electronic conductivity b' of the powder material was then tested.

[0157] Electronic conductivity of the first lithium-containing active material: The interface between the first and second positive electrode active layers can be observed by slicing the positive electrode sheet. The second positive electrode active layer is completely scraped off, and then a portion of the first positive electrode active layer is scraped off and immersed in the solvent NMP to wash out the binder in the first positive electrode active layer, thus obtaining the powder material. The electronic conductivity b of the powder material is then tested.

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

[0159] Example of test method: At 25℃, after the battery has completed formation and capacity testing, let it stand for 30 minutes, then discharge it at a constant current of 0.1C to 2.5V. After standing for 1 hour, charge it at a constant current of 0.1C to 4.25V. Then, let it stand for 30 minutes, discharge it at a constant current of 0.1C to 2.5V, stand for 1 hour, charge it at a constant current of 0.1C to 4.25V, and then charge it at a constant voltage to 0.02C. Record its actual capacity as C0. Next, discharge it at a constant current of 0.2C to 2.0V, stand for 1 hour, charge it at a constant current of 0.1C to 4.25V, and then charge it at a constant voltage to 0.02C. Let it stand for 30 minutes, then discharge it at a constant current of 1C to 2.5V. Record its actual capacity as C1. Use C1 / C0 as the rate capability at 1C. Next, let it stand for 1 hour, then charge it at a constant current of 0.1C to 4.25V, then charge it at a constant voltage of 0.02C, let it stand for 30 minutes, then discharge it at a constant current of 0.5C to 2.5V, and let it stand for 1 hour. Then, charge it at a constant current of 0.1C to 4.25V, then charge it at a constant voltage of 0.02C, let it stand for 30 minutes, then discharge it at a constant current of 1C to 2.5V, let it stand for 1 hour, then charge it at a constant current of 0.1C to 4.25V, then charge it at a constant voltage of 0.02C, let it stand for 30 minutes, then discharge it at a constant current of 2C to 2.5V, and let it stand for 1 hour. Record the actual capacity C2 at this point, and use C2 / C0 as the rate capability at 2C.

[0160] The performance of the individual battery cells is shown in Table 2:

[0161] Table 2. Parameters of the positive electrode and performance of the battery cell

[0162]

[0163] As can be seen from the contents of Tables 1 and 2, the rate performance of the battery provided in this application embodiment is better than that of the battery provided in the comparative example. This indicates 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] A comparison of Examples 1 to 9 shows 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 -9At a ratio of S / cm, the rate performance of the battery is further improved. A comparison of Example 1 with Examples 10-13 shows that, with the same values ​​of a'-a and b-b', a ratio of the thickness of the second positive electrode active layer to the thickness of the first positive electrode active layer of 1.2-1.6 can further improve the rate performance of the battery.

[0165] The embodiments described above are some, but not all, of the embodiments of this application. The detailed description of the embodiments of this application is not intended to limit the scope of the claimed application, but merely to illustrate selected embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of this application without inventive effort are within the scope of protection of this application.

Claims

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

2. The positive electrode sheet according to claim 1, characterized by a and a' are related as follows: a' - a > 9 x 10 -10 S / cm.

3. The cathode electrode according to claim 2, wherein 9 x 10 -10 S / cm < a' - a < 8 x 10 -9 S / cm.

4. The cathode electrode according to claim 2, wherein 1 x 10 -11 S / cm≤a≤9 x 10 -11 S / cm; 1 x 10 -9 S / cm≤a'≤1 x 10 -8 S / cm.

5. The cathode sheet of claim 1, wherein, The relationship of b and b' is: b - b' > 9 x 10 -10 S / cm.

6. The cathode electrode of claim 5, wherein, 9 x 10 -10 S / cm ≤ b - b' ≤ 8 x 10 -9 S / cm.

7. The cathode electrode according to claim 5, wherein b' is 1 x 10 -10 S / cm ~8x10 -9 S / cm, b is 1 x 10 -8 S / cm ~4x10 -8 S / cm.

8. The positive electrode plate according to any one of claims 1 to 7, characterized by, The first lithium-containing active material includes at least one of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium nickel cobalt manganese aluminate.

9. The positive electrode plate according to any one of claims 1 to 7, characterized by, The second lithium-containing active material includes a phosphate system material and / or a vanadate system material.

10. The cathode electrode of claim 9, wherein, The phosphate system material includes LiMPO4, wherein M includes Mn and a non-Mn element, and the non-Mn element includes a manganese site doping element.

11. The cathode electrode of claim 10, wherein, 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.

12. The cathode electrode of claim 10, wherein, The manganese site doping element includes at least two of Fe, Ti, V, Ni, Co, and Mg.

13. The cathode sheet of claim 10, wherein, The non-Mn element further includes a phosphorus site doping element.

14. The cathode electrode of claim 13, wherein, The phosphorus site doping element includes one or more elements of B, S, Si, and N.

15. The cathode sheet of claim 10, wherein, The second lithium-containing active material includes a compound of the formula Li a Mn 1-b A b P 1-c R c O4, 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 of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Fe, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and R includes one or more elements of B, S, Si, and N.

16. The cathode sheet of claim 10, wherein, the second lithium-containing active material includes a compound of the formula Li d A x Mn 1-y B y P 1-z C z O 4-n D n 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, n is selected from the range of 0.001 to 0.100; A includes one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W, B includes one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge, C includes one or more elements selected from the group consisting of B, S, Si, and N, and D includes one or more elements selected from the group consisting of S, F, Cl, and Br.

17. The cathode sheet of claim 10, wherein, The phosphate system material further includes lithium iron phosphate.

18. The cathode sheet of claim 10, wherein, The vanadate system material includes Li3VO4 or / and Li2VO3.

19. The positive electrode plate of any one of claims 1-7, 10-18, wherein, 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. or 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 of the formula: 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, n is selected from the range of 0.001 to 0.100; A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W, B comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge, C comprises one or more elements selected from the group consisting of B, S, Si, and N, and D comprises one or more elements selected from the group consisting 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 of the formula: 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, n is selected from the range of 0.001 to 0.100; A comprises one or more elements selected from the group consisting of Zn, Al, Na, K, Mg, Nb, Mo, and W, B comprises one or more elements selected from the group consisting of Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge, C comprises one or more elements selected from the group consisting of B, S, Si, and N, and D comprises one or more elements selected from the group consisting of S, F, Cl, and Br.

20. The positive electrode plate of any one of claims 1-7, 10-18, wherein, The addition amount of the second lithium-containing active material is greater than the addition amount of the first lithium-containing active material.

21. The cathode sheet of claim 20, wherein, The ratio of the addition amount of the second lithium-containing active material to the addition amount of the first lithium-containing active material is 1.2 to 1.

6.

22. A battery, characterized by The positive electrode plate includes a positive electrode current collector and a first positive electrode active layer and a second positive electrode active layer arranged in sequence on at least one side of the positive electrode current collector; the active material of the first positive electrode active layer is a first lithium-containing active material, the ion conductivity of the first lithium-containing active material is a, and the electronic conductivity of the first lithium-containing active material is b, the active material of the second positive electrode active layer is a second lithium-containing active material, the ion 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 < a', and b > b'; 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.

23. An electrical device, comprising: The positive electrode plate includes a positive electrode current collector and a first positive electrode active layer and a second positive electrode active layer arranged in sequence on at least one side of the positive electrode current collector; the active material of the first positive electrode active layer is a first lithium-containing active material, the ion conductivity of the first lithium-containing active material is a, and the electronic conductivity of the first lithium-containing active material is b, the active material of the second positive electrode active layer is a second lithium-containing active material, the ion 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 < a', and b > b'; 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.

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