Electrode assembly, battery, and electric device

Abstract

The application relates to an electrode assembly, a battery and an electric device. The electrode assembly has a winding structure and a central axis, and comprises a positive electrode sheet, which comprises a current collector layer, a first material layer and a second material layer. The first material layer is arranged on one side of the current collector layer facing the central axis. The first material layer comprises a first sub-layer and a second sub-layer. The first sub-layer is closer to the central axis than the second sub-layer. The first sub-layer comprises a first active substance. The first active substance comprises a core and a protective layer. The core comprises lithium iron phosphate and a first doping element. The second sub-layer comprises a second active substance. The second active substance comprises lithium iron phosphate and a second doping element. The second material layer is arranged on the side of the current collector layer away from the central axis. The second material layer comprises a third active substance. The third active substance comprises lithium iron phosphate and a third doping element. The mass content of the first doping element is less than the mass content of the second doping element and the mass content of the third doping element.

Description

Technical Field

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

[0002] With the continuous development of lithium-ion batteries, lithium iron phosphate is widely used as a positive electrode active material. Its crystal structure belongs to olivine, which has good safety and stability. At present, lithium-ion batteries are increasingly pursuing high capacity indicators, but this will lead to some problems such as material processing and electrical performance degradation, resulting in lithium plating on the surface of the negative electrode, thus affecting the battery's service life. Summary of the Invention

[0003] In view of this, this application provides an electrode assembly, a battery, and an electrical device, wherein the electrode assembly can mitigate the occurrence of lithium plating, thereby extending the battery's lifespan.

[0004] This application provides an electrode assembly with a wound structure having a central axis. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The separator is located between the positive and negative electrode. The positive electrode includes a current collector layer, a first material layer, and a second material layer. The first material layer is disposed on the side of the current collector layer facing the central axis. The first material layer includes a first sub-layer and a second sub-layer. The first sub-layer is closer to the central axis than the second sub-layer. The first sub-layer includes a first active material with a core-shell structure, comprising a core and a protective layer. A second sublayer covers the outer periphery of the core, the core comprising lithium iron phosphate and a first dopant element; the second sublayer comprises a second active material comprising lithium iron phosphate and a second dopant element; the mass content of the first dopant element in the first active material is less than the mass content of the second dopant element in the second active material; a second material layer is disposed on the side of the current collector layer away from the central axis, the second material layer comprising the third active material comprising lithium iron phosphate and a third dopant element; the mass content of the first dopant element in the first active material is less than the mass content of the third dopant element in the third active material.

[0005] Furthermore, the core of the first active substance has the chemical formula LiFe. (1-x) M1 x PO4 / C, the chemical formula of the second active substance is LiFe (1-y) M2 y PO4 / C, the chemical formula of the third active substance is LiFe (1-z) M3 zPO4 / C, wherein M1 is the first doping element, which is selected from at least one of titanium, vanadium, magnesium or niobium; M2 is the second doping element, which is selected from at least one of titanium, vanadium, magnesium or niobium; and M3 is the third doping element, which is selected from at least one of titanium, vanadium, magnesium or niobium, and satisfies the relationship: x < y, x < z.

[0006] Furthermore, in the first active substance, the range of x is 0.01≤x≤0.03; and in the second active substance, the range of y is 0.04≤y≤0.06.

[0007] Furthermore, in the third active substance, the range of z is: 0.04≤z≤0.06.

[0008] Furthermore, if the thickness of the first sub-layer is d1 and the thickness of the second sub-layer is d2, then the following relationship is satisfied: 0.1≤d1 / d2≤0.5.

[0009] Furthermore, if the thickness of the second material layer is d3, then the following relationship is satisfied: 0.85≤(d1+d2) / d3≤1.

[0010] Furthermore, the median particle size D1 of the first active substance is in the range of 1.1 μm ≤ D1 ≤ 1.3 μm, the median particle size D2 of the second active substance is in the range of 0.8 μm ≤ D2 ≤ 1.0 μm, and the median particle size D3 of the third active substance is in the range of 0.8 μm ≤ D3 ≤ 1.0 μm.

[0011] Furthermore, the first active substance has a core-shell structure, comprising a core and a protective layer, wherein the protective layer covers the outer periphery of the core, and the core has the chemical formula LiFe. (1-x) M1 x PO4 / C, where the range of x is: 0.02≤x≤0.03.

[0012] Furthermore, the protective layer is an inorganic metal oxide layer, and the protective layer is selected from at least one of aluminum oxide layer, calcium oxide layer, and titanium oxide layer.

[0013] This application also provides a battery, the battery comprising: an electrode assembly provided in this application and an electrolyte, the electrolyte being used to wet at least a portion of the electrode assembly.

[0014] This application also provides an electrical device, which includes: a device body and a battery provided in this application, wherein the battery supplies power to the device body.

[0015] In this application, the first sub-layer, the second sub-layer, the current collector layer, and the second material layer are sequentially arranged. When the positive electrode, the separator, and the negative electrode are wound together to form the wound structure, at the bend of the same turn of the wound structure, in the direction from the central axis to the outside, the first sub-layer, the second sub-layer, the current collector layer, and the second material layer are arranged sequentially. At corresponding positions, i.e., at the bend and along any straight line from the central axis to the outside, the curvature of the first sub-layer, the second sub-layer, the current collector layer, and the second material layer gradually decreases. The first active material, the second active material, and the third active material are all active materials. The first dopant element, the second dopant element, and the third dopant element are all dopant elements. When dopant elements are added to the active material, and the mass content of the dopant element is large, the bond energy of the Li-O bond in the active material can be weakened, thereby reducing the diffusion resistance of lithium ions in the active material. This results in a faster rate of lithium ion insertion / extraction in the active material, and consequently, the active material can exhibit a higher specific capacity. Therefore, the specific capacity of the active material can be adjusted by regulating the mass content of the doping element. Specifically, in this application, if the mass content of the first doping element in the first active material is less than the mass content of the second doping element in the second active material, the Li-O bond energy in the first active material is stronger, the diffusion resistance of lithium ions in the first active material is greater, the rate of lithium ion insertion / extraction in the first active material is slower, and the specific capacity of the first active material is lower. Conversely, if the Li-O bond energy in the second active material is weaker, the diffusion resistance of lithium ions in the second active material is smaller, and the rate of lithium ion insertion / extraction in the second active material is faster, then the specific capacity of the second active material is greater than that of the first active material. When the positive electrode sheet is used... When the electrode assembly is a wound structure, within the same turn of the wound structure, the first sub-layer is closer to the central axis than the second sub-layer. The curvature of the first sub-layer is greater than that of the second sub-layer. The area of ​​the first sub-layer at corresponding positions is smaller, and the specific capacity of the first active material is less than that of the second active material. This balances the specific capacity per unit area at corresponding positions of the first and second sub-layers, ensuring that the specific capacity per unit area at corresponding positions of the first and second sub-layers is close to or equal. This prevents excessive lithium ion deintercalation from the first sub-layer, which would then deposit on the surface of the adjacent negative electrode, thus mitigating lithium plating on the surface of the negative electrode. Furthermore, the second sub-layer still has a higher specific capacity, ensuring that the first material layer still has a high capacity. The cooperation between the first and second sub-layers ensures that the first material layer has a high capacity while also mitigating lithium plating on the surface of the negative electrode.Similarly, if the mass content of the first dopant element in the first active material is less than the mass content of the third dopant element in the third active material, then the specific capacity of the third active material is greater than that of the first active material. In the same turn of the winding structure, the first sub-layer is closer to the central axis than the second material layer, and the curvature of the first sub-layer is greater than that of the second material layer. Therefore, the specific capacity of the first active material is less than that of the third active material, which balances the specific capacity per unit area at corresponding positions of the first and second material layers. This prevents excessive lithium ions from being extracted from the first sub-layer and deposited on the surface of the adjacent negative electrode, thus mitigating lithium plating on the surface of the negative electrode. Furthermore, the second material layer still has a high specific capacity, ensuring that the positive electrode still has a high capacity. Consequently, the positive electrode provided in this application enables the battery to have a high energy density while mitigating lithium plating on the negative electrode, thus extending the battery's lifespan. Furthermore, in this embodiment, the protective layer covers the outer periphery of the core. This protective layer increases the resistance to lithium ions entering and exiting the core, thereby increasing the difficulty of lithium ion deintercalation / intercalation in the first active material and reducing its performance, thus further reducing the specific capacity of the first active material. Within the same turn of the winding structure, the specific capacity per unit area of ​​the first sublayer can be reduced to balance the specific capacity per unit area at corresponding positions of the first sublayer and the second sublayer and / or the second material layer. This avoids excessive lithium ion deintercalation / intercalation from the first sublayer, mitigating lithium plating on the surface of the negative electrode and extending the battery's lifespan. By setting the protective layer and setting the mass content of the first dopant element to a low level, the two work synergistically to create a difference in lithium ion diffusion capacity between the side of the positive electrode near the central axis and the side away from the central axis. This results in a weaker lithium ion diffusion capacity on the side of the positive electrode near the central axis compared to the side away from the central axis, further mitigating lithium plating. Attached Figure Description

[0016] To more clearly illustrate the technical solutions of the embodiments of this application, the drawings used in the implementation will be briefly introduced below. Obviously, the drawings described below are some implementations of this application. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0017] Figure 1 This is a top view of a battery according to an embodiment of this application;

[0018] Figure 2 This is a schematic cross-sectional view of the positive electrode sheet according to an embodiment of this application;

[0019] Figure 3 This is a schematic diagram of the structure of the first active substance according to an embodiment of this application;

[0020] Figure 4 This is a partial cross-sectional structural diagram of a battery according to an embodiment of this application;

[0021] Figure 5 An electron scanning microscope of the first active substance according to an embodiment of this application;

[0022] Figure 6 An electron scanning microscope of the second active substance according to an embodiment of this application;

[0023] Figure 7 This is a schematic diagram of the structure of an electrical device according to an embodiment of this application;

[0024] Figure 8 This is a circuit block diagram of an electrical device according to an embodiment of this application.

[0025] Explanation of reference numerals in the attached figures:

[0026] 100 - Electrode assembly, 101 - Central axis, 110 - Positive electrode, 111 - Current collector layer, 112 - First material layer, 1121 - First sub-layer, 1122 - Second sub-layer, 113 - Second material layer, 120 - Separator, 130 - Negative electrode, 140 - First active material, 141 - Core, 142 - Protective layer, 200 - Battery, 210 - Electrolyte, 220 - Housing, 221 - Receptacle, 300 - Electrical device, 310 - Device body. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of this application.

[0028] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the listed steps or units, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to these processes, methods, products, or apparatuses.

[0029] In this document, references to "embodiment" or "implementation" mean that a particular feature, structure, or characteristic described in connection with an embodiment or implementation 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.

[0030] With the continuous development of lithium-ion batteries, lithium iron phosphate is widely used as a positive electrode active material. Its crystal structure belongs to olivine, which has good safety and stability. At present, lithium-ion batteries are increasingly pursuing high capacity indicators, but this will lead to some problems such as material processing and deterioration of electrical performance. In addition, the positive electrode, separator and negative electrode form a wound structure. The curvature of the inner side of the wound structure is larger, which leads to the difference in the content of active lithium ions on the inner and outer sides of the wound structure. More lithium ions are deposited per unit area on the inner side of the positive electrode closer to the wound structure, while the graphite used in the negative electrode expands more in volume, resulting in a smaller distance between the negative electrode and the positive electrode. This causes lithium deposition on the surface of the negative electrode and ultimately affects the service life of the battery.

[0031] Please see Figures 1 to 3This application provides an electrode assembly 100, which has a wound structure with a central axis 101. The electrode assembly 100 includes a positive electrode 110, a separator 120, and a negative electrode 130. The separator 120 is located between the positive electrode 110 and the negative electrode 130. The positive electrode 110 includes a current collector layer 111, a first material layer 112, and a second material layer 113. The first material layer 112 is disposed on the side of the current collector layer 111 facing the central axis 101. The first material layer 112 includes a first sub-layer 1121 and a second sub-layer 1122. The first sub-layer 1121 is closer to the central axis 101 than the second sub-layer 1122. The first sub-layer 1121 includes a first active material 140, which has a core-shell structure. The first active material 140 includes a core 141 and a protective layer 142, the protective layer 142 covering the outer periphery of the core 141. The first active material 140 includes lithium iron phosphate and a first dopant element. The second sublayer 1122 includes a second active material, the second active material including lithium iron phosphate and a second dopant element. The mass content of the first dopant element in the first active material 140 is less than the mass content of the second dopant element in the second active material. The second material layer 113 is disposed on the side of the current collector layer 111 away from the central axis 101. The second material layer 113 includes the third active material, the third active material including lithium iron phosphate and a third dopant element. The mass content of the first dopant element in the first active material 140 is less than the mass content of the third dopant element in the third active material.

[0032] Understandably, the positive electrode 110, the separator 120, and the negative electrode 130 are stacked and then wound to form the wound structure. Specifically, in the same turn of the wound structure, the positive electrode 110, the separator 120, and the negative electrode 130 are arranged sequentially in the direction from the central axis 101 outward.

[0033] Understandably, the first material layer 112, the current collector layer 111, and the second material layer 113 are stacked in sequence and then wound together, with the first material layer 112 being closer to the central axis 101 of the winding structure than the second material layer 113.

[0034] Understandably, the first sub-layer 1121, the second sub-layer 1122, the current collector layer 111 and the second material layer 113 are stacked sequentially, with the first sub-layer 1121 being closer to the central axis 101 of the winding structure than the second sub-layer 1122.

[0035] Optionally, the first active material 140 includes lithium iron phosphate and a first doping element, wherein the first doping element is used to dope the lithium iron phosphate; the second active material includes lithium iron phosphate and a second doping element, wherein the second doping element is used to dope the lithium iron phosphate; and the third active material includes lithium iron phosphate and a third doping element, wherein the third doping element is used to dope the lithium iron phosphate. In other words, the raw materials for the first active material 140, the second active material, and the third active material all include lithium iron phosphate.

[0036] In this embodiment, the first sub-layer 1121, the second sub-layer 1122, the current collector layer 111, and the second material layer 113 are arranged sequentially. When the positive electrode 110, the separator 120, and the negative electrode 130 are wound to form the winding structure, at the bend of the same turn of the winding structure, in the direction from the central axis 101 to the outside, the first sub-layer 1121, the second sub-layer 1122, the current collector layer 111, and the second material layer 113 are arranged sequentially. Then, at the corresponding position, that is, at the bend and on any straight line from the central axis 101 to the outside, the curvature of the first sub-layer 1121, the curvature of the second sub-layer 1122, the curvature of the current collector layer 111, and the curvature of the second material layer 113 gradually decrease. The first active material 140, the second active material, and the third active material are all active materials. The first dopant element, the second dopant element, and the third dopant element are all dopant elements. When dopant elements are added to the active materials, and the mass content of the dopant elements is relatively large, the bond energy of the Li-O bonds in the active materials can be weakened, thereby reducing the diffusion resistance of lithium ions in the active materials. This results in a faster rate of lithium ion insertion / extraction in the active materials, and consequently, the active materials can exhibit a higher specific capacity. Therefore, the specific capacity of the active materials can be adjusted by regulating the mass content of the dopant elements.Specifically, in this embodiment, the mass content of the first doped element in the first active material 140 is less than the mass content of the second doped element in the second active material. Therefore, the Li-O bond energy in the first active material 140 is stronger, resulting in greater diffusion resistance of lithium ions and a slower rate of lithium ion insertion / extraction in the first active material 140, thus leading to a lower specific capacity. Conversely, the Li-O bond energy in the second active material is weaker, resulting in less diffusion resistance of lithium ions and a faster rate of lithium ion insertion / extraction in the second active material. This makes the specific capacity of the second active material greater than that of the first active material 140. When the positive electrode 110 is applied to the electrode assembly 100 and the electrode assembly 100 is rolled up... During the winding process, within the same turn of the winding structure, the first sub-layer 1121 is closer to the central axis 101 than the second sub-layer 1122. The curvature of the first sub-layer 1121 is greater than that of the second sub-layer 1122. At corresponding positions of the first and second sub-layers 1121, the area of ​​the first sub-layer 1121 is smaller, and the specific capacity of the first active material 140 is less than that of the second active material. This balances the specific capacity per unit area at corresponding positions of the first and second sub-layers 1121, ensuring that the specific capacity per unit area at corresponding positions of the first and second sub-layers 1122 is close to or equal. This prevents excessive lithium ions from being extracted from the first sub-layer 1121 and deposited on the surface of the adjacent negative electrode 130, thereby mitigating lithium deposition on the surface of the negative electrode 130. Furthermore, the second sub-layer 1122 still has a high specific capacity, ensuring that the first material layer 112 still has a high capacity. The first sub-layer 1121 and the second sub-layer 1122 work together to ensure that the first material layer 112 has a high capacity and to mitigate lithium plating on the surface of the negative electrode 130. Similarly, the mass content of the first dopant element in the first active material 140 is less than the mass content of the third dopant element in the third active material, resulting in a greater specific capacity of the third active material than that of the first active material 140. In the same turn of the winding structure, the first sub-layer 1121 is closer to the central axis 101 than the second material layer 113, and the curvature of the first sub-layer 1121 is greater than that of the second material layer 113. The specific capacity of the first active material 140 is less than that of the third active material, which balances the specific capacity per unit area at corresponding positions of the first material layer 112 and the second material layer 113. This prevents excessive lithium ions from being extracted from the first sub-layer 1121 and deposited on the surface of the adjacent negative electrode 130, thereby mitigating lithium plating on the surface of the negative electrode 130.Furthermore, the second material layer 113 still has a high specific capacity, thus ensuring that the positive electrode 110 still has a high capacity. Consequently, the positive electrode 110 provided in this embodiment not only enables the battery 200 to have a high energy density but also mitigates lithium plating on the negative electrode 130, which helps extend the lifespan of the battery 200. Further, in this embodiment, the protective layer 142 covers the outer periphery of the core 141. The protective layer 142 increases the resistance of lithium ions entering and exiting the core 141, thereby increasing the difficulty of lithium ion intercalation / deintercalation in the first active material 140, reducing the performance of lithium ion intercalation / deintercalation in the first active material 140, and further reducing the specific capacity of the first active material 140. Within the same turn of the winding structure, the specific capacity per unit area of ​​the first sub-layer 1121 can be reduced to balance the specific capacity per unit area at corresponding positions of the first sub-layer 1121, the second sub-layer 1122, and / or the second material layer 113. This avoids excessive lithium ion deintercalation from the first sub-layer 1121, thus mitigating lithium plating on the surface of the negative electrode 130 and extending the lifespan of the battery 200. By setting the protective layer 142 and setting the mass content of the first dopant element to be relatively low, the two work synergistically to create a difference in lithium ion diffusion capacity between the side of the positive electrode 110 near the central axis 101 and the side away from the central axis 101. This results in a weaker lithium ion diffusion capacity on the side of the positive electrode 110 near the central axis 101 compared to the side away from the central axis 101, thereby better mitigating lithium plating.

[0037] Understandably, in the terminology of this application, when the positive electrode 110, the diaphragm 120 and the negative electrode 130 are stacked and arranged with multiple turns around the central axis 101, and the positive electrode 110, the diaphragm 120 and the negative electrode 130 have the same number of turns around the central axis 101, it is referred to as "the same turn in the winding structure".

[0038] Understandably, in the terminology of this application, the "specific capacity" of an active material refers to the ratio of the electrical capacity that the active material can release to the mass of the active material. Therefore, the higher the specific capacity of the active material, the better the rate and performance of lithium ion insertion / extraction of the active material.

[0039] Understandably, the winding structure is wound around the central axis 101, with the innermost loop being the one closest to the central axis 101 and the outermost loop being the one furthest from the central axis 101. The number of winding turns gradually increases from the innermost loop to the outermost loop. Suppose that in the nth turn of the winding structure, the first sublayer 1121 de-intercalates too many lithium ions. During the charging and discharging process of the battery 200, the volume of the negative electrode 130 expands, causing the distance between the first sublayer 1121 in the nth turn and the negative electrode 130 in the (n-1)th turn to decrease. As a result, the excess lithium ions deposited in the first sublayer 1121 in the nth turn will be deposited on the surface of the negative electrode 130 in the (n-1)th turn of the winding structure.

[0040] Optionally, the first doping element is selected from a metallic element. The second doping element is selected from a metallic element. The third doping element is selected from a metallic element. It can be understood that the first doping element is doped into at least one lithium site and at least one iron site in the first active material 140; the second doping element is doped into at least one lithium site and at least one iron site in the second active material; and the third doping element is doped into at least one lithium site and at least one iron site in the third active material.

[0041] Optionally, the ionic resistivity of the first sublayer 1121 is greater than that of the second sublayer 1122, and the ionic resistivity of the first sublayer 1121 is greater than that of the second material layer 113. In this embodiment, the rate of lithium ion insertion / extraction of the first active material 140 in the first sublayer 1121 is less than the rate of lithium ion insertion / extraction of the second active material in the second sublayer 1122, and the rate of lithium ion insertion / extraction of the first active material 140 in the first sublayer 1121 is less than the rate of lithium ion insertion / extraction of the third active material in the second material layer 113. This can effectively slow down the lithium plating phenomenon of the negative electrode 130 and improve the cycle performance of the battery 200.

[0042] In some embodiments, the core 141 of the first active substance 140 has the chemical formula LiFe. (1-x) M1 x PO4 / C, the chemical formula of the second active substance is LiFe (1-y) M2 y PO4 / C, the chemical formula of the third active substance is LiFe (1-z) M3 z PO4 / C, wherein M1 is the first doping element, which is selected from at least one of titanium (Ti), vanadium (V), magnesium (Mg) or niobium (Nb); M2 is the second doping element, which is selected from at least one of titanium, vanadium, magnesium or niobium; and M3 is the third doping element, which is selected from at least one of titanium, vanadium, magnesium or niobium, and satisfies the relationship: x < y, x < z.

[0043] Understandably, x represents the mass content of the first dopant element in the core 141 of the first active material 140. y represents the mass content of the second dopant element in the second active material. z represents the mass content of the third dopant element in the third active material.

[0044] Understandably, in some embodiments, the first dopant element, the second dopant element, and the third dopant element are selected from the same type of titanium, vanadium, magnesium, or niobium. In other embodiments, the first dopant element, the second dopant element, and the third dopant element are selected from different types of titanium, vanadium, magnesium, or niobium.

[0045] Understandably, the core 141 of the first active substance 140 has the chemical formula LiFe. (1-x) M1 x If PO4 / C, then the first active material 140 is a mixture of lithium iron phosphate and carbon after being doped with the first doping element.

[0046] Understandably, the chemical formula of the second active substance is LiFe. (1-y) M2 y If PO4 / C, then the second active material is a mixture of lithium iron phosphate and carbon after being doped with a second doping element.

[0047] Understandably, the chemical formula of the third active substance is LiFe. (1-z) M3 z If PO4 / C, then the third active material is a mixture of lithium iron phosphate and carbon after being doped with a third doping element.

[0048] In this embodiment, the core 141 of the first active material 140 has the chemical formula LiFe. (1-x) M1 x PO4 / C, the chemical formula of the second active substance is LiFe (1-y) M2 yIf the ratio of PO4 / C satisfies the relationship x < y, then the mass content of the first doped element is less than that of the second doped element. Therefore, the resistance to lithium ion diffusion in the first active material 140 is greater than that in the second active material, resulting in a smaller specific capacity of the first active material 140 compared to the second active material. This balances the specific capacity per unit area at corresponding positions in the first sublayer 1121 and the second sublayer 1122, preventing excessive lithium ion deintercalation from the first sublayer 1121 and subsequent deposition on the surface of the adjacent negative electrode 130, thus mitigating lithium deposition on the surface of the negative electrode 130. Furthermore, the second sublayer 1122 still has a high specific capacity, ensuring that the first material layer 112 still has a high capacity. Similarly, the chemical formula of the third active material is LiFe. (1-z) M3 z If PO4 / C and the relationship x < z is satisfied, then the mass content of the first doped element is less than the mass content of the third doped element. The resistance to the diffusion of lithium ions in the first active material 140 is greater than the resistance to the diffusion in the third active material, thereby making the specific capacity of the first active material 140 less than that of the third active material. In the same turn of the winding structure, the first sub-layer 1121 is closer to the central axis 101 than the second material layer 113. The curvature of the first sub-layer 1121 is greater than that of the second material layer 113. The specific capacity of the first active material 140 is less than that of the third active material, which can balance the specific capacity per unit area at the corresponding positions of the first material layer 112 and the second material layer 113, so as to avoid excessive lithium ions being extracted from the first sub-layer 1121 and deposited on the surface of the adjacent negative electrode 130, thereby slowing down the phenomenon of lithium plating on the surface of the negative electrode 130. Furthermore, the second material layer 113 still has a high specific capacity, which allows the positive electrode 110 to still have a high capacity. Consequently, the positive electrode 110 provided in this embodiment can not only enable the battery 200 to have a high energy density, but also reduce the lithium plating phenomenon of the negative electrode 130, which is beneficial to extending the service life of the battery 200.

[0049] Preferably, in some embodiments, the second active material is the same as the third active material; in other words, the second active material and the third active material satisfy the relationship y = z, and the second dopant element M2 and the third dopant element M3 are selected from the same element.

[0050] In this embodiment, when the second active material is the same as the third active material, the active materials in the second sub-layer 1122 and the second material layer 113 are the same, which is beneficial to improving the consistency of the positive electrode 110. On the one hand, it facilitates the processing of the positive electrode 110, and on the other hand, it is beneficial to improve the cycle performance of the battery 200.

[0051] In some embodiments, in the first active substance 140, the range of x is: 0.01≤x≤0.03.

[0052] Specifically, the value of x can be, but is not limited to, 0.01, 0.012, 0.014, 0.015, 0.018, 0.02, 0.021, 0.022, 0.023, 0.024, 0.025, 0.026, 0.027, 0.028, 0.029, and 0.03.

[0053] In the first active material 140 provided in this embodiment, when x satisfies the range 0.01≤x≤0.03, the mass content of the first dopant element is within a reasonable range. On the one hand, in the first active material 140, the bond energy of the Li-O bond is within a reasonable range, the diffusion resistance of lithium ions in the first active material 140 is small, the rate of lithium ion insertion / extraction in the first active material 140 is slow, and the specific capacity of the first active material 140 is low. In the same turn of the winding structure, the specific capacity per unit area of ​​the first sublayer 1121 can be reduced to balance the specific capacity per unit area at the corresponding positions of the first sublayer 1121 and the second sublayer 1122 and / or the second material layer 113, thereby avoiding excessive lithium ion insertion / extraction from the first sublayer 1121, thus slowing down the phenomenon of lithium plating on the surface of the negative electrode 130 and extending the service life of the battery 200. On the other hand, the specific capacity of the first active material 140 is not so low that the capacity of the positive electrode 110 is too low, thus enabling the battery 200 to have both high capacity, energy density, and good safety performance. When the value of x is too large, the mass content of the first dopant element is too large, and the bond energy of the Li-O bond in the first active material 140 is still relatively weak. The diffusion resistance of lithium ions in the first active material 140 is too small, the rate of lithium ion insertion and extraction in the first active material 140 is too fast, and the specific capacity of the first active material 140 is too high. In the winding structure, the excessive lithium ions extracted from the first active material 140 of the first sublayer 1121 form lithium plating on the surface of the adjacent negative electrode 130, resulting in poor cycle performance of the battery 200. When the value of x is too small, the mass content of the first doped element is too small, and correspondingly, the specific capacity of the first active material 140 is too low. Although it can alleviate the lithium plating phenomenon of the negative electrode 130 to a certain extent, it also makes the capacity of the positive electrode 110 too low, thus making the capacity and energy density of the battery 200 low.

[0054] Preferably, in the first active substance 140, the range of x is: 0.02≤x≤0.03.

[0055] In some embodiments, in the second active substance, the range of y is: 0.04≤y≤0.06.

[0056] Specifically, the value of y can be, but is not limited to, 0.04, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, 0.05, 0.052, 0.054, 0.056, 0.058, and 0.06.

[0057] In the second active material provided in this embodiment, when y satisfies the range 0.04≤y≤0.06, the mass content of the second dopant element is within a reasonable range. In the second active material, the second dopant element causes lattice distortion in lithium iron phosphate, and the degree of lattice distortion is within a reasonable range. The bond energy of the Li-O bond in the second active material doped with the second dopant element is weaker, the diffusion resistance of lithium ions in the second active material is smaller, and the rate of lithium ion insertion / extraction in the second active material is faster, resulting in a larger specific capacity of the second active material. Consequently, the first material layer 112 has a larger specific capacity, and the positive electrode 110 has a larger capacity. When the electrode assembly 100 is applied to the battery 200, the battery 200 has a higher capacity and energy density. When the value of y is too large, the mass content of the second dopant element is too high. Given that the distortion of the crystal structure is finite, excessive second dopant elements in the second active material may cause the formation of impurity compounds, thereby reducing the lithium-ion intercalation / deintercalation performance of the second active material. This, in turn, reduces the capacity performance of the positive electrode 110 and the electrode assembly 100, resulting in a lower capacity and energy density of the battery 200. When the value of y is too small, the mass content of the second dopant element is too small, resulting in a low specific capacity of the second active material in the second sublayer 1122. If the specific capacity of the first active material 140 is low, the specific capacity of the first material layer 112 will also be low, reducing the capacity of the positive electrode 110. This, in turn, results in a low capacity and energy density of the battery 200, thus reducing the overall performance of the battery 200.

[0058] Preferably, in the second active substance, the range of y is: 0.04≤y≤0.05.

[0059] In some embodiments, the range of z in the third active substance is: 0.04≤z≤0.06.

[0060] Specifically, the value of z can be, but is not limited to, 0.04, 0.041, 0.042, 0.043, 0.044, 0.045, 0.046, 0.047, 0.048, 0.049, 0.05, 0.052, 0.054, 0.056, 0.058, and 0.06.

[0061] In the third active material provided in this embodiment, when z satisfies the range 0.04≤z≤0.06, the mass content of the third doping element is within a reasonable range. In the third active material, the third doping element causes lattice distortion in lithium iron phosphate, and the degree of lattice distortion is within a reasonable range. The bond energy of the Li-O bond in the third active material doped with the third doping element is weaker, the diffusion resistance of lithium ions in the third active material is smaller, and the rate of lithium ion insertion / extraction in the third active material is faster, resulting in a larger specific capacity of the third active material. Consequently, the second material layer 113 has a larger specific capacity, and the positive electrode 110 has a larger capacity. When the electrode assembly 100 is applied to the battery 200, the battery 200 has a higher capacity and energy density. When the value of z is too large, the mass content of the third dopant element is too high. Excessive third dopant element in the third active material may cause the formation of impurity compounds, thus reducing the lithium-ion intercalation / deintercalation performance of the third active material. This, in turn, reduces the capacity performance of the positive electrode 110 and the electrode assembly 100, resulting in a lower capacity and energy density of the battery 200. When the value of z is too small, the mass content of the third dopant element is too small. This results in a low specific capacity of the third active material in the second material layer 113. If the specific capacity of the second material layer 113 is too low, given the relatively low capacity of the first material layer 112, the capacity of the positive electrode 110 will be too low, leading to a lower capacity and energy density of the battery 200, thus reducing the overall performance of the battery 200.

[0062] Preferably, in the third active substance, the range of z is: 0.04≤z≤0.05.

[0063] In some embodiments, the protective layer 142 is an inorganic metal oxide layer, and the protective layer 142 is selected from at least one of aluminum oxide layer, calcium oxide layer, and titanium oxide layer.

[0064] In this embodiment, the protective layer 142 is an inorganic metal oxide layer, selected from at least one of aluminum oxide, calcium oxide, and titanium oxide. The protective layer 142 has a low ionic conductivity to further reduce the rate of lithium ion insertion or extraction from the core 141, thereby reducing the specific capacity of the first active material 140. Within the same turn of the winding structure, the specific capacity per unit area of ​​the first sublayer 1121 can be reduced to balance the specific capacity per unit area at corresponding positions of the first sublayer 1121 and the second sublayer 1122 and / or the second material layer 113. This prevents excessive lithium ion insertion / extraction from the first sublayer 1121, thus mitigating lithium plating on the surface of the negative electrode 130 and extending the lifespan of the battery 200.

[0065] Please see Figure 2 In some embodiments, the thickness of the first sublayer 1121 is d1 and the thickness of the second sublayer 1122 is d2, which satisfies the relationship: 0.1≤d1 / d2≤0.5.

[0066] Specifically, the value of d1 / d2 can be, but is not limited to, 0.1, 0.12, 0.14, 0.16, 0.18, 0.2, 0.22, 0.24, 0.26, 0.28, 0.3, 0.32, 0.35, 0.38, 0.4, 0.42, 0.45, 0.48, 0.49, and 0.5.

[0067] In this embodiment, when the thickness d1 of the first sublayer 1121 and the thickness d2 of the second sublayer 1122 satisfy the relationship 0.1≤d1 / d2≤0.5, the thicknesses of the first sublayer 1121 and the second sublayer 1122 are within a reasonable range. The first sublayer 1121 includes a first active material 140, and the mass content of the first dopant element in the first active material 140 is relatively low, resulting in a low specific capacity of the first active material 140 and a low capacity of the first sublayer 1121. The second sublayer 1122 includes a second active material, and the mass content of the second dopant element in the second active material is relatively high, resulting in a high specific capacity of the second active material and a high capacity of the second sublayer 1122. On the one hand, in the winding structure, the rate of lithium ion insertion / extraction in the first sublayer 1121 can be slowed down, preventing excessive lithium ions from being extracted from the first sublayer 1121 and deposited on the surface of the negative electrode 130, thereby mitigating lithium deposition on the surface of the negative electrode 130 and improving the safety performance of the battery 200. On the other hand, this avoids the first sub-layer 1121 being too thick, which would result in an excessively low capacity of the first material layer 112, thus ensuring that the positive electrode 110 still has a high capacity, allowing the electrode assembly 100 to possess both high capacity and high safety performance. When the value of d1 / d2 is too large, the thickness of the first sub-layer 1121 becomes too large or the thickness of the second sub-layer 1122 becomes too small. The capacity of the first sub-layer 1121 is low, and the first sub-layer 1121 occupies too much space in the first material layer 112. Although the capacity of the second sub-layer 1122 is high, the second sub-layer 1122 occupies too little space in the first material layer 112, thereby reducing the capacity of the positive electrode 110. Although this can better mitigate the lithium plating phenomenon on the surface of the negative electrode 130, when the electrode assembly 100 is applied to the battery 200, the capacity and energy density of the battery 200 are too low. When the value of d1 / d2 is too small, the thickness of the first sub-layer 1121 is too small or the thickness of the second sub-layer 1122 is too large. Consequently, in the positive electrode 110, there is less of the first active material 140, and the first sub-layer 1121 is unable to play a role in mitigating lithium plating. In the same turn of the winding structure, both the first material layer 112 and the second material layer 113 deposit a large number of lithium ions. This results in an excessive specific capacity per unit area of ​​the first material layer 112. The excessive lithium ions deposited in the first material layer 112 are easily deposited on the surface of the negative electrode 130, thereby affecting the cycle performance of the battery 200.

[0068] Optionally, the thickness d1 of the first sublayer 1121 is in the range of 3μm≤d1≤25μm.

[0069] Specifically, the thickness d1 of the first sublayer 1121 can be, but is not limited to, 3μm, 5μm, 8μm, 10μm, 12μm, 14μm, 16μm, 17μm, 18μm, 20μm, 21μm, 23μm and 25μm.

[0070] In this embodiment, when the thickness d1 of the first sublayer 1121 satisfies the range of 3μm≤d1≤25μm, the thickness of the first sublayer 1121 is within a reasonable range. The first sublayer 1121 includes a first active material 140, and the mass content of the first dopant element in the first active material 140 is relatively low, resulting in a relatively low specific capacity of the first active material 140. On the one hand, the relatively low specific capacity of the first active material 140 in the first sublayer 1121 slows down the rate of lithium ion insertion / extraction in the first sublayer 1121 in the winding structure, preventing excessive lithium ions from being extracted from the first sublayer 1121 and deposited on the surface of the negative electrode 130, thereby mitigating lithium deposition on the surface of the negative electrode 130 and improving the safety performance of the battery 200. On the other hand, it avoids the first sublayer 1121 being too thick, which would result in an excessively low capacity of the first material layer 112, thus ensuring that the positive electrode 110 still has a high capacity, allowing the electrode assembly 100 to have both high capacity and high safety performance. When the thickness of the first sub-layer 1121 is too large, it occupies too much space in the first material layer 112, resulting in a lower capacity of the first material layer 112 and thus reducing the capacity of the positive electrode 110. Although it can better mitigate lithium plating on the surface of the negative electrode 130, when the electrode assembly 100 is applied to the battery 200, the capacity and energy density of the battery 200 are too low. When the thickness of the first sub-layer 1121 is too small, the first active material 140 is less in the positive electrode 110, and the first sub-layer 1121 is less effective in mitigating lithium plating. In the same turn of the winding structure, both the first material layer 112 and the second material layer 113 deposit a large amount of lithium ions, resulting in an excessive specific capacity per unit area of ​​the first material layer 112. The excessive lithium ions deposited in the first material layer 112 are prone to deposit on the surface of the negative electrode 130, thus affecting the cycle performance of the battery 200.

[0071] Optionally, the thickness d2 of the second sublayer 1122 is in the range of 35μm≤d2≤55μm.

[0072] Specifically, the thickness d2 of the second sublayer 1122 can be, but is not limited to, 35μm, 36μm, 38μm, 40μm, 42μm, 44μm, 45μm, 47μm, 48μm, 50μm, 52μm, 53μm, 54μm and 55μm.

[0073] In this embodiment, when the thickness d2 of the second sublayer 1122 satisfies the range of 35μm≤d2≤55μm, the thickness of the second sublayer 1122 is within a reasonable range. On the one hand, when the capacity of the first sublayer 1121 is low, the mass content of the second dopant element of the second active material in the second sublayer 1122 is high, resulting in a higher specific capacity of the second active material, thus giving the second sublayer 1122 a higher capacity. This allows the first material layer 112 to have both a high capacity and to mitigate lithium plating. On the other hand, it avoids the second sublayer 1122 from being too thick, which would lead to an excessively thick positive electrode 110, thereby ensuring better performance of the electrode assembly 100. When the thickness of the second sublayer 1122 is too large, it will result in an excessively large thickness of the positive electrode 110, reducing the performance of the electrode assembly 100. When the thickness of the second sub-layer 1122 is too small, the capacity of the second sub-layer 1122 will also be low if the capacity of the first sub-layer 1121 is low. This results in the capacity of the first material layer 112 being too low, which is not conducive to improving the capacity of the positive electrode 110 and ultimately reduces the capacity performance and energy density of the battery 200.

[0074] In some embodiments, the thickness of the second material layer 113 is d3, which satisfies the relationship: 0.85≤(d1+d2) / d3≤1.

[0075] Understandably, d1+d2 represents the thickness of the first material layer 112.

[0076] Understandably, the thickness of the first material layer 112 is less than or equal to the thickness of the second material layer 113.

[0077] Specifically, the value of (d1+d2) / d3 can be, but is not limited to, 0.85, 0.86, 0.87, 0.88, 0.89, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, and 1.

[0078] In this embodiment, when the electrode assembly 100 satisfies the relationship 0.85≤(d1+d2) / d3≤1, the thicknesses of the second material layer 113 and the first material layer 112 are both within a reasonable range. On the one hand, this allows for a difference in the capacity utilization of the first material layer 112 and the second material layer 113. That is, in the same turn of the winding structure, the rate of lithium ion insertion / extraction in the first material layer 112 is less than the rate of lithium ion insertion / extraction in the second material layer 113. This prevents excessive lithium ions from being deposited on the surface of the negative electrode 130 due to the first sublayer 1121 of the first material layer 112, thereby ensuring better safety performance of the positive electrode 110. On the other hand, the first material layer 112 and the second material layer 113 still maintain a high capacity, resulting in a high capacity for the positive electrode 110. Consequently, when the electrode assembly 100 is applied to the battery 200, the battery 200 has a high capacity and energy density. When (d1+d2) / d3 is too large, the thickness of the first material layer 112 is too large and the thickness of the second material layer 113 is too small. The first material layer 112 includes a first sub-layer 1121 and a second sub-layer 1122. If the first sub-layer 1121 is too large, it may result in the capacity of the first material layer 112 being too low, and the thickness of the second material layer 113 being too small. Consequently, the capacity of the positive electrode 110 is too low, which reduces the capacity and energy density of the battery 200 when the electrode assembly 100 is applied to the battery 200. When (d1+d2) / d3 is too small, the thickness of the first material layer 112 is too small and the thickness of the second material layer 113 is too large. If the thickness of the first sub-layer 1121 in the first material layer 112 is too small, the first sub-layer 1121 will be unable to play a role in mitigating the lithium plating phenomenon. In the same turn of the winding structure, both the first material layer 112 and the second material layer 113 will deposit a large number of lithium ions, which will result in an excessive specific capacity per unit area of ​​the first material layer 112. The excessive lithium ions deposited in the first material layer 112 are easy to deposit on the surface of the negative electrode 130, thereby affecting the cycle performance of the battery 200.

[0079] Optionally, the thickness d3 of the second material layer 113 is in the range of 30μm≤d3≤60μm.

[0080] Specifically, the thickness d3 of the second material layer 113 can be, but is not limited to, 30μm, 32μm, 35μm, 38μm, 40μm, 42μm, 45μm, 50μm, 52μm, 53μm, 56μm and 60μm.

[0081] In this embodiment, when the thickness d3 of the second material layer 113 satisfies the range of 30μm≤d3≤60μm, the thickness of the second material layer 113 is within a reasonable range, and the second material layer 113 has a suitable capacity, so that when the electrode assembly 100 is applied to the battery 200, the battery 200 has a high capacity and energy density. When the thickness of the second material layer 113 is too large, it will result in an excessively large thickness of the positive electrode 110, reducing the performance of the electrode assembly 100. When the thickness of the second material layer 113 is too small, it will result in an excessively low capacity of the second material layer 113, which is not conducive to improving the capacity of the positive electrode 110, and ultimately reduces the capacity performance and energy density of the battery 200.

[0082] In some embodiments, the median particle size D1 of the first active substance 140 is in the range of 1.1 μm ≤ D1 ≤ 1.3 μm.

[0083] Specifically, the median particle size D1 of the first active substance 140 can be, but is not limited to, 1.1 μm, 1.11 μm, 1.13 μm, 1.15 μm, 1.18 μm, 1.2 μm, 1.21 μm, 1.23 μm, 1.24 μm, 1.26 μm, 1.28 μm, and 1.3 μm.

[0084] Understandably, in some embodiments, when the mass content of the first dopant element in the first active material 140 is low, the median particle size of the first active material 140 is large.

[0085] In this embodiment, when the median particle size D1 of the first active material 140 satisfies the range 1.1μm≤D1≤1.3μm, the median particle size of the first active material 140 is within a reasonable range. On the one hand, this facilitates the placement of the first active material 140 on the first sub-layer 1121, so that the first sub-layer 1121 can play a role in mitigating the occurrence of lithium plating. On the other hand, the median particle size of the first active material 140 is larger than that of the second active material and the third active material, and the median particle size of the first active material 140 is negatively correlated with the mass content of the first dopant element. In other words, the mass content of the first dopant element in the first active material 140 is low and within a reasonable range. In the first active material 140, the bond energy of the Li-O bond is within a reasonable range, the diffusion resistance of lithium ions in the first active material 140 is small, the rate of lithium ion insertion / extraction in the first active material 140 is slow, and the specific capacity of the first active material 140 is low. In the same turn of the winding structure, the specific capacity per unit area of ​​the first sublayer 1121 can be reduced to balance the specific capacity per unit area at the corresponding positions of the first sublayer 1121 and the second sublayer 1122 and / or the second material layer 113, thereby avoiding excessive lithium ion insertion / extraction from the first sublayer 1121, thus slowing down the phenomenon of lithium plating on the surface of the negative electrode 130 and extending the service life of the battery 200. Furthermore, the specific capacity of the first active material 140 is not so low that the capacity of the positive electrode 110 is too low, thus enabling the battery 200 to possess both high capacity, energy density, and good safety performance. When the median particle size of the first active material 140 is too large, on the one hand, it is not conducive to placing the first active material 140 in the first sublayer 1121. On the other hand, if the median particle size of the first active material 140 is too large, the mass content of the first dopant element in the first active material 140 will be too low. Although this can alleviate the lithium plating phenomenon of the negative electrode 130 to a certain extent, it also makes the capacity of the positive electrode 110 too low, resulting in a lower capacity and energy density of the battery 200. When the median particle size of the first active material 140 is too small, the mass content of the first dopant element in the first active material 140 is too high, and the specific capacity of the first active material 140 is too high. In the winding structure, the excessive lithium ions released from the first active material 140 of the first sub-layer 1121 form lithium plating on the surface of the adjacent negative electrode 130, thereby making the cycle performance of the battery 200 too poor.

[0086] In some embodiments, the median particle size D2 of the second active substance is in the range of 0.8 μm ≤ D2 ≤ 1.0 μm.

[0087] Specifically, the median particle size D2 of the second active substance can be, but is not limited to, 0.8 μm, 0.82 μm, 0.83 μm, 0.85 μm, 0.88 μm, 0.9 μm, 0.92 μm, 0.93 μm, 0.95 μm, 0.96 μm, 0.97 μm, 0.99 μm, and 1.0 μm.

[0088] Understandably, in some embodiments, when the mass content of the second dopant element in the second active material is high, the median particle size of the first active material 140 is small.

[0089] In this embodiment, when the median particle size D2 of the second active material satisfies the range 0.8 μm ≤ D2 ≤ 1.0 μm, the median particle size of the second active material is within a reasonable range. On the one hand, this facilitates the placement of the second active material on the second sub-layer 1122, allowing the second sub-layer 1122 to cooperate with the first sub-layer 1121, so that the first material layer 112 can both mitigate lithium plating on the surface of the negative electrode 130 and have a high capacity. On the other hand, the median particle size of the second active material is negatively correlated with the mass content of the second dopant element. In other words, if the mass content of the second dopant element in the second active material is high and within a reasonable range, the bond energy of the Li-O bond in the second active material doped with the second dopant element is weaker, the diffusion resistance of lithium ions in the second active material is smaller, and the rate of lithium ion insertion / extraction in the second active material is faster, resulting in a larger specific capacity of the second active material. Consequently, the first material layer 112 has a larger specific capacity, and the positive electrode 110 has a larger capacity. When the electrode assembly 100 is applied to the battery 200, the battery 200 has a high capacity and energy density. When the median particle size of the second active material is too large, the mass content of the second dopant element in the second active material is correspondingly low. If the specific capacity of the first active material 140 is low, the specific capacity of the first material layer 112 will also be low, thereby reducing the capacity of the positive electrode 110, and consequently, the capacity and energy density of the battery 200 will be too low, reducing the performance of the battery 200. When the median particle size of the second active material is too small, on the one hand, it increases the difficulty of preparing the second active material, thus increasing the processing cost of the electrode assembly 100. On the other hand, correspondingly, the mass content of the second dopant element in the second active material is too high. Excessive second dopant elements may cause the second active material to form impurity compounds, thereby reducing the lithium-ion intercalation / deintercalation performance of the second active material, and consequently reducing the capacity performance of the positive electrode 110 and the electrode assembly 100, resulting in a lower capacity and energy density of the battery 200.

[0090] In some embodiments, the median particle size D3 of the third active substance is in the range of 0.8 μm ≤ D3 ≤ 1.0 μm.

[0091] Specifically, the median particle size D3 of the third active substance can be, but is not limited to, 0.8 μm, 0.82 μm, 0.83 μm, 0.85 μm, 0.88 μm, 0.9 μm, 0.92 μm, 0.93 μm, 0.95 μm, 0.96 μm, 0.97 μm, 0.99 μm, and 1.0 μm.

[0092] Understandably, in some embodiments, when the mass content of the second dopant element in the second active material is high, the median particle size of the first active material 140 is small.

[0093] In this embodiment, when the median particle size D3 of the third active material satisfies the range of 0.8 μm ≤ D3 ≤ 1.0 μm, the median particle size of the third active material is within a reasonable range. On the one hand, this facilitates the placement of the third active material on the second material layer 113, allowing the second material layer 113 to cooperate with the first material layer 112, so that the positive electrode 110 can both mitigate lithium plating on the surface of the negative electrode 130 and have a higher capacity. On the other hand, the median particle size of the third active material is negatively correlated with the mass content of the third dopant element. In other words, if the mass content of the third dopant element in the third active material is relatively high and within a reasonable range, the bond energy of the Li-O bond in the third active material doped with the third dopant element is weaker, the diffusion resistance of lithium ions in the third active material is smaller, and the rate of lithium ion insertion / extraction in the third active material is faster, resulting in a larger specific capacity of the third active material and a larger capacity for the positive electrode 110. When the electrode assembly 100 is applied to the battery 200, the battery 200 has a high capacity and energy density. When the median particle size of the third active material is too large, the mass content of the third dopant element in the third active material is correspondingly low, thereby reducing the capacity of the positive electrode 110, and consequently, the capacity and energy density of the battery 200 are too low, reducing the performance of the battery 200. When the median particle size of the third active material is too small, on the one hand, it increases the difficulty of preparing the third active material, thus increasing the processing cost of the electrode assembly 100. On the other hand, correspondingly, the mass content of the third dopant element in the third active material is too high. Excessive third dopant elements may cause the third active material to form impurity compounds, thereby reducing the lithium-ion intercalation / deintercalation performance of the third active material, and consequently reducing the capacity performance of the positive electrode 110 and the electrode assembly 100, resulting in a lower capacity and energy density of the battery 200.

[0094] Please see also Figures 1 to 4 This application also provides a battery 200, which includes an electrode assembly 100 provided in this application and an electrolyte 210, wherein the electrolyte 210 is used to wet at least a portion of the electrode assembly 100.

[0095] In this embodiment, the electrode assembly 100 includes a positive electrode 110 provided in this application. In the positive electrode 110, the first sub-layer 1121, the second sub-layer 1122, the current collector layer 111, and the second material layer 113 are sequentially stacked and wound. Furthermore, the mass content of the first dopant element in the first active material 140 is less than the mass content of the second dopant element in the second active material, and the mass content of the first dopant element in the first active material 140 is less than the mass content of the third dopant element in the third active material. Therefore, the specific capacity exerted by the first active material 140 is less than the specific capacity exerted by the second active material, and the specific capacity exerted by the first active material 140 is less than the specific capacity exerted by the third active material. In the same turn of the winding structure, the first sub-layer 1121 is closer to the central axis 101 than the second sub-layer 1122 and the second material layer 113. The specific capacity of the first active material 140 is less than that of the second active material, which can balance the specific capacity per unit area at the corresponding positions of the first sub-layer 1121 and the second sub-layer 1122. The specific capacity of the first active material 140 is less than that of the third active material, which can balance the specific capacity per unit area at the corresponding positions of the first material layer 112 and the second material layer 113. This is to avoid excessive lithium ions being extracted from the first sub-layer 1121 and deposited on the surface of the adjacent negative electrode 130, thereby slowing down the phenomenon of lithium plating on the surface of the negative electrode 130. Furthermore, the second sub-layer 1122 still has a high specific capacity, which in turn makes the first material layer 112 have a high capacity, which in turn makes the positive electrode 110 have a high specific capacity, and ultimately makes the battery 200 have both high energy and good safety performance, thus making the battery 200 have a long service life.

[0096] Optionally, the battery 200 further includes a housing 220 having a receiving cavity 221 for receiving the electrode assembly 100 and the electrolyte 210.

[0097] The technical solution of this application will be further described below with reference to several embodiments:

[0098] Examples 1 to 13, Comparative Example 1 and Comparative Example 2:

[0099] 1. Preparation of positive electrode 110:

[0100] (1) Preparation of the first active substance 140:

[0101] ① Weigh out iron source, phosphorus source, lithium source, carbon source, titanium source, etc., and weigh out an appropriate amount of inorganic oxide source (10% of the total amount of iron source, phosphorus source, lithium source, carbon source, and titanium source). Mix them evenly in a ball mill, add an appropriate amount of pure water as a dispersant, and then perform high-energy ball milling (ball-to-material ratio of 5:2, rotation speed of 2000 r / min, time of 15 h) to mill the raw materials into particles of appropriate size. The iron source is ferrous oxalate, ferric phosphate, or ferric oxide; the phosphorus source is lithium dihydrogen phosphate or ammonium dihydrogen phosphate; the lithium source is lithium carbonate or lithium hydroxide; the carbon source is glucose, sucrose, or citric acid; the titanium source is titanium dioxide. The protective layer 142 in Examples 1 to 12 is an alumina layer, sourced from aluminum hydroxide; the protective layer 142 in Example 13 is a calcium oxide layer, sourced from calcium hydroxide. The first active substance 140 used in Comparative Example 2 does not include the protective layer 142.

[0102] ② Spray dry the ball-milled material (pump speed 10mL / min, drying temperature set at 200℃) to form powder with a certain particle size;

[0103] ③ The dried powder was placed in a vacuum atmosphere sintering furnace for high-temperature calcination (protective atmosphere: nitrogen, 700°C, 15h), and then ball-milled to obtain the first active material 140 of Examples 1 to 13, Comparative Example 1 and Comparative Example 2. The first active material 140 has a core-shell structure, comprising a core 141 and a protective layer 142, wherein the protective layer 142 covers the outer periphery of the core 141. The chemical formula of the core 141 of the first active material 140 is LiFe. (1-x) M1 x PO4 / C, wherein M1 is the first doping element and the first doping element is selected from at least one of titanium, vanadium, magnesium or niobium, and the range of x is: 0.01≤x≤0.03.

[0104] ④ The particle morphology of the first active substance 140 was obtained by scanning electron microscopy, such as... Figure 5 As shown, the particle size distribution of the first active material 140 was obtained using a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000). The testing standard used was particle size distribution laser diffraction method GB / T19077-2016, to determine the median particle size D1 of the first active material 140.

[0105] In the first active substance 140 of Examples 1 to 13, Comparative Examples 1 and 2, the values ​​of x, the types of M1 and the values ​​of D1 are shown in Table 1.

[0106] (2) Preparation of the second and third active substances:

[0107] ① Weigh out iron source, phosphorus source, lithium source, carbon source, titanium source, etc., and mix them evenly in a ball mill. Then add an appropriate amount of pure water as a dispersant, and then perform high-energy ball milling (ball-to-material ratio of 5:2, rotation speed of 2000 r / min, time of 15 h) to mill the raw materials into particles of appropriate size. The iron source is ferrous oxalate, ferric phosphate, or ferric oxide; the phosphorus source is lithium dihydrogen phosphate or ammonium dihydrogen phosphate; the lithium source is lithium carbonate or lithium hydroxide; the carbon source is glucose, sucrose, or citric acid; and the titanium source is titanium dioxide.

[0108] ② Spray dry the ball-milled material (pump speed 10mL / min, drying temperature set at 200℃) to form powder with a certain particle size;

[0109] ③ The dried powder was placed in a vacuum atmosphere sintering furnace for high-temperature calcination (protective atmosphere: nitrogen, 700℃, 15h), and then ball-milled to obtain the second active material of Examples 1 to 13, Comparative Examples 1 and 2, and the third active material of Examples 1 to 13, Comparative Examples 1 and 2. The chemical formula of the second active material is LiFe. (1-y) M2 y PO4 / C, wherein M2 is the second doping element selected from at least one of titanium, vanadium, magnesium, or niobium, and y ranges from 0.04 to 0.06; the chemical formula of the third active material is LiFe. (1-z) M3 z PO4 / C, where M3 is the third doping element and the third doping element is selected from at least one of titanium, vanadium, magnesium or niobium, and the range of z is: 0.04≤z≤0.06.

[0110] ④ Obtain the particle morphology of the second or third active substance using an electron scanning microscope, such as... Figure 6 As shown. The particle size distribution map of the median particle size of the first active material 140 was obtained by a laser diffraction particle size distribution measuring instrument (Malvern Mastersizer 3000). The test standard used was particle size distribution laser diffraction method GB / T19077-2016, to test the median particle size D2 of the second active material and / or the median particle size D3 of the third active material.

[0111] Understandably, in the above embodiments, the second active substance and the third active substance are formed through the same preparation process, that is, the component parameters and structural parameters of the second active substance and the third active substance are the same. Figure 6The examples can characterize both the scanning electron microscope (SEM) spectra of the second active substance and the scanning electron microscope (SEM) spectra of the third active substance.

[0112] Understandably, by Figure 5 and Figure 6 It can be seen that, Figure 5 The median particle size of the first active substance 140 shown is greater than [missing information]. Figure 6 The median particle size of the second active substance shown, and / or, Figure 5 The median particle size of the first active substance 140 shown is greater than [missing information]. Figure 6 The median particle size of the third active substance is shown.

[0113] In the second active substances of Examples 1 to 13, Comparative Examples 1 and 2, the values ​​of y, the types of M2 and D2 are shown in Table 1; in the third active substances of Examples 1 to 13, Comparative Examples 1 and 2, the values ​​of z, the types of M3 and D3 are shown in Table 1.

[0114] (3) Preparation of the positive electrode 110 of Examples 1 to 13 and Comparative Example 2:

[0115] ① The second material layer 113 is disposed on the surface of the current collector layer 111: Weigh the corresponding amounts of the third active material, conductive carbon black and polyvinylidene fluoride in a mixing tank at a mass ratio of 95%:2%:3%, and then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 6 hours to obtain a uniform slurry with suitable viscosity; the slurry is uniformly coated on the current collector layer 111 (aluminum foil) on the specified side by extrusion coating to form the second material layer 113, the thickness of the second material layer 113 being d3.

[0116] ② The second sublayer 1122 is disposed on the surface of the current collector layer 111 away from the second material layer 113: Weigh the corresponding amounts of the second active material, conductive carbon black and polyvinylidene fluoride in a mixing tank at a mass ratio of 95%:2%:3%, and then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 6 hours to obtain a uniform slurry with suitable viscosity; the slurry is uniformly coated on the surface of the current collector layer 111 away from the second material layer 113 by extrusion coating to form the second sublayer 1122, the thickness of the second sublayer 1122 being d2.

[0117] ③ The first sublayer 1121 is disposed on the surface of the second sublayer 1122 away from the current collector layer 111: The corresponding amounts of the first active material 140, conductive carbon black, and polyvinylidene fluoride are weighed into a mixing tank at a mass ratio of 95%:2%:3%, and an appropriate amount of N-methylpyrrolidone (NMP) is added and stirred for 6 hours to obtain a uniform slurry with suitable viscosity. The slurry is then uniformly coated onto the surface of the second sublayer 1122 away from the current collector layer 111 by extrusion coating to form the first sublayer 1121, the thickness of which is d1. The thicknesses d1 of the first sublayer 1121, d2 of the second sublayer 1122, and d3 of the second material layer 113 satisfy: d3 = d1 + d2.

[0118] Through the above steps, positive electrode sheets 110 of Examples 1 to 13 and Comparative Example 2 are obtained. In the positive electrode sheets 110 of Examples 1 to 13 and Comparative Example 2, the thickness d1+d2 of the first material layer 112 is 60 μm, and the thickness of the second material layer 113 is 60 μm. The positive electrode sheet 110 includes a current collector layer 111, a first material layer 112, and a second material layer 113. The first material layer 112 is disposed on the side of the current collector layer 111 facing the central axis 101. The first material layer 112 includes a first sub-layer 1121 and a second sub-layer 1122. The first sub-layer 1121 is closer to the central axis 101 than the second sub-layer 1122. The second material layer 113 is disposed on the side of the current collector layer 111 away from the central axis 101.

[0119] Specifically, the first active substance 140 used in Comparative Example 2 does not include the protective layer 142.

[0120] In the positive electrode sheet 110 of Examples 1 to 13 and Comparative Example 2, the values ​​of the thickness d1 of the first sub-layer 1121, the thickness d2 of the second sub-layer 1122, and the thickness d3 of the second material layer 113 are shown in Table 1.

[0121] (4) Preparation of the positive electrode 110 of Comparative Example 1:

[0122] ① The second material layer 113 is disposed on the surface of the current collector layer 111: Weigh the corresponding amounts of the third active material, conductive carbon black and polyvinylidene fluoride in a mixing tank at a mass ratio of 95%:2%:3%, and then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 6 hours to obtain a uniform slurry with suitable viscosity; the slurry is uniformly coated on the current collector layer 111 (aluminum foil) on the specified side by extrusion coating to form the second material layer 113, the thickness of the second material layer 113 being d3.

[0123] ② The first material layer 112 is disposed on the surface of the current collector layer 111 away from the second material layer 113: Weigh the corresponding amounts of the second active material, conductive carbon black and polyvinylidene fluoride in a mixing tank at a mass ratio of 95%:2%:3%, and then add an appropriate amount of N-methylpyrrolidone (NMP) and stir for 6 hours to obtain a uniform slurry with suitable viscosity; The slurry is uniformly coated on the surface of the current collector layer 111 away from the second material layer 113 by extrusion coating to form the first material layer 112, the thickness of the first material layer 112 being d1+d2.

[0124] Through the above steps, the positive electrode 110 of Comparative Example 1 is obtained. In the positive electrode 110 of Comparative Example 1, the thickness of the first material layer 112 and the thickness of the second material layer 113 are both 60 μm. The positive electrode 110 includes a current collector layer 111, a first material layer 112, and a second material layer 113. The first material layer 112 is disposed on the side of the current collector layer 111 facing the central axis 101, and the second material layer 113 is disposed on the side of the current collector layer 111 away from the central axis 101. In other words, in the positive electrode 110 of Comparative Example 1, the first material layer 112 is not divided into a first sublayer 1121 and a second sublayer 1122, and the first material layer 112 includes a second active material, in which the mass content of the second dopant element is relatively high.

[0125] 2. Preparation of negative electrode sheet 130:

[0126] Weigh out the corresponding amounts of artificial graphite, conductive carbon black, and sodium carboxymethyl cellulose in a mixing tank at a mass ratio of 95%:2.5%:2.5%. Add an appropriate amount of deionized water and stir for 6 hours to obtain a uniform slurry with suitable viscosity. Then, coat the slurry onto copper foil and place it in a vacuum oven. Dry it at 150°C for 20 hours to obtain the negative electrode sheet 130.

[0127] 3. Preparation of diaphragm 120:

[0128] A 16µm polyethylene film is used as the diaphragm 120.

[0129] 4. Preparation of Battery 200:

[0130] (1) The positive electrode 110, the separator 120, and the negative electrode 130 are placed in a press for pressing, and then a cutter is used to cut the positive electrode 110, the separator 120, and the negative electrode 130 to a certain size. The cut positive electrode 110, the separator 120, and the negative electrode 130 are stacked in sequence and then wound to form an electrode assembly 100. The electrode assembly 100 has a wound structure with a central axis 101. In the electrode assembly 100 of Examples 1 to 13, the first material layer 112 of the positive electrode 110 is disposed on... The current collector layer 111 faces the central axis 101. The first sub-layer 1121 is closer to the central axis 101 than the second sub-layer 1122. The second material layer 113 is disposed on the side of the current collector layer 111 away from the central axis 101. In the electrode assembly 100 of Comparative Examples 1 and 2, the first material layer 112 of the positive electrode 110 is disposed on the side of the current collector layer 111 facing the central axis 101, and the second material layer 113 is disposed on the side of the current collector layer 111 away from the central axis 101. Then, positive and negative electrode tabs are soldered, dried, and then encapsulated with an aluminum-plastic film to form the electrode assemblies 100 of Examples 1 to 13, Comparative Examples 1 and 2.

[0131] A solution obtained by dissolving 1 mol / L lithium hexafluorophosphate in a mixed solvent of ethylene carbonate and diethyl carbonate in a molar ratio of 1:1 was injected into the cell as electrolyte 210. Finally, the cells were packaged to form experimental cells 1 to 13, control cell 1 and control cell 2.

[0132] In this embodiment, the positive electrode 110 of Example 1 is applied to the electrode assembly 100 of Example 1 and assembled in the implementation battery 1; the positive electrode 110 of Example 2 is applied to the electrode assembly 100 of Example 2 and assembled in the implementation battery 2; the positive electrode 110 of Comparative Example 1 is applied to the electrode assembly 100 of Comparative Example 1 and assembled in the control battery 1, and so on.

[0133] Table 1 below shows the composition and structural parameters of the positive electrode 110 of Examples 1 to 13, Comparative Example 1 and Comparative Example 2.

[0134] Table 1: Composition and structural parameters of the positive electrode 110 of Examples 1 to 13, Comparative Examples 1 and 2.

[0135]

[0136]

[0137] The difference between Example 1 and Example 13 is that the protective layer 142 in Example 1 is an aluminum oxide layer, which is derived from aluminum hydroxide; while the protective layer 142 in Example 13 is a calcium oxide layer, which is derived from calcium hydroxide.

[0138] Battery 200 performance test:

[0139] 1. Rate discharge capacity test of batteries 1 to 13, control battery 1, and control battery 2:

[0140] At 25°C, the experimental batteries 1 to 13, control battery 1 and control battery 2 were charged to 3.65V at a rate of 0.5C, and then discharged to 2.5V at a rate of 0.5C. After the discharge was completed, the discharge capacity at 0.5C was recorded.

[0141] The 0.5C discharge capacity values ​​of the experimental batteries 1 to 13, the comparative battery 1, and the comparative battery 2 are shown in Table 2.

[0142] 2. Testing of interface lithium plating in batteries 1 to 13, control battery 1, and control battery 2:

[0143] At 25°C, the experimental batteries 1 to 13, control battery 1 and control battery 2 were charged to 3.65V at a 1C rate, then discharged to 2.5V at a 1C rate, and then charged to 3.65V at a 1C rate. Then the battery 200 was disassembled to observe the lithium plating at the interface of the negative electrode 130.

[0144] The interface lithium plating of experimental batteries 1 to 13, comparative battery 1 and comparative battery 2 are shown in Table 2.

[0145] Table 2 below shows the performance parameters of implementation batteries 1 to 13, comparison battery 1, and comparison battery 2.

[0146] Table 2: Performance parameters of implementation batteries 1 to 13, comparative battery 1 and comparative battery 2.

[0147]

[0148]

[0149] Please refer to Tables 1 and 2. From the data of Example 1 and Comparative Example 1, it can be seen that the positive electrode 110 of Example 1 includes a current collector layer 111, a first material layer 112, and a second material layer 113. The first material layer 112 includes a first sublayer 1121 and a second sublayer 1122. The doping content of the first doped element of the first active material 140 in the first sublayer 1121 is less than the doping content of the second doped element of the second active material in the second sublayer 1122. Furthermore, the doping content of the first doped element of the first active material 140 is also less than the doping content of the third doped element of the third active material in the second material layer 113. In contrast, the positive electrode 110 of Comparative Example 1 includes a current collector layer 111, a first material layer 112, and a second material layer 113. The first material layer 112 does not divide into first sublayers 1121 and second sublayers 1122; instead, it is directly composed of the second active material. This results in the 0.5C discharge capacity of Example 1 being slightly lower than that of Comparative Example 1. The 0.5C discharge capacity of the experimental battery 1 is not observed, but lithium plating does not occur in the control battery 1. This is because: in Example 1, the doping content of the first doping element of the first active material 140 in the first sublayer 1121 is relatively low, and the specific capacity of the first active material 140 is relatively low, while the specific capacity of the second and third active materials is relatively high. In the same turn of the winding structure, the first sublayer 1121 is closer to the central axis 101 than the second sublayer 1122 and the second material layer 113. The specific capacity of the first active material 140 is less than that of the second active material, which can balance the specific capacity per unit area at the corresponding positions of the first sublayer 1121 and the second sublayer 1122, so as to avoid excessive lithium ion deintercalation from the first sublayer 1121 and deposition on the surface of the adjacent negative electrode 130, thereby slowing down the lithium plating phenomenon on the surface of the negative electrode 130 and making the service life of the experimental battery 1 longer than that of the control battery 1.

[0150] As can be seen from the data of Example 1 and Comparative Example 2, under the same conditions, the first active material 140 used in Comparative Example 2 does not include the protective layer 142, resulting in lithium plating at the interface of the comparative battery 2. This is because: the first active material 140 of the battery 1 has a protective layer 142, which increases the resistance of lithium ions entering and leaving the core 141, thereby increasing the difficulty of lithium ion insertion and extraction from the first active material 140, reducing the performance of lithium ion insertion and extraction from the first active material 140, and further reducing the specific capacity of the first active material 140. In the same turn of the winding structure, the specific capacity per unit area of ​​the first sub-layer 1121 can be reduced to balance the specific capacity per unit area at the corresponding positions of the first sub-layer 1121 and the second sub-layer 1122 and / or the second material layer 113, thereby avoiding excessive lithium ion insertion and extraction from the first sub-layer 1121, thus slowing down the phenomenon of lithium plating on the surface of the negative electrode 130 and extending the service life of the battery 200. This indicates that by setting the protective layer 142 and setting the mass content of the first dopant element to be relatively low, the two can work synergistically to make the lithium ion diffusion capacity of the positive electrode 110 closer to the central axis 101 and the side farther from the central axis 101 different. This means that the lithium ion diffusion capacity of the positive electrode 110 closer to the central axis 101 is worse than that of the side farther from the central axis 101, so as to better mitigate the occurrence of lithium plating.

[0151] As can be seen from the data of Examples 1 to 3, under the same conditions, the doping content y of the second doped element in the second active material of Examples 1 and 2 satisfies the range 0.04≤y≤0.06, and the doping content z of the third doped element in the third active material satisfies the range 0.04≤z≤0.06. However, the values ​​of y and z in Example 3 are both too large. Although Example 1 to Example 3 all show no lithium plating, the discharge capacity of Example 3 at 0.5C is significantly smaller than that of Example 1 and Example 2 at 0.5C. This is because, within a certain range, as the value of y gradually increases, it is beneficial to improve the capacity of the second sublayer 1122, and as the value of z gradually increases, it is beneficial to improve the capacity of the second material layer 113, thereby making the positive electrode 110 have a higher capacity, that is, Example 1 and Example 2 have a higher capacity. However, when the value of y or z is too large, the distortion of the crystal structure reaches a certain limit. In the second active material, excessive second doping elements may cause the formation of impurity compounds, thereby reducing the lithium-ion insertion / extraction performance of the second active material. Similarly, in the third active material, excessive third doping elements may cause the formation of impurity compounds, thereby reducing the lithium-ion insertion / extraction performance of the third active material, and ultimately causing the capacity of the implemented battery 3 to be lower than that of the implemented batteries 1 and 2. Therefore, preferably, the range of y values ​​is 0.04 ≤ y ≤ 0.05, and the range of z values ​​is 0.04 ≤ z ≤ 0.05.

[0152] Data from Examples 1, 4, and 5 show that, under the same conditions, the mass content x of the first dopant element in the first active material 140 of Examples 1, 4, and 5 all satisfy the range 0.01 ≤ x ≤ 0.03. This results in all three batteries (1, 4, and 5) exhibiting no lithium plating. Furthermore, as the mass content of the first dopant element gradually increases, the 0.5C discharge capacity of the corresponding battery 200 also gradually increases. Correspondingly, the 0.5C discharge capacity of battery 5 is significantly lower than that of batteries 1 and 4. This indicates that increasing the mass content of the first dopant element also benefits the capacity of the positive electrode 110. Therefore, it is necessary to control the value of the doping amount x of the first dopant element so that the positive electrode 110 can have both good capacity and slow down lithium plating, thereby enabling the corresponding battery 200 to have both high capacity and good safety performance. Therefore, preferably, the range of x is 0.02 ≤ x ≤ 0.03.

[0153] As can be seen from the data of Examples 1, 6 to 9, when the thickness d1 of the first sublayer 1121 and the thickness d2 of the second sublayer 1122 are constant, the value of d1 / d2 increases as the thickness d1 of the first sublayer 1121 gradually increases. Although all of the embodiments 1, 6 to 9 exhibit no lithium plating, their 0.5C discharge capacity gradually decreases, which is detrimental to the overall performance improvement of the battery 200. Therefore, preferably, the value of d1 / d2 satisfies the range 0.1 ≤ d1 / d2 ≤ 0.5.

[0154] As can be seen from the data of Examples 1, 10 to 13, in the first aspect, the first doping element in Example 1 is Ti, the first doping element in Example 10 is V, the first doping element in Example 11 is Mg, and the first doping element in Example 12 is Nb. All of the cells 1, 10 to 12 have a high 0.5C discharge capacity and no lithium plating phenomenon occurs at the interface. This indicates that when the first doping element is selected from at least one of titanium, vanadium, magnesium or niobium, the first sublayer 1121 can play a role in mitigating the occurrence of lithium plating, so that the corresponding cell 200 has better applicability and a longer service life. Secondly, in Example 1, the protective layer 142 is an aluminum oxide layer, and in Example 13, the protective layer 142 is a calcium oxide layer. Both the battery 1 and the battery 13 have a high 0.5C discharge capacity and no lithium plating occurs at the interface. This indicates that when a protective layer 142 is provided and the protective layer 142 is selected from inorganic metal oxide layers, such as aluminum oxide or calcium oxide, the first sublayer 1121 can play a role in mitigating the occurrence of lithium plating, so that the corresponding battery 200 has better applicability and a longer service life.

[0155] Please see Figure 7 and Figure 8 This application also provides an electrical device 300, which includes a device body 310 and a battery 200 provided in this application, wherein the battery 200 supplies power to the device body 310.

[0156] Understandably, the battery 200 is electrically connected to the device body 310.

[0157] In this embodiment, the battery 200 combines high energy density with good safety performance and has a long service life. When the battery 200 is applied to the electrical device 300, it can provide stable power to the device body 310, which helps to improve the user experience.

[0158] Optionally, the electrical device 300 in this application embodiment can be, but is not limited to, portable electronic devices such as mobile phones, tablets, laptops, desktop computers, smart bracelets, smartwatches, e-readers, and game consoles. It can also be a vehicle such as a car, truck, sedan, van, freight train, high-speed train, or electric vehicle. Furthermore, it can be various household appliances. Figure 7 In this embodiment, the electrical equipment 300 is an energy storage battery cabinet.

[0159] It is understood that the electrical device 300 described in this embodiment is merely one form of the electrical device 300 used by the battery 200, and should not be construed as a limitation on the electrical device 300 provided in this application, nor should it be construed as a limitation on the electrical device 300 provided in various embodiments of this application.

[0160] In this application, the terms "embodiment" and "implementation" mean that a specific feature, structure, or characteristic described in connection with an embodiment can be included in at least one embodiment of this application. The appearance of these phrases in various locations throughout the specification does not necessarily refer to the same embodiment, nor are they independent or alternative embodiments mutually exclusive with other embodiments. Those skilled in the art will understand, explicitly and implicitly, that the embodiments described in this application can be combined with other embodiments. Furthermore, it should be understood that the features, structures, or characteristics described in the various embodiments of this application can be arbitrarily combined to form another embodiment that does not depart from the spirit and scope of the technical solution of this application, provided there is no contradiction between them.

[0161] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit it. Although this application has been described in detail with reference to the above preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions to the technical solutions of this application should not depart from the spirit and scope of the technical solutions of this application.

Claims

1. An electrode assembly, characterized in that, The electrode assembly has a wound structure with a central axis. The electrode assembly includes a positive electrode, a separator, and a negative electrode. The separator is located between the positive and negative electrode. The positive electrode includes: Current collector layer; A first material layer is disposed on the side of the current collector facing the central axis. The first material layer includes a first sub-layer and a second sub-layer. The first sub-layer is closer to the central axis than the second sub-layer. The first sub-layer includes a first active material with a core-shell structure, comprising a core and a protective layer. The protective layer covers the outer periphery of the core. The core includes lithium iron phosphate and a first dopant element. The second sub-layer includes a second active material, which also includes lithium iron phosphate and a second dopant element. The mass content of the first dopant element in the first active material is less than the mass content of the second dopant element in the second active material. The thickness of the first sub-layer is d1, and the thickness of the second sub-layer is d2, satisfying the relationship: 0.1 ≤ d1 / d2 ≤ 0.5; and A second material layer is disposed on the side of the current collector layer away from the central axis. The second material layer includes a third active material, which includes lithium iron phosphate and a third dopant element. The mass content of the first dopant element in the first active material is less than the mass content of the third dopant element in the third active material. The median particle size D1 of the first active material ranges from 1.1 μm to 1.3 μm, the median particle size D2 of the second active material ranges from 0.8 μm to 1.0 μm, and the median particle size D3 of the third active material ranges from 0.8 μm to 1.0 μm. The core of the first active substance has the chemical formula LiFe. (1-x) M1 x PO4 / C, the chemical formula of the second active substance is LiFe (1-y) M2 y PO4 / C, the chemical formula of the third active substance is LiFe (1-z) M3 z PO4 / C, wherein M1 is the first doping element, which is selected from at least one of titanium, vanadium, magnesium or niobium; M2 is the second doping element, which is selected from at least one of titanium, vanadium, magnesium or niobium; and M3 is the third doping element, which is selected from at least one of titanium, vanadium, magnesium or niobium, and satisfies the relationship: x < y, x < z.

2. The electrode assembly according to claim 1, characterized in that, In the first active substance, the range of x is: 0.01≤x≤0.03; in the second active substance, the range of y is: 0.04≤y≤0.

06.

3. The electrode assembly according to claim 2, characterized in that, In the third active substance, the range of z is: 0.04≤z≤0.

06.

4. The electrode assembly according to claim 1, characterized in that, If the thickness of the second material layer is d3, then the following relationship is satisfied: 0.85≤(d1+d2) / d3≤1.

5. The electrode assembly according to any one of claims 1 to 4, characterized in that, The protective layer is an inorganic metal oxide layer, and the protective layer is selected from at least one of aluminum oxide layer, calcium oxide layer, and titanium oxide layer.

6. A battery, characterized in that, The battery includes: The electrode assembly according to any one of claims 1 to 5; and An electrolyte used to wet at least a portion of the electrode assembly.

7. An electrical appliance, characterized in that, The electrical equipment includes: The equipment itself; and The battery of claim 6, wherein the battery supplies power to the device body.

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