Cathode pole piece, battery and electric equipment

Abstract

The invention provides a cathode pole piece, a battery and electric equipment, the cathode pole piece comprises a first area, a second area and a third area which are sequentially distributed along the width direction of the cathode pole piece, the capacity of the first area in unit area is C1mAh, the capacity of the second area in unit area is C2mAh, the capacity of the third area in unit area is C3mAh, C2 / C1 is greater than or equal to 1 / 3 and less than or equal to 99 / 100, and C2 / C3 is greater than or equal to 1 / 3 and less than or equal to 99 / 100. Therefore, the cycling stability of the battery comprising the cathode plate is improved.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a cathode electrode, a battery and an electrical device. Background Art

[0002] Batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. During the battery cycle, the temperature of the middle area of ​​the battery cell is higher than that of the two end areas, and the expansion force of the middle area of ​​the battery cell is greater than that of the two end areas, resulting in the polarization degree of the middle area of ​​the pole piece being less than that of the two end areas of the pole piece. Affected by the uneven polarization degree, during the charging process, the lithium ions from the cathode pole piece are more inclined to diffuse and embed lithium in the middle area of ​​the anode pole piece, that is, the lithium ions embedded in the middle area of ​​the anode pole piece include not only the lithium ions from the middle area of ​​the cathode pole piece, but also some lithium ions from the edge area of ​​the cathode pole piece, which easily causes the amount of lithium embedded in the middle area of ​​the anode pole piece to exceed the lithium accommodation capacity of the area, thereby causing lithium precipitation and reducing the cycle stability of the battery. Summary of the invention

[0003] In view of the technical problems existing in the background technology, the present application provides a cathode electrode that can reduce the problem of lithium deposition in the middle of the anode electrode, thereby improving the cycle stability of the battery.

[0004] In a first aspect, the present application provides a cathode electrode, comprising a first zone, a second zone and a third zone sequentially distributed along its width direction, wherein the capacity per unit area of ​​the first zone is C1mAh, the capacity per unit area of ​​the second zone is C2mAh, and the capacity per unit area of ​​the third zone is C3mAh, wherein 1 / 3≤C2 / C1≤99 / 100, 1 / 3≤C2 / C3≤99 / 100.

[0005] In the present application, the capacity per unit area of ​​the second zone of the cathode electrode piece is smaller than the capacity per unit area of ​​the first zone and the capacity per unit area of ​​the third zone, so that the active lithium content in the second zone of the cathode electrode piece is smaller than the active lithium content per unit area of ​​the first zone and the third zone, and the total amount of active lithium embedded from the second zone of the cathode electrode piece into the corresponding area of ​​the anode electrode piece is small, and the corresponding area of ​​the anode electrode piece can accommodate more lithium ions from the first zone and the third zone of the cathode electrode piece, thereby reducing the risk of lithium precipitation in the corresponding area of ​​the anode electrode piece due to uneven polarization and improving the cycle stability of the battery. In the present application, 1 / 3≤C2 / C1≤99 / 100, 1 / 3≤C2 / C3≤99 / 100, while improving the cycle stability of the battery, can reduce the distance between the second zone of the cathode electrode piece and the corresponding area of ​​the anode electrode piece, reduce the difficulty of exhaust during the battery formation process, and improve the energy density of the battery.

[0006] In some embodiments, 0.5≤C2 / C1≤0.9. Thus, the risk of lithium deposition in the region corresponding to the anode electrode is reduced, the cycle stability of the battery is improved, the difficulty of exhaust during battery formation is reduced, and the energy density of the battery is improved.

[0007] In some embodiments, 0.5≤C2 / C3≤0.9. Thus, the risk of lithium deposition in the region corresponding to the anode electrode is reduced, the cycle stability of the battery is improved, the difficulty of exhaust during battery formation is reduced, and the energy density of the battery is improved.

[0008] In some embodiments, the cathode plate includes a cathode active layer, the cathode active layer includes a cathode active material, the gram capacity of the cathode active material in the first region is D1mAh / g, the gram capacity of the cathode active material in the second region is D2mAh / g, and the gram capacity of the cathode active material in the third region is D3mAh / g, 0.5≤D2 / D1≤0.9, 0.5≤D2 / D3≤0.9. Thus, the active lithium content in the second region of the cathode plate is less than the active lithium content in the first region and the third region at the same time, so that during the charging process of the battery cell, the total amount of active lithium embedded from the second region of the cathode plate into the corresponding region of the anode plate is less, and the corresponding region of the anode plate can accommodate more lithium ions from the first region and the third region of the cathode plate, thereby reducing the risk of lithium precipitation in the corresponding region of the anode plate due to uneven polarization and improving the cycle stability of the battery.

[0009] In some embodiments, 150 mAh / g ≤ D1 ≤ 160 mAh / g.

[0010] In some embodiments, 120 mAh / g ≤ D2 ≤ 150 mAh / g.

[0011] In some embodiments, 150 mAh / g ≤ D3 ≤ 160 mAh / g.

[0012] This improves the cycle stability of the battery and at the same time increases the energy density of the battery.

[0013] In some embodiments, the cathode active material includes lithium iron phosphate and a carbon coating layer coated on at least a portion of the surface of the lithium iron phosphate, the carbon coating amount of the cathode active material in the first region is m1, the carbon coating amount of the cathode active material in the second region is m2, and the carbon coating amount of the cathode active material in the third region is m3, m2>m1, m2>m3. Thus, by making the carbon coating amount of the cathode active material in the second region greater than the carbon coating amount of the cathode active material in the first region and the carbon coating amount of the cathode active material in the third region at the same time, the active lithium content in the second region is lower than the active lithium content in the first region and the third region, reducing the risk of lithium precipitation in the corresponding area of ​​the anode pole piece due to uneven polarization, and improving the cycle stability of the battery.

[0014] In some embodiments, 1.1%≤m1≤1.3%.

[0015] In some embodiments, 1.3%≤m2≤1.6%.

[0016] In some embodiments, 1.1%≤m3≤1.3%.

[0017] Therefore, by making the carbon coating amount of the cathode active material in the second zone greater than the carbon coating amount of the cathode active material in the first zone and the carbon coating amount of the cathode active material in the third zone, the active lithium content in the second zone is made lower than the active lithium content in the first zone and the third zone, thereby reducing the risk of lithium deposition in the corresponding area of ​​the anode electrode due to uneven polarization and improving the cycle stability of the battery.

[0018] In some embodiments, the thickness of the cathode active layer in the second region is less than that in the first region, and the thickness of the cathode active layer in the second region is less than that in the third region. Thus, the active lithium content in the second region is lower than that in the first region and the third region, reducing the risk of lithium deposition in the corresponding region of the anode plate due to uneven polarization and improving the cycle stability of the battery.

[0019] In some embodiments, the cathode active layer in the first region has a thickness T1, 110 μm≤T1≤261 μm.

[0020] In some embodiments, the cathode active layer in the second region has a thickness T2, 85 μm≤T1≤235 μm.

[0021] In some embodiments, the cathode active layer in the third region has a thickness T3, 110 μm≤T3≤261 μm.

[0022] Therefore, when T1, T2 and T3 meet the above conditions, the cycle stability of the battery is improved while the energy density of the battery is improved.

[0023] In some embodiments, the width of the cathode electrode piece is b, and along the width direction of the cathode electrode piece, the size of the second region is a, 1 / 15≤a / b≤3 / 4. Thus, the active lithium content of the second region is lower than that of the first region and the third region, reducing the risk of lithium deposition in the corresponding region of the anode electrode piece due to uneven polarization, improving the cycle stability of the battery, and at the same time, improving the energy density of the battery.

[0024] The second aspect of the present application provides a battery, comprising the cathode electrode sheet provided in the first aspect of the present application. Thus, the battery has excellent cycle stability and high energy density.

[0025] In some embodiments, the battery further comprises an anode electrode sheet arranged opposite to the cathode electrode sheet, the anode electrode sheet having a fourth region, the fourth region being arranged corresponding to the second region, and the lithium removal capacity per unit area of ​​the second region in a fully discharged state under the condition that the battery SOH is 100% is dmAh / mm 2 The lithium removal capacity per unit area of ​​the fourth zone is fmAh / mm 2 The SOH of the battery is greater than 70% and less than 100%, and the lithium removal capacity per unit area of ​​the second zone is gmAh / mm under the fully discharged condition. 2 The lithium removal capacity per unit area of ​​the fourth zone is hmAh / mm 2 ; (g+h) / (d+f)≤1. Thus, the probability that the active lithium content in the second zone after battery attenuation is greater than the active lithium content in the second zone in the initial state can be reduced, the risk of lithium deposition in the anode electrode can be reduced, and the cycle stability of the battery can be improved.

[0026] In some embodiments, when the battery is fully discharged, the lithium removal capacity per unit area in the first region and the third region is independently cmAh / mm 2 The lithium removal capacity per unit area in the second zone is dmAh / mm 2 , 1 / 3≤d / c≤99 / 100. Therefore, during the charging process of the battery cell, the total amount of active lithium embedded from the second area of ​​the cathode electrode piece into the corresponding area of ​​the anode electrode piece is small, and the corresponding area of ​​the anode electrode piece can accommodate more lithium ions from the first and third areas of the cathode electrode piece, thereby reducing the risk of lithium deposition in the corresponding area of ​​the anode electrode piece due to uneven polarization and improving the cycle stability of the battery.

[0027] In some embodiments, 0.5≤d / c≤0.9.

[0028] The third aspect of the present application provides an electric device, comprising the battery provided in the second aspect of the present application. Thus, the electric device has a longer service life.

[0029] Additional aspects and advantages of the present application will be given in part in the description below, and in part will become apparent from the description below, or will be learned through the practice of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Various other advantages and benefits will become apparent to those of ordinary skill in the art by reading the detailed description of the preferred embodiments below. The accompanying drawings are only for the purpose of illustrating the preferred embodiments and are not to be considered as limiting the present application. Moreover, the same reference numerals are used throughout the drawings to represent the same components. In the drawings:

[0031] Figure 1This is a schematic structural diagram of a cathode electrode sheet according to an embodiment of the present application from one viewing angle;

[0032] Figure 2 yes Figure 1 A schematic diagram of the structure of the cathode electrode from another perspective;

[0033] Figure 3 is a schematic structural diagram of a battery according to one embodiment of the present application;

[0034] Figure 4 is a schematic structural diagram of a battery module according to an embodiment of the present application;

[0035] Figure 5 is a schematic structural diagram of a battery pack according to an embodiment of the present application;

[0036] Figure 6 yes Figure 5 Exploded diagram of

[0037] Figure 7 It is a schematic diagram of an embodiment of an electric device in which a battery is used as a power source.

[0038] Description of reference numerals:

[0039] 10: cathode electrode; 110: current collector; 101: first zone; 102: second zone; 103: third zone; 1: battery; 2: battery module; 3: battery pack; 4: upper case; 5: lower case. DETAILED DESCRIPTION

[0040] The following is a detailed description of the embodiments of the technical solution of the present application. The following embodiments are only used to more clearly illustrate the technical solution of the present application, and are therefore only used as examples, and cannot be used to limit the scope of protection of the present application.

[0041] Reference to "embodiments" herein means that a particular feature, structure, or characteristic described in conjunction with the embodiments may be included in at least one embodiment of the present application. The appearance of the phrase in various locations in the specification does not necessarily refer to the same embodiment, nor is it an independent or alternative embodiment that is mutually exclusive with other embodiments. It is explicitly and implicitly understood by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0042] For simplicity, only some numerical ranges are specifically disclosed herein. However, any lower limit can be combined with any upper limit to form an undefined range; and any lower limit can be combined with other lower limits to form an undefined range, and any upper limit can be combined with any other upper limit to form an undefined range. In addition, each separately disclosed point or single value itself can be combined as a lower limit or upper limit with any other point or single value or with other lower limits or upper limits to form an undefined range.

[0043] In the description of the embodiments of the present application, the term "and / or" is only a description of the association relationship of the associated objects, indicating that there may be three relationships. For example, A and / or B can represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " in this article generally indicates that the associated objects before and after are in an "or" relationship.

[0044] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field to which this application belongs; the terms used herein are only for the purpose of describing specific embodiments and are not intended to limit this application; the terms "including" and "having" in the specification and claims of this application and the above-mentioned figure descriptions and any variations thereof are intended to cover non-exclusive inclusions.

[0045] At present, from the perspective of market development, the application of batteries is becoming more and more extensive. Batteries are not only used in energy storage power systems such as hydropower, thermal power, wind power and solar power stations, but also widely used in electric vehicles such as electric bicycles, electric motorcycles, electric cars, as well as military equipment and aerospace and other fields. With the continuous expansion of battery application areas, its market demand is also constantly expanding.

[0046] The battery includes a cathode plate, an anode plate, a separator separating the cathode plate and the anode plate, and an electrolyte located between the cathode plate and the anode plate. The cathode plate includes a cathode current collector and a cathode coating located on at least one surface of the cathode current collector, and the anode plate includes an anode current collector and an anode coating located on at least one surface of the anode current collector, wherein the cathode coating contains a cathode active material, and the anode coating contains an anode active material. When the lithium-ion battery is charged, lithium ions are released from the cathode active material, migrate to the anode plate through the electrolyte under the action of the electric field, and are embedded in the anode active material; when the lithium-ion battery is discharged, lithium ions are released from the anode active material, migrate to the cathode plate through the electrolyte under the action of the electric field, and are embedded in the cathode active material.

[0047] Usually, the coating composition on the surface of the electrode has a high uniformity, that is, the thickness, active material content and lithium content at different positions in the coating are basically the same, which makes the capacity of different positions of the coating the same. During the battery cell cycle, affected by the heat dissipation effect, the temperature of the middle area of ​​the battery cell is higher than the temperature of the two end areas, and the expansion force of the middle area of ​​the battery cell is also greater than the expansion force of the two end areas. The uneven distribution of temperature and expansion force leads to uneven polarization of the electrode. Specifically, the cathode electrode includes a first area, a second area and a third area distributed in sequence along its width direction, and the anode electrode includes a fourth area, a fifth area and a sixth area distributed along its width direction. The fifth area and the sixth area are arranged on both sides of the fourth area along the width direction of the anode electrode. During the battery charging process, the lithium ions in the first area of ​​the cathode electrode are embedded in the fifth area of ​​the anode electrode, the lithium ions in the second area of ​​the cathode electrode are embedded in the fourth area of ​​the anode electrode, and the lithium ions in the third area of ​​the cathode electrode are embedded in the sixth area of ​​the anode electrode. Affected by the uneven degree of polarization, during the charging process, lithium ions from the first and third zones of the cathode electrode are more inclined to diffuse and embed lithium in the fourth zone of the anode electrode. That is, the lithium ions embedded in the fourth zone of the anode electrode include not only lithium ions from the second zone of the cathode electrode, but also some lithium ions from the first and third zones. This can easily cause the amount of lithium embedded in the fourth zone of the anode electrode to exceed the lithium accommodation capacity of this area, resulting in lithium deposition, which increases the safety hazard of the battery.

[0048] In order to avoid lithium plating in the fourth area of ​​the anode electrode, the present application sets 1 / 3≤C2 / C1≤99 / 100 and 1 / 3≤C2 / C3≤99 / 100. Since the capacity per unit area of ​​the second area is smaller than the capacity per unit area of ​​the first area and the third area, during the charging process of the battery cell, the total amount of active lithium embedded from the second area of ​​the cathode electrode into the fourth area of ​​the anode electrode is small, and the fourth area of ​​the anode electrode can accommodate more lithium ions from the first and third areas of the cathode electrode, thereby reducing the risk of lithium plating in the fourth area of ​​the anode electrode due to the amount of embedded lithium exceeding the lithium accommodation capacity of the area, thereby improving the cycle stability of the battery cell and reducing the impact on the battery energy density.

[0049] The cathode electrode sheet disclosed in the embodiment of the present application can be used for a battery, and the battery disclosed in the embodiment of the present application can be used for an electrical device that uses a battery as a power source or various energy storage systems that use a battery as an energy storage element. Electrical devices may include, but are not limited to, mobile phones, tablets, laptops, electric toys, electric tools, battery cars, electric cars, ships, spacecraft, and the like. Among them, electric toys may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the like, and spacecraft may include airplanes, rockets, space shuttles, and spacecraft, and the like.

[0050] The first aspect of the present application provides a cathode electrode 10, referring to Figure 1, the cathode electrode 10 includes a first area 101, a second area 102 and a third area 103 sequentially distributed along its width direction, the capacity per unit area of ​​the first area 101 is C1mAh, the capacity per unit area of ​​the second area 102 is C2mAh, and the capacity per unit area of ​​the third area 103 is C3mAh, wherein 1 / 3≤C2 / C1≤99 / 100, 1 / 3≤C2 / C3≤99 / 100. Specifically, when only one surface of the cathode electrode 10 in the thickness direction includes active materials, the first area 101, the second area 102 and the third area 103 are located only on one surface of the cathode electrode 10; when both surfaces of the cathode electrode 10 in the thickness direction include active materials, the first area 101, the second area 102 and the third area 103 are located on both surfaces of the cathode electrode 10 (reference Figure 2 ), the first region 101, the second region 102 and the third region 103 on both sides of the cathode electrode 10 all satisfy: 1 / 3≤C2 / C1≤99 / 100, 1 / 3≤C2 / C3≤99 / 100.

[0051] In the present application, the capacity per unit area of ​​the second zone 102 of the cathode electrode 10 is smaller than the capacity per unit area of ​​the first zone 101 and the capacity per unit area of ​​the third zone 103, so that the active lithium content of the second zone 102 of the cathode electrode 10 is smaller than the active lithium content per unit area of ​​the first zone 101 and the third zone 103. During the charging process of the battery cell, the total amount of active lithium embedded from the second zone 102 of the cathode electrode 10 into the fourth zone of the anode electrode is small, and the fourth zone of the anode electrode can accommodate more lithium ions from the first zone 101 and the third zone 103 of the cathode electrode 10, thereby reducing the risk of lithium plating in the fourth zone of the anode electrode due to the amount of embedded lithium exceeding the lithium accommodation capacity of the area, thereby improving the cycle stability of the battery.

[0052] Since the capacity per unit area of ​​the second area 102 of the cathode electrode 10 is smaller than the capacity per unit area of ​​the first area 101 and the third area 103, the amount of lithium embedded in the fourth area of ​​the anode electrode is smaller than that in the fifth and sixth areas, and the expansion degree of the fourth area of ​​the anode electrode is smaller than that of the fifth and sixth areas, resulting in the distance between the fourth area of ​​the anode electrode and the second area 102 of the cathode electrode 10 being greater than the distance between the fifth area of ​​the anode electrode and the first area 101 of the cathode electrode 10, and the distance between the fourth area of ​​the anode electrode and the second area 102 of the cathode electrode 10 being greater than the distance between the sixth area of ​​the anode electrode and the third area 103 of the cathode electrode 10. In the present application, 1 / 3≤C2 / C1≤99 / 100, 1 / 3≤C2 / C3≤99 / 100, while improving the cycle stability of the battery, can reduce the distance between the second area 102 of the cathode electrode 10 and the fourth area of ​​the anode electrode, and reduce the probability of the gas generated during the battery formation process remaining between the second area and the fourth area to generate interface black spots.

[0053] In some embodiments, 1 / 3≤C2 / C1≤99 / 100, for example, C2 / C1 can be 1 / 3, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.99, etc., or can be a range composed of any of the above values. Thus, the capacity per unit area of ​​the second region 102 is less than the capacity per unit area of ​​the first region 101. During the battery cycle, the total amount of active lithium embedded in the middle region of the anode electrode from the second region 102 of the cathode electrode 10 is less, and the fourth region of the anode electrode can accommodate more lithium ions from the first region 101 of the cathode electrode 10, thereby reducing the risk of lithium precipitation in the fourth region of the anode electrode due to the amount of lithium embedded exceeding the lithium accommodation capacity of the region, thereby improving the cycle stability of the battery. In some specific embodiments, 0.5≤C2 / C1≤0.9.

[0054] In some embodiments, 1 / 3≤C2 / C3≤99 / 100, for example, C2 / C3 can be 1 / 3, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.99, etc., or can be a range composed of any of the above values. Thus, the capacity per unit area of ​​the second region 102 is less than the capacity per unit area of ​​the third region 103. During the battery cycle, the total amount of active lithium embedded in the fourth region of the anode electrode from the second region 102 of the cathode electrode 10 is less, and the fourth region of the anode electrode can accommodate more lithium ions from the third region 103 of the cathode electrode 10, thereby reducing the risk of lithium precipitation in the fourth region of the anode electrode due to uneven polarization and improving the cycle stability of the battery. In some specific embodiments, 0.5≤C2 / C3≤0.9.

[0055] The test method for the capacity per unit area of ​​the cathode electrode piece in the present application is: assemble the cathode electrode piece and the anode electrode piece into a button battery, charge the button battery to obtain the charging capacity, and divide the charging capacity by the area of ​​the cathode electrode piece to obtain the capacity per unit area.

[0056] It should be noted that C2 / C1 and C2 / C3 may be the same or different, and those skilled in the art may select according to the design of the battery. In some specific embodiments, in order to improve the preparation efficiency of the cathode electrode sheet, C2 / C1 and C2 / C3 are the same.

[0057] In some embodiments, reference Figure 1The cathode electrode sheet 10 includes a current collector 110, and the current collector 110 includes a cathode active layer, and the cathode active layer includes a cathode active material. The gram capacity of the cathode active material in the first area 101, the second area 102, and the third area 103 can be adjusted so that the capacity per unit area of ​​the second area 102 is simultaneously smaller than the capacity per unit area of ​​the first area 101 and the third area 103. Specifically, the gram capacity of the cathode active material in the first area 101 is D1mAh / g, the gram capacity of the cathode active material in the second area 102 is D2mAh / g, and the gram capacity of the cathode active material in the third area 103 is D3mAh / g, 0.5≤D2 / D1≤0.9, 0.5≤D2 / D3≤0.9. For example, D2 / D1 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85 or 0.9, etc., or can be a range consisting of any of the above values; D2 / D3 can be 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85 or 0.9, etc., or can be a range consisting of any of the above values. Therefore, since the capacity per unit area of ​​the second zone 102 is smaller than the capacity per unit area of ​​the first zone 101, and the capacity per unit area of ​​the second zone 102 is smaller than the capacity per unit area of ​​the third zone 103, the gram capacity of the cathode active material of the second zone 102 is smaller than the gram capacity of the cathode active material of the first zone 101 and the third zone 103, so that the active lithium content of the second zone 102 is smaller than the active lithium content of the first zone 101 and the third zone 103. During the charging process of the battery, the total amount of active lithium embedded from the second zone 102 of the cathode electrode 10 into the fourth zone of the anode electrode is small, and the fourth zone of the anode electrode can accommodate more lithium ions from the first zone 101 and the third zone 103 of the cathode electrode 10, thereby reducing the risk of lithium precipitation in the fourth zone of the anode electrode due to uneven polarization and improving the cycle stability of the battery.

[0058] The test method for "gram capacity" in this application is: assemble the cathode electrode and the anode electrode into a button battery, charge the button battery to obtain the charging capacity, and divide the charging capacity by the mass of the active material of the cathode electrode to obtain the gram capacity of the cathode active material.

[0059] It should be noted that, when 0.5≤D2 / D1≤0.9 and 0.5≤D2 / D3≤0.9, the thicknesses of the cathode active layer of the first region 101, the cathode active layer of the second region 102 and the cathode active layer of the third region 103 are not particularly limited. For example, when the thicknesses of the cathode active layer of the first region 101, the cathode active layer of the second region 102 and the cathode active layer of the third region 103 are the same, the capacity per unit area of ​​the second region 102 can be made smaller than the capacity per unit area of ​​the first region 101 and the third region 103 by specifically adjusting the sizes of D1, D2 and D3; when the thicknesses of the cathode active layers of the first region 101 and the third region 103 are greater than the thickness of the cathode active layer of the second region 102, the sizes of D1, D2 and D3 can also be adjusted to make the capacity per unit area of ​​the second region 102 smaller than the capacity per unit area of ​​the first region 101 and the third region 103.

[0060] In some embodiments, 150mAh / g≤D1≤160mAh / g, for example, it can be 150mAh / g, 152mAh / g, 154mAh / g, 156mAh / g, 158mAh / g or 160mAh / g, or can be a range consisting of any of the above values.

[0061] In some embodiments, 120 mAh / g≤D2≤150 mAh / g, for example, it can be 120 mAh / g, 130 mAh / g, 140 mAh / g or 150 mAh / g, or can be a range consisting of any of the above values.

[0062] In some embodiments, 150mAh / g≤D3≤160mAh / g, for example, it can be 150mAh / g, 152mAh / g, 154mAh / g, 156mAh / g, 158mAh / g or 160mAh / g, or it can be a range consisting of any of the above values.

[0063] Therefore, when D1, D2 and D3 meet the above conditions, the energy density of the battery is improved while the cycle stability of the battery is improved.

[0064] In some embodiments, the carbon coating amount on the surface of the cathode active material in the first region 101, the second region 102, and the third region 103 can be adjusted so that the capacity per unit area of ​​the second region 102 is simultaneously smaller than the capacity per unit area of ​​the first region 101 and the third region 103. Specifically, the cathode active material may include lithium iron phosphate and a carbon coating layer coated on at least a portion of the surface of the lithium iron phosphate, the carbon coating amount of the cathode active material in the first region 101 is m1, the carbon coating amount of the cathode active material in the second region 102 is m2, and the carbon coating amount of the cathode active material in the third region 103 is m3, m2>m1, m2>m3. Therefore, by making the carbon coating amount of the cathode active material in the second zone 102 greater than the carbon coating amount of the cathode active material in the first zone 101 and the carbon coating amount of the cathode active material in the third zone 103, the active lithium content in the second zone 102 is lower than the active lithium content in the first zone 101 and the third zone 103, thereby reducing the risk of lithium deposition in the corresponding area of ​​the anode electrode due to uneven polarization and improving the cycle stability of the battery.

[0065] In some embodiments, 1.1%≤m1≤1.3%, for example, it can be 1.1%, 1.12%, 1.14%, 1.16%, 1.18%, 1.2%, 1.22%, 1.24%, 1.26%, 1.28% or 1.3%, etc., or it can be a range consisting of any of the above values.

[0066] In some embodiments, 1.3%≤m2≤1.6%, for example, it can be 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, 1.55% or 1.6%, etc., or it can be a range consisting of any of the above values.

[0067] In some embodiments, 1.1%≤m3≤1.3%, for example, it can be 1.1%, 1.12%, 1.14%, 1.16%, 1.18%, 1.2%, 1.22%, 1.24%, 1.26%, 1.28% or 1.3%, etc., or it can be a range consisting of any of the above values.

[0068] The "carbon coating amount" referred to in this application refers to: the percentage of the mass of the carbon coating layer in the total mass of the lithium iron phosphate and the carbon coating layer. The carbon coating amount can be obtained by inductively coupled plasma (ICP) testing.

[0069] In some embodiments, the thicknesses of the cathode active layers of the first zone 101, the second zone 102, and the third zone 103 can be adjusted so that the capacity per unit area of ​​the second zone 102 is simultaneously smaller than the capacity per unit area of ​​the first zone 101 and the third zone 103. Specifically, the thickness of the cathode active layer of the second zone 102 is smaller than the thickness of the cathode active layer of the first zone 101, and the thickness of the cathode active layer of the second zone 102 is smaller than the thickness of the cathode active layer of the third zone 103. Specifically, since the capacity per unit area of ​​the second zone 102 is smaller than the capacity per unit area of ​​the first zone 101, and the capacity per unit area of ​​the second zone 102 is smaller than the capacity per unit area of ​​the third zone 103, the thickness of the cathode active layer of the second zone 102 is smaller, and the active lithium content of the second zone 102 can be reduced. During the charging process of the battery cell, the total amount of active lithium embedded from the second zone 102 of the cathode electrode 10 into the fourth zone of the anode electrode is smaller, and the fourth zone of the anode electrode can accommodate more lithium ions from the first zone 101 and the third zone 103 of the cathode electrode 10, thereby reducing the risk of lithium plating in the fourth zone of the anode electrode due to uneven polarization and improving the cycle stability of the battery.

[0070] In the present application, the thickness of the cathode active layer can be measured by a micrometer.

[0071] It should be noted that the thickness of the cathode active layer in the first area 101 may be the same as or different from the thickness of the cathode active layer in the third area 103. According to some specific embodiments of the present application, the thickness of the cathode active layer in the second area 102 is less than the thickness of the cathode active layer in the first area 101, the thickness of the cathode active layer in the second area 102 is less than the thickness of the cathode active layer in the third area 103, and the thickness of the cathode active layer in the first area 101 is the same as the thickness of the cathode active layer in the third area 103.

[0072] It should be noted that, since the thickness of the cathode active layer of the second zone 102 is smaller than the thickness of the cathode active layer of the first zone 101 and the third zone 103, the gram capacity of the cathode active material in the second zone 102 may be greater than the gram capacity of the cathode active material in the first zone 101 and the third zone 103, or the gram capacity of the cathode active material in the second zone 102 is smaller than the gram capacity of the cathode active material in the first zone 101 and the third zone 103, as long as the capacity per unit area of ​​the second zone 102 is smaller than the capacity per unit area of ​​the first zone 101 and the third zone 103.

[0073] It should be noted that, since the thickness of the cathode active layer of the second zone 102 is smaller than the thickness of the cathode active layer of the first zone 101 and the third zone 103, the carbon coating amount on the surface of the cathode active material in the second zone 102 can be greater than the carbon coating amount on the surface of the cathode active material in the first zone 101 and the third zone 103, or the carbon coating amount on the surface of the cathode active material in the second zone 102 is smaller than the carbon coating amount on the surface of the cathode active material in the first zone 101 and the third zone 103, as long as the capacity per unit area of ​​the second zone 102 is smaller than the capacity per unit area of ​​the first zone 101 and the third zone 103.

[0074] In some embodiments, reference Figure 1 The thickness of the cathode active layer of the first zone 101 is T1, 110μm≤T1≤261μm, for example, it can be 110μm, 130μm, 150μm, 170μm, 190μm, 210μm, 230μm, 250μm or 261μm, etc., or can be a range composed of any of the above values.

[0075] In some embodiments, reference Figure 1 The thickness of the cathode active layer of the second zone 102 is T2, 85μm≤T2≤235μm, for example, it can be 85μm, 105μm, 125μm, 145μm, 165μm, 185μm, 205μm, 225μm or 235μm, etc., or can be a range composed of any of the above values.

[0076] In some embodiments, reference Figure 1 The thickness of the cathode active layer of the third zone 103 is T3, 110μm≤T3≤261μm, for example, it can be 110μm, 130μm, 150μm, 170μm, 190μm, 210μm, 230μm, 250μm or 261μm, etc., or can be a range composed of any of the above values.

[0077] Therefore, when T1, T2 and T3 meet the above conditions, the cycle stability of the battery is improved while the energy density of the battery is improved.

[0078] In some embodiments, reference Figure 2, the width of the cathode electrode sheet 10 is b, and along the width direction of the cathode electrode sheet 10, the size of the second area 102 is a, 1 / 15≤a / b≤3 / 4, for example, it can be 1 / 15, 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7 or 0.75, or it can be any range of the above values. Therefore, since the capacity per unit area of ​​the second area 102 is less than the capacity per unit area of ​​the first area 101, and the capacity per unit area of ​​the second area 102 is less than the capacity per unit area of ​​the third area 103, when the width of the second area 102 and the width of the electrode sheet satisfy 1 / 15≤a / b≤3 / 4, the influence of the second area 102 on the battery energy density can be reduced while improving the battery cycle stability, thereby improving the battery energy density.

[0079] The width of the cathode electrode in the present application can be measured by a ruler or a tape measure.

[0080] In some embodiments, the cathode current collector may be a metal foil, a foamed metal or a composite current collector. For example, as the metal foil, aluminum or stainless steel, stainless steel, copper, aluminum, nickel, carbon electrode, carbon or titanium with a silver surface treatment may be used. The composite current collector may include a polymer material base and a metal layer. The foamed metal may be a nickel foam, a copper foam, an aluminum foam, an alloy foam or carbon foam. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0081] In some embodiments, the cathode active layer may also include a binder, a conductive agent, and other optional auxiliary agents.

[0082] As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, SuperP (SP), graphene, and carbon nanofibers.

[0083] As an example, the adhesive may include one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyacrylic acid (PAA), carboxymethyl cellulose (CMC), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0084] The second aspect of the present application provides a battery, comprising the cathode electrode 10 provided in the first aspect of the present application. Therefore, the battery has excellent cycle stability and high energy density.

[0085] In some embodiments, the battery further comprises an anode electrode sheet arranged opposite to the cathode electrode sheet 10, the anode electrode sheet having a fourth region, the fourth region being arranged corresponding to the second region 102, and the lithium removal capacity per unit area of ​​the second region 102 in the fully discharged state under the condition that the battery SOH is 100% is dmAh / mm 2 The lithium removal capacity per unit area of ​​the fourth zone is fmAh / mm 2 The SOH of the battery is greater than 70% and less than 100%, and the lithium removal capacity per unit area of ​​the second area 102 is gmAh / mm under the fully discharged condition. 2 The lithium removal capacity per unit area of ​​the fourth zone is hmAh / mm 2 ; (g+h) / (d+f)≤1. Thus, the probability that the active lithium content in the second zone after battery attenuation is greater than the active lithium content in the second zone in the initial state can be reduced, the risk of lithium deposition in the anode electrode can be reduced, and the cycle stability of the battery can be improved.

[0086] It should be noted that, the “fourth region is arranged corresponding to the second region” mentioned here means that the orthographic projection of the fourth region of the cathode electrode piece on the anode electrode piece at least partially overlaps with the second region.

[0087] In this application, "SOH" refers to the battery capacity retention rate. The test method for battery SOH is as follows: at a certain temperature, the battery is first charged at a constant current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour) to a voltage of 3.65V, and then charged at a constant voltage of 3.65V to a current of 0.05C. After standing for 5 minutes, the battery is discharged at a constant current of 1C to a voltage of 2.5V. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The battery is subjected to multiple cycle charge and discharge tests according to the above method, and the discharge capacity of multiple cycles is detected. The capacity retention rate of the battery after multiple cycles = (discharge capacity of multiple cycles / discharge capacity of the first cycle) × 100%.

[0088] In this application, "full charge state" means that the battery power is completely exhausted.

[0089] In this application, "lithium removal capacity" refers to the capacity of lithium ions removed within the operating voltage range. The testing method for the lithium removal capacity is: the cathode electrode and the anode electrode are prepared into a button battery, and the button battery is charged and tested, and the charged capacity is the lithium removal capacity.

[0090] In some embodiments, when the battery is fully discharged, the lithium removal capacity per unit area in the first area 101 and the third area 103 is independently cmAh / mm 2 The lithium removal capacity per unit area in the second zone 102 is dmAh / mm 2, 1 / 3≤d / c≤99 / 100, for example, it can be 1 / 3, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9 or 0.99, etc., or it can be a range composed of any of the above values. In some specific embodiments, 0.5≤d / c≤0.9. As a result, the lithium desorption capacity per unit area of ​​the second region 102 is less than the lithium desorption capacity per unit area of ​​the first region 101 and the third region 103. During the battery charging process, the total amount of active lithium embedded in the fourth region of the anode electrode from the second region 102 of the cathode electrode 10 is small, and the fourth region of the anode electrode can accommodate more lithium ions from the first region 101 and the third region 103 of the cathode electrode 10, thereby reducing the risk of lithium precipitation in the fourth region of the anode electrode due to uneven polarization and improving the cycle stability of the battery.

[0091] In some embodiments, the anode pole piece includes an anode current collector, and the anode current collector can be a metal foil, a foam metal or a composite current collector. For example, as the metal foil, aluminum or stainless steel with a silver surface treatment, stainless steel, copper, aluminum, nickel, carbon electrode, carbon or titanium, etc. can be used. The foam metal can be a nickel foam, a copper foam, an aluminum foam, a foam alloy or a carbon foam, etc. The composite current collector may include a polymer material base layer and a metal layer, and the composite current collector may be formed by arranging a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene, polyethylene terephthalate, polybutylene terephthalate, polystyrene, polyethylene, etc.).

[0092] In some embodiments, the anode electrode plate may further include an anode active layer, and the anode active layer includes an anode active material. The specific type of the anode active material is not limited, and active materials known in the art that can be used for battery anodes can be used. Those skilled in the art can select according to actual needs.

[0093] As an example, the anode active material may include, but is not limited to, one or more of artificial graphite, natural graphite, hard carbon, soft carbon, silicon-based materials and tin-based materials. The silicon-based material may include one or more of elemental silicon, silicon oxide compounds (e.g., silicon monoxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. The tin-based material may include one or more of elemental tin, tin oxide compounds, and tin alloys. These materials can all be obtained commercially.

[0094] In some embodiments, to further increase the energy density of the battery, the anode active material may include a silicon-based material.

[0095] The anode active layer may also optionally include a binder, a conductive agent and other optional auxiliary agents.

[0096] As an example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0097] As an example, the adhesive may include one or more of styrene-butadiene rubber (SBR), water-based acrylic resin, polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), ethylene-vinyl acetate copolymer (EVA), polyvinyl alcohol (PVA) and polyvinyl butyral (PVB).

[0098] As examples, other optional additives may include thickeners and dispersants (eg, sodium carboxymethylcellulose CMC-Na), and PTC thermistor materials.

[0099] Generally, the battery includes a cathode plate 10, an anode plate, a separator and an electrolyte. During the battery charging and discharging process, active ions are embedded and removed back and forth between the cathode plate 10 and the anode plate. The separator is arranged between the cathode plate 10 and the anode plate to play a role of isolation. The electrolyte plays a role of conducting ions between the cathode plate 10 and the anode plate.

[0100] As the above-mentioned isolation membrane, the present application has no special restrictions, and any known porous structure isolation membrane with electrochemical stability and mechanical stability can be selected according to actual needs. For example, it can be a single-layer or multi-layer film containing one or more of glass fiber, non-woven fabric, polyethylene, polypropylene and polyvinylidene fluoride.

[0101] The electrolyte may include an electrolyte salt and a solvent.

[0102] As an example, when the battery is a lithium ion battery, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorooxalatoborate (LiDFOB), lithium dioxalatoborate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalatophosphate) (LiDFOP) and lithium tetrafluorooxalatophosphate (LiTFOP).

[0103] As an example, the solvent may include one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and diethyl sulfone (ESE).

[0104] In some embodiments, the electrolyte further includes additives, such as an anode film-forming additive, a cathode film-forming additive, or an additive capable of improving certain battery properties, such as an additive for improving battery overcharge performance, an additive for improving battery high temperature performance, or an additive for improving battery low temperature performance.

[0105] The embodiment of the present application has no particular limitation on the shape of the battery, which can be cylindrical, square or any other shape. Figure 3 A square-structured battery 1 is shown as an example.

[0106] In some embodiments, the battery 1 may include an outer packaging for packaging the cathode electrode sheet 10 , the anode electrode sheet and the electrolyte.

[0107] In some embodiments, the outer package may include a shell and a cover plate. The shell may include a bottom plate and a side plate connected to the bottom plate, and the bottom plate and the side plate enclose a receiving cavity. The shell has an opening connected to the receiving cavity, and the cover plate can be covered on the opening to close the receiving cavity.

[0108] The cathode electrode sheet 10, the anode electrode sheet and the separator can be wound or laminated to form an electrode assembly. The electrode assembly is encapsulated in the receiving cavity. The electrolyte is infiltrated in the electrode assembly. The number of electrode assemblies contained in the battery can be one or more, which can be adjusted according to demand.

[0109] In some embodiments, the outer packaging of the battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell.

[0110] The outer packaging of the battery may also be a soft package, such as a bag-type soft package. The material of the soft package may be plastic, such as one or more of polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0111] In some embodiments, the batteries may be assembled into a battery module. The battery module may contain multiple batteries, and the specific number may be adjusted according to the application and capacity of the battery module.

[0112] Figure 4 2 is an example of a battery module 2. Figure 4 In the battery module 2, the multiple batteries 1 can be arranged in sequence along the length direction of the battery module 2. Of course, they can also be arranged in any other manner. Further, the multiple batteries 1 can be fixed by fasteners.

[0113] The battery module 2 may also include a housing having a storage space, in which a plurality of batteries 1 are stored. In some embodiments, the battery modules may be assembled into a battery pack, and the number of battery modules contained in the battery pack may be adjusted according to the application and capacity of the battery pack.

[0114] Figure 5 and 6 The battery pack 3 is used as an example. Figure 5 and 6 The battery pack 3 may include a battery box and a plurality of battery modules 2 disposed in the battery box. The battery box includes an upper box body 4 and a lower box body 5. The upper box body 4 can cover the lower box body 5 and form a closed space for accommodating the battery modules 2. The plurality of battery modules 2 can be arranged in the battery box in any manner.

[0115] The third aspect of the present application provides an electrical device, comprising the battery provided in the second aspect of the present application, thereby extending the life cycle of the electrical device.

[0116] As an example, the power-consuming device includes at least one of the battery, battery module and battery pack. The battery, battery module or battery pack can be used as a power source for the power-consuming device, or as an energy storage unit for the power-consuming device. The power-consuming device may be, but is not limited to, a mobile device (such as a mobile phone, a laptop computer), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck), an electric train, a ship and a satellite, and an energy storage system.

[0117] The electrical equipment can select the battery 1, the battery module 2 or the battery pack 3 according to its usage requirements.

[0118] Figure 7 The power consumption device is used as an example. The power consumption device includes a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. In order to meet the high power and high energy density requirements of the power consumption device for the battery, a battery pack or a battery module can be used.

[0119] As another example, the electric device may include a mobile phone, a tablet computer, and a notebook computer. The electric device is usually required to be thin and light, and a battery may be used as a power source.

[0120] In order to make the technical problems, technical solutions and beneficial effects solved by the embodiments of the present application clearer, the following will be further described in detail with reference to the embodiments and the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present application and its applications. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present application.

[0121] Example 1

[0122] 1. Preparation of cathode electrode

[0123] The cathode active material lithium iron phosphate, the conductive agent acetylene black, and the binder PVDF were mixed in a weight ratio of 96:2:2, and the solvent N-methylpyrrolidone was added. The mixture was fully stirred and mixed to obtain a cathode active slurry. The cathode active slurry was coated on both surfaces of the cathode current collector. The formed cathode electrode sheet is shown in Table 1.

[0124] 2. Preparation of anode electrode

[0125] The anode active material artificial graphite (gram capacity of 340 mAh / g), the conductive agent acetylene black, and the binder SBR+CMC were mixed in a weight ratio of 95:1.5:3.1:0.4, and the solvent deionized water was added. The mixture was stirred and mixed to obtain the negative electrode slurry, which was then coated on both surfaces of the negative electrode current collector copper foil. The coating weight of the negative electrode slurry was 0.108 g / 1540.25 mm 2 (measured by weight excluding solvent), and after drying and cold pressing, an anode electrode sheet is obtained.

[0126] 3. Preparation of electrolyte

[0127] In an argon atmosphere glove box with a water content of <10ppm, EC, PC, and DMC were mixed in a weight ratio of EC:PC:DMC=3:3:3, and then LiPF6, vitamin C (VC), vinyl sulfate (DTD) and polystyrene (PS) were added to the mixed organic solvent and stirred evenly to obtain an electrolyte, wherein the concentration of LiPF6 in the lithium-ion battery electrolyte was 1mol / L, and the mass percentages of VC, DTD and PS were 3%, 1% and 1%, respectively.

[0128] 4. Isolation film

[0129] A polyethylene porous membrane was used as the isolation membrane.

[0130] 5. Preparation of batteries

[0131] The cathode electrode sheet, the separator, and the anode electrode sheet are stacked in order, so that the separator is placed between the cathode electrode sheet and the anode electrode sheet to play an isolating role, and then wound to obtain a bare cell. The bare cell is placed in an outer package, injected with a prepared electrolyte, and packaged for formation to obtain a lithium-ion battery.

[0132] The preparation methods of the batteries in Examples 2 to 14 and Comparative Examples 1 to 4 are the same as those in Example 1, except that the structures of the cathode plates are different, as shown in Table 1.

[0133]

[0134] Test Method

[0135] 1. Test method for the number of cycles at which the capacity decays to 80% at 25°C

[0136] At 25°C, the lithium-ion battery is first charged at a constant current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour) to a voltage of 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C. After standing for 5 minutes, the lithium-ion battery is discharged at a constant current of 1C to a voltage of 2.5V. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The lithium-ion battery is subjected to multiple cycle charge and discharge tests according to the above method until the discharge capacity of the lithium-ion battery decays to 80%, and the number of cycles of the lithium-ion battery is recorded.

[0137] 2. High temperature cycle performance test of lithium-ion batteries

[0138] At 60°C, the lithium-ion battery is first charged at a constant current of 1C (i.e., the current value that completely discharges the theoretical capacity within 1 hour) to a voltage of 3.65V, then charged at a constant voltage of 3.65V to a current of 0.05C. After standing for 5 minutes, the lithium-ion battery is discharged at a constant current of 1C to a voltage of 2.5V. This is a charge and discharge cycle process, and the discharge capacity this time is the discharge capacity of the first cycle. The lithium-ion battery is subjected to multiple cycle charge and discharge tests according to the above method, and the discharge capacity of the 500th cycle is detected.

[0139] The capacity retention rate of the lithium ion battery after 500 cycles at 60° C. = (discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0140] The test results of Examples 1 to 14 and Comparative Examples 1 to 4 are shown in Table 2.

[0141] Table 2

[0142]

[0143]

[0144] Conclusion: It can be seen from Table 2 that the number of cycles when the capacity of the battery in Example 1-14 decays to 80% at 25°C is greater than that of Comparative Example 1-4, and the capacity retention rate of the battery in Example 1-14 after 500 cycles at 60°C is higher than that of Comparative Example 1-4, indicating that the battery of the present application has excellent cycle stability.

[0145] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them; although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application, and they should all be included in the scope of the claims and specification of the present application. In particular, as long as there is no structural conflict, the various technical features mentioned in the various embodiments can be combined in any way. The present application is not limited to the specific embodiments disclosed herein, but includes all technical solutions that fall within the scope of the claims.

Claims

1. A cathode electrode, characterized in that: It includes a first area, a second area and a third area distributed in sequence along its width direction, the capacity per unit area of ​​the first area is C1mAh, the capacity per unit area of ​​the second area is C2mAh, the capacity per unit area of ​​the third area is C3mAh, wherein 1 / 3≤C2 / C1≤99 / 100, 1 / 3≤C2 / C3≤99 / 100.

2. The cathode electrode according to claim 1, characterized in that: 0.5≤C2 / C1≤0.

9.

3. The cathode electrode according to claim 1 or 2, characterized in that: 0.5≤C2 / C3≤0.

9.

4. The cathode electrode according to any one of claims 1 to 3, characterized in that: It includes a cathode active layer, the cathode active layer includes a cathode active material, the gram capacity of the cathode active material in the first zone is D1mAh / g, the gram capacity of the cathode active material in the second zone is D2mAh / g, the gram capacity of the cathode active material in the third zone is D3mAh / g, 0.5≤D2 / D1≤0.9, 0.5≤D2 / D3≤0.

9.

5. The cathode electrode according to claim 4, characterized in that: Satisfy at least one of the following conditions: 150mAh / g≤D1≤160mAh / g; 120mAh / g≤D2≤150mAh / g; 150mAh / g≤D3≤160mAh / g.

6. The cathode electrode according to claim 4 or 5, characterized in that: The cathode active material includes lithium iron phosphate and a carbon coating layer coated on at least a portion of the surface of the lithium iron phosphate, the carbon coating amount of the cathode active material in the first zone is m1, the carbon coating amount of the cathode active material in the second zone is m2, and the carbon coating amount of the cathode active material in the third zone is m3, m2>m1, m2>m3.

7. The cathode electrode according to claim 6, characterized in that: Satisfy at least one of the following conditions: 1.1％≤m1≤1.3％； 1.3％≤m2≤1.6％； 1.1％≤m3≤1.3％。 8. The cathode electrode according to any one of claims 4 to 7, characterized in that: The thickness of the cathode active layer in the second region is smaller than that in the first region, and the thickness of the cathode active layer in the second region is smaller than that in the third region.

9. The cathode electrode according to any one of claims 4 to 8, characterized in that: Satisfy at least one of the following conditions: The thickness of the cathode active layer in the first region is T1, 110 μm≤T1≤261 μm; The thickness of the cathode active layer in the second region is T2, 85 μm≤T2≤235 μm; The thickness of the cathode active layer in the third region is T3, 110 μm≤T3≤261 μm.

10. The cathode electrode according to any one of claims 1 to 9, characterized in that: The width of the cathode electrode piece is b, and along the width direction of the cathode electrode piece, the size of the second region is a, 1 / 15≤a / b≤3 / 4.

11. A battery, characterized in that: Comprising a cathode pole piece according to any one of claims 1-10.

12. The battery according to claim 11, characterized in that It also includes an anode electrode sheet arranged opposite to the cathode electrode sheet, the anode electrode sheet has a fourth area, the fourth area is arranged corresponding to the second area, and the lithium removal capacity per unit area of ​​the second area in a fully discharged state is dmAh / mm under the condition that the battery SOH is 100%. 2 The lithium removal capacity per unit area of ​​the fourth zone is fmAh / mm 2 The SOH of the battery is greater than 70% and less than 100%, and the lithium removal capacity per unit area of ​​the second zone is gmAh / mm under the fully discharged condition. 2 The lithium removal capacity per unit area of ​​the fourth zone is hmAh / mm 2 ; (g+h) / (d+f)≤1.

13. The battery according to claim 11 or 12, characterized in that: When the battery is fully discharged, the lithium removal capacity per unit area in the first area and the third area is independently cmAh / mm 2 The lithium removal capacity per unit area in the second zone is dmAh / mm 2 , 1 / 3≤d / c≤99 / 100, preferably 0.5≤d / c≤0.

9.

14. An electrical device, characterized in that: Comprising a battery according to any one of claims 11-13.

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