Positive plate and preparation method thereof, lithium ion battery and power utilization device

Abstract

The invention discloses a positive plate and a preparation method thereof, a lithium ion battery and a power utilization device, the positive plate is provided with a middle area and at least one outer side area located at the periphery of the middle area, and the polarizability of the middle area is greater than that of the outer side area. The polarizability of the middle area of the positive plate is greater than that of the outer area, so that the phenomena of high temperature, large expansive force and small polarization of the middle part of the pole plate, low temperature, small expansive force and large polarization of the head part and the bottom part of the pole plate due to the influence of heat dissipation in a battery cell circulation process are counteracted, and the polarizability uniformity of the middle area and the outer area of the pole plate is improved; the problem that the lithium intercalation amount in the outer side area of the pole piece is lower than that in the middle area is solved, and the problem of lithium precipitation in the middle of a battery cell is solved.

Description

Technical Field

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

[0002] During the battery cell cycle, the polarization in the height direction of the electrode is different due to uneven temperature and expansion force. Affected by heat dissipation, the temperature in the middle of the electrode is high, the expansion force is large, and the polarization is small; the temperature at the head and bottom of the electrode is low, the expansion force is small, and the polarization is large; under the influence of uneven polarization distribution, lithium ions tend to diffuse and embed lithium in the middle of the electrode, making the amount of lithium embedded in the outer area of ​​the electrode lower than that in the middle area, thus causing lithium deposition in the middle of the battery cell. Summary of the invention

[0003] The present application is made in view of the above-mentioned problems, and its purpose is to provide a positive electrode sheet to reduce lithium deposition in the middle of the battery cell.

[0004] In order to achieve the above-mentioned objectives, the embodiments of the present application provide a positive electrode sheet and a preparation method thereof, a lithium-ion battery and an electrical device.

[0005] In a first aspect, an embodiment of the present application provides a positive electrode sheet, wherein the positive electrode sheet has a central region and at least one outer region located outside the central region, and the polarizability of the central region is greater than the polarizability of the outer region.

[0006] Therefore, in the technical solution of the embodiment of the present application, the polarizability of the middle area of ​​the positive electrode sheet is greater than the polarizability of the outer area, so as to offset the influence of heat dissipation during the cycle of the battery cell, the temperature in the middle of the electrode sheet is high, the expansion force is large, the polarization is small, and the temperature at the head and bottom of the electrode sheet is low, the expansion force is small, and the polarization is large. The uniformity of the polarizability of the middle and outer areas of the electrode sheet is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer area of ​​the electrode sheet is lower than the amount of lithium inserted in the middle area is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved.

[0007] In any embodiment, the resistivity of the active material in the middle region is greater than the resistivity of the active material in the outer region. By setting the resistivity of the active material in the middle region of the positive electrode sheet to be greater than the resistivity of the active material in the outer region, the polarization performance of the middle region of the positive electrode sheet is improved, and under the influence of temperature and expansion force, the consistency of the polarization performance of the middle region and the outer region is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer region of the electrode sheet is lower than the amount of lithium inserted in the middle region is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved; and / or,

[0008] The carbon coating content of the active material in the middle region is less than that of the active material in the outer region. By setting the carbon coating content of the active material in the middle region of the positive electrode sheet to be less than that of the active material in the outer region, the polarization performance of the middle region of the positive electrode sheet is improved, and under the influence of temperature and expansion force, the consistency of the polarization performance of the middle region and the outer region is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer region of the electrode sheet is lower than that in the middle region is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved; and / or,

[0009] The median particle size of the active material in the middle region is smaller than the median particle size of the active material in the outer region. By setting the median particle size of the active material in the middle region of the positive electrode sheet smaller than the median particle size of the active material in the outer region, the polarization performance of the middle region of the positive electrode sheet is improved. Under the influence of temperature and expansion force, the consistency of the polarization performance of the middle region and the outer region is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer region of the electrode sheet is lower than the amount of lithium inserted in the middle region is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved.

[0010] In any embodiment, the size of the middle region in the width direction of the positive electrode sheet is a 1 The dimension of the positive electrode sheet in the width direction is a 2 , where: 0<a 1 / a 2 <1; By setting a middle area in the width direction of the positive electrode sheet, the polarization performance of the middle area is higher than that of the outer area, thereby improving the uniformity of the polarization of the middle and outer areas of the electrode sheet, improving the uniformity of lithium insertion from the positive electrode to the negative electrode, alleviating the problem that the amount of lithium inserted in the outer area of ​​the electrode sheet is lower than that in the middle area, and improving the problem of lithium deposition in the middle of the battery cell. When a 1 / a 2 When it is less than 1 / 10, the middle area is narrow and lithium deposition still occurs in some local areas. 1 / a 2 When it is greater than 3 / 4, the middle area is too wide and lithium is deposited in some local areas. 1 / a 2 ≤3 / 4.

[0011] In any embodiment, the resistivity of the active material in the middle region is greater than the resistivity of the active material in the outer region, and the resistivity of the active material in the middle region is R 1 The resistivity of the active material in the outer region is R 2 , where: 0Ωcm<R 1 -R 2< 55 Ωcm; By controlling the resistivity of the active material in the middle region to be greater than that of the active material in the outer region, the polarization of the middle region is made greater than that of the outer region. At the same time, the resistivity difference is controlled within a suitable range, which is beneficial to improving the consistency of the polarization performance between the middle region and the outer region. Among them, R 1 -R 2 ≥ 55 Ωcm, when the resistivity difference between the active material in the middle region and the active material in the outer region is too large, it will increase the probability of lithium plating in the outer region. Optionally, 5 Ωcm < R 1 -R 2 < 25 Ωcm.

[0012] In any embodiment, the resistivity of the active material in the middle region is greater than that of the active material in the outer region. The resistivity of the active material in the middle region is R 1 , and the resistivity of the active material in the outer region is R 2 , where: 0 Ωcm < R 1 < 60 Ωcm; and / or, 0 Ωcm < R 2 < 60 Ωcm. By controlling the resistivity of the active materials in the appropriate middle region and outer region, the electron transport ability can be improved. When R 1 ≥ 60 Ωcm, the resistivity of the active material in the middle region is too large, affecting the electron transport ability. When R 2 ≥ 60 Ωcm, the resistivity of the outer region itself is too large, affecting the electron transport ability.

[0013] In any embodiment, the carbon coating content of the active material in the middle region is greater than that of the active material in the outer region. The carbon coating content of the active material in the middle region is W 1 , and the carbon coating content of the active material in the outer region is W 2 , where: 0% < W 2 -W 1 < 3%; By controlling the difference in the appropriate carbon coating content, the polarization of the middle region is made greater than that of the outer region, which is beneficial to improving the consistency of the polarization performance between the middle region and the outer region. When W 2 -W 1 ≥ 3%, the difference in the carbon coating content between the active materials in the middle region and the outer region is too large, which will increase the probability of lithium plating in the outer region. Optionally, 0.3% < W 2 -W 1 < 1.2%.

[0014] In any embodiment, the carbon coating content of the active material in the middle region is greater than that of the active material in the outer region. The carbon coating content of the active material in the middle region is W 1, the carbon coating content of the active material in the outer region is W 2 , where: 0% < W 1 < 3%; and / or, 0% < W 2 < 3%. By controlling the appropriate carbon coating content of the active materials in the middle region and the outer region, the electron transport ability can be improved. When W 1 ≥ 3%, the carbon coating content of the active material in the middle region itself is too large, reducing the energy density of the battery cell and affecting the electron transport ability. When W 2 ≥ 3%, the carbon coating content of the outer region itself is too large, reducing the energy density of the battery cell and affecting the electron transport ability.

[0015] In any embodiment, the median particle size of the active material in the middle region is greater than the median particle size of the active material in the outer region. The median particle size of the active material in the middle region is d 1 , and the median particle size of the active material in the outer region is d 2 , where: 0 μm < d 2 - d 1 < 3 μm; by controlling the appropriate difference in the median particle size, the polarization of the middle region is made greater than that of the outer region, which is beneficial to improving the consistency of the polarization performance of the middle region and the outer region. When d 2 - d 1 ≥ 3 μm, the difference in the median particle size of the active materials in the middle region and the outer region is too large, which will increase the probability of lithium plating in the outer region. Optionally, 0.2 μm < d 2 - d 1 < 1 μm.

[0016] In any embodiment, the median particle size of the active material in the middle region is greater than the median particle size of the active material in the outer region. The median particle size of the active material in the middle region is d 1 , and the median particle size of the active material in the outer region is d 2 , where: 0 μm < d 1 < 3 μm; and / or, 0 μm < d 2 < 3 μm. By controlling the appropriate median particle sizes of the active materials in the middle region and the outer region, the electron and ion transport abilities of the middle positive electrode can be regulated. When d 1 ≥ 3 μm, the median particle size of the middle region itself is too large, affecting the electron and ion transport abilities. When d 2 ≥ 3 μm, the median particle size of the outer region itself is too large, affecting the electron and ion transport abilities.

[0017] In any embodiment, the positive electrode sheet includes at least two outer regions, and in the width direction of the positive electrode sheet, the two outer regions are located on both sides of the middle region. By respectively arranging the outer regions on both sides of the middle region in the width direction, after the electrode sheet is wound, the polarization performance at the upper and lower ends is less than the polarization performance at the middle position, and the effect of improving lithium deposition in the middle of the battery cell is better.

[0018] In any embodiment, the positive electrode sheet includes a current collector, a middle coating layer is provided in a middle region on the current collector, an outer coating layer is provided in a peripheral region on the current collector and located on at least one side of the middle region of the current collector, and the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer. By forming a middle region and a peripheral region on the current collector to form corresponding middle regions and outer regions, the polarizability of the middle region can be greater than the polarizability of the outer region by changing the polarizability of the coating layer.

[0019] In any embodiment, the material of the middle coating layer includes: lithium iron phosphate with a first carbon coating content, wherein the mass percentage of the carbon coating layer in the lithium iron phosphate with the first carbon coating content is 0.01 to 0.5 wt.%;

[0020] The material of the outer coating layer includes: lithium iron phosphate with a second carbon coating content, wherein the mass percentage of the carbon coating layer in the lithium iron phosphate with the second carbon coating content is 0.01 to 1.5 wt.%;

[0021] The mass percentage of the carbon coating layer in the lithium iron phosphate having the first carbon coating content is less than the mass percentage of the carbon coating layer in the lithium iron phosphate having the second carbon coating content.

[0022] By making the mass percentage of the carbon coating layer in the lithium iron phosphate with the first carbon coating content smaller than the mass percentage of the carbon coating layer in the lithium iron phosphate with the second carbon coating content, the polarization performance of the middle region is higher than that of the outer region.

[0023] In a second aspect, the present application provides a method for preparing a positive electrode sheet, comprising the following steps:

[0024] providing a current collector;

[0025] A middle coating layer is arranged in the middle area of ​​at least one side of the current collector, the periphery of the middle area of ​​the current collector has at least one peripheral area, the peripheral area is arranged with an outer coating layer, the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer, and a positive electrode sheet is obtained.

[0026] By providing a middle coating layer in the middle area of ​​at least one side of the current collector, the periphery of the middle area of ​​the current collector has at least one peripheral area, and the peripheral area is provided with an outer coating layer, a positive electrode sheet can be obtained in which the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer.

[0027] In a third aspect, an embodiment of the present application provides a lithium-ion battery, comprising the positive electrode sheet of the first aspect of the present application.

[0028] In any embodiment, the lithium ion battery includes a lithium ion primary battery and a lithium ion secondary battery.

[0029] In a fourth aspect, an embodiment of the present application provides an electrical device, comprising the lithium-ion battery of the third aspect of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without paying creative work.

[0031] Figure 1 A schematic diagram of the structure of a positive electrode sheet of one or more embodiments;

[0032] Figure 2 A schematic diagram of the structure of a positive electrode sheet of one or more embodiments;

[0033] Figure 3 A schematic diagram of the size structure of the middle area of ​​the positive electrode sheet of one or more embodiments.

[0034] Description of the accompanying drawings of the embodiments of the present application:

[0035] Label name Label name 100 Positive electrode <![CDATA[a 1 ]]> The size of the middle area in the width direction of the positive electrode sheet 1 Central Region <![CDATA[a 2 ]]> The width of the positive electrode 2 Outer area

[0036] The purpose, features and advantages of the present invention will be further described with reference to the accompanying drawings in conjunction with the embodiments. DETAILED DESCRIPTION

[0037] The following specifically discloses the implementation methods of the positive electrode sheet, the preparation method of the positive electrode sheet, the solar power generation device and the power-consuming device of the present application. However, there may be cases where unnecessary detailed descriptions are omitted. For example, there are cases where detailed descriptions of well-known matters and repeated descriptions of actually the same structure are omitted. This is to avoid the following description from becoming unnecessarily lengthy and to facilitate the understanding of those skilled in the art. In addition, the drawings and the following descriptions are provided for those skilled in the art to fully understand the present application and are not intended to limit the subject matter described in the claims.

[0038] "Scope" disclosed in the present application is limited in the form of lower limit and upper limit, and a given range is limited by selecting a lower limit and an upper limit, and the selected lower limit and upper limit define the boundary of a special range. The scope limited in this way can be including end values ​​or not including end values, and can be arbitrarily combined, that is, any lower limit can be combined with any upper limit to form a scope. For example, if the scope of 60-120 and 80-110 is listed for a specific parameter, it is understood that the scope of 60-110 and 80-120 is also expected. In addition, if the minimum range values ​​1 and 2 are listed, and if the maximum range values ​​3, 4 and 5 are listed, the following scope can be all expected: 1-3, 1-4, 1-5, 2-3, 2-4 and 2-5. In the present application, unless otherwise specified, the numerical range "ab" represents the abbreviation of any real number combination between a and b, wherein a and b are real numbers. For example, the numerical range "0-5" means that all real numbers between "0-5" are listed in this document, and "0-5" is just an abbreviation of these numerical combinations. In addition, when a parameter is expressed as an integer ≥ 2, it is equivalent to disclosing that the parameter is, for example, an integer of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0039] Unless otherwise specified, all embodiments and optional embodiments of the present application can be combined with each other to form a new technical solution.

[0040] Unless otherwise specified, all technical features and optional technical features of this application can be combined with each other to form a new technical solution.

[0041] If there is no special explanation, all steps of the present application can be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), which means that the method may include steps (a) and (b) performed sequentially, or may include steps (b) and (a) performed sequentially. For example, the method may further include step (c), which means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b) and (c), or may include steps (a), (c) and (b), or may include steps (c), (a) and (b), etc.

[0042] If there is no special explanation, the "include" and "comprising" mentioned in this application are open-ended or closed-ended. For example, the "include" and "comprising" may mean that other components not listed may also be included or only the listed components may be included or only the listed components may be included.

[0043] If not specifically stated, in this application, the term "or" is inclusive. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, any of the following conditions satisfies the condition "A or B": A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0044] During the battery cell cycle, the polarization in the height direction of the electrode is different due to uneven temperature and expansion force. Affected by heat dissipation, the temperature in the middle of the electrode is high, the expansion force is large, and the polarization is small; the temperature at the head and bottom of the electrode is low, the expansion force is small, and the polarization is large; under the influence of uneven polarization distribution, lithium ions tend to diffuse and embed lithium in the middle of the electrode, making the amount of lithium embedded in the head and bottom of the electrode lower than that in the middle, thus causing lithium deposition in the middle of the battery cell.

[0045] Therefore, there are endless technologies for improving lithium deposition in the middle of the battery cell. For example, a negative electrode plate has a higher negative electrode capacity per unit area of ​​the edge layer than that of the middle layer. When the negative electrode capacity per unit area of ​​the middle layer is equal to the designed negative electrode capacity per unit area of ​​the negative electrode plate, it is equivalent to increasing the negative electrode capacity of the edge layer. In this way, even if the thickness of the outer edge of the edge layer gradually decreases due to the flow of the slurry, it can ensure that the negative electrode capacity of the edge layer is not less than the designed negative electrode capacity, thereby avoiding the negative electrode capacity of the negative electrode plate due to the casting or edge effect of the edge area of ​​the dressing layer, thereby reducing the risk of lithium deposition of the negative electrode plate. However, due to the high specific capacity of the edge graphite, the interlayer spacing is often smaller than that of the middle graphite with low specific capacity, the degree of graphitization is higher, and the limit charging capacity is lower. The lithium deposition caused by insufficient CB is improved by increasing the specific capacity of graphite, but it may further lead to lithium deposition due to insufficient charging capacity of the graphite material itself.

[0046] Unexpectedly, by setting the polarization performance of the middle area of ​​the positive electrode sheet to be higher than the polarization performance of at least one outer area, the difference in polarization performance between the middle area and the outer area of ​​the positive electrode sheet caused by inconsistent temperature and expansion force can be alleviated, thereby improving the uniformity of the polarization of the middle and outer areas of the electrode sheet, improving the uniformity of lithium insertion from the positive electrode to the negative electrode, alleviating the problem of lower lithium insertion amount in the outer area of ​​the electrode sheet than in the middle area, and improving the problem of lithium deposition in the middle of the battery cell.

[0047] Based on this, the embodiments of the present application provide a positive electrode sheet and a preparation method thereof, a lithium-ion battery and an electrical device.

[0048] See also Figure 1 and Figure 2In the first aspect, an embodiment of the present application proposes a positive electrode sheet 100, wherein the positive electrode sheet 100 has a central region 1 and at least one outer region 2 located outside the central region 1, and the polarizability of the central region 1 is greater than the polarizability of the outer region 2.

[0049] Therefore, in the technical solution of the embodiment of the present application, the polarizability of the middle region 1 of the positive electrode sheet 100 is greater than the polarizability of the outer region 2, so as to offset the influence of heat dissipation during the cycle of the battery cell, the high temperature in the middle of the electrode sheet, the large expansion force, the small polarization, and the low temperature at the head and bottom of the electrode sheet, the small expansion force, and the large polarization. The uniformity of the polarizability of the middle and outer regions 2 of the electrode sheet is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer region of the electrode sheet is lower than the amount of lithium inserted in the middle region is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved.

[0050] In any embodiment, the resistivity of the middle region 1 is greater than the resistivity of the outer region 2. By setting the resistivity of the middle region 1 of the positive electrode sheet 100 to be greater than the resistivity of the outer region 2, the polarization performance of the middle region 1 of the positive electrode sheet 100 is improved, and under the influence of temperature and expansion force, the consistency of the polarization performance of the middle region and the outer region 2 is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer region of the electrode sheet is lower than the amount of lithium inserted in the middle region is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved; and / or,

[0051] The carbon coating content of the middle region 1 is less than that of the outer region 2. By setting the carbon coating content of the middle region 1 of the positive electrode sheet 100 to be less than that of the outer region 2, the polarization performance of the middle region 1 of the positive electrode sheet 100 is improved, and under the influence of temperature and expansion force, the consistency of the polarization performance of the middle region and the outer region 2 is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer region of the electrode sheet is lower than that in the middle region is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved; and / or,

[0052] The median particle size of the middle region 1 is smaller than the median particle size of the outer region 2. By setting the median particle size of the middle region 1 of the positive electrode sheet 100 smaller than the median particle size of the outer region 2, the polarization performance of the middle region 1 of the positive electrode sheet 100 is improved. Under the influence of temperature and expansion force, the consistency of the polarization performance of the middle region and the outer region 2 is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer region of the electrode sheet is lower than the amount of lithium inserted in the middle region is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved.

[0053] See also Figure 3 In any embodiment, the size of the middle region 1 in the width direction of the positive electrode sheet 100 is a 1 The dimension of the positive electrode sheet 100 in the width direction is a 2 , where: 0<a1 / a 2 <1, a 1 / a 2 It can be 1 / 20, 1 / 15, 1 / 10, 1 / 5, 1 / 3, 1 / 2, 3 / 4, 4 / 5; and / or, 1 / 4 ≤ a 1 / a 2 ≤ 3 / 4. By setting a central region 1 with a certain size in the width direction of the positive electrode sheet 100, the polarization performance of the central region 1 is higher than that of the outer region 2, thereby improving the uniformity of the polarization of the central part and the outer region 2 of the electrode sheet, improving the uniformity of lithium intercalation from the positive electrode to the negative electrode, alleviating the problem that the amount of lithium intercalation in the outer region of the electrode sheet is lower than that in the central region, and improving the problem of lithium deposition in the central part of the battery cell.

[0054] In any embodiment, the resistivity of the active material in the central region is greater than the resistivity of the active material in the outer region, and the resistivity of the active material in the central region is R 1 and the resistivity of the active material in the outer region is R 2 where: 0 Ω·cm < R 1 -R 2 <55 Ω·cm; R 1 -R 2 can be 2 Ω·cm, 5 Ω·cm, 10 Ω·cm, 15 Ω·cm, 20 Ω·cm, 25 Ω·cm, 30 Ω·cm, 35 Ω·cm, 40 Ω·cm, 45 Ω·cm, 50 Ω·cm, 54 Ω·cm. By controlling the resistivity of the active material in the central region to be greater than the resistivity of the active material in the outer region, the polarization of the central region 1 is made greater than the polarization of the outer region 2. At the same time, the resistivity difference is controlled within a suitable range, which is beneficial to improving the consistency of the polarization performance of the middle region and the outer region 2. Among them, when R 1 -R 2 ≥ 55 Ω·cm, the resistivity difference between the active materials in the central region and the outer region is too large, which will increase the probability of lithium deposition in the outer region. Optionally, 5 Ω·cm < R 1 -R 2 <25 Ω·cm.

[0055] In any embodiment, the resistivity of the active material in the central region is greater than the resistivity of the active material in the outer region, and the resistivity of the active material in the central region is R 1 and the resistivity of the active material in the outer region is R 2 where: 0 Ω·cm < R 1 <60 Ω·cm; and / or, 0 Ω·cm < R 2 <60 Ω·cm. By controlling the resistivity of the appropriate central region 1 and outer region 2, the electron transport ability can be improved, R 1When it is ≥ 60 Ωcm, the resistivity of the middle region 1 itself is too high, affecting the electron transport ability, R 2 When it is ≥ 60 Ωcm, the resistivity of the outer region 2 itself is too high, affecting the electron transport ability.

[0056] In any implementation, the carbon coating content of the active material in the middle region is greater than that of the active material in the outer region. The carbon coating content of the active material in the middle region is W 1 , and the carbon coating content of the active material in the outer region is W 2 , where: 0% < W 2 -W 1 < 3%; By controlling the appropriate difference in carbon coating content, the polarization of the middle region 1 is made greater than that of the outer region 2, which is beneficial to improving the consistency of the polarization performance of the middle region and the outer region 2. W 2 -W 1 ≥ 3%, the difference in carbon coating content between the active materials in the middle region and the outer region is too large, which will increase the probability of lithium plating in the outer region. W 2 -W 1 can be 0.1%, 0.2%, 0.3%, 0.5%, 0.8%, 1.0%, 1.2%, 1.5%, 2.0%, 2.5%, 2.9%. Optionally, 0.3% < W 2 -W 1 < 1.2%.

[0057] In any implementation, the carbon coating content of the active material in the middle region is greater than that of the active material in the outer region. The carbon coating content of the active material in the middle region is W 1 , and the carbon coating content of the active material in the outer region is W 2 , where: 0% < W 1 < 3%; and / or, 0% < W 2 < 3%. By controlling the appropriate carbon coating content of the middle region 1 and the outer region 2, the electron transport ability can be improved. W 1 ≥ 3%, the carbon coating content of the active material in the middle region itself is too high, reducing the energy density of the battery cell and affecting the electron transport ability. W 2 ≥ 3%, the carbon coating content of the outer region itself is too high, reducing the energy density of the battery cell and affecting the electron transport ability.

[0058] In any implementation, the median particle size of the active material in the middle region is greater than that of the active material in the outer region. The median particle size of the active material in the middle region is d 1 , and the median particle size of the active material in the outer region is d 2 , where: 0 μm < d 2 -d1 <3μm;d 2 -d 1 It can be 0.1μm, 0.2μm, 0.5μm, 0.8μm, 1μm, 1.5μm, 2.0μm, 2.5μm, 2.9μm. By controlling the difference in the appropriate median particle size, the polarizability of the middle region 1 is greater than that of the outer region 2, which is beneficial to improving the consistency of the polarization performance of the middle region and the outer region 2. 2 -d 1 When d is ≥3μm, the difference between the median particle size of the active material in the middle region and the outer region is too large, which will increase the probability of lithium deposition in the outer region. 2 -d 1 <1μm.

[0059] In any embodiment, the median particle size of the active material in the middle region is greater than the median particle size of the active material in the outer region, and the median particle size of the active material in the middle region is d 1 , the median particle size of the active material in the outer region is d 2 , where: 0μm<d 1 <3μm; and / or, 0μm<d 2 <3μm. By controlling the median particle size of the active materials in the middle and outer regions, the electron and ion transport capacity of the middle positive electrode can be adjusted. 1 When the particle size is ≥3μm, the median particle size in the middle region is too large, which affects the transmission capacity of electrons and ions. 2 When the particle size is ≥3μm, the median particle size of the outer region itself is too large, which affects the transmission capacity of electrons and ions.

[0060] In any embodiment, the positive electrode sheet 100 includes at least two outer regions 2, and in the width direction of the positive electrode sheet 100, the two outer regions 2 are located on both sides of the middle region 1. By respectively arranging the outer regions 2 on both sides of the middle region 1 in the width direction, after the electrode sheet is wound, the polarization properties of the upper and lower ends are less than the polarization properties of the middle position, and the effect of improving lithium deposition in the middle of the battery cell is better.

[0061] In any embodiment, the positive electrode sheet 100 includes a current collector, a middle coating layer is provided in the middle region of the current collector, and an outer coating layer is provided in the outer region of the current collector and located on at least one side of the middle region of the current collector, and the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer. By forming the middle region and the outer region on the current collector to form the corresponding middle region 1 and outer region 2, the polarizability of the middle region can be greater than the polarizability of the outer region by changing the polarizability of the coating layer.

[0062] In any embodiment, the material of the middle coating layer includes: lithium iron phosphate with a first carbon coating content, wherein the mass percentage of the carbon coating layer in the lithium iron phosphate with the first carbon coating content is 0.01 to 0.5 wt.%;

[0063] The material of the outer coating layer includes: lithium iron phosphate with a second carbon coating content, wherein the mass percentage of the carbon coating layer in the lithium iron phosphate with the second carbon coating content is 0.01 to 1.5 wt.%;

[0064] The mass percentage of the carbon coating layer in the lithium iron phosphate having the first carbon coating content is less than the mass percentage of the carbon coating layer in the lithium iron phosphate having the second carbon coating content.

[0065] By making the mass percentage of the carbon coating layer in the lithium iron phosphate with the first carbon coating content smaller than the mass percentage of the carbon coating layer in the lithium iron phosphate with the second carbon coating content, the polarization performance of the middle region is higher than that of the outer region.

[0066] In any embodiment, the material of the middle coating layer includes but is not limited to at least one of lithium cobalt oxide, lithium manganese oxide, nickel cobalt lithium manganese oxide, lithium iron phosphate and nickel cobalt aluminum oxide. The polarizability of the middle region can be higher than that of the outer region by changing the type of active material of the middle coating layer, changing the particle size or carbon coating content of the active material of the middle coating layer.

[0067] In a second aspect, an embodiment of the present application provides a method for preparing a positive electrode sheet, which is used to prepare the positive electrode sheet of the first aspect of the present application, comprising the following steps:

[0068] providing a current collector;

[0069] A middle coating layer is arranged in the middle area of ​​at least one side of the current collector, the periphery of the middle area of ​​the current collector has at least one peripheral area, the peripheral area is arranged with an outer coating layer, the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer, and a positive electrode sheet is obtained.

[0070] By providing a middle coating layer in the middle area of ​​at least one side of the current collector, the periphery of the middle area of ​​the current collector has at least one peripheral area, and the peripheral area is provided with an outer coating layer, a positive electrode sheet can be obtained in which the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer.

[0071] In a third aspect, an embodiment of the present application provides a lithium-ion battery, comprising the positive electrode sheet of the first aspect of the present application.

[0072] In any embodiment, the lithium ion battery includes a lithium ion primary battery and a lithium ion secondary battery.

[0073] In a fourth aspect, an embodiment of the present application provides an electrical device, comprising the lithium-ion battery of the third aspect of the present application.

[0074] The technical solution of the present invention is further described in detail below in conjunction with specific embodiments. It should be understood that the following embodiments are only used to explain the present invention, and are not used to limit the present invention.

[0075] Example 1

[0076] A positive electrode sheet, wherein the polarizability of the middle region is greater than that of the outer region.

[0077] Example 2

[0078] A positive electrode sheet, wherein the polarizability of a central region is greater than the polarizability of an outer region.

[0079] The parameters of the positive electrode sheets of Examples 3 to 35 of the present application and Comparative Examples 1 to 3 are as shown in Table 1.

[0080] Table 1 Parameters of positive electrode sheets of Examples 3 to 26 and Comparative Examples 1 to 6

[0081]

[0082]

[0083] Embodiment 27

[0084] A method for preparing a positive electrode sheet comprises the following steps:

[0085] providing a current collector;

[0086] A middle coating layer is arranged in the middle area of ​​at least one side of the current collector, the periphery of the middle area of ​​the current collector has at least one peripheral area, the peripheral area is arranged with an outer coating layer, the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer, and a positive electrode sheet is obtained.

[0087] The positive electrode sheets of Examples 1 to 26 and Comparative Examples 1 to 6 are prepared into lithium ion secondary batteries, wherein the negative electrode sheet, the electrolyte, the separator and the lithium ion secondary battery can be prepared by the following preparation method:

[0088] Preparation of negative electrode:

[0089] The negative electrode active material artificial graphite (gram capacity of 340 mAh / g), the conductive agent acetylene black, and the binder SBR+CMC were mixed according to 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 a 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, a negative electrode sheet is obtained.

[0090] Electrolyte preparation:

[0091] 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, VC, DTD, and 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 1 mol / L, and the mass percentages of VC, DTD, and PS were 3%, 1%, and 1%, respectively.

[0092] Preparation of isolation membrane:

[0093] A polyethylene porous membrane was used as the isolation membrane.

[0094] Preparation of lithium-ion secondary batteries:

[0095] The positive electrode sheet, the separator, and the negative electrode sheet are stacked in order, the separator is placed between the positive and negative electrodes to play a role of isolation, and then wound to obtain a bare cell. The bare cell is placed in an outer package, the prepared electrolyte is injected, and the package is packaged for formation to obtain a lithium-ion secondary battery.

[0096] Perform the following test:

[0097] Room temperature cycle performance test of lithium-ion secondary batteries

[0098] At 25°C, the lithium-ion secondary 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 secondary 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 secondary battery is subjected to multiple cycle charge and discharge tests according to the above method until the discharge capacity of the lithium-ion secondary battery decays to 80%, and the number of cycles of the lithium-ion secondary battery is recorded.

[0099] High temperature cycle performance test of lithium-ion secondary batteries

[0100] At 60°C, the lithium-ion secondary 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 secondary 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 secondary battery is subjected to multiple cycle charge and discharge tests according to the above method, and the discharge capacity of the 1000th cycle is detected.

[0101] Capacity retention rate of the lithium ion secondary battery after 500 cycles at 60° C.=(discharge capacity at the 500th cycle / discharge capacity at the first cycle)×100%.

[0102] The statistical experimental results are shown in Table 2.

[0103] Table 2 Performance measurement of positive electrode sheets of Examples 1 to 26 and Comparative Examples 1 to 6

[0104]

[0105]

[0106] It can be seen from Table 2 that, through Examples 1 to 2 and Comparative Examples 1 to 6, it can be seen that by setting the polarizability of the middle portion of the positive electrode sheet to be greater than that of the outer region, the probability of lithium deposition in the middle portion of the battery cell can be reduced.

[0107] It can be seen from Examples 3 to 7 that by setting the middle region in the width direction of the positive electrode sheet, the polarization performance of the middle region is higher than that of at least one outer region, thereby improving the uniformity of the polarization of the middle and outer regions of the electrode sheet, improving the uniformity of lithium insertion from the positive electrode to the negative electrode, alleviating the problem that the amount of lithium inserted in the outer region of the electrode sheet is lower than that in the middle region, and improving the problem of lithium deposition in the middle of the battery cell. The ratio of the middle region in the width direction of the positive electrode sheet to the width of the positive electrode sheet affects the effect of improving lithium deposition in the middle. When a 1 / a 2 When it is less than 1 / 10, the middle area is narrow and lithium deposition still occurs in some local areas. 1 / a 2 When it is greater than 3 / 4, the middle area is too wide and lithium is deposited in some local areas.

[0108] It can be seen from Examples 8 to 13 that by controlling the resistivity of the active material in the middle region to be greater than that of the active material in the outer region, the polarizability of the middle region is greater than that of the outer region, and at the same time, the resistivity difference is controlled within a suitable range, which is conducive to improving the consistency of the polarization performance of the middle region and the outer region. 1 -R 2 When ≥55Ωcm, the resistivity difference between the active materials in the middle region and the outer region is too large, which will increase the probability of lithium deposition in the outer region.

[0109] It can be seen from Examples 14 to 19 that by controlling the appropriate difference in carbon coating content, the polarizability of the middle region is greater than that of the outer region, which is beneficial to improving the consistency of the polarization performance of the middle region and the outer region. 2 -W 1When it is ≥3%, the difference in carbon coating content between the active materials in the middle region and the outer region is too large, which will increase the probability of lithium precipitation in the outer region.

[0110] It can be seen from Examples 20 to 25 that by controlling the appropriate difference in median particle size, the polarizability of the middle region is greater than that of the outer region, which is beneficial to improving the consistency of the polarization performance of the middle region and the outer region. 2 -d 1 When the particle size is ≥3μm, the difference between the median particle size of the active materials in the middle region and the outer region is too large, which will increase the probability of lithium deposition in the outer region.

[0111] To summarize, in the positive electrode sheet proposed in the present application, the polarizability of the middle area of ​​the positive electrode sheet is greater than the polarizability of the outer area, so as to offset the influence of heat dissipation during the cycle of the battery cell, the temperature in the middle of the electrode sheet is high, the expansion force is large, the polarization is small, and the temperature at the head and bottom of the electrode sheet is low, the expansion force is small, and the polarization is large. The uniformity of the polarizability of the middle and outer areas of the electrode sheet is improved, the uniformity of lithium insertion from the positive electrode to the negative electrode is improved, the problem that the amount of lithium inserted in the outer area of ​​the electrode sheet is lower than the amount of lithium inserted in the middle area is alleviated, and the problem of lithium precipitation in the middle of the battery cell is improved.

[0112] The above are only preferred embodiments of the present invention, and do not limit the patent scope of the present invention. For those skilled in the art, the present invention may have various changes and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the patent protection scope of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The invention has a middle region and at least one outer region located at the periphery of the middle region, wherein the polarizability of the middle region is greater than the polarizability of the outer region.

2. The positive electrode sheet according to claim 1, characterized in that: The resistivity of the active material in the middle region is greater than the resistivity of the active material in the outer region; and / or, The carbon coating content of the active material in the middle region is less than the carbon coating content of the active material in the outer region; and / or, The median particle size of the active material in the middle region is smaller than the median particle size of the active material in the outer region.

3. The positive electrode sheet according to claim 1 or 2, characterized in that: The size of the middle area in the width direction of the positive electrode sheet is a1, and the size of the middle area in the width direction of the positive electrode sheet is a2, wherein: 0<a1 / a2<1; optionally, 1 / 4≤a1 / a2≤3 / 4.

4. The positive electrode sheet according to any one of claims 1 to 3, characterized in that: The resistivity of the active material in the middle region is greater than that of the active material in the outer region. The resistivity of the active material in the middle region is R1, and the resistivity of the active material in the outer region is R2, wherein: 0Ωcm<R1-R2<55Ωcm; optionally, 5Ωcm<R1-R2<25Ωcm.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The resistivity of the active material in the middle region is greater than that of the active material in the outer region. The resistivity of the active material in the middle region is R1, and the resistivity of the active material in the outer region is R2, wherein: 0Ωcm<R1<60Ωcm;and / or, 0Ωcm<R2<60Ωcm.

6. The positive electrode sheet according to any one of claims 1 to 5, characterized in that: The carbon coating content of the active material in the middle region is less than that of the active material in the outer region. The carbon coating content of the active material in the middle region is W1, and the carbon coating content of the active material in the outer region is W2, wherein: 0%<W2-W1<3%; alternatively, 0.3%<W2-W1<1.2%.

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that: The carbon coating content of the active material in the middle region is less than that of the active material in the outer region. The carbon coating content of the active material in the middle region is W1, and the carbon coating content of the active material in the outer region is W2, wherein: 0%<W1<3%; and / or, 0％＜W2＜3％。 8. The positive electrode sheet according to any one of claims 1 to 7, characterized in that: The median particle size of the active material in the middle region is smaller than the median particle size of the active material in the outer region. The median particle size of the active material in the middle region is d1, and the median particle size of the active material in the outer region is d2, wherein: 0μm<d2-d1<3μm; optionally, 0.2μm<d2-d1<1μm.

9. The positive electrode sheet according to any one of claims 1 to 8, characterized in that: The median particle size of the active material in the middle region is smaller than the median particle size of the active material in the outer region. The median particle size of the active material in the middle region is d1, and the median particle size of the active material in the outer region is d2, wherein: 0 μm<d1<3 μm; and / or, 0μm<d2<3μm.

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: It comprises at least two outer regions, and in the width direction of the positive electrode sheet, the two outer regions are located on both sides of the middle region.

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that: The positive electrode sheet includes a current collector, a middle coating layer is arranged in the middle area of ​​the current collector, and an outer coating layer is arranged in the outer area of ​​the current collector and located on at least one side of the middle area of ​​the current collector, and the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer.

12. The positive electrode sheet according to claim 11, characterized in that: The material of the middle coating layer includes: lithium iron phosphate with a first carbon coating content, wherein the mass percentage of the carbon coating layer in the lithium iron phosphate with the first carbon coating content is 0.01-0.5wt.%; The material of the outer coating layer includes: lithium iron phosphate with a second carbon coating content, wherein the mass percentage of the carbon coating layer in the lithium iron phosphate with the second carbon coating content is 0.01 to 1.5 wt.%; The mass percentage of the carbon coating layer in the lithium iron phosphate having the first carbon coating content is less than the mass percentage of the carbon coating layer in the lithium iron phosphate having the second carbon coating content.

13. A method for preparing a positive electrode sheet, characterized in that: The following steps are involved: providing a current collector; A middle coating layer is arranged in the middle area of ​​at least one side of the current collector, the periphery of the middle area of ​​the current collector has at least one peripheral area, the peripheral area is arranged with an outer coating layer, the polarizability of the middle coating layer is greater than the polarizability of the outer coating layer, and a positive electrode sheet is obtained.

14. A lithium ion battery, characterized in that: Comprising the positive electrode sheet as described in any one of claims 1 to 12.

15. The lithium ion battery according to claim 14, characterized in that The lithium ion battery includes a lithium ion primary battery and a lithium ion secondary battery.

16. An electrical device, characterized in that: Comprising a lithium ion battery as claimed in claim 14 or 15.

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