Positive electrode sheet, secondary battery, battery module, battery pack, and electric device including the same

Abstract

The application provides a positive electrode sheet, a secondary battery, a battery module, a battery pack and a power utilization device comprising the same. The positive electrode sheet comprises a current collector, a resistance layer and a positive active material layer, wherein the current collector comprises a coated area and a non-coated area outside the coated area, the resistance layer comprises a conductive agent and a binder but does not comprise a positive active material, the positive active material layer comprises a positive active material, a conductive agent and a binder, the resistance of the resistance layer is greater than that of the positive active material layer, and the resistance layer is arranged on the current collector. In the cross section of the positive electrode sheet, the projection of a part of the positive active material layer on the current collector overlaps with the projection of the resistance layer on the current collector, and the projection of another part of the positive active material layer on the current collector does not overlap with the projection of the resistance layer on the current collector.

Description

Technical Field

[0001] This application relates to the field of secondary battery technology, and in particular to a positive electrode sheet that can be used in secondary batteries, as well as secondary batteries, battery modules, battery packs and electrical devices including the positive electrode sheet. Background Technology

[0002] In recent years, with the vigorous promotion of new energy electric vehicles, their market share has been continuously increasing. Currently, the most widely used energy storage battery in new energy electric vehicles is the lithium-ion secondary battery. With the continuous development of lithium-ion secondary batteries and their increasingly widespread application, higher requirements are being placed on their energy density, cycle performance, and safety performance.

[0003] However, the cycle life of current lithium-ion rechargeable batteries is generally around 800-900 charge-discharge cycles, after which their capacity decays to about 80% of their initial value. Currently, effective methods to increase battery life include: improving the surface coating of active materials to reduce surface side reactions; increasing the content of conductive materials to reduce resistance; etc. However, existing methods all bring significant cost increases and technical challenges. Therefore, existing lithium-ion rechargeable batteries still need improvement in terms of lifespan. Summary of the Invention

[0004] In view of the above problems, the purpose of this application is to provide a positive electrode sheet for a secondary battery, as well as a secondary battery, battery module, battery pack and power device including the positive electrode sheet, wherein by controlling the release of lithium ions, the battery capacity decay is slowed down while ensuring the battery power performance, thereby extending the service life.

[0005] To achieve the above objectives, this application provides a positive electrode sheet for a secondary battery, comprising: a current collector, a resistive layer, and a positive electrode active material layer, wherein...

[0006] The current collector includes a coated area and an uncoated area outside the coated area.

[0007] The resistive layer includes a conductive agent and a binder, but does not include a positive electrode active material.

[0008] The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0009] The resistance of the resistive layer is greater than the resistance of the positive electrode active material layer, and the resistive layer is disposed on the current collector.

[0010] In the cross-section of the positive electrode sheet, the projection of a portion of the positive active material layer onto the current collector (in this application, projection refers to the orthographic projection perpendicular to the main surface of the current collector) overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion onto the current collector does not overlap with the projection of the resistive layer onto the current collector.

[0011] In some embodiments, the polarization parameter P of the positive electrode is in the range of 0.5 to 70.0, preferably in the range of 0.5 to 36.0, and more preferably in the range of 0.5 to 10.0. The polarization parameter P = ((1-S) / S)·(R1 / R2), where S is the area ratio of the resistive layer to the coating area of ​​the current collector, R1 is the film resistance value of the portion of the positive electrode where the resistive layer is disposed, and R2 is the film resistance value of the portion of the positive electrode in the coating area where the resistive layer is not disposed.

[0012] In some embodiments, the area ratio S of the resistive layer relative to the coated area of ​​the current collector is in the range of 0.20 to 0.80, preferably in the range of 0.40 to 0.60.

[0013] In some embodiments, the projection of the positive electrode active material layer onto the current collector completely covers the projection of the resistive layer onto the current collector.

[0014] In some embodiments, the mass ratio of the binder to the conductive agent in the resistive layer is greater than the mass ratio of the binder to the conductive agent in the positive electrode active material layer; preferably, in the resistive layer, the mass ratio of the binder to the conductive agent is in the range of 2.2 to 50.0, more preferably in the range of 4.0 to 20.0; and / or preferably, in the positive electrode active material layer, the mass ratio of the binder to the conductive agent is in the range of 1.6 to 10.0, more preferably in the range of 2.0 to 3.4.

[0015] In some embodiments, the conductive agent in the resistive layer has a mass content of 2.0 to 30.0% based on the total weight of the resistive layer, and the binder has a mass content of 70.0 to 98.0% based on the total weight of the resistive layer.

[0016] In some embodiments, a conductive agent layer is further disposed on the current collector, the projection of the conductive agent layer on the current collector not overlapping the projection of the resistive layer on the current collector, and the resistance of the conductive agent layer is less than the resistance of the positive electrode active material layer. Preferably, the projections of the conductive agent layer and the resistive layer on the current collector completely cover the projection of the positive electrode active material layer on the current collector. Preferably, R3 / R1 is in the range of 0.10 to 0.95, where R1 is the film resistance value of the positive electrode sheet in the portion where the resistive layer is disposed, and R3 is the film resistance value of the positive electrode sheet in the portion where the conductive agent layer is disposed.

[0017] In some embodiments, R1 / R2 is in the range of 1.15 to 26.00, where R1 is the film resistance value of the portion of the positive electrode sheet where the resistive layer is disposed, and R2 is the film resistance value of the portion of the positive electrode sheet in the coating area where the resistive layer is not disposed; preferably, R1 is in the range of 0.3 to 9.0 Ω; and / or preferably, R2 is in the range of 0.3 to 4.0 Ω.

[0018] In some embodiments, the positive electrode active material includes one or more selected from lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium nickel manganese oxide; the conductive agent includes one or more selected from graphite, carbon black, acetylene black, graphene, and carbon nanotubes; and the binder includes one or more selected from polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, and polyimide.

[0019] In other embodiments, the first positive electrode active material and the second positive electrode active material respectively comprise one or more selected from layered transition metal oxides, polyanionic compounds, Prussian blue compounds, sulfides, nitrides, carbides, and titanates.

[0020] In some embodiments, the compaction density of the positive electrode sheet is 1.5–4.0 g / cm³. 3 Preferably, it is 2.3–3.5 g / cm³. 3 .

[0021] In some embodiments, the thickness of the current collector is 8–14 μm, preferably 10–13 μm; the thickness of the positive electrode is 100–200 μm; and / or the thickness of the resistive layer is 1–30 μm, preferably 10–13 μm.

[0022] In some embodiments, the D of the positive electrode active material v 50 is 1-20 μm, preferably 3-15 μm.

[0023] On the other hand, this application also provides a secondary battery, including a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode may include the positive electrode sheet for the secondary battery of this application as described above.

[0024] On the other hand, this application also provides a battery module. The battery module of this application may include the secondary battery of this application as described above.

[0025] On the other hand, this application also provides a battery pack. The battery pack of this application may include the battery module of this application as described above.

[0026] On the other hand, this application also provides an electrical device. The electrical device of this application may include the secondary battery of this application as described above, or the battery module of this application as described above, or the battery pack of this application as described above, or a combination thereof.

[0027] In the secondary battery of this application, by applying the positive electrode sheet with a resistive layer as described in this application, the rate of active lithium ion release in a certain region of the positive electrode sheet is slowed down, thereby retaining some lithium in that region (because during charging, compared with conventional positive electrode active material layers, the rate of active lithium ion release in this region is slower, thus retaining some lithium at the end of charging). During subsequent battery cycles, as the battery gradually ages, the active lithium retained in the aforementioned positive electrode sheet region is gradually released, and the battery capacity shows a trend of first increasing and then gradually decreasing, thereby increasing the battery's lifespan. Attached Figure Description

[0028] Figure 1 This is a schematic cross-sectional view of the positive electrode sheet in the thickness direction according to an embodiment of this application.

[0029] Figure 2 yes Figure 1 The diagram shown is a top view of the positive electrode sheet according to one embodiment of this application.

[0030] Figure 3 This is a top view schematic diagram of the positive electrode sheet according to one embodiment of this application.

[0031] Figure 4 This is a schematic cross-sectional view of the positive electrode sheet in the thickness direction according to an embodiment of this application.

[0032] Figure 5 This is a schematic cross-sectional view of the positive electrode sheet in the thickness direction according to an embodiment of this application.

[0033] Figure 6 This is a schematic diagram of a secondary battery according to one embodiment of this application.

[0034] Figure 7 yes Figure 6An exploded view of a secondary battery according to one embodiment of this application is shown.

[0035] Figure 8 This is a schematic diagram of a battery module according to one embodiment of this application.

[0036] Figure 9 This is a schematic diagram of a battery pack according to one embodiment of this application.

[0037] Figure 10 yes Figure 9 An exploded view of a battery pack according to one embodiment of this application is shown.

[0038] Figure 11 This is a schematic diagram of an electrical device that uses a secondary battery as a power source according to one embodiment of this application.

[0039] Figure 12 This is a graph showing the cycle performance of the secondary battery obtained in Example 19.

[0040] Explanation of reference numerals in the attached figures:

[0041] 10 positive electrode sheets

[0042] 11 Positive electrode active material layer

[0043] 22 current collectors

[0044] 33 resistive layers

[0045] 44 conductive agent layer

[0046] 1 battery pack

[0047] 2 upper box

[0048] 3 lower cabinets

[0049] 4 battery modules

[0050] 5 Secondary batteries

[0051] 51 housing

[0052] 52 Electrode Assembly

[0053] 53 Top Cover Assembly Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of the application will be described in detail below with reference to the accompanying drawings. However, those skilled in the art should understand that these embodiments are only used to illustrate the technical solutions of this application and not to limit it.

[0055] For the sake of brevity, this application specifically discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form an unspecified range; and any lower limit can be combined with other lower limits to form an unspecified range, just as any upper limit can be combined with any other upper limit to form an unspecified range. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and be combined with any other point or single value or with other lower or upper limits to form an unspecified range.

[0056] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0057] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0058] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0059] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0060] Unless otherwise specified, in this application, terms indicating direction or positional relationship such as "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "lateral," "longitudinal," "axial," "radial," and "circumferential" refer to the direction or positional relationship shown in the accompanying drawings. They are merely simplified descriptions for the convenience of describing the embodiments of this application and do not indicate or imply that the device or element referred to must have a specific direction or positional relationship or must be constructed and operated in a specific direction or positional relationship. Therefore, they should not be construed as limitations on the embodiments of this application.

[0061] In existing technologies, it is generally recognized that reducing the impedance of the electrode sheets, including the active material layer and the current collector, can reduce the internal resistance of the cell and help improve the cycle performance of lithium-ion secondary batteries. The kinetic performance of the battery is affected by the lithium-ion intercalation / deintercalation rate of the positive electrode sheet. The faster the lithium-ion intercalation / deintercalation rate, that is, the faster the lithium ions move from the positive electrode active material layer to the negative electrode, the better the kinetic performance.

[0062] However, the inventors of this application have discovered that by setting a resistive layer with a higher resistance than the positive electrode active material layer on the current collector of the positive electrode sheet for secondary batteries in a prescribed manner, the cycle performance of the secondary battery can be improved and the battery life extended. Specifically, the projection of the resistive layer on the current collector does not overlap with the projection of at least a portion of the positive electrode active material layer on the current collector. Therefore, when the battery begins charging, the potential is equal at all points on the positive electrode sheet, and lithium ions are released from the positive electrode active material layer and move towards the negative electrode. During charging, due to the presence of the resistive layer, a portion of lithium is retained in the positive electrode active material layer located above the resistive layer (where the projections overlap) (i.e., some lithium is retained without being released from the positive electrode active material), while the positive electrode active material layer not located above the resistive layer (where the projections do not overlap) is not affected by this. As lithium-ion secondary batteries are charged and discharged, the lithium retained in the positive electrode active material layer above the resistive layer continuously replenishes the lithium consumed by the negative electrode. During the cycle, as the battery polarization is gradually eliminated and the battery ages, the battery capacity shows a trend of first increasing and then gradually decreasing. Ultimately, this slows down the overall capacity decay of the battery, thereby extending the battery's lifespan.

[0063] Based on the above findings, this application provides a positive electrode sheet for secondary batteries, comprising: a current collector, a resistive layer, and a positive electrode active material layer, wherein...

[0064] The current collector includes a coated area and an uncoated area outside the coated area.

[0065] The resistive layer includes a conductive agent and a binder, but does not include a positive electrode active material.

[0066] The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0067] The resistance of the resistive layer is greater than the resistance of the positive electrode active material layer, and the resistive layer is disposed on the current collector.

[0068] In the cross-section of the positive electrode sheet (in this application, the cross-section refers to the cross-section perpendicular to the main surface of the current collector), the projection of a portion of the positive electrode active material layer onto the current collector overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion onto the current collector does not overlap with the projection of the resistive layer onto the current collector.

[0069] As described above, in this application, the current collector includes a coated area and optionally an uncoated area other than the coated area. In the coated area, a positive electrode active material layer and a resistive layer may be disposed on the current collector. The uncoated area may be located at both ends or around the coated area. In this application, the uncoated area is described only to illustrate that the area used as a reference for the area ratio of the resistive layer is the area of ​​the coated region on the current collector (not the entire area of ​​the current collector). In other words, if the surface of the current collector is completely coated, the current collector may only include the coated area.

[0070] As described above, in this application, in the cross-section of the positive electrode sheet, the projection of a portion of the positive electrode active material layer onto the current collector overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion onto the current collector does not overlap with the projection of the resistive layer onto the current collector. Thus, the projection of the resistive layer onto the current collector does not overlap with the projection of at least a portion of the positive electrode active material layer onto the current collector. This structural feature can impart polarization capability to the positive electrode sheet, thereby slowing down battery capacity decay and extending battery life. Specifically, as described above, during battery charging, a portion of lithium that was not extracted from the positive electrode active material layer due to the influence of the resistive layer can be retained in the positive electrode active material layer above the resistive layer (projection overlap), while the positive electrode active material layer not above the resistive layer (projection non-overlapping) is not affected by the above. As lithium-ion secondary batteries are charged and discharged, the lithium retained in the positive electrode active material layer above the resistive layer continuously replenishes the lithium consumed by the negative electrode. During the cycle, as the battery polarization is gradually eliminated and the battery ages, the battery capacity shows a trend of first increasing and then gradually decreasing. Ultimately, this slows down the overall capacity decay of the battery and extends its service life.

[0071] In this application, the resistive layer does not completely cover the coating area of ​​the current collector. In other words, the area ratio S of the resistive layer relative to the coating area of ​​the current collector is less than 1.

[0072] By setting a resistive layer with a higher resistance as described above, the positive electrode of this application will have different film resistance values ​​in the portion where the resistive layer is set and in the portion where the resistive layer is not set. In this application, the film resistance value of the positive electrode in the portion where the resistive layer is set is denoted as R1, and the film resistance value of the positive electrode in the coating area of ​​the current collector where the resistive layer is not set is denoted as R2, and R1 / R2 is greater than 1.

[0073] Those skilled in the art can adjust the polarization capability of the positive electrode by varying the area and resistance of the resistive layer. When the area of ​​the resistive layer is appropriately increased, the area ratio of the resistive layer to the coating area of ​​the current collector increases accordingly, which can appropriately increase the amount of active lithium retained in the positive electrode. When the resistance of the resistive layer is appropriately increased, the resistance difference between the resistive layer and the positive electrode active material layer increases accordingly, thereby appropriately increasing the ratio R1 / R2 between the film resistance value R1 of the portion of the positive electrode where the resistive layer is provided and the film resistance value R2 of the portion of the positive electrode where the resistive layer is not provided in the coating area of ​​the current collector, which can also appropriately increase the amount of active lithium retained in the positive electrode. On the other hand, when the area of ​​the resistive layer is appropriately reduced, excessive amounts of lithium ions retained in the portion of the positive electrode where the resistive layer is provided on the current collector can be avoided. Moreover, by appropriately reducing the area of ​​the resistive layer or appropriately lowering the resistance of the resistive layer, desirable power performance of the battery can be ensured. Therefore, in this application, the area and / or resistance of the resistive layer can be appropriately adjusted as needed. When adjusting the polarization capability of the positive electrode, the area and resistance of the resistive layer can also be adjusted simultaneously, thereby flexibly adjusting the amount of active lithium retained in the positive electrode while ensuring the power performance of the battery.

[0074] As mentioned above, both the area and resistance of the resistive layer affect the polarization capability of the positive electrode. In this application, the polarization capability of the positive electrode can be characterized by the following polarization parameter P: P = ((1-S) / S)·(R1 / R2), where S is the area ratio of the resistive layer to the coating area of ​​the current collector, R1 is the film resistance value of the portion of the positive electrode where the resistive layer is provided, and R2 is the film resistance value of the portion of the positive electrode in the coating area where the resistive layer is not provided. Furthermore, in this application, when the film resistance value R1 of the portion of the positive electrode where the resistive layer is provided or the film resistance value R2 of the portion of the positive electrode in the coating area where the resistive layer is not provided is inconsistent in different regions, R1 and R2 refer to average values.

[0075] In this application, the amount of active lithium retained by the positive electrode can be adjusted by appropriately adjusting the polarization parameter P of the positive electrode. As a non-limiting example, the polarization parameter P of the positive electrode can be adjusted to a range of 0.5 to 70.0.

[0076] Optionally, by adjusting the area ratio of the resistive layer on the current collector to the coating area of ​​the current collector, and / or adjusting the ratio R1 / R2 of the film resistance value R1 of the positive electrode sheet in the portion with the resistive layer and the film resistance value R2 of the portion of the positive electrode sheet in the coating area without the resistive layer, the polarization parameter P of the positive electrode sheet can be appropriately adjusted so that the polarization capability of the positive electrode sheet and the power performance of the battery both reach the required levels, ensuring the power performance of the battery while retaining an appropriate amount of active lithium in the positive electrode sheet. Therefore, while ensuring power performance, battery capacity decay can be reduced and cycle performance can be significantly improved. For example, the number of cycles to maintain 80% battery capacity is significantly increased to over 1500, while the 60s pulse discharge power of the battery remains above 950W.

[0077] In some embodiments, the polarization parameter P of the positive electrode can be adjusted to be not less than 0.5. In some embodiments, the polarization parameter P of the positive electrode can be adjusted to be not greater than 36.0, and optionally, not greater than 10.0. In some embodiments, for example, the polarization parameter P of the positive electrode can be adjusted to a range of 0.5 to 70.0, optionally, to a range of 0.5 to 36.0, and optionally, to a range of 0.5 to 10.0. Optionally, the polarization parameter P of the positive electrode can be 0.5–60.0, 0.5–50.0, 0.5–40.0, 0.5–30.0, 0.5–25.0, 0.5–12.0, 0.8–60.0, 0.9–50.0, 1.2–40.0, 1.5–30.0, 2.5–25.0, 3.5–12.0, 4.0–32.0, 6.0–22.0, 7.0–22.0, 8.0–32.0, 9.0–18.0, 10.0–18.0, 11.0–17.0, 12.0–19.0, 15.0–19.0, or 15.0–26.0.

[0078] In some embodiments, the area ratio S of the resistive layer relative to the coating area of ​​the current collector can be adjusted to a range of 0.20 to 0.80. Furthermore, by combining the ratio R1 / R2 between the film resistance value R1 of the portion of the positive electrode where the resistive layer is provided and the film resistance value R2 of the portion of the positive electrode where the resistive layer is not provided in the coating area, adjusting the area ratio of the resistive layer relative to the coating area of ​​the current collector within an appropriate range can also regulate the amount of lithium retained in the positive electrode active material layer above the resistive layer. This allows for adjustment of the amount of active lithium retained in the positive electrode to regulate the battery's lifespan.

[0079] In some embodiments, the area ratio S of the resistive layer relative to the coating area of ​​the current collector may be not less than 0.20, optionally not less than 0.30, optionally not less than 0.40. In some embodiments, the area ratio S of the resistive layer relative to the coating area of ​​the current collector may be not greater than 0.80, optionally not greater than 0.70, optionally not greater than 0.60. In some embodiments, for example, the area ratio S of the resistive layer relative to the coating area of ​​the current collector may be in the range of 0.20 to 0.60, optionally in the range of 0.20 to 0.70, optionally in the range of 0.30 to 0.60, optionally in the range of 0.30 to 0.70, optionally in the range of 0.30 to 0.80, optionally in the range of 0.40 to 0.60, optionally in the range of 0.40 to 0.70, optionally in the range of 0.40 to 0.80. In a preferred embodiment, the area ratio S of the resistive layer relative to the coating area of ​​the current collector can be in the range of 0.30 to 0.70, and optionally in the range of 0.40 to 0.60.

[0080] The resistive layer can be disposed on the current collector in any manner, as long as the ratio between the area of ​​the resistive layer and the area of ​​the coating area of ​​the current collector meets the requirements. As a non-limiting example, see [reference needed]. Figure 1 and Figure 2 The resistive layer 33 can be one or more parallel coatings disposed on the current collector 22, parallel to the longitudinal direction of the positive electrode. As a non-limiting example, refer to... Figure 3 The resistive layer 33 can also be multiple parallel coatings disposed on the current collector 22 in a direction perpendicular to the longitudinal direction of the positive electrode.

[0081] In this application, the projection of a portion of the positive electrode active material layer 11 onto the current collector 22 overlaps with the projection of the resistive layer 33 onto the current collector 22, while the projection of another portion onto the current collector 22 does not overlap with the projection of the resistive layer 33 onto the current collector 22. Optionally, as... Figure 4 As shown, the projection of the positive electrode active material layer 11 onto the current collector 22 completely covers the projection of the resistive layer 33 onto the current collector 22.

[0082] In the resistive layer of this application, the higher the mass ratio of the binder to the conductive agent, the greater the resistance of the resistive layer, and consequently, the greater the film resistance value of the positive electrode sheet in the portion where the resistive layer is disposed. Therefore, optionally, the mass ratio of the binder to the conductive agent in the resistive layer is greater than the mass ratio of the binder to the conductive agent in the positive electrode active material layer. That is, the relative mass content of the binder to the conductive agent in the resistive layer is greater than the relative mass content of the binder to the conductive agent in the positive electrode active material layer. By adjusting the material composition of the resistive layer in the above manner, the resistance value of the resulting resistive layer can be appropriately greater than the resistance value of the active material layer, thereby generating a desired level of resistance difference between the portion of the positive electrode sheet in which the resistive layer is disposed and the portion of the positive electrode sheet in the coating area where the resistive layer is not disposed.

[0083] Optionally, in the resistive layer, the mass ratio of the adhesive to the conductive agent is in the range of 2.2 to 50.0, preferably in the range of 4.0 to 20.0. Optionally, in the resistive layer, the mass ratio of the adhesive to the conductive agent can be 2.2 to 40.0, 2.2 to 30.0, 2.2 to 20.0, 2.8 to 50.0, 2.8 to 40.0, 2.8 to 30.0, 2.8 to 20.0, 3.4 to 50.0, 3.4 to 40.0, 3.4 to 30.0, 3.4 to 20.0, 4.0 to 50.0, 4.0 to 40.0, and 4.0 to 30.0.

[0084] Optionally, in the positive electrode active material layer, the mass ratio of the binder to the conductive agent is in the range of 1.6 to 10.0, preferably in the range of 2.0 to 3.4. Optionally, the positive electrode active material layer can be a conventional positive electrode active material layer commonly used in the art. Therefore, the mass content of both the binder and the conductive agent in the positive electrode active material layer can also be conventional contents commonly used in the art. As a non-limiting example, in the positive electrode active material layer, the mass ratio of the binder to the conductive agent is in the range of 1.6 to 10.0, preferably in the range of 2.0 to 3.4. Optionally, in the positive electrode active material layer, the mass ratio of the binder to the conductive agent can be 1.6–8.0, 1.6–6.0, 1.6–4.0, 1.8–10.0, 1.8–8.0, 1.8–6.0, 1.8–4.0, 2.0–10.0, 2.0–8.0, 2.0–6.0, and 2.0–4.0.

[0085] Optionally, the mass content of the conductive agent in the resistive layer can be 2.0 to 30.0% by weight based on the total weight of the resistive layer. Alternatively, the mass content of the conductive agent in the resistive layer can be 2.0 to 25.0% by weight, 2.0 to 20.0% by weight, 3.0 to 30.0% by weight, 3.0 to 25.0% by weight, 3.0 to 20.0% by weight, 4.0 to 30.0% by weight, 4.0 to 25.0% by weight, or 4.0 to 20.0% by weight based on the total weight of the resistive layer.

[0086] Optionally, the mass content of the adhesive in the resistive layer may be 70.0% to 98.0% by weight based on the total weight of the resistive layer. Alternatively, the mass content of the adhesive in the resistive layer may be 70.0% to 95.0% by weight, 70.0% to 90.0% by weight, 75.0% to 98.0% by weight, 75.0% to 95.0% by weight, 75.0% to 90.0% by weight, 80.0% to 98.0% by weight, 80.0% to 95.0% by weight, or 80.0% to 90.0% by weight based on the total weight of the resistive layer.

[0087] In some embodiments, a conductive agent layer may also be disposed on the current collector. The projection of the conductive agent layer on the current collector does not overlap with the projection of the resistive layer on the current collector, and the resistance of the conductive agent layer is less than the resistance of the positive electrode active material layer. The presence of the conductive agent layer can further reduce the resistance of the portion of the current collector on which the conductive agent layer is disposed, thereby increasing the charge and discharge rate and mitigating the power performance degradation caused by the presence of the resistive layer, ultimately further improving the power performance of the battery.

[0088] As a non-restrictive example, such as Figure 5 As shown, the projections of the conductive agent layer 44 and the resistive layer 33 onto the current collector 22 completely cover the projection of the positive electrode active material layer 11 onto the current collector 22.

[0089] In this embodiment, the film resistance value of the positive electrode sheet in the portion where the conductive agent layer 44 is disposed is denoted as R3. Preferably, the ratio R3 / R1 between the film resistance value R3 of the positive electrode sheet in the portion where the conductive agent layer 44 is disposed and the film resistance value R1 of the positive electrode sheet in the portion where the resistive layer 33 is disposed is in the range of 0.10 to 0.95. Optionally, R3 / R1 can be 0.10 to 0.90, 0.10 to 0.85, 0.10 to 0.80, 0.20 to 0.95, 0.20 to 0.90, 0.20 to 0.85, 0.20 to 0.80, 0.30 to 0.95, 0.30 to 0.90, 0.30 to 0.85, or 0.30 to 0.80.

[0090] In some embodiments, the ratio R1 / R2 between the film resistance R1 of the positive electrode sheet where the resistive layer is provided and the film resistance R2 of the positive electrode sheet where the resistive layer is not provided in the coated area can be set in the range of 1.15 to 26.00. Setting the R1 / R2 ratio within a specified range ensures that the resistance difference between the portion of the positive electrode sheet with the resistive layer and the portion without the resistive layer in the coated area is within a certain range. On the one hand, this ensures that the ion migration rate of the portion of the positive electrode sheet without the resistive layer on the current collector is not too high, thus undesirably leading to excessive lithium ion retention in the portion of the electrode sheet with the resistive layer on the current collector, reducing battery capacity. On the other hand, it prevents the difference between the two portions from being too small, resulting in almost no retention of active lithium. By adjusting the R1 / R2 ratio within an appropriate range in conjunction with the area ratio of the resistive layer to the coated area of ​​the current collector, it can also regulate the amount of active lithium retained in the positive electrode active material layer above the resistive layer, thereby flexibly adjusting the battery's lifespan. Optionally, R1 / R2 can be 1.15–20.00, 1.15–15.00, 1.15–10.00, 2.00–26.00, 2.00–20.00, 2.00–15.00, 2.00–10.00, 3.00–26.00, 3.00–20.00, 3.00–15.00, or 3.00–10.00.

[0091] Optionally, the ratio of R1 / R2 is adjusted primarily by adjusting the film resistance value R1 of the portion of the positive electrode where the resistive layer is located. As mentioned above, the positive active material layer of the positive electrode can be a conventional positive active material layer commonly used in the art. In this case, the adjustment of R1 is mainly determined by adjusting the resistance of the resistive layer.

[0092] As a non-limiting example, R1 can be in the range of 0.3 to 9.0 Ω. Optionally, R1 can be 0.5 to 7.0 Ω, 1.0 to 7.0 Ω, 1.0 to 6.0 Ω, 1.0 to 5.0 Ω, 2.0 to 8.0 Ω, 2.0 to 7.0 Ω, 2.0 to 6.0 Ω, 3.0 to 8.0 Ω, 3.0 to 7.0 Ω, 3.0 to 6.0 Ω, or 3.0 to 5.0 Ω. As a non-limiting example, R2 can be in the range of 0.3 to 4.0 Ω. Optionally, R2 can be 0.3 to 3.5 Ω, 0.3 to 2.0 Ω, 0.3 to 1.0 Ω, 0.3 to 0.5 Ω, 0.2 to 3.5 Ω, 0.2 to 2.0 Ω, 0.2 to 1.0 Ω, or 0.2 to 0.5 Ω.

[0093] In some embodiments, when the positive electrode sheet of the present invention is applied to a lithium-ion secondary battery, the positive electrode active material may include one or more selected from lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium nickel manganese oxide. As a non-limiting example, the first positive electrode active material and the second positive electrode active material may respectively include materials selected from LiNi 0.55 Co 0.05 Mn 0.4 O2, LiCoO2, LiNiO2, LiMnO2, LiMn2O4, LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2(NCM333), LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523), LiNi 0.6 Co 0.2 Mn 0.2 O2(NCM622), LiNi 0.8 Co 0.1 Mn 0.1 O2(NCM811), LiNi 0.85 Co 0.15 Al 0.05 One or more of O2, LiFePO4 (LFP), and LiMnPO4.

[0094] In some embodiments, when the positive electrode sheet of the present invention is applied to a sodium-ion secondary battery, the first positive electrode active material and the second positive electrode active material may each comprise one or more selected from layered transition metal oxides, polyanionic compounds, Prussian blue compounds, sulfides, nitrides, carbides, and titanates. As a non-limiting example, the first positive electrode active material and the second positive electrode active material may each comprise one or more selected from NaCrO2, Na2Fe2(SO4)3, molybdenum disulfide, tungsten disulfide, vanadium disulfide, titanium disulfide, hexagonal boron nitride, carbon-doped hexagonal boron nitride, titanium carbide, tantalum carbide, molybdenum carbide, silicon carbide, Na2Ti3O7, and Na2Ti6O7. 13 Na4Ti5O 12 Li4Ti5O 12 One or more of NaTi2(PO4)3.

[0095] Optionally, the conductive agent may include one or more selected from graphite, carbon black, acetylene black, graphene, and carbon nanotubes. Optionally, the binder may include one or more selected from polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, and polyimide.

[0096] In some embodiments, the compaction density of the positive electrode sheet can be 1.5–4.0 g / cm³.3 The preferred concentration is 2.3–3.5 g / cm³. 3 Setting the compaction density of the electrode within a specified range can not only reduce the electrode thickness and increase the battery energy density, but also reduce the active lithium shuttle path and improve the charge / discharge rate and power. Optionally, the compaction density of the positive electrode can be 1.5–3.3 g / cm³. 3 1.5~3.5g / cm 3 1.5~4.0g / cm 3 2.2~3.3g / cm 3 2.2~3.5g / cm 3 3.0~4.0g / cm 3 3.0~3.3g / cm 3 Or 2.2~3.5g / cm 3 .

[0097] In some embodiments, the thickness of the current collector is 8–14 μm, preferably 10–13 μm. Setting the thickness of the current collector within a specified range can reduce the weight of the current collector and increase the energy density without hindering current flow due to an excessively thin current collector. Optionally, the thickness of the current collector can be 8–13 μm, 9–14 μm, 9–13 μm, or 10–14 μm. Optionally, the thickness of the positive electrode is 100–200 μm. As a non-limiting example, the thickness of the positive electrode can be 100–180 μm, 100–160 μm, 120–200 μm, 120–180 μm, or 120–160 μm. Optionally, the thickness of the resistive layer is 1–30 μm, preferably 10–13 μm. As a non-limiting example, the thickness of the resistive layer can be 1–25 μm, 1–20 μm, 4–30 μm, 4–25 μm, 4–20 μm, 7–30 μm, 7–25 μm, 7–20 μm, 10–30 μm, 10–25 μm, or 10–20 μm.

[0098] In some implementations, the D of the positive electrode active material v50 represents 1–20 μm. Setting the particle size of the positive electrode active material within a specified range can further ensure that the positive electrode retains an appropriate amount of active lithium. Specifically, when the particle size is large, the migration of lithium ions from the inside to the outside of the particle causes polarization. Therefore, a larger particle size can be used to increase polarization. At the beginning of charging, some lithium ions have an excessively long path to escape from the outside of the particle, resulting in some remaining inside the particle after charging. The remaining lithium ions are gradually released as the migration path shortens due to particle breakage during cycling, thereby further slowing down the battery capacity decay and further increasing the battery's cycle life. When the particle size becomes too large, the increased polarization caused by the increased particle size may not be able to offset the adverse effects of the accompanying reduced particle dispersion on battery performance. Therefore, in a preferred embodiment, the D of the positive electrode active material... v The diameter (D) of the positive electrode active material can be 3–15 μm. Optionally, the D of the positive electrode active material... v 50 can be 1~18μm, 1~15μm, 2~20μm, 2~18μm, 2~15μm, 3~20μm or 3~18μm.

[0099] In the positive electrode, the current collector has two opposing surfaces along its own thickness direction. In some embodiments, the coating area of ​​the current collector can be disposed on either or both of the opposing surfaces of the positive electrode current collector.

[0100] The positive electrode current collector may include a metal foil or a composite current collector. As a non-limiting example, the metal foil may include aluminum foil. In some embodiments, the composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. As a non-limiting example, the composite current collector can be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0101] In the preparation of the positive electrode sheet of this application, the resistive layer of this application can be formed first on the current collector, and then the positive active material layer can be formed on the current collector on which the resistive layer is formed.

[0102] As an example, a method for forming the resistive layer of this application on a current collector may include the following steps: mixing a conductive agent and a binder in a certain mass ratio, adding them to, for example, N-methylpyrrolidone (NMP), and stirring uniformly under the action of a vacuum mixer to obtain a resistive layer slurry with a certain solid content. The resistive layer slurry is then uniformly coated onto the target area of ​​the current collector using a conventional coating method (e.g., using an extrusion coater or a transfer coater), and dried at an appropriate temperature (e.g., 85°C) to form the resistive layer of this application on the current collector.

[0103] As an example, a method for forming a positive electrode active material layer on a current collector having a resistive layer may include the following steps: mixing a positive electrode active material, a conductive agent, and a binder in a certain mass ratio, adding them to, for example, N-methylpyrrolidone (NMP), and stirring uniformly under vacuum to obtain a slurry for the positive electrode active material layer having a certain solid content (e.g., 60% by weight). The slurry for the positive electrode active material layer is then uniformly coated onto a target area of ​​the current collector having the resistive layer using a conventional coating method (e.g., using an extrusion coater or a transfer coater), and dried at an appropriate temperature (e.g., 85°C), thereby forming a positive electrode active material layer on the current collector having the resistive layer.

[0104] On the other hand, this application also provides a secondary battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator, wherein the positive electrode includes the positive electrode sheet for secondary electrodes of this application as described above.

[0105] This application also provides a battery module that includes the secondary battery of this application as described above.

[0106] This application also provides a battery pack that includes the battery module of this application as described above.

[0107] This application also provides an electrical device, which includes the secondary battery of this application as described above, or the battery module of this application as described above, or the battery pack of this application as described above, or a combination thereof.

[0108] In the secondary battery of this application, by applying the positive electrode sheet with a resistive layer as described in this application, the rate of active lithium ion release in a certain region of the positive electrode sheet is slowed down, thereby retaining some lithium in that region (because during charging, compared with conventional positive electrode active material layers, the rate of active lithium ion release in this region is slower, thus retaining some lithium at the end of charging). During subsequent battery cycles, as the battery gradually ages, the lithium ions retained in the aforementioned positive electrode sheet region are gradually released, and the battery capacity shows a trend of first increasing and then gradually decreasing, thereby slowing down the capacity decay of the battery and increasing its lifespan.

[0109] The secondary battery, battery module, battery pack, and device of this application will be described below with appropriate reference to the accompanying drawings.

[0110] In one embodiment of this application, a secondary battery is provided.

[0111] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0112] [Negative electrode plate]

[0113] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on at least one surface of the negative current collector, wherein the negative active material layer includes a negative active material.

[0114] In the secondary battery of this application, the negative electrode active material can be any negative electrode active material commonly used in the art for preparing the negative electrode of a secondary battery. Examples of negative electrode active materials include artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate. Silicon-based materials can be selected from one or more of elemental silicon, silicon oxide compounds (e.g., silicon suboxide), silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials can be selected from one or more of elemental tin, tin oxide compounds, and tin alloys.

[0115] The negative electrode current collector has two surfaces opposite each other in its own thickness direction. As an example, the negative electrode active material layer can be disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0116] In the secondary battery of this application, the negative electrode current collector may include a metal foil or a composite current collector. As a non-limiting example, the metal foil may include copper foil. In some embodiments, the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. As a non-limiting example, the composite current collector may be formed by forming 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 (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0117] In the secondary battery of this application, the negative electrode active material layer typically includes a negative electrode active material, an optional binder, an optional conductive agent, and other optional additives, and is usually formed by coating the negative electrode active material layer with a slurry and drying it. The slurry for the negative electrode active material layer is typically formed by dispersing the negative electrode active material, optional conductive agent, and binder in a solvent and stirring until homogeneous. The solvent can be N-methylpyrrolidone (NMP) or deionized water.

[0118] As an example, the conductive agent may be selected from one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0119] As an example, the adhesive may be selected from one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS).

[0120] Other optional additives include thickeners (such as sodium carboxymethyl cellulose (CMC-Na)).

[0121] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0122] [Electrolytes]

[0123] This application does not impose specific limitations on the type of electrolyte; it can be selected according to requirements. For example, the electrolyte can be solid or liquid.

[0124] In some implementations, the electrolyte is liquid and typically comprises an electrolyte salt and a solvent.

[0125] As an example, the electrolyte salt may be selected from 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 difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0126] As an example, the solvent may be selected from one or more of the following: fluoroethylene carbonate (FEC), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butyl carbonate (BC), 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), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0127] In some embodiments, the electrolyte may optionally include additives. For example, the electrolyte may include negative electrode film-forming additives, positive electrode film-forming additives, additives to improve battery overcharge performance, additives to improve battery high-temperature performance, additives to improve battery low-temperature performance, etc.

[0128] [Septum]

[0129] The separator separates the positive and negative electrodes, preventing short circuits inside the battery, while allowing active ions to move between the positive and negative electrodes. In the secondary battery of this application, there are no particular restrictions on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0130] In some embodiments, the diaphragm material may be selected from one or more of the following: glass fiber film, nonwoven fabric film, polyethylene (PE) film, polypropylene (PP) film, polyvinylidene fluoride film, and multilayer composite films comprising one or more of these. The diaphragm may be a single-layer diaphragm or a multilayer composite diaphragm, without particular limitation. When the diaphragm is a multilayer composite diaphragm, the materials of each layer may be the same or different, without particular limitation.

[0131] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0132] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte as described above.

[0133] In some implementations, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene (PP), polybutylene terephthalate (PBT), and polybutylene succinate (PBS).

[0134] This application does not impose any particular limitation on the shape of the secondary battery; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 6 This is an example of a square-structured secondary battery 5.

[0135] In some implementations, refer to Figure 7 The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. Electrolyte is immersed in the electrode assembly 52. ​​The secondary battery 5 may contain one or more electrode assemblies 52, which can be selected by those skilled in the art according to specific practical needs.

[0136] In some implementations, the secondary batteries can be assembled into a battery module, and the number of secondary batteries contained in the battery module can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery module.

[0137] Figure 8 This is battery module 4, used as an example. (See reference...) Figure 8 In battery module 4, multiple secondary batteries 5 can be arranged sequentially along the length of battery module 4. Alternatively, the secondary batteries 5 can be arranged in any other manner. Furthermore, the multiple secondary batteries 5 can be secured with fasteners.

[0138] Optionally, the battery module 4 may also include a housing with a receiving space in which a plurality of secondary batteries 5 are received.

[0139] In some embodiments, the battery modules can also be assembled into a battery pack. The number of battery modules included in the battery pack can be selected by those skilled in the art based on the application of the battery pack.

[0140] Figure 9 and Figure 10 This is battery pack 1 as an example. (See reference...) Figure 9 and Figure 10 The battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper body 2 and a lower body 3, with the upper body 2 covering the lower body 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0141] In addition, this application also provides an electrical device, which includes one or more of the secondary battery, battery module, or battery pack provided in this application. The secondary battery, battery module, or battery pack can be used as the power source of the electrical device or as the energy storage unit of the electrical device. The electrical device can be, but is not limited to, mobile devices (such as mobile phones, laptops, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0142] As an electrical device, a secondary battery, battery module, or battery pack can be selected according to its usage requirements.

[0143] Figure 11 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the secondary battery for this electrical device, a battery pack or battery module can be used.

[0144] Another example of an electrical device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use rechargeable batteries as their power source.

[0145] The foregoing description of this invention is not intended to describe every disclosed embodiment or implementation. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. In each example, the examples are listed only as representative groups and should not be construed as exhaustive.

[0146] Example

[0147] In the following examples, unless specific conditions are specified, the steps described are performed under standard conditions or conditions recommended by the manufacturer. Reagents or instruments used, unless otherwise specified, are commercially available products. A general method for battery preparation (hereinafter referred to as the general method) is described below.

[0148] Preparation of positive electrode sheet

[0149] (1) Preparation of resistive layer paste

[0150] The conductive agent Super P and the binder polyvinylidene fluoride (PVDF) are mixed at a certain mass ratio. The resulting mixture is added to the solvent N-methylpyrrolidone (NMP) and stirred evenly in a lithium-ion battery slurry mixer (Shanghai Baomian Electromechanical Equipment Co., Ltd., model BMXJ5-2000L) to obtain a slurry for the resistive layer.

[0151] (2) Preparation of slurry for positive electrode active material layer

[0152] LiNi, the positive electrode active material 0.55 Co 0.05 Mn 0.4 O2, conductive agent Super P, and binder polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 96:2.5:1.5 and added to the solvent N-methylpyrrolidone (NMP). The mixture was stirred evenly under vacuum to obtain a slurry for the positive electrode active material layer. The solid content of the slurry was 60% by weight.

[0153] (3) Preparation of positive electrode sheet

[0154] The resistive layer slurry prepared as described above was uniformly coated onto the target area of ​​the current collector using an extrusion coating machine. Specifically, a lithium battery slot extrusion coating machine (Guangdong Hongbao Technology Co., Ltd., HB-TBY750) was used to uniformly coat the positive electrode active material layer slurry prepared as described above onto an aluminum foil with a thickness of 8–14 μm at a coating speed of 36 m / min, with a coating weight of 0.9 mg / cm³. 2 The length of the slurry nozzle of the extrusion coating machine is controlled by controlling the coating pad with a specific width opening, thereby obtaining a base coating layer with a controlled width arranged along the longitudinal length of the aluminum foil. Alternatively, the pressure switch of the nozzle extrusion can be controlled intermittently to obtain a base coating layer with a controlled width arranged in a direction perpendicular to the longitudinal length of the aluminum foil. The obtained positive electrode current collector aluminum foil with the base coating layer is dried at 85°C to form a resistive layer with a thickness of 1–30 μm on the positive electrode current collector aluminum foil.

[0155] Next, the positive electrode active material layer slurry prepared as described above is uniformly coated onto the target area of ​​the positive electrode current collector aluminum foil on which the resistive layer is formed. The coating of the positive electrode active material layer slurry can be performed by the same method as the coating method for the resistive layer slurry described above. Alternatively, a transfer coating machine can be used for coating. Specifically, using a transfer coating machine (Yakang Precision Machinery Co., Ltd., DT600 / 750), the positive electrode active material layer slurry is uniformly coated onto the target area of ​​the current collector on which the resistive layer of this application is formed using conventional processes in the art, and then dried at 85°C, thereby forming a positive electrode active material layer on the current collector aluminum foil on which the resistive layer is formed.

[0156] Then, the obtained laminate is cold-pressed, trimmed, cut, and slit using conventional processes to obtain a positive electrode sheet with a thickness of 100–200 μm.

[0157] Measurement of Dv50 of positive electrode active material

[0158] In this application, the Dv50 value of the positive electrode active material refers to the median particle size of the positive electrode active material. Specifically, a particular Dv50 value indicates that 50% of the particles by volume have a diameter greater than that value, and another 50% of the particles by volume have a diameter smaller than that value.

[0159] The Dv50 value of the positive electrode active material can be measured according to the method specified in GB / T19077-2016. More specifically, the Dv50 value can be measured according to the following method.

[0160] Sample pretreatment: Take a clean beaker, add an appropriate amount of the sample to be tested, add sodium dodecyl sulfate as a surfactant, then add deionized water as a dispersant, and sonicate (120W / 5min) to ensure that the sample is completely dispersed in the dispersant.

[0161] Test: The Dv50 was measured using an LS-909 laser particle size analyzer (Omec). After the sample was poured into the injection tower, it circulated with the solution to the test optical path system. The scattered light emitted by the particles under the irradiation of the laser beam was received and its energy distribution was measured to obtain the particle size distribution characteristics (shading degree: 8-12%), and finally the Dv50 value of the material was obtained.

[0162] Measurement of film resistance of positive electrode

[0163] The film resistance values ​​of the positive electrode sheet in the portion with the resistive layer and the portion of the positive electrode sheet in the coated area without the resistive layer were measured using a conventional electrode resistance meter (Yuaneng Technology, IEST BER1000 model). Specifically, a 10cm × 10cm square test sample was cut from the portion of the positive electrode sheet to be measured. At the measurement location, the test sample was clamped between the two conductive terminals of the resistance meter on both the top and bottom sides, and a certain pressure was applied to fix it in place. The resistance R of the test sample was then measured. The diameter of the conductive terminals of the resistance meter was 14mm, the pressure applied during the measurement was 5MPa to 27MPa, and the sampling time ranged from 5s to 17s. R is the resistance value of the sample read by the resistance meter. The film resistance value measured in the portion with the resistive layer was recorded as R1. The film resistance value measured in the portion of the coated area without the resistive layer was recorded as R2.

[0164] Battery manufacturing

[0165] (1) Preparation of negative electrode sheet

[0166] Artificial graphite (anode active material), Super P (conductive agent), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber latex (SBR) (binder) were mixed in a mass ratio of 97:0.7:1.8:0.5 and added to deionized water as a solvent. The mixture was stirred evenly under vacuum to obtain anode slurry. The solid content of the anode slurry was 56% by weight.

[0167] Using conventional processes, the negative electrode slurry is uniformly coated onto the negative electrode current collector copper foil using an extrusion coating machine or a transfer coating machine, and then dried at 85°C. After cold pressing, edge trimming, cutting, and slitting, the negative electrode sheet is obtained.

[0168] (2) Preparation of electrolyte

[0169] In an argon-atmospheric glove box with a water content of <10 ppm, thoroughly dried lithium salt (LiPF6) was dissolved in a mixed solvent of ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) in a volume ratio of 20:20:60. Then, vinylene carbonate (VC) was added as an additive, and the mixture was thoroughly mixed to obtain the electrolyte. The concentration of lithium salt was 1 mol / L.

[0170] (3) Preparation of the diaphragm

[0171] Using a 7 μm thick polyethylene (PE) membrane as the base membrane for the separator, alumina, sodium carboxymethyl cellulose (CMC), and acrylate in a weight ratio of 93%:3%:4% were added to deionized water and stirred evenly under vacuum to obtain a slurry. The solid content of the slurry was 55% by weight. The obtained slurry was then uniformly sprayed onto both sides of the base membrane to a thickness of 2 μm on each side to obtain the separator.

[0172] (4) Assembly of lithium-ion batteries

[0173] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes for isolation. The resulting laminate is then wound into a square bare cell, tabs are welded on, and the bare cell is installed in a square aluminum casing. The top cover is laser-welded. After vacuum baking at 80°C to remove water, electrolyte is injected and the casing is sealed. Following this, the battery undergoes a series of processes including standing at 45°C, formation (0.02C constant current charging to 3.3V, then 0.1C constant current charging to 3.6V), shaping, and capacity testing to obtain the finished hard-shell lithium-ion battery, with a thickness of 28mm, a width of 97.5mm, and a length of 148mm.

[0174] Battery performance measurement

[0175] (1) Measurement of the number of cycles

[0176] The cycle performance of the battery including the positive electrode of this application was evaluated at 25°C under 0.5C / 0.5C conditions. Specifically, the cell was placed in the Nebula Battery Charge-Discharge Test System (model BAT-NEEFLCT-05300-V012), charged at a constant current and constant voltage rate of 0.5C to the charging cutoff voltage of 4.4V, allowed to stand for 5 minutes, and then discharged at a constant current rate of 0.5C to the discharge cutoff voltage of 2.5V. The discharge capacity was recorded, and the cell was allowed to stand for another 5 minutes. This cycle was repeated. The number of cycles in which the discharge capacity remained above 80% of the initial capacity was recorded.

[0177] (2) Measurement of 60s pulse discharge power

[0178] The power performance of a battery can be determined by measuring its 60-second pulse discharge power. Specifically, the battery cell is placed in a Nebula battery charge-discharge test system at 25°C and charged at a constant current and constant voltage rate of 0.5C to the charging cutoff voltage of 4.4V. After resting for 5 minutes, it is discharged at a specific power, ensuring that the battery voltage reaches exactly 2.5V and stops discharging at 60 seconds. The power at this point is the 60-second pulse discharge power.

[0179] Examples 1-6 and Control Examples

[0180] The positive electrode and battery were prepared according to the general method described above. In Examples 1-6, the thickness of the aluminum foil used as the current collector was 12 μm. The thickness of the resistive layer disposed on the current collector was 10 μm. The Dv50 of the positive electrode active material in the positive electrode active material layer was 4 μm. The thickness of the positive electrode sheet was 120 μm, and the compaction density was 3.4 g / cm³. 3 .

[0181] Furthermore, the projection of a portion of the positive electrode active material layer onto the current collector overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion does not overlap with the projection of the resistive layer onto the current collector, such as... Figure 4 As shown.

[0182] The composition of the resistive layer in the positive electrode, the area ratio S of the resistive layer relative to the coating area of ​​the current collector, the film resistance value R1 of the part with the resistive layer, the film resistance value R2 of the part without the resistive layer, the corresponding R1 / R2 value, the polarization parameter P value, and the number of battery cycles and 60s pulse discharge power measured by the performance test method described above are all shown in Table 1 below.

[0183] In the comparative example, the resistive layer of the present invention was not disposed on the current collector. Therefore, the positive electrode only includes the current collector and the positive electrode active material layer. The performance test results of the comparative example are also shown in Table 1 below.

[0184] Table 1

[0185]

[0186] As can be seen from the results shown in Table 1, compared with the control example without a resistive layer, by setting a resistive layer on the current collector, and with part of the projection of the positive electrode active material layer on the current collector overlapping with the projection of the resistive layer on the current collector, while the projection of another part on the current collector does not overlap with the projection of the resistive layer on the current collector, the cycle performance of the secondary batteries in Examples 1 to 6 is significantly improved. The number of cycles in which the discharge capacity remains above 80% of the initial capacity is significantly increased from 835 to over 1500, greatly extending the battery's lifespan. At the same time, it can ensure that the battery maintains good power performance, with the 60s pulse discharge power of the battery remaining above 1050W.

[0187] In Examples 1-6, by applying a higher mass content of binder, a higher resistance value can be achieved in the resistive layer. This results in the film resistance (R1) of the positive electrode sheet where the resistive layer is provided being greater than the film resistance (R2 = 0.35 Ω) of the portion without the resistive layer, thus generating appropriate lithium-ion polarization in the positive electrode sheet. Consequently, the rate of active lithium-ion extraction is slowed in the portion of the positive electrode sheet where the resistive layer is provided, thereby retaining some lithium in this portion. During subsequent battery cycles, as the battery gradually ages, the active lithium retained in this region is gradually released, and the battery capacity initially increases and then gradually decreases, thereby slowing down the capacity decay and increasing the battery's lifespan.

[0188] In addition, by adjusting the composition of the resistive layer, specifically by adjusting the mass content of the binder in the resistive layer to adjust the resistance value of the resistive layer, the amount of lithium retained in the positive electrode active material layer above the resistive layer can be adjusted, thereby adjusting the amount of active lithium retained in the positive electrode sheet, and the battery life can be adjusted as needed.

[0189] Furthermore, compared to Example 6, in Examples 1 to 5, by adjusting the composition of the resistive layer, the polarization parameter P of the positive electrode sheet is adjusted to a preferred range of 0.5 to 70.0, which can achieve additional technical effects of fully maintaining the battery power performance while further increasing the battery life. The number of cycles in which the discharge capacity is maintained at more than 80% of the initial capacity is further increased to more than 1900 times, and the 60s pulse discharge power of the battery is maintained at more than 1100W.

[0190] Examples 7-21

[0191] The positive electrode and battery were prepared according to the general method described above. In Examples 7-21, based on the total weight of the resistive layer, the mass content of the conductive agent was 15%, and the mass content of the binder was 85%. The thickness of the aluminum foil used as the current collector was 12 μm. The thickness of the resistive layer disposed on the current collector was 10 μm. The Dv50 of the positive electrode active material in the positive electrode active material layer was 4 μm. The thickness of the positive electrode sheet was 120 μm, and the compaction density was 3.4 g / cm³. 3 .

[0192] In the positive electrode, the film resistance R1 of the portion with the resistive layer and the film resistance R2 of the portion without the resistive layer are 1.98Ω and 0.35Ω, respectively. Accordingly, R1 / R2 = 5.66.

[0193] Furthermore, the projection of a portion of the positive electrode active material layer onto the current collector overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion does not overlap with the projection of the resistive layer onto the current collector, such as... Figure 4 As shown.

[0194] The area ratio S of the resistive layer relative to the coating area of ​​the current collector, the corresponding polarization parameter P, and the number of battery cycles and 60s pulse discharge power measured by the performance testing method described above are all shown in Table 2 below.

[0195] Table 2

[0196] S P Number of cycles 60s pulse discharge power (W) Example 7 0.20 8.8 1851 1056.5 Example 8 0.25 6.6 1973 1126.1 Example 9 0.30 5.1 2115 1207.2 Example 10 0.35 4.1 2387 1362.4 Example 11 0.40 3.3 2500 1426.9 Example 12 0.45 2.7 2639 1506.3 Example 13 0.50 2.2 2552 1456.6 Example 14 0.55 1.8 2364 1349.3 Example 15 0.60 1.5 2226 1270.6 Example 16 0.65 1.2 2189 1249.4 Example 17 0.70 0.9 2109 1203.8 Example 18 0.75 0.7 2078 1186.1 Example 19 0.80 0.6 2050 1170.1 Example 20 0.05 41.8 1569 1224.0 Example 21 0.90 0.2 1722 982.9

[0197] As an example, the cycle curve of the battery in Example 19 is as follows: Figure 12 As shown. From Figure 12 It can be clearly seen that during the cycling process, as the battery polarization gradually ages and is eliminated, the battery capacity shows a trend of first increasing and then gradually decreasing, thereby slowing down the battery capacity decay and increasing the battery's cycle life. The number of cycles in which the discharge capacity is maintained at more than 80% of the initial capacity reaches 2050.

[0198] As can be seen from the results shown in Table 2, compared with the control example without a resistive layer, by setting a resistive layer on the current collector, the projection of part of the positive electrode active material layer on the current collector overlaps with the projection of the resistive layer on the current collector, while the projection of another part on the current collector does not overlap with the projection of the resistive layer on the current collector. The cycle performance of the secondary batteries in Examples 7 to 21 is significantly improved. The number of cycles in which the discharge capacity is maintained at more than 80% of the initial capacity is significantly increased from 835 cycles to more than 1500 cycles, which greatly extends the battery life. At the same time, it can ensure that the battery maintains good power performance, and the 60s pulse discharge power of the battery is maintained at more than 950W.

[0199] In Examples 7-21, the film resistance (R1) of the positive electrode portion with the resistive layer is greater than that of the portion without the resistive layer (R2 = 0.35 Ω), resulting in appropriate lithium-ion polarization in the positive electrode. Therefore, the rate of active lithium-ion release is slowed in the portion of the positive electrode with the resistive layer, thus retaining some lithium in that area. During subsequent battery cycles, as the battery ages, the active lithium retained in this region is gradually released, causing the battery capacity to initially increase and then gradually decrease, thereby slowing down capacity decay and increasing battery life.

[0200] In addition, by adjusting the area ratio S of the resistive layer relative to the coating area of ​​the current collector, the amount of lithium retained in the positive electrode active material layer above the resistive layer can be adjusted, thereby adjusting the amount of active lithium retained in the positive electrode sheet, and the battery life can be adjusted as needed.

[0201] Moreover, compared with Examples 20 and 21, in Examples 7 to 19, by adjusting the area ratio S of the resistive layer relative to the coating area of ​​the current collector, the polarization parameter P of the positive electrode can be adjusted to a preferred range of 0.5 to 70.0, thereby achieving additional technical effects of maintaining battery power performance while further increasing battery life. The number of cycles in which the discharge capacity is maintained at more than 80% of the initial capacity is further increased to more than 1800, and the 60s pulse discharge power of the battery is maintained at more than 1000W.

[0202] In summary, by setting a resistive layer on the current collector, appropriate lithium-ion polarization can be generated in the positive electrode. Compared with the control example without a resistive layer on the current collector, the battery cycle performance of Examples 1-21 is significantly improved, with the discharge capacity maintained at more than 80% of the initial capacity for more than 1500 cycles, greatly extending the battery life. Simultaneously, it also ensures that the battery maintains good power performance, with the 60s pulse discharge power remaining above 950W.

[0203] Example 22

[0204] The positive electrode and battery were prepared according to the general method described above. In Example 22, the composition of the resistive layer was the same as in Example 3. Furthermore, the area ratio S of the resistive layer relative to the coating area of ​​the current collector was 0.70. The thickness of the aluminum foil serving as the current collector was 12 μm. The thickness of the resistive layer disposed on the current collector was 10 μm. The Dv50 of the positive electrode active material in the positive electrode active material layer was 4 μm. The thickness of the positive electrode sheet was 120 μm, and the compaction density was 3.4 g / cm³. 3 .

[0205] Furthermore, the projection of a portion of the positive electrode active material layer onto the current collector overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion does not overlap with the projection of the resistive layer onto the current collector; and a conductive agent layer is also disposed on the current collector, the projection of which does not overlap with the projection of the resistive layer onto the current collector, such as... Figure 5 As shown.

[0206] In this embodiment, the film resistance R3 of the positive electrode sheet where the conductive agent layer is disposed is 0.25Ω. The film resistance R1 of the positive electrode sheet where the resistive layer is disposed and the film resistance R2 of the portion where the resistive layer is not disposed are 2.12Ω and 0.35Ω, respectively. The polarization parameter P is 8.48.

[0207] As measured by the performance testing methods described above, in Example 22, the additional conductive agent layer compensated for the power reduction caused by the resistive layer, resulting in significantly improved cycle performance and excellent power performance. Compared to Examples 1-21 without a conductive agent layer, the battery prepared in Example 22 exhibits superior cycle and power performance, with the number of cycles maintaining over 80% of the initial capacity further increased to 2680, and the 60s pulse discharge power reaching 1529.7W, comparable to the control example without a resistive layer.

[0208] Examples 23-26

[0209] The positive electrode and battery were prepared using essentially the same method as in Example 7, except that the positive electrode was prepared with a different compaction density, resulting in different electrode thicknesses, as shown in Table 3. The battery performance measurement results are also shown in Table 3.

[0210] Table 3

[0211]

[0212] As shown in Table 3, compared with Example 23, when the compaction density is between 2.0 and 4.0 g / cm³... 3 When within the preferred range, the following additional effects can also be achieved: the electrode thickness is reduced, the battery energy density is increased, and the active lithium shuttle path is reduced, thereby improving the battery power performance while improving the battery cycle life, maintaining the discharge capacity at more than 80% of the initial capacity for more than 1850 cycles, and maintaining the 60s pulse discharge power at more than 1050W.

[0213] Examples 27-37

[0214] The positive electrode and battery were prepared according to the general method described above. In the resistive layer, based on the total weight of the resistive layer, the mass content of the conductive agent was 2%, and the mass content of the binder was 98%. The thickness of the aluminum foil serving as the current collector was 12 μm. The thickness of the resistive layer disposed on the current collector was 10 μm. The thickness of the positive electrode was 120 μm, and the compaction density was 3.4 g / cm³. 3 .

[0215] In Examples 27-37, the film resistance values ​​R1 of the portion with the resistive layer and R2 of the portion without the resistive layer are 5.81Ω and 0.35Ω, respectively. Furthermore, the area ratio of the resistive layer to the current collector coating area is 0.55. Correspondingly, the polarization parameter P is 13.6.

[0216] Furthermore, the projection of a portion of the positive electrode active material layer onto the current collector overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion does not overlap with the projection of the resistive layer onto the current collector, such as... Figure 4 As shown.

[0217] The Dv50 of the positive electrode active material in the positive electrode active material layer and the performance measurement results of the battery are shown in Table 4.

[0218] Table 4

[0219]

[0220] As shown in Table 4, the results demonstrate that by increasing the particle size of the positive electrode active material in the present application, polarization can be generated within the particles of the positive electrode active material, further enhancing the polarization capability of the positive electrode and thereby improving the battery cycle performance. Compared to Examples 33-37, in Examples 27-32, the Dv50 of the positive electrode active material is within the preferred range of 3-15 μm, and the particles are more fully dispersed. As the particle size of the positive electrode active material increases, both the cycle life and power performance of the battery show an increasing trend.

[0221] In summary, by adjusting the composition of the resistive layer on the current collector of the positive electrode sheet, the film resistance of the portion of the positive electrode sheet with the resistive layer is adjusted. This ensures that, on the cross-section of the positive electrode sheet, the projection of a portion of the positive active material layer onto the current collector overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion does not overlap. This imparts a certain polarization capability to the positive electrode sheet, thereby reducing battery capacity decay and maintaining the discharge capacity at more than 80% of the initial capacity for more than 1500 cycles, greatly extending the battery's lifespan. At the same time, it ensures good power performance, with the battery's 60s pulse discharge power remaining above 950W.

[0222] Industrial application

[0223] The positive electrode with a resistive layer on the current collector, as described in this application, increases lithium-ion polarization when applied to secondary batteries. During cycling, as the battery polarization gradually ages and diminishes, the battery capacity initially increases and then gradually decreases, thus increasing the battery's cycle life while ensuring power performance. Therefore, this application is suitable for industrial applications.

Claims

1. A positive electrode sheet for a secondary battery, comprising: The current collector, resistive layer, and positive electrode active material layer, among which, The current collector includes a coated area and an uncoated area outside the coated area. The resistive layer includes a conductive agent and a binder, but does not include a positive electrode active material. The positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder. The resistance of the resistive layer is greater than the resistance of the positive electrode active material layer, and the resistive layer is disposed on the current collector. In the cross-section of the positive electrode sheet, the projection of a portion of the positive electrode active material layer onto the current collector overlaps with the projection of the resistive layer onto the current collector, while the projection of another portion onto the current collector does not overlap with the projection of the resistive layer onto the current collector. A conductive agent layer is also disposed on the current collector. The projections of the conductive agent layer and the resistive layer on the current collector completely cover the projection of the positive electrode active material layer on the current collector. R3 / R1 is in the range of 0.10~0.95, where R1 is the film resistance value of the portion of the positive electrode sheet where the resistive layer is disposed, and R3 is the film resistance value of the portion of the positive electrode sheet where the conductive agent layer is disposed.

2. The positive electrode sheet for a secondary battery according to claim 1, wherein, The polarization parameter P of the positive electrode is in the range of 0.5 to 70.

0. The polarization parameter P = ((1-S) / S)•(R1 / R2), where S is the area ratio of the resistive layer to the coating area of ​​the current collector, R1 is the film resistance value of the portion of the positive electrode where the resistive layer is provided, and R2 is the film resistance value of the portion of the positive electrode in the coating area where the resistive layer is not provided.

3. The positive electrode sheet for a secondary battery according to claim 2, wherein, The polarization parameter P of the positive electrode is in the range of 0.5 to 36.

0.

4. The positive electrode sheet for a secondary battery according to claim 3, wherein, The polarization parameter P of the positive electrode is in the range of 0.5 to 10.

0.

5. The positive electrode sheet for a secondary battery according to claim 1, wherein, The area ratio of the resistive layer to the coated area of ​​the current collector is in the range of 0.20 to 0.

80.

6. The positive electrode sheet for a secondary battery according to claim 5, wherein, The area ratio of the resistive layer to the coated area of ​​the current collector is in the range of 0.40 to 0.

60.

7. The positive electrode sheet for a secondary battery according to claim 1, wherein, The projection of the positive electrode active material layer onto the current collector completely covers the projection of the resistive layer onto the current collector.

8. The positive electrode sheet for a secondary battery according to claim 1, wherein, The ratio of the mass of the binder to the mass of the conductive agent in the resistive layer is greater than the ratio of the mass of the binder to the mass of the conductive agent in the positive electrode active material layer.

9. The positive electrode sheet for a secondary battery according to claim 8, wherein, In the resistive layer, the ratio of the mass of the adhesive to the mass of the conductive agent is in the range of 2.2 to 50.

0.

10. The positive electrode sheet for a secondary battery according to claim 9, wherein, In the resistive layer, the ratio of the mass of the adhesive to the mass of the conductive agent is in the range of 4.0 to 20.

0.

11. The positive electrode sheet for a secondary battery according to claim 10, wherein, In the positive electrode active material layer, the ratio of the mass of the binder to the mass of the conductive agent is in the range of 1.6 to 10.

0.

12. The positive electrode sheet for a secondary battery according to claim 11, wherein, In the positive electrode active material layer, the ratio of the mass of the binder to the mass of the conductive agent is in the range of 2.0 to 3.

4.

13. The positive electrode sheet for a secondary battery according to claim 11, wherein, In the resistive layer, the mass content of the conductive agent is 2.0 to 30.0% by weight based on the total weight of the resistive layer; the mass content of the binder is 70.0 to 98.0% by weight based on the total weight of the resistive layer.

14. The positive electrode sheet for a secondary battery according to claim 1, wherein, The projection of the conductive agent layer onto the current collector does not overlap with the projection of the resistive layer onto the current collector, and the resistance of the conductive agent layer is less than the resistance of the positive electrode active material layer.

15. The positive electrode sheet for a secondary battery according to claim 14, wherein, R1 / R2 is in the range of 1.15 to 26.00, where R1 is the film resistance value of the positive electrode sheet in the portion where the resistive layer is provided, and R2 is the film resistance value of the positive electrode sheet in the coating area where the resistive layer is not provided.

16. The positive electrode sheet for a secondary battery according to claim 15, wherein, R1 is in the range of 0.3 to 9.0 Ω.

17. The positive electrode sheet for a secondary battery according to claim 16, wherein, R2 is in the range of 0.3~4.0 Ω.

18. The positive electrode sheet for a secondary battery according to any one of claims 1 to 17, wherein, The positive electrode active material includes one or more selected from lithium cobalt oxide, lithium manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, and lithium nickel manganese oxide; the conductive agent includes one or more selected from graphite, carbon black, acetylene black, graphene, and carbon nanotubes; the binder includes one or more selected from polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, and polyimide.

19. The positive electrode sheet for a secondary battery according to any one of claims 1 to 17, wherein, The positive electrode active material includes one or more selected from layered transition metal oxides, polyanionic compounds, Prussian blue compounds, sulfides, nitrides, carbides, and titanates; the conductive agent includes one or more selected from graphite, carbon black, acetylene black, graphene, and carbon nanotubes; and the binder includes one or more selected from polyvinylidene fluoride, polyacrylic acid, polytetrafluoroethylene, and polyimide.

20. The positive electrode sheet for a secondary battery according to any one of claims 1 to 17, wherein, The compaction density of the positive electrode sheet is 1.5~4.0 g / cm³. 3 .

21. The positive electrode sheet for a secondary battery according to claim 20, wherein, The compaction density of the positive electrode sheet is 2.3~3.5 g / cm³. 3 .

22. The positive electrode sheet for a secondary battery according to any one of claims 1 to 17, wherein, The thickness of the current collector is 8~14 μm; the thickness of the positive electrode is 100~200 μm; and / or the thickness of the resistive layer is 1~30 μm.

23. The positive electrode sheet for a secondary battery according to claim 22, wherein, The thickness of the current collector is 10~13 μm; the thickness of the positive electrode is 100~200 μm; and / or the thickness of the resistive layer is 10~13 μm.

24. The positive electrode sheet for a secondary battery according to any one of claims 1 to 17, wherein the D of the positive electrode active material... v 50 represents 1~20 μm.

25. The positive electrode sheet for a secondary battery according to claim 24, wherein the D of the positive electrode active material... v 50 is 3~15 μm.

26. A secondary battery comprising a positive electrode, said positive electrode comprising a positive electrode sheet for a secondary battery according to any one of claims 1 to 25.

27. A battery module comprising the secondary battery of claim 26.

28. A battery pack comprising the battery module of claim 27.

29. An electrical device comprising at least one of the secondary battery of claim 26, the battery module of claim 27, and the battery pack of claim 28.

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