Electrochemical and electronic devices

Abstract

The electrochemical device includes an electrode assembly, positive electrode tabs, and negative electrode tabs. In the electrode assembly, a separator is disposed between the positive and negative electrode pieces. The positive electrode tabs are connected to the positive electrode pieces, and the negative electrode tabs are connected to the negative electrode pieces. The positive electrode pieces include a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. The number of positive electrode tabs a and the number of layers b of the positive electrode pieces satisfy the relationship 0.25≦a / b≦1.25. The mole percentage X of nickel in the positive electrode active material satisfies the relationship X≧60%. The thickness h1 of the positive electrode active material layer satisfies the relationship 10 μm≦h1≦30 μm. Increasing the number of positive electrode tabs effectively reduces the current density per positive electrode tab. Reducing the thickness of the positive electrode active material layer shortens the lithium ion transport distance. Increasing the mole percentage of nickel in the positive electrode active material layer improves the energy density of the electrochemical device and effectively suppresses temperature rise during high-rate discharge of the electrochemical device.

Description

[Technical Field]

[0001] FIELD OF THE INVENTION Embodiments of the present invention relate to the field of electrochemical devices, and more particularly to electrochemical devices and electronic equipment. [Background technology]

[0002] With the development of electronic technology, electronic devices such as smart wearable devices, smartphones, computers, drones, and electric vehicles are increasingly being used in daily life. As important power storage devices, the power storage performance and safety performance of electrochemical devices must be strictly controlled.

[0003] Taking lithium-ion batteries as an example, conventional lithium-ion batteries are prone to a rapid temperature rise during high-rate discharge, which significantly affects the lifespan of the lithium-ion battery after multiple charge-discharge cycles. Therefore, how to suppress the temperature rise during high-rate discharge of lithium-ion batteries is an issue that needs to be resolved urgently. Summary of the Invention

[0004] The technical problem to be solved by the embodiments of the present invention is to provide an electrochemical device and an electronic device that can effectively solve the problem of the temperature of the electrochemical device rising too high during charging.

[0005] In order to solve the above technical problems, one technical solution adopted by embodiments of the present invention provides an electrochemical device including an electrode assembly, a positive electrode tab, and a negative electrode tab. The electrode assembly includes positive electrode pieces, a separator, and negative electrode pieces. The separator is disposed between the positive electrode pieces and the negative electrode pieces. The positive electrode pieces include a positive electrode current collector and a positive electrode active material layer. The positive electrode active material layer is disposed on at least one surface of the positive electrode current collector. The positive electrode active material layer includes a positive electrode active material. The positive electrode tab is connected to the positive electrode current collector. The negative electrode tab is connected to the negative electrode pieces. The number of positive electrode tabs a and the number of positive electrode piece layers b satisfy 0.25≦a / b≦1.25. The mole percentage X of nickel in the positive electrode active material satisfies X≧60%. The thickness h1 of the positive electrode active material layer satisfies 10 μm≦h1≦30 μm.

[0006] In some embodiments, the number a of positive electrode tabs and the number b of layers of positive electrode pieces satisfy 0.5≦a / b≦1. In some embodiments, the mole percentage X of nickel in the positive electrode active material satisfies 80%≦X≦95%. In some embodiments, the number a of positive electrode tabs satisfies 5≦a≦40. The number b of layers of positive electrode pieces satisfies 20≦b≦40. In some embodiments, the thickness h2 of the positive electrode current collector satisfies 7 μm≦h2≦15 μm. In some embodiments, the positive electrode active material layer contains carbon nanotubes that satisfy at least one of the following conditions: (1) the length of the carbon nanotubes is 0.1 μm to 6 μm; (2) the diameter of the carbon nanotubes is 10 nm to 20 nm; and (3) the Dv90 of the carbon nanotubes is 3 μm to 10 μm.

[0007] In some embodiments, the positive electrode active material has a Dv90 of 12 μm to 30 μm. In some embodiments, the positive electrode piece further includes a functional layer, the functional layer and the positive electrode active material layer being located on the same surface of the positive electrode current collector, the functional layer being provided on the side of the surface of the positive electrode current collector closer to the positive electrode tab, and the functional layer having a thickness of 10 μm to 25 μm. In some embodiments, the functional layer comprises inorganic particles and an adhesive.

[0008] To solve the above technical problems, another technical solution adopted by the embodiments of the present invention is to provide an electronic device including the above electrochemical device.

[0009] The electrochemical device according to an embodiment of the present invention includes an electrode assembly, a positive electrode tab, and a negative electrode tab, wherein the electrode assembly includes a separator disposed between the positive electrode piece and the negative electrode piece, the positive electrode tab connected to the positive electrode piece, and the negative electrode tab connected to the negative electrode piece, and the positive electrode piece includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector. When the mole percentage of nickel in the positive electrode active material is high, the temperature rise during high-rate discharge of the lithium-ion battery can be effectively suppressed by rationally optimizing the relationship between the number of layers of the positive electrode piece, the number of tabs, and the thickness of the positive electrode active material layer. The positive electrode active material comprises a nickel-containing material, the mole percentage X of nickel in the positive electrode active material satisfies X≧60%, the number a of positive electrode tabs and the number b of positive electrode piece layers satisfy 0.25≦a / b≦1.25, and the thickness h1 of the positive electrode active material layer satisfies 10μm≦h1≦30μm, thereby effectively suppressing the temperature rise during high-rate discharge of the electrochemical device and improving the safety and stability of the electrochemical device. [Brief explanation of the drawings]

[0010] In order to more clearly describe specific embodiments of the present invention or technical solutions in the prior art, the drawings necessary for describing the specific embodiments or prior art will be briefly described below. Throughout the drawings, similar elements or parts are generally designated by similar reference numerals. In the drawings, each element or part is not necessarily drawn to scale. [Figure 1] FIG. 1 is a schematic diagram of an electrochemical device according to an embodiment of the present invention. [Figure 2] FIG. 2 is a schematic cross-sectional view taken along the line AA in FIG. [Figure 3] FIG. 3 is a schematic diagram of a positive electrode piece in an electrochemical device according to an embodiment of the present invention. [Figure 4] FIG. 4 is a schematic cross-sectional view taken along line BB in FIG. DETAILED DESCRIPTION OF THE INVENTION

[0011] To facilitate understanding of the present invention, the present invention will be described in more detail below with reference to the accompanying drawings and specific embodiments. When an element is described as being "fixed" to another element, it may be directly connected to the other element, or there may be one or more intermediate elements between them. When an element is described as being "connected" to another element, it may be directly connected to the other element, or there may be one or more intermediate elements between them. As used herein, orientations or positional relationships indicated by terms such as "upper," "lower," "inner," "outer," "vertical," and "horizontal" are based on the orientations or positional relationships shown in the drawings and are intended solely to facilitate and simplify the description of the present invention. They do not imply or indicate that the associated devices or elements must have a particular orientation, be configured, or operate in a particular orientation, and should not be construed as limiting the present invention. Furthermore, terms such as "first," "second," and the like are used for descriptive purposes only and do not imply or indicate relative importance.

[0012] Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention pertains. Terms used in the present specification are intended to describe specific embodiments only and are not intended to limit the present invention. The term "and / or" used herein includes any and all combinations of one or more of the associated listed items. In addition, the technical features of different embodiments of the present invention described below can be combined with each other unless they are mutually inconsistent.

[0013] Referring to FIG. 1, the electrochemical device 100 includes an electrode assembly 10, a positive electrode tab 20, a negative electrode tab 30, and a case 40. A receiving cavity is provided in the case 40. The electrode assembly 10 is provided in the receiving cavity. One end of the positive electrode tab 20 and one end of the negative electrode tab 30 are electrically connected to the electrode assembly 10. The other end of the positive electrode tab 20 and the other end of the negative electrode tab 30 both extend outward from the receiving cavity. Of course, the receiving cavity also contains an electrolyte for the electrode assembly 10 to generate an electrochemical reaction.

[0014] Referring to FIG. 2 , the electrode assembly 10 includes a positive electrode piece 11, a separator 12, and a negative electrode piece 13. The positive electrode piece 11, the separator 12, and the negative electrode piece 13 are stacked to form the stacked electrode assembly 10. Here, the positive electrode piece 11 and the negative electrode piece 13 are separated by the separator 12. One end of the positive electrode tab 20 is electrically connected to the positive electrode piece 11, and one end of the negative electrode tab 30 is connected to the negative electrode piece 13. Of course, in other embodiments, the positive electrode piece 11, the separator 12, and the negative electrode piece 13 may be stacked and then wound to form the wound electrode assembly 10. The present invention does not limit the formation method of the electrode assembly 10. When the electrode assembly 10 has a stacked structure, the number of layers of positive electrode pieces is the same as the number of positive electrode pieces, i.e., the number of layers of positive electrode pieces is the same as the number of positive electrode pieces in the electrode assembly 10. When the electrode assembly 10 has a wound structure, the positive electrode piece is unfolded along the winding direction of the electrode assembly 10, and the number of layers on the positive electrode piece side is determined based on the number of times the positive electrode piece is bent.

[0015] The number a of positive electrode tabs 20 satisfies 2≦a≦40, the number b of positive electrode pieces 11 satisfies 20≦b≦40, and the ratio of the number a of positive electrode tabs 20 to the number b of positive electrode pieces 11 satisfies 0.25≦a / b≦1.25. To ensure sufficient capacity for the electrochemical device 100, the number b of positive electrode pieces 11 in the electrode assembly 10 is typically 20 to 40, and the number a of positive electrode tabs 20 is at least two. To reduce the current load on the positive electrode pieces 11, the number a of positive electrode tabs 20 may be a multiple number, such as 5, 10, or 15, with the ratio of the number of positive electrode tabs 20 to the number of positive electrode pieces 11 being 0.25 or greater, i.e., one-fourth. The use of a structure with multiple positive electrode tabs 20 reduces the density of the current output from each positive electrode tab 20, reduces the resistance of the electrode assembly, reduces heat generation, and suppresses the temperature rise in the electrochemical device 100 due to current flow. In another embodiment, the number a of the positive electrode tabs 20 and the number b of the positive electrode pieces 11 satisfy 0.5≦a / b≦1.

[0016] 3 and 4, the positive electrode piece 11 includes a positive electrode current collector 111 and a positive electrode active material layer 112. The positive electrode active material layer 112 is provided on the surface of the positive electrode current collector 111. One end of a positive electrode tab 20 is connected to the positive electrode current collector 111. The positive electrode active material layer 112 includes a positive electrode active material, and a mole percentage X of nickel in the positive electrode active material satisfies X≧60%.

[0017] The higher the nickel content in the positive electrode active material, the higher the capacity per gram of the positive electrode active material. For a given designed capacity, using a positive electrode active material with a higher nickel content results in a lighter weight of the single layer coated on the surface of the positive electrode current collector 111. For the same compaction density, the thickness of the positive electrode pieces 11 is thinner, the lithium ion transmission path is shorter, the resistance of the electrode assembly 10 is reduced, and the amount of heat generated during the discharge process of the electrochemical device 100 is reduced. Furthermore, the reduced thickness of the positive electrode pieces 11 is more advantageous for heat dissipation, thereby suppressing the temperature rise of the electrochemical device 100. In another embodiment, the mole percentage X of nickel in the positive electrode active material satisfies the range of 80%≦X≦95%.

[0018] 3 and 4, the thickness h1 of the positive electrode active material layer 112 satisfies 10 μm≦h1≦30 μm along the thickness direction of the positive electrode piece 11. By reducing the thickness h1 of the positive electrode active material layer 112, the distance that lithium ions travel between the positive electrode piece 11 and the negative electrode piece 13 can be shortened, the requirement for high-speed lithium ion transport under high-rate discharge conditions can be met, and the electrochemical device 100 has a high discharge capacity retention rate.

[0019] The Dv90 of the positive electrode active material is 12 μm to 30 μm. The magnitude of the Dv90 of the positive electrode active material affects the performance of the positive electrode pieces 11. If the Dv90 of the positive electrode active material is too large, it becomes difficult to apply the positive electrode active material well to the surface of the positive electrode current collector 111, and the surface of the positive electrode pieces 11 is likely to be scratched. If the specific surface area of ​​the positive electrode active material is too small, the kinetic performance of the positive electrode active material deteriorates, and the temperature difference is likely to increase during high-rate charging and discharging of the electrochemical device 100. If the Dv90 of the positive electrode active material is too small, the positive electrode active material is likely to aggregate, which reduces the electrical performance of the positive electrode pieces 11 and is disadvantageous to the high-temperature performance of the positive electrode pieces 11.

[0020] The positive electrode active material layer 112 contains carbon nanotubes that satisfy at least one of the following conditions: (1) the length of the carbon nanotubes is 0.1 μm to 6 μm; (2) the diameter of the carbon nanotubes is 10 nm to 20 nm; and (3) the Dv90 of the carbon nanotubes is 3 μm to 10 μm.

[0021] A large aspect ratio of carbon nanotubes is advantageous for forming a conductive network between carbon nanotube particles and improving the conductive performance of the positive electrode piece 11. The Dv90 of carbon nanotubes is advantageous for dispersing the carbon nanotubes. If the Dv90 is too large, the carbon nanotubes themselves tend to aggregate, while if it is too small, the carbon nanotubes and binders tend to aggregate, both of which are unfavorable for forming a conductive network. Therefore, adding carbon nanotubes to the positive electrode active material layer 112 and restricting the morphology of the carbon nanotubes according to the above conditions is advantageous for reducing the internal resistance of the positive electrode piece 11 and further improving the internal resistance of the entire electrochemical device 100. For the same current, the smaller the internal resistance of the electrochemical device 100, the less heat is generated, thereby further suppressing the temperature rise of the electrochemical device 100 during high-rate discharge.

[0022] 3 and 4, the thickness h2 of the positive electrode current collector 111 along the thickness direction of the positive electrode piece 11 satisfies 7 μm≦h2≦15 μm. The positive electrode current collector 111 is used to carry the positive electrode active material layer 112 and the functional layer 113. By improving the nickel content and electrical conductivity of the positive electrode active material layer 112, the thickness of the positive electrode current collector 111 can be reduced, thereby improving the energy density of the electrochemical device 100.

[0023] 3 and 4, the positive electrode piece 11 further includes a functional layer 113. The functional layer 113 and the positive electrode active material layer 112 are located on the same surface of the positive electrode current collector 111. In addition, along the width direction of the positive electrode current collector 111, the functional layer 113 is located closer to the positive electrode tab 20 of the positive electrode current collector 111 than the positive electrode active material layer 112. The functional layer 113 is used to cover burrs and debris generated when cutting the positive electrode piece 11 and the positive electrode tab 20, and prevents the burrs and debris from breaking through the separator 12 and causing direct contact between the positive electrode piece 11 and the negative electrode piece 13, thereby causing an internal short circuit in the electrode assembly 10.

[0024] The thickness d of the functional layer 113 is equal to or less than the thickness h1 of the positive electrode active material layer 112. After the application of the positive electrode active material layer 112 and the functional layer 113 to the positive electrode current collector 111 is completed, the positive electrode active material layer 112 is subjected to a compaction process, in which a press roll simultaneously compacts the positive electrode active material layer 112 and the functional layer 113. Because the functional layer 113 primarily contains inorganic particles and adhesive, its hardness is greater than that of the positive electrode active material layer 112. If the thickness d of the functional layer 113 is greater than the thickness h1 of the positive electrode active material layer 112, the positive electrode active material layer 112 cannot be properly compacted, and the positive electrode current collector 111 may even break. Of course, the thickness d of the functional layer 113 cannot be too thin, otherwise it will not be able to cover burrs and debris on the positive electrode current collector 111.

[0025] The electrochemical device 100 of this embodiment includes an electrode assembly 10, positive electrode tabs 20, and negative electrode tabs 30. In the electrode assembly 10, a separator 12 is disposed between a positive electrode piece 11 and a negative electrode piece 13. The positive electrode tabs 20 are connected to the positive electrode piece 11, and the negative electrode tabs 30 are connected to the negative electrode piece 13. The positive electrode piece 11 includes a positive electrode current collector 111 and a positive electrode active material layer 112 disposed on the positive electrode current collector 111. Here, the number a of the positive electrode tabs 20 and the number b of the positive electrode pieces 11 satisfy the relationship 0.25≦a / b≦1.25. The positive electrode active material includes a nickel-containing material, and its nickel mole percentage X satisfies the relationship X≧60%. The thickness h1 of the positive electrode active material layer 112 satisfies the relationship 10 μm≦h1≦30 μm. Increasing the number of positive electrode tabs 20 can effectively reduce the current density of each positive electrode tab 20, thereby reducing the amount of heat generated by the current flow. Furthermore, by reducing the thickness of the positive electrode active material layer 112, the lithium ion transmission distance can be shortened, thereby meeting the requirement for high-speed lithium ion transmission under high-rate discharge conditions of the electrochemical device 100 and providing the electrochemical device 100 with a high discharge capacity retention rate. Furthermore, by increasing the mole percentage of nickel in the positive electrode active material layer 112, the energy density of the electrochemical device 100 can be increased. This arrangement effectively suppresses temperature rise during high-rate discharge of the electrochemical device 100, thereby improving the safety and stability of the electrochemical device 100.

[0026] In order for those skilled in the art to more easily understand the technical solution and beneficial effects of the present invention, the following description takes a lithium ion battery as an example. (Measurement method) 1. Measurement method for Dv90 of cathode materials (1) Starting up the instrument: First, turn on the instrument and enter the sample injector system, then turn on the optical path system and computer, and preheat for 30 minutes. (2) Cleaning the sample injector system: Fill the sample injector with water, adjust the rotation speed to maximum, and clean for 5 seconds. Then, adjust the rotation speed to 0. This cleaning was repeated three times to ensure the sample injector was clean. (3) Enter the "Manual Measurement" screen and set the parameters such as material name, refractive index, material type, measurement time, and number of measurements in order. (4) Click “start” to perform light calibration and background light measurement. (5) The positive electrode material was dispersed in an aqueous solution (10 mL) and measured using a laser diffraction / scattering particle size distribution analyzer (Master Sizer 3000). The sample was added to the sample cell, and the shading rate increased with the amount of sample added. When the shading rate reached 8% to 12%, the addition of the sample was stopped, and the measurement was initiated by clicking "start" until the shading rate stabilized (generally no fluctuations for 30 s). After the measurement was completed, Dv90 was obtained. (6) Three parallel samples were measured and the average Dv90 was calculated.

[0027] 2.Method for measuring cycle maintenance rate After allowing the test battery to stand for 5 minutes at a temperature of 25±3°C, it was charged at a constant current rate of 0.5C until the voltage reached 4.50V, and then charged at a constant voltage of 4.50V until the voltage reached 0.025C. After allowing the battery to stand for 5 minutes, it was discharged at a constant current rate of 0.5C until the voltage reached 3.0V, and then allowed to stand for 5 minutes. The capacity at this point was recorded as D0. This charge / discharge cycle was repeated 600 times, and the final discharge capacity was recorded as D1. After cycling at 25±3°C, the capacity decay rate was calculated as D1 / D0 in %.

[0028] 3. Battery temperature rise measurement method The battery in this example was placed in an environment with a temperature of 25±3°C. A temperature sensor was placed at the geometric center of the battery to monitor the cell surface temperature. The battery was charged at a constant current rate of 1C until the voltage reached 4.50V, and then continued to charge at a constant voltage of 4.50V until the current reached ≦0.025C. The battery temperature was monitored throughout the charging process using a temperature sensor. The battery was discharged at a constant current rate of 15C until the voltage reached ≦2.8V. The battery temperature was monitored throughout the discharging process using a temperature sensor, and the maximum temperature value T1 during the discharging process was extracted. The discharge temperature rise △T = T1-25, in °C.

[0029] Example 1 1. <Positive Electrode Piece Preparation>: Carbon nanotubes (CNTs) and PVDF binder were mixed in the specified ratio, and NMP was added to prepare a conductive adhesive solution (7% solids). After mixing was complete, lithium nickel cobalt manganese oxide (NICKM) was added as the positive electrode active material, and the mixture was stirred with a vacuum stirrer until the mixture was homogeneous, resulting in a positive electrode slurry with a solids content of approximately 75%. The mole percentage (X) of nickel in the positive electrode active material was 80%, and the mass ratio of each component was NCM:conductive carbon nanotubes:binder = 97:1:2. The positive electrode slurry and functional layer (inorganic particles and adhesive) were applied to the surface of 12 μm aluminum foil (positive electrode current collector), dried, and cold-pressed. Then, a tab was die-cut, cut, and the positive electrode tab was welded to obtain a positive electrode piece. Here, the thickness h1 of the positive electrode active material layer was 25 μm, the thickness d of the functional layer was 25 μm, and the width L1 of the functional layer was 1.5 μm.

[0030] 2. <Preparation of negative electrode pieces>: Artificial graphite, styrene-butadiene rubber, and sodium carboxymethylcellulose were mixed with deionized water and additives in a mass ratio of 96%:2%:2% and stirred to obtain a negative electrode slurry. This negative electrode slurry was applied to the surface of 12 μm copper foil, dried, cold pressed, and then die-cut and cut to form a tab. The negative electrode tab was then welded to obtain a negative electrode piece.

[0031] 3. Preparation of electrolyte: Under a dry argon gas environment, ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) (weight ratio 1:1:1) were mixed, and lithium hexafluorophosphate (LiPF6) was added and mixed uniformly to form a base electrolyte. Here, the concentration of LiPF6 was 1.15 mol / L.

[0032] 4. Preparation of separator: A porous polyethylene (PE) polymer film was used as the separator. 5. <Preparation of Lithium-ion Battery>: Positive electrode pieces, separators, and negative electrode pieces were stacked in order and then wound to form an electrode assembly. Here, the number of layers of positive electrode pieces was 40, and the number of positive electrode tabs was 20. The electrode assembly was placed in an outer foil, leaving a liquid filling port. Electrolyte was poured through the liquid filling port, and the assembly was sealed. After undergoing processes such as formation and capacity measurement, a lithium-ion battery was obtained. Here, the ratio of the number of positive electrode tabs (a) to the number of layers of positive electrode pieces (b) was 0.25.

[0033] In Examples 2 to 8 and Comparative Examples 1 and 2: <Preparation of positive electrode pieces>, different numbers of positive electrode tabs and the number of layers of positive electrode pieces were selected according to Table 1 to adjust the ratio of the number of positive electrode tabs a to the number of layers of positive electrode pieces b. Other parameter settings were the same as in Example 1, and when the number of layers of positive electrode pieces changed, the number of layers of the corresponding negative electrode pieces and separator was adjusted according to the number of layers of the positive electrode pieces.

[0034] Examples 9 to 11 and Comparative Example 3: In <Preparation of Positive Electrode Pieces>, the molar percentage X of nickel in the positive electrode active material was adjusted according to Table 1, but other parameters were set the same as in Example 3. Examples 12 and 13, Comparative Examples 4 and 5: In <Preparation of Positive Electrode Pieces>, the thickness h1 of the positive electrode active material layer was adjusted according to Table 1 so as to vary, but other parameters were set in the same manner as in Example 3.

[0035] Examples 14 to 17: In <Preparation of Positive Electrode Pieces>, the thickness h2 of the positive electrode current collector was adjusted to be different according to Table 1, but other parameter settings were the same as in Example 1. Examples 18 to 21: The conductive carbon nanotubes were different from those in Example 3, but other parameter settings were the same as in Example 3. See Table 2 for details.

[0036] [Table 1]

[0037] [Table 2]

[0038] The above experimental data reveal the following: As can be seen from Examples 1 to 13 and Comparative Examples 1 to 5, when the mole percentage of nickel in the positive electrode active material is high, the temperature rise during high-rate discharge of a lithium-ion battery can be effectively suppressed by rationally setting and optimizing the relationship between the number of positive electrode tabs, the number of positive electrode tabs, and the thickness of the positive electrode active material layer. If the ratio of the number of positive electrode tabs to the number of positive electrode tab layers is too small, the temperature rise during high-rate discharge of a lithium-ion battery cannot be effectively suppressed. If the ratio of the number of positive electrode tabs to the number of positive electrode tab layers is too large, there is a limit to the effectiveness of suppressing the temperature rise during high-rate discharge of a lithium-ion battery, and at the same time, it affects the capacity retention rate of the lithium-ion battery. Furthermore, if the thickness of the positive electrode tabs is too thin, it affects the capacity retention rate, and if it is too thick, it increases the internal resistance of the positive electrode tabs and positive electrode tabs, weakening the temperature rise improvement effect brought about by the number of positive electrode tabs and positive electrode tab layers.

[0039] As can be seen from Examples 3 and 14 to 17, as the thickness of the positive electrode current collector gradually increases, the effect of suppressing the temperature rise during high-rate discharge of the lithium-ion battery increases and then decreases, so the thickness of the positive electrode current collector should be maintained within a reasonable range.

[0040] As can be seen from Examples 3 and 18 to 21, increasing the aspect ratio of carbon nanotubes can effectively suppress temperature rise. This is because carbon nanotubes with a high aspect ratio are advantageous for forming a conductive network between particles, improving the conductive performance of the positive electrode pieces. The Dv90 of carbon nanotubes is advantageous for dispersion of the carbon nanotubes. If the Dv90 is too large, the carbon nanotubes themselves tend to aggregate, while if it is too small, the carbon nanotubes and binders tend to aggregate, both of which are disadvantageous for forming a conductive network. Therefore, adding carbon nanotubes to the positive electrode active material layer and restricting the morphology of the carbon nanotubes according to the above conditions is advantageous for reducing the internal resistance of the positive electrode pieces and further improving the internal resistance of the entire electrochemical device. Furthermore, the amount of heat generated for the same current is reduced, thereby further suppressing temperature rise during high-rate discharge of the electrochemical device.

[0041] The above are merely examples of the present invention and do not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by utilizing the contents of the specification and drawings of the present invention, or any directly or indirectly applicable to other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. 1. An electrochemical device comprising: the positive electrode assembly includes a positive electrode tab and a negative electrode tab, the electrode assembly includes a positive electrode piece, a separator and a negative electrode piece, the separator is disposed between the positive electrode piece and the negative electrode piece, the positive electrode piece includes a positive electrode current collector and a positive electrode active material layer, the positive electrode active material layer is disposed on a surface of the positive electrode current collector, the positive electrode active material layer includes a positive electrode active material, the positive electrode tab is connected to the positive electrode current collector, and the negative electrode tab is connected to the negative electrode piece, the number a of the positive electrode tabs and the number b of the positive electrode piece layers satisfy 0.25≦a / b≦1.25, a mole percentage X of nickel in the positive electrode active material satisfies X≧60%, The electrochemical device, wherein the thickness h1 of the positive electrode active material layer satisfies 10 μm≦h1≦30 μm.

2. 2. The electrochemical device according to claim 1, wherein the number a of the positive electrode tabs and the number b of the layers of the positive electrode pieces satisfy 0.5≦a / b≦1.

3. 3. The electrochemical device according to claim 2, wherein a mole percentage X of nickel in the positive electrode active material satisfies 80%≦X≦95%.

4. the number a of the positive electrode tabs satisfies 5≦a≦40, 4. The electrochemical device according to claim 3, wherein the number b of layers of the positive electrode pieces satisfies 20≦b≦40.

5. 5. The electrochemical device according to claim 4, wherein the thickness h2 of the positive electrode current collector satisfies 7 μm≦h2≦15 μm.

6. the positive electrode active material layer contains carbon nanotubes, The carbon nanotubes are (1) The length of the carbon nanotube is 0.1 μm to 6 μm; (2) the diameter of the carbon nanotube is 10 nm to 20 nm; and (3) The carbon nanotube has a Dv90 of 3 μm to 10 μm.

5. The electrochemical device according to claim 4.

7. 2. The electrochemical device according to claim 1, wherein the positive electrode active material has a Dv90 of 12 μm to 30 μm.

8. The electrochemical device according to claim 5, wherein the positive electrode piece further includes a functional layer, the functional layer and the positive electrode active material layer are located on the same surface of the positive electrode current collector, the functional layer is provided on a side of the surface of the positive electrode current collector that is closer to the positive electrode tab, and the thickness of the functional layer is 10 μm to 25 μm.

9. 9. The electrochemical device according to claim 8, wherein the functional layer comprises inorganic particles and an adhesive.

10. An electronic device comprising the electrochemical device according to any one of claims 1 to 9.

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