Electrochemical device and electronic device

Abstract

The invention provides an electrochemical device and an electronic device, the electrochemical device comprises an electrode assembly of a winding structure, the electrode assembly comprises a positive pole piece, and the positive pole piece comprises a positive current collector, a first coating and a positive material layer; wherein the surface, opposite to the winding center, of the positive current collector is a first surface; in the winding direction of the positive pole piece, the first surface comprises a coating area and an uncoated area which are connected with each other, the coating area is provided with a first coating and a positive pole material layer, and the first coating is arranged between the positive pole current collector and the positive pole material layer; the uncoated region is provided with a first coating and is positioned on the outermost ring of the positive current collector; the thickness of the first coating in the uncoated area is D1 [mu] m, the thickness of the first coating in the coated area is D2 [mu] m, 0.9 < = D1 < = 6, and 0 < = D1-D2 < = 3.6. The safety performance of the electrochemical device is improved, and meanwhile, the electrochemical device has good rate capability.

Description

Technical Field

[0001] This application relates to the field of electrochemistry technology, and particularly to an electrochemical device and an electronic device. Background Art

[0002] During the use of a mobile phone, due to misoperations such as slipping, flying off and hitting the ground or a sharp object, or knocking against a hard object, the lithium-ion battery is subjected to mechanical impact, which easily damages the positive electrode plate and the negative electrode plate of the lithium-ion battery, resulting in the positive electrode plate and the negative electrode plate breaking to form debris and triggering a short circuit, thus causing the lithium-ion battery to catch fire or even explode.

[0003] Currently, during the short-circuit failure process, the outer positive electrode plate has a larger damaged area, and more positive electrode plate debris is formed. The positive electrode plate debris in series forms a short circuit or the exposed positive current collector and the intruder form a short circuit, which will bring great potential safety hazards to the lithium-ion battery. Therefore, improving the protection of the outer positive electrode plate, reducing the probability of debris generation or increasing the contact resistance is extremely important for the safe use of the lithium-ion battery. Summary of the Invention

[0004] The purpose of this application is to provide an electrochemical device and an electronic device to improve the safety performance of the electrochemical device, and at the same time, the electrochemical device has good rate performance.

[0005] It should be noted that in the summary of the invention of this application, the lithium-ion battery is used as an example of the electrochemical device to explain this application, but the electrochemical device of this application is not limited to the lithium-ion battery. The specific technical solutions are as follows:

[0006] The first aspect of the present application provides an electrochemical device, which includes a wound electrode assembly. The electrode assembly includes a positive electrode tab, and the positive electrode tab includes a positive electrode current collector, a first coating layer, and a positive electrode material layer. Among them, the surface of the positive electrode current collector facing away from the winding center is the first surface. Along the winding direction of the positive electrode tab, the first surface includes a connected coating area and an uncoated area. The coating area is provided with the first coating layer and the positive electrode material layer, and the first coating layer is disposed between the positive electrode current collector and the positive electrode material layer. The uncoated area is provided with the first coating layer, and the uncoated area is located in the outermost circle of the positive electrode current collector. The thickness of the first coating layer in the uncoated area is D1 μm, and the thickness of the first coating layer in the coating area is D2 μm, where 0.9 ≤ D1 ≤ 6 and 0 ≤ D1 - D2 ≤ 3.6. By providing the positive electrode material layer and the first coating layer in the coating area of the positive electrode current collector, and only providing the first coating layer in the uncoated area of the positive electrode current collector, and controlling the values of D1 and D1 - D2 within the above ranges, the generation probability of outer circle debris can be effectively reduced, the risk of short circuit formed by the series connection of outer circle debris or the risk of short circuit formed by the exposed positive electrode current collector and outer circle debris can be reduced, and the safety performance of the electrochemical device can be improved. At the same time, the first coating layer can increase the short circuit resistance, reduce the short circuit power, and by setting different thicknesses of the first coating layer in the uncoated area and the coating area, the internal resistance of the electrochemical device can be reduced, so that while the safety performance of the electrochemical device is improved, it has good rate performance. On the other hand, only providing the first coating layer in the uncoated area of the positive electrode current collector can reduce the consumption of the positive electrode active material and lower the production cost.

[0007] In an embodiment of the present application, 0.9 ≤ D2 ≤ 3. By controlling the value of D2 within the above range, the short circuit resistance can be increased, the safety performance of the electrochemical device can be further improved, at the same time, the energy density of the electrochemical device can be increased, and the internal resistance of the electrochemical device can also be reduced, so that while the safety performance of the electrochemical device is improved, it has good rate performance.

[0008] In an embodiment of the present application, the coating weight of the first coating layer in the uncoated area is CW1 mg / 1540.25mm 2 , 3 ≤ CW1 ≤ 14. By controlling the value of CW1 within the above range, the generation probability of outer circle debris can be reduced, the risk of short circuit formed by the series connection of outer circle debris or the risk of short circuit formed by the exposed positive electrode current collector and outer circle debris can be reduced, and the safety performance of the electrochemical device can be further improved.

[0009] In an embodiment of the present application, the coating weight of the first coating layer in the coating area is CW2 mg / 1540.25mm 2, 3 ≤ CW2 ≤ 8. By adjusting the value of CW2 within the above range, the short-circuit resistance can be increased, the safety performance of the electrochemical device can be further improved, the energy density of the electrochemical device can be increased, and the internal resistance of the electrochemical device can be reduced. Therefore, while the safety performance of the electrochemical device is improved, it has good rate performance.

[0010] In one embodiment of the present application, 0 ≤ CW1 - CW2 ≤ 6. By adjusting the value of CW1 - CW2 within the above range, the generation probability of outer ring debris can be effectively reduced. At the same time, the first coating can increase the short-circuit resistance, reduce the short-circuit power, and by differentiating the coating weights of the first coating in the uncoated area and the coated area, the internal resistance of the electrochemical device can be reduced. Therefore, while the safety performance of the electrochemical device is further improved, it has good rate performance.

[0011] In one embodiment of the present application, along the length direction of the positive electrode tab after unfolding, the length of the uncoated area is x cm, and the length of the positive electrode current collector is L cm, 0.07 ≤ x / L ≤ 0.12. By adjusting the value of x / L within the above range, the energy density and rate performance of the electrochemical device can be improved.

[0012] In one embodiment of the present application, along the winding direction of the positive electrode tab, the first coating in the uncoated area connects the first coating in the coated area and the positive electrode material layer; along the width direction of the positive electrode tab after unfolding, the width of the first coating in the uncoated area is the same as the width of the positive electrode material layer in the coated area. Through the above setting, the safety performance of the electrochemical device can be improved.

[0013] In one embodiment of the present application, the first coating includes ceramic particles, and the ceramic particles include at least one of alumina, boehmite, silica, zirconia, titanium dioxide, magnesium oxide, zinc oxide, or calcium oxide; based on the mass of the first coating, the mass percentage content of the ceramic particles is W1%, 80 ≤ W1 ≤ 99.2. By selecting the above ceramic particles and adjusting the value of W1 within the above range, the first coating has high mechanical strength and short-circuit resistance, further improving the safety performance of the electrochemical device.

[0014] In one embodiment of the present application, the average particle size of the ceramic particles is d nm, 100 ≤ d ≤ 1500. By adjusting the value of d within the above range, a relatively dense first coating can be formed on the surface of the positive electrode current collector, reducing the risk of short circuit formed by the exposed positive electrode current collector and outer ring debris, and further improving the safety performance of the electrochemical device.

[0015] In an embodiment of the present application, 200 ≤ d ≤ 500. A relatively dense first coating can be formed on the surface of the positive current collector, further reducing the risk of short circuit formation between the exposed positive current collector and the outer debris, and further improving the safety performance of the electrochemical device.

[0016] In an embodiment of the present application, the first coating further includes a first binder, and the first binder includes at least one of polyacrylic acid binders, styrene-acrylic binders, or styrene-butadiene rubber binders; based on the mass of the first coating, the mass percentage content of the first binder is W2%, and 0.6 ≤ W2 ≤ 10. By selecting the above first binder and controlling the value of W2 within the above range, the overall adhesion of the first coating can be improved, and the adhesion between the first coating and the positive current collector can be enhanced, thereby further improving the safety performance of the electrochemical device.

[0017] In an embodiment of the present application, the first coating further includes a first conductive agent, and the first conductive agent includes at least one of conductive carbon black, artificial graphite, activated carbon, carbon nanotubes, or carbon nanofibers; based on the mass of the first coating, the mass percentage content of the first conductive agent is W3%, and 0.2 ≤ W3 ≤ 10. By selecting the above first conductive agent and controlling the value of W3 within the above range, the first coating has good conductivity while having a high short-circuit resistance, taking into account the cycle performance while improving the safety performance of the electrochemical device.

[0018] The second aspect of the present application provides an electronic device, which includes the electrochemical device in any of the foregoing embodiments. The electronic device of the present application has good rate performance while having good safety performance.

[0019] Advantages of the present application:

[0020] The present application provides an electrochemical device and an electronic device. The electrochemical device includes a wound electrode assembly, and the electrode assembly includes a positive electrode tab. The positive electrode tab includes a positive current collector, a first coating, and a positive electrode material layer; wherein, the surface of the positive current collector facing away from the winding center is the first surface; along the winding direction of the positive electrode tab, the first surface includes a connected coating area and an uncoated area. The coating area is provided with the first coating and the positive electrode material layer, and the first coating is disposed between the positive current collector and the positive electrode material layer; the uncoated area is provided with the first coating, and the uncoated area is located in the outermost circle of the positive current collector. The thickness of the first coating in the uncoated area is D1 μm, and the thickness of the first coating in the coating area is D2 μm, 0.9 ≤ D1 ≤ 6, 0 ≤ D1 - D2 ≤ 3.6. By controlling the values of D1 and D1 - D2 within the scope of the present application, the safety performance of the electrochemical device can be improved, and the rate performance of the electrochemical device is better.

[0021] Of course, it is not necessary for any product or method implementing this application to achieve all the above-mentioned advantages simultaneously. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] To more clearly illustrate the technical solutions in the embodiments of this application, the following briefly introduces the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of this application, and those of ordinary skill in the art can also obtain other embodiments based on these drawings.

[0023] Figure 1 Partial cross-sectional view of the positive electrode tab along its thickness direction in the electrode assembly with a winding structure of an implementation scheme of this application;

[0024] Figure 2 Graph of the coating weight of the first coating in the uncoated area and the resistance of the first coating electrode tab in some implementation schemes of this application;

[0025] Figure 3 Graph of the coating weight of the first coating in the uncoated area and the film resistance of the cold-pressed positive electrode tab in some implementation schemes of this application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] The following will clearly and completely describe the technical solutions in this application in conjunction with the embodiments and drawings of this application. Obviously, the described embodiments are only some embodiments of this application, rather than all embodiments. All other embodiments obtained by those skilled in the art based on this application belong to the scope of protection of this application.

[0027] It should be noted that in the specific implementation of this application, a lithium-ion battery is used as an example of the electrochemical device to explain this application, but the electrochemical device of this application is not limited to lithium-ion batteries.

[0028] The first aspect of this application provides an electrochemical device, which includes an electrode assembly with a winding structure. The electrode assembly includes a positive electrode tab, such as Figure 1As shown in the figure, the positive electrode plate includes a positive electrode current collector 11, a first coating layer 12, and a positive electrode material layer 13; wherein, the surface of the positive electrode current collector facing away from the winding center is the first surface 11a; along the winding direction of the positive electrode plate, the first surface 11a includes a connected coating area 112 and an uncoated area 111. The coating area 112 is provided with the first coating layer 12 and the positive electrode material layer 13, and the first coating layer 12 is disposed between the positive electrode current collector 11 and the positive electrode material layer 13; the uncoated area 111 is provided with the first coating layer 12, and the uncoated area 111 is located in the outermost circle of the positive electrode current collector. The thickness of the first coating layer in the uncoated area is D1 μm, and the thickness of the first coating layer in the coating area is D2 μm, 0.9 ≤ D1 ≤ 6, 0 ≤ D1 - D2 ≤ 3.6. For example, the value of D1 can be 0.9, 1, 2, 3, 4, 5, 6 or a range composed of any two of these numerical values; the value of D1 - D2 can be 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.3, 3.57, 3.6 or a range composed of any two of these numerical values. In this application, the "coating area" refers to the area on the positive electrode current collector in the positive electrode plate where the positive electrode material layer is coated; the "uncoated area" refers to the area on the positive electrode current collector in the positive electrode plate where the positive electrode material layer is not coated.

[0029] In an embodiment of the present application, as Figure 1 shown, the surface of the positive electrode current collector 11 facing the winding center is the second surface 11b, and the second surface is provided with the first coating layer 12 and the positive electrode material layer 13, and the first coating layer 12 is disposed between the positive electrode current collector 11 and the positive electrode material layer 13.

[0030] The inventors have found through research that by setting the positive electrode material layer and the first coating layer in the coating area of the positive electrode current collector, and only setting the first coating layer in the uncoated area of the positive electrode current collector, by adjusting the values of D1 and D1 - D2 within the above ranges, the generation probability of outer ring debris can be effectively reduced, the risk of short circuit formed by the series connection of outer ring debris or the risk of short circuit formed by the exposed positive electrode current collector and outer ring debris can be reduced, and the safety performance of the electrochemical device can be improved; at the same time, the first coating layer can increase the short circuit resistance and reduce the short circuit power, and by setting different thicknesses of the first coating layer in the uncoated area and the coating area, the internal resistance of the electrochemical device can be reduced, so that while the safety performance of the electrochemical device is improved, it has good rate performance. On the other hand, only setting the first coating layer in the uncoated area of the positive electrode current collector can reduce the amount of positive electrode active material used and reduce the production cost.

[0031] In an embodiment of the present application, 0.9 ≤ D2 ≤ 3. For example, the value of D2 can be 0.9, 1, 1.5, 2, 2.5, 3 or a range composed of any two of these numerical values. By adjusting the value of D2 within the above range, the short-circuit resistance can be increased, the short-circuit power can be reduced, and the safety performance of the electrochemical device can be further improved; at the same time, the relatively thin thickness of the first coating in the coated area can reduce the overall thickness of the electrochemical device, improve the energy density of the electrochemical device, and can also reduce the internal resistance of the electrochemical device, so that while the safety performance of the electrochemical device is improved, it has good rate performance.

[0032] The present application does not particularly limit the method for adjusting the value of D1, as long as the purpose of the present application can be achieved. For example, the value of D1 can be adjusted by adjusting the coating weight of the first coating in the uncoated area. Exemplarily, when the coating weight of the first coating in the uncoated area increases, the value of D1 increases, and when the coating weight of the first coating in the uncoated area decreases, the value of D1 decreases.

[0033] The present application does not particularly limit the method for adjusting the value of D2, as long as the purpose of the present application can be achieved. For example, the value of D2 can be adjusted by adjusting the coating weight of the first coating in the coated area. Exemplarily, when the coating weight of the first coating in the coated area increases, the value of D2 increases, and when the coating weight of the first coating in the coated area decreases, the value of D2 decreases.

[0034] The present application does not particularly limit the method for adjusting the value of D1 - D2, as long as the purpose of the present application can be achieved. For example, the value of D1 - D2 can be adjusted by adjusting the respective values of D1 and D2, and the adjustment method is as described above.

[0035] In an embodiment of the present application, the coating weight of the first coating in the uncoated area is CW1 mg / 1540.25mm 2 , 3 ≤ CW1 ≤ 14. For example, the value of CW1 can be 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14 or a range composed of any two of these numerical values. The value of CW1 reflects the thickness of the first coating in the uncoated area. By adjusting the value of CW1 within the above range, the generation probability of outer ring debris can be reduced, the risk of short circuit formed by the series connection of outer ring debris or the risk of short circuit formed by the exposed positive current collector and outer ring debris can be reduced, and the safety performance of the electrochemical device can be further improved.

[0036] In an embodiment of the present application, the coating weight of the first coating in the coated area is CW2 mg / 1540.25mm 2, 3 ≤ CW2 ≤ 8. For example, the value of CW2 can be 3, 4, 5, 6, 7, 8, or a range composed of any two of these numerical values. The value of CW2 reflects the thickness of the first coating in the coating area. By controlling the value of CW2 within the above range, the short-circuit resistance can be increased, the short-circuit power can be reduced, and the safety performance of the electrochemical device can be further improved; at the same time, the relatively thin thickness of the first coating in the coating area can reduce the overall thickness of the electrochemical device, improve the energy density of the electrochemical device, and also reduce the internal resistance of the electrochemical device, so that while the safety performance of the electrochemical device is improved, it has good rate performance.

[0037] In an embodiment of the present application, 0 ≤ CW1 - CW2 ≤ 6. For example, the value of CW1 - CW2 can be 0, 1, 2, 3, 4, 5, 6, or a range composed of any two of these numerical values. By controlling the value of CW1 - CW2 within the above range, the generation probability of outer-ring debris can be reduced, the risk of short circuit formed by the series connection of outer-ring debris or the risk of short circuit formed by the exposed positive current collector and outer-ring debris can be reduced; at the same time, the first coating can increase the short-circuit resistance, reduce the short-circuit power, and by differentially setting the coating weights of the first coating in the non-coating area and the coating area, the internal resistance of the electrochemical device can be reduced, so that while the safety performance of the electrochemical device is further improved, it has good rate performance.

[0038] The method for controlling the value of CW1 in the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the value of CW1 can be controlled by adjusting the coating amount of the first coating slurry in the non-coating area. Exemplarily, when the coating amount of the first coating slurry in the non-coating area increases, the value of CW1 increases, and when the coating amount of the first coating slurry in the non-coating area decreases, the value of CW1 decreases.

[0039] The method for controlling the value of CW2 in the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the value of CW2 can be controlled by adjusting the coating amount of the first coating slurry in the coating area. Exemplarily, when the coating amount of the first coating slurry in the coating area increases, the value of CW2 increases, and when the coating amount of the first coating slurry in the coating area decreases, the value of CW2 decreases.

[0040] The method for controlling the value of CW1 - CW2 in the present application is not particularly limited as long as the purpose of the present application can be achieved. For example, the value of CW1 - CW2 can be controlled by adjusting the respective values of CW1 and CW2, and the control method is as described above.

[0041] In an embodiment of the present application, along the length direction after the positive electrode tab is unfolded, the length of the uncoated area is x cm, and the length of the positive current collector is L cm, where 0.07 ≤ x / L ≤ 0.12. For example, the value of x / L can be 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, or a range composed of any two of these values. The value of x / L reflects the proportion of the length of the outermost circle of the positive electrode tab to the total length. By controlling the value of x / L within the above range, the proportion of the length of the outermost circle of the positive electrode tab to the total length is appropriate, the electrode assembly has an appropriate number of winding turns, the volume utilization rate of the positive active material can be improved, and the energy density of the electrochemical device can be increased; at the same time, the wetting degree of the electrolyte on the positive electrode tab during the cycling process and the stress release ability of the electrochemical device can be improved, thereby reducing the cyclic swelling of the electrochemical device, and the internal resistance of the electrochemical device can also be reduced, thereby improving the rate performance of the electrochemical device.

[0042] In an embodiment of the present application, 12 ≤ x ≤ 17.5 and 100 ≤ L ≤ 250. For example, the value of x can be 12, 12.5, 13, 13.5, 14, 14.5, 15, 15.5, 16, 16.5, 17, 17.5, or a range composed of any two of these values; the value of L can be 100, 120, 140, 160, 180, 200, 220, 240, 250, or a range composed of any two of these values. By controlling the values of x and L within the above range, the positive electrode tab has appropriate dimensions, the stability of the positive electrode tab preparation process is relatively high, and the production cost of the positive electrode tab is relatively low; at the same time, the energy density of the electrochemical device can be controlled within an effective range of 700 Wh / L to 950 Wh / L, improving the capacity of the electrochemical device.

[0043] The present application does not particularly limit the method for controlling the value of L, as long as the purpose of the present application can be achieved. For example, commercially available positive current collectors with different lengths can be selected.

[0044] The present application does not particularly limit the method for controlling the value of x, as long as the purpose of the present application can be achieved. For example, the value of x can be controlled by controlling the length of the outermost circle of the positive electrode tab.

[0045] The present application does not particularly limit the method for controlling the value of x / L, as long as the purpose of the present application can be achieved. For example, the value of x / L can be controlled by controlling the respective values of x and L, and the control method is as described above.

[0046] In an embodiment of the present application, along the winding direction of the electrode assembly, the first coating in the uncoated area connects the first coating in the coated area and the positive electrode material layer; along the width direction of the positive electrode tab after unfolding, the width of the first coating in the uncoated area is the same as the width of the positive electrode material layer in the coated area. Through the above settings, the generation probability of outer ring debris can be effectively reduced, the risk of short circuit formed by the series connection of outer ring debris or the risk of short circuit formed by the exposed positive electrode current collector and outer ring debris can be reduced, and the safety performance of the electrochemical device can be improved.

[0047] In an embodiment of the present application, the first coating includes ceramic particles, and the ceramic particles include at least one of aluminum oxide, boehmite, silicon dioxide, zirconium dioxide, titanium dioxide, magnesium oxide, zinc oxide or calcium oxide; based on the mass of the first coating, the mass percentage content of the ceramic particles is W1%, 80 ≤ W1 ≤ 99.2. For example, the value of W1 can be 80, 82, 84, 86, 88, 90, 92, 94, 96, 98, 99, 99.2 or a range composed of any two of these values. By selecting the above ceramic particles and controlling the value of W1 within the above range, the first coating has high mechanical strength and short circuit resistance, reduces the short circuit power, and further improves the safety performance of the electrochemical device.

[0048] In an embodiment of the present application, the average particle size of the ceramic particles is d nm, 100 ≤ d ≤ 1500, preferably, 200 ≤ d ≤ 500. For example, the value of d can be 100, 200, 300, 400, 500, 700, 900, 1100, 1300, 1500 or a range composed of any two of these values. By controlling the value of d within the above range, the packing density between particles can be increased, a relatively dense first coating can be formed on the surface of the positive electrode current collector, the pressure resistance of the first coating can be improved, the protection effect on the positive electrode current collector under abnormal conditions such as nail penetration and impact can be enhanced, the generation probability of outer ring debris can be reduced, and the risk of short circuit formed by the series connection of outer ring debris or the risk of short circuit formed by the exposed positive electrode current collector and outer ring debris can be reduced, further improving the safety performance of the electrochemical device.

[0049] The present application does not particularly limit the method for controlling the value of d, as long as the purpose of the present application can be achieved. For example, commercially available ceramic particles with different average particle sizes can be selected according to needs.

[0050] In an embodiment of the present application, the first coating further includes a first binder, and the first binder includes at least one of polyacrylic acid binders, styrene-acrylic binders or styrene-butadiene rubber binders. The polyacrylic acid binders include at least one of sodium polyacrylate, lithium polyacrylate, potassium polyacrylate or ammonium polyacrylate. The styrene-acrylic binders include styrene-acrylic polymers (C8H8) y (C3H4O2) z, carboxyl styrene-acrylic rubber, hydroxy styrene-acrylic rubber or epoxy styrene-acrylic rubber, wherein 500≤y≤2500, 500≤z≤2500. The styrene-butadiene rubber adhesive includes a styrene-butadiene rubber polymer (C8H8) m (C4H6) n , acrylonitrile-styrene-butadiene rubber, carboxylated styrene-butadiene rubber or hydroxystyrene-butadiene rubber, wherein 500≤m≤2500, 500≤n≤2500. Based on the mass of the first coating, the mass percentage of the first binder is W2%, 0.6≤W2≤10. For example, the value of W2 can be 0.6, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two of the values. By selecting the above-mentioned first binder and regulating the value of W2 within the above-mentioned range, the overall adhesion of the first coating can be improved, and the adhesion between the first coating and the positive electrode collector can be improved, thereby further improving the safety performance of the electrochemical device.

[0051] In one embodiment of the present application, the first coating layer also includes a first conductive agent, and the first conductive agent includes at least one of conductive carbon black, artificial graphite, activated carbon, carbon nanotubes or carbon nanofibers. Conductive carbon black may include but is not limited to at least one of Super P, acetylene black or Ketjen black; carbon nanotubes may include but are not limited to at least one of single-walled carbon nanotubes or multi-walled carbon nanotubes. Based on the mass of the first coating layer, the mass percentage of the first conductive agent is W3%, 0.2≤W3≤10. For example, the value of W3 can be 0.2, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or a range consisting of any two of the values. By selecting the above-mentioned first conductive agent and adjusting the value of W3 within the above-mentioned range, the first coating layer has good conductivity while having a higher short-circuit resistance, improving the safety performance of the electrochemical device while taking into account the cycle performance.

[0052] The present application has no particular restrictions on the preparation method of the positive electrode sheet, as long as the purpose of the present application can be achieved. For example, the preparation method of the positive electrode sheet may include but is not limited to the following steps: mixing the ceramic particles, the first binder and the first conductive agent according to a mass ratio of (80 to 99.2): (0.6 to 10): (0.2 to 10), adding the first solvent, and stirring evenly to obtain a first coating slurry with a solid content of 40wt% to 50wt%. Then the first coating slurry is 3mg / 1540.25mm 2 Up to 8mg / 1540.25mm 2The coating weight is coated on the second surface of the positive current collector, and after drying under the conditions of 90°C to 150°C, a positive electrode sheet with the first coating on the second surface is obtained. Then, an uncoated area with a length of x cm is reserved on the first surface of the positive current collector, and the above steps are repeated in the coated area on the first surface to obtain a positive electrode sheet with the first coating on the coated area of the first surface. Then, the first coating slurry is coated on the reserved uncoated area on the first surface of the positive current collector at a coating weight of 3 mg / 1540.25 mm 2 to 14 mg / 1540.25 mm 2 of the coating weight, and after drying under the conditions of 90°C to 150°C, a positive electrode sheet with the first coating on both sides is obtained. Then, a positive electrode material layer slurry is prepared, the positive electrode material layer slurry is coated on the surface of the first coating in the coated area, dried, and then the positive electrode material layer slurry is coated on the surface of the first coating on the second surface of the positive current collector and dried to obtain a positive electrode sheet with the first coating and the positive electrode material layer on both sides. Among them, the first solvent may include but is not limited to at least one of pure water or N-methylpyrrolidone.

[0053] This application has no special limitation on the positive current collector, as long as the purpose of this application can be achieved. For example, it may include aluminum foil, aluminum alloy foil, or composite current collector (such as aluminum-carbon composite current collector), etc.

[0054] In this application, the positive electrode material layer includes a positive electrode active material. This application has no special limitation on the positive electrode active material, as long as the purpose of this application can be achieved. For example, the positive electrode active material may include but is not limited to at least one of lithium nickel cobalt manganese oxide (such as NCM811, NCM622, NCM523, NCM111), lithium nickel cobalt aluminate, lithium iron phosphate, lithium-rich manganese-based material, lithium cobalt oxide (LiCoO2), lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0055] In this application, the positive electrode material layer may further include a second conductive agent and a second binder. There are no particular limitations on the types of the second conductive agent and the second binder in this application, as long as the objectives of this application can be achieved. For example, the second conductive agent may include, but is not limited to, at least one of conductive carbon black, carbon nanotubes (CNTs), carbon fibers, flake graphite, graphene, metal materials, or conductive polymers. The above-mentioned carbon fibers may include, but are not limited to, vapor-grown carbon fibers (VGCF) and / or carbon nanofibers. The above-mentioned metal materials may include, but are not limited to, metal powders and / or metal fibers. Specifically, the metal may include, but is not limited to, at least one of copper, nickel, aluminum, or silver. The above-mentioned conductive polymers may include, but are not limited to, at least one of polyphenylene derivatives, polyaniline, polythiophene, polyacetylene, or polypyrrole. For example, the second binder may include, but is not limited to, at least one of polyacrylic acid, sodium polyacrylate, potassium polyacrylate, lithium polyacrylate, polyimide, polyvinyl alcohol, carboxymethyl cellulose, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, polyimide, polyamideimide, styrene-butadiene rubber, or polyvinylidene fluoride. There are no particular limitations on the mass ratio of the positive electrode active material, the second conductive agent, and the second binder in the positive electrode material layer in this application. Those skilled in the art can select according to actual needs as long as the objectives of this application can be achieved.

[0056] There are no particular limitations on the thickness of the positive electrode current collector and the thickness of the positive electrode material layer in this application, as long as the objectives of this application can be achieved. For example, the thickness of the positive electrode current collector is 5 μm to 20 μm, and the thickness of the single-sided positive electrode material layer is 30 μm to 90 μm.

[0057] In this application, the electrode assembly further includes a negative electrode tab, and the negative electrode tab includes a negative electrode current collector and a negative electrode material layer disposed on at least one surface of the negative electrode current collector. The above-mentioned "negative electrode material layer disposed on at least one surface of the negative electrode current collector" means that the negative electrode material layer may be disposed on one surface of the negative electrode current collector along its own thickness direction, or may be disposed on two surfaces of the negative electrode current collector along its own thickness direction. It should be noted that the "surface" here may be the entire area of the surface of the negative electrode current collector, or may be a partial area of the surface of the negative electrode current collector. There are no particular limitations in this application as long as the objectives of this application can be achieved.

[0058] There are no particular limitations on the negative electrode current collector in this application, as long as the objectives of this application can be achieved. For example, it may include copper foil, copper alloy foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, or composite current collector. Exemplarily, the composite current collector may be a lithium-copper composite current collector, a carbon-copper composite current collector, a nickel-copper composite current collector, or a titanium-copper composite current collector, etc.

[0059] In the present application, the negative electrode material layer includes a negative electrode active material. There is no particular limitation on the negative electrode active material in the present application, as long as the object of the present application can be achieved. For example, the negative electrode active material may include, but is not limited to, natural graphite, artificial graphite, mesophase microbeads, hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, lithiated TiO2-Li4Ti5O with a spinel structure 12 or at least one of Li-Al alloy. In some embodiments of the present application, the negative electrode material layer may further include a second conductive agent and / or a second binder, for example, it may be at least one of the above-mentioned second conductive agent and the above-mentioned second binder. There is no particular limitation on the mass ratio of the negative electrode active material, the second conductive agent, and the second binder in the negative electrode material layer in the present application, and those skilled in the art can select according to actual needs as long as the object of the present application can be achieved.

[0060] There is no particular limitation on the thickness of the negative electrode current collector and the thickness of the negative electrode material layer in the present application, as long as the object of the present application can be achieved. For example, the thickness of the negative electrode current collector is 4 μm to 15 μm, and the thickness of the single-sided negative electrode material layer is 40 μm to 100 μm.

[0061] Optionally, the negative electrode plate may further include a conductive layer, and the conductive layer is located between the negative electrode current collector and the negative electrode material layer. There is no particular limitation on the composition of the conductive layer in the present application, and it may be a commonly used conductive layer in the art. For example, the conductive layer includes a second conductive agent and a second binder. There is no particular limitation on the second conductive agent and the second binder in the conductive layer in the present application, and for example, it may be at least one of the above-mentioned second conductive agent and the above-mentioned second binder.

[0062] In the present application, the electrode assembly further includes a separator. There is no particular limitation on the separator in the present application, as long as the object of the present application can be achieved. For example, the material of the separator may include, but is not limited to, at least one of polyolefins (PO) mainly composed of polyethylene (PE) and polypropylene (PP), polyester (for example, polyethylene terephthalate (PET) film), cellulose, polyimide (PI), polyamide (PA), spandex or aramid. The type of the separator may include at least one of a woven film, a non-woven film, a microporous film, a composite film, a rolled film or a spun film.

[0063] In some embodiments of the present application, the separator membrane may include a substrate layer and a surface treatment layer. The substrate layer may be a non-woven fabric or a composite membrane having a porous structure, and the material of the substrate layer may include at least one of polyethylene, polypropylene, polyethylene terephthalate, or polyimide. Optionally, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be used. Optionally, a surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by mixing a polymer and an inorganic substance. In some embodiments of the present application, the inorganic layer includes inorganic particles and a second binder. The present application places no particular limitation on the inorganic particles. For example, the inorganic particles may include at least one of silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, or barium sulfate. The present application places no particular limitation on the second binder. For example, it may be at least one of the above-mentioned second binders. In some embodiments of the present application, the polymer layer includes a polymer, and the material of the polymer includes at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene ether, polyvinylidene fluoride, or poly(vinylidene fluoride-hexafluoropropylene). In the present application, there is no particular limitation on the thickness of the separator membrane, as long as the object of the present application can be achieved. For example, the thickness of the separator membrane may be 3 μm to 30 μm.

[0064] In the present application, the electrochemical device further includes an electrolyte solution, which includes a lithium salt and a non-aqueous solvent. There is no particular limitation on the lithium salt in the present application, as long as the object of the present application can be achieved. For example, the lithium salt may include, but is not limited to, at least one of LiPF6, LiBF4, LiAsF6, LiClO4, LiB(C6H5)4, LiCH3SO3, LiCF3SO3, LiN(SO2CF3)2, LiC(SO2CF3)3, Li2SiF6, lithium bis(oxalato)borate (LiBOB), or lithium difluoroborate. There is no particular limitation on the mass percentage content of the lithium salt in the electrolyte solution in the present application, as long as the object of the present application can be achieved. For example, based on the mass of the electrolyte solution, the mass percentage content of the lithium salt is 8% to 20%. There is no particular limitation on the non-aqueous solvent in the present application, as long as the object of the present application can be achieved. For example, the non-aqueous solvent may include, but is not limited to, at least one of carbonate compounds, carboxylate compounds, ether compounds, or other organic solvents. The above-mentioned carbonate compounds may include, but are not limited to, at least one of linear carbonate compounds, cyclic carbonate compounds, or fluorinated carbonate compounds. The above-mentioned linear carbonate compounds may include, but are not limited to, at least one of dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), or methyl ethyl carbonate (MEC). The above-mentioned cyclic carbonate compounds may include, but are not limited to, at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), or vinylene ethylene carbonate (VEC). The fluorinated carbonate compounds may include, but are not limited to, at least one of fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, or trifluoromethyl ethylene carbonate. The above-mentioned carboxylate compounds may include, but are not limited to, at least one of methyl formate, methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, or caprolactone. The above-mentioned ether compounds may include, but are not limited to, at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, 1-ethoxy-1-methoxyethane, 2-methyltetrahydrofuran, or tetrahydrofuran. The above-mentioned other organic solvents may include, but are not limited to, at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methyl sulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, or trioctyl phosphate.The present application does not particularly limit the mass percentage of the non-aqueous solvent in the electrolyte, as long as the object of the present application can be achieved.

[0065] The electrochemical device further includes a housing for accommodating the electrode assembly and the electrolyte, as well as other components known in the field of electrochemical devices. The present application does not limit the above-mentioned other components. The present application does not particularly limit the housing, and it can be a housing well-known in the art, as long as the object of the present application can be achieved. For example, the housing can be a hard shell housing or a flexible housing. The material of the hard shell housing can be metal. The present application does not limit the type of metal, and a metal hard shell housing known in the art can be used, as long as the object of the present application can be achieved. The flexible housing can be a metal plastic film, such as an aluminum plastic film, a steel plastic film, etc.

[0066] The preparation process of the electrochemical device of the present application is well-known to those skilled in the art. The present application has no special limitations. For example, the preparation process of the electrochemical device can include, but is not limited to, the following steps: stacking the positive electrode sheet, the separator, and the negative electrode sheet in sequence, and performing operations such as winding and folding according to needs to obtain a wound electrode assembly, placing the electrode assembly in the housing, injecting the electrolyte into the housing and sealing it to obtain the electrochemical device. In addition, an overcurrent protection element, a guide plate, etc. can be placed in the housing according to needs to prevent the pressure inside the electrochemical device from rising and overcharging and discharging.

[0067] The second aspect of the present application provides an electronic device, and the electronic device includes the electrochemical device in any of the foregoing embodiments. The electronic device of the present application has good safety performance and good rate performance at the same time.

[0068] The electronic device of the present application is not particularly limited, and it can be any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, a laptop computer, a pen input computer, a mobile computer, an e-book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, a liquid crystal TV, a portable cleaner, a portable CD player, a minidisc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a moped, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flash, a camera, a large household battery, and a lithium-ion capacitor, etc.

[0069] Examples

[0070] Hereinafter, examples and comparative examples are given to more specifically illustrate the embodiments of the present application. Various tests and evaluations are carried out according to the following methods. In addition, unless otherwise specified, "parts" and "%" are based on mass.

[0071] Testing method and device:

[0072] First coating thickness test:

[0073] Disassemble the lithium-ion battery in the example or comparative example to obtain the positive electrode sheet. Perform plasma longitudinal cutting on the positive electrode sheet along the thickness direction, polish it using argon ion polishing technology to obtain a flat cross-section, then observe the above cross-section using a scanning electron microscope (model: OXFORD·EDS), measure the thickness of the first coating at 15 test points in the uncoated area, with an interval of 2 mm between adjacent test points. After taking the average of the thicknesses of the first coating at the 15 test points in the uncoated area, it is the thickness D1 of the first coating in the uncoated area; measure the thickness of the first coating at 15 test points in the coated area, with an interval of 2 mm between adjacent test points. After taking the average of the thicknesses of the first coating at the 15 test points in the coated area, it is the thickness D2 of the first coating in the coated area. Calculate the value of D1 - D2.

[0074] Average particle size test of ceramic particles:

[0075] Charge the lithium-ion battery at a constant current of 0.5C to 4.35V, and then charge it at a constant voltage of 4.35V to 0.05C. At this time, the lithium-ion battery reaches a fully charged state. Disassemble the fully charged lithium-ion battery to obtain the positive electrode sheet. Perform plasma longitudinal cutting on the positive electrode sheet along the thickness direction, polish it using argon ion polishing technology to obtain a flat cross-section, then observe the above cross-section using a scanning electron microscope (model: OXFORD·EDS), measure the size of the ceramic particles in the first coating, and take the average of the diameter sizes at 30 test points as the average particle size d of the ceramic particles.

[0076] Stud penetration test:

[0077] Take 10 lithium-ion batteries from each group of examples or comparative examples and fully charge them in an environment of 25 ± 3°C. The specific steps are as follows: Charge the lithium-ion battery at a constant current of 0.5C to 4.35V, and then charge it at a constant voltage of 4.35V to 0.05C.

[0078] Perform a stud penetration test on the lithium-ion battery under the condition of 25 ± 3°C. Use a steel stud with a diameter of 4 mm, made of carbon steel, a taper of 16.5 mm, and a total length of 100 mm. Perform the stud penetration test from the center position of the plane formed by the length and width of the lithium-ion battery, set the stud penetration speed to 150 mm / s, and stop the stud penetration after the steel stud passes through the lithium-ion battery. Then observe the state of the lithium-ion battery for 5 minutes. Taking the non-combustion and non-explosion of the lithium-ion battery as the judgment standard, the passing rate (%) of the stud penetration test = the number of lithium-ion batteries that do not burn and do not explode in the stud penetration test / 10 × 100%.

[0079] The safety performance of lithium-ion batteries is characterized by the passing rate of the nail penetration test of lithium-ion batteries. The higher the passing rate of the nail penetration test of lithium-ion batteries, the better the safety performance of lithium-ion batteries.

[0080] First coating electrode sheet resistance test:

[0081] Test equipment: The equipment used is the electrode sheet resistor BER2500 produced by Yuanneng Technology.

[0082] Test conditions: Under 400 kgf, keep the pressure for 15 s and record the resistance data.

[0083] The first coating slurry prepared in each example or comparative example was coated on the surface of a 9-μm-thick positive current collector aluminum foil with the coating weight CW1 in the uncoated area shown in Table 1. After drying at 120 °C for 12 h, a positive current collector with a single-sided first coating was obtained. It was cut into 12 first coating samples with a size of 5 cm × 5 cm. Then, the first coating samples were placed on the sample stage of the electrode sheet resistor to measure the electrode sheet resistance of the first coating. One electrode sheet resistance of the first coating was obtained for each first coating sample, and the average value of the test results was taken to obtain the first coating electrode sheet resistance R1.

[0084] Taking the coating weight CW1 of the first coating in the uncoated area of Examples 1-3 to 1-6 as the abscissa and the first coating electrode sheet resistance R1 obtained by testing as the ordinate, a curve was fitted to obtain Figure 2 . From Figure 2 it can be seen the influence of different coating weights of the first coating in the uncoated area on the first coating electrode sheet resistance R1.

[0085] Cold-pressed positive electrode sheet film resistance test:

[0086] Test equipment: The equipment used is the electrode sheet resistor BER2500 produced by Yuanneng Technology.

[0087] Test conditions: Under 400 kgf, keep the pressure for 15 s and record the resistance data.

[0088] Take the cold-pressed positive electrode sheets prepared in each example or comparative example, cut out 12 positive electrode sheet samples with a size of 5 cm × 5 cm from the cold-pressed positive electrode sheets, place the positive electrode sheet samples on the sample stage of the electrode sheet resistor, and one film resistance was obtained for each positive electrode sheet sample. The average value of the test results was taken to obtain the cold-pressed positive electrode sheet film resistance R2.

[0089] Taking the coating weight CW1 of the first coating in the uncoated area of Examples 1-3 to 1-6 as the abscissa and the cold-pressed positive electrode sheet film resistance R2 obtained by testing as the ordinate, a curve was fitted to obtain Figure 3 . From Figure 3It can be seen the influence of different coating weights of the first coating in the uncoated area on the film resistance R2 of the cold-pressed positive electrode sheet.

[0090] Full charge time test of lithium-ion battery:

[0091] Discharge the lithium-ion battery at a constant current of 0.5C until 3.0V. At this time, the lithium-ion battery reaches the full discharge state, then charge it at a constant current of 3C until 4.35V, and then charge it at a constant voltage of 4.35V until 0.05C. At this time, the lithium-ion battery reaches the full charge state. Measure the charging time and record it as the full charge time of the lithium-ion battery.

[0092] Use the full charge time of the lithium-ion battery to characterize the rate performance of the lithium-ion battery. The shorter the full charge time of the lithium-ion battery, the better the rate performance of the lithium-ion battery.

[0093] Example 1-1

[0094] <Preparation of positive electrode sheet>

[0095] Mix ceramic particle boehmite, the first binder sodium polyacrylate and the first conductive agent Super P according to a mass ratio of 85:10:5, add pure water as the first solvent, and stir evenly to obtain a first coating slurry with a solid content of 45wt%. Then coat the first coating slurry on the second surface of the positive electrode current collector aluminum foil with a thickness of 9μm at a coating weight of 3mg / 1540.25mm 2 and dry it at 120°C for 12h to obtain a positive electrode sheet with the first coating coated on the second surface. Then reserve an uncoated area with a length of 15cm on the first surface of the aluminum foil, repeat the above steps in the coated area on the first surface to obtain a positive electrode sheet with the first coating coated in the coated area on the first surface. Then coat the uncoated area reserved on the first surface of the aluminum foil at a coating weight of 9mg / 1540.25mm 2Coat the first coating slurry with a coating weight, and after drying at 120 °C, a positive electrode sheet with a double-sided first coating is obtained. Mix the positive electrode active material lithium cobaltate, the second conductive agent Super P, and the second binder polyvinylidene fluoride in a mass ratio of 97.6:1.1:1.3, add N-methylpyrrolidone (NMP) as the positive electrode solvent, and stir evenly with a vacuum mixer to obtain a positive electrode material layer slurry with a solid content of 75 wt%. Coat the positive electrode material layer slurry evenly on the surface of the first coating in the coating area, and after drying at 120 °C, a positive electrode sheet with a double-sided first coating and a first surface-coated positive electrode material layer is obtained. Then, coat the positive electrode material layer slurry on the surface of the first coating on the second surface of the positive electrode current collector, and after drying at 120 °C, a positive electrode sheet with a double-sided first coating and a positive electrode material layer is obtained. Then, after cold pressing, cutting, and welding the tabs, bake at 85 °C under vacuum conditions for 12 h to obtain a positive electrode sheet with a specification of 74 mm × 1350 mm for use. Among them, the length L of the positive electrode current collector is 135 cm, the length x of the uncoated area is 15 cm, and the coating weight of the positive electrode material layer is 267.8 mg / 1540.25 mm 2 , and the thickness of the single-sided positive electrode material layer after cold pressing is 45.55 μm.

[0096] <Preparation of negative electrode sheet>

[0097] Mix the negative electrode active material artificial graphite, the second binder styrene-butadiene rubber (SBR), and the second binder carboxymethyl cellulose (CMC) in a mass ratio of 97.6:1.1:1.3, then add deionized water as the negative electrode solvent, and stir evenly with a vacuum mixer to obtain a negative electrode material layer slurry with a solid content of 70 wt%. Coat the negative electrode material layer slurry evenly on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dry at 120 °C to obtain a negative electrode sheet with a single-sided negative electrode material layer. The coating weight of the negative electrode material layer is 142 mg / 1540 mm 2 . Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided negative electrode material layer. After drying at 120 °C, cold press, then cut and weld the tabs to obtain a negative electrode sheet with a specification of 78 mm × 1351 mm for use. Among them, the thickness of the single-sided negative electrode material layer after cold pressing is 60 μm.

[0098] <Preparation of electrolyte>

[0099] In a glove box under an argon atmosphere with a water content of less than 10 ppm, mix ethylene carbonate (EC), propylene carbonate (PC), and diethyl carbonate (DEC) evenly in a mass ratio of 1:3:6 to obtain a basic solvent, add the lithium salt LiPF6 and stir evenly to obtain an electrolyte. Among them, based on the total mass of the electrolyte, the mass percentage content of the lithium salt is 12.5%, and the balance is the basic solvent.

[0100] <Separator film>

[0101] Use a polyethylene porous polymer film with a thickness of 8 μm as the separator film.

[0102] <Preparation of lithium-ion battery>

[0103] Stack the positive electrode sheet, separator film, negative electrode sheet, and separator film in sequence, with the separator film in the middle of the positive electrode sheet and the negative electrode sheet to play a role in isolation, and wind them to obtain an electrode assembly. Put the electrode assembly into an aluminum-plastic film packaging bag, remove moisture at 80 °C, inject the prepared electrolyte, and obtain a lithium-ion battery through vacuum packaging, standing, forming, and shaping processes. Among them, the upper limit voltage of forming is 4.35 V, the forming temperature is 85 °C, and the forming time is 50 min.

[0104] Examples 1-2 to Examples 1-15

[0105] Except that in the <Preparation of positive electrode sheet>, the coating amount of the first coating slurry in the uncoated area and the coating amount of the first coating slurry in the coated area are adjusted, so that the coating weight CW1 of the first coating in the uncoated area and the coating weight CW2 of the first coating in the coated area are as shown in Table 1, and the thickness D1 of the first coating in the uncoated area and the thickness D2 of the first coating in the coated area change accordingly, the rest is the same as Example 1-1.

[0106] Example 1-16

[0107] Except for preparing the positive electrode sheet and the negative electrode sheet according to the following method, the rest is the same as Example 1-1.

[0108] <Preparation of positive electrode sheet>

[0109] Mix ceramic particle boehmite, first binder sodium polyacrylate, and first conductive agent Super P according to a mass ratio of 85:10:5, add pure water as the first solvent, and stir evenly to obtain a first coating slurry with a solid content of 45 wt%. Then coat the first coating slurry on the second surface of a positive electrode current collector aluminum foil with a thickness of 9 μm at a coating weight of 3 mg / 1540.25 mm 2 and dry it at 120 °C for 12 h to obtain a positive electrode sheet with the first coating on the second surface. Then leave an uncoated area with a length of 12 cm on the first surface of the aluminum foil, and repeat the above steps in the coated area on the first surface to obtain a positive electrode sheet with the first coating in the coated area on the first surface. Then coat the uncoated area reserved on the first surface of the aluminum foil at a coating weight of 9 mg / 1540.25 mm 2Coat the first coating slurry with a coating weight, and after drying at 120 °C, a positive electrode sheet with a double-sided first coating is obtained. Mix the positive active material lithium cobaltate, the second conductive agent Super P, and the second binder polyvinylidene fluoride according to a mass ratio of 97.6:1.1:1.3, add N-methylpyrrolidone (NMP) as the positive electrode solvent, and stir evenly with a vacuum mixer to obtain a positive electrode material layer slurry with a solid content of 75 wt%. Coat the positive electrode material layer slurry evenly on the surface of the first coating in the coating area, and after drying at 120 °C, a positive electrode sheet with a double-sided first coating and a first surface-coated positive electrode material layer is obtained. Then, coat the positive electrode material layer slurry on the surface of the first coating on the second surface of the positive electrode current collector, and after drying at 120 °C, a positive electrode sheet with a double-sided first coating and a positive electrode material layer is obtained. Then, after cold pressing, slitting, and welding the tabs, bake at 85 °C under vacuum for 12 h to obtain a positive electrode sheet with a specification of 74 mm × 2400 mm for use. Among them, the length L of the positive electrode current collector is 240 cm, the length x of the uncoated area is 12 cm, and the coating weight of the positive electrode material layer is 267.8 mg / 1540.25 mm 2 , and the thickness of the single-sided positive electrode material layer after cold pressing is 45.55 μm.

[0110] <Preparation of negative electrode sheet>

[0111] Mix the negative active material artificial graphite, the second binder styrene-butadiene rubber (SBR), and the second binder carboxymethyl cellulose (CMC) according to a mass ratio of 97.6:1.1:1.3, then add deionized water as the negative electrode solvent, and stir evenly with a vacuum mixer to obtain a negative electrode material layer slurry with a solid content of 70 wt%. Coat the negative electrode material layer slurry evenly on one surface of a negative electrode current collector copper foil with a thickness of 6 μm, and dry at 120 °C to obtain a negative electrode sheet with a single-sided coating of the negative electrode material layer. The coating weight of the negative electrode material layer is 142 mg / 1540 mm 2 . Then repeat the above steps on the other surface of the copper foil to obtain a negative electrode sheet with a double-sided coating of the negative electrode material layer. After drying at 120 °C, cold press, then slit and weld the tabs to obtain a negative electrode sheet with a specification of 78 mm × 2410 mm for use. Among them, the thickness of the single-sided negative electrode material layer after cold pressing is 60 μm.

[0112] Examples 1-17

[0113] Except for adjusting the relevant preparation parameters according to Table 1 in <Preparation of positive electrode sheet>, the rest are the same as in Examples 1-16

[0114] Examples 1-18

[0115] Except for adjusting the relevant preparation parameters according to Table 1 in <Preparation of positive electrode sheet>, the rest are the same as in Example 1-1.

[0116] Examples 2-1 to 2-10

[0117] Except for regulating the relevant preparation parameters according to Table 2 in the <Preparation of Positive Electrode Sheets>, the rest is the same as in Example 1-1.

[0118] Comparative Example 1

[0119] Except for preparing the positive electrode sheet according to the following method, the rest is the same as in Example 1-1.

[0120] <Preparation of Positive Electrode Sheets>

[0121] Mix the positive active material lithium cobaltate, the second conductive agent Super P, and the second binder polyvinylidene fluoride in a mass ratio of 97.6:1.1:1.3, add N-methylpyrrolidone (NMP) as the positive electrode solvent, and stir evenly by a vacuum mixer to obtain a positive electrode material layer slurry with a solid content of 75 wt%. Coat the positive electrode material layer slurry evenly on one surface of a positive electrode current collector aluminum foil with a thickness of 9 μm, and dry it at 120 °C to obtain a positive electrode sheet with a single-sided coated positive electrode material layer. Then repeat the above steps on the other surface of the aluminum foil to obtain a positive electrode sheet with a double-sided coated positive electrode material layer. Then, after cold pressing, cutting, and welding the tab, bake it in a vacuum at 85 °C for 12 h to obtain a positive electrode sheet with a specification of 74 mm × 1350 mm for use. Among them, the length L of the positive electrode current collector is 135 cm, and the coating weight of the positive electrode material layer is 267.8 mg / 1540.25 mm 2 , and the thickness of the single-sided positive electrode material layer after cold pressing is 45.55 μm.

[0122] Comparative Examples 2 and 3

[0123] Except for regulating the coating amount of the first coating slurry in the uncoated area and the coating amount of the first coating slurry in the coated area in the <Preparation of Positive Electrode Sheets> so that the coating weight CW1 of the first coating in the uncoated area and the coating weight CW2 of the first coating in the coated area are as shown in Table 1, and the thickness D1 of the first coating in the uncoated area and the thickness D2 of the first coating in the coated area change accordingly, the rest is the same as in Example 1-1.

[0124] Comparative Example 4

[0125] Except for preparing the positive electrode sheet according to the following method, the rest is the same as in Example 1-1.

[0126] <Preparation of Positive Electrode Sheets>

[0127] Mix ceramic particles boehmite, the first binder sodium polyacrylate, and the first conductive agent Super P in a mass ratio of 85:10:5. Add pure water as the first solvent and stir evenly to obtain a first coating slurry with a solid content of 45 wt%. Reserve an uncoated area with a length of 15 cm on the first surface of the aluminum foil, and coat the first coating slurry at a coating weight of 24.64 mg / 1540.25 mm 2 on the reserved uncoated area. After drying at 120 °C, a positive electrode sheet with the first coating only coated on the uncoated area is obtained. Mix the positive electrode active material lithium cobaltate, the second conductive agent Super P, and the second binder polyvinylidene fluoride in a mass ratio of 97.6:1.1:1.3. Add N-methylpyrrolidone (NMP) as the positive electrode solvent and stir evenly with a vacuum mixer to obtain a positive electrode material layer slurry with a solid content of 75 wt%. Coat the positive electrode material layer slurry evenly on the surface of the positive electrode current collector in the coated area. After drying at 120 °C, a positive electrode sheet with the positive electrode material layer coated on the first surface and the first coating only coated on the uncoated area is obtained. Then coat the positive electrode material layer slurry on the second surface of the positive electrode current collector. After drying at 120 °C, a positive electrode sheet with the positive electrode material layer coated on both sides and the first coating only coated on the uncoated area is obtained. Then, through cold pressing, slicing, welding the tab, and baking in a vacuum at 85 °C for 12 h, a positive electrode sheet with a specification of 74 mm × 1350 mm is obtained for use. Among them, the length L of the positive electrode current collector is 135 cm, the length x of the uncoated area is 15 cm, and the coating weight of the positive electrode material layer is 267.8 mg / 1540.25 mm 2 , and the thickness of the single-sided positive electrode material layer after cold pressing is 45.55 μm.

[0128] Comparative Example 5

[0129] Except for preparing the positive electrode sheet according to the following method, the rest is the same as in Examples 1-1.

[0130] <Preparation of Positive Electrode Sheet>

[0131] Mix ceramic particles boehmite, the first binder sodium polyacrylate, and the first conductive agent Super P in a mass ratio of 85:10:5. Add pure water as the first solvent and stir evenly to obtain a first coating slurry with a solid content of 45 wt%. Then coat the first coating slurry at 9.24 mg / 1540.25 mm 2The coating weight is coated on the second surface of the positive current collector aluminum foil with a thickness of 9 μm, and after drying at 120 °C for 12 h, a positive electrode sheet with the first coating on the second surface is obtained. Then, an uncoated area with a length of 15 cm is reserved on the first surface of the aluminum foil, and the above steps are repeated in the coated area on the first surface to obtain a positive electrode sheet with the coated area and the first coating on the second surface. The positive active material lithium cobaltate, the second conductive agent Super P, and the second binder polyvinylidene fluoride are mixed according to a mass ratio of 97.6:1.1:1.3, and N-methylpyrrolidone (NMP) is added as the positive electrode solvent. After being stirred evenly by a vacuum mixer, a positive electrode material layer slurry with a solid content of 75 wt% is obtained. The positive electrode material layer slurry is evenly coated on the surface of the first coating in the coated area, and after drying at 120 °C, a positive electrode sheet with the coated area, the first coating on the second surface, and the positive electrode material layer coated on the coated area is obtained. Then, the positive electrode material layer slurry is coated on the surface of the first coating on the second surface of the positive current collector, and after drying at 120 °C, a positive electrode sheet with the coated area, the first coating, and the positive electrode material layer on the second surface is obtained. Then, it is cold-pressed, sliced, and the tab is welded, and baked at 85 °C under vacuum for 12 h to obtain a positive electrode sheet with a specification of 74 mm × 1350 mm for use. Among them, the length L of the positive current collector is 135 cm, the length x of the uncoated area is 15 cm, and the coating weight of the positive electrode material layer is 267.8 mg / 1540.25 mm 2 , and the thickness of the single-sided positive electrode material layer after cold pressing is 45.55 μm.

[0132] The preparation parameters and performance test results of each example and comparative example are shown in Table 1 and Table 2.

[0133]

[0134] As can be seen from Examples 1-1 to 1-18 and Comparative Examples 1 to 5, the positive electrode tab of the lithium-ion battery in the embodiments of the present application includes a first coating. By controlling the thickness D1 of the first coating in the uncoated area and the value of D1-D2 within the scope of the present application, the lithium-ion battery obtained has a relatively high passing rate in the nail penetration test and a short full charge time, indicating that the safety performance of the lithium-ion battery in the embodiments of the present application is improved, and at the same time, it has good rate performance. In Comparative Example 1, the positive electrode tab of the lithium-ion battery does not include the first coating, and the obtained lithium-ion battery has a relatively low passing rate in the nail penetration test, indicating that the lithium-ion battery in Comparative Example 1 cannot balance good safety performance and rate performance. In Comparative Examples 2 to 4, the value of the thickness D1 of the first coating in the uncoated area and / or D1-D2 is not within the scope of the present application, and the obtained lithium-ion battery has a relatively low passing rate in the nail penetration test or a long full charge time, indicating that the lithium-ion batteries in Comparative Examples 2 to 4 cannot balance good safety performance and rate performance. In Comparative Example 5, the first coating is not provided in the uncoated area and the value of D1-D2 is not within the scope of the present application, and the obtained lithium-ion battery has a relatively low passing rate in the nail penetration test, indicating that the lithium-ion battery in Comparative Example 5 cannot balance good safety performance and rate performance.

[0135] The thickness D2 of the first coating in the coated area usually affects the safety performance of the lithium-ion battery. As can be seen from Examples 1-1, 1-2, 1-11 to 1-15, when the value of D2 is within the scope of the present application, the obtained lithium-ion battery has a relatively high passing rate in the nail penetration test and a short full charge time, indicating that the safety performance of the lithium-ion battery is improved, and at the same time, it has good rate performance.

[0136] The coating weight CW1 of the first coating in the uncoated area usually affects the safety performance of the lithium-ion battery. As can be seen from Examples 1-1 to 1-11 and 1-15, when the value of CW1 is within the scope of the present application, the obtained lithium-ion battery has a relatively high passing rate in the nail penetration test and a short full charge time, indicating that the safety performance of the lithium-ion battery is improved, and at the same time, it has good rate performance.

[0137] The coating weight CW2 of the first coating in the coated area usually affects the safety performance of the lithium-ion battery. As can be seen from Examples 1-1, 1-2, 1-11 to 1-15, when the value of CW2 is within the scope of the present application, the obtained lithium-ion battery has a relatively high passing rate in the nail penetration test and a short full charge time, indicating that the safety performance of the lithium-ion battery is improved, and at the same time, it has good rate performance.

[0138] The value of CW1 - CW2 usually affects the safety performance of lithium - ion batteries. It can be seen from Examples 1 - 1 to 1 - 15 that when the value of CW1 - CW2 is within the scope of this application, the passing rate of the nail - penetration test of the obtained lithium - ion battery is relatively high and the full - charge time is relatively short, indicating that the safety performance of the lithium - ion battery is improved and it also has good rate performance.

[0139] From Figure 2 it can be seen that the resistance R1 of the first - coated electrode increases with the increase of the coating weight CW1 of the first coating in the uncoated area. From Figure 3 it can be seen that the membrane resistance R2 of the cold - pressed positive - electrode sheet increases with the increase of the coating weight CW1 of the first coating in the uncoated area.

[0140] The value of x / L usually affects the safety performance and rate performance of lithium - ion batteries. It can be seen from Examples 1 - 1, 1 - 16 to 1 - 18 that when the value of x / L is within the scope of this application, the passing rate of the nail - penetration test of the obtained lithium - ion battery is relatively high and the full - charge time is relatively short, indicating that the safety performance and rate performance of the lithium - ion battery are improved.

[0141] Table 2

[0142]

[0143] The value of d usually affects the safety performance of lithium - ion batteries. It can be seen from Examples 1 - 1, 2 - 1 to 2 - 4 that when the value of d is within the scope of this application, the passing rate of the nail - penetration test of the obtained lithium - ion battery is relatively high and the full - charge time is relatively short, indicating that the safety performance of the lithium - ion battery is improved and it also has good rate performance.

[0144] The type of ceramic particles and the value of W1 usually affect the safety performance of lithium - ion batteries. It can be seen from Examples 1 - 1, 2 - 5 to 2 - 7 that when the type of ceramic particles and the value of W1 are within the scope of this application, the passing rate of the nail - penetration test of the obtained lithium - ion battery is relatively high and the full - charge time is relatively short, indicating that the safety performance of the lithium - ion battery is improved and it also has good rate performance.

[0145] The type of the first binder and the value of W2 usually affect the safety performance of lithium - ion batteries. It can be seen from Examples 1 - 1, 2 - 5 to 2 - 6, 2 - 8 to 2 - 9 that when the type of the first binder and the value of W2 are within the scope of this application, the passing rate of the nail - penetration test of the obtained lithium - ion battery is relatively high and the full - charge time is relatively short, indicating that the safety performance of the lithium - ion battery is improved and it also has good rate performance.

[0146] The type of the first conductive agent and the value of W3 generally affect the safety performance of the lithium-ion battery. It can be seen from Examples 1-1, 2-5 to 2-6, and 2-10 that when the type of the first conductive agent and the value of W3 are within the scope of the present application, the passing rate of the nail penetration test of the obtained lithium-ion battery is relatively high and the full charge time is relatively short, indicating that the safety performance of the lithium-ion battery is improved and it has good rate performance at the same time.

[0147] It should be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that a process, method or article including a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method or article.

[0148] Each embodiment in this specification is described in a related manner. For the same or similar parts among the embodiments, reference can be made to each other. The differences between each embodiment and other embodiments are emphasized.

[0149] The above are only the preferred embodiments of the present application and are not intended to limit the present application. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present application shall be included within the scope of protection of the present application.

Claims

1. An electrochemical device, which includes a wound electrode assembly, and the electrode assembly includes a positive electrode tab, and the positive electrode tab includes a positive electrode current collector, a first coating layer, and a positive electrode material layer; Among them, The surface of the positive electrode current collector facing away from the winding center is the first surface; along the winding direction of the positive electrode tab, the first surface includes a connected coating area and an uncoated area, the coating area is provided with the first coating layer and the positive electrode material layer, and the first coating layer is disposed between the positive electrode current collector and the positive electrode material layer; the uncoated area is provided with the first coating layer, and the uncoated area is located in the outermost circle of the positive electrode current collector; The thickness of the first coating layer in the uncoated area is D1 μm, the thickness of the first coating layer in the coating area is D2 μm, 0.9 ≤ D1 ≤ 6, 0 ≤ D1 - D2 ≤ 3.

6.

2. The electrochemical device according to claim 1, wherein, 0.9≤D2≤3。 3. The electrochemical device according to claim 1, wherein, The coating weight of the first coating in the uncoated area is CW1 mg / 1540.25mm 2 , where 3 ≤ CW1 ≤ 14.

4. The electrochemical device according to claim 3, wherein, The coating weight of the first coating in the coating area is CW2 mg / 1540.25mm 2 , where 3 ≤ CW2 ≤ 8.

5. The electrochemical device according to claim 4, wherein, 0 ≤ CW1 - CW2 ≤ 6.

6. The electrochemical device according to claim 1, wherein, Along the length direction of the positive electrode tab after being unfolded, the length of the uncoated area is x cm, and the length of the positive electrode current collector is L cm, 0.07 ≤ x / L ≤ 0.

12.

7. The electrochemical device according to claim 1, wherein, Along the winding direction of the positive electrode tab, the first coating layer in the uncoated area connects the first coating layer in the coating area and the positive electrode material layer; along the width direction of the positive electrode tab after being unfolded, the width of the first coating layer in the uncoated area is the same as the width of the positive electrode material layer in the coating area.

8. The electrochemical device according to claim 1, wherein, The first coating layer includes ceramic particles, and the ceramic particles include at least one of alumina, boehmite, silica, zirconia, titanium dioxide, magnesium oxide, zinc oxide, or calcium oxide; based on the mass of the first coating layer, the mass percentage content of the ceramic particles is W1%, 80 ≤ W1 ≤ 99.

2.

9. The electrochemical device according to claim 8, wherein The average particle size of the ceramic particles is d nm, 100 ≤ d ≤ 1500.

10. The electrochemical device according to claim 9, wherein, 200≤d≤500。 11. The electrochemical device according to claim 8, wherein, The first coating layer further includes a first binder, and the first binder includes at least one of polyacrylic acid-based binders, styrene-acrylic binders, or styrene-butadiene rubber-based binders; based on the mass of the first coating layer, the mass percentage content of the first binder is W2%, 0.6 ≤ W2 ≤ 10.

12. The electrochemical device according to claim 11, wherein, The first coating layer further includes a first conductive agent, and the first conductive agent includes at least one of conductive carbon black, artificial graphite, activated carbon, carbon nanotubes, or carbon nanofibers; based on the mass of the first coating layer, the mass percentage content of the first conductive agent is W3%, 0.2 ≤ W3 ≤ 10.

13. An electronic device, which includes the electrochemical device according to any one of claims 1 to 12.

Images