Electrochemical and Electronic Devices

Abstract

The present invention provides an electrochemical device and an electronic device. The electrochemical device includes a positive electrode piece, which includes a positive electrode current collector, a positive electrode active material layer, and a positive electrode coating layer. The positive electrode current collector includes a first region, a second region, and a third region. The positive electrode active material layer includes a first portion, a second portion, and a third portion provided in the first region, the second region, and the third region, respectively. The positive electrode coating layer includes a fourth portion and a fifth portion provided in the first region and the second region, respectively. The combined impedance of the first portion and the fourth portion is greater than the impedance of the third portion, and the combined impedance of the second portion and the fifth portion is greater than the impedance of the third portion. The present invention optimizes the uniformity of lithium absorption during the charging process of the electrode piece, improves lithium deposition issues at the edge of the electrode piece, and widens the lithium deposition window, thereby improving the rate performance of the electrochemical device.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS The present invention is based on a Chinese patent application having application number 202110662766.6, filing date June 15, 2021, and title "Electrochemical Device and Electronic Device", and claims priority to the Chinese patent application, the entire contents of which are incorporated herein by reference. The present invention relates to the field of electrochemical energy storage, in particular to electrochemical and electronic devices. [Background technology]

[0002] During charging and discharging of an electrochemical device (e.g., a lithium ion battery), there is a difference in dynamic performance between the edge region and the middle region of the pole piece, particularly during a fast charging process. The edge region is prone to lithium deposition during a high-power fast charging process, which limits the improvement of the fast charging performance of the electrochemical device. Summary of the Invention

[0003] An embodiment of the present invention provides an electrochemical device, the electrochemical device including a positive electrode piece, the positive electrode piece including a positive electrode current collector, a positive electrode active material layer, and a positive electrode coating layer. The positive electrode current collector includes a first region, a second region, and a third region located between the first region and the second region along the width direction of the positive electrode piece. The positive electrode active material layer includes a first positive electrode active material, and the positive electrode active material layer includes a first portion, a second portion, and a third portion provided in the first region, the second region, and the third region, respectively. The positive electrode coating layer includes a fourth portion and a fifth portion provided in the first region and the second region, respectively. The fourth portion is located between the first portion and the first region, or the first portion is located between the fourth portion and the first region. The fifth portion is located between the second portion and the second region, or the second portion is located between the fifth portion and the second region. The combined impedance of the first and fourth portions is greater than the impedance of the third portion, and the combined impedance of the second and fifth portions is greater than the impedance of the third portion.

[0004] In some embodiments, the ratio of the combined impedance of the fourth portion and the first portion to the impedance of the third portion is 1.02 to 5, and the ratio of the combined impedance of the fifth portion and the second portion to the impedance of the third portion is 1.02 to 5. In some embodiments, the ratio of the width of the fourth portion to the width of the positive electrode active material layer is 0.01 to 0.25, and the ratio of the width of the fifth portion to the width of the positive electrode active material layer is 0.01 to 0.25. In some embodiments, the thickness of the fourth portion is more than 0.5 μm and less than 8 μm. In some embodiments, the thickness of the fifth portion is more than 0.5 μm and less than 8 μm. In some embodiments, the thickness of the third portion is more than 20 μm and less than 200 μm. In some embodiments, the positive electrode coating layer includes at least one of conductive carbon, ceramic, and lithium iron phosphate and a first binder. In some embodiments, the mass content of the first binder in the positive electrode coating layer is more than 20%. In some embodiments, the first binder comprises at least one of polyvinylidene fluoride, copolymers of vinylidene fluoride-fluorinated olefin, polyvinylpyrrolidone, polyacrylonitrile, polymethylacrylate, polytetrafluoroethylene, sodium carboxymethylcellulose, styrene butadiene rubber, polyurethane, fluorinated rubber, and polyvinyl alcohol. In some embodiments, the conductive carbon comprises at least one of conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black, and nanocarbon fibers. In some embodiments, the combined thickness of the first portion and the fourth portion is the same as the thickness of the third portion, and the combined thickness of the second portion and the fifth portion is the same as the thickness of the third portion.

[0005] Another embodiment of the present invention provides an electrochemical device, the electrochemical device including a negative electrode piece, the negative electrode piece including a negative electrode current collector, a negative electrode active material layer, and a negative electrode coating layer. The negative electrode current collector includes a first region, a second region, and a third region located between the first region and the second region along the width direction of the negative electrode piece. The negative electrode active material layer includes a first negative electrode active material, and the negative electrode active material layer includes a first portion, a second portion, and a third portion provided in the first region, the second region, and the third region, respectively. The negative electrode coating layer is located between the third portion and the third region, or the third portion is located between the negative electrode coating layer and the third region. The combined impedance of the negative electrode coating layer and the third portion is greater than the impedance of the first portion and greater than the impedance of the second portion.

[0006] In some embodiments, the ratio of the impedance of the first portion to the combined impedance of the negative electrode coating layer and the third portion is 0.5 to 0.99, and the ratio of the impedance of the second portion to the combined impedance of the negative electrode coating layer and the third portion is 0.5 to 0.99. In some embodiments, the ratio of the width of the negative electrode coating layer to the width of the negative electrode active material layer is 0.75 to 0.99. In some embodiments, the thickness of the negative electrode coating layer is more than 0.5 μm and less than 8 μm. In some embodiments, the negative electrode coating layer includes at least one of conductive carbon and ceramic and a first binder. In some embodiments, the thickness of the first portion and the thickness of the second portion are both more than 20 μm and less than 200 μm.

[0007] In some embodiments, the mass content of the first binder in the negative electrode coating layer is greater than 20%. In some embodiments, the first binder comprises at least one of polyvinylidene fluoride, copolymers of vinylidene fluoride and fluorinated olefin, polyvinylpyrrolidone, polyacrylonitrile, polymethylacrylate, polytetrafluoroethylene, sodium carboxymethylcellulose, styrene butadiene rubber, polyurethane, fluorinated rubber, and polyvinyl alcohol. In some embodiments, the conductive carbon comprises at least one of conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black, and nanocarbon fibers. In some embodiments, the combined thickness of the third portion and the negative electrode coating layer is the same as the thickness of the first portion, and the combined thickness of the third portion and the negative electrode coating layer is the same as the thickness of the second portion.

[0008] In some embodiments of the present invention, there is provided an electronic device comprising any of the electrochemical devices described above.

[0009] In the embodiment of the present invention, the positive electrode coating layer is provided on the positive electrode piece, or the negative electrode coating layer is provided on the negative electrode piece, thereby optimizing the uniformity of lithium absorption during the charging process of the electrode piece, improving the lithium deposition problem at the edge of the electrode piece, and widening the lithium deposition window, which is favorable to improving the rate performance of the electrochemical device. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 shows a cross-sectional view of a positive pole piece 10 of an electrochemical device according to some embodiments of the present invention, taken along a plane defined by its width and thickness directions. [Diagram 2] FIG. 2 shows a cross-sectional view of a positive pole piece 10 of an electrochemical device according to another embodiment of the invention, taken along a plane defined by its width and thickness directions. [Diagram 3]FIG. 3 shows a cross-sectional view of a negative pole piece 12 of an electrochemical device according to some embodiments of the present invention, taken along a plane defined by its width and thickness directions. [Figure 4] FIG. 4 shows a cross-sectional view of a negative pole piece 12 of an electrochemical device according to another embodiment of the invention, taken along a plane defined by its width and thickness directions. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] The following examples will enable those skilled in the art to more fully understand the present invention, but are not intended to limit the present invention.

[0012] 1 and 2 show cross-sectional views of a positive electrode piece 10 of an electrochemical device according to some embodiments of the present invention along a plane defined by its width and thickness directions. An embodiment of the present invention provides an electrochemical device, and as shown in FIG. 1, the electrochemical device includes a positive electrode piece 10, which includes a positive electrode current collector 101, a positive electrode active material layer 102, and a positive electrode coating layer 103. It should be understood that, although FIG. 1 shows the positive electrode active material layer 102 and the positive electrode coating layer 103 located on both sides of the positive electrode current collector 101, this is merely exemplary, and the positive electrode active material layer 102 and the positive electrode coating layer 103 may be located on only one side of the current collector 101.

[0013] In some embodiments, as shown in FIG. 1, the positive electrode current collector 101 includes a first region 1011, a second region 1012, and a third region 1013 located between the first region 1011 and the second region 1012 along the width direction of the positive electrode piece 10. In some embodiments, the positive electrode active material layer 102 includes a first positive electrode active material, and the positive electrode active material layer 102 includes a first portion 1021, a second portion 1022, and a third portion 1023 provided in the first region 1011, the second region 1012, and the third region 1013, respectively. In some embodiments, the positive electrode coating layer 103 may or may not include a second positive electrode active material, and the positive electrode coating layer 103 includes a fourth portion 1031 and a fifth portion 1032 provided in the first region 1011 and the second region 1012, respectively.

[0014] In some embodiments, as shown in FIG. 1, the first portion 1021 is located between the fourth portion 1031 and the first region 1011. In some embodiments, as shown in FIG. 2, the fourth portion 1031 is located between the first portion 1021 and the first region 1011. In some embodiments, as shown in FIG. 1, the second portion 1022 is located between the fifth portion 1032 and the second region 1012. In some embodiments, as shown in FIG. 2, the fifth portion 1032 is located between the second portion 1022 and the second region 1012. Thus, the difference between FIG. 2 and FIG. 1 is the relative positions of the positive electrode active material layer 102 and the positive electrode coating layer 103, and other details refer to FIG. 1. It should be understood that in FIG. 1, the first region 1011, the second region 1012, and the third region 1013 of the positive electrode collector 101 are divided by dotted lines, and the first portion 1021, the second portion 1022, and the third portion 1023 of the positive electrode active material layer 102 are divided by dotted lines, but in reality there may be no interface, and the entire positive electrode collector 101 may be continuous, or the entire positive electrode active material layer 102 may be continuous.

[0015] In some embodiments, the combined impedance of the first portion 1021 and the fourth portion 1031 is greater than the impedance of the third portion 1023, and the combined impedance of the second portion 1022 and the fifth portion 1032 is greater than the impedance of the third portion 1023. That is, the impedance of the edge region of the positive pole piece 10 is greater than the impedance of the middle region of the positive pole piece 10. This can reduce the release rate of lithium ions from the edge region of the positive pole piece 10 (e.g., the combination of the first portion 1021 and the fourth portion 1031, or the combination of the second portion 1022 and the fifth portion 1032), and can reduce the charging current density of the edge region during the charging process. In contrast, lithium deposition is relatively easy to occur at the edges of the negative electrode pieces, and reducing the charging current density in the edge regions is beneficial to optimizing the uniformity of lithium absorption in the corresponding negative electrode pieces during the charging process, improving the lithium deposition problem at the edges of the negative electrode pieces, widening the lithium deposition window, and thereby improving the rate performance of the electrochemical device.

[0016] The impedance measurement method is as follows, and it may be DC impedance or AC impedance. Regardless of the measurement method, the measured impedance is always within the above impedance range. The specific impedance measurement method is as follows. To measure the DC impedance, the corresponding area to be measured (when measuring the combined impedance of two parts, they are taken out together and measured) is taken out and assembled into a lithium ion battery as a positive electrode. Then, it is attached to New Era to charge and discharge, and the voltage and current of the lithium ion battery are monitored to obtain the DC impedance value of the lithium ion battery. Specifically, the lithium ion battery is charged at a constant current of 0.5C to the full charge voltage, and then charged at a constant voltage of 0.05C. Furthermore, the lithium ion battery is discharged at a current of 1C for 30 minutes to a charge rate of 50%, and the voltage V1 is recorded, and the battery is left to stand for 60 minutes, and the voltage V2 is recorded. Discharge is performed at a current of 0.1C for 10 seconds, and the voltage V3 is recorded. Discharge is performed at a current of 1C for 1 second, and the voltage V4 is recorded. The DC impedance R of the lithium ion battery isT and DCR is calculated using the following formula.

number

[0017] The method for measuring the AC impedance is as follows. The corresponding areas are taken out to make a symmetrical battery in which the positive electrode piece corresponds to the positive electrode piece and the negative electrode piece corresponds to the negative electrode piece. An electrochemical workstation is used to perform EIS measurement on the symmetrical battery, where the measurement temperature is 25°C, the measurement frequency range is 30mHz-500kHz, and the disturbance voltage is 5mV. After obtaining the EIS spectrum, the AC impedance Rz of the symmetrical battery is read from the spectrum.

[0018] In some embodiments, the ratio of the combined impedance of the fourth portion 1031 and the first portion 1011 to the impedance of the third portion 1023 is 1.02 to 5. In some embodiments, the ratio of the combined impedance of the fifth portion 1032 and the second portion 1022 to the impedance of the third portion 1023 is 1.02 to 5. That is, the ratio of the impedance of the edge region of the positive pole piece 10 to the impedance of the middle region is 1.02 to 5. If the impedance difference between the edge region and the middle region is too large, it may affect the rate performance of the middle region (i.e., the third portion 1023), and thus may affect the improvement of the rate performance of the entire electrochemical device.

[0019] In some embodiments, the ratio of the width w1 of the fourth portion 1031 to the width W of the positive electrode active material layer 102 is 0.01 to 0.25. In some embodiments, the ratio of the width w2 of the fifth portion 1032 to the width W of the positive electrode active material layer 102 is 0.01 to 0.25. If this ratio is too small, the effect of improving lithium deposition by the fourth portion 1031 or the fifth portion 1032 is relatively limited, and if this ratio is too large, the overall impedance of the positive electrode piece 10 increases excessively, which is disadvantageous to improving the rate performance of the electrochemical device. In some embodiments, the width w1 of the fourth portion 1031 is the same as the width w2 of the fifth portion 1032 (for example, the following specific examples), but the present invention is not limited thereto, and the width w1 and the width w2 may be different. It should be understood that, due to the existence of an error, the term "same" here means that if the error is within 5%, it can be considered to be "same".

[0020] In some embodiments, the thickness h1 of the fourth portion 1031 is greater than 0.5 μm and less than 8 μm. In some embodiments, the thickness h2 of the fifth portion 1032 is greater than 0.5 μm and less than 8 μm. If the thickness h1 of the fourth portion 1031 or the thickness h2 of the fifth portion 1032 is too small, the effect of improving lithium deposition by the fourth portion 1031 or the fifth portion 1032 is relatively limited, and if the thickness h1 of the fourth portion 1031 or the thickness h2 of the fifth portion 1032 is too large, the overall impedance of the positive electrode piece 10 increases excessively, which is detrimental to the improvement of the rate performance of the electrochemical device. In some embodiments, the thickness h1 of the fourth portion 1031 is the same as the thickness h2 of the fifth portion 1032 (for example, the specific examples below), but the present invention is not limited thereto, and the thickness h1 and the thickness h2 may be different. It should be understood that, due to the existence of an error, the term "same" here means that if the error is within 5%, it can be considered as "same".

[0021] In some embodiments, the thickness of the third portion 1023 is more than 20 μm and less than 200 μm. If the thickness of the third portion 1023 is too small, it is disadvantageous for improving the energy density of the electrochemical device, and if the thickness of the third portion 1023 is too large, the lithium ion transport path of the positive electrode active material layer 102 in the portion close to the positive electrode current collector 101 becomes long, which is disadvantageous for improving the rate performance of the electrochemical device.

[0022] In some embodiments, the positive electrode coating layer 103 includes at least one of conductive carbon, ceramic, and lithium iron phosphate, and a first binder. The conductive carbon is advantageous for increasing the electrical conductivity of the positive electrode coating layer 103. The ceramic is advantageous for increasing the structural strength of the positive electrode coating layer 103. The lithium iron phosphate belongs to the positive electrode active material and is advantageous for improving the energy density of the electrochemical device. The presence of the first binder in the positive electrode coating layer 103 is advantageous for binding various materials in the positive electrode coating layer 103 together.

[0023] In some embodiments, the mass content of the first binder in the positive electrode coating layer 103 is greater than 20%. This can improve the structural stability of the positive electrode coating layer 103, and the positive electrode coating layer 103 is less likely to peel off. In some embodiments, the first binder includes at least one of polyvinylidene fluoride, vinylidene fluoride-fluorinated olefin copolymer, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene butadiene rubber, polyurethane, fluorinated rubber, and polyvinyl alcohol. In some embodiments, the conductive carbon includes at least one of conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black, and nanocarbon fibers.

[0024] In some embodiments, the combined thickness of the first portion 1021 and the fourth portion 1031 is the same as the thickness of the third portion 1023. In some embodiments, the combined thickness of the second portion 1022 and the fifth portion 1032 is the same as the thickness of the third portion 1023. It should be understood that due to the presence of tolerance, the term "same" herein means that the tolerance is within 5% and can be considered to be "same". This allows the combined thickness of the positive electrode active material layer 102 and the positive electrode coating layer to be uniform throughout, which facilitates subsequent processing of the electrochemical device, such as winding or stacking. In some embodiments, after forming a positive electrode active material layer 102 of uniform thickness on a positive electrode current collector 101 and forming a positive electrode coating layer 103, cold pressing can be performed to make the combined thickness of the positive electrode active material layer 102 and the positive electrode coating layer 103 uniform overall, but the compression density is higher in a partial region where the positive electrode active material layer 102 and the positive electrode coating layer 103 are present than in a region where only the positive electrode active material layer 102 is present.

[0025] In some embodiments, the first positive electrode active material and the second positive electrode active material may each independently include at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, and lithium manganese oxide. In some embodiments, the positive electrode active material layer 102 may further include a conductive agent and a binder, and the conductive agent in the positive electrode active material layer 102 may include at least one of conductive carbon black, ketjen black, layered graphite, graphene, carbon nanotubes, and carbon fibers, and the binder in the positive electrode active material layer 102 may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene butadiene rubber, epoxy resin, polyester resin, polyurethane resin, and polyfluorene. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the first binder in the positive electrode active material layer 102 may be (80 to 99): (0.1 to 10): (0.1 to 10). In some embodiments, the positive electrode coating layer 103 may include a conductive agent (e.g., conductive carbon) and a first binder, the mass content of the conductive agent in the positive electrode coating layer 103 may be 30% to 80%, and the mass content of the first binder in the positive electrode coating layer 103 may be 20% to 70%. It should be understood that the above are merely examples, and the positive electrode active material layer 102 may adopt any other suitable materials, thicknesses, and mass ratios.

[0026] In some embodiments, the positive electrode current collector may be an Al foil, and of course, other current collectors commonly used in this field may be used. In some embodiments, the thickness of the positive electrode current collector may be 1 μm to 50 μm.

[0027] As shown in Fig. 3, another embodiment of the present invention provides an electrochemical device, which includes a negative electrode piece 12, and the negative electrode piece 12 includes a negative electrode current collector 121, a negative electrode active material layer 122, and a negative electrode coating layer 123. It should be understood that, although Fig. 3 shows that the negative electrode active material layer 122 and the negative electrode coating layer 123 are located on both sides of the negative electrode current collector 121, this is merely exemplary, and the negative electrode active material layer 122 and the negative electrode coating layer 123 may be located on only one side of the negative electrode current collector 121.

[0028] In some embodiments, the negative electrode current collector 121 includes a first region 1211, a second region 1212, and a third region 1213 located between the first region 1211 and the second region 1212 along the width direction of the negative electrode piece 12. In some embodiments, the negative electrode active material layer 122 includes a first negative electrode active material, and includes a first portion 1221, a second portion 1222, and a third portion 1223 provided in the first region 1211, the second region 1212, and the third region 1213, respectively. In some embodiments, the negative electrode coating layer 123 may or may not include a second negative electrode active material.

[0029] In some embodiments, as shown in FIG. 3, the third portion 1223 is located between the negative electrode coating layer 123 and the third region 1213. In some embodiments, as shown in FIG. 4, the negative electrode coating layer 123 is located between the third portion 1223 and the third region 1213. Therefore, the difference between FIG. 4 and FIG. 3 is that the relative positions of the negative electrode active material layer 122 and the negative electrode coating layer 123 are different, and other details are referred to FIG. 3. It should be understood that in FIG. 3, the first region 1211, the second region 1212, and the third region 1213 of the negative electrode current collector 121 are divided by dotted lines, and the first portion 1221, the second portion 1222, and the third portion 1223 of the negative electrode active material layer 122 are divided by dotted lines, but in reality, there may be no interface, and the entire negative electrode current collector 121 may be continuous, and the entire negative electrode active material layer 122 may be continuous.

[0030] In some embodiments, the combined impedance of the negative electrode coating layer 123 and the third portion 1223 is greater than the impedance of the first portion 1221 and greater than the impedance of the second portion 1222. That is, the impedance of the edge region of the negative electrode piece 12 is smaller than the impedance of the middle region of the negative electrode piece 12. This allows the lithium ion absorption rate of the edge region of the negative electrode piece 12 (e.g., the first portion 1221 or the second portion 1222) to be faster than the middle region of the negative electrode piece 12 (e.g., the combination of the third portion 1223 and the negative electrode coating layer 123). In addition, the edge region of the negative electrode piece is relatively prone to lithium deposition, and the lithium ion absorption rate of the edge region of the negative electrode piece is relatively improved, which is favorable to optimizing the uniformity of lithium absorption of the negative electrode piece 12 during charging, improving the lithium deposition problem of the edge of the negative electrode piece, widening the lithium deposition window, and thereby favoring the rate performance of the electrochemical device.

[0031] In some embodiments, the ratio of the impedance of the first portion 1221 to the combined impedance of the anode coating layer 123 and the third portion 1223 is 0.5 to 0.99. In some embodiments, the ratio of the impedance of the second portion 1222 to the combined impedance of the anode coating layer 123 and the third portion 1223 is 0.5 to 0.99. If the ratio is too small, the effect of improving lithium deposition in the edge region of the anode pole piece 12 is relatively limited.

[0032] In some embodiments, the ratio of the width w of the negative electrode coating layer 123 to the width Y of the negative electrode active material layer 122 is 0.75 to 0.99. If the ratio is too small, the effect of the negative electrode coating layer 123 in improving the uniformity of lithium absorption is relatively limited.

[0033] In some embodiments, the thickness of the negative electrode coating layer 123 is greater than 0.5 μm and less than 8 μm. If the thickness of the negative electrode coating layer 123 is too small, the effect of improving the uniformity of lithium absorption by the negative electrode coating layer 123 is relatively limited. If the thickness of the negative electrode coating layer 123 is too large, it will have too much effect on the overall impedance of the negative electrode piece 12, which will in turn affect the overall rate performance of the electrochemical device.

[0034] In some embodiments, the negative electrode coating layer 123 includes at least one of conductive carbon and ceramic and a second binder. The conductive carbon is advantageous for improving the electrical conductivity of the negative electrode coating layer 123. The ceramic is advantageous for increasing the structural strength of the negative electrode coating layer 123. The presence of the second binder in the negative electrode coating layer 123 is advantageous for binding together various materials in the negative electrode coating layer 123. In some embodiments, the mass content of the second binder in the negative electrode coating layer 123 is greater than 20%. If the mass content of the second binder in the negative electrode coating layer 123 is too small, it is disadvantageous for improving the binding strength of the negative electrode coating layer 123, and the negative electrode coating layer 123 is likely to peel off. In some embodiments, the second binder comprises at least one of polyvinylidene fluoride, vinylidene fluoride-fluorinated olefin copolymer, polyvinylpyrrolidone, polyacrylonitrile, polymethylacrylate, polytetrafluoroethylene, sodium carboxymethylcellulose, styrene butadiene rubber, polyurethane, fluorinated rubber, and polyvinyl alcohol. In some embodiments, the conductive carbon in the anode coating layer 123 comprises at least one of conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black, and nanocarbon fibers.

[0035] In some embodiments, the thickness of the first portion 1221 and the thickness of the second portion 1222 are both greater than 20 μm and less than 200 μm. If the thickness of the first portion 1221 or the thickness of the second portion 1222 is too small, that is, if the thickness of the negative electrode active material layer 122 is too small, it is disadvantageous in improving the energy density of the electrochemical device. If the thickness of the negative electrode active material layer 12 is too large, the lithium ion transport path of the negative electrode active material layer 122 becomes long in the portion close to the negative electrode current collector 121, which is disadvantageous in improving the rate performance of the electrochemical device.

[0036] In some embodiments, the combined thickness of the third portion 1223 and the negative electrode coating layer 123 is the same as the thickness of the first portion 1221. In some embodiments, the combined thickness of the third portion 1223 and the negative electrode coating layer 123 is the same as the thickness of the second portion 1222. It should be understood that due to the presence of tolerance, the term "same" herein means that the tolerance is within 5% and can be considered as "same". This allows the combined thickness of the negative electrode active material layer 122 and the negative electrode coating layer 123 to be generally uniform, which facilitates subsequent processing of the electrochemical device, such as winding or stacking. In some embodiments, after forming the negative electrode active material layer 122 of uniform thickness on the negative electrode current collector 121 and forming the negative electrode coating layer 123, cold pressing can be performed to make the combined thickness of the negative electrode active material layer 122 and the negative electrode coating layer 123 uniform overall, but the compression density is higher in a partial region where the negative electrode active material layer 122 and the negative electrode coating layer 123 are present than in a region where only the negative electrode active material layer 122 is present.

[0037] In some embodiments, the first negative electrode active material and the second negative electrode active material each independently include at least one of graphite, hard carbon, silicon, silicon monoxide, and silicone. In some embodiments, the negative electrode active material layer 122 may further include a conductive agent and a binder, and the conductive agent in the negative electrode active material layer 122 may include at least one of conductive carbon black, ketjen black, layered graphite, graphene, carbon nanotubes, and carbon fibers, and the binder in the negative electrode active material layer 122 may include at least one of carboxymethyl cellulose (CMC), polyacrylic acid, polyvinylpyrrolidone, polyaniline, polyimide, polyamideimide, polysiloxane, styrene butadiene rubber, epoxy resin, polyester resin, polyurethane resin, and polyfluorene. In some embodiments, the mass ratio of the positive electrode active material, the conductive agent, and the binder in the negative electrode active material layer 122 may be (80 to 99):(0.1 to 10):(0.1 to 10). It should be understood that the above are merely examples, and the negative electrode active material layer 122 may adopt any other suitable materials, thicknesses and mass ratios. In some embodiments, the negative electrode coating layer 123 may include a conductive agent (e.g., conductive carbon) and a second binder, the mass content of the conductive agent in the negative electrode coating layer 123 may be 30% to 80%, and the mass content of the second binder in the negative electrode coating layer 123 may be 20% to 70%.

[0038] In some embodiments, the negative electrode current collector may include at least one of a copper foil, a nickel foil, and a carbon-based current collector. In some embodiments, the negative electrode current collector may have a thickness of 1 μm to 50 μm.

[0039] In some embodiments, the electrochemical device may further include a separator located between the positive electrode piece and the negative electrode piece. In some embodiments, the separator includes at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, and aramid. For example, the polyethylene includes at least one selected from the group consisting of high density polyethylene, low density polyethylene, and ultra-high molecular weight polyethylene. In particular, polyethylene and polypropylene have excellent short circuit prevention effects and can improve the stability of the battery due to the shutdown effect. In some embodiments, the thickness of the separator is in the range of about 5 μm to 50 μm.

[0040] In some embodiments, the separator may further include a porous layer on a surface thereof, the porous layer being provided on at least one surface of the separator, the porous layer including inorganic particles and a binder, the inorganic particles being aluminum oxide (Al 2 O 3 ), silicon oxide (SiO 2 ), magnesium oxide (MgO), titanium oxide (TiO 2 ), hafnium dioxide (HfO 2 ), tin oxide (SnO 2 ), cerium oxide (CeO 2 ), Nickel oxide (NiO), Zinc oxide (ZnO), Calcium oxide (CaO), Zirconium oxide (ZrO 2 ), yttrium oxide (Y 2 O 3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. In some embodiments, the pores of the separator have a diameter in the range of about 0.01 μm to 1 μm. The binder contained in the porous layer is at least one selected from the group consisting of polyvinylidene fluoride, copolymers of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylic acid esters, polyacrylic acid, polyacrylates, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethylmethacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The porous layer on the surface of the separator can enhance the heat resistance, oxidation prevention, and electrolyte wettability of the separator, and strengthen the bond between the separator and the pole pieces.

[0041] In some embodiments, the electrochemical device includes a lithium ion battery, but the invention is not limited thereto. In some embodiments, the electrochemical device further includes an electrolyte. The electrolyte can be at least one of a gel electrolyte, a solid electrolyte, and an electrolyte solution, and the electrolyte solution includes a lithium salt and a non-aqueous solvent. The lithium salt can be LiPF 6 , LiBF 4 , LiAsF 6 , LiClO 4 , LiB(C 6 H 5 ) 4 , LiCH 3 SO 3 , LiCF 3 SO 3 , LiN(SO 2 CF 3 ) 2 , LiC(SO 2 CF 3 ) 3 , LiSiF 6 , LiBOB, and lithium difluoroborate. For example, LiPF is used as the lithium salt because it has high ionic conductivity and can improve cycle characteristics. 6is preferred.

[0042] The non-aqueous solvent can be a carbonate compound, a carboxylic acid ester compound, an ether compound, another organic solvent, or a combination thereof.

[0043] The carbonate compound can be a linear carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.

[0044] Specific examples of the chain carbonate compound include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), ethyl methyl carbonate (MEC), or a combination thereof.Specific examples of the cyclic carbonate compound include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), or a combination thereof. Specific examples of the fluorocarbonate compound include 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, trifluoromethylethylene carbonate, or a combination thereof.

[0045] Specific examples of the carboxylate compound are methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, γ-butyrolactone, decanolide, valerolactone, mevalonolactone, caprolactone, methyl formate, or a combination thereof.

[0046] Specific examples of the ether compound are dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, or a combination thereof.

[0047] Specific examples of other organic solvents are dimethylsulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphate esters or combinations thereof.

[0048] In some embodiments of the present invention, a lithium ion battery is taken as an example, and a positive electrode, a separator, and a negative electrode are wound or stacked in order to form an electrode member, which is then placed in, for example, an aluminum laminate and sealed, and an electrolyte is injected, formed, and sealed to manufacture a lithium ion battery. An embodiment of the present invention further provides an electronic device including the electrochemical device described above. The electronic device of the embodiment of the present invention is not particularly limited and can be used in any electronic device known in the prior art. In some embodiments, the electronic device can include, but is not limited to, notebook computers, pen-input computers, mobile computers, electronic book players, mobile phones, portable facsimiles, portable copy machines, portable printers, stereo headsets, video recorders, LCD televisions, portable cleaners, portable CD players, mini discs, transceivers, electronic notebooks, calculators, memory cards, portable tape recorders, radios, backup power sources, motors, automobiles, motorcycles, auxiliary bicycles, bicycles, lighting equipment, toys, game machines, watches, power tools, flashlights, cameras, large household storage batteries, and lithium ion capacitors.

[0049] In the following, in order to better illustrate the present invention, some specific examples and comparative examples are given, in which a lithium ion battery is taken as an example. Example 1

[0050] Preparation of positive electrode pieces: Lithium cobalt oxide, a positive electrode active material, a conductive agent, and polyvinylidene fluoride (PVDF), a binder, were dissolved in an N-methylpyrrolidone (NMP) solution in a weight ratio of 97.6:1.1:1.3 to form a positive electrode active material layer slurry. Aluminum foil was used as a positive electrode current collector, and the positive electrode active material layer slurry was applied to the positive electrode current collector, with a coating thickness of 50 μm and a width of the electrode piece of 100 mm. Polyvinylidene fluoride (PVDF), a binder, and conductive carbon black were dissolved in an N-methylpyrrolidone (NMP) solution in a ratio of 6:4 to form a positive electrode coating layer slurry. A positive electrode coating layer was applied to two edges of the electrode piece, with each coating width being 5 mm and each thickness being 3 μm. The positive electrode piece was obtained through drying, cold pressing, and cutting.

[0051] Preparation of negative electrode pieces: The negative electrode active materials, artificial graphite, conductive carbon, and styrene butadiene rubber, which is a binder, were dissolved in deionized water in a weight ratio of 97.5:0.5:2 to form a negative electrode active material layer slurry. Copper foil was used as the negative electrode current collector, and the negative electrode active material layer slurry was applied to the negative electrode current collector, with a coating thickness of 60 μm and a width of the electrode piece of 100 mm. After drying, cold pressing, and cutting, a negative electrode piece was obtained.

[0052] Preparation of the separator: The separator substrate is polyethylene (PE) with a thickness of 8 μm, and a 2 μm aluminum oxide ceramic layer is coated on both sides of the separator substrate, and finally, 2.5 mg / cm2 aluminum oxide ceramic layers are coated on both sides of the ceramic layer. 2 The binder, polyvinylidene fluoride (PVDF), was applied to the substrate and then dried.

[0053] Preparation of electrolyte: In an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC): propylene carbonate (PC): polypropylene (PP): diethyl carbonate (DEC) = 1:1:1:1, weight ratio) were prepared as a base electrolyte, where LiPF 6 The concentration was 1.15 mol / L.

[0054] Preparation of lithium ion battery: Positive electrode piece, separator, and negative electrode piece are stacked in order, the separator is placed between the positive electrode and the negative electrode to play the role of isolation, and then wound to obtain an electrode assembly. The electrode assembly is placed in an exterior aluminum laminate, and after removing moisture at 80°C, the above-mentioned electrolyte is poured in, sealed, and processed through formation, degassing, shaping, etc. to obtain a lithium ion battery.

[0055] In the other examples and comparative examples, the parameters are changed based on the steps of Example 1 or Example 12, and the specific parameters to be changed are as follows:

[0056] In Comparative Example 1, the positive electrode coating layer was not applied. (1031+1021) / R 1023 is different from Example 1, and in the example, the impedance ratio R (1031+1021) / R 1023 In the sixth to eighth embodiments, the impedance ratio R (1031+1021) / R 1023 and the width of the positive electrode coating layer was different from that of Example 1. In Examples 9 to 11, the impedance ratio R (1031+1021) / R 1023 In addition, the thickness of the positive electrode coating layer was different from that in Example 1.

[0057] In Example 12, no positive electrode coating layer was applied, and the preparation of the negative electrode piece was different from that in Example 1.

[0058] Preparation of negative electrode piece: Negative electrode active material artificial graphite, conductive carbon and binder styrene butadiene rubber were dissolved in deionized water in a weight ratio of 97.5:0.5:2 to form a negative electrode active material layer slurry. Copper foil was used as a negative electrode current collector, and the negative electrode active material layer slurry was applied to the negative electrode current collector, with a coating thickness of 50 μm and a width of the electrode piece of 100 mm. Binders sodium carboxymethylcellulose, styrene butadiene rubber and conductive carbon black were dissolved in water in a ratio of 5:90:5 to form a negative electrode coating layer slurry. The negative electrode coating layer slurry was applied to the negative electrode active material layer, with a coating width of 90 mm, and was applied to the middle of the electrode piece, with a distance of 5 mm on both sides, and a coating thickness of 2 μm. After coating was completed, the negative electrode piece was obtained through drying and cold pressing.

[0059] In Examples 13 to 14, the impedance ratio R 1221 / R (1223+123) The other parameters were the same as those of Example 12. In Examples 15 and 16, the width of the negative electrode coating layer was different from that of Example 12. In Examples 17 to 19, the thickness of the negative electrode coating layer was different from that of Example 12.

[0060] The method for measuring each parameter of the present invention will be described below.

[0061] Lithium Deposition Window Measurement: First, the electrochemical device was discharged to a fully discharged state, and then set to a certain temperature (e.g., 25°C), and normal charging (constant current + constant voltage) was performed at different rates, such as 1C, 1.1C, 1.2C..., according to the design of the electrochemical device, that is, charging to the cut-off voltage of the battery at a certain rate, charging to 0.05C at a constant voltage and stopping charging, charging, and then fully discharging at 0.2C, and the above charge and discharge process was repeated 10 cycles. Finally, the electrochemical device was fully charged and then disassembled, and the negative electrode piece was observed to see whether lithium was precipitated, and the maximum current when lithium was not precipitated (there was no white spot on the surface of the negative electrode piece) was defined as the maximum non-lithium precipitation rate of the battery, that is, the lithium precipitation window.

[0062] Full charge time measurement: The lithium-ion battery under test was left at 25°C for 30 minutes, then charged at a constant current of 0.5 C until the voltage reached the rated voltage, and then charged at a constant voltage until the charge / discharge rate reached 0.05 C, after which charging was stopped. The time from when charging started to when charging was stopped was counted as the full charge time.

[0063] Energy density measurement: Battery energy density: The lithium-ion battery to be measured was left at 25°C for 30 minutes, charged at a constant current of 0.5C until the voltage reached the rated voltage, then charged at a constant voltage until the charge / discharge rate reached 0.05C, after which charging was stopped and the electrochemical device to be measured was left for 30 minutes. After that, the battery was discharged to 3.0V at 0.2C, and the lithium-ion battery to be measured was left for 30 minutes. Finally, the discharge capacity was taken as the actual battery capacity C of the battery. When the length, width and height of the measured lithium-ion battery are L, W and H, respectively, and the discharge platform voltage of the battery is V, the energy density of the battery VED = C × V / (L × W × H).

[0064] The parameters and evaluation results of Examples 1 to 19 and Comparative Example 1 are shown in Table 1.

[0065] [Table 1]

[0066] It can be seen from the comparison between Example 1 and Comparative Example 1 that after the positive electrode coating layer is formed, it is favorable to improve the charging capacity of the electrochemical device, and the full charge time and energy density of the electrochemical device are basically unchanged. Similarly, it can be seen from the comparison between Example 14 and Comparative Example 1 that after the negative electrode coating layer is formed, it is favorable to improve the charging capacity of the electrochemical device, and the full charge time and energy density of the electrochemical device are basically unchanged.

[0067] As can be seen from the comparison of Examples 1 to 5, the impedance ratio R (1031+1021) / R 1023 As the impedance ratio R increases, the charge capacity of the electrochemical device first increases and then levels off, the time to full charge of the electrochemical device first levels off and then increases, and the energy density of the electrochemical device first levels off and then decreases. (1031+1021) / R 1023 If it exceeds 5, the charging ability does not improve, the full charge time becomes long, and the energy density decreases.

[0068] As can be seen from the comparison of Examples 6 to 8, as the width of the positive electrode coating layer increases, the charging capacity of the electrochemical device first increases and then becomes constant, the full charge time of the electrochemical device tends to increase, and the energy density of the electrochemical device tends to decrease. When the ratio of the width of the positive electrode coating layer to the width of the positive electrode active material layer is more than 0.25, the charging capacity of the electrochemical device becomes basically constant, the full charge time of the electrochemical device becomes longer, and the energy density of the electrochemical device decreases.

[0069] As can be seen from the comparison of Examples 9 to 11, as the thickness of the positive electrode coating layer increases, the charging capacity of the electrochemical device first increases and then becomes constant, the full charge time of the electrochemical device is basically constant, and the energy density of the electrochemical device tends to decrease. When the thickness of the positive electrode coating layer is more than 8 μm, the charging capacity and full charge time of the electrochemical device are basically constant, and the energy density of the electrochemical device decreases.

[0070] As can be seen from the comparison of Examples 12 to 14, the impedance ratio R 1221 / R (1223+123) As the charge capacity of the electrochemical device increases, the charging time of the electrochemical device tends to decrease, the energy density of the electrochemical device tends to increase, and the charging time of the electrochemical device tends to decrease.

[0071] It can be seen from the comparison between Examples 15 and 16 that with increasing width of the negative electrode coating layer, the charging capacity of the electrochemical device increases, the full charging time of the electrochemical device increases slightly, and the energy density of the electrochemical device remains essentially constant. When the ratio of the width of the negative electrode coating layer to the width of the negative electrode active material layer is less than 0.75 or exceeds 0.99, the charging capacity of the electrochemical device is relatively decreased.

[0072] As can be seen from the comparison of Examples 17 to 19, as the thickness of the negative electrode coating layer increases, the charging capacity and full charge time of the electrochemical device are basically constant, and the energy density of the electrochemical device tends to decrease. When the thickness of the positive electrode coating layer is more than 8 μm, the charging capacity and full charge time of the electrochemical device are basically constant, and the energy density of the electrochemical device decreases.

[0073] The above description is merely a description of the preferred embodiments and applied technical principles of the present invention. It should be understood by those skilled in the art that the scope of the disclosure included in the present invention is not limited to the technical solution consisting of a specific combination of the above technical features, but also includes other technical solutions consisting of any combination of the above technical features or features equivalent thereto. For example, the technical solutions obtained by mutually modifying the above features and the technical features having similar functions disclosed in the present invention are also included.

Claims

1. 1. An electrochemical device including a positive electrode piece, the electrochemical device being a lithium ion battery, the positive electrode piece comprising: a positive electrode current collector including a first region, a second region, and a third region located between the first region and the second region along a width direction of the positive electrode piece; a positive electrode active material layer including a first portion, a second portion, and a third portion provided in the first region, the second region, and the third region, respectively; a positive electrode coating layer including a fourth portion and a fifth portion provided on the first region and the second region, respectively; the fourth portion is located between the first portion and the first region, or the first portion is located between the fourth portion and the first region, the fifth portion is located between the second portion and the second region, or the second portion is located between the fifth portion and the second region, an impedance of a combination of the first portion and the fourth portion is greater than an impedance of the third portion, and an impedance of a combination of the second portion and the fifth portion is greater than an impedance of the third portion; an impedance ratio of the combination of the fourth portion and the first portion to the impedance of the third portion is 1.02 to 5, and an impedance ratio of the combination of the fifth portion and the second portion to the impedance of the third portion is 1.02 to 5.

2. The positive electrode piece is a ratio of a width of the fourth portion to a width of the positive electrode active material layer is 0.01 to 0.25, and a ratio of a width of the fifth portion to a width of the positive electrode active material layer is 0.01 to 0.25; The thickness of the fourth portion is greater than 0.5 μm and less than 8 μm; The thickness of the fifth portion is greater than 0.5 μm and less than 8 μm; The electrochemical device according to claim 1 , wherein the third portion has a thickness that satisfies at least one of the following: greater than 20 μm and less than 200 μm.

3. 10. The electrochemical device of claim 1, wherein the positive electrode coating layer comprises at least one of conductive carbon and ceramic and a first binder.

4. The positive electrode piece is The mass content of the first binder in the positive electrode coating layer is greater than 20%; and the first binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and a fluorinated olefin, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene butadiene rubber, polyurethane, a fluorinated rubber, and polyvinyl alcohol; 4. The electrochemical device according to claim 3, wherein the conductive carbon satisfies at least one of the following: conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black, and nanocarbon fibers.

5. 2. The electrochemical device of claim 1 , wherein a combined thickness of the first portion and the fourth portion is the same as a thickness of the third portion, and a combined thickness of the second portion and the fifth portion is the same as a thickness of the third portion.

6. 1. An electrochemical device including a negative electrode piece, the electrochemical device being a lithium ion battery, the negative electrode piece comprising: a negative electrode current collector including a first region, a second region, and a third region located between the first region and the second region along a width direction of the negative electrode piece; a negative electrode active material layer including a first portion, a second portion, and a third portion provided in the first region, the second region, and the third region, respectively; a negative electrode coating layer; the negative electrode coating layer is located between the third portion and the third region, or the third portion is located between the negative electrode coating layer and the third region; an impedance of the combination of the negative electrode coating layer and the third portion is greater than an impedance of the first portion and greater than an impedance of the second portion; an impedance ratio of the first portion to an impedance of a combination of the negative electrode coating layer and the third portion is 0.5 to 0.99, and an impedance ratio of the second portion to an impedance of a combination of the negative electrode coating layer and the third portion is 0.5 to 0.

99.

7. The negative electrode piece is a ratio of a width of the negative electrode coating layer to a width of the negative electrode active material layer is 0.75 to 0.99; The thickness of the negative electrode coating layer is more than 0.5 μm and less than 8 μm; the negative electrode coating layer comprises at least one of conductive carbon and ceramic and a second binder; The electrochemical device according to claim 6 , wherein the thickness of the first portion and the thickness of the second portion each satisfy at least one of the following: greater than 20 μm and less than 200 μm.

8. The negative electrode piece is The mass content of the second binder in the negative electrode coating layer is more than 20%; and the second binder includes at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and a fluorinated olefin, polyvinylpyrrolidone, polyacrylonitrile, polymethyl acrylate, polytetrafluoroethylene, sodium carboxymethyl cellulose, styrene butadiene rubber, polyurethane, a fluorinated rubber, and polyvinyl alcohol; 8. The electrochemical device according to claim 7, wherein the conductive carbon satisfies at least one of the following: conductive carbon black, carbon nanotubes, conductive graphite, graphene, acetylene black, and nanocarbon fibers.

9. An electronic device comprising an electrochemical device according to any one of claims 1 to 8.

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