Electrode and method for manufacturing same, electrochemical device and electronic device

Abstract

The present invention provides an electrode, a method for manufacturing the same, an electrochemical device, and an electronic device. The electrode includes a current collector and an active material layer located on one or both sides of the current collector. The active material layer includes a first region and a second region. Along the thickness direction of the electrode, the first region is located between the current collector and the second region. The first region is a region from the current collector side to two-thirds of the thickness of the active material layer, and the second region is a region from two-thirds of the thickness of the active material layer to the electrode surface. Thermogravimetric analysis is performed on the active material layer at a heating rate of 10°C / min in an inert atmosphere. The thermogravimetric analysis result shows that the difference in the number of thermal weight loss peaks at 200°C to 800°C between the first region and the second region is ≧1. This shows that the second region of the active material layer in the present invention has good electrical conductivity, so that ions and electrons can be transmitted to the first region via the second region, which is advantageous in increasing the electrical conductivity of the entire electrode and further improving the capacity and energy density of the electrochemical device using the electrode.

Description

[Technical Field]

[0001] The present invention relates to the field of electrochemical energy storage, and in particular to electrodes and methods for their fabrication, electrochemical devices and electronic devices. [Background technology]

[0002] Electrochemical devices, such as lithium-ion batteries, have advantages such as high energy density, high output, and long cycle life, and are widely used in various fields. With technological developments, the demand for energy density of electrochemical devices is increasing. To improve the energy density of electrochemical devices, some techniques increase the capacity or voltage of the active material, while others increase the content of active material per unit volume and reduce the content of inactive material. Reducing the content of inactive material can be achieved by reducing the thickness of the current collector or separator, reducing the content of inactive material in the formulation, and manufacturing thicker electrodes. However, in practical applications, the thickness of both the current collector and separator is approaching its limit, so the only option is to increase the electrode thickness. However, excessive electrode thickness can adversely affect the performance of the electrochemical device, so the electrode thickness cannot be increased significantly. Therefore, increasing the electrode thickness as much as possible to increase the capacity of the electrochemical device while maintaining the performance of the electrochemical device is an urgent issue that needs to be resolved. Summary of the Invention [Means for solving the problem]

[0003] Some embodiments of the present invention provide an electrode, a method for fabricating the same, an electrochemical device, and an electronic device. Thermogravimetric analysis was performed on the active material layer in an inert atmosphere at a heating rate of 10°C / min. The results showed that the difference in the number of thermal weight loss peaks between the first and second regions was ≥ 1. This improves the conductivity of the second region of the active material layer, and is advantageous for increasing the thickness of the active material layer, thereby increasing the energy density of the electrochemical device.

[0004] An electrode according to some embodiments of the present invention includes a current collector and an active material layer located on one or both sides of the current collector, the active material layer including a first region and a second region, the first region being located between the current collector and the second region along the thickness direction of the electrode, the first region being a region extending from the current collector to two-thirds of the thickness of the active material layer, and the second region being a region extending from two-thirds of the thickness of the active material layer to the electrode surface, and the active material layer being subjected to thermogravimetric analysis in an inert atmosphere at a heating rate of 10°C / min. The results of the thermogravimetric analysis show that the difference in the number of thermal weight loss peaks between the first region and the second region at temperatures between 200°C and 800°C is ≥ 1. This indicates that the second region has better electrical conductivity than the first region, and is advantageous for electronic conduction.

[0005] In some examples of the present invention, thermogravimetric analysis was performed on the active material layer in an inert atmosphere at a heating rate of 10°C / min. The results of the thermogravimetric analysis showed that the first region had one or more weight loss peaks between 200°C and 800°C, and the second region had zero to two weight loss peaks between 200°C and 800°C. This indicates that the second region of the active material layer in the present invention has good electrical conductivity. This is advantageous for increasing the thickness of the electrode, and further advantageous for improving the capacity and energy density of the electrochemical device.

[0006] In some embodiments of the present invention, the thermogravimetric analysis results indicate that the mass change of the first region from 200°C to 800°C is 0.21% to 13%, and the thermogravimetric analysis results indicate that the mass change of the second region from 200°C to 800°C is 0% to 2.4%. This indicates that the second region of the active material layer in the present invention has zero or an extremely low content of polymer compound. This is advantageous for increasing ionic and electronic conductivity in the second region of the active material layer, allowing ions and electrons to be transferred to the first region of the active material layer, improving overall conductivity. In some embodiments, the polymer compound is a binder and / or thickener. In some embodiments of the present invention, the thermogravimetric analysis results indicate that the mass change of the first region from 200°C to 800°C is 1.6% to 4.02%.

[0007] In some embodiments of the present invention, the electrode is a positive electrode or a negative electrode. In some embodiments, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and the current collector is a negative electrode current collector. In some embodiments, the compressed density ρ1 of the negative electrode active material layer is ρ1≧0.6 g / cm 3 and a higher compaction density is advantageous for increasing the energy that the electrochemical device can store per unit volume. In some embodiments, the thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector is h1≧10 μm, and a larger thickness is advantageous for supporting more active material and increasing the energy density of the electrochemical device. In some embodiments, the negative electrode active material layer includes a negative electrode material, and the negative electrode material includes at least one of lithium titanate, silicon monoxide, graphite, silicon, and hard carbon.

[0008] In some embodiments of the present invention, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, the current collector is a negative electrode current collector, and the compressed density ρ1 of the negative electrode active material layer is 1.85 g / cm 3 ≧ρ1≧0.65g / cm 3This is advantageous for increasing the energy density. In some embodiments, the thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector satisfies 1500 μm≧h1≧15 μm. This is advantageous for increasing the energy density and preventing the negative electrode active material layer from falling off.

[0009] In some embodiments of the present invention, the compressed density ρ1 of the negative electrode active material layer is 1.83 g / cm 3 ≧ρ1≧1.0g / cm 3 In some embodiments of the present invention, the thickness h1 of the negative electrode active material layer on one side of the negative electrode current collector satisfies 150 μm≧h1≧30 μm.

[0010] In some embodiments of the present invention, the electrode is the positive electrode, the current collector is a positive electrode current collector, the active material layer is a positive electrode active material layer, and the compressed density ρ of the positive electrode active material layer is ρ≧2 g / cm 3 This is advantageous for increasing energy density. In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector is h2≧20 μm. This is advantageous for supporting more positive electrode material and increasing capacity. In some embodiments, the positive electrode active material layer includes a positive electrode material, and the positive electrode material includes at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide.

[0011] In some embodiments of the present invention, the electrode is a positive electrode, the current collector is a positive electrode current collector, the active material layer is a positive electrode active material layer, and the compressed density ρ2 of the positive electrode active material layer is 4.25 g / cm 3 ≧ρ2≧2.3g / cm 3This increases the energy density and prevents particle crushing. In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies 1500 μm ≧ h2 ≧ 30 μm. This increases the battery capacity and prevents the positive electrode active material layer from falling off the current collector. In some embodiments of the present invention, the electrode is a positive electrode, the current collector is a positive electrode current collector, and the active material layer is a positive electrode active material layer, and the compressed density ρ2 of the positive electrode active material layer is 4.23 g / cm 3 ≧ρ2≧4.0g / cm 3 In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies 130 μm≧h2≧26 μm.

[0012] In some embodiments of the present invention, the active material layer includes a conductive agent, wherein the mass percentage of the conductive agent in the first region is B and the mass percentage of the conductive agent in the second region is A, and A is greater than B. This increases the conductivity of the second region, allowing ions and electrons to be transmitted to the first region. In some embodiments, the mass percentage of the conductive agent in the first region is B and the mass percentage of the conductive agent in the second region is A, and (AB) / B is greater than or equal to 20%. In some embodiments, the conductive agent includes at least one of carbon nanotubes, carbon fibers, acetylene black, graphene, ketjen black, and conductive carbon black. In some embodiments, the mass percentage of the conductive agent in the active material layer is 0% to 2% relative to the total mass of the active material layer.

[0013] In some embodiments of the present invention, the first region includes a polymeric compound, and the polymeric compound includes at least one of polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polysiloxane, polyacrylic acid, polypropylene derivatives, sodium carboxymethylcellulose, lithium carboxymethylcellulose, polymethylpyrrolidone, polyvinylpyrrolidone, styrene acrylate, and styrene butadiene rubber. In some embodiments, the weight percentage of the polymeric compound in the active material layer is 0.42% to 14%. In some embodiments, the weight percentage of the polymeric compound in the active material layer is 2.0% to 5.0%.

[0014] Some embodiments of the present invention provide an electrode fabrication method capable of fabricating any of the electrodes of the present invention. The electrode fabrication method includes applying an active material layer slurry to at least one surface of a current collector, drying the slurry, and cold-pressing the slurry to obtain an initial electrode, and then treating the initial electrode to obtain an electrode. Here, the treatment of the initial electrode includes plasma treatment of the initial electrode in a vacuum environment, heat treatment of the initial electrode in a vacuum or inert gas environment, or laser bombardment of the initial electrode in a vacuum or inert gas environment. In the plasma treatment of the initial electrode in a vacuum environment, the plasma output is 0.5 kW to 5 kW, the gas source includes at least one of nitrogen gas, argon gas, and carbon tetrafluoride, the gas flow rate is 3000 sccm to 5000 sccm, the temperature is 20°C to 60°C, and the treatment time is 0.5 min to 1 min. In the heat treatment of the initial electrode in a vacuum or inert gas environment, the heat treatment temperature is higher than 200°C, and the heat treatment time is 1 min to 3 min. In the laser bombardment of the initial electrode in a vacuum or inert gas environment, the laser intensity is 30 W to 100 W, and the treatment time is 0.5 s to 1 s.

[0015] In some embodiments of the present invention, there is provided a method for producing an electrode, which can produce any of the electrodes of the present invention. The method for producing an electrode includes applying an active material layer slurry to at least one surface of a current collector, drying the slurry, and cold-pressing the slurry to obtain an initial electrode, and treating the initial electrode to obtain an electrode. Here, the treatment of the initial electrode includes heat-treating the initial electrode in a vacuum or inert gas environment. Here, the heat-treatment temperature is 350°C to 600°C, and the heat-treatment time is 1 minute to 3 minutes. In some embodiments of the present invention, there is provided an electrochemical device including an electrode. The electrode is any of the electrodes of the present invention. Or, the electrode is an electrode produced by the method for producing the electrode of the present invention.

[0016] In some embodiments of the present invention, an electronic device is provided that includes an electrochemical device according to the present invention. [Effects of the Invention]

[0017] An electrode according to an embodiment of the present invention includes a current collector and an active material layer located on one or both sides of the current collector. The active material layer includes a first region and a second region. The first region is located between the current collector and the second region. The first region extends from the current collector to two-thirds of the active material layer's thickness along the thickness direction, and the second region extends from two-thirds of the active material layer's thickness to the electrode surface along the thickness direction. Thermogravimetric analysis of the active material layer was performed at a heating rate of 10°C / min in an inert atmosphere. The results showed that the difference in the number of thermal weight loss peaks between the first and second regions at temperatures between 200°C and 800°C was ≥ 1. This indicates that the second region of the active material layer according to the present invention has good electrical conductivity. This allows ions and electrons to be transferred to the first region via the second region, thereby increasing the overall electrical conductivity of the electrode, which is advantageous for increasing the electrode's thickness and further improving the capacity and energy density of electrochemical devices using the electrode. [Brief explanation of the drawings]

[0018] The above and other features, advantages, and aspects of the embodiments of the present invention will become more apparent with reference to the drawings and the following specific embodiments. Throughout the drawings, the same or similar reference numerals represent the same or similar elements. It should be understood that the drawings are schematic and that elements are not necessarily drawn to scale.

[0019] [Figure 1] FIG. 1 is a schematic diagram of an electrode according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0020] The following examples will enable those skilled in the art to fully understand the present invention, but are not intended to limit the present application in any way.

[0021] To increase the energy density of electrochemical devices, some techniques have increased the thickness of the active material layer in the electrode, but increasing the thickness of the active material layer in the electrode can result in a deterioration in the conductivity of the active material layer due to its excessive thickness. To increase the conductivity of the active material layer, some techniques have adopted a multilayer active material layer structure, but the composite cold-pressing process for multiple single-layer structures is complex, and changes in the original compaction density and porosity of each single layer cannot be avoided during the re-cold-pressing process. Furthermore, insufficient bonding at the bonded points between layers can easily lead to peeling, affecting electron and ion conduction and deteriorating cycle performance. Another technique has involved drilling holes in the active material layer using a laser, but laser drilling is inefficient, costly, and prone to losing energy density during drilling. Another technique has involved applying a pore-forming agent solution to the electrode surface, but this inevitably dissolves the electrode surface, and the depth of the pores formed by the pore-forming agent is limited, limiting the improvement to the side closer to the current collector. Although the above techniques have solved the problem of ion transmission from the electrolyte to the active material surface by different methods, the ion transmission from the active material surface to the inside of the active material layer remains unchanged, and the ion transmission obstruction still exists, so the improvement effect is not good.

[0022] Some embodiments of the present invention provide an electrode that is advantageous for increasing the energy density of an electrochemical device by improving the conductivity of the active material layer of the electrode. In some embodiments, an electrode is provided. The electrode may be an electrode for an electrochemical device. The electrode includes a current collector and an active material layer located on one or both sides of the current collector. The active material layer includes a first region and a second region. Along the thickness direction of the electrode, the first region is located between the current collector and the second region. The first region is a region from the current collector side to two-thirds of the thickness of the active material layer, and the second region is a region from two-thirds of the thickness of the active material layer to the electrode surface. Thermogravimetric analysis of the active material layer is performed in an inert atmosphere at a heating rate of 10°C / min, and the thermogravimetric analysis result shows that the difference in the number of thermal weight loss peaks between the first region and the second region at 200°C to 800°C is ≥ 1. In some embodiments, the thickness of the first region accounts for two-thirds of the total thickness of the active material layer, the thickness of the second region accounts for one-third of the total thickness of the active material layer, and the number of weight loss peaks in the second region is less than the number of weight loss peaks in the first region. This indicates that the type or content of the polymer compound contained in the second region is less than that in the first region. This is advantageous for the conductivity of the second region, and electrons are transmitted to the first region via the second region, which is advantageous for increasing the conductivity of the entire pole piece.

[0023] In some examples of the present invention, thermogravimetric analysis was performed on the active material layer in an inert atmosphere at a heating rate of 10°C / min. The results showed that the first region had one or more weight loss peaks between 200°C and 800°C, and the second region had zero to two weight loss peaks between 200°C and 800°C. In some examples, the second region was located on one side of the first region away from the current collector, and ions and electrons must pass through the second region. Therefore, the conductivity of the second region significantly affects the conductivity of the electrode. In some examples of the present invention, the second region had zero to two weight loss peaks between 200°C and 800°C. This indicates that the second region does not contain polymeric compounds such as polymeric thickeners and binders, or that the content of such polymeric compounds is extremely low. This prevents the polymeric compounds in the active material layer from affecting the conductivity of the second region of the active material layer, thereby improving the ion and electron conductivity of the entire active material layer. Thus, when the energy density of the electrochemical device is increased by increasing the thickness of the active material layer, the active material layer has good electrical conductivity, so increasing the thickness of the active material layer does not deteriorate the electrical characteristics of the electrochemical device. Meanwhile, in the present invention, the number of weight loss peaks in the first region of the active material layer at 200°C to 800°C is one or more. This indicates the presence of a polymer compound in the first region of the active material layer of the present invention. This is because a polymer compound must be used in the active material layer so that the materials in the active material layer are bound to each other and adhere to the current collector. As can be seen from this, in the electrochemical device according to the embodiment of the present invention, the active material layer has good electrical conductivity, which is advantageous for the performance of the electrochemical device and for increasing the energy density. Furthermore, the present invention limits the thicknesses of the first and second regions. The reasons for this are as follows. If the thickness of the second region is too small, there will be no significant improvement in the conductivity of the active material layer; if the thickness of the second region is too large, there is a risk that the active material layer will fall off during compaction; if the thickness of the first region is too small, the capacity of the entire active material layer will be insufficient; and if the thickness of the first region is too large, the binding strength between the active material layer and the current collector will be insufficient, making it difficult to support the active material layer.

[0024] In some examples of the present invention, the results of thermogravimetric analysis indicate that the mass change of the first region from 200°C to 800°C is 0.21% to 13%. In some examples, the results of thermogravimetric analysis indicate that the mass change of the second region from 200°C to 800°C is 0% to 2.4%. In some examples, the detection accuracy of the thermogravimetric analyzer is 0.2%, and the low mass change of the second region of the active material layer from 200°C to 800°C in these examples indicates that the content of the polymer compound in the second region of the active material layer of the present invention is zero or extremely low. This is advantageous for increasing the conduction of ions and electrons in the second region of the active material layer and for improving the electrical properties of the electrochemical device. A non-zero content of the polymer compound in the first region is advantageous for ensuring the polymerization strength of the entire active material layer and the binding strength with the current collector. In some examples, the results of thermogravimetric analysis indicate that the mass change of the first region from 200°C to 800°C is 1.6% to 4.02%. In some embodiments, the polymeric compound is a binder and / or thickener, and the second region has a binder and / or thickener content of substantially zero to ensure electrical conductivity.

[0025] In some embodiments of the present invention, the electrode may be a negative electrode or a positive electrode, and may be a negative electrode or a positive electrode of an electrochemical device. In some embodiments, the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and the current collector is a negative electrode current collector, and the current collector may be, but is not limited to, copper foil, aluminum foil, steel foil, etc. In some embodiments, the compressed density ρ1 of the negative electrode active material layer is ρ1≧0.6 g / cm 3 A higher compressed density indicates a larger mass of the active material layer supported per unit volume of the electrode. The larger the mass of the negative electrode active material layer, the higher the energy that can be stored per unit volume of the electrochemical device, thereby increasing the energy density. In some examples, the compressed density ρ1 of the active material layer is 1.85 g / cm 3 ≧ρ1≧0.65g / cm 3In some embodiments, the viscosity satisfies 1.83 g / cm 3 ≧ρ1≧1.0g / cm 3 In some embodiments, the compressed density of the negative electrode active material layer is 1.0 g / cm. 3 By limiting the compressed density of the negative electrode active material layer to 1.83 g / cm or more, the energy density of the electrochemical device can be further ensured. 3 By limiting the compressed density to be equal to or less than this value, it is possible to prevent the particles in the active material layer from being crushed due to an excessively large compressed density, thereby preventing increased consumption of the electrolyte and deterioration of cycle performance.

[0026] In some embodiments of the present invention, the thickness h1 of one side of the negative electrode active material layer on the negative electrode current collector satisfies h1≧10 μm. In some embodiments, a thicker negative electrode active material layer is advantageous for increasing the proportion of the negative electrode active material layer in the electrochemical device and for increasing the energy density of the electrochemical device. In some embodiments of the present invention, the thickness h1 of one side of the negative electrode active material layer on the negative electrode current collector satisfies 1500 μm≧h1≧15 μm. In some embodiments, the thickness h1 is 150 μm≧h1≧30 μm. By limiting the thickness of the negative electrode active material layer to 30 μm or more, the thickness of the negative electrode active material layer can be ensured, thereby increasing the energy density of the entire electrochemical device. By limiting the thickness of the negative electrode active material layer to 150 μm or less, separation between the negative electrode active material layer and the current collector due to an excessively thick negative electrode active material layer can be prevented.

[0027] In some embodiments of the present invention, the negative electrode active material layer includes a negative electrode material, and the negative electrode material includes at least one of lithium titanate, silicon monoxide, graphite, and hard carbon.

[0028] In some embodiments of the present invention, the electrode is a positive electrode, the current collector is a positive electrode current collector, the active material layer is a positive electrode active material layer, and the compressed density ρ of the positive electrode active material layer is ρ≧2 g / cm 3Limiting the compressed density of the positive electrode active material layer can increase the energy density. Preferably, the compressed density ρ2 of the positive electrode active material layer is 4.25 g / cm 3 ≧ρ2≧2.3g / cm 3 In some embodiments, the viscosity satisfies 4.23 g / cm 3 ≧ρ2≧4.0g / cm 3 Further limiting the compression density of the positive electrode active material layer can further increase the energy density and prevent problems of material particle crushing and insufficient electrolyte infiltration caused by an excessively high compression density.

[0029] In some embodiments of the present invention, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies h2≧20 μm. In some embodiments, increasing the thickness of the positive electrode active material on one side of the positive electrode current collector allows the positive electrode to carry more active material, thereby increasing capacity. In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies 1500 μm≧h2≧30 μm. In some embodiments, the thickness h2 of the positive electrode active material layer on one side of the positive electrode current collector satisfies 130 μm≧h2≧26 μm. By further limiting the thickness of the positive electrode active material layer, capacity can be increased and separation of the positive electrode active material layer from the positive electrode current collector due to excessive thickness can be prevented.

[0030] In some embodiments of the present invention, the positive electrode active material layer includes a positive electrode material, which may include at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide, and may include two or more of these materials in combination.

[0031] In some embodiments of the present invention, the active material layer includes a conductive agent, wherein the mass percentage of the conductive agent in the first region is B and the mass percentage of the conductive agent in the second region is A, and A is greater than B. In some embodiments, the second region is located on one side of the first region away from the current collector, and increasing the content of the conductive agent in the second region improves conductivity, allowing ions and electrons to be transported within the active material layer.

[0032] In some embodiments of the present invention, the mass percentage of the conductive material in the first region is B, the mass percentage of the conductive material in the second region is A, and (AB) / B is 20% or more. In some embodiments, the mass percentage of the conductive material in the second region is significantly higher than that in the first region. Because the second region is closer to the exterior of the active material layer and the transmission paths of ions and electrons must pass through the second region, the conductivity of the first region can be ensured by having the mass percentage of the conductive material in the second region at least 20% higher than that in the first region.

[0033] In some embodiments of the present invention, the conductive agent comprises at least one of carbon nanotubes, carbon fiber, acetylene black, graphene, ketjen black, and conductive carbon black. In some embodiments of the present invention, the mass percentage of the conductive agent in the active material layer is 0% to 2% of the total mass of the active material layer. The carbon nanotubes in the conductive agent may be single-walled carbon nanotubes or multi-walled carbon nanotubes, and can increase long-range electron conduction.

[0034] In some embodiments of the present invention, the first region comprises a polymeric compound, and the polymeric compound may comprise a binder and / or a thickener, and the polymeric compound comprises at least one of polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polysiloxane, polyacrylic acid, polypropylene derivatives, sodium carboxymethylcellulose, lithium carboxymethylcellulose, polymethylpyrrolidone, polyvinylpyrrolidone, styrene acrylate, and styrene butadiene rubber.

[0035] In some embodiments of the present invention, the mass percentage of the polymer compound in the active material layer is 0.42% to 14%, and in some embodiments, the mass percentage of the polymer compound in the active material layer is 2.0% to 5.0%. If the mass percentage of the polymer compound is too low, the adhesion between the active material layer and the current collector may be insufficient, and if the mass percentage of the binder is too high, the conductivity of the active material layer may be affected.

[0036] In some embodiments of the present invention, the polymer compound is distributed in a dotted or planar form on the surface of the active material (e.g., a negative electrode material) of the active material layer, and gathers on the surface of the active material or between particles of the active material. A large amount of exposed active material is advantageous in ensuring conductivity by reducing the interference with the transmission of electrons and ions.

[0037] Referring to FIG. 1, in some embodiments of the present invention, an electrode includes a current collector 10 and an active material layer, the active material layer including a first region and a second region, and the active material layer including an active material 20 (which may be a positive electrode material or a negative electrode material), a conductive agent 30, and a polymer compound 40, where the active material 20 may include a first active material and a second active material, the particle size of the first active material being larger than the particle size of the second active material, and by blending active materials of different particle sizes, the gaps can be sufficiently filled.

[0038] In some embodiments of the present invention, increasing the mass percentage of the conductive agent in the second region improves the electronic conductivity of the second region, and decreasing the content of polymeric compounds (e.g., binders and / or thickeners) in the second region reduces interference with ionic transport and improves electrode kinetics.

[0039] Some embodiments of the present invention provide a method for fabricating an electrode, which can be used to fabricate any of the electrodes of the present invention. The method includes applying an active material layer slurry to at least one surface of a current collector, drying the slurry, and cold-pressing the slurry to obtain an initial electrode, and then treating the initial electrode to obtain an electrode. Here, the treatment of the initial electrode includes plasma treatment of the initial electrode in a vacuum environment, heat treatment of the initial electrode in a vacuum or inert gas environment, or laser bombardment of the initial electrode in a vacuum or inert gas environment. In the plasma treatment of the initial electrode in a vacuum environment, the plasma output is 0.5 kW to 5 kW, the gas source includes at least one of nitrogen gas, argon gas, and carbon tetrafluoride, the gas flow rate is 3000 sccm to 5000 sccm, the temperature is 20°C to 60°C, and the treatment time is 0.5 min to 1 min. In the heat treatment of the initial electrode in a vacuum or inert gas environment, the heat treatment temperature is higher than 200°C and the heat treatment time is 1 to 3 minutes. In the laser shock treatment of the initial electrode in a vacuum or inert gas environment, the laser intensity is 30 W to 100 W and the treatment time is 0.5 to 1 s.

[0040] In an embodiment of the present invention, the initial electrode is treated to remove the polymer compound in the second region, which is the surface layer of the active material layer in the initial electrode. For example, by removing the binder and / or thickener in the second region, the fabricated electrode has better conductivity, reduces the coverage area of ​​the polymer compound on the active material, reduces interference with ion conduction, improves dynamic properties, and is advantageous for increasing the thickness of the active material layer without degrading electrode performance.

[0041] In some embodiments of the present invention, a method for fabricating the electrode is provided. The method includes applying an active material layer slurry to at least one surface of a current collector, drying the slurry, and cold-pressing the slurry to obtain an initial electrode. The initial electrode treatment includes heat-treating the initial electrode in a vacuum or inert gas environment. The heat-treating temperature for the initial electrode in a vacuum or inert gas environment is 350°C to 600°C, and the heat-treating time is 1 minute to 3 minutes.

[0042] In some embodiments of the present invention, an electrochemical device is provided that includes an electrode, the electrode being any of the electrodes of the present invention, or the electrode being an electrode fabricated by a fabrication method according to the present invention.

[0043] An electrochemical device according to some embodiments of the present invention includes a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode. In some embodiments, the negative electrode and the positive electrode are any one of the above-described electrodes. In some embodiments, the current collector of the positive electrode may be an Al foil, although other current collectors commonly used in this field may also be used.

[0044] 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 high-density polyethylene, low-density polyethylene, and ultra-high molecular weight polyethylene. Among them, polyethylene and polypropylene play an important role in preventing short circuits and can improve battery stability through the off-state effect. In some embodiments, the thickness of the separator is within a range of about 5 μm to 50 μm.

[0045] In some embodiments, the separator surface may include a porous layer, 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 including at least one selected from aluminum oxide (Al2O3), silicon oxide (SiO2), magnesium oxide (MgO), titanium oxide (TiO2), hafnium dioxide (HfO2), tin oxide (SnO2), cerium dioxide (CeO2), nickel oxide (NiO), zinc oxide (ZnO), calcium oxide (CaO), zirconium oxide (ZrO2), yttrium oxide (YO3), silicon carbide (SiC), boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate. In some embodiments, the pores in the separator have a diameter ranging from about 0.01 μm to 1 μm. The porous layer binder includes at least one selected from the group consisting of polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, sodium carboxymethylcellulose, polyvinylpyrrolidone, polyvinyl ether, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The porous layer on the separator surface improves the separator's heat resistance, antioxidant properties, and electrolyte penetration performance, and strengthens the adhesion between the separator and the pole pieces.

[0046] In some embodiments of the present invention, the electrochemical device may have a wound structure or a stacked structure. In some embodiments, the positive electrode and / or negative electrode of the electrochemical device may have a multi-layer structure formed by winding or stacking, or may have a single-layer structure in which a single-layer positive electrode, a separator, and a single-layer negative electrode are stacked. In some embodiments, the electrochemical device includes a lithium-ion battery, although the present invention is not limited thereto. In some embodiments, the electrochemical device may further include an electrolyte. The electrolyte may be one or more 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 may be one or more selected from LiPF, LiBF, LiAsF, LiClO, LiB(CH), LiCHSO, LiCFSO, LiN(SOCF), LiC(SOCF), LiSiF, LiBOB, and lithium difluoroborate. For example, LiPF is selected as the lithium salt because of its high ionic conductivity and its ability to improve cycle characteristics.

[0047] The non-aqueous solvent may be a carbonate compound, a carboxylate compound, an ether compound, another organic solvent, or a combination thereof. The carbonate compound may be a chain carbonate compound, a cyclic carbonate compound, a fluorocarbonate compound, or a combination thereof.

[0048] Examples of linear carbonate compounds include diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), and combinations thereof. Examples of cyclic carbonate compounds include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinyl ethylene carbonate (VEC), and combinations thereof. Illustrative 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, and combinations thereof.

[0049] Illustrative examples of carboxylate compounds include methyl acetate, ethyl acetate, n-propyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, propyl propionate, gamma-butyrolactone, decalactone, valerolactone, mevalonolactone, caprolactone, methyl formate, and combinations thereof.

[0050] Illustrative examples of ether compounds include dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, tetrahydrofuran, and combinations thereof.

[0051] Examples of other organic solvents include dimethyl sulfoxide, 1,2-dioxolane, cyclobutane sulfone, methylcyclobutane sulfone, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidone, formamide, dimethylformamide, acetonitrile, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, phosphate esters, and combinations thereof.

[0052] In some embodiments of the present invention, for example, a lithium ion battery is fabricated by sequentially winding or stacking a positive electrode, a separator, and a negative electrode to form an electrode assembly, which is then sealed in, for example, an aluminum plastic film, and an electrolyte is injected, formed, and sealed to fabricate a lithium ion battery. The fabricated lithium ion battery is then subjected to a performance test.

[0053] It should be understood by those skilled in the art that the above-described method for fabricating an electrochemical device (e.g., a lithium ion battery) is merely an example, and other methods commonly used in the art may be employed without departing from the scope of the present disclosure.

[0054] The present invention provides an electronic device including an electrochemical device. The electrochemical device is any one of the electrochemical devices of the present invention. The electronic device of the present invention is not particularly limited and may be used in any electronic device known in the art. In some embodiments, the electronic device may include, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a mobile phone, a portable facsimile machine, a portable copier, a portable printer, a stereo headset, a video recorder, an LCD television, a portable vacuum cleaner, a portable CD player, a minidisc player, a walkie-talkie, an electronic organizer, a calculator, a memory card, a portable tape recorder, a radio, a backup power supply, a motor, an automobile, a motorcycle, an electric bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, a power tool, a flashlight, a camera, and a large-scale household battery.

[0055] In the following, some specific examples and comparative examples are given to better illustrate the present invention, in which a lithium ion battery is used as an example.

[0056] Example 1

[0057] Positive electrode fabrication: The positive electrode material, lithium cobalt oxide, polyvinylidene fluoride (PVDF), and carbon nanotubes (CNTs) were mixed in a mass ratio of 97.5:1.5:1.0, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry. The mixture was stirred uniformly to form a positive electrode active material layer. The slurry was uniformly applied to an aluminum foil positive electrode current collector and dried to obtain a positive electrode piece.

[0058] Preparation of negative electrode pieces: Graphite as the negative electrode material, carbon nanotubes as the conductive agent, and binders (styrene acrylate and lithium carboxymethyl cellulose) are mixed in a predetermined mass ratio, and deionized water is added as a solvent to form a negative electrode active material layer slurry. Copper foil is used as the negative electrode current collector, and the negative electrode active material layer slurry is applied to the negative electrode current collector and dried at 90°C. The dried electrode pieces are then heat-treated at a heat treatment temperature of 350°C for 2 minutes. After heat treatment, negative electrode pieces are obtained.

[0059] Separator fabrication: The separator is polyethylene (PE) with a thickness of 8 μm.

[0060] Preparation of electrolyte solution: In an environment with a water content of less than 10 ppm, lithium hexafluorophosphate and a nonaqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): vinylene carbonate (VC) = 20:30:20:28:2, weight ratio) were mixed in a weight ratio of 8:92 to obtain an electrolyte solution.

[0061] Fabrication of lithium-ion battery: The positive electrode, separator, and negative electrode were stacked and wound in this order so that the separator was interposed between the positive and negative electrodes to act as an insulator. The electrode assembly was placed in an outer aluminum plastic film, and after removing moisture at 80°C, the above electrolyte solution was injected and sealed. After undergoing processes such as formation, degassing, and trimming, a lithium-ion battery was obtained.

[0062] The relevant parameters of Example 1 are as follows: the positive electrode active material layer contains lithium cobalt oxide, PVDF, and CNT, with mass percentages of 97.5%, 1.5%, and 1%, respectively; the thickness of the positive electrode active material layer on one side of the positive electrode current collector is 63 μm; and the compressed density of the positive electrode active material layer on one side of the positive electrode current collector is 4.1 g / cm. 3 The negative electrode active material layer contains graphite, styrene acrylate, carboxymethyl cellulose lithium, and CNT, with the mass percentages of these being 97.4%, 1%, 1%, and 0.6%, respectively. The compressed density of the negative electrode active material layer is 1.74 g / cm 3 The negative electrode active material layer on one side of the negative electrode current collector has a thickness of 75 μm. The negative electrode material is graphite, the first region of the negative electrode active material layer has a thickness of 50 μm, and the second region of the negative electrode active material layer has a thickness of 25 μm. The mass percentage A of the conductive agent in the second region of the negative electrode is 0.6%, and the mass percentage B of the conductive agent in the first region of the negative electrode is 0.4%. The conductive agent in the negative electrode is carbon nanotubes, the binder in the first region of the negative electrode is styrene acrylate, and the mass percentage of the binder in the first region of the negative electrode is 2.5%. The number of thermal weight loss peaks in the first region of the negative electrode active material layer at 200°C to 800°C is 1, and the mass change of the first region of the negative electrode is 1.6%. The number of thermal weight loss peaks in the second region of the negative electrode active material layer at 200°C to 800°C is 0, and the mass change of the second region of the negative electrode is 0.1%.

[0063] Examples 2 to 36 are obtained by changing the parameters above the steps of Example 1. The changed parameters are specifically shown in the table below.

[0064] Example 37

[0065] Positive electrode fabrication: Lithium cobalt oxide (positive electrode material), polyvinylidene fluoride (PVDF), and carbon nanotubes (CNT) were mixed in a mass ratio of 97.5:1.5:1.0, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry. The mixture was then stirred uniformly to form a positive electrode active material layer. The slurry was then uniformly coated onto an aluminum foil positive electrode current collector and dried at 90°C. The dried electrode was then heat-treated at 350°C for 2 minutes. After heat treatment, positive electrode pieces were obtained.

[0066] Preparation of negative electrode pieces: Graphite as the negative electrode material, carbon nanotubes as the conductive agent, and binders (styrene acrylate and lithium carboxymethyl cellulose) were mixed in a predetermined mass ratio, and deionized water was added as a solvent to form a slurry of the negative electrode active material layer. Copper foil was used as the negative electrode current collector, and the slurry of the negative electrode active material layer was applied to the negative electrode current collector and dried at 90°C to obtain a negative electrode piece.

[0067] Other steps in Example 37 were the same as in Example 1.

[0068] The relevant parameters of Example 37 are as follows: the positive electrode active material layer contains lithium cobalt oxide, PVDF, and CNT, with mass percentages of 97.5%, 1.5%, and 1%, respectively; the thickness of the positive electrode active material layer on one side of the positive electrode current collector is 63 μm; and the compressed density of the positive electrode active material layer on one side of the positive electrode current collector is 4 g / cm. 3The thickness of the first region of the positive electrode active material layer is 42 μm, and the thickness of the second region of the positive electrode active material layer is 21 μm. The mass percentage A of the conductive agent in the second region of the positive electrode is 1%, and the mass percentage B of the conductive agent in the first region of the positive electrode is 0.67%. The conductive agent in the positive electrode is carbon nanotubes, the binder in the first region of the positive electrode is PVDF, and the mass percentage of the binder in the first region of the positive electrode is 1.5%. The number of thermal weight loss peaks in the first region of the positive electrode active material layer at 200°C to 800°C is 1, and the mass change of the first region of the positive electrode is 1.2%. The number of thermal weight loss peaks in the second region of the positive electrode active material layer at 200°C to 800°C is 0, and the mass change of the second region of the positive electrode is 0.1%.

[0069] The negative electrode active material layer contains graphite, styrene acrylate, lithium carboxymethyl cellulose, and CNTs, with the mass percentages of these being 97.4%, 1%, 1%, and 0.6%, respectively. The compressed density of the negative electrode active material layer is 1.74 g / cm. 3 The thickness of the negative electrode active material layer on one side of the negative electrode current collector is 73 μm. The negative electrode material is graphite.

[0070] Examples 38 to 48 are obtained by changing the parameters above the steps of Example 34. The changed parameters are specifically shown in the table below.

[0071] Example 49

[0072] Positive electrode fabrication: Lithium cobalt oxide (positive electrode material), polyvinylidene fluoride (PVDF), and carbon nanotubes (CNT) were mixed in a mass ratio of 97.5:1.5:1.0, and N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry. The mixture was then stirred uniformly to form a positive electrode active material layer. The slurry was then uniformly coated onto an aluminum foil positive electrode current collector and dried at 90°C. The dried electrode was then heat-treated at 350°C for 2 minutes. After heat treatment, positive electrode pieces were obtained.

[0073] Preparation of negative electrode pieces: Graphite as the negative electrode material, carbon nanotubes as the conductive agent, and binders (styrene acrylate and lithium carboxymethyl cellulose) are mixed in a predetermined mass ratio, and deionized water is added as a solvent to form a negative electrode active material layer slurry. Copper foil is used as the negative electrode current collector, and the negative electrode active material layer slurry is applied to the negative electrode current collector and dried at 90°C. The dried electrode pieces are then heat-treated at a heat treatment temperature of 350°C for 2 minutes. After heat treatment, negative electrode pieces are obtained.

[0074] Other steps in Example 49 were the same as in Example 1.

[0075] The relevant parameters of Example 49 are as follows: the positive electrode active material layer contains lithium cobalt oxide, PVDF, and CNTs, with mass percentages of 97.5%, 1.5%, and 1%, respectively; the thickness of the positive electrode active material layer on one side of the positive electrode current collector is 63 μm; and the compressed density of the positive electrode active material layer on one side of the positive electrode current collector is 4.1 g / cm. 3 The thickness of the first region of the positive electrode active material layer is 42 μm, and the thickness of the second region of the positive electrode active material layer is 21 μm. The mass percentage A of the conductive agent in the second region of the positive electrode is 1%, and the mass percentage B of the conductive agent in the first region of the positive electrode is 0.67%. The conductive agent in the positive electrode is carbon nanotubes, the binder in the first region of the positive electrode is PVDF, and the mass percentage of the binder in the first region of the positive electrode is 1.5%. The number of thermal weight loss peaks in the first region of the positive electrode active material layer at 200°C to 800°C is 1, and the mass change of the first region of the positive electrode is 1.2%. The number of thermal weight loss peaks in the second region of the positive electrode active material layer at 200°C to 800°C is 0, and the mass change of the second region of the positive electrode is 0.1%. The negative electrode active material layer contains graphite, styrene acrylate, lithium carboxymethyl cellulose, and CNTs, with the mass percentages of these being 97.4%, 1%, 1%, and 0.6%, respectively. The compressed density of the negative electrode active material layer is 1.74 g / cm. 3The thickness of the negative electrode active material layer on one side of the negative electrode current collector is 75 μm. The negative electrode material is graphite, the thickness of the first region of the negative electrode active material layer is 50 μm, the thickness of the second region of the negative electrode active material layer is 25 μm, the mass percentage A of the conductive agent in the second region of the negative electrode is 0.6%, and the mass percentage B of the conductive agent in the first region of the negative electrode is 0.4%. The conductive agent in the negative electrode is carbon nanotubes, and the binder in the first region of the negative electrode is styrene acrylate and lithium carboxymethyl cellulose, with the mass ratio of these two binders being 1:1. The mass percentage of the binder in the first region of the negative electrode is 2%, the number of thermal weight loss peaks at 200°C to 800°C in the first region of the negative electrode is 2, and the mass change of the first region of the negative electrode is 1.6%. The number of thermal weight loss peaks in the second region of the negative electrode active material layer at temperatures between 200°C and 800°C is 0, and the mass change of the second region in the negative electrode is 0.1%.

[0076] Comparative Example 1

[0077] Preparation of positive electrode pieces: The positive electrode material (lithium cobalt oxide), the binder (PVDF), and the conductive agent (carbon nanotubes) were mixed in a mass ratio of 97.5%:1.5%:1%. N-methylpyrrolidone (NMP) was added as a solvent to prepare a slurry, which was then stirred uniformly to form a positive electrode active material layer. The slurry was uniformly applied to an aluminum foil positive electrode current collector and dried at 90°C to obtain positive electrode pieces.

[0078] Preparation of negative electrode pieces: Graphite as the negative electrode material, styrene acrylate as the binder, lithium carboxymethyl cellulose as the binder, and CNT as the conductive agent were mixed in a ratio of 97.5%:1%:1%:0.5%, and deionized water was added as the solvent to form a slurry of the negative electrode active material layer. Copper foil was used as the negative electrode current collector, and the slurry of the negative electrode active material layer was applied to the negative electrode current collector and dried at 90°C to obtain a negative electrode piece.

[0079] Other manufacturing steps of Comparative Example 1 were the same as those of Example 1, and the differences in parameters between Comparative Example 1 and Example 1 are shown in the table below.

[0080] In Comparative Examples 2 and 3, the parameters were changed above the steps of Comparative Example 1. The changed parameters are specifically shown in the table below.

[0081] The test method of the present invention will be explained below.

[0082] 1. Thermogravimetric test

[0083] The battery was discharged to 3.0 V and disassembled to obtain negative electrode pieces. The electrode pieces were soaked in DMC (dimethyl carbonate) for 12 to 24 hours, the DMC was replaced, and the electrode pieces were soaked for another 12 to 24 hours. They were then dried at 80 to 100°C, and the active material layer powder at the corresponding position on the electrode piece surface was scraped and measured. Thermogravimetric analysis was performed on the negative electrode active material layer of the fabricated lithium-ion battery using thermogravimetric analysis to measure the mass change and the number of weight loss peaks during the thermogravimetric analysis process. The measurement range was 200 to 800°C, the heating rate was 10°C / min, and the test atmosphere was an inert atmosphere.

[0084] 2. Resistivity test

[0085] The resistivity of the active material layer was measured using a resistance meter. The electrode pieces were directly measured using a top-bottom flat pressure-controllable probe. An AC current was applied to the test positive or negative electrode piece, and a constant pressure (0.35 T) was applied to the test active material layer to obtain the overall resistance across the thickness of the electrode piece. The area (A) and thickness (l) of the test electrode piece were also collected, and the resistivity of the test electrode piece was calculated using the resistivity calculation formula (ρ = R * A / l).

[0086] 3. AC resistance test

[0087] A small AC current of 1 kHz was applied to the positive and negative electrodes of the battery, and the AC resistance of the battery was obtained by measuring the voltage response.

[0088] 4. 25℃ DC resistance DCR test

[0089] At 25°C, a lithium-ion battery was charged at a constant current of 0.5C to 4.45V, then at a constant voltage of 0.05C, allowed to stand for 30 minutes, discharged at 0.1C for 3 hours until the battery reached 70% SOC (the corresponding voltage value U1 was recorded), and then discharged at 1C for 1 second (the corresponding voltage value U2 was recorded). Here, "1C" refers to the current value at which the battery capacity is fully discharged within 1 hour. The DCR of the battery at 70% SOC was calculated using the following formula: DCR = (U1 - U2) / (1C - 0.1C).

[0090] 5. Rate performance test

[0091] At 25°C, the battery was discharged at a constant current to 3V, then charged and discharged for the first time. The battery was then charged at a constant current of 0.7C until the upper voltage reached 4.48V, then charged at a constant voltage of 0.05C, and then discharged at a constant current of 0.2C until the final voltage reached 3V. The discharge capacity at 0.2C was recorded. The battery was then repeatedly charged at a constant current of 0.7C until the upper voltage reached 4.48V, then charged at a constant voltage of 0.05C, and finally discharged at a constant current of 3C. The discharge rate was set to discharge the battery until the final voltage reached 3V, and the discharge capacity at 3C was recorded.

[0092] 3C discharge capacity maintenance rate = (3C discharge capacity / 0.2C discharge capacity) x 100%

[0093] [Table 1(1)] [Table 1(2)] [Table 1(3)]

[0094] [Table 2(1)] [Table 2(2)]

[0095] Tables 1 and 2 show the manufacturing parameters and performance test results for Examples 1 to 15 and Comparative Examples 1 to 3. All ratios in the tables are mass ratios.

[0096] Referring to Tables 1 and 2, in Examples 1 to 15, the difference between the number of weight loss peaks in the first region of the negative electrode at 200°C to 800°C and the number of weight loss peaks in the second region of the negative electrode at 200°C to 800°C was 1 or more. In Comparative Examples 1 to 3, the difference between the number of weight loss peaks in the first region of the negative electrode at 200°C to 800°C and the number of weight loss peaks in the second region of the negative electrode at 200°C to 800°C was 0. Examples 1 to 15 had lower AC resistance and DC resistance than Comparative Examples 1 to 3, and higher 3C discharge capacity retention than Comparative Examples 1 to 3. This is thought to be because when the difference between the number of thermal weight loss peaks in the first region and the second region at 200°C to 800°C is ≥ 1, the second region has better conductivity, making it easier for ions and electrons to pass through the second region and reach the first region, thereby improving the dynamic properties of the pole piece.

[0097] Referring to Examples 1 to 3, with the change in the number of weight loss peaks in the first region of the negative electrode at 200°C to 800°C, the AC resistance, DC resistance, and 3C discharge capacity of the lithium ion battery are still superior to those of Comparative Examples 1 to 3. As can be seen, as long as the difference in the number of weight loss peaks between the first region and the second region is 1 or more, the technical effects described in the present invention can be achieved.

[0098] In Comparative Examples 1 to 3, the content of the conductive agent in the first region was higher than that in the second region, resulting in poor conductivity in the second region, which affected the transmission of electrons and ions from the second region to the first region and affected dynamic performance. On the other hand, in Examples 1 to 12, the content of the conductive agent in the second region was higher than that in the first region, which was advantageous for improving dynamic properties.

[0099] Examples 1, 4 to 6 show the effects of different binder components. As can be seen, different binders have some effect on the DC resistance, AC resistance, and 3C discharge capacity retention rate of the lithium ion battery. The performance of the lithium ion battery is best when the binder is styrene acrylate and carboxymethyl cellulose lithium.

[0100] Examples 7 to 9 and 11 to 12 demonstrate the effect of varying the mass percentage of the binder in the first region of the negative electrode on lithium-ion batteries. As the mass percentage of the binder increases, the thermogravimetric change of the first region at temperatures between 200°C and 800°C increases. This is because the binder is decomposed and oxidized during the thermogravimetric analysis process. The AC and DC resistances increase, and the 3C discharge capacity retention rate decreases. This is because the presence of the binder interferes with the transmission of ions and electrons, reducing conductivity.

[0101] Examples 9 and 10 show that changing the binder component ratio affects the performance of lithium-ion batteries when the binder components are unchanged.

[0102] In Examples 13 to 15, the time and / or temperature of the heat treatment for the negative electrode was appropriately adjusted so that the number of weight loss peaks in the second region of the negative electrode between 200°C and 800°C was different from those in Examples 2, 3, and 11. This indicates that the performance of the lithium-ion battery is best when the number of weight loss peaks in the second region of the negative electrode between 200°C and 800°C is controlled to be zero.

[0103] [Table 3(1)] [Table 3(2)]

[0104] [Table 4(1)] [Table 4(2)]

[0105] Tables 3 and 4 show the manufacturing parameters and performance test results for Examples 8 and 20 to 27. The ratios in the tables are all mass ratios.

[0106] Examples 8, 16 to 19 demonstrate the effect of the thickness of the negative electrode active material layer. As the thickness of the negative electrode active material layer increases, the AC resistance and DC resistance of the lithium-ion battery increase, and the 3C discharge capacity retention rate decreases. This is because the increased thickness lengthens the transmission paths of ions and electrons, resulting in a decrease in dynamic characteristics. However, if the negative electrode active material layer is too thin, too little negative electrode active material is supported, which is detrimental to energy density.

[0107] Examples 8 and 20 to 23 demonstrate the effect of the thickness of the positive electrode active material layer. As with the negative electrode, increasing the thickness of the positive electrode active material increases the DC resistance and AC resistance, and reduces the 3C discharge capacity retention rate. However, if the thickness of the positive electrode active material layer is too small, it also affects the energy density.

[0108] Examples 8, 24 to 27 show the effect of the components of the negative electrode active material layer. As can be seen, when the negative electrode material is selected from silicon monoxide, lithium cobalt oxide, graphite, silicon, and hard carbon, all of them can achieve good results. However, when different negative electrode materials are selected, the compression density of the negative electrode active material layer varies, and when the negative electrode material is graphite, the overall performance is excellent.

[0109] [Table 5(1)] [Table 5(2)]

[0110] [Table 6(1)] [Table 6(2)]

[0111] Tables 5 and 6 show the manufacturing parameters and performance test results for Examples 8 and 28 to 36. The ratios in the tables are all mass ratios.

[0112] Examples 8, 28, and 29 demonstrate the effect of the mass percentage of the conductive agent in the negative electrode active material layer. As the mass percentage of the conductive agent increases, both the DC resistance and the AC resistance decrease, and the 3C discharge capacity retention rate increases. This is because the conductive agent increases the conductivity of the entire negative electrode active material layer. However, if the mass percentage of the conductive agent is too high, the energy density of the lithium-ion battery decreases.

[0113] Examples 8, 30, and 31 demonstrate the effect of the conductive agent distribution in the negative electrode active material layer. As can be seen, when (AB) / B is greater than 20%, the DC resistance and AC resistance are significantly reduced and the rate performance is improved. This is because the increased content of the conductive agent in the second region allows ions and electrons to be transferred to the first region, improving the dynamic characteristics.

[0114] Examples 8, 32 to 36 demonstrate the effect of the type of conductive agent in the negative electrode active material layer. When the conductive agent is conductive carbon black, acetylene black, ketjen black, carbon nanotubes, graphene, or carbon fiber, the performance of the lithium ion battery is excellent, and the performance is best when the conductive agent is carbon nanotubes.

[0115] [Table 7(1)] [Table 7(2)]

[0116] [Table 8(1)] [Table 8(2)]

[0117] Tables 7 and 8 show the fabrication parameters and performance test results for Examples 37 to 49. All ratios in the tables are mass ratios. In Examples 37 to 49, the positive electrode was heat-treated. In Example 49, both the positive electrode and the negative electrode were heat-treated.

[0118] Examples 37 to 41 demonstrate the effect of the compression density of the positive electrode active material layer. As the compression density of the positive electrode active material layer increases, the AC resistance and DC resistance increase, and the 3C discharge capacity retention rate decreases. This is because the increase in compression density increases the amount of positive electrode material per unit volume, reducing the infiltration of the electrolyte and the dynamic characteristics.

[0119] Examples 42 to 44 show the effect of the thickness of the positive electrode active material layer: As the thickness of the positive electrode active material layer increases, the dynamic characteristics decrease, the resistance increases, and the rate performance deteriorates.

[0120] Examples 45 to 48 demonstrate the influence of the positive electrode active material. All of the active materials used in these examples exhibited excellent performance, with lithium cobalt oxide exhibiting superior overall performance. In Example 49, both the positive and negative electrodes were heat-treated, resulting in excellent dynamic characteristics, the lowest AC and DC resistances, and the best 3C discharge performance.

[0121] The above description merely describes preferred embodiments of the present invention and the technical principles used. Those skilled in the art should understand that the scope of the present invention is not limited to the technical solution based on the specific combination of the above-mentioned technical features, but also encompasses other technical solutions formed by any combination of the above-mentioned technical features or equivalent features. For example, the above features are formed by replacing technical features having similar functions disclosed in the present invention with each other.

Claims

1. An electrode comprising a current collector and an active material layer located on one or both sides of the current collector, the active material layer includes a first region and a second region, the first region is located between the current collector and the second region along a thickness direction of the electrode, the first region being a region extending from the current collector side to two-thirds of the thickness of the active material layer, and the second region being a region extending from two-thirds of the thickness of the active material layer to a surface of the electrode, an electrode, characterized in that: a thermogravimetric analysis is performed on the active material layer in an inert atmosphere at a heating rate of 10°C / min; and the result of the thermogravimetric analysis shows that the difference in the number of thermal weight loss peaks between the first region and the second region at 200°C to 800°C is ≧1, the number of weight loss peaks in the second region is smaller than the number of weight loss peaks in the first region; and the result of the thermogravimetric analysis shows that the mass change in the second region at 200°C to 800°C is 0% to 0.97%.

2. 2. The electrode according to claim 1, wherein a thermogravimetric analysis is performed on the active material layer in an inert atmosphere at a heating rate of 10°C / min, and the results of the thermogravimetric analysis show that the number of weight loss peaks in the first region from 200°C to 800°C is 1 or more, and the number of weight loss peaks in the second region from 200°C to 800°C is 0 to 2.

3. An electrode as described in claim 1, characterized in that the results of the thermogravimetric analysis show that the mass change of the first region at temperatures between 200°C and 800°C is 0.21% to 13%.

4. 2. The electrode of claim 1, wherein the results of the thermogravimetric analysis show that the mass change of the first region from 200°C to 800°C is 1.6% to 4.02%.

5. 2. The electrode according to claim 1, wherein the electrode is a negative electrode, the active material layer is a negative electrode active material layer, and the current collector is a negative electrode current collector.

6. The electrode is (c) the compressed density ρ of the negative electrode active material layer １ is ρ １ ≧0.6 g / cm ３ That is, (d) The thickness h of the negative electrode active material layer on one side of the negative electrode current collector １ Is, h １ ≧10 μm; (e) the negative electrode active material layer contains a negative electrode material, and the negative electrode material contains at least one of lithium titanate, silicon monoxide, graphite, silicon, and hard carbon; 6. The electrode according to claim 5, wherein at least one of the following is satisfied:

7. The electrode is (f) the compressed density ρ of the negative electrode active material layer １ is 1.85 g / cm ３ ≧ρ １ ≧0.65 g / cm ３ and (g) The thickness h of the negative electrode active material layer on one side of the negative electrode current collector １ is 1500 μm ≧ h １ ≧15 μm; 6. The electrode according to claim 5, wherein at least one of the following is satisfied:

8. The electrode is (h) the compressed density ρ of the negative electrode active material layer １ is 1.83 g / cm ３ ≧ρ １ ≧1.0 g / cm ３ and (i) The thickness h of the negative electrode active material layer on one side of the negative electrode current collector １ is 150 μm ≧ h １ ≧30 μm; 6. The electrode according to claim 5, wherein at least one of the following is satisfied:

9. the electrode is a positive electrode, the current collector is a positive electrode current collector, and the active material layer is a positive electrode active material layer; The electrode is (j) the compressed density ρ of the positive electrode active material layer ２ is ρ ２ ≧2 g / cm ３ That is, (k) The thickness h of the positive electrode active material layer on one side of the positive electrode current collector ２ Is, h ２ ≧20 μm; (l) the positive electrode active material layer contains a positive electrode material, and the positive electrode material contains at least one of lithium iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, lithium cobalt oxide, and lithium nickel cobalt aluminum oxide; Satisfy at least one of the following: Electrode according to claim 1 , characterized in that

10. the electrode is a positive electrode, the current collector is a positive electrode current collector, and the active material layer is a positive electrode active material layer; The electrode is (m) the compressed density ρ of the positive electrode active material layer ２ is 4.25 g / cm ３ ≧ρ ２ ≧2.3 g / cm ３ and (n) The thickness h of the positive electrode active material layer on one side of the positive electrode current collector ２ is 1500 μm ≧ h ２ ≧30 μm; Satisfy at least one of the following: Electrode according to claim 1 , characterized in that

11. the electrode is a positive electrode, the current collector is a positive electrode current collector, and the active material layer is a positive electrode active material layer; The electrode is (o) the compressed density ρ of the positive electrode active material layer ２ is 4.23 g / cm ３ ≧ρ ２ ≧4.0 g / cm ３ and (p) The thickness h of the positive electrode active material layer on one side of the positive electrode current collector ２ is 130 μm ≧ h ２ ≧26 μm; Satisfy at least one of the following: Electrode according to claim 1 , characterized in that

12. The active material layer contains a conductive agent, and The active material layer is (q) the mass percentage of the conductive agent in the first region is B, the mass percentage of the conductive agent in the second region is A, and A is greater than B; (r) the mass percentage of the conductive agent in the first region is B, the mass percentage of the conductive agent in the second region is A, and (A-B) / B≧20%; (s) the conductive agent includes at least one of carbon nanotubes, carbon fibers, acetylene black, graphene, ketjen black, and conductive carbon black; (t) the mass percentage of the conductive agent in the active material layer is 0 to 2% with respect to the total mass of the active material layer; Satisfy at least one of the following: Electrode according to claim 1 , characterized in that

13. the first region includes a polymer compound, and The first region is (u) the polymer compound includes at least one of polyethylene oxide, polypropylene oxide, polyvinylidene fluoride, polytetrafluoroethylene, polyacrylonitrile, polyimide, polysiloxane, polyacrylic acid, polypropylene derivatives, sodium carboxymethylcellulose, lithium carboxymethylcellulose, polymethylpyrrolidone, polyvinylpyrrolidone, styrene acrylate, and styrene-butadiene rubber; (v) the mass percentage of the polymer compound in the active material layer is 0.42% to 14%; Satisfy at least one of the following: Electrode according to claim 1 , characterized in that

14. The electrode according to claim 1 , wherein the first region contains a polymer compound, and the mass percentage of the polymer compound in the active material layer is 2.0% to 5.0%.

15. A method for producing an electrode according to any one of claims 1 to 14, comprising the steps of: applying the active material layer slurry to at least one surface of a current collector, drying it, and cold pressing it to obtain an initial electrode; and performing a process on the initial electrode to obtain the electrode. the treatment of the initial electrode includes plasma treatment of the initial electrode in a vacuum environment, heat treatment of the initial electrode in a vacuum or inert gas environment, or laser bombardment of the initial electrode in a vacuum or inert gas environment; In the plasma treatment of the initial electrode in a vacuum environment, the plasma output is 0.5 kW to 5 kW, the gas source contains at least one of nitrogen gas, argon gas, and carbon tetrafluoride, the gas flow rate is 3000 sccm to 5000 sccm, the temperature is 20°C to 60°C, and the treatment time is 0.5 min to 1 min; In the heat treatment of the initial electrode under a vacuum or inert gas environment, the heat treatment temperature is higher than 200°C and the heat treatment time is 1 minute to 3 minutes; In the laser impact on the initial electrode under vacuum or inert gas environment, the laser intensity is 30W to 100W, and the treatment time is 0.5s to 1s; A manufacturing method characterized by:

16. A method for producing an electrode according to any one of claims 1 to 14, comprising the steps of: applying the active material layer slurry to at least one surface of a current collector, drying it, and cold pressing it to obtain an initial electrode; and performing a process on the initial electrode to obtain the electrode. The treatment of the initial electrode includes heat treatment of the initial electrode in a vacuum or inert gas environment, the heat treatment temperature is 350°C to 600°C, and the heat treatment time is 1 minute to 3 minutes. A manufacturing method characterized by:

17. 1. An electrochemical device comprising an electrode, An electrochemical device, characterized in that the electrode is the electrode according to any one of claims 1 to 14.

18. An electronic device comprising the electrochemical device of claim 17.

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