Composite pole piece, preparation method and application thereof

Abstract

The application discloses a kind of composite pole piece and its preparation method and application, belong to battery material technical field.The composite pole piece includes current collector, the surface of current collector has active material layer, active material layer simultaneously has low voltage platform active area and high voltage platform active area;Low voltage platform active area and current collector have microcrystalline lattice formed by functional additive between them;Functional additive includes electric polymer.By setting low voltage and high voltage platform active area on the same current collector, the advantages of different active materials can be concentrated on the same pole piece and make full use of their performance advantages;When battery is in overcharge environment, microcrystalline lattice arranged in composite pole piece can directly absorb and consume conversion overcharge current on current collector, quickly respond to overcharge protection of participating material.Battery with the above-mentioned composite pole piece can have higher battery energy density and rate, longer cycle life and better safety.

Description

Technical Field

[0001] This invention relates to the field of battery materials technology, and more specifically, to a composite electrode, its preparation method, and its application. Background Technology

[0002] Currently, commonly used cathode materials in lithium batteries include lithium cobalt oxide, lithium nickel cobalt aluminum oxide, lithium iron phosphate, lithium manganese oxide, lithium nickel manganese oxide, and lithium nickel cobalt manganese oxide. Commonly used anode materials are broadly classified into two categories: carbon materials and non-carbon materials. Carbon materials specifically refer to carbon-based systems, mainly including artificial graphite, natural graphite, mesophase carbon microspheres, and hard carbon. Non-carbon materials mainly include silicon-based materials (such as silicon-based silicon suboxide, elemental silicon, and silicon-carbon composites), tin-based materials, titanium-based materials, nitrides, composite oxides, and metallic lithium.

[0003] However, each single material system used in batteries has its own advantages and disadvantages. For example, lithium manganese oxide, a cathode material, has good rate performance and high compaction density, but low actual specific capacity; lithium iron phosphate has good cycle performance and high safety performance, but low actual energy density; lithium cobalt oxide has high compaction density and high energy density, but high cost, and poor safety and thermal stability; ternary nickel-cobalt-manganese materials have high specific capacity and high energy density, but poor high-temperature performance, cycle performance, and safety performance. For example, graphite, a cathode material, has a long cycle life, but low specific capacity; hard carbon has good rate performance, but low compaction density; lithium titanate has good low-temperature performance and is suitable for high-rate charge and discharge, but low specific capacity and serious gas generation during charge and discharge; silicon has a high theoretical specific capacity, but low inherent conductivity and high volume expansion.

[0004] Currently, there is no existing technology that can simultaneously use different material systems in the current collector and achieve a battery with high energy density and rate capability, long cycle life, and good safety.

[0005] In view of this, the present invention is proposed. Summary of the Invention

[0006] The purpose of this invention is to provide a composite electrode, its preparation method, and its application, so as to solve or improve the above-mentioned technical problems.

[0007] This invention can be implemented as follows: In a first aspect, the present invention provides a composite electrode, the composite electrode comprising a current collector, the surface of the current collector having an active material layer, the active material layer having both a low-voltage plateau active region and a high-voltage plateau active region; and, between the low-voltage plateau active region and the current collector, there is a microcrystalline lattice formed by functional additives. Functional additives include electropolymers.

[0008] In an optional embodiment, the current collector has a first surface and a second surface disposed opposite to each other along the thickness direction of the current collector, and the active material layer includes a first active material layer and a second active material layer; wherein, the first active material layer is disposed on the first surface, and the second active material layer is disposed on the second surface; The first active material layer consists entirely of low-voltage plateau active regions, while the second active material layer consists entirely of high-voltage plateau active regions. Alternatively, the first active material layer may consist entirely of high-voltage plateau active regions, and the second active material layer may consist entirely of high-voltage plateau active regions. Alternatively, the first active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, while the second active material layer consists entirely of low-voltage plateau active regions. Alternatively, the first active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, while the second active material layer consists entirely of high-voltage plateau active regions. Alternatively, the first active material layer may consist entirely of low-voltage plateau active regions, while the second active material layer may contain both low-voltage plateau active regions and high-voltage plateau active regions. Alternatively, the first active material layer may consist entirely of high-voltage plateau active regions, while the second active material layer may contain both low-voltage plateau active regions and high-voltage plateau active regions. Alternatively, the first active material layer contains both a low-voltage plateau active region and a high-voltage plateau active region, and the second active material layer contains both a low-voltage plateau active region and a high-voltage plateau active region.

[0009] In an optional embodiment, when the same active material layer contains both a low-voltage plateau active region and a high-voltage plateau active region, the connection position between the low-voltage plateau active region and the high-voltage plateau active region has at least one of the following characteristics: Feature 1: The connection between the low-voltage plateau active region and the high-voltage plateau active region is wedge-shaped; Feature 2: The connection between the low-voltage plateau active region and the high-voltage plateau active region is an overlapping method; Feature 3: The length of the active region of the high-voltage platform gradually increases along the direction away from the current collector; Feature 4: The acute angle between the active region of the low-voltage platform and the current collector is 15°~45°; preferably, the acute angle is 30°. Feature 5: The projected length of the side of the low-voltage platform active region connected to the high-voltage platform active region on the current collector surface is 50μm~930μm.

[0010] In an optional embodiment, the first active material layer includes m first active material sub-regions, and the second active material layer includes n second active material sub-regions, where m ≥ 1, n ≥ 1, and m and n are both integers. The active material used in the m-th first active material sub-region is denoted as x. m The active material used in the nth second active material sub-region is denoted as y. n ; Different first active material sub-regions may use the same or different active materials, and different second active material sub-regions may use the same or different active materials. m With y n They may be the same or different; and at least one active material sub-region has an active material that is a low-voltage platform active material, and at least one active material sub-region has an active material that is a high-voltage platform active material.

[0011] In a second aspect, the present invention provides a method for preparing a composite electrode as described in any of the foregoing embodiments, comprising the following steps: preparing a microcrystalline lattice in a predetermined region of a current collector by mixing a mixture containing functional additives; preparing a low-voltage plateau active region of an active material layer on the surface of the microcrystalline lattice; and preparing a high-voltage plateau active region of an active material layer on the remaining surface of the current collector where the microcrystalline lattice has not been prepared.

[0012] In an optional embodiment, the current collector is tractioned at both ends and passes sequentially on the rollers through a spray section, a crystallization section, a coating section, and a drying section. In the spraying section, the mixture is applied to a predetermined position on the current collector by spraying. Then, in the crystallization section, the mixture applied to the surface of the current collector is heated to form a solid microcrystalline lattice. In the coating section, different active slurries are applied to the surface of the solid microcrystalline lattice and the remaining surface of the current collector without microcrystalline lattice. In the drying section, the active slurries are dried to form low-voltage plateau active regions and high-voltage plateau active regions, respectively.

[0013] In an optional embodiment, the preparation of the microcrystalline lattice includes at least one of the following features: Feature 6: The droplet size of the spray is 500μm~1000μm; Feature 7: Droplet density is 40 droplets / cm³ 2 ~300 pieces / cm 2 ; Feature 8: The temperature of the crystallization zone is 80℃~120℃; Feature 9: The amount of functional additives used is 0.5mg / Ah~15mg / Ah, where Ah is a unit of battery capacity; Feature 10: The mass fraction of the mixture is 0.5%~2%; Feature 11: The electropolymer includes at least one of metallocene compounds, heterocyclic compounds, substituted or unsubstituted aromatic compounds; Feature 12: The area of ​​the microcrystalline lattice is 50% to 70% of the total area of ​​the current collector.

[0014] In optional embodiments, the metallocene compound includes at least one of ferrocene (dicyclopentadienyl iron), butylferrocene (di-n-butylcyclopentadienyl iron), nickel diacene (dicyclopentadienyl nickel), and cobalt diacene (dicyclopentadialkyl cobalt); Alternatively, the heterocyclic compound includes at least one of aza-benzobenzene, aza-benzotetrabenzene, aza-benzopentabenzene derivatives, halosiloxane-modified 2-aminothiophene-3-carboxynitrile, thiathracene, phenothiazine derivatives, and N,N-dialkyl-dihydrophenazine. Alternatively, the unsubstituted aromatic compounds include at least one of naphthalene and anthracene; Alternatively, the substituted aromatic compounds include at least one of difluorophenyl-phenylphosphonate, dimethoxybenzene derivatives, anisole, and 2,2,6,6-tetramethylpiperidine oxide.

[0015] In optional embodiments, the electropolymer includes difluorophenyl-phenylphosphonate, azidobenzene, azidotetraphenyl and azidopentabenzene derivatives, halosiloxane-modified 2-aminothiophene-3-carboxynitrile, dimethoxybenzene derivatives, naphthalene, anthracene, thiaanthracene, anisole, phenothiazine derivatives, N,N-dialkyl-dihydrophenazine, and 2,2,6,6-tetramethylpiperidine oxide.

[0016] In an optional embodiment, the dimethoxybenzene derivative includes at least one selected from 1,4-di-tert-butyl-2,5-dimethoxybenzene, 4-tert-butyl-1,2-dimethoxybenzene, and 2,5-di-tert-butyl-1,4-dimethoxybenzene.

[0017] In an optional embodiment, the thiathane includes at least one of 2,7-diacetylthiathane, 2,7-dibromothiathane, 2,7-diisobutyrylthiathane, and 2-acetylthiathane.

[0018] In an optional embodiment, the solvent in the mixture includes ethanol.

[0019] In an optional embodiment, in the coating section, along the direction of movement of the current collector, the coating width of the active slurry is 1mm to 2mm smaller than the width of the current collector. Alternatively, in the drying section, the drying temperature is 90℃~130℃.

[0020] Thirdly, the present invention provides a battery cell having a composite electrode as described in any of the foregoing embodiments.

[0021] In an optional implementation, the battery cell is a wound battery cell.

[0022] Fourthly, the present invention provides a battery comprising the cell of the foregoing embodiments.

[0023] The beneficial effects of this invention include: This invention, by setting low-voltage plateau active regions and high-voltage plateau active regions on the same current collector, can concentrate the advantages of different active materials on the same electrode and allow them to fully utilize their respective performance advantages. The microcrystalline lattice formed between the low-voltage plateau active region and the current collector can directly absorb and dissipate the overcharge current on the current collector when the battery is in an overcharge environment, quickly responding to the overcharge protection of the participating materials. Batteries with the above-mentioned composite electrode can have higher battery energy density, rate capability, longer cycle life, and better safety. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0025] Figure 1 A schematic diagram of a design scheme for the active material in the composite electrode provided by the present invention; Figure 2 A schematic diagram showing the connection between the low-voltage plateau active region and the high-voltage plateau active region in the same active layer of the composite electrode provided by the present invention. Figure 3 This is a schematic diagram of the structure of the surface active material layer for current collectors in the prior art; Figure 4 This is a schematic diagram illustrating the fabrication process of the composite electrode provided by the present invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0027] The composite electrode provided by this invention, its preparation method, and its application are described in detail below.

[0028] This invention proposes a composite electrode, combining Figure 1 and Figure 2The composite electrode includes a current collector, the surface of which has an active material layer, and the active material layer has both a low-voltage plateau active region and a high-voltage plateau active region; and there is a microcrystalline lattice formed by functional additives between the low-voltage plateau active region and the current collector. Functional additives include electropolymers (also known as "redox shuttle pairs O / R").

[0029] In this article, "low" and "high" are relative concepts and do not specifically limit the scope of "low" and "high".

[0030] It should be noted that currently, increasing the upper limit voltage of batteries can meet the actual market demand for high power and high energy density. However, excessively high voltage can easily lead to overcharging of the cathode material and cause thermal runaway. Existing technologies attempt to improve this problem by using functional additives. However, the conventional approach in existing technologies is to add functional additives to the electrolyte or active materials. This reduces the proportion of active materials and affects their performance. Furthermore, mixing them into the active material or electrolyte can crowd out lithium-ion channels, leading to increased internal resistance. When the battery is about to be overcharged, the additives mixed in the electrolyte or active materials diffuse to the electrode side to absorb and consume the overcharge current. From a kinetic perspective, this process takes a certain amount of time, and the additives cannot participate in overcharge potential clamping protection in time. Moreover, as the number of battery cycles increases, the electrolyte is consumed, which affects the diffusion of the additives, thereby reducing their overcharge protection.

[0031] This invention creatively uses additives to be spray-deposited and crystallized on the surface of the current collector in the form of microcrystalline particles. After the slurry is applied, the crystals temporarily dissolve and then recrystallize after drying, forming a microcrystalline lattice distributed between the current collector and the low-voltage platform active region. When the battery is in an overcharged environment, the additives can directly absorb and consume the overcharge current on the current collector, quickly responding to the overcharge protection of the participating materials.

[0032] The composite electrode in this paper can be either a positive or negative electrode. The current collector can be aluminum foil, copper foil, or a composite current collector with aluminum or copper as the main conductive layer. Aluminum foil and current collectors with aluminum as the main conductive layer correspond to the positive electrode, while copper foil and current collectors with copper as the main conductive layer correspond to the negative electrode. When the composite electrode is a positive electrode, the active material used in the active material layer is the positive active material; when the composite electrode is a negative electrode, the active material used in the active material layer is the negative active material.

[0033] The current collector has a first surface and a second surface disposed opposite to each other along the thickness direction of the current collector, and the active material layer includes a first active material layer and a second active material layer; wherein the first active material layer is disposed on the first surface and the second active material layer is disposed on the second surface.

[0034] In some alternative embodiments, the first active material layer is entirely composed of low-voltage plateau active regions, and the second active material layer is entirely composed of high-voltage plateau active regions.

[0035] In some alternative embodiments, the first active material layer is entirely composed of high-voltage plateau active regions, and the second active material layer is entirely composed of high-voltage plateau active regions.

[0036] In some alternative embodiments, the first active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, while the second active material layer consists entirely of low-voltage plateau active regions.

[0037] In some alternative embodiments, the first active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, while the second active material layer consists entirely of high-voltage plateau active regions.

[0038] In some alternative embodiments, the first active material layer is entirely composed of low-voltage plateau active regions, and the second active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions.

[0039] In some alternative embodiments, the first active material layer is entirely composed of high-voltage plateau active regions, and the second active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions.

[0040] In some alternative embodiments, the first active material layer simultaneously contains both a low-voltage plateau active region and a high-voltage plateau active region, and the second active material layer simultaneously contains both a low-voltage plateau active region and a high-voltage plateau active region (e.g., Figure 2 (As shown).

[0041] For example, the active material used in the low-voltage platform active region can be lithium iron phosphate (platform voltage 3.4V, voltage range 3.2V~3.7V), and the active material used in the high-voltage platform active region can be lithium cobalt oxide (platform voltage 3.7V, voltage range 3.0V~4.5V).

[0042] When the same active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, the low-voltage plateau active region is formed by at least one low-voltage plateau active sub-region, and the high-voltage plateau active region is formed by at least one high-voltage plateau active sub-region. Different low-voltage plateau active sub-regions can be arranged continuously or intermittently; similarly, different high-voltage plateau active sub-regions can be arranged continuously or intermittently.

[0043] Unlike traditional systems that continuously coat a single material across a wide area of ​​the current collector surface (such as...), Figure 3 In some embodiments of the present invention, by using active materials different from the original single material system to interweave and replace part of the coating area of ​​the original single material system, composite electrode sheets of different types of materials are formed, which can improve the overall performance of the battery.

[0044] In some embodiments, when the same active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, the connection between the low-voltage plateau active regions and the high-voltage plateau active regions is wedge-shaped (e.g., Figure 2 (As shown). This wedge-shaped connection method can also be understood as an overlapping joint between two interconnected areas.

[0045] In other words, the above method can also be understood as wedge-shaped thickness reduction treatment at the beginning and end of the coating of low-voltage active material. Correspondingly, the beginning and end of the coating of low and high voltage plateau active materials are overlapped, that is, the coating of active material with relatively high voltage plateau overlaps on the active material with relatively low voltage plateau, so as to continuously coat low and high voltage plateau materials on the same current collector to obtain composite electrode.

[0046] In some alternative embodiments, the length of the high-voltage platform active region for connection with the low-voltage platform active region gradually increases along the direction away from the current collector, so as to... Figure 2 Taking the orientation as an example, it has a shape that is narrow at the bottom and wide at the top on the upper surface of the current collector.

[0047] It should be noted that existing technologies use different patterns as units, splicing different active materials onto the current collector surface by spraying or jetting. However, due to the complexity of the patterns and the large number of splices, the yield and production efficiency are low. Furthermore, the numerous edges or corners at the contact points between different active material coatings, coupled with varying shrinkage rates during the drying process of the wet slurry, result in micro-gaps or cracks at the splices. This affects the uniformity, consistency, and integrity of the electrolyte interphase (CEI) film formed on the positive electrode or the solid electrolyte interphase (SEI) film formed on the negative electrode during the battery's activation and formation stage. This leads to increased internal resistance of the electrode, increased heat generation, and reduced cycle performance. In particular, after splicing multiple materials on the current collector surface, the different currents that the active materials in different pattern units withstand during charging and discharging can easily cause overcharging or over-discharging in certain areas, thus reducing battery safety performance.

[0048] This invention, by setting a microcrystalline lattice between the low-voltage plateau active region and the current collector, enables the direct absorption and conversion of overcharge current on the current collector when the battery is in an overcharge environment, thus rapidly responding to the overcharge protection of the participating materials. Furthermore, by setting the connection between the low-voltage plateau active region and the high-voltage plateau active region in a wedge-shaped manner, the coating positions at the beginning and end of adjacent two different active material systems adopt a wedge-shaped thickness reduction and overlapping method (e.g., ...). Figure 4 As shown, the current collector passes between the two roller surfaces and adheres to the lower roller surface. During coating, the upper roller surface is coated with a uniform slurry. When the upper roller adheres to the upper surface of the current collector, the current collector, driven by the traction machine, causes the slurry to adhere evenly to its surface through friction. The upper roller can adjust the coating thickness by setting the gap value between itself and the lower roller in stages through the control system. Therefore, a dried wedge-shaped coating area with reduced thickness can be obtained at the beginning and end of coating. When other material slurries are coated again in the middle of the beginning and end of adjacent electrodes, it is not necessary to set the gap value between the two roller surfaces in stages. During coating, the slurry adheres to the upper surface of the dried wedge-shaped coating area, completing the overlapping operation. This effectively avoids microcracks or gaps at the joint of the active material coating area caused by the drying of different active material systems, as well as uneven, inconsistent or incomplete film formation of the electrodes, and high film resistance, which affect the electrochemical performance of the finished battery, such as cycle and rate performance.

[0049] In some optional embodiments, the acute angle between the active region of the low-voltage platform and the current collector can be 15° to 45°, such as 15°, 18°, 20°, 22°, 25°, 28°, 30°, 32°, 35°, 38°, 40°, 42°, or 45°, or any other value within the range of 15° to 45°. In some more typical embodiments, the acute angle between the active region of the low-voltage platform and the current collector can be 30°.

[0050] If the acute angle between the active area of ​​the low-voltage platform and the current collector is less than 15°, the starting area of ​​the active material coating on the current collector surface is too thin, resulting in low adhesion and easy material detachment after drying. If the acute angle between the active area of ​​the low-voltage platform and the current collector is greater than 45°, the upper surface of the wedge-shaped coating area formed by the low-voltage platform is too steep, which is not conducive to the overlapping of the active material of the high-voltage platform on its surface.

[0051] In some optional embodiments, the projected length of the side of the low-voltage platform active region connected to the high-voltage platform active region on the current collector surface can be 50 μm to 930 μm (wherein, the projected length of the positive electrode active region on the current collector surface is 500 μm to 930 μm; the projected length of the negative electrode active region on the current collector surface is 50 μm to 740 μm, preferably 500 μm for both), such as 50 μm, 80 μm, 120 μm, 200 μm, 740 μm, 900 μm, or 930 μm, or any other value within the range of 50 μm to 930 μm. In some more typical embodiments, the projected length of the side of the low-voltage platform active region connected to the high-voltage platform active region on the current collector surface is 300 μm to 600 μm.

[0052] If the projection length is less than 300μm, the overlap area due to the limited precision of the coating machine will be too small, resulting in poor overlap and increased material contact resistance. If the projection length is greater than 600μm, the active material will be coated too thickly on the current collector surface, which is not conducive to the performance of the active material.

[0053] In some optional embodiments, the first active material layer includes m first active material sub-regions, and the second active material layer includes n second active material sub-regions, where m ≥ 1, n ≥ 1, and m and n are both natural numbers. The active material used in the m-th first active material sub-region is denoted as x. m The active material used in the nth second active material sub-region is denoted as y. n ; The active materials used in the different first active material sub-regions mentioned above may be the same or different, and the active materials used in the different second active material sub-regions may be the same or different. m With y n They may be the same or different; and at least one active material sub-region has an active material that is a low-voltage platform active material, and at least one active material sub-region has an active material that is a high-voltage platform active material.

[0054] The aforementioned composite electrodes can be used alone or in combination in wound-structured batteries.

[0055] For example, when the total number of turns of the positive and negative electrodes is greater than 2, the composite electrode structure can be as follows: Figure 1 As shown, the first surface of the current collector is coated with a first active material layer, which is divided into x1, x2, ..., x... m The first active material sub-region has a second active material layer coated on the second surface of the current collector. The second active material layer is divided into y1, y2, ..., y n The second active material sub-region, x1, x2, ..., x m y1, y2, ..., y n The combination of active material sub-regions includes, but is not limited to, the following: (1) x1, x2, ..., x m The active materials in the first active material sub-region are the same active material a (a single material system or a multi-material system), y1, y2, ..., y n The second active material sub-region may contain one or more independent single active material systems or multi-material systems, which may or may not contain active material a. (2) x1, x2, ..., x m The first active material sub-region may or may not contain active material a, y1, y2, ..., y nThe second active material sub-region contains an active layer composed of one or more independent single active material systems or multi-material systems, with or without active material a; that is, in x1, x2, ..., x m y1, y2, ..., y n The active material sub-regions can be composed of multiple single active material systems or multi-component material systems.

[0056] As an example, the aforementioned "single material system" can be a lithium iron phosphate system, and the aforementioned "multi-material system" can be a mixed system of lithium iron phosphate and lithium manganese oxide.

[0057] Furthermore, if x1, x2, ..., x m y1, y2, ..., y n When the active material used in the active material sub-region is a low-voltage platform material, it needs to be spray-dried and crystallized to form a microcrystalline lattice.

[0058] In some embodiments, the positive / negative composite electrode sheet prepared in a battery cell has a total of 2 or 3 active layer types composed of single active material systems and multi-element active material systems on both sides of the current collector.

[0059] Specifically, the above x1, x2, ..., x m With y1, y2, ..., y n There is no one-to-one correspondence; it is only used for detailed explanation.

[0060] As for active materials, active materials can be a single material system or a multi-material system composed of single material systems with the same polarity. The multi-material system should contain two or more material systems.

[0061] In some optional embodiments, the positive electrode active material comprises at least three metallic elements and at least one non-metallic element. The metallic elements include, but are not limited to, lithium, iron, manganese, cobalt, nickel, aluminum, sodium, molybdenum, tungsten, chromium, vanadium, magnesium, zinc, potassium, titanium, copper, platinum, gold, zirconium, silver, or calcium. The non-metallic elements include, but are not limited to, oxygen, phosphorus, sulfur, carbon, silicon, fluorine, boron, or nitrogen. In some typical embodiments, the positive electrode active material may be lithium iron phosphate containing lithium, iron, phosphorus, and oxygen; lithium manganese oxide containing lithium, manganese, and oxygen; lithium cobalt oxide containing lithium, cobalt, and oxygen; or a ternary nickel-cobalt-manganese material containing lithium, nickel, cobalt, manganese, and oxygen.

[0062] In some optional embodiments, the negative electrode active material comprises at least one metallic or non-metallic element. The metallic element includes, but is not limited to, tin, titanium, lithium, copper, antimony, manganese, aluminum, zinc, iron, nickel, calcium, germanium, sodium, potassium, chromium, cobalt, manganese, or molybdenum. The non-metallic element includes, but is not limited to, silicon, carbon, nitrogen, phosphorus, or fluorine. In some typical embodiments, the negative electrode active material may be artificial graphite containing carbon, a silicon-carbon composite material containing carbon and silicon, lithium titanate containing lithium, titanium, and oxygen, or lithium metal containing lithium.

[0063] Accordingly, the present invention also provides a method for preparing the above-mentioned composite electrode, which includes the following steps: preparing a microcrystalline lattice in a predetermined region of a current collector by mixing a mixture containing functional additives; preparing a low-voltage platform active region of an active material layer on the surface of the microcrystalline lattice; and preparing a high-voltage platform active region of an active material layer on the remaining surface of the current collector where the microcrystalline lattice has not been prepared.

[0064] In some alternative embodiments, the current collector is tractioned at both ends and passed sequentially on a roller shaft through a spray section, a crystallization section, a coating section, and a drying section (e.g., ...). Figure 4 (As shown).

[0065] In the spraying section, the mixture is applied to a predetermined position on the current collector by spraying. Then, in the crystallization section, the mixture applied to the surface of the current collector is heated to form a solid microcrystalline lattice. In the coating section, different active slurries are applied to the surface of the solid microcrystalline lattice and the remaining surface of the current collector without microcrystalline lattice. In the drying section, the active slurries are dried to form low-voltage plateau active regions and high-voltage plateau active regions, respectively.

[0066] In an optional embodiment, the particle size of the spray droplets used to prepare the microcrystalline lattice can be 500μm to 1000μm, such as 500μm, 600μm, 700μm, 800μm, 900μm or 1000μm, or any other value in the range of 500μm to 1000μm.

[0067] The droplet density can be 40 droplets / cm³ 2 ~300 pieces / cm 2 For example, 40 pieces / cm 2 50 pieces / cm 2 80 pieces / cm 2 100 pieces / cm 2 120 pieces / cm 2 150 pieces / cm 2 180 pieces / cm2 200 pieces / cm 2 220 pieces / cm 2 250 pieces / cm 2 280 pieces / cm 2 Or 300 pieces / cm 2 Alternatively, it can be 40 pieces / cm. 2 ~300 pieces / cm 2 Any other value within the range.

[0068] The temperature of the crystallization zone can be 80℃~120℃, such as 80℃, 85℃, 90℃, 95℃, 100℃, 105℃, 110℃, 115℃ or 120℃, or other values ​​within the range of 80℃~120℃.

[0069] The dosage of functional additives can range from 0.5 mg / Ah to 15 mg / Ah, such as 0.5 mg / Ah, 1 mg / Ah, 5 mg / Ah, 10 mg / Ah, or 15 mg / Ah, or other values ​​within the range of 0.5 mg / Ah to 15 mg / Ah. The "Ah" mentioned above refers to the unit of battery capacity.

[0070] The mass fraction of the mixture can be 0.5% to 2%, such as 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8% or 2%, or other values ​​within the range of 0.5% to 2%.

[0071] In some embodiments, the electropolymer may, by way of example but not by way of limitation, include at least one of metallocene compounds, heterocyclic compounds, substituted or unsubstituted aromatic compounds.

[0072] The metallocene compounds may, by way of example but not by way of limitation, include at least one of ferrocene (dicyclopentadienyl iron), butylferrocene (di-n-butylcyclopentadienyl iron), nickel diacene (dicyclopentadienyl nickel), and cobalt diacene (dicyclopentadialkyl cobalt).

[0073] Heterocyclic compounds may, by way of example but not by way of limitation, include at least one of azircon, azircon-tetrabenzene, azircon-pentabenzene derivatives, halosiloxane-modified 2-aminothiophene-3-carboxynitrile, thiaanthracene, phenothiazine derivatives, and N,N-dialkyl-dihydrophenazine.

[0074] Unsubstituted aromatic compounds may, by way of example but not by way of limitation, include at least one of naphthalene and anthracene.

[0075] The substituted aromatic compounds may, by way of example but not by way of limitation, include at least one of difluorophenyl-phenylphosphonate, dimethoxybenzene derivative, anisole, and 2,2,6,6-tetramethylpiperidine oxide.

[0076] In some more specific alternatives, the electropolymer may, by way of example but not by way of limitation, include difluorophenyl-phenylphosphonate, azidobenzene, azidotetraphenyl and azidopentabenzene derivatives, halosiloxane-modified 2-aminothiophene-3-carboxynitrile, dimethoxybenzene derivatives, naphthalene, anthracene, thiaanthracene, anisole, phenothiazine derivatives, N,N-dialkyl-dihydrophenazine, and 2,2,6,6-tetramethylpiperidine oxide.

[0077] The dimethoxybenzene derivative may, by way of example but not limitation, include at least one of 1,4-di-tert-butyl-2,5-dimethoxybenzene, 4-tert-butyl-1,2-dimethoxybenzene, and 2,5-di-tert-butyl-1,4-dimethoxybenzene. The thiazolium may, by way of example but not limitation, include at least one of 2,7-diacetylthiazolium, 2,7-dibromothiazolium, 2,7-diisobutyrylthiazolium, and 2-acetylthiazolium.

[0078] The aforementioned electropolymer can directly convert to its oxidized form O on the overcharged positive electrode side. Electropolymerization occurs under high voltage, consuming the overcharge current and excess charge. Then, through diffusion in the electrolyte, it is reduced to its original state R on the negative electrode side. The reversible nature of the redox shuttle couple O / R will maintain the aforementioned "oxidation-diffusion-reduction-diffusion" cycle indefinitely, thereby locking the positive electrode potential at the oxidation potential of R until the charge terminates. Its characteristic oxidation potential (3.7V-4.7V & Li / Li) + The oxidation potential should be higher than that of the positive electrode and lower than that of the electrolyte decomposition potential. It should have high kinetic reversibility on both the positive and negative electrodes, good solubility in the electrolyte and no negative impact on battery performance, and sufficient chemical and electrochemical stability.

[0079] In an optional embodiment, the solvent in the mixture includes ethanol to facilitate removal during the crystallization process. The ethanol may be industrial-grade alcohol with a purity of 99%.

[0080] In some alternative implementations, the area of ​​the microcrystalline lattice is 50% to 70% of the total area of ​​the current collector, such as 50%, 55%, 60%, 65% or 70%, or other values ​​within the range of 50% to 70%.

[0081] If the area of ​​the microcrystalline lattice is less than 50% of the total area of ​​the current collector, it is not conducive to weakening the protection of the active material at low voltage platforms when the amount of electropolymer is small; if the area of ​​the microcrystalline lattice is more than 70% of the total area of ​​the current collector, it is not conducive to increasing the contact resistance between the active material and the surface of the current collector due to excessive electropolymer.

[0082] In an optional embodiment, in the coating section, along the direction of movement of the current collector, the coating width of the active slurry is 1mm to 2mm smaller than the width of the current collector, for example, it can be 1mm, 1.5mm or 2mm smaller.

[0083] In the drying section, the drying temperature can be 90℃~130℃, such as 90℃, 95℃, 100℃, 105℃, 110℃, 115℃, 120℃, 125℃ or 130℃, or other values ​​within the range of 90℃~130℃.

[0084] Furthermore, taking the positive electrode active slurry as an example, the positive electrode active slurry can be composed of positive electrode active material, conductive agent, binder, and solvent. Converted to the total weight percentage of the active dry material, the positive electrode active material can be 70wt%~98wt%, the conductive agent can be 0.2wt%~25wt%, and the binder can be 1wt%~10wt%. Specifically, the positive electrode active material can be at least one of lithium iron phosphate, lithium manganese oxide, lithium cobalt oxide, and ternary nickel-cobalt-manganese alloys; the conductive agent can be at least one of conductive graphite, conductive carbon black, carbon nanotubes, and graphene; the binder can be at least one of PVDF (polyvinylidene fluoride), modified PVDF systems, and PAA (polyacrylic acid); and the solvent can be at least one of NMP (NN-dimethylpyrrolidone) and deionized water.

[0085] Similarly, taking negative electrode active slurry as an example, negative electrode active slurry can be composed of negative electrode active material, conductive agent, binder, and solvent. Converted to the total weight percentage of active dry material, the negative electrode active material can be 70wt%~98wt%, the conductive agent can be 0.2wt%~25wt%, and the binder can be 2.5wt%~10wt%. Specifically, the negative electrode active material can be at least one of natural graphite, artificial graphite, silicon oxide, hard carbon, lithium titanate, silicon-carbon composite materials, and metallic lithium; the conductive agent can be at least one of conductive graphite, conductive carbon black, carbon nanotubes, and graphene; the binder can be a CMC (carboxymethyl cellulose) + SBR (styrene-butadiene rubber) system, a CMC + PAA system, a pure PAA system, a CMC + modified PAA or modified SBR system, or a PVDF + oxalic acid system; and the solvent can be at least one of NMP and deionized water.

[0086] Thirdly, the present invention provides a battery cell having a composite electrode as described in any of the foregoing embodiments.

[0087] In an optional implementation, the battery cell is a wound battery cell.

[0088] Fourthly, the present invention provides a battery comprising the cell of the foregoing embodiments.

[0089] For example, the battery also includes a casing, a separator, and an electrolyte. The casing can be made of aluminum-plastic film or aluminum shell; the separator can be made of single-layer PE, single-layer PP, PP / PE / PP composite film, or composite separator coated with functional coatings such as ceramic coating; the electrolyte can be composed of solvent, solute, or reinforcing agent. The solvent can be carbonate, carboxylic acid ester, sulfite, or fluorinated solvent, etc.; the solute can be LiPF6 (lithium hexafluorophosphate), LiDFP (lithium difluorophosphate), LiBF4 (lithium tetrafluoroborate), LiBOB (lithium bis(oxalate-borate)), LiODFB (lithium bis(oxalate-borate)), LiFSI (lithium bis(fluorosulfonyl)imide), or LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), etc.; the reinforcing agent can be film-forming additive, flame retardant additive, stabilizer, high and low temperature additive, rate-enhancing additive, or wetting accelerator, etc.

[0090] In some embodiments, the positive and negative composite electrode sheets can be prepared into a single wound battery by separately processing the materials through pulping, coating, baking, rolling, slitting, sheet making, winding, casing, top and side sealing, re-baking, liquid injection, vacuum settling, pre-top sealing, activation, formation, vacuum double sealing, capacity sorting, and finished product.

[0091] It should be noted that for other preparation processes and technologies of "cells" and "batteries" not mentioned in detail in this article, please refer to the relevant existing technologies, which will not be elaborated on here.

[0092] The features and performance of the present invention will be further described in detail below with reference to the embodiments. Other undisclosed processes and conditions shall be operated in accordance with conventional practices in the art.

[0093] The following comparative examples and embodiments all use aluminum-cased soft-pack wound batteries, model number 435868, with a designed capacity of 2000mAh. The active slurry formulation of the positive electrode composite sheet is: positive active material: conductive agent: binder = 95%: 2.5%: 2.5% (mass ratio). The positive active material uses one or more of lithium iron phosphate, lithium cobalt oxide, and ternary nickel-cobalt-manganese, etc. The conductive agent is conductive carbon black, the binder is PVDF, and the solvent is NMP. The active slurry formulation of the negative electrode composite sheet is: negative active material: conductive agent: binder = 95%: 2.5%: 2.5% (mass ratio). The composition is 3%:2.5%:4.5% (mass ratio). The negative electrode active material is artificial graphite, the conductive agent is conductive carbon black, and the binder is CMC (2%) + SBR (2.5%). A PP / PE / PP composite membrane with a thickness of 23μm is used as the separator. The electrolyte is obtained by dissolving LiPF6 electrolyte in a system composed of EC, EMC and DMC in a volume ratio of 1:1:1, and the concentration of LiPF6 is 1mol / L. The positive electrode current collector uses 16μm aluminum foil, and the negative electrode current collector uses 8μm copper foil.

[0094] The above-mentioned aluminum-cased soft-pack wound battery preparation process mainly includes: the positive and negative composite electrode sheets are prepared by slurry preparation, coating, baking, rolling, slitting, sheet making, winding, casing, top and side sealing, baking again, liquid injection, vacuum standing, pre-top sealing, activation, formation, vacuum double sealing, capacity sorting, and finished product, etc., to prepare a single wound battery.

[0095] The preparation process of the electrode with a solid microcrystalline lattice includes: the current collector is tractioned at both ends and passed sequentially on a roller through a spray section, a crystallization section (temperature 80℃~120℃), a coating section, and a drying section (temperature 90℃~130℃). In the spray section, the mixture is sprayed onto a predetermined position on the current collector; in the crystallization section, the mixture adhering to the surface of the current collector is heated to form a solid microcrystalline lattice; in the coating section, different active slurries are coated on the surface of the solid microcrystalline lattice and the remaining surface of the current collector without microcrystalline lattice (the coating width of the active slurry is 1mm~2mm smaller than the width of the current collector); in the drying section, the active slurries are dried to form low-voltage plateau active regions and high-voltage plateau active regions, respectively.

[0096] The preparation process of electrodes that do not have a solid microcrystalline lattice can be carried out without the above-mentioned spraying and crystallization processes.

[0097] Comparative Example 1 In this comparative example, the aluminum foil has a first surface and a second surface arranged opposite each other in the thickness direction. Both the first and second surfaces of the aluminum foil are uniformly coated with a positive electrode active slurry using lithium iron phosphate as the positive electrode active material. The copper foil also has a first surface and a second surface arranged opposite each other in the thickness direction. Both the first and second surfaces of the copper foil are uniformly coated with a negative electrode active slurry using artificial graphite as the negative electrode active material.

[0098] Comparative Example 2 The difference between this comparative example and Comparative Example 1 is that the first (or second) surface of the aluminum foil is uniformly coated with a positive electrode active slurry made of lithium iron phosphate and lithium cobalt oxide mixed in a mass ratio of 1:1 as the positive electrode active material.

[0099] Comparative Example 3 The difference between this comparative example and Comparative Example 1 is that the first surface (or second surface) of the aluminum foil is provided with a first active material layer, which includes 12 first active material sub-regions. The positive electrode active materials used in the 12 first active material sub-regions are denoted as x1, x2, ..., x 12In the first active material sub-region x, the positive electrode active materials with odd-numbered subscripts are all lithium iron phosphate, and the positive electrode active materials with even-numbered subscripts are all lithium cobalt oxide. Furthermore, within the same active material layer, there is no wedge-shaped thickness reduction treatment between adjacent active material sub-regions, and no microcrystalline lattice formed by functional additives is set between the active region corresponding to the positive electrode active material lithium iron phosphate and the current collector.

[0100] Comparative Example 4 The difference between this comparative example and comparative example 3 is that the positive electrode active slurry with lithium iron phosphate as the positive electrode active material is mixed with 1.0 mg / Ah of functional additives (design capacity 2000 mAh). The functional additives are a mixture of difluorophenyl-phenylphosphonic acid, N,N-dialkyl-dihydrophenazine and 2,2,6,6-tetramethylpiperidine oxide in a mass ratio of 1:1:1.

[0101] Comparative Example 5 The difference between this comparative example and Comparative Example 1 is that the first surface (second surface) of the aluminum foil is uniformly coated with a positive electrode active slurry made of lithium iron phosphate and lithium cobalt oxide mixed in a mass ratio of 1:1 (lithium iron phosphate and ternary nickel cobalt manganese 811 in a mass ratio of 1:1) as the positive electrode active material.

[0102] Comparative Example 6 The difference between this comparative example and Comparative Example 3 is that: the first and second surfaces of the aluminum foil are respectively provided with first and second active material layers, and the first and second active material layers include 12 first and 12 second active material sub-regions. The positive electrode active materials used for the 12 first active material sub-regions are denoted as x1, x2, ..., x 12 The positive electrode active materials used in the 12 second active material sub-regions are denoted as y1, y2, ..., y3, respectively. 12 For the first and second active material sub-regions, the positive electrode active materials used when the x and y indices are odd are both lithium iron phosphate, while for the first and second active material sub-regions, the positive electrode active materials used when the x and y indices are even are lithium cobalt oxide and ternary nickel-cobalt-manganese 811, respectively.

[0103] Comparative Example 7 The difference between this comparative example and comparative example 6 is that the y-subscript of the second active material sub-region is odd, and the positive electrode active material is lithium manganese oxide. Comparative Example 8 The difference between this comparative example and Comparative Example 1 is that the positive electrode active material is lithium cobalt oxide. Comparative Example 9 The difference between this comparative example and Comparative Example 1 is that the positive electrode active material is ternary nickel-cobalt-manganese 811. Comparative Example 10 The difference between this comparative example and Comparative Example 1 is that the positive electrode active material is lithium manganese oxide. Example 1 The difference between this embodiment and Comparative Example 1 is that the first (or second) surface of the aluminum foil is uniformly coated with a positive electrode active slurry using lithium cobalt oxide as the positive electrode active material.

[0104] Example 2 The difference between this embodiment and Embodiment 1 is that a microcrystalline matrix formed by functional additives is provided between the active region corresponding to lithium iron phosphate and the current collector. The functional additives are a mixture of difluorophenyl-phenylphosphonic acid, N,N-dialkyl-dihydrophenazine, and 2,2,6,6-tetramethylpiperidine oxide in a mass ratio of 1:1:1. In the preparation of the microcrystalline matrix, the mixture is obtained by mixing the above functional additives with ethanol, with the functional additives accounting for 2% of the mixture by mass; the amount of functional additives used is 2.0 mg / Ah; the droplet size is 800 μm, and the droplet density is 50 droplets / cm³. 2 The coverage (by area) of the solid microcrystalline lattice is 60%.

[0105] Example 3 The difference between this embodiment and Comparative Example 2 is that a microcrystalline matrix formed by functional additives is provided between the active region of the lithium iron phosphate that is not mixed with lithium cobalt oxide and the current collector. The process parameters are the same as those of Example 2. The difference between this embodiment and Example 2 is that the amount of functional additives used is 1.0 mg / Ah.

[0106] Example 4 The difference between this embodiment and Comparative Example 3 is that a microcrystalline matrix formed by functional additives is provided between the active region corresponding to lithium iron phosphate and the current collector, and its process parameters are the same as those in Example 3.

[0107] Example 5 The difference between this embodiment and embodiment 4 is that: in the same active material layer, adjacent active material sub-regions overlap at the beginning and end to perform wedge-shaped thickness reduction treatment, that is, the active material sub-region corresponding to lithium cobalt oxide overlaps on the active material sub-region corresponding to lithium iron phosphate, the wedge angle of the wedge-shaped thickness reduction is 15°, and the projected length of the wedge surface is 690μm.

[0108] Example 6 The difference between this embodiment and embodiment 4 is that the subscript number of the first active material sub-region x uses positive electrode active materials including lithium iron phosphate, lithium cobalt oxide and ternary nickel cobalt manganese 811, where adjacent numbers correspond to different positive electrode active materials used. In this embodiment, the positive electrode active materials used in the active material sub-regions with subscript number combinations of x 1 / 4 / 7 / 10, 2 / 5 / 8 / 11 and 3 / 6 / 9 / 12 are lithium iron phosphate, lithium cobalt oxide and ternary nickel cobalt manganese 811, respectively. The difference from embodiment 3 is that the amount of functional additive is 2.0 mg / Ah.

[0109] Example 7 The difference between this embodiment and embodiment 6 is that: in the same active material layer, adjacent active material sub-regions are overlapped end to end for wedge-shaped thickness reduction treatment, that is, the active material sub-regions corresponding to lithium cobalt oxide (or ternary nickel cobalt manganese 811) overlap on the active material sub-regions corresponding to lithium iron phosphate, and the active material sub-regions corresponding to ternary nickel cobalt manganese 811 overlap on the active material sub-regions corresponding to lithium cobalt oxide. The wedge-shaped thickness reduction process parameters are the same as those in embodiment 5.

[0110] Example 8 The difference between this embodiment and Comparative Example 5 is that: the second surface of the aluminum foil is provided with a second active material layer, which includes 12 second active material sub-regions. The positive electrode active materials used in the 12 second active material sub-regions are respectively denoted as y1, y2, ..., y 12 The second active material sub-region y, with odd and even subscripts, uses lithium iron phosphate and ternary nickel-cobalt-manganese 811 as the positive electrode active materials, respectively. A microcrystalline lattice formed by functional additives is disposed between the active region corresponding to lithium iron phosphate and the current collector, with the same process parameters as in Example 2.

[0111] Example 9 The difference between this embodiment and embodiment 8 is that the adjacent active material sub-regions are overlapped end to end to perform wedge-shaped thickness reduction treatment, and the process parameters are the same as those in embodiment 5.

[0112] Example 10 The difference between this embodiment and Comparative Example 6 is that a microcrystalline matrix formed by functional additives is provided between the active region corresponding to lithium iron phosphate and the current collector, and its process parameters are the same as those in Example 2.

[0113] Example 11 The difference between this embodiment and embodiment 10 is that the adjacent active material sub-regions are overlapped end to end to perform wedge-shaped thickness reduction treatment, and the process parameters are the same as those in embodiment 5.

[0114] Example 12 The difference between this embodiment and Comparative Example 7 is that a microcrystalline matrix formed by functional additives is provided between the active region corresponding to lithium iron phosphate and the current collector. The amount of functional additives used is 2.5 mg / Ah, and the other process parameters are the same as in Example 2.

[0115] Example 13 The difference between this embodiment and embodiment 12 is that the adjacent active material sub-regions are overlapped end to end to perform wedge-shaped thickness reduction treatment, and the process parameters are the same as those in embodiment 5.

[0116] Comparative Example 1 The difference between this comparative example and Example 2 is that the functional additive is a mixture of difluorophenyl-phenylphosphonic acid, 2-aminothiophene-3-carboxynitrile and 1,4-di-tert-butyl-2,5-dimethoxybenzene in a mass ratio of 1:1:1.

[0117] Comparative Example 2 The difference between this comparative example and Example 2 is that the droplet size of the spray is 200 μm.

[0118] Comparative Example 3 The difference between this comparative example and Example 2 is that the droplet size of the spray is 1500 μm.

[0119] Comparative Example 4 The difference between this comparative example and Example 2 is that the droplet density is 10 droplets / cm³. 2 .

[0120] Comparative Example 5 The difference between this comparative example and Example 2 is that the droplet density is 500 droplets / cm³. 2 .

[0121] Comparative Example 6 The difference between this comparative example and Example 2 is that the amount of functional additive used is 0.5 mg / Ah.

[0122] Comparative Example 7 The difference between this comparative example and Example 2 is that the amount of functional additive used is 15 mg / Ah.

[0123] Comparative Example 8 The difference between this comparative example and Example 2 is that the area of ​​the microcrystalline lattice is 40% of the total area of ​​the current collector.

[0124] Comparative Example 9 The difference between this comparative example and Example 2 is that the area of ​​the microcrystalline lattice is 70% of the total area of ​​the current collector.

[0125] Comparative Example 10 The difference between this comparative example and Example 5 is that the wedge angle of the wedge thickness reduction is 30° and the projected length of the wedge surface is 320μm.

[0126] Comparative Example 11 The difference between this comparative example and Example 5 is that the wedge angle of the wedge thickness reduction is 45° and the projected length of the wedge surface is 184μm.

[0127] Experimental Example 1 Taking Comparative Examples 1-10 and Examples 1-13 as examples, at room temperature, the electrode sheets and assembled soft-pack batteries were tested for internal resistance, energy density, cycle performance, needle penetration, overcharge, and heating using equipment such as a four-probe, charge-discharge equipment, high-temperature chamber, and needle penetration machine, in accordance with national standards such as GB / T31485-2015 Safety Requirements and Test Methods for Power Batteries for Electric Vehicles. The number of cycles was carried out under charge-discharge conditions at a rate of 0.5C. The results are detailed below.

[0128] Table 1 Comparison Results

[0129] As can be seen from Comparative Examples 1, 8-10, 2-7, and 1-13 in Table 1, a slurry prepared by mixing or simultaneously containing different single active materials (such as lithium cobalt oxide, lithium iron phosphate, and ternary nickel cobalt manganese 811) with binary or multi-component active materials (such as lithium cobalt oxide: lithium iron phosphate = 1:1, ternary nickel cobalt manganese 811: lithium iron phosphate = 1:1) can be coated on both sides of the current collector to construct a composite electrode. In this way, the advantages of good cycle performance and high heat resistance of a single system (such as lithium iron phosphate) can be utilized to improve the poor performance of other materials (such as lithium cobalt oxide, ternary nickel cobalt manganese 811) in terms of cycle performance, thermal stability, and needle penetration test. At the same time, it can also significantly compensate for and improve the low energy density of the original single system (such as lithium iron phosphate), thereby improving the overall performance of the battery cell.

[0130] Specifically, as can be seen from Comparative Example 4 and Example 4 in Table 1, compared to mixing functional additives into the active material, by setting a functional additive microcrystalline lattice functional layer between the low-voltage active region and the current collector, the overcharge current is directly absorbed, consumed, and converted on the current collector, thereby increasing the upper limit of the cell's voltage operation range. The energy density and cycle performance of the individual cell are also significantly increased. From Examples 4, 6, 8, 12 and Examples 5, 7, 9, 11, 13 in Table 1, it can be seen that the wedge-shaped thickness reduction and overlap treatment at the beginning and end of the two active layers can improve the coupling at the joint of the active layers, reduce microcracks caused by drying shrinkage after coating different active material slurries, thereby reducing the internal resistance of the electrode surface, reducing the resistance of the finished cell, and significantly improving its cycle performance. Experimental Example 2 Taking Examples 2 and 5 and Comparative Examples 1 to 11 as examples, the performance was tested according to the method in Test Example 1, and the results are shown in Table 2.

[0131] Table 2 Comparison Results

[0132] As can be seen from Examples 2 and 5, and Comparative Examples 1 to 11, the same effect can be achieved by selecting other functional additives to prepare microcrystalline lattices, namely, widening the voltage range of the battery cell, increasing the voltage platform of the battery cell, thereby increasing the energy density of the battery cell, and its overcharge reaction mechanism can enable the battery cell to obtain superior cycle characteristics in a wide voltage range. When some preparation conditions and structural characteristics are changed, such as reducing (small) or increasing (large) the amount of functional additives and their mass fraction dissolved in the mixture, spray particle size, droplet density, wedge contact angle, etc., the resulting battery performance improvement is not very obvious.

[0133] In summary, this invention leverages the complementarity of materials to combine the advantages of different active materials onto the same electrode, allowing them to fully utilize their respective performances and improving the efficiency of sheet coating. The composite electrode prepared according to specific structures, preparation methods, and conditions can significantly enhance battery safety while simultaneously improving battery energy density, rate capability, and cycle life.

[0134] The above are merely preferred embodiments of the present invention and are not intended to limit the present invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A composite electrode, characterized in that, The composite electrode includes a current collector, the surface of which has an active material layer. The current collector has a first surface and a second surface disposed opposite to each other along its thickness direction. The active material layer includes a first active material layer and a second active material layer. The first active material layer is disposed on the first surface, and the second active material layer is disposed on the second surface. The first active material layer consists entirely of low-voltage plateau active regions, and the second active material layer consists entirely of high-voltage plateau active regions. Alternatively, the first active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, and the second active material layer consists entirely of low-voltage plateau active regions. Or, the first active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, and the second active material layer consists entirely of high-voltage plateau active regions. Furthermore, a microcrystalline lattice formed by functional additives exists between the low-voltage plateau active regions and the current collector. The functional additive includes an electropolymer that is converted to an oxidized state on the overcharged positive electrode side and undergoes electropolymerization under high voltage, consuming the overcharge current.

2. The composite electrode according to claim 1, characterized in that, When the same active material layer contains both low-voltage plateau active regions and high-voltage plateau active regions, the connection position between the low-voltage plateau active regions and the high-voltage plateau active regions has at least one of the following characteristics: Feature 1: The connection between the low-voltage platform active region and the high-voltage platform active region is wedge-shaped; Feature 2: The connection between the low-voltage platform active region and the high-voltage platform active region is an overlapping connection. Feature 3: The length of the active region of the high-voltage platform gradually increases along the direction away from the current collector; Feature 4: The acute angle between the active region of the low-voltage platform and the current collector is 15°~45°; Feature 5: The projected length of the side of the low-voltage platform active region connected to the high-voltage platform active region on the current collector surface is 50μm~930μm.

3. The composite electrode according to claim 1 or 2, characterized in that, The first active material layer includes m first active material sub-regions, and the second active material layer includes n second active material sub-regions, where m ≥ 1, n ≥ 1, and m and n are both integers. The active material used in the m-th first active material sub-region is denoted as x. m The active material used in the nth second active material sub-region is denoted as y. n ; Different first active material sub-regions may use the same or different active materials, and different second active material sub-regions may use the same or different active materials. m With y n They may be the same or different; and at least one active material sub-region has an active material that is a low-voltage platform active material, and at least one active material sub-region has an active material that is a high-voltage platform active material.

4. A method for preparing a composite electrode as described in any one of claims 1 to 3, characterized in that, Includes the following steps: A microcrystalline lattice is prepared in a predetermined region of a current collector by mixing a liquid containing functional additives. A low-voltage plateau active region of the active material layer is prepared on the surface of the microcrystalline lattice, and a high-voltage plateau active region of the active material layer is prepared on the remaining surface of the current collector where the microcrystalline lattice is not prepared.

5. The preparation method according to claim 4, characterized in that, The current collector is tractioned at both ends and passes sequentially on the roller shaft through the spray section, crystallization section, coating section and drying section; In the spraying section, the mixture is applied to a predetermined position on the current collector using a spray method; in the crystallization section, the mixture applied to the surface of the current collector is heated to form a solid microcrystalline lattice; in the coating section, different active slurries are applied to the surface of the solid microcrystalline lattice and the remaining surface of the current collector without microcrystalline lattice preparation; in the drying section, the active slurries are dried to form a low-voltage plateau active region and a high-voltage plateau active region, respectively.

6. The preparation method according to claim 5, characterized in that, The preparation of the microcrystalline lattice includes at least one of the following features: Feature 6: The droplet size of the spray is 500μm~1000μm; Feature 7: Droplet density is 40 droplets / cm³ 2 ~300 pieces / cm 2 ; Feature 8: The temperature of the crystallization zone is 80℃~120℃; Feature 9: The amount of the functional additive is 0.5 mg / Ah to 15 mg / Ah, where Ah is a unit of battery capacity; Feature 10: The mass fraction of the mixture is 0.5%~2%; Feature 11: The electropolymer comprises at least one of metallocene compounds, heterocyclic compounds, and substituted or unsubstituted aromatic compounds; Feature 12: The area of ​​the microcrystalline lattice is 50% to 70% of the total area of ​​the current collector.

7. The preparation method according to claim 5, characterized in that, In the coating section, along the direction of movement of the current collector, the coating width of the active slurry is 1mm to 2mm smaller than the width of the current collector. Alternatively, in the drying section, the drying temperature is 90℃~130℃.

8. A battery cell, characterized in that, The battery cell has the composite electrode as described in any one of claims 1 to 3.

9. A battery, characterized in that, The battery includes the cell as described in claim 8.

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