Composite pole piece, preparation method thereof and battery

Abstract

The embodiment of the invention discloses a composite pole piece, a preparation method thereof and a battery. The composite pole piece comprises a current collector; the safety bottom coating is arranged on the current collector, and the safety bottom coating comprises ceramic particles; the ion conducting coating is arranged on one side, far away from the current collector, of the safe bottom coating, the ion conducting coating comprises a solid electrolyte, and the ionic conductivity of the solid electrolyte is greater than or equal to 10 <-4 > S / cm; and the active material layer is arranged on one side, far away from the safety bottom coating, of the ion-conducting coating, and the active material layer comprises an active material. The ion conducting coating is additionally arranged between the safe bottom coating and the active material layer, the ion conducting coating is rich in the solid electrolyte with the ionic conductivity larger than or equal to 10 <-4 > S / cm, the ion conducting coating has high ion transmission capacity, the transmission efficiency of lithium ions in the battery is improved, the internal resistance of the battery is reduced, and the cycle performance of the battery is improved.

Description

Technical Field

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

[0002] With the widespread application of lithium-ion batteries in 3C electronics, power, and energy storage, high energy density and high safety performance have become core requirements. Currently, coating the electrode surface with a safety undercoating (such as ceramic coating or polymer coating) can effectively improve the thermal stability and mechanical strength of the battery and suppress the risk of thermal runaway.

[0003] However, the internal resistance of the battery increases significantly after the safety base coating is applied, which in turn leads to problems such as battery cycle capacity decay and rate performance degradation. Summary of the Invention

[0004] This application provides a composite electrode sheet and its preparation method, as well as a battery, aiming to solve the problem of significant increase in battery internal resistance after the application of a safety undercoating.

[0005] This application provides a composite electrode sheet, comprising: current collector; A safety primer coating is disposed on the current collector, the safety primer coating comprising ceramic particles; An ion-conducting coating is disposed on the side of the safety base layer away from the current collector, and the ion-conducting coating comprises a solid electrolyte with an ionic conductivity ≥10. -4 S / cm; and An active material layer is disposed on the side of the ion-conducting coating away from the safety base coating, and the active material layer includes an active material.

[0006] The composite electrode provided in this application embodiment has a safety undercoat layer on the current collector. By utilizing the thermal barrier effect of the ceramic particles in the safety undercoat layer, the thermal stability and mechanical strength of the battery can be improved, reducing the risk of battery thermal runaway. Furthermore, an ion-conducting coating is added between the safety undercoat layer and the active material layer. The ion-conducting coating is rich in ions and has a conductivity ≥10. -4 Solid electrolytes with a S / cm ratio and ion-conducting coatings have strong ion transport capabilities, improving the transport efficiency of lithium ions within the battery, thereby reducing the battery's internal resistance and improving cycle performance.

[0007] Optionally, in some embodiments of this application, the thickness of the safety primer layer is 1 μm to 5 μm.

[0008] A safety undercoat thickness of less than 1 μm will reduce the heat insulation effect of the safety undercoat and decrease the safety of the battery; while a safety undercoat thickness of more than 5 μm will cause the internal resistance of the battery to increase sharply and the cycle performance of the battery to decrease.

[0009] Optionally, in some embodiments of this application, the thickness of the ion-conducting coating is 0.5 μm to 2 μm.

[0010] If the thickness of the ion-conducting coating is less than 0.5 μm, it will be difficult for the ion-conducting coating to uniformly cover the safety base layer, affecting the lithium-ion transport efficiency in the battery. If the thickness of the ion-conducting coating is greater than 2 μm, the lithium-ion transport path will be too long, which will also affect the lithium-ion transport efficiency in the battery. Consequently, the internal resistance of the battery will increase and the cycle performance will decrease.

[0011] Optionally, in some embodiments of this application, the thickness of the active material layer is 50 μm to 150 μm.

[0012] The thickness of the active material layer directly affects the energy density of the battery. Increasing the thickness of the active material layer is beneficial to improving the energy density of the battery. However, if the thickness of the active material layer is too large, it will increase the mass transfer resistance and the wetting effect of the electrolyte on the active material layer, thereby increasing concentration polarization and deteriorating the cycle performance of the battery.

[0013] Optionally, in some embodiments of this application, the ceramic particles include at least one of alumina, magnesium hydroxide, and boehmite; and / or, The solid electrolyte includes Li7La3Zr2O 12 Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 1.3 Al 0.3 Ti 1.7 At least one of (PO4)3, and / or, The active material includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium phosphate.

[0014] Optionally, in some embodiments of this application, the safety primer further includes a first binder and a first conductive agent; wherein the content of the ceramic particles is 80wt%~90wt%, the content of the first binder is 5wt%~10wt%, and the content of the first conductive agent is 3wt%~10wt%.

[0015] The main material in the safety primer is ceramic particles. Controlling the content of ceramic particles helps to ensure the heat insulation effect of the safety primer. The use of the first binder can improve the reliability of the bond between the safety primer and the current collector. The addition of the first conductive agent is used to reduce the internal resistance of the safety primer.

[0016] Optionally, in some embodiments of this application, the ion-conducting coating further includes a second binder, wherein the content of the solid electrolyte is 90wt%~95wt% and the content of the second binder is 5wt%~10wt%.

[0017] The main material of the ion-conducting coating is a solid electrolyte. Controlling the content of the solid electrolyte helps to ensure the lithium-ion transport efficiency of the ion-conducting coating. The addition of a second binder can improve the bonding effect between the ion-conducting coating and the safety base layer.

[0018] Optionally, in some embodiments of this application, the active material layer further includes a third binder and a second conductive agent; wherein the content of the active material is 90wt%~95wt%, the content of the third binder is 2wt%~5wt%, and the content of the second conductive agent is 2wt%~5wt%.

[0019] The main material in the active material layer is the active material. Increasing the content of the active material helps to improve the energy density of the battery. The use of the third binder can improve the bonding effect between the active material layer and the ion-conducting coating. The addition of the second conductive agent is used to construct a conductive network in the active material layer and improve the cycle performance of the battery.

[0020] Optionally, in some embodiments of this application, the compaction density of the composite electrode is 3.2 g / cm³. 3 ~4.2 g / cm 3 .

[0021] Accordingly, this application also provides a method for preparing the above-mentioned composite electrode, including: Provide current collectors; A first slurry is provided, the first slurry comprising ceramic particles and a first solvent, and the first slurry is subjected to a first film-forming treatment and a first drying treatment on the current collector to form a safety base coating; A second slurry is provided, the second slurry comprising a solid electrolyte and a second solvent, and the second slurry is subjected to a second film-forming treatment and a second drying treatment on the safety base layer to form an ion-conducting coating; A third slurry is provided, the third slurry comprising an active material and a third solvent, and the third slurry is subjected to a third film-forming treatment and a third drying treatment on the ion-conducting coating to form an active material layer, thereby obtaining a composite electrode.

[0022] The composite electrode preparation method provided in this application is a wet process, which is simple to operate and suitable for large-scale mass production.

[0023] Optionally, in some embodiments of this application, the first slurry further comprises a first binder and a first conductive agent, and the solid content of the first slurry is 30wt%~40wt%; and / or, the second slurry further comprises a second binder, and the solid content of the second slurry is 20wt%~30wt%; and / or, the third slurry further comprises a third binder and a second conductive agent, and the solid content of the third slurry is 60wt%~75wt%.

[0024] In addition, this application also provides a battery comprising the above-described composite electrode or a composite electrode prepared by the above-described composite electrode preparation method. Attached Figure Description

[0025] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a schematic diagram of the structure of the composite electrode provided in an exemplary embodiment of this application. Detailed Implementation

[0027] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0028] This application provides a composite electrode, a method for preparing the same, and a battery. Detailed descriptions are provided below. It should be noted that the order of description of the following embodiments is not intended to limit the preferred order of the embodiments. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative and do not impose numerical requirements or establish an order. Various embodiments of the present invention may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a rigid limitation on the scope of the invention; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges, such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Additionally, whenever a numerical range is indicated herein, it means including any referenced number (fraction or integer) within the indicated range.

[0029] This application provides a battery, which refers to a device that can convert chemical energy into electrical energy. The battery can have different forms, such as, but not limited to, a battery cell, a battery module, and a battery pack. Typically, a battery module and a battery pack each independently include multiple battery cells connected in series or parallel. Optionally, a battery module includes battery cells, and a battery pack includes battery modules.

[0030] In some embodiments of this application, the battery is a single battery cell. A single battery cell (also called a battery cell) is the basic unit for converting chemical energy into electrical energy. Optionally, the single battery cell is a secondary battery, such as a lithium-ion battery, in which case the single battery cell can realize the mutual conversion of chemical energy and electrical energy. Specifically, the single battery cell includes a positive electrode and a negative electrode, which are arranged opposite to each other.

[0031] In some embodiments of this application, the battery cell further includes a separator disposed between the positive and negative electrode plates to prevent short circuits caused by contact between the positive and negative electrode plates. The separator can be selected from one or more of polyolefin separators, non-woven fabric separators, ceramic-coated separators, and composite separators. As an example, a polyolefin separator includes at least one of polyethylene (PE) film and polypropylene (PP) film. The separator can be a dry-process separator or a wet-process separator, and is not limited thereto.

[0032] In some embodiments of this application, the positive electrode sheet includes a positive electrode film layer containing a positive electrode active material. As an example, the positive electrode sheet also includes a positive electrode current collector, with the positive electrode film layer disposed on the current collector; in another example, the positive electrode sheet is a self-supporting structure, comprising only the positive electrode film layer without a current collector. Further, the positive electrode film layer also includes a conductive agent and a binder. In the positive electrode sheet, the conductive agent includes at least one of carbon black, graphite, carbon nanotubes (CNTs), graphene, and carbon fiber; the binder includes polyvinylidene fluoride (PVDF); the current collector includes aluminum foil; and the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel manganese oxide, lithium cobalt oxide, lithium-rich manganese-based oxide, and lithium manganese oxide.

[0033] In some embodiments of this application, the negative electrode sheet includes a negative electrode film layer, which contains a negative electrode active material. The negative electrode active material can be selected from at least one of carbon-based and silicon-based negative electrode materials. Carbon-based negative electrode materials not only have good structural stability, effectively buffering volume changes and thus extending the cycle life of individual battery cells, but also have high conductivity, improving the charge and discharge efficiency of the battery. Common carbon-based negative electrode materials include graphite-based materials, such as natural graphite, artificial graphite, and mesophase carbon microspheres (MCI); hard carbon materials, such as amorphous carbon; soft carbon materials, such as graphene and carbon nanotubes; and nanocarbon materials, such as graphene, carbon nanotubes, and carbon fibers. Silicon-based negative electrode materials are another type of negative electrode material different from carbon-based negative electrode materials. Silicon-based negative electrode materials use silicon as the main active material and achieve energy storage through a chemical reaction with lithium ions. Silicon-based anode materials have a theoretical specific capacity far exceeding that of carbon-based anode materials, allowing the anode sheet to provide greater energy storage capacity and significantly improve battery life. Furthermore, silicon-based anode materials have a lower delithiation potential, which helps to inhibit lithium deposition, thus reducing the risk of lithium plating. Common silicon-based anode materials include silicon-oxygen composites, silicon-carbon composites, and silicon-based alloys. However, silicon-based anode materials have low conductivity and experience significant volume expansion during charge and discharge, which can easily lead to pulverization of the anode film and instability of the SEI film, thereby affecting the cycle performance and safety of the battery cell. Optionally, the anode film also includes a conductive agent and a binder. As an example, in the anode sheet, the conductive agent includes at least one of carbon black, graphite, carbon nanotubes (CNTs), graphene, and carbon fiber, and the binder includes at least one of styrene-butadiene rubber (SBR) and polyacrylic acid (PAA). In some examples, the anode sheet is a self-supporting structure, consisting only of the anode film without a negative current collector. In other examples, the negative electrode sheet also includes a negative current collector, on which a negative electrode film layer is disposed. As an example, the negative current collector includes copper foil.

[0034] In some embodiments of this application, the battery cell further includes an electrolyte used to wet the positive and negative electrode plates. The electrolyte provides ion channels during the charging and discharging process of the battery cell, enabling charge transfer between the positive and negative electrode plates, thereby completing energy storage and release. The electrolyte mainly includes a non-aqueous organic solvent and an electrolyte salt. Taking a lithium-ion battery cell as an example, the electrolyte salt includes lithium salts, which may include at least one of lithium hexafluorophosphate (LiPF6), lithium perchlorate, lithium bis(oxalato)borate (LiBOB), lithium difluorooxalato)borate (LiODFB), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), and lithium bis(fluorosulfonyl)imide (LiFSI); the non-aqueous organic solvent includes at least one of carbonate solvents, carboxylic acid ester solvents, and ether solvents. Optionally, the electrolyte also includes functional additives. Functional additives are generally diverse and have different functions. As examples, functional additives include film additives, overcharge protection additives, flame retardant additives, high and low temperature additives, conductive additives, and additives for controlling water and HF content, etc. The film additive includes at least one of vinylene carbonate (VC) and fluoroethylene carbonate (FEC). The flame retardant additive includes at least one of organophosphorus compounds, organofluorine compounds, and haloalkyl phosphates.

[0035] In some embodiments of this application, the battery cell further includes a solid electrolyte membrane disposed between the positive and negative electrode plates. The solid electrolyte membrane can also prevent the positive and negative electrode plates from conducting. Optionally, the solid electrolyte membrane includes at least one of oxide solid electrolyte, sulfide solid electrolyte, and polymer solid electrolyte. If the solid electrolyte membrane can be used to completely replace the electrolyte and separator in the battery cell, then the battery cell is an all-solid-state battery.

[0036] Of course, in other embodiments, the battery cell may also be a semi-solid-state battery or a liquid battery.

[0037] Please see Figure 1 This application also provides a composite electrode 10, which can be either a positive or negative electrode. Specifically, the composite electrode 10 includes a current collector 1, a safety base coating 2, an ion-conducting coating 3, and an active material layer 4. The safety base coating 2 is disposed on the current collector 1. The safety base coating 2 includes ceramic particles. The ion-conducting coating 3 is disposed on the side of the safety base coating 2 away from the current collector 1. The ion-conducting coating 3 includes a solid electrolyte with an ionic conductivity ≥10. - 4 S / cm. The active material layer 4 is disposed on the side of the ion-conducting coating 3 away from the safety base coating 2. The active material layer 4 includes active material.

[0038] The composite electrode 10 provided in this embodiment has a safety undercoat 2 in the current collector 1. By utilizing the thermal barrier effect of the ceramic particles in the safety undercoat 2, the thermal stability and mechanical strength of the battery can be improved, reducing the risk of battery thermal runaway. Furthermore, an ion-conducting coating 3 is added between the safety undercoat 2 and the active material layer 4. The ion-conducting coating 3 is rich in ions and has a conductivity ≥10. -4 The solid electrolyte with S / cm has a strong ion transport capability, which improves the transport efficiency of lithium ions in the battery, thereby reducing the internal resistance of the battery and improving cycle performance.

[0039] In some embodiments of this application, the thickness of the safety base coating 2 is 1 μm to 5 μm. A thickness less than 1 μm reduces the heat insulation effect of the safety base coating 2, decreasing battery safety; while a thickness greater than 5 μm causes a sharp increase in the battery's internal resistance, reducing its cycle performance. As an example, the thickness of the safety base coating 2 is any one or a range between 1 μm, 2 μm, 3 μm, 4 μm, and 5 μm.

[0040] In some embodiments of this application, the thickness of the ion-conducting coating 3 is 0.5 μm to 2 μm. A thickness less than 0.5 μm makes it difficult for the ion-conducting coating 3 to uniformly cover the safety undercoat 2, affecting the lithium-ion transport efficiency within the battery. Conversely, a thickness greater than 2 μm results in an excessively long lithium-ion transport path, also affecting the lithium-ion transport efficiency within the battery, thereby increasing the battery's internal resistance and decreasing cycle performance. As an example, the thickness of the ion-conducting coating 3 is 0.5 μm, 1 μm, 1.5 μm, or 2 μm.

[0041] In some embodiments of this application, the thickness of the active material layer 4 is 50 μm to 150 μm. The thickness of the active material layer 4 directly affects the energy density of the battery. Increasing the thickness of the active material layer 4 is beneficial to improving the energy density of the battery. However, if the thickness of the active material layer 4 is too large, it will increase the mass transfer resistance and the wetting effect of the electrolyte on the active material layer 4, thereby leading to increased concentration polarization and deterioration of the battery's cycle performance. As an example, the thickness of the active material layer 4 is 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 110 μm, 120 μm, 130 μm, 140 μm, or 150 μm.

[0042] In some embodiments of this application, the ceramic particles include at least one selected from alumina (Al2O3), magnesium hydroxide (Mg(OH)2), and boehmite (γ-AlOOH). Alumina is a high thermal conductivity ceramic material with a room temperature thermal conductivity of 25 W / (m·K) to 35 W / (m·K), while magnesium hydroxide and boehmite are low thermal conductivity ceramic materials, wherein the thermal conductivity of magnesium hydroxide is less than 0.2 W / (m·K), and the thermal conductivity of boehmite is 2.0 W / (m·K) to 4.0 W / (m·K).

[0043] In some embodiments of this application, the solid electrolyte includes Li7La3Zr2O 12 (LLZO), Li 1.5 Al 0.5 Ge 1.5 (PO4)3(LAGP), Li 1.3 Al 0.3 Ti 1.7 At least one of (PO4)3(LATP). LLZO and LAGP belong to the NASICON structural system, and LLZO has an ionic conductivity ≥10. -4 S / cm, LAGP has an ionic conductivity of 10. -4 S / cm~10 -3 S / cm; LATP belongs to the perovskite structure system, and the ionic conductivity of LATP is 10. -4 S / cm~10 -3 S / cm.

[0044] In some embodiments of this application, the active material includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium phosphate. Lithium cobalt oxide (LCO) has ultra-high energy density, lithium phosphate (LFP) has excellent thermal stability, while lithium nickel cobalt manganese oxide (NCM) combines the advantages of high energy density and good thermal stability, and also has a cost advantage.

[0045] In some embodiments of this application, the safety primer 2 further includes a first binder and a first conductive agent; wherein the content of ceramic particles is 80wt%~90wt%, the content of the first binder is 5wt%~10wt%, and the content of the first conductive agent is 3wt%~10wt%. The main material in the safety primer 2 is ceramic particles. Controlling the content of ceramic particles helps to ensure the heat-insulating effect of the safety primer 2. The use of the first binder can improve the reliability of the bond between the safety primer 2 and the current collector 1. The addition of the first conductive agent is used to reduce the internal resistance of the safety primer 2. As an example, the content of ceramic particles in the safety primer 2 is 80wt%, 82wt%, 84wt%, 86wt%, 88wt%, or 90wt%, the content of the first binder is 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%, and the content of the first conductive agent is 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. As an example, the first binder is polyvinylidene fluoride (PVDF), and the first conductive agent is conductive carbon black Super P (SP).

[0046] In some embodiments of this application, the ion-conducting coating 3 further includes a second binder, wherein the content of the solid electrolyte is 90wt%~95wt%, and the content of the second binder is 5wt%~10wt%. The main material of the ion-conducting coating 3 is the solid electrolyte; controlling the content of the solid electrolyte helps ensure the lithium-ion transport efficiency of the ion-conducting coating 3. The addition of the second binder can improve the bonding effect between the ion-conducting coating 3 and the safety undercoat 2. As an example, the content of the solid electrolyte in the ion-conducting coating 3 is 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, or 95wt%, and the content of the second binder is 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, or 10wt%. The second binder can be the same as or different from the first binder. As an example, the second binder is polyacrylic acid (PAA).

[0047] In some embodiments of this application, the active material layer 4 further includes a third binder and a second conductive agent; wherein the content of the active material is 90wt%~95wt%, the content of the third binder is 2wt%~5wt%, and the content of the second conductive agent is 2wt%~5wt%. The main material in the active material layer 4 is the active material; increasing the content of the active material is beneficial to improving the energy density of the battery. The use of the third binder can improve the bonding effect between the active material layer 4 and the ion-conducting coating 3. The addition of the second conductive agent is used to construct a conductive network within the active material layer 4, improving the cycle performance of the battery. As an example, the content of the active material in the active material layer 4 is 90wt%, 91wt%, 92wt%, 93wt%, 94wt%, or 95wt%, the content of the third binder is 2wt%, 3wt%, 4wt%, or 5wt%, and the content of the second conductive agent is 2wt%, 3wt%, 4wt%, or 5wt%. The third binder and the first binder can be the same or different; the third binder and the second binder can be the same or different. The second conductive agent and the first conductive agent can be the same or different. As an example, the third binder is polyvinylidene fluoride (PVDF), and the second conductive agent includes conductive carbon black SP and carbon nanotubes (CNTs).

[0048] In some embodiments of this application, the compaction density of the composite electrode 10 is 3.2 g / cm³. 3 ~4.2 g / cm 3 As an example, the compaction density of composite electrode 10 is 3.2 g / cm³. 3 3.4g / cm 3 3.6g / cm 3 3.8g / cm 3 4.0g / cm 3 Or 4.2 g / cm 3 .

[0049] Accordingly, this application also provides a method for preparing the above-mentioned composite electrode 10, including: Provide current collector 1; A first slurry is provided, the first slurry comprising ceramic particles and a first solvent, and the first slurry is subjected to a first film-forming treatment and a first drying treatment on a current collector to form a safety primer 2; A second slurry is provided, the second slurry comprising a solid electrolyte and a second solvent, and the second slurry is subjected to a second film-forming treatment and a second drying treatment on a safety primer to form an ion-conducting coating 3; A third slurry is provided, which contains an active material and a third solvent. The third slurry is subjected to a third film-forming treatment and a third drying treatment on an ion-conducting coating to form an active material layer 4, thereby obtaining a composite electrode 10.

[0050] It can be seen that the preparation method of the composite electrode 10 provided in this application embodiment is a wet process, which is simple to operate and suitable for large-scale mass production.

[0051] The first solvent, the second solvent, and the third solvent can be the same or different from each other. As an example, the first solvent is N-methyl-2-pyrrolidone (NMP), the second solvent is deionized water, and the third solvent is also NMP.

[0052] The first film-forming treatment, the second film-forming treatment, and the third film-forming treatment can be the same or different from each other. For example, the first film-forming treatment, the second film-forming treatment, and the third film-forming treatment can each be independently selected from a blade coating process and a microgravure coating process.

[0053] After undergoing a first film-forming treatment, a first wet film layer is formed from the first slurry. A first drying treatment is then performed to remove a first solvent from the first wet film layer. After undergoing a second film-forming treatment, a second wet film layer is formed from the second slurry. After undergoing a third film-forming treatment, a third wet film layer is formed from the third slurry. A third drying treatment is then performed to remove a third solvent from the third wet film layer. As an example, both the first and third drying treatments are vacuum drying at a temperature of 70°C to 90°C; the second drying treatment is forced-air drying at a temperature of 55°C to 65°C.

[0054] In some embodiments of this application, the first slurry further comprises a first binder and a first conductive agent, and the solid content of the first slurry is 30wt%~40wt%; the second slurry further comprises a second binder, and the solid content of the second slurry is 20wt%~30wt%; the third slurry further comprises a third binder and a second conductive agent, and the solid content of the third slurry is 60wt%~75wt%. The solid content of the slurry refers to the total mass percentage of substances other than the solvent in the slurry. As an example, the solid content of the first slurry is 30wt%, 32wt%, 34wt%, 36wt%, 38wt%, or 40wt%; the solid content of the second slurry is 20wt%, 22wt%, 24wt%, 26wt%, 28wt%, or 30wt%; and the solid content of the third slurry is 60wt%, 62wt%, 64wt%, 66wt%, 68wt%, 70wt%, 72wt%, 74wt%, or 75wt%. Generally, the higher the solid content of the slurry, the greater its viscosity. Higher viscosity is more conducive to the fabrication of thick films, while lower viscosity is more conducive to the fabrication of thin and uniform films. In the composite electrode 10, the thickness of the ion-conducting coating 3 is relatively small, while the thickness of the active material layer 4 is relatively large. Therefore, the solid content of the second slurry is relatively low, thereby improving the uniformity of the thickness of the prepared ion-conducting coating 3 and improving the internal resistance of the battery. The solid content of the third slurry is relatively high, which is conducive to the fabrication of a thicker active material layer 4 and improves the energy density of the battery.

[0055] The following description is based on specific embodiments.

[0056] Example 1 This embodiment provides a composite electrode, the structure of which is as follows: Current collector: Aluminum foil; Safety base coating: Coated on the surface of the current collector, with a thickness of 2.5μm, and composed of boehmite (average particle size 0.5μm) + PVDF + SP (mass ratio of 80%:10%:10%). Ion-conducting coating: Coated on the surface of the safety primer, with a thickness of 1μm, and composed of LLZO (average particle size 0.3μm) + PAA (mass ratio of 95%:5%). Active material layer: coated on the surface of the ion-conducting coating, with a thickness of 75μm, and composed of lithium cobalt oxide active material (average particle size 5μm) + PVDF + SP + CNT (mass ratio of 90%:5%:4.9%:0.1%).

[0057] The preparation process of the composite electrode includes: coating a safety base coating onto the surface of the current collector aluminum foil, coating an ion-conducting coating onto the surface of the safety base coating, coating an active material layer onto the surface of the ion-conducting coating, drying, and then roll forming to obtain the composite electrode.

[0058] Example 2 This embodiment provides a composite electrode, the structure of which is as follows: Current collector: Aluminum foil; Safety base coating: Coated on the surface of the current collector, with a thickness of 3μm, and composed of alumina (average particle size 0.8μm) + PVDF + SP (mass ratio of 80%:10%:10%). Ion-conducting coating: Coated on the surface of the safety primer, with a thickness of 1.5 μm, and composed of LAGP (average particle size 0.25 μm) + PAA (mass ratio of 95%:5%). Active material layer: coated on the surface of the ion-conducting coating, with a thickness of 100μm, and composed of NCM (average particle size 10μm, LiNiCoMnO2) + PVDF + SP + CNT (mass ratio of 90%:5%:4.9%:0.1%).

[0059] Please refer to Example 1 for the preparation process of the composite electrode.

[0060] Example 3 This embodiment provides a composite electrode, the structure of which is as follows: Current collector: Aluminum foil; Safety primer coating: coated on the surface of the current collector, with a thickness of 3.5μm, and composed of magnesium hydroxide (average particle size 1μm) + PVDF + SP (mass ratio of 80%:10%:10%). Ion-conducting coating: Coated on the surface of the safety primer, with a thickness of 2μm, and composed of LATP (average particle size 0.2μm) + PAA (mass ratio of 95%:5%). Active material layer: coated on the surface of the ion-conducting coating, with a thickness of 125μm, and composed of lithium manganese oxide (average particle size 15μm) + PVDF + SP + CNT (mass ratio of 90%:5%:4.9%:0.1%).

[0061] Please refer to Example 1 for the preparation process of the composite electrode.

[0062] Comparative Example 1 This comparative example provides a composite electrode, the structure of which differs from that of the composite electrode in Example 1 in that the ion-conducting coating is omitted, that is, the composite electrode includes a current collector, a safety base coating and an active material layer stacked sequentially.

[0063] The preparation process of the composite electrode includes: coating a safety base coating onto the surface of the current collector aluminum foil, coating an active material layer onto the surface of the safety base coating, drying, and then rolling to obtain the composite electrode.

[0064] Comparative Example 2 This comparative example provides a composite electrode sheet whose structure differs from that of the composite electrode sheet in Example 1 in that the ion-conducting coating is disposed on the side of the active material layer away from the safety undercoat layer, that is, the composite electrode sheet includes a current collector, a safety undercoat layer, an active material layer and an ion-conducting coating layer stacked sequentially.

[0065] The preparation process of the composite electrode includes: coating a safety base coating onto the surface of the current collector aluminum foil, coating an active material layer onto the surface of the safety base coating, coating an ion-conducting coating onto the surface of the active material layer, drying, and then roll forming to obtain the composite electrode.

[0066] Comparative Example 3 This comparative example provides a composite electrode, the structure of which differs from the composite electrode in Example 1 in that: the ion-conducting coating is removed, and a solid electrolyte Li7La3Zr2O is added to the safety undercoat. 12 The content of solid electrolyte is 95 wt%.

[0067] The preparation process of the composite electrode includes: coating a safety base coating containing a solid electrolyte onto the surface of the current collector aluminum foil, coating an active material layer onto the surface of the safety base coating, drying, and then rolling to obtain the composite electrode.

[0068] Performance testing 1. Lithium-ion battery manufacturing: Negative electrode preparation: 90% traditional artificial graphite, 5% conductive agent SP and 5% binder SBR by mass ratio are evenly dispersed in solvent H2O to prepare a negative electrode slurry. The negative electrode slurry is coated onto the current collector copper foil, dried and then rolled to obtain a negative electrode sheet.

[0069] Lithium-ion battery preparation: The above-mentioned negative electrode sheet, electrolyte (EC / PC system electrolyte) and composite electrode sheet (as positive electrode) provided in Examples 1-3 and Comparative Examples 1-3 were respectively assembled to obtain lithium-ion batteries 1#-6#.

[0070] 2. The prepared lithium-ion batteries were subjected to safety and electrochemical performance tests under the following conditions: 2.1 Internal resistance test: Under a voltage of 4.2V, the AC impedance of the battery is measured using an AC internal resistance tester at a test frequency of 1±0.1KHz.

[0071] 2.2 Cyclic test: At 25±3 ℃, the battery is charged at a constant current of 1C to the upper limit voltage, then constant voltage to 0.05C, rested for 5 minutes, and then discharged at a constant current of 1C to the cutoff voltage of 3.0V. The charge and discharge cycle is repeated 50 times, the remaining capacity is recorded, and the capacity retention rate is calculated based on the remaining capacity.

[0072] 2.3 Needle penetration test: At 25±3 ℃, the battery is charged at a constant current of 1C to the upper limit voltage, and then the constant voltage is reduced to 0.05C. The battery is then placed horizontally in an environment of 45±2℃. A steel nail with a diameter of 3mm is inserted through the battery in the center of the battery in a direction perpendicular to the battery surface to short-circuit it until the battery explodes, catches fire, or the surface temperature returns to normal.

[0073] 2.4 Thermal abuse test: At 25±3 ℃, the battery is charged at a constant current of 1C to the upper limit voltage, and then the voltage is kept constant at 0.05C. The battery is then placed in a temperature shock chamber, and the temperature of the shock chamber is increased to 150℃±2℃ at a rate of 5℃±2℃ / min and maintained for 30min. The state of the battery is observed. If it does not catch fire or explode, it is OK; if it catches fire or explodes, it is NG. 2.5 Short-circuit test: At 25±3 ℃, charge the battery at a constant current of 1C to the upper limit voltage, then maintain the constant voltage to 0.05C. Place the battery in an environment of 25±3 ℃ and leave it for 30 minutes after the battery surface temperature is reached. Then connect the positive and negative terminals of the battery cell with wires, ensuring that all wires with an external resistance of 50mΩ±20mΩ are short-circuited to the positive and negative terminals of the battery pack. Monitor the battery temperature change during the test. Terminate the test if any of the following conditions occur; a) The battery temperature drops to 20% below its peak value; b) The short circuit time reaches 24 hours.

[0074] Please refer to Table 1 for the test results of each test item.

[0075] Table 1

[0076] Results analysis: The test results of Examples 1-3 and Comparative Examples 1-3 show that setting a safety undercoat on the current collector surface can greatly improve the pass rate of the battery's nail penetration test, thermal abuse test, and short circuit test, thus improving the battery's safety performance. However, comparing Example 1 with Comparative Example 1, the battery in Comparative Example 1 has a higher internal resistance of 120 mΩ, while the battery in Example 1 has an internal resistance of 28 mΩ. This indicates that setting an ion-conducting coating in the composite electrode has a positive effect on reducing the battery's internal resistance. Furthermore, comparing Example 1 with Comparative Example 2, the battery in Comparative Example 2 has an internal resistance of 85 mΩ, which is still significantly higher than the battery in Example 1. This indicates that the location of the ion-conducting coating in the composite electrode also affects the battery's internal resistance. Comparing Example 1 with Comparative Example 3, it can be seen that adding a solid electrolyte to the safety undercoat in Comparative Example 3 improves the lithium-ion transport efficiency of the safety undercoat, but the internal resistance of the battery in Comparative Example 3 (50 mΩ) is still higher than that of the battery in Example 1.

[0077] It is speculated that in Example 1, an ion-conducting coating is placed between the safety base layer and the active material layer. The high lithium-ion transport capacity of the ion-conducting coating reduces the contact resistance between the two layers, thus significantly lowering the battery's internal resistance. Although Comparative Example 2 also has an ion-conducting coating, it is not located between the safety base layer and the active material layer, failing to effectively improve the contact resistance. Therefore, the battery's internal resistance remains high. Comparative Example 3 reduces the internal resistance of the safety base layer by adding a solid electrolyte, but the contact resistance between the safety base layer and the active material layer remains high, resulting in a still relatively high battery internal resistance.

[0078] The above provides a detailed description of a composite electrode, its preparation method, and the battery provided in the embodiments of this application. Specific examples have been used to illustrate the principles and implementation methods of this application. The descriptions of the above embodiments are only for the purpose of helping to understand the methods and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A composite electrode, characterized in that, include: current collector; A safety primer coating is disposed on the current collector, the safety primer coating comprising ceramic particles; An ion-conducting coating is disposed on the side of the safety base layer away from the current collector, and the ion-conducting coating comprises a solid electrolyte with an ionic conductivity ≥10. -4 S / cm; and An active material layer is disposed on the side of the ion-conducting coating away from the safety base coating, and the active material layer includes an active material.

2. The composite electrode according to claim 1, characterized in that, The thickness of the safety primer coating is 1 μm to 5 μm; and / or, The thickness of the ion-conducting coating is 0.5 μm to 2 μm; and / or, The thickness of the active material layer is 50 μm to 150 μm.

3. The composite electrode according to claim 1 or 2, characterized in that, The ceramic particles comprise at least one of alumina, magnesium hydroxide, and boehmite; and / or, The solid electrolyte includes Li7La3Zr2O 12 Li 1.5 Al 0.5 Ge 1.5 (PO4)3, Li 1.3 Al 0.3 Ti 1.7 At least one of (PO4)3, and / or, The active material includes at least one of lithium nickel cobalt manganese oxide, lithium cobalt oxide, and lithium phosphate.

4. The composite electrode according to any one of claims 1 to 3, characterized in that, The safety primer layer further includes a first binder and a first conductive agent; wherein the content of the ceramic particles is 80wt%~90wt%, the content of the first binder is 5wt%~10wt%, and the content of the first conductive agent is 3wt%~10wt%.

5. The composite electrode according to any one of claims 1 to 4, characterized in that, The ion-conducting coating further includes a second binder, wherein the content of the solid electrolyte is 90wt%~95wt% and the content of the second binder is 5wt%~10wt%.

6. The composite electrode according to any one of claims 1 to 5, characterized in that, The active material layer further includes a third binder and a second conductive agent; wherein the content of the active material is 90wt%~95wt%, the content of the third binder is 2wt%~5wt%, and the content of the second conductive agent is 2wt%~5wt%.

7. The composite electrode according to any one of claims 1 to 6, characterized in that, The compaction density of the composite electrode is 3.2 g / cm³. 3 ~4.2 g / cm 3 .

8. The method for preparing the composite electrode according to any one of claims 1 to 7, characterized in that, include: Provide current collectors; A first slurry is provided, the first slurry comprising ceramic particles and a first solvent, and the first slurry is subjected to a first film-forming treatment and a first drying treatment on the current collector to form a safety base coating; A second slurry is provided, the second slurry comprising a solid electrolyte and a second solvent, and the second slurry is subjected to a second film-forming treatment and a second drying treatment on the safety base layer to form an ion-conducting coating; A third slurry is provided, the third slurry comprising an active material and a third solvent, and the third slurry is subjected to a third film-forming treatment and a third drying treatment on the ion-conducting coating to form an active material layer, thereby obtaining a composite electrode.

9. The method for preparing the composite electrode according to claim 8, characterized in that, The first slurry further comprises a first binder and a first conductive agent, and the solid content of the first slurry is 30wt%~40wt%; and / or, The second slurry further comprises a second binder, and the solid content of the second slurry is 20wt%~30wt%; and / or, The third slurry further comprises a third binder and a second conductive agent, and the solid content of the third slurry is 60wt%~75wt%.

10. A battery, characterized in that, This includes composite electrodes prepared according to any one of claims 1 to 7 or by any one of claims 8 or 9.

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