Positive electrode material and preparation method thereof, positive plate and battery

Abstract

The invention relates to the technical field of lithium ion batteries, and discloses a positive electrode material which comprises a positive electrode active material and a composite conductive agent. Active particles of the positive electrode active material are subjected to in-situ polymerization double-layer coating; wherein the positive active material comprises one or more of nickel cobalt lithium manganate, nickel cobalt lithium aluminate, nickel lithium manganate and lithium iron phosphate materials; the composite conductive agent comprises a carbon nanotube and a metal nanowire which are formed by compounding, wherein the imidazolium ionic liquid is used as a dispersing agent of the carbon nano tube and the metal nano wire, and the tail end of the metal nano wire is embedded into the particle surface of the positive electrode active material. By optimizing the proportion of the positive electrode material, the conductivity of the conductive agent and the stability of the conductive slurry can be effectively improved, so that the comprehensive performance of the battery is improved. The invention also discloses a preparation method of the positive electrode material, a positive plate and a battery.

Description

Technical Field

[0001] The present application relates to the technical field of lithium - ion batteries, and particularly to a positive electrode material, a preparation method thereof, a positive electrode sheet, and a battery. Background Art

[0002] Currently, with the rapid development of the electric vehicle industry and the continuous innovation of smart grids, high - performance power tools, and robotics technology, the demand for the comprehensive performance of lithium - ion batteries has reached a new height, so as to adapt to a wider range of application scenarios and high - performance requirements.

[0003] In positive electrode materials, carbon black or graphite with a relatively high addition amount is used as a conductive agent to improve its energy density; a highly efficient conductive network is formed through the one - dimensional structure of carbon nanotubes; high - nickel ternary materials or a blend of ternary and lithium manganate are used to increase its specific capacity; at the same time, by adjusting the positive and negative electrode capacity ratio, its cycle life is improved. In related technologies, to further improve the comprehensive performance, the slurry processability can also be improved through composite conductive agents or pre - dispersion processes.

[0004] In the process of implementing the embodiments of the present disclosure, it is found that at least the following problems exist in related technologies:

[0005] The positive electrode material prepared by the above - mentioned method has a complex process, resulting in a high cost, low control accuracy of the solid content, affecting the consistency of the electrode sheet compaction density, and poor stability of the prepared conductive slurry, resulting in significant fluctuations in the conductive performance; in addition, when the positive and negative electrode matching is poorly optimized, lithium metal precipitation or loss of active lithium will be caused, affecting the cycle life; on this basis, in the process of increasing the specific capacity, poor interfacial compatibility is likely to occur, resulting in hindered lithium - ion migration and decreased rate performance, thus affecting the comprehensive performance of the battery.

[0006] It should be noted that the information disclosed in the above background art section is only used to enhance the understanding of the background of the present application, and thus may include information that does not constitute the prior art known to those of ordinary skill in the art. Summary of the Invention

[0007] To have a basic understanding of some aspects of the disclosed embodiments, a simple summary is given below. This summary is not a general review, nor is it intended to identify key / important constituent elements or delineate the protection scope of these embodiments, but rather serves as a preface to the subsequent detailed description.

[0008] The embodiments of the present disclosure provide a positive electrode material, a preparation method thereof, a positive electrode sheet, and a battery. By optimizing the ratio of the positive electrode material, the conductivity of the conductive agent and the stability of the conductive slurry can be effectively improved, thereby improving the comprehensive performance of the battery.

[0009] In some embodiments, the positive electrode material includes a positive electrode active material and a composite conductive agent. The positive electrode active material has its active particles coated with a double layer in-situ polymerization. Among them, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium nickel manganese oxide, and lithium iron phosphate materials; the composite conductive agent includes carbon nanotubes and metal nanowires with a composite composition; wherein, an imidazole-based ionic liquid is used as a dispersant for the carbon nanotubes and metal nanowires, and the ends of the metal nanowires are embedded on the surface of the particles of the positive electrode active material.

[0010] In some embodiments, the porosity range on the surface of the particles of the positive electrode active material is 20% to 40%.

[0011] In some embodiments, the oxygen content of the imidazole-based ionic liquid ≤ 50 ppm.

[0012] In some embodiments, by controlling the oxidant concentration and surfactant distribution in stages, and combining the method of directional adsorption-in-situ polymerization, a hydrophilic sulfate-doped structure is formed in the inner layer of the active particles, and a hydrophobic dodecylbenzenesulfonate structure is formed in the outer layer of the active particles to form a double-layer coating structure of the inner layer and the outer layer.

[0013] In some embodiments, the thickness range of the double-layer coating structure is 5 nm to 50 nm.

[0014] In some embodiments, the distribution of sulfate in the inner layer and the distribution of dodecylbenzenesulfonate in the outer layer of the active particles are analyzed by a measuring device; wherein, the content of sulfate in the inner layer is 10% to 30%, and the content of dodecylbenzenesulfonate in the outer layer is 5% to 15%.

[0015] In some embodiments, ammonium persulfate and ferric chloride are used as initiators for in-situ polymerization; wherein, the molar ratio is 1:1 to 1:3.

[0016] In some embodiments, the mass ratio range of the carbon nanotubes and the metal nanowires is 1:3 to 3:1.

[0017] In some embodiments, the diameter range of the carbon nanotubes is 50 nm to 200 nm, and the length-to-diameter ratio ≥ 500.

[0018] In some embodiments, the diameter range of the metal nanowires is 10 nm to 50 nm, and the length range is 1 μm to 10 μm.

[0019] In some embodiments, the imidazole-based ionic liquid includes 1-butyl-3-methylimidazolium tetrafluoroborate, and its concentration range is 0.5 wt% to 5 wt%.

[0020] In some embodiments, the carbon nanotubes are treated by refluxing with nitric acid, and the density range of oxygen-containing functional groups on their surface is 0.5 mmol / g to 2.0 mmol / g; wherein, the nitric acid concentration range is 30% to 60%, and the reflux treatment duration is 2 h to 6 h.

[0021] In some embodiments, the metal nanowires include one or more of silver nanowires, copper nanowires, aluminum fluoride nanowires, copper sulfide nanowires, titanium dioxide nanowires, nitride nanowires, and lithium nickel cobalt manganese oxide nanowires.

[0022] In some embodiments, the lithium nickel cobalt manganese oxide material includes a high-nickel ternary lithium nickel cobalt manganese oxide material, with the chemical formula Li a Ni x Co y Mn z M b O2; where 0.9 < a < 1.1, 0.7 < x ≤ 0.94, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1; the M element is a combination of one or more of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

[0023] In some embodiments, the lithium nickel cobalt manganese oxide material includes a medium-nickel ternary lithium nickel cobalt manganese oxide material, with the chemical formula Li a1 Ni x1 Co y1 Mn z1 M1 b1 O2; where 0.9 < a1 < 1.1, 0.4 ≤ x1 ≤ 0.7, 0.1 ≤ y1 < 0.4, 0.05 ≤ z1 < 0.4, 0 ≤ b1 ≤ 0.1, and M1 is a combination of one or more of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

[0024] In some embodiments, the positive electrode material further includes a binder; wherein, the mass percentage of the positive electrode active material is 96% to 98%, the mass percentage of the composite conductive agent is 1% to 3%, and the mass percentage of the binder is 1% to 3%.

[0025] In some embodiments, the method for preparing the positive electrode material includes the following steps:

[0026] Prepare a conductive paste from carbon nanotubes and metal nanowires through a disperser;

[0027] Perform in-situ polymerization coating on the positive electrode active material through a reaction kettle to prepare a positive electrode active material with a double-layer coating structure;

[0028] Mix the conductive paste, the cathode active material with a double-layer coating structure, and the binder and decompose them in an organic solvent to form a cathode paste with a solid content of 40 wt% to 60 wt%. The cathode paste is the cathode material.

[0029] In some embodiments, the carbon nanotubes are refluxed with nitric acid in a concentration range of 30% to 60% to make the density range of oxygen-containing functional groups on their surface be 0.5 mmol / g to 2.0 mmol / g; wherein, the reflux time is 2 h to 6 h.

[0030] In some embodiments, when preparing the conductive paste from carbon nanotubes and metal nanowires, it further includes: using an imidazole-based ionic liquid as a dispersant for the carbon nanotubes and metal nanowires, and its oxygen content ≤ 50 ppm.

[0031] In some embodiments, in-situ polymerization coating is performed on the cathode active material, including:

[0032] Adding aniline monomer to a sulfuric acid solution with a set concentration to form a first solution; wherein, the mass ratio of the aniline monomer is 5 wt%.

[0033] Immerse the cathode active material in the first solution.

[0034] Add ammonium persulfate to the first solution and control the concentration of ammonium persulfate so that sulfate ions electrostatically adsorb on the defect sites on the surface of the carbon nanotubes, so that the active particles form an inner hydrophilic sulfate-doped structure.

[0035] In some embodiments, in-situ polymerization coating is performed on the cathode active material, and it further includes:

[0036] Rinse with ethanol and deionized water with a volume ratio of 1:1 to form the cathode active material, so that the cathode active material removes the unreacted monomers.

[0037] Use FeCl3 with a concentration of 0.05 mol / L as an initiator to spray a 5 wt% ethanol solution, so that Fe 3+ Induce the directional growth of aniline on the surface of the dodecylbenzenesulfonate micelles, so that the active particles form an outer hydrophobic dodecylbenzenesulfonate structure.

[0038] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector. The positive electrode coating includes the positive electrode material as described in the foregoing embodiments.

[0039] In some embodiments, the positive electrode material is coated on the positive electrode current collector, dried and heat-treated to obtain the positive electrode coating.

[0040] In some embodiments, the battery includes: a positive electrode sheet as described in the foregoing embodiments; a negative electrode sheet including a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector, and the negative electrode coating includes a negative electrode active material.

[0041] In some embodiments, the negative electrode active material includes at least two of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-carbon material, and silicon-oxygen material in admixture, and the silicon content in the negative electrode active material ranges from 5 wt% to 40 wt%.

[0042] In some embodiments, the diameter of the battery ranges from 20 mm to 50 mm, and the height ranges from 60 mm to 180 mm, wherein the ratio of the diameter to the height of the battery > 1.6.

[0043] The positive electrode material, its preparation method, positive electrode sheet, and battery provided by the embodiments of the present disclosure can achieve the following technical effects:

[0044] In this application, a conductive agent is formed by compounding carbon nanotubes and metal nanowires, and the ends of the metal nanowires are embedded on the surface of the particles of the positive electrode active material, improving the conductivity; at the same time, an imidazole-based ionic liquid is used as a dispersant for the carbon nanotubes and metal nanowires, improving the stability of the slurry and the stability of the homogenization process; on this basis, in-situ polymerization double-layer coating is performed on the active particles of the positive electrode active material, optimizing the conductive network. In this way, the electronic conductivity of the positive electrode material is improved, thereby enhancing the fast charge and discharge performance and long cycle performance of the battery, and further improving the comprehensive performance of the battery.

[0045] The above general description and the following description are only exemplary and explanatory and are not used to limit this application. Description of the Drawings

[0046] One or more embodiments are exemplarily illustrated by corresponding drawings. These exemplary illustrations and the drawings do not constitute limitations on the embodiments. Elements with the same reference numerals in the drawings are shown as similar elements. The drawings do not constitute a scale limitation, and among them:

[0047] Figure 1 is a schematic structural diagram of a battery provided by an embodiment of the present disclosure;

[0048] Figure 2 is a schematic coating diagram of a positive electrode sheet of a battery provided by an embodiment of the present disclosure;

[0049] Figure 3 is a schematic coating diagram of a negative electrode sheet of a battery provided by an embodiment of the present disclosure;

[0050] Figure 4 is a flowchart of a preparation method of a positive electrode material provided by an embodiment of the present disclosure;

[0051] Figure 5 It is a comparative graph of discharge capacity cycle life provided by an embodiment of the present disclosure.

[0052] Reference numerals:

[0053] 10 - housing;

[0054] 20 - positive electrode terminal; 21 - positive electrode post; 22 - positive electrode coating area; 23 - positive electrode empty foil area;

[0055] 30 - negative electrode terminal; 31 - negative electrode coating area; 32 - negative electrode empty foil area. Detailed implementation manners

[0056] In order to be able to understand the features and technical content of the embodiments of the present disclosure in more detail, the implementation of the embodiments of the present disclosure will be described in detail below in conjunction with the accompanying drawings. The attached drawings are only for reference and explanation purposes and are not used to limit the embodiments of the present disclosure. In the following technical descriptions, for the sake of explanation, multiple details are provided to provide a full understanding of the disclosed embodiments. However, one or more embodiments can still be implemented without these details. In other cases, well-known structures and devices can be shown in a simplified manner.

[0057] The terms "first", "second", etc. in the description and claims of the embodiments of the present disclosure and the above-mentioned accompanying drawings are used to distinguish similar objects and do not have to be used to describe a specific order or sequence. It should be understood that such data can be interchanged under appropriate circumstances so as to implement the embodiments of the present disclosure described here. In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion.

[0058] In the embodiments of the present disclosure, the orientation or positional relationship indicated by terms such as "upper", "lower", "inner", "middle", "outer", "front", "rear", etc. is based on the orientation or positional relationship shown in the accompanying drawings. These terms are mainly used to better describe the embodiments of the present disclosure and their embodiments, and are not used to limit that the indicated devices, elements or components must have a specific orientation or be constructed and operated in a specific orientation. And, in addition to being able to represent the orientation or positional relationship, some of the above terms may also be used to represent other meanings. For example, the term "upper" may also be used to represent a certain attachment relationship or connection relationship in some cases. For those of ordinary skill in the art, the specific meanings of these terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0059] In addition, the terms "arranged", "connected", and "fixed" should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, or there can be internal communication between two devices, components, or parts. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present disclosure can be understood according to specific circumstances.

[0060] Unless otherwise specified, the term "plurality" means two or more.

[0061] In the embodiments of the present disclosure, the character " / " indicates that the objects before and after are in an "or" relationship. For example, A / B means: A or B.

[0062] The term "and / or" is an associative relationship describing an object, indicating that there can be three relationships. For example, A and / or B means: A or B, or, A and B these three relationships.

[0063] It should be noted that, without conflict, the embodiments in the embodiments of the present disclosure and the features in the embodiments can be combined with each other.

[0064] In the conductive agent in the related art, carbon black or graphite with an addition amount of ≥3 wt% is generally used as the conductive agent. In this way, the proportion of the positive electrode active material decreases, restricting the improvement of the energy density. Among them, although carbon nanotubes (CNT) can form an efficient conductive network through a one-dimensional structure, their characteristics of easy agglomeration and uneven dispersion result in poor slurry stability, and the conductivity fluctuates significantly in practical applications. For example, the difference in the resistivity of the electrode sheet is >20%. In improving the specific capacity, high-nickel ternary materials are used in the related art. Although the specific capacity can be improved, the cost is high and the thermal stability is poor. To reduce the cost, a blending scheme of ternary materials and lithium manganate materials can also be adopted, but the interfacial compatibility is poor, resulting in hindered lithium ion migration and a decrease in the rate performance. In the positive and negative electrode matching, the positive and negative electrode capacity ratio (N / P) in the related art is generally 1:1.1 to 1:1.2. In this way, lithium metal precipitation or loss of active lithium is easily caused, affecting the cycle life.

[0065] In the above problems, in the related art, a composite conductive agent is made of carbon nanotubes and carbon black, or a pre-dispersion process is used to improve the processability of the slurry. However, there are still the following problems. For example, when carbon nanotubes are directly mixed with polyvinylidene difluoride (PVDF) colloidal solution, due to the difference in solvent polarity, secondary agglomeration may occur, and its particle size distribution D 50> 500 nm. In addition, the process of adding conductive agents step by step is complex, requiring 4 mixing steps, and the control accuracy of the solid content is low, with an error of ±5%. In this way, the consistency of the compaction density of the electrode sheet will be affected. On this basis, if the negative electrode material uses oil-based carbon, the kinetic matching with the highly conductive positive electrode is poor, which will also exacerbate the polarization effect and deteriorate the comprehensive performance of the battery.

[0066] Therefore, to further improve the comprehensive performance of the battery, the embodiments of the present disclosure provide a positive electrode material, including a positive electrode active material and a composite conductive agent. The positive electrode active material, whose active particles are coated with an in-situ polymerization double layer, wherein the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminate, lithium nickel manganese oxide, and lithium iron phosphate materials; the composite conductive agent includes carbon nanotubes and metal nanowires with a composite composition; wherein, an imidazole-based ionic liquid is used as a dispersant for the carbon nanotubes and metal nanowires, and the ends of the metal nanowires are embedded in the particle surface of the positive electrode active material.

[0067] Using the positive electrode material provided by the embodiments of the present disclosure, a conductive agent is formed by the composite of carbon nanotubes and metal nanowires, and the ends of the metal nanowires are embedded in the particle surface of the positive electrode active material, which improves the conductivity; at the same time, an imidazole-based ionic liquid is used as a dispersant for the carbon nanotubes and metal nanowires, which improves the stability of the slurry and the stability of the homogenization process; on this basis, the active particles of the positive electrode active material are coated with an in-situ polymerization double layer, optimizing the conductive network. In this way, the electronic conductivity of the positive electrode material is improved, thereby enhancing the fast charge and discharge performance and long cycle performance of the battery, and further improving the comprehensive performance of the battery.

[0068] In the embodiments of the present disclosure, the surface polarity of the carbon nanotubes can be regulated by controlling the density of oxygen-containing functional groups, affecting the compatibility with the dispersant ionic liquid and the anchoring effect of the metal nanowires. Here, a high density enhances dispersion, but an excessive amount will cause self-aggregation.

[0069] In some embodiments, the porosity range of the particle surface of the positive electrode active material is 20% to 40%.

[0070] In the embodiments of the present disclosure, the porosity mainly affects the pore impedance. Among them, when the porosity is too low, the pore impedance will be increased, and when the porosity is too high, the energy density will be affected. Therefore, the porosity range of the particle surface of the positive electrode active material is controlled between 20% and 40% to balance the pore impedance and the energy density.

[0071] In the embodiments of the present disclosure, the conductive agent is composed of carbon nanotubes and metal nanowires. The carbon nanotubes provide a framework support, and the metal nanowires fill the pores. If the ratio of the two is unbalanced, the conductive network will be discontinuous, thereby reducing the conductive efficiency.

[0072] In the embodiments of the present disclosure, the conductive network of the electrode sheet is composed of a carbon paste layer formed by a conductive agent and a binder. Here, if the metal nanowires cannot be embedded on the surface of the active particles, they may be covered by the paste in the carbon paste layer, thus failing to achieve the due conductive effect. Therefore, the ends of the metal nanowires being embedded on the surface of the particles of the positive electrode active material can ensure its conductive effect.

[0073] In some embodiments, the oxygen content of the imidazole-based ionic liquid is ≤50 ppm.

[0074] In some embodiments, by controlling the oxidant concentration and the surfactant distribution in stages, and combining the methods of directional adsorption-in-situ polymerization, a hydrophilic sulfate-doped structure is formed in the inner layer of the active particles, and a hydrophobic dodecylbenzenesulfonate structure is formed in the outer layer of the active particles to form a double-layer coating structure of the inner layer and the outer layer; wherein, the thickness range of the double-layer coating structure is 5 nm to 50 nm.

[0075] In the embodiments of the present disclosure, the sulfate group is a strong hydrophilic group, and the dodecylbenzenesulfonate group is an amphoteric group, where the sulfonate group is hydrophilic and the dodecylbenzene is a hydrophobic group, and its long-chain alkyl group and benzene ring are non-polar. Therefore, the interfacial bonding can be improved through the hydrophilic sulfate group in the inner layer, and the penetration of the electrolyte can be promoted through the hydrophobic dodecylbenzenesulfonate group in the outer layer.

[0076] In some embodiments, the distribution of sulfate groups in the inner layer of the active particles and the distribution of dodecylbenzenesulfonate groups in the outer layer are analyzed by a measuring device; wherein, the content of sulfate groups in the inner layer is 10% to 30%, and the content of dodecylbenzenesulfonate groups in the outer layer is 5% to 15%.

[0077] In the embodiments of the present disclosure, the measuring device is a Time of Flight Secondary Ion Mass Spectrometry (TOF-SIMS), which can analyze the distribution of sulfate groups in the inner layer and the distribution of dodecylbenzenesulfonate groups in the outer layer.

[0078] In some embodiments, ammonium persulfate and ferric chloride are used as initiators for in-situ polymerization; wherein, the molar ratio is 1:1 to 1:3.

[0079] In some embodiments, the mass ratio range of carbon nanotubes to metal nanowires is 1:3 to 3:1.

[0080] In some embodiments, the diameter range of the carbon nanotubes is 50 nm to 200 nm, and the length-to-diameter ratio ≥500; the diameter range of the metal nanowires is 10 nm to 50 nm, and the length range is 1 μm to 10 μm.

[0081] In some embodiments, the imidazole-based ionic liquid includes 1-butyl-3-methylimidazolium tetrafluoroborate, and its concentration ranges from 0.5 wt% to 5 wt%.

[0082] In some embodiments, the carbon nanotubes are treated by refluxing with nitric acid, so that the density range of oxygen-containing functional groups on their surface is from 0.5 mmol / g to 2.0 mmol / g; wherein, the concentration range of nitric acid is from 30% to 60%, and the reflux treatment duration is from 2 h to 6 h.

[0083] In some embodiments, the metal nanowires include one or more of silver nanowires, copper nanowires, aluminum fluoride nanowires, copper sulfide nanowires, titanium dioxide nanowires, and lithium nickel cobalt manganese oxide nanowires.

[0084] In the embodiments of the present disclosure, the aluminum fluoride nanowires can generate an interfacial layer rich in LiF through a conversion reaction, which can guide uniform lithium deposition and inhibit dendrite growth, and improve the stability of the interface between the positive electrode and the electrolyte. The copper sulfide nanowires have a high specific surface area and excellent ion / electron transport properties, and can be used as a carrier for the positive electrode composite material, enhancing the conductivity of the positive electrode material and alleviating the volume expansion problem. The titanium dioxide nanowires shorten the ion diffusion path through a one-dimensional structure, can inhibit the structural collapse of the positive electrode material during cycling, and improve the rate performance. The lithium nickel cobalt manganese oxide nanowires, as a self-supporting positive electrode skeleton, can directly load active substances, optimize electron transport through a one-dimensional continuous conductive network, and are suitable for high-energy density ternary positive electrode systems.

[0085] In some embodiments, the lithium nickel cobalt manganese oxide material includes a high-nickel ternary lithium nickel cobalt manganese oxide material, and its chemical formula is Li a Ni x Co y Mn z M b O2; wherein 0.9 < a < 1.1, 0.7 < x ≤ 0.94, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1; the M element is any one or a combination of more than one of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

[0086] In some embodiments, the lithium nickel cobalt manganese oxide material includes a medium-nickel ternary lithium nickel cobalt manganese oxide material, and its chemical formula is Li a1 Ni x1 Co y1 Mn z1 M1 b1 O2; wherein, 0.9 < a1 < 1.1, 0.4 ≤ x1 ≤ 0.7, 0.1 ≤ y1 < 0.4, 0.05 ≤ z1 < 0.4, 0 ≤ b1 ≤ 0.1, and M1 is any one or a combination of more than one of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

[0087] In some embodiments, the positive electrode material further includes a binder; wherein, the mass percentage of the positive electrode active material is 96% to 98%, the mass percentage of the composite conductive agent is 1% to 3%, and the mass percentage of the binder is 1% to 3%.

[0088] Meanwhile, in combination with Figure 4 As shown, the embodiments of the present disclosure further provide a method for preparing a positive electrode material, including the following steps:

[0089] S401. Prepare a conductive paste from carbon nanotubes and metal nanowires through a disperser;

[0090] S402. Perform in-situ polymerization coating on the positive electrode active material through a reaction kettle to prepare a positive electrode active material with a double-layer coating structure;

[0091] S403. Mix and decompose the conductive paste, the positive electrode active material with a double-layer coating structure, and the binder in an organic solvent to form a positive electrode material with a solid content of 40 wt% to 60 wt%.

[0092] In the embodiments of the present disclosure, the positive electrode material includes a positive electrode paste.

[0093] In some embodiments, the carbon nanotubes are refluxed with nitric acid in a concentration range of 30% to 60% so that the density range of oxygen-containing functional groups on the surface is 0.5 mmol / g to 2.0 mmol / g; wherein, the reflux treatment duration is 2 h to 6 h.

[0094] In some embodiments, when preparing the conductive paste from carbon nanotubes and metal nanowires, it further includes: using an imidazole-based ionic liquid as a dispersant for the carbon nanotubes and metal nanowires, and its oxygen content ≤ 50 ppm.

[0095] In some embodiments, the in-situ polymerization coating on the positive electrode active material includes:

[0096] Adding aniline monomer to a sulfuric acid solution with a set concentration to form a first solution; wherein, the mass ratio of the aniline monomer is 5 wt%;

[0097] Immerse the positive electrode active material in the first solution for treatment;

[0098] Adding ammonium persulfate to the first solution and controlling the concentration of ammonium persulfate so that sulfate ions electrostatically adsorb on the surface defect sites of the carbon nanotubes to form an inner hydrophilic sulfate-doped structure with active particles.

[0099] In some embodiments, the in-situ polymerization coating on the positive electrode active material further includes:

[0100] Rinse the formed positive electrode active material with ethanol and deionized water with a volume ratio of 1:1 to remove unreacted monomers from the positive electrode active material;

[0101] Using FeCl3 with a concentration of 0.05 mol / L as an initiator, spray a 5 wt% ethanol solution to make Fe 3+ initiate the directional growth of aniline on the surface of dodecylbenzenesulfonate micelles, forming an outer hydrophobic dodecylbenzenesulfonate structure.

[0102] An embodiment of the present disclosure also provides a positive electrode sheet, which includes a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector. The positive electrode coating includes the positive electrode material as described in the foregoing embodiments.

[0103] In some embodiments, the positive electrode material is a positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector, dried and heat-treated to obtain the positive electrode coating.

[0104] Combined with Figure 1 As shown, an embodiment of the present disclosure also provides a battery, which includes: the positive electrode sheet as described in the foregoing embodiments; a negative electrode sheet, which includes a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector. The negative electrode coating includes a negative electrode active material.

[0105] In an embodiment of the present disclosure, the battery includes a positive electrode sheet, a negative electrode sheet and a separator stacked. Among them, a cylindrical battery core is formed by winding. The end of the electrode sheet at the initial winding is at the axis of the cylinder, and the end of the electrode sheet at the end of winding is at the outer surface of the cylinder. It also includes a cylindrical housing 10, the inside of which is used to accommodate the battery core, the top is the positive electrode end 20, the bottom is the negative electrode end 30, and a positive electrode post 21 is provided on the positive electrode end 20.

[0106] Here, a positive electrode tab and a negative electrode tab are respectively provided at both ends of the battery. The battery core is connected to the negative electrode bus bar by welding, the negative electrode bus bar is connected to the housing 10 by welding, the battery core is connected to the positive electrode bus bar by welding, an insulating sheet is placed on the positive electrode bus bar, the positive electrode bus bar is connected to the cap by welding, and the cap is connected to the housing 10 by a rolling groove.

[0107] In an embodiment of the present disclosure, combined with Figure 2 As shown, the positive electrode sheet includes a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector. The positive electrode current collector includes a positive electrode coating area 22 and a positive electrode bare foil area 23. At least a part of the positive electrode bare foil area 23 serves as a positive electrode tab, and the positive electrode bare foil area 23 accounts for 1% to 10% of the area of the positive electrode current collector. Specifically, the positive electrode sheet includes a strip-shaped positive electrode foil and a positive electrode coating area 22 and a positive electrode bare foil area 23 coated on the surface of the strip-shaped positive electrode foil.

[0108] Combined with Figure 3As shown, the negative electrode sheet includes a negative electrode current collector and a negative electrode coating applied to at least one surface of the negative electrode current collector. The negative electrode current collector includes a negative electrode coating area 31 and a negative electrode bare foil area 32. At least a part of the negative electrode bare foil area 32 serves as a negative electrode tab, and the negative electrode bare foil area 32 accounts for 2% to 11% of the area of the negative electrode current collector. Specifically, the negative electrode sheet includes a strip-shaped negative electrode foil and a negative electrode coating area 31 and a negative electrode bare foil area 32 coated on the surface of the strip-shaped negative electrode foil.

[0109] In the embodiments of the present disclosure, the positive electrode bare foil area 23 and the negative electrode bare foil area 32 are perpendicular to the winding direction, and the top end face or the bottom end face of the battery is formed by methods such as flattening or cutting and laminating.

[0110] In some embodiments, the negative electrode active material includes at least two mixtures of artificial graphite, natural graphite, soft carbon, hard carbon, silicon-carbon material, and silicon-oxygen material, and the silicon content in the negative electrode active material ranges from 5 wt% to 40 wt%.

[0111] In some embodiments, in the above structure, the tab can be a single tab, multiple tabs, or a full tab, preferably a full tab; its housing 10 can be a steel shell or an aluminum shell. The diameter range of the battery is 20 mm to 50 mm, and the height range is 60 mm to 180 mm. Among them, the ratio of the diameter to the height of the battery > 1.6.

[0112] On this basis, the embodiments of the present disclosure provide a method for preparing a battery, including:

[0113] Preparing a positive electrode sheet: Mixing positive electrode coating materials, applying them to at least one surface of the aluminum foil, and obtaining the positive electrode sheet after drying and cold pressing;

[0114] Preparing a negative electrode sheet: Mixing negative electrode coating materials, applying them to at least one surface of the aluminum foil, and obtaining the negative electrode sheet after drying and cold pressing;

[0115] Preparing a battery core: After rolling and slitting the positive electrode sheet and the negative electrode sheet respectively, winding them together with the separator to obtain a battery core;

[0116] Assembling the battery: Welding the tabs of the battery core to the electrical connection piece, loading it into the battery housing, and performing electrolyte injection, sealing, and formation processes to obtain the battery.

[0117] In addition, the embodiments of the present disclosure provide an electrical device including a battery for providing power as described in this application.

[0118] The following continues to further explain and illustrate the present invention with embodiments.

[0119] Preparation of composite conductive agent: In a constant-temperature oil bath reactor, the surface of carbon nanotubes is treated by nitric acid reflux. Its process parameters include: the concentration of nitric acid is 50%, and its volume ratio of HNO3:H2O = 1:1; the reaction temperature is 60°C ± 2°C, the reaction time is 4 h, and the stirring speed is 300 rpm. It is centrifugally washed with deionized water to make its pH = 7, and then vacuum dried to obtain the composite conductive agent.

[0120] Preparation of conductive paste: Using 1-butyl-3-methylimidazolium tetrafluoroborate with a concentration of 0.5 wt% to 5 wt% as a dispersant, and its oxygen content ≤ 50 ppm, carbon nanotubes and silver nanowires are dispersed in 1-butyl-3-methylimidazolium tetrafluoroborate according to a certain mass ratio.

[0121] Preparation of cathode active material: Aniline monomer is added to 0.5 M H2SO4, and the pH of H2SO4 is 1.2, and the mass ratio of aniline monomer is 5 wt%; the cathode active material is placed in the above solution for impregnation, and ammonium persulfate is added as an initiator to a certain concentration to form an inner hydrophilic sulfate-doped structure. The obtained cathode active material is cyclically rinsed 3 times with ethanol and deionized water with a volume ratio of 1:1 to remove unreacted monomers, and a 5 wt% ethanol solution and a 0.05 mol / L FeCl3 solution are simultaneously sprayed using an electrostatic spraying machine; among them, the 5 wt% ethanol solution contains 0.1% cross-linking agent KH-560, and the 5 wt% ethanol solution forms a micelle template to guide the growth of aniline along the hydrophobic chain to form an outer hydrophobic dodecylbenzenesulfonate structure, thereby forming a double-layer coating structure.

[0122] Preparation of cathode plate: It includes a cathode current collector aluminum foil and a cathode coating coated on both surfaces of the aluminum foil; among them, calculated by weight percentage, the cathode coating includes 97% of cathode active material, 0.4% of composite conductive agent, 1.6% of SP conductive agent, and 1% of PVDF binder. The above substances are added to NMP and stirred to form a cathode paste with a solid content of 60%, which is coated on the cathode current collector to form a cathode plate.

[0123] Preparation of anode plate: It includes an anode current collector copper foil and an anode coating coated on both surfaces of the copper foil; among them, calculated by weight percentage, the anode coating includes 96% of artificial graphite, 1.0% of conductive agent acetylene black, 1% of thickener CMC, and 2% of anode binder polyacrylate LA133. The above substances are added to deionized water and stirred to form an anode paste with a solid content of 40%, which is coated on the anode current collector to form an anode plate.

[0124] Preparation of electrolyte: Ethylene carbonate (EC), ethyl methyl carbonate (EMC), and diethyl carbonate (DEC) were mixed in a volume ratio of 1:1:1 to obtain an organic solvent. Then, the fully dried lithium salt LiPF6 was dissolved in the mixed organic solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0125] Preparation of separator: A high-porosity dynamic separator was selected. The thickness of the base film PE was 9 μm, the thickness of the ceramic coatings on both sides was 1 μm, and the thickness of the PVDF coating was 1 μm. The air permeability of the separator was ≥100 s / 100 mL.

[0126] Assembly of battery: After the positive electrode sheet and the negative electrode sheet were respectively roll-pressed, slit, and die-cut, they were wound together with the separator simultaneously to obtain a battery core. After the battery core was welded to the electrical connection piece, it was placed into a battery case, and then the processes of injecting liquid, sealing, and forming were completed. The battery of this example was obtained. The case of the battery was cylindrical, and its dimensional parameters were diameter: 21.0 mm, length: 70.0 mm.

[0127] Testing the viscosity rebound of the slurry: Using a rotational viscometer of model DV2T, with rotor CPE-40 and a rotation speed of 50 rpm, the viscosity at 25 °C was 5000 ± 500 mPa·s (GB / T 22235). The viscosity of the positive electrode slurry was measured at 0 h and after standing for 24 h. The viscosity rebound rate was calculated through the following formula:

[0128]

[0129] where V Δ is the viscosity rebound rate, V1 is the viscosity of the positive electrode slurry after standing for 24 h, and V2 is the viscosity of the positive electrode slurry at 0 h.

[0130] Testing the stability of the slurry: Using a rheometer of model MCR 302, performing a dynamic frequency sweep from 0.1 Hz to 100 Hz, with G' / G” = 1.05 (ISO 6721-10), the G' / G” value of the positive electrode slurry was measured.

[0131] Testing the resistivity of the positive electrode sheet: Using a 46-probe tester of model RTS-9, applying the probe to the positive electrode sheet with a constant pressure of 10 Mpa, the resistivity of the positive electrode sheet was measured. Among them, the resistivity of the positive electrode sheet included the resistivity of the material area and the interfacial contact resistivity.

[0132] Testing the cycle stability: Using a blue electrochemical test system of model CT-4008, the experimental battery was charged and discharged at 1C from 2.5 V to 4.2 V, and the capacity retention rate after 500 cycles was calculated.

[0133] Example 1

[0134] Example 1 provides a battery, which is prepared by the following method:

[0135] Preparation of composite conductive paste: The aspect ratio of carbon nanotubes is 600:1; the density of oxygen-containing functional groups of carbon nanotubes treated by nitric acid reflux is 1.2 mmol / g; the mass ratio of carbon nanotubes to silver nanowires is 2:1; 1-butyl-3-methylimidazolium tetrafluoroborate (BMIM-BF4) with an oxygen content of 30 ppm is used as a dispersant; it is dispersed in NMP at 2500 rpm for 30 min using a high-speed shear disperser to obtain a composite conductive paste with a solid content of 5 wt%.

[0136] Preparation of cathode active material: Aniline monomer with a purity of 99.5% is added to 0.5 M H2SO4, and the pH of H2SO4 is 1.2, and the mass ratio of aniline monomer is 5 wt%. The high-nickel ternary cathode material (NCM811) is placed in the above solution for impregnation, and ammonium persulfate (APS) with a concentration of 0.3 mol / l is added as an initiator; at a temperature of 5°C ± 1°C, polymerization is carried out for 2 h to form a hydrophilic sulfate-doped structure with a thickness of 15 nm on the inner layer. The obtained cathode active material is rinsed 3 times in a circulating manner with ethanol and deionized water with a volume ratio of 1:1 to remove unreacted monomers. An electrostatic spraying machine is used to spray a 5 wt% ethanol solution and a 0.05 mol / L FeCl3 solution simultaneously; among them, the 5 wt% ethanol solution contains 0.1% cross-linking agent KH-560, and the 5 wt% ethanol solution forms a micelle template to guide the growth of aniline along the hydrophobic chain to form a hydrophobic dodecylbenzenesulfonate structure with a thickness of 50 nm on the outer layer. Among them, the thickness of the coating layer is monitored in real time by a quartz crystal microbalance.

[0137] Preparation of cathode plate: The cathode active material, composite conductive agent, and polyvinylidene fluoride (PVDF) binder are mixed in a mass ratio of 97:1.5:1.5, and NMP is used as an organic solvent to form a cathode paste with a solid content of 65%. It is coated on a positive current collector, dried and heat-treated to obtain a cathode plate.

[0138] The anode plate and separator are made according to the above embodiments and will not be elaborated here.

[0139] Assembly of the battery: The cathode plate, anode plate, and separator are wound by a winding machine to form a core. The core is cut and stacked for the positive and negative electrode tabs, and then the positive and negative current collector foils are welded to the core respectively. Then the negative current collector foil is welded to the steel shell, an insulating sheet is placed above the positive current collector foil, and the positive current collector foil is welded to the cap. Then grooving, liquid injection, and sealing are completed to obtain the battery of Example 1.

[0140] Here, the relevant parameter settings involved in this embodiment are as shown in Table 1 below:

[0141] Battery type <![CDATA Full tab Cylindrical battery]]> Aspect ratio of carbon nanotubes 600∶1 Mass ratio of carbon nanotubes to metal nanowires 2∶1 Density of oxygen-containing functional groups in the pretreatment of carbon nanotubes <![CDATA[1.2 mmol / g]]> Types of dispersant ionic liquids BMIM-BF4 (oxygen content 30 ppm) Oxidant gradient of the coating layer <![CDATA[Inner layer APS 0.3 mol / L, outer layer FeCl 3 0.05 mol / L]]> Gradient of the coating layer <![CDATA[Inner layer sulfate doping (15 nm ) and outer layer SDBS hydrophobic (50 nm )]]> Positive electrode active material NCM811 Negative electrode active material 90% artificial graphite + 10% silicon oxide

[0142] Table 1

[0143] Example 2

[0144] Example 2 provides a battery. The difference between this example and Example 1 is that the density of oxygen-containing functional groups after the pretreatment of carbon nanotubes is 0.5 mmol / L, and the others are the same as those in Example 1.

[0145] Example 3

[0146] Example 3 provides a battery. The difference between this example and Example 1 is that the density of oxygen-containing functional groups after the pretreatment of carbon nanotubes is 2 mmol / L, and the others are the same as those in Example 1.

[0147] Example 4

[0148] Example 4 provides a battery. The difference between this example and Example 1 is that the aspect ratio of the carbon nanotubes used is 500:1, and the others are the same as those in Example 1.

[0149] Example 5

[0150] Example 5 provides a battery. The difference between this example and Example 1 is that the aspect ratio of the carbon nanotubes used is 900:1, and the others are the same as those in Example 1.

[0151] Example 6

[0152] Example 6 provides a battery. The difference between this example and Example 1 is that the mass ratio of carbon nanotubes to silver nanowires is 3:1, and the others are the same as those in Example 1.

[0153] Example 7

[0154] Example 7 provides a battery. The difference between this example and Example 1 is that the mass ratio of carbon nanotubes to silver nanowires is 1:1, and the others are the same as those in Example 1.

[0155] Example 8

[0156] Example 8 provides a battery. The difference between this example and Example 1 is that the type of the dispersant ionic liquid becomes 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide ionic liquid (EMIM-TFSI), and the others are the same as those in Example 1.

[0157] Example 9

[0158] Example 9 provides a battery. The difference between this example and Example 1 is that the gradient concentration of the coating initiator is set to 0.5 mol / L of ammonium persulfate APS in the inner layer, and the others are the same as those in Example 1.

[0159] Example 10

[0160] Example 10 provides a battery. The difference between this example and Example 1 is that the gradient concentration of the coating initiator is set to 0.1 mol / L of FeCl3 in the outer layer, and the others are the same as in Example 1.

[0161] Example 11

[0162] Example 11 provides a battery. The difference between this example and Example 1 is that the impregnation time is adjusted so that the inner layer coating thickness is 25 nm, and the others are the same as in Example 1.

[0163] Example 12

[0164] Example 12 provides a battery. The difference between this example and Example 1 is that the concentration of the sprayed ethanol solution is adjusted to 7%, and the others are the same as in Example 1.

[0165] Example 13

[0166] Example 13 provides a battery. The difference between this example and Example 1 is that the carbon nanotube pretreatment acid is changed from HNO3 to H2SO4 of the same concentration, and the others are the same as in Example 1.

[0167] Example 14

[0168] Example 14 provides a battery. The difference between this example and Example 1 is that the metal nanowires are replaced by copper nanowires from silver nanowires, and the others are the same as in Example 1.

[0169] Example 15

[0170] Example 15 provides a battery. The difference between this example and Example 1 is that the cathode material is selected as lithium iron phosphate LiFePO4, and the others are the same as in Example 1.

[0171] Example 16

[0172] Example 16 provides a battery. The difference between this example and Example 1 is that the cathode material is selected as large single crystal lithium nickel cobalt manganate LiNi 0.5 Co 0.2 Mn 0.3 O2, and the others are the same as in Example 1.

[0173] Example 17

[0174] Example 17 provides a battery. The difference between this example and Example 1 is that the cathode material is selected as LiNi 0.5 Co 0.2 Al 0.3 O2, and the others are the same as in Example 1.

[0175] Example 18

[0176] Example 18 provides a battery. The difference between this example and Example 1 is that the metal nanowires are replaced by aluminum fluoride nanowires, and the others are the same as those in Example 1.

[0177] Example 19

[0178] Example 19 provides a battery. The difference between this example and Example 1 is that the metal nanowires are replaced by copper sulfide nanowires, and the others are the same as those in Example 1.

[0179] Example 20

[0180] Example 20 provides a battery. The difference between this example and Example 1 is that the metal nanowires are replaced by titanium dioxide nanowires, and the others are the same as those in Example 1.

[0181] Comparative Example 1

[0182] Comparative Example 1 provides a battery. The difference between this comparative example and Example 1 is that the density of oxygen-containing functional groups after pretreatment of carbon nanotubes is 0.2 mmol / L, and the others are the same as those in Example 1.

[0183] Comparative Example 2

[0184] Comparative Example 2 provides a battery. The difference between this comparative example and Example 1 is that the density of oxygen-containing functional groups after pretreatment of carbon nanotubes is 3 mmol / L, and the others are the same as those in Example 1.

[0185] Comparative Example 3

[0186] Comparative Example 3 provides a battery. The difference between this comparative example and Example 1 is that the aspect ratio of the selected carbon nanotubes is 250:1, and the others are the same as those in Example 1.

[0187] Comparative Example 4

[0188] Comparative Example 4 provides a battery. The difference between this comparative example and Example 1 is that the mass ratio of carbon nanotubes to silver nanowires is 5:1, and the others are the same as those in Example 1.

[0189] Comparative Example 5

[0190] Comparative Example 5 provides a battery. The difference between this comparative example and Example 1 is that no dispersant is added, and the others are the same as those in Example 1.

[0191] Comparative Example 6

[0192] Comparative Example 6 provides a battery. The difference between this comparative example and Example 1 is that the oxygen content of the added ionic liquid dispersant is 100 ppm, and the others are the same as those in Example 1.

[0193] Comparative Example 7

[0194] Comparative Example 7 provides a battery. The difference between this comparative example and Example 1 is that only ammonium persulfate APS is used and no outer layer spraying is performed, and the others are the same as those in Example 1.

[0195] Comparative Example 8

[0196] Comparative Example 8 provides a battery. The difference between this comparative example and Example 1 is that the environmental temperature is set to 60 °C during inner layer coating for high-temperature polymerization, and the others are the same as those in Example 1.

[0197] Comparative Example 9

[0198] Comparative Example 9 provides a battery. The difference between this comparative example and Example 1 is that only an ethanol solution with the same concentration is sprayed, and the others are the same as those in Example 1.

[0199] Comparative Example 10

[0200] Comparative Example 10 provides a battery. The difference between this comparative example and Example 1 is that the carbon nanotubes are not pretreated, and the others are the same as those in Example 1.

[0201] Comparative Example 11

[0202] Comparative Example 11 provides a battery. The difference between this comparative example and Example 1 is that the diameter of the silver nanowires is 150 nm, and the others are the same as those in Example 1.

[0203] The capacity performance of the cylindrical batteries of Examples 1 to 14 and Comparative Examples 1 to 11 was evaluated, and the evaluation method was as follows:

[0204] Test the capacity retention rate: Test the capacity retention rate after 600 cycles at a 3C rate. Taking the cylindrical battery with a high-nickel ternary material NCM811 and a graphite-mixed silicon anode as an example, for other types of batteries, the voltage range for testing needs to be corrected.

[0205] Take a 5 Ah battery, place it in a 25 °C constant temperature oven for more than 4 h, and perform the test according to the following steps:

[0206] (11) Discharge the battery at a constant current of 0.1C until it cuts off at 2.5V, and let it stand for 5 min;

[0207] (12) The battery is charged at a constant current to 4.2 V under the condition of 0.1 C, and charged at a constant current of 0.01 C until it reaches 4.2 V and then cut off, and then left standing for 5 min;

[0208] (13) The battery is discharged at a constant current until it reaches 2.5 V under the condition of 0.1 C and then cut off, and then left standing for 5 min;

[0209] (14) The battery is charged at a constant current to 4.2 V under the condition of 3 C, and charged at a constant current of 0.01 C until it reaches 4.2 V and then cut off, and then left standing for 5 min;

[0210] (15) The battery is discharged at a constant current until it reaches 2.5 V under the condition of 3 C, left standing for 5 min, the capacity value C0 at this time is read, and then left standing for 5 min;

[0211] (16) Repeat steps (14) and (15) 600 times;

[0212] (17) Through the ratio of the 600th discharge capacity to the 1st discharge capacity C0 in steps (14) and (15), the cycling performance of a single battery, that is, the capacity retention rate, is obtained.

[0213] If the positive electrode of the battery is lithium iron phosphate, then change to the following test steps:

[0214] Take a cylindrical battery, such as 21700 3Ah, place it in a constant temperature oven at 25 °C for more than 4 h, and conduct tests according to the following steps:

[0215] (21) The battery is discharged at a constant current until it reaches 2.0 V under the condition of 0.1 C and then cut off, and then left standing for 5 min;

[0216] (22) The battery is charged at a constant current to 3.6 V under the condition of 0.1 C, and charged at a constant voltage until it reaches 0.05 C and then cut off, and then left standing for 5 min;

[0217] (23) The battery is discharged at a constant current until it reaches 2.0 V under the condition of 0.1 C and then cut off, and then left standing for 5 min, and the capacity value C1 at this time is read;

[0218] (24) The battery is charged at a constant current to 3.6 V under the condition of 3 C, and charged at a constant voltage until it reaches 0.05 C and then cut off, and left standing for 5 min;

[0219] (25) The battery is discharged at a constant current until it reaches 2.0 V under the condition of 3 C and then cut off, and left standing for 5 min;

[0220] (26) Repeat steps (24) and (25) 600 times;

[0221] (27) The cycling performance of a single cell, i.e., the capacity retention rate, is obtained by the ratio of the 600th discharge capacity to the 1st discharge capacity in steps (24) and (25).

[0222] The test results of the 24-hour viscosity rebound rate of the positive electrode slurries, the resistivity of the positive electrode sheets, and the electrochemical performance of the corresponding batteries for Examples 1 to 20 are shown in Table 2. Among them, the 24-hour viscosity rebound rate of the positive electrode slurries is between 5% and 23%, the resistivity of the positive electrode sheets is between 0.8 Ω·cm and 6.5 Ω·cm, and the capacity retention rate after 600 cycles at 3C rate is between 83% and 94%.

[0223]

[0224] Table 2

[0225] The test results of the 24-hour viscosity rebound rate of the positive electrode slurries, the resistivity of the positive electrode sheets, and the electrochemical performance of the corresponding batteries for Comparative Examples 1 to 11 are shown in Table 3. Among them, the 24-hour viscosity rebound rate of the positive electrode slurries is between 2% and 58%, the resistivity of the positive electrode sheets is between 3.5 Ω·cm and 6.5 Ω·cm, and the capacity retention rate after 600 cycles at 3C rate is between 70% and 83%.

[0226]

[0227] Table 3

[0228] From the test results in Table 2, Table 3, and the attached Figure 5 it can be seen that by using the positive electrode material of the present application, whether in the process of homogenizing the composite conductive agent or in the prepared battery, it has good processing performance, low resistivity, and good battery capacity retention rate at different rates.

[0229] Combining and comparing Examples 1 to 3, Comparative Examples 1 and 2, and Figure 5 it can be known that if the density of oxygen-containing functional groups is too low, it will lead to poor dispersion of carbon nanotubes and ineffective binding with metal nanowires, thus increasing the resistivity. But if it is too high, it will cause self-aggregation of carbon nanotubes, reducing the processing performance of the slurry and the resistivity of the electrode sheet. Therefore, the comprehensive performance in Examples 2 and 3 and Comparative Examples 1 and 2 is lower than that in Example 1.

[0230] Comparing Comparative Example 4, Example 5 and Comparative Example 3, it can be seen that the resistivity of Example 5 is slightly lower than that of Example 1. This is because the increase in the aspect ratio enhances the penetration of the three-dimensional conductive network, which helps to improve the conductivity of the overall composite material. However, the viscosity rebound rate of the slurry in Example 5 after 24 hours is relatively high, because when the aspect ratio of carbon nanotubes is relatively high, it is difficult to disperse and easy to agglomerate. Moreover, the resistivity of the electrode sheet in Comparative Example 3 increases significantly, because when the aspect ratio is insufficient, the long-range connection of the conductive network will be disconnected, and an efficient conductive network cannot be formed.

[0231] Comparing Comparative Example 6, Example 7 and Comparative Example 4, it can be seen that when the proportion of metal nanowires is insufficient, the number of conductive nodes between particle gaps will decrease, resulting in an increase in the resistivity of the electrode sheet. However, when the proportion of metal nanowires increases, they will spontaneously adsorb and agglomerate, affecting the processing performance of the slurry and the stability during long cycling, manifested as a slightly worse cycle capacity retention rate at high rates.

[0232] Comparing Comparative Example 8 and Comparative Example 5, it can be seen that when EMIM-TFSI is selected as the dispersant, compared with BMIM-BF4, the - TFSI anion has a larger volume and better dispersion stability, but it will reduce the conductive performance of the electrode sheet and increase the resistivity of the electrode sheet.

[0233] Comparing Comparative Example 9 to Example 11, as well as Comparative Example 9 and Comparative Example 10, it can be seen that a high initiator concentration can increase the inner layer polymerization rate, form a dense coating layer, resulting in an increase in the cycle capacity retention rate. At the same time, the thickness of the coating layer should be controlled to be sufficient to cover the surface defects of carbon nanotubes. However, in the case of being too thick, such as when the coating layer thickness > 20 nm, it will hinder electron conduction, increase the resistivity of the electrode sheet, and thus reduce the cycle stability.

[0234] In Example 14, copper nanowires are used to replace silver nanowires, and both the resistivity of the electrode sheet and the capacity retention rate decrease compared with Example 1. This is because the conductivity of copper is weaker than that of silver, and at the same time, the positive electrode potential is relatively high, and the surface of copper nanowires is easily oxidized, which is not conducive to cycle stability.

[0235] In summary, through the positive electrode material provided by this application, by optimizing the ratio of the positive electrode material, the conductivity of the conductive agent and the stability of the conductive slurry can be effectively improved, thereby improving the comprehensive performance of the battery.

[0236] The above description and the accompanying drawings sufficiently illustrate embodiments of the present disclosure such that those skilled in the art can practice them. Other embodiments may include structural and other changes. The embodiments represent only possible variations. Unless explicitly required, individual components and functions are optional, and the order of operations may vary. Parts and features of some embodiments may be included in or substituted for parts and features of other embodiments. Embodiments of the present disclosure are not limited to the structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present disclosure is limited only by the appended claims.

Claims

1. A cathode material, characterized in that, Comprising: A positive electrode active material, the active particles of which are coated with an in-situ polymerization double layer; wherein, the positive electrode active material includes one or more of lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium nickel manganese oxide, and lithium iron phosphate materials; A composite conductive agent, comprising carbon nanotubes and metal nanowires with a composite composition; Wherein, an imidazole-based ionic liquid is used as a dispersant for the carbon nanotubes and metal nanowires, and the ends of the metal nanowires are embedded in the surface of the particles of the positive electrode active material.

2. The cathode material according to claim 1, wherein The thickness range of the double-layer coating structure is 5 nm to 50 nm.

3. The cathode material according to claim 1, wherein The diameter range of the carbon nanotubes is 50 nm to 200 nm, and the aspect ratio ≥ 500.

4. The cathode material according to claim 1, characterized in that, The diameter range of the metal nanowires is 10 nm to 50 nm, and the length range is 1 μm to 10 μm.

5. The cathode material according to claim 1, characterized in that, The metal nanowires include one or more of silver nanowires, copper nanowires, aluminum fluoride nanowires, copper sulfide nanowires, titanium dioxide nanowires, and lithium nickel cobalt manganese oxide nanowires.

6. The cathode material according to claim 1, wherein The carbon nanotubes are treated by refluxing with nitric acid so that the density range of oxygen-containing functional groups on the surface is 0.5 mmol / g to 2.0 mmol / g; wherein, the nitric acid concentration range is 30% to 60%, and the reflux treatment duration is 2 h to 6 h.

7. The cathode material according to any one of claims 1 to 6, characterized in that, The lithium nickel cobalt manganese oxide material includes a high-nickel ternary lithium nickel cobalt manganese oxide material, and its chemical formula is Li a Ni x Co y Mn z M b O2; where 0.9 < a < 1.1, 0.7 < x ≤ 0.94, 0.1 ≤ y < 0.4, 0.05 ≤ z < 0.4, 0 ≤ b ≤ 0.1; the M element is one or a combination of more than one of Al, Mg, Zr, Ti, W, Nb, Mo, B.

8. The cathode material according to any one of claims 1 to 6, characterized in that, The lithium nickel cobalt manganese oxide material includes a medium-nickel ternary lithium nickel cobalt manganese oxide material with the chemical formula Li a1 Ni x1 Co y1 Mn z1 M1 b1 O2; wherein, 0.9 < a1 < 1.1, 0.4 ≤ x1 ≤ 0.7, 0.1 ≤ y1 < 0.4, 0.05 ≤ z1 < 0.4, 0 ≤ b1 ≤ 0.1, and M1 is one or a combination of more than one of Al, Mg, Zr, Ti, W, Nb, Mo, and B.

9. A method for preparing the positive electrode material according to any one of claims 1 to 8, characterized in that, Including the following steps: Preparing a conductive paste from carbon nanotubes and metal nanowires by a disperser; Performing in-situ polymerization coating on the positive electrode active material by a reaction kettle to prepare a positive electrode active material with a double-layer coating structure; Mixing and dispersing the conductive paste, the positive electrode active material with a double-layer coating structure, and a binder in an organic solvent to form a positive electrode material with a solid content of 40 wt% to 60 wt%.

10. A positive electrode sheet, characterized in that, Including a positive electrode current collector and a positive electrode coating coated on at least one surface of the positive electrode current collector, and the positive electrode coating includes the positive electrode material according to any one of claims 1 to 8.

11. A battery, characterized in that, Comprising: The positive electrode sheet according to claim 10; A negative electrode sheet, including a negative electrode current collector and a negative electrode coating coated on at least one surface of the negative electrode current collector, and the negative electrode coating includes a negative electrode active material.

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