Polymer-based negative electrode current collector and its preparation method

Abstract

A polymer-based negative electrode current collector and its preparation method are disclosed. The current collector comprises a support layer and a protective conductive composite layer located on the surface of the support layer. The protective conductive composite layer contains a conductive material with a larger particle size and a protective material with a smaller particle size, and the bonding force between the protective material and the support layer is not less than 500 N / m. Furthermore, the support layer is made of a high-strength conductive polymer with abundant unsaturated functional groups, which can reduce the thickness of the support layer and ensure sufficient adhesion to the conductive protective composite layer. This preparation method involves mixing the protective and conductive materials and forming them on this surface in a single step. Utilizing the self-alignment effect caused by the different particle sizes, the conductive and protective material particles not only move towards the sides closer to and away from the support layer, respectively, but also avoid interference between the bonding forces between the conductive and protective materials.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and more specifically to a polymer-based negative electrode current collector and its preparation method, which uses polymer materials to form a support layer and forms a protective conductive composite layer by forming a protective material and a conductive material on the surface of the support layer in a one-time process. Background Technology

[0002] In recent years, to address the problems of fossil fuel consumption and environmental pollution brought about by the increasing demand for energy, countries have actively developed new energy technologies. Among these, lithium-ion batteries, due to their advantages such as high energy density, low environmental risk, high output power, and long cycle life, have been widely used in chemical energy storage, new energy vehicles, power tools, portable electronic devices, and electronic products. Furthermore, with the rapid development of these industries and the continuous expansion of the application scope of lithium-ion batteries, the requirements for their gravimetric and volumetric energy densities are becoming increasingly stringent.

[0003] Current lithium-ion battery technology generally uses metal current collectors with large thickness and high density in both the positive and negative electrodes. However, this results in relatively low energy density in the secondary battery, which cannot meet the increasingly demanding requirements of the market. Therefore, how to improve the energy density of lithium-ion secondary batteries by improving the current collector while ensuring good conductivity and current collection performance has become an urgent technical challenge.

[0004] To obtain rechargeable batteries with high gravimetric energy density, the weight of various components can be reduced. Improving the current collector typically involves choosing a lighter one, such as a plastic current collector coated with a protective conductive layer. However, while weight reduction is achieved with plastic current collectors coated with metal layers, it also leads to some performance degradation, affecting the performance of the electrodes and the battery itself. Furthermore, the commonly used current collector structure, consisting of an alternating protective layer / conductive layer / support layer / conductive layer / protective layer, not only affects the volumetric energy density due to its accumulated thickness, but its internal resistance also reduces the electrochemical performance of the lithium-ion battery.

[0005] Therefore, continuous improvements are still needed to obtain current collectors with better performance. Summary of the Invention

[0006] This invention provides a polymer-based negative electrode current collector, comprising a support layer and a protective conductive composite layer located on the surface of the support layer. The bonding force between the protective conductive composite layer and the support layer is not less than 500 N / m (Newtons per meter). The support layer is made of a conductive polymer, and the particle size of the protective material is smaller than that of the conductive material. Furthermore, in a portion of the protective conductive composite layer near the support layer, the conductive material outweighs the protective material, while in another portion of the conductive protective layer away from the support layer, the protective material outweighs the conductive material.

[0007] Alternatively, the ratio between the particle size of the protective material particles and the particle size of the conductive material particles may be between 3 and 5, or the ratio may be between 2.5 and 3.3.

[0008] Alternatively, the protective material has a particle size between 10 nm and 100 nm, and the conductive material has a particle size between 50 nm and 300 nm.

[0009] Alternatively, the protective material has a particle size between 30 nm and 80 nm and the conductive material has a particle size between 100 nm and 200 nm.

[0010] Alternatively, the protective material may be at least one of metal oxides, metallic materials, and carbon materials.

[0011] Alternatively, the resistivity of the conductive material is not greater than 7.0 × 10⁻⁶ at 25°C. -8 The Ω·m (ohm-per meter) and the thickness of the conductive material in the protective conductive composite layer is between 1.3 μm (micrometer) and 3 μm.

[0012] Alternatively, the metal oxide may be one or more of aluminum oxide, cobalt oxide, chromium oxide, and nickel oxide; the metal material may be one or more of nickel, chromium, tin, nickel-based alloys, and copper-based alloys; the carbon material may be one or more of graphite, acetylene black, carbon black, carbon nanotubes, graphene, and carbon fiber; or the conductive material may be one or more of copper, nickel, stainless steel, silver, and titanium.

[0013] Optionally, the thickness of the protective conductive composite layer is between 2 μm and 5 μm, the thickness of the conductive material is between 1.3 μm and 3 μm, and the thickness of the protective material is between 0.7 μm and 2 μm.

[0014] Optionally, the thickness of the protective conductive composite layer is between 3 μm and 4 μm, the thickness of the conductive material is between 1.6 μm and 2 μm, and the thickness of the protective material is between 1.4 μm and 2 μm.

[0015] Alternatively, the support layer may have a 1.4 10 -9 The resistivity is Ω·m, or the supporting layer may have a Young's modulus between 5 GPa and 25 GPa.

[0016] Alternatively, the support layer may have an elongation at break between 4.5% and 6.7%, or the elongation at break of the support layer may be not less than the elongation at break of the protective conductive composite layer.

[0017] Alternatively, the conductive polymer can be a conductive polymer or a composite conductive polymer material made from a blend of a polymer and a conductive agent.

[0018] Optionally, the conductive polymer may have a polymer structure with a conjugated long chain structure, or the conductive polymer may be one or more of polyaniline, polythiophene, polypyrrole, polysulfide, or aliphatic conjugated polymers.

[0019] Alternatively, the composite conductive polymer material is a conductive polymer material formed by blending various conductive agents with intrinsically non-conductive conventional polymer materials using different processing techniques. Here, the intrinsically non-conductive conventional polymer material is one or more of polyethylene, polypropylene, polytetrafluoroethylene, vinylidene fluoride, and polystyrene, and the conductive agent is one or more of graphite, carbon nanotubes, carbon fibers, high-purity conductive carbon black, graphene, activated carbon, and conductive carbon black.

[0020] Alternatively, the thickness of the support layer may be between 2 μm and 15 μm, or between 3 μm and 12 μm, or between 5 μm and 8 μm.

[0021] This invention provides a lithium-ion battery, comprising a positive electrode and a negative electrode. Here, the negative electrode comprises the polymer-based negative electrode current collector described above.

[0022] This invention provides a method for preparing the above-mentioned polymer-based negative electrode current collector. First, a support layer is provided, wherein the material of the support layer is a conductive polymer. Next, a protective material and a conductive material are mixed together in a solvent to form a protective conductive composite slurry, and the protective conductive composite slurry is formed on the surface of the support layer in a single step, thereby forming a protective conductive composite layer.

[0023] Optionally, one or more coupling agents and crosslinking agents can be co-mixed into the solvent. Furthermore, the amounts of the coupling agent and the crosslinking agent used can be adjusted to achieve the desired separation between the protective material and the conductive material; the more coupling agent and crosslinking agent used, the longer it takes to achieve the desired separation.

[0024] Optionally, the protective conductive composite paste comprises a protective material with a mass fraction between 45% and 58%, a conductive material with a mass fraction between 35% and 50%, a coupling agent with a mass fraction between 5.5% and 10%, and a crosslinking agent with a mass fraction between 2.5% and 5%. Furthermore, the solvent has a solid content between 35% and 45%.

[0025] Alternatively, the crosslinking agent may be one or more of vinylidene fluoride, sodium alginate, styrene-butadiene rubber, and polytetrafluoroethylene; the coupling agent may be one or more of trichlorovinylsilane, triethoxyvinylsilane, γ-aminopropyltriethoxysilane, trichloropropylene silane, etc.; tetrabutyl titanate, triisostearoyl titanate isopropyl, diisostearoyl phthaloate ethyl ester, and methacryloyl chromium complex; or the solvent may be one or more of ethanol, dimethylacetamide, acetonitrile, methanol, and polycarbonate.

[0026] Alternatively, the method for forming the protective conductive composite paste on the surface of the support layer can be one or both of rolling and bonding. Furthermore, the settling time of the protective conductive composite paste can be adjusted to regulate the separation between the protective material and the conductive material within the protective conductive composite layer; the longer the settling time, the more the protective material and the conductive material separate from each other.

[0027] This invention has at least the following beneficial effects. First, the current collector support layer is made of a conductive polymer, which is not only cheaper than the traditionally used metal support layer, but also has high strength and ductility, significantly improving the tensile strength and processing performance of the current collector, thereby reducing the thickness of the support layer. This reduces the overall weight of the battery and the volume of the bare cell, increasing the battery's specific energy. Furthermore, its high conductivity also improves the battery's electrochemical performance. In addition, the conductive polymer has abundant unsaturated functional groups, which can fully bond with the protective conductive composite layer, strengthening the overall strength of the current collector and improving electron permeability, thus reducing the battery's internal resistance. Furthermore, compared to existing methods that sequentially form the conductive layer and protective layer on the support layer surface, this invention first mixes the protective material particles and conductive material particles and forms them on the support layer surface in one step. Then, the protective conductive composite layer is formed through the self-alignment of different particles caused by their different particle sizes. This not only reduces the overall thickness of the current collector but also avoids interference between the bonding forces of the conductive and protective materials, further reducing the current collector's internal resistance and improving the battery's electrochemical performance. Attached Figure Description

[0028] Figure 1A This is a cross-sectional schematic diagram showing the polymer-based negative electrode current collector of the first embodiment of the present invention;

[0029] Figures 1B to 1DFor illustrative purposes, three possible variations of the first embodiment of the present invention are presented.

[0030] Figure 2 This is a flowchart illustrating the preparation method of the polymer-based negative electrode current collector according to the second embodiment of the present invention;

[0031] Figures 3A to 3C This is a cross-sectional schematic diagram illustrating the mechanism of the polymer-based negative electrode current collector preparation method proposed in this invention.

[0032] Component labeling explanation

[0033] 100…Polymer-based negative electrode current collector

[0034] 101… Support layer

[0035] 102… Protective conductive composite layer

[0036] 1021…conductive material particles

[0037] 1022… Protective material particles

[0038] 103… Protective Conductive Composite Paste

[0039] Steps S1~S3… Detailed Implementation

[0040] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0041] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and such ranges or values ​​should be understood to include values ​​close to such ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0042] In summary, this invention proposes a polymer-based negative electrode current collector, comprising a support layer and a protective conductive composite layer located on the surface of the support layer. Here, the support layer is made of a conductive polymer. In the protective conductive composite layer, a portion near the support layer is predominantly composed of conductive material (i.e., this portion is mainly conductive material, or even entirely conductive material), while the remaining portion of the conductive protective layer away from the support layer is predominantly composed of protective material (i.e., this portion is mainly protective material, or even entirely protective material). The bonding force between the protective conductive composite layer and the support layer is not less than 500 N / m. This invention also proposes a method for preparing the polymer-based negative electrode current collector, which involves first forming a protective conductive slurry by combining a protective material, a conductive material, and a solvent (even a coupling agent and / or a crosslinking agent), and then forming this protective conductive slurry on the surface of the polymer support layer. Utilizing the self-alignment effect resulting from the smaller particle size of the protective material and the larger particle size of the conductive material, the conductive material and the protective material are arranged separately to form the protective conductive composite layer.

[0043] like Figure 1A As shown, a first embodiment of the present invention provides a polymer-based negative electrode current collector (100), comprising: a support layer (101) and a protective conductive composite layer (102). The protective conductive composite layer (102) is located on the surface of the support layer (101). Here, the bonding force between the protective conductive composite layer (102) and the support layer (101) is not less than 500 N / m, the particle size of the protective material is smaller than the particle size of the conductive material, and a portion of the protective conductive composite layer near the support layer has more conductive material than protective material, while another portion of the conductive protective layer away from the support layer has more protective material than conductive material.

[0044] The reason for ensuring that the bonding force between the protective conductive composite layer (102) and the support layer (101) is not less than 500 N / m is to ensure the strength of the negative electrode (or negative electrode) and control the internal resistance of the negative electrode. Otherwise, when the negative electrode is immersed in the electrolyte inside the lithium-ion battery for a period of time, especially after the lithium-ion battery has been operating for a period of time, the protective conductive composite layer (102) and the support layer (101) are prone to separate from each other, causing the negative electrode to lose its normal function.

[0045] The reason for using a protective material as the primary component in the portion of the protective conductive composite layer furthest from the support layer and a conductive material as the primary component in the portion closer to the support layer is the same as the reason for using a conductive layer on the surface of the support layer and a protective layer on top of the conductive layer in existing commercial negative electrode current collectors, and therefore does not need to be repeated. However, compared to existing commercial negative electrode current collectors where the protective layer and conductive layer are formed sequentially on the support layer, and are adjacent but clearly separated layers (or the conductive material is completely located between the protective material and the support layer), this invention does not require such strict limitation. For example, in some embodiments of this invention, the protective material is completely located on top of the conductive material, that is, a portion of the protective conductive composite layer is 100% conductive material and another portion is 100% protective material. For example, in other embodiments of this invention, the protective material is generally located on top of the conductive material, but there is a transition zone where both protective and conductive materials coexist, that is, the two sides of the protective conductive composite layer are 100% conductive material and 100% protective material respectively, but in the middle portion of the protective conductive composite layer, the proportions of protective and conductive materials gradually change in opposite directions. Furthermore, in some embodiments of the present invention, the proportions of the protective material and the conductive material in the entire protective conductive composite layer gradually change in opposite directions. Here, Figures 1B to 1D For illustrative purposes, these three possible variations in the distribution of the protective material and the conductive material inside the protective conductive composite layer in the first embodiment of the present invention are presented respectively.

[0046] In contrast, the protective material has a smaller particle size while the conductive material has a larger particle size, which is a feature of this invention. This allows the self-alignment effect between particles of different sizes to be utilized to separate the protective material and the conductive material, and to reduce interference between their bonding forces or even other factors on the negative electrode current collector.

[0047] Furthermore, to ensure that the two types of particles can be properly aligned (or move to opposite sides of the protective conductive composite layer), the particle sizes of both materials have appropriate ranges. In fact, there is a suitable ratio range between the particle sizes of the protective material and the conductive material to allow the self-alignment effect to be fully realized. For example, in some embodiments of the invention, the particle size of the protective material is between 10 nm and 100 nm, while the particle size of the conductive material is between 50 and 300 nm. For example, in other embodiments of the invention, the particle size of the protective material is between 30 nm and 80 nm, while the particle size of the conductive material is between 100 nm and 200 nm. For example, in some embodiments of the invention, the ratio between the particle sizes of the protective material and the conductive material is between 3 and 5. In still other embodiments of the invention, the ratio between the particle sizes of the protective material and the conductive material is between 2.5 and 3.3.

[0048] Of course, the particle size of the two materials also needs to take into account the properties of the materials used, such as whether they are easy to process into small particles and the influence of different particle sizes on their resistance or mechanical strength. Different practical applications have different suitable ranges for the particle size of protective materials and conductive materials.

[0049] In addition to the above, the distribution patterns of the protective and conductive materials in the protective conductive composite layer, such as the thickness of the distribution area, also affect the performance of the negative electrode current collector. Generally speaking, the smaller the total thickness of the portion where the conductive material particles are distributed in the protective conductive composite layer, the better it is to reduce the mass of the negative electrode current collector and thus improve the energy density of the battery. However, if the total thickness of the portion where the conductive material particles are distributed is too small, it will reduce its conductivity and current collection effect, thus negatively affecting the electrochemical performance of the battery. On the other hand, if the total thickness of the portion where the conductive material particles are distributed is too large, these conductive material particles are more likely to mix excessively with these protective material particles, which is not conducive to the concentrated distribution of the protective material particles on the outer side of the protective conductive composite layer, thus negatively affecting the protective function of the protective conductive composite layer. Therefore, in some embodiments, when the resistivity of the conductive material is not greater than 7.0 × 10⁻⁸ Ω·m (at 25°C), the total thickness of the portion of the conductive material distributed in the conductive protective composite layer is between 1.3 μm and 3 μm. This is because the entire conductive protective composite layer can effectively reduce the weight of the current collector while enabling the lithium-ion battery to have better rate performance, charge and discharge performance, etc.

[0050] The thicknesses of the support layer, protective conductive composite layer, conductive material (or the thickness of the portion of the protective conductive composite layer where the conductive material is distributed), and protective material (or the thickness of the portion of the protective conductive composite layer where the protective material is distributed) depend on their intended function and the side effects to be avoided. An excessively thin support layer is difficult to bond with the protective conductive composite layer, while an excessively thick support layer is prone to breakage. Thinner conductive and protective material thicknesses (i.e., thinner protective conductive composite layer thickness) are more conducive to reducing the overall mass of the negative electrode current collector, thereby improving the overall energy density of the lithium-ion battery. However, excessively thin protective material thickness (or excessively thin conductive composite layer thickness) is prone to breakage during negative electrode processing (or even damage during lithium-ion battery use due to impact or overheating), and excessively thin conductive material thickness will result in poor conductivity and current collection performance, thus negatively affecting the overall electrochemical performance of the lithium-ion battery.

[0051] For example, in some embodiments, the thickness of the protective conductive composite layer is between 2 μm and 5 μm, the thickness of the conductive material is between 1.3 μm and 3 μm, and the thickness of the protective material is between 0.7 μm and 2 μm. For example, in other embodiments, when the thickness of the protective conductive composite layer is adjusted to between 3 μm and 4 μm, the thickness of the conductive material is correspondingly adjusted to between 1.6 μm and 2 μm, and the thickness of the protective material is correspondingly adjusted to between 1.4 μm and 2 μm.

[0052] The types of protective and conductive materials are not particularly limited, as long as particles of appropriate size can be produced and adequate protective and conductive functions can be provided. For example, in some embodiments, the protective material is a metal oxide, such as aluminum oxide, cobalt oxide, chromium oxide, or nickel oxide, or a combination of these. For example, in some embodiments, the protective material is a metallic material, such as nickel, chromium, tin, nickel-based alloys, or copper-based alloys, or a combination of these. For example, in some embodiments, the protective material is a carbon material, such as graphite, acetylene black, carbon black, carbon nanotubes, graphene, or carbon fibers, or a combination of these. For example, in some embodiments, the conductive material is copper, nickel, stainless steel, silver, or titanium, or a combination of these.

[0053] The main reason for using conductive polymers to form the support layer is their advantage over metal current collectors commonly used in commercial anodes, including lower cost, ease of processing and high plasticity, and conductivity comparable to metals. In particular, conductive polymers have abundant unsaturated functional groups, making them easy to integrate with the protective conductive composite layer (or protective conductive paste). The type of conductive polymer used is not particularly limited, as long as it provides the aforementioned advantages and is appropriately matched with the protective conductive composite layer.

[0054] For example, in some embodiments, the conductive polymer is a conductive high molecular weight polymer (or a conductive polymer with a molecular weight greater than 10,000). In other embodiments, the conductive polymer is a composite conductive high molecular weight polymer material made from a blend of a polymer and a conductive agent. In still other embodiments, the conductive polymer can be a mixture of the two. Furthermore, in yet another embodiment, the bulk resistivity of the support layer is 1.4 × 10⁻⁶. -9 Ω·m (approximately no higher than the volume resistivity of the metal current collector).

[0055] For example, in some embodiments, the conductive polymer structure is a long-chain structure with conjugated molecules. This is because delocalized π electrons on the double bonds can migrate along the molecular chain to form an electric current, making the polymer structure itself conductive. In other embodiments, the conductive polymer can be polyaniline, polythiophene, polypyrrole, polysulfide, or an aliphatic conjugated polymer, or even a combination of several of these.

[0056] For example, in some embodiments, the composite conductive polymer material is a conductive polymer material formed by blending various conductive agents with intrinsically non-conductive conventional polymer materials using different processing techniques. Here, the intrinsically non-conductive conventional polymer material can be polyethylene, polypropylene, polytetrafluoroethylene, vinylidene fluoride, or polystyrene, or a combination of these. Here, the conductive agent can be one of graphite, carbon nanotubes, carbon fibers, high-purity conductive carbon black, graphene, activated carbon, or conductive carbon black, or a combination of these.

[0057] To ensure good conductivity and current collection performance, and to prevent delamination between the protective conductive composite layer and the support layer, it is necessary to reduce the probability of breakage or cracking of the protective conductive composite layer and to improve the bonding strength between the support layer and the conductive material. Therefore, in some embodiments, the material and thickness of the support layer are such that the elongation at break of the support layer is not less than that of the protective conductive composite layer. In other embodiments, the material and thickness of the support layer are such that the elongation at break of the support layer is between 4.5% and 6.7%.

[0058] To prevent delamination between the protective conductive composite layer and the support layer, the support layer must provide adequate support to the protective conductive composite layer, thereby enhancing the bonding strength between them. Conversely, to prevent excessive stretching or deformation of the support layer during the processing of the negative electrode current collector, it is necessary to prevent breakage of the protective conductive composite layer. Therefore, the support layer needs to possess both good toughness and appropriate rigidity. For this reason, in some embodiments, the Young's modulus of the support layer is between 5 GPa and 25 GPa.

[0059] To facilitate adhesion between the support layer and the protective conductive composite layer, the thickness of the support layer cannot be too thin. Conversely, to prevent breakage, the thickness of the support layer cannot be too thick. Therefore, in some embodiments, the thickness of the support layer is between 2 μm and 15 μm. In other embodiments, the thickness is between 3 μm and 12 μm. In still other embodiments, the thickness is between 5 μm and 8 μm.

[0060] like Figure 2As shown, the second embodiment of the present invention provides a method for preparing a polymer-based negative electrode current collector, particularly the method for preparing a polymer-based negative electrode current collector provided in the first embodiment, comprising: a support layer step (S1): providing a support layer, wherein the material of the support layer is a conductive polymer; a protective conductive composite slurry step (S2): mixing the protective material and the conductive material together in a solvent to form a protective conductive composite slurry; and a protective conductive composite layer step (S3): forming the protective conductive composite slurry on the surface of the support layer in one step, thereby forming a protective conductive composite layer.

[0061] In the support layer step (S1), the provided support layer has a surface.

[0062] In the protective conductive composite slurry step (S2), to ensure thorough mixing of the protective material and the conductive material, to make the protective conductive composite slurry suitable for formation (or transfer) on the surface of the support layer in the protective conductive composite layer step (S3), and to allow relative movement and rearrangement of the protective material particles and conductive material particles within the protective conductive composite slurry, coupling agents and / or crosslinking agents may be co-mixed into the solvent. In some embodiments, the protective conductive composite slurry comprises at least: a protective material with a mass fraction between 45% and 58%, a conductive material with a mass fraction between 35% and 50%, a coupling agent with a mass fraction between 5.5% and 10%, and a crosslinking agent with a mass fraction between 2.5% and 5%. Furthermore, the solid content of the solvent is between 35% and 45%.

[0063] Here, there are many possible options for the crosslinking agent, coupling agent, and solvent, depending on the protective and conductive materials used, the support layer used, the properties of the protective-conductive composite layer to be formed, and how the protective conductive paste is formed on (or transferred to) the surface of the support layer, etc. For example, in some embodiments, the crosslinking agent is one or more of vinylidene fluoride, sodium alginate, styrene-butadiene rubber, and polytetrafluoroethylene. For example, in other embodiments, the coupling agent is one or more of trichlorovinylsilane, triethoxyvinylsilane, γ-aminopropyltriethoxysilane, trichloropropylene silane, tetrabutyl titanate, triisostearoyl titanate isopropyl triisostearoyl phthalate, diisostearoyl phthalate ethyl ester, and chromium methacryloyl complex. For example, in still other embodiments, the solvent is one or more of ethanol, dimethylacetamide, acetonitrile, methanol, and polycarbonate.

[0064] There is more than one way to form (or transfer) the protective conductive paste on (or to) the surface of the support layer, as long as the quality of the protective conductive paste is not damaged during the process, especially the amount of protective conductive paste is not excessively consumed or the overall process rate is not excessively reduced. For example, in some embodiments, the protective conductive composite paste is formed on the surface of the support layer by one or two of rolling and bonding.

[0065] Furthermore, after mixing the protective material and conductive material together in a solvent to form a protective conductive composite slurry, the protective conductive composite material can be left to stand for a period of time to adjust the distribution of the protective and conductive materials. Alternatively, the protective and conductive materials can be allowed to self-align for a period of time to adjust the degree of separation between them in the protective conductive composite slurry. Whether the protective conductive composite slurry is formed on the support layer first and then left to stand for a period of time, or vice versa, obviously, the longer the standing time, the more the protective and conductive materials will separate, meaning that the final protective conductive composite layer will have less of the protective and conductive materials mixed together. For example, after preparing the protective conductive composite slurry, if it is left to stand for only one hour, the protective and conductive materials in the resulting protective conductive composite layer are often still mixed without significant stratification. However, if the slurry is left to stand for twelve hours, the resulting protective conductive composite layer will often consist of two distinct layers: one layer of protective material and the other of conductive material. Of course, the specific standing time and degree of stratification depend on many factors, such as the particle size and profile of the protective and conductive materials, the temperature of the protective conductive composite slurry during the standing period, and the type and quantity of the crosslinking agent, crosslinking aid, and solvent used in the protective conductive composite slurry. For instance, the amount of solvent used often has an inverse effect on the separation speed between the protective and conductive material particles; the more solvent used, the longer it takes for the protective and conductive material particles to achieve complete separation.

[0066] like Figures 3A to 3C As shown, the mechanism of this preparation method includes three stages. First, as... Figure 3A As shown, a protective conductive composite paste (103) is formed on the surface of the support layer (101) in one step, and the protective conductive composite paste (103) contains a large number of conductive material particles (1021) and a large number of protective material particles (1022), wherein the particle size of the conductive material particles (1021) is larger than the particle size of the protective material particles (1022). Next, as... Figure 3BAs shown, due to the different particle sizes of the conductive material particles (1021) and the protective material particles (1022), the conductive material particles (1021) gradually settle and move towards the surface of the support layer (101), while the smaller protective material particles (1022) gradually move away from the surface of the support layer (101). Finally, as... Figure 3C As shown, given sufficient time and an appropriate particle size ratio, the conductive material particles (1021) and the protective material particles (1022) can move due to their different particle sizes. For example, in the final formed protective conductive composite layer (102), the conductive material particles (1021) will self-align on one side adjacent to the support layer (101), while the protective material particles (1022) will self-align on the other side away from the support layer (101). That is, although the conductive material particles (1021) and the protective material particles (1022) are formed simultaneously on the surface of the support layer (101) and are initially mixed together, the self-alignment effect caused by the different particle sizes allows the conductive material particles (1021) and the protective material particles (1022) to eventually separate from each other, resulting in the two opposing parts of the protective conductive composite layer (102) being dominated by protective material or conductive material, respectively.

[0067] In contrast, existing commercial negative electrode current collector manufacturing methods generally involve first forming a conductive layer on the surface of a support layer (regardless of whether the support layer is made of metal, plastic, or other materials), and then forming a protective layer on top of the conductive layer. In this case, because the physical and chemical properties of the conductive material used in the conductive layer often differ significantly from those of the protective material used in the protective layer, in addition to the inevitable difficulties in forming the conductive layer on the support layer and the protective layer on top of the conductive layer, the bonding force between the protective layer and the conductive layer (or between the protective material and the conductive material) can also interfere with the flowing current.

[0068] In contrast, this invention utilizes the self-alignment effect between a large number of protective material particles and a large number of conductive material particles within the protective conductive paste. This not only simplifies the process of forming the protective material / conductive material / support layer / conductive material / protective material structure and reduces the interference of the bonding force between the protective and conductive materials on the flowing current, but can even eliminate the structural micro-defects between these conductive and protective material particles after self-alignment. Whether in terms of improving the performance of the negative electrode current collector (such as reducing resistance or even homogenizing the electric field) or improving the preparation method of the negative electrode current collector (requiring only one-time formation of the protective conductive paste and waiting for the self-alignment effect to occur), it has significant advantages over existing commercial negative electrode current collectors and their preparation methods.

[0069] A third embodiment of the present invention is a lithium-ion battery comprising a positive electrode and a negative electrode, wherein the negative electrode uses a polymer-based negative electrode current collector provided by the present invention. Here, the relative relationship between the positive and negative electrodes, and the manner in which the negative electrode uses this polymer-based negative electrode current collector, are the same as in the prior art. Since those skilled in the art will understand this, it will not be elaborated upon here, nor will it be shown in the accompanying drawings.

[0070] The present invention will now be illustrated using the following embodiments and comparative examples:

[0071] As shown in Tables 1 and 2, Examples 1 to 5 all relate to polymer-based negative electrode current collectors. Here, the support layer material is polyaniline, and both the protective and conductive materials are copper oxide. However, the particle size of the copper oxide particles used as the protective material differs significantly from that used as the conductive material. Between different examples, the thickness and Young's modulus of the support layer vary, as do the particle size and thickness of the protective material in the protective-conductive composite layer, the particle size and thickness of the conductive material in the protective-conductive composite layer, and even the overall thickness of the current collector, thus providing multiple points of comparison.

[0072] Furthermore, to highlight the advantages of the polymer-based negative electrode current collector of the present invention, Comparative Examples 1 to 6 were used as controls. Here, Comparative Examples 1 and 2 did not have a protective conductive composite layer, while Comparative Examples 3 to 6, like Examples 1 to 6, used a polyaniline support layer, a copper oxide protective material, and a copper oxide conductive material. However, the particle size of the copper oxide protective material and the particle size of the copper oxide conductive material were significantly different from those of Examples 1 to 6.

[0073]

[0074]

[0075] Example 1

[0076] A support layer made of polyaniline with a thickness of 3 μm and a Young's modulus of 5 GPa is used. A protective conductive composite layer is located on the support layer. The conductive material particles used are copper oxide particles with a particle size of 10 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 1.4 μm. The protective material particles used are copper oxide particles with a particle size of 50 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 0.6 μm. The total thickness of the current collector is 5 μm.

[0077] Example 2

[0078] A support layer made of polyaniline with a thickness of 5 μm and a Young's modulus of 17 GPa is used to protect the conductive composite layer on the support layer. The conductive material particles used are copper oxide particles with a particle size of 100 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 3 μm. The protective material particles used are copper oxide particles with a particle size of 300 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 3 μm. The total thickness of the current collector is 11 μm.

[0079] Example 3

[0080] A support layer made of polyaniline with a thickness of 5 μm and a Young's modulus of 17 GPa is used to protect the conductive composite layer. The conductive material particles used are copper oxide particles with a particle size of 10 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 1.4 μm. The protective material particles used are copper oxide particles with a particle size of 50 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 1.6 μm. The total thickness of the current collector is 8 μm.

[0081] Example 4

[0082] A support layer made of polyaniline with a thickness of 8 μm and a Young's modulus of 18 GPa is used to protect the conductive composite layer on the support layer. The conductive material particles used are copper oxide particles with a particle size of 100 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 2 μm. The protective material particles used are copper oxide particles with a particle size of 300 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 2 μm. The total thickness of the current collector is 12 μm.

[0083] Example 5

[0084] A support layer made of polyaniline with a thickness of 12 μm and a Young's modulus of 6 GPa is used to protect the conductive composite layer. The conductive material particles used are copper oxide particles with a particle size of 10 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 1.4 μm. The protective material particles used are copper oxide particles with a particle size of 50 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 1.6 μm. The total thickness of the current collector is 15 μm.

[0085] Comparative Example 1

[0086] The support layer is made of copper foil with a thickness of 8 μm and a Young's modulus of 90 GPa. However, no conductive layer, protective layer or even a protective conductive composite layer is formed on the surface of the support layer. The thickness of the entire current collector is 8 μm.

[0087] Comparative Example 2

[0088] Only a support layer made of polyaniline with a thickness of 12μm and a Young's modulus of 15GPa is used, but no conductive layer, protective layer or even protective conductive composite layer is formed on the surface of the support layer, and the entire current collector thickness is 12μm.

[0089] Comparative Example 3

[0090] A support layer made of polyaniline with a thickness of 14 μm and a Young's modulus of 26 GPa is used. A protective conductive composite layer is located on the support layer. The conductive material particles used are copper oxide particles with a particle size of 10 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 1.4 μm. The protective material particles used are copper oxide particles with a particle size of 50 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 0.6 μm. The total thickness of the current collector is 16 μm.

[0091] Comparative Example 4

[0092] A support layer made of polyaniline with a thickness of 2 μm and a Young's modulus of 3 GPa is used to protect the conductive composite layer. The conductive material particles used are copper oxide particles with a particle size of 10 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 1.4 μm. The protective material particles used are copper oxide particles with a particle size of 50 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 0.6 μm. The total thickness of the current collector is 4 μm.

[0093] Comparative Example 5

[0094] A support layer made of polyaniline with a thickness of 8 μm and a Young's modulus of 15 GPa is used. A protective conductive composite layer is located on the support layer. The conductive material particles used are copper oxide particles with a particle size of 8 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 1.4 μm. The protective material particles used are copper oxide particles with a particle size of 40 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 0.6 μm. The total thickness of the current collector is 10 μm.

[0095] Comparative Example 6

[0096] A support layer made of polyaniline with a thickness of 8 μm and a Young's modulus of 15 GPa is used to protect the conductive composite layer. The conductive material particles used are copper oxide particles with a particle size of 8 nanometers and the total thickness of the conductive material (or the thickness of the conductive material particle distribution) is 1.4 μm. The protective material particles used are copper oxide particles with a particle size of 400 nanometers and the total thickness of the protective material (or the thickness of the protective material particle distribution) is 0.6 μm. The total thickness of the current collector is 10.4 μm.

[0097] The test results for these embodiments and comparative examples are shown in Tables 3 and 4.

[0098]

[0099]

[0100] Clearly, as shown in Table 3, the elongation at break of the polymer-based negative electrode current collectors proposed in this invention is between 156% and 163%. In contrast, the elongation at break of the negative electrode current collectors not proposed in this invention is between 112% and 159%, and in particular, except for Comparative Example 35, it is between 112% and 141%. In other words, the polymer-based negative electrode current collectors proposed in this invention are easier to process and manufacture and less prone to cracking due to impact, heating, etc.

[0101] Clearly, as shown in Table 4, batteries made using the polymer-based negative electrode current collector proposed in this invention can maintain a capacity retention rate of not less than 80% and a 4C rate discharge capacity retention rate of not less than 49%. In contrast, batteries using several negative electrode current collectors not proposed in this invention not only have a capacity retention rate of less than 80%, but also a 4C rate discharge capacity retention rate of less than 46%. In other words, batteries using the polymer-based negative electrode current collector proposed in this invention (at least those using these embodiments of this invention) exhibit good cycle life and rate performance, comparable to batteries using conventional negative electrode current collectors. That is, using the polymer-based negative electrode current collector proposed in this invention (at least those using these embodiments of this invention) does not have a significant adverse effect on the electrochemical performance of the negative electrode and the battery. In particular, batteries made using negative electrode current collectors with a protective layer can further improve their capacity retention rate and 4C rate capacity retention rate after 1000 cycles at 45°C and 1C / 1C, providing lithium-ion batteries with better reliability.

[0102] Incidentally, these embodiments and comparative examples employ methods known in the art to determine the Young's modulus of the support layer (such as a polymer-based negative electrode current collector). For example, the support layer is first cut into square samples with side lengths of 15 mm and 200 mm, then the thickness (μm) of the samples is measured with a micrometer, and a tensile test is performed on the samples using a high-speed rail tensile testing machine at room temperature and pressure (25 degrees Celsius, 0.1 MPa). Initially, the sample length between the clamps is set to 50 mm, and then a tensile speed of 50 mm per minute is applied, and the load (Newtons) and equipment displacement (mm) at the point of sample fracture are recorded. Since stress (Pa) equals the load divided by the product of a side length and thickness, and strain equals the equipment displacement divided by the tensile speed = y / 50, the initial linear region curve can be calculated by plotting the stress and strain values ​​based on the measured values, and the slope of this curve is the Young's modulus.

[0103] Incidentally, these embodiments and comparative examples used the following method to test the size of copper-based grains (such as copper oxide grains) in the conductive layer. First, X-ray diffraction analysis was performed on the negative electrode current collector to determine the diffraction peaks of the copper-based conductive layer, such as the diffraction peaks of the Cu(111) crystal plane. Then, based on the diffraction angle and full width at half maximum (FWHM) of the diffraction peaks, the size of the copper-based grains was calculated using the Scherrer formula. Specifically, the size of the copper-based grains is equal to the product of the Scherrer constant and the X-ray wavelength divided by the product of the FWHM of the diffraction peak and cos(θ). Here, θ is the diffraction angle, and the FWHM of the diffraction peak needs to be converted to radians.

[0104] Incidentally, these embodiments and comparative examples involved X-ray diffraction analysis of the negative electrode current collector using instruments and methods known in the art. For instance, an X-ray powder diffractometer was used, and the X-ray diffraction spectrum was determined according to JIS K0131-1996 General Rules for X-ray Diffraction Analysis. For example, a Bruker D8 Discover X-ray diffractometer from Bruker AxS (Germany) was used, with CuKα rays as the radiation source, the ray wavelength scanning 2θ angle ranging from 20 degrees to 80 degrees, and the scanning rate at 0.05 degrees per second.

[0105] It should be noted that these embodiments and comparative examples were tested using Xinwei charging and discharging equipment for electrical performance testing. For example, the 1C / 1C cycle test (or a test that first charges the battery to its rated capacity within one hour and then discharges it to its rated capacity within one hour) is conducted at 25 degrees Celsius. The lithium-ion battery is first charged to 4.2 volts using a constant current that allows it to be fully charged within one hour, then charged at a constant voltage until the current is less than or equal to 0.05 hours, and finally discharged to 3.0 volts using a constant current that allows it to be fully discharged within one hour. This process yields the 1C discharge capacity of the lithium-ion battery. Similarly, the 4C rate discharge test is conducted at 25 degrees Celsius. The lithium-ion battery is first charged to 4.2 volts using a constant current that allows it to be fully charged within one hour, then charged at a constant voltage until the current is less than or equal to 0.05 hours, and finally discharged to 3.0 volts using a constant current that allows it to be fully discharged within four hours. This process yields the 4C discharge capacity of the lithium-ion battery. Here, the 4C rate capacity retention rate (percentage / %) of a lithium-ion secondary battery is equal to the percentage obtained by converting the ratio of the 4C rate discharge capacity to the 1C rate discharge capacity.

[0106] The above content involving common knowledge will not be described in detail, as those skilled in the art will understand.

[0107] The above descriptions are merely some specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention. The technical scope of this invention is not limited to the contents of the specification, but must be determined according to the scope of the claims.

Claims

1. A polymer-based negative electrode current collector, comprising: A support layer, wherein the material of the support layer is a conductive polymer; and A protective conductive composite layer is located on the surface of the support layer, and the material of the protective conductive composite layer includes a protective material and a conductive material; Here, the bonding force between the protective conductive composite layer and the support layer is not less than 500 N / m; Here, the particle size of the protective material is smaller than that of the conductive material; Here, in the part of the protective conductive composite layer near the support layer, the conductive material is greater than the protective material, while in the other part of the protective conductive composite layer away from the support layer, the protective material is greater than the conductive material. Here, the particle size of the protective material is between 10 nm and 100 nm, and the particle size of the conductive material is between 50 nm and 300 nm. Here, the Young's modulus of the support layer is between 5 GPa and 25 GPa.

2. The polymer-based negative electrode current collector according to claim 1, characterized in that, Includes one of the following: The ratio between the particle size of the conductive material and the particle size of the protective material is between 3 and 5; and The ratio between the particle size of the conductive material and the particle size of the protective material is between 2.5 and 3.

3.

3. The polymer-based negative electrode current collector according to claim 1, characterized in that, The particle size of the protective material is between 30 nm and 80 nm, and the particle size of the conductive material is between 100 nm and 200 nm.

4. The polymer-based negative electrode current collector according to claim 1, characterized in that, Includes one of the following: All of the conductive materials are closer to the support layer than all of the protective materials; The distribution of the protective material gradually increases from the side of the protective conductive composite layer closer to the support layer towards the side of the protective conductive composite layer farther from the support layer, while the distribution of the conductive material gradually decreases from the side of the protective conductive composite layer closer to the support layer towards the side of the protective conductive composite layer farther from the support layer. and The portion of the protective conductive composite layer adjacent to the support layer is made entirely of the conductive material, while the portion of the protective conductive composite layer away from the support layer is made entirely of the protective material. The proportion of the conductive material within the protective conductive composite layer gradually decreases from the side of the protective conductive composite layer closer to the support layer towards the side of the protective conductive composite layer away from the support layer, while the proportion of the protective material within the protective conductive composite layer gradually increases from the side of the protective conductive composite layer closer to the support layer towards the side of the protective conductive composite layer away from the support layer.

5. The polymer-based negative electrode current collector according to claim 1, characterized in that, The protective material is at least one of metal oxides, metallic materials, and carbon materials.

6. The polymer-based negative electrode current collector according to claim 5, characterized in that, Includes at least one of the following: The metal oxide is one or more of the following: copper oxide, aluminum oxide, cobalt oxide, chromium oxide, and nickel oxide. The metallic material is one or more of nickel, chromium, tin, nickel-based alloys, and copper-based alloys; The carbon material is one or more of graphite, carbon black, carbon nanotubes, graphene, and carbon fiber; and The conductive material is one or more of copper, nickel, stainless steel, silver, and titanium.

7. The polymer-based negative electrode current collector according to claim 1, characterized in that... The resistivity of the conductive material is no greater than 7.0 × 10⁻⁶ at 25°C. -8 The thickness of the conductive material in the protective conductive composite layer is between 1.3 μm and 3 μm.

8. The polymer-based negative electrode current collector according to claim 1, characterized in that, Including one of the following: The thickness of the protective conductive composite layer is between 2 μm and 5 μm, the thickness of the conductive material is between 1.3 μm and 3 μm, and the thickness of the protective material is between 0.7 μm and 2 μm; and The thickness of the protective conductive composite layer is between 3 μm and 4 μm, the thickness of the conductive material is between 1.6 μm and 2 μm, and the thickness of the protective material is between 1.4 μm and 2 μm.

9. The polymer-based negative electrode current collector according to claim 1, characterized in that, The conductive polymer includes one or more of the following: conductive polymer, composite conductive polymer material made from polymer and conductive agent blend.

10. The polymer-based negative electrode current collector according to claim 9, characterized in that... Includes one of the following: The conductive polymer structure is a long-chain structure with conjugated molecules; and The conductive polymer is one or more of polyaniline, polythiophene, polypyrrole, polysulfide, and aliphatic conjugated polymers.

11. The polymer-based negative electrode current collector according to claim 9, characterized in that, The composite conductive polymer material is a conductive polymer material formed by blending various conductive agents with intrinsically non-conductive conventional polymer materials using different processing techniques. The intrinsically non-conductive conventional polymer materials are one or more of polyethylene, polypropylene, polytetrafluoroethylene, polyvinylidene fluoride, and polystyrene. The conductive agents are one or more of graphite, carbon nanotubes, carbon fibers, graphene, activated carbon, and conductive carbon black.

12. The polymer-based negative electrode current collector according to claim 1, characterized in that... : The volume resistivity of the support layer is 1.4 × 10⁻⁶. -9 Ω•m.

13. The polymer-based negative electrode current collector according to claim 1, characterized in that, Includes at least one of the following: The elongation at break of the support layer is between 4.5% and 6.7%. The elongation at break of the support layer is not less than the elongation at break of the protective conductive composite layer; The thickness of the support layer is between 2 μm and 15 μm; The thickness of the support layer is between 3 μm and 12 μm; and The thickness of the support layer is between 5 μm and 8 μm.

14. A lithium-ion battery comprising a positive electrode and a negative electrode, wherein the negative electrode has a polymer-based negative electrode current collector according to any one of claims 1 to 13.

15. A method for preparing a polymer-based negative electrode current collector according to any one of claims 1 to 13, comprising: The support layer is provided, wherein the material of the support layer is a conductive polymer; The protective material and the conductive material are mixed together in a solvent to form a protective and conductive composite slurry. and A protective conductive composite slurry is formed on the surface of the support layer in a single step, thereby forming the protective conductive composite layer.

16. The method according to claim 15, characterized in that, Includes at least one of the following: The coupling agent and one or more of the crosslinking agents are mixed together in the solvent; and The amount of coupling agent and crosslinking agent used is adjusted to achieve the desired separation between the protective material and the conductive material. The more coupling agent and crosslinking agent used, the longer it takes to achieve the desired separation.

17. The method according to claim 16, characterized in that... : The protective conductive composite paste contains a protective material with a mass fraction between 45% and 58%, a conductive material with a mass fraction between 35% and 50%, a coupling agent with a mass fraction between 5.5% and 10%, and a crosslinking agent with a mass fraction between 2.5% and 5%; and The solid content of the solvent is between 35% and 45%.

18. The method according to claim 17, characterized in that, Includes at least one of the following: The crosslinking agent is one or more of vinylidene fluoride, sodium alginate, styrene-butadiene rubber, and polytetrafluoroethylene. The coupling agent is one or more of the following: trichlorovinylsilane, triethoxyvinylsilane, γ-aminopropyltriethoxysilane, trichloropropenylsilane, tetrabutyl titanate, isopropyl triisostearoyl titanate, diisostearoyl phthalate ethyl ester, and chromium methacryloyl complex; and The solvent is one or more of ethanol, dimethylacetamide, acetonitrile, methanol, and polycarbonate.

19. The method according to claim 15, characterized in that, Includes at least one of the following: The protective conductive composite paste is formed on the surface of the support layer using one or two of rolling, bonding, or other methods; and Adjusting the settling time of the protective conductive composite slurry can adjust the separation between the protective material and the conductive material inside the protective conductive composite layer. The longer the settling time, the more the protective material and the conductive material will separate from each other.

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