WO2023202666A1

WO2023202666A1 - Negative electrode electron-rich current collectors, methods for preparing the same, electrode plates, and batteries

Info

Publication number: WO2023202666A1
Application number: PCT/CN2023/089504
Authority: WO
Inventors: Chenghao WANG; Xuefa Li; Guoping Zhang
Original assignee: Jiangyin Nanopore Innovative Materials Technology Ltd
Priority date: 2022-04-20
Filing date: 2023-04-20
Publication date: 2023-10-26
Also published as: CN114725394A; WO2023201844A1

Abstract

The present application relates to an electron-rich current collector for use in a negative electrode, a method for preparing the same, an electrode plate, and a battery. In the present application, the nano copper layer is electron-rich and has the energy distribution of electric charges ranging, for example, from 200 eV/mm² to 500 eV/mm². By disposing the nano copper layers on the surfaces of the polymer substrate layer, there is no need for an additional zinc or chromium anti-oxidation layer, and the oxidation of copper can be prevented or minimized.

Description

NEGATIVE ELECTRODE ELECTRON-RICH CURRENT COLLECTORS, METHODS FOR PREPARING THE SAME, ELECTRODE PLATES, AND BATTERIES

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to and benefits of Chinese patent application No. 2022104143634, filed April 20, 2022, and International Application No. PCT/CN2022/095416, filed May 27, 2022, all of which are incorporated herein by reference in their entireties.

TECHNICAL FIELD

The present application relates to the field of new materials, and in particular to an electron-rich current collector for use in a negative electrode, a method for preparing the same, an electrode plate, and a battery.

BACKGROUND

Copper has good electrical conductivity and is relatively inexpensive, so it is widely used to prepare current collectors for use in negative electrodes of non-aqueous secondary batteries, such as lithium batteries. However, copper in air is highly susceptible to oxidation. Hence, a copper current collector for use in a negative electrode needs to be subjected to an anti-oxidation treatment to avoid or minimize oxidation that affects its performance. In the conventional art, the anti-oxidation treatment for copper current collectors for use in negative electrodes involves forming a layer of zinc or chromium as a barrier layer on a surface of the copper current collectors to keep copper away from air, so that the storage life of the negative electrode copper current collectors can be prolonged to about 3 months. However, use of zinc or chromium will not only cause an increase in production costs, but also increase the interfacial resistance between the current collectors and the electrode plates, leading to a larger internal resistance of the batteries, which affects the capacity and cycling performance of the batteries. In addition, zinc plating and chromium plating produce large volumes of industrial waste water. The chromium plating, in particular, could cause serious environmental pollution due to toxicity of chromium, which is not compatible with the green environmental protection concept.

In addition, the conventional current collector for use in a negative electrode is usually made entirely of metal. Due to the high density of the metal, the resulting battery has higher weight and lower energy density for the same volume.

SUMMARY OF THE DISCLOSURE

Thus, there is a need to provide an electron-rich current collector for use in a negative electrode, a method for preparing the same, an electrode plate, and a battery, which can reduce pollution to environment, reduce the interfacial resistance, and increase the energy density and oxidation resistance.

In an aspect of the present application, a negative electrode electron-rich current collector is provided, which includes a polymer substrate layer and a nano copper layer disposed on a surface of the polymer substrate layer.

In another aspect of the present application, a negative electrode electron-rich current collector is provided, which includes a polymer substrate layer and two nano copper layers respectively disposed on two sides of the polymer substrate layer.

The nano copper layer is a deposited film or a deposited layer of copper nanoparticles. The nano copper layer carries electrons. An energy distribution of electric charges in the nano copper layers ranges, for example, from 200 eV/mm² to 500 eV/mm².

In some embodiments, an average particle size of the copper nanoparticles in the nano copper layers ranges from 10 nm to 50 nm.

In some embodiments, a material of the polymer substrate layer is one or more selected from polyethylene glycol terephthalate, polyethylene, polypropylene, and polymethylpentene.

In some embodiments, a weight-average molecular weight of the material of the polymer substrate layer ranges from 1,000 kDa to 1,500 kDa.

In some embodiment, a surface roughness of the polymer substrate layer ranges from 150 nm to 200 nm.

In some embodiments, a thickness of the electron-rich current collector for use in a negative electrode ranges from 3 μm to 30 μm.

In some embodiments, a thickness of the polymer substrate layer ranges from 1 μm to 25 μm.

In some embodiments, a thickness of the nano copper layer ranges from 10 nm to 3 μm.

In some embodiments, the electron-rich current collector for use in a negative electrode further comprises a non-nano copper layer disposed between the polymer substrate layer and the nano copper layer.

In some embodiments, the electron-rich current collector for use in a negative electrode further comprises two non-nano copper layers disposed between the polymer substrate layer and the two nano copper layers on two sides of the polymer substrate layer.

In some embodiments, the thickness of the nano copper layer ranges from 10 nm to 50 nm. In some embodiments, the thickness of the non-nano copper layer ranges from 0.25 μm to 2.99 μm.

In another aspect of the present application, a method for preparing the electron-rich current collector for use in a negative electrode disclosed herein is further provided, comprising:

providing a polymer substrate layer; and

depositing electron-rich copper nanoparticles onto one or two surfaces of the polymer substrate layer by using a vacuum magnetron sputtering method, thereby forming one or two nano copper layers.

The electron-rich copper nano-particles are prepared by a method comprising:

mixing [Gd₂C] ²⁺·2e^- electrets, a bivalent copper salt, and an alcohol solvent to react at a temperature ranging, for example, from 60 ℃ to 120 ℃, and then adsorbing the [Gd₂C] ²⁺·2e^- electrets onto a magnetic substance to separate the [Gd2C] ²⁺·2e^- electrets from a remaining reaction system;

subjecting the remaining reaction system to a solid-liquid separation to collect a solid product; and

drying the solid product.

In some embodiments, in the method for preparing the electron-rich copper nanoparticles, the reaction time of the mixed [Gd₂C] ²⁺·2e^- electrets, the bivalent copper salt, and the alcohol solvent ranges from 40 min to 60 min.

In some embodiments, the vacuum magnetron sputtering method comprises:

forming a target by the electron-rich copper nanoparticles;

fixing the target at a cathode of a magnetron sputtering apparatus, and placing a polymer substrate layer at an anode of the magnetron sputtering apparatus;

evacuating the magnetron sputtering apparatus to a vacuum degree of less than or equal to 5×10^-2 Pa, and filling the magnetron sputtering apparatus with a non-reactive gas having a gas pressure ranging, for example, from 1 Pa to 10 Pa; and

applying a voltage ranging, for example, from 2500 V to 3500 V between the cathode and the anode, thereby allowing atoms in the target to move towards the anode under the electric field and to deposit onto a surface of the polymer substrate layer, thereby forming the nano copper layer.

In another aspect of the present application, an electrode plate is further provided, which comprises the electron-rich current collector for use in a negative electrode as disclosed herein.

The present application further provides a battery including the electrode plate as disclosed herein.

In the present application, the nano copper layer is electron-rich and has an energy distribution of electric charges ranging, for example, from 200 eV/mm² to 500 eV/mm². By disposing the nano copper layer on a surface of the polymer substrate layer, it is possible to not include an additional zinc or chromium anti-oxidation layer, and the oxidation of copper can still be minimized. Thus, the interfacial resistance between different metal layers in the conventional art can be reduced, and the performance of the current collector as disclosed herein can be improved. The method does not require a step of zinc or chromium plating on the surfaces of the copper current collector, which can reduce the production costs and the pollution to the environment, and thus is more environmentally friendly. Further, use of the polymer in combination with metal in the current collector as disclosed herein can increase the energy density of the battery and thus can make the battery lighter and thinner than the conventional all-metal current collector.

The electron-rich copper nanoparticles are prepared via a reaction of the [Gd2C] ²⁺·2e^- electrets and a divalent copper salt precursor, in which spontaneous transfer of electrons occurs. As such, the amount of electric charges on the surfaces of the copper nanoparticles can be controlled under certain reaction conditions, so as to further control the distribution of electric charges in the nano copper layer. In addition, no additional stabilizer needs to be added during the reaction. The resulting copper nanoparticles can have a good dispersibility, and the post-processing can be simple. The electrets can be removed by using a magnet, after the routine operations such as the solid-liquid separation and the drying that can be performed to obtain the electron-rich copper nanoparticles. The electron-rich copper nanoparticles can be deposited onto a surface of the polymer substrate layer by using the vacuum magnetron sputtering method to form a film, so that the electron-rich and oxidation-resistant negative electrode current collector is obtained. The whole preparation method is simple, controllable, and easy for industrial production.

By using the current collector in a negative electrode disclosed herein, an electrode plate can have a high energy density, a small interface resistance, and an improved performance. By using the electrode plate including the negative electrode current collector disclosed herein, a battery may have improved capacity and cycling performance.

DETAILED DESCRIPTION

In order to facilitate understanding of the present application, the present application will be described more thoroughly with reference to the related embodiments. However, the present application can be embodied in many different forms and is not limited to the embodiments disclosed herein. These embodiments are provided to make the understanding of the disclosure of the present application more thorough and comprehensive.

In addition, the terms “first” and “second” are used merely as labels to distinguish one element having a certain name from another element having the same name, and cannot be understood as indicating or implying any priority, precedence, or order of one element over another, or indicating the quantity of the element. Therefore, the element modified by “first” or “second” may explicitly or implicitly includes at least one of the elements. In the description of the present application, “a plurality of” means “at least two” , such as two, three, etc., unless otherwise specifically defined. In the description of the present application, the article “a” or “an” means “at least one” , for example, one, two, etc., unless otherwise specifically defined.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by one of ordinary skill in the art of the present application. The terms used in the description of the present application are only for the purpose of describing specific embodiments, and are not used to limit the present application. The term “and/or” used herein refers to any and all combinations of one or more of the associated listed items.

In the present application, when technical features are described in a non-exclusive manner, a technical solution with an exclusive inclusion of the listed features and a technical solution with a non-exclusive inclusion of the listed features are both applicable.

Unless otherwise specified, when a numerical range is disclosed in the present application, that numerical range is considered continuous and includes the minimum and maximum values of that range and every value therebetween. Further, when a range is referred for integers, every integer between the minimum value and the maximum value of the range is included. Furthermore, when multiple ranges are provided to describe a feature or characteristic, such ranges may be combined. In other words, unless otherwise stated, all ranges disclosed herein are to be understood to encompass any and all sub-ranges subsumed therein.

Unless otherwise specified, percentage content used in the present application refers to mass percentage for solid-liquid mixing and solid-solid mixing and refer to volume percentages for liquid-liquid mixing.

Unless otherwise specified, percentage concentration used in the present application refers to final concentration which is a percentage of a component in a system when addition of the component is completed.

Unless otherwise defined, when a temperature range is mentioned in the present application, both a constant temperature in the range and a temperature varied in the range are allowed. The constant temperature allows the temperature to fluctuate within the accuracy range of the instrument.

In the present application, the term “non-reactive gas” refers to a gas that does not affect the deposition of film and does not react with the target during magnetron sputtering, which can be, for example, an inert gas such as argon gas.

In an aspect of the present application, an electron-rich current collector for use in a negative electrode is provided, which includes a polymer substrate layer and a nano copper layer disposed on a surface of the polymer substrate layer.

The nano copper layer is a deposited film or a deposited layer of copper nanoparticles. The nano copper layer carries electrons. An energy distribution of electric charges in the nano copper layer ranges, for example, from 200 eV/mm² to 500 eV/mm².

The nano copper layer is electron-rich and has the energy distribution of electric charges ranging, for example, from 200 eV/mm² to 500 eV/mm². By disposing the nano copper layer on a surface of the polymer substrate layer, it is possible to not include an additional zinc or chromium anti-oxidation layer, and the oxidation of copper can be minimized. The storage lifetime can be prolonged to 7 months, which is longer than the 3-month storage lifetime in the conventional art using the zinc or chromium anti-oxidation layer. In addition, the interfacial resistance between different metal layers in the conventional art can be reduced, and the performance of the current collector disclosed herein can be improved. The method disclosed herein does not require a step of zinc or chromium plating on the surfaces of the copper current collector, which can reduce the production costs and the pollution to the environment, and thus is more environmentally friendly. Further, the use of polymer in combination with metal in the current collector disclosed herein can increase the energy density of the battery and thus can make the battery lighter and thinner than the conventional all-metal current collector. In general, the present application provides a current collector for use in a negative electrode having improved oxidation resistance and good overall performance, including, for example, one or more properties selected from: a puncture strength greater than or equal to 50 gram-force (gf) , a tensile strength greater than or equal to 150 MPa in the machine direction (MD) , a tensile strength greater than or equal to 150 MPa in the transverse direction (TD) , an elongation greater than or equal to 10%in the MD, an elongation greater than or equal to 10%in the TD, a surface roughness (Ra) less than or equal to 2.5 μm, a square resistance less than or equal to 38 mΩ on both surfaces, and a peeling force greater than or equal to 2 N/m between the nano copper layer and the polymer substrate layer.

In some embodiments, the energy distribution of electric charges in the nano copper layer ranges, for example, from 320 eV/mm² to 380 eV/mm², or is, for example, 200 eV/mm², 250 eV/mm², 300 eV/mm², 350 eV/mm², 400 eV/mm², or 450 eV/mm². The energy distribution of electric charges in the nano copper layer directly affects the performance of the current collector for use in a negative electrode. Sufficient number of electric charges can improve the oxidation resistance of the nano copper layer and reduce the electrical resistance of the current collector. However, an excessive number of electric charges can cause an excessive amount of static electric charges on the nano copper layer, resulting in contamination of the nano copper layer in storage and thus negatively affecting the performance. Therefore, only appropriate amount of electric charges can well balance the oxidation resistance and the electrical conductivity with the static electricity issue so as to optimize the overall performance of the current collector.

In some embodiments, an average particle size of the copper nanoparticles in the nano copper layer ranges from 10 nm to 50 nm. The average particle size of the copper nanoparticles ranges, for example, from 28 nm to 43 nm, or is, for example, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, or 45 nm. By controlling the average particle size of the copper nanoparticles in the suitable range, the processing difficulty can be controlled, and the resulting nano copper layer can have a higher compactness, so that the amount of electric charges in the nano copper layer can be sufficient to achieve the anti-oxidation effect, and the mechanical strength of the nano copper layer can be greater, which can enhance the safety of the battery.

In some embodiments, a material of the polymer substrate layer is one or more selected from polyethylene glycol terephthalate, polyethylene, polypropylene, and polymethylpentene. By using the low-density polymers, such as polyethylene glycol terephthalate, polyethylene, polypropylene, and polymethylpentene, the current collector for use in a negative electrode disclosed herein can have a lower density, thereby further increasing the energy density of the battery.

In some embodiments, the weight-average molecular weight of the material of the polymer substrate layer ranges from 1,000 kDa to 1,500 kDa. The weight-average molecular weight of the material of the polymer substrate layer is, for example, 1,100 kDa, 1,200 kDa, 1,300 kDa, or 1,400 kDa. The appropriate weight-average molecular weight can better balance the strength with the density of the polymer substrate layer, thereby further improving the overall performance of the current collector.

In some embodiments, a surface roughness of the polymer substrate layer ranges from 150 nm to 200 nm. The surface roughness of the polymer substrate layer is, for example, 155 nm, 160 nm, 165 nm, 170 nm, 175 nm, 180 nm, 185 nm, 190 nm, or 195 nm. The polymer substrate layer having the appropriate roughness can bind more tightly with the above-described nano copper layer, thereby preventing the peeling between layers.

In some embodiments, the thickness of the electron-rich current collector for use in a negative electrode ranges from 3 μm to 30 μm. The thickness of the electron-rich current collector for use in a negative electrode ranges, for example, from 6 μm to 24 μm, or is, for example, 5 μm, 10 μm, 15 μm, 20 μm, or 25 μm.

In some embodiments, the thickness of the polymer substrate layer ranges from 1 μm to 25 μm, such as from 4 μm to 20 μm, or is, for example, 5 μm, 10 μm, or 15 μm.

In some embodiments, the thickness of the nano copper layer ranges from 10 nm to 3 μm. Further, the thickness of the nano copper layer independently ranges, for example, from 0.5 μm to 2.5 μm, or is, for example, 0.4 μm, 0.6 μm, 0.8 μm, 1.0 μm, 1.2 μm, 1.4 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.4 μm, 2.6 μm or 2.8 μm.

In some embodiments, a non-nano copper layer is further disposed between the polymer substrate layer and the nano copper layer on at least one side of the polymer substrate layer. The thickness of the nano copper layer ranges, for example, from 10 nm to 50 nm. The thickness of the non-nano copper layer ranges, for example, from 0.25 μm to 2.99 μm. In order to further reduce the cost, a part of the nano copper layer disclosed herein can be replaced with an ordinary non-nano copper layer, which plays a basic function of electron collecting, while the thickness of the nano copper layer, which plays a role of anti-oxidation, ranges, for example, from 10 nm to 50 nm. In some embodiments, the thickness of the nano copper layer is, for example, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, or 45 nm. In some embodiments, the thickness of the non-nano copper layer is, for example, 0.3 μm, 0.5 μm, 0.7 μm, 0.9 μm, 1.1 μm, 1.3 μm, 1.5 μm, 1.7 μm, 1.9 μm, 2.1 μm, 2.3 μm, 2.5 μm, 2.7 μm, or 2.9 μm.

In some embodiments, the non-nano copper layer is prepared by the following method. Copper with a purity equal to or lager than 99.9%, water, and sulfuric acid are mixed to prepare a copper sulfate electrolyte liquid. Then the divalent copper in the copper sulfate electrolyte liquid is reduced to elementary copper by electroplating to prepare the above-described non-nano copper layer. The copper layer prepared by this method can have a high purity, a good quality, and a good binding ability with the polymer substrate layer.

providing a polymer substrate layer; and

depositing electron-rich copper nanoparticles onto a surface of the polymer substrate layer by using a vacuum magnetron sputtering method, thereby forming the nano copper layer.

In another aspect of the present application, a method for preparing the negative electrode electron-rich current collector disclosed herein is further provided, comprising:

providing a polymer substrate layer; and

depositing electron-rich copper nanoparticles onto the two sides of the polymer substrate layer by using a vacuum magnetron sputtering method, thereby forming the two nano copper layers.

The electron-rich copper nanoparticles are prepared by a method, comprising:

mixing [Gd2C] ²⁺·2e^- electrets, a divalent copper salt, and an alcohol solvent to react at a temperature ranging, for example, from 60℃ to 120℃, and then adsorbing the [Gd2C] ²⁺·2e^- electrets onto a magnetic substance to separate the [Gd2C] ²⁺·2e^- electrets from a remaining reaction system;

drying the solid product.

In some embodiments, the magnetic substance is a magnet.

The electron-rich copper nanoparticles are prepared via a reaction of the [Gd2C] ²⁺·2e^- electrets and the divalent copper salt precursor, in which spontaneous transfer of electrons occurs. As such, the amount of electric charges on the surfaces of the copper nanoparticles can be controlled under the certain reaction conditions, so as to further control the distribution of electric charges in the nano copper layer. In addition, no additional stabilizer needs to be added during the reaction. The resulting copper nanoparticles can have a good dispersibility, and the post-processing can be simple. The electrets can be removed by using the magnet, and then the routine operations such as the solid-liquid separation and the drying can be performed to obtain the electron-rich copper nanoparticles. The electron-rich copper nanoparticles can be deposited onto the surfaces of the polymer substrate layer by using the vacuum magnetron sputtering method to form films, so that the electron-rich and oxidation-resistant negative electrode current collector is obtained. The preparation method disclosed herein is simple, controllable, and easy for industrial production.

The electret is a dielectric material, which itself carries electric charges, and the electric charges quasi-permanently exist in the electret. In the present application, by using the [Gd2C] ²⁺·2e^- electrets, the divalent copper precursor can be reduced to elemental nano copper with the appropriate particle size, and the electrons can be transferred to the surface of the nano copper, so that the nano copper carries negative electric charges and has high oxidation resistance. In the present application, the [Gd2C] ²⁺·2e^- electrets can be prepared by the following method. Under argon gas protection, a sheet of Gd metal (99.9%) and graphite with a molar ratio of 2: 1 are subjected to arc melting and cooling. The melting and cooling process can be repeated three times to ensure the uniformity. After that, the resulting [Gd₂C] ²⁺·2e^- ingot is transferred to a glove box, ground to remove the surface oxide layer, and then ground into powder to obtain the [Gd₂C] ²⁺·2e^- electrets.

In some embodiments, the divalent copper salt is, for example, one or more selected from copper chloride, copper sulfate, and copper nitrate In some embodiments, the divalent copper salt is copper chloride.

In some embodiments, the alcohol solvent is selected from, for example, hexanol, ethanol, and isopropanol. In some embodiments, the alcohol solvent is hexanol.

In some embodiments, the reaction temperature is, for example, 70 ℃, 90 ℃, 100 ℃ or 110 ℃. In some embodiments, the reaction temperature is 80 ℃. A suitable reaction temperature allows the divalent copper to be reduced to nano copper with a suitable particle size.

In some embodiments, the molar ratio of the [Gd₂C] ²⁺·2e^- electrets to the divalent copper salt is (1.5 to 2.5) : 1. In some embodiments, the molar ratio of the [Gd₂C] ²⁺·2e^- electrets to the divalent copper salt is 2 : 1.

In some embodiments, the concentration of the divalent copper salt in the alcohol solvent ranges from 0.05 mol/L to 0.15 mol/L. In some embodiments, the concentration of the divalent copper salt in the alcohol solvent is 0.1 mol/L.

The spontaneous transfer of electrons can be better controlled by using the suitable concentration and the suitable molar ratio of the electrets to the divalent copper salt precursor, so as to make the copper nanoparticles carry an appropriate amount of electrons.

In some embodiments, in the method for preparing the electron-rich copper nanoparticles, the reaction time ranges from 40 min to 60 min. Further, the reaction time is, for example, 45 min, 50 min, or 55 min. A suitable reaction time enables the surface of the nano copper to carry a suitable amount of electrons, which can further enable a more suitable energy distribution of electric charges on the surface of the formed nano copper layers.

In some embodiments, the vacuum magnetron sputtering method further comprises: forming a target by the electron-rich copper nanoparticles; fixing the target onto a cathode of a magnetron sputtering apparatus, and placing the polymer substrate layer onto an anode of the magnetron sputtering apparatus; evacuating the magnetron sputtering apparatus to a vacuum degree less than or equal to 5×10^-2 Pa, and filling the magnetron sputtering apparatus with a non-reactive gas having a gas pressure ranging, for example, from 1 Pa to 10 Pa; and then applying a voltage ranging, for example, from 2500 V to 3500 V between the cathode and the anode, thereby allowing atoms in the target to move towards the anode under the action of electric field and to deposit onto the surface of the polymer substrate layer, thereby forming the nano copper layer. Further, the gas pressure of the non-reactive gas is, for example, 2 Pa, 4 Pa, 6 Pa, or 8 Pa. The voltage between the cathode and the anode is, for example, 2750 V, 3000 V, or 3250 V. The suitable magnetron sputtering parameters allow the resulting copper nano-layer to have a suitable energy distribution of electric charges, so that the negative electrode current collector can have relatively good oxidation resistance while the amount of static electric charges is not too large.

In some embodiments, the unwinding tension for providing the polymer substrate layer ranges, for example, from 6 N to 25 N, such as 8 N, 10 N, 12 N, 14 N, 16 N, 18 N, 20 N, 22 N, or 24 N.

In some embodiments, the winding tension for winding the above-described electron-rich current collector ranges, for example, from 4 N to 15 N, such as 6 N, 8 N, 10 N, 12 N, or 14 N.

In some embodiments, either or both of the unwinding speed and the winding speed range, for example, from 25 m/min to 35 m/min, such as 30 m/min.

The suitable unwinding and winding tensions and speeds can further improve the quality of the electron-rich current collector for use in a negative electrode.

In yet another aspect of the present application, an electrode plate is further provided, which comprises the electron-rich current collector for use in a negative electrode disclosed herein.

The present application further provides a battery comprising the electrode plate disclosed herein.

By using the current collector for use in a negative electrode disclosed herein, the electrode plate can have a high energy density, a small interface resistance, and an improved performance. By using the electrode plate comprising the negative electrode current collector disclosed herein, the battery can have improved capacity and cycling performance.

The present application are described further in detail below with reference to specific examples and comparative examples. For the experimental parameters not specified in the following examples, firstly refer to the above description in the present application, and also refer to the experimental manuals in the art or other experimental methods known in the art, or refer to the experimental conditions recommended by the manufacturers. It is to be understood that the instruments and the raw materials used in the following examples are relatively specific, and other specific examples are not limited thereto. The weights of the relevant components disclosed herein not only refer to the specific contents of the components, but can also represent the proportional relationship between the weights of components. Therefore, the scaling up or down of the weights of the relevant components disclosed herein is within the scope of the present application. Specifically, the unit of weight disclosed herein can be μg, mg, g, kg, or other well-known mass unit in the chemical industry.

Preparation of [Gd₂C] ²⁺·2e^- electrets: Under argon gas protection, a sheet of Gd metal (99.9%) and graphite with a molar ratio of 2: 1 are subjected to arc melting. The cooling and melting process can be repeated three times to ensure the uniformity. After the melting, the resulting [Gd₂C] ²⁺·2e^- ingot is transferred to a glove box, ground to remove the surface oxide layer, and then ground into powder to obtain the [Gd₂C] ²⁺·2e^- electrets.

Example 1

(1) 1 mmol [Gd₂C] ²⁺·2e^- electrets, 0.5 mmol copper chloride, and 5 mL hexanol were mixed and reacted at 80 ℃ for 50 min to form the copper nanoparticles in the reaction system. A magnet was used to adsorb the [Gd₂C] ²⁺·2e^- electrets, thereby removing the [Gd₂C] ²⁺·2e^- electrets from the reaction system. The remaining reaction system was subjected to a solid-liquid separation to collect the solid product, which was dried to obtain the copper nanoparticles. An average particle size of the copper nanoparticles was 30 nm.

(2) The copper nanoparticles obtained in step (1) were processed to form a target. The target was fixed at a cathode of a magnetron sputtering apparatus. A polyethylene glycol terephthalate substrate layer with a thickness of 4 μm and a surface roughness of 150 nm was placed at an anode of the magnetron sputtering apparatus. A weight-average molecular weight of the polyethylene glycol terephthalate was 100,000 Da. The magnetron sputtering apparatus was evacuated to a vacuum degree less than or equal to 5×10^-2 Pa and then filled with argon gas having a gas pressure of 10 Pa. A voltage of 3000 V was applied between the cathode and the anode so that atoms in the target moved towards the anode under the electric field and deposited onto a surface of the polyethylene glycol terephthalate substrate layer, forming a nano copper layer with a thickness of 1 μm and a charge energy distribution of 350 eV/mm². The above-described steps were repeated to form another nano copper layer with a thickness of 1 μm and a charge energy distribution of 350 eV/mm² on another surface of the polyethylene glycol terephthalate substrate layer. As such, a negative electrode electron-rich current collector was obtained.

(3) The negative electrode electron-rich current collector obtained in step (2) was wound with a winding tension of 6 N and a winding speed of 30 m/min and stored.

Example 2

Example 2 is substantially the same as Example 1, except that the reaction temperature in step (1) was 60 ℃, and the average particle size of the copper nanoparticles was 45 nm.

Example 3

Example 3 is substantially the same as Example 1, except that the reaction time in step (1) was 60 min, and the charge energy distribution of the nano copper layer obtained in step (2) was 450 eV/mm².

Example 4

Example 4 is substantially the same as Example 1, except that a part of the nano copper target was replaced with an ordinary non-nano copper target, and the obtained negative electrode electron-rich current collector sequentially included a nano copper layer with a thickness of 10 nm, a non-nano copper layer with a thickness of 0.99 μm, a substrate layer of polyethylene glycol terephthalate with a thickness of 4 μm, another non-nano copper layer with a thickness of 0.99 μm, and another nano copper layer with a thickness of 10 nm.

Example 5

(1) 1 mmol [Gd₂C] ²⁺·2e^- electrets, 0.5 mmol copper chloride, and 5 mL hexanol were mixed and reacted at 120 ℃ for 45 min. A magnet was used to adsorb the [Gd₂C] ²⁺·2e^- electrets, thereby removing the [Gd₂C] ²⁺·2e^- electrets from the reaction system. The remaining reaction system was subjected to a solid-liquid separation to collect the solid product, which was dried to obtain the copper nanoparticles. An average particle size of the copper nanoparticles was 10 nm.

(2) The copper nanoparticles obtained in step (1) were processed to form a target. The target was fixed at a cathode of a magnetron sputtering apparatus. A polypropylene substrate layer with a thickness of 8 μm and a surface roughness of 200 nm was placed at an anode of the magnetron sputtering apparatus. A weight-average molecular weight of the polypropylene was 100,000 Da. The magnetron sputtering apparatus was evacuated to a vacuum degree less than or equal to 5×10^-2 Pa and then filled with argon gas having a gas pressure of 10 Pa. A voltage of 3000 V was applied between the cathode and the anode so that atoms in the target moved towards the anode under the electric field and deposited onto a surface of the polypropylene substrate layer, forming a nano copper layer with a thickness of 0.5 μm and a charge energy distribution of 250 eV/mm². The above-described steps were repeated to further form another nano copper layer which had a thickness of 0.5 μm and a charge energy distribution of 250 eV/mm² on another surface of the polypropylene substrate layer. As such, a negative electrode electron-rich current collector was obtained.

Comparative Example 1

Comparative Example 1 is substantially the same as Example 1, except that the reaction time in step (1) was 100 min, and the charge energy distribution of the nano copper layer obtained in step (2) was 600 eV/mm².

Comparative Example 2

Comparative Example 2 is substantially the same as Example 1, except that the reaction time in step (1) was 20 min, and the charge energy distribution of the nano copper layer obtained in step (2) was 100 eV/mm².

Comparative Example 3

Comparative Example 3 is substantially the same as Example 1, except that the reaction temperature in step (1) was 55 ℃, and the average particle size of the copper nanoparticles was 60 nm.

Comparative Example 4

Comparative Example 4 is substantially the same as Example 1, except that the voltage in step (2) was 4,500 V.

Comparative Example 5

Comparative Example 5 is substantially the same as Example 4, except that the two nano copper layers with the thickness of 10 nm were respectively replaced with two protective layers. The two protective layers were respectively a zinc metal barrier layer with a thickness of 7 nm and a chromium metal anti-oxidation layer with a thickness of 3 nm.

Comparative Example 6

Comparative Example 6 is substantially the same as Example 1, except that the surface roughness of the polyethylene glycol terephthalate substrate layer was 100 nm.

Comparative Example 7

Comparative Example 7 is substantially the same as Example 1, except that the surface roughness of the polyethylene glycol terephthalate substrate layer was 300 nm.

Comparative Example 8

Comparative Example 8 is substantially the same as Example 5, except that the surface roughness of the polypropylene substrate layer was 100 nm.

Comparative Example 9

Comparative Example 9 is substantially the same as Example 5, except that the surface roughness of the polypropylene substrate layer was 300 nm.

The term “surface roughness” used in the present application is defined as an absolute arithmetic average (Ra) of the deviations of the profile relative to the base length.

Performance characterization and tests:

The energy distribution of electric charges was tested as follows. The surface energy of copper was measured by photoelectron spectroscopy, which includes the following steps:

A surface of a sample of the composite current collector to be measured was ultrasonicated to clean the surface. A monochromator was selected as the light source. The sample was irradiated by the light source, and the spectrum of electrons escaping from the copper surface was measured by an electron spectrometer to obtain a XPS spectrum. The XPS spectrum was scanned and analyzed to determine parameters such as the location and intensity of the copper peaks. The area of the copper peaks was calculated by using peak fitting software or manually. The area of the copper peaks was divided by the actual area of the measured region to obtain the energy distribution of electric charges in unit area. The energy of the light source ranged from 50 eV to 1500 eV. The irradiation time was from 1 to 3 hours. The testing temperature ranged from 20 ℃ to 30 ℃.

The current collectors prepared in the examples and the comparative examples were characterized and tested according to GB/T 36363-2018 standard. The 100 ampere-hour (Ah) lithium batteries assembled herein had the following structure: the positive electrode was NCM811 ternary material, the negative electrode was graphite, and the electrolyte was a liquid lithium salt solution, which was lithium hexafluorophosphate dissolved in a liquid solvent. The separator was a PE separator prepared by a wet process. The batteries were soft pack batteries with aluminum-plastic film housing. The test results are shown in Table 1.

(1) Surface static electricity measurement: An electrostatic voltmeter was disposed on and in close contact with the metal surface of the current collector to be measured. Then the electrostatic voltmeter was turned on and adjusted to have an appropriate sensitivity. When a stable test value was shown by the electrostatic voltmeter, this value was read as the electrostatic voltage value of the metal surface. By comparing the electrostatic voltage values of different metal surfaces, whether electrostatic charges existed between the different metal surfaces can be known.

(2) Tensile strength and elongation measurements: The test was performed by using a tensile testing machine. The two ends of the current collector to be measured were clamped respectively by an upper clamp and a lower clamp of the tensile testing machine, and were kept in the same axis during the test. The parameters such as sample size, clamp moving speed, and unit of measure were set, and the extension length and load value of the sample were recorded during the test. Then the tensile strength and elongation were calculated according to the test results.

(3) Puncture strength measurement: The current collector to be measured was cut into a fixed-size rectangle, which was then fixed on a table. The surface of the sample was ensured to be flat. A needle with a round cross-section (with a diameter of 3.0 mm) was used to apply pressure to the sample at a speed of 1 mm/suntil the pressure reached a specified peak value or the sample was broken. The maximum force applied by the needle at each puncture spot was recorded. By analyzing the test results, the puncture strength and puncture index of the sample were calculated.

(4) Roughness measurement: The surface of the current collector to be measured was scanned by using a profilometer to obtain surface’s profile data, and the surface roughness was quantified by calculation or other methods.

(5) Sheet resistance measurement: The current collector to be measured was cut into a square. Four probes were fixed at the four corners of the square current collector, wherein two opposite probes were respectively connected to the electrodes of a sheet resistance meter, and the other two probes were connected to a power supply as testing probes. The sheet resistance meter was turned on, and the position and spacing of the four probes were adjusted, so that the four probes were perpendicular and parallel to sample surface, and kept stable, during which the sheet resistance meter can automatically apply a current to the sample and measure the voltage of the sample, and calculate the sheet resistance value of the sample.

(6) Oxidation resistance measurement: The oxidation resistance test was performed by visual observation. The oxidized copper foil gradually became red and then turned to be black as the oxidation continues.

(7) Internal resistance measurement (100 Ah lithium battery) : The lithium battery to be measured was fully charged to a fixed state. A load with a known resistance value was connected to the positive and negative electrodes of the lithium battery. The voltage between two ends of the load was measured while the circuit was closed. The internal resistance of the battery was calculated according to the Ohm's law, i.e., internal resistance = measured voltage /measured current.

(8) Energy density measurement (100 Ah lithium battery) : The energy density can be calculated by the following equation: energy density (Wh/liter) = capacity × platform voltage ÷ volume ÷ 1000. The capacity refers to the charge capacity of the battery, the unit is Ah, and the value of the capacity is 100 Ah in the test. The platform voltage refers to the open circuit voltage of the lithium battery, that is, the voltage measured without load. The volume is the physical volume of the lithium battery, and the unit is liter.

Table 1

As can be seen from Table 1, the current collectors for use in a negative electrode prepared in Examples 1 to 5 had moderate surface static electricity and good oxidation resistance, all started to be oxidized after 200 days or longer. In addition, the basic performances such as mechanical strength and energy density were good. As compared to Example 1, the particle size of the copper nanoparticles in Example 2 was larger, which might cause a certain degree of decrease in strength of the current collector and a slight increase in roughness, and the energy density was also lower due to a certain degree of decrease in compactness. The energy of electric charges in Example 3 was higher, which caused a limited improvement in oxidation resistance but a higher surface static electricity, so the storage difficulty was slightly larger, and a difference between sheet resistances at two surfaces might occur due to an improper storage. In Example 4, a part of nano copper is replaced with a non-nano copper, so the cost was significantly decreased.

In Comparative Examples 1 and 2, the energy distributions of electric charges were not suitable. An excessively high energy distribution of charges resulted in excessive surface static electricity, making storage challenging and leading to a sizable discrepancy in sheet resistance between the two sides. An inadequate energy distribution of electric charges resulted in a significant decrease in oxidation resistance of the current collector. In Example 3, the average particle size of the copper nanoparticles was too large, which had a negative effect on oxidation resistance and other properties of the current collector. In Example 4, the voltage in step (2) was too high, causing the loss of electrons from the surfaces of the current collector. This resulted in a low energy distribution of electric charges, which negatively affected the oxidation resistance and the mechanical property. In Comparative Example 5 which employed the conventional method, the barrier layer was made of zinc and the anti-oxidation layer was made of chromium, the oxidation resistance was worse than that in other examples, the electrical performance was also poor due to the significant interface resistance. Furthermore, since several materials were used together, the integration property was also poor, resulting in poor elongation.

For the composite current collectors obtained in Example 1, Example 5, and Comparative Examples 6-9, the peeling force was tested and the results are shown in Table 2. The peeling force was tested as follows: A tape with a length of 11 cm was attached onto a steel plate, and then the composite current collector with a length of 10 cm was attached onto the tape. After that, another tape with a length of 22 cm was attached onto the composite current collector. The steel plate was fixed in an instrument for measuring the peeling force. The tape with the length of 22 cm was folded into a U-shape, and then the free end thereof was clamped by a clamper of the instrument for measuring the peeling force. Thereafter, the instrument for measuring the peeling force was started to pull the tape to peel the copper layer off from the substrate layer and to measure the peeling force.

Table 2

According to the comparisons between Example 1 and Comparative Example 6 and between Example 5 and Comparative Example 8, the smaller the surface roughness of the substrate layer, the easier the nano copper layer to be peeled off from the substrate layer, and the poorer the binding force. According to the comparisons between Example 1 and Comparative Example 7 and between Example 5 and Comparative Example 9, when the surface roughness of the substrate layer was larger, the nano copper layer was slightly easier to be peeled off from the substrate layer, which may due to the excessive large roughness of the substrate layer making the copper layer in some areas with deep depressions unable to be completely bond with the substrate layer. In addition, the surface of the electron-rich current collector for use in a negative electrode tended to form bumps in the raised areas of the substrate, resulting in defects on the surface of the current collector.

The technical features of the embodiments disclosed herein can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features are disclosed herein. However, as long as there is no contradiction in the combination of these technical features, the combinations should be considered as within the scope of the present application.

The embodiments disclosed herein should not be construed as limiting the scope of the present application. It should be understood by those of ordinary skill in the art that various modifications and improvements can be made without departing from the concept of the present application, and all fall within the protection scope of the present application.

Claims

An electron-rich current collector for use in a negative electrode, comprising:

a polymer substrate layer; and

a nano copper layer disposed on a surface of the polymer substrate layer;

wherein the nano copper layer is a deposited film or a deposited layer of copper nanoparticles, wherein the nano copper layer carries electrons, and wherein an energy distribution of electric charges in the nano copper layer ranges from 200 eV/mm² to 500 eV/mm².
The electron-rich current collector of claim 1, wherein an average particle size of the copper nanoparticles in the nano copper layers ranges from 10 nm to 50 nm.
The electron-rich current collector of claim 1, wherein a material of the polymer substrate layer is one or more selected from polyethylene glycol terephthalate, polyethylene, polypropylene, and polymethylpentene; and/or

a surface roughness of the polymer substrate layer is 150 nm to 200 nm.
The electron-rich current collector of claim 3, wherein a weight-average molecular weight of the material of the polymer substrate layer ranges from 1,000 kDa to 1,500 kDa.
The electron-rich current collector of any one of claims 1 to 4, wherein the electron-rich current collector has at least one property selected from:

a thickness of the electron-rich current collector ranging from 3 μm to 30 μm,

a thickness of the polymer substrate layer ranging from 1 μm to 25 μm, and

a thickness of the nano copper layer ranging from 10 nm to 3 μm.
The electron-rich current collector of any one of claims 1 to 4, further comprising a non-nano copper layer, wherein the non-nano copper layer is disposed between the polymer substrate layer and the nano copper layer, wherein the thickness of the nano copper layer ranges from 10 nm to 50 nm, and wherein the thickness of the non-nano copper layer ranges from 0.25 μm to 2.99 μm.
A method for preparing an electron-rich current collector, comprising:

providing a polymer substrate layer; and

depositing electron-rich copper nanoparticles onto a surface of the polymer substrate layer by using a vacuum magnetron sputtering method, thereby forming a nano copper layer;

wherein the electron-rich copper nanoparticles are prepared by a method comprising:

mixing [Gd₂C] ²⁺·2e^-electrets, a bivalent copper salt, and an alcohol solvent to react at a temperature ranging from 60 ℃ to 120 ℃, and then adsorbing the [Gd₂C] ²⁺·2e^-electrets onto a magnetic substance to separate the [Gd₂C] ²⁺·2e^-electrets from a remaining reaction system;

subjecting the remaining reaction system to a solid-liquid separation to collect a solid product; and

drying the solid product.
The method of claim 7, wherein the reaction time of the mixed [Gd₂C] ²⁺·2e^-electrets, the bivalent copper salt, and the alcohol solvent ranges from 40 min to 60 min, and/or

the vacuum magnetron sputtering method comprises:

forming a target by the electron-rich copper nanoparticles;

fixing the target at a cathode of a magnetron sputtering apparatus, and placing the polymer substrate layer at an anode of the magnetron sputtering apparatus;

evacuating the magnetron sputtering apparatus to a vacuum degree less than or equal to 5×10^-2 Pa, and filling the magnetron sputtering apparatus with a non-reactive gas having a gas pressure ranging from 1 Pa to 10 Pa; and

applying a voltage ranging from 2500 V to 3500 V between the cathode and the anode, thereby allowing atoms in the target to move towards the anode under an electric field and to deposit onto a surface of the polymer substrate layer, thereby forming the nano copper layer.
An electrode plate comprising the electron-rich current collector of any one of claims 1 to 6.
A battery comprising the electrode plate of claim 9.