Passivated metal powder and applications

Abstract

This application relates to the field of batteries, specifically to a metal powder passivated with an organic passivating agent. After sintering in an inert gas atmosphere, the passivated metal powder has a post-sintering oxygen content of less than 800 ppm, preferably less than 500 ppm. Passivated metal powders with post-sintering oxygen content within this range exhibit high conductivity and stable resistivity, thereby yielding passivated metal powders with high conductivity and stable resistivity, as well as related conductive materials such as metal electrodes and solar cells.

Description

Technical Field

[0001] This application relates to the field of solar cells, and more specifically to a passivated metal powder, a conductive material containing the metal powder, and a solar cell. Background Technology

[0002] With increasingly serious environmental problems and the depletion of traditional fossil fuels, sustainable green energy has become a common development direction for the world. Solar energy, as a widely available and easily accessible renewable energy source, is considered one of the most valuable clean energy sources. Conductive paste, as a crucial component of solar cells, significantly impacts their photoelectric conversion efficiency and cost per kilowatt-hour. Traditional conductive pastes mainly consist of silver paste, which offers good conductivity and stability; however, silver is expensive, greatly increasing the cost of solar cells. Therefore, finding a conductive paste that is highly conductive, inexpensive, and readily available is urgently needed.

[0003] Although some low-cost metals have been discovered for preparing conductive pastes, the surfaces of some metal powders are easily oxidized to form non-conductive metal oxides, which severely affect the conductivity of the paste. Take copper as an example. Copper is one of the earliest metals used by humans, belongs to the same group as silver, and has a similar outermost electron structure. Therefore, the electrical properties of copper are close to those of silver. Due to the low cost of copper, copper paste can significantly reduce the cost of solar cells by replacing silver paste. However, copper powder forms non-conductive copper oxides upon contact with oxygen. Furthermore, in humid environments, copper powder is accelerated to oxidize due to moisture, and the copper oxides on the surface of the copper powder severely affect the electrical properties of the paste. Currently, the main way to delay or inhibit the oxidation of metal powders is to coat the surface of the metal powder with one or more layers of organic passivating agents to isolate or block oxygen. Summary of the Invention

[0004] In the prior art, passivated metal powders have poor oxidation resistance. To address this, the inventors of this application discovered that by controlling the oxygen content of the passivated metal powder to a low range after sintering, metal powders with higher oxidation resistance can be obtained, thereby yielding metal powders with higher electrical conductivity and resistance stability, thus completing this invention.

[0005] Therefore, in a first aspect of this application, a passivated metal powder is provided, the metal powder having a post-sintering oxygen content of less than 800 ppm, the post-sintering oxygen content referring to the oxygen content of the metal powder after sintering the passivated metal powder in an inert gas atmosphere.

[0006] In a second aspect, a metal conductive paste is provided, comprising the passivated metal powder and dispersion medium described in the first aspect.

[0007] In a third aspect, a metal electrode is provided, which is prepared from the metal conductive paste described in the second aspect.

[0008] In a fourth aspect, a solar cell is provided, which includes the metal electrode described in the third aspect.

[0009] This application provides a passivated metal powder, which, after sintering in an inert gas atmosphere, has an oxygen content of less than 800 ppm, preferably less than 500 ppm, as tested in a test. That is, it has a post-sintering oxygen content of less than 800 ppm, preferably less than 500 ppm. The inventors have discovered that passivated metal powders with a post-sintering oxygen content within this defined range exhibit high conductivity and stable resistivity, thereby obtaining conductive materials such as metal electrodes with high conductivity and stable resistivity. Detailed Implementation

[0010] The present application will be described in detail below. It should be understood that the following description is merely illustrative and is not intended to limit the scope of the application; the scope of protection of the present application is determined by the appended claims. Furthermore, those skilled in the art will understand that modifications can be made to the technical solutions of the present application without departing from its spirit and intent. Unless otherwise specified, the technical means used in the embodiments are conventional means well known to those skilled in the art.

[0011] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the subject matter of this application pertains. Before a detailed description of this application, the following definitions are provided to better understand it.

[0012] In cases where numerical ranges are provided, such as concentration ranges, percentage ranges, or ratio ranges, it should be understood that, unless the context explicitly specifies otherwise, all intermediate values ​​between the upper and lower limits of the range, up to one-tenth of the lower limit unit, and any other values ​​or intermediate values ​​within the range are included in the subject matter. The upper and lower limits of these smaller ranges may be independently included in the smaller ranges, and such embodiments are also included in the subject matter, limited by any specific excluded limit values ​​within the range. Where the range includes one or two limit values, the range excluding any one or both of those included limit values ​​is also included in the subject matter.

[0013] In the context of this application, many embodiments use the expressions "comprising," "including," or "basically / mainly composed of...". The expressions "comprising," "including," or "basically / mainly composed of..." are generally understood as open-ended expressions, indicating that they include not only the elements, components, parts, or method steps specifically listed after the expression, but also other elements, components, parts, or method steps. However, in this document, the expressions "comprising," "including," or "basically / mainly composed of..." can also be understood as closed-ended expressions in certain situations, indicating that they only include the elements, components, parts, or method steps specifically listed after the expression, and exclude any other elements, components, parts, or method steps. In this case, the expression is equivalent to the expression "composed of...".

[0014] Current research has revealed the following problems during the passivation of copper powder: Some organic passivating agents, even after curing at high temperatures, can still cause oxidation of the organically modified copper surface by oxygen, leading to a sharp increase in the resistivity of the copper powder. Furthermore, for organic passivating agents with poor hydrophobicity, moisture can easily cause secondary oxidation and corrosion of the copper surface under heating conditions. A small amount of organic passivating agent coating is insufficient to prevent oxygen erosion, while an excessive amount, although improving the oxidation resistance of the copper powder, can affect the conductivity of the slurry and electrodes prepared from the copper powder. Moreover, during the preparation of the conductive slurry, some of the organic passivating agent in the coating layer on the copper powder surface can dissolve into the slurry, affecting the viscosity of the slurry or causing coating failure, resulting in unstable resistance of the electrodes prepared after curing. When using a single organic passivating agent to treat copper powder, partial oxidation of the copper powder surface is unavoidable.

[0015] Therefore, in a first aspect of this application, a passivated metal powder is provided, the passivated metal powder having a post-sintering oxygen content of less than 800 ppm, wherein the post-sintering oxygen content refers to the oxygen content of the metal powder after sintering the passivated metal powder in an inert gas atmosphere. Specifically, the post-sintering oxygen content of the metal powder can be less than 10 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, 450 ppm, 500 ppm, 550 ppm, 600 ppm, 650 ppm, 700 ppm, 750 ppm, or 800 ppm, or a range consisting of any two of these values.

[0016] In one specific implementation, the metal powder has a post-sintering oxygen content of less than 500 ppm.

[0017] In this application, metal powder can be used to prepare metal conductive paste after passivation with an organic passivating agent. Because the passivated metal powder has residual organic passivating agent or water vapor on its surface after passivation that has not been adsorbed with the metal powder or has a weak adsorption effect, sintering in an inert gas atmosphere can make the passivated metal powder have a stable surface oxygen content. The inventors found that whether the oxygen content after sintering is less than 800 ppm (or 500 ppm) can be used to determine whether the metal powder can be effectively used to prepare metal conductive paste with high conductivity and low resistivity.

[0018] If the oxygen content is too high after sintering, it indicates that the surface of the metal powder may not be sufficiently passivated, resulting in copper oxidation, which will reduce the conductivity of the electrode made from the metal powder. Alternatively, if the surface of the metal powder is coated with too much organic passivating agent, the organic passivating agent will react with the surface of the metal powder during sintering, leaving more oxygen on the surface of the metal powder. Excessive organic passivating agent will dissolve into the slurry, affecting the viscosity of the slurry, and thus affecting the stability and printability of the slurry.

[0019] In this application, the oxygen content after sintering refers to the oxygen content obtained by first sintering the passivated metal powder in an inert atmosphere, for example, at 500℃-600℃, and then measuring the oxygen content of the metal powder. As an example, the specific steps of sintering the passivated metal powder in an inert gas atmosphere may include: (1) The passivated metal powder is placed in a closed high-temperature furnace (e.g., a muffle furnace) and heat-treated at a certain temperature under a nitrogen atmosphere for a certain time, and then the muffle furnace is allowed to cool naturally. The temperature and time of the heat treatment can be determined by the measurement deviation of the oxygen content after sintering, as long as the oxygen content value after sintering is kept constant after heat treatment. When the oxygen content value after sintering is constant, the deviation is within 50 ppm, preferably 30 ppm. As a specific implementation scheme, the heat treatment temperature is 500℃-600℃, for example, any one of 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, or a range consisting of any two of these values. The treatment time is 30min-60min, for example, any one of 30min, 40min, 50min, 60min, or a range consisting of any two of these values.

[0020] (2) After the high-temperature furnace cools to room temperature, the powder is quickly transferred to a nitrogen atmosphere and pressed into powder. The oxygen content after sintering is measured by non-dispersive infrared spectroscopy (NDIR). As a specific implementation method, the powder can be pressed into powder in a glove box.

[0021] In one specific implementation, the passivated oxygen content of the metal powder after passivation is 800 ppm to 3000 ppm. Herein, the passivated oxygen content refers to the oxygen content measured by, for example, non-dispersive infrared spectroscopy (NDIR) after the metal powder has been passivated with an organic passivating agent. If the passivated oxygen content is greater than 3000 ppm, it indicates that there are many oxides on the surface of the metal powder or that there is an excessive amount of organic passivating agent on the surface of the metal powder, which will affect the resistivity of the electrode prepared from the metal powder and the stability of the conductive paste. If the passivated oxygen content is less than 800 ppm, the organic passivating agent on the surface of the metal powder is insufficient, which will affect the oxidation resistance and low-temperature sintering properties of the copper powder.

[0022] In one specific implementation, the passivated metal powder includes metal powder and an organic passivating agent coated on the surface of the metal powder. Passivating the metal powder with an organic passivating agent allows the agent to coat the surface of the metal powder, forming an antioxidant layer that isolates oxygen and moisture, thus solving the problem of easy oxidation of the metal powder and reducing the oxygen content of the passivated metal powder after sintering.

[0023] In a further specific embodiment, the organic passivating agent is selected from one or more of organic amine compounds, organic acid compounds, imidazole compounds, thiazole compounds, and thiol compounds.

[0024] In a more specific embodiment, the organic amine compound may include, but is not limited to, linear or branched C6-C6 compounds. 22 Aliphatic amines, such as n-octylamine, n-hexylamine, dodecylamine, tetradecylamine, hexadecylamine, stearylamine, oleylamine, etc., can be used alone or in combination of two or more.

[0025] In a more specific embodiment, the organic acid compound can be a fatty acid compound, which may include, but is not limited to, linear or branched C6-C fatty acids. 22 Saturated fatty acids or unsaturated fatty acids, these fatty acid compounds can be used alone or in combination of two or more.

[0026] In a more specific embodiment, the imidazole compound may include, but is not limited to, imidazole, benzimidazole, 2-thiobenzimidazole, alkyl imidazole (alkyl carbon atoms numbered 1-20), etc., and these imidazole compounds may be used alone or in combination of two or more.

[0027] In a more specific embodiment, the thiazole compound may include, but is not limited to, 2-thiobenzothiazole.

[0028] In a more specific implementation, the thiol compounds may include, but are not limited to, ethanethiol, methanethiol, propanethiol, butanethiol, mercaptoethanol, etc., and these thiol compounds may be used alone or in combination of two or more.

[0029] The above are merely examples, and no special limitations are made on organic passivating agents, as long as the metal powder has the oxygen content within the above range after sintering.

[0030] In yet another specific embodiment, the passivated metal powder may include flake powder. Flake powder refers to metal powder having a sheet-like two-dimensional planar structure, i.e., a small thickness and a large aspect ratio. Specifically, "flake powder" refers to powder with an aspect ratio (shortest diameter / thickness) greater than or equal to 2. In this invention, the ratio of the longest diameter to the shortest diameter of the flake powder is 1-10.

[0031] In yet another specific implementation, the D of the flake powder 50 The particle size can be 1 μm – 10 μm, and the median thickness can be 100 nm – 500 nm. The D... 50 The particle size can be measured using a laser particle size analyzer, and the median thickness can be measured using a SEM (Semiconductor Electron Microscope). Specifically, the D of the flake powder... 50 The particle size can be 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm, 3.5 μm, 4 μm, 4.5 μm, 5 μm, 5.5 μm, 6 μm, 6.5 μm, 7 μm, 7.5 μm, 8 μm, 8.5 μm, 9 μm, 9.5 μm, or 10 μm, or a range consisting of any two of these values. More specifically, the median thickness of the powder flakes can be 100 nm, 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, or 500 nm, or a range consisting of any two of these values.

[0032] In yet another specific implementation, the specific surface area of ​​the flake powder can be 0.1 - 0.9 m². 2 / g. More specifically, the specific surface area of ​​the flake powder can be 0.1 m². 2 / g, 0.2 m 2 / g, 0.3 m 2 / g, 0.4 m 2 / g, 0.5 m 2 / g, 0.6m 2 / g, 0.7 m 2 / g, 0.8 m 2 / g or 0.9 m 2 / g, or a range consisting of any two of these values. In the context of this application, the term "specific surface area" refers to the surface area per unit mass of a porous solid material, commonly expressed in square meters per gram (m² / g). 2 The specific surface area (g) can be measured using conventional methods, such as the determination of specific surface area of ​​metal powders according to GB / T 13390-2008. If the specific surface area of ​​the metal powder is within the above range, it ensures that the metal powder has good oxidation resistance. The larger the specific surface area, for example, above the upper limit, the higher the surface activity and the easier it is to be oxidized. The smaller the specific surface area, for example, below the lower limit, the larger the particle size of the metal powder, which will affect the low-temperature sintering properties of the metal conductive paste prepared from the metal powder, resulting in insufficient sintering at low temperatures or poor bonding between the metal powder and the substrate after sintering.

[0033] In another specific embodiment, the oxygen content of the sintered powder can be between 10 ppm and 450 ppm, for example, 10 ppm, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, 400 ppm, or 450 ppm, or a range consisting of any two of these values. If the oxygen content of the sintered powder is within this range, it can ensure that the surface of the powder has a suitable oxygen content and an organic passivating agent with strong adhesion to the surface of the metal powder.

[0034] In one specific implementation, the ratio of the oxygen content to the specific surface area of ​​the sintered powder is expressed as Q (oxygen content after sintering / BET specific surface area, unit ppm·g / m²). 2 And the range of Q can be: 10 ppm·g / m 2 <Q<550ppm·g / m 2 The Q value represents the oxygen content per unit specific surface area after sintering and can be used to measure or compare the oxygen content after sintering of metal powders with different specific surface areas. When the Q value of the powder is within the specified range, the stability of the conductive metal paste prepared from the powder is better, thereby further improving the conductivity of the electrode prepared from the metal powder. However, if the Q value is too high, for example, exceeding 550 ppm·g / m 2 This indicates that there are many oxides on the surface of the metal powder, which in turn affects the stability of the conductive metal slurry prepared from the metal powder and the conductivity of the electrode prepared from the metal powder.

[0035] In yet another specific embodiment, the passivated metal powder may include spherical powder. Hereinafter, "spherical powder" refers to powder with an aspect ratio (shortest diameter / thickness) of less than 2.

[0036] In yet another specific implementation, the D of the ball powder 50 The particle size can be 100 nm - 800 nm. The D 50 Particle size can be measured using a laser particle size analyzer. Specifically, the D of the spherical powder... 50 The particle size can be 100 nm, 150 nm, 200 nm, 250 nm, 300 nm, 350 nm, 400 nm, 450 nm, 500 nm, 550 nm, 600 nm, 650 nm, 700 nm, 750 nm or 800 nm, or a range consisting of any two of these values.

[0037] In yet another specific implementation, the specific surface area of ​​the spherical powder can be 0.5-8 m². 2 / g. Specifically, the specific surface area of ​​the spherical powder can be 0.5 m². 2 / g, 0.8 m 2 / g、1 m 2 / g、2 m 2 / g、3 m 2 / g、4 m 2 / g、5 m 2 / g、6 m 2 / g、7 m 2 / g or 8 m 2 / g, or a range consisting of any two of these values.

[0038] In another specific embodiment, the oxygen content of the sintered spherical powder can be between 15 ppm and 400 ppm, for example, 15 ppm, 20 ppm, 25 ppm, 30 ppm, 35 ppm, 40 ppm, 45 ppm, 50 ppm, 100 ppm, 150 ppm, 200 ppm, 250 ppm, 300 ppm, 350 ppm, or 400 ppm, or a range consisting of any two of these values. If the oxygen content of the sintered spherical powder is within this range, it can ensure that the surface of the spherical powder has a suitable amount of organic passivating agent that has a strong bonding force with the surface of the metal powder.

[0039] In one specific embodiment, the ratio of oxygen content to specific surface area of ​​the sintered spherical powder is expressed as Q, and the range of Q is: 1 ppm·g / m 2 <Q<350 ppm·g / m 2For example, 1 ppm·g / m 2 15 ppm·g / m 2 30ppm·g / m 2 40 ppm·g / m 2 60 ppm·g / m 2 80 ppm·g / m 2 100 ppm·g / m 2 120 ppm·g / m 2 140 ppm·g / m 2 160 ppm·g / m 2 180 ppm·g / m 2 200 ppm·g / m 2 220 ppm·g / m 2 240 ppm·g / m 2 260 ppm·g / m 2 280 ppm·g / m 2 300 ppm·g / m 2 320 ppm·g / m 2 350 ppm·g / m 2 When the Q value is within the specified range, the stability of the conductive metal paste prepared from the spherical powder is better, and the conductivity of the electrode prepared from the spherical powder can be further improved. In some cases, the Q value of the spherical powder is lower than that of the flake powder, and in this case, the oxidation resistance of the spherical powder may be slightly inferior to that of the flake powder.

[0040] In a further specific embodiment, the passivated metal powder may include spherical powder and flake powder.

[0041] It is understood that in this invention, when the metal powder includes spherical powder and flake powder, the spherical powder and flake powder can be mixed first and then passivated, or the spherical powder and flake powder can be passivated separately and then mixed. There are no special requirements for this, as long as the obtained passivated metal spherical powder has the required properties, such as the oxygen content after sintering within the defined range.

[0042] In a preferred embodiment, the passivated metal powder may consist of spherical powder and flake powder, preferably consisting of 35%-60% flake powder and 40%-65% spherical powder by mass percentage.

[0043] In one specific implementation, the mass percentage of the ball powder can be 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60%, or a range consisting of any two of these values.

[0044] In one specific implementation, the mass percentage of the flake powder can be 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, 50%, 51%, 52%, 53%, 54%, 55%, 56%, 57%, 58%, 59%, or 60%, or a range consisting of any two of these values.

[0045] In this application, the metal powder in flake form and the metal powder in spherical form are matched in shape and / or mass, so that metal powder particles of various sizes and shapes are densely packed, and the conductive channels between the metal powder particles are more unobstructed.

[0046] In one specific embodiment, the metal powder is a powder of at least one metal selected from copper, nickel, zinc, aluminum, or an alloy thereof.

[0047] In a preferred embodiment, the metal powder is copper powder. Copper is inexpensive and has electrical conductivity close to that of silver; therefore, copper powder offers greater cost-effectiveness and superior conductivity.

[0048] In yet another specific implementation, the copper powder may be copper powder in flake form.

[0049] In a further specific embodiment, the tap density of the copper powder in flake form is 4.4–5.2 g / ml. Specifically, the tap density of the copper powder in flake form can be 4.4 g / ml, 4.5 g / ml, 4.6 g / ml, 4.7 g / ml, 4.8 g / ml, 4.9 g / ml, 5 g / ml, 5.1 g / ml, or 5.2 g / ml, or a range consisting of any two of these values. In the context of this application, the term "tap density" refers to the bulk density of powder after it has been tapped, meaning the density of the powder after it has been packed into a specific container and the container has been vibrated to break down the voids in the powder and bring it into a tightly packed state. By measuring the tap density, the flowability and porosity of the powder can be determined. The tap density can be calculated by measuring the volume after vibrating the BT-301 vibrator 1000 times. When the tap density of the copper powder in flake form is within this range, the metal electrode formed by the copper powder has a high density and a low porosity, thereby exhibiting a low resistivity.

[0050] In yet another specific embodiment, the copper powder in flake form has a particle size of 0.4-0.7 μm. 2 The specific surface area is 0.4 m² / g. Specifically, the specific surface area of ​​the copper powder in flake form can be 0.4 m² / g. 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.55m 2 / g, 0.6 m 2 / g, 0.65 m 2 / g or 0.7 m 2 / g, or a range consisting of any two of these values. If the specific surface area of ​​the copper powder in flake form is within the above range, it can ensure that the copper powder has good oxidation resistance; the larger the specific surface area, for example, exceeding the upper limit, the higher the surface activity and the easier it is to be oxidized; while the smaller the specific surface area, for example, below the lower limit, the larger the particle size of the metal powder, which will affect the low-temperature sintering properties of the metal conductive paste prepared from the metal powder, resulting in insufficient sintering at low temperatures or poor bonding between the metal powder and the substrate after sintering.

[0051] In yet another specific implementation, the copper powder may be copper powder in the form of spherical powder.

[0052] In a further specific embodiment, the tap density of the copper powder in spherical form is 4.3-4.9 g / ml. Specifically, the tap density of the copper powder in spherical form can be 4.3 g / ml, 4.4 g / ml, 4.5 g / ml, 4.6 g / ml, 4.7 g / ml, 4.8 g / ml, or 4.9 g / ml, or a range consisting of any two of these values. When the tap density of the copper powder in spherical form is within this range, the metal electrode formed by the copper powder has high density, low porosity, and thus low resistivity.

[0053] In yet another specific embodiment, the copper powder in spherical form has a particle size of 0.5-4.0 μm. 2 The specific surface area is 0.5 m² / g. Specifically, the specific surface area of ​​the copper powder in spherical form can be 0.5 m² / g. 2 / g, 0.7 m 2 / g, 0.9 m 2 / g, 1.0 m 2 / g, 1.2 m 2 / g, 1.4 m 2 / g, 1.6 m 2 / g, 1.8 m 2 / g, 2.0 m 2 / g、2.2 m 2 / g、2.4 m 2 / g, 2.5 m 2 / g, 2.6m 2 / g、2.8 m 2 / g, 3.0 m 2 / g、3.2 m 2 / g、3.4 m 2 / g, 3.6 m 2 / g、3.8 m 2 / g or 4.0 m 2 / g, or a range consisting of any two of these values. If the specific surface area of ​​the copper powder in spherical form is within the above range, the copper powder can be ensured to have good oxidation resistance; if the specific surface area is larger, for example, greater than the upper limit, the surface activity is high and it is easily oxidized; if the specific surface area is smaller, for example, lower than the lower limit, the particle size of the metal powder is larger, which will affect the low-temperature sintering properties of the metal conductive paste prepared from the metal powder, resulting in insufficient sintering at low temperatures or poor bonding between the metal powder and the substrate after sintering.

[0054] Taking copper powder as an example, the passivation process of the metal powder in this application may include the following steps: (1) Copper powder pretreatment: Step a: Add copper powder to acid for pickling. The hydrogen ion molar concentration of the acid is between 0.1-5 mol / L. The temperature during the pickling process is 20-60 ℃, and the pickling time is 30 min to 2 h. Step b: Wash the acid-washed copper powder by centrifugation with water and ethanol until the pH reaches 7.

[0055] In the copper powder pretreatment step, the acid may be one or more acids selected from hydrochloric acid, hydrobromic acid, hydroiodic acid, sulfuric acid, nitric acid, perchloric acid, sulfurous acid, phosphoric acid, hydrofluoric acid, acetic acid, carbonic acid, hydrosulfuric acid, and hypochlorous acid. (2) Passivation treatment: An organic passivating agent was mixed with water and alcohol to prepare a passivation solution. Pretreated copper powder was then placed into the passivation solution and stirred at room temperature. The solution was then washed with ethanol until the conductivity was less than 30 μS / cm. In the passivation treatment step, the alcohol includes, but is not limited to, one or more of ethanol, ethylene glycol, methanol, glycerol, tetramethylethylene glycol, n-propanol, isopropanol, n-butanol, sec-butanol, isobutanol, n-pentanol, sec-pentanol, 3-pentanol, tert-pentanol, and n-hexanol; the organic passivating agent can be the organic passivating agent listed above, but is not limited to it.

[0056] In the passivation process of metal powder, the thickness of the passivation layer on the surface of the metal powder can be controlled by adjusting the pretreatment temperature, pretreatment time, type of organic passivating agent, passivation treatment temperature, and passivation treatment time, thereby adjusting the oxygen content of the passivated metal powder after passivation and after sintering. It is understood that the selection of multiple parameters in the above passivation process can be adjusted for different metal systems, and this application does not impose specific limitations on this.

[0057] In one specific implementation, from the viewpoint of reducing metal oxides on the surface of the metal powder, the metal powder of this application can also be treated with a reducing agent. More specifically, the reducing agent can be added to the passivation solution to perform reduction treatment simultaneously with passivation. Alternatively, after passivation, the passivated metal powder can be placed in an alcohol solution containing a reducing agent for reduction treatment.

[0058] In a preferred embodiment, passivation and reduction are performed in the same solution to simplify the processing steps.

[0059] In a further specific embodiment, the reducing agent is an organic reducing agent or an inorganic reducing agent, such as at least one of borohydrides, hypophosphorous acid and its salts, phosphorous acid and its salts, borane compounds, reducing organic acid compounds, phenolic compounds, aldehyde compounds, and hydrazine hydrate.

[0060] In a more specific embodiment, the borohydride may be sodium borohydride or lithium borohydride; the hypophosphite and its salt may be hypophosphite or sodium hypophosphite; the phosphorous acid and its salt may be phosphorous acid or sodium phosphite; the borane compound may be dimethylamineborane or amineborane; the reducing organic acid compound may be ascorbic acid, formic acid, oxalic acid, citric acid, salicylic acid, glyoxylic acid, glycolic acid, succinic acid, maleic acid, tartaric acid, methanesulfonic acid, fumaric acid, ricinoleic acid, malic acid, oleic acid, etc.; the phenolic compound may be selected from aromatic compounds having one or more hydroxyl substituents or heteroaromatic compounds having one or more hydroxyl substituents, wherein the aromatic compounds... The compound can be benzene, naphthalene, anthracene, fluorene, etc., with 6-18 carbon atoms. The heteroaromatic compound can be pyridine, furan, thiophene, imidazole, quinoline, isoquinoline, etc., with 5-18 carbon atoms. The aromatic compound or heteroaromatic compound can be further substituted by other substituents, which can be hydrogen, alkyl, alkenyl, alkynyl, halogen, or cyano. The phenolic compound can have 1-5 hydroxyl substituents. Phenolic compounds with two or more hydroxyl substituents are, for example, one of catechol, hydroquinone, resorcinol, catechol, and dopamine. Phenolic compounds with one hydroxyl substituent can be tert-butylphenol or 2,6-di-tert-butyl-p-methylphenol.

[0061] In a preferred embodiment, the reducing agent may be a reducing organic acid, which is beneficial to the storage stability of the slurry.

[0062] In a second aspect of this application, a metal conductive paste is provided, comprising the passivated metal powder and dispersion medium of the first aspect.

[0063] In a preferred embodiment, the metal conductive paste comprises 80%-95% passivated metal powder and 5%-20% dispersion medium.

[0064] In one specific embodiment, the dispersion medium includes a resin, a curing agent, a dispersant, a solvent, and optionally a curing accelerator.

[0065] In yet another specific implementation, the resin may be one or more of epoxy resin, phenolic resin, phenoxy resin, acrylic resin, aldehyde-ketone resin, polyurethane, and polyester, but is not limited thereto.

[0066] In a further specific embodiment, the epoxy resin may be a thermosetting resin, selected from one or more of bisphenol A type epoxy resin, bisphenol F epoxy resin, hydrogenated bisphenol A type epoxy resin, polyurethane modified epoxy resin, dimer acid modified epoxy resin, siloxane modified epoxy resin, phenolic epoxy resin, polyol glycidyl ether type epoxy resin, and polyacid glycidyl ester type epoxy resin. Of course, other resins known in the art that can be used in this application may also be selected, and this application does not further limit them.

[0067] In another specific embodiment, the curing agent may be one or more selected from dicyandiamide curing agents, tertiary amine curing agents, isocyanates, imidazole curing agents, acid anhydride curing agents, and latent imidazole curing agents, such as triethanolamine, blocked isocyanates, 1-butyl-3-methylimidazolium dibutyl phosphate, and Busington (Lanxess) 7982. Isocyanates may be selected from one or more selected from Trixene BI 7982 (a blocked isocyanate based on HDI), MF-K60X (a blocked polyisocyanate HDI curing agent), ketoxime-terminated isocyanates, hexamethylene diisocyanate-terminated with hexamethylene hexamethylene diisocyanate, and dodecyl mercaptan-terminated diphenyl diisocyanate. Of course, other curing agents known in the art that can be used in this application may also be selected, and this application does not further limit their use.

[0068] In another specific embodiment, the dispersant may be an ether, amine, carboxylic acid, or other dispersant with 16-20 carbon atoms and an amino group at the end or a polar group such as a hydroxyl group, for example, Tween, OP series, oleic acid, and Span. Of course, other dispersants known in the art that can be used in this application may also be selected, and this application does not further limit them.

[0069] In yet another specific embodiment, the solvent may be selected from esters, ethers, ketones, and alcohols, such as amyl acetate, cyclohexanone, amyl propionate, isopropyl lactate, divalent esters (DBE), amyl acetate, diethylene glycol acetate, diethylene glycol butyl ether acetate, ethylene glycol carbonate, propylene glycol carbonate, tributyl borate, triphenyl phosphate, tricresyl phosphate, butyl acetate, diethyl carbonate, ethylene glycol ethyl ether acetate, ethylene glycol butyl ether acetate, γ-butyrolactone, butyl carbitol acetate, and ethyl carbitol acetate. Diethylene glycol monoethyl ether acetate, diethylene glycol monobutyl ether acetate, ethylene glycol monoethyl ether, ethylene glycol monomethyl ether, ethylene glycol butyl ether, ethylene glycol diethyl ether, diethylene glycol butyl ether, ethylene glycol monoisopropyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, dipropylene glycol propyl ether, dipropylene glycol butyl ether, dipropylene glycol ether, ethylene glycol dimethyl ether, tripropylene glycol methyl ether, tripropylene glycol dimethyl ether, diethylene glycol monobutyl ether, 4-heptanone, sec-pentanol, ethylene glycol, propylene glycol, pentanol, hexanol, heptanol, octanol, methylpentanol, butyl carbitol, terpineol, dihydroterpineol.

[0070] In another specific embodiment, the metallic conductive paste may or may not contain a curing accelerator. The curing accelerator catalyzes the curing of the resin, lowers the curing temperature, and shortens the curing time. The curing accelerator is selected from quaternary ammonium salts, imidazole esters, imidazole onium salts, and substituted ureas. Specifically, quaternary ammonium salts may include benzyltriethylammonium chloride, and substituted ureas may include N-p-chlorophenyl-N,N'-dimethylurea, N-(3,4-dichlorophenyl)-N,N'-dimethylurea, N-(3-phenyl)-N,N'-dimethylurea, N-(4-phenyl)-N,N '-Dimethylurea, 2-methylimidazolidinylurea, etc.; imidazoles and their esters or imidazolidinium salts can be imidazolidinyl sulfonate / salt, imidazolidinyl phosphate / salt, or imidazolidinyl acetate / salt, such as imidazolidinyl dibutyl phosphate, 1-ethyl-3-methylimidazolidinyl acetate, 1-ethyl-3-methylimidazolidinyl methane sulfonate, trimellitic acid 1-cyanoethyl-2-undecapidazolidinium, isocyanurate 2-methylimidazolidinium, tetraphenylboronic acid 2-ethyl-4-methylimidazolidinium and tetraphenylboronic acid 2-ethyl-1,4-dimethylimidazolidinium.

[0071] When the metal powder is copper powder, i.e., for copper paste, the conductive metal paste may include copper powder, resin, curing agent, dispersant, solvent, and optional curing accelerator. In this case, the weight percentage of the copper powder is 80-95 parts, the weight percentage of the resin is 5-15 parts, the weight percentage of the solvent is 5-15 parts, the weight percentage of the curing agent is 1-5 parts, and the weight percentage of the optional curing accelerator is 1-5 parts. By using copper powder with the tap density and specific surface area defined above, and by mixing flake powder and spherical powder in a suitable mass ratio, copper particles of various sizes and shapes are densely packed, and the conductive channels between the conductive particles are more unobstructed, thereby improving the conductivity of the paste.

[0072] In yet another specific embodiment, the shear viscosity of the metallic conductive paste at 25°C and 0-100 rpm is 1-100 Pa·s, for example, 1 Pa·s, 5 Pa·s, 10 Pa·s, 15 Pa·s, 20 Pa·s, 25 Pa·s, 30 Pa·s, 35 Pa·s, 40 Pa·s, 45 Pa·s, 50 Pa·s, 60 Pa·s, 70 Pa·s, 80 Pa·s, 85 Pa·s, 90 Pa·s, 100 Pa·s, or a range of any two of these values. The shear viscosity of this application was obtained by rotational rheometer testing.

[0073] Taking copper powder as an example, the preparation method of the copper paste in this application may include the following steps: 1) Provide copper powder; 2) Copper powder, resin, solvent, curing agent, dispersant and optional curing accelerator are mixed in a certain proportion and ground by a three-roll mill.

[0074] In a third aspect of this application, a metal electrode is provided, which is prepared from the metal conductive paste described in the second aspect.

[0075] Taking copper paste as an example, an exemplary preparation method of the copper electrode of this application may include the following steps: placing the aforementioned copper paste in a nitrogen atmosphere for heating and curing to obtain the electrode. The curing temperature can be 100-220℃, for example, 100℃, 110℃, 120℃, 130℃, 140℃, 150℃, 160℃, 170℃, 180℃, 190℃, 200℃, 210℃, 220℃, etc., and the curing time can be 10min-60min, for example, 10min, 15min, 20min, 25min, 30min, 35min, 40min, 45min, 50min, 55min, 60min, etc.

[0076] Taking copper paste as an example, the preparation method of copper electrode in this application may also include the following steps: applying the pre-prepared copper paste to the battery cell (e.g., HJT / HBC / TBC) by screen printing, so that the grid line width is 40 μm - 120 μm, and then heating and curing it in a nitrogen oven, the curing temperature is generally 100-220℃, and the curing time is 10 min - 60 min, thereby forming the electrode grid line.

[0077] In a fourth aspect of this application, a solar cell is provided, which includes the metal electrode described in the third aspect.

[0078] In yet another specific embodiment, the surface of the solar cell may have a textured surface, with the metal electrode located on top of the textured surface of the solar cell.

[0079] In one specific implementation, the solar cell may be selected from BC cells, HJT cells, or perovskite / crystalline silicon tandem cells.

[0080] In yet another specific implementation, the solar cell may be a crystalline silicon cell, and a conductive barrier layer exists between the metal electrode and the crystalline silicon cell.

[0081] Example The following embodiments illustrate the preparation method and characterization of the related properties of the product of this application. Unless otherwise specified, all test methods used are conventional methods, and all test materials used in the following embodiments were purchased from conventional reagent stores. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs.

[0082] Example 1 Acid washing procedure: Add 500 g of copper powder to 1 L of sulfuric acid solution (hydrogen ion molar concentration of 1 mol / L), ultrasonically stir the copper powder for 15 min, wash the treated copper powder several times with water until pH neutral, wash twice with ethanol, and dry at 60℃ for 12 h. The copper powder can be flake powder or spherical powder; the D of the flake powder... 50 The particle size is 2 μm and the thickness is 100 nm. The D of the spherical powder 50 The particle size is 150 nm, and the flake powder or spherical powder is acid washed separately.

[0083] Passivation step: Add 1g of citric acid and 1g of octadecylamine to a mixed solution of 3L water and 3L ethanol, stir for 15min, then add the flake powder and ball powder treated in the acid washing step to the above solution, stir magnetically for 30min (the entire reaction is protected under N2 atmosphere), transfer the above solvent to a three-necked flask, keep at 100℃ for 10h, then wash twice with water, ethanol and low-boiling-point petroleum ether respectively, and dry overnight in a vacuum desiccator.

[0084] Example 2 The pickling steps are the same as in Example 1.

[0085] Passivation step: Add 1g of salicylic acid and 1g of tetradecylamine to a mixed solution of 3L water and 3L ethanol, stir for 15min, then add the flake powder and ball powder treated in the acid washing step to the above solution, stir magnetically for 30min (the entire reaction is protected under N2 atmosphere), transfer the above solvent to a three-necked flask, keep at 100℃ for 10h, then wash twice with water, ethanol and low-boiling-point petroleum ether respectively, and dry overnight in a vacuum desiccator.

[0086] Example 3 The pickling steps are the same as in Example 1.

[0087] Passivation step: Add 1g of salicylic acid and 1g of tetradecylamine to a mixed solution of 3L water and 3L ethanol, stir for 15min, then add the flake powder and ball powder treated in the acid washing step to the above solution, stir magnetically for 30min (the entire reaction is protected under N2 atmosphere), transfer the above solvent to a three-necked flask, keep at 60℃ for 10h, then wash twice with water, ethanol and low-boiling-point petroleum ether respectively, and dry overnight in a vacuum desiccator.

[0088] Example 4 The pickling steps are the same as in Example 1.

[0089] Passivation step: Add 1g of salicylic acid and 1g of tetradecylamine to a mixed solution of 3L water and 3L ethanol, stir for 15 min, then add the treated flake powder and ball powder to the above solution, stir magnetically for 30 min (the entire reaction is protected under N2 atmosphere), transfer the above solvent to a three-necked flask, keep at 100℃ for 2 h, then wash twice with water, ethanol and low-boiling-point petroleum ether respectively, and dry overnight in a vacuum desiccator.

[0090] Example 5 In addition to D 50 Replace spherical powder with a particle size of 150 nm with D 50 Apart from the spherical powder with a particle size of 300 nm, the other conditions for the acid washing and passivation steps are the same as in Example 1.

[0091] Comparative Example 1 The pickling steps are the same as in Example 1.

[0092] Passivation step: Add 1g of benzoic acid and 6mL of n-hexylamine to a mixed solution of 3L water and 3L ethanol, stir for 15min, then add the flake powder and spherical powder treated in the acid washing step to the above solution, stir magnetically for 30min (the entire reaction is protected under N2 atmosphere), transfer the above solvent to a three-necked flask, keep at 100℃ for 10h, then wash twice with water, ethanol and low-boiling-point petroleum ether respectively, and dry overnight in a vacuum desiccator.

[0093] Example 6 In this embodiment, an oxygen-nitrogen analyzer was first used to measure the oxygen content of the passivated copper powder obtained in Examples 1-5 and Comparative Example 1 using non-dispersive infrared (NDIR) technology. The measurement results are shown in Tables 1 and 2.

[0094] Then, the oxygen content of the passivated copper powder obtained in Examples 1-5 and Comparative Example 1 after sintering was tested, including the following steps: (1) Weigh an appropriate amount of passivated copper powder (ball powder or flake powder) from Examples 1-5 and Comparative Example 1, put it into a small crucible, and place the small crucible in a sealed muffle furnace.

[0095] (2) Replace the nitrogen in the sealed muffle furnace 6 times, evacuate for one minute each time, and fill with gas to a slightly positive pressure. Be careful to evacuate and fill slowly to avoid blowing the powder away.

[0096] (3) Raise the muffle furnace to 500°C to 600°C, hold for 40 minutes, and then wait for the muffle furnace to cool down naturally.

[0097] (4) After the muffle furnace reaches room temperature, quickly transfer the powder to the glove box and replace the gas three times to avoid oxidation of the powder. At this time, the powder has been sintered into blocks. Transfer the block powder to a sealed centrifuge tube and take it out for later use.

[0098] (5) The blocky powder was pressed into powder, shaken evenly, and then the oxygen content after sintering was measured using an oxygen and nitrogen analyzer and non-dispersive infrared (NDIR) technology. The results are shown in Table 1 and Table 2 below.

[0099] Example 7 90 parts by weight of passivated copper powder obtained in Examples 1-5 and Comparative Example 1, 5 parts by weight of hydrogenated bisphenol A type epoxy resin as resin, 2 parts by weight of blocked isocyanate as curing agent, and 3 parts by weight of diethylene glycol butyl ether solvent are provided; after the above materials are prepared in the above proportions, they are ground into copper paste by a three-roll mill.

[0100] The prepared copper paste was screen-printed into a copper film, then heated and cured in a nitrogen oven at 190°C. The resistivity of the copper film was then tested.

[0101] Resistivity was measured using the four-probe method. Four equally spaced probes were placed on the semiconductor surface. A small current I was supplied to the two outer probes by a constant current source, and the voltage V between the two middle probes was measured to determine the resistivity of the semiconductor. For a thin semiconductor wafer with a thickness of W (much smaller than its length and width), the resistivity was calculated as ρ = ηW(V / I), where η is a correction factor. The relevant measurement results are shown in Tables 1 and 2 below.

[0102] Viscosity testing method: The prepared copper paste was centrifuged at 2000 rpm in a planetary centrifuge to remove air bubbles and allowed to stand for 1 hour. Then, the copper paste was added to the rheometer testing platform, and the shear viscosity at 50 rpm was measured. The rheometer model was Thermo Scientific HAAKE Mars40; temperature 20-25℃, humidity 30-45%. The relevant measurement results are shown in Tables 1 and 2 below.

[0103] Table 1: Relevant Measurement Results of Copper Powder in Spherical Form

[0104] Table 2: Relevant Measurement Results of Copper Powder in Flake Form

[0105] As shown in Table 1, the oxygen content of the sintered copper powder in spherical form is 55-350 ppm, and the Q value (the ratio of oxygen content to specific surface area after sintering) is 15.67-300.75 ppm. g / m 2 In Examples 1-5, the electrodes prepared from this spherical powder exhibited high conductivity and stable resistivity; the results of Examples 1-5 show that the specific surface area of ​​the spherical copper powder is between 0.5 and 4 m². 2 The / g range is beneficial for obtaining metal electrodes with high conductivity and stability. As shown in Table 2, the oxygen content of sintered copper powder in flake form is 15-450 ppm, and / or the Q value is 18.29-529.41 ppm. g / m 2 It can exhibit high conductivity and stable resistivity, thereby obtaining a metal electrode with high conductivity and stable resistivity.

[0106] It should be noted that the terminology used in this application's specification is for the purpose of describing specific embodiments only and is not intended to limit the application. The foregoing summary section and the following detailed description are for illustrative purposes only and are not intended to limit the application in any way. Without departing from the spirit and intent of this application, the scope of this application is defined by the appended claims.

Claims

1. A passivated metal powder, wherein the passivated metal powder has a post-sintering oxygen content of less than 800 ppm, preferably less than 500 ppm, wherein the post-sintering oxygen content refers to the oxygen content of the metal powder after sintering the passivated metal powder in an inert gas atmosphere.

2. The metal powder according to claim 1, wherein, The passivated metal powder has an oxygen content of 800 ppm to 3000 ppm after passivation.

3. The metal powder according to claim 1 or 2, wherein, The passivated metal powder includes metal powder and an organic passivating agent coated on the surface of the metal powder; preferably, the organic passivating agent is selected from one or more of organic amine compounds, organic acid compounds, imidazole compounds, thiazole compounds, and thiol compounds.

4. The metal powder according to any one of claims 1-3, wherein, The passivated metal powder includes flake powder, the flake powder having a D... 50 The particle size is 1 μm - 10 μm, and the median thickness is 100 nm - 500 nm.

5. The metal powder according to any one of claims 1-3, wherein, The passivated metal powder includes flake powder, the specific surface area of ​​which is 0.1-0.9 m². 2 / g.

6. The metal powder according to any one of claims 1-3, wherein, The passivated metal powder includes flake powder, the oxygen content of which is 10 ppm to 450 ppm after sintering.

7. The metal powder according to any one of claims 1-3, wherein, The passivated metal powder includes flake powder, and the ratio of oxygen content to specific surface area after sintering of the flake powder is expressed as Q, and the range of Q is 10 ppm. g / m 2 <Q<550 ppm g / m 2 .

8. The metal powder according to any one of claims 1-3, wherein, The passivated metal powder includes spherical powder, the D of which is... 50 The particle size is 100 nm - 800 nm.

9. The metal powder according to any one of claims 1-3, wherein, The passivated metal powder includes spherical powder with a specific surface area of ​​0.5 m². 2 / g - 8 m 2 / g.

10. The metal powder according to any one of claims 1-3, wherein, The passivated metal powder includes spherical powder, and the oxygen content of the sintered spherical powder is 15 ppm to 400 ppm.

11. The metal powder according to any one of claims 1-3, wherein, The passivated metal powder includes spherical powder, and the ratio of oxygen content to specific surface area of ​​the sintered spherical powder is expressed as Q, and the range of Q is 1 ppm. g / m 2 <Q<350 ppm g / m 2 .

12. The metal powder according to any one of claims 1-11, wherein, The passivated metal powder includes spherical powder and flake powder.

13. The metal powder according to claim 12, wherein, The passivated metal powder consists of spherical powder and flake powder, preferably consisting of 35%-60% flake powder and 40%-65% spherical powder by mass percentage.

14. The metal powder according to any one of claims 1-13, wherein, The passivated metal powder is a powder of at least one of copper, nickel, zinc, and aluminum or an alloy thereof.

15. The metal powder according to any one of claims 1-14, wherein, The passivated metal powder is copper powder.

16. The metal powder according to claim 15, wherein, The copper powder is in flake form, preferably with a particle size of 0.4-0.7 μm. 2 Specific surface area per g.

17. The metal powder according to claim 15, wherein, The copper powder is in the form of spherical powder, preferably, the spherical copper powder has a particle size of 0.5-4.0 μm. 2 Specific surface area per g.

18. A metal conductive paste comprising passivated metal powder and a dispersion medium as described in any one of claims 1-17, preferably comprising 80%-95% passivated metal powder and 5%-20% dispersion medium.

19. The metallic conductive paste according to claim 18, wherein, The dispersion medium includes a resin, a curing agent, a dispersant, a solvent, and an optional curing accelerator.

20. The metallic conductive paste according to claim 19, wherein, The metal powder is copper powder, and the metal conductive paste includes: 80-95 parts by weight of copper powder, 5-15 parts by weight of resin, 5-15 parts by weight of solvent, 1-5 parts by weight of curing agent, and optionally 1-5 parts by weight of curing accelerator.

21. The metallic conductive paste according to any one of claims 18-20, wherein, At 25°C, the shear viscosity of the metal conductive paste at 0-100 rpm is 1-100 Pa·s.

22. A metal electrode prepared from any one of the metal conductive pastes according to claims 18-21.

23. A solar cell comprising the metal electrode of claim 22; said solar cell is selected from BC cells, HJT cells, and perovskite / crystalline silicon tandem cells.

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