A kind of pore plugging silver paste for MWT battery and preparation method thereof

Abstract

The present invention discloses a pore-plugging silver paste for MWT batteries and a preparation method thereof, belonging to the field of battery electrode pastes. The pore-plugging silver paste for MWT batteries comprises the following components by weight: 89%-92% silver powder, 1.2%-3.0% glass powder, 0.3%-2% organic resin, 3%-5% solvent, 0%-2% thixotropic agent, and 0%-2.5% other additives; the silver powder is spherical or quasi-spherical, and the glass powder has a softening point of 680°C or higher. By limiting the silver powder and glass powder, the present invention enables the paste to form uniform and minimal corrosion on the passivation film, ensuring lower leakage current, better welding tensile strength, and higher reliability. Furthermore, by adjusting the rheological properties of the paste, the paste has good fluidity during printing and complete pore plugging, thus solving the problem of poor pore plugging.

Description

Technical Field

[0001] The present invention relates to the field of battery electrode slurry, and in particular to a pore-plugging silver paste for MWT batteries and a preparation method thereof. Background Art

[0002] Metal Wrap Through (MWT) high-efficiency back-contact cells use laser punching and printing of plugging silver paste to conduct the current collected by the front fine grid lines to the back through the silver paste filled in the circular holes. The advantages of MWT cells are: the positive and negative electrode points of the battery are distributed on the back of the cell, the front electrode does not require a main grid line, the shading area can be reduced by 3%, and at the same time, the back wiring technology avoids the performance degradation caused by welding stress and micro cracks. The requirements of MWT cells for plugging paste are: (1) good density and low resistance after sintering; (2) good rheological properties, and the plugging effect is complete and full after printing; (3) the paste is less corrosive, with less corrosion to the passivation film, while ensuring good welding tension.

[0003] The existing plugging silver paste technology used in MWT batteries has problems such as high paste viscosity, poor plugging, and high transmittance. In addition, the corrosiveness and adhesion of the plugging paste cannot be balanced: for pastes with low corrosiveness, the welding tensile strength is poor; while pastes with good welding tensile strength have the problems of high corrosiveness and large leakage current.

[0004] Therefore, developing a silver paste for MWT batteries with complete pore plugging, low corrosion, low leakage current and good welding tensile strength is a current research hotspot. Summary of the Invention

[0005] The purpose of the present invention is to overcome the shortcomings of the prior art and provide a silver paste for MWT batteries with complete pore plugging, low corrosiveness, low leakage current and good welding tension, and a preparation method thereof.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is: a pore-plugging silver paste for MWT batteries, comprising the following components in weight percentage: 89%-92% silver powder, 1.2%-3.0% glass powder, 0.3%-2% organic resin, 3%-5% solvent, 0-2% thixotropic agent, and 0-2.5% other additives; the silver powder is spherical silver powder and quasi-spherical silver powder, and the softening point of the glass powder is ≥680°C.

[0007] The silver powder of the present invention is spherical silver powder and quasi-spherical silver powder. This is because the spherical silver powder has a smooth surface, large particles, and a good bulk density, but the activity of the spherical silver powder is relatively low, while the quasi-spherical silver powder has an uneven surface but a large surface energy and a high activity. Therefore, the present invention adopts a mixture of the two types of silver powder, which can retain a certain sintering activity of the silver powder and make the silver powder have a better bulk density, thereby making the resistance of the silver powder smaller and reducing the corrosion of the slurry to the passivation film.

[0008] The inventor unexpectedly discovered that the use of glass powder with a softening point ≥ 680° C. in the present invention can improve the welding tensile strength of the final slurry, increase reliability, and reduce corrosion to the passivation film.

[0009] Preferably, the weight percentage of spherical silver powder in the silver powder is 10%-80%. The inventors have found through experiments that when the weight percentage of spherical silver powder in the silver powder is within this range, the resistance of the obtained silver powder can be smaller, so that after the final plugging silver paste is printed into the gate line, the resistance value at both ends of the gate line is smaller.

[0010] More preferably, the weight percentage of spherical silver powder in the silver powder is 30%-60%. The inventors have found through experiments that the weight percentage of spherical silver powder in the silver powder within this range can minimize the resistance of the obtained silver powder, thereby minimizing the resistance value at both ends of the gate line after the final plugging silver paste is printed into the gate line.

[0011] Preferably, the median diameter D of the silver powder is 50 0.8-3.5um.

[0012] More preferably, the median diameter D of the spherical silver powder in the silver powder is 50 The median diameter D of the spherical silver powder is 2.0-3.5um. 50 0.8-2.5um.

[0013] Preferably, the spherical silver powder is prepared by a physical spray method, and the quasi-spherical silver powder is prepared by a chemical redox method; the chemical redox method is to use a reducing agent to reduce silver ions or silver complex ion solutions into silver atoms in an aqueous solution or an organic system, and to deposit and grow silver particles. This method can obtain silver particles with different properties by selecting a solvent system, a reducing agent and a protective agent, and can prepare smaller silver particles with a richer surface structure and greater activity; the physical spray method is to use a medium to atomize molten silver. According to the different atomizing media, it can be divided into high-pressure gas atomization method, high-pressure water atomization method, ultrasonic atomization method, rotating disk atomization method, electrodynamic atomization method, etc. The silver powder obtained by this method has a smooth surface, low activity and slightly larger particles; by combining the two silver powders, a certain sintering activity of the silver powder can be retained, and the silver powder can have a better bulk density, lower resistance and lower corrosion performance.

[0014] Preferably, the glass powder comprises the following components in parts by weight: 13-18 parts of PbO, 28-35 parts of SiO2, 18-25 parts of Bi2O3, and 10-15 parts of B2O3.

[0015] More preferably, the glass powder further comprises 2-12 parts by weight of at least one of ZnO, ZrO, and Li2O.

[0016] More preferably, the glass powder is prepared by air flow milling. The present invention adopts air flow milling to prepare glass powder. Air flow milling can make the glass powder particles more uniform, thereby making the glass powder contact sites more uniform, and can make the slurry form uniform and small corrosion on the passivation film, ensuring that the leakage current of the slurry is lower; therefore, using glass powder with a softening point ≥680°C and preparing glass powder by air flow milling can balance the problems of excessive slurry corrosion and poor welding tensile strength.

[0017] Most preferably, the preparation steps of the glass powder are: mixing various raw materials and then melting them to obtain glass blocks, and using compressed gas to make the glass blocks repeatedly impact, collide and crush in a certain space to obtain the glass powder.

[0018] More preferably, the median diameter D of the glass powder 50 0.8-3.0μm.

[0019] Preferably, the organic resin includes at least one of EC (ethyl cellulose), acrylic resin, epoxy resin, CA (cellulose acetate), and PVB (polyvinyl butyral).

[0020] More preferably, the organic resin comprises the following components in weight percentage: EC 30%-60%, CA 40%-70%; using this weight percentage of EC and CA to adjust the rheological properties of the slurry can make the pore plugging of the slurry more complete.

[0021] Preferably, the solvent comprises at least one of alcohol ester lauryl, terpineol, butyl carbitol, butyl carbitol acetate, acetyl tributyl citrate, propylene glycol phenyl ether, and diethylene glycol methyl ether.

[0022] Preferably, the thixotropic agent comprises at least one of fumed silica, hydrogenated castor oil, and polyamide wax.

[0023] More preferably, the thixotropic agent is polyamide wax, which can make the slurry reach a higher thixotropic index when used in a smaller amount. The higher thixotropic index can make the slurry have good fluidity during printing, completely plug the holes without leaking the slurry, and solve the problem of poor plugging.

[0024] Preferably, the other additive is a bismuth-tin alloy. In the present invention, the bismuth-tin alloy is added to the slurry to improve the welding performance of the slurry, including soldering ability and solder resistance.

[0025] More preferably, the mass ratio of bismuth to tin in the bismuth-tin alloy is Sn:Bi=42:58.

[0026] More preferably, the bismuth-tin alloy has a particle size of 300 mesh and a melting point of 130-140°C.

[0027] The present invention also provides a preparation method of the pore-plugging silver paste for MWT batteries, comprising the following steps: mixing and stirring the components of the pore-plugging silver paste until there is no dry powder, grinding and dispersing them uniformly, and then obtaining the pore-plugging silver paste for MWT batteries.

[0028] The beneficial effects of the present invention are as follows: the present invention provides a pore-plugging silver paste for an MWT battery, which adopts a mixture of spherical silver powder and quasi-spherical silver powder to make the silver powder have higher activity while ensuring a larger bulk density, thereby reducing the resistance of the silver powder and making the slurry less corrosive to the battery passivation film; the present invention adopts glass powder with a softening point of ≥680°C and adopts a jet mill method to prepare the glass powder, which can make the slurry form uniform and small corrosion on the passivation film, thereby ensuring a lower leakage current of the slurry, and at the same time, can also make the welding tensile force of the slurry better and the reliability higher, thereby balancing the problem of excessive corrosion of the slurry and poor welding tensile force; the rheological properties of the slurry are adjusted by adding ethyl cellulose in combination with cellulose acetate, and the thixotropic index of the slurry is increased by adding polyamide wax, so that the slurry has good fluidity during printing, the pores are completely plugged without leakage, and the problem of poor pore plugging of the slurry is solved. DETAILED DESCRIPTION

[0029] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments.

[0030] Example 1

[0031] An embodiment of the pore-plugging silver paste for MWT batteries according to the present invention, the formula of the glass powder in this embodiment is shown in Table 1, and the formula of the pore-plugging silver paste for MWT batteries is shown in Table 2.

[0032] In Example 1, the glass powder is prepared by the following method: (1) weighing various raw materials and mixing them uniformly; placing the mixed materials in a crucible and melting them in a high-temperature muffle furnace at a melting temperature of 1000°C; (2) quenching the melt with water and cooling it into a glass block; (3) using compressed gas to repeatedly impact and collide the glass block in a certain space to crush it to a median diameter D of the glass powder. 50 When the particle size is 0.8-3.0 μm, the glass powder is obtained.

[0033] In Example 1, the preparation method of the pore-plugging silver paste for MWT batteries is as follows: the ingredients are prepared in weight percentage according to the formula in Table 2, the components are mixed, and then pre-mixed with a rapid dispersing device. After stirring until there is no dry powder, the mixture is ground with a three-roll grinder to obtain the pore-plugging silver paste for MWT batteries.

[0034] The mass percentage of the spherical silver powder in the silver powder is 10%, and the mass percentage of the quasi-spherical silver powder is 90%.

[0035] Example 2

[0036] The formula of the glass powder described in this embodiment is shown in Table 1, and the formula of the pore-plugging silver paste for the MWT battery is shown in Table 2.

[0037] The preparation method of the glass powder is the same as that of Example 1, and the preparation method of the pore-plugging silver paste for MWT batteries is the same as that of Example 1.

[0038] The mass percentage of the spherical silver powder in the silver powder is 80%, and the mass percentage of the quasi-spherical silver powder is 20%.

[0039] Example 3

[0040] The formula of the glass powder described in this embodiment is shown in Table 1, and the formula of the pore-plugging silver paste for the MWT battery is shown in Table 2.

[0041] The preparation method of the glass powder is the same as that of Example 1, and the preparation method of the pore-plugging silver paste for MWT batteries is the same as that of Example 1.

[0042] The mass percentage of the spherical silver powder in the silver powder is 30%, and the mass percentage of the quasi-spherical silver powder is 70%.

[0043] Example 4

[0044] The formula of the glass powder described in this embodiment is shown in Table 1, and the formula of the pore-plugging silver paste for the MWT battery is shown in Table 2.

[0045] The preparation method of the glass powder is the same as that of Example 1, and the preparation method of the pore-plugging silver paste for MWT batteries is the same as that of Example 1.

[0046] The mass percentage of the spherical silver powder in the silver powder is 60%, and the mass percentage of the quasi-spherical silver powder is 40%.

[0047] Table 1

[0048]

[0049]

[0050] Table 2

[0051]

[0052] Comparative Example 1

[0053] A comparative example of the pore-plugging silver paste for MWT batteries according to the present invention is provided. The difference between this comparative example and Example 1 is that all the silver powders are prepared by a chemical oxidation-reduction method, i.e., all are spherical silver powders. The formula of the glass powder and the formula of the pore-plugging silver paste for MWT batteries in this comparative example are the same as those in Example 1.

[0054] The preparation method of the glass powder in this comparative example is the same as that in Example 1, and the preparation method of the pore-plugging silver paste for MWT batteries is the same as that in Example 1.

[0055] Comparative Example 2

[0056] The only difference between this comparative example and Example 1 is that all the silver powders are prepared by physical spraying, that is, all are spherical silver powders. The formula of the glass powder and the formula of the pore-plugging silver paste for MWT batteries in this comparative example are the same as those in Example 1.

[0057] The preparation method of the glass powder in this comparative example is the same as that in Example 1, and the preparation method of the pore-plugging silver paste for MWT batteries is the same as that in Example 1.

[0058] Comparative Example 3

[0059] The only difference between this comparative example and Example 1 is that the glass powder is prepared by water grinding. The specific preparation steps of the glass powder are as follows: the ingredients are prepared according to the glass formula (weight percentage) in Table 1, (1) the various raw materials are weighed and mixed evenly, and the mixed materials are placed in a crucible and placed in a high-temperature muffle furnace for melting at a melting temperature of 1000°C; (2) the melt is quenched with water and cooled into a glass block; (3) zirconium beads and the melted glass block are added to water, and the large glass particles are collided into small particles with a particle size of 0.6-1.5 μm by collision between the grinding balls and the glass, thereby obtaining the glass powder.

[0060] The formula of the glass powder and the formula of the pore-plugging silver paste for MWT batteries in this comparative example are the same as those in Example 1. The preparation method of the pore-plugging silver paste for MWT batteries in this comparative example is the same as that in Example 1.

[0061] Effect Examples

[0062] The plugging silver pastes of Examples 1-4 and Comparative Examples 1-3 were respectively made into MWT batteries, and the leakage current of the batteries was tested using an IV tester. The plugging silver pastes of Examples 1-4 and Comparative Examples 1-3 were printed into a section of gate lines, and the resistance between the ends of the gate lines was tested using a multimeter. The gate line screen printing parameters were: length 10 mm, width 1 mm, film thickness 32 μm, and printing thickness ≤12 μm. The test results are shown in Table 3.

[0063] Table 3

[0064]

[0065]

[0066] The results are shown in Table 3. In Comparative Example 1, the silver powder is prepared only by the chemical oxidation-reduction method, and the silver powder is more active, resulting in a larger leakage current of the final plugging silver paste. In Comparative Example 2, the silver powder is prepared only by the physical spray method, resulting in a larger resistance value between the head and tail of the gate line after the final plugging silver paste is printed into the gate line. In Examples 1-4, since the silver powder is prepared by a mixture of the chemical oxidation-reduction method and the physical spray method, it can be ensured that the leakage current of the plugging silver paste is small, and the resistance value after printing into the gate line is small. In Comparative Example 3, the glass powder is prepared by the water grinding method, resulting in a larger leakage current of the final slurry. In addition, in Example 4, since bismuth-tin alloy is not added, the solderability of the final slurry is poor, and the welding tension is 0.5N lower than that of Examples 1-4.

[0067] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A silver paste for plugging holes in MWT batteries, characterized in that: The invention comprises the following components in weight percentage: 89%-92% silver powder, 1.2%-3.0% glass powder, 0.3%-2% organic resin, 3%-5% solvent, 0-2% thixotropic agent, and 0-2.5% other additives; the silver powder is spherical silver powder or quasi-spherical silver powder, and the softening point of the glass powder is ≥680°C; The median diameter D of the silver powder 50 0.8-3.5 μm; wherein the spherical silver powder is prepared by physical spraying method, and the median diameter D 50 The spherical silver powder is prepared by chemical oxidation-reduction method, and the median diameter D 50 0.8-2.5μm; The weight percentage of spherical silver powder in the silver powder is 30%-60%; the glass powder is prepared by air jet milling; The organic resin consists of ethyl cellulose and cellulose acetate, the mass percentage of the ethyl cellulose is 30%-60%, and the mass percentage of the cellulose acetate is 40%-70%. The thixotropic agent is polyamide wax.

2. The pore-plugging silver paste for MWT batteries according to claim 1, wherein: The glass powder contains the following components in weight percentage: the glass powder contains the following components in weight: 13-18 parts of PbO, 28-35 parts of SiO2, 18-25 parts of Bi2O3, and 10-15 parts of B2O3.

3. The pore-plugging silver paste for MWT batteries according to claim 2, wherein: The glass powder further comprises 2-12 parts by weight of at least one of ZnO, ZrO, and Li2O.

4. The pore-plugging silver paste for MWT batteries according to claim 1, wherein: The preparation steps of the glass powder are as follows: mixing various raw materials and then melting them to obtain glass blocks, and using compressed gas to make the glass blocks repeatedly impact, collide and crush in space to obtain the glass powder.

5. The pore-plugging silver paste for MWT batteries according to claim 1, wherein: The other auxiliary agent is bismuth-tin alloy.

6. The method for preparing the pore-plugging silver paste for MWT batteries according to any one of claims 1 to 5, characterized in that: The method comprises the following steps: mixing and stirring the components of the pore-plugging silver paste until there is no dry powder, grinding and dispersing the components uniformly, and thus obtaining the pore-plugging silver paste for the MWT battery.

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