Method for manufacturing a battery cell and battery cell

Abstract

The application discloses a battery piece manufacturing method and a battery piece. The battery piece manufacturing method comprises the following steps: rough polishing and fine polishing are sequentially performed on the edges of a silicon piece to obtain a polished silicon piece; the polishing liquid used in the fine polishing contains polishing wax; the polished silicon piece is annealed and cooled to obtain an annealed silicon piece; the annealed silicon piece is subjected to primary plasma cleaning to obtain a primary cleaned silicon piece; an AlO thin film is generated in situ on the surface of the primary cleaned silicon piece to obtain a passivated silicon piece; a battery thin film is deposited on the surface of the passivated silicon piece to obtain a gridless battery piece; a grid line is formed on the surface of the gridless battery piece to obtain a battery piece to be cleaned; and secondary plasma cleaning is performed on the battery piece to be cleaned to obtain the battery piece. The battery piece manufacturing method is more conducive to improving the mechanical properties of the silicon piece due to polishing and annealing, so that the mechanical properties and the qualified rate of the battery piece prepared by the manufacturing method are improved.

Description

Technical Field

[0001] This invention relates to the field of battery cell technology, and more specifically, to a method for manufacturing battery cells and battery cells themselves. Background Technology

[0002] During the manufacturing process of monocrystalline silicon heterojunction solar cells, a small amount of silver paste overflow occurs during the silver paste printing process, forming an organic contaminant layer. This organic contaminant layer significantly reduces the photoelectric conversion efficiency of the heterojunction cell. However, due to the difficulty in removing organic contaminants, coupled with the low mechanical strength and high fragility of monocrystalline silicon heterojunction cells, the removal process easily damages the cells, resulting in a low yield of finished cells. Therefore, it is crucial to find a way to effectively remove the organic contaminant layer while simultaneously improving the yield of finished cells.

[0003] In view of this, the present invention is proposed. Summary of the Invention

[0004] The purpose of this invention is to provide a method for manufacturing battery cells and battery cells that improve the strength of battery cells.

[0005] This invention is implemented as follows:

[0006] In a first aspect, the present invention provides a method for manufacturing a battery cell, comprising:

[0007] Polishing involves sequentially coarse and fine polishing the edges of the silicon wafer to obtain a polished silicon wafer; the polishing solution used for fine polishing contains polishing wax.

[0008] Annealing involves annealing and cooling the polished silicon wafer to obtain an annealed silicon wafer.

[0009] A single plasma cleaning process is performed on the annealed silicon wafer to obtain a single-cleaned silicon wafer.

[0010] Al2O3 passivation: An Al2O3 film is generated in situ on the surface of the silicon wafer after the first cleaning to obtain a passivated silicon wafer;

[0011] A grid-free solar cell is formed by depositing a thin film on the passivated silicon wafer surface.

[0012] A grid line is formed on the surface of the grid-free solar cell to obtain a solar cell to be cleaned.

[0013] Secondary plasma cleaning: The battery cell to be cleaned is subjected to secondary plasma cleaning to obtain the battery cell.

[0014] In an optional embodiment, the polishing process is performed using a wool felt mechanical polishing machine;

[0015] And / or, the edge roughness of the silicon wafer after rough polishing is ≤0.05um, and the edge roughness of the silicon wafer after fine polishing is ≤0.025um.

[0016] In an optional embodiment, the polishing liquid used for rough polishing includes 90.5-91.5 parts by weight of 5500-6500 grit diamond polishing paste, 4.5-5.5 parts by weight of deionized water, and 3.5-4.5 parts by weight of anhydrous ethanol.

[0017] And / or, the polishing liquid used for fine polishing includes 93.5-94.5 parts by weight of 9000-11000 grit diamond polishing paste, 2.5-3.5 parts by weight of deionized water, 1.5-2.5 parts by weight of anhydrous ethanol and 1.8-2.2 parts by weight of polishing wax.

[0018] In an optional embodiment, the annealing step is performed at a temperature of 295-305°C for 18-22 minutes and a vacuum degree of ≤1×10-3Pa.

[0019] In an optional implementation, the cooling rate of the cooling step is ≤5℃ / min, and nitrogen gas is introduced at a flow rate of 45-55 sccm during the cooling process.

[0020] In an optional embodiment, in the first plasma cleaning step, the process gas is oxygen, the oxygen flow rate is 30-50 sccm, the temperature is 25℃~28℃, the vacuum degree is 50-100Pa, the plasma power is 90-110W, and the cleaning time is 45-55s.

[0021] And / or, the water droplet angle on the surface of the battery cell during the first cleaning is 5° to 15°;

[0022] And / or, in the secondary plasma cleaning step, the process gas is nitrogen or argon, the process gas flow rate is 30-150 sccm, the temperature is 25℃~28℃, the vacuum degree is 50-100Pa, the plasma power is 50-150W, and the cleaning time is 45-120s.

[0023] In an optional embodiment, the thickness of the Al2O3 film is 0.5 nm to 2 nm;

[0024] And / or, the Al2O3 thin film is formed by atomic layer deposition;

[0025] And / or, the Vickers hardness of the Al2O3 film is 15-25 GPa.

[0026] In an optional embodiment, the parameters for the atomic layer deposition include: deposition temperature of 120°C to 200°C and pressure of 180 Pa to 230 Pa.

[0027] Secondly, the present invention provides a battery cell manufactured by the method described in any one of the foregoing embodiments.

[0028] In an optional embodiment, the solar cell includes a silicon wafer and an Al2O3 film disposed on the surface of the silicon wafer, wherein hydroxyl and carboxyl groups are present between the silicon wafer and the Al2O3 film.

[0029] The present invention has the following beneficial effects:

[0030] The method for manufacturing solar cells in this application uses polishing wax in the polishing step, which, combined with the annealing step, is more conducive to improving the mechanical properties of the silicon wafer. As a result, the mechanical properties and yield of the solar cells prepared by this method are improved. Attached Figure Description

[0031] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is an image of the edge of the silicon wafer before polishing in Example 1;

[0033] Figure 2 This is an image of the edge of the polished silicon wafer in Example 1;

[0034] Figure 3 This is an image of the silicon wafer to be cleaned in Example 1;

[0035] Figure 4 This is a picture of the battery cell in Example 1. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0037] During the manufacturing process of monocrystalline silicon heterojunction solar cells, a small amount of silver paste overflows during printing and forms an organic layer, leading to a decrease in cell efficiency. Therefore, it is necessary to clean the overflowed silver paste. Simultaneously, the applicant discovered that microcracks exist at the edges of the silicon wafer after cutting, which is a significant cause of reduced mechanical strength. This reduced mechanical strength makes the cells more susceptible to damage during the cleaning of overflowing silver paste, further reducing the yield of finished cells. To address this issue, this application proposes the following solution:

[0038] This application provides a method for manufacturing a battery cell, including:

[0039] Polishing involves sequentially coarse and fine polishing the edges of the silicon wafer to obtain a polished silicon wafer. The fine polishing process uses a polishing slurry containing polishing wax for annealing and cooling, resulting in an annealed silicon wafer.

[0040] A single plasma cleaning process is performed on the annealed silicon wafer to obtain a single-cleaned silicon wafer.

[0041] Al2O3 passivation: An Al2O3 film is generated in situ on the surface of the silicon wafer after the first cleaning to obtain a passivated silicon wafer;

[0042] A grid-free solar cell is formed by depositing a thin film on the passivated silicon wafer surface.

[0043] A grid line is formed on the surface of the grid-free solar cell to obtain a solar cell to be cleaned.

[0044] Secondary plasma cleaning: The battery cell to be cleaned is subjected to secondary plasma cleaning to obtain the battery cell.

[0045] In this application, the polishing process is carried out under the condition of polishing liquid containing polishing wax. On the one hand, polishing wax can reduce scratches on the silicon wafer surface and improve smoothness. On the other hand, it can form a polishing wax protective film on the battery surface. During the subsequent annealing process, the presence of the polishing wax protective film can effectively remove the internal stress generated during the silicon wafer polishing process, thereby helping to improve the strength of the silicon wafer to be cleaned and further improve the yield of the battery cells.

[0046] To prevent the presence of polishing wax protective film from affecting the formation of passivation film, the annealed silicon wafer is subjected to a plasma cleaning before nitrogen passivation to remove polishing wax and other organic matter.

[0047] After the grid lines are formed, a second plasma cleaning is performed to remove the overflow silver paste from the grid line formation process, thereby improving the efficiency of the solar cell.

[0048] The method for manufacturing solar cells in this application uses polishing wax in the polishing step, which, combined with the annealing step, is more conducive to improving the mechanical properties of the silicon wafer. As a result, the mechanical properties and yield of the solar cells prepared by this method are improved.

[0049] In an optional embodiment, the polishing process is performed using a wool felt mechanical polishing machine;

[0050] And / or, the edge roughness of the silicon wafer after rough polishing is ≤0.05um, and the edge roughness of the silicon wafer after fine polishing is ≤0.025um.

[0051] The edges of the silicon wafers are first rough polished and then fine polished. Rough polishing helps improve efficiency, while fine polishing helps reduce defects on the polished surface. The combination of the two helps to balance efficiency and effectiveness.

[0052] In an optional embodiment, the polishing liquid used for rough polishing includes 90.5-91.5 parts by weight of 5500-6500 grit diamond polishing paste, 4.5-5.5 parts by weight of deionized water, and 3.5-4.5 parts by weight of anhydrous ethanol.

[0053] And / or, the polishing liquid used for fine polishing includes 93.5-94.5 parts by weight of 9000-11000 grit diamond polishing paste, 2.5-3.5 parts by weight of deionized water, 1.5-2.5 parts by weight of anhydrous ethanol and 1.8-2.2 parts by weight of polishing wax.

[0054] During polishing, diamond polishing paste provides efficient cutting force, while deionized water and ethanol adjust the viscosity of the polishing slurry and aid in heat dissipation. Meanwhile, in fine polishing, the polishing slurry contains polishing wax. Compared to directly applying polishing wax to the edge of the silicon wafer after polishing to form a protective layer, forming a protective layer during polishing allows the polishing paste to penetrate the shallow surface of the polished area more effectively. Furthermore, during annealing, this process is more conducive to mitigating the internal stress of the silicon wafer.

[0055] It should be noted that the polishing wax in this application may be beeswax, paraffin wax or carnauba wax.

[0056] In an optional embodiment, the annealing step is performed at a temperature of 295-305°C for 18-22 minutes and a vacuum degree of ≤1×10-3Pa.

[0057] In an optional implementation, the cooling rate of the cooling step is ≤5℃ / min, and nitrogen gas is introduced at a flow rate of 45-55 sccm during the cooling process.

[0058] In this application, annealing is performed at a relatively low temperature, and the cooling rate after annealing should not be too high to facilitate the full release of internal stress. Typically, the cooling step only needs to cool the silicon wafer to room temperature.

[0059] In an optional embodiment, in the first plasma cleaning step, the process gas is oxygen, the oxygen flow rate is 30-50 sccm, the temperature is 25℃~28℃, the vacuum degree is 50-100Pa, the plasma power is 90-110W, and the cleaning time is 45-55s. The process gas in the first plasma cleaning step is oxygen, which can remove organic matter and weakly bonded oxides from the silicon wafer surface. On the other hand, the oxidation effect of oxygen can form polar oxygen-containing groups, such as -OH and -COOH, on the silicon wafer surface, which can increase the hydrophilicity of the silicon wafer surface. This reduces the water droplet angle on the silicon wafer surface from 50°~80° to 5°~15°. Al2O3 film has strong hydrophilicity, and the increased hydrophilicity of the silicon wafer surface after the first cleaning is conducive to more complete contact between the silicon wafer and the Al2O3 film.

[0060] In an optional embodiment, in the secondary plasma cleaning step, the process gas is nitrogen or argon, the process gas flow rate is 30-150 sccm, the temperature is 25℃~28℃, the vacuum degree is 50-100Pa, the plasma power is 50-150W, and the cleaning time is 45-120s.

[0061] In the secondary plasma cleaning step, a moderate process gas flow rate helps ensure uniformity, room temperature prevents thermal damage to the silicon wafer, and a moderate vacuum level combined with power helps adjust the etching rate to a suitable range. The combination of process gas and parameters helps avoid over-cleaning of the silicon wafer.

[0062] In an optional embodiment, the thickness of the Al2O3 film is 0.5 nm to 2 nm;

[0063] And / or, Al2O3 films formed by atomic layer deposition (ALD) are denser, growing layer by layer in the form of atomic arrangement to form high-density films, with fewer defects such as pinholes and grain boundaries compared to Al2O3 films formed by CVD.

[0064] And / or, the Vickers hardness of the Al2O3 film is 15-25 GPa.

[0065] In an optional embodiment, the parameters for the atomic layer deposition include: deposition temperature of 120°C to 200°C and pressure of 180 Pa to 230 Pa.

[0066] This application also provides a battery cell, which is manufactured by the method described in any of the foregoing embodiments.

[0067] In an optional embodiment, the battery cell includes a silicon wafer and an Al2O3 film disposed on the surface of the silicon wafer, wherein hydroxyl and carboxyl groups are present between the silicon wafer and the Al2O3 film.

[0068] The -OH and -COOH groups on the surface of the silicon wafer during the first cleaning process can form covalent bonds with oxygen ions in the Al2O3 film preparation process, further enhancing the bonding force between Al2O3 and the surface of the silicon wafer during the first cleaning process, which in turn helps to improve the mechanical properties and efficiency of the silicon wafer.

[0069] The features and performance of the present invention will be further described in detail below with reference to embodiments.

[0070] Example 1

[0071] This embodiment provides a method for manufacturing a battery cell, including the following steps:

[0072] Polishing involves using a wool felt mechanical polisher to coarsely and finely polish the edges of the silicon wafer to be processed, resulting in a polished silicon wafer. An image of the wafer edge before polishing is shown below. Figure 1 As shown, the silicon wafer edges were not smooth and had high roughness before polishing. Mechanical strength data included a maximum force of 11.3 N, a maximum deformation of 24.77 mm, and a maximum bending strength of 244.18 MPa. Images of the silicon wafer edges after polishing are shown below. Figure 2 As shown, the edges of the polished silicon wafer are smooth, and the mechanical strength data include a maximum force of 11.4 N, a maximum deformation of 24.85 mm, and a maximum bending strength of 268.15 MPa. The polishing slurry used for rough polishing consists of 91 parts by weight of 6000-grit diamond polishing paste, 5 parts by weight of deionized water, and 4 parts by weight of anhydrous ethanol. The polishing slurry used for fine polishing consists of 94 parts by weight of 10000-grit diamond polishing paste, 3 parts by weight of deionized water, 2 parts by weight of anhydrous ethanol, and 2 parts by weight of polishing wax. The edge roughness Ra of the silicon wafer after rough polishing is 0.05 μm, and the edge roughness Ra of the polished silicon wafer is 0.025 μm.

[0073] Annealing: The solar cell is placed in a vacuum annealing furnace to anneal and cool the polished silicon wafer to obtain an annealed silicon wafer. The annealing temperature is 300℃±2℃, the time is 20min, and the vacuum degree is ≤1×10-3Pa. The cooling rate is 3℃ / min. Nitrogen gas is introduced at a flow rate of 50sccm during the cooling process until it is cooled to room temperature.

[0074] In a single plasma cleaning process, the solar cell is placed on the heated stage of a vacuum plasma cleaner to uniformly expose its surface. The heated stage is then purged with oxygen for plasma cleaning. This process is repeated to obtain a cleaned silicon wafer. The water droplet angle on the surface of the cleaned silicon wafer is 10°. The process gas is oxygen, with a flow rate of 40 sccm, a temperature of 27°C, a vacuum degree of 80 Pa, a plasma power of 100 W, and a cleaning time of 50 s.

[0075] Al2O3 passivation is achieved by in-situ generation of a 15nm thick Al2O3 film on the surface of a cleaned silicon wafer using atomic layer deposition, resulting in a passivated silicon wafer. The parameters for atomic layer deposition include: process temperature 180℃; process vacuum pressure 150Pa.

[0076] A grid-free solar cell is formed by depositing a thin film on the passivated silicon wafer surface.

[0077] Printed grid lines are formed on the surface of the gridless solar cell to obtain the solar cell to be cleaned. Figure 3 As shown, a small amount of silver paste overflows from the edge of the grid line;

[0078] A secondary plasma cleaning process is performed on the battery cells to be cleaned, resulting in the battery cells, as shown below. Figure 4 As shown, the overflowing silver paste was removed; the process gas was nitrogen or argon, the process gas flow rate was 120 sccm, the temperature was 28℃, the vacuum degree was 100Pa, the plasma power was 150W, and the cleaning time was 100s.

[0079] Example 2

[0080] This embodiment provides a method for manufacturing a battery cell. The main difference from Comparative Example 1 is that the weight percentage of polishing wax in the polishing liquid used for fine polishing is increased to 2.5.

[0081] Example 3

[0082] This embodiment provides a method for manufacturing a battery cell. The main difference from Comparative Example 1 is that the weight percentage of polishing wax in the polishing liquid used for fine polishing is reduced to 1.7.

[0083] Example 4

[0084] This embodiment provides a method for manufacturing a battery cell. The main difference from Comparative Example 1 is that the process gas in the first plasma cleaning step is replaced with argon.

[0085] Example 5

[0086] This embodiment provides a method for manufacturing a battery cell. The main difference from Embodiment 1 is that the annealing step parameters are unreasonable. Specifically, the annealing temperature is 295°C, the time is 20 min, and the vacuum degree is ≤1×10-3 Pa.

[0087] Comparative Example 1

[0088] This comparative example provides a method for manufacturing a battery cell. The main difference from Example 1 is that polishing wax is not added to the polishing liquid used for fine polishing, while the proportions of other components remain unchanged.

[0089] Comparative Example 2

[0090] This comparative example provides a method for manufacturing a solar cell. The main difference from Comparative Example 1 is that a plasma cleaning step is omitted, and the annealed silicon wafer is passivated with Al2O3.

[0091] Comparative Example 3

[0092] This comparative example provides a method for manufacturing a battery cell, the main difference from Example 1 being that the passivation film is replaced with Si3N4.

[0093] Comparative Example 4

[0094] This comparative example provides a method for manufacturing a solar cell, which differs from Example 1 mainly in that: polishing, annealing, and a first plasma cleaning are omitted, and Al2O3 passivation is directly applied to the silicon wafer to be treated.

[0095] The mechanical properties of the cleaned silicon wafers and the yield rate of the fabricated solar cells in the above embodiments and comparative examples were tested using the following methods:

[0096] Three-point testing was performed on silicon wafers or solar cells. The silicon wafer was placed parallel to two parallel support rods, with the center of the silicon wafer along its length located at the center of the two parallel rods. The pressure knife was positioned directly above the center of the two parallel rods and automatically pressed down to apply external force to the solar cell. The test results are shown in Table 1. The number of samples tested at the three points was 80, and the average value of the results was taken.

[0097] Table 1

[0098]

[0099]

[0100] Note: When calculating the pass rate in the table, the pass standard is:

[0101] 1. The battery cells have no color difference, no hidden cracks, and no obvious scratches on the edges;

[0102] 2. Maximum force ≥11.9N, maximum bending strength ≥25mm, maximum bending strength ≥240MPa.

[0103] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for manufacturing a battery cell, characterized in that, include: Polishing involves sequentially performing coarse and fine polishing on the edges of the silicon wafer to obtain a polished silicon wafer. The polishing solution used in fine polishing contains polishing wax, which forms a protective polishing wax film on the battery surface; Annealing involves annealing and cooling a polished silicon wafer with a protective polishing wax film to obtain an annealed silicon wafer. A single plasma cleaning process is performed on the annealed silicon wafer to obtain a single-cleaned silicon wafer. Al2O3 passivation: An Al2O3 film is generated in situ on the surface of the silicon wafer after the first cleaning to obtain a passivated silicon wafer; A grid-free solar cell is formed by depositing a thin film on the surface of the passivated silicon wafer. A grid line is formed on the surface of the grid-free solar cell to obtain a solar cell to be cleaned. Secondary plasma cleaning: The battery cell to be cleaned is subjected to secondary plasma cleaning to obtain the battery cell.

2. The method for manufacturing a battery cell according to claim 1, characterized in that, The polishing was performed using a wool felt mechanical polishing machine; And / or, the edge roughness of the silicon wafer after rough polishing is ≤0.05um, and the edge roughness of the silicon wafer after fine polishing is ≤0.025um.

3. The method for manufacturing a battery cell according to claim 2, characterized in that, The polishing solution used for rough polishing includes 90.5-91.5 parts by weight of 5500-6500 grit diamond polishing paste, 4.5-5.5 parts by weight of deionized water, and 3.5-4.5 parts by weight of anhydrous ethanol. And / or, the polishing liquid used for fine polishing includes 93.5-94.5 parts by weight of 9000-11000 grit diamond polishing paste, 2.5-3.5 parts by weight of deionized water, 1.5-2.5 parts by weight of anhydrous ethanol and 1.8-2.2 parts by weight of polishing wax.

4. The method for manufacturing a battery cell according to claim 1, characterized in that, The annealing process involves a temperature of 295-305℃, a time of 18-22 minutes, and a vacuum degree ≤1×10⁻⁶. - ³Pa.

5. The method for manufacturing a battery cell according to claim 1, characterized in that, The cooling rate is ≤5℃ / min, and nitrogen gas is introduced at a flow rate of 45-55 sccm during the cooling process.

6. The method for manufacturing a battery cell according to claim 1, characterized in that, In the first plasma cleaning step, the process gas is oxygen, the oxygen flow rate is 30-50 sccm, the temperature is 25℃~28℃, the vacuum degree is 50-100Pa, the plasma power is 90-110W, and the cleaning time is 45-55s. And / or, the water droplet angle on the surface of the battery cell during the first cleaning is 5°~15°; And / or, in the secondary plasma cleaning step, the process gas is nitrogen or argon, the process gas flow rate is 30-150 sccm, the temperature is 25℃~28℃, the vacuum degree is 50-100Pa, the plasma power is 50-150W, and the cleaning time is 45-120s.

7. The method for manufacturing a battery cell according to claim 1, characterized in that, The thickness of the Al2O3 film is 0.5nm-2nm; And / or, the Al2O3 thin film is formed by atomic layer deposition; And / or, the Vickers hardness of the Al2O3 film is 15-25 GPa.

8. The method for manufacturing a battery cell according to claim 7, characterized in that, The parameters for atomic layer deposition include: deposition temperature of 120℃~200℃ and pressure of 180pa~230pa.

9. A battery cell, characterized in that, It is produced by the method described in any one of claims 1-8.

10. The battery cell according to claim 9, characterized in that, The solar cell includes a silicon wafer and an Al2O3 film disposed on the surface of the silicon wafer, wherein hydroxyl and carboxyl groups exist between the silicon wafer and the Al2O3 film.

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