Lithium ion battery cell and method of manufacture

Abstract

This invention discloses a lithium-ion battery cell and its preparation method. The battery cell includes a cell housing and a battery electrode assembly located within the cell housing. The battery electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a non-adhesive separator located between the positive and negative electrode sheets. The positive electrode sheet includes a positive current collector; the upper and lower surfaces of the positive current collector are respectively coated with a positive active material coating. The negative electrode sheet includes a negative current collector; the upper and lower surfaces of the negative current collector are respectively coated with a negative active material coating. A finishing tape is provided on the battery electrode assembly for fixing the battery electrode assembly. A hot melt adhesive sheet is provided on the outer surface of the battery electrode assembly for fixing the battery electrode assembly and bonding the battery electrode assembly to the cell housing. This invention can effectively solve the alignment problem of large soft-pack lithium-ion battery cells using low-cost non-adhesive separators and avoid the problem of current collector breakage at the root of the battery tabs due to cell drops.

Description

Technical Field

[0001] This invention relates to the field of battery technology, and in particular to a lithium-ion battery cell and its preparation method. Background Technology

[0002] Lithium-ion battery cells have advantages such as high specific energy, high cycle life, and long storage time. They are widely used not only in portable electronic devices (such as mobile phones, digital cameras, and laptops), but also in large and medium-sized electric equipment such as electric vehicles, electric bicycles, and power tools. Therefore, the performance requirements for lithium-ion battery cells are becoming increasingly stringent.

[0003] For large pouch lithium-ion cells used in current electric vehicles or two-wheeled vehicles, as applications deepen and market competition intensifies, there is a continuous pursuit of higher energy density and lower cost in technology.

[0004] Currently, low-cost, adhesive-free separators are increasingly being used in large, pouch-type lithium-ion battery cells. The cost of adhesive-free separators is generally significantly lower than that of oil-coated separators (statistically, it can reduce costs by 1 yuan / m³). 2 (Above), and the cost is also significantly lower than that of water-based coated diaphragms (according to statistics, it can reduce the cost by 0.5 yuan / m). 2 (Above), and usually has better rate performance, and also has certain advantages in thickness.

[0005] However, cells using uncoated separators lack adhesion between the separator and the electrode, preventing them from being bonded together as a whole. This results in a relatively loose internal structure within the cell, making it prone to misalignment.

[0006] Furthermore, in actual use, because the internal structure of the battery cell is relatively loose, hot melt adhesive cannot be used to bond the entire electrode assembly to the outer shell. As a result, in the event of a battery cell being dropped, the electrode plates are very prone to misalignment, or the current collector at the base of the electrode tab may break due to the drop, affecting the normal use of the battery cell.

[0007] Therefore, there is an urgent need to develop a technology that can solve the above-mentioned technical problems. Summary of the Invention

[0008] The purpose of this invention is to address the technical deficiencies of existing technologies by providing a lithium-ion battery cell and its preparation method.

[0009] Therefore, the present invention provides a lithium-ion battery cell, comprising a hollow cell housing and a battery electrode assembly located within the cell housing;

[0010] A battery electrode assembly includes a positive electrode plate, a negative electrode plate, and a separator located between the positive electrode plate and the negative electrode plate;

[0011] The diaphragm is an adhesive-free diaphragm;

[0012] The positive electrode includes a positive current collector; the upper and lower surfaces of the positive current collector are coated with a positive active material coating.

[0013] The negative electrode sheet includes a negative current collector; the upper and lower surfaces of the negative current collector are coated with a negative active material coating.

[0014] The battery electrode assembly is provided with a finishing tape, which is used to fix the battery electrode assembly.

[0015] A hot melt adhesive sheet is provided on the outer surface of the battery electrode assembly. This hot melt adhesive sheet is used to fix the battery electrode assembly and to bond the battery electrode assembly to the cell housing.

[0016] Furthermore, the present invention also provides a method for preparing a lithium-ion battery cell as described above, which includes the following steps:

[0017] Step S1: Prepare a positive electrode sheet;

[0018] Step S2: Prepare the negative electrode sheet;

[0019] Step S3, preparing the battery electrode assembly: The positive electrode sheet, negative electrode sheet and uncoated separator are prepared by winding or stacking to obtain the battery electrode assembly;

[0020] Step S4: Apply finishing tape to the battery terminal assembly to secure it and prevent it from coming apart.

[0021] Step S5: Perform hot pressing shaping on the battery electrode assembly, and then continue welding the positive and negative tabs.

[0022] Step S6: Apply hot melt adhesive to the outer surface of the battery electrode assembly to further fix the battery electrode assembly.

[0023] Step S7: The battery electrode assembly is placed into the hollow cell housing made of aluminum-plastic film, and then the encapsulation operation is performed to obtain the encapsulated battery electrode assembly.

[0024] In step S8, the packaged battery electrode assembly undergoes electrode assembly drying, liquid injection and sealing, standing, formation, degassing and sealing, as well as edge cutting and folding operations to obtain the finished lithium-ion battery cell.

[0025] As can be seen from the technical solution provided by the present invention above, compared with the prior art, the present invention provides a lithium-ion battery cell and its preparation method. Its design is scientific and applicable to scenarios using adhesive-free separators. By applying adhesive to the thinned areas of the positive and negative electrode sheets, all electrode sheets and separators are bonded into a whole, ensuring a compact internal structure of the battery cell. At the same time, by attaching hot melt adhesive sheets to the outer surface of the electrode assembly, the electrode assembly can be bonded to the battery cell shell. This effectively solves the problem of poor alignment (overhang) in existing large soft-pack lithium-ion batteries using low-cost adhesive-free separators, and avoids the problem of current collector breakage at the root of the battery cell tab due to battery cell drops. It has significant practical significance. Attached Figure Description

[0026] Figure 1a A top view of the coating state of the positive electrode sheet in a lithium-ion battery cell provided by the present invention;

[0027] Figure 1b A side view of the coating state of the positive electrode sheet in a lithium-ion battery cell provided by the present invention;

[0028] Figure 2 A schematic diagram showing the distribution of the adhesive layer on the positive electrode sheet of a lithium-ion battery cell provided by the present invention;

[0029] Figure 3a A top view of the coating state of the negative electrode sheet in a lithium-ion battery cell provided by the present invention;

[0030] Figure 3b A side view of the coating state of the negative electrode sheet in a lithium-ion battery cell provided by the present invention;

[0031] Figure 4 A schematic diagram showing the distribution of the adhesive layer on the negative electrode sheet of a lithium-ion battery cell provided by the present invention;

[0032] Figure 5 A schematic diagram of a lithium-ion battery cell provided by the present invention, wherein a finishing tape is provided on the cell;

[0033] Figure 6 This invention provides a schematic diagram of the structure of a hot melt adhesive sheet used in a lithium-ion battery cell.

[0034] Figure 7 This is a schematic diagram of the working state of a lithium-ion battery cell provided by the present invention, in which hot melt adhesive sheets have been attached to the outside of the battery electrode assembly. Detailed Implementation

[0035] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0037] In the description of this patent, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection or setting, a detachable connection or setting, or an integral connection or setting. Those skilled in the art can understand the specific meaning of the above terms in this patent according to the specific circumstances.

[0038] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this invention, "a plurality of" means two or more, unless otherwise explicitly specified.

[0039] See Figures 1a to 1b , Figure 2 , Figures 3a to 3b , Figures 4 to 7 The present invention provides a lithium-ion battery cell, comprising a hollow battery cell housing and a battery electrode assembly 20 located within the battery cell housing;

[0040] The battery electrode assembly 20 includes a positive electrode 1, a negative electrode 2, and a separator located between the positive electrode and the negative electrode;

[0041] The diaphragm is an uncoated diaphragm (i.e., a diaphragm without any adhesive coating);

[0042] The positive electrode 1 includes a positive electrode current collector 101; the upper and lower surfaces of the positive electrode current collector 101 are respectively coated with a positive electrode active material coating (i.e., positive electrode material area) 102;

[0043] The negative electrode sheet 2 includes a negative electrode current collector 201; the upper and lower surfaces of the negative electrode current collector 201 are respectively coated with a negative electrode active material coating (i.e., negative electrode material area) 202;

[0044] Among them, the battery electrode assembly 20 is provided with a finishing tape 3, which is used to fix the battery electrode assembly.

[0045] A hot melt adhesive sheet 4 is provided on the outer surface of the battery electrode assembly. The hot melt adhesive sheet 4 is used to fix the battery electrode assembly and to bond and fix the battery electrode assembly to the cell housing.

[0046] In this invention, specifically, the battery electrode group 20 is a wound battery electrode group or a stacked battery electrode group.

[0047] The battery electrode assembly is prepared by winding or stacking positive electrode 1, negative electrode 2 and separator.

[0048] In practice, when the battery electrode assembly 20 is a wound battery electrode assembly, the finishing tape 3 is pasted on the winding end of the battery electrode assembly to fix the shape of the battery electrode assembly and prevent the battery electrode assembly from spreading out.

[0049] Furthermore, when the battery electrode assembly 20 is a wound battery electrode assembly, the starting end of one side of the finishing tape 3 is pasted to the winding termination end of the battery electrode assembly, and the termination end of the other side of the finishing tape 3 is pasted to the outer surface of the winding main body of the battery electrode assembly.

[0050] In practice, when the battery electrode assembly 20 is a stacked battery electrode assembly, multiple finishing tapes 3 are respectively pasted on the left and right ends of the battery electrode assembly to fix the shape of the battery electrode assembly and prevent the battery electrode assembly from falling apart.

[0051] Furthermore, when the battery electrode assembly 20 is a stacked battery electrode assembly, each tail tape 3 is bonded to the left and right outer walls and the front and rear edges of the battery electrode assembly; the tail tape 3 is shaped like a "U".

[0052] In this invention, specifically, the battery cell casing is a casing made of aluminum-plastic film.

[0053] The aluminum-plastic film comprises a PET (polyethylene terephthalate) material layer, an aluminum layer, and a PP (polypropylene) material layer, with the PET and PP material layers covering the inner and outer sides of the aluminum layer, respectively. The aluminum-plastic film can also have other structures, not limited to the above-described design.

[0054] In this invention, specifically, there is no adhesive-coated diaphragm, only a base film is included;

[0055] The base film includes, but is not limited to, any one of materials such as polyethylene (PE) and polypropylene (PP);

[0056] In this invention, specifically, the finishing tape 3 includes a base film and an adhesive layer covering one side of the base film.

[0057] The base film includes, but is not limited to, any one of materials such as polyethylene (PE) and polypropylene (PP);

[0058] In practice, the adhesive in the adhesive layer can be an existing adhesive that is viscous and resistant to high temperatures.

[0059] In this invention, specifically, the hot melt adhesive sheet 4 includes a base film and an adhesive layer covering the inner and outer surfaces of the base film.

[0060] In specific implementation, the base film includes, but is not limited to, any one of materials such as polyethylene (PE) and polypropylene (PP);

[0061] The adhesive in the coating layer can be an existing adhesive that is viscous and heat-resistant.

[0062] In this invention, specifically, an electrolyte is injected into the cell casing;

[0063] The electrolyte of the lithium-ion battery cell of the present invention can use existing conventional electrolyte formulations, which will not be described in detail here.

[0064] In this invention, specifically, the battery electrode assembly 20 is provided with positive electrode tabs 501 and negative electrode tabs 502 spaced apart.

[0065] Positive tab 501 is connected to positive electrode 1; negative tab 502 is connected to negative electrode 2.

[0066] Furthermore, the positive electrode 501 is made of aluminum, and the negative electrode 502 is made of copper or copper plated with nickel.

[0067] In this invention, specifically, the positive current collector is an aluminum foil.

[0068] In this invention, specifically, the positive electrode active material coating (i.e., the positive electrode material region) 102 includes a positive electrode active material material, a conductive agent, a binder, and a dispersant;

[0069] The mass ratio of the positive electrode active material, conductive agent, binder, and dispersant is (90–99.7):(0.1–4):(0.1–4)(0.1–2).

[0070] In practice, the positive electrode active material can be a conventional material, such as a ternary lithium-containing material (e.g., a ternary lithium-containing compound Li(Ni)). 0.33 Co 0.33 Mn 0.33Materials such as O2), lithium iron phosphate (e.g., lithium iron phosphate), and lithium cobalt (e.g., lithium cobalt oxide).

[0071] In practice, the binder for the positive electrode active material coating is polyvinylidene fluoride (PVDF).

[0072] The dispersant can be nitrile rubber or other nitrile rubber;

[0073] The conductive agent can be carbon nanotubes or graphene.

[0074] In this invention, specifically, the negative electrode current collector is a copper foil.

[0075] In this invention, specifically, the negative electrode active material coating (i.e., the positive electrode material region) 202 includes a negative electrode active material material, a conductive agent, a binder, and a dispersant;

[0076] The mass ratio of the negative electrode active material, conductive agent, binder, and dispersant is (90–99.7): (0.1–4): (0.1–4): (0.1–2).

[0077] In practice, the negative electrode active material can be any existing conventional material, including but not limited to at least one of graphite (artificial graphite, natural graphite) and silicon carbide.

[0078] In practice, for the negative electrode active material coating, the binder is carboxymethyl cellulose (CMC) and / or styrene-butadiene rubber (SBR).

[0079] The dispersant can be carboxymethyl cellulose (CMC), which also acts as a binder.

[0080] The conductive agent can be carbon nanotubes or graphene.

[0081] To prepare the lithium-ion battery cell provided by the present invention, the present invention also provides a method for preparing a lithium-ion battery cell, comprising the following steps:

[0082] Step S1: Prepare positive electrode 1;

[0083] Step S2: Prepare negative electrode 2;

[0084] Step S3, preparing battery electrode assembly 20: The positive electrode 1, negative electrode 2 and uncoated separator are prepared by winding or stacking to obtain the battery electrode assembly;

[0085] Step S4: Attach finishing tape 3 to the battery electrode assembly 20 to fix the battery electrode assembly and prevent it from coming apart.

[0086] Step S5: Perform hot pressing shaping operation on battery electrode assembly 20, and then continue welding operation on positive electrode tab and negative electrode tab.

[0087] It should be noted that, in this invention, by hot-pressing the battery electrode assembly, the positive electrode sheet, negative electrode sheet, and uncoated separator are better bonded together. The hot-pressing process can also initially bond the coated positive and negative electrode sheets and the separator into a whole, preventing loosening, improving interface adhesion, reducing contact resistance, and ensuring that the cell thickness meets the requirements.

[0088] Step S6: Apply hot melt adhesive sheet 4 to the outer surface of the battery electrode assembly 20 to further fix the battery electrode assembly.

[0089] Step S7: The battery electrode assembly 20 is placed into the hollow cell housing made of aluminum-plastic film, and then a sealing operation is performed to obtain the sealed battery electrode assembly.

[0090] In step S8, the packaged battery electrode assembly undergoes electrode assembly drying, liquid injection and sealing, standing, formation, degassing and sealing, as well as edge cutting and folding operations to obtain the finished lithium-ion battery cell.

[0091] In this invention, step S1 specifically includes the following steps:

[0092] Step S11: Perform the positive electrode slurry preparation operation;

[0093] Specifically, the positive electrode active material, conductive agent, binder and dispersant are mixed together in a preset mass ratio, placed in a mixing tank, and then solvent is added and stirred evenly to prepare a positive electrode slurry. The positive electrode slurry is a uniform suspension containing the positive electrode active material.

[0094] In specific implementation, in step S11, for the solute included in the positive electrode slurry, the mass ratio between the positive electrode active material, conductive agent, binder and dispersant is (90~99.7):(0.1~4):(0.1~4)(0.1~2).

[0095] In specific implementation, in step S11, the viscosity of the positive electrode slurry is 1000-15000 cp, and the solid content is 60-70%.

[0096] In specific implementation, in step S11, the positive electrode active material can be a conventional material, such as a ternary lithium-containing material (e.g., a ternary lithium-containing compound Li(Ni)). 0.33 Co 0.33 Mn 0.33 Materials such as O2), lithium iron phosphate (e.g., lithium iron phosphate), and lithium cobalt (e.g., lithium cobalt oxide).

[0097] In specific implementation, in step S11, for the positive electrode slurry, the binder is polyvinylidene fluoride (PVDF);

[0098] The solvent is N-methylpyrrolidone (NMP);

[0099] The dispersant can be nitrile rubber or other nitrile rubber;

[0100] The conductive agent can be carbon nanotubes or graphene.

[0101] Step S12: Perform the preparation of PVDF adhesive solution;

[0102] Specifically, PVDF and NMP are mixed together, placed in a mixing tank and stirred evenly to prepare a suspension of PVDF adhesive;

[0103] In specific implementation, in step S12, the mass proportion of PVDF in the PVDF adhesive suspension is 3 to 9%, that is, within the range of 6 ± 3%.

[0104] Step S13: Perform the positive electrode coating and drying operation;

[0105] Specifically, the positive electrode slurry obtained in step S12 is uniformly coated on the upper and lower surfaces of the positive electrode current collector (e.g., aluminum foil), and then dried to obtain positive electrode sheet 1.

[0106] In specific implementation, in step S13, the positive electrode slurry is injected into the spraying equipment, and then the positive electrode slurry is uniformly sprayed onto the aluminum foil that serves as the positive electrode current collector through the spraying equipment.

[0107] In specific implementation, in step S13, a drying operation is performed using an oven to obtain a dry positive electrode sheet.

[0108] In specific implementation, in step S13, the coating and drying operation of the positive electrode slurry on one side (e.g., the upper surface) of the positive electrode current collector (e.g., aluminum foil) is completed first, and then the coating and drying operation on the other side is performed.

[0109] In specific implementation, in step S13, see... Figures 1a to 1b As shown, for the positive electrode 1, a positive active material coating (i.e., positive electrode material region) 102 is coated on the upper and lower sides of the positive current collector 101.

[0110] Each positive electrode active material coating (i.e., positive electrode material area) 102 includes a positive electrode central material area 1021 and a positive electrode thinning material area 1022, wherein the positive electrode central material area 1021 is located at the center of the positive electrode active material coating and has a positive electrode thinning material area 1022 on its front and rear sides respectively.

[0111] Each positive electrode empty foil region 104 is connected to the positive electrode thinning material region 1022 in the adjacent positive electrode active material coating 102;

[0112] It should be noted that in this invention, the width of the positive electrode empty foil region 103 is between 15 and 30 mm, and the width of the positive electrode thinning material region 1022 is between 10 and 20 mm.

[0113] The positive electrode thinning region 1022 is 5-10 μm thinner than the positive electrode center region 1021 of the positive electrode active material coating (i.e., positive electrode region) 102. The width of the positive electrode active material coating (i.e., positive electrode region) 102 depends on the cell size.

[0114] Step S14: Perform positive electrode cold pressing operation;

[0115] Specifically, the positive electrode sheet 1 is rolled to reduce the thickness difference between the positive electrode thinning area 1022 and the positive electrode center area 1021 of the positive electrode active material coating 102.

[0116] It should be noted that in this invention, the coated and dried positive electrode sheet 1 is installed on a cold press, and the pressure and the gap between the rollers are set to compact the positive electrode sheet. The thickness difference between the positive electrode thinning material area 1022 and the positive electrode active material coating (i.e., the positive electrode material area) 102 of the positive electrode center material area 1021 is reduced to 2-7 μm.

[0117] Step S15: Perform the positive electrode coating operation;

[0118] Specifically, the PVDF adhesive suspension prepared in step S12 is injected into a spray coating machine, and the positive electrode sheet obtained in step S14 (i.e., the dried and compacted positive electrode sheet) is loaded onto the spray coating machine. The PVDF adhesive suspension prepared in step S12 is sprayed onto the positive electrode thinning area 1022 of the positive electrode sheet 1, and a positive electrode coating layer 104 is formed on the positive electrode thinning area 1022 by spraying.

[0119] In specific implementation, in step S15, PVDF adhesive is first sprayed onto one side and then both sides of the positive electrode sheet in the thinned material areas 1022 on both sides. That is, the PVDF adhesive is first sprayed onto one side (e.g., the upper surface) of the positive electrode sheet, and then the spraying operation is performed on the other side. See [link to relevant documentation]. Figure 2 As shown, a positive electrode coating layer 104 is formed on the positive electrode thinning area 1022 by spraying.

[0120] In specific implementation, in step S15, the positive electrode coating layer 104 is 0-3 μm thicker than the positive electrode active material coating (i.e., the positive electrode material region) 102 in the positive electrode center material region 1021.

[0121] The longitudinal width of the positive electrode coating layer 104 is smaller than the longitudinal width of the positive electrode thinning area 1022.

[0122] It should be noted that, in this invention, the PVDF adhesive is sprayed onto the upper layer of the positive electrode thinning region 1022. The thickness of the positive electrode adhesive layer 104 can be 0-3 μm thicker than the thickness of the positive electrode active material coating (i.e., the positive electrode material region) 102's positive electrode central material region 1021, and its width is less than or equal to the width of the positive electrode thinning region 1022. The single-sided adhesive coating weight is 0.1-1.0 g / m². 2 After drying in a high-temperature oven, the NMP solution evaporates, and the PVDF particles remain in the positive electrode thinning area of ​​the positive electrode sheet. The temperature setting of the oven (i.e., the drying oven) should be lower than that of the coating area, generally controlled at 60±20℃.

[0123] Step S16: Perform positive electrode punching operation;

[0124] Specifically, the positive electrode 1 is punched according to the pre-designed dimensions to obtain the finished positive electrode.

[0125] It should be noted that in step S16, the positive electrode sheet 1 is fed onto the punching machine and punched according to the dimensions of the designed mold. The punching must include the area with the tabs, and key dimensions such as the length and width of the electrode sheet must be controlled.

[0126] In this invention, step S2 specifically includes the following steps:

[0127] Step S21: Perform the negative electrode slurry preparation operation;

[0128] Specifically, the negative electrode active material, conductive agent, binder and dispersant are mixed together in a preset mass ratio, placed in a mixing tank, and then solvent is added and stirred evenly to prepare a negative electrode slurry. The negative electrode slurry is a uniform suspension containing the negative electrode active material.

[0129] In specific implementation, in step S21, the mass ratio of the negative electrode active material, conductive agent, binder and dispersant in the solute included in the negative electrode slurry is (90~99.7):(0.1~4):(0.1~4):(0.1~2).

[0130] In specific implementation, in step S21, the viscosity of the negative electrode slurry is 1000-10000 cp, and the solid content is 45-60%.

[0131] In specific implementation, in step S21, the negative electrode active material can be a conventional material, including but not limited to at least one of graphite (artificial graphite, natural graphite) and silicon carbide.

[0132] In specific implementation, in step S21, for the negative electrode slurry, the binder is styrene-butadiene rubber (SBR);

[0133] The solvent is deionized water;

[0134] The dispersant can be carboxymethyl cellulose (CMC);

[0135] The conductive agent can be carbon nanotubes or graphene.

[0136] Step S22: Perform the preparation of PVDF adhesive solution;

[0137] Specifically, PVDF and NMP are mixed together, placed in a mixing tank and stirred evenly to prepare a suspension of PVDF adhesive;

[0138] In specific implementation, in step S22, the mass ratio of PVDF in the PVDF adhesive suspension is 3 to 9%, that is, within the range of 6 ± 3%.

[0139] It should be noted that, in this invention, the PVDF adhesive of the negative electrode is not limited to the polyvinylidene fluoride PVDF adhesive and the above-mentioned ratio, but can be other organic solvent adhesives. The PVDF adhesive of the positive electrode cannot be an aqueous adhesive. The PVDF adhesive of the negative electrode is not limited to the polyvinylidene fluoride PVDF adhesive, but can be an aqueous adhesive.

[0140] Step S23: Perform the negative electrode coating and drying operation;

[0141] Specifically, the negative electrode slurry obtained in step S22 is uniformly coated on the upper and lower surfaces of the negative electrode current collector (e.g., copper foil), and then dried to obtain the negative electrode sheet 2.

[0142] In specific implementation, in step S23, the negative electrode slurry is injected into the spraying equipment, and then the negative electrode slurry is uniformly sprayed onto the copper foil that serves as the negative electrode current collector through the spraying equipment.

[0143] In specific implementation, in step S23, a drying operation is performed using an oven to obtain a dry positive electrode sheet.

[0144] In specific implementation, in step S23, the coating and drying operation of the negative electrode slurry on one side (e.g., the upper surface) of the negative electrode current collector (e.g., copper foil) is completed first, and then the coating and drying operation on the other side is performed.

[0145] In specific implementation, see step S23. Figures 3a to 3b As shown, for the negative electrode 2, a negative electrode active material coating (i.e., negative electrode material area) 202 is coated on the upper and lower sides of the negative electrode current collector 201.

[0146] Each negative electrode active material coating (i.e., negative electrode material area) 202 includes a negative electrode central material area 2021 and a negative electrode thinning material area 2022, wherein the negative electrode central material area 2021 is located at the center of the negative electrode active material coating and has a negative electrode thinning material area 2022 on its front and rear sides respectively.

[0147] Each negative electrode empty foil region 204 is connected to the negative electrode thinning material region 2022 in the adjacent negative electrode active material coating 202;

[0148] It should be noted that in this invention, the width of the negative electrode empty foil area 203 is between 15 and 30 mm, and the width of the negative electrode thinning material area 2022 is between 10 and 20 mm.

[0149] The negative electrode thinning area 2022 is 5-10 μm thinner than the negative electrode center area 2021 of the negative electrode active material coating (i.e., the positive electrode material area) 202. The width of the negative electrode active material coating (i.e., the negative electrode material area) 202 depends on the cell size.

[0150] Step S24: Perform negative electrode cold pressing operation;

[0151] Specifically, the negative electrode sheet 2 is rolled to reduce the thickness difference between the negative electrode thinning material area 2022 and the negative electrode center material area 2021 of the negative electrode active material coating 202.

[0152] It should be noted that in this invention, the coated and dried negative electrode sheet 2 is installed on a cold press, and the pressure and the gap between the rollers are set to compact the negative electrode sheet 2. The thickness difference between the negative electrode thinning material area 2022 and the negative electrode active material coating (i.e., the negative electrode material area) 202 of the negative electrode center material area 2021 is reduced to 2-7 μm.

[0153] Step S25: Perform the negative electrode coating operation;

[0154] Specifically, the PVDF adhesive suspension prepared in step S22 is injected into a spray coating machine, and the negative electrode sheet obtained in step S24 (i.e., the dried and compacted negative electrode sheet) is loaded onto the spray coating machine. The PVDF adhesive suspension prepared in step S22 is sprayed onto the negative electrode thinning area 2022 of the negative electrode sheet 2, and a negative electrode coating layer 2104 is formed on the negative electrode thinning area 2022 by spraying.

[0155] In specific implementation, in step S25, the negative electrode thinning areas 2022 on both the upper and lower sides of the negative electrode sheet are first coated with PVDF adhesive on one side and then on both sides. That is, the PVDF adhesive is first coated on one side (e.g., the upper surface) of the negative electrode sheet, and then the coating operation is performed on the other side. See [link to relevant documentation]. Figure 4 As shown, a negative electrode coating layer 204 is formed on the negative electrode thinning material area 2022 by spraying.

[0156] In specific implementation, in step S25, the negative electrode coating layer 204 is 0-3 μm thicker than the negative electrode active material coating (i.e., the negative electrode material area) 202 in the negative electrode center material area 1021.

[0157] The longitudinal width of the negative electrode coating layer 304 is smaller than the longitudinal width of the negative electrode thinning area 2022.

[0158] It should be noted that, in this invention, the coating size of the thinned material area at the edge of the positive and negative electrode sheets is less than or equal to the size of the thinned material area, and the thickness should be 0 to 3 μm thicker than the size of the compacted central material area.

[0159] It should be noted that, in this invention, when the PVDF adhesive is sprayed onto the upper layer of the negative electrode thinning area 2022, the thickness of the negative electrode adhesive layer 204 can be 0-3 μm thicker than the thickness of the negative electrode active material coating (i.e., the negative electrode material area) 202's negative electrode center material area 2021, and the width is less than or equal to the width of the negative electrode thinning area 2022, with a single-sided adhesive coating weight of 0.1-1.0 g / m². 2 After drying in a high-temperature oven, the NMP solution evaporates, and the PVDF particles remain in the thinned material area of ​​the negative electrode sheet. The temperature setting of the oven (i.e., the drying oven) should be lower than that of the coating material area, generally controlled at 60±20℃.

[0160] Step S26: Perform negative electrode punching operation;

[0161] Specifically, the negative electrode 2 is punched according to the pre-designed dimensions to obtain the finished negative electrode.

[0162] It should be noted that in step S26, the negative electrode 2 is fed onto the punching machine and punched according to the dimensions of the designed mold. The punching must include the area with the tabs, and key dimensions such as the length and width of the electrode must be controlled.

[0163] In this invention, specifically in step S3, the positive electrode 1, the negative electrode 2, and the uncoated separator are stacked in the order of uncoated separator, negative electrode, uncoated separator, positive electrode, uncoated separator, negative electrode, and uncoated separator to prepare a battery electrode assembly.

[0164] In this invention, specifically in step S4, multiple (e.g., three) finishing tapes 3 are respectively pasted to the left and right ends of the battery electrode assembly 20. See [link to relevant documentation]. Figure 5 As shown.

[0165] It should be noted that, see Figure 5As shown, the stacked battery electrode assembly 20 may include a head adhesive coating area 2001 or a bottom adhesive coating area 2002, or both. Adhesive is applied to the head adhesive coating area 2001 and the bottom adhesive coating area 2002.

[0166] In this invention, specifically in step S5, the hot pressing operation involves placing the stacked battery electrode assembly on a hot press and hot pressing it. The pressure is typically a surface pressure of 1 ± 0.5 MPa, the temperature is 60–80°C, and the time is 1–3 minutes. This allows the adhesive particles in the thinned areas of the electrode sheets to dissolve, and under pressure, each layer of electrode sheet and the uncoated separator bond together, ultimately bonding all the electrode sheets into a complete and robust electrode assembly.

[0167] It should be noted that when performing a hot pressing process on the stacked or wound battery electrode assembly, the hot pressing should ensure that the adhesive particles in the coating area of ​​the electrode assembly are activated, bonding the positive electrode sheet, negative electrode sheet, separator, etc. together, so that the electrode assembly can become a whole.

[0168] In this invention, specifically in step S5, the welding operation of the positive electrode tab and the negative electrode tab includes pre-welding and final welding, specifically: pre-welding multiple positive current collectors together and pre-welding multiple negative current collectors together, and then cutting; then welding the positive electrode tab (e.g., taking the positive aluminum electrode tab) and the negative electrode tab (e.g., the negative copper electrode tab) together with the positive current collector and the negative current collector respectively.

[0169] In this invention, specifically in step S6, hot melt adhesive sheets 4 are respectively attached to the outer surface of at least one of the front and rear sides of the battery electrode assembly 20. (See [link to relevant documentation]). Figure 6 Figure 7 As shown.

[0170] In specific implementation, the hot melt adhesive sheet 4 includes at least one of the following: a hot melt adhesive head protection zone 401, a hot melt adhesive body area 402, and a hot melt adhesive bottom protection zone 403;

[0171] Among them, the hot melt adhesive head protection zone 401 and the hot melt adhesive bottom protection zone 403 are used to restrict the movement of the positive electrode, negative electrode and separator included inside the battery electrode assembly (e.g., restricting from both the top and bottom ends).

[0172] The hot melt adhesive main body area 402, through the hot melt adhesive on its inner and outer surfaces, can bond and fix the battery electrode assembly 20 and the cell housing together, reduce the relative movement and impact of the battery electrode assembly 20 in the cell housing, and effectively improve the drop resistance performance of the cell.

[0173] Furthermore, when the hot melt adhesive sheet 4 includes a hot melt adhesive head protection zone 401, a hot melt adhesive body area 402, and a hot melt adhesive bottom protection zone 403, the hot melt adhesive head protection zone 401 and the hot melt adhesive bottom protection zone 403 are respectively connected to the upper and lower ends of the hot melt adhesive body area 402.

[0174] It should be noted that, for the present invention, the shape of the hot melt adhesive sheet 4 is not limited to... Figure 6 , Figure 7 The shape shown should include at least one of the following three areas: the hot melt adhesive head protection zone, the hot melt adhesive body area, and the hot melt adhesive bottom protection zone.

[0175] Furthermore, the hot melt adhesive head protection zone 401 has at least one (e.g., three) hot melt adhesive strips 4011 that bypass the head region (i.e., the top region, which is folded back and then attached to the rear side of the battery electrode assembly 20), and the maximum distance between the portion of the hot melt adhesive strip 4011 that bypasses the head region of the battery electrode assembly 20 (i.e., the portion that is folded back and attached to the rear side of the battery electrode assembly 20) and the head region of the battery electrode assembly 20 is greater than 2 cm.

[0176] It should be noted that the hot melt adhesive strips 4011 on the left and right sides can be long strips, while the hot melt adhesive strip 4011 in the middle can be T-shaped.

[0177] Furthermore, the hot melt adhesive head protection zone 401 has a tab exposure opening (i.e., tab vacancy) 4012 at a position corresponding to the positive tab and negative tab on the battery electrode assembly 20.

[0178] Furthermore, the hot melt adhesive bottom protection zone 403 bypasses the bottom area (i.e., the bottom surface area) of the battery electrode assembly 20, and after bypassing, it folds back and adheres to the rear side of the battery electrode assembly 20. In addition, the width of the hot melt adhesive bottom protection zone 403 is at least 30% greater than the bottom edge width of the battery electrode assembly 20, and the distance between the part of the hot melt adhesive bottom protection zone 403 that bypasses the bottom area of ​​the battery electrode assembly 20 (i.e., the part that folds back and adheres to the rear side of the battery electrode assembly 20) and the edge of the bottom area (i.e., the bottom surface area) of the battery electrode assembly 20 is greater than 2 cm.

[0179] Furthermore, the area of ​​at least one hot melt adhesive body area 402 is greater than 30% of the area of ​​the side of the battery electrode assembly to which it is adhered (e.g., the front or rear side), and it can be adhered to both sides or only one side.

[0180] Furthermore, the hot melt adhesive head protection zone, the hot melt adhesive body area, and the hot melt adhesive bottom protection zone can be separate areas, or they can be a whole composed of three areas, or a whole composed of two adjacent areas; one area can be applied alone, or two or three areas can be applied.

[0181] In this invention, step S7 specifically includes the following steps:

[0182] First, punching: punching out a pit (i.e., a recess) in the aluminum-plastic film to accommodate the battery electrode assembly, thus obtaining the cell casing;

[0183] Then, packaging: the battery electrode assembly is placed into the recess of the cell casing (i.e., aluminum-plastic film) and then placed on a packaging machine for sealing.

[0184] In this invention, the electrode drying operation in step S8 specifically involves placing the packaged battery electrode assembly into an oven to dry and remove moisture.

[0185] The electrolyte injection and sealing process involves injecting the electrolyte into the dried battery cell and then sealing it.

[0186] The specific process of the settling operation is as follows: the battery cell is settling at a high temperature (e.g., 50-80°C) or a normal temperature (e.g., 15-25°C) for a preset time (e.g., 24 hours) to ensure that the electrolyte fully wets the positive and negative electrode plates;

[0187] The formation process specifically involves charging and discharging the battery cell with a small current (e.g., 0.1–0.2C) to ensure activation and the formation of a complete negative electrode interface film. The formation temperature is typically 40–80°C, and the formation pressure is 1.0 ± 0.5 MPa.

[0188] The degassing and sealing process involves placing the battery cell that generates gas during formation onto a degassing machine and performing degassing and sealing operations sequentially.

[0189] The specific steps for cutting and folding the edges are as follows: cut the aluminum and plastic on both sides of the battery cell (for example, cut to 4-10mm), and then fold the edges.

[0190] It should be noted that, regarding the formation process of this invention: the formation process should ensure that all parts of the battery electrode assembly, such as the positive electrode, negative electrode, and separator, are completely bonded together to form a complete and non-loose whole. Simultaneously, the formation process should ensure a good bond between the hot melt adhesive and the cell casing, allowing the hot melt adhesive to restrict relative movement between the electrode assembly and the casing.

[0191] This invention can improve drop resistance by using the thinning and coating technology of the positive and negative electrode sheets alone, or by applying hot melt adhesive sheets to the outer layer of the battery electrode assembly alone, or by using both in combination. However, it is not possible to apply hot melt adhesive only to one or two sides of the main body area of ​​the battery electrode assembly, that is, it is not possible to apply the hot melt adhesive sheet 4 to only one area of ​​the main body area 402 of the battery electrode assembly, otherwise there will be no improvement effect.

[0192] It should be noted that, for the present invention, the battery cell involved is not limited to a battery cell with a tab on one side, but can also be a battery cell with tabs on opposite sides (e.g., the upper and lower sides).

[0193] In this invention, specifically, after step S8, the following steps may also be included:

[0194] Step S9, test K value: First, let the cell stand at high temperature for a preset first time t1, and measure the first voltage value V1 of the cell (specifically, the open circuit voltage). Then, let it stand at room temperature for a preset second time t2, and measure the second voltage value V2 of the cell (specifically, the open circuit voltage).

[0195] Based on the difference between the first voltage value V1 and the second voltage value V2, and the difference between the preset first time duration t1 and the preset second time duration t2, a quotient operation is performed to obtain the self-discharge rate K value of the lithium-ion battery cell.

[0196] It's important to note that the K-value of a lithium-ion battery cell, i.e., the cell's self-discharge rate, is a crucial indicator of its performance. It represents the voltage drop of the cell per unit time, typically expressed in mV / d (millivolts per day). The formula for calculating the K-value is: K = (V1 - V2) / (t2 - t1), where V1 and V2 are the open-circuit voltages measured at times t1 and t2, respectively. By measuring the open-circuit voltage of the cell at different time points and using this formula, the K-value of the lithium-ion battery cell can be obtained. The battery K-value is a physical quantity that measures the cell's self-discharge rate. Self-discharge refers to the phenomenon where the battery's charge gradually decreases due to internal chemical reactions or physical effects when the cell is at rest. A smaller K-value indicates a lower self-discharge rate and better cell performance.

[0197] In this invention, specifically, after step S8, further operations such as casing voltage detection, X-ray detection, voltage internal resistance detection, and appearance inspection can be arranged.

[0198] Compared with existing technologies, the lithium-ion battery cell and its preparation method provided by this invention have the following beneficial effects:

[0199] 1. This invention utilizes the thickness difference between the thinned material areas at the edges of the positive and negative electrode sheets to apply adhesive, bonding all internal components of the entire electrode assembly (positive electrode sheet, negative electrode sheet, and separator) into a single unit. This improves the problem of unevenness (thinness) at the head and bottom of the battery cell. Simultaneously, this feature completely eliminates the problem of loose internal components in uncoated separator cells. It also mitigates the issues of electrode misalignment and current collector breakage at the base of the electrode tabs caused by excessive relative movement during cell drops. Furthermore, the use of PVDF adhesive is low, resulting in lower costs and increased market competitiveness.

[0200] 2. In this invention, the head and bottom protection zones of the hot melt adhesive sheet on the outer layer of the battery electrode assembly can effectively restrict the movement of each part in the battery electrode assembly. The hot melt adhesive in the main area of ​​the hot melt adhesive can fix the battery electrode assembly and the cell housing together, reduce the relative movement and impact of the battery electrode assembly in the cell housing, and effectively improve the drop resistance of the cell.

[0201] It should be noted that the low-cost, adhesive-free separator of this invention is merely a base film and cannot be bonded to the positive and negative electrode sheets. Therefore, during the manufacturing process, given the lack of adhesion between the electrode sheets, they are very prone to loosening or slipping during transportation, resulting in misalignment. Therefore, this invention employs adhesive coating on the thinned areas of the electrode sheets to re-bond and fix the positive and negative electrode sheets and the separator together, effectively reducing the relative loosening of the electrode sheets. Then, a hot-melt adhesive sheet is bonded to the outside of the electrode assembly, fixing the entire electrode assembly to the cell housing. This effectively solves the misalignment problem (overhang) in existing large soft-pack lithium-ion cells using low-cost, adhesive-free separators and significantly improves the cell's drop resistance.

[0202] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A lithium-ion battery cell, characterized in that, It includes a hollow battery cell housing and a battery electrode assembly (20) located inside the battery cell housing; The battery electrode assembly (20) includes a positive electrode sheet (1), a negative electrode sheet (2), and a separator located between the positive electrode sheet and the negative electrode sheet; The separator is a non-coated separator; The positive electrode sheet (1) includes a positive electrode current collector (101); positive electrode active material coatings (102) are respectively coated on the upper and lower surface of the positive electrode current collector (101); The negative electrode sheet (2) includes a negative electrode current collector (201); negative electrode active material coatings (202) are respectively coated on the upper and lower surface of the negative electrode current collector (201); Among them, a finishing tape (3) is provided on the battery electrode assembly (20), and the finishing tape (3) is used to fix the battery electrode assembly; A hot-melt film (4) is provided on the outer surface of the battery electrode assembly, and the hot-melt film (4) is used to fix the battery electrode assembly and bond and fix the battery electrode assembly to the battery cell housing together.

2. The lithium-ion battery cell as described in claim 1, characterized in that, The battery electrode assembly 20 is a wound battery electrode assembly or a stacked battery electrode assembly; The battery electrode assembly is obtained by winding or stacking the positive electrode sheet (1), the negative electrode sheet (2), and the separator.

3. The lithium-ion battery cell as described in claim 1, characterized in that, When the battery electrode assembly (20) is a wound battery electrode assembly, the finishing tape (3) is pasted at the winding termination end of the battery electrode assembly to fix the shape of the battery electrode assembly and prevent the battery electrode assembly from spreading; When the battery electrode assembly (20) is a stacked battery electrode assembly, multiple finishing tapes (3) are respectively pasted at the left and right ends of the battery electrode assembly to fix the shape of the battery electrode assembly and prevent the battery electrode assembly from spreading.

4. The lithium-ion battery cell as described in claim 3, characterized in that, When the battery electrode assembly (20) is a wound battery electrode assembly, the starting end of one side of the finishing tape (3) is pasted at the winding termination end of the battery electrode assembly, and the termination end of the other side of the finishing tape (3) is pasted on the outer surface of the winding main body part of the battery electrode assembly; When the battery electrode assembly (20) is a stacked battery electrode assembly, each finishing tape (3) is bonded to the left and right outer walls and the front and rear edges of the battery electrode assembly; the shape of the finishing tape (3) is "U" shape.

5. The lithium-ion battery cell as described in claim 1, characterized in that, The battery cell housing is a housing made of an aluminum-plastic film; and / or The non-coated separator only includes a base film; the base film includes any one of polyethylene (PE) and polypropylene (PP).

6. The lithium-ion battery cell as described in claim 1, characterized in that, The finishing tape (3) includes a base film and a glue layer covering one surface of the base film; and / or The hot-melt film (4) includes a base film and glue layers covering the inner and outer surfaces of the base film.

7. A method for preparing a lithium-ion battery cell as described in any one of claims 1 to 6, characterized in that, It includes the following steps: Step S1, obtaining the positive electrode sheet (1); Step S2, obtaining the negative electrode sheet (2); Step S3, preparing the battery electrode assembly (20): obtaining the battery electrode assembly by winding or stacking the positive electrode sheet (1), the negative electrode sheet (2), and the non-coated separator; Step S4, pasting the finishing tape (3) on the battery electrode assembly (20) to fix the battery electrode assembly and prevent the battery electrode assembly from spreading; Step S5, performing a hot pressing and shaping operation on the battery electrode assembly (20), and successively continuing with the welding operations of the positive electrode tab and the negative electrode tab; Step S6, pasting the hot-melt film (4) on the outer surface of the battery electrode assembly (20) to further fix the battery electrode assembly through the hot-melt film (4); Step S7: The battery electrode assembly (20) is placed into the hollow cell housing made of aluminum-plastic film, and then the encapsulation operation is performed to obtain the encapsulated battery electrode assembly. In step S8, the packaged battery electrode assembly undergoes electrode assembly drying, liquid injection and sealing, standing, formation, degassing and sealing, as well as edge cutting and folding operations to obtain the finished lithium-ion battery cell.

8. The method for preparing a lithium-ion battery cell as described in claim 7, characterized in that, Step S1 specifically includes the following steps: Step S11: Perform the positive electrode slurry preparation operation; Specifically, the positive electrode active material, conductive agent, binder and dispersant are mixed together in a preset mass ratio, placed in a mixing tank, and then solvent is added and stirred evenly to prepare a positive electrode slurry. The positive electrode slurry is a uniform suspension containing the positive electrode active material. Step S12: Perform the preparation of PVDF adhesive solution; Specifically, PVDF and NMP are mixed together, placed in a mixing tank and stirred evenly to prepare a suspension of PVDF adhesive; Step S13: Perform the positive electrode coating and drying operation; Specifically, the positive electrode slurry obtained in step S12 is uniformly coated on the upper and lower surfaces of the positive electrode current collector, and then dried to obtain the positive electrode sheet (1). In step S13, for the positive electrode sheet (1), a positive active material coating (102) is coated on the upper and lower sides of the positive current collector (101); Each positive electrode active material coating (102) includes a positive electrode central material region (1021) and a positive electrode thinning material region (1022), wherein the positive electrode central material region (1021) is located at the center of the positive electrode active material coating and has a positive electrode thinning material region (1022) on its front and rear sides respectively; Each positive electrode empty foil region (104) is connected to the positive electrode thinning material region (1022) in the adjacent positive electrode active material coating (102); Step S14: Perform positive electrode cold pressing operation; Specifically, the positive electrode sheet (1) is rolled to reduce the thickness difference between the thinned material area (1022) and the central material area (1021) of the positive electrode active material coating (102). Step S15: Perform the positive electrode coating operation; Specifically, the PVDF adhesive suspension prepared in step S12 is injected into a spray coating machine, and the positive electrode sheet obtained in step S14 is loaded onto the spray coating machine. The PVDF adhesive suspension prepared in step S12 is sprayed onto the positive electrode thinning area (1022) of the positive electrode sheet (1), and a positive electrode coating layer (104) is formed on the positive electrode thinning area (1022) by spraying. Step S16: Perform positive electrode punching operation; Specifically, the positive electrode sheet (1) is punched according to the pre-designed dimensions to obtain the finished positive electrode sheet; And / or, Step S2 specifically includes the following steps: Step S21: Perform the negative electrode slurry preparation operation; Specifically, the negative electrode active material, conductive agent, binder and dispersant are mixed together in a preset mass ratio, placed in a mixing tank, and then solvent is added and stirred evenly to prepare a negative electrode slurry. The negative electrode slurry is a uniform suspension containing the negative electrode active material. Step S22: Perform the preparation of PVDF adhesive solution; Specifically, PVDF and NMP are mixed together, placed in a mixing tank and stirred evenly to prepare a suspension of PVDF adhesive; Step S23: Perform the negative electrode coating and drying operation; Specifically, the negative electrode slurry obtained in step S22 is uniformly coated on the upper and lower surfaces of the negative electrode current collector, and then dried to obtain the negative electrode sheet (2). In step S23, for the negative electrode sheet (2), a negative electrode active material coating (202) is coated on the upper and lower sides of the negative electrode current collector (201); Each negative electrode active material coating (202) includes a negative electrode central material area (2021) and a negative electrode thinning material area (2022), wherein the negative electrode central material area (2021) is located at the center of the negative electrode active material coating and has a negative electrode thinning material area (2022) on its front and rear sides respectively; Each negative electrode empty foil region (204) is connected to the negative electrode thinning material region (2022) in the adjacent negative electrode active material coating (202); Step S24: Perform negative electrode cold pressing operation; Specifically, the negative electrode sheet (2) is rolled to reduce the thickness difference between the negative electrode thinning material area (2022) and the negative electrode center material area (2021) of the negative electrode active material coating (202). Step S25: Perform the negative electrode coating operation; Specifically, the PVDF adhesive suspension prepared in step S22 is injected into a spray coating machine, and the negative electrode sheet obtained in step S24 is loaded onto the spray coating machine. The PVDF adhesive suspension prepared in step S22 is sprayed onto the negative electrode thinning area (2022) of the negative electrode sheet (2), and a negative electrode coating layer (2104) is formed on the negative electrode thinning area (2022) by spraying. Step S26: Perform negative electrode punching operation; Specifically, the negative electrode sheet (2) is punched according to the pre-designed dimensions to obtain the finished negative electrode sheet.

9. The method for preparing a lithium-ion battery cell as described in claim 7, characterized in that, Hot melt adhesive sheets (4) are attached to the outer surface of at least one of the front and rear sides of the battery electrode assembly (20); The hot melt adhesive sheet (4) includes at least one of a hot melt adhesive head protection zone (401), a hot melt adhesive body area (402), and a hot melt adhesive bottom protection zone (403); The hot melt adhesive head protection zone (401) has at least one hot melt adhesive strip (4011) that bypasses the head region of the battery electrode assembly (20); The hot melt adhesive head protection zone (401) has an electrode tab exposure opening (4012) at the position corresponding to the positive electrode tab and the negative electrode tab on the battery electrode assembly (20); The hot melt adhesive bottom protection zone (403) bypasses the bottom region of the battery electrode assembly (20).

10. The method for preparing a lithium-ion battery cell according to any one of claims 7 to 9, characterized in that, Following step S8, the following steps are also included: Step S9, test K value: First, let the cell stand at high temperature for a preset first time t1 and measure the first voltage value V1 of the cell. Then, let it stand at room temperature for a preset second time t2 and measure the second voltage value V2 of the cell. Based on the difference between the first voltage value V1 and the second voltage value V2, and the difference between the preset first time duration t1 and the preset second time duration t2, a quotient operation is performed to obtain the self-discharge rate K value of the lithium-ion battery cell.

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