Preparation method of soft package battery

Abstract

The invention relates to a preparation method of a soft package battery, which comprises the following steps: S1, carrying out pressurization treatment and stretching extension treatment on a dry battery cell to obtain a first intermediate; s2, performing liquid injection treatment and packaging treatment on the first intermediate to obtain a second intermediate; s3, performing formation treatment on the second intermediate to obtain a soft package battery; the formation treatment comprises the following steps: S310, charging the second intermediate, wherein the state of charge of the second intermediate after charging is 100% SOC; s320, keeping the temperature at 42-48 DEG C, and standing for 1-3 hours; s330, discharging the second intermediate, wherein the state of charge of the second intermediate after discharging is 0% SOC; charging and discharging are carried out for multiple times in the formation treatment, and the steps S310-S330 are adopted for at least the first to second times of charging and discharging. According to the scheme provided by the invention, the soft package battery has excellent safety performance and cycle performance.

Description

Technical Field

[0001] The present application relates to the field of battery technology, and in particular to a method for preparing a soft-pack battery. Background Art

[0002] Lithium-ion batteries are widely used in 3C digital, power tools, aerospace, energy storage, power vehicles and other fields due to their advantages such as high specific energy, no memory effect and long cycle life. The rapid development of electronic information technology and consumer products has put forward higher requirements on the electrochemical performance of lithium-ion batteries.

[0003] In the related technologies, pouch cells, as a mainstream packaging form of lithium-ion batteries, have been widely used in many fields due to their high energy density and high volume utilization. At the same time, negative electrodes containing silicon materials have attracted widespread attention and research due to their advantages such as high theoretical capacity, low lithium insertion potential, abundant raw materials, non-toxicity and environmental protection. However, silicon materials will expand and contract to a large extent during the charging and discharging process. When silicon materials are used in pouch cells, the expansion of silicon materials is prone to cause burrs to form on the edges of the electrode pieces, resulting in broken corners in the pouch cells, deteriorating the safety performance of the pouch cells, and causing the electrode particles to pulverize and the active material to fall off, thereby reducing the conductivity of the negative electrode active material layer, and ultimately leading to a significant deterioration in the cycle performance of the pouch cells.

[0004] In summary, it is urgent to develop a method that can improve the safety and cycle performance of soft-pack batteries. Summary of the Invention

[0005] In order to solve or partially solve the problems existing in the related art, the present application provides a method for preparing a soft-pack battery, which can enable the soft-pack battery to exhibit excellent safety performance and cycle performance.

[0006] The present application provides a method for preparing a soft-pack battery, which includes the following steps: S1. Pressurizing and stretching the dry cell to obtain a first intermediate; The pressurizing treatment and the stretching treatment are performed simultaneously; the pressurizing direction of the pressurizing treatment is perpendicular to the maximum cross-sectional direction of the dry battery cell; the stretching direction of the stretching treatment is parallel to the maximum cross-sectional direction of the dry battery cell; S2. injecting and packaging the first intermediate to obtain a second intermediate; S3. Performing a formation treatment on the second intermediate to obtain a soft-pack battery; Wherein, the chemical conversion treatment comprises the following steps: S310, charging the second intermediate at a rate of 0.05C to 0.15C, wherein the state of charge of the second intermediate is 100% SOC after charging is completed; S320, keep at 42℃~48℃ for 1h~3h; S330, discharging the second intermediate at a rate of 0.05C to 0.2C, wherein the state of charge of the second intermediate is 0% SOC after the discharge is completed; The formation treatment is performed multiple times of charge and discharge, and at least the first and second charge and discharges are performed using steps S310 to S330.

[0007] In the method for preparing the soft-pack battery as described above, the formation treatment is performed by multiple charge and discharge, and at least the first to third charge and discharges use steps S310 to S330.

[0008] In the method for preparing the soft-pack battery as described above, the formation treatment is performed 2 to 3 times of charge and discharge, and each charge and discharge adopts steps S310 to S330.

[0009] The preparation method of the soft-pack battery as described above, wherein the dry battery cell is a laminated battery cell or a wound battery cell; and the stretching and stretching direction of the stretching and stretching treatment is the width direction of the dry battery cell.

[0010] In the method for preparing the soft-pack battery as described above, the side length of the first intermediate exceeds the side length of the dry cell by 0.5% to 1%.

[0011] The preparation method of the soft-pack battery as described above, wherein the dry battery cell includes a negative electrode sheet, the negative electrode sheet includes a negative electrode collector and a negative electrode active material layer arranged on at least one side of the negative electrode collector; the porosity of the negative electrode active material layer of the dry battery cell is b, and the porosity of the negative electrode active material layer of the first intermediate is (1.1~1.35)b.

[0012] The method for preparing the soft-pack battery as described above, wherein the pressurizing pressure of the pressurizing treatment is 0.5 MPa to 1.2 MPa, and the pressurizing time is 8 h to 12 h.

[0013] The method for preparing the soft-pack battery as described above, wherein the stretching force of the stretching treatment is 0.2 kN to 1 kN.

[0014] In the method for preparing the soft-pack battery as described above, the pressurizing treatment and the stretching and extending treatment are performed at a temperature of 38° C. to 45° C.

[0015] In the method for preparing the soft-pack battery as described above, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of silicon-carbon material, graphite, soft carbon, hard carbon, tin-based alloy and silicon-oxygen material.

[0016] In the method for preparing the soft-pack battery as described above, the negative electrode active material layer includes a negative electrode binder, and the negative electrode binder includes at least one of polyacrylic acid, carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, and polyvinylidene fluoride.

[0017] The technical solution provided by the present application may include the following beneficial effects: the present application adopts a preparation method for soft-pack batteries, which firstly pre-expands the negative electrode active material layer in the dry battery cell through pressurization treatment and stretching and extension treatment, releases part of the lattice stress of the negative electrode active material in advance, and adjusts the pore distribution of the negative electrode active material layer, thereby avoiding the expansion of the negative electrode active material during the cycle, causing burrs on the edge of the negative electrode sheet, avoiding the burrs piercing the soft-pack battery and causing broken corners, reducing the corner breakage rate of the soft-pack battery, and being able to form a uniform microcrack network inside the negative electrode active material layer, alleviating the volume change stress of the negative electrode active material layer during the cycle, reducing the risk of pulverization and falling off of the negative electrode active material layer, and ensuring the negative electrode activity. The conductivity of the material layer improves the cycle performance of the battery. Subsequently, through multiple long-term charge and discharge cycles at low rates and storage at high temperatures for chemical formation reactions, the formation of the SEI film can be promoted. At the same time, the SEI film is promoted to self-repair during the expansion-contraction process, making the SEI film denser, reducing the interfacial impedance of the battery, and avoiding direct contact between the negative electrode active material and the electrolyte during the battery cycle, reducing side reactions such as electrolyte decomposition and gas production. Moreover, at high temperatures, the components in the negative electrode active material layer can participate in the construction of the SEI film, improve the elasticity of the SEI film, avoid the damage of the SEI film caused by the expansion of the negative electrode active material, ensure the stability of the negative electrode active material layer and the electrolyte, and improve the cycle performance of the battery.

[0018] It should be understood that the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the present application. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is used for pressurization and stretching treatment of dry battery cells. DETAILED DESCRIPTION

[0020] To facilitate understanding of the present application, the present application will be described in detail below. However, before describing the present application in detail, it should be understood that the present application is not limited to the specific embodiments described. It should also be understood that the terms used herein are for the purpose of describing specific embodiments only and are not intended to be limiting.

[0021] Where a range of values is provided, it is understood that each intervening value between the upper and lower limits of the range and any other specified or intervening values in the specified range is encompassed herein. The upper and lower limits of these smaller ranges may independently be included in the smaller ranges and are also encompassed herein, subject to any express exclusions in the specified range. Where a specified range includes one or both limits, ranges excluding either or both of those included limits are also encompassed herein.

[0022] Unless otherwise defined, all terms used herein have the same meaning as commonly understood by those of ordinary skill in the art to which this application belongs. Although any methods and materials equivalent to those described herein can also be used in the practice or testing of this application, preferred methods and materials are now described.

[0023] In related technologies, silicon materials will expand and contract to a large extent during the charging and discharging process. When silicon materials are used in soft-pack batteries, the expansion of silicon materials is likely to cause burrs to form on the edges of the electrodes, resulting in broken corners in the soft-pack batteries, deteriorating the safety performance of the soft-pack batteries, and causing the electrode particles to pulverize and the active materials to fall off, thereby reducing the conductivity of the negative electrode active material layer, and ultimately leading to a significant deterioration in the cycle performance of the soft-pack batteries.

[0024] In order to solve the above problems, the present invention provides a method for preparing a soft-pack battery, which includes the following steps: S1. Performing pressurization and stretching treatment on the dry battery cell to obtain a first intermediate.

[0025] The pressurizing treatment and the stretching and extending treatment are carried out simultaneously; the pressurizing direction of the pressurizing treatment is perpendicular to the maximum cross-sectional direction of the dry battery cell; and the stretching and extending direction of the stretching and extending treatment is parallel to the maximum cross-sectional direction of the dry battery cell.

[0026] Specifically, if Figure 1 As shown, the dry battery cell is pressurized in the direction perpendicular to the maximum cross-section of the dry battery cell for pressurization treatment, and at the same time, the dry battery cell is stretched and extended in the direction parallel to the maximum cross-section of the dry battery cell to increase the side length of the dry battery cell to obtain a first intermediate.

[0027] The dry cell in this application refers to the cell in a soft-pack battery that is not soaked in electrolyte. The dry cell can be produced using a lamination process or a winding process. The dry cell includes a positive electrode sheet, a separator, and a negative electrode sheet stacked in sequence, but does not include a casing. The cell in this application is preferably rectangular in shape, i.e., the maximum cross-section of the cell is the plane formed by the cell's length × width, and the cell's thickness is perpendicular to this plane.

[0028] The positive electrode sheet of the present application includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The present application does not limit the choice of positive electrode current collector, which can be selected based on actual needs, such as aluminum foil. The present application does not limit the composition of the positive electrode active material layer, which can be selected based on actual needs, such as including positive electrode active material, positive electrode conductive agent, positive electrode binder, etc.

[0029] The negative electrode sheet of the present application includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The present application does not limit the choice of the negative electrode current collector; it can be selected based on actual needs, such as copper foil. The present application does not limit the composition of the negative electrode active material layer; it can be selected based on actual needs, such as including negative electrode active material, negative electrode conductive agent, negative electrode binder, etc.

[0030] Specifically, the negative electrode active material in the negative electrode active material layer may be a silicon material, a carbon material, or a silicon-carbon material.

[0031] This application does not limit the choice of diaphragm, which can be selected according to actual needs, for example, polyethylene diaphragm, polypropylene diaphragm, etc.

[0032] S2. Performing liquid injection and packaging treatments on the first intermediate to obtain a second intermediate.

[0033] Specifically, the first intermediate is placed in a soft-pack battery shell, an electrolyte is injected, and then a sealing and packaging process is performed to obtain a second intermediate.

[0034] This application does not limit the choice of the shell of the soft-pack battery, and it can be selected according to actual needs, such as a multi-layer aluminum-plastic composite film shell.

[0035] This application does not limit the selection of electrolyte components, which can be selected according to actual needs. For example, the electrolyte is an electrolyte known in the art that can be used in batteries and has excellent electrochemical performance of the battery, including lithium salts and organic solvents.

[0036] This application does not limit the specific parameters of the sealed package, as long as the first intermediate and the electrolyte can be sealed in the soft-pack battery shell, which can be selected according to actual needs.

[0037] S3. Performing a formation treatment on the second intermediate to obtain a soft-pack battery.

[0038] Specifically, the second intermediate is subjected to a formation treatment so that the battery constructs an interface film to obtain a soft-pack battery.

[0039] The chemical treatment includes the following steps: S310 , charging the second intermediate at a rate of 0.05C to 0.15C. After charging, the state of charge of the second intermediate is 100% SOC.

[0040] Specifically, the second intermediate is charged at a rate of 0.05C to 0.15C. For example, the charge rate may be 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, 0.1C, 0.11C, 0.12C, 0.13C, 0.14C or 0.15C, etc. After charging, the second intermediate is fully charged (i.e., the state of charge is 100% SOC).

[0041] S320, keep warm at 42℃~48℃ and let stand for 1h~3h.

[0042] Specifically, the second intermediate is subjected to a standing treatment at a standing temperature of 42°C to 48°C, for example, the standing temperature may be 42°C, 43°C, 44°C, 45°C, 46°C, 47°C or 48°C, and the standing time is 1h to 3h, for example, the standing time may be 1h, 1.2h, 1.4h, 1.6h, 1.8h, 2h, 2.2h, 2.4h, 2.6h, 2.8h or 3h, etc.

[0043] S330 , discharging the second intermediate at a rate of 0.05C to 0.2C. After the discharge is completed, the state of charge of the second intermediate is 0% SOC.

[0044] Specifically, the second intermediate after standing is discharged at a discharge rate of 0.05C~0.2C. For example, the discharge rate can be 0.05C, 0.06C, 0.07C, 0.08C, 0.09C, 0.1C, 0.11C, 0.12C, 0.13C, 0.14C, 0.15C, 0.16C, 0.17C, 0.18C, 0.19C or 0.2C, etc., and the discharge is stopped after the state of charge of the second intermediate is 0% SOC.

[0045] The formation treatment is performed by multiple charge and discharge cycles, and at least the first and second charge and discharge cycles use steps S310 to S330 .

[0046] Specifically, in the formation treatment, steps S310, S320, and S330 are first repeated at least 1 to 2 times to charge and discharge the second intermediate at least 1 to 2 times, and then the charge and discharge treatment is performed according to other rate parameters or the charge and discharge treatment is stopped to obtain a soft-pack battery.

[0047] This application does not limit the parameters of the charge and discharge processing after steps S310, S320, and S330. As long as steps S310, S320, and S330 are used for charge and discharge at least for the first or second time, the purpose of constructing a high-performance SEI film can be achieved.

[0048] The present application adopts a preparation method of a soft-pack battery. First, through pressurization treatment and stretching and extension treatment, the negative electrode active material layer in the dry battery cell can be pre-expanded, the lattice stress of part of the negative electrode active material can be released in advance, and the pore distribution of the negative electrode active material layer can be adjusted, so as to avoid burrs on the edge of the negative electrode sheet caused by the expansion of the negative electrode active material during the cycle, and avoid burrs piercing the soft-pack battery to cause broken corners, thereby reducing the corner breakage rate of the soft-pack battery, and can form a uniform microcrack network inside the negative electrode active material layer, thereby alleviating the volume change stress of the negative electrode active material layer during the cycle, reducing the risk of pulverization and falling off of the negative electrode active material layer, ensuring the conductivity of the negative electrode active material layer, and improving the battery performance. The cycle performance of the battery is improved, and then the formation reaction is carried out through multiple low-rate long-term charge and discharge and storage at high temperature, which can promote the formation of the SEI film and promote the self-repair of the SEI film during the expansion-contraction process, making the SEI film denser, reducing the interfacial impedance of the battery, and avoiding direct contact between the negative electrode active material and the electrolyte during the battery cycle, reducing side reactions such as electrolyte decomposition and gas production, and the components in the negative electrode active material layer at high temperature can participate in the construction of the SEI film, improve the elasticity of the SEI film, avoid the damage of the SEI film caused by the expansion of the negative electrode active material, ensure the stability of the negative electrode active material layer and the electrolyte, and improve the cycle performance of the battery.

[0049] In a preferred embodiment, the formation treatment is performed multiple times of charge and discharge, and at least the first to third charge and discharge adopt steps S310 to S330. Specifically, in the formation treatment, steps S310, S320, and S330 are first repeated at least 1 to 3 times, so that the second intermediate is charged and discharged at least 1 to 3 times, and then the charge and discharge treatment is performed according to other rate parameters or the charge and discharge treatment is stopped to obtain a soft-pack battery. Through this formation treatment, the SEI film in the soft-pack battery of the present application is better in self-repair during the expansion-contraction process, making the density and elasticity of the SEI film better, thereby greatly improving the cycle performance of the battery.

[0050] Preferably, the formation treatment is performed 2 to 3 times of charge and discharge, with steps S310 to S330 being used for each charge and discharge. In this case, the self-healing properties of the SEI film in the soft-pack battery are enhanced, resulting in an improved density and elasticity of the SEI film, thereby further reducing the interfacial impedance of the battery and ensuring the stability of the negative electrode active material layer and the electrolyte. On the one hand, this can avoid the situation where a small number of charge and discharge cycles lead to poor density and elasticity of the SEI film, which results in insufficient improvement in the lithium conductivity of the SEI film and the stability of the negative electrode active material layer and the electrolyte. On the other hand, this can also avoid the situation where a large number of charge and discharge cycles lead to excessive density of the SEI film, which in turn reduces the lithium conductivity of the SEI film, thereby significantly improving the battery's cycle performance.

[0051] More preferably, the formation treatment is performed three times of charge and discharge, each time using steps S310 to S330. This solution adopted by the present application can greatly improve the density and conductivity of the SEI film in the soft-pack battery, thereby improving the cycle performance of the battery.

[0052] In a specific embodiment, the dry cell is a laminated cell or a wound cell; the stretching and stretching direction of the stretching and stretching treatment is the width direction of the dry cell. The dry cell of the present application is prepared by a lamination process or a winding process, which is conducive to the preparation of soft-pack batteries with high energy density and high safety, and is also conducive to the pressurization treatment and stretching and stretching treatment of the dry cell of the present application, simplifying the preparation process. The stretching and stretching direction of the stretching and stretching treatment of the present application is the width direction of the dry cell, which can perform reasonable pre-expansion treatment on the negative active material layer of the dry cell, avoiding the collapse and pulverization problems of the negative active material layer during pressurization treatment and stretching and stretching treatment, thereby improving the stability of the soft-pack battery.

[0053] In a specific embodiment, the side length of the first intermediate exceeds the side length of the dry battery cell by 0.5% to 1%, that is, the side length of the first intermediate is 100.5% to 101% of the side length of the dry battery cell, for example, the side length of the first intermediate exceeds the side length of the dry battery cell by 0.5%, 0.6%, 0.7%, 0.8%, 0.9% or 1%, etc. The side length of the dry battery cell in the present application refers to the size of the dry battery cell parallel to the stretching and extension direction of the stretching and extension treatment. Similarly, the side length of the first intermediate refers to the size of the first intermediate parallel to the stretching and extension direction of the stretching and extension treatment. When the side length ratio of the first intermediate and the dry battery cell is within the above range, the negative electrode active material layer can achieve sufficient pre-expansion, so that the lattice stress of the negative electrode active material is released, and the pore distribution of the negative electrode active material layer can be better adjusted, reducing the occurrence of edge burrs on the negative electrode sheet and the probability of pulverization and falling off of the negative electrode active material layer, thereby making the battery safety performance and cycle performance better.

[0054] In a specific embodiment, the porosity of the negative electrode active material layer of the dry cell is b, and the porosity of the negative electrode active material layer in the first intermediate is (1.1-1.35) b. For example, the porosity of the negative electrode active material layer in the first intermediate can be 1.1 b, 1.15 b, 1.2 b, 1.25 b, 1.3 b, or 1.35 b, etc. When the increase rate of the porosity of the negative electrode active material layer after the pressurization treatment and the stretching treatment is within the above range, it is beneficial to reduce the edge burrs of the negative electrode sheet and alleviate the volume change stress of the negative electrode active material layer during the cycle. It can also greatly reduce the probability of broken corners in the battery and the probability of pulverization and shedding of the negative electrode active material layer, improve the stability of the negative electrode active material layer, and at the same time increase the rate of lithium ion deintercalation in the negative electrode active material layer, thereby further improving the safety and cycle performance of the battery.

[0055] In a specific embodiment, the pressurization pressure of the pressurization treatment is 0.5MPa~1.2MPa, for example, the pressurization pressure is 0.5MPa, 0.6MPa, 0.7MPa, 0.8MPa, 0.9MPa, 1MPa, 1.1MPa or 1.2MPa, and the pressurization time is 8h~12h, for example, the pressurization time is 8h, 8.5h, 9h, 9.5h, 10h, 10.5h, 11h, 11.5h or 12h, etc. When the pressurization pressure and pressurization time of the pressurization treatment are within the above ranges, it is beneficial to control the increase rate of the side length of the dry battery cell and the increase rate of the porosity of the negative electrode active material layer, thereby reducing the probability of problems such as broken corners and pulverization and shedding of the negative electrode active material layer in the battery, and ensuring the structural stability of the battery cell, avoiding the collapse of the battery cell structure due to excessive pressurization pressure, thereby ensuring the improvement of the safety performance and cycle performance of the battery.

[0056] In a specific embodiment, the stretching force of the stretching and extension treatment is 0.2kN to 1kN, for example, the stretching force can be 0.2kN, 0.3kN, 0.4kN, 0.5kN, 0.6kN, 0.7kN, 0.8kN, 0.9kN or 1kN, etc. When the stretching force of the stretching and extension treatment is within the above range, the increase rate of the side length of the dry battery cell and the increase rate of the porosity of the negative electrode active material layer can be controlled within the above range by controlling the time of the stretching and extension treatment, so that the probability of problems such as broken corners and pulverization and shedding of the negative electrode active material layer in the battery is lowered, and the collapse of the battery cell structure or damage to the negative electrode current collector caused by excessive stretching force can be avoided, thereby greatly improving the safety performance and cycle performance of the battery.

[0057] In a specific embodiment, the pressurization treatment and the stretching and extension treatment are performed at a temperature of 38°C to 45°C, for example, the temperature may be 38°C, 39°C, 40°C, 41°C, 42°C, 43°C, 44°C, or 45°C. When the pressurization treatment and the stretching and extension treatment are performed at a high temperature, it is beneficial to the extension of the battery cell, thereby helping to increase the porosity of the negative electrode active material layer in the battery cell, thereby reducing the edge burrs of the negative electrode sheet and reducing the corner breakage rate of the battery. At the same time, it can ensure the conductivity of the negative electrode active material layer, further improving the cycle performance of the battery.

[0058] In one specific embodiment, the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of a silicon-carbon material, graphite, soft carbon, hard carbon, a tin-based alloy, and a silicon-oxygen material. When the negative electrode active material is selected from the above materials, it helps to improve the energy density of the battery. At the same time, the soft-pack battery preparation method can alleviate the problems of corner breakage and cycle performance degradation caused by the expansion of the negative electrode active material, thereby improving the battery's energy density while also improving the safety and cycle performance of the battery.

[0059] In one specific embodiment, the negative electrode active material layer includes a negative electrode binder, which includes at least one of polyacrylic acid, carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinyl alcohol (PVA), and polyvinylidene fluoride (PVDF). When the negative electrode binder is selected from the above binders, during the battery formation process, the negative electrode binder, such as polyacrylic acid (PAA), can react with lithium hexafluorophosphate in the electrolyte at high temperatures to form a resilient Li-PAA composite SEI film. This enhances the SEI film's elasticity, prevents SEI film damage caused by expansion of the negative electrode active material, and reduces the likelihood of side reactions between the negative electrode active material layer and the electrolyte, thereby improving the battery's cycling performance.

[0060] In a specific embodiment, the negative electrode active material layer includes a negative electrode conductive agent, and the negative electrode conductive agent includes at least one of carbon nanotubes, conductive carbon black, graphene, vapor-grown carbon fibers, and lamellar graphite.

[0061] In one specific embodiment, the positive electrode active material layer of the present application includes a positive electrode active material, and the positive electrode active material includes at least one of lithium manganese oxide, a ternary material of nickel-cobalt-lithium manganese oxide, lithium nickel manganese oxide, a lithium-rich manganese-based material, and a ternary material of nickel-cobalt-aluminum. When the positive electrode active material is selected from the above compounds, the positive electrode active material can fully demonstrate its performance and improve the electrochemical performance of the lithium-ion battery.

[0062] In the embodiments of the present application, there are no particular restrictions on the type of positive electrode current collector; it can be any known material suitable for use as a positive electrode current collector. In one embodiment, the positive electrode current collector includes a metal material such as aluminum, stainless steel, nickel plating, titanium, tantalum, or a carbon material such as carbon cloth or carbon paper. Preferably, the positive electrode current collector is a metal material.

[0063] In one specific embodiment, the positive electrode coating further comprises a positive electrode conductive agent and a positive electrode binder. The positive electrode conductive agent comprises at least one carbon material selected from natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, vapor-grown carbon fiber (VGCF), and the like. The positive electrode binder comprises at least one selected from polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, nitrocellulose, polyvinylidene fluoride, and polytetrafluoroethylene.

[0064] In a specific embodiment, the soft-pack battery also includes a diaphragm. The embodiment of the present application has no special restrictions on the material and shape of the diaphragm, as long as it does not significantly damage the effect of the present application. It can include porous sheet-like or non-woven fabric-like materials with excellent liquid retention, etc. The materials of the resin or glass fiber diaphragm include but are not limited to polyolefins, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, etc., and can be specifically set according to needs.

[0065] The present application also provides a soft-pack battery, which is prepared by the above-mentioned soft-pack battery preparation method. The soft-pack battery prepared by the preparation method of the present application exhibits excellent safety performance and cycle performance.

[0066] In a specific embodiment, the corner breakage rate of the soft-pack battery is no more than 1%.

[0067] In a specific embodiment, after the soft-pack battery is cycled at 1C / 0.5C for 100 cycles, that is, charged at a charge rate of 1.0C and discharged at a discharge rate of 0.5C, after repeated charge and discharge 100 times, the capacity retention rate of the battery is not less than 90% and the expansion rate is not higher than 8%.

[0068] Hereinafter, the present application will be further described in detail through specific embodiments.

[0069] Example 1 1. Preparation of positive electrode The positive electrode active material lithium cobalt oxide (LCO), the conductive agent CNT, and the adhesive PVDF are fully stirred and mixed in NMP solvent at a weight ratio of 97:1.5:1.5. The slurry is coated on aluminum foil and then processed through drying, cold pressing, slitting, sheet making, welding, tab lamination and other processes to make a positive electrode sheet that meets the winding requirements.

[0070] 2. Preparation of negative electrode sheet Anode active material (graphite and carbon-coated silicon material, with a silicon content of 10%), binder (polyacrylic acid PAA), and conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare anode slurry. This slurry was coated onto the cathode current collector Cu foil. After drying, cold pressing, slitting, sheeting, welding, and tab gluing, negative electrode sheets meeting winding requirements were produced.

[0071] 3. Preparation of electrolyte Ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed and stirred in a mass ratio of 1:1:2.5:5.5 to form a mixed solvent, 13.5% of lithium hexafluorophosphate (LiPF6) and 15% of fluoroethylene carbonate (FEC) were added, and the mixture was mixed evenly to obtain an electrolyte.

[0072] 4. Production of soft pack batteries S1. The positive electrode sheet, separator, and negative electrode sheet are stacked to obtain a dry cell; the dry cell is subjected to a pressurization treatment and a stretching treatment at 42° C. to obtain a first intermediate; The pressurization pressure of the pressurization treatment is 0.8 MPa and the pressurization time is 10 h; the tensile force of the tensile stretching treatment is 0.6 kN; The side lengths of the dry cell and the first intermediate are measured, and the side length of the first intermediate exceeds the side length of the dry cell by 0.8%; The porosity of the negative electrode active material layer in the dry cell and the first intermediate was measured. The porosity of the negative electrode active material layer in the dry cell was b, and the porosity of the negative electrode active material layer in the first intermediate was 1.25b; S2, placing the first intermediate into an aluminum-plastic film, injecting the prepared electrolyte, completing a sealing and packaging process, and obtaining a second intermediate; S3, performing a formation treatment on the second intermediate to obtain a soft-pack battery; The chemical conversion treatment is carried out according to the following steps: S310, charging the second intermediate at a rate of 0.1C for 10 hours, and after the charging is completed, the state of charge of the second intermediate is 100% SOC; S320, keep at 45℃ for 2h; S330, discharging the second intermediate at a rate of 0.1C, and after the discharge is completed, the state of charge of the second intermediate is 0% SOC; During the chemical conversion treatment, steps S310 to S330 are repeated three times.

[0073] The preparation methods of the soft-pack batteries provided in Examples 2 to 19 and Comparative Examples 3 to 16 are substantially the same as those in Example 1. Specific parameters are shown in Tables 1 and 2.

[0074] Comparative Example 1 1. Preparation of positive electrode The positive electrode active material lithium cobalt oxide (LCO), the conductive agent CNT, and the adhesive PVDF are fully stirred and mixed in NMP solvent at a weight ratio of 97:1.5:1.5. The slurry is coated on aluminum foil and then processed through drying, cold pressing, slitting, sheet making, welding, tab lamination and other processes to make a positive electrode sheet that meets the winding requirements.

[0075] 2. Preparation of negative electrode sheet Anode active material (graphite and carbon-coated silicon material, with a silicon content of 10%), binder (polyacrylic acid PAA), and conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare anode slurry. This slurry was coated onto the cathode current collector Cu foil. After drying, cold pressing, slitting, sheeting, welding, and tab gluing, negative electrode sheets meeting winding requirements were produced.

[0076] 3. Preparation of electrolyte Ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed and stirred in a mass ratio of 1:1:2.5:5.5 to form a mixed solvent, 13.5% of lithium hexafluorophosphate (LiPF6) and 15% of fluoroethylene carbonate (FEC) were added, and the mixture was mixed evenly to obtain an electrolyte.

[0077] 4. Production of soft pack batteries S1, stacking the above-mentioned positive electrode sheet, separator and negative electrode sheet to obtain a dry battery cell; S2, placing the first intermediate into an aluminum-plastic film, injecting the prepared electrolyte, completing a sealing and packaging process, and obtaining a second intermediate; S3, performing a formation treatment on the second intermediate to obtain a soft-pack battery; Among them, the formation treatment is carried out according to the following steps: at 80°C, charge to 35% SOC at a charge rate of 0.2C, then charge to 70% SOC at a charge rate of 0.5C, and finally charge to 100% SOC at a charge rate of 1C, that is, the formation is completed.

[0078] Comparative Example 2 1. Preparation of positive electrode The positive electrode active material lithium cobalt oxide (LCO), the conductive agent CNT, and the adhesive PVDF are fully stirred and mixed in NMP solvent at a weight ratio of 97:1.5:1.5. The slurry is coated on aluminum foil and then processed through drying, cold pressing, slitting, sheet making, welding, tab lamination and other processes to make a positive electrode sheet that meets the winding requirements.

[0079] 2. Preparation of negative electrode sheet Anode active material (graphite and carbon-coated silicon material, with a silicon content of 10%), binder (polyacrylic acid PAA), and conductive agent (carbon black) were added to water as a solvent at a weight ratio of 95:3.5:1.5 to prepare anode slurry. This slurry was coated onto the cathode current collector Cu foil. After drying, cold pressing, slitting, sheeting, welding, and tab gluing, negative electrode sheets meeting winding requirements were produced.

[0080] 3. Preparation of electrolyte Ethylene carbonate (EC), propylene carbonate (PC), ethyl propionate (EP), and propyl propionate (PP) were mixed and stirred in a mass ratio of 1:1:2.5:5.5 to form a mixed solvent, 13.5% of lithium hexafluorophosphate (LiPF6) and 15% of fluoroethylene carbonate (FEC) were added, and the mixture was mixed evenly to obtain an electrolyte.

[0081] 4. Production of soft pack batteries S1, stacking the above-mentioned positive electrode sheet, separator and negative electrode sheet to obtain a dry battery cell; S2, placing the first intermediate into an aluminum-plastic film, injecting the prepared electrolyte, completing a sealing and packaging process, and obtaining a second intermediate; S3, performing a formation treatment on the second intermediate to obtain a soft-pack battery; The chemical conversion treatment is carried out according to the following steps: S310, charging the second intermediate at a rate of 0.1C for 10 hours, and after the charging is completed, the state of charge of the second intermediate is 100% SOC; S320, keep at 45℃ for 2h; S330, discharging the second intermediate at a rate of 0.1C, and after the discharge is completed, the state of charge of the second intermediate is 0% SOC; During the chemical conversion treatment, steps S310 to S330 are repeated three times.

[0082] Table 1

[0083] Table 2

[0084] Test example The batteries prepared in the above embodiments and comparative examples were tested for the following items.

[0085] Battery performance test: 1. Corner breakage rate test In a constant temperature chamber at (25±2)°C, the soft-pack battery was charged to 4.53V at a constant current and constant voltage of 1.0C, then charged to 0.05C at a constant voltage, and then discharged to 3.0V at 0.5C after standing for 5 minutes. A cycle test was performed using a 1.0C charge / 0.5C discharge cycle. Multiple charge and discharge cycles were performed under the above conditions for up to 100 cycles. The corners of the soft-pack battery cells were then visually inspected to see if the aluminum-plastic film was damaged. The proportion of batteries with damaged corners in the entire batch of cycled cells was also calculated.

[0086] 2. Cycle performance test In a constant temperature box at (25±2)°C, the soft-pack battery was charged to 4.53V at 1.0C constant current and constant voltage, then charged to 0.05C at constant voltage. After standing for 5 minutes, it was discharged to 3.0V at 0.5C. The capacity obtained in this step was taken as the initial capacity. The thickness of the soft-pack battery was measured with a screw micrometer, which was the initial thickness. The cycle test was performed using 1.0C charging / 0.5C discharging. Multiple charge and discharge cycles were performed under the above conditions, and the capacity retention rate and expansion rate of the battery after 100 cycles were calculated: Capacity retention (%) = discharge capacity (mAh) after the corresponding number of cycles / initial capacity (mAh) × 100%; Expansion rate (%) = (thickness of the soft-pack battery corresponding to the number of cycles (cm) - initial thickness (cm)) / initial thickness (cm) × 100%.

[0087] Each group of 100 batteries has an average value of the calculated capacity retention rate and is recorded in Table 3.

[0088] Table 3

[0089] From Tables 1 to 3, we can see that: According to the comparison between Examples 1 to 18 and Comparative Examples 1 and 2, it can be seen that the preparation method of the soft-pack battery of the present application can prepare a battery with better safety performance and cycle performance.

[0090] According to the comparison between Examples 1 to 3 and Comparative Examples 3 and 4, when the pressurization pressure of the pressurization treatment is 0.5 MPa to 1.2 MPa and the pressurization time is 8 h to 12 h, the safety performance and cycle performance of the battery are improved.

[0091] According to the comparison between Examples 1, 4, 5 and Comparative Examples 5 and 6, it can be seen that when the tensile force of the stretching treatment is 0.2 kN to 1 kN, it is beneficial to improve the safety performance and cycle performance of the battery.

[0092] According to the comparison between Examples 1, 6, 7 and Comparative Examples 7 and 8, when the pressurization treatment and the stretching and extending treatment are performed at a temperature of 38° C. to 45° C., the safety performance and cycle performance of the battery can be further improved.

[0093] According to the comparison between Examples 1, 8, 9 and Comparative Examples 9 and 10, it can be seen that when the side length of the first intermediate exceeds the side length of the dry battery cell by 0.5% to 1%, and the porosity of the negative electrode active material layer of the first intermediate is 1.1 to 1.35 times the porosity of the negative electrode active material layer of the dry battery cell, the safety performance and cycle performance of the battery are higher.

[0094] According to the comparison between Examples 1, 10, and 11 and Comparative Examples 11 and 12, it can be seen that when the charge rate in the formation treatment is within the range of 0.05C to 0.15C, the safety performance and cycle performance of the battery can be improved.

[0095] According to the comparison between Examples 1, 12, 13 and Comparative Examples 13 and 14, it can be seen that when the standing temperature and standing time in the formation treatment are within the range of 42°C to 48°C and 1h to 3h, respectively, the safety performance and cycle performance of the battery can be improved.

[0096] According to the comparison between Examples 1, 14, and 15 and Comparative Examples 15 and 16, it can be seen that when the discharge rate in the formation treatment is within the range of 0.05C to 0.2C, the safety performance and cycle performance of the battery can be improved.

[0097] Comparison of Examples 1 and 16-19 shows that when steps S310-S330 are used for at least the first to second charge-discharge cycles of the formation treatment, the battery's cycle performance is improved. Furthermore, when steps S310-S330 are used for at least the first to third charge-discharge cycles of the formation treatment, the battery's cycle performance is even better.

[0098] The embodiments of the present application have been described above. The above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Many modifications and variations will be apparent to those skilled in the art without departing from the scope and spirit of the described embodiments. The terminology used herein is selected to best explain the principles of the embodiments, their practical applications, or improvements to the technology in the market, or to enable other persons skilled in the art to understand the embodiments disclosed herein.

Claims

1. A method for preparing a soft pack battery, characterized in that: The following steps are involved: S1. Pressurizing and stretching the dry cell to obtain a first intermediate; The pressurizing treatment and the stretching treatment are performed simultaneously; the pressurizing direction of the pressurizing treatment is perpendicular to the maximum cross-sectional direction of the dry battery cell; the stretching direction of the stretching treatment is parallel to the maximum cross-sectional direction of the dry battery cell; S2. injecting and packaging the first intermediate to obtain a second intermediate; S3. Performing a formation treatment on the second intermediate to obtain a soft-pack battery; Wherein, the chemical conversion treatment comprises the following steps: S310, charging the second intermediate at a rate of 0.05C to 0.15C, wherein the state of charge of the second intermediate is 100% SOC after charging is completed; S320, keep at 42℃~48℃ for 1h~3h; S330, discharging the second intermediate at a rate of 0.05C to 0.2C, wherein the state of charge of the second intermediate is 0% SOC after the discharge is completed; The formation treatment is performed multiple times of charge and discharge, and at least the first and second charge and discharges are performed using steps S310 to S330.

2. The method for preparing a soft pack battery according to claim 1, wherein: The formation treatment is performed multiple times of charge and discharge, and at least the first to third charge and discharges are performed using steps S310 to S330; Preferably, the formation treatment is performed 2 to 3 times of charge and discharge, and each charge and discharge adopts steps S310 to S330.

3. The method for preparing a soft pack battery according to claim 1, wherein: The dry battery cell is a laminated battery cell or a wound battery cell; the stretching and stretching direction of the stretching and stretching treatment is the width direction of the dry battery cell.

4. The method for preparing a soft pack battery according to claim 2, wherein: The side length of the first intermediate exceeds the side length of the dry cell by 0.5% to 1%.

5. The method for preparing a soft pack battery according to claim 2, wherein: The dry battery cell includes a negative electrode sheet, which includes a negative electrode current collector and a negative electrode active material layer arranged on at least one side of the negative electrode current collector; the porosity of the negative electrode active material layer of the dry battery cell is b, and the porosity of the negative electrode active material layer of the first intermediate is (1.1~1.35)b.

6. The method for preparing a soft pack battery according to claim 4, wherein: The pressurization pressure of the pressurization treatment is 0.5 MPa to 1.2 MPa, and the pressurization time is 8 h to 12 h.

7. The method for preparing a soft pack battery according to claim 4, wherein: The tensile force of the stretching and extending treatment is 0.2kN~1kN.

8. The method for preparing a soft pack battery according to claim 1, wherein: The pressurizing treatment and the stretching and extending treatment are performed at a temperature of 38° C. to 45° C.

9. The method for preparing a soft pack battery according to claim 5, wherein: The negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes at least one of silicon-carbon material, graphite, soft carbon, hard carbon, tin-based alloy, and silicon-oxygen material.

10. The method for preparing a soft pack battery according to claim 5, wherein: The negative electrode active material layer includes a negative electrode binder, and the negative electrode binder includes at least one of polyacrylic acid, carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl alcohol, and polyvinylidene fluoride.

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