A soft-pack lithium-ion battery and preparation method thereof

Abstract

The present invention provides a soft-package lithium-ion battery and a preparation method thereof, the method comprising the following steps: (1) winding a positive electrode sheet, a negative electrode sheet and a diaphragm to obtain a winding core; (2) hot-cold pressing the winding core obtained in step (1), and then sequentially performing packaging, liquid injection, pressurized formation and pressurized volume separation; in step (2), the hot-cold pressing comprises sequentially performing hot pressing and cold pressing; the hot pressing conditions comprise: a temperature of 75-90° C., a pressure of 0.3-0.6 MPa and a time of 8-10 s; the cold pressing conditions comprise: a temperature of 22-26° C., a pressure of 0.3-0.6 MPa and a time of 8-10 s; the preparation method of the present invention can avoid the problems of difficulty in water baking, low electrolyte retention, and decreased bonding force between the diaphragm and the electrode sheet after liquid injection caused by hot pressing before packaging; the present invention performs hot-cold pressing once after winding to shape the winding core, which has the technical effect of bonding the diaphragm and the electrode sheet and hardening the bare battery cell.

Description

Technical Field

[0001] The present invention relates to the technical field of batteries, and in particular to a soft-pack lithium-ion battery and a preparation method thereof. Background Art

[0002] Soft-pack wound batteries are widely favored by the market due to their good safety, high specific energy, flexible design and many other advantages. However, soft-pack lithium-ion batteries have the problem of easy deformation due to the lack of strong binding force, which is a problem that all major soft-pack lithium-ion battery cell companies need to solve. Silicon-based negative electrodes are known as the most likely negative electrode materials to replace graphite because of their high theoretical specific capacity (up to 4200mAh / g) and the ability to significantly increase the energy density of batteries. However, their volume expansion can theoretically reach 300%, which is about ten times that of graphite negative electrodes. The expansion of the pole piece cannot stretch, which will cause the deformation of the negative pole piece, and further cause deformation of the battery, which will not only affect the battery performance, but also damage digital devices.

[0003] In the prior art, the square lithium battery shaping method adopts the method of optimizing the winding tension, preheating and hot pressing the wound battery cell, and then performing normal packaging, baking, liquid injection, formation, capacity division and other processes, which can effectively improve the deformation problem.

[0004] The above method is applicable to the winding structure of stacked sheets or non-welded pole ears, but not to the winding structure of welded pole ears. After welding the pole ears, the one-time shaping after winding can easily lead to overpressure and blockage of the diaphragm at the pole ears, lithium deposition at the pole sheets and pole ears after battery cycling, and one-time hot pressing after winding can easily lead to problems such as difficulty in electrolyte infiltration and low liquid retention. Therefore, how to overcome the above-mentioned technical problems and defects has become a key issue that needs to be solved. Summary of the invention

[0005] Aiming at the problems that existing soft-pack batteries are easily difficult to infiltrate electrolyte, have low liquid retention, and have overpressure at the tab after one-time hot pressing, the present invention provides a soft-pack lithium-ion battery and a preparation method thereof.

[0006] The technical solution adopted by the present invention to solve the above technical problems is as follows: In one aspect, the present invention provides a method for preparing a soft-pack lithium-ion battery, the method comprising the following steps: (1) Winding the positive electrode sheet, the negative electrode sheet and the separator to obtain a winding core; (2) hot and cold pressing the core obtained in step (1), and then sequentially performing packaging, liquid injection, pressurized chemical formation, and pressurized volume separation; In step (2), the hot and cold pressing includes hot pressing and cold pressing performed sequentially; the conditions of the hot pressing include: temperature of 75-90°C, pressure of 0.3-0.6MPa, and time of 8-10s; the conditions of the cold pressing include: temperature of 22-26°C, pressure of 0.3-0.6MPa, and time of 8-10s.

[0007] Optionally, in step (2), the pressurized chemical forming process includes the following steps: (2.1) Place the battery cell in a pressurized forming cabinet for forming, or clamp the battery cell with a pressurized fixture for forming; during this process, fully charge the battery cell once and then discharge it to 80%-90% SOC; (2.2) Place the battery cells in step (2.1) in a pressurized formation cabinet for capacity separation, or clamp the battery cells with a pressurized fixture for capacity separation.

[0008] Optionally, in step (2), the pressure of the pressurized formation is 0.6-1.0 MPa, the temperature of the pressurized formation is 22-85° C., and the time of the pressurized formation is 2h-21h.

[0009] Optionally, in step (2), the pressure of the pressurized separation is 0.3-0.4 MPa, the temperature of the pressurized separation is 22-26° C., and the time of the pressurized separation is 7 h-20 h.

[0010] Optionally, in step (1), the diaphragm includes a base film, a first film layer and a second film layer, the first film layer and the second film layer are stacked on at least one side of the base film, and the first film layer is arranged between the base film and the second film layer.

[0011] Optionally, the first film layer and the second film layer are stacked on one side of the base film, and the second film layer is stacked on the other side of the base film.

[0012] Optionally, the first film layer is a ceramic layer, and the second film layer is a rubber coating layer.

[0013] Optionally, in step (1), one side of the base film on which the ceramic layer and the adhesive layer are stacked is bonded to the positive electrode plate, and the other side of the base film on which the adhesive layer is stacked is bonded to the negative electrode plate.

[0014] Optionally, the adhesive layer is made by coating an oily adhesive or a water-based adhesive on the ceramic layer by roller coating or spraying, and the adhesive layer is selected from one or more of polyvinylidene fluoride and polymethyl methacrylate.

[0015] Optionally, the ceramic layer is made by coating ceramic slurry on the surface of the base film, and the adhesive in the ceramic slurry is selected from one or more of polyvinyl alcohol and polyacrylic acid.

[0016] Another aspect of the present invention provides a soft-pack lithium-ion battery, which is prepared by the above-mentioned method for preparing a soft-pack lithium-ion battery.

[0017] The preparation method of the soft-pack lithium-ion battery provided by the present invention can avoid the difficulty of baking water and low electrolyte retention due to hot pressing before packaging. If the pole piece is welded with a pole ear metal strip, the thickness of the metal strip is larger than that of the surface. When pressure is applied, the pole ear is subjected to concentrated force, resulting in overpressure of the pole piece at the pole ear, difficulty in electrolyte infiltration, and lithium precipitation problem at the pole ear in the late cycle. At the same time, the bonding force between the diaphragm and the pole piece will also decrease after liquid injection. The present invention performs hot and cold pressing once after winding to shape the winding core, which has the technical effect of bonding the diaphragm and the pole piece and hardening the bare battery cell. The formation and capacity division adopt a pressurized method to restrain the expansion and deformation of the negative pole piece during charging. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0019] Figure 1 It is a schematic diagram of a method for preparing a soft-pack lithium-ion battery provided by one embodiment of the present invention; Figure 2 is a line graph of the battery cycle thickness increase rate of comparative example 1; Figure 3 It is a line graph of the battery cycle thickness increase rate of Example 1. DETAILED DESCRIPTION

[0020] In order to make the technical problems, technical solutions and beneficial effects solved by the present invention clearer, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not intended to limit the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0021] Unless otherwise specified, the experimental methods used in the following examples are all conventional methods; the materials and reagents used are reagents and materials that can be obtained from commercial channels unless otherwise specified.

[0022] like Figure 1 As shown, in one embodiment, the present invention provides a method for preparing a soft-pack lithium-ion battery, the method comprising the following steps: (1) Winding the positive electrode sheet, the negative electrode sheet and the separator to obtain a winding core; (2) hot and cold pressing the core obtained in step (1), and then sequentially performing packaging, liquid injection, pressurized chemical formation, and pressurized volume separation; In step (2), the hot-cold pressing comprises hot pressing and cold pressing performed sequentially; the conditions of the hot pressing comprise: a temperature of 75-90°C, a pressure of 0.3-0.6 MPa, and a time of 8-10 s; the conditions of the cold pressing comprise: a temperature of 22-26°C, a pressure of 0.3-0.6 MPa, and a time of 8-10 s.

[0023] In some embodiments, the positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material, a conductive agent, and a binder.

[0024] In some embodiments, the positive electrode active material includes one or more of lithium iron phosphate (LFP), lithium iron manganese phosphate (LMFP), lithium cobalt oxide (LCO), lithium manganese oxide (LMO), lithium nickel oxide (LNO), ternary materials (NCM, NCA), lithium manganese-rich base (LMR), lithium nickel manganese oxide (LNMO), and lithium vanadium phosphate (Li3V2(PO4)3, LiVOPO4).

[0025] In a preferred embodiment, the positive electrode active material includes one or more of lithium iron phosphate (LFP), lithium cobalt oxide (LCO), ternary material (NCM), and lithium manganese oxide (LMO); In some embodiments, the positive electrode conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, carbon nanofibers, metal powders, metal fibers, and polyphenylene derivatives.

[0026] In some embodiments, the positive electrode binder includes one or more of polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorine-containing acrylic resin.

[0027] In some embodiments, the mass percentage of each component in the positive electrode active material layer is: 96-98 wt % of positive electrode active material, 0.5-2 wt % of conductive agent, and 1.0-2.0 wt % of binder.

[0028] When the mass ratio of the positive electrode active material in the positive electrode active material layer is within the above range, the positive electrode plate can have a higher lithium removal and lithium insertion capacity, and the battery can have a higher capacity.

[0029] The positive electrode current collector is selected from a metal material that can conduct electrons. Preferably, the positive electrode current collector includes one or more of copper, nickel, tin, copper, and stainless steel. In a more preferred embodiment, the positive electrode current collector is selected from aluminum foil.

[0030] The positive electrode sheet can be prepared according to conventional methods in the art. For example, the positive electrode active material layer is usually prepared by coating a positive electrode slurry made of a positive electrode active material, a positive electrode conductive agent, a positive electrode binder and any other components on a positive electrode current collector, followed by drying and cold pressing. The solvent can be N-methylpyrrolidone (NMP), but is not limited thereto.

[0031] In one embodiment, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer coated on one or both sides of the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, a conductive agent, a binder and a thickener.

[0032] In one embodiment, the negative electrode active material includes one or more of a graphite negative electrode material, a silicon-oxygen negative electrode material, a silicon-carbon negative electrode material, and a silicon negative electrode material.

[0033] In a preferred embodiment, the negative electrode active material includes one or more of silicon-carbon negative electrode material, silicon negative electrode material, silicon-oxygen negative electrode material or silicon-based doped graphite.

[0034] In some embodiments, the negative electrode conductive agent includes one or more of graphite, superconducting carbon, acetylene black, carbon black, carbon nanotubes, graphene, and carbon nanofibers.

[0035] In some embodiments, the negative electrode binder includes one or more of styrene-butadiene rubber and polyacrylic acid.

[0036] In some embodiments, the thickener includes one or more of polyacrylic acid and sodium carboxymethyl cellulose.

[0037] In some embodiments, the mass percentage of each component in the negative electrode active material layer is: 91%-97% of negative electrode active material, 0.5%-3% of conductive agent, 1%-2% of binder and 0.5%-1.5% of thickener.

[0038] The negative electrode current collector is selected from metal materials that can conduct electrons. Preferably, the negative electrode current collector includes one or more of Al, Ni, tin, copper, and stainless steel. In a more preferred embodiment, the negative electrode current collector is selected from copper foil.

[0039] The negative electrode sheet can be prepared according to conventional methods in the art. For example, the negative electrode active material layer is usually prepared by coating a negative electrode slurry made of a negative electrode active material, a negative electrode conductive agent, a negative electrode binder and any other components on a negative electrode current collector, followed by drying and cold pressing. The solvent can be an aqueous solvent, but is not limited thereto.

[0040] In some embodiments, the manufacture of the battery includes the following steps: The positive electrode sheet, the separator and the negative electrode sheet are arranged in order, so that the separator is located between the positive and negative electrodes to play an isolating role, and the roll core is obtained by winding; the roll core is hot-cold pressed, and then the roll core is placed in the aluminum-plastic film bag formed by punching and shelling, and then packaged, baked, injected, pre-charged with a clamp, and placed at high temperature for 8-12 hours; second sealing, clamp capacity division and third sealing are performed to obtain a soft-pack lithium-ion battery.

[0041] Specifically, the temperature of hot pressing is any point value among 75°C, 76°C, 77°C, 78°C, 79°C, 80°C, 81°C, 82°C, 83°C, 84°C, 85°C, 86°C, 87°C, 88°C, 89°C or 90°C, or a range value consisting of any two point values; in a preferred embodiment, the temperature of hot pressing is 80-85°C.

[0042] Specifically, the pressure of hot pressing is any point value among 0.3MPa, 0.35MPa, 0.4MPa, 0.45MPa, 0.5MPa, 0.55MPa or 0.6MPa, or a range value consisting of any two point values; in a preferred embodiment, the pressure of hot pressing is 0.4-0.5MPa.

[0043] Specifically, the hot pressing time is any point value among 8s, 8.2s, 8.4s, 8.6s, 8.8s, 9s, 9.2s, 9.4s, 9.6s, 9.8 or 10s, or a range value consisting of any two point values; in a preferred embodiment, the hot pressing time is 8.6-9.6s.

[0044] When the hot pressing temperature is 75-90℃, the pressure is 0.3-0.6MPa, and the time is 8-10s, it has the technical effect of inhibiting the deformation of the negative electrode sheet due to the expansion of lithium insertion during charging and then causing deformation of the battery; at the same time, during the use of the battery, the battery liquid retention is high, the battery cell cycle thickness increases slowly, the battery cycle life is long, and there is no lithium plating problem at the pole ear.

[0045] When the hot pressing temperature is lower than 75°C, or the hot pressing pressure is lower than 0.3MPa, or the hot pressing time is lower than 8s, the battery cell may be easily deformed during use.

[0046] When the hot pressing temperature is greater than 90°C, when the hot pressing pressure is greater than 0.6MPa, and when the hot pressing time is greater than 10s, excessive pressure will occur during battery use, and the tabs will also be prone to overpressure, resulting in lithium deposition during the cycle, shortening the battery cycle life.

[0047] Specifically, the temperature of cold pressing is any point value among 22°C, 22.5°C, 23°C, 23.5°C, 24°C, 24.5°C, 25°C, 25.5°C or 26°C, or a range value consisting of any two point values; in a preferred embodiment, the temperature of cold pressing is 23-25°C.

[0048] Specifically, the cold pressing pressure is any point value among 0.3MPa, 0.35MPa, 0.4MPa, 0.45MPa, 0.5MPa, 0.55MPa or 0.6MPa, or a range value consisting of any two point values; in a preferred embodiment, the cold pressing pressure is 0.4-0.5MPa.

[0049] Specifically, the cold pressing time is any point value among 8s, 8.2s, 8.4s, 8.6s, 8.8s, 9s, 9.2s, 9.4s, 9.6s, 9.8 or 10s, or a range value consisting of any two point values; in a preferred embodiment, the cold pressing temperature is 8.6-9.6s.

[0050] Compared with the prior art, the preparation method of the soft-package lithium-ion battery cell of the present invention has the following advantages: it can avoid the difficulty of baking water and low electrolyte retention due to hot pressing before packaging. If the pole piece is welded with a pole ear metal strip, the thickness of the metal strip is larger than that of the surface. When pressure is applied, the pole ear is subjected to concentrated force, resulting in overpressure of the pole piece at the pole ear, difficulty in electrolyte infiltration, lithium precipitation problem at the pole ear in the late cycle, and the bonding force between the diaphragm and the pole piece will also decrease after liquid injection. The present invention performs hot and cold pressing once after winding to shape the winding core, which has the technical effect of bonding the diaphragm and the pole piece and hardening the bare battery cell. The formation and capacity division adopt a pressurized method to restrain the expansion and deformation of the negative pole piece during charging.

[0051] The present invention performs hot and cold pressing once after winding to shape the winding core, which has the technical effect of bonding the diaphragm and the pole piece and hardening the bare battery core.

[0052] In one embodiment, in step (2), the process of pressurizing and forming comprises the following steps: (2.1) Place the battery cell in a pressurized forming cabinet for forming, or clamp the battery cell with a pressurized fixture for forming; during this process, fully charge the battery cell once and then discharge it to 80%-90% SOC; (2.2) Place the battery cells in step (2.1) in a pressurized formation cabinet for capacity separation, or clamp the battery cells with a pressurized fixture for capacity separation.

[0053] The present invention performs hot and cold pressing on the core, and then sequentially performs encapsulation and liquid injection to obtain a battery cell, and then pressurizes the battery cell for formation and pressure separation; The present invention places the battery cell in a pressurized formation cabinet for formation, or clamps the battery cell with a pressurized clamp for formation. The present application adopts pressurized restraint formation during formation, performs a full charge during formation, and then discharges to 80%-90% SOC, which can improve the deformation of the battery under the cabinet and the problem of subsequent cycle deformation.

[0054] In one embodiment, in step (2), the pressure of the pressurized formation is 0.6-1.0 MPa, the temperature of the pressurized formation is 22-85° C., and the time of the pressurized formation is 2h-21h.

[0055] Specifically, the pressure of the pressurized formation is any point value among 0.6MPa, 0.65MPa, 0.7MPa, 0.75MPa, 0.8MPa, 0.85MPa, 0.9MPa, 0.95MPa or 1MPa, or a range value consisting of any two point values; in a preferred embodiment, the pressure of the pressurized formation is 0.7-0.8MPa.

[0056] Specifically, the temperature of the pressurized formation is any point value among 22°C, 25°C, 30°C, 35°C, 40°C, 45°C, 50°C, 55°C, 60°C, 65°C, 70°C, 75°C, 80°C or 85°C, or a range value consisting of any two point values; in a preferred embodiment, the temperature of the pressurized formation is 30-50°C.

[0057] Specifically, the time for pressurized formation is any point value among 2h, 3h, 4h, 5h, 6h, 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h, 20h or 21h, or a range value consisting of any two point values; in a preferred embodiment, the time for pressurized formation is 8h-18h.

[0058] When the pressure of pressurized formation is 0.6-1.0MPa, the temperature is 22-85℃, and the time is 2h-21h, it has the technical effect of inhibiting the deformation of the negative electrode sheet due to the expansion of charging lithium insertion, which in turn causes the deformation of the battery; at the same time, during the use of the battery, the battery retains a high amount of liquid, the battery cell cycle thickness increases slowly, the battery cycle life is long, and there is no lithium plating problem at the pole ear.

[0059] When the pressure of pressurized formation is less than 0.6MPa, or the temperature of pressurized formation is less than 22°C, or the time of pressurized formation is less than 2h, the battery cell may be easily deformed during use.

[0060] When the pressure of pressurized formation is greater than 1.0MPa, or the temperature of pressurized formation is greater than 85℃, or the time of pressurized formation is greater than 21h, excessive pressure will occur during the use of the battery, and the tabs are prone to overpressure, which will cause lithium deposition during the cycle and shorten the battery cycle life.

[0061] In one embodiment, in step (2), the pressure of the pressurized separation is 0.3-0.4 MPa, the temperature of the pressurized separation is 22-26° C., and the time of the pressurized separation is 7 h to 20 h.

[0062] Specifically, the temperature of pressurized separation is any point value among 22°C, 22.5°C, 23°C, 23.5°C, 24°C, 24.5°C, 25°C, 25.5°C or 26°C, or a range value consisting of any two point values; in a preferred embodiment, the temperature of pressurized separation is 23-25°C.

[0063] Specifically, the pressure of the pressurized separation is any point value among 0.3MPa, 0.31MPa, 0.32MPa, 0.33MPa, 0.34MPa, 0.35MPa, 0.36MPa, 0.37MPa, 0.38MPa, 0.39MPa or 0.4MPa, or a range value consisting of any two point values; in a preferred embodiment, the pressure of the pressurized separation is 0.32-0.38MPa.

[0064] Specifically, the time for pressurized volume separation is any point value among 7h, 8h, 9h, 10h, 11h, 12h, 13h, 14h, 15h, 16h, 17h, 18h, 19h or 20h, or a range value consisting of any two point values; in a preferred embodiment, the time for pressurized volume separation is 10h-15h.

[0065] In one embodiment, in step (1), the diaphragm includes a base film, a first film layer and a second film layer, the first film layer and the second film layer are stacked on at least one side of the base film, and the first film layer is arranged between the base film and the second film layer.

[0066] Specifically, in one embodiment, a first film layer and a second film layer are stacked on one side of the base film, and the first film layer or the second film layer is stacked on the other side of the base film; In another embodiment, the first film layer and the second film layer are stacked on both sides of the base film, and the first film layer is arranged between the base film and the second film layer.

[0067] In a preferred embodiment, the first film layer and the second film layer are stacked on one side of the base film, and the second film layer is disposed on the other side of the base film.

[0068] In one embodiment, the first film layer is a ceramic layer, and the second film layer is a rubber coating layer.

[0069] In one embodiment, the thickness of the first film layer is 1-5um; specifically, the thickness of the first film layer is any point value of 1um, 2um, 3um, 4um or 5um, or a range value consisting of any two point values; in a preferred embodiment, the thickness of the first film layer is 2-3um.

[0070] In one embodiment, the thickness of the second film layer is 1-5um; specifically, the thickness of the second film layer is any point value of 1um, 2um, 3um, 4um or 5um, or a range value consisting of any two point values; in a preferred embodiment, the thickness of the second film layer is 1-3um.

[0071] The adhesive layer has the function of bonding the diaphragm and the electrode; the ceramic layer has the functions of reducing the thermal shrinkage of the diaphragm, dissipating heat, improving safety, increasing liquid retention and absorbing side reaction products.

[0072] In one embodiment, in step (1), one side of the base film laminated with the ceramic layer and the adhesive layer is bonded to the positive electrode plate, and the other side of the base film laminated with the adhesive layer is bonded to the negative electrode plate.

[0073] Specifically, one side of the base film laminated with a ceramic layer and a coating layer is bonded to the positive electrode sheet, which has the functions of reducing thermal shrinkage of the diaphragm, dissipating heat, improving safety, increasing liquid retention and absorbing side reaction products; the other side of the base film laminated with a coating layer is bonded to the negative electrode sheet, which has the function of inhibiting deformation of the negative electrode sheet.

[0074] In one embodiment, the adhesive layer is made by coating an oily adhesive or a water-based adhesive on the ceramic layer by roller coating or spraying, and the adhesive layer is selected from one or more of polyvinylidene fluoride and polymethyl methacrylate.

[0075] The use of polyvinylidene fluoride or polymethyl methacrylate has the effect of bonding the pole piece and the diaphragm and inhibiting the deformation of the pole piece.

[0076] In one embodiment, the ceramic layer is made by coating ceramic slurry on the surface of the base film, and the binder in the ceramic slurry is selected from one or more of polyvinyl alcohol (PVA) and polyacrylic acid (PAA).

[0077] Polyvinyl alcohol (PVA), polyacrylic acid (PAA) and the like are selected to enable the ceramic to adhere to the base film surface.

[0078] In one embodiment, the present invention provides a soft-pack lithium-ion battery on the other hand. The soft-pack lithium-ion battery is prepared by the above-mentioned method for preparing the soft-pack lithium-ion battery.

[0079] The battery of the present invention is a soft-pack lithium-ion battery, which is prepared by the above-mentioned preparation method of the soft-pack lithium-ion battery, and can avoid the problems of difficulty in baking moisture, low electrolyte retention, and decreased adhesion between the diaphragm and the pole piece after liquid injection due to the hot pressing before packaging. It can also effectively solve the problems that due to the welding of the pole ear metal strip, the thickness of the metal strip is larger and the surface is thicker, and when pressure is applied, the pole ear is subjected to concentrated force, resulting in overpressure of the pole piece at the pole ear, difficulty in electrolyte infiltration, and lithium precipitation in the late cycle.

[0080] The present invention performs a hot and cold pressing after winding to shape the winding core, which has the technical effect of bonding the diaphragm and the pole piece and hardening the bare battery cell, thereby improving the problem of easy deformation of the battery lower cabinet, and can reduce the moisture inside the battery, increase the battery liquid retention, and slow down the thickness increase during the battery cell cycle.

[0081] The beneficial effects of the present invention are further illustrated below in conjunction with embodiments.

[0082] In order to make the invention purpose, technical scheme and beneficial technical effect of the present invention clearer, the present invention is further described in detail below in conjunction with examples. However, it should be understood that the examples of the present invention are only for explaining the present invention, not for limiting the present invention, and the examples of the present invention are not limited to the examples given in the specification. The specific experimental conditions or operating conditions not specified in the examples are made under conventional conditions, or are made under the conditions recommended by the material supplier.

[0083] In addition, it should be understood that one or more method steps mentioned in the present invention do not exclude the existence of other method steps before or after the combination step or the insertion of other method steps between these explicitly mentioned steps, unless otherwise specified; it should also be understood that the combination connection relationship between one or more devices / apparatuses mentioned in the present invention does not exclude the existence of other devices / apparatuses before or after the combination device / apparatus or the insertion of other devices / apparatuses between these explicitly mentioned two devices / apparatuses, unless otherwise specified. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0084] In the following examples, the reagents, materials and instruments used, unless otherwise specified, can be purchased commercially or obtained by synthetic methods known in the art.

[0085] Table 1 Battery parameter design of Examples 1-25 and Comparative Examples 1-7;

[0086] Example 1 This embodiment is used to illustrate the soft-pack lithium-ion battery and the preparation method thereof disclosed in the present invention; it includes the following steps: (1) Preparation of diaphragm A 3um thick ceramic layer and a 3um thick PVDF coating layer are coated on one side of the base film, and a 3um thick PVDF coating layer is coated on the other side of the base film to obtain a diaphragm.

[0087] (2) Preparation of negative electrode The negative electrode active material SIC, the conductive agent CNT, the conductive agent SP, and the binder PAA are mixed in a mass ratio of 93%:3%:1%:3%. The mixture is fully stirred and mixed in an aqueous solvent to form a uniform negative electrode slurry. The slurry is applied to at least one side of the negative electrode current collector copper foil, and after drying, rolling, die-cutting and other processes, a positive electrode sheet that meets the requirements is obtained.

[0088] (3) Preparation of positive electrode The positive electrode active material LCO, the conductive agent CNT, and the adhesive PVDF are mixed in a mass ratio of 98%:0.6%:1.4%. They are fully stirred and mixed in NMP solvent to form a uniform positive electrode slurry. The slurry is applied to at least one side of the positive electrode current collector aluminum foil, and after drying, rolling, die-cutting and other processes, a positive electrode sheet that meets the requirements is obtained.

[0089] (4) Preparation of batteries The positive electrode sheet, the separator and the negative electrode sheet are stacked in order, so that the separator is located between the positive and negative electrodes to play a role of isolation, and the side of the separator laminated with the ceramic layer and the rubber layer is attached to the positive electrode sheet, and the rubber layer on the other side of the separator is attached to the negative electrode sheet, and then the sheets are stacked and wound to obtain a winding core; The core is hot pressed at 80°C and 0.4MPa for 8s; then cold pressed at 25°C and 0.4MPa for 8s; then packaged, baked, and injected in sequence to obtain a battery cell; Then the battery cell is placed in a pressurized forming cabinet for forming at a pressure of 0.8MPa and a temperature of 35°C for 15h. During this process, the battery cell is fully charged once and then discharged to 80% SOC. The battery cell is then placed at high temperature for 12h and sealed for the second time. The battery cell is then pressurized and divided into different volumes, the pressure for pressurization and division is 0.8 MPa, the temperature for division is 25° C., and the time for division is 12 h. Finally, three seals are performed to obtain a soft-pack lithium-ion battery cell.

[0090] Example 2-25 Examples 2-25 are used to illustrate the battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that: The hot pressing parameters, cold pressing parameters, charging degree, discharging degree, pressurized formation parameters, pressurized capacity separation parameters and diaphragm structure in the battery preparation process shown in Table 1 were used.

[0091] Comparative Examples 1-7 Comparative Examples 1-7 are used to illustrate the battery and the preparation method thereof disclosed in the present invention, and include most of the operation steps in Example 1, except that: The hot pressing parameters, cold pressing parameters, charging degree, discharging degree, pressurized formation parameters, pressurized capacity separation parameters and diaphragm structure in the battery preparation process shown in Table 1 were used.

[0092] Performance Testing The following performance tests were performed on the batteries prepared in the above Examples 1-25 and Comparative Examples 1-7: (1) Lower cabinet deformation test: visually inspect the degree of deformation.

[0093] (2) Battery cell cycle thickness increase rate performance test: the ratio of the battery cell cycled to 80% of the initial capacity and fully charged to the battery cell cycled to half-charged for the first time.

[0094] (3) Battery cycle life test: The battery is charged and discharged using a standard charging and discharging method. One full charge and one discharge is defined as one cycle.

[0095] (4) Test for lithium deposition at the tab: Disassemble the battery at the end of its cycle life and observe whether there is lithium deposition at each tab of the negative electrode.

[0096] The test results are shown in Table 2.

[0097] Table 2 Test results of Examples 1-25 and Comparative Examples 1-7

[0098] like Figure 2-Figure 3 As shown, and it can be seen from Table 2 that compared with Examples 1-10, when the battery is subjected to hot and cold pressing; and the conditions of hot pressing include: temperature of 75-90°C, pressure of 0.3-0.6MPa, and time of 8-10s; the conditions of cold pressing include: temperature of 22-26°C, pressure of 0.3-0.6MPa, and time of 8-10s, the battery is not easy to deform, and the internal moisture of the battery is reduced, the battery has a high liquid retention capacity, the cell cycle thickness increases slowly, the battery cycle life is longer, and there is no lithium precipitation problem at the pole ear.

[0099] When the hot pressing temperature is lower than 75°C, or the hot pressing pressure is lower than 0.3MPa, or the hot pressing time is lower than 8s, the battery cell may be easily deformed during use.

[0100] When the hot pressing temperature is greater than 90°C, when the hot pressing pressure is greater than 0.6MPa, and when the hot pressing time is greater than 10s, excessive pressure will occur during battery use, and the tabs will also be prone to overpressure, resulting in lithium deposition during the cycle, shortening the battery cycle life.

[0101] Compared with Examples 1-12, when the battery charge is insufficient, the deformation of the battery lower cabinet and the subsequent cycle deformation problem cannot be effectively improved; the battery cycle life is short.

[0102] Comparative Examples 13-20, when the pressure of the pressurized formation of the battery is 0.6-1.0 MPa, the temperature of the pressurized formation is 22-85° C., and the time of the pressurized formation is 2h-21h, the battery deformation is suppressed, the thickness of the battery cell increases slowly, the battery cycle life is longer, and there is no lithium precipitation at the tab; When the pressure of the pressurized formation of the battery is less than 0.6MPa, or the temperature of the pressurized formation is less than 22°C, or the time of the pressurized formation is less than 2h, the battery cell may be easily deformed during use.

[0103] When the pressure of pressurized formation is greater than 1.0MPa, or the temperature of pressurized formation is greater than 85℃, or the time of pressurized formation is greater than 21h, excessive pressure will occur during the use of the battery, and the tabs are prone to overpressure, which will cause lithium deposition during the cycle and shorten the battery cycle life.

[0104] Comparative Examples 21-25, when the pressure of the pressurized capacity separation of the battery is 0.3-0.4MPa, the temperature of the pressurized capacity separation is 22-26°C, and the time of the pressurized capacity separation is 7h-20h, the battery deformation is suppressed, the battery liquid retention is high during the use of the battery, the thickness of the battery cell increases slowly, the battery cycle life is long, and there is no lithium precipitation at the tab; When the pressure of the pressurized capacity separation of the battery is less than 0.3MPa, or the temperature of the pressurized capacity separation is less than 22℃, or the time of the pressurized capacity separation is less than 7h, the battery cell may be easily deformed during use.

[0105] When the pressure of the pressurized capacity separation of the battery is greater than 0.4MPa, or the temperature of the pressurized capacity separation is greater than 26℃, or the time of the pressurized capacity separation is greater than 20h, the pressure will be too high during the use of the battery, the pole ear is also prone to overpressure, lithium is deposited during the cycle, and the battery cycle life is shortened.

[0106] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a soft-pack lithium-ion battery, characterized in that: The method comprises the following steps: (1) Winding the positive electrode sheet, the negative electrode sheet and the separator to obtain a winding core; (2) hot and cold pressing the core obtained in step (1), and then sequentially performing packaging, liquid injection, pressurized chemical formation, and pressurized volume separation; In step (2), the hot and cold pressing includes hot pressing and cold pressing performed sequentially; the conditions of the hot pressing include: temperature of 75-90°C, pressure of 0.3-0.6MPa, and time of 8-10s; the conditions of the cold pressing include: temperature of 22-26°C, pressure of 0.3-0.6MPa, and time of 8-10s.

2. The method for preparing a soft-pack lithium-ion battery according to claim 1, characterized in that: In step (2), the pressurized forming process includes the following steps: (2.1) Place the battery cell in a pressurized forming cabinet for forming, or clamp the battery cell with a pressurized fixture for forming; during this process, fully charge the battery cell once and then discharge it to 80%-90% SOC; (2.2) Place the battery cells in step (2.1) in a pressurized formation cabinet for capacity separation, or clamp the battery cells with a pressurized fixture for capacity separation.

3. The method for preparing a soft-pack lithium-ion battery according to claim 1, characterized in that: In step (2), the pressure of the pressurized formation is 0.6-1.0 MPa, the temperature of the pressurized formation is 22-85° C., and the time of the pressurized formation is 2h-21h.

4. The method for preparing a soft-pack lithium-ion battery according to claim 1, characterized in that: In step (2), the pressure of the pressurized separation is 0.3-0.4 MPa, the temperature of the pressurized separation is 22-26° C., and the time of the pressurized separation is 7 h to 20 h.

5. The method for preparing a soft-pack lithium-ion battery according to claim 1, characterized in that: In step (1), the diaphragm includes a base film, a first film layer and a second film layer, the first film layer and the second film layer are stacked on at least one side of the base film, and the first film layer is arranged between the base film and the second film layer.

6. The method for preparing a soft-pack lithium-ion battery according to claim 5, characterized in that: The first film layer and the second film layer are stacked on one side of the base film, and the second film layer is stacked on the other side of the base film.

7. The method for preparing a soft-pack lithium-ion battery according to claim 6, characterized in that: The first film layer is a ceramic layer, and the second film layer is a rubber coating layer.

8. The method for preparing a soft-pack lithium-ion battery according to claim 7, characterized in that: In step (1), one side of the base film on which the ceramic layer and the adhesive layer are stacked is bonded to the positive electrode plate, and the other side of the base film on which the adhesive layer is stacked is bonded to the negative electrode plate.

9. The method for preparing a soft-pack lithium-ion battery according to claim 6, characterized in that: The adhesive coating layer is made by coating an oily adhesive or a water-based adhesive on the ceramic layer by roller coating or spraying. The adhesive coating layer is selected from one or more of polyvinylidene fluoride and polymethyl methacrylate.

10. The method for preparing a soft-pack lithium-ion battery according to claim 6, characterized in that: The ceramic layer is made by coating ceramic slurry on the surface of the base film, and the adhesive in the ceramic slurry is selected from one or more of polyvinyl alcohol and polyacrylic acid.

11. A soft-pack lithium-ion battery, characterized in that: The soft-pack lithium-ion battery is prepared by the method for preparing a soft-pack lithium-ion battery according to any one of claims 1 to 10.

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