A preparation method and application of a square laminated lithium ion battery capable of improving stress

Abstract

The application discloses a preparation method of a square laminated lithium ion battery capable of improving stress, and comprises the following steps: first, preparing positive electrode slurry; second, coating the positive electrode; third, preparing negative electrode slurry; fourth, coating the negative electrode; fifth, performing punching operation to obtain cut positive electrode sheet and cut negative electrode sheet C1; and sixth, sequentially performing existing laminating, welding of pole lug, shell entering, drying, liquid injection, exhaust, formation, aging and capacity distribution processes on the cut positive electrode sheet and the cut negative electrode sheet C1 obtained in the fifth step to obtain a finished square laminated lithium ion battery. The application is scientific in design, the coating process of the positive electrode sheet is improved, ceramic glue and positive electrode slurry are scientifically coated on both sides of the positive electrode sheet in a preset mode, the binding force of the bottom corner of the battery shell on the battery pole group assembled therein can be effectively reduced, the stress concentration problem existing in the square laminated lithium ion battery can be relieved, and the cycle performance of the square laminated lithium ion battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion battery, in particular to a preparation method and application of a square laminated lithium ion battery capable of improving stress. BACKGROUND

[0002] Lithium ion batteries are increasingly widely used in the field of electric vehicles due to their high energy density, long cycle life, high power density and no pollution. With the continuous improvement of the endurance mileage of electric vehicles, the requirement for the energy density of lithium ion power batteries is also increasing.

[0003] In order to pursue higher energy density, lithium ion batteries are increasingly converted from a wound structure to a laminated structure. The pole group of the laminated lithium ion power battery is usually thick, and as the cycle progresses, the pole group will continuously expand, resulting in an increase in the expansion force of the battery. Due to the limitation of the shell structure of the square laminated battery, the bottom and edges of the battery shell cannot deform, and the binding force (i.e. the binding stress) of the battery shell on the battery pole group assembled therein is more obvious, so that the problem of uneven stress on the pole group occurs during the cycle. The uneven stress on the pole group leads to different reaction degrees of the pole piece and the electrolyte. For example, the side reaction in the area where the pole piece is stressed is serious, which further increases the thickness of the pole piece, and thus increases the binding force of the battery shell, causing lithium precipitation in the negative pole piece, resulting in serious degradation of the cycle performance of the battery.

[0004] Therefore, there is an urgent need to develop a technology that can effectively reduce the binding force (i.e. the binding stress) of the battery shell bottom corner on the battery pole group assembled therein, thereby effectively alleviating the stress concentration problem of the square laminated lithium ion battery and improving the cycle performance of the square laminated lithium ion battery. SUMMARY

[0005] The purpose of the present application is to overcome the technical defects of the prior art and provide a preparation method and application of a square laminated lithium ion battery capable of improving stress.

[0006] To this end, the present application provides a preparation method of a square laminated lithium ion battery capable of improving stress, which comprises the following steps:

[0007] Firstly, the positive electrode slurry is prepared: the positive electrode active material, the conductive agent and the binder are mixed in a mass ratio of 96:2:2, then put into a solvent and fully stirred to obtain a positive electrode slurry;

[0008] Secondly, the positive electrode is coated: the positive electrode slurry and the ceramic glue are coated on the upper and lower sides of the positive electrode current collector 1 by a preset coating method, and then dried in an oven and rolled by a pole piece rolling machine to obtain an initial positive electrode piece;

[0009] Third step, negative electrode slurry preparation: the negative electrode active material, conductive agent, binder and dispersing agent, according to the mass ratio 96:2:1:1 ratio, then put into the solvent and stir evenly, mixed to obtain negative electrode slurry;

[0010] Fourth step, negative electrode coating: the negative electrode slurry obtained in the third step is uniformly coated on the negative electrode current collector, and then dried in an oven and rolled by a pole piece roller, to obtain an initial negative electrode piece C;

[0011] Fifth step, perform the punching operation: the initial positive electrode piece obtained in the second step is cut into a first fixed size of a cut positive electrode piece meeting the preset condition using a punch knife; at the same time, the initial negative electrode piece C is cut into a second fixed size of a cut negative electrode piece C1 using a punch knife;

[0012] Sixth step, the cut positive electrode piece and the cut negative electrode piece C1 obtained in the fifth step are sequentially subjected to existing processes of laminating, welding the pole lug, entering the shell, drying, liquid injection, exhaust, formation, aging and containerization, to obtain a finished square laminated lithium ion battery.

[0013] In addition, the application also provides an application of the preparation method of the square laminated lithium ion battery capable of improving stress as described above to the square laminated lithium ion battery.

[0014] From the technical solutions provided by the application, compared with the prior art, the application provides a preparation method of a square laminated lithium ion battery capable of improving stress and application, which is scientific in design, improves the coating process of the positive electrode piece, and scientifically coats the ceramic glue and the positive electrode slurry on both sides of the positive electrode piece in a predetermined manner, which can effectively reduce the restraint force (i.e. stress) of the bottom corner of the battery shell on the battery pole group assembled therein, thereby effectively relieving the stress concentration problem of the square laminated lithium ion battery, improving the cycle performance of the square laminated lithium ion battery, and having great practical significance. BRIEF DESCRIPTION OF DRAWINGS

[0015] Figure 1 The basic flowchart of the preparation method of the square laminated lithium ion battery capable of improving stress provided by the application;

[0016] Figure 2 In the preparation method of the square laminated lithium ion battery capable of improving stress provided by the application, the cross-sectional view of the first initial positive electrode piece A is shown;

[0017] Figure 3 In the preparation method of the square laminated lithium ion battery capable of improving stress provided by the application, the cross-sectional view of the second initial positive electrode piece B is shown;

[0018] In the figure: 1, positive electrode current collector (i.e. positive electrode foil), 2, positive electrode slurry area, 3, ceramic adhesive area;

[0019] 21, normal positive electrode slurry coating area, 22, positive electrode slurry thinning coating area. DETAILED DESCRIPTION

[0020] The technical solutions of the present application will be described in detail below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, not all. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0021] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application. In addition, the terms "first", "second" and the like are only for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined with "first", "second" and the like can explicitly or implicitly include one or more of the features. In the description of the present application, unless otherwise specified, the meaning of "a plurality of" is two or more.

[0022] In the description of the present application, it should be noted that unless otherwise specified and limited, the terms "mounting", "connection", "connection" should be understood broadly, for example, it can be fixedly connected, or it can be detachably connected, or integrally connected; it can be mechanically connected, or it can be electrically connected; it can be directly connected, or it can be indirectly connected through an intermediate medium; it can be the communication between the two elements inside. For those skilled in the art, the specific meaning of the above terms in the present application can be understood through specific circumstances.

[0023] The present application will be described in detail below with reference to the drawings and in conjunction with the embodiments.

[0024] Referring to Figures 1 to 3 The present application provides a preparation method of a square laminated lithium ion battery capable of improving stress, comprising the following steps:

[0025] The first step is to prepare the positive electrode slurry: the positive electrode active material (such as the positive electrode lithium iron phosphate material), the conductive agent, and the binder are mixed in a mass ratio of 96:2:2, then put into a solvent and stirred uniformly to obtain the positive electrode slurry;

[0026] In the first step, the solute of the positive electrode slurry includes the positive electrode active material, the conductive agent, and the binder. The solvent is N-methyl pyrrolidone or water.

[0027] The solid content of the positive electrode slurry is 50-65%.

[0028] In the first step, the positive electrode active material includes, but is not limited to, any one of lithium iron phosphate, nickel-cobalt-manganese ternary, nickel-cobalt-aluminum ternary, lithium cobaltate, nickelate, and manganate, and the mass of the positive electrode active material accounts for 88-98% of the total mass of the solute in the positive electrode slurry (i.e., the mass fraction).

[0029] In the first step, the conductive agent includes, but is not limited to, at least one of conductive carbon black, carbon nanotubes, and graphene, and the mass of the conductive agent accounts for 1-6% of the total mass of the solute in the positive electrode slurry.

[0030] In the first step, the binder includes, but is not limited to, polyvinylidene fluoride or an acrylic binder, and the mass of the binder accounts for 1-6% of the total mass of the solute in the positive electrode slurry.

[0031] In the first step, the binder of the positive electrode mainly functions to tightly bond the positive electrode active material (such as the positive electrode lithium iron phosphate material), the conductive agent, and the positive electrode current collector.

[0032] The second step is to coat the positive electrode: the positive electrode slurry (i.e., obtained by the first step) and the ceramic adhesive are coated on the upper and lower sides of the positive electrode current collector (such as an aluminum foil) 1 in a preset coating mode, and then the initial positive electrode sheet (which can be a first initial positive electrode sheet or a second initial positive electrode sheet) is obtained after drying in an oven and rolling in a sheet rolling machine.

[0033] In the present application, in the second step, the preset coating mode can be a first coating mode or a second coating mode.

[0034] The first coating mode is as follows:

[0035] The upper and lower sides of the positive electrode current collector 1 are each provided with a positive electrode slurry area 2 and two ceramic adhesive areas 3, and the two ceramic adhesive areas 3 are located on the left and right sides of the positive electrode slurry area 2 (i.e., at the two ends of the positive electrode current collector).

[0036] The positive electrode slurry area 2 is uniformly coated with the positive electrode slurry obtained in the first step (for example, the coating amount is 40 mg / cm2).

[0037] The ceramic adhesive area 3 is uniformly coated with ceramic adhesive;

[0038] After the coating of the positive electrode slurry and the ceramic adhesive on the upper and lower sides of the positive electrode current collector 1 (for example, an aluminum foil) is completed according to the first coating mode, and then the drying in the oven and the rolling in the electrode sheet rolling machine are performed, a first initial positive electrode sheet A is obtained.

[0039] The second coating mode is specifically as follows:

[0040] The upper and lower sides of the positive electrode current collector are each provided with a ceramic adhesive area 3, a normal positive electrode slurry coating area 21, and a thinned positive electrode slurry coating area 22;

[0041] The ceramic adhesive area 3 and the thinned positive electrode slurry coating area 22 are respectively located on the left and right sides of the normal positive electrode slurry coating area 21;

[0042] The ceramic adhesive area 3 is uniformly coated with ceramic adhesive;

[0043] The normal positive electrode slurry coating area 21 and the thinned positive electrode slurry coating area 22 are coated with the positive electrode slurry obtained in the first step;

[0044] For the thinned positive electrode slurry coating area 22, the coating amount (i.e., the coating mass per unit area) of the positive electrode slurry thereon gradually decreases (i.e., gradient decrease) from near to far according to the interval distance between the thinned positive electrode slurry coating area 22 and the normal positive electrode slurry coating area 21;

[0045] The coating amount of the positive electrode slurry at all positions of the thinned positive electrode slurry coating area 22 is less than the coating amount of the positive electrode slurry on the normal positive electrode slurry coating area 21;

[0046] After the coating of the positive electrode slurry and the ceramic adhesive on the upper and lower sides of the positive electrode current collector (for example, an aluminum foil) is completed according to the second coating mode, and then the drying in the oven and the rolling in the electrode sheet rolling machine are performed, a second initial positive electrode sheet B is obtained.

[0047] In the second step, the ceramic adhesive includes a solute and a solvent;

[0048] The solute includes ceramic and a binder;

[0049] The ceramic adhesive has a solid content of 30-40%.

[0050] In the second step, the ceramic adhesive specifically includes ceramic, a binder, and a solvent;

[0051] The ceramic is specifically aluminum oxide or bormite, and the mass of the ceramic accounts for 25-35% of the total mass of the ceramic adhesive (i.e., mass fraction);

[0052] The binder is specifically polyvinylidene fluoride, and the mass of the binder accounts for 5-15% of the total mass of the ceramic adhesive.

[0053] The solvent is N-methyl pyrrolidone, and the mass of the solvent accounts for 60-70% of the total mass of the ceramic adhesive.

[0054] In the second step, specifically, the preparation of the ceramic adhesive is specifically as follows: first, the binder and the solvent are mixed and stirred to obtain a glue solution, and then the ceramic and the glue solution are mixed and stirred, so that the ceramic adhesive is obtained.

[0055] It should be noted that in the present application, the ceramic adhesive used in the first coating method is completely the same as the ceramic adhesive used in the second coating method.

[0056] In the present application, specifically, for the first coating method, the coating amount of the positive electrode slurry area 2 is uniform, and the coating amount is set to ensure a proper N / P ratio (i.e., the ratio of the actual capacity of the negative electrode and the positive electrode material per unit area, for example, between 1.1-1.5), so as to avoid the battery from lithium precipitation due to the lack of sufficient lithium ion receiving sites in the negative electrode.

[0057] It should be noted that if the N / P ratio is less than 1.0, there will not be enough sites in the negative active material to insert lithium ions, which will cause the battery to precipitate lithium. If the N / P ratio is too large, there will be too much negative active material, which will not only cause the electrolyte to be consumed quickly, affecting the cycle performance, but also reduce the energy density of the battery. Therefore, the N / P ratio is generally set to be between 1.1-1.5.

[0058] Specifically, the coating amount of the positive electrode slurry area 2 can be set to ensure the desired N / P ratio according to the following formula (1).

[0059]

[0060] Specifically, for the first coating method, the ceramic adhesive area 3 is adjacent to the positive electrode slurry area 2.

[0061] The overlapping area of the ceramic adhesive area 3 and the positive electrode slurry area 2 is 0-3 mm, so as to ensure that there is no gap between them.

[0062] Specifically, for the first coating method, the transverse width of a single ceramic adhesive area 3 Figure 2 There are four ceramic adhesive areas 3 in total.

[0063] Specifically, for the first coating method, the ratio of the transverse width of a single ceramic adhesive area 3 to the transverse width of the positive electrode current collector 1 (such as aluminum foil) is preferably 0.5%-3%;

[0064] The ratio of the transverse width of a single ceramic adhesive area 3 to the transverse width of a single positive electrode slurry area 2 is preferably greater than 0 and less than 2%.

[0065] In a specific implementation, for the first coating method, the thickness of the ceramic adhesive during coating is lower than the thickness of the positive electrode slurry on the positive electrode slurry area 2 during coating, so as to avoid cracks and broken strips during rolling.

[0066] In the present application, in a specific implementation, for the second coating method, the coating amount of the positive electrode slurry on the normal positive electrode slurry coating area 21 is set to 40 mg / cm 2 ;

[0067] The positive electrode slurry thinning coating area 22 is adjacent to the normal positive electrode slurry coating area 21.

[0068] The coating amount of the positive electrode slurry thinning coating area 22 gradually decreases (i.e. gradient decrease) from the initial 40 mg / cm 2 to 36 mg / cm 2 , according to the interval distance between the positive electrode slurry thinning coating area 22 and the normal slurry coating area 21.

[0069] In a specific implementation, for the second coating method, the coating amount of the positive electrode slurry thinning coating area 22 gradually decreases by 0.8-1.2 mg / cm 2 for each centimeter of interval distance, according to the interval distance between the positive electrode slurry thinning coating area 22 and the normal slurry coating area 21.

[0070] In a specific implementation, for the second coating method, the lateral width of a single ceramic adhesive area 3 is 1-10 mm.

[0071] In a specific implementation, for the second coating method, the ratio of the lateral width of a single ceramic adhesive area 3 to the lateral width of the positive electrode current collector 1 (such as aluminum foil) is preferably 0.5%-3%.

[0072] The ratio of the lateral width of a single ceramic adhesive area 3 to the lateral width of a single normal positive electrode slurry coating area 21 is preferably greater than 0 and less than 2%.

[0073] In a specific implementation, for the second coating method, the thickness of the ceramic adhesive during coating is lower than the thickness of the positive electrode slurry on the normal positive electrode slurry coating area 21 during coating, so as to avoid cracks and broken strips during rolling.

[0074] In the present application, in a specific implementation, for the second coating method, the N / P ratio (i.e. the actual capacity ratio of the negative electrode and the positive electrode material per unit area) of the positive electrode slurry thinning coating area 22 is greater than the N / P ratio of the normal positive electrode slurry coating area 21.

[0075] It should be noted that the final purpose of the thinning area (i.e., the positive slurry thinning coating area 22) is to reduce the thickness of the area. Under the condition that the solid content of the slurry is constant, the lower the coating amount, the thinner the coating thickness. N / P is inversely proportional to the positive coating amount. The coating amount of the thinning area (i.e., the positive slurry thinning coating area 22) is lower than that of the normal coating area (i.e., the positive slurry normal coating area 21), so the N / P ratio of the thinning area is naturally greater than that of the normal coating area. The greater the N / P, the less likely the battery is to lithiumize.

[0076] In a specific implementation, the coating amount can be adjusted by the coating equipment, as long as the coating amount of the thinning area (i.e., the positive slurry thinning coating area 22) is less than that of the normal coating area (i.e., the positive slurry normal coating area 21), the N / P ratio of the thinning area can be ensured to be greater than that of the normal coating area.

[0077] In a specific implementation, for the second coating mode, the positive slurry coating amount on the positive slurry normal coating area 21 is set to ensure a suitable N / P ratio (for example, between 1.1 and 1.5) to avoid battery lithiumization.

[0078] It should be noted that an N / P ratio less than 1.0 will result in insufficient sites in the negative active material for embedding lithium ions, thus causing the battery to lithiumize. If the N / P ratio is too large, there is too much negative active material, which on the one hand will cause the electrolyte to be consumed quickly, affecting the cycle performance, and on the other hand will reduce the energy density of the battery. Therefore, the N / P ratio is generally set to be between 1.1 and 1.5.

[0079] As described above, the coating amount of the positive slurry normal coating area 21 can be set according to the above formula (1) to ensure that the desired N / P ratio is obtained.

[0080] Third step, negative slurry preparation: the negative active material (for example, graphite material), conductive agent, binder and dispersant are mixed in a mass ratio of 96:2:1:1, then put into a solvent and fully stirred to obtain a negative slurry;

[0081] In the third step, the solute of the negative slurry includes the negative active material, the conductive agent, the binder and the dispersant;

[0082] The solvent is deionized water;

[0083] The solid content of the negative slurry is 40-50%.

[0084] In the third step, the negative active material includes, but is not limited to, at least one of graphite and silicon, and the mass of the negative active material accounts for 86-97% of the total mass of the solute in the negative slurry;

[0085] In the third step, the conductive agent, including but not limited to at least one of conductive carbon black and graphene, accounts for 1-5% of the total mass of the solute in the negative electrode slurry;

[0086] In the third step, the dispersant, including but not limited to sodium carboxymethyl cellulose, accounts for 1-4% of the total mass of the solute in the negative electrode slurry.

[0087] In the third step, the binder, including but not limited to at least one of styrene-butadiene rubber and acrylic binder, accounts for 1-5% of the total mass of the solute in the negative electrode slurry.

[0088] It should be noted that the binder of the negative electrode can be styrene-butadiene rubber, polyacrylic acid, etc., and its function is to tightly bond the negative electrode active material, the conductive agent, and the negative electrode current collector.

[0089] In the fourth step, the negative electrode is coated: the negative electrode slurry obtained in the third step is uniformly coated on the negative electrode current collector (such as a copper foil, for example, with a coating amount of 18.6 mg / cm 2 ) and then dried in an oven and rolled by a pole piece roller to obtain an initial negative electrode piece C;

[0090] In the fifth step, the punching operation is performed: the initial positive electrode piece obtained in the second step is cut into a first fixed size of a cut positive electrode piece that meets the preset conditions using a punch; at the same time, the initial negative electrode piece C is cut into a second fixed size of a cut negative electrode piece C1 using a punch.

[0091] In the fifth step, the size of the cut negative electrode piece C1 (i.e., the second fixed size) is larger (e.g., one circle larger) than the size of the cut positive electrode piece (i.e., the first fixed size), and the purpose is to ensure that the cut negative electrode piece C1 can completely cover the cut positive electrode piece, with a covering amount of 1-5 mm.

[0092] In the fifth step, when the initial positive electrode piece obtained in the second step is the first initial positive electrode piece A obtained by the first coating method, the first initial positive electrode piece A is cut into a first fixed size of a first cut positive electrode piece A1 that meets the preset conditions using a punch.

[0093] At this time, the preset condition is that in the first cut positive electrode piece A1 obtained by cutting, the ceramic adhesive area 3 (i.e., the remaining ceramic adhesive area after cutting) that is still coated with ceramic adhesive is located at one end of the first cut positive electrode piece A1 as the bottom (i.e., the bottom of the battery pole group), and at this time, the total area of the ceramic adhesive area 3 (including the surface area of the upper and lower sides) accounts for 1-3% of the total area of the entire first cut positive electrode piece A1 (including the surface area of the upper and lower sides).

[0094] In the fifth step, specifically, when the initial positive plate obtained in the second step is the second initial positive plate B obtained by the second coating method, the second initial positive plate B is cut into the second cut positive plate B1 of the first fixed size and meeting the preset condition by using a punch knife.

[0095] At this time, the preset condition is that, in the second cut positive plate B1 obtained after cutting, the positive slurry thinning coating area 22 is located at one end of the second cut positive plate B1 as a bottom (i.e., the bottom of the battery pole group), and the coating amount of the positive slurry on the positive slurry thinning coating area 22 is less than the coating amount of the positive slurry on the positive slurry normal coating area 21, and at this time, the total area (including the upper and lower surface areas) of the positive slurry thinning coating area 22 accounts for 5-15% of the total area (including the upper and lower surface areas) of the entire second cut positive plate B1.

[0096] In the sixth step, the cut positive plate (for example, the first cut positive plate A1 or the second cut positive plate B1) obtained in the fifth step and the cut negative plate C1 are sequentially subjected to the existing processes of lamination, welding of the tab, entering the shell, drying, liquid injection, exhaust, formation, aging, and containerization (all using the existing conventional lamination battery production processes) to obtain a finished square lamination lithium ion battery.

[0097] It should be noted that, for the finished square lamination lithium ion battery, the existing Arbin, Hangke, and other conventional charge-discharge cycle test equipment can be used for charge-discharge cycle test, and the existing expansion force test equipment can be used to test the maximum expansion force of the finished square lamination lithium ion battery.

[0098] In order to more clearly understand the technical solutions of the present application, the technical solutions of the present application will be described below through specific embodiments.

[0099] Reference Example:

[0100] For a finished lamination battery, the following preparation steps (which are the preparation process of an existing ordinary battery) are included:

[0101] 1. The positive slurry and the ceramic adhesive are simultaneously and uniformly coated on the positive current collector to obtain a positive plate after drying and rolling. The positive plate is provided with a positive slurry area and an upper ceramic adhesive area. In order to ensure the N / P ratio, the positive slurry area is uniformly coated, and the coating amount is set to 40 mg / cm 2 . The upper ceramic adhesive area is adjacent to the slurry area, the width of the ceramic adhesive area is 6 mm, and the ceramic adhesive area overlaps the positive slurry area by 0.5 mm.

[0102] 2. The negative slurry is uniformly coated on the negative current collector to obtain a negative plate after drying and rolling. The coating amount of the negative plate is 18.6 mg / cm 2.

[0103] 3) The positive electrode sheet is cut by a punch knife, and the height of the ceramic glue reserved at the top end of the cut electrode sheet is 3 mm. The negative electrode sheet is cut by a punch knife to obtain an electrode sheet.

[0104] 4) The positive and negative electrode sheets are laminated, the tabs are welded, the shell is entered, dried, liquid injected, degassed, formed, aged, and divided to obtain a finished laminated battery.

[0105] 5) The finished laminated battery is tested by 1C (i.e. 100% discharge depth), 45℃ cycle test on the existing Arbin device, and the test results are shown in Table 1.

[0106] Example 1:

[0107] Based on the first coating method of the positive electrode sheet provided by the present application, a finished laminated battery is prepared. Specifically, the following steps are included:

[0108] 1) The positive electrode slurry and ceramic glue are simultaneously and uniformly coated on the positive current collector, and after drying and rolling, a positive electrode sheet is obtained. The positive electrode sheet is provided with an upper ceramic glue area, a slurry area and a lower ceramic glue area. The positive electrode slurry area is adjacent to the upper and lower ceramic areas, and the width of the positive electrode slurry area is uniformly coated with a positive electrode slurry area coating amount of 40 mg / cm 2 . The ceramic glue area is adjacent to the positive electrode slurry area, and the width of the upper and lower ceramic glue area is 6 mm, and the ceramic glue area overlaps the positive electrode slurry area by 0.5 mm.

[0109] It should be noted that the ceramic glue coating amount has no special requirements, and the thickness of the dried ceramic glue should be lower than the thickness of the positive electrode slurry.

[0110] 2) The negative electrode slurry is uniformly coated on the negative current collector, and after drying and rolling, a negative electrode sheet is obtained. The coating amount of the negative electrode sheet is 18.6 mg / cm 2 .

[0111] 3) The positive electrode sheet is cut by a punch knife, and the height of the ceramic glue reserved at the top end of the cut electrode sheet is 3 mm. The negative electrode sheet is cut by a punch knife to obtain an electrode sheet.

[0112] 4) The positive and negative electrode sheets are laminated, the tabs are welded, the shell is entered, dried, liquid injected, degassed, formed, aged, and divided to obtain a finished square laminated lithium ion battery.

[0113] 5) The finished square laminated lithium ion battery is tested by 1C, 100% DOD (i.e. 100% discharge depth), 45℃ cycle test on the existing Arbin device, and the test results are shown in Table 1.

[0114] Example 2:

[0115] Based on the second coating method of the positive electrode sheet provided by the present application, a finished product of a stacked battery is prepared. Specifically, the following steps are included:

[0116] 1. The positive electrode slurry is coated on the current collector, and after drying in an oven and rolling, a positive electrode sheet is obtained. The positive electrode sheet is provided with a ceramic adhesive area, a normal positive electrode slurry coating area, and a positive electrode slurry thinning coating area. The coating amount of the positive electrode sheet is set to ensure a suitable N / P ratio to avoid lithium precipitation in the battery. The normal positive electrode slurry coating area is adjacent to the ceramic adhesive area and the positive electrode slurry thinning coating area, wherein the coating amount gradient of the normal positive electrode slurry coating area to the positive electrode slurry thinning coating area decreases, and the N / P ratio of the positive electrode slurry thinning coating area is greater than that of the normal coating area. The normal coating amount is set to 40 mg / cm 2 , the positive electrode slurry thinning coating area is adjacent to the normal positive electrode slurry coating area, and the coating amount gradient decreases from 40 mg / cm 2 to 36 mg / cm 2 .

[0117] It should be noted that there is no special requirement for the coating amount of the ceramic adhesive, and it is only required that the thickness of the dried ceramic adhesive is lower than that of the positive electrode slurry.

[0118] 2. The negative electrode slurry is uniformly coated on the negative electrode current collector, and after drying and rolling, a negative electrode sheet is obtained. The coating amount of the negative electrode sheet is 18.6 mg / cm2.

[0119] 3. The positive and negative electrode sheets are cut using a punch knife.

[0120] 4. The cut electrode sheets are stacked, the tabs are welded, the shell is entered, dried, liquid injected, degassed, formed, aged, and separated to obtain a finished product of a square stacked lithium ion battery.

[0121] 5. The finished product of the square stacked lithium ion battery is tested on the existing Arbin device at 1C, 100% DOD (i.e. 100% discharge depth), and 45°C. The test results are shown in Table 1.

[0122] Table 1:

[0123] Temperature Cycle number Capacity retention rate Maximum swelling force Reference example 45 degrees 1000 87％ 9 KN Example 1 45 degrees 1000 89％ 6.7 KN Example 2 45 degrees 1000 89％ 6.5 KN

[0124] It should be noted that the maximum expansion force in Table 1 refers to the maximum expansion force generated by the expansion of the electrode group during the cycling process of the finished battery.

[0125] As can be seen from the test results in Table 1 above, under the same number of cycles, both of the two improvement methods (including the first coating method of the positive electrode sheet and the second coating method of the positive electrode sheet) of the present application can reduce the cycle expansion force (obtained by existing measurement means) of the battery, thereby improving the cycle performance of the battery.

[0126] It should be noted that in the above embodiment 1, the first coating method in the application is introduced, and the difference between the comparative example is that the ceramic glue is coated on the bottom of the positive plate, which increases the distance between the positive paste and the bottom of the shell, and the other parts are the same. Because the bottom of the shell is not easy to deform, the stress of the battery is greater near the bottom of the shell. After increasing the distance between the positive paste and the bottom of the shell, the positive plate at the position with the greatest stress is removed, so the overall battery stress is reduced.

[0127] In the above embodiment 2, the second coating method in the application is introduced, and the difference between the comparative example is that the coating amount of the positive plate bottom is reduced, and the other parts are the same. After thinning the bottom of the pole group, the excess space at the bottom of the battery is increased, and the bottom of the pole group has enough expansion space to ensure that it is not restricted by the shell, thereby reducing the stress of the battery.

[0128] It should be noted that in the application, the stress of the battery is the stress generated by the expansion of the pole group but restricted by the shell during the cycle process. The greater the expansion force of the pole group, the greater the stress of the battery.

[0129] In the application, in a specific implementation, the application provides a preparation method of a square stacked lithium ion battery capable of improving stress, which is applied to the square stacked lithium ion battery.

[0130] Compared with the prior art, the preparation method of the square stacked lithium ion battery capable of improving stress and the application provided by the application have the following beneficial effects:

[0131] The application does not need to change the battery structure or add new equipment, only needs to make scientific changes in the coating process of the positive plate, so that the stress at the bottom of the stacked lithium ion battery can be reduced, and the cycle performance of the stacked lithium ion battery can be improved.

[0132] For the application, the principle of reducing the stress at the bottom of the battery is that the insulating ceramic glue is coated on the bottom of the positive plate (i.e. one end of the bottom of the battery pole group), or the coating amount of the positive paste in the bottom area of the positive plate is reduced, the shell ratio of the bottom of the battery (i.e. the ratio between the volume of the battery pole group and the volume of the battery shell) is reduced, and enough expansion space is given to the bottom of the battery pole group, so that the lithium ion is difficult to be inserted and extracted due to the stress restriction of the external battery shell at the bottom of the battery pole group.

[0133] It should be noted that for the application, based on the first coating method, the ceramic glue is coated on the bottom of the positive plate, which increases the distance between the positive paste and the bottom of the shell, effectively reduces the restriction of the battery shell on the pole group, and thus reduces the stress.

[0134] For the present application, based on the second coating method, the coating amount of the positive plate bottom is reduced, the thickness of the positive group bottom is reduced, the entry shell ratio is reduced, and enough expansion space can be given to the positive group, thereby reducing the stress.

[0135] In summary, compared with the prior art, the present application provides a preparation method and application of a square stacked lithium ion battery capable of improving stress, which is scientifically designed. By improving the coating process of the positive plate, the ceramic glue and the positive paste are coated on both sides of the positive plate in a predetermined manner, which can effectively reduce the restraint force (i.e. restraint stress) of the bottom corner of the battery shell on the battery group assembled therein, thereby effectively relieving the stress concentration problem of the square stacked lithium ion battery, improving the cycle performance of the square stacked lithium ion battery, and having great practical significance.

[0136] The above description is only the preferred embodiments of the present application, and it should be pointed out that for ordinary skilled in the art, without departing from the principles of the present application, a number of improvements and refinements can be made, and these improvements and refinements should be considered as the protection scope of the present application.

Claims

1. A method for producing a square-shaped laminated lithium-ion battery for stress improvement, characterized by, The method comprises the following steps: The first step is to make the positive electrode slurry: the positive electrode active material, the conductive agent and the binder are mixed in a mass ratio of 96:2:2, then put into the solvent and fully stirred to obtain the positive electrode slurry; The second step is to coat the positive electrode: the positive electrode slurry and the ceramic adhesive are coated on the upper and lower sides of the positive electrode current collector (1) by a preset coating method, then dried in an oven and rolled by a pole piece roller, and the initial positive electrode piece is obtained; The third step is to make the negative electrode slurry: the negative electrode active material, the conductive agent, the binder and the dispersing agent are mixed in a mass ratio of 96:2:1:1, then put into the solvent and fully stirred to obtain the negative electrode slurry; The fourth step is to coat the negative electrode: the negative electrode slurry obtained in the third step is uniformly coated on the negative electrode current collector, then dried in an oven and rolled by a pole piece roller, and the initial negative electrode piece C is obtained; The fifth step is to perform the punching operation: the initial positive electrode piece obtained in the second step is cut into a first fixed size by a punch knife, and the initial negative electrode piece C is cut into a second fixed size by a punch knife; The sixth step is to perform the existing stacking, welding of the tab, shell entering, drying, liquid injection, exhaust, formation, aging and containerization procedures on the cut positive electrode piece and the cut negative electrode piece C1 obtained in the fifth step, and the finished square stacked lithium ion battery is obtained; The positive electrode piece is located at the bottom of the battery shell in the battery, the distance between the positive electrode slurry and the bottom of the shell is increased by the ceramic adhesive at the bottom of the positive electrode piece, or the coating area (22) at the bottom of the positive electrode piece is thinned, the bottom of the pole group is thinned, the expansion space is reserved for the bottom of the pole group, and the constraint of the shell is prevented; The preset coating method is the first coating method or the second coating method; In the first coating method, the positive electrode piece has two ceramic adhesive areas (3) and one positive electrode slurry area (2), and the two ceramic adhesive areas (3) are located on the left and right sides of the positive electrode slurry area (2); the total area of the ceramic adhesive area (3) of the positive electrode piece formed by the first coating method accounts for 1-3% of the total area of the first cut positive electrode piece A1. In the second coating mode, the positive electrode sheet has one ceramic adhesive area (3) and one positive electrode slurry thinning coating area (22) and one positive electrode slurry normal coating area (21), the ceramic adhesive area (3) and the positive electrode slurry thinning coating area (22) are respectively located on the left and right sides of the positive electrode slurry normal coating area (21); for the positive electrode slurry thinning coating area (22), the coating amount of the positive electrode slurry thereon gradually decreases from near to far according to the interval distance between the positive electrode slurry thinning coating area (22) and the slurry normal coating area (21); the coating amount of the positive electrode slurry at all positions of the positive electrode slurry thinning coating area (22) is less than the coating amount of the positive electrode slurry on the positive electrode slurry normal coating area (21), the N / P ratio of the positive electrode slurry thinning coating area (22) is greater than the N / P ratio of the positive electrode slurry normal coating area (21), the thickness of the ceramic adhesive area (3) formed by the second coating mode is lower than the thickness of the positive electrode slurry on the positive electrode slurry normal coating area (21) during coating; the total area of the positive electrode slurry thinning coating area (22) of the positive electrode sheet formed by the second coating mode accounts for 5-15% of the total area of the second cut positive electrode sheet B1.

2. The method for preparing a square stacked lithium-ion battery with improved stress as described in claim 1, characterized in that, Wherein, The first coating mode is specifically as follows: The upper and lower sides of the positive electrode current collector (1) are each provided with one positive electrode slurry area (2) and two ceramic adhesive areas (3); The positive electrode slurry area (2) is uniformly coated with the positive electrode slurry obtained in the first step; The ceramic adhesive area (3) is uniformly coated with ceramic adhesive; After completing the coating of the positive electrode slurry and the ceramic adhesive on the upper and lower sides of the positive electrode current collector according to the first coating mode, and then drying in an oven and rolling in a sheet rolling machine, a first initial positive electrode sheet A is obtained; Wherein, the second coating mode is specifically as follows: The upper and lower sides of the positive electrode current collector (1) are each provided with one ceramic adhesive area (3), one positive electrode slurry normal coating area (21) and one positive electrode slurry thinning coating area (22); The ceramic adhesive area (3) is uniformly coated with ceramic adhesive; The positive electrode slurry normal coating area (21) and the positive electrode slurry thinning coating area (22) are coated with the positive electrode slurry obtained in the first step; After completing the coating of the positive electrode slurry and the ceramic adhesive on the upper and lower sides of the positive electrode current collector according to the second coating mode, and then drying in an oven and rolling in a sheet rolling machine, a second initial positive electrode sheet B is obtained.

3. The method of claim 1, wherein the method is for preparing a stress-improved square-shaped lithium ion battery. In the first step, the solute of the positive electrode slurry includes positive electrode active material, conductive agent and binder; the solvent is N-methyl pyrrolidone or water; The solid content of the positive electrode slurry is 50-65%; In the first step, the positive electrode active material includes any one of lithium iron phosphate, nickel cobalt manganese ternary, nickel cobalt aluminum ternary, lithium cobaltate, nickelate and manganate, and the mass of the positive electrode active material accounts for 88-98% of the total mass of the solute in the positive electrode slurry; In the first step, the conductive agent includes at least one of conductive carbon black, carbon nanotube and graphene, and the mass of the conductive agent accounts for 1-6% of the total mass of the solute in the positive electrode slurry; In the first step, the binder includes polyvinylidene fluoride or acrylic binder, and the mass of the binder accounts for 1-6% of the total mass of the solute in the positive electrode slurry.

4. The method of claim 2, wherein the method is a method of preparing a stress-improved square-shaped laminated lithium ion battery, characterized by, In the second step, for the second coating mode, the coating amount of the positive electrode slurry on the normal positive electrode slurry coating area (21) is set to 40 mg / cm2 2 ; The positive electrode slurry thinning coating area (22) is adjacent to the positive electrode slurry normal coating area (21); The coating amount of the positive electrode slurry thinning coating area (22) is gradually reduced from the initial 40 mg / cm 2 to 36 mg / cm 2 from near to far according to the interval distance of the positive electrode slurry thinning coating area (22) and the slurry normal coating area (21).

5. The method for preparing a square stacked lithium-ion battery with improved stress as described in claim 2, characterized in that, In the second step, for the first coating mode, the ceramic adhesive area (3) is immediately adjacent to the positive electrode slurry area (2); The overlapping area of the ceramic adhesive area (3) and the positive electrode slurry area (2) is 0-3mm, ensuring that there is no gap between the two; For the first coating mode, the lateral width of a single ceramic adhesive area (3) is 1-10mm; For the first coating mode, the ratio of the lateral width of a single ceramic adhesive area (3) to the lateral width of the positive electrode current collector (1) is 0.5%-3%; The ratio of the lateral width of a single ceramic adhesive area (3) to the lateral width of a single positive electrode slurry area (2) is greater than 0 and less than 2%.

6. The method for preparing a square stacked lithium-ion battery with improved stress as described in claim 2, characterized in that, For the second coating mode, the lateral width of a single ceramic adhesive area (3) is 1-10mm; For the second coating mode, the ratio of the lateral width of a single ceramic adhesive area (3) to the lateral width of the positive electrode current collector (1) is 0.5%-3%; The ratio of the lateral width of a single ceramic adhesive area (3) to the lateral width of a single positive electrode slurry normal coating area (21) is greater than 0 and less than 2%.

7. The method of claim 1, wherein the method is for preparing a stress-improved square-shaped lithium ion battery. In the third step, the solute of the negative electrode slurry includes a negative electrode active material, a conductive agent, a binder, and a dispersant; The solvent is deionized water; The solid content of the negative electrode slurry is 40-50%; In the third step, the negative electrode active material includes at least one of graphite and silicon, and the mass of the negative electrode active material accounts for 86-97% of the total mass of the solute in the negative electrode slurry; In the third step, the conductive agent includes at least one of conductive carbon black and graphene, and the mass of the conductive agent accounts for 1-5% of the total mass of the solute in the negative electrode slurry; In the third step, the dispersant includes sodium carboxymethyl cellulose, and the mass of the dispersant accounts for 1-4% of the total mass of the solute in the negative electrode slurry; In the third step, the binder includes at least one of styrene-butadiene rubber and an acrylic binder, and the mass of the binder accounts for 1-5% of the total mass of the solute in the negative electrode slurry.

8. The method of claim 1, wherein the method is for preparing a stress-improved square-shaped lithium ion battery. In the fifth step, the second fixed size of the cut negative electrode sheet C1 is larger than the first fixed size of the cut positive electrode sheet. The cut negative electrode sheet C1 can completely cover the cut positive electrode sheet.

9. The method of claim 2, wherein the method is for improving stress of a square- shaped laminated lithium ion battery. In the fifth step, when the initial positive electrode sheet obtained in the second step is a first initial positive electrode sheet A obtained by the first coating mode, the first initial positive electrode sheet A is cut into a first cut positive electrode sheet A1 of a first fixed size that meets the preset condition using a punch knife. At this time, the preset condition is that, in the first cut positive electrode sheet A1 obtained after cutting, the ceramic adhesive area (3) where the ceramic adhesive is still coated is located at one end of the first cut positive electrode sheet A1 as a bottom end. Alternatively, in the fifth step, when the initial positive electrode sheet obtained in the second step is a second initial positive electrode sheet B obtained by the second coating mode, the second initial positive electrode sheet B is cut into a second cut positive electrode sheet B1 of a first fixed size that meets the preset condition using a punch knife. At this time, the preset condition is that, in the second cut positive electrode sheet B1 obtained after cutting, the positive electrode slurry thinning coating area (22) is located at one end of the second cut positive electrode sheet B1 as a bottom end, and the coating amount of the positive electrode slurry on the positive electrode slurry thinning coating area (22) is less than the coating amount of the positive electrode slurry on the positive electrode slurry normal coating area (21).

10. Use of a stress-improved square-laminate lithium-ion battery according to any one of claims 1 to 9 for the preparation of a method for the production of a square-laminate lithium-ion battery. Application to prismatic laminated lithium-ion batteries. Application to prismatic laminated lithium-ion batteries.

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