Preparation method of secondary battery, secondary battery, energy storage system and electric equipment

Abstract

The invention relates to the field of batteries, and provides a preparation method of a secondary battery, the secondary battery, an energy storage system and electric equipment.The method comprises the steps that under the condition that a historical batch and an initial batch are different and a target viscosity difference value is larger than a second difference value threshold value, an injection step is executed; an injection step of injecting a predetermined mass of a solvent into the initial slurry to reduce the target viscosity difference to obtain a first target slurry, the predetermined mass being calculated according to a formula m = a * [delta] [mu] + b * [mu] 1; obtaining the viscosity of the first target slurry to obtain a prepared viscosity, and determining whether the prepared viscosity is equal to the target viscosity or not; and coating the surface of at least one of the positive pole piece and the negative pole piece with the second target slurry to obtain a target pole piece. According to the method, the technical problem of how to improve the adjustment accuracy of the viscosity of the slurry in the preparation process of the secondary battery is solved.

Description

Technical Field

[0001] The present application relates to the field of batteries, and more particularly, to a method for preparing a secondary battery, a secondary battery, an energy storage system, and an electrical device. Background Art

[0002] Slurry preparation is a key step in the manufacturing process of secondary batteries. Currently, in the slurry manufacturing process, after the slurry is prepared, the viscosity of the slurry is detected. If the viscosity does not meet the standard, it is adjusted, but the accuracy of the adjustment is relatively low.

[0003] Therefore, there is an urgent need for a method for preparing a secondary battery that can solve the problem of how to improve the accuracy of slurry viscosity adjustment.

[0004] The above information disclosed in the background art is only used to enhance the understanding of the background art of the technology described in this article. Therefore, the background art may contain certain information that is not prior art known to those skilled in the art in their own country. Summary of the Invention

[0005] The main object of the present application is to provide a method for preparing a secondary battery, a secondary battery, an energy storage system, and an electrical device, so as to solve the problem of how to accurately adjust the viscosity of the slurry during the preparation of the secondary battery in the prior art.

[0006] To achieve the above object, according to one aspect of the present application, a method for preparing a secondary battery is provided, including: a first obtaining step of obtaining a target viscosity difference of an initial slurry, a current viscosity of the initial slurry, and a historical batch of the initial slurry, where the target viscosity difference is the difference between the actual viscosity and the target viscosity of the initial slurry, the current viscosity is the viscosity of the initial slurry at the current moment, and the historical batch is the batch of the material of the previous cylinder of the initial slurry; a first determining step of determining whether the historical batch and the initial batch are the same and the magnitude relationship between the target viscosity difference and a first difference threshold and a second difference threshold, where the initial batch is the batch of the material of the initial slurry, the second difference threshold is greater than the first difference threshold, and in the case where the historical batch and the initial batch are different and the target viscosity difference is greater than the second difference threshold, an injection step is executed, and in the case where the historical batch and the initial batch are the same or the historical batch and the initial batch are different and the target viscosity difference is greater than or equal to the first difference threshold and less than or equal to the second difference threshold, a processing step is executed; the injection step of injecting a predetermined mass of solvent into the initial slurry to reduce the target viscosity difference and obtain a first target slurry, where the predetermined mass is calculated according to the formula m = a×Δμ + b×μ1, m is the predetermined mass, Δμ is the target viscosity difference, μ1 is the current viscosity, the value range of a is -0.03 to -0.01, and the value range of b is 120 to 130; the processing step of performing a predetermined treatment on the initial slurry to reduce the target viscosity difference and obtain the first target slurry; a second obtaining step of obtaining the viscosity of the first target slurry to obtain a preliminary viscosity and determining the magnitude relationship between the difference between the preliminary viscosity and the target viscosity and a third difference threshold; a repeating step of, in the case where the difference between the preliminary viscosity and the target viscosity is greater than the third difference threshold, sequentially repeating the first obtaining step, the first determining step, the injection step or the processing step, and the second obtaining step at least once until the preliminary viscosity is equal to the target viscosity, and determining the first target slurry as a second target slurry; a coating step of coating the second target slurry on the surface of at least one of a positive electrode plate and a negative electrode plate to obtain a target electrode plate.

[0007] Further, obtaining the target viscosity difference of the initial slurry includes: obtaining the target viscosity and the target temperature, where the target viscosity is the ideal viscosity of the initial slurry, and the target temperature is the temperature preset to enable the initial slurry to reach the viscosity corresponding to the target viscosity; obtaining the mapping relationship between the viscosity of the slurry and the temperature of the slurry; according to the mapping relationship and the target temperature, determining the viscosity of the initial slurry corresponding to the target temperature as the actual viscosity; calculating the difference between the actual viscosity and the target viscosity to obtain the target viscosity difference.

[0008] Further, obtaining the mapping relationship between the viscosity of the slurry and the temperature of the slurry includes: obtaining a plurality of historical viscosities of the slurry and a plurality of historical temperatures of the slurry, where the historical viscosities and the historical temperatures correspond one by one, and the temperature range of the historical temperatures is 20°C to 50°C; fitting the plurality of historical viscosities and the plurality of historical temperatures to obtain the expression of the mapping relationship as: μ = x×T y , where μ is the viscosity of the initial slurry, T is the temperature of the initial slurry, x > 0, y < 0.

[0009] Further, the predetermined treatment includes at least one of the following: increasing the stirring duration of the initial slurry to a predetermined duration, where the predetermined duration is 30 to 120 min; increasing the stirring speed of the initial slurry to a first predetermined speed, where the first predetermined speed is 5 to 18 m / s; increasing the dispersion speed of the initial slurry to a second predetermined speed, where the second predetermined speed is 500 to 2000 rmp.

[0010] Further, after the second obtaining step and before the coating step, the method further includes: when the preliminary viscosity is equal to the target viscosity, determining the first target slurry as the second target slurry.

[0011] Further, the ratio of the second difference threshold to the first difference threshold is 1 to 1.5.

[0012] Further, after the coating step, the method further includes: rolling the target electrode sheet, and winding the rolled target electrode sheet and the separator to obtain an electric core; encapsulating and injecting electrolyte into the electric core to obtain a secondary battery.

[0013] To achieve the above object, according to one aspect of the present application, there is provided a secondary battery, which is prepared by using any one of the preparation methods of the secondary battery.

[0014] According to another aspect of the present application, there is provided an energy storage system including a plurality of the secondary batteries.

[0015] According to another aspect of the present application, there is provided an electrical device including the secondary battery or the energy storage system described above.

[0016] Applying the technical solution of the present application, first, in the first acquisition step, the target viscosity difference of the initial slurry, the current viscosity of the initial slurry, and the historical batch of the initial slurry are acquired. The target viscosity difference is the difference between the actual viscosity and the target viscosity of the initial slurry. The current viscosity is the viscosity of the initial slurry at the current moment. The historical batch is the batch of the material of the previous cylinder of the initial slurry; then, in the first determination step, it is determined whether the historical batch and the initial batch are the same and the magnitude relationship between the target viscosity difference and the first difference threshold and the second difference threshold. Among them, the initial batch is the batch of the material of the initial slurry, and the second difference threshold is greater than the first difference threshold. In the case where the historical batch and the initial batch are different and the target viscosity difference is greater than the second difference threshold, the injection step is executed. In the case where the historical batch and the initial batch are the same or the historical batch and the initial batch are different and the target viscosity difference is greater than or equal to the first difference threshold and less than or equal to the first difference threshold, the processing step is executed; in the injection step, a predetermined mass of solvent is injected into the initial slurry to reduce the target viscosity difference to obtain a first target slurry. The predetermined mass is calculated according to the formula m = a×Δμ + b×μ1, where m is the predetermined mass, Δμ is the target viscosity difference, μ1 is the current viscosity, the value range of a is -0.03 to -0.01, and the value range of b is 120 to 130; in the processing step, the initial slurry is further subjected to a predetermined treatment to reduce the target viscosity difference to obtain a first target slurry; in the second acquisition step, the viscosity of the first target slurry is acquired to obtain a preliminary viscosity, and it is determined whether the preliminary viscosity is equal to the target viscosity; finally, in the repetition step, in the case where the difference between the preliminary viscosity and the target viscosity is greater than the third difference threshold, the first acquisition step, the first determination step, the injection step or the processing step, and the second acquisition step are sequentially repeated at least once until the preliminary viscosity is equal to the target viscosity, and the first target slurry is determined as the second target slurry; in the coating step, the second target slurry is coated on the surface of at least one of the positive electrode sheet and the negative electrode sheet to obtain a target electrode sheet. The beneficial effects of the present application are:

[0017] Determine the specific adjustment method of the slurry viscosity according to the batch of the initial slurry and the magnitude relationship between the difference between the actual viscosity and the target viscosity and the first difference threshold and the second difference threshold; when the historical batch is different from the initial batch and the target viscosity difference is greater than the second difference threshold, adjust the slurry viscosity by increasing the solvent, and according to the solvent mass calculation formula m = a×Δμ + b×μ1, combined with the target viscosity difference Δμ and the current viscosity μ1, the precise solvent mass can be calculated, and the solvent of this mass is injected into the initial slurry, thereby improving the adjustment accuracy of the slurry viscosity. Further, after adjusting the viscosity of the slurry to obtain the first target slurry, obtain the viscosity of the first target slurry again. If the viscosity deviates from the target viscosity, repeat the above judgment process until the slurry viscosity reaches the target viscosity, thereby realizing the closed-loop adjustment of the slurry viscosity. Through the solvent mass calculation formula, the precise solvent injection mass can be calculated. Through the above repeated judgment process, the closed-loop adjustment of the slurry viscosity can be realized. Combining the above two methods can comprehensively improve the adjustment accuracy of the slurry viscosity. Description of the Drawings

[0018] The accompanying drawings forming a part of this application are used to provide a further understanding of this application. The schematic embodiments and descriptions thereof of this application are used to explain this application and do not constitute an improper limitation of this application. In the drawings:

[0019] Figure 1 A flowchart showing a method for preparing a secondary battery according to an embodiment of this application is shown. Detailed Embodiments

[0020] It should be noted that, without conflict, the embodiments in this application and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine the embodiments to detail this application.

[0021] In order to enable those skilled in the art to better understand the solution of this application, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the drawings in the embodiments of this application. Obviously, the described embodiments are only a part of the embodiments of this application, rather than all the embodiments. Based on the embodiments in this application, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the scope of protection of this application.

[0022] It should be noted that the terms "first", "second", etc. in the description, claims and above-mentioned drawings of the present application are used to distinguish similar objects, and do not necessarily describe a specific order or sequence. It should be understood that the data used in this way can be interchanged under appropriate circumstances, so as to implement the embodiments of the present application described herein. In addition, the terms "comprising" and "having" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product or device comprising a series of steps or units does not necessarily have to be limited to those steps or units clearly listed, but may include other steps or units not clearly listed or inherent to these processes, methods, products or devices.

[0023] As introduced in the background art, the accuracy of adjusting the viscosity of the slurry in the prior art is relatively low. To solve the above technical problems, the present application proposes a method for preparing a secondary battery, a secondary battery, an energy storage system and an electrical equipment.

[0024] Figure 1 It is a schematic flow chart of a method for manufacturing a solar cell according to an embodiment of the present application. As Figure 1 shown, it includes:

[0025] Step S201, the first acquisition step, acquiring the target viscosity difference of the initial slurry, the current viscosity of the initial slurry, and the historical batch of the initial slurry. The target viscosity difference is the difference between the actual viscosity of the initial slurry and the target viscosity of the initial slurry. The current viscosity is the viscosity of the initial slurry at the current moment. The historical batch is the batch of the material of the previous tank of the initial slurry;

[0026] In practical applications, the actual viscosity refers to the viscosity value of the slurry measured during the actual production process. The actual viscosity will be affected by various factors and may deviate from the target viscosity. The factors affecting the actual viscosity include the raw material batch, stirring speed and time, temperature, humidity, and surface tension. The material of the slurry is related to the polarity of the slurry. The positive electrode slurry material includes positive electrode active material, conductive agent, binder, additive, and solvent, etc. Among them, the positive electrode active material includes lithium cobalt oxide ( ), lithium nickel cobalt manganese oxide (NMC), lithium iron phosphate ( ), etc.; the positive electrode conductive agent is used to improve the conductivity of the electrode, and materials such as carbon black (such as SuperP), conductive graphite, carbon nanotubes (CNT), graphene, etc. can be used; the binder is used to adhere the active material and the conductive agent to the current collector, and the binder includes polyvinylidene fluoride (PVDF), styrene-butadiene rubber latex (SBR), polyacrylic acid (PAA), etc.; the auxiliary agent is used to improve the performance of the slurry, such as a copolymer of a lubricating unit and an acrylate structural unit; the solvent is used to adjust the viscosity and fluidity of the slurry, including N-methylpyrrolidone (NMP) and water. The negative electrode slurry material includes a negative electrode active material, a conductive agent, a binder, a dispersant, and a solvent. Among them, the materials of the negative electrode active material include graphite, hard carbon, soft carbon, silicon-based materials, and tin-based materials, etc.; the conductive agent is used to improve the conductivity of the electrode, including carbon black, carbon fiber, conductive graphite, and carbon nanotubes; the binder is used to adhere the active material and the conductive agent to the current collector, including styrene-butadiene rubber latex (SBR), nitrile rubber, polyacrylic acid (PAA), etc.; the dispersant is used to improve the dispersibility of the slurry, and common dispersants include sodium carboxymethyl cellulose (CMC), sodium polyacrylate, etc.; the solvent is used to adjust the viscosity and fluidity of the slurry, and common solvents include water and organic alcohol solvents.

[0027] Step S202, the first determination step, determines whether the above-mentioned historical batch and the initial batch are the same and the magnitude relationship between the above-mentioned target viscosity difference and the first difference threshold and the second difference threshold. Among them, the above-mentioned initial batch is the batch of the materials of the above-mentioned initial slurry, and the above-mentioned second difference threshold is greater than the above-mentioned first difference threshold. In the case where the above-mentioned historical batch and the above-mentioned initial batch are different and the above-mentioned target viscosity difference is greater than the above-mentioned second difference threshold, the injection step is executed. In the case where the above-mentioned historical batch and the above-mentioned initial batch are the same or the above-mentioned historical batch and the above-mentioned initial batch are different and the above-mentioned target viscosity difference is greater than or equal to the above-mentioned first difference threshold and less than or equal to the above-mentioned second difference threshold, the processing step is executed;

[0028] It should be noted that both the positive electrode slurry and the negative electrode slurry include multiple materials. Therefore, the above-mentioned initial batch and historical batch both refer to the batches of multiple materials. The same of the above-mentioned historical batch and the above-mentioned initial batch indicates that the batches of multiple materials of the slurry are all the same, and the difference between the above-mentioned historical batch and the above-mentioned initial batch indicates that any one of the batches of multiple materials of the slurry is different. Since the first difference threshold is less than the above-mentioned second difference threshold, when the above-mentioned target viscosity difference is greater than the above-mentioned second difference threshold, it indicates that the target viscosity difference is relatively large, and the target viscosity difference can be reduced by the injection step. When the above-mentioned target viscosity difference is greater than or equal to the above-mentioned first difference threshold and less than or equal to the above-mentioned second difference threshold, it indicates that the target viscosity difference is relatively small, and the target viscosity difference can be reduced by the processing step.

[0029] Step S203, the above injection step, injecting a predetermined mass of solvent into the above initial slurry to reduce the above target viscosity difference, obtaining a first target slurry, where the above predetermined mass is calculated according to the formula m = a×Δμ + b×μ1, m is the above predetermined mass, Δμ is the above target viscosity difference, μ1 is the above current viscosity, the value range of a is -0.03 to -0.01, and the value range of b is 120 to 130;

[0030] Specifically, when the initial slurry is a positive electrode slurry, the above solvent can be N-methylpyrrolidone (NMP) and water. When the initial slurry is a negative electrode slurry, the above solvent can be water and an organic alcohol solvent. The value ranges of the above a and b are related to the polarity of the slurry, and the above a and b can be semi-empirical coefficients, and the initial values can be empirical values. By continuously collecting the solvent mass, the target viscosity difference, and the current viscosity to continuously calibrate the above a and b, the value ranges of a and b are obtained.

[0031] Step S204, the above treatment step, performing a predetermined treatment on the above initial slurry to reduce the above target viscosity difference, obtaining the above first target slurry;

[0032] Specifically, the above predetermined treatment can be implemented by at least one of the following methods: reducing the amount of binder, as the binder will increase the viscosity of the slurry, appropriately reducing the amount of binder can reduce the target viscosity difference; adjusting the ratio of the conductive agent and the active material to avoid particle agglomeration, which helps to reduce the target viscosity difference; reasonably optimizing the stirring parameters, determining the optimal stirring speed, time, temperature and other process parameters through experiments to avoid over-stirring or insufficient stirring; controlling the environmental conditions, controlling the humidity in the production environment can avoid the change of slurry viscosity caused by moisture absorption of the slurry, keeping the temperature of the production environment stable to avoid the influence of temperature fluctuation on the slurry viscosity. Adjusting the pH value of the slurry can affect the charge distribution on the particle surface, thereby changing the interaction force between particles and reducing the target viscosity difference.

[0033] Step S205, the second acquisition step, acquiring the viscosity of the above first target slurry, obtaining a preliminary viscosity, and determining the magnitude relationship between the difference between the above preliminary viscosity and the above target viscosity and a third difference threshold;

[0034] Specifically, a rotational viscometer, a capillary viscometer, a rheometer, an on-line viscometer, or a falling ball viscometer can be used to acquire the viscosity of the above first target slurry.

[0035] Step S206: Repeat the steps. When the difference between the above-mentioned preliminary viscosity and the above-mentioned target viscosity is greater than the above-mentioned third difference threshold, successively repeat the above-mentioned first acquisition step, the above-mentioned first determination step, the above-mentioned injection step or the above-mentioned treatment step, and the above-mentioned second acquisition step at least once until the preliminary viscosity is equal to the target viscosity, and determine the above-mentioned first target slurry as the second target slurry.

[0036] Specifically, the above-mentioned third difference threshold is a value approaching 0. In another specific embodiment, the above-mentioned third difference threshold can be 0. That is to say, when the preliminary viscosity is different from the target viscosity, continuously repeat the above-mentioned first acquisition step, the above-mentioned first determination step, the above-mentioned injection step or the above-mentioned treatment step, and the above-mentioned second acquisition step at least once to adjust the preliminary viscosity.

[0037] Step S207: Coating step. Coat the above-mentioned second target slurry on the surface of at least one of the positive electrode plate and the negative electrode plate to obtain a target electrode plate.

[0038] Specifically, the above-mentioned coating step can adopt one of blade coating, roll coating transfer coating, and slit extrusion coating. First, the current collector (such as aluminum foil or copper foil) is unrolled from the coil, and tabbing is performed to ensure continuous production. The tension control system is used to ensure that the current collector maintains an appropriate tension during the coating process; then, the slurry is evenly coated on the current collector, and the coating thickness and uniformity are controlled according to the selected coating method; then, the solvent in the slurry is removed by hot air drying and other methods to ensure that the coating is dry; finally, a deviation correction device is used to ensure that the edge of the coating is neat and avoid coating deviation; the coated electrode plate is rolled up and prepared for subsequent processes. The above-mentioned target electrode plate can be a positive electrode plate or a negative electrode plate. That is to say, the viscosity of the slurry of at least one of the positive electrode plate and the negative electrode plate is adjusted by the above-mentioned method of the present application.

[0039] For the method for preparing the secondary battery of the present application, according to the batch of the initial slurry and the magnitude relationship between the difference between the actual viscosity and the target viscosity and the first difference threshold and the second difference threshold, the specific adjustment method of the slurry viscosity is determined; when the historical batch is different from the initial batch and the target viscosity difference is greater than the second difference threshold, the slurry viscosity is adjusted by increasing the solvent, and according to the solvent mass calculation formula m = a×Δμ + b×μ1, combined with the target viscosity difference Δμ and the current viscosity μ1, the precise solvent mass can be calculated, and the solvent of this mass is injected into the initial slurry, thereby improving the adjustment accuracy of the slurry viscosity. Further, after adjusting the viscosity of the slurry to obtain the first target slurry, the viscosity of the first target slurry is obtained again. If the viscosity deviates from the target viscosity, the above judgment process is repeated until the slurry viscosity reaches the target viscosity, thereby realizing the closed-loop adjustment of the slurry viscosity. Through the solvent mass calculation formula, the precise solvent injection mass can be calculated, and through the above repeated judgment process, the closed-loop adjustment of the slurry viscosity can be realized. Combining the above two methods can comprehensively improve the adjustment accuracy of the slurry viscosity.

[0040] In some other embodiments, the above step S201 can be implemented through the following steps: Step S2011, obtain the above target viscosity and target temperature, where the above target viscosity is the ideal viscosity of the initial slurry, and the above target temperature is the temperature preset to make the above initial slurry reach the viscosity corresponding to the above target viscosity; Step S2012, obtain the mapping relationship between the viscosity of the slurry and the temperature of the above slurry; Step S2013, according to the above mapping relationship and the above target temperature, determine that the viscosity of the above initial slurry corresponding to the above target temperature is the above actual viscosity; Step S2014, calculate the difference between the above actual viscosity and the above target viscosity to obtain the above target viscosity difference. This method can quickly determine the actual viscosity through the mapping relationship between the slurry viscosity and the temperature in combination with the target temperature, and further quickly determine the difference between the above actual viscosity and the above target viscosity to obtain the above target viscosity difference.

[0041] Specifically, the target viscosity refers to the ideal viscosity value preset according to process requirements and battery performance requirements during the manufacturing process of battery slurry. It is determined based on the formulation of the slurry, equipment parameters, and the requirements of subsequent processes (such as coating). In practical applications, the viscosity decreases as the temperature increases. As the temperature rises, the molecular motion in the slurry becomes more intense, and the intermolecular interaction force weakens, resulting in a decrease in the viscosity of the slurry. In addition, the influence of temperature on viscosity has a non-linear characteristic. The change in the viscosity of the slurry with temperature is not a simple linear relationship. In some temperature ranges, the change in viscosity may be relatively significant, while in other ranges it is relatively stable. It should be noted that the above mapping relationship can be obtained by experimentally measuring the viscosity of the slurry at different temperatures, and a curve of viscosity change with temperature can be obtained. These data can be used to establish the mapping relationship between viscosity and temperature.

[0042] To further obtain an accurate mapping relationship, in some embodiments, the above step S2012 can be specifically implemented through the following steps: Step S20121, obtain a plurality of historical viscosities of the above slurry and a plurality of historical temperatures of the above slurry, where the above historical viscosities and historical temperatures correspond one by one, and the temperature range of the above historical temperatures is 20°C to 50°C; Step S20122, fit the plurality of above historical viscosities and a plurality of above historical temperatures to obtain the expression of the above mapping relationship as: μ = x × Ty, where μ is the viscosity of the above initial slurry, T is the temperature of the above initial slurry, x > 0, and y < 0. By fitting a plurality of historical temperatures and a plurality of historical viscosities, the accuracy of the above mapping relationship can be further improved.

[0043] Specifically, in practical applications, due to the large rheological differences in slurries with different formulations or materials, the specific value ranges of x and y in the expression of the above mapping relationship are related to the specific formulation of the slurry and the selection of materials. Taking the slurry of the cathode electrode as an example, the corresponding historical viscosity and historical temperature data are as follows: (45.4, 3000), (42.8, 3500), (39.6, 3800), (36.5, 4000), (30.9, 4200), (26.8, 4500), (21.6, 5000), (18.1, 6500), where the first value in the parentheses is the temperature and the second value is the viscosity. The unit of viscosity is mPa·s, and the unit of temperature is °C. Fit the above historical viscosities and historical temperatures to obtain the mapping relationship, where the range of the above x is 0 to 10000, and the value range of y is 0 to 5. In addition, due to the existence of the above differences, it is also possible to obtain according to μ = x 1 ×T y +x 2 ×T y-1 +x 3 ×T y-2 +…+x n-1×T + x n , where x 1、 x 2、… x n has the same value range as that of x, and n is a positive integer. During the production process of the secondary battery slurry, the temperature of the actual operating environment is generally between 20°C and 50°C. This temperature range covers the operating temperatures of various factory workshops. Therefore, selecting the historical data in this interval can better reflect the situation in actual production. At the same time, within this temperature range, the viscosity of the slurry changes significantly with temperature, which can reflect the regulation effect of temperature on viscosity. In practical applications, when the temperature is lower than 20°C, the slurry may become too viscous and difficult to coat evenly; when the temperature is higher than 50°C, it may cause rapid volatilization of the solvent in the slurry, affecting the stability of the slurry.

[0044] In some other embodiments, step S204 can be implemented through the following steps: step S2041, increase the stirring duration of the above-mentioned initial slurry to a predetermined duration, and the above-mentioned predetermined duration is 30 - 120 min; step S2042, increase the stirring speed of the above-mentioned initial slurry to a first predetermined speed, and the above-mentioned first predetermined speed is 5 - 18 m / s; step S2043, increase the dispersion speed of the above-mentioned initial slurry to a second predetermined speed, and the above-mentioned second predetermined speed is 500 - 2000 rmp. This method can further quickly adjust the viscosity of the initial slurry by adjusting one of the stirring duration, stirring speed, and stirring and dispersion speed to achieve a reduction in the target viscosity difference.

[0045] Specifically, the dispersion speed refers to the speed at which stirring is carried out after adding the slurry materials to ensure that the materials can be fully dispersed. The dispersion speed includes an initial dispersion stage, a main material mixing stage, and a final dispersion stage. Among them, the initial dispersion stage refers to that after adding the conductive agent and part of the solvent, the dispersion speed can be set at 500 - 1500 rpm to ensure that the conductive agent can be fully dispersed; the main material mixing stage refers to that when adding the positive electrode main material (such as NCM or LFP), the dispersion speed can be increased to 1200 - 1500 rpm to ensure full mixing of the main material and the adhesive; the final dispersion stage refers to that after adding the remaining solvent, the dispersion speed can be further increased to 1350 - 1500 rpm to ensure the uniformity of the slurry and reduce the viscosity. The stirring speed refers to the speed of the stirring paddle, including the revolution speed and the rotation speed.

[0046] In some embodiments, after the above step S205 and before the above step S207, the above method further includes: step S208, when the above preliminary viscosity is equal to the above target viscosity, determining the above first target slurry as the above second target slurry. When the preliminary viscosity is equal to the target viscosity, directly determining the first target slurry as the second target slurry without performing subsequent repeated steps can further reduce the complexity of the preparation method of the secondary battery.

[0047] In practical applications, the detection of the above preliminary viscosity can be achieved by setting a first communication pipeline, a detection chamber, a second communication pipeline, a first valve, and a second valve on the basis of an existing slurry stirring tank. The two ends of the first communication pipeline are respectively communicated with the slurry stirring tank and the detection chamber, and the second communication pipeline is respectively communicated with the detection chamber and the above slurry stirring tank. The detection chamber is used to detect the viscosity of the first target slurry. The first valve is arranged on the first communication pipeline, and the second valve is arranged on the second communication pipeline. The inclination angles of the first communication pipeline and the second communication pipeline are 45 to 60°, and the detection chamber has a conical structure. The specific detection steps are as follows: after the pulping is completed, the first valve and the second valve are opened simultaneously, and the slurry flows through the stirring tank - the first valve - the first communication pipeline - the detection chamber - the second valve - the second communication pipeline - the stirring tank in sequence; the first valve and the second valve are closed simultaneously, the viscometer is started, and the viscosity of the slurry in the detection chamber is measured. If the viscosity test parameters do not meet the corresponding viscosity range, the matching viscometer parameters are automatically selected to measure the viscosity again; after the detection is completed and when the above preliminary viscosity is equal to the above target viscosity, the valve 1 and the valve 2 are opened simultaneously, and the slurry remains in a flowing state.

[0048] In other embodiments, the ratio of the above second difference threshold to the above first difference threshold is 1 to 1.5. Setting the ratio of the above second difference threshold to the first difference threshold within the above range can improve the accuracy of the judgment based on the target viscosity difference and the first difference threshold and the second difference threshold.

[0049] Specifically, for example, the above first difference threshold is 1 and the second difference threshold is 1.2.

[0050] After the above step S207, the following steps are further included: step S209, rolling the above-mentioned target electrode sheet, and winding the rolled target electrode sheet and the separator to obtain an electric core; step S2010, encapsulating and injecting electrolyte into the above-mentioned electric core to obtain a secondary battery. The above rolling step can make the contact between the active material and the current collector closer, thereby further improving the conductivity of the electrode sheet; thereafter, through the winding method, a higher energy density can be achieved in a limited space, thereby further improving the space utilization rate inside the battery; then, the wound electric core is placed in a housing and sealed to prevent the influence of the external environment on the electric core, thereby further extending the service life of the secondary battery; by injecting the electrolyte into the electric core, the electrolyte can fully infiltrate the electrode material to ensure good contact between the electrode material and the electrolyte, thereby further improving the electrochemical performance of the battery.

[0051] Specifically, the complete preparation process of the secondary battery includes three parts: the front-end process, the middle-end process, and the back-end process. Among them, the front-end process is the electrode sheet manufacturing, which includes preparing the slurry, coating, rolling, and slitting into sheets. Specifically: Mix the cathode material, anode material, conductive agent, binder, and solvent in proportion and put them into a high-speed mixer to stir evenly; the stirred slurry needs to be tested for viscosity, density, and uniformity to ensure meeting the requirements of subsequent processes. Coat the stirred slurry evenly on the current collector to form an electrode sheet coating; the coated electrode sheet needs to be dried to remove the solvent; pass the coated electrode sheet through a rolling press to compact it and control the thickness and compaction density of the electrode sheet; the rolled electrode sheet needs to be inspected for thickness and surface quality to ensure uniformity and consistency; slit the rolled electrode sheet into the required size and shape. During the sheet-making process, it is necessary to ensure that the edges of the electrode sheet are neat to avoid burrs and cracks. The middle-end process is the battery cell synthesis, which includes winding or laminating, welding the tabs, inserting into the case, and encapsulating. Specifically: Wind the positive electrode sheet, negative electrode sheet, and separator into a battery cell in a certain order, which is mainly used for producing square and circular batteries; stack the positive electrode sheet, negative electrode sheet, and separator into a battery cell in a certain order, which is suitable for soft-pack batteries; then use the ultrasonic welding process to connect the tabs to the positive and negative electrodes of the battery cell; put the wound or laminated battery cell into the battery case and perform welding or riveting; encapsulate the battery cell to ensure isolation between the inside of the battery and the external environment and prevent moisture and air from entering. The back-end process is the formation and encapsulation, which includes injecting electrolyte, formation, aging and testing, assembly and testing. Specifically: Inject the electrolyte into the encapsulated battery cell in a drying room, usually using vacuum injection to ensure that the electrolyte fully infiltrates the battery cell; perform small-current charge and discharge on the battery cell after injection to activate the battery and form a SEI film. Gas will be generated during the formation process and needs to be removed through a degassing process; leave the formed battery at a certain temperature, monitor indicators such as voltage, internal resistance, and capacity, and eliminate unqualified batteries; assemble the single cells into a battery module or battery pack in a certain series-parallel manner and perform performance testing on the battery module or battery pack to ensure that it meets the requirements.

[0052] The above solar cell of the present application will be specifically described below in conjunction with specific embodiments and comparative examples.

[0053] Example 1

[0054] This example provides a method for preparing a secondary battery, including:

[0055] Step S11: The first acquisition step, acquiring the target viscosity difference of the initial slurry, the current viscosity of the initial slurry, and the historical batch of the initial slurry. The target viscosity difference is the difference between the actual viscosity and the target viscosity of the initial slurry. The current viscosity is the viscosity of the initial slurry at the current moment. The historical batch is the batch of the material of the previous tank of the initial slurry;

[0056] Step S12: First determination step, determining whether the above-mentioned historical batch and the initial batch are the same and the magnitude relationship between the above-mentioned target viscosity difference and the first difference threshold and the second difference threshold, where the above-mentioned initial batch is the batch of the material of the above-mentioned initial slurry, the above-mentioned second difference threshold is greater than the above-mentioned first difference threshold, and in the case where the above-mentioned historical batch and the above-mentioned initial batch are different and the above-mentioned target viscosity difference is greater than the above-mentioned second difference threshold, the injection step is executed, and in the case where the above-mentioned historical batch and the above-mentioned initial batch are the same or the above-mentioned historical batch and the above-mentioned initial batch are different and the above-mentioned target viscosity difference is greater than or equal to the above-mentioned first difference threshold and less than or equal to the above-mentioned second difference threshold, the processing step is executed;

[0057] Step S13: The above-mentioned injection step, injecting a predetermined mass of solvent into the above-mentioned initial slurry to reduce the above-mentioned target viscosity difference and obtain a first target slurry, where the above-mentioned predetermined mass is calculated according to the formula m = -0.03×Δμ + 120×μ1, m is the above-mentioned predetermined mass, Δμ is the above-mentioned target viscosity difference, and μ1 is the above-mentioned current viscosity;

[0058] Step S14: The above-mentioned processing step, performing a predetermined treatment on the above-mentioned initial slurry to reduce the above-mentioned target viscosity difference and obtain the above-mentioned first target slurry, and the above-mentioned predetermined treatment includes increasing the stirring duration of the above-mentioned initial slurry to 30 min, increasing the stirring speed of the above-mentioned initial slurry to 5 m / s, and increasing the dispersion speed of the above-mentioned initial slurry to 500 rmp;

[0059] Step S15: Second acquisition step, acquiring the viscosity of the above-mentioned first target slurry to obtain a preliminary viscosity and determining the magnitude relationship between the difference between the above-mentioned preliminary viscosity and the above-mentioned target viscosity and the third difference threshold;

[0060] Step S16: Repeating step, in the case where the difference between the above-mentioned preliminary viscosity and the above-mentioned target viscosity is greater than the above-mentioned third difference threshold, sequentially repeating the above-mentioned first acquisition step, the above-mentioned first determination step, the above-mentioned injection step or the above-mentioned processing step, and the above-mentioned second acquisition step at least once until the above-mentioned preliminary viscosity is equal to the above-mentioned target viscosity, and determining the above-mentioned first target slurry as the second target slurry.

[0061] Example 2

[0062] This example provides a method for preparing a secondary battery. The only difference between this method for preparing a secondary battery and Example 1 is that the above-mentioned predetermined mass is calculated according to the formula m = -0.02×Δμ + 125×μ1.

[0063] Example 3

[0064] This embodiment provides a method for preparing a secondary battery. The only difference between this method for preparing a secondary battery and that of Embodiment 1 is that the above-mentioned predetermined mass is calculated according to the formula m = -0.01×Δμ + 130×μ1.

[0065] Embodiment 4

[0066] This embodiment provides a method for preparing a secondary battery. The only difference between this method for preparing a secondary battery and that of Embodiment 1 is that the above-mentioned predetermined treatment includes increasing the stirring duration of the above-mentioned initial slurry to 75 min, increasing the stirring speed of the above-mentioned initial slurry to 11 m / s, and increasing the dispersion speed of the above-mentioned initial slurry to 1200 rmp.

[0067] Embodiment 5

[0068] This embodiment provides a method for preparing a secondary battery. The only difference between this method for preparing a secondary battery and that of Embodiment 1 is that the above-mentioned predetermined treatment includes increasing the stirring duration of the above-mentioned initial slurry to 120 min, increasing the stirring speed of the above-mentioned initial slurry to 18 m / s, and increasing the dispersion speed of the above-mentioned initial slurry to 2000 rmp.

[0069] Comparative Example 1

[0070] This embodiment provides a method for preparing a secondary battery, including:

[0071] Step S21: Detect the viscosity of the slurry in an offline manner. Usually, after the pulp making is completed, the slurry is manually taken out and detected by an offline viscometer;

[0072] Step S22: In the case where the viscosity does not meet the requirements, manually adjust the viscosity based on experience;

[0073] Step S23: If the viscosity still does not meet the requirements, discard this part of the slurry. If the viscosity meets the requirements, obtain the second target slurry.

[0074] Comparative Example 2

[0075] This embodiment provides a method for preparing a secondary battery. The only difference between this method for preparing a secondary battery and that of Embodiment 1 is that the above-mentioned predetermined mass is calculated according to the formula m = -0.04×Δμ + 100×μ1.

[0076] Comparative Example 3

[0077] This embodiment provides a method for preparing a secondary battery. The only difference between this method for preparing a secondary battery and that of Embodiment 1 is that the above-mentioned predetermined treatment includes increasing the stirring duration of the above-mentioned initial slurry to 150 min, increasing the stirring speed of the above-mentioned initial slurry to 28 m / s, and increasing the dispersion speed of the above-mentioned initial slurry to 2500 rmp.

[0078] The viscosity and surface density of the second target slurry prepared by using the preparation methods in the above-mentioned Examples 1-5 and Comparative Examples 1-3 were tested, and the test results are shown in Table 1:

[0079] Table 1

[0080]

[0081] It can be seen from the above experimental data that the viscosity of Example 1 is significantly greater than that of Comparative Example 1, and the surface density of Example 1 is significantly greater than that of Comparative Example 1, indicating that compared with the method of manually adjusting the viscosity of the slurry in the prior art, the viscosity of the second target slurry prepared by the preparation method of the secondary battery of the present application is large, and the problem of excessive viscosity can be improved. Moreover, compared with Comparative Example 2, the viscosities of Examples 1-3 are greater and the surface densities are greater, indicating that calculating the predetermined mass of the solvent by using the values within the value ranges of a and b of the present application and performing the corresponding injection steps can make the viscosity and surface density greater. In addition, according to the data of Comparative Example 2 and Examples 1-3, if a smaller a value (such as -0.04) and b value (such as 100) are used to form the formula and calculate the predetermined mass of the solvent, its viscosity and surface density will not be significantly better than those of Examples 1-3. Therefore, the value ranges of a and b set in the present application are relatively reasonable and can ensure a large viscosity and surface density.

[0082] It can also be seen from the above experimental data that compared with Comparative Example 3, the viscosities of Example 1 and Examples 4-5 are greater and the surface densities are greater, indicating that performing the above-mentioned predetermined treatment by using the values within the predetermined time range, the first predetermined rotation speed range and the second predetermined rotation speed range of the present application can make the viscosity and surface density greater. In addition, according to the data of Comparative Example 3, Example 1 and Examples 4-5, if a larger predetermined time (such as 150 min), a first predetermined rotation speed (such as 28 m / s) and a second predetermined rotation speed (such as 2500 rmp) are used to perform the above-mentioned predetermined treatment, its viscosity and surface density will not be significantly better than those of Example 1 and Examples 4-5, and the energy consumption and man-hour consumption caused are much higher than those of Example 1. Therefore, the value ranges of the predetermined time, the first predetermined rotation speed and the second predetermined rotation speed set in the present application are relatively reasonable, which can not only ensure a large viscosity and surface density, but also avoid waste of energy and man-hours.

[0083] In another specific embodiment of the present application, a secondary battery is provided, and the secondary battery is prepared by using any one of the above-mentioned preparation methods of the secondary battery. The secondary battery includes a positive electrode, a negative electrode, an electrolyte and a separator, and the slurry prepared by the above-mentioned preparation method is used for coating at least one of the positive electrode and the negative electrode.

[0084] Specifically, the secondary battery may be one of a lithium-ion battery, a lead-acid battery, a nickel-metal hydride battery, a nickel-cadmium battery, and a nickel-metal hydride battery.

[0085] In another specific embodiment of the present application, an energy storage system is provided, including a plurality of the above-mentioned secondary batteries.

[0086] Specifically, the energy storage system may be one of a grid energy storage system, a renewable energy storage system, a microgrid energy storage system, and a distributed energy storage system.

[0087] In another specific embodiment of the present application, an electrical device is provided, including the above-mentioned secondary battery or the above-mentioned energy storage system.

[0088] Specifically, the electrical device can be applied to personal consumption fields, energy storage fields, transportation fields, medical fields, aerospace fields, etc. Among them, electrical devices in the personal consumption field include portable electronic devices such as smart phones, tablet computers, and laptop computers, and smart wearable devices such as smart watches and health monitoring devices; electrical devices in the transportation field include electric vehicles, hybrid vehicles, and drones, etc. Electrical devices in the energy storage field include renewable energy storage systems, smart grid systems, and uninterruptible power supplies, etc.; electrical devices in the medical field include medical devices such as cardiac pacemakers, insulin pumps, portable ventilators, defibrillators, blood glucose monitors, portable B-ultrasound machines, and electrocardiographs.

[0089] From the above description, it can be seen that the above embodiments of the present application achieve the following technical effects:

[0090] According to the batch of the initial slurry and the magnitude relationship between the difference between the actual viscosity and the target viscosity and the first difference threshold and the second difference threshold, determine the specific adjustment method of the slurry viscosity; when the historical batch is different from the initial batch and the target viscosity difference is greater than the second difference threshold, adjust the slurry viscosity by increasing the solvent, and according to the solvent mass calculation formula m = a×Δμ + b×μ1, combined with the target viscosity difference Δμ and the current viscosity μ1, the precise solvent mass can be calculated, and the solvent of this mass is injected into the initial slurry, thereby improving the adjustment accuracy of the slurry viscosity. Further, after adjusting the viscosity of the slurry to obtain the first target slurry, obtain the viscosity of the first target slurry again. If the viscosity deviates from the target viscosity, repeat the above judgment process until the slurry viscosity reaches the target viscosity, thereby realizing the closed-loop adjustment of the slurry viscosity. Through the solvent mass calculation formula, the precise solvent injection mass can be calculated. Through the above repeated judgment process, the closed-loop adjustment of the slurry viscosity can be realized. Combining the above two methods can comprehensively improve the adjustment accuracy of the slurry viscosity.

[0091] The above are only the preferred embodiments of the present application and are not intended to limit the present application. For those skilled in the art, the present application may have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for preparing a secondary battery, characterized in that: include: A first acquisition step is to acquire a target viscosity difference of the initial slurry, a current viscosity of the initial slurry, and a historical batch of the initial slurry, wherein the target viscosity difference is a difference between an actual viscosity of the initial slurry and a target viscosity of the initial slurry, the current viscosity is a viscosity of the initial slurry at a current moment, and the historical batch is a batch of material of a cylinder of slurry before the initial slurry; A first determining step is to determine whether the historical batch and the initial batch are the same and the magnitude relationship between the target viscosity difference and the first difference threshold and the second difference threshold, wherein the initial batch is a batch of materials for the initial slurry, the second difference threshold is greater than the first difference threshold, and when the historical batch and the initial batch are different and the target viscosity difference is greater than the second difference threshold, an injecting step is performed, and when the historical batch and the initial batch are the same or the historical batch and the initial batch are different and the target viscosity difference is greater than or equal to the first difference threshold and less than or equal to the second difference threshold, a processing step is performed; The injecting step injects a predetermined mass of solvent into the initial slurry to reduce the target viscosity difference to obtain a first target slurry, wherein the predetermined mass is calculated according to the formula m=a×Δμ+b×μ1, m is the predetermined mass, Δμ is the target viscosity difference, μ1 is the current viscosity, a ranges from -0.03 to -0.01, and b ranges from 120 to 130; The processing step performs a predetermined processing on the initial slurry to reduce the target viscosity difference and obtain the first target slurry.

2. The method for preparing a secondary battery according to claim 1, characterized in that: Obtain the target viscosity difference of the initial slurry, including: Obtaining the target viscosity and target temperature, wherein the target viscosity is an ideal viscosity of the initial slurry, and the target temperature is a preset temperature that enables the initial slurry to reach the target viscosity; Acquire a mapping relationship between the viscosity of the slurry and the temperature of the slurry; According to the mapping relationship and the target temperature, determining the viscosity of the initial slurry corresponding to the target temperature as the actual viscosity; The difference between the actual viscosity and the target viscosity is calculated to obtain the target viscosity difference.

3. The method for preparing a secondary battery according to claim 2, characterized in that: Obtaining a mapping relationship between the viscosity of the slurry and the temperature of the slurry includes: Acquire multiple historical viscosities of the slurry and multiple historical temperatures of the slurry, wherein the historical viscosities correspond to the historical temperatures one by one, and wherein the temperature range of the historical temperatures is 20° C. to 50° C.; Fitting the plurality of historical viscosities and the plurality of historical temperatures to obtain the expression of the mapping relationship is: μ=x×T y , μ is the viscosity of the initial slurry, T is the temperature of the initial slurry, x>0, y<0.

4. The method for preparing a secondary battery according to claim 1, characterized in that: The predetermined processing includes at least one of the following: Increasing the stirring time of the initial slurry to a predetermined time, wherein the predetermined time is 30 to 120 minutes; Increasing the stirring speed of the initial slurry to a first predetermined speed, wherein the first predetermined speed is 5-18 m / s; The dispersion speed of the initial slurry is increased to a second predetermined speed, wherein the second predetermined speed is 500-2000 rpm.

5. The method for preparing a secondary battery according to claim 1, characterized in that: The ratio of the second difference threshold to the first difference threshold is 1-1.

5.

6. The method for preparing a secondary battery according to claim 1, characterized in that: After the processing step, the method further comprises: A second acquisition step, acquiring the viscosity of the first target slurry to obtain a preliminary viscosity, and determining a magnitude relationship between a difference between the preliminary viscosity and the target viscosity and a third difference threshold; a repeating step, in which, when the difference between the preliminary viscosity and the target viscosity is greater than the third difference threshold, the first obtaining step, the first determining step, the injecting step or the processing step, and the second obtaining step are sequentially repeated at least once until the preliminary viscosity is equal to the target viscosity, and the first target slurry is determined to be the second target slurry; The second determining step is to determine the first target slurry as the second target slurry when the preliminary viscosity is equal to the target viscosity.

7. The method for preparing a secondary battery according to claim 6, characterized in that: After the repeating step or the second determining step, the method further includes: A coating step, coating the second target slurry on a surface of at least one of the positive electrode sheet and the negative electrode sheet to obtain a target electrode sheet; Rolling the target pole piece, and winding the rolled target pole piece and the separator to obtain a battery cell; The battery core is packaged and injected with liquid to obtain a secondary battery.

8. A secondary battery, characterized in that: The secondary battery is prepared by the method for preparing a secondary battery according to any one of claims 1 to 7.

9. An energy storage system, characterized in that: The invention comprises a plurality of secondary batteries according to claim 8.

10. An electrical device, characterized in that: Includes the secondary battery according to claim 8 or the energy storage system according to claim 9.

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