Pole piece coating and baking directional impurity removal method

Abstract

The invention discloses a method for coating, baking and directionally removing impurities of a pole piece. The method comprises the following steps: feeding the coated pole piece into a coating oven for baking; calculating the saturated vapor pressure and the saturated vapor concentration of the binder according to the slurry parameters on the surface of the pole piece and the operating parameters of the coating oven; binder saturated steam is injected from one end of the coating drying oven, so that the gas partial pressure of the binder in the coating drying oven reaches the saturated steam pressure of the binder, and gas after impurity removal is discharged from the other end of the coating drying oven; the concentration of the dispersing agent steam in the exhausted gas is obtained in real time, the injection rate of the binder saturated steam is adjusted according to the change rate of the concentration of the dispersing agent steam, and the impurity removal progress is monitored. According to the invention, by injecting the binder saturated steam into the coating oven, the volatilization of the binder is inhibited, the preferential volatilization of the dispersant is promoted, the impurity removal is realized, the pole piece defect caused by the volatilization loss of the binder in the pole piece baking process is avoided, and the battery manufacturing yield and the product performance are further improved.

Description

Technical Field

[0001] The invention belongs to the technical field of battery core manufacturing, and in particular relates to a method for directional impurity removal by coating and baking a pole piece. Background Art

[0002] In the traditional electrode coating and baking process, when the content of the dispersant is higher than the specified concentration of the electrode slurry, the baking time needs to be extended to allow the dispersant to volatilize due to heating, thereby achieving the purpose of removing impurities.

[0003] For example, invention patent application CN117012893A discloses a sodium ion battery negative electrode sheet and a sodium ion battery containing the same, wherein the sodium ion battery negative electrode sheet comprises a negative electrode active material, a conductive agent, a dispersant, an auxiliary agent and a binder; the preparation method of the sodium ion battery negative electrode sheet comprises the following steps: S1: first stirring and mixing the solvent and the dispersant evenly; S2: after stirring and mixing evenly in step S1, adding the negative electrode material and the conductive agent, stirring and mixing evenly; S3: after completing step S2, adding the binder, stirring and mixing evenly; S4: after completing step S3, adding the auxiliary agent, stirring and mixing; S5: coating the obtained slurry on the current collector, drying, and die-cutting to obtain the negative electrode sheet.

[0004] The above-mentioned electrodes of the prior art all contain dispersants and binders. During preparation, impurities such as dispersants and excess solvents can be removed by extending the coating and drying time. However, due to the tension effect and its own volatility, if the coating and baking time is too long, the binder will float or even volatilize, which will cause the slurry to peel off from the substrate. In addition, premature volatilization of the binder will also affect the mechanical and electrochemical properties of the electrode sheet, resulting in a decrease in battery performance. There is currently no method to solve the above problems. Summary of the invention

[0005] The purpose of the present invention is to overcome the deficiencies in the prior art and provide a method for directional impurity removal during pole piece coating and baking, by injecting saturated steam of binder into the coating oven so that the gas partial pressure of the binder in the coating oven reaches the saturated vapor pressure of the binder, or even exceeds the saturated vapor pressure of the binder, thereby inhibiting the volatilization of the binder, promoting the preferential volatilization of the dispersant, achieving impurity removal, avoiding pole piece defects caused by binder volatilization loss in the pole piece baking process, and further improving the battery manufacturing yield and product performance.

[0006] The present invention provides the following technical solutions: A method for directional impurity removal during pole piece coating and baking, comprising the following steps: Obtaining the slurry parameters of the coated electrode surface and the operating parameters of the coating oven, and sending the coated electrode into the coating oven for baking; Calculate the saturated vapor pressure and saturated vapor concentration of the binder according to the slurry parameters on the electrode surface and the operating parameters of the coating oven; Inject saturated steam of adhesive from one end of the coating oven so that the gas partial pressure of the adhesive in the coating oven reaches the saturated vapor pressure of the adhesive, and discharge the impurity-free gas from the other end of the coating oven; Real-time acquisition of the concentration of dispersant vapor in the exhaust gas, and adjustment of the injection rate of the saturated vapor of the binder according to the change rate of the concentration of dispersant vapor in the exhaust gas; When the change rate of the dispersant vapor concentration in the exhausted gas is lower than a preset value, the directional impurity removal is completed.

[0007] Furthermore, the slurry parameters on the electrode surface include the type of binder, the type of dispersant, the concentration of the binder and the concentration of the dispersant; the operating parameters of the coating oven include the coating temperature. The confirmation of each parameter is used for the subsequent calculation of the saturated vapor pressure and saturated vapor concentration of the binder.

[0008] Furthermore, the method also includes: determining whether the concentration of the dispersant in the slurry parameters on the electrode surface is higher than the preset requirements of the slurry on the electrode surface; if the concentration of the dispersant is higher than the preset requirements of the slurry on the electrode surface, there is a need for impurity removal.

[0009] By judging whether impurities need to be removed, it is decided whether it is necessary to extend the coating baking time and inject saturated steam of adhesive, thereby avoiding the waste of raw materials caused by injecting saturated steam of adhesive into the coating oven when there is no need for impurities removal.

[0010] Furthermore, the method for calculating the saturated vapor pressure of the binder includes: lg P = A - B / (T +C); Wherein, P is the saturated vapor pressure of the binder; T is the maximum temperature when the coating oven is running; A, B, and C are Antoine constants.

[0011] Furthermore, the method for calculating the saturated vapor concentration of the binder includes: According to the ideal gas equation: PV=nRT; It can be obtained that: c = P / RT; Wherein, P is the saturated vapor pressure of the binder, V is the volume of the saturated vapor of the binder, n is the amount of substance of the saturated vapor of the binder, R is the standard gas constant, T is the maximum temperature when the coating oven is running, and c is the mass concentration of the saturated vapor of the binder.

[0012] Furthermore, the step of adjusting the injection rate of the saturated binder steam according to the change rate of the dispersant steam concentration in the exhausted gas includes: When the change rate of dispersant vapor concentration is ≥500ppm / min, the injection rate of binder saturated vapor is 10~15L / m 2 ; When the change rate of dispersant vapor concentration is 500ppm / min>≥100ppm / min, the injection rate of saturated binder vapor is 1~2L / m 2 ; When the change rate of dispersant vapor concentration is less than 100ppm / min, the injection rate of saturated binder vapor is 0.4~0.5L / m 2 ; The unit is L / m 2 Refers to the amount of saturated vapor of adhesive corresponding to each square meter of electrode.

[0013] By adjusting the injection rate of the saturated binder steam according to the change rate of the dispersant vapor concentration in the exhausted gas, when the change rate is large, more saturated binder steam needs to be injected, and when the change rate gradually becomes smaller, the injection rate of the saturated binder steam can be adaptively reduced. While effectively suppressing the volatilization of the binder, the emission of the dispersant can be stabilized and the purpose of saving raw materials can be achieved.

[0014] Furthermore, the method for determining whether the directional impurity removal is completed includes: When the change rate of each dispersant vapor concentration in the exhausted gas is lower than 20 ppm / min, it is considered that the directional impurity removal is completed.

[0015] Furthermore, the coating oven is a vacuum tunnel furnace, and the baking process of the coated electrode is carried out in an oxygen-free environment, thereby avoiding the risk of oxidation of the electrode and slurry.

[0016] Furthermore, the coating oven temperature is set to step heating, and the temperature range is 80-180° C. This temperature range can ensure the effective volatilization of the dispersant without affecting other components such as the binder.

[0017] Further, the slurry includes an active substance, a binder and a dispersant; The binder includes one or more of cellulose sodium hydroxyethyl methylcellulose (CMC), polyvinylidene fluoride (PVDF), and styrene-butadiene rubber (SBR); The dispersant includes one or more of N-methylpyrrolidone (NMP) and water.

[0018] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention calculates the saturated vapor pressure and saturated vapor concentration of the binder according to the slurry parameters on the electrode surface and the operating parameters of the coating oven, and then injects the saturated vapor of the binder having the aforementioned saturated vapor concentration from one end of the coating oven, so that the gas partial pressure of the binder in the coating oven reaches the saturated vapor pressure of the binder, or even exceeds the saturated vapor pressure of the binder, thereby inhibiting the volatilization of the binder. At the same time, due to the injection of the saturated vapor of the binder, the gas partial pressure of the dispersant is much lower than the saturated vapor pressure of the dispersant, thereby promoting the preferential volatilization of the dispersant and achieving impurity removal. The gas after impurity removal is also discharged from the other end of the coating oven, thereby avoiding electrode defects caused by the loss of binder volatilization during the electrode baking process, and further improving the battery manufacturing yield and product performance; (2) The present invention obtains the concentration of dispersant vapor in the exhaust gas in real time and adjusts the injection rate of the saturated binder vapor according to the change rate of the dispersant vapor concentration in the exhaust gas, thereby avoiding the waste of the saturated binder vapor and achieving the purpose of reducing costs and increasing efficiency; when the change rate of the dispersant vapor concentration in the exhaust gas is lower than the preset value, the directional impurity removal is completed. The method is simple, effective and easy to operate. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 It is a schematic flow chart of a method for directional impurity removal by coating, baking and coating of a pole piece according to an embodiment of the present invention; Figure 2 is a curve diagram showing the relationship between the saturated vapor pressure of the binder and the temperature in an embodiment of the present invention; Figure 3 4 is a curve diagram showing the relationship between the saturated vapor concentration of the binder and the temperature in the embodiment of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the protection scope of the present invention.

[0021] In the description of the present invention, unless otherwise specified, "plurality" means two or more.

[0022] Example 1

[0023] like Figure 1 As shown, this embodiment provides a method for directional impurity removal by coating and baking a pole piece, comprising the following steps: Step 1: Obtain the slurry parameters of the coated electrode surface and the operating parameters of the coating oven, and send the coated electrode into the coating oven for baking.

[0024] The slurry used for the pole piece includes active material, binder and dispersant; the binder includes one or more of CMC, PVDF and SBR; the dispersant includes one or more of NMP and water.

[0025] The coating oven is a vacuum tunnel furnace, and the baking process of the coated electrode is carried out in an oxygen-free environment, thereby avoiding the risk of oxidation of the electrode and slurry. The temperature of the coating oven is set to step heating, and the temperature range is 80~180℃. This temperature range can ensure the effective volatilization of the dispersant without affecting other components such as the binder.

[0026] The slurry parameters on the surface of the pole piece include the type of binder, the type of dispersant, the concentration of the binder and the concentration of the dispersant; the operating parameters of the coating oven include the coating temperature. The confirmation of each parameter is used for the subsequent calculation of the saturated vapor pressure and saturated vapor concentration of the binder.

[0027] Step 2: Determine whether the concentration of the dispersant in the slurry parameters on the electrode surface is higher than the preset requirements of the slurry on the electrode surface. If the concentration of the dispersant is higher than the preset requirements of the slurry on the electrode surface, there is a need for impurity removal and proceed to the subsequent steps.

[0028] By judging whether impurities need to be removed, it is decided whether it is necessary to extend the coating baking time and inject saturated steam of adhesive, thereby avoiding the waste of raw materials caused by injecting saturated steam of adhesive into the coating oven when there is no need for impurities removal.

[0029] Step 3: Calculate the saturated vapor pressure and saturated vapor concentration of the binder according to the slurry parameters on the electrode surface and the operating parameters of the coating oven.

[0030] (1) The method for calculating the saturated vapor pressure of the binder comprises: lg P = A - B / (T +C); Wherein, P is the saturated vapor pressure of the binder, in mmHg; T is the maximum temperature of the coating oven when it is running, in °C; A, B, C are antoine constants, without units, which can be found in books such as "Principles of Chemical Engineering" and "Handbook of Vapor Pressure".

[0031] (2) For ease of calculation, the pressure unit of the saturated vapor pressure P of the binder is converted from mmHg to the standard unit Pa.

[0032] (3) A method for calculating the saturated vapor concentration of the binder, comprising: According to the ideal gas equation: PV=nRT; After deformation, we can get: c=P / RT; Where P is the saturated vapor pressure of the binder, in Pa; V is the volume of the saturated vapor of the binder, in m 3 ; n is the amount of substance of the saturated vapor of the binder, in mol; R is the standard gas constant, R=8.314J / (mol·K); T is the maximum temperature of the coating oven during operation, in K; c is the mass concentration of the saturated vapor of the binder, in g / m 3 .

[0033] (4) In order to facilitate calculation and statistics, the unit of mass concentration c of saturated vapor of binder is changed from g / m 3 Convert to ppm (parts per million).

[0034] Step 4: According to the saturated vapor concentration of the binder calculated in step 3, inject saturated vapor of the binder from one end of the coating oven so that the gas partial pressure of the binder in the coating oven reaches the saturated vapor pressure of the binder, and discharge the decontaminated gas at the same flow rate from the other end of the coating oven.

[0035] Step 5: Real-time acquisition of the concentration of the dispersant vapor in the exhaust gas, and adjustment of the injection rate of the saturated vapor of the binder according to the change rate of the concentration of the dispersant vapor in the exhaust gas. When the change rate of dispersant vapor concentration is ≥500ppm / min, the injection rate of binder saturated vapor is 10~15L / m 2 ; When the change rate of dispersant vapor concentration is 500ppm / min>≥100ppm / min, the injection rate of saturated binder vapor is 1~2L / m 2 ; When the change rate of dispersant vapor concentration is less than 100ppm / min, the injection rate of saturated binder vapor is 0.4~0.5L / m 2 ; The unit is L / m 2 Refers to the amount of saturated vapor of adhesive corresponding to each square meter of electrode.

[0036] By adjusting the injection rate of the saturated binder steam according to the change rate of the dispersant vapor concentration in the exhausted gas, when the change rate is large, more saturated binder steam needs to be injected, and when the change rate gradually becomes smaller, the injection rate of the saturated binder steam can be adaptively reduced. While effectively suppressing the volatilization of the binder, the emission of the dispersant can be stabilized and the purpose of saving raw materials can be achieved.

[0037] In order to achieve the above steps, sensors should be installed in the coating oven to continuously monitor the temperature, gas composition changes and gas pressure of each component in the coating oven as a basis for controlling the input parameters of the saturated steam of the binder.

[0038] Step 6: When the change rate of the dispersant vapor concentration in the exhausted gas is lower than a preset value, the directional impurity removal is completed.

[0039] In this embodiment, when the change rate of each dispersant vapor concentration in the exhausted gas is lower than 20 ppm / min, it is determined that the directional impurity removal is completed.

[0040] Example 2

[0041] This embodiment adopts the method described in Example 1 to carry out electrode coating, baking and directional doping removal.

[0042] The positive electrode slurry mainly includes positive electrode active material, binder and dispersant. Based on the weight of powder, the binder is 5%wt, the dispersant is 5%wt, and the positive electrode active material is 90%wt. Among them, the positive electrode active material component is doped lithium iron phosphate, the binder component is PVDF, and the dispersant component is NMP and water.

[0043] The coated electrode was sent to the coating oven for baking. The coating oven was a vacuum tunnel furnace. The temperature was set to step heating. The temperature range was 80-120°C. The electrode movement speed was 2m / s. The concentration of binder and dispersant in the slurry on the surface of the electrode was measured, and the slurry parameters before impurity removal were obtained as shown in Table 1 below.

[0044] Table 1 Concentration of binder and dispersant before and after impurity removal project PVDF concentration NMP concentration <![CDATA[H2O concentration]]> Before cleaning 5549ppm 3684ppm 2560ppm After removing impurities 5320ppm 1960ppm 1035ppm The saturated vapor pressure and saturated vapor concentration of the binder are calculated according to the method in step 3 of Example 1, and the related Antoine constants are shown in Table 2. Among them, the relationship between the saturated vapor pressure of the binder and the temperature is as follows: Figure 2 As shown in the figure, the relationship between the saturated vapor concentration of the binder and the temperature is as follows Figure 3 shown.

[0045] Table 2 Antoine constants of binders and dispersants Type of substance A B C PVDF 6.9 695.5 256.29 NMP 7.7 1655.3 224 <![CDATA[H2O]]> 8.1 1723.6 233 Based on the maximum temperature of 120°C in the coating oven during production, it can be calculated that the saturated vapor concentration of the binder is 7229ppm. Therefore, saturated or supersaturated (concentration ≥7229ppm) binder vapor is injected from one end of the coating oven, and the same flow rate of decontaminated gas is discharged from the other end of the coating oven. The changes in the partial pressures of the binder and dispersant in the coating oven and the concentration of the dispersant vapor in the discharged gas are monitored in real time.

[0046] After monitoring, about 70 minutes later, in the gas discharged from the discharge side, the concentration change rate of NMP was less than 10ppm / min, and the concentration change rate of water was less than 20ppm / min. At this time, it can be considered that the concentration value of the dispersant has not changed for a long time or the change rate is too low, and the impurity removal is completed. The parameters of the electrode surface slurry after impurity removal are shown in Table 1.

[0047] It can be seen from Table 1 that before and after impurity removal, the concentration of NMP dropped from 3684ppm to 1960ppm, and the water concentration dropped from 2560ppm to 1035ppm. The removal rate of NMP reached 46.8%, and the water removal rate reached 59.6%. The dispersant removal effect was good, and only a small amount of binder volatilized, which can be ignored and will not affect the performance of the electrode.

[0048] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for directional impurity removal during pole piece coating and baking, characterized in that: The following steps are involved: Obtaining the slurry parameters of the coated electrode surface and the operating parameters of the coating oven, and sending the coated electrode into the coating oven for baking; Calculate the saturated vapor pressure and saturated vapor concentration of the binder according to the slurry parameters on the electrode surface and the operating parameters of the coating oven; Inject saturated steam of adhesive from one end of the coating oven so that the gas partial pressure of the adhesive in the coating oven reaches the saturated vapor pressure of the adhesive, and discharge the impurity-free gas from the other end of the coating oven; Real-time acquisition of the concentration of dispersant vapor in the exhaust gas, and adjustment of the injection rate of the saturated vapor of the binder according to the change rate of the concentration of dispersant vapor in the exhaust gas; When the change rate of the dispersant vapor concentration in the exhausted gas is lower than a preset value, the directional impurity removal is completed.

2. The method for directional impurity removal by coating and baking of pole pieces according to claim 1, characterized in that: The slurry parameters on the surface of the pole piece include the type of binder, the type of dispersant, the concentration of the binder and the concentration of the dispersant; the operating parameters of the coating oven include the coating temperature.

3. The method for directional impurity removal by coating and baking of pole pieces according to claim 1, characterized in that: The method also includes: determining whether the concentration of the dispersant in the slurry parameters on the surface of the pole piece is higher than the preset requirements of the slurry on the surface of the pole piece; if the concentration of the dispersant is higher than the preset requirements of the slurry on the surface of the pole piece, there is a need for impurity removal.

4. The method for directional impurity removal by coating and baking of pole pieces according to claim 1, characterized in that: The method for calculating the saturated vapor pressure of the binder comprises: lg P = A - B / (T +C); Wherein, P is the saturated vapor pressure of the binder; T is the maximum temperature when the coating oven is running; A, B, and C are Antoine constants.

5. The method for directional impurity removal during pole piece coating and baking according to claim 1, characterized in that: The method for calculating the saturated vapor concentration of the binder comprises: According to the ideal gas equation: PV=nRT; It can be obtained that: c = P / RT; Wherein, P is the saturated vapor pressure of the binder, V is the volume of the saturated vapor of the binder, n is the amount of substance of the saturated vapor of the binder, R is the standard gas constant, T is the maximum temperature when the coating oven is running, and c is the mass concentration of the saturated vapor of the binder.

6. The method for directional impurity removal during pole piece coating and baking according to claim 1, characterized in that: The step of adjusting the injection rate of the saturated binder steam according to the change rate of the dispersant steam concentration in the exhausted gas comprises: When the change rate of dispersant vapor concentration is ≥500ppm / min, the injection rate of binder saturated vapor is 10~15L / m 2 ; When the change rate of dispersant vapor concentration is 500ppm / min>≥100ppm / min, the injection rate of saturated binder vapor is 1~2L / m 2 ; When the change rate of dispersant vapor concentration is less than 100ppm / min, the injection rate of saturated binder vapor is 0.4~0.5L / m 2 ; The unit is L / m 2 Refers to the amount of saturated vapor of adhesive corresponding to each square meter of electrode.

7. The method for directional impurity removal by coating and baking of pole pieces according to claim 1, characterized in that: The method for determining whether the directional impurity removal is completed comprises: When the change rate of each dispersant vapor concentration in the exhausted gas is lower than 20 ppm / min, it is considered that the directional impurity removal is completed.

8. The method for directional impurity removal by coating and baking of pole pieces according to claim 1, characterized in that: The coating oven is a vacuum tunnel furnace, and the baking process of the coated electrode is carried out in an oxygen-free environment.

9. The method for directional impurity removal during pole piece coating and baking according to claim 1, characterized in that: The coating oven temperature is set to step heating, and the temperature range is 80~180℃.

10. The method for directional impurity removal during pole piece coating and baking according to claim 1, characterized in that: The slurry includes an active substance, a binder and a dispersant; The binder includes one or more of cellulose sodium hydroxyethyl methyl cellulose, polyvinylidene fluoride, and styrene-butadiene rubber; The dispersant includes one or more of N-methylpyrrolidone and water.

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