A method for directional impurity removal during electrode coating and baking

Abstract

This invention discloses a method for directional impurity removal during electrode coating and baking, comprising the following steps: feeding the coated electrode into a coating oven for baking; calculating the saturated vapor pressure and concentration of the binder based on the slurry parameters on the electrode surface and the operating parameters of the coating oven; injecting binder saturated vapor from one end of the coating oven to bring the gas partial pressure of the binder in the oven to the saturated vapor pressure of the binder, and discharging the purified gas from the other end of the coating oven; acquiring the concentration of dispersant vapor in the discharged gas in real time, and adjusting the injection rate of binder saturated vapor and monitoring the impurity removal progress based on the rate of change of dispersant vapor concentration. This invention, by injecting binder saturated vapor into the coating oven, suppresses binder volatilization and promotes preferential volatilization of the dispersant, achieving impurity removal and avoiding electrode defects caused by binder volatilization loss during the electrode baking process, further improving battery manufacturing yield and product performance.

Description

Technical Field

[0001] This invention belongs to the field of battery cell manufacturing technology, specifically relating to a method for directional impurity removal during electrode coating and baking. Background Technology

[0002] In the traditional electrode coating and baking process, when the content of dispersant is higher than the specified concentration of electrode slurry, the baking time needs to be extended so that the dispersant volatilizes 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 electrode sheet. The sodium-ion battery negative electrode sheet includes a negative electrode active material, a conductive agent, a dispersant, an additive, and a binder. The preparation method of the sodium-ion battery negative electrode sheet includes the following steps: S1: First, stir and mix the solvent and dispersant evenly; S2: After stirring and mixing evenly in step S1, add the negative electrode material and the conductive agent, stir and mix evenly; S3: After completing step S2, add the binder, stir and mix evenly; S4: After completing step S3, add the additive, stir and mix; S5: Coat the obtained slurry onto the current collector, dry and die-cut to obtain the negative electrode sheet.

[0004] The electrodes in the aforementioned 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 surface tension and its own volatility, if the coating and baking time is too long, the binder may float or even volatilize, leading to the slurry peeling off from the substrate. In addition, premature volatilization of the binder can also affect the mechanical and electrochemical properties of the electrode, resulting in a decrease in battery performance. Currently, there is no way to solve the above problems. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for directional impurity removal during electrode coating and baking. By injecting saturated vapor of binder into the coating oven, the gas partial pressure of the binder in the coating oven reaches or even exceeds the saturated vapor pressure of the binder, thereby inhibiting the volatilization of the binder and promoting the preferential volatilization of the dispersant, thus achieving impurity removal. This avoids electrode defects caused by binder volatilization loss during the electrode baking process, and further improves the battery manufacturing yield and product performance.

[0006] This invention provides the following technical solution:

[0007] A method for directional impurity removal during electrode coating and baking includes the following steps:

[0008] Obtain the slurry parameters on the surface of the coated electrode and the operating parameters of the coating oven, and then send the coated electrode into the coating oven for baking.

[0009] The saturated vapor pressure and saturated vapor concentration of the binder are calculated based on the slurry parameters on the electrode surface and the operating parameters of the coating oven.

[0010] Saturated vapor of binder is injected from one end of the coating oven to make the gas partial pressure of binder in the coating oven reach the saturated vapor pressure of binder, and the impurity-removed gas is discharged from the other end of the coating oven.

[0011] The concentration of dispersant vapor in the discharged gas is acquired in real time, and the injection rate of binder saturated vapor is adjusted according to the rate of change of the concentration of dispersant vapor in the discharged gas.

[0012] When the rate of change of dispersant vapor concentration in the discharged gas is lower than the preset value, directional impurity removal is completed.

[0013] Furthermore, the slurry parameters on the electrode surface include the type of binder, the type of dispersant, the binder concentration, and the dispersant concentration; the operating parameters of the coating oven include the coating temperature. Confirmation of these parameters is used for subsequent calculations of the binder's saturated vapor pressure, saturated vapor concentration, etc.

[0014] 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, then there is a need for impurity removal.

[0015] By determining whether impurity removal is required, it is then decided whether to extend the coating baking time and inject saturated steam for the binder. This avoids the waste of raw materials caused by injecting saturated steam for the binder into the coating oven when there is no need for impurity removal.

[0016] Furthermore, the method for calculating the saturated vapor pressure of the adhesive includes:

[0017] lg P = A - B / (T +C);

[0018] In the formula, P is the saturated vapor pressure of the binder; T is the highest temperature during the operation of the coating oven; and A, B, and C are Antoin constants.

[0019] Furthermore, the method for calculating the saturated vapor concentration of the adhesive includes:

[0020] According to the ideal gas equation: PV = nRT;

[0021] Therefore: c = P / RT;

[0022] In the formula, 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 highest temperature of the coating oven during operation, and c is the mass concentration of the saturated vapor of the binder.

[0023] Furthermore, adjusting the injection rate of the binder saturated vapor based on the rate of change of the dispersant vapor concentration in the discharged gas includes:

[0024] When the rate of change of dispersant vapor concentration is ≥500ppm / min, the injection rate of binder saturated vapor is 10~15L / m. 2 ;

[0025] When the rate of change of dispersant vapor concentration is greater than 100 ppm / min (500 ppm / min), the injection rate of saturated binder vapor is 1~2 L / m. 2 ;

[0026] When the rate of change of dispersant vapor concentration is <100 ppm / min, the injection rate of binder saturated vapor is 0.4~0.5 L / m. 2 ;

[0027] Wherein, the unit is L / m 2 This refers to the amount of saturated vapor in the binder per square meter of electrode sheet.

[0028] By adjusting the injection rate of binder saturated steam according to the rate of change of dispersant vapor concentration in the discharged gas, when the rate of change is large, more binder saturated steam needs to be injected, while when the rate of change gradually decreases, the injection rate of binder saturated steam can be adaptively reduced. This effectively suppresses binder volatilization, stabilizes the emission of dispersant, and achieves the goal of saving raw materials.

[0029] Furthermore, the method for determining whether directional impurity removal has been completed includes:

[0030] When the rate of change of the vapor concentration of each dispersant in the discharged gas is less than 20 ppm / min, the directional impurity removal is considered to be completed.

[0031] 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.

[0032] Furthermore, the coating oven temperature is set to tiered heating, with a temperature range of 80~180℃. This temperature range can ensure the effective volatilization of the dispersant without affecting other components such as the binder.

[0033] Furthermore, the slurry includes active substances, binders, and dispersants;

[0034] The adhesive includes one or more of sodium hydroxyethyl methyl cellulose (CMC), polyvinylidene fluoride (PVDF), and styrene-butadiene rubber (SBR);

[0035] The dispersant includes one or more of N-methylpyrrolidone (NMP) and water.

[0036] Compared with the prior art, the beneficial effects of the present invention are:

[0037] (1) The present invention calculates the saturated vapor pressure and saturated vapor concentration of the binder based on the slurry parameters on the electrode surface and the operating parameters of the coating oven. Then, the binder saturated vapor with the aforementioned saturated vapor concentration is injected 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 binder saturated vapor, the gas partial pressure of the dispersant is much lower than the saturated vapor pressure of the dispersant, thus promoting the preferential volatilization of the dispersant and achieving impurity removal. The impurity-removed gas is also discharged from the other end of the coating oven, thereby avoiding electrode defects caused by binder volatilization loss in the electrode baking process, and further improving the battery manufacturing yield and product performance.

[0038] (2) This invention obtains the concentration of dispersant vapor in the discharged gas in real time and adjusts the injection rate of saturated binder vapor according to the rate of change of dispersant vapor concentration in the discharged gas, thereby avoiding the waste of saturated binder vapor and achieving the purpose of cost reduction and efficiency improvement; when the rate of change of dispersant vapor concentration in the discharged gas is lower than the preset value, directional impurity removal is completed. The method is simple, effective and easy to operate. Attached Figure Description

[0039] Figure 1 This is a schematic flowchart of the electrode coating, baking, and directional impurity removal method in an embodiment of the present invention;

[0040] Figure 2 This is a graph showing the relationship between the saturated vapor pressure of the adhesive and temperature in an embodiment of the present invention;

[0041] Figure 3 This is a graph showing the relationship between the saturated vapor concentration of the binder and temperature in an embodiment of the present invention. Detailed Implementation

[0042] The present invention will be further described below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0043] In the description of this invention, unless otherwise stated, "multiple" means two or more.

[0044] Example 1

[0045] like Figure 1 As shown, this embodiment provides a method for directional impurity removal during electrode coating and baking, including the following steps:

[0046] Step 1: Obtain the slurry parameters on the surface of the coated electrode and the operating parameters of the coating oven, and send the coated electrode into the coating oven for baking.

[0047] The slurry used in the electrode 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.

[0048] 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 stepped heating, with a temperature range of 80~180℃. This temperature range can ensure the effective volatilization of the dispersant without affecting other components such as the binder.

[0049] The slurry parameters on the electrode surface include the type of binder, the type of dispersant, the binder concentration, and the dispersant concentration; the operating parameters of the coating oven include the coating temperature. Confirmation of these parameters is used for subsequent calculations of the binder's saturated vapor pressure, saturated vapor concentration, etc.

[0050] Step 2: Determine whether the concentration of dispersant in the slurry parameters on the electrode surface is higher than the preset requirements of the electrode surface slurry. If the concentration of dispersant is higher than the preset requirements of the electrode surface slurry, then impurity removal is required, and proceed to the next step.

[0051] By determining whether impurity removal is required, it is then decided whether to extend the coating baking time and inject saturated steam for the binder. This avoids the waste of raw materials caused by injecting saturated steam for the binder into the coating oven when there is no need for impurity removal.

[0052] Step 3: Calculate the saturated vapor pressure and saturated vapor concentration of the binder based on the slurry parameters on the electrode surface and the operating parameters of the coating oven.

[0053] (1) The method for calculating the saturated vapor pressure of the adhesive includes:

[0054] lg P = A - B / (T +C);

[0055] In the formula, P is the saturated vapor pressure of the binder, in mmHg; T is the highest operating temperature of the coating oven, in °C; A, B, and C are Antoin constants, which have no units and can be found in books such as "Chemical Engineering Principles" and "Handbook of Vapor Pressure".

[0056] (2) For ease of calculation, the pressure unit of the saturated vapor pressure P of the adhesive is changed from mmHg to the standard unit Pa.

[0057] (3) The method for calculating the saturated vapor concentration of the adhesive includes:

[0058] According to the ideal gas equation: PV = nRT;

[0059] After deformation, we get: c = P / RT;

[0060] In the formula, P is the saturated vapor pressure of the binder, in Pa; V is the volume of the saturated vapor of the binder, in m³. 3 n is the amount of substance of the saturated binder vapor, in mol; R is the standard gas constant, R = 8.314 J / (mol·K); T is the highest operating temperature of the coating oven, in K; c is the mass concentration of the saturated binder vapor, in g / m³. 3 .

[0061] (4) For ease of calculation and statistics, the unit of the mass concentration c of the binder saturated vapor is changed from g / m³. 3 Converted to ppm (parts per million).

[0062] Step 4: Based on the saturated vapor concentration of the binder calculated in Step 3, inject saturated vapor of the binder into 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 purified gas from the other end of the coating oven at the same flow rate.

[0063] Step 5: Real-time acquisition of the concentration of dispersant vapor in the discharged gas, and adjustment of the injection rate of binder saturated vapor based on the rate of change in the concentration of dispersant vapor in the discharged gas. Specifically:

[0064] When the rate of change of dispersant vapor concentration is ≥500ppm / min, the injection rate of binder saturated vapor is 10~15L / m. 2 ;

[0065] When the rate of change of dispersant vapor concentration is greater than 100 ppm / min (500 ppm / min), the injection rate of saturated binder vapor is 1~2 L / m. 2 ;

[0066] When the rate of change of dispersant vapor concentration is <100 ppm / min, the injection rate of binder saturated vapor is 0.4~0.5 L / m. 2 ;

[0067] Wherein, the unit is L / m 2 This refers to the amount of saturated vapor in the binder per square meter of electrode sheet.

[0068] By adjusting the injection rate of binder saturated steam according to the rate of change of dispersant vapor concentration in the discharged gas, when the rate of change is large, more binder saturated steam needs to be injected, while when the rate of change gradually decreases, the injection rate of binder saturated steam can be adaptively reduced. This effectively suppresses binder volatilization, stabilizes the emission of dispersant, and achieves the goal of saving raw materials.

[0069] 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 inside the coating oven, serving as the basis for controlling the input parameters of the binder saturated vapor.

[0070] Step 6: When the rate of change of the dispersant vapor concentration in the discharged gas is lower than the preset value, the directional impurity removal is completed.

[0071] In this embodiment, when the rate of change of the vapor concentration of each dispersant in the discharged gas is less than 20 ppm / min, it is considered that the directional impurity removal has been completed.

[0072] Example 2

[0073] This embodiment uses the method described in Example 1 to perform electrode coating, baking, and directional impurity removal.

[0074] The positive electrode slurry mainly consists of positive electrode active material, binder, and dispersant. By powder weight, the binder is 5% wt, the dispersant is 5% wt, and the positive electrode active material is 90% wt. The positive electrode active material is doped lithium iron phosphate, the binder is PVDF, and the dispersant is NMP and water.

[0075] The coated electrodes were placed in a coating oven (a vacuum tunnel furnace) for baking. The temperature was set to gradient heating, with a range of 80–120°C, and the electrode movement speed was 2 m / s. The concentrations of binder and dispersant in the slurry on the electrode surface were measured, and the slurry parameters before impurity removal are shown in Table 1 below.

[0076] Table 1 Concentrations of binder and dispersant before and after impurity removal

[0077] project PVDF concentration NMP concentration <![CDATA[H2O concentration]]> Before cleaning 5549ppm 3684ppm 2560ppm After removing impurities 5320ppm 1960ppm 1035ppm

[0078] The saturated vapor pressure and saturated vapor concentration of the adhesive were calculated according to the method in step 3 of Example 1, and the relevant Antoine constants are shown in Table 2. The relationship between the saturated vapor pressure of the adhesive and temperature is as follows: Figure 2 As shown, the relationship between the saturated vapor concentration of the adhesive and temperature is as follows: Figure 3 As shown.

[0079] Table 2. Antoin constants of binders and dispersants

[0080] Types of matter A B C PVDF 6.9 695.5 256.29 NMP 7.7 1655.3 224 <![CDATA[H2O]]> 8.1 1723.6 233

[0081] Based on the fact that the highest temperature inside the coating oven during production is 120℃, the saturated vapor concentration of the binder can be calculated to be 7229ppm. Therefore, binder vapor containing saturated or supersaturated (concentration ≥7229ppm) is injected from one end of the coating oven, while the same flow rate of purified gas is discharged from the other end of the coating oven. The partial pressure changes of the binder and dispersant inside the coating oven and the concentration of dispersant vapor in the discharged gas are monitored in real time.

[0082] After monitoring, approximately 70 minutes later, the concentration change rate of NMP in the gas discharged from the exhaust side was less than 10 ppm / min, and the concentration change rate of moisture was less than 20 ppm / min. At this point, it can be considered that the concentration of the dispersant has not changed for a long time or the change rate is too low, and the impurity removal can be considered complete. The parameters of the slurry on the electrode surface after impurity removal are shown in Table 1.

[0083] As shown in Table 1, before and after purification, the concentration of NMP decreased from 3684 ppm to 1960 ppm, and the moisture concentration decreased from 2560 ppm to 1035 ppm. The removal rate of NMP reached 46.8%, and the removal rate of moisture reached 59.6%. The dispersant removal effect was good, while only a small amount of binder volatilized, which was negligible and would not affect the performance of the electrode.

[0084] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for directional impurity removal during electrode coating and baking, characterized in that, Includes the following steps: Obtain the slurry parameters on the surface of the coated electrode and the operating parameters of the coating oven, and then send the coated electrode into the coating oven for baking. The saturated vapor pressure and saturated vapor concentration of the binder are calculated based on the slurry parameters on the electrode surface and the operating parameters of the coating oven. Saturated vapor of binder is injected from one end of the coating oven to make the gas partial pressure of binder in the coating oven reach the saturated vapor pressure of binder, and the impurity-removed gas is discharged from the other end of the coating oven. The concentration of dispersant vapor in the discharged gas is acquired in real time, and the injection rate of binder saturated vapor is adjusted according to the rate of change of the concentration of dispersant vapor in the discharged gas. When the rate of change of dispersant vapor concentration in the discharged gas is lower than the preset value, directional impurity removal is completed.

2. The electrode coating, baking, and directional impurity removal method according to claim 1, characterized in that, 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.

3. The electrode coating, baking, and directional impurity removal method according to claim 1, characterized in that, The method further includes: determining whether the concentration of 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 dispersant is higher than the preset requirements of the slurry on the electrode surface, then there is a need for impurity removal.

4. The electrode coating, baking, and directional impurity removal method according to claim 1, characterized in that, The method for calculating the saturated vapor pressure of the adhesive includes: lg P = A - B / (T +C); In the formula, P is the saturated vapor pressure of the binder; T is the highest temperature during the operation of the coating oven; and A, B, and C are Antoin constants.

5. The electrode coating, baking, and directional impurity removal method according to claim 1, characterized in that, The step of adjusting the injection rate of binder saturated vapor based on the rate of change of dispersant vapor concentration in the discharged gas includes: When the rate of change of dispersant vapor concentration is ≥500ppm / min, the injection rate of binder saturated vapor is 10~15L / m. 2 ; When the rate of change of dispersant vapor concentration is greater than 100 ppm / min (500 ppm / min), the injection rate of binder saturated vapor is 1~2 L / m. 2 ; When the rate of change of dispersant vapor concentration is <100 ppm / min, the injection rate of binder saturated vapor is 0.4~0.5 L / m. 2 ; Wherein, the unit is L / m 2 This refers to the amount of saturated binder vapor per square meter of electrode sheet.

6. The electrode coating, baking, and directional impurity removal method according to claim 1, characterized in that, The method for determining whether targeted impurity removal is complete includes: When the rate of change of the vapor concentration of each dispersant in the discharged gas is less than 20 ppm / min, the directional impurity removal is considered to be completed.

7. The electrode coating, baking, and directional impurity removal method 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.

8. The electrode coating, baking, and directional impurity removal method according to claim 1, characterized in that, The coating oven is set to a stepped heating temperature range of 80~180℃.

9. The electrode coating, baking, and directional impurity removal method according to claim 1, characterized in that, The slurry includes active substances, binders, and dispersants; The adhesive includes one or more of polyvinylidene fluoride and styrene-butadiene rubber; The dispersant includes one or more of N-methylpyrrolidone and water.

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