Low internal resistance ceramic coated separator and manufacturing method thereof, lithium ion battery

Abstract

The present disclosure provides a low-internal-resistance ceramic-coated separator, a manufacturing method thereof, and a lithium-ion battery. The low-internal-resistance ceramic-coated separator of the present disclosure includes a polymer base film and a ceramic layer formed by coating one or both sides of the polymer base film. The ceramic layer uses low-sodium boehmite and does not contain sodium carboxymethylcellulose (CMC), and the sodium content of the ceramic layer is less than 1000 ppm. As a result, the separator exhibits a significantly reduced increase in air permeability. When used in a lithium-ion battery, the separator significantly reduces the internal resistance of the core and further improves the battery's power performance and discharge efficiency.

Description

[Technical Field]

[0001] [CROSS-REFERENCE TO RELATED APPLICATIONS] This disclosure claims priority to a Chinese patent application bearing application number CN202211374693.1 and entitled "Low internal resistance ceramic coated separator and manufacturing method thereof for lithium ion batteries," filed with the China Patent Office on November 4, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present disclosure relates to the technical field of separators for lithium ion batteries, and more particularly to a low internal resistance ceramic coated separator and its manufacturing method, and a lithium ion battery. [Background technology]

[0003] In recent years, new energy vehicles have increasingly required high-rate charge and discharge performance from power batteries. Internal resistance is a key factor affecting battery power performance and discharge efficiency, and its initial value is primarily determined by the battery's structural design, raw material characteristics, and manufacturing process. As lithium batteries are used, their performance continues to deteriorate, primarily manifesting as a decrease in capacity, an increase in internal resistance, and a decrease in power. Changes in battery internal resistance are affected by various usage conditions, such as temperature and depth of discharge.

[0004] The main factors that affect the ionic impedance of the separator include the electrolyte distribution within the separator, the separator's area, thickness, pore size, porosity, and buckling coefficient. Ion conduction within the battery depends on the diffusion of Li ions in the electrolyte through the separator's pores. The separator's liquid absorption and wetting ability are key to creating good ion flow paths. A separator with higher liquid absorption and a porous structure can improve conductivity, reduce battery impedance, and improve the battery's rate performance.

[0005] Compared with conventional base membranes, ceramic separators and rubber-coated separators can significantly improve the separator's high-temperature shrinkage resistance as well as the separator's liquid absorption and wetting capabilities. However, the internal resistance of conventional ceramic-coated separators still needs to be further reduced.

[0006] Currently, the internal resistance of ceramic-coated separators is controlled primarily by adjusting the thickness and air permeability of the separator. Generally, the thinner the separator, the lower the resistance encountered by solvated lithium ions passing through. The better the ionic conductivity, the lower the internal resistance. The higher the air permeability, the higher the internal resistance. However, little attention has been paid to the effect of the composition ratio of the coating slurry on the internal resistance of the coating.

[0007] In the prior art, the usual method for producing boehmite is the Bayer process, which involves treating bauxite with sodium hydroxide to obtain a sodium aluminate solution, and then re-precipitating aluminum hydroxide to obtain boehmite, which introduces a certain amount of sodium element during the process.When preparing boehmite ceramic slurry, CMC solution is usually added to strengthen the adhesion between the boehmite and the base film and improve the peel strength of the separator.CMC also serves as a suspending agent, improving the settling of particles after the slurry is prepared. Summary of the Invention [Problem to be solved by the invention]

[0008] An object of the present disclosure is to provide a ceramic-coated separator having low internal resistance, which can reduce the internal resistance of the core and further improve the power performance and discharge efficiency of the battery, a method for manufacturing the same, and a lithium-ion battery equipped with the separator. [Means for solving the problem]

[0009] The present disclosure is realized as follows.

[0010] First, the present disclosure provides a ceramic substrate comprising a polymer base film and a ceramic layer formed by coating one or both sides of the polymer base film, the ceramic layer has a sodium content of less than 1000 ppm and does not contain sodium carboxymethylcellulose (CMC); Provided is a low internal resistance ceramic coated separator, in which the peel strength between the ceramic layer and the polymer base film is 20 N / m or more, optionally 20 to 70 N / m, optionally 30 N / m to 70 N / m, optionally 40 N / m to 70 N / m, for example, 45 N / m, 50 N / m, 55 N / m, 60 N / m, or 65 N / m.

[0011] By adjusting the formulation, the low internal resistance ceramic coated separator of the present disclosure can achieve an ionic conductivity of 1.4 mS / cm or more, and can even achieve an ionic conductivity of 1.5 mS / cm or more.

[0012] Optionally, the ceramic layer is formed by applying a ceramic slurry, and since the CMC is omitted, the viscosity of the ceramic slurry is less than that of a normal ceramic slurry, and is 10 to 40 mPa·S. -1 , e.g., 35 mPa·S -1 Below, 30mPa·S -1 Below, 25mPa·S -1 The solid content of the ceramic slurry is 25% to 35%.

[0013] Optionally, the ceramic slurry comprises as components: 2 to 6 parts of a dispersant; 292 parts low-sodium boehmite powder; 20 to 60 binders and 1 to 4 parts of a wetting agent; The low-sodium boehmite powder has a sodium content of 100 ppm or less.

[0014] Optionally, the ceramic slurry further comprises 30 to 50 parts of a leveling agent. In one alternative embodiment, the model number of the leveling agent is UNISAFE WHS-10.

[0015] Optionally, the ceramic layer has a thickness of 1 to 5 μm and an areal density of 8 to 10 g / m 2 is.

[0016] Optionally, the low internal resistance ceramic coated separator has an air permeability value of 75 to 175 sec / mL.

[0017] Optionally, the low internal resistance ceramic coated separator has a moisture content of less than 1000 ppm, optionally less than 700 ppm, optionally less than 500 ppm.

[0018] Optionally, the polymer base film is a polyolefin microporous film. Optionally, the polyolefin microporous film is a polyethylene microporous film, a polypropylene microporous film, or a bi-layer or multi-layer composite film consisting of a polyethylene microporous film and a polypropylene microporous film.

[0019] The present disclosure further provides a method for producing the above-mentioned low internal resistance ceramic coated separator, which includes the following steps 1 to 3.

[0020] In step 1, ceramic slurry is prepared: 292 parts of low-sodium boehmite powder, 2-6 parts of D-3019 dispersant, 20-60 parts of BM-900B binder, and 1-4 parts of 202E type wetting agent are added to water, and each component is stirred in the water to uniformly disperse and obtain a stable ceramic slurry.

[0021] Step 2: Applying the slurry: A polymer base film is provided, and a gravure roll is used to coat the surface of the base film to form a ceramic layer. The operating parameters of the gravure roll are adjusted according to the viscosity and solid content of the ceramic slurry so that the coating thickness and areal density of the ceramic layer meet the requirements.

[0022] Optionally, the gravure roll has a line count of 140 to 189, a cell depth of 30 to 50 μm, a coating speed of 80 to 140 s / m, and a speed ratio of 90% to 100%, where the speed ratio is the ratio between the operating speed of the gravure roll and the operating speed of the coater.

[0023] In step 3, the ceramic layer is dried to obtain the low internal resistance ceramic coated separator.

[0024] Optionally, in step 2, the ceramic slurry is continuously stirred at a low rotation speed of 10 to 30 r / min before being applied to the base film, thereby preventing the low-viscosity ceramic slurry from settling before application.

[0025] Optionally, during manufacturing, the environmental humidity is controlled to 1% or less, thereby reducing the moisture content of the low internal resistance ceramic coated separator.

[0026] The present disclosure further provides a lithium battery including a positive electrode, a negative electrode, a non-aqueous electrolyte, and the low internal resistance ceramic-coated separator described above, or a low internal resistance ceramic-coated separator obtained by the manufacturing method described above. [Effects of the Invention]

[0027] The present disclosure has the following beneficial effects:

[0028] In the low internal resistance ceramic coated separator disclosed herein, the ceramic layer formed by coating one or both sides of the polymer base film uses low-sodium boehmite and does not contain sodium carboxymethylcellulose, and the sodium content of the ceramic layer is less than 1000 ppm, which allows the separator to significantly reduce the increase in air permeability. When used in a lithium-ion battery, this can significantly reduce the internal resistance of the cell, further improving the power performance and discharge efficiency of the battery, and significantly reducing the internal resistance of the separator, thereby providing the separator with good usage performance.

[0029] In order to more clearly explain the technical solutions of the embodiments of the present disclosure, the following briefly introduces drawings that need to be used in the embodiments, it should be understood that the following drawings only illustrate some embodiments of the present disclosure, and therefore should not be considered as limiting the scope, and those skilled in the art can obtain further related drawings based on these drawings without creative efforts. [Brief explanation of the drawings]

[0030] [Figure 1] FIG. 1 is a structural schematic diagram of a low internal resistance ceramic coated separator according to the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0031] In order to clarify the objectives, technical solutions, and advantages of the embodiments of the present disclosure, the technical solutions in the embodiments of the present disclosure are described below clearly and completely. In addition, unless conditions are specified in the examples, the procedures are carried out according to standard conditions or manufacturer's recommended conditions. For reagents and equipment used without a specified manufacturer, all are commercially available general products.

[0032] As shown in Figure 1, the low-internal-resistance ceramic-coated separator of the present disclosure includes a polymer base film 1 and a ceramic layer 2 formed by coating one or both sides of the polymer base film 1. The present disclosure considers the formulation of the ceramic layer and employs a powder with a low sodium (Na) content to eliminate the impact of sodium on lithium-ion batteries. This involves the use of low-sodium boehmite powder with a Na content of less than 100 ppm. Furthermore, the currently mainstream sodium carboxymethyl cellulose (CMC) solution is eliminated from the ceramic slurry. On the one hand, the introduction of Na into CMC can affect lithium-ion batteries, making it necessary to remove it. On the other hand, CMC has many hydrophilic groups, namely carboxymethyl and hydroxyl, in its main chain, making it a highly water-absorbent substance. Its equilibrium moisture content increases with increasing ambient humidity and decreases with increasing temperature. By eliminating the use of CMC in the separator, the proportion of water-absorbent materials is significantly reduced, reducing the separator's moisture content and the impact of moisture on the separator's internal resistance.

[0033] The present disclosure achieves the effect of reducing the internal resistance of the separator by minimizing the sodium content in the slurry while satisfying other physical property requirements for the ceramic-coated separator, thereby imparting good separator performance. The reason for this is that sodium and lithium are the same main group elements, and a high sodium content in the slurry affects the diffusion of lithium ions in the battery. However, the present disclosure limits the sodium content in the separator to 1000 ppm or less, thereby suppressing the effect of sodium ions on the diffusion of lithium ions. When used in lithium-ion batteries, the ceramic-coated separator of the present disclosure can achieve an ionic conductivity of 1.4 mS / cm or higher, and even 1.5 mS / cm or higher.

[0034] Optionally, the present disclosure adjusts the formulation and process of the ceramic layer slurry to reduce the internal resistance of the ceramic-coated separator while ensuring that other physical properties of the ceramic-coated separator meet usage requirements. This is mainly reflected in the following: First, when CMC is removed, the solids content gradient of the ceramic slurry is set to meet the coating thickness requirements of the ceramic layer. Second, the content of binders and additives is adjusted to reduce the increase in air permeability and increase it to an appropriate range. Third, during the production of the ceramic layer, the coating process parameters are adjusted and a continuous stirring step is added to prevent the slurry from settling. Fourth, the additives are adjusted to resolve the problem of reduced peel strength caused by the omission of CMC, ensuring that the peel strength meets usage requirements.

[0035] The features and performance of the present disclosure will be described in more detail below with reference to examples and comparative examples. Example 1

[0036] (1) Preparation of ceramic slurry: Low-sodium boehmite powder (Model BG-611D), pure water, and a dispersant (Model D-3019) were added to a double planetary mixing tank and stirred to disperse, after which a binder (Model BM-900B), a leveling agent (UNISAFE WHS-10), and a wetting agent (Model 202E) were added in that order. (2) Preparation of low internal resistance ceramic-coated separator: The ceramic slurry was applied to both sides of a 12 μm-thick PE microporous substrate, with a coating thickness of 1.5 μm on each side to form a ceramic layer. The gravure roll had a line count of 150, a cell depth of 40 μm, and a speed ratio of 90%. After drying, an ultra-low internal resistance ceramic-coated separator was obtained. Example 2

[0037] (1) Preparation of ceramic slurry: Low-sodium boehmite powder (Model BG-611D), pure water, and a dispersant (Model D-3019) were added to a double planetary mixing tank and stirred to disperse, after which a binder (Model BM-900B), a leveling agent (UNISAFE WHS-10), and a wetting agent (Model 202E) were added in that order. (2) Production of low internal resistance ceramic-coated separator: Using a gravure roll, the ceramic slurry was applied to both sides of a 12 μm-thick PE porous separator, resulting in a 1.5 μm coating thickness on each side, forming a ceramic layer. The gravure roll had a line count of 150, a cell depth of 40 μm, and a speed ratio of 90%. After drying, an ultra-low internal resistance ceramic-coated separator was obtained. Example 3

[0038] (1) Preparation of ceramic slurry: Low-sodium boehmite powder (Model BG-611D), pure water, and a dispersant (Model D-3019) were added to a double planetary mixing tank and stirred to disperse, after which a binder (Model BM-900B), a leveling agent (UNISAFE WHS-10), and a wetting agent (Model 202E) were added in that order. (2) Production of low internal resistance ceramic-coated separator: Using a gravure roll, the ceramic slurry was applied to both sides of a 12 μm-thick PE porous separator, resulting in a 1.5 μm coating thickness on each side, forming a ceramic layer. The gravure roll had a line count of 150, a cell depth of 40 μm, and a speed ratio of 90%. After drying, an ultra-low internal resistance ceramic-coated separator was obtained. Example 4

[0039] (1) Preparation of ceramic slurry: Low-sodium boehmite powder (Model BG-611D), pure water, and a dispersant (Model D-3019) were added to a double planetary mixing tank and stirred to disperse, after which a binder (Model BM-900B), a leveling agent (UNISAFE WHS-10), and a wetting agent (Model 202E) were added in that order. (2) Production of low internal resistance ceramic-coated separator: Using a gravure roll, the ceramic slurry was applied to both sides of a 12 μm-thick PE porous separator, resulting in a 1.5 μm coating thickness on each side, forming a ceramic layer. The gravure roll had a line count of 150, a cell depth of 40 μm, and a speed ratio of 90%. After drying, an ultra-low internal resistance ceramic-coated separator was obtained. Comparative Example 1

[0040] (1) Preparation of ceramic slurry: Low-sodium boehmite powder (BG-611D model), pure water, and dispersant (D-3019 model) were added to a double planetary mixing tank and stirred to disperse, and then binder (BM-900B model), B1-CMC1220 solution, and wetting agent (202E model) were added in sequence. (2) Preparation of low internal resistance ceramic-coated separator: The ceramic slurry was applied to both sides of a 12 μm thick PE porous separator, with a coating thickness of 1.5 μm on each side, forming a ceramic layer. The gravure roll had a line count of 180, a cell depth of 30 μm, and a speed ratio of 90%. After drying, the ceramic-coated separator was obtained. Comparative Example 2

[0041] (1) Preparation of ceramic slurry: Low-sodium boehmite powder (BG-611D model), pure water, and dispersant (D-3019 model) were added to a double planetary mixing tank and stirred to disperse, and then binder (BM-900B model) and wetting agent (202E model) were added in sequence. (2) Preparation of low internal resistance ceramic-coated separator: The ceramic slurry was applied to both sides of a 12 μm thick PE porous separator, with a coating thickness of 1.5 μm on each side, forming a ceramic layer. The gravure roll had a line count of 180, a cell depth of 30 μm, and a speed ratio of 90%. After drying, the ceramic-coated separator was obtained. Comparative Example 3

[0042] (1) Preparation of ceramic slurry: Low-sodium boehmite powder (BG-611D model), pure water, and dispersant (D-3019 model) were added to a double planetary mixing tank and stirred to disperse, and then binder (BM-900B model), B1-CMC1220 solution, and wetting agent (202E model) were added in sequence. (2) Preparation of low internal resistance ceramic-coated separator: The ceramic slurry was applied to both sides of a 12 μm thick PE porous separator, with a coating thickness of 1.5 μm on each side, forming a ceramic layer. The gravure roll had a line count of 180, a cell depth of 30 μm, and a speed ratio of 90%. After drying, the ceramic-coated separator was obtained.

[0043] The ceramic slurry formulations and process parameters for the above examples and comparative examples are shown in Table 1 below.

[0044] Table 1. Table summarizing the ceramic slurry formulations and process parameters in the examples and comparative examples. JPEG2025541954000002.jpg103170

[0045] <Evaluation method> (1) Peel strength between the ceramic layer and the base film A 12 mm wide, 15 cm long adhesive tape (Scotch, model number 550R-12) was attached to the surface of one of the ceramic layers of the separator, and the separator was cut so that its width and length matched those of the adhesive tape to prepare a measurement sample. When attaching the adhesive tape to the separator, its longitudinal direction was aligned with the MD direction of the separator. The adhesive tape was used as a support for peeling off one of the ceramic layers. The measurement sample was left in an atmosphere of 23±1°C temperature and 50±5% relative humidity for 24 hours or more, and the following measurements were carried out in the same atmosphere. The adhesive tape was peeled off along with the adjacent ceramic layer directly below it by about 10 cm, separating the laminate (1) of the adhesive tape and ceramic layer from the laminate (2) of the porous substrate and the other ceramic layer by about 10 cm. The end of the laminate (1) was fixed to the upper chuck of a TENSILON (RTC-1210A, manufactured by Orientec Co., Ltd.), and the end of the laminate (2) was fixed to the lower chuck of the TENSILON. The measurement sample was suspended in the direction of gravity so that the tensile angle (the angle of the laminate (1) relative to the measurement sample) was 180°. The laminate (1) was pulled at a pulling rate of 20 mm / min, and the load applied when peeling the laminate (1) from the porous substrate was measured. After the start of the measurement, load readings were obtained at 0.4 mm intervals from 10 mm to 40 mm, and the average value was taken as the peel strength.

[0046] (2) Internal resistance and ionic conductivity of the separator Measurements were carried out using electrochemical impedance spectroscopy (EIS). The separator sample was assembled into a button battery in the following order: positive electrode shell, separator, stainless steel plate gasket, spring gasket, and negative electrode shell. Using an electrochemical workstation, measurements were carried out at frequencies from 0.01 Hz to 10 Hz. 6 An AC impedance scan was performed at 50 Hz and a voltage amplitude of 5 mV to obtain the internal resistance Rb of the separator. The formula for calculating the ionic conductivity of the separator is K = d / (S * Rb), where K is the ionic conductivity of the separator (mS / cm), d is the thickness of the separator (cm), and S is the effective working area of ​​the separator (cm). 2 )

[0047] (3) Gurley air permeability value A 100 mm x 100 mm composite separator sample was cut out and tested using a US Gurley 4110N air permeability tester in a 100 cc test gas mode. The time required for the test gas to completely permeate the composite separator sample was recorded and used as the Gurley value.

[0048] Referring to Table 2, the performance test results of the separators manufactured in the above examples and comparative examples are compared as follows:

[0049] Table 2: Performance parameters of ceramic coated separators manufactured in Examples and Comparative Examples JPEG2025541954000003.jpg53170

[0050] As can be seen from the results in Tables 1 and 2, the present disclosure uses low-sodium boehmite and eliminates the addition of CMC solution, thereby increasing the separator's air permeability and reducing the sodium content. This significantly reduces the separator's internal resistance and improves its operating performance. The problem of slurry settling due to the elimination of CMC solution can be resolved by adjusting the parameters of the ceramic layer manufacturing process. After preparation, slow stirring is performed to prevent settling, and the ideal thickness and areal density of the ceramic layer can be achieved by adjusting the operating parameters of the gravure roll. Furthermore, the elimination of the addition of CMC solution reduces the adhesion of the ceramic slurry to some extent, which in turn reduces the peel strength of the ceramic coating layer to some extent. However, by adjusting the formulation of the ceramic layer slurry, the present disclosure can still meet the usage requirement of a ceramic layer peel strength of greater than 20 N / m. Furthermore, as can be seen from a comparison of Example 2 and Example 1, the addition of a leveling agent solution can further improve the ceramic peel strength, increasing the ceramic layer peel strength to 40 N / m or more.

[0051] The above contents are only the selectable embodiments of the present disclosure, and do not limit the present disclosure, and those skilled in the art may have various modifications and changes to the present disclosure. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present disclosure should be included in the protection scope of the present disclosure.

Claims

1. A low internal resistance ceramic coated separator, a polymer base film and a ceramic layer formed by coating one or both sides of the polymer base film; the ceramic layer has a sodium content of less than 1000 ppm and is free of sodium carboxymethylcellulose; The peel strength between the ceramic layer and the polymer base film is 20 N / m or more; The low internal resistance ceramic coated separator is characterized in that the ionic conductivity of the low internal resistance ceramic coated separator is 1.4 mS / cm or more.

2. 2. The low internal resistance ceramic coated separator according to claim 1, wherein the peel strength between the ceramic layer and the polymer base film is 20 to 70 N / m.

3. The ceramic layer is formed by applying a ceramic slurry, and the viscosity of the ceramic slurry is 10 to 40 mPa·S. －１ 2. The low internal resistance ceramic coated separator according to claim 1, wherein the solid content of the ceramic slurry is 25% to 35%.

4. The ceramic slurry contains the following components: 2 to 6 parts of a dispersant; 292 parts low-sodium boehmite powder; 20 to 60 parts of binder; 1 to 4 parts of a wetting agent; 4. The low internal resistance ceramic coated separator according to claim 3, wherein the low sodium boehmite powder has a sodium content of 100 ppm or less.

5. 5. The low internal resistance ceramic coated separator according to claim 4, wherein the ceramic slurry further comprises 30 to 50 parts of a leveling agent.

6. The ceramic layer has a thickness of 1 to 5 μm and an areal density of 8 to 10 g / m ２ 2. The low internal resistance ceramic coated separator according to claim 1, wherein

7. 2. The low internal resistance ceramic coated separator according to claim 1, wherein the low internal resistance ceramic coated separator has an air permeability value of 75 to 175 sec / mL.

8. 2. The low internal resistance ceramic coated separator according to claim 1, wherein the moisture content of the low internal resistance ceramic coated separator is less than 1000 ppm.

9. 2. A method for producing the low internal resistance ceramic coated separator according to claim 1, comprising: Preparation of ceramic slurry: Step 1: Stirring each component in water to uniformly disperse it and obtain a stable ceramic slurry; Step 2: applying a slurry to a polymer base film and coating the surface of the base film with a gravure roll to form a ceramic layer; and step 3. drying the ceramic layer to obtain the low internal resistance ceramic coated separator.

10. 2. The method for producing a low internal resistance ceramic coated separator according to claim 1, wherein in step 2, before coating the ceramic slurry on the base film, the ceramic slurry is continuously stirred at a rotation speed of 10 to 30 r / min, and the gravure roll has a line count of 140 to 189, a cell depth of 30 to 50 μm, a coating speed of 80 to 140 s / m, and a speed ratio of 90% to 100%.

11. 2. The method for manufacturing a low internal resistance ceramic coated separator according to claim 1, wherein the environmental humidity is controlled to 1% or less during manufacturing.

12. A lithium battery, A lithium battery comprising a positive electrode, a negative electrode, a non-aqueous electrolyte, and the low internal resistance ceramic-coated separator according to any one of claims 1 to 8, or a low internal resistance ceramic-coated separator obtained by the manufacturing method according to any one of claims 9 to 11.

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