Patent Description:
With the increasing technology development and the growing demand for mobile devices, the demand for secondary batteries as an energy source is rapidly increasing, and secondary batteries essentially include an electrode assembly which is a power generation element. The electrode assembly includes a positive electrode, a separator, and a negative electrode stacked at least once, and the positive electrode and the negative electrode are manufactured by coating and drying a positive electrode active material slurry and a negative electrode active material slurry on a current collector made of an aluminum foil and a current collector made of a copper foil, respectively. In general, the secondary battery includes the positive electrode active material, for example, lithium containing cobalt oxide (LiCoO<NUM>) of layered crystal structure, lithium containing manganese oxide such as LiMnO<NUM> of layered crystal structure, LiMn<NUM>O<NUM> of spinel crystal structure, and lithium containing nickel oxide (LiNiO<NUM>). Additionally, the negative electrode active material primarily includes carbon based materials, and recently, with the growing demand for high energy lithium secondary batteries, proposals have been made to mix with silicon based materials and silicon oxide based materials having effective capacity at least <NUM> times higher than carbon based materials. For the uniform charging/discharging characteristics of the secondary batteries, it is necessary to uniformly coat the positive electrode active material slurry and the negative electrode active material slurry on the current collector.

To improve the performance of the secondary batteries, attention is directed to the development of an electrode structure having an active material layer of double layer structure on the current collector. To form the active material layer of double layer structure on the current collector, a dual slot die coater capable of simultaneously coating two types of electrode active material slurries may be used.

<FIG> shows an example of a coating method using the dual slot die coater, and <FIG> is an enlarged diagram of section A in <FIG>.

Referring to <FIG> and <FIG>, an electrode active material layer may be formed in a double layer on the current collector <NUM> at the same time by delivering two types of electrode active material slurries <NUM>, <NUM> from the dual slot die coater <NUM> while moving the current collector <NUM> by rotation of a coating roll <NUM>. The electrode active material slurries <NUM>, <NUM> delivered from the dual slot die coater <NUM> are coated over one surface of the current collector <NUM> to form the electrode active material layer.

The dual slot die coater <NUM> is constructed by assembling three plate members, i.e., three die blocks <NUM>, <NUM>, <NUM>. A slot is formed between the adjacent die blocks, totaling two slots, to simultaneously deliver two types of electrode active material slurries <NUM>, <NUM> through exit ports <NUM>, <NUM>, each in communication with each slot, so the first electrode active material slurry <NUM> is coated earlier and the additional second electrode active material slurry <NUM> is continuously coated on the first electrode active material slurry <NUM>, to simultaneously form the double-layered electrode active material layer. The reference numbers <NUM> and <NUM> indicate manifolds in which a coating solution is received.

However, the process using the dual slot die coater <NUM> has some difficulties in forming each electrode active material layer to a desired thickness due to the use of the electrode active material slurries <NUM>, <NUM> simultaneously delivered from different exit ports <NUM>, <NUM>.

The gap G from the exit ports <NUM>, <NUM> to the surface of the current collector <NUM> is a coating gap, and is a very important variable in determining the coating quality of the electrode active material layer. In general, the thickness of each electrode active material layer is affected by the amount of the electrode active material slurry delivered through the exit ports <NUM>, <NUM>, the type of the electrode active material slurry and the coating gap. Additionally, stable coating requires a uniform coating gap in the widthwise direction (TD direction) of the current collector, and a widthwise coating gap deviation significantly affects the coating width and the uncoated region boundary shape. The thickness of the electrode active material layer is a very small value of a few tens of µm to a few hundreds of µm, and even a few µm change significantly affects the coating quality, so very strict management is required, and to stably achieve uniform coating in the widthwise direction of the current collector, it is necessary to control very strictly in order to achieve uniform dimensional precision in the widthwise direction. However, to increase the production amount, as the width of the dual slot die coater <NUM> increases with the increasing width of the current collector, it is more difficult to uniformly coat in the widthwise direction and precise control of the coating gap is more necessary.

Additionally, the coating process using the dual slot die coater <NUM> has a problem such as leaking and side ring because of simultaneously delivering the electrode active material slurries <NUM>, <NUM> from different exit ports <NUM>, <NUM>. Among them, leaking refers to instability caused by the loss of some of the coating solution upstream outside of a die lip 21a as shown in <FIG>. This refers to a loss of the pre-metered coating solution, which makes it impossible to estimate the final coating thickness. Due to the leaking, the coating solution may reside for a long time and turn into a solid or a widthwise coating thickness deviation may occur. In particular, when the coating solution is delivered under high pressure with the coating gap G reduced down to a few hundreds of µm to achieve thin film coating or reduce the widthwise thickness deviation of the coating layer, leaking may get severer.

When drying the electrode active material slurries <NUM>, <NUM> after coating, the coating layer may change in shape due to the surface tension of a liquid component of the slurry, and thus this fact should be considered when coating. For example, the Marangoni flow takes place inwards from the edges of the coating layer during drying, and after drying, a fat-edge pattern defect may occur, resulting in fat edges. To prevent the fat-edge pattern defect, it is necessary to coat the edge thinner. When the exit ports <NUM>, <NUM> are closer to the current collector <NUM> with the smaller coating gap G, the edge may be coated thinner. However, as the coating gap G is smaller, leaking gets severer.

A window margin exists between a leaking area and a side ring area. The wider the window margin, the higher the productivity. Since the above-mentioned coating gap G significantly affects the size and shape of coating beads formed between the current collector <NUM> and the die lip 21a during coating and the location of the dynamic contact line, the conventional slot coating process prevents leaking by repeatedly adjusting the initial conditions such as the coating gap, the properties of the coating solution, and the volume and rate of the flow of the coating solution. However, it is not easy to set the initial conditions and it takes a long time to find the optimal process conditions. Accordingly, the wider window margin makes it easier to control the coating gap or set the initial conditions.

<CIT> , <CIT> and <CIT> disclose dual slot die coaters.

The present disclosure is designed to solve the above-described problem, and therefore the present disclosure is directed to providing a dual slot die coater with high productivity by reducing the occurrence of leaking and widening the window margin and a method for coating an electrode active material slurry using the same.

However, the problems to be solved by the present disclosure are not limited to the above problems, and other problems will be clearly understood by those skilled in the art from the following detailed description.

The invention is as defined by the claims.

To solve the above-described problem, a dual slot die coater according to the present disclosure is a dual slot die coater comprising a lower slot and an upper slot, for extrusion coating of an electrode active material slurry on a surface of a continuously moving current collector through at least one of the lower slot or the upper slot, the dual slot die coater comprising a lower plate, an intermediate plate positioned on the lower plate and an upper plate positioned on the intermediate plate, the lower slot being formed between the lower plate and the intermediate plate, and the upper slot being formed between the intermediate plate and the upper plate, wherein the lower plate, the intermediate plate and the upper plate have a lower die lip, an intermediate die lip and an upper die lip, each forming an front end with respect to the current collector, respectively, and a thickness of the lower die lip is larger than a thickness of the upper die lip and a thickness of the intermediate die lip.

According to the invention, the thickness of the lower die lip : the thickness of the upper die lip is <NUM> : <NUM> or more, or
the thickness of the lower die lip : the thickness of the intermediate die lip is <NUM> : <NUM> or more.

In the present disclosure, a lower exit port in communication with the lower slot may be formed between the lower die lip and the intermediate die lip, an upper exit port in communication with the upper slot may be formed between the intermediate die lip and the upper die lip, the slurry forming a lower slurry layer may be delivered on the current collector through the lower exit port, and the slurry forming an upper slurry layer may be delivered on the lower slurry layer on the current collector through the upper exit port, the upper exit port being spaced apart from the lower exit port downstream in a coating direction.

In the present disclosure, a thinner die lip between the upper die lip and the intermediate die lip is preferably <NUM> µm or more in thickness.

In the present invention, a thinner die lip between the upper die lip and the intermediate die lip is <NUM> µm or more in thickness.

In the present disclosure, a distance between the current collector and the upper die lip may be larger than a distance between the current collector and the lower die lip and a distance between the current collector and the intermediate die lip.

In the present disclosure, preferably, the current collector is moved by rotation of a circular coating roll having a diameter of <NUM> to <NUM>, and the current collector has a curvature by the coating roll, and the lower die lip, the intermediate die lip and the upper die lip have such thickness that an average of increases of the curvature at a location corresponding to a lower plate top which is a region of the lower die lip located on the most downstream side along a movement direction of the current collector, an intermediate plate bottom which is a region of the intermediate die lip located on the most upstream side along the movement direction of the current collector, an intermediate plate top which is a region of the intermediate die lip located on the most downstream side along the movement direction of the current collector, and an upper plate bottom which is a region of the upper die lip located on the most upstream side along the movement direction of the current collector does not exceed <NUM> µm.

In the present disclosure, the thickness of the upper die lip may range from <NUM> to <NUM>, the thickness of the intermediate die lip may range from <NUM> to <NUM>, and the thickness of the lower die lip may range from <NUM> to <NUM>. According to the present invention, the thickness of the upper die lip may range from <NUM> to <NUM>, the thickness of the intermediate die lip may range from <NUM> to <NUM>, and the thickness of the lower die lip may range from <NUM> to <NUM>.

A method for coating an electrode active material slurry according to the present disclosure comprises forming an electrode active material slurry layer on a current collector using the dual slot die coater according to the present disclosure by supplying an electrode active material slurry while moving the current collector from the lower die lip to the upper die lip.

In the method for coating an electrode active material slurry according to the present disclosure, the electrode active material slurry layer may be formed with a thickness of <NUM> µm or more.

In the method for coating an electrode active material slurry according to the present disclosure, the electrode active material slurry may have a viscosity of <NUM> cps (mPa-s) or more.

Another method for coating an electrode active material slurry according to the present disclosure is as follows. The method for coating an electrode active material slurry using a dual slot die coater including a lower slot and an upper slot, for simultaneous extrusion coating of two types of electrode active material slurries on a surface of a continuously moving current collector through the lower slot and the upper slot, the dual slot die coater including a lower plate, an intermediate plate positioned on the lower plate and an upper plate positioned on the intermediate plate, the lower slot being formed between the lower plate and the intermediate plate, and the upper slot being formed between the intermediate plate and the upper plate, wherein the lower plate, the intermediate plate and the upper plate have a lower die lip, an intermediate die lip and an upper die lip, each forming a front end with respect to the current collector, respectively, and a thickness of the lower die lip is larger than a thickness of the upper die lip and a thickness of the intermediate die lip, the method comprises simultaneously delivering the two types of electrode active material slurries on the current collector moving from the lower die lip to the upper die lip direction through a lower exit port and an upper exit port to form a double layer structure including a lower slurry layer and an upper slurry layer coated on the lower slurry layer, wherein the lower exit port in communication with the lower slot is formed between the lower die lip and the intermediate die lip, the upper exit port in communication with the upper slot is formed between the intermediate die lip and the upper die lip, and the upper exit port is spaced apart from the lower exit port downstream in a coating direction.

Here, a flow ratio of the electrode active material slurry forming the lower slurry layer and the electrode active material slurry forming the upper slurry layer may be <NUM> : <NUM>.

According to the present disclosure, among the lower die lip, the intermediate die lip and the upper die lip of the dual slot die coater, the thickness of the lower die lip is the largest. As the thickness of the lower die lip is larger, the window margin is wider. Accordingly, according to the present disclosure, the productivity increases, and the dynamic contact line may be used in a wide range of coating applications according to the intended coated product and quality.

According to the present disclosure, it is possible to raise the leaking limit. Additionally, it is possible to reduce the side ring area. When the coating gap reduces, the dynamic contact line moves in a direction that is opposite to the coating direction, and when it exceeds a predetermined level, leaking occurs, but the present disclosure achieves the wide window margin by increasing the thickness of the lower die lip, thereby preventing leaking even when the coating gap reduces. It is because the electrode active material slurry does not leak and a larger amount of electrode active material slurry resides in the lower die lip. According to the present disclosure, it is possible to prevent leaking when the coating gap is small or the slurry is supplied in a large amount relative to the movement speed of the current collector, thereby forming an electrode active material slurry layer with good coating quality.

According to the present disclosure, it is possible to prevent leaking without having to repeatedly adjust the initial conditions such as the coating gap, the properties of the coating solution, and the volume and speed of the flow of the coating solution to prevent leaking. To prevent a fat-edge caused by the Marangoni flow during drying from the edge, it is necessary to coat the edge thin in the coating step, but when the coating gap or the distance between the coating roll and the die lip is smaller, leaking gets severer. According to the present disclosure, since leaking is prevented even when the coating gap reduces, it is possible to prevent a pattern defect such as a fat-edge.

The accompanying drawings illustrate a preferred embodiment of the present disclosure and together with the detailed description of the present disclosure, serve to provide further understanding of the technical features of the present disclosure, and thus, the present disclosure is not construed as being limited to the drawings.

Prior to the description, it should be understood that the terms or words used in the specification and the appended claims should not be construed as limited to general and dictionary meanings, but interpreted based on the meanings and concepts corresponding to technical aspects of the present disclosure on the basis of the principle that the inventor is allowed to define terms appropriately for the best explanation. Therefore, the embodiments described herein and illustrations in the drawings are just some preferred embodiments of the present disclosure and do not fully describe the technical features of the present disclosure, so it should be understood that a variety of other equivalents and modifications could have been made thereto at the time of filing the patent application.

A dual slot die coater of the present disclosure is an apparatus including a lower slot and an upper slot to coat a coating solution in a double layer on a substrate. The 'substrate' described below is a current collector and the coating solution is an 'electrode active material slurry'. The slurry delivered through the lower slot and the slurry delivered through the upper slot may be electrode active material slurries having the same or different compositions (types of an active material, a conductive material and a binder), amounts (amounts of the active material, the conductive material and the binder) or properties. The dual slot die coater of the present disclosure is optimized for electrodes manufactured by simultaneous coating of two types of electrode active material slurries, or pattern coating by coating two types of electrode active material slurries in an alternating manner, or intermittent coating by the supply and stop of two types of electrode active material slurries in an alternating manner. However, the scope of the present disclosure is not necessarily limited thereto.

<FIG> is a schematic cross-sectional view of the dual slot die coater according to an embodiment of the present disclosure. <FIG> is a schematic exploded perspective view of the dual slot die coater according to an embodiment of the present disclosure. <FIG> is an enlarged diagram of section B in <FIG>, showing an electrode active material slurry coating process using the dual slot die coater according to an embodiment of the present disclosure.

Referring to <FIG>, the dual slot die coater <NUM> according to the present disclosure includes a lower slot <NUM> and an upper slot <NUM>, and is an apparatus capable of simultaneously, alternately or intermittently coating a same type of electrode active material slurry or two different types of electrode active material slurries on a current collector <NUM> through the lower slot <NUM> and the upper slot <NUM>.

The dual slot die coater <NUM> includes a lower plate <NUM>, an intermediate plate <NUM> positioned on the lower plate <NUM> and an upper plate <NUM> positioned on the intermediate plate <NUM>. The lower plate <NUM>, the intermediate plate <NUM> and the upper plate <NUM> are assembled together through fasteners such as bolts. The lower plate <NUM> is the lowermost block among the blocks of the dual slot die coater <NUM>, and the surface facing the intermediate plate <NUM> is inclined at an angle of approximately <NUM>° to <NUM>° to the bottom surface (X-Z plane).

The lower slot <NUM> may be formed at a location in which the lower plate <NUM> and the intermediate plate <NUM> face each other. For example, a first spacer <NUM> is interposed between the lower plate <NUM> and the intermediate plate <NUM> to form a gap between, and the lower slot <NUM> corresponding to a passage for the flow of a first electrode active material slurry <NUM> may be formed. In this case, the thickness of the first spacer <NUM> determines the vertical width (Y-axis direction, a slot gap) of the lower slot <NUM>.

As shown in <FIG>, the first spacer <NUM> has a first opening portion 113a which is cut at an area, and may be interposed in the remaining portion except one side in the edge area of the facing surface of each of the lower plate <NUM> and the intermediate plate <NUM>. Accordingly, a lower exit port 101a through which the first electrode active material slurry <NUM> emerges is only formed between the front end of the lower plate <NUM> and the front end of the intermediate plate <NUM>. The front end of the lower plate <NUM> and the front end of the intermediate plate <NUM> are defined as a lower die lip <NUM> and an intermediate die lip <NUM>, respectively, and in other words, the lower exit port 101a is formed by the spacing between the lower die lip <NUM> and the intermediate die lip <NUM>.

For reference, the first spacer <NUM> acts as a gasket to prevent the leakage of the first electrode active material slurry <NUM> through the gap between the lower plate <NUM> and the intermediate plate <NUM> except the area where the lower exit port 101a is formed, and thus the first spacer <NUM> is preferably made of a material having sealing ability.

The lower plate <NUM> includes a first manifold <NUM> having a predetermined depth on the surface facing the intermediate plate <NUM>, and the first manifold <NUM> is in communication with the lower slot <NUM>. Although not shown in the drawing, the first manifold <NUM> is connected to a first electrode active material slurry supply chamber (not shown) installed outside with a supply pipe and is supplied with the first electrode active material slurry <NUM>. When the first manifold <NUM> is fully filled with the first electrode active material slurry <NUM>, the flow of the first electrode active material slurry <NUM> is guided along the lower slot <NUM> and comes out of the lower exit port 101a.

The intermediate plate <NUM> is a block disposed in the middle of the die blocks of the dual slot die coater <NUM>, and is interposed between the lower plate <NUM> and the upper plate <NUM> to form a dual slot. The intermediate plate <NUM> of this embodiment is a right-angled triangle in cross section, but is not necessarily limited thereto, and for example, the intermediate plate <NUM> may be, for example, an isosceles triangle in cross section.

The upper plate <NUM> is positioned facing the upper surface of the intermediate plate <NUM> parallel to the bottom surface. As described above, the upper slot <NUM> is formed at a location in which the intermediate plate <NUM> and the upper plate <NUM> face each other.

In the same way as the lower slot <NUM> described above, a second spacer <NUM> may be interposed between the intermediate plate <NUM> and the upper plate <NUM> to form a gap between. Accordingly, the upper slot <NUM> corresponding to a passage for the flow of a second electrode active material slurry <NUM> is formed. In this case, the vertical width (Y-axis direction, a slot gap) of the upper slot <NUM> is determined by the second spacer <NUM>.

In addition, the second spacer <NUM> having the similar structure to the first spacer <NUM> has a second opening portion 133a which is cut at an area, and is interposed in the remaining portion except one side in the edge area of the facing surface of each of the intermediate plate <NUM> and the upper plate <NUM>. Likewise, the circumferential direction except the front side of the upper slot <NUM> is blocked, and the upper exit port 102a is only formed between the front end of the intermediate plate <NUM> and the front end of the upper plate <NUM>. The front end of the upper plate <NUM> is defined as an upper die lip <NUM>, and in other words, the upper exit port 102a is formed by the spacing between the intermediate die lip <NUM> and the upper die lip <NUM>.

In addition, the upper plate <NUM> includes a second manifold <NUM> having a predetermined depth on the surface facing the intermediate plate <NUM>, and the second manifold <NUM> is in communication with the upper slot <NUM>. Although not shown in the drawings, the second manifold <NUM> is connected to a supply chamber for the second electrode active material slurry <NUM> installed outside with a supply pipe and is supplied with the second electrode active material slurry <NUM>. When the second electrode active material slurry <NUM> is supplied from the external source along the supply pipe, and the second manifold <NUM> is fully filled with the second electrode active material slurry <NUM>, the flow of the second electrode active material slurry <NUM> is guided along the upper slot <NUM> in communication with the second manifold <NUM> and comes out of the upper exit port 102a.

The upper slot <NUM> and the lower slot <NUM> form a predetermined angle, and the angle may be approximately <NUM>° to <NUM>°. The upper slot <NUM> and the lower slot <NUM> may intersect at one point, and the upper exit port 102a and the lower exit port 101a may be provided near the intersection point. Accordingly, the locations at which the first electrode active material slurry <NUM> and the second electrode active material slurry <NUM> emerge may converge to approximately one point.

The first and second manifolds <NUM>, <NUM> are formed in the lower plate <NUM> and the upper plate <NUM>, respectively. In this case, the intermediate plate <NUM> that is the most structurally vulnerable may be less prone to deformation.

Meanwhile, the dual slot die coater <NUM> may further include a first valve to open/close the delivery through the lower exit port 101a, a second valve to open/close the delivery through the upper exit port 102a, and a valve control unit to control the opening/closing of the first and second valves.

According to the dual slot die coater <NUM> having the above-described configuration, a rotatable coating roll <NUM> is positioned on the front side of the dual slot die coater <NUM>, and the coating roll <NUM> may be rotated to move the current collector <NUM> to be coated, while continuously contacting the first electrode active material slurry <NUM> and the second electrode active material slurry <NUM> with the surface of the current collector <NUM>, and thereby the current collector <NUM> may be simultaneously coated in a double layer structure. Alternatively, pattern coating may be intermittently formed on the current collector <NUM> by performing the supply and stop of the first electrode active material slurry <NUM> and the supply and stop of the second electrode active material slurry <NUM> in an alternating manner by the closing/opening control of the first and second valves through the valve control unit.

The first electrode active material slurry <NUM> is coated on the current collector <NUM> to form a lower slurry layer, and almost at the same time, the second electrode active material slurry <NUM> is coated on the lower slurry layer to form an upper slurry layer.

Referring further to <FIG>, the structure of the die lip of the dual slot die coater according to an embodiment of the present disclosure and a method for coating an electrode active material slurry using the dual slot die coater will be described in detail. The dual slot die coater <NUM> according to the present disclosure has a difference in lip thickness between the upper/intermediate/lower plates.

The lower die lip thickness D1 is larger than the upper die lip thickness D3, and the lower die lip thickness D1 is larger than the intermediate die lip thickness D2. Accordingly, the lower die lip thickness D1 is larger than the average thickness of the upper die lip thickness D3 and the intermediate die lip thickness D2. As described above, the lower die lip thickness D1 is the largest. D1>D2, D1>D3, D1>(D2+D3)/<NUM>. The upper die lip thickness D3 may be equal to the intermediate die lip thickness D2.

The lower die lip thickness D1 : the upper die lip thickness D3 is <NUM> : <NUM> or more. That is, the lower die lip thickness D1 is at least <NUM> times larger than the upper die lip thickness D3. When the lower die lip thickness D1 is larger than the upper die lip thickness D3, the window margin is wider as intended, but when the lower die lip thickness D1 is at least <NUM> times larger than the upper die lip thickness D3, it is possible to prevent leaking. When the lower die lip thickness D1 is equal to the upper die lip thickness D3 or the upper die lip thickness D3 is larger than the lower die lip thickness D1, leaking occurs.

The lower die lip thickness D1 : the intermediate die lip thickness D2 may be <NUM> : <NUM> or more. That is, the lower die lip thickness D1 is at least <NUM> times larger than the intermediate die lip thickness D2. When the lower die lip thickness D1 is larger than the intermediate die lip thickness D2, the window margin is wider as intended, but when the lower die lip thickness D1 is at least <NUM> times larger than the intermediate die lip thickness D2, it is possible to prevent leaking. When the lower die lip thickness D1 is equal to the intermediate die lip thickness D2, leaking occurs. When the intermediate die lip thickness D2 is larger than the lower die lip thickness D1, leaking does not occur, but a pattern defect occurs.

According to the present disclosure, the thickness of the lower die lip <NUM> is the largest. The inventors found that as the lower die lip <NUM> is thicker, the window margin is wider. Accordingly, it may be easier to control the coating gap or set the initial condition. Accordingly, according to the present disclosure, productivity increases, and the dynamic contact line coating may be used in a wide range of coating applications according to the intended coated product and quality.

According to the present disclosure, with the wider window margin, it is possible to raise the leaking limit. Additionally, it is possible to reduce the side ring area. As the coating gap reduces, the dynamic contact line moves in a direction that is opposite to the coating direction, and when it exceeds a predetermined level, leaking occurs, but the present disclosure may reduce leaking by increasing the thickness of the lower die lip <NUM>. It is because the electrode active material slurry does not leak and the electrode active material slurry in a large amount resides in the lower die lip <NUM>. According to the present disclosure, it is possible to reduce leaking even when the coating gap is small or the slurry is supplied a large amount relative to the movement speed of the current collector <NUM>.

According to the dual slot die coater according to the present disclosure and the method for coating an electrode active material slurry using the same, the formation of the active material layer of double layer structure on the current collector may increase the procedural efficiency and reduce the defect rate.

It is desirable that the thickness condition of the lower die lip <NUM>, the upper die lip <NUM> and the intermediate die lip <NUM> is satisfied, and the thickness of the thinnest die lip among the upper die lip <NUM> and the intermediate die lip <NUM> is equal to or larger than <NUM> µm (<NUM>). When the thickness of the thinnest die lip is smaller than <NUM> µm, the die block is too thin and the slot gap changes, which makes uniform coating difficult. Thus, the thickness is at least <NUM> µm. When the thickness of the thinnest die lip is <NUM> µm, the thickness of the lower die lip <NUM> may be equal to or larger than <NUM> µm that is <NUM> times larger than the thickness of the thinnest die lip.

In the invention, the thickness of the thinnest die lip is equal to or larger than <NUM> µm. It may be a value that takes into account the pressure of the electrode active material slurry coming out. More preferably, the thickness of the thinnest die lip is equal to or larger than <NUM>. This may be a value set for precise machining. When the thickness of the thinnest die lip is <NUM> µm, the thickness of the lower die lip <NUM> may be equal to or larger than <NUM> that is <NUM> times larger than the thickness of the thinnest die lip. More preferably, the thickness of the thinnest die lip is equal to or larger than <NUM>. This may be also a value set for precise machining. The distance H3 between the current collector <NUM> and the upper die lip <NUM> may be larger than the distance H2 between the current collector <NUM> and the intermediate die lip <NUM> and the distance H1 between the current collector <NUM> and the lower die lip <NUM>. This distance difference may be formed by moving back the upper die lip <NUM> which is the lip of the upper plate <NUM> in a direction that is opposite to the delivery direction than the lower die lip <NUM> which is the lip of the lower plate <NUM> and the intermediate die lip <NUM> which is the lip of the intermediate plate <NUM>, far away from the current collector <NUM>, to form the lip step. It is possible to reduce the loading out area through the step between the lips. The distance H1 between the current collector <NUM> and the lower die lip <NUM> may be equal to the distance H2 between the current collector <NUM> and the intermediate die lip <NUM>.

To form the lip step, the dual slot die coater <NUM> may further include a control unit to individually move back the upper die lip <NUM> after placing the lower die lip <NUM>, the intermediate die lip <NUM> and the upper die lip <NUM> in linear alignment with respect to the current collector <NUM>. In this configuration, the upper die lip <NUM> is disposed at a more rearward position from the current collector <NUM> than the lower die lip <NUM> and the intermediate die lip <NUM>.

Accordingly, the predetermined step is formed between the lower exit port 101a and the upper exit port 102a. The step is a result of subtracting the distance H1 between the current collector <NUM> and the lower die lip <NUM> from the distance H3 between the current collector <NUM> and the upper die lip <NUM>. The lower exit port 101a and the upper exit port 102a are spaced by the step apart from each other along the horizontal direction, thereby preventing the second electrode active material slurry <NUM> coming out of the upper exit port 102a from entering the lower exit port 101a, or the first electrode active material slurry <NUM> coming out of the lower exit port 101a from entering the upper exit port 102a. In addition, the intermediate die lip <NUM> presses down the first electrode active material slurry <NUM>, but the upper die lip <NUM> does not press down the second electrode active material slurry <NUM>, and thus the width of the lower slurry layer coated with the first electrode active material slurry <NUM> is equal to the width of the upper slurry layer coated with the second electrode active material slurry <NUM>.

As shown in the drawing, when the lip positions are set, the upper exit port 102a is spaced apart from the lower exit port 101a downstream in the coating direction. An active material layer may be formed with a double layer structure on the current collector <NUM> by simultaneously delivering the first and second electrode active material slurries <NUM>, <NUM> through the lower exit port 101a and the upper exit port 102a while moving the current collector <NUM> from the lower die lip <NUM> to the upper die lip <NUM>.

The first electrode active material slurry <NUM> issuing from the lower exit port 101a is coated on the current collector <NUM> to form the lower slurry layer, and at the same time, the second electrode active material slurry <NUM> issuing from the upper exit port 102a is coated thereon to form the upper slurry layer. The dual slot die coater <NUM> of the present disclosure can form a double layer structure including the upper slurry layer on the lower slurry layer.

Each of the average thickness of the lower slurry layer formed by the first electrode active material slurry <NUM> emerging through the lower exit port 101a and the average thickness of the upper slurry layer formed by the second electrode active material slurry <NUM> emerging through the upper exit port 102a may be <NUM> µm or more. Each average thickness may be <NUM> µm or less. In general, the average particle size of the secondary battery active material is about <NUM> µm, but the particle size follows the commonly used normal distribution, so it is general that d(<NUM>) or d(max) is larger than <NUM> µm (here, the average particle size is d(<NUM>), and may be defined as a particle size corresponding to <NUM>% cumulative mass percentage in the particle size distribution curve measured by laser diffraction. It will be understood that d(<NUM>) indicates that <NUM>% of the total particle have a particle size that is equal to or smaller than the above-described value). Since the slurry layer includes the active material, it is difficult to form the slurry layer less than <NUM> µm in thickness. Additionally, when the thickness of the slurry layer is equal to or larger than <NUM> µm, it is possible to smoothly coat without active material clogging at the coating gap usually maintained. Additionally, when the thickness of the slurry layer is equal to or larger than <NUM> µm, it may be advantageous, but it is difficult to realistically achieve the coating amount actually used in the secondary battery of more than <NUM> µm.

For example, the method for coating an electrode active material slurry of the present disclosure may be applied to the manufacture of the positive electrode of the secondary battery. The positive electrode includes a current collector and a positive electrode active material layer formed on the surface of the current collector. The current collector may include any material which exhibits electrical conductivity, for example, Al, Cu, and a proper one may be used according to the polarity of the current collector of the electrode well known in the field of secondary batteries. The positive electrode active material layer may further include at least one of a positive electrode active material particles, a conductive material or a binder. Additionally, the positive electrode may further include various types of additives to enhance or improve the electoral and chemical properties.

The active material is not limited to a particular type and may include any material used for positive electrode active materials of lithium ion secondary batteries. Its nonlimiting example may include at least one of layered compounds or compounds with one or more transition metal substitution such as lithium manganese composite oxide (LiMn<NUM>O<NUM>, LiMnO<NUM>), lithium cobalt oxide (LiCoO<NUM>), lithium nickel oxide (LiNiO<NUM>); lithium manganese oxide of formula Li<NUM>+xMn<NUM>-xO<NUM> (x is <NUM> ~ <NUM>), LiMnO<NUM>, LiMn<NUM>O<NUM>, LiMnO<NUM>; lithium copper oxide (Li<NUM>CuO<NUM>); vanadium oxide, for example, LiV<NUM>O<NUM>, LiV<NUM>O<NUM>, V<NUM>O<NUM>, Cu<NUM>V<NUM>O<NUM>; Ni site lithium nickel oxide represented by formula LiNi<NUM>-xMxO<NUM> (M = Co, Mn, Al, Cu, Fe, Mg, B or Ga, x = <NUM> ~ <NUM>); lithium manganese composite oxide represented by formula LiMn<NUM>-xMxO<NUM> (M = Co, Ni, Fe, Cr, Zn or Ta, x = <NUM> ~ <NUM>) or Li<NUM>Mn<NUM>MO<NUM> (M = Fe, Co, Ni, Cu or Zn); LiMn<NUM>O<NUM> with partial substitution of alkali earth metal ion for Li in the formula; disulfide compounds; or Fe<NUM>(MoO<NUM>)<NUM>. In the present disclosure, the positive electrode may include a solid electrolyte material, for example, at least one of a polymer based solid electrolyte, an oxide based solid electrolyte or a sulfide based solid electrolyte.

The conductive material may be typically added in an amount of <NUM> wt% to 20wt% based on the total weight of the mixture including the electrode active material. The conductive material is not limited to a particular type, and may include any material having conductive properties without causing any chemical change to the corresponding battery, for example, at least one selected from graphite, for example, natural graphite or artificial graphite; carbon black, for example, carbon black, acetylene black, ketjen black, channel black, furnace black, lamp black, thermal black; conductive fibers, for example, carbon fibers or metal fibers; metal powder, for example, carbon fluoride, aluminum and nickel powder; conductive whiskers, for example, zinc oxide and potassium titanate; conductive metal oxide, for example, titanium oxide; and conductive materials, for example, polyphenylene derivatives.

The binder is not limited to a particular type and may include any material which assists in bonding the active material and the conductive material and bonding to the current collector, for example, polyvinylidene fluoride polyvinylalcohol, carboxymethylcellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylenepropylene-diene monomer (EPDM), sulfonated EPDM, styrene butadiene rubber, fluoro rubber and a variety of copolymers thereof. The binder may be typically included in the range of <NUM> wt% to <NUM> wt% or <NUM> wt% to <NUM> wt% based on <NUM> wt% of the electrode layer.

The electrode may be a negative electrode. The negative electrode includes a current collector and a negative electrode active material layer formed on the surface of the current collector. The negative electrode active material layer may further include at least one of negative electrode active material particles, a conductive material or a binder. Additionally, the negative electrode may further include a variety of additives to enhance or improve the electrical and chemical properties.

The negative electrode active material may include carbon materials, for example, graphite, amorphous carbon, diamond phase carbon, fullerene, carbon nanotubes and carbon nanohorns, lithium metal materials, alloy based materials, for example, silicon or tin alloy based materials, oxide based materials, for example, Nb<NUM>O<NUM>, Li<NUM>Ti<NUM>O<NUM>, TiO<NUM>, or a composite thereof. For the conductive material, the binder and the current collector of the negative electrode, a reference may be made to the positive electrode.

In particular, the electrode manufactured according to the present disclosure is preferably a positive electrode. Preferably, the positive electrode has a structure in which a lower active material layer and an upper active material layer are formed on a current collector in a sequential order. The lower active material layer contains a conductive material in a larger amount, and the upper active material layer contains a conductive material in a smaller amount. In this case, the amount of the conductive material in the lower active material layer may be adjusted to the range between <NUM> and <NUM> weight%. It is possible to increase the amount of the active material on the electrode surface and reduce the electrical conductivity at a predetermined level by reducing the amount the conductive material in the upper active material layer. In particular, when the amount of the conductive material in the upper active material layer is controlled to a very low level of <NUM> weight% or less, it is possible to reduce the heat generation reaction in the event of an internal short circuit of the cell.

In another example, the average particle size P1 of the active material that forms the lower active material layer ranges between <NUM> and <NUM>% of the average particle size P2 of the active material that forms the upper active material layer. In this case, a smaller particle size active material is applied to the lower active material layer, and a larger particle size active material is applied to the upper active material layer, which makes electrolyte solution wetting easy and induces the smooth movement of ions or holes.

Here, a flow ratio of the first electrode active material slurry <NUM> and the second electrode active material slurry <NUM> may be <NUM> : <NUM>. The first and second electrode active material slurries <NUM>, <NUM> may include graphite, a conductive material, CMC and a binder. The viscosity of the first and second electrode active material slurries <NUM>, <NUM> may be equal to or higher than <NUM> cps (mPa-s).

The viscosity of the slurry for forming a secondary battery electrode may be <NUM> cps (mPa-s) to <NUM> cps (mPa-s).

For example, the negative electrode active material slurry may have viscosity of <NUM> cps (mPa-s) to <NUM> cps (mPa-s). The positive electrode active material slurry may have viscosity of <NUM> cps (mPa-s) to <NUM> cps (mPa-s). Since the dual slot die coater <NUM> of the present disclosure is configured to coat a coating solution having the viscosity of <NUM> cps (mPa-s) or more, the dual slot die coater <NUM> of the present disclosure is different from the structure of a device for coating a coating solution having lower viscosity such as a commonly used resin solution, for example, a photosensitive emulsion, a magnetic fluid, an antireflective solution, an antiglare solution, a solution for improving the viewing angle and a dye solution for color filter, and cannot be arrived at by modifying such device. Since the dual slot die coater <NUM> of the present disclosure is configured to coat the slurry including the secondary battery active material having the average particle size of about <NUM> µm, the dual slot die coater <NUM> of the present disclosure is different from the structure of a device for coating a coating solution without particles of the above-described particle size and cannot be arrived at by modifying such device. The dual slot die coater <NUM> of the present disclosure is optimal for a coater for an electrode.

Although <FIG> is shown irrespective of the curvature of the coating roll <NUM>, actually the current collector <NUM> placed on the coating roll <NUM> also has a curvature due to the curvature of the coating roll <NUM>, and thus the coating gap between the die lips <NUM>, <NUM>, <NUM> and the current collector <NUM> varies depending on the location. As the lower die lip <NUM> is thicker, the window margin is wider, but the coating gap deviation increases. This is the same case with the other die lips <NUM>, <NUM>. Accordingly, the inventors propose the preferred thickness range of each die lip <NUM>, <NUM>, <NUM> including the thickest lower die lip <NUM>. That is, since the coating roll <NUM> is circular, when the die lips <NUM>, <NUM>, <NUM> are too thick, the coating gap at each position changes. To achieve coating uniformity while preventing fat-edge by making the lower die lip <NUM> thickest, the present disclosure proposes an appropriate maximum value of the thickness of each die lip <NUM>, <NUM>, <NUM>.

<FIG> is a diagram illustrating the thickness range of each die lip in the dual slot die coater according to an embodiment of the present disclosure.

The die lips <NUM>, <NUM>, <NUM> are aligned in line. A region of the lower die lip <NUM> located on the most upstream side along the movement direction of the current collector is defined as a lower plate bottom 111a, and a region of the lower die lip <NUM> located on the most downstream side is defined as a lower plate top 111b. A region of the intermediate die lip <NUM> located on the most upstream side along the movement direction of the current collector is defined as an intermediate plate bottom 121a, and a region of the intermediate die lip <NUM> located on the most downstream side is defined as an intermediate plate top 121b. A region of the upper die lip <NUM> located on the most upstream side along the movement direction of the current collector is defined as an upper plate bottom 131a, and a region of the upper die lip <NUM> located on the most downstream side is defined as an upper plate top 131b.

An intermediate plate bottom coating gap G2a which is the coating gap at the intermediate plate bottom 121a is the target coating gap PV + a curvature increase at a location corresponding to the intermediate plate bottom 121a. Likewise, a lower plate top coating gap G1b which is the coating gap at the lower plate top 111b is the target coating gap PV + a curvature increase at a location corresponding to the lower plate top 111b. An upper plate bottom coating gap G3a which is the coating gap at the upper plate bottom 131a is the target coating gap PV + a curvature increase at a location corresponding to the upper plate bottom 131a. Likewise, an intermediate plate top coating gap G2b which is the coating gap at the intermediate plate top 121b is the target coating gap PV + a curvature increase at a location corresponding to the intermediate plate top 121b.

When an average of the curvature increase at the location corresponding to the intermediate plate bottom 121a and the curvature increase at the location corresponding to the lower plate top 111b is AV', and an average of the curvature increase at the location corresponding to the upper plate bottom 131a and the curvature increase at the location corresponding to the intermediate plate top 121b is AV, AV' and AV change depending on the diameter of the coating roll <NUM>, the thickness of each die lip <NUM>, <NUM>, <NUM>, the thickness of the spacer <NUM>, <NUM> used, and which part of the dual slot die coater <NUM> at which the coating roll <NUM> is centered.

In case that the thickness of the spacer <NUM>, <NUM> is <NUM> to <NUM>, the diameter of the coating roll <NUM> is <NUM> to <NUM>, and the coating roll <NUM> is centered on the upper plate bottom 131a or the lower plate top 111b, when AV' and AV are equal to or smaller than <NUM> µm, the coating quality is not affected. When AV' and AV do not exceed <NUM> µm, the maximum of the thickness D3 of the upper die lip <NUM> is <NUM>. The maximum of the thickness D2 of the intermediate die lip <NUM> is <NUM>. The maximum of the thickness D1 of the lower die lip <NUM> is <NUM>.

Accordingly, when considering together with the minimum value of each die lip described above, the thickness D3 of the upper die lip <NUM> may range from <NUM> to <NUM>, the thickness D2 of the intermediate die lip <NUM> may range from <NUM> to <NUM>, and the thickness D1 of the lower die lip <NUM> may range from <NUM> to <NUM>.

Hereinafter, the present disclosure will be described in more detail through experimental examples.

For electrode quality evaluation, an electrode active material slurry layer of double layer structure is formed with varying thicknesses of the die lips <NUM>, <NUM>, <NUM>. The electrode active material slurries <NUM>, <NUM> are a mixture of graphite : conductive material : CMC : binder at a ratio of <NUM> : <NUM> : <NUM> : <NUM> in water. The coating gap is <NUM> µm, and the flow ratio of the upper layer slurry and the lower layer slurry is <NUM> : <NUM>. The coating rate is <NUM>/min.

Table <NUM> summarizes the die lip thickness and the thickness ratio, and the electrode quality results.

In experimental example <NUM>, as opposed to the present disclosure, the upper die lip <NUM>, the intermediate die lip <NUM> and the lower die lip <NUM> are equally <NUM> in thickness. As a result of simulation and actual test, leaking occurred. A Carreau-Yasuda viscosity model was used in the simulation.

In experimental example <NUM>, each of the upper die lip <NUM>, the intermediate die lip <NUM> and the lower die lip <NUM> is <NUM> in thickness. Each die lip is twice thicker than experimental example <NUM>, but its ratio is equally <NUM> : <NUM> : <NUM>. In the same way as experimental example <NUM>, as a result of simulation and actual test, leaking occurred. (c) of <FIG> shows that leaking of the first electrode active material slurry <NUM> occurred in the lower die lip <NUM> as a result of simulation of experimental example <NUM>.

In experimental examples <NUM> to <NUM>, the lower die lip <NUM> is the thickest. That is, the die lip thickness requirement of the present disclosure is met. As a result of simulation and actual test in experimental examples <NUM> to <NUM>, leaking or side ring did not occur, and the coating quality is good. (a) of <FIG> shows experimental example <NUM>, and (b) shows experimental example <NUM>. The arrow indicates the dynamic contact line. The lower die lip <NUM> of experimental example <NUM> is thicker than experimental example <NUM>. In experimental example <NUM>, it can be seen that the dynamic contact line is disposed at the inner position than the lower die lip <NUM>. That is, the window margin is wider. Accordingly, according to the present disclosure, as shown in experimental examples <NUM> to <NUM>, it is possible to prevent leaking and achieve the wider window margin with the increasing thickness of the lower die lip <NUM>. The thickness of the lower die lip <NUM> does not increase without limit, and is adjusted to place the dynamic contact line at an appropriate position according to the intended coated product and quality when coating.

In experimental example <NUM>, as opposed to the present disclosure, the upper die lip <NUM> is the thickest. As a result of simulation, leaking occurred.

In experimental example <NUM>, as opposed to the present disclosure, the thickness of the intermediate die lip <NUM> is the largest. As a result of simulation, leaking did not occur, but in the actual test, a fat-edge pattern defect occurred, resulting in fat electrode edge.

While the present disclosure has been described with respect to a limited number of embodiments and drawings, the present disclosure is not limited thereto, and it is obvious to those skilled in the art that a variety of changes and modifications may be made thereto within the technical aspects of the present disclosure and the appended claims and their equivalent scope.

Claim 1:
A dual slot die coater (<NUM>) comprising a lower slot (<NUM>) and an upper slot (<NUM>), for extrusion coating of an electrode active material slurry on a surface of a continuously moving current collector (<NUM>) through at least one of the lower slot (<NUM>) or the upper slot (<NUM>), the dual slot die coater (<NUM>) comprising:
a lower plate (<NUM>), an intermediate plate (<NUM>) positioned on the lower plate (<NUM>) and an upper plate (<NUM>) positioned on the intermediate plate (<NUM>), the lower slot (<NUM>) being formed between the lower plate (<NUM>) and the intermediate plate (<NUM>), and the upper slot (<NUM>) being formed between the intermediate plate (<NUM>) and the upper plate (<NUM>),
wherein the lower plate (<NUM>), the intermediate plate (<NUM>) and the upper plate (<NUM>) have a lower die lip (<NUM>), an intermediate die lip (<NUM>) and an upper die lip (<NUM>), each forming a front end with respect to the current collector (<NUM>), respectively, and characterized in that
a thickness D1 of the lower die lip (<NUM>) is larger than a thickness D3 of the upper die lip (<NUM>) and a thickness D2 of the intermediate die lip (<NUM>),
wherein the thickness D1 of the lower die lip is <NUM> times the thickness D3 of the upper die lip or more, or
wherein the thickness D1 of the lower die lip is <NUM> times the thickness D2 of the intermediate die lip or more, and
wherein a thinner die lip between the upper die lip (<NUM>) and the intermediate die lip (<NUM>) is <NUM> µm or more in thickness.