阅读说明：本技术 用于电化学应用的箔的无溶剂涂层工艺 (Solvent-free coating process for foils for electrochemical applications ) 是由 J·M·奥菲 A·乌尔西格 于 2021-05-25 设计创作，主要内容包括：本发明提供制造具有包含活性材料和可熔聚合物的功能性涂层的箔的无溶剂工艺、具有功能性涂层的箔,及其用作电极箔、固态电池中的电解质或用于电化学存储装置的分隔器的用途。所述工艺包括将干粉混合物散布到箔上,熔融干粉混合物,并压延覆盖有熔融粉末的箔。(The present invention provides a solvent-free process for manufacturing a foil with a functional coating comprising an active material and a fusible polymer, a foil with a functional coating, and its use as an electrode foil, an electrolyte in a solid-state battery or a separator for an electrochemical storage device. The process includes spreading a dry powder mixture onto a foil, melting the dry powder mixture, and calendaring the foil covered with the molten powder.)

1. A process for manufacturing a foil having a functional coating comprising an active material and a fusible polymer, wherein the foil having the functional coating is used as an electrode foil, an electrolyte in a solid-state battery, or a separator for an electrochemical storage device, the process comprising the steps of:

(a) providing a dry powder mixture comprising (i) active material particles and (ii) fusible polymer particles,

(b) dispersing the dry powder mixture onto a foil to form a powder-coated foil,

(c) melting the powder of the powder-covered foil to form a powder-covered foil,

(d) calendering the foil covered with the molten powder to form a calendered structure; and

(e) cooling the rolled structure to form a foil having a functional coating.

2. The process of claim 1, wherein step (c) is performed before step (d).

3. The process of claim 1, wherein steps (c) and (d) are performed simultaneously by hot calendering.

4. A process according to any preceding claim, wherein the volume average particle diameter D of the particles (i) in the dry powder mixture₅₀Greater than 5.0 μm, the volume-average particle diameter D of the particles (ii)₅₀Is 5.0 μm or less.

5. The process of any one of the preceding claims, wherein steps (b) through (e) are carried out continuously.

6. A process according to any one of the preceding claims, wherein the dry powder mixture further comprises electrically conductive additive particles.

7. The process of any preceding claim, wherein after the dry powder mixture is spread onto the foil in step (b) and before being melted in step (c), the dry powder mixture does not adhere to the foil, but rests on the foil solely by the action of gravity.

8. The process according to any of the preceding claims, wherein the scattering of the dry powder mixture onto the foil in step (b) is the only process step of dispensing the powder on the foil until melting in step (c).

9. The process according to any one of the preceding claims, wherein step (b) is performed by applying the dry powder mixture onto a spreading roller, brushing the dry powder mixture off the spreading roller by using a vibrating brush, and sprinkling the dry powder mixture onto the foil by at least one vibrating distribution plate.

10. The process according to any of the preceding claims, which is a process for producing a metal foil with a functional coating for use as an electrode foil.

11. The process according to any one of the preceding claims, wherein the active material is at least one material selected from the group consisting of metal oxides, activated carbon, graphite, metal phosphates and silicon compounds, and/or the fusible polymer is at least one polymer selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene and polysiloxanes.

12. The process of claim 1, wherein steps (b) through (e) are performed continuously and step (c) is performed before step (d).

13. The process of claim 1, wherein steps (b) through (e) are performed continuously, the scattering of the dry powder mixture onto the foil in step (b) is the only step of dispensing the powder onto the foil until melted in step (c), and steps (c) and (d) are performed simultaneously by hot calendaring.

14. A foil having a coating comprising an active material and a polymer and produced by the process of any one of claims 1-13.

15. Use of the coated foil according to claim 14 as an electrode foil or separator for an electrochemical storage device.

Technical Field

The present invention relates to a process for the solventless production of coated foils which can be used as electrode foils, electrolytes in solid-state batteries or separators for secondary batteries or other electrochemical storage devices, to the foils produced by this process and to the use of the foils.

Background

The production of lithium ion batteries involves many different process steps, which can be optimized to save costs. One process step in manufacturing is the production of electrode foils. For this purpose, the active material is first dispersed in a binder solution together with various conductive additives. Water or N-methyl-2-pyrrolidone (NMP) was used as the solvent. In a further step, the resulting paste-like mass is then applied to a metal foil by means of a coating head in a coating system and then dried. The disadvantage of this process is that the drying process step is energy consuming and requires a long drying line. In addition, the solvent used, NMP, is considered to be harmful to health and reproduction, and therefore this substance is of high interest. In addition, due to legal requirements, the use of NMP as a solvent in the electrode coating will be excluded in the future.

Various methods for solvent-free production of electrode foils are known. In a calender-based process, the powdered functional material mixture is introduced into a roll nip and a foil is produced, which is pressed onto a current collector in a subsequent process step or the current collector is additionally introduced directly into the roll nip, so that the finished electrode is produced from the calender. Another possibility is based on powder spray processes and electrostatically assisted powder coating processes, wherein the material mixture is transferred to the current collector in a high voltage induced electric field.

US 2016/181651 a1 describes a sieving application in which particles containing active material and binder are sieved onto a current collector and then compacted by a roller system.

WO 2014/155168 a1 describes a process for producing a coated electrode foil in which particles containing an active material and a binder are dispersed on the foil and then calendered.

Problems to be solved by the invention

However, the methods known in the prior art are laborious and slow and often require special equipment to achieve a uniform coating.

It is therefore an object of the present invention to provide a process with which solvent-free and uniform coating of a foil can be carried out in a simple and efficient manner.

Disclosure of Invention

The stated object is achieved by providing a process which comprises simply applying a solvent-free starting material, melting the starting material and calendering.

More specifically, the subject matter of the present invention is described in the following points:

[1] a process for manufacturing a foil having a functional coating comprising an active material and a fusible polymer, wherein the foil having the functional coating is used as an electrode foil, an electrolyte in a solid-state battery, or a separator for an electrochemical storage device, the process comprising the steps of:

(a) providing a dry powder mixture comprising (i) active material particles and (ii) fusible polymer particles,

(b) dispersing the dry powder mixture onto a foil to form a powder-coated foil,

(c) melting the powder of the powder-covered foil to form a powder-covered foil,

(d) calendering the foil covered with the molten powder to form a calendered structure; and

(e) cooling the rolled structure to form a foil having a functional coating.

[1-1] preferably, the particles (i) and/or (ii) in the dry powder mixture provided in step (a) of point [1] are present at least partly as individual particles.

[2] The process according to the point [1] or [1-1], wherein the step (c) is carried out before the step (d).

[3] The process according to the point [1] or [1-1], wherein the steps (c) and (d) are simultaneously carried out by hot calendering.

[4]According to the aforementioned point [1]]、[1-1]、[2]Or [3]]The process of any of the preceding claims, wherein the volume average particle diameter D of the particles (i) in the dry powder mixture₅₀Greater than 5.0 μm, volume average particle diameter D of the particles (ii)₅₀Is 5.0 μm or less.

Preferred embodiments in the process according to the point [4] are those according to the following point: [4-1] the size of the particles (i) is at least twice the size of the particles (ii); [4-2] the size of the particles (i) is greater than 20 μm.

[5] The process according to any of the preceding points, wherein steps (b) to (e) are carried out continuously.

[6] The process according to any of the preceding points, wherein the dry powder mixture further comprises conductive additive particles.

[7] The process according to any of the preceding points, wherein after the dispersion of the dry powder mixture onto the foil in step (b) and before the melting in step (c), the dry powder mixture does not adhere to the foil but stays on the foil only by gravity. Here, the plane of the foil must be substantially perpendicular to the direction of gravity.

[7-1] the combination of the features of [1], [1-1] and [7] is preferable. [7-2] the combination of the features of [2] and [7], that is, specifically [1], [2] and [7] or [1-1], [2] and [7], may also be preferable.

[8] The process according to any of the preceding points, wherein the scattering of the dry powder mixture onto the foil in step (b) is the only process step of dispensing the powder onto the foil until melting in step (c).

[8-1] the combination of the features of the points [7] and [8] is preferable. [8-2] the point [7-1] or a combination of the features of [7-2] and [8] is more preferable.

[9] The method according to any of the preceding points, wherein step (b) is performed by applying the dry powder mixture to a spreading roller, brushing the dry powder mixture off the spreading roller by using a vibrating brush, and sprinkling the dry powder mixture onto the foil by at least one vibrating distribution plate.

Embodiments according to the following points are preferred: [9-1] combination of the features of [9] and [7] or [7-1] or [7-2 ]; [9-2] combination of the features of [9] and [8-1] or [8-2 ]; [9-3] combination of the features of the points [9] and [4-1 ]; [9-4] a combination of the features of the essential points [9-2] and [9-3 ]; [9-5] combination of the features of [9], [8-2] and [4-1 ].

[10] The process according to any one of the preceding points, which is a process for producing a metal foil with a functional coating for use as an electrode foil.

[11] The method according to any one of the preceding points, wherein the active material is at least one material selected from the group consisting of metal oxides, activated carbon, graphite, metal phosphates, and silicon compounds, and/or the fusible polymer is at least one polymer selected from the group consisting of polyvinylidene fluoride, polytetrafluoroethylene, and polysiloxane.

[12] The process according to the point [1] or [1-1], wherein the steps (b) to (e) are continuously carried out, and the step (c) is carried out before the step (d).

Embodiments according to the following points are preferred: [12-1] combination of the features of [12] and [8-1] or [8-2 ]; [12-2] combination of the features of the points [12] and [9-1 ]; [12-3] combination of the features of the points [12] and [9-2 ]; [12-4] combination of the features of the points [12] and [9-3 ]; [12-5] combination of the features of [12] and [9-4] or [9-5 ].

[13] The process according to the point [1] or [1-1], wherein the steps (b) to (e) are continuously performed, the scattering of the dry powder mixture onto the foil in the step (b) is the only step of distributing the powder on the foil until melting in the step (c), and the steps (c) and (d) are simultaneously performed by hot calendering.

Embodiments according to the following points are preferred: [13-1] combination of the features of the points [13] and [8-1 ]; [13-2] combination of the features of the points [13] and [9-1 ]; [13-3] combination of the features of the points [13] and [9-2 ]; [13-4] combination of the features of the points [13] and [9-3 ]; [13-5] combination of the features of [13] and [9-4 ].

[14] A foil having a coating layer comprising an active material and a polymer, which can be produced by the process according to any one of the points [1] to [13] and [1-1] to [13-5 ].

[15] Use of the foil with a coating according to point [14] as an electrode foil or separator for an electrochemical storage device.

Advantages of the invention

Compared to solvent based processes, the process according to the invention has the following advantages: material costs are reduced by omitting the solvent during coating and drying is no longer required, thereby reducing costs. By eliminating the solvent NMP, there is no need to forcibly recover NMP, thereby reducing the environmental burden.

The process according to the invention enables easy production of a uniform foil coating compared to other solvent-free processes. In cold calendering, the melting of the binder prior to calendering allows for a higher speed of the process to be run continuously. In the hot calendering, the step of melting in advance may be omitted.

The process according to the invention can be used for solvent-free coating of electrode foils of accumulators or capacitors, separators of accumulators or capacitors, electrodes of solid-state batteries, solid-state electrolytes of solid-state batteries or mixed electrolytes of solid-state batteries.

Modes for carrying out the invention

The process according to the invention is used to produce a foil according to the invention with a functional coating.

The foil may be a current collector, such as a metal foil, and may be used as an electrode foil. The foil may also be a porous foil, such as a plastic foil, and may be used as a separator for a battery or capacitor. The foil may also be a ready-made electrode foil, on which further functional coatings are applied.

The functional coating comprises an active material, a fusible polymer and, if desired, a conductive additive. The starting material of the functional coating is a dry powder mixture wherein the components of the functional coating are contained in particulate form. Herein, the particles of the active material may be simply referred to as particles (i), and the particles of the meltable polymer may be simply referred to as particles (ii). Any type of particle used in the preparation of the dry powder mixture, such as particles (i) and particles (ii), is also referred to herein in general terms as starting material particles.

Preferred active materials for the positive electrode are oxides of lithium and transition metals, such as lithium nickel oxide, lithium cobalt oxide, lithium manganese oxide, and compounds of these oxides; lithium and transition metal phosphates such as lithium manganese phosphate and lithium iron phosphate and lithium manganese iron phosphate. Preferred active materials for the negative electrode are carbonaceous materials, such as artificial or natural graphite, amorphous carbon; a lithium transition metal oxide; and a silicon compound.

Examples of fusible polymers include PVDF (polyvinylidene fluoride), PTFE (polytetrafluoroethylene), and polysiloxanes.

Examples of the conductive additive include carbon black, porous carbon, carbon nanotube, graphene, graphite, and carbon fiber.

The process according to the invention can be used for solvent-free coating of electrode foils of accumulators or capacitors, separators of accumulators or capacitors, electrodes of solid-state batteries, solid-state electrolytes of solid-state batteries or mixed electrolytes of solid-state batteries. The coated foil according to the invention can be used for these applications.

The steps of the process according to the invention are described below.

Step (a)

A dry powder mixture is provided comprising at least particles (i) and particles (ii). Additionally, a conductive additive may be included.

The dry powder mixture is dry and preferably contains less than 5 wt%, more preferably less than 3 wt% water. The dry powder mixture is free of solvents and therefore also free of organic solvents such as NMP.

Dry powder blending can be performed by, for example, thoroughly mixing or blending the components in a mill such as a ball mill or a mortar mill or a planetary mixer. The preparation of the dry powder mixture is carried out in a solvent-free manner.

Dry-powder mixtures (Trockenpulvermischung) can be prepared as Dry-blended mixtures (Dry-Blend-Mischung) without the use of solvents. For this purpose, the components used in the mixing process are dried under vacuum under the influence of temperature in order to remove the residual water. This is done in a dryer or vacuum dryer. The materials may be mixed first by diffusion mixing, for example by means of a drum mixer and then by means of a propeller mill. In the case of adhesive powders, the average particle size should preferably not be greater than 5 μm, since otherwise a very high proportion of adhesive must be used in order to obtain sufficient adhesion subsequently when applied to the foil. The agglomerates can be broken up using a propeller mixer so that the particles can be refined.

The particles of the dry powder mixture may be present as individual particles such that, for example, the starting material particles are separate and do not adhere to each other by physical or chemical interactions. However, the particles of the dry powder mixture may also adhere to each other and thus form larger units. For example, intensive dry mixing, possibly under heating, can produce small agglomerates comprising different types of particles of starting material (e.g., particles (i) and particles (ii)). The particle size in the agglomerates is preferably constant compared to the size of the starting material particles. To ensure uniform coating, the agglomerates are preferably small and contain only a small amount of starting material particles. For example, the small cluster of particles may be particles (i) covered by particles (ii). Preferably, the particles (i) and/or (ii) of the dry powder mixture provided in step (a) are at least partially present in the form of separate particles, i.e. in a proportion of at least 30 wt% or at least 50 wt% based on the total amount of particles (i) and (ii) provided.

The different types of starting material particles preferably have different sizes. The particle diameter of the particles (i) is preferably 5 to 200. mu.m, more preferably 10 to 100. mu.m. The particle size of the particles (ii) is preferably less than 10 μm, more preferably 5 μm or less. In the dry powder mixture used according to the invention, the particles (i) are preferably larger than the particles (ii), more preferably at least twice as large, even more preferably at least five times as large as the particles (ii). The combination of particles (i) having a size greater than 5.0 μm and particles (ii) having a size equal to or less than 5.0 μm is preferred, and more preferably, the size of particles (i) is at least twice as large as particles (ii). Even more preferred is a combination of particles (i) having a size greater than 20 μm and particles (ii) having a size equal to or less than 5.0 μm. Particle size as referred to herein is D by volume₅₀The value is obtained.

A typical dry powder mixture comprises 80 to 99 parts by mass of particles (i) and 1 to 20 parts by mass of particles (ii) in 100 parts by mass of the sum of particles (i) and particles (ii).

In the dry powder mixture, the smaller particles (ii) may fill the voids of the larger particles (i). In case the dry powder mixture consists partly of individual particles (i) and (ii) and partly of small agglomerates of particles (i) and (ii), the individual particles, in particular the very small particles (ii), may fill the voids. As a result, after the particles (ii) or the small agglomerates, respectively, have melted and subsequently cooled, a polymer network can be formed which serves as a binder and which, in the case of the embedded conductive additive, is also suitable for conducting electricity.

Step (b)

Dispersing the dry powder mixture prepared in step (a) onto a foil. This means that the application of the dry powder mixture to the foil is only performed under the influence of gravity. Other forces are excluded during application.

The dry powder mixture is preferably applied via a metering hopper to a spreading roller which has a specially structured coating. The vibrating brush sweeps the powder down the spreading roller. In order to ensure the uniformity of the powder application and to break up any lumps, the powder passes through at least one vibrating distributor screen without contact, depending on the flowability, falling onto the passing foil. The application speed of the powder can be precisely adjusted by adjusting the rotation speed of the spreading roller, the vibration speed of the brush, and the passing speed of the foil. Depending on the active material used, it may be necessary to adjust the powder dispersion device used (different spreading rolls (Streuwalze), brush bars (Ausb ü rstbecken), bridge crushers (Br ü ckenbrecher) may be used, among others), due to the difference in particle size and morphology.

During the use of the applicator roll and the brush, preferably only low shear forces act on the powder particles. This has the advantage that the particles are not crushed into non-uniform fragments. Such chips will have a lower flow and will therefore result in an uneven application to the foil.

In a preferred embodiment, the dry powder mixture does not adhere to the foil after being spread onto the foil in step (b), but rests on the foil only by gravity until it melts in step (c). Therefore, between step (b) and step (c), preferably no action is performed which would result in a physical or chemical interaction between the dry powder mixture and the foil and thus in adhesion of the dry powder mixture to the foil. This requires that the dry powder mixture is placed on the upper side of the foil, i.e. the side facing the direction of gravity, so that the resting of the dry powder mixture on the foil under the influence of gravity is the only physical interaction between the dry powder mixture and the foil. Since the dry powder mixture is still completely free flowing after the step of scattering, the plane of the foil must be placed substantially horizontally, i.e. perpendicular to the direction of gravity. The term "substantially" means a deviation of at most 20 °, preferably at most 10 °, more preferably at most 5 °. In a particularly preferred embodiment, the particles rest on the foil solely by the action of gravity, as described above, and furthermore the particles are present at least partially as individual particles. Since the particles on the foil are free flowing and smaller in this embodiment, the smaller particles can more easily fill the voids of the larger particles, so that a more compact structure can be obtained.

In a preferred embodiment, the scattering of the dry powder mixture onto the foil in step (b) is the only process step for dispensing the powder onto the foil until melted in step (c). This means that other means of distributing the powder, for example using a scraper (Rakel), are excluded.

Step (c)

The melting of the powder can be carried out, for example, thermally or under IR radiation. In this process, a meltable polymer, preferably a thermoplastic polymer, is at least partially melted. Thus, the melting in step (c) is at least partially melting. Partial melting means that only part of the polymer melts or that the polymer does not completely melt but only softens. Thus, as used herein, melting refers to heating to at least the glass transition temperature Tg, and melting a polymer refers to a polymer that has been heated to at least its glass transition temperature Tg. For example, the melt may be heated to a temperature between the softening point and the melting point of the polymer. However, the fusible polymer can also be heated above its melting point and thus completely melted.

Since the powder comprises an at least partially molten polymer, the foil obtained in step (c) and covered by the molten powder has an at least partially molten powder covering.

The melting of the powder results in particles, particularly particles of a meltable polymer, at least partially dissolving in the dry powder mixture. Thus, the surface is smooth and fills the spaces between the particles, thereby making the powder layer on the foil more dense. In addition, this results in the powder layer adhering to the foil.

Step (d)

The firm bonding of the molten powder obtained in step (c) to the foil is carried out in a calender having counter-rotating rolls with substantially parallel axes of rotation. The contact pressure of the rollers is adjustable, in particular by the distance between the axes of rotation of the two rollers being adjustable and/or the speed of rotation of the rollers being adjustable. The roller may be heatable to thermally fix the functional coating to the foil to increase adhesion.

Step (e)

Cooling is most easily achieved by cooling the rolled structure at ambient temperature. Alternatively, cooling can also be carried out by means of suitable cooling devices. In cold rolling, cooling has already been carried out at least partially in step (d).

With respect to steps (c), (d) and (e), the following two variations are possible.

In thatModification 1 of the aboveStep (c) is carried out before step (d), for example by cold calendering. For example, in step (c), the foil is brought into pre-contact with the powder layer by at least partially melting the binder by means of high temperature or other types of energy input (e.g. IR radiation). The cooling in step (e) may be at least partially performed during the cold calendering in step (d), such that steps (d) and (e) are performed at least partially simultaneously. Variant 1 may be preferred over variant 2 because melting prior to the calendering step may be faster than with hot calendering.

In thatModification 2 of the aboveAnd steps (c) and (d) are carried out simultaneously by hot calendering. Thus, the contacting of the applied powder mixture is performed by hot calendering. Variant 2 differs from variant 1 mainly in that the melting of the powder mixture applied to the foil is carried out by hot calendering, rather than by two successive process steps. In order to be able to melt, the temperature of the calendering rolls must be adjusted accordingly. By saving one process step, variant 2 may be preferred. By adjusting the temperature and the compaction pressure, the properties of the coating can be controlled during the hot calendering process.

However, variations 1 and 2 are not mutually exclusive. In one embodiment, the melting step (c) may be performed before step (d), which may be performed as hot calendering. In this case, for example, only partial melting or softening of the polymer may occur in step (c), so that the molten layer on the foil does not become too fluid. This combination allows the advantages of both variants to be combined, namely the advantage of a higher processing speed due to the previous melting, and the advantage of simultaneous melting under pressure during the hot pressing delay.