Method and system for producing a dry mixture of conductive carbon black and active material

Abstract

The invention relates to a method for producing a dry mixture consisting of conductive carbon black (16) and an active material for producing anode material for an electrochemical cell, in particular a battery cell, in which, in a first step, only the conductive carbon black (16) is set, by means of shearing, to a bulk density of <0.05 g / cm3, preferably < 0.03g / cm3 and in a second, subsequent step, is mixed with the active material.

Description

[0001] Process and plant for producing a dry mixture consisting of conductive carbon black and an active material

[0002] DESCRIPTION

[0003] The invention relates to a method for producing a dry mixture consisting of conductive carbon black and an active material for producing anode material for an electrochemical cell, in particular a battery or accumulator cell, such as for a lithium-ion accumulator.

[0004] The functional components of a coating for anodes of lithium-ion batteries include an electrochemically active material, the so-called active material, which is typically formed from graphite, additives that increase electrical conductivity, the so-called conductive additives, which are primarily formed from conductive carbon blacks, and the electrically / electrochemically inactive binder.

[0005] The production of anode material often begins with a dry mixing process in which the powdered components graphite and conductive carbon black are mixed. A typical dry mixing process is described in US 2016 / 0013473 A1. This is followed by a dispersion process in which the binder is dissolved and interacts with the graphite and conductive carbon black to form a suspension. This is followed by coating conductive foils with the suspension, drying, and compacting the resulting composite layer.

[0006] A somewhat different mixing process is described in DE 10 2017 213403 A1, according to which a binder is first mixed with a first electrode component under high shear stress, whereby the binder is intended to fibrillate due to relative movement of the electrode component and the binder. A second electrode component is then added to the mixture under lower shear stress.

[0007] The inventors have recognized that the deposition of the conductive carbon black particles on the particles of the active material has a positive effect on the electrode conductivity of the finished anode material and have therefore set themselves the task of providing the dry mixing process with a view to an improved result of the mixing of conductive carbon black particles and active material and at the same time an efficient dry mixing process.

[0008] The problem is solved by a method according to claim 1 and a system according to claim 12.

[0009] The process according to the invention for producing the dry mixture of conductive carbon black and an active material provides, in a first step, that the conductive carbon black is isolated to a bulk density of <0.1 g / cm 3 , preferably < 0.08 g / cm 3 , particularly preferably 0.05 g / cm 3 and more preferably < 0.03g / cm 3and in a second, subsequent step the conductive carbon black is mixed with the active material.

[0010] The invention is based on the finding that the state of the conductive carbon black, even at the moment of initial contact with the active material during mixing, plays a significant role in the distribution of the conductive carbon black particles along the particle surface of the active material. Conductive carbon black typically has a primary particle size of 10 to 50 nm, which, due to van der Waals interactions, initially combine to form so-called aggregates with a size of 100 to 300 nm and then further to form agglomerates with dimensions in the micrometer range. In its as-delivered state, the conductive carbon black therefore generally has a bulk density of approximately 0.1 g / cm3 due to the aggregates and agglomerates formed during storage and transport. 3or more. It is suspected that this property makes it difficult to achieve a homogeneous distribution of the conductive carbon black particles in the dry mixture.

[0011] Therefore, the process according to the invention provides for the isolated pretreatment of the conductive carbon black in the first step of the process. "Isolated" in this context means that the conductive carbon black is treated in the first step without the presence of particles of the active material or any other substance. In particular, the agglomerates are thus comminuted in the first step. This process step is also referred to as destructuring. The inventors have discovered that destructuring is accompanied by an increase in the volume of the conductive carbon black. A measure of the success of this first process step is therefore the bulk density of the conductive carbon black, where bulk density is understood to be the bulk density determined according to DIN ISO 697 / EN ISO 60. As a result of the first process step, this is below 0.1 g / cm 3, preferably below 0.08 g / cm 3 , more preferably below 0.05 g / cm 3 and most preferably below 0.03 g / cm 3 .

[0012] The conductive carbon black is preferably formed from primary particles with an average size (d50) of 10 to 50 nm. The bulk density can be easily adjusted by mechanically loading the conductive carbon black in its initial state, preferably by subjecting it to reproducible shear or impact stress. (Fine) impact mills are preferably used for this purpose, and blowers, particularly a radial blower, are particularly preferred. The conductive carbon black is preferably metered into an intake line of the blower. This is preferably done gravimetrically.

[0013] The destructuring of the conductive carbon black is particularly preferably carried out in the first step by means of a shear load at a shear rate of at least 10,000 s -1 , furthermore preferably of at least 12,000 s -1and most preferably of at least 15,000 s -1 .

[0014] For this purpose, it has proven advantageous to feed the conductive carbon black to a fan, preferably a radial fan, which has a stator and rotating fan blades, wherein the shear stress is achieved with the said shear velocities in the gap between the rotating fan blades and the stator within the housing.

[0015] The inventors have further recognized that by destructuring the conductive carbon black beforehand, the subsequent mixing can be carried out with significantly lower mechanical stress on the components than if the conductive carbon black is added to the active material in the mixing container in untreated form, and that the electrical conductivity of the finished anode material can thereby be increased even further compared to the known mixing processes.

[0016] Only in the second, downstream step is the destructured conductive carbon black mixed with the active material. The active material is preferably graphite. Amorphous carbon or lithium titanate are also possible options, but play a less important role in practice.

[0017] The graphite preferably comprises pretreated, rounded graphite particles in order to achieve the highest possible particle density in the anode coating, which, in contrast, cannot be achieved with particles with an angular geometry (splintered). Rounded here means that the edges and corners of the particles are broken, which means that the particles are less likely to entangle with one another in a bed. Compared to spattered particles, they are easily mobile relative to one another and can therefore be compressed into a denser sphere packing without the application of destructive force. This ultimately leads to a higher energy density of the anode material. Graphite particles with an average size (d50) of 12 to 20 pm are particularly preferably used initially.

[0018] The degree of rounding is best parameterized using the BET surface area and the tamped density of the graphite particle material. Graphite is the preferred starting material, which, before mixing with conductive carbon black, has a BET surface area of ​​6 m according to DIN ISO 9277. 2 / g up to 12 m 2 / g and a tapped density determined according to DIN ISO 787-11 of greater than 0.8 g / ml, preferably greater than 0.85 g / ml, particularly preferably greater than 0.9 g / ml and further preferably greater than 0.95 g / ml.

[0019] To achieve the desired properties, 1 to 5 wt.% conductive carbon black and 95 to 99 wt.% graphite are preferably mixed.

[0020] The goal in the second process step is to maintain the degree of rounding as much as possible. To achieve this, it has proven advantageous to conduct the mixing process gently, particularly in a second step that is independent of the destructuring of the conductive carbon black. Surprisingly, it has been found that such a mixing process, despite the minimal stress on the mix, does not result in any significant deterioration in the mixing result.

[0021] Advantageously, the mixing of the conductive carbon black with the active material in the second step is carried out by means of a mixer at a shear rate of at least 1,000 s' 1 and preferably at least 2,000 s -1 . Furthermore, the shear rate during mixing is preferably at most 5,000 s' 1 .

[0022] Also preferably, the mixing under these conditions takes place over a mixing time of at least 200 seconds, preferably at least 400 seconds.

[0023] By mixing the conductive carbon black with the graphite in the second step, a dry mixture with a tamped density according to DIN EN ISO 787-11 of at least 0.8 g / cm 3 , preferably at least 0.85 g / cm 3 which, due to the gentle mixing, is virtually unchanged from the starting material graphite (0.9 g / ml). Ideally, the tapped density of the powder mixture is higher than the tapped density of the starting graphite, namely when the soot particles fill the voids between and within the unchanged, rounded graphite particles, thereby increasing the mass but not the volume of the powder mixture.

[0024] Advantageously, by mixing the conductive carbon black with the graphite in the second step, a dry mixture with a specific BET surface area according to DIN ISO 9277 of at most 7 m 2 / g, preferably not more than 5.2 m 2 / g. This value is also virtually unchanged from that of the pure starting material, graphite, and ideally even lower. A low specific BET surface area indicates an ideal powder form of the conductive carbon black, which exhibits optimal coating or wetting behavior and deposits itself in a uniform layer on the particles of the active material, ideally even filling its pores. The properties of the dry mixture can be summarized in the following matrix:

[0025] The first case is evidence of excessive shear during mixing, which damages the active material and reduces the tamped density despite good wetting by an approximately ideal powdered conductive carbon black.

[0026] In the second case, it can be assumed that excessive shear during mixing on the one hand and insufficiently destructured conductive carbon black on the other hand are the cause, with the result that the active material can no longer be optimally compacted and at the same time the conductive carbon black does not optimally wet the active material.

[0027] The third case is the one achieved by the dry mixing process according to the invention. The conductive carbon black is sufficiently destructured by the upstream first process step to coat the active material particles almost uniformly in the second process step, which, in turn, do not experience any structural impairment during mixing.

[0028] In the fourth case, although the mixture is gentle, the conductive carbon black is not sufficiently destructured, which leads to an increased specific surface area due to the conductive carbon black aggregates and agglomerates.

[0029] Advantageously, after the first step, the destructured conductive soot is subjected to a separation process in which the conductive soot is separated from the carrier gas from the radial blower by means of a separator and then fed to the mixer. The destructured conductive soot is thus transported to the separator, preferably by means of the gas flow from the radial blower. From there, the conductive soot simply falls into the mixer by gravity. The first process step can be carried out very efficiently due to the very short residence time of the conductive soot in the blower. The conductive soot particles are then transferred to the second process step for coating the active material without intermediate storage, so that the risk of re-agglomeration or re-aggregation can be largely eliminated.The plant according to the invention for producing a dry mixture consisting of conductive carbon black and an active material for producing anode material for an electrochemical cell, in particular a battery cell, comprises a destructuring agent which is designed to subject the conductive carbon black in isolation to a shear or compressive stress which is sufficient to reduce the bulk density of the conductive carbon black to <0.1 g / cm. 3 , preferably <0.08 g / cm 3 , particularly preferably <0.05 g / cm 3 , still preferably < 0.03g / cm 3 and a mixer downstream of the destructuring agent, which is configured to mix the destructured conductive carbon black with the active material.

[0030] Preferably, the destructuring means is formed by a fan, particularly preferably a radial fan, which has a stator and rotating fan blades and which is designed to generate a shear rate of at least 10,000 s' in a gap between the rotating fan blades and the stator. 1 , preferably at least 12,000 s' 1 and particularly preferably of at least 15,000 s -1 to generate.

[0031] The mixer is preferably designed to achieve a shear rate of at least 1,000 s -1 and preferably at least 2,000 s' 1 and still preferably maximum 5000 s -1To this end, it preferably comprises, similar to the blower, a housing with a stator and mixing tools rotating therein, wherein the shear stress is achieved at the aforementioned shear rates in the gap between the rotating mixing tools and the stator within the housing.

[0032] The blower is connected to the mixer via a fluid line. A separator is preferably integrated into the fluid flow within this fluid line between the radial blower and the mixer. This separator is designed to separate the conductive soot, i.e., conductive soot particles and / or aggregates and / or agglomerates, from the carrier gas stream from the radial blower. The separator is preferably a filter, a cyclone separator, or an electrostatic precipitator, or a combination of these.

[0033] Accordingly, the radial fan is preferably further configured to generate a sufficient gas flow to transport the conductive soot through the fluid line and the separator to the mixer. Thus, in addition to destructuring the conductive soot, the fan also has the function of providing a sufficient volume flow to transport the conductive soot to the subsequent processing step.

[0034] Further advantages and features of the invention are described below with reference to the figures. Figure 1 shows an embodiment of the system according to the invention;

[0035] Figure 2 is a schematic representation of the dry mix after simple mixing;

[0036] Figure 3 is a schematic representation of the dry mix after intensive mixing;

[0037] Figure 4 is a schematic representation of the dry mixture in which ideal powdered conductive carbon black is homogeneously deposited on the particles of the active material and

[0038] Figure 5 is a schematic representation of the dry mixture of ideal powdered conductive carbon black with active material in which the cavities between the particles of the active material are also filled with conductive carbon black.

[0039] The plant according to the invention for producing a dry mix, as shown in Figure 1, has a metering device 10 with a container 12 and a conveyor device 14 for the conductive carbon black 16 on the inlet side. The conveyor device 14 is shown here as a screw conveyor, but is not fundamentally limited to such a conveyor system. Dosing can be carried out using the metering device either volumetrically or gravimetrically. In the latter case, a scale is also provided, with which, for example, the container 12 is weighed. The conveying speed of the conveyor device 14 can then be regulated based on the determined mass reduction.

[0040] The conductive carbon black 16 is thus metered into an intake duct 18 of a radial fan 20, through which a carrier gas 22, preferably air, is simultaneously sucked in. In the radial fan 20, the conductive carbon black 16 is subjected to a shear rate of at least 10,000 s' in the first process step. 1, preferably at least 12,000 s' 1 and particularly preferably of at least 15,000 s~ 1 This is selected for a given fan geometry by setting and / or regulating a specific fan speed. In this way, the bulk density of the conductive carbon black can be reduced to <0.1 g / cm 3 , preferably <0.08 g / cm 3 , particularly preferably <0.05 g / cm 3 , still preferably < 0.03g / cm 3 to set.

[0041] On the output side, a fluid line 24 connects to the radial fan 20, through which the now destructured conductive soot 16 is pneumatically transported in the flow of the carrier gas 22 to a connected separator 26. In the example shown, this is a cyclone separator, although the system according to the invention is not limited to the use of a cyclone separator. In the separator 26, the destructured conductive soot 16 is separated from the carrier gas 22. The carrier gas 22 passes through an exhaust line 28 to a filter 30, through which it is purified of any residual conductive soot and released into the environment.

[0042] Through the fluid line 24, the conductive carbon black 16 from the separator 26 is fed to a mixer 32, to which rounded active material 36 is additionally fed through another fluid line 34 or optionally also the same fluid line 24 (not shown here). In the second process step, the conductive carbon black 16 is mixed in the mixer 32 together with the active material 36 at a shear rate of at least 1,000 s 1 , preferably at least 2,000 s -1 Mixed for a period of at least 200 seconds, preferably at least 400 seconds. The mechanical stress causes the materials to blend, causing the conductive carbon black particles to partially adhere to the active material particles and form a coating on them, which increases the contact area of ​​the graphite particles.

[0043] Further parts of the conductive carbon black, especially aggregates that were not completely crushed in the first process step, fill the spaces between the active material particles and thus again increase the contact area of ​​neighboring active material particles, which explains the overall improved particle conductivity of the dry mixture.

[0044] Figures 2 to 5 schematically illustrate four different states of the dry mixture. In each case, the active material particles 40 are idealized as circular spheres. Cavities 42 are enclosed between adjacent active material particles. The purpose of the conductive carbon black is to improve the contact between the active material particles.

[0045] Figure 2 depicts the idealized case in which the conductive carbon black is enclosed in the form of agglomerates 44 in some of the cavities 42 between the active material particles 40. Where conductive carbon black is enclosed, the agglomerates form electrical bridges, increasing the number of contacts between neighboring active material particles. The conductive carbon black agglomerates have a diameter that is approximately the same order of magnitude as that of the active material particles. As a result, conductive carbon black is not found in all cavities 42, and the increase in contact points does not occur between all neighboring active material particles, which is expected to result in only a slight improvement in powder conductivity.

[0046] Figure 3 also shows, as an idealized representation, a case in which the conductive carbon black is present in the form of smaller aggregates 46. The aggregates 46 are approximately an order of magnitude smaller than the active material particles and therefore fit into the majority of the cavities 42 between the active material particles 40, where they, like the agglomerates 44, form electrical bridges. This further increases the number of contacts between neighboring active material particles, but does not achieve a significant improvement in powder conductivity.

[0047] Figure 4 shows an idealized representation with conductive carbon black in the form of pure primary particles 48, which are several orders of magnitude smaller than the active material particles 40. The conductive carbon black particles 48 adhere evenly to the surface of the active material particles 40. Although this does not form additional electrical bridges, the individual contact points are enlarged, which contributes to improved powder conductivity. Finally, Figure 5 shows the state in which the conductive carbon black not only adheres evenly to the surface of the active material particles, but also free conductive carbon black fills the cavities between the active material particles. Here, too, the conductive carbon black particles 48 adhere evenly to the surface of the active material particles 40, creating larger contact areas. They provide additional electrical bridges in the cavities between the active material particles.

[0048] List of reference symbols

[0049] 10 Appendix

[0050] 12 containers

[0051] 14 Conveyor system

[0052] 16 Conductive carbon black

[0053] 18 intake duct

[0054] 20 radial fans

[0055] 22 Carrier gas

[0056] 24 Fluid line

[0057] 26 separators

[0058] 28 exhaust pipe

[0059] 30 filters

[0060] 32 mixers

[0061] 34 second channel

[0062] 36 active material

[0063] 40 active material particles

[0064] 42 cavity

[0065] 44 Conductive carbon black agglomerate

[0066] 46 Power unit

[0067] 48 conductive soot particles

Claims

Patent claims 1 . A method for producing a dry mixture consisting of conductive carbon black (16) and an active material for producing anode material for an electrochemical cell, in particular a battery cell, in which, in a first step, the conductive carbon black (16) is isolated to a bulk density of <0.1 g / cm 3 , preferably <0.08 g / cm 3 , particularly preferably <0.05 g / cm 3 , still preferably < 0.03g / cm 3 and in a second, subsequent step the conductive carbon black is mixed with the active material.

2. Method according to claim 1, characterized in that the conductive carbon black (16) is formed from primary particles with an average size (d50) of 10 to 50 nm.

3. Method according to one of the preceding claims, characterized in that the active material consists of graphite (36).

4. Method according to one of the preceding claims, characterized in that 1 to 5 wt.% of conductive carbon black (16) and 95 to 99 wt.% of the graphite (36) are mixed.

5. Method according to one of the preceding claims, characterized in that in the first step the bulk density of the conductive carbon black (16) is determined by means of a shear rate in the range of 10,000 s -1 , preferably at least 12,000 s' 1 and particularly preferably of at least 15,000 s -1 is set.

6. The method according to claim 5, characterized in that in the first step the conductive soot (16) is fed to a fan, preferably a radial fan (20), with a stator and with rotating fan blades, wherein the shear velocity is generated in a gap between the rotating fan blades and the stator.

7. Method according to one of the preceding claims, characterized in that the mixing of the conductive carbon black (16) with the active material (36) in the second step is carried out by means of a mixer (32) at a shear rate of at least 1,000 s 1 and preferably at least 2,000 s -1 occurs.

8. Method according to claim 6 and 7, characterized in that after the first step, the conductive soot (16) is subjected to a separation process in which the conductive soot (16) is separated from a carrier gas from the blower (20) and is then fed to the mixer (32).

9. Method according to one of the preceding claims, characterized in that by mixing the conductive carbon black (16) with the graphite (36) in the second step, a mixture with a tamped density according to DIN EN ISO 787-11 of at least 0.8 g / cm 3 , preferably at least 0.85 g / cm 3 is manufactured.

10. Method according to one of the preceding claims, characterized in that by mixing the conductive carbon black (16) with the graphite (36) in the second step, a mixture with a specific BET surface area of ​​at most 7 m 2 / g, preferably not more than 5.2 m 2 / g is produced. 11 . Method according to one of the preceding claims, characterized in that by mixing the conductive carbon black (16) with the graphite (36) in the second step, a mixture with a powder conductivity of at least 3.5x10' 2 S / cm, preferably at least 3.7x10 -2 S / cm is produced.

12. Plant (10) for producing a dry mixture consisting of conductive carbon black (16) and an active material for producing anode material for an electrochemical cell, in particular a battery cell, comprising: - a destructuring agent which is designed to subject the conductive carbon black (16) in isolation to a shear or compressive load which is sufficient to reduce the bulk density of the conductive carbon black to <0.1 g / cm 3 , preferably <0.08 g / cm 3 , particularly preferably <0.05 g / cm 3 , still preferably < 0.03g / cm 3 to set, and - a mixer (32) downstream of the destructuring agent, which is arranged to mix the conductive carbon black (16) with the active material.

13. Plant according to claim 12, characterized in that the destructuring means is a fan, preferably a radial fan (20), with a stator and with rotating fan blades, which is designed to generate a shear rate of at least 10,000 s in a gap between the rotating fan blades and the stator -1 , preferably at least 12,000 s' 1 and particularly preferably of at least 15,000 s -1 to generate.

14. Plant according to claim 12 or 13, characterized in that the mixer (32) is arranged to have a shear rate of at least 1,000 s' 1 and preferably at least 2,000 s' 1 to generate.

15. Plant according to claim 13 and 14, characterized in that in the fluid flow between the blower and the mixer (32) a separator (26), preferably a filter, a cyclone separator or a total separator, is switched on, which is designed to separate the conductive soot (16) from a carrier gas (22) from the blower.

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