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

Abstract

The present invention relates to a method and system for producing a dry mixture of conductive carbon black (16) and an active material for the production of anode materials for electrochemical cells, particularly battery cells. The method includes a first step of shearing the conductive carbon black (16) to a volume density of 0.05 g / cm. 3 less than 0.03 g / cm 3 The viscosity is adjusted to less than 1000 ppm and in a second step mixed with the active ingredient.

Description

[Background technology]

[0001] The present invention relates to a method for producing a dry mixture of conductive carbon black and an active material for the production of a positive electrode material for electrochemical cells, in particular batteries or accumulator cells, such as lithium-ion accumulators.

[0002] The functional components of the anode coating of lithium-ion accumulators include an electrochemically active material (the so-called active material), which is usually made of graphite, an additive that improves electrical conductivity (the so-called conductive additive), which is mainly made of conductive carbon black, and an electrically / electrochemically inactive binder.

[0003] The initial stage of anode material production typically involves a dry mixing process in which the powdered components graphite and conductive carbon black are mixed. A typical example of this process is described in US 2016 / 0013473 A1. This is followed by a dispersion step in which the binder is dissolved and reacted with the graphite and conductive carbon black to form a suspension. The suspension is then coated onto a current collector foil, dried, and the resulting layer composite is compressed.

[0004] DE 10 2017 213 403 A1 describes a different mixing process in which a binder is treated with a first electrode component under high shear stress to form a mixture. The relative movement between the electrode component and the binder is intended to cause fiberization of the binder. The second electrode component is then added to the mixture under low shear stress.

[0005] The inventors recognized that adhesion between conductive carbon black particles and particles of active material has a positive effect on the electrode conductivity of the finished positive electrode material, and set out to provide an efficient dry mixing process while improving the results of the mixture of conductive carbon black particles and active material. Summary of the Invention

[0006] This problem is solved by a method according to claim 1 and a system according to claim 12.

[0007] In the method for producing a dry mixture of conductive carbon black and an active material of the present invention, in the first step, the conductive carbon black is isolated and has a volume density of less than 0.1 g / cm 3 , preferably <0.08 g / cm 3 , particularly preferably 0.05 g / cm 3 , more preferably <0.03 g / cm 3 and in the second step, the conductive carbon black is mixed with the active material.

[0008] The present invention is based on the finding that the state of conductive carbon black at the time of initial contact with the active material during mixing has a significant impact on the distribution of conductive carbon black particles along the surface of the active material particles. Conductive carbon black typically has a primary particle size of 10-50 nm, and forms so-called aggregates of 100-300 nm due to van der Waals forces, which then further aggregate into micrometer-scale aggregates. Therefore, due to aggregation and agglomeration during storage and transportation, conductive carbon black typically has a volume density of about 0.1 g / cm as shipped. 3 This characteristic is believed to prevent uniform distribution of the conductive carbon black particles in the dry mix.

[0009] Thus, in the method of the present invention, the conductive carbon black is pretreated alone in the first step of the method. "Alone" in this context means that the conductive carbon black is treated in the first step without the presence of particles of active material or other substances. In particular, agglomerates are broken down in this first step. This step is also called "destructuring." The inventors have discovered that destructuring causes a volume increase in the conductive carbon black. An indicator of the success of this first step is the "volume density" of the conductive carbon black, which is measured according to DIN ISO 697 / EN ISO 60. This value is calculated as a result of the first step if the conductive carbon black has a volume density of 0.1 g / cm. 3 less than 0.08 g / cm 3 less than 0.05 g / cm 3 less than, most preferably 0.03 g / cm 3 is less than.

[0010] Preferably, the conductive carbon black is formed from primary particles with a median particle size (d50) of 10 to 50 nm.

[0011] The volume density can be easily adjusted by applying mechanical stress to the initial conductive carbon black. Preferably, the conductive carbon black is subjected to a reproducible shear or impact stress. For this purpose, a (fine) impact mill is preferably used, more preferably a blower, especially a radial blower. Preferably, the conductive carbon black is metered into the suction tube of the blower. This operation is preferably carried out gravimetrically.

[0012] The first step of the structural breakdown of conductive carbon black is when the shear rate is at least 10,000 s 1 , more preferably at least 12000s -1 , most preferably at least 15,000 s— 1 The shear stress is

[0013] For this purpose, it has been found effective to supply the conductive carbon black to a blower in a first step, preferably a radial blower, which has a stationary part and a rotating blower blade, and is configured so that a shear stress at the above shear rate is obtained in the gap between the rotating blower blade and the stationary part in the housing.

[0014] The inventors further recognized that by pre-structuring the conductive carbon black, subsequent mixing can be performed with significantly less mechanical stress on the components than when untreated conductive carbon black is added to the active material in a mixing vessel, thereby further improving the electrical conductivity of the finished anode material compared to known mixing processes.

[0015] The destructed conductive carbon black is mixed with an active material in a second downstream step. The active material preferably consists of graphite. Amorphous carbon or lithium titanate can also be considered, but their practical role is limited.

[0016] It is desirable to use pre-processed, rounded graphite particles to achieve the highest possible particle density in the anode coating, a property that cannot be achieved with angular (irregular) particles. "Rounded" means that the particle edges and corners are broken, reducing interlocking in agglomerates. Compared to angular particles, rounded particles are relatively more mobile and can be compressed into a tighter spherical packing without destructive forces. This improves the energy density of the anode material. Particularly preferred are primary graphite particles with a mean particle size (d50) of 12 to 20 μm.

[0017] The degree of roundness can best be parameterized by the BET specific surface area and tap density of the graphite particle material. Preferably, the graphite particle material has a BET specific surface area of ​​6 m according to DIN ISO 9277 before being mixed with the conductive carbon black. 2 / g~12m 2Graphite is used as the substrate, having a tap density according to DIN ISO 787-11 of more than 0.8 g / ml, preferably more than 0.85 g / ml, more preferably more than 0.9 g / ml, and even more preferably more than 0.95 g / ml.

[0018] To obtain the desired physical properties, it is preferable to mix 1 to 5% by weight of conductive carbon black with 95 to 99% by weight of graphite.

[0019] The purpose of the second step is to maintain the roundness as much as possible. It has been found to be advantageous to carry out the mixing step gently, especially in the second step, which is independent of the structural destruction of the conductive carbon black. Surprisingly, it has been found that such a mixing step does not result in significant defects in the mixing result, despite the gentle processing of the mixture.

[0020] Preferably, in the second step, the conductive carbon black and the active material are mixed at a shear rate of at least 1000 s- 1 and preferably at least 2000 s 1 Furthermore, the shear rate during mixing is preferably 5000 s−1. 1 The following is the result.

[0021] Also preferably, the mixing time under these conditions is at least 200 seconds, preferably at least 400 seconds.

[0022] In a second step, conductive carbon black is mixed with graphite to achieve a tap density of at least 0.8 g / cm according to DIN EN ISO 787-11. 3 , preferably at least 0.85 g / cm 3This preferably produces a dry mixture of 0.9 g / ml, which upon gentle mixing will approximate the tap density of the original graphite material at 0.9 g / ml. Ideally, if the tap density of the powder mixture is higher than that of the base graphite, the soot particles will fill the voids between and within the remaining rounded graphite particles, increasing the mass of the powder mixture without increasing its volume.

[0023] In the second step, conductive carbon black is mixed with graphite to achieve a BET surface area of ​​up to 7 m according to DIN ISO 9277. 2 / g, preferably up to 5.2m 2 / g of dry mixture is desirable. This value is similar to that of pure substrate graphite, and ideally should be even lower. A low specific BET surface area indicates an ideal powder morphology for the conductive carbon black, with optimal coating or wetting behavior, forming a uniform layer on the active material particles and ideally filling their pores.

[0024] The properties of the dry mix can be summarized in the following matrix: [Table 1]

[0025] In the first case, excessive shear forces during mixing can damage the active material and reduce tap density despite good wetting by near-ideal powdered carbon black.

[0026] In the second case, it is hypothesized that excessive shear forces during mixing on the one hand and insufficient destructuring of the carbon black on the other hand result in suboptimal compaction of the active material, while at the same time the carbon black is unable to optimally wet the active material.

[0027] The third case is realized by the dry mixing process of the invention: the carbon black is sufficiently broken down in the first upstream step, and then coated almost uniformly on the active material particles in the second step, preventing structural damage during mixing.

[0028] In the fourth case, it is hypothesized that even with gentle mixing, the carbon black is not sufficiently broken down, resulting in an increase in the specific surface area due to carbon black agglomerates and aggregates.

[0029] Preferably, after the first step, the broken carbon black is subjected to a separation step, where it is separated from the carrier gas supplied by the radial blower in a separator and then fed to a mixer. The broken carbon black is preferably transported to the separator by the gas flow from the radial blower. From there, the carbon black falls by gravity into the mixer. The first step can be carried out very efficiently due to the very short residence time of the carbon black in the blower. The carbon black particles are sent directly to the second step without intermediate storage and used to coat the active material, virtually eliminating the risk of reagglomeration or re-agglomeration.

[0030] The system of the present invention is for producing a dry mixture of conductive carbon black and active material for the production of anode materials for electrochemical cells, particularly battery cells, by isolating the carbon black and subjecting it to a shear or pressure load to reduce its density to less than 0.1 g / cm 3 less than 0.08 g / cm 3 less than 0.05 g / cm 3 less than 0.03 g / cm 3 and a mixer disposed downstream of the breaker for mixing the mixture supplied from the breaker.

[0031] Preferably, the destruction device is formed by a blower, more preferably a radial blower, having a stationary part and a rotating blower blade, and in a gap between the rotating blower blade and the stationary part, the destruction device is formed by a blower, more preferably a radial blower, having a rotation speed of at least 10,000 s- 1 , preferably at least 12,000 s— 1 , particularly preferably at least 15,000 s 1 is configured to generate a shear rate of

[0032] The mixing device preferably has a mixing time of at least 1000 s 1 and preferably at least 2000 s- 1 , and preferably up to 5000 s 1 For this purpose, similar to a blower, the mixing device has a structure with a stationary part and a rotating mixing tool in a housing, and is configured to generate shear stress at a specified shear rate in the gap between the rotating mixing tool and the stationary part in the housing.

[0033] The blower is connected to the mixer via a fluid line. A separator configured to separate carbon black (i.e., carbon black particles and / or agglomerates and / or agglomerates) from the carrier gas stream supplied from the radial blower is preferably disposed in the fluid flow line between the radial blower and the mixer. The separator is preferably a filter, a cyclone separator, or an electrostatic filter, or a combination thereof.

[0034] Therefore, the radial blower is preferably configured to generate a sufficient gas flow to transport the carbon black through the fluid lines and separator to the mixing device, so that the blower not only functions to disrupt the carbon black structure but also to provide a sufficient flow rate to transport the carbon black to the next processing step.

[0035] Further advantages and features of the invention are explained below with reference to the drawings. [Brief explanation of the drawings]

[0036] [Figure 1] FIG. 1 shows an embodiment of the system of the present invention. [Figure 2] FIG. 2 is a schematic diagram of the dry mixture after simple mixing. [Figure 3] Figure 3 is a schematic diagram of the dry mix after intensive mixing. [Figure 4] FIG. 4 is a schematic diagram of a dry mixture in which ideally the powdered conductive carbon black is uniformly attached to the particles of the active material. [Figure 5] FIG. 5 is a schematic diagram of an idealized dry mixture of powdered conductive carbon black and active material, in which the voids between the particles of active material are also filled with conductive carbon black. DETAILED DESCRIPTION OF THE INVENTION

[0037] The dry mix production system of the present invention (see FIG. 1) comprises a metering device (10) at the inlet side, which comprises a transport device (14) for conductive carbon black (16) and a container (12). The transport device (14) is shown here as a screw conveyor, but is not limited to such a transport system. The metering can be performed volumetrically or gravimetrically by the metering device. In the latter case, for example, a scale is provided to measure the weight of the container (12). Based on the measured mass loss, the transport speed of the transport device (14) can be adjusted.

[0038] In this way, the conductive carbon black (16) is fed into the suction channel (18) of the radial blower (20) while a carrier gas (22) (preferably air) is sucked in. In the radial blower (20), the conductive carbon black (16) is, in a first step, sucked in for at least 10,000 s -1 Preferably, the shear rate is at least 12,000 s -1 , particularly preferably at least 15,000 s -1 This is selected by setting and / or adjusting the blower speed depending on the blower geometry. By this method, the volume density of the conductive carbon black can be reduced to 0.1 g / cm. 3 less than 0.08 g / cm 3 less than 0.05 g / cm 3 less than 0.03 g / cm 3 It is possible to adjust it to less than

[0039] At the outlet side, the radial blower (20) is connected to a fluid line (24), through which the now-decomposed conductive carbon black (16) is transported by airflow in a carrier gas (22) and sent to a connected separator (26). In the illustrated example, this is a cyclone separator, but the system of the present invention is not limited to the use of a cyclone separator. In the separator (26), the destroyed conductive carbon black (16) is separated from the carrier gas (22). The carrier gas (22) flows through an exhaust pipe (28) to a filter (30) to remove any remaining conductive carbon black before being discharged into the environment.

[0040] Via fluid line (24), the conductive carbon black (16) is fed from the separator (26) to a mixer (32), which also feeds round active material (36) via another fluid line (34) or optionally the same fluid line (24) (not shown here). In the mixer (32), the conductive carbon black (16) is mixed with the active material (36) in a second step at a shear rate of at least 1000 s -1 , preferably at least 2000 s -1 The mixture is mixed for at least 200 seconds, preferably at least 400 seconds, under conditions of 0.15 to 1.05° C. The mechanical stress causes the materials to mix and the particles of conductive carbon black to partially adhere to the particles of active material, thereby forming a coating that increases the contact surface area of ​​the graphite particles.

[0041] A further portion of the conductive carbon black, especially the agglomerates that were not completely broken down in the first step, fills the voids between the active material particles, further increasing the contact surface area between adjacent active material particles, which explains the improvement in the overall particle conductivity of the dry mixture.

[0042] Figures 2-5 show four different states of the dry mixture. In each case, the active material particles (40) are idealized as cross-sections of spheres. The voids (42) between adjacent active material particles are enclosed. The role of the conductive carbon black is to improve contact between the active material particles.

[0043] Figure 2 shows an idealized case where conductive carbon black is present in the form of agglomerates (44) that surround some of the voids (42) between active material particles (40). Where the carbon black is surrounded, the agglomerates form electrical bridges, increasing the number of contact points between adjacent active material particles. The carbon black agglomerates are on the order of the same diameter as the active material particles. As a result, not all of the voids (42) contain carbon black, increasing the number of contact points between adjacent active material particles, suggesting a marginal improvement in the powder's conductivity.

[0044] Also shown in Figure 3 is an idealized schematic of the conductive carbon black present in the form of smaller agglomerates (46). These agglomerates (46) are approximately an order of magnitude smaller than the active material particles and fit into most of the voids (42) between the active material particles (40), forming electrical bridges similar to agglomerates (44). This further increases the number of contacts between adjacent active material particles, but does not significantly improve powder conductivity.

[0045] Figure 4 shows an idealized schematic diagram of conductive carbon black in the form of pure primary particles (48). These conductive carbon black particles (48) are several orders of magnitude smaller in size than the active material particles (40). The conductive carbon black particles (48) are uniformly attached to the surfaces of the active material particles (40). This does not create additional electrical bridges, but rather increases the individual contact points, contributing to improved powder conductivity.

[0046] Figure 5 shows that the conductive carbon black not only adheres uniformly to the surface of the active material particles, but also fills the voids between them. The carbon black particles (48) adhere uniformly to the surface of the active material particles (40), increasing the contact surface area. In the voids between the active material particles, additional electrical bridges are formed. [Explanation of symbols]

[0047] 10 Systems 12 containers 14 Transport equipment 16 Conductive carbon black 18 Suction duct 20 Radial Blower 22 Carrier gas 24 Fluid Piping 26 Separator 28 Exhaust line 30 filters 32 Mixing equipment 34 Second Duct 36 Active materials 40 active material particles 42 void 44 Conductive carbon black aggregates 46 Conductive carbon black aggregates 48 Conductive carbon black particles

Claims

1. A method for producing a dry mixture of conductive carbon black (16) and an active material for the production of an anode material for an electrochemical cell, in particular a battery cell, is provided, wherein in a first step, the conductive carbon black (16) is treated alone to reduce the volume density to 0.1 g / cm 3 less than 0.08 g / cm 3 less than 0.05 g / cm 3 less than, more preferably <0.03 g / cm 3 and in a second step, mixing the conductive carbon black with an active material.

2. 2. The method of claim 1, wherein the conductive carbon black (16) is formed from primary particles with a median particle size (d50) of 10 to 50 nm.

3. 3. The method of claim 1 or 2, characterized in that the active material consists of graphite (36).

4. 4. The method according to claim 1, wherein 1 to 5% by weight of conductive carbon black (16) and 95 to 99% by weight of graphite (36) are mixed.

5. In the first step, the volume density of the conductive carbon black (16) is determined by a shear rate of 10,000 s -1 , preferably at least 12000 s -1 , particularly preferably at least 15,000 s -1 The method according to any one of claims 1 to 4, characterized in that the temperature is adjusted in the range of

6. 6. The method according to claim 5, characterized in that in the first step, the conductive carbon black (16) is fed to a blower, preferably a radial blower (20), having a stationary part and a rotating blower blade, and a shear velocity is generated in the gap between the rotating blower blade and the stationary part.

7. In the second step, the conductive carbon black (16) and the active material (36) are mixed for at least 1000 s- 1 at a shear rate of preferably at least 2000 s 1 7. The method according to claim 1, wherein the method is carried out using a mixing device (32) at a shear rate of 0.1 to 1.0 MPa.

8. 8. The method according to claims 6 and 7, characterized in that after the first step, the conductive carbon black (16) is subjected to a separation step in which it is separated from the carrier gas supplied by the blower (20) and then fed to the mixer (32).

9. In the second step, the conductive carbon black (16) and the graphite (36) are mixed to produce a mixture having a tap density according to DIN EN ISO 787-11 of at least 0.8 g / cm 3 , preferably at least 0.85 g / cm 3 9. The method according to claim 1, wherein a mixture of

10. In the second step, the conductive carbon black (16) and the graphite (36) are mixed to form a conductive carbon black having a BET specific surface area of ​​7 m 2 / g or less, preferably 5.2m 2 10. The method according to claim 1, wherein a mixture of 0.1 to 0.5 wt % or less is produced.

11. In the second step, the conductive carbon black (16) and the graphite (36) are mixed together to provide a powder conductivity of at least 3.5×10 -2 S / cm, preferably at least 3.7×10 -2 11. The method according to claim 1, wherein a mixture is obtained in which the viscosity is 0.5 S / cm.

12. A system (10) for producing a dry mixture of conductive carbon black (16) and an active material for the production of anode materials for electrochemical cells, particularly battery cells, comprising: The conductive carbon black (16) is subjected to a shear force or pressure load alone to reduce its volume density to 0.1 g / cm 3 less than 0.08 g / cm 3 less than 0.05 g / cm 3 less than 0.03 g / cm 3 a disruptive device for adjusting the a mixer (32) disposed downstream of the breaker and configured to mix the conductive carbon black (16) with the active material; A system comprising:

13. The destruction device is a blower, preferably a radial blower (20), having a stationary part and a rotating blower blade, and a gap between the rotating blower blade and the stationary part that is at least 10,000 s -1 , preferably at least 12000 s -1 , particularly preferably at least 15,000 s -1 13. The system of claim 12, configured to generate a shear rate of

14. The mixing device (32) is -1 , preferably at least 2000 s -1 14. The system of claim 12 or 13, configured to generate a shear rate of

15. 15. The system according to claims 13 and 14, characterized in that a separator (26), preferably a filter, cyclone separator or total separator, is integrated in the fluid flow path between the blower and the mixer (32), and is configured to separate the conductive carbon black (16) from the carrier gas (22) supplied by the blower.

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