Use of conductive proteins as conductive additives in electrode pastes

Abstract

The invention relates to the use of an electrically conductive protein as a conductive additive in an electrode paste (10), wherein pili (22) of bacteria (32) are used as the protein.

Description

Technical Field

[0001] The invention relates to the use of an electrically conductive protein as a conductive additive in an electrode paste and to three methods for producing such an electrode paste. Background Art

[0002] Motor vehicles that are driven or can be driven electrically or electrically, such as electric vehicles, hybrid vehicles, plug-in vehicles or fuel cell vehicles, usually include an electric motor, by which one or two axles can be driven. To provide electrical energy, the electric motor is usually connected to a (high-voltage) battery inside the vehicle as an electrical energy storage device.

[0003] In particular, electrochemical cells are understood here and below to mean so-called secondary batteries of motor vehicles. In such (secondary) vehicle batteries, the consumed chemical energy can be restored by means of a charging process. Such vehicle batteries are designed, for example, as electrochemical accumulators, in particular as lithium-ion accumulators.

[0004] In order to generate or provide a sufficiently high operating voltage, such vehicle batteries usually have at least one battery module (battery cell module) in which a plurality of individual battery cells are connected in a modular manner. Alternatively, a so-called Cell2Pack design (module-free design) is possible, in which the battery cells are directly connected together, in particular in parallel, as a vehicle battery and are not previously combined into modules.

[0005] The battery of the type described has a cathode and an anode as well as a separator and an electrolyte on the battery cell plane. The electrodes, i.e. the anode and the cathode, are made of corresponding (electrode) active materials. The active material is a prerequisite for high-power batteries. In order to improve the electrical properties, conductive particles are usually added to the active material as a conductive additive or conductive agent. Carbon-based conductive particles, such as conductive soot (Leitruβ) or conductive graphite, are important components of lithium-ion batteries due to their high electrical conductivity (or conductivity). They assist in the transfer of electrons to or from the active material and thus reduce the electrode resistance, i.e. the internal resistance of the battery.

[0006] Extrusion methods can be used for the production of batteries, in which the electrodes of a battery cell are produced from a plastic material that is pressed (extruded) out of a nozzle element. By integrating a continuous extrusion process into the production of lithium-ion battery cells, the process time and the energy requirement in the production of the battery can be significantly reduced due to the higher efficiency of the mixing process. The electrodes of the battery or battery cell are produced here by means of an extruded electrode paste, the quality of the paste being determined by special standards or product parameters, for example by the particle size of the conductive particles. The electrode paste is then applied, for example, to a corresponding current arrester, in particular a copper or aluminum film.

[0007] For conductive additives for electrode pastes, the following properties are especially desirable:

[0008] - a high electrical conductivity, for example similar to that of carbon nanotubes. The conductive additive preferably has a specific resistance of 1 Ohm cm or less;

[0009] - Smaller particle size of about 10 nm and larger (particle) length of about 1 μm to achieve a larger range of conductivity;

[0010] -Easily dispersed in active materials without excessive shear stress (mixing speed);

[0011] - can be developed economically and easily in large quantities;

[0012] - not harmful to health, i.e. not toxic;

[0013] - High Oil Absorption Number (OAN) to ensure the highest possible electrolyte absorption;

[0014] Even a relatively small proportion should be sufficient to achieve a relatively high electrical conductivity in the electrode paste material, thereby ensuring a relatively high energy density.

[0015] - the smallest possible proportion of metallic impurities;

[0016] - Lower moisture and gas absorption, and lower binder and solvent consumption. In addition, to achieve simple coatings the coating should have a higher solids content at a lower viscosity; and

[0017] -Good antioxidant properties.

[0018] It is difficult to achieve the previously required properties in a single product. Therefore, the current industrial solution is to use a combination of conductive soot, compressible porous graphite, carbon nanotubes and graphene. However, conductive additives made of carbon, especially conductive soot (such as carbon black), have multiple problems when used in electrode pastes.

[0019] One problem with conductive carbon is the high specific resistance of about 0.25 Ohm cm (ohm-centimeter), which leads to a high internal resistance and voltage drop within the battery cell. The electrode resistance can be expressed in Ohm / cm, for example. 2 It is measured in Ohms per square centimeter and is usually around 70 Ohm / cm depending on the carbon content. 2 Up to 250Ohm / cm 2 Therefore, the specific resistance is much higher than that of metals. However, since metals cannot be used as conductive agents, the only option available is to use non-metals such as carbon as conductive agents.

[0020] Conductive additives should have as small a surface as possible in order to improve the electrical conductivity. On the other hand, the surface influences the rheological curve. Therefore, an additional problem of conductive additives is the increase in the surface of the electrode paste material, thereby increasing the viscosity of the electrode paste. The extrusion process is thus adversely affected. This problem usually occurs in conductive soot with a relatively small particle size, which is used, for example, in electrode pastes for high-energy batteries.

[0021] Another problem with conductive carbon is that it exists in the form of agglomerates or aggregates, which each have a large surface area. The specific surface area (BET surface area) of an agglomerate is, for example, 63 m 2 / g (square meter per gram) and can be increased to 130m as the particle size decreases. 2 / g. With increasing surface area, the oxidation rate disadvantageously increases. However, higher aggregate lengths are desirable so that the connection does not disappear during (thermal) expansion of the battery cell or the battery electrode.

[0022] Conductive soot also has the problem that the greater surface area creates the risk of absorbing vapors and / or gases, which in turn affects the application-related properties of the electrode paste. It is therefore recommended that conductive soot is always stored without potential sources of dirt or contamination. In this case, the storage temperature should not exceed 50° C. (degrees Celsius). Conductive soot should therefore be stored under cold and dry conditions, which disadvantageously increases the storage costs.

[0023] Another problem with carbon blacks with a higher BET surface area is the higher binder solution requirement. The larger the surface area of ​​the conductive carbon black, the more binder and solvent are needed. This reduces the energy density of the electrode paste or battery electrode.

[0024] An additional problem with conductive soot is the presence of metal impurities, especially iron, which should be minimized. Metal impurities in conductive additives or electrode pastes are particularly important for the safety of use in battery electrodes due to the risk of oxidation and the risk of electrical short circuits. There are different sources for carbon soot. Boiler soot (combustion soot) has a higher proportion of metal impurities than acetylene soot. Acetylene soot usually has an iron proportion of less than 5 ppm (parts per million) and other heavy metal proportions. Disadvantageously, the cost of acetylene-based conductive carbon without impurities is particularly high.

[0025] Additional problems arise due to the small aspect ratio (length to diameter) of the conductive soot aggregates. The distance between the conductive particles is typically about 40 nm (nanometers). If after a number of cycles, the average distance between the active materials increases by an amount greater than the length of the conductive particles, the conductivity is disrupted. This reduces the service life of the battery.

[0026] In order to solve the above problems, the proportion of conductive soot is increased to improve the conductivity. The soot content can usually vary between 1% and 4%, wherein the increase in soot content improves the conductivity. However, the increase in soot content also increases the demand for binders and solvents and reduces the energy density.

[0027] Smaller carbon particle sizes require high compression during the calendering process during electrode manufacturing to establish a connection from the conductive additive to the active material. High compression in turn reduces the porosity required for electrical diffusion. In order to compensate for this loss of porosity, other solutions, for example, porous, highly compressible (compressible) graphite (Porocarb) is added to the anode and cathode in the same proportion as conductive soot. Here, graphite achieves an electrode with a higher density and sufficient porosity for electrolyte diffusion. The combination of compressible graphite and conductive carbon improves the conductivity of the electrode paste through additional electrical connection to the active material. Compressible graphite is usually added to the active material of the cathode. Disadvantageously, the addition of graphite increases costs and reduces energy density.

[0028] Other solutions are conductive soot made from acetylene with tightly controlled metal impurities (Fe, Co, Ni, Mn, Cr and Cu), sulfur impurities and ash content. Tightly controlled impurities and acetylene as a soot source are cheaper than burning carbon (which has more impurities).

[0029] An additional solution is to improve the dispersibility of the conductive particles. For this purpose, dry mixing (English: dry mixing, or dry mixing) or wet mixing (English: wet mixing, or wet mixing) is carried out, for example, at different rotation speeds (shear load) in batch mixing or extrusion. The dispersibility of carbon soot depends on the particle size and surface area. Smaller particles require less dispersibility. In this case, good dispersibility corresponds to a uniform conductivity of the electrode paste.

[0030] Another solution is, for example, to replace semi-crystalline carbon with conductive soot having a higher degree of crystallinity and better uniformity of particle size. This results in improved conductivity and more connection points to the active material. In addition, there are fewer hot spots in the battery electrodes, which increases the service life. The disadvantage is that crystalline conductive carbon is relatively expensive.

[0031] Instead of conductive soot there are other conductive additives which can be used to achieve better conductivity.

[0032] An alternative is, for example, the use of linear or filamentary carbon structures, such as carbon nanotubes (CNT) or carbon fibers (CF), which are usually used as conductive additives in combination with conductive soot.

[0033] As an alternative or supplement to the conductive soot, for example, carbon nanotubes are used. Carbon nanotubes can be single-walled or multi-walled, wherein multi-walled carbon nanotubes have a higher conductivity. The advantage of carbon nanotubes is that the tube has a relatively small diameter of about 10 nm and a relatively large (axial) length of about 1.5 μm (micrometer). Due to the long length, the connection between the active materials is maintained even when the distance between the materials increases during the expansion of the single cell. Therefore, carbon nanotubes achieve conductivity over a large area or over a large length, so the conductivity is also called line-to-point conductivity.

[0034] Carbon nanotubes have a high electrical conductivity, which is more than twice that of conductive soot. The specific resistance of carbon nanotubes is 5 to 10 Ohm cm. Therefore, only 1% of carbon nanotubes is required to achieve the same conductivity as that achieved by 3 to 4% of conductive soot.

[0035] Other alternatives are, for example, the use of graphene (conductive graphene, conductive graphite) as a conductive additive. Graphene has a flaky conductive structure and provides a higher conductivity than bare carbon and carbon nanotubes. Due to the flaky conductive structure, the conductivity is also referred to as face-to-face conductivity. Graphene is mainly used in combination with carbon nanotubes and conductive soot to achieve greater conductivity. Graphene is mainly used as an additive for conductive soot and compressible graphite. Here, the addition of graphene helps to reduce the soot content and therefore improve the energy density of the electrode paste or electrode.

[0036] Both graphene and carbon nanotubes have high electronic conductivity, but these conductive additives have relatively high costs. In addition, there are problems with uniform or consistent dispersion within the electrode paste material. In addition, graphene and carbon nanotubes have lower OAN values ​​(Oil Absorption Number) than conductive soot, which results in lower electrolyte absorption and thus increased charging resistance (lithium ions). Summary of the invention

[0037] The technical problem to be solved by the present invention is to provide a new conductive additive having the desired properties mentioned above. In particular, a particularly suitable use of conductive proteins as conductive additives in electrode pastes should be provided. The technical problem to be solved by the present invention is also to provide a method for producing an electrode paste having such a conductive additive. The technical problem to be solved by the present invention is also to provide a particularly suitable battery cell.

[0038] According to the invention, the technical problem is solved in terms of use by the use of an electrically conductive protein as a conductive additive in an electrode paste, and in terms of a method by a method for producing an electrode paste, and in terms of a battery cell by a battery cell. The advantages and configurations described with respect to the use can also be transferred to the method and / or the battery cell and vice versa.

[0039] According to the invention, electrically conductive proteins are used as conductive additives in the electrode paste, wherein in particular bacterial pili, preferably gram-negative anaerobic bacteria, are used as proteins. This results in a conductive additive that is particularly suitable for the electrode paste. The (bacterial) pili can be used as the sole conductive additive or in combination with conductive soot to achieve a metal-like conductivity of the electrode paste.

[0040] Electrode paste is understood here and below to mean in particular a suspension or slurry (English: slurry) consisting of active material (of the electrode) and binder (binder) as well as conductive additives.

[0041] Fimbrien (Pilus, plural: Pili, also known as Fimbrien) is a thread-like, protein-containing appendage that is located outside the bacterial cell as a cell protrusion.

[0042] Electrode pastes are used, for example, to produce capacitors, fuel cells or conductive adhesives or elastomers. Electrode pastes are preferably provided for producing battery electrodes for battery cells, in particular lithium-ion battery cells. The electrode paste is extruded onto the arrester in an extrusion process, in particular as an extrudate, by means of an extruder.

[0043] The present invention is based on the recognition that electrically conductive proteins can be used alone or in combination with conductive soot to achieve better conductivity than the combination of conductive soot and carbon nanotubes. The amino acids contained in proteins have good electrical conductivity.

[0044] The manufacturing cost of synthetic proteins is relatively high, but there are a large number of microorganisms with conductive proteins in nature. Generally, Gram-negative bacteria have conductive proteins in the form of pili. The pili are composed of very conductive proteins (aromatic amino acids) and have a specific resistance of about 1 Ohm cm. Bacteria such as Pseudomonas aeruginosa, Shewanella oneidensis, Geobacter sulfurreducens, etc. have suitable pili. The pili have, for example, a diameter of about 12 to 16 nm and a length of about 800 nm, so that the pili are effectively formed like nanotubes or nanowires. The long-range conductivity of electrons is better than that of carbon nanotubes.

[0045] Furthermore, the maximum roughness of the pili was 5 nm. Here, the rough surface provides more space for the attachment of other pili or nanofibers and the formation of interconnected bacterial nanotubes or bacterial nanofibers of greater length. The roughness of the nanowires is important because it plays a role in the effective surface bonding with other materials.

[0046] Natural electrically conductive proteins in the form of bacterial pili can be produced in large quantities at room temperature in bioreactors from inexpensive, renewable raw materials with significantly lower energy consumption. In this case, in particular, the end product contains no toxic or health-damaging components.

[0047] The pili not only transfer electrons to the electrode and the active material, but also store electrons on their surface. This means that the pili can be used as a local capacitor in the electrode. These electrons can be released when a higher rate (C-Rate) of the battery is required, for example.

[0048] According to the invention, the conductivity of the electrode is thus improved by using Gram-negative anaerobic bacteria and the conductivity of their pili. According to the invention, the pili of the bacteria are therefore used as a conductive agent or conductive additive. The pili of the bacteria can produce a higher conductivity in the electrode paste material. The pili can be used as a separate additive. The pili are preferably used in combination with conductive soot, wherein the conductive soot additionally assists the lithium ion transport.

[0049] By using pili as conductive additive, the conductivity of the electrode produced by means of the electrode paste is increased. This means that the electrode has a lower voltage drop. In addition, the pili can be produced easily and at low cost by means of a cultured bacterial culture. The pili therefore have lower production costs than graphene or carbon nanotubes, thereby achieving a particularly cost-effective electrode paste. In addition, a uniform dispersion of the conductive bacteria or pili can be achieved during dry mixing or direct cultivation in graphite. In addition, bacterial pili do not have any metallic impurities.

[0050] Particularly high electrode energy densities can be achieved by using bacterial pili, since the proportion of soot and binders is reduced. In addition, higher capacitive discharge rates (C-rates) can be achieved through the capacitor effect of the pili for holding the electrons. Since pili adhere to other pili due to their surface roughness, long-distance electrocoating is also possible.

[0051] In order to separate or separate the pili from the rest of the bacterial cell, a simple and cost-effective mechanical separation method can be used. Alternatively, bacteria with pili can also be used as conductive nanotubes, so there is no need to separate the pili from the rest of the bacteria. Bacteria used as conductive nanotubes are harmless to health. After the drying process in the coating device, the bacteria in the solid slurry or solid electrode paste are already dead. Here, the electrode can additionally perform a cleaning process by ultraviolet radiation or plasma to prevent bacterial growth in the electrode. Unlike biological or microbial electrodes, according to the present invention, the bacteria in the finished product are dead or biologically inactive. Even after cell death, bacteria with pili can conduct electricity.

[0052] The processes for processing or treating the electrode paste, such as dry mixing, wet mixing, degassing, wet coating of a substrate and final drying, are the same for the electrode paste according to the invention as for conventional electrode production.

[0053] Different processes are conceivable for using bacterial pili as conductive additives in electrode pastes. Three methods according to the invention for producing such electrode pastes are described in more detail below, wherein conductive pili are mixed with the active material of the cathode and / or anode to achieve a higher conductivity.

[0054] The cultivation of bacteria requires good control of temperature, pH, hypoxia and nutrition. The cultivation of bacteria is preferably achieved under a nitrogen atmosphere.

[0055] In the first method, the pili are separated by mechanical separation and then introduced into the active material. In the second and third methods, the bacteria are cultivated and grown, for example, in graphite (active material of the electrode). The pili are better conductors than the rest of the bacterial cell, but their mechanical stability is increased by the connection to the battery cell. The combination of pili and bacterial cells allows for longer lengths of conductive tubes, which exceed the length of carbon nanotubes.

[0056] For example, glucose and nitrates are added to graphite to accelerate the growth of bacteria. Here, the alcohol produced during the growth of the bacteria is preferably evaporated.

[0057] For the second and third methods, additional processes such as UV radiation or cold plasma cleaning are necessary when using the electrode paste in order to completely kill the bacteria after the electrode paste has dried.

[0058] Three production methods according to the invention are explained in more detail below.

[0059] In the first method for producing electrode paste, a bacterial culture is first cultivated from bacteria with conductive or conducting pili. In this case, the bacteria are cultivated in an incubator, for example. Next, the bacteria are placed in a saline solution (salt solution) and subjected to a vibration and centrifugation process. In the saline solution, the pili are mechanically, preferably by vibration, separated from the bacterial cells. In the subsequent centrifugation process, the separated pili with a weight less than the cell body of the bacteria are collected in the center and filtered out. Short or broken pili are also separated during the filtration process. Finally, the pili are washed or cleaned with distilled water. Here, the pili have a diameter of about 15nm and a length of about 400nm to 800nm. The length of the pili depends on the mechanical separation method, wherein the maximum possible length of the pili is desired for long-distance conductivity.

[0060] The pili are then mixed with conductive soot, in particular with conductive carbon aggregates. Conductive pili are used in combination with conductive soot to achieve point-to-point and line-to-point conductivity of the electrode paste. Preferably, about 0.5% of the total weight of the solids in the electrode paste or slurry is added as pili. In other words, the electrode paste has 0.5% by weight (weight percentage) of conductive pili. Pili are a better substitute for carbon nanotubes here because they have significantly better conductivity. Here, the proportion of conductive carbon or conductive soot is, for example, between 2% by weight and 3% by weight. The mixture formed by pili and conductive soot is then mixed with an active material (cathode or anode material) and a binder to form an electrode paste or electrode paste material.

[0061] The binder is, for example, polyvinylidene fluoride PVDF for the cathode and styrene butadiene rubber SBR for the anode. The solvent is, for example, water (for the anode) or N-methyl-2-pyrrolidone (NMP) for the cathode. The active material is, for example, graphite for the anode or a metal oxide for the cathode, in particular lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (LNMC, NMC), lithium iron phosphate (LFP), lithium nickel cobalt aluminum oxide (NCA), etc.

[0062] In order to distribute the conductive soot and pili evenly, the conductive soot and pili are first dry mixed, wherein the roughness of the pili surface is increased so that the conductive soot adheres better to the pili. The dry mixing ensures that the carbon adheres evenly to the pili. Afterwards, adhesives and solvents can be added to wet mix the conductive additive with the active material. The wet slurry or electrode paste is then applied or extruded onto a film-like substrate (aluminum for the cathode and copper for the anode) during the electrode manufacturing process. Finally, the (electrode paste) coating is dried to remove the solvent. The pili have a relatively low tensile strength, so this electrode paste is loaded with as little shear stress as possible in the extrusion mixing process.

[0063] The pili can also be added to the carbon nanotube and conductive soot solution to further increase the electronic conductivity and hold the electrons on the pili surface like in a capacitor. Thus, the pili increase the capacity and energy density of the battery electrode.

[0064] According to the invention, the advantages and embodiments described with respect to the first method can also be transferred to the second method and vice versa.

[0065] In the second method for producing electrode paste, a bacterial culture is grown in a graphite material by bacteria having pili capable of conducting electricity, so that the bacteria cover the graphite material. The graphite material covered with bacteria is mixed with a binder and a solvent to form a suspension. An active material is added to the suspension and mixed to form an electrode paste or an electrode paste material.

[0066] To grow in nature or in the laboratory, bacteria require a source of energy, carbon and other required nutrients, as well as a range of permissive physical conditions, such as oxygen concentration, temperature and pH.

[0067] Bacteria are classified into organisms or groups based on their growth patterns under different chemical (nutritional) or physical conditions. For example, phototrophic bacteria are organisms that use light as an energy source, anaerobes are organisms that grow in the absence of oxygen, and thermophiles are organisms that grow at high temperatures. Bacteria that can conduct electricity or have pili that can conduct electricity are mainly anaerobes.

[0068] The carbon requirement of the organisms is met by organic carbon (a compound with carbon-hydrogen bonds). Here, the addition of glucose helps to accelerate the growth of the bacterial colony exponentially. Sometimes nitrates can also be added as a nitrogen source. In the second method, heterotrophic anaerobes are preferably cultivated in graphite, wherein only less carbon-hydrogen bonds (e.g. glucose) and, if necessary, nitrates are added.

[0069] The graphite used in the cathode is in particular a compressible or compressible porous graphite (porocarb). The graphite content here is about 2% of the total mass of the cathode. This means that the graphite content in the cathode electrode paste is about 2% by weight. Due to the high porosity of the graphite, bacterial cultures can also grow in the pores. In the anode, in addition to the 2% by weight, this porous graphite can also be used. Since the anode is made of more than 90% graphite, the same graphite can also be used for bacterial growth.

[0070] It is advantageous to maintain an anaerobic atmosphere during bacterial cultivation. This is maintained by carrying out bacterial cultivation in a tank where the nitrogen pressure is maintained slightly above atmospheric pressure. For example, the nitrogen pressure is 15 mbar (millibar) to 20 mbar higher than atmospheric pressure, so that air is not sucked into the tank. The nitrogen pressure prevents oxygen and air from entering the cultivation solution. Bacterial cultivation normally takes about 16 to 18 hours to complete. Byproducts such as alcohols produced during cell growth are removed by means of a drying process before further processing.

[0071] The bacteria evenly cover the graphite and improve conductivity without dispersion problems. Therefore, no complicated dry mixing is required for uniform dispersion.

[0072] Once the bacterial culture is grown in the graphite, a binder and solvent are added, followed by the same mixing and coating process as in conventional battery manufacturing.

[0073] Unlike the pili in the first method, the bacteria in the second method are present in a slurry or electrode paste. The electrode paste is usually extruded and then dried. After the slurry is dried at, for example, 100° C. to remove the solvent, the bacteria die. Additional UV radiation can also be used to kill the bacteria after the coating process. It is important to note that even biologically dead bacteria can conduct electricity, so dead bacteria can remain in the active material. The dead bacteria form long chains in the form of conductive nanotubes with their pili.

[0074] In a third method according to the invention for producing an electrode paste, a bacterial culture of bacteria having electrically conductive pili is mixed with the electrode paste material. This means that the bacterial culture is mixed into a slurry or suspension consisting of an active material and a binder as well as a solvent and, if necessary, other conductive additives such as conductive soot. The bacterial culture is then incubated in the electrode paste material, wherein the bacterial culture and the electrode paste material are moved during the incubation period by means of a rotating spindle. Here, the statements relating to the first and / or second method also apply according to the invention to the third method and vice versa.

[0075] Here, in a third variant of the method, the bacterial culture is added directly to the slurry solution. Here, the bacteria require carbon nutrients in the slurry. The carbon nutrients are, for example, in the form of graphite, which is present in the anode or in the active material of the anode. In the cathode, about 2% by weight of porous graphite is added as bacterial nutrients. Additional glucose and possible nitrates can help to further accelerate bacterial growth. In order to accelerate the cultivation, the suspension consisting of bacteria and electrode paste material is kept at about 37° C. for, for example, 18 hours. The slurry is constantly stirred by a rotating spindle to avoid precipitation. Since it is an anaerobic bacterium, a nitrogen pressure slightly above atmospheric pressure is maintained in the mixing container.

[0076] For example, the bacterial culture forms within two days and is evenly distributed on the added graphite. In this way, a uniform distribution of the conductive bacteria can be achieved without a great deal of mixing effort. During the growth of the bacterial culture and during the mixing process of the active material, gases are generated, which are preferably removed by a degassing device.

[0077] The finished slurry or electrode paste still contains active bacteria. Once the electrode paste is applied to the substrate during further processing, it passes through different drying zones. The solvent evaporates during the drying at about 100° C. Here, the heat also kills the bacteria. After the last drying zone, the coating is cleaned, for example, by UV radiation or cold plasma. These two processes can also kill all active bacteria. Although the bacteria in the finished battery electrodes are dead cells, they are still conductive. Here, the bacteria achieve point-to-point conductivity over long distances, as in carbon nanotubes.

[0078] Bacteria can be added in combination with conductive soot as a conductive additive. Under normal circumstances, 0.5% by weight of bacteria and 2% by weight of conductive carbon are sufficient to achieve better conductivity than the combination of carbon nanotubes and conductive soot.

[0079] The battery cell according to the invention is designed in particular as a lithium-ion battery. The battery cell is preferably provided and suitable and arranged for a vehicle battery, in particular for an electrically driven or electrically driven motor vehicle, such as a traction battery of an electric or hybrid vehicle. Here, the battery cell has a battery electrode, which is made of an electrode paste produced according to the method. This means that the electrode material of the battery electrode has bacteria and / or pili as a conductive additive. This achieves a particularly suitable battery cell with particularly high conductivity and energy density. Here, the advantages and configurations described with respect to the use and / or the method can also be transferred to the battery cell according to the invention and vice versa. BRIEF DESCRIPTION OF THE DRAWINGS

[0080] Embodiments of the present invention are described in more detail below with reference to the accompanying drawings. In the accompanying drawings, in a schematic and simplified view:

[0081] Figure 1 A method for manufacturing a battery electrode for a battery cell is shown;

[0082] Figure 2 An electrode paste material with active material and conductive soot and bacterial pili is shown;

[0083] Figure 3 The separation process used to separate the pili from the bacterial body is shown;

[0084] Figure 4 A first method for making an electrode paste is shown;

[0085] Figure 5 A second method for making an electrode paste is shown; and

[0086] Figure 6 A third method for making an electrode paste is shown.

[0087] In all the figures, corresponding parts and dimensions are always provided with the same reference symbols. DETAILED DESCRIPTION

[0088] exist Figure 1 1 shows a schematic diagram of a method for producing a battery electrode 2 for a battery cell of a vehicle battery (not shown in detail). In this case, the battery cell is in particular a lithium-ion battery cell.

[0089] The production takes place essentially in three method steps 4 , 6 , 8 . In a first method step 4 , a slurry is produced as electrode paste 10 .

[0090] In a second method step 6 , the film-shaped current arrester 12 is coated with the electrode paste 10 , dried, calendered and formed into an electrode coil 14 . In a third method step 10 , the electrode coil 14 is singulated into battery electrodes 2 .

[0091] The electrode paste 10 is applied as a coating on the current arrester 12 in method step 6, for example, by an extrusion method in a coating or extrusion step 15. The current arrester 12 is, for example, a copper film or an aluminum film. After coating, the electrode paste 10 is dried in a drying step 16, for example, in order to remove solvents from the electrode paste 10. The coated electrode paste or electrode layer is calendered or rolled in a calendering step 18, so that an electrical connection is produced between the active material 24 and the conductive additives 20, 22 compressed in the electrode layer. Thus, a strip-shaped or band-shaped electrode strip material or electrode substrate is produced, which is produced as a continuous material or coil in the form of an electrode roll 14 and is further processed in method step 8.

[0092] The singulation in method step 8 is carried out by a separating device 16 which is designed, for example, as a dicing blade or a separating blade or as a laser.

[0093] exist Figure 2 Schematically, an electrode paste 10 or an electrode layer of a battery electrode 2 is shown in detail in FIG.

[0094] exist Figure 2 The electrode paste 10 shown in FIG. 1 has, for example, LCO, in particular LiCoO2, as an active material 24, wherein conductive soot 20 (carbon black) and (bacterial) pili 22 are added as conductive additives. The conductive soot 20 is present in the form of aggregates or agglomerates, wherein thread-like or fibrous pili 22 extend between the active material 24 and the conductive soot 20 in the form of a fabric or a felt.

[0095] The pili 22 are made of a very conductive protein (aromatic amino acids) and have a specific resistance of about 1 Ohm cm. The pili 22 have, for example, a diameter of about 12 to 16 nm and a length of about 800 nm.

[0096] The conductive bacterial pili 22 are used in combination with the conductive soot 20 to achieve point-to-point and line-to-point conductivity in the electrode paste 10. The conductive additives 20, 22 assist the electron transport and thus improve the conductivity of the electrode paste 10. Figure 228a, 28b, 28c. Arrow 28a represents electron transport from active material 24 to pili 22. Arrow 28b represents electron transport along pili 22, wherein arrow 28c represents electron transport along conductive soot aggregates. Even if conductive soot 20 does not form contact, electron transport between active materials 24 may be achieved through pili 22.

[0097] In order to use bacterial pili 22 as a conductive additive in electrode paste 10, different processes can be considered. Figures 3 to 6 Three methods according to the invention for producing such an electrode paste 10 are explained in more detail.

[0098] The following is based on Figure 2 and Figure 3 A first method for producing an electrode paste 10 is explained in more detail. In a method step not shown in detail, a bacterial culture 30 is first grown from bacteria 32 having electrically conductive or conductive pili 22. The bacteria 32 are in particular gram-negative anaerobic bacteria, such as Pseudomonas aeruginosa, Shewanella oneida or Geobacter sulfurreducens. For example, the bacteria 32 or the bacterial culture 30 are grown in an incubator. The bacteria 32 and pili 22 are only provided with reference numerals in the figures as examples.

[0099] Next, the bacteria 32 are placed in a saline solution 34 (salt solution) and subjected to a vibration and centrifugation process 36. In the saline solution 34, the pili 22 are mechanically separated from the bacteria 32. In the subsequent centrifugation process, the separated pili 22 with a weight less than the cell body of the bacteria 32 are collected in the center and filtered out. Short or broken pili 22 are also separated during the filtration process. Finally, the pili 22 are washed or cleaned with distilled water. Here, the pili 22 have a diameter of about 15 nm and a length of about 400 nm to 800 nm. The length of the pili depends on the mechanical separation method, wherein the largest possible length of the pili 22 is desired for long-range conductivity.

[0100] The pili 22 are then mixed with the conductive soot 20 and, for example, compressible graphite 38. Preferably, about 0.5% by weight of electrically conductive pili 22 and between 2% and 3% by weight of conductive soot 20 and about 2% by weight of graphite are used. In order to distribute the conductive soot 20 and pili 22 and graphite 38 uniformly, a dry mixing process 40 is carried out, in which the roughness of the pili surface is increased so that the conductive soot adheres better to the pili. The dry mixing ensures that the carbon adheres uniformly to the pili.

[0101] The resulting mixture 42 is then mixed with a slurry or suspension consisting of active material 24 and binder 46 and solvent 48 in a wet mixing process 44 to form an electrode paste 10 or electrode paste material. Here, constant rotation during the wet mixing process 44 prevents sedimentation and ensures a uniform distribution of pili 22, conductive soot 20 and graphite 38 in the active material 24. During electrode manufacturing, the resulting electrode paste 10 is applied or extruded onto a substrate film of the current arrester 12. The (electrode paste) coating is then dried to remove the solvent 48.

[0102] Binder 46 is, for example, polyvinylidene fluoride PVDF for cathode and styrene butadiene rubber SBR for anode. Solvent 48 is, for example, water (for anode) or N-methyl-2-pyrrolidone (NMP) for cathode. Active material 24 is, for example, graphite for anode or metal oxide for cathode, in particular lithium cobalt oxide (LCO), lithium nickel manganese cobalt oxide (LNMC, NMC), lithium iron phosphate (LFP), lithium nickel cobalt aluminum oxide (NCA), etc.

[0103] Here, the wet mixing process 44 is preferably carried out in a nitrogen atmosphere having a nitrogen pressure maintained above atmospheric pressure. For this purpose, nitrogen 50 is introduced into the mixing tank. When the electrode paste 10 is mixed, gas is generated, and the gas is preferably removed by a degassing mechanism 52.

[0104] exist Figure 5 In the second method shown for producing the electrode paste 10, a bacterial culture 30 of bacteria 32 with electrically conductive pili 22 is grown through porous graphite 38, so that the bacteria 32 cover the graphite material. Thus, the carbon requirement of the bacteria 32 is met, for example, by adding glucose 54, wherein nitrates 56 can additionally assist bacterial growth as a nitrogen source.

[0105] In the second method, heterotrophic anaerobic bacteria are therefore preferably cultivated in graphite 38, wherein only a small amount of carbon-hydrogen bonds (e.g. glucose 54) and, if necessary, nitrates 56 are added. Here, the bacterial cultivation is carried out in a dry mixing process 58 to prevent precipitation. For the bacterial cultivation, an anaerobic atmosphere is maintained by keeping the nitrogen pressure slightly above atmospheric pressure. The nitrogen pressure prevents oxygen and air from entering the cultivation solution. Bacterial growth is carried out, for example, at a temperature of 37° C., wherein the dry mixing process 58 lasts, for example, one to two days, depending on the type of bacteria and the amount of graphite, glucose and nitrates.

[0106] The resulting graphite 38 coated with bacteria 32 is dried, for example, at 50° C., to remove byproducts produced during cell growth, such as alcohols, prior to further processing.

[0107] The bacteria-covered graphite 38 is mixed with the binder 46 and the solvent 48 in a wet mixing process 60 to form a suspension 62. In this case, the suspension 62 has a dispersion of the bacteria-covered graphite 38 in the binder 46 that is as homogeneous as possible.

[0108] The suspension 62 is introduced into a second wet mixing process 64 and mixed with the active material 24 dissolved in the solvent 48 to form the electrode paste 10. The wet mixing is performed until the binder 46 and the solvent 48 are uniformly dispersed with the active material 24 and the desired viscosity of the electrode paste 10 is achieved. The mixing is preferably performed in a nitrogen atmosphere, wherein the gas generated during the mixing is removed by the degassing mechanism 52.

[0109] exist Figure 6 In the third method for producing the electrode paste 10 shown, a bacterial culture 30 of bacteria 32 having electrically conductive pili 22 is mixed with the electrode paste material. This means that the bacterial culture 30 is mixed in a wet mixing process 64 into a slurry or suspension consisting of active material 24 and binder 46 as well as solvent 48 and optionally other conductive additives, such as conductive soot 20. The bacterial culture 30 is then incubated in the electrode paste material, wherein the bacterial culture 30 and the electrode paste material are moved during the incubation by means of a rotating spindle 66. This means that the bacteria 32 are incubated during the wet mixing process 64.

[0110] Therefore, in a third variant of the method, the bacterial culture 30 is added directly to the slurry solution of the electrode paste 10. Here, the bacteria 32 require carbon nutrients in the slurry. The carbon nutrients are, for example, in the form of graphite, which is present in the active material of the anode. In the cathode, about 2% by weight of porous graphite is added as bacterial nutrients. Additional glucose 54 and possible nitrates 56 can help to further accelerate the growth of bacteria 30. In order to accelerate the cultivation, the slurry is kept at about 37° C. for example for 18 hours and is constantly stirred by a rotating spindle 66 to avoid precipitation. Due to the anaerobic bacteria 32, a nitrogen pressure slightly above atmospheric pressure is maintained in the mixing container.

[0111] Prior to the extrusion step 15, the electrode paste 10 is preferably dried at about 50°C in order to remove by-products such as alcohol.

[0112] Unlike the pili 22 in the first method, the bacteria 30 are present in the slurry or electrode paste 10 in the second and third methods. The electrode paste 10 is dried in a drying step 16, for example at 100° C., during electrode production, in order to remove the solvent 48. Depending on the type of bacteria, the bacteria 30 are killed in the drying step 16. In addition or alternatively, an additional step 68 can also be connected after the drying step (see Figure 6), which additional step serves to kill the bacteria 30, for example by UV radiation or by plasma treatment of the electrode layer (plasma cleaning).

[0113] The claimed invention is not limited to the above-described embodiments. On the contrary, those skilled in the art can also derive other variants of the invention within the scope of the disclosed claims without departing from the technical solution of the claimed invention. In addition, all individual features described in conjunction with the different embodiments can also be combined in other ways within the scope of the disclosed claims without departing from the technical solution of the claimed invention.

[0114] List of Reference Numerals

[0115] 2 Battery Electrodes

[0116] 4, 6, 8 Method steps

[0117] 10. Electrode paste

[0118] 12 Current discharger

[0119] 14 Electrode roll

[0120] 15 Extrusion Steps

[0121] 16 Drying Steps

[0122] 18 Calendering Steps

[0123] 20 Conductive additives / conductive soot

[0124] 22 Conductive additives / pilus

[0125] 24 Active Materials

[0126] 26 Separation device

[0127] 28a, 28b, 28c Arrows

[0128] 30 Bacterial cultures

[0129] 32 Bacteria

[0130] 34 Saline solution

[0131] 36 Vibration / centrifugal process

[0132] 38 Graphite

[0133] 40 Dry Mixing Process

[0134] 42 Mixture

[0135] 44 Wet Mixing Process

[0136] 46 Adhesive

[0137] 48 Solvent

[0138] 50 Nitrogen

[0139] 52 Degassing mechanism

[0140] 54 Glucose

[0141] 56 Nitrate

[0142] 58 Dry Mixing Process

[0143] 60 Wet Mixing Process

[0144] 62 Suspension

[0145] 64 Wet Mixing Process

[0146] 66 Spindle

[0147] 68 Steps

Claims

1. A use of a conductive protein as a conductive additive in an electrode paste (10), wherein: The pili (22) of bacteria (32) were used as proteins.

2. The use according to claim 1, It is characterized in that The pili (22) of Gram-negative anaerobic bacteria (32) were used.

3. A method for producing an electrode paste (10), wherein the bacterial culture (30) is grown from bacteria (32) having pili (22) capable of conducting electricity, -in, Adding a saline solution (34) to the bacterial culture (30), wherein the pili (22) are separated from the bacteria (32) mechanically and by centrifugation, wherein the separated pili (22) are mixed with the conductive soot (20) to form a mixture (42), - wherein an active material (24), a binder (46) and a solvent (48) are added to the mixture (42) and mixed into an electrode paste (10).

4. The method according to claim 3, It is characterized in that Mechanical separation of pili (22) and bacteria (32) is achieved by means of vibration.

5. A method for producing an electrode paste (10), wherein a bacterial culture (30) of bacteria (32) having pili (22) capable of conducting electricity is grown in a graphite material (38), so that the bacteria (32) cover the graphite material (38), -in, The bacteria-covered graphite material (38) is mixed with a binder (46) and a solvent (48) to form a suspension (62), - wherein the active material (24) is added to the suspension (62) and mixed into an electrode paste (10).

6. A method for producing an electrode paste (10), -in, A bacterial culture (30) of bacteria (32) having pili (22) capable of conducting electricity is mixed with an electrode paste material, - wherein a bacterial culture (30) is grown in the electrode paste material, and - During the incubation period, the bacterial culture (30) and the electrode paste material are moved by means of a rotating spindle (66).

7. The method according to claim 6, It is characterized in that In addition to the bacterial culture, conductive soot is mixed into the electrode paste material.

8. The method according to any one of claims 3 to 7, It is characterized in that The cultivation of the bacterial culture (30) is performed in a tank with a nitrogen atmosphere, in which a nitrogen pressure higher than atmospheric pressure is maintained.

9. The method according to any one of claims 3 to 7, It is characterized in that The gases formed are removed by means of a degassing device (52).

10. A battery cell having at least one battery electrode produced from an electrode paste produced according to a method as claimed in any one of claims 3 to 9.

11. The battery cell according to claim 10, wherein: The battery cell is a battery cell for a vehicle battery.

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