DE102023111490A1 - Electrode for a battery, battery and method for producing an electrode for a battery - Google Patents

Abstract

The invention relates to an electrode (12, 14) for a battery (10), in particular a lithium-ion battery, wherein the electrode (12, 14) has a first layer (18, 22) made of a first active material composition and a second layer (20, 24) made of a second active material composition. The layers (18, 20, 22, 24) are arranged adjacent to one another in a planar manner with their main extension directions oriented at right angles to the direction of current flow that results when the electrode (12, 14) is used as intended as part of a battery (10), wherein the first layer (18, 22) and the second layer (20, 24) differ in at least one property.

Description

The invention relates to an electrode for a battery, a battery and a method for producing an electrode for a battery.

There are various parameters used to measure the performance of a battery. The parameter that is decisive for the suitability of a battery for the respective application depends on the intended use of the battery. These parameters can be, for example, an energy density if the greatest possible amount of energy is to be stored in the smallest possible space. Alternatively and/or additionally, it can also be a specific energy. This is interesting if the greatest possible amount of energy is to be stored with the lowest possible weight of the battery.

In other applications, the amount of stored energy may be less important, but the highest possible performance must be provided. In that case, the performance parameter that determines the suitability of a battery for a specific application may be the power density of the battery, if a battery is to provide the highest possible performance in the smallest possible space. Alternatively and/or additionally, it may be the specific performance of a battery, if a battery is to provide the highest possible performance in relation to its weight.

In practice, this has led to batteries of the type in question being optimized for a wide range of different applications. The resulting batteries have a property profile that is based on the parameter(s) that are essential for the respective application.

However, there are limits to the optimization of such a battery. With conventional batteries, for example, it is therefore difficult to optimize a battery for applications where the primary requirement is to store as much energy as possible with low weight and/or volume, but at the same time there is the requirement to only provide a certain part of the stored energy at a high specific power or power density.

The invention is therefore based on the object of demonstrating an electrode for a battery, a battery and a method for producing an electrode for a battery, which make it possible to make available, by means of a battery at a high energy density and/or specific energy of the battery, a portion of the energy stored in the battery at a comparatively high power density and/or specific power.

The object is achieved by an electrode, a battery and a method having the features of the independent claims. The features of the dependent claims relate to advantageous embodiments.

The electrode has a first layer of a first active material composition and a second layer of a second active material composition.

The layers are arranged adjacent to one another with their main extension directions oriented at right angles to the direction of current flow that arises when the electrode is used as intended as part of a battery. The first and second layers differ in at least one property. In this way, it is possible to create an electrode for a battery that, compared to the prior art, enables new optimization options through the two layers that differ in at least one property.

In particular, the layers are arranged adjacent to one another in such a way that a flat interface is formed between the first layer and the second layer. In this context, an interface is understood to mean in particular an area at which at least one property of the material of the electrode changes abruptly.

The layers and/or the interface extend in particular at right angles to the direction of current flow that results from the intended use of the electrode as a component of a battery.

It has been shown that it is possible to arrange two discrete layers of active material compositions on top of each other. This makes it possible to adjust the properties of both layers in a targeted manner and independently of each other. In this way, the layers can be optimized independently of each other in terms of their properties. In particular, this makes it possible to optimize both layers so that one layer can provide high performance and the other layer can store the largest possible amount of energy.

Depending on the arrangement of the electrode in the battery, the specific When the electrode is used as intended, the layers and/or the interface between the first and the second layer take on a design in which they do not extend in just one plane. For example, the electrodes can be wound in a spiral shape in order to produce a substantially circular-cylindrical battery. Alternatively and/or additionally, the electrodes in the battery can be folded so that the layers and/or the interface extend predominantly in a plurality of planes parallel to one another. Therefore, the direction of current flow when used as intended is to be understood as the local direction of current flow at a specific point on the interface. In other words, the directions of current flow at different points on the interface when the electrode is used as intended can differ significantly from one another with regard to their absolute spatial orientation.

The electrode can be designed in such a way that the first layer has a higher power density and/or a higher specific power than the second layer when the electrode is used as intended as part of a battery. In this way, a battery can be created using the electrode in which electrical energy can be provided at different power levels through the differently designed layers.

Alternatively and/or additionally, the electrode can be designed in such a way that the first layer has a lower energy density and/or a lower specific energy than the second layer when the electrode is used as intended as part of a battery. In this way, batteries can be made with electrodes whose layers can each store different amounts of energy.

The first active material composition of the first layer and the second active material composition of the second layer can be chemically different from one another. By using different chemical compositions, the active material composition can be optimized with regard to either the highest possible power output or the highest possible energy storage capacity.

The active material composition of the respective layer preferably comprises an active material and further components. The active material refers to the chemically active substances in an electrode that are responsible for energy storage by undergoing chemical transformations with the release and/or absorption of electrical charge carriers when the battery is charged and/or discharged. The further components can comprise one or more binders and/or one or more conductivity additives.

For example, the conductivity additive can be selected from graphite, carbon black, carbon fibers such as carbon fibers, graphite fibers or so-called "carbon nanotubes", metal powders such as silver powder, metal fibers such as stainless steel fibers and/or mixtures thereof. The conductivity additive is different from the cathode-active materials. The mass fraction of the conductivity additive in the active material composition can be at least 1% and/or at most 5%.

The first layer can have a higher mass fraction of conductivity additive than the second layer. A higher mass fraction of conductivity additive increases the electrical conductivity and is therefore particularly suitable for realizing high power densities or high specific powers. Layers with a lower mass fraction of conductivity additive, on the other hand, are particularly suitable for storing comparatively large amounts of energy, since the layer can contain correspondingly more active material for storing the electrical energy.

The first layer can have a finer-grained structure than the second layer. A finer-grained structure is better suited to achieving high power densities or high specific powers. Layers with a coarser-grained structure, on the other hand, are better suited to storing comparatively large amounts of energy and are more cost-effective.

For example, the binder can comprise a polymer, in particular polyvinylidene fluoride, polyethylene oxide, polyethylene, polypropylene, polytetrafluoroethylene, polyacrylate, ethylene-propylene-diene rubber (EPDM) and/or mixtures and/or copolymers thereof. The mass fraction of the binder in the active material composition can be at least 1%, in particular at least 3%, and/or at most 7%, in particular at most 5%.

The mass fraction of the active material in the active material composition is preferably at least 88% and/or at most 97%.

The active material can be, for example, graphite and related carbons in which lithium intercalation takes place. The active material of the anode can alternatively and/or additionally be a compound selected from the group consisting of nanocrystalline, amorphous silicon as a lithium alloy, lithium titanates, tin dioxide (SnO2) and combinations thereof. With such active materials, the electrode is particularly suitable for intended use as an anode of a battery.

In particular, the active materials of the active material composition of the first layer and the second layer may differ chemically from each other.

The first layer can in particular have a lithium iron phosphate (LFP) as an active material in the active material composition. The lithium iron phosphate can in particular be a lithium manganese iron phosphate. Lithium iron phosphates as an active material are particularly suitable for achieving high electrical outputs. With such active materials, the electrode is particularly suitable for intended use as a cathode of a battery.

The second layer can in particular comprise a lithium nickel manganese cobalt oxide (NMC) as an active material in the active material composition. Such a lithium nickel manganese cobalt oxide offers the advantage as an active material that batteries with this active material are particularly well suited to storing large amounts of energy, i.e. in particular to enabling high energy densities and/or high specific energies. With such active materials, the electrode is particularly suitable for intended use as a cathode of a battery.

The layer thicknesses of the first and second layers can differ from one another. By using different layer thicknesses, it is possible to further optimize the battery for a specific application by adjusting the ratio of the layers with the different properties to one another.

The first layer and the second layer together can have a total thickness of at least 30 µm, preferably at least 50 µm, and/or at most 140 µm, preferably at most 100 µm. It has been shown that good properties can be achieved with "double layers" in this thickness range, also with regard to the manufacturability of the layers.

The first layer can have a higher porosity than the second layer. A higher porosity enables a higher electrolyte content of the layer in the battery and thus better internal ion conductivity. Therefore, a layer with a comparatively low porosity is well suited to realizing high power densities or high specific powers. The second layer in particular can have a porosity of less than 30 vol.%. Layers with such low porosities, on the other hand, are particularly well suited to storing comparatively large amounts of energy.

The second layer can be arranged between the first layer and a carrier material. The carrier material can in particular be a current collector. Such current collectors can be formed, for example, from a metal foil. Nickel, aluminum, steel, copper or an alloy based on one of the above metals is preferably used as the metal. For a cathode, a current collector made of aluminum or an aluminum alloy is preferred. For an anode, a current collector made of copper or a copper alloy is preferred.

The battery has at least one electrode of the type described above. The battery can have an electrode of the type described above as a cathode. Alternatively and/or additionally, the battery can have an electrode of the type described above as an anode. The battery is in particular a lithium-ion battery.

The battery may further comprise a separator arranged between the electrodes. The separator spatially and electrically separates the anode compartment from the cathode compartment. The separator may be a porous non-conductive or insulating material that allows the transport of ions through the separator between the anode and cathode compartments of the cell. The separator may be made of porous glass, porous ceramic and/or porous polymer.

Furthermore, the battery can comprise a lithium-ion (Li-ion) conductive liquid electrolyte system. The liquid Li-ion conductive electrolyte system can comprise, for example, a solvent and an electrolyte salt containing Li-ions. The solvent can comprise, for example, water, N-methylacetamide, acetonitrile, carbonates, sulfolanes, sulfones, N-substituted pyrrolidones, acyclic and/or cyclic ethers, xylene, polyether, siloxane or mixtures thereof.

The method for producing an electrode of the type described above or a battery of the type described above provides that the first layer and the second layer are first produced separately from one another and then combined to produce the electrode.

Creating the layers separately allows different properties to be set for the two layers The two layers can thus be optimized separately with regard to the resulting requirement profile.

The layers can be produced in particular by extruding the respective layer. In this case, the extrusion can in particular take place onto a carrier material. The carrier material can be a carrier material onto which the layer is extruded only for the purpose of production and which is then removed, in particular after the layers have been brought together, and in particular does not become part of the battery to be produced. Alternatively and/or additionally, the carrier material can also be a carrier material that is intended to become part of the battery, in particular a current collector. In this context, in particular the second layer is extruded onto a current collector as a carrier material.

The first and/or the second layer can be compacted after their respective production and separately from the other layer. In this case, compaction is carried out in particular by calendering. Compacting the layers separately in this way makes it possible to influence the properties of the respective layers in a targeted and independent manner. In particular, different porosities of the respective layers can be set in a targeted manner.

Alternatively, a layer, in particular the second layer, can be compacted after it has been created and before the layers are combined, and after the layers are combined, the combined layers can be compacted together. The compaction of one layer and/or the compaction of the layers together can be carried out by calendering. In particular, if the one layer in this context is the second layer, it can be exposed to a higher pressure during compaction than the combined layers during compaction together. With such a process, it is particularly possible to create a layer, in particular the first layer, directly on the other, already compacted layer when the layers are created, in particular to extrude it onto it and then to compact the layers together. Due to the lower pressure during compaction together, the density of the already compacted layer is no longer influenced, or at least not significantly, so that different densities of the layers can also be specifically set in this way.

In particular, the compaction increases the density of at least the first layer and/or the second layer by at least 10%, preferably by at least 30%, particularly preferably by at least 50%.

During compaction, the electrode is in particular in the dried state. The percentage values given for the reduction in thickness or increase in density refer to the electrode in the dried state. For the purposes of this invention, a material is in the dried state when any solvents and/or volatile auxiliaries that are not intended to become part of the battery have been at least substantially removed from the material.

Accordingly, the method can provide that the active material composition contains a solvent during the production of the respective layer. The solvent can in particular be ethylene carbonate. The solvent improves the processability of the respective active material composition during the production of the layer. In this context, the use of ethylene carbonate in particular has proven to be advantageous.

In this context, the method provides in particular that the proportion of solvent in the active material composition during the production of the layer is at least 10% by weight, in particular at least 15% by weight, and/or at most 30% by weight, in particular at most 25% by weight, based on the total weight of the active material composition.

In particular, the combination of these comparatively low solvent contents with ethylene carbonate as a solvent enables a comparatively environmentally friendly production of the electrodes.

The production of the layer, in particular the extrusion, can take place at a temperature of at least 120°C and/or a temperature of at most 160°C. It has been shown that active material compositions can be processed particularly well at these temperatures. In particular, corresponding processes in which the flowability required for the production of the layer only sets in at such a temperature range allow "free-standing" layers to be produced, i.e. layers that have a certain dimensional stability. These are particularly suitable for realizing the "double layers" according to the invention.

The removal of the solvent, which takes place in particular after the production and/or before the compaction of the respective layer, takes place in in particular by heating the respective layer. The respective layer is in particular heated to a temperature of at least 140°C and/or at most 200°C.

The layers are joined together in particular by lamination. Furthermore, the layers can also be joined together with a current collector by lamination. The first and second layers or a layer and a current collector are joined together in particular at a temperature of at least 80° and/or at most 90°C.

• 1 eine Schnittdarstellung durch eine beispielhafte Batterie

Further practical embodiments and advantages of the invention are described below in connection with the drawing. It shows:

• 1 a cross-section of an example battery

The in 1 The battery 10 shown has an anode 12 and a cathode 14. Anode 12 and cathode 14 are separated from each other by a separator 16.

As in the example shown, the anode 12 can have a first layer 18 and a second layer 20. The first layer 18 and the second layer 20 differ in at least one property.

As in the example shown, the cathode 14 can also have a first layer 22 and a second layer 24. The first layer 22 and the second layer 24 also differ in at least one property.

The anode 12 and the cathode 14 can each have a current collector 26 or 28, as in the example shown. In particular, the second layer 20 of the anode 12 is arranged between the first layer 18 and the current collector 26 of the anode 12. Furthermore, in particular, the second layer 24 of the cathode 14 is arranged between the first layer 22 and the current collector 28 of the cathode 14.

In the 1 The battery is shown in a very simplified manner and is essentially reduced to the electrode arrangement. In practice, a battery can be a 1 For simplicity, housing not shown and/or in 1 For the sake of simplicity, they also have means for electrically contacting the current collectors 26 and 28, which are also not shown.

In the case of the anode 12, the first layer 18 and the second layer 20 can consist of active material compositions, each of which has graphite as the active material. The property in which the first layer 18 of the anode 12 and the second layer 20 of the anode 12 differ can be, for example, the porosity. For example, the first layer 18 can have a higher porosity than the second layer 20. Due to the higher porosity, the first layer 18 therefore has a higher ion conductivity, which improves the suitability of the first layer 18 for providing high power. However, due to the lower porosity of the second layer 20, a higher energy density can be achieved by means of this layer. In the case of the cathode 14, the first layer 22 can also advantageously have a higher porosity than the second layer 24.

Furthermore, the active material of the first layer 22 can be, for example, an LFP, while the active material of the second layer can be an NMC. Such a combination has the further advantage that, due to the different voltages resulting from the different active materials, the characteristic that the LFP as an active material tends to be better suited to delivering high power, while the NMC tends to enable higher energy densities, is further reinforced.

Since the NMC typically enables higher cell voltages, the NMC will supply the electrical energy in an operating state in which only low power is required. Only when the cell voltage drops due to high power output from the battery will the LFP also release electrical energy and thus enable the battery to deliver high power. If the power output from the battery drops again, the cell voltage rises again. The electrical energy is now again released by the NMC.

Due to the high cell voltage made possible by the NMC, charges can also be transferred to the LFP. In other words, the first layer 22 with the LFP as active material is charged again by the second layer 24 with the NMC as active material in phases in which only very low power is delivered.

In this way, even a comparatively thin layer 22, the active material composition of which has LFP as the active material, can significantly increase the ability of the battery 10 to deliver comparatively large electrical power over short, spaced-apart periods of time, while at the same time the NMC enables an overall high energy density of the battery 10.

The features of the invention disclosed in the present description, in the drawings and in the claims can be essential for the realization of the invention in its various embodiments both individually and in any combination. The invention is not limited to the embodiments described. It can be varied within the scope of the claims and taking into account the knowledge of the competent person skilled in the art.

list of reference symbols

10

battery

12

anode

14

cathode

16

separator

18

first layer, anode

20

second layer, anode

22

first layer, cathode

24

second layer, cathode

26

current collector

28

current collector

Claims (18)

Electrode (12, 14) for a battery (10), in particular a lithium-ion battery, wherein the electrode (12, 14) has a first layer (18, 22) made of a first active material composition and a second layer (20, 24) made of a second active material composition, wherein the layers (18, 20, 22, 24) are arranged adjacent to one another in a planar manner with their main extension directions oriented at right angles to the current flow direction that results when the electrode (12, 14) is used as intended as a component of a battery (10), wherein the first layer (18, 22) and the second layer (20, 24) differ in at least one property. Electrode (12, 14) after claim 1 , characterized in that the layers (1, 20, 22, 24) are arranged adjacent to one another in such a way that a flat interface is formed between the first layer (1, 22) and the second layer (20, 24), which extends in particular at right angles to the direction of current flow which results when the electrode (12, 14) is used as intended as part of a battery (10). Electrode (12, 14) after claim 1 or 2 , characterized in that the electrode (12, 14) is designed such that the first layer (18, 22) has a higher power density and/or a higher specific power than the second layer (20, 24) when the electrode (12, 14) is used as intended as a component of a battery. Electrode (12, 14) according to one of the preceding claims, characterized in that the electrode (12, 14) is designed such that the first layer (18, 22) has a lower energy density and/or a lower specific energy than the second layer (20, 24) when the electrode (12, 14) is used as intended as a component of a battery (10). Electrode (12, 14) according to one of the preceding claims, characterized in that the first active material composition of the first layer (18, 22) and the second active material composition of the second layer (20, 24) differ chemically from one another. Electrode (12, 14) according to one of the preceding claims, characterized in that the active materials of the active material compositions of the first layer (18, 22) and the second layer (20, 24) differ chemically from one another, in particular wherein the first layer (18, 22) comprises a lithium iron phosphate, in particular a lithium manganese iron phosphate, and/or the second layer (20, 24) comprises a lithium nickel manganese cobalt oxide as active material in the active material composition. Electrode (12, 14) according to one of the preceding claims, characterized in that the layer thicknesses of the first layer (18, 20) and the second layer (20, 24) differ from one another and/or wherein the first layer (18, 20) and the second layer (20, 24) together have a total thickness of at least 30 µm, preferably of at least 50 µm, and/or of at most 80 µm, preferably of at most 70 µm. Electrode (12, 14) according to one of the preceding claims, characterized in that the first layer (18, 22) has a higher porosity than the second layer (20, 24), in particular wherein the second layer (20, 24) has a porosity of less than 30 vol.%. Electrode (12, 14) according to one of the preceding claims, characterized in that the first layer (18, 22) has a higher mass fraction of conductivity additive than the second layer (20, 24). Electrode (12, 14) according to one of the preceding claims, characterized in that the first layer (18, 22) has a finer-grained structure than the second layer (20, 24). Electrode (12, 14) according to one of the preceding claims, characterized in that the second layer (20, 24) is arranged between the first layer (18, 22) and a carrier material, in particular a current collector. Battery (10), in particular a lithium-ion battery, with an anode (12) and a cathode (14), characterized in that the cathode (14) is an electrode (14) according to one of the preceding claims. Battery (10), in particular lithium-ion battery, with an anode (12) and a cathode (14), in particular battery (10) according to claim 12 , characterized in that the anode (12) is an electrode (12) according to one of the preceding Claims 1 until 11 is. Method for producing an electrode (12, 14) according to one of the Claims 1 until 11 , in particular an electrode (12, 14) for a battery (10) according to claim 12 or 13 , wherein the first layer (18, 22) and the second layer (20, 24) are initially produced separately from one another and then combined to produce the electrode (12, 14). procedure according to claim 14 , characterized in that the layers (18, 20, 22, 24) are produced by extruding the respective layer (18, 20, 22, 24), in particular onto a carrier material. procedure according to claim 14 or 15 , wherein the first and/or the second layer (18, 20, 22, 24) are compacted, in particular calendered, separately from the other layer (18, 20, 22, 24) after their respective production and before the layers (18, 20, 22, 24) are brought together. procedure according to claim 14 or 15 , wherein the second layer (20, 24) is compacted, in particular calendered, after its production and before the layers (18, 20, 22, 24) are brought together, and after the layers (18, 20, 22, 24) are brought together, the layers (18, 20, 22, 24) are compacted together, in particular calendered, in particular when the second layer (20, 24) is compacted, it is exposed to a higher pressure than the layers (18, 20, 22, 24) when they are compacted together. procedure according to Claims 14 until 17 , wherein the first and/or the second layer (18, 20, 22, 24) is produced, in particular extruded, at a temperature of the respective active material composition of at least 120 °C and/or at most 160 °C.

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