EP2396840A1

EP2396840A1 - Power-optimized and energy-density-optimized flat electrodes for electrochemical energy stores

Info

Publication number: EP2396840A1
Application number: EP10703072A
Authority: EP
Inventors: Gerold Neumann; Andreas Wuersig; Peter Gulde
Original assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Current assignee: Fraunhofer Gesellschaft zur Forderung der Angewandten Forschung eV
Priority date: 2009-02-10
Filing date: 2010-02-09
Publication date: 2011-12-21
Also published as: JP2012517660A; WO2010092059A1; KR20110128855A; US20120094176A1

Abstract

The invention relates to an electrode layer composite for forming planar electrodes (1, 2) in electrochemical storage elements, wherein the electrode layer composite comprises at least one first layer (6, 8) containing electrode material and one second layer (7, 9) containing electrode material, wherein the first layer (6, 8) has a higher energy density (specific or area capacity) than the second layer (7, 9), while the second layer (7, 9) has a higher power density (current carrying capability) per unit area than the first layer (6, 8).

Description

Power and energy density optimized surface electrodes for electrochemical energy storage

The present invention relates to an electrode layer composite for the formation of planar electrodes in electrochemical storage elements such as batteries and accumulators, an electrochemical storage element for storing and emitting electrical energy with a flat anode, a separator and a flat cathode, comprising such an electrode layer composite, and a method for producing such Electrode layer composites and thus provided memory elements.

Electrochemical storage elements constructed from sheet-like electrode and separator layers, in particular based on film technologies, are well known. They have as electrodes planar anodes and cathodes which are separated by a separator and each connected to a current conductor, via which a Ankontaktierung takes place. In lithium-ion cells, the films are usually processed into a multilayer winding body and pressed into a solid metal housing. In this then the liquid electrolyte is added and then hermetically sealed the battery case. Lithium polymer cells are flat cells, also called prismatic cells. Here, the electrodes, usually in the form of films, typically stacked and intimately connected under pressure and possibly temperature or by gluing together. The battery body is placed in a housing, usually in a metallized plastic film, filled with electrolyte and then sealed by sealing the Gehäusefolienberandung. Inside the housing, a vacuum is set during the final closure. The electrolyte in this cell type is incorporated in the battery body into micropores present in the electrode and separator structure or absorbed and immobilized in the layers by gelation of the polymer binder.

The electrochemically active materials for electrode films are generally powdery and have a certain particle size distribution. They are processed into slides by means of a binder. In US Pat. No. 5,219,680 A, for example, a carbon-polymer electrode is described as the anode consisting of amorphous carbon particles bound in a polymer matrix. In order to produce the ionic conductivity between the carbon particles in the electrode, the anode is filled with a liquid electrolyte. This is absorbed in pores or in the polymer matrix. Materials for the cathode, such as LiCoO 2, are described in manufacturing technology comparable as described in US 5,219,680 for the anode described in films.

For separators, various ways of producing are known. So there is the possibility to gelify liquid electrolytes and to make them so in films. Such a way is e.g. known from the patent US 5,009,970. Another

The procedure is to produce a film with a fine-pored sponge structure and to make it ionically conductive after completion of the film composite by impregnation in a liquid electrolyte. This method is known from the patent US 5,464,000. DE 198 39 217 A1 describes a possibility of incorporating solid-phase conductors into a polymer matrix and thus producing a separator film.

Pasty materials, electrodes and solid electrolytes in lithium technology and electrochemical cells produced using these materials, in particular accumulator cells, are known inter alia from WO 00/13249, WO 00/63984, WO 01/33656 A1 and WO 01/41246 A1. Electrochemical energy storage based on lithium batteries have gained a very large economic importance. They are currently considered one of the most promising options for the introduction of hybrid or even fully electric vehicles. The energy storage must meet numerous requirements. While in consumer applications primarily a high volumetric and gravimetric energy density is in the foreground, vehicle applications include, among others, fast charging capability and high pulse load capacity, ie high power density, and wide temperature ranges as well as high intrinsic safety.

In particular, the requirements of high power density, e.g. high pulse load capacity, and high gravimethscher and volumetric energy density can not be realized simultaneously in a memory cell or for an electrode according to the prior art. This will be explained using the example of a lithium battery:

In such a charging lithium ions are shifted from the cathode via the separator to the anode under the action of an externally applied electric field. The separator as a separating layer between the anode and cathode is purely ion-conducting, so that electrons only the way through the external circuit to the anode is possible to maintain the charge balance in the accumulator. As a result, it is inevitable that in the electrodes over their layer thickness away until the separator facing the phase boundary, a good ion and electron conduction must be ensured.

The electronic and ionic conductivities in the structure of the electrochemical storage element are based on various mechanisms with different values for conductivity and possibly temperature dependencies. There are both material-dependent contributions, such as particle size of the electrode material, as well as by the cell design certain proportions, such as the dimensions of the electrode. By choosing the material morphology as well as the cell design, however, the cells can only be designed either in the direction of a high load capacity (correspondingly low internal resistance) or in the direction of a high energy density.

From the lattice structure of the solid particles of the electrochemically active material, lithium atoms are reversibly inserted or removed as ions in a battery or accumulator assembly during charging or discharging processes. These migrate in the solid state to the surface of the particle by solid-state diffusion. Since lithium ions are moved in the solid state, for reasons of charge neutrality, sufficient electronic conductivity is additionally required, which as a rule deviates significantly from the ionic conductivity. Using the example of data of the conductivities of the cathode material LiCoθ2 the problem becomes clear:

Electronic conductivity: 0.43 to 4,800 mS / cm (depending on state of charge) Ionic conductivity: approx. 3 * 10 ^~ 4 mS / cm

The indicated conductivities refer to the mobility of the electrons or ions in the active material particles of the electrode material. For use in a cell, a total conductivity of the cell of at least 1 to 10 mS / cm is usually required. The required conductivities can be generated by the addition of conductivity improvers such as carbon black for the electronic and of electrolyte for the ionic conductivity. However, the conductivity improvers only act outside of the solid particle, ie only when the ion or the electron has been transferred from the solid to the surrounding matrix of soot and electrolyte. Since the solid-state diffusion proceeds more slowly than the diffusion in the surrounding matrix, a high power density is favored by short paths in the solid, ie the smallest possible particle size. Furthermore, a high power density is favored by short paths in the matrix. Heavy-duty electrodes, ie electrodes with a high power density, therefore generally have an electrode material with small particle diameters up to down to the nanometer range and additionally low electrode thicknesses or thicknesses.

Materials with small particle sizes usually require a high binder content when processing to form the battery electrode in order to ensure the mechanical cohesion of the electrode. Since binder in the electrode represents a largely inactive substance, the energy density of the cell is reduced by a high binder content in relation to the active material. If, in order to achieve a desired target capacity, a larger number of cell elements of a specific thickness are connected in parallel, there is a further reduction of the energy density compared to thicker electrodes, since comparatively much separator material and metallic current conductors must be processed in the cell, based on the storage capacity represent dead material to the cell. A heavy duty electrode of the prior art as a whole has a reduced energy density.

A high energy density can be favored by a high thickness of the electrode as well as large particle diameters of the active materials corresponding to a high amount of active mass in the composite electrode, since the electrode can thereby contain larger amounts of charge carriers, whereby their storage capacity is increased. However, a high electrode thickness and large particle diameters lead to longer paths for the electrons and ions, which in turn reduces the power density.

The above-described incompatibility of high load capacity, ie high power density, while maintaining a high energy density in the electrochemical storage element is dissolved in the prior art, for example, characterized in that accumulators high energy density either with so-called supercapacitors (SuperCaps), but a very low energy density have extremely high power density, or be paired with accumulators that are optimized for high power density. The disadvantage in the configuration with supercaps is that the discharge characteristics of accumulators and SuperCaps differ significantly, so that usually has to be done via an adjustment electronics. Such an arrangement is described, for example, in US Pat

EP 1 391 961 A1. However, this means unwanted overhead on electronics. Parallel circuits of high-energy and high-power cells have also been described variously, for example in WO 03/088375 A2 and in WO 03/088375 A2. Again, costly electronic equalization circuits are required. Based on the above-described prior art, the present invention has the object, a sheet-like electrode, in particular an electrode foil, and to provide an electrochemical energy storage, the or both a high volumetric and gravimethsche energy density and a high pulse power density and rapid discharge - Charging or simultaneously allows, without the need for additional external measures such as electronic circuits are necessary.

The solution of the above-described object is the device side in an electrode layer composite for forming in particular foil-shaped electrodes in electrochemical storage elements having at least a first layer and a second layer, wherein the first layer ("high energy layer") has a higher energy density and thus a higher surface capacitance (mAh / cm ² ) as the second layer, while the second layer ("high-power layer") has a higher power density and thus a higher current-carrying capacity (mA / cm ² ) than the first layer.

It is further solved by an electrochemical storage element for storing and delivering electrical energy with a flat, in particular foil-shaped anode, a separator and a flat, in particular foil-shaped cathode, wherein the anode and / or the cathode has or have a layer composite according to the invention.

In terms of the method, the object is achieved by a method for producing a surface electrode according to the invention or an electrochemical storage element according to the invention, in which the first layer and the second layer are produced separately and laminated under the effect of pressure and temperature, or by first applying one of the two layers in a tapecasting process. Process is deposited on a substrate and the other layer is subsequently deposited on the one layer in a further tapecasting process. Such an electrode configuration is advantageously connected to a metallic current collector. This is e.g. as a preferably primed film which can be used as a substrate for the coating process or which is bonded by lamination to the double-layer electrode. In another embodiment, a preferably primed open-pore current conductor is inserted between the high energy layer and the high-power layer. In this configuration, it is favorable if the open-pore structure has an open area fraction of at least 50%. Under a surface electrode in the context of the present invention are

Electrode flat body or flat materials in a flat or curved shape understand. The films can be both flexible and inflexible (in the latter case rigid or difficult to bend). According to the invention, "flat materials" or "flat structures" are materials whose length and width have a significantly greater dimension than their thickness, ie their dimension in both surface directions at least twice, and usually at least ten times in at least one direction of the surface plane , preferably at least 100 times or even at least 1000 times the thickness diameter. Foil materials are mostly flexible.

The present invention relates to electrochemical energy stores, in particular in the form of flat (also stacked) or wound batteries and accumulators, the flat, in particular foil-like electrodes, in particular lithium-ion cells and lithium polymer cells. In both cases, fabrics serve as the starting product for the electrodes as well as the separator which separates anode and cathode. As cathode materials for electrodes in lithium batteries and lithium accumulators, a number of materials are available. Examples which may be mentioned here as cathode materials are LiCoO ₂ , LiMn ₂ O ₄ , LiMePO ₄ (Me: metal, eg Fe, Co), LiNiO ₂ , LiMn _x Ni _y Co _z O ₂ (x + y + z = 1), LiNi _x COyO ₂ (x + y = 1), V ₂ O ₅ and LiAlχNi _y Co _z O ₂ (x + y + z = 1). The skilled person is aware of other materials. A number of materials are also available as anode materials for foil electrodes in lithium batteries or lithium accumulators. Exemplary here as graphite anode materials, preferably in different modifications, hard carbon, tin compounds, silicon, metallic lithium, TiO ₂ , Li ₄ Ti ₅ Oi ₂ and mixtures thereof. The skilled person is aware of other materials. The materials are produced as powders with a certain particle size distribution. From these particles is formed - usually by embedding in a binder - a layer from which lithium in a battery or Akkumulatoraufbau reversible can be installed or removed.

Suitable binders are all materials known from the prior art. Suitable are solvent-free, but especially solvent and / or swelling agent-containing binder. Particularly suitable are fluorinated hydrocarbon polymers such as Teflon, polyvinylidene fluoride (PVDF) or polyvinyl chloride. Films or layers which are produced with these binder agents are particularly good water-repellent, which gives the electrochemical components thus produced a particularly good long-term stability. Further examples are polystyrene or polyurethane. Examples of copolymers include copolymers of Teflon and amorphous fluoropolymer and

Polyvinylidene fluoride / hexafluoropropylene called. Regardless of whether the binder contains a solvent and / or swelling agent or not, a plasticizer (also Called plasticizer) for the polymer material (s) used. "Plasticizers" are substances whose molecules are bound to the polymer molecules by secondary valences (van der Waals forces). They reduce the interaction forces between the macromolecules and thereby lower the softening temperature and the brittleness and hardness of the plastics. Due to their lower volatility, however, they often can not be removed by evaporation from the plastic, but may have to be dissolved out by an appropriate solvent. The incorporation of a plasticizer causes a high mechanical flexibility of the films produced therewith.

As further binders also come e.g. synthetic rubbers such as SBC (styrene

Butadiene rubber) or CMC (carboxymethylcellulose) or mixtures of both. These are water-soluble.

However, there are special cases where a binder can be completely eliminated, e.g. when the solid particles for the electrode or solid electrolyte material have sufficient cohesion, as may be the case with some nanoparticles, see WO 00/63984. The layer or film is then formed from a paste consisting of the nanoparticles in a suitable suspending agent.

The invention provides a new concept for the construction of sheet-like electrodes and electrochemical energy storage and for manufacturing processes for such

Energy storage, with the same high energy densities and high power densities can be achieved in a device simultaneously. The fulfillment of these two properties in one component is essential for energy storage, for example in hybrid vehicles. High weight-related energy densities allow high vehicle ranges in the pure electric vehicle by reducing weight.

Space saving in the vehicle is achieved by a low volume and a high power density allows good recuperation in braking mode and high load capacity during acceleration. The high power density is therefore required primarily in pulse mode of the cells. Such Pulsprofilen with high energy density of the cell, the invention takes into account.

For this purpose, the electrodes have at least two partial areas or layers with different properties. The first subregion or the first layer is designed for high energy density and is also referred to as high energy layer. The second subregion or the second layer is designed for high power density and is also referred to as a high-power layer. In particular, the first layer has a higher energy density than the second layer, while the second layer has a has higher power density than the first layer. The first layer, due to its relatively high energy density, represents a large storage volume of the electrode for charge carriers. However, as stated above, the first layer has only a relatively low power density. However, this has the second layer, which, however, has only a relatively low energy density. The combination of the two layers creates a foil-shaped electrode which advantageously has both a high power density and a high energy density.

Short-term high loads (pulsed operation) are mainly absorbed by charge carrier shifts in the high-power layer, long-lasting, uniform loads due to charge carrier shifts in the high-energy layer. If pulsed operation leads to a greater emptying of the high-power layer in relation to the high-energy layer, this imbalance is compensated for by a charge carrier exchange between the high-energy layer and the high-power layer.

According to one embodiment of the invention, the first layer (high-energy layer) has a greater layer thickness than the second layer (high-performance layer). Alternatively or additionally, the first layer comprises an electrode material which has a larger particle diameter than the electrode material of the second layer. The composite electrode formed therefrom thus contains a highly loadable part with electrode materials having the smallest possible particle diameters and a small layer thickness, as well as another part with a high energy density, which generally has large particle diameters and the highest possible layer thicknesses.

The electrode material of the two layers may be chemically different; however, it preferably consists of the same chemical composition.

Suitable particle diameter (average primary particle size at low

Agglomerate state) of the electrode material for the high-energy layer are advantageously in the range of about 0.5 to 10 microns, preferably at about 0.7 to 6 microns. The particle diameters for the high-performance layer are advantageously in the range of about 1 nm to 1 μm, preferably about 50-700 nm. The ratio of the particle diameter of high-energy material to high-performance material is generally in the range from 1.2: 1 to 20: 1. Often one will choose a ratio of 1.5: 1 to 7.5: 1 and most preferably of about 5: 1.

An inventive electrochemical storage element for storing and delivering electrical energy has an anode, a separator and a cathode, wherein the anode and / or cathode at least one layer composite according to the invention have, as described herein. In a known manner, the anode and the cathode are connected to current collectors via which an external contact takes place. The respective electrodes have a finite thickness, typically between about 50 .mu.m and 200 .mu.m, contain, among other active material, usually also Leitruß and binder. The electronic conductivity is ensured by the Leitruß. The separator consists either of a neutral material, for example a binder optionally stabilized by electrochemically inert, insoluble particles (of SiO 2 or the like), as known from the prior art. The binder may instead or in addition also be embedded particles of a material which is a solid electrolyte _, such as Lii _{, 3} Al _0.3 Tii _{, 7} (PO ₄ ) ₃ ,

LiTaO ₃ XSrTiO ₃ , LiTi ₂ (PO ₄ ) ₃ xLi ₂ O or Li ₄ SiO ₄ XLi ₃ PO ₄ , as described in WO 01/41246 A1. Alternatively, for example, microperforated polymeric films having a thickness typically between 10 and 35 microns of polypropylene or polyethylene or composite films of both may be used. Another embodiment is nonwovens, which are coated with ceramic, for example. The ionic conductivity is usually achieved by adding a liquid electrolyte into the assembled cell. The electrolyte typically consists of a conducting salt which is dissolved in an organic solvent or a solvent mixture. This electrolyte can be incorporated in each case in the individual films of the composite; Preferably, however, it is absorbed only after the lamination of the individual layers in the layer composite, for example by the binder, optionally supported by said inert, insoluble particles, provided that they are able to improve the transport and storage of electrolyte fluid, by a concentration gradient of plasticizer in the binder and in the electrolyte or by a resulting in the film production microporous structure (eg obtained by dissolving out plasticizer from the binder material) or by a mixture of two or all of the effects mentioned.

The layers according to the invention are preferably in the form of films. To produce both self-supporting layers (films, tapes) as well as resting on a substrate layers can be made of the usual, known in the prior art method, which are applicable for the corresponding binder materials. Important techniques are the so-called tape casting, the so-called "reverse roll-on-coating", casting, spraying, brushing or rolling. Depending on the material, solidification of the matrix takes place, for example, by curing (of resins or other precondensates as binder), by crosslinking of prepolymers or linear polymers as binders, by evaporation of solvent or in a similar manner. To obtain self-supporting films, for example, a suitable pasty mass can be formed on calenders in the appropriate thickness. Here can be referred to standard technology. Self-supporting layers can also be formed by applying a pasty mass to a substrate and peeling off the layer produced after its solidification. The coating can be carried out by conventional paste application methods. By way of example, painting, knife coating, spraying, spin coating and the like may be mentioned here. Also printing techniques are possible. The lamination of films linking is carried out at a suitable temperature, for example in the integrated system PVDF suitably at 100-250 ⁰ C, preferably in the range of 135-150 ⁰ C. Optionally, the temperature gradient can be driven. Continuous films can be laminated dynamically-continuously, eg with a roll laminator. The line pressure is preferably about 10 - 100 kg / cm.

The advantages of producing film technology are obvious: film technology is a very economical production process that offers a high degree of freedom of forming. In addition to the possibility of reeling can be realized without much effort changing other, even planar geometries. In addition, this technology ensures a very large contact surface between the layers of different functionality such. B. between electrodes and electrolyte in accumulators with respect to the volume of electrochemically active material used. This results in this application particularly favorable loading and unloading.

Preferably, a current collector is arranged directly or indirectly on the first layer (high-energy layer). The reason for this is the

Carrier mobilities in the respective layers. The ion mobility in the electrodes is lower than that of the electrons. A charge imbalance caused by electron displacement has to be compensated for by ion flux, since otherwise an electric field is created which inhibits further electron shifts in the electrode. If the current collector is arranged on the high energy layer, which - as stated above - has a relatively high storage capacity, but only a relatively low power density, that is to say release of charge carriers per time, charge shifts and

Imbalances are compensated because there is sufficient time for charge balance by ion flux. Preferably, the second layer is connected to the current collector via the first layer. A pulsed short-term high power density is effected via an electron flow from the high-power layer via the high-energy layer to the current collector. Preferably, the respective high-energy and high-power layer are intimately connected to each other, so that advantageously no additional current conductor is necessary. The intimate connection can be brought about in various ways. One possibility is to separately prepare each layer separately in separate tapecasting processes and then to process them in a lamination process, ie under

Influence of pressure and temperature, to connect with each other and if necessary with a current conductor. Alternatively, it is possible to completely process a layer, such as the high-energy layer, first by way of a tapecasting process and then to deposit it in a second tapecasting process onto the other layer, ie in the example on the high-performance layer. From the electrode foils prepared in this way, the complete cell can then be constructed either as a wound round cell or as a prismatic stacking or wound cell.

In FIG. 2, the current flows and the mobilities of the individual charge carriers in such a layer sequence are shown by way of example during the discharge process. The abbreviations HL and HE stand for the currents in the high-performance or

High-energy layer. The stronger an arrow, the higher the required mobility of the charge carrier in the respective layer. Since the electrons in each case, i. under low load of the accumulator as well as at high power draw, the entire circuit must pass through the electrodes via the current collector and the counter electrode, a high electron conductivity in all layers (with the exception of the separator) is required. Increased ionic conductivity is required only in the part of the layer system which is dimensioned for high load capacity.

In a further embodiment, the current collector is arranged between the first and the second layer. He contacts these preferably directly. The separator may be disposed between the second layer (high-power layer) of the anode and the second layer of the cathode, preferably in direct contact with them. In this way it is possible to advantageously shorten the electron flow paths through the films. With unchanged energy density, the power density of a memory element according to the invention is thus increased. The separator is a purely ion-conducting membrane which is introduced between anode and cathode as a thin separating layer. Typically, these are either microperforated membranes or microporous membranes resulting from the combination of a filler with a polymeric binder. By the addition of electrolyte, the ion conductivity is produced in the separator. In particular, in the embodiment described above, it is advantageous if the current collector preferably has an open-pore structure of each electrode, so that lithium ions can pass through the current collector. This is particularly easy to achieve if the current conductor consists essentially of a perforated metal foil or a perforated expanded metal or the like. Disadvantage of this arrangement, however, is that the passage area for lithium ions is reduced by the open-pore current collector and thus the charge exchange between the high-energy and the high-performance layer is slowed down. The current flows in the case of discharge in this configuration are shown by way of example in FIG. Thickness and direction of the arrows also symbolize the current directions as well as the necessary mobility of the charge carriers.

Further advantages and features of the present invention will become apparent from the following non-limiting description of exemplary embodiments with reference to FIGS. Showing:

FIG. 1 shows a schematic sectional view of an electrochemical storage element,

FIG. 2 shows the electrochemical storage element of FIG. 1 with charge transfers shown;

FIG. 3 shows another embodiment of an electrochemical storage element in a schematic sectional representation,

FIG. 4 shows the electrochemical storage element of FIG. 3 with charge shifts and FIG

5 shows a diagram of the voltage curve over time during charging and discharging of a memory element according to the invention and of a conventional memory element.

In the figures 1 to 4 flat cells are exemplified for the invention. The first embodiment of a flat cell shown in FIG. 1 has an anode 1 and a cathode 2. Anode 1 and cathode 2 are separated from each other by means of a separator 3. The anode 1 has a two-layer structure and has an anode high-energy layer 6 and an anode high-power layer 7. Similarly, the cathode 2 is also constructed in two layers and has a cathode high energy layer 8 and a cathode high-power layer 9. The layers of anode 1 and cathode 2 are arranged such that the anode high-power layer 7 and the cathode high-power layer 9 adjoin the separator 3. On the opposite side of the separator 3 of the Anode high-energy layer 7 and the cathode high-power layer 9, the anode high-energy layer 6 and the cathode high-energy layer 8 is arranged.

On the anode high-power layer 7 opposite side of the anode high-energy layer 6, an anode current collector 4 is arranged. On the opposite side of the cathode high power layer 9

Cathode high energy layer 8, a cathode current collector 5 is arranged. The current collectors 4, 5 serve for external contacting of the flat cell.

FIG. 2 shows the current flows and the mobilities of the charge carriers for each layer during the discharge process of the flat cell. The strength of the drawn arrows stands for the required mobility of the charge carrier in the respective layer. The required mobility of the electrons is relatively high in all layers of the flat cell. The reason for this is that the electrons have to go through the entire circuit both under low load and under high load of the flat cell.

The electron flow must be compensated by a corresponding ion flux. If this is not done, internal electric fields are built up in the flat cell, which makes further charge shifts more difficult or weaker. In the laid out to a high load capacity layers, d. H. The anode high-power layer 7 and the cathode high-power layer 9, and in the pure ion-conducting separator 3, a high ion mobility is required to compensate for the relatively large charge transfer by electrons and to prevent or minimize the structure of an electric field in the high-performance layers 7, 9. In the anode high energy layer 6 and the cathode high energy layer 8, only a relatively small ion mobility is required, since only shifts of electrons of the respective high energy layer have to be compensated thereby.

The electron mobility in the high-energy layers 6, 8 must be relatively high in order to pass the relatively large charge quantities of the electrons originating from the respective high-power layer 7, 9 through the respective high-energy layer 6, 8.

FIG. 3 shows an alternative embodiment of the flat cell. It differs from the embodiment shown in Figures 1 and 2 by a different layer sequence. In the same way, an anode high-power layer 7 and a cathode high-power layer 9 are arranged adjacent to a separator 3. Likewise, an anode high energy layer 6 and a Cathode high energy layer 8 is provided. However, unlike the embodiment shown in FIGS. 1 and 2, the anode current collector 4 is interposed between the anode high-power layer 7 and the anode high-energy layer 6 and the cathode current collector 5 between the cathode high-power layer 9 and the cathode high-energy layer 8. By this arrangement, it is advantageously possible to shorten the electron flow paths through the film layers. This difference becomes clear when looking at FIG. 3. In this, the respective mobilities of the charge carriers are drawn in a similar manner as in FIG. The required electron and ion mobility in the high-power layers 7, 9 are relatively high. As with the first embodiment shown in Figure 2, the ion mobility in the respective high energy layers 6, 8 is relatively low. Unlike in this embodiment, the electron mobility in the two high energy layers 6, 8 is low. The reason for this is that due to the high-energy layers 6, 8 no electrons originating from the high-power layers 7, 9 have to pass through and the ion current in the high-energy layers 6, 8 only has to compensate for charge shifts due to shifts of the electrons originating from the material of the high-energy layers 6, 8 ,

Hereinafter, an exemplary experimental setup of the present invention will be described. In this cell cells were prepared with a 2-layer lithium titanate film in the negative electrode and with LP30 (EC / DMC 1: 1, 1 M LiPF ₆ ) based electrolyte and measured.

The positive electrode was prepared by dissolving PVDF as a binder (Kynar LBG2) in acetone. To this solution was then added lithium cobalt oxide powder (42% by weight) with 6 μm average grain size, graphite (2% by weight) and acetylene black

(2 wt .-%) added, the whole intimately mixed with a stirrer and processed to a viscous, uniform paste. This paste was then drawn with a squeegee on a glass plate and the solvent evaporated. The film thus produced had a surface charge of 3.5 mAh / cm ² at a thickness of 120 microns. The negative electrode had the two-layer structure according to the invention. Their high energy layer was prepared by dissolving the binder PVDF (Kynar LBG2) in acetone. Thereafter, Li ₄ Ti ₅ Oi ₂ (28 wt%) and acetylene black (5 wt%) were added and intimately mixed. The added lithium titanate is a high energy material with an average primary particle size of about 1 .mu.m and a low degree of agglomeration. The pasty mass thus obtained was drawn with a doctor blade on a glass plate and the solvent evaporated. The thus produced film with a thickness of 140 microns had a surface capacity of 2.6 mAh / cm ² .

The high performance layer was prepared by dissolving the binder PVDF (Kynar LBG2) in acetone. Thereafter, Li ₄ Ti ₅ O ₃ (25 wt%) and acetylene black (5 wt%) were added and intimately mixed. The added lithium titanate is a high-performance material, which is reflected in a significantly lower mean primary particle size of about 500 nm and an increased degree of agglomeration compared to the lithium titanate used in the high-energy layer. This agglomeration leads to good processability while retaining the properties of very small primary particles. The area capacity of the film designed for high load capacities was 0.9 mAh / cm ² , the layer thickness 118 μm.

Both films (high-performance layer, high-energy layer) were connected after the drying process with a roller laminator and a line pressure of 120 kg / cm miteinender at a temperature of 155 ⁰ C.

For the Separatorlage 75 wt .-% Lii _{, 3} Alo _{, 3} Tii _{, 7} (PO ₄ ) ₃ powder was intimately mixed with dissolved in acetone PVDF (25 wt.%) And a film having a thickness of about 50 microns moved out. As the electrolyte, a 1 M solution of the conductive salt LiPF ₆ in a mixture of ethylene carbonate (EC) and dimethyl carbonate (DMC) 1: 1 (standard electrolyte, type name LP30) was used.

In this example, the current collector was attached as shown in FIG. The lamination to the cell body by means of static lamination at a temperature of 160 ⁰ C and a pressure of 1, 9 MPa. The battery body was hermetically sealed in a metallized plastic film. This method is known to those skilled in the art as pouch or coffee bag technology.

As a reference, a second cell was constructed whose electrodes each had no multilayer structure. Its positive electrode was prepared by dissolving PVDF as a binder (Kynar LBG2) in acetone. Lithium cobalt oxide powder (42% by weight), graphite (2% by weight) and acetylene black (2% by weight) were then added to this solution, all intimately mixed with a stirrer and processed to a viscous, uniform paste. This paste was then drawn with a squeegee on a glass plate and the solvent evaporated. The film thus produced had a surface charge of 3.05 mAh / cm ² at a thickness of 103 microns.

The negative electrode was prepared by dissolving the same binder PVDF (Kynar LBG2) in acetone. Thereafter, Li ₄ Ti ₅ O ₂ (28% by weight) with a medium Particle size of 1 micron and acetylene black (1, 7 wt.%) Was added and intimately mixed. The paste thus obtained was then drawn with a doctor blade on a glass plate and the solvent evaporated. The capacity was adjusted to 3.1 mAh / cm ^{2 of} the cathode capacity, the thickness was 165 microns.

For the Separatorlage 75 wt .-% Lii _{, 3} Alo _{, 3} Tii _{, 7} (PO ₄ ) ₃ powder was intimately mixed with dissolved in acetone PVDF (25 wt.%) And a film having a thickness of about 50 microns moved out.

Test cells were also prepared with a standard electrolyte LP30, in the anode, separator and cathode before the addition of electrolyte with a static laminator at 160 ⁰ C and a pressure of 1 MPa 9 have been welded together from these films.

After completion, the cells were packaged in a pouch technology known to those skilled in the art and compared with respect to their electrical behavior. FIG. 5 shows the voltage curve of both test cell types after a multiple charging / discharging load of 10 C (charge or discharge within 6 minutes, 1/10 of an hour). At the end of each discharge, the cells are discharged to 1, 8V. This is the starting point on the voltage axis in Figure 5. By diffusion-related compensation processes, which are due to the internal resistance of the cell, and restoring the cell equilibrium, the voltage slowly increases after the complete discharge to 1, 8 V in the rest phase until the next charging step at. The higher the internal resistance, the higher the voltage increase. In the case of the thick, 2-layer electrodes (referred to as 2-layer in FIG. 5), the voltage jumps to approximately 2.55 V, while in the thinner 1-layer electrode structure (referred to as 1-layer in FIG. 5) in the same Time the voltage rises to approx. 2.7V. This is a surprising result, since

Understanding the state of the art, the behavior was expected to be exactly the opposite, since thick electrodes cause increased internal resistance. If you start charging after the rest period of 30 minutes, the voltage in the 1-layer system increases much faster compared to the 2-layer system, which also does not correspond to the expected behavior. This is all the more surprising since the measurement of the internal resistance by means of impedance spectroscopy provides no indication of a significantly improved behavior of the 2-layer system under high load. The 2-layer cell has an impedance of 808 milliohms at 1 kHz and the 1-layer cell has 793.3 milliohms. This difference is so small that no seriously different electrical behavior, in particular with regard to the load, would have been expected. LIST OF REFERENCE NUMBERS

1 anode

2 cathode 3 separator

4 current collector anode

5 current collector cathode

6 anode high energy layer A

7 anode high-power layer K 8 cathode high-energy layer A

9 cathode high-power layer K

10 arrow for electron mobility

11 arrow for ion mobility

Claims

Claims:

1 . Electrode layer composite for forming planar electrodes (1, 2) in electrochemical storage elements, comprising at least a first electrodematehalhaltige layer (6, 8) and a second electrode material-containing

5 layer (7, 9), wherein the first layer (6, 8) has a higher specific

Capacity as the second layer (7, 9), while the second layer (7, 9) has a higher power density or surface current carrying capacity than the first layer (6, 8).

2. Electrode layer composite according to claim 1, characterized in that the first layer (6, 8) has a greater layer thickness than the second layer (7, 9).

3. An electrode layer composite according to claim 1 or 2, characterized in that the electrode material of both layers is in the form of particles and the material of the first layer (6, 8) has a larger particle diameter than i5 the material of the second layer (7, 9).

4. The electrode layer composite according to claim 3, wherein the particle diameter of the electrode material of the first layer is from 1.5 times to 7.5 times the particle diameter of the electrode material of the second layer.

The electrode-layer composite of any one of the preceding claims, wherein the electrode material of the first and second layers is chemically identical.

The electrode layer composite of any one of the preceding claims, wherein each of the layers further comprises a binder.

7. An electrode layer composite according to claim 6, wherein the binder contains a polymer material and optionally a plasticizer.

8. Electrode layer composite according to one of the preceding claims in the form of a film composite.

9. electrode layer composite according to claim 8, characterized in that the composite further comprises a flat current collector, preferably

30 directly or indirectly at the first layer (6, 8) with higher specific

Capacity is arranged.

10. Electrode layer composite according to claim 9, characterized in that the second layer (7, 9) via the first layer (6, 8) is connected to the current collector.

1 1. Electrode layer composite according to claim 9, characterized in that the current collector is arranged between the first (6, 8) and the second layer (7, 9), preferably contacting them directly.

12. An electrochemical storage element for storing and emitting electrical energy with a sheet-like anode, a separator and a sheet-like cathode, wherein the anode and / or the cathode has a lo electrode layer composite according to one of claims 1 to 1 1 or have.

13. An electrochemical storage element according to claim 12, characterized in that the separator between the second layer (7) (high-performance layer) of the anode and the second layer (9) i5 (high-power layer) of the cathode is arranged and preferably in direct contact with them.

14. An electrochemical storage element according to any one of claims 12 or 13, characterized in that the current collector has an open-pore structure, so that lithium ions pass through the current collector

20, wherein the current conductor is in particular a perforated metal foil or an expanded metal.

15. A method for producing an electrode layer composite according to one of claims 1 to 11 or an electrochemical storage element according to one of claims 12 to 14, characterized in that the first layer (6, 8)

25 and the second layer (7, 9) are prepared separately and then laminated under pressure and / or temperature.

16. A method for producing an electrode layer composite according to one of claims 1 to 11 or an electrochemical storage element according to one of claims 12 to 14, characterized in that first one of

30 two layers (6, 7, 8, 9) is produced in a tapecasting process and the other layer (6, 7, 8, 9) subsequently in a further tapecasting process on the one layer (6, 7, 8, 9) is deposited.