DE102009055944A1 - Separator for electrochemical cell i.e. lithium ion cell, utilized in energy storage system of e.g. electric vehicle, has regular or disorder patterns comprising variety of projections and/or recesses and arranged on side of single layer - Google Patents

Abstract

The separator (1) has an electronically insulating separator layer comprising pores for receiving an electrolyte and a single layer (2). A regular or disorder patterns comprising variety of projections and/or recesses such as burl (3), crater (3'), grooves, rib and/or honeycomb-like structures and arranged on a side of the single layer by a shaping process such as rolling or pressing process. The separation layer is made of alumina, silica, spodumene, phosphate, silicon carbide, silicon nitride, boron nitride, boron carbide, titanium diboride and zirconium diboride. An independent claim is also included for an electrochemcial cell with a positive electrode.

Description

The invention relates to a separator for an electrochemical cell and an electrochemical cell with such a separator, in particular a lithium-ion cell.

Electrochemical cells are used in many areas of technology as energy storage. In particular, they are used in vehicle technology in energy storage systems of electric and hybrid vehicles, but also in the stationary area, such as for buffering peak loads or energy storage for decentralized energy supply.

An electrochemical cell includes two electrodes, which can exchange ions with one another via an electrolyte, usually ions of a metal. Between the two electrodes, a separator is arranged, which serves a spatial separation and electrical insulation of the two electrodes. In addition, the separator has the task to absorb the electrolyte in it and in this way to allow the internal exchange between the electrodes through the separator. In order to achieve the most compact possible structure and a particularly high energy density of the electrochemical cell, the separator is usually in touching contact with the electrodes or is arranged at least in a direct vicinity of the two electrodes.

When using the electrochemical cell for the purpose of energy extraction, the two electrodes are electrically connected to each other via an external circuit, through which a voltage between the two electrodes is tapped. The two electrodes differ by a respective electrode potential, which is often referred to as redox potential, which is a measure of how easily and how quickly the respective electrode can deliver the ions (in the electrolyte). The smaller the potential of an electrode, the easier and faster the electrode will deliver the respective ions (in the electrolyte). An electrochemical cell therefore includes two electrodes having different electrode potentials with respect to ionization of a chemical element (usually a metal), the electrode having the smaller potential being referred to as the negative electrode and the electrode having the larger potential being referred to as the positive electrode. A maximum achievable voltage of an electrochemical cell, which can be tapped via the above-mentioned circuit, is limited by the difference between the two electrode potentials. In order to achieve the highest possible voltage and thus the highest possible energy density in the electrochemical cell, it is endeavored to develop electrode materials, also referred to as active materials, which are distinguished by particularly large or particularly small electrode potentials. Particularly in the case of lithium-ion cells, very different electrode materials can be used for this purpose.

For safety and durability of the electrochemical cell, mechanical stability, thermal stability (stability at high temperatures) and electrochemical stability of the separator are crucial. If the separator is damaged, for example, by a mechanical force, in particular by a pressing or tearing of the separator, it can lead to an electrical short circuit of the two electrodes. This usually results in the destruction of the cell and is usually accompanied by a very strong evolution of heat, which can lead to the development of a fire. Such short circuits can also be caused by deformation of the separator due to high temperatures, or dendrites puncture the separator, which can arise, for example, in crystallization processes (copper on the negative lead-off electrode) within the cell. Furthermore, swelling of the separator should be prevented by the absorption of the electrolyte as much as possible.

The mechanical stability of the separator, in particular in the form of a stiffness (stability to kinking and folding) of the separator, has the particular advantage that the separator, the thickness of which is generally in the micrometer range, is less easily foldable or foldable in a production process, which can reduce defective production or stagnation during the production process. Handling of the separator, for example when installed in an electrochemical cell, is also simplified with increased stiffness of the separator. Overall, the importance of the mechanical stability of the separator in applications in particularly large and flat electrochemical cells is too.

It is known in the prior art that the mechanical stability of plastic-based separators can be increased by adding ceramic or inorganic components into the plastic. So will be in about EP 1 942 000 A1 an admixture of inorganic fillers, for example given by a magnesium oxide, described in a layer of the separator based on plastic, such as polypropylene.

The electrochemical stability of the separator prevents the separator itself from undergoing chemical conversion processes such as oxidation or reduction in the process Separator contained shares. In particular, in electrochemical cells with electrodes which have particularly high or particularly low redox potentials, there is a risk of oxidation or reduction of constituents in the separator.

It is therefore the object of the present invention to propose a separator for an electrochemical cell, which solves the problems mentioned or at least mitigated.

Such a separator should therefore be particularly stable and easy to produce mechanically, electrochemically as well as thermally. In addition, an electrochemical cell with such a separator to propose, which is characterized by a particularly long shelf life, maximum safety and ease of manufacture.

This object is achieved by a separator with the features of the main claim and by an electrochemical cell having the features of claim 14. Specific embodiments and further developments are subject matters of the subclaims.

Accordingly, in a separator according to the invention for an electrochemical cell having an electronically insulating separating layer, which has a plurality of pores for receiving an electrolyte and at least one layered single layer, provided that on at least one side of the at least one single layer a regular or random, from a variety of surveys and / or depressions existing pattern is applied.

The invention is therefore based on the idea to increase mechanical stability of the separator by applying the pattern from the elevations and / or depressions. In comparison with a separator without this pattern, the separator according to the invention has a greater rigidity, which, as already described above, in particular simplifies its manufacturability and processability in an electrochemical cell.

The invention is also based on the recognition that chemical reactions between solid substances take place at contact surfaces between these substances, ie where there is direct physical contact between the substances. By applied to the relevant at least one single layer pattern, a contact surface between this single layer can be reduced with adjoining layers, so that chemical reactions between the individual layer and another adjacent to the single layer layer, such as an electrode, only at the by the pattern reduced contact surface can run off. Thus, chemical changes of the individual layer in question can be spatially limited to the area of the reduced contact area by the pattern. This results in greater chemical stability _{[BP1] of} the single _layer provided with the pattern and thus of the entire separator.

In one embodiment, therefore, the pattern is applied to an outer surface of the separation layer of the separator. This outer surface usually acts as a contact surface with an electrode of an electrochemical cell. Since, as already described above, such electrodes frequently have active materials with particularly high or particularly low redox potentials, there is generally a particularly great risk that the separation layer of the separator on this outer surface is oxidized or reduced by the active material of the electrode. Therefore, the above-mentioned patterns on the outer surface of the separation layer contribute greatly to the increase of the electrochemical stability of the separator due to the described reduction of the contact area.

While the contact area between the separator and an electrode may be reduced by the pattern (for improved electrochemical stability of the separator), the pattern simultaneously enlarges a surface of the separator and, with it, wettability of the separator with a liquid, such as the electrolyte , In this way, a further significant advantage of the pattern described here results from the improved wettability of the separator by the electrolyte. By a high wettability of the separator with the electrolyte at the same time a complete and uniform penetration and wetting of the separating layer of the separator with the electrolyte is facilitated and improved. Such as complete as possible penetration of the separation layer with the electrolyte is necessary for the best possible and uniform ion conductivity of the separator through the separation layer, which in turn is a prerequisite for high performance and durability of an electrochemical cell.

An embodiment of the invention provides that the elevations and / or depressions are configured as nubs, craters, grooves, ribs and / or honeycomb-shaped structures. As a rule, such structures can be produced particularly easily, for example by rolling or pressing in. Furthermore, with such structures, in particular by honeycomb-shaped structures, a particularly high stability and rigidity of the separator can be achieved. In addition, the structures mentioned are suitable for interlocking or interlocking with one another when they are applied to mutually facing sides of two individual layers of the separator arranged directly next to one another, so that the abovementioned Structures of a single layer are in physical contact with the structures of the other single layer. By interlocking or hooking the structures, improved adhesion of these individual layers to one another can be achieved. As a result, in particular, a displacement, warping or deformation of the individual layers relative to one another can be reduced, so that overall a greater mechanical stability of the separator can be achieved. In particular, can in this way a single layer, which consists of a plastic and which tends to deformation at certain temperatures, such as a contraction, by an adjacent dimensionally stable single layer, such as a certain inorganic content, particularly well by the interlocked or wedged pattern be supported. In addition, facilitates in this way, the production of such a separator, since such individual layers can not easily slip against each other after a juxtaposition.

An embodiment which can be produced particularly easily provides that said pattern is applied to the at least one individual layer by a forming process, in particular by rolling or impressions, for example integrated in a casting process. Such transformations are also particularly suitable for individual layers in a sequence following a preceding extrusion, coating, stretching, drawing or screen printing of the single layer. It is also advantageous that, in this way, dimensions of the structures, such as, for example, a height of the elevations, a depth of the depressions and a mean distance between these structures, can be set independently of other parameters of the separator, in particular of the pore size. In this way, therefore, the advantageous properties of these structures can be adjusted separately from other properties of the separator, such as a thickness, length and width, a porosity and the pore size. Another possibility of generating said pattern is in the pressing and laminating of individual layers with each other, in which at the same time a pattern can be pressed onto the individual layers.

These patterns can also be caused by the surface roughness with ups and downs created by the morphology of the ceramic grains _[BP2] . In one embodiment, it is therefore provided that the elevations and / or depressions are given by a surface roughness of a ceramic coating applied to the single layer. The elevations are formed by ceramic granules.

In a further embodiment, it is provided that a mean distance between two adjacent elevations or a mean distance between two adjacent depressions is greater by a factor X than an average pore size, wherein the factor X in a range of 1 to 10,000, preferably in one area from 50 to 1000 lies. In one embodiment, a mean height of the pits or a mean depth of the pits is greater by a factor Y than the average pore size, wherein the factor Y is in a range of 1 to 10,000, preferably in a range of 50 to 1000. In a further embodiment, furthermore, a mean diameter of the elevations or a mean diameter of the depressions is greater by a factor Z than the mean pore size, the factor Z is in a range from 1 to 10,000, preferably in a range from 50 to 1000.

The mean pore size of the separating layer of the separator, which is given by an average value of a Gaussian distribution over measured pore sizes, is generally in a range between 10 nm and 2 μm. In one embodiment, it is provided that the elevations have a height in a range between 0.01 μm and 100 μm, preferably in a range between 0.1 μm and 10 μm, and / or the depressions have a depth in a range between 0, 01 .mu.m and 100 .mu.m, preferably in a range between 0.1 .mu.m and 10 .mu.m, wherein in addition a mean distance between the elevations and / or depressions in a range between 0.01 .mu.m and 100 .mu.m, preferably in a range between 0.1 μm and 10 μm. In a further embodiment, it is provided that the elevations and / or the depressions have a diameter in a range between 0.01 μm and 100 μm, preferably in a range between 0.1 μm and 10 μm.

The described patterns with elevations and / or depressions having the dimensions and distances from each other, in particular in the particular preferred range of 0.1 .mu.m and 10 .mu.m, are particularly well suited for simultaneously achieving the above-mentioned advantages, ie the increase of the mechanical Stability (in particular the rigidity) as well as the electrochemical stability and the wettability of the separator.

One embodiment provides that the separating layer comprises at least two individual layers which lie loosely against each other flatly or are firmly connected to one another in a planar manner, in particular by lamination or by coating a first single layer with a second single layer. An embodiment provides that the separator via a shut-down | mechanism | _[BP3] , where, for example, a low-molecular-weight plastic layer melts at a certain critical temperature, thus reducing its ion permeability loses (becomes high impedance). Another high molecular weight plastic layer with a higher melting point (higher thermal stability) remains mechanically stable and serves as a carrier layer to maintain dimensional stability and integrity of the separator (typically, a melting single layer tends to shrink) and thus the spatial separation and electrical isolation of two electrodes.

Another advantage of a multi-layered structure of a separator is a particularly high level of safety against short circuits or fines due to production errors within a single layer. A production error in a single position, such as a small hole (a defect) in the single layer, in the case of several individual layers usually covered by a further single layer, so that no harmful effects of production error arise, such as short circuits or fine circuits (leakage currents through small Defects or pinholes) and the production error is thus corrected. In this way, a scrap amount during the production of such separators can be reduced, which can reduce the overall manufacturing cost of such separators. Likewise, defects within a single layer can be corrected or compensated, which arise during use, such as within an electrochemical cell, for example, in a partial piercing of the separating layer, for example by a dendrite.

An embodiment provides that the separating layer contains at least one single layer, which has an inorganic portion. Here and below, a proportion always means a mass fraction within the particular individual position. The remaining portion of such a single layer is usually a plastic, see below. An inorganic fraction within a single layer has the ability to increase the mechanical stability of the individual layer relative to external forces, so that the single layer is more stable against buckling, folding, puncturing, crushing, tearing, with the advantages described above. Such a layer is thus particularly suitable as a supporting single layer within the separating layer, which also counteracts swelling of the separating layer by contact with an electrolyte. Furthermore, a single layer with a sufficiently high inorganic content selected has a particularly high thermal stability, so that even in the case that further layers melt within the separating layer of the separator, a secure electrical insulation of two electrodes is still ensured, see description of the shut-down Mechanism above. Such an inorganic portion within a single layer also has the advantages described herein in a separator having no embossed pattern of the type proposed herein.

In one exemplary embodiment, two outer individual layers of polyethylene (melting point about 130 ° C.-140 ° C.) and a further individual layer of polypropylene arranged between these individual layers (melting point about 160 ° C.) are at least above 160 ° C. for stabilization at high temperatures a coating of one of these individual layers is provided, in such a way that this coating is arranged between two of these individual layers.This coating preferably consists of an aluminum oxide or a silicon dioxide ceramic In this way, a shrinkage of the separator is counteracted even when the individual layers are melted , so a separation of two electrodes is still guaranteed.

In one embodiment, it is provided that the inorganic portion of the separating layer is replaced by a ceramic, in particular by aluminum oxide, silicon dioxide, spodumene (LiAlSi ₂ O ₆ ), a phosphate (for example a lithium phosphate such as Li _1.3 Al _0.3 Ti _1.7 ( PO ₄ ) ₃ ), silicon carbide, silicon nitride, boron nitride, boron carbide, titanium diboride, zirconium diboride or by a mixture material consisting thereof, by lithium-conducting solid compounds (in lithium-ion cells), and / or glass fibers is given. In this case, the respective inorganic components are adjusted so that, for a given electrode material (active material), a particularly high electrochemical stability of the individual individual layer and thus of the entire separator results.

The basic idea is to choose on one side of the separator, which is intended to face the negative electrode, an inorganic material which is as electrochemically stable to a reduction (which therefore can not be easily reduced), such as Alumina, and on one side of the separator, which is intended to face the positive electrode to choose an inorganic material which is as electrochemically stable to oxidation (which therefore can not be easily oxidized), such as silica. In addition to the choice of substance for the inorganic portion is also intended to tune the respective inorganic mass fractions within individual layers of a separator in each case to the active materials within the electrodes of an electrochemical cell. This leads, in particular in the case of lithium-ion cells, for which a large number of different active materials is known, to different sequences of individual layers, each with different proportions (possibly) of different inorganic materials. This further essential basic idea of the invention will be concretized below on the basis of further exemplary embodiments of the invention. In general, the inorganic content is in a range between 0.001 and 100%.

In one embodiment, it is provided that the separating layer has at least one individual layer with a portion based on a plastic. Such a single layer can be adjusted (regardless of a subsequently applied pattern here proposed type) by stretching or extrusion with an oil and subsequent dissolution of the oil to a predetermined, uniform as possible porosity, average pore size and layer thickness, which is the best possible conductivity at the same time allow high security against a short circuit formation by this single layer. In one embodiment, it is provided that the plastic-based portion of the release layer by polyolefin, in particular polyethylene, polypropylene or a combination thereof, by polyvinylidene difluoride (PVDF), hexafluoropropylene (HFP) or a combination of the latter (PVDF-HFP), Teflon , Polycarbonates, polyethylene terephthalate, polyvinyl chloride, polyurethane and / or by a non-woven or by a combination thereof. In general, the remaining portion of the single layer is given by an inorganic material, for example by one of the above. In this case, in turn, the respective components of a single layer based on a plastic or an inorganic material are adjusted such that a particularly high thermal, mechanical and for a given electrode material (active material) results in a particularly high electrochemical stability of this single layer or of the entire separator. For this purpose, specific embodiments are given below.

In a further development, it is provided that the separating layer of the separator comprises at least one or a combination of basic building blocks B1, B2 and B3, wherein basic building block B1 is constructed from a first single layer with an inorganic portion and a second single-layer based exclusively on plastic, basic module B2 a first single layer with an inorganic portion and a second and a third each based solely on plastic individual layers is constructed, wherein the first single layer between the second and the third single layer is arranged, and basic block B3 of a first and a second single layer with different inorganic components is constructed. In this case, the respective remaining portions of said individual layers with an inorganic portion are preferably given by a material based on a plastic.

The mentioned individual layers of the basic building blocks B1, B2 and B3 can lie loosely against one another or a single layer, in particular a ceramic, can also be present as coatings of another single layer. In the latter case, the single layer applied as a coating can be designed to be particularly thin in order to achieve a particularly good ion conductivity and a high energy density within an electrochemical cell with such a separator. In a preferred embodiment, the individual layers are firmly connected within a separator, in particular by lamination.

In basic module B2, the single layer is arranged with the inorganic portion between two plastic-based individual layers and preferably completely enclosed by them, and thus particularly well protected against attrition, such as during further processing, whereby a particularly long shelf life and security of the separator is achieved. By combining the mentioned basic components, the mechanical stability of the separator can be increased and the risk of a short circuit can be reduced. Separators with three or more individual layers are therefore particularly advantageous in the case of particularly large and planar electrochemical cells in which the mechanical stability and the short-circuit safety occupy a particularly high level, even if a resulting greater thickness of the separator results in a somewhat reduced ionic conductivity and energy density of the electrochemical cell Cell results.

The invention also provides an electrochemical cell, in particular for electric or hybrid vehicles or stationary applications such as for decentralized power supply, with a negative and a positive electrode, in which a separator of the type proposed here is arranged with an electrolyte between the negative and the positive electrode wherein the electrolyte is wholly or partly taken up by the pores of the separation layer, a first outer surface of the separation layer is in physical contact with the negative electrode, and a second outer surface of the positive electrode separation layer is in physical contact for establishing an ion conductive connection between the second electrode negative and positive electrode.

In one embodiment, the electrochemical cell is a nickel-cadmium, nickel-metal hydride, nickel-zinc, lithium, or Li-ion cell or a double-layer capacitor.

In a further development it is provided that the pattern on the first outer surface and / or on the second outer surface of the separating layer is arranged to improve a wettability of the separation layer with the electrolyte and to reduce a contact area between the separation layer and the electrodes for increasing an electrochemical stability of the separation layer.

A further embodiment provides that an inorganic mass fraction of the separating layer, starting from the first outer layer in a direction toward the second outer layer, increases to improve an electrochemical stability of the separating layer, in particular to avoid a reduction of inorganic portions of the separating layer at the negative electrode. In a preferred embodiment, said percentage mass fraction increases by 20-70 percentage points, in a particularly preferred embodiment by 40-60 percentage points. In a further development, it is further provided that said mass fraction decreases again after an increase towards the positive electrode, in particular for avoiding an oxidation of inorganic portions of the separation layer at the negative electrode.

In one embodiment, a single layer of the separating layer forming the first outer layer has an inorganic mass fraction in a range between 10% and 98%. In a further embodiment, a single layer of the separating layer forming the second outer layer has an inorganic mass fraction in a range between 10% and 98%. A further development provides that the separating layer has a third single layer arranged between a first single layer forming the first outer layer and a second single layer forming the second outer layer with an inorganic mass fraction in a range between 10% and 98%.

A remaining proportion in the individual layers mentioned is generally based in each case on one of the above-mentioned plastics, which produces a flexibility of the individual individual layer and counteracts a tearing of the single layer.

In a further development, the electrochemical cell is a lithium-ion cell with a negative electrode with an electrode material from one of the material groups A (graphite, soft-carbon, hard-carbon), B (silicon, tin) or C (lithium titanate) and / or a positive electrode having an electrode material of one of the material groups D (Li-Co compounds), E (Li-Ni compounds, Li-Mn compounds, Li-Co-Ni-Mn compounds), F (Li-Fe -P compounds, Li-Mn-P compounds, Li-Co-P compounds). In one embodiment of such a lithium-ion cell with an electrochemically particularly stable separation layer is provided that an inorganic portion of a first outer layer forming single layer of the separation layer at a negative electrode with an electrode material of A between 40% and 98%, from B between 60% and 98%, or from C between 0% and 25%. In a further embodiment of the lithium-ion cell described is provided that an inorganic portion of the second outer layer forming single layer is at a positive electrode with an electrode material of D between 40% and 98%, from E between 30% and 98% or F is between 10% and 98%. These ranges of values for the respective mass fractions are particularly suitable for improving an electrochemical stability of the separating layer.

In the following, specific embodiments of the invention will be described with reference to FIG 1 to 6 described in more detail. It shows:

1 Separators of a type proposed here, with patterns in a top view,

2 a cross section through an electrochemical cell with a separator which includes a basic building block B2,

3 a cross section through an electrochemical cell with a separator which includes a basic building block B2,

4 a cross section through an electrochemical cell with a separator which includes a base module B1,

5 a cross section through an electrochemical cell with a separator, which includes a base module B3,

6 a cross section through an electrochemical cell with a separator, which includes two basic building blocks B3,

In 1a to 1c is in each case a section of a separator 1 here proposed type shown schematically in a plan view. In the embodiments shown here is in each case a single layer 2 a separation layer 1 of the separator 1 shown. Here and below, the separating layer and the separator each carry the same reference numeral 1 because in the embodiments shown, the separator is given by the separating layer.

In 1a is on the single position 2 a pattern applied by rollers, which by as nubs 3 formed elevations and through as a crater 3 ' shaped recesses is given. An average diameter d _{1 of} the nubs shown 3 and craters 3 ' has a value of about 20 microns and a mean distance d ₂ between adjacent pimples 3 or craters 3 ' has a value of about 5 microns. An average pore size d _p of pores (not shown here) Single Location 2 has a value of 100 nm. An average depth of the craters 3 ' and a mean height of the pimples 3 is 50 microns each. Thus, the average diameter d _{1 of} the nubs 3 and craters 3 ' by a factor Z = 200 greater than the average pore size, the average distance d _{2 of} the nubs 3 and craters 3 ' by a factor of X = 50 greater than the mean pore size and finally the mean depth of the craters 3 ' and the average height of the pimples 3 by a factor Y = 100 greater than the average pore size.

In 1b is on the single position 2 a pattern applied by impressions, which by as ribs 4 shaped elevations is given (which at the same time as grooves 4 ' molded recesses are formed). A mean diameter d _{1 of} the shown ribs 4 has a value of about 0.1 microns and a mean distance d ₂ between adjacent ribs has a value of about 0.2 microns. A mean pore size d _p of pores (not shown here) of the single layer 2 has a value of 10 nm. A mean height of the ribs 4 is 0.1 μm. Thus, the mean diameter d _{1 of} the ribs 4 by a factor Z = 10 greater than the average pore size, the average distance d _{2 of} the ribs 3 is a factor X = 20 greater than the mean pore size and finally the average height of the ribs 4 by a factor Y = 10 greater than the average pore size.

In 1c is on the single position 2 applied a pattern by rolling during a Castevefahrens, which as through honeycomb 5 shaped surveys is given. A mean diameter d _{1 of} the honeycombs shown has a value of about 100 μm and a mean distance d ₂ between adjacent honeycombs 5 has a value of about 10 microns. A mean pore size d _p of pores (not shown here) of the single layer 2 has a value of 1 μm. An average height of the honeycomb is 20 μm. Thus, the mean diameter d _{1 of} the honeycomb by a factor Z = 100 is greater than the average pore size, the average distance d _{2 of} the honeycomb 5 by a factor X = 10 greater than the average pore size and finally the mean height of the honeycomb is a factor Y = 10 greater than the average pore size.

In 2 is a section of a cross section of a separator 1 here proposed type shown schematically, which by areas 6 an outer surface of an outer single layer 2 of the separator 1 in contact with an electrode 7 stands. The named areas 6 Together they serve as a contact surface 6 between electrode 7 and separator 1 , The areas 6 are through tops of pimples 3 given, which in the form of a pattern on the single layer 2 are applied. The through these areas 6 given contact surface 6 of the separator 1 with the electrode 6 is thus smaller than an entire outer surface of the single layer, which except the areas mentioned 6 especially intermediate areas 6 ' which covers itself between the pimples 3 located. That through the pimples 3 given patterns increased by the reduction of the contact area 6 an electrochemical stability of the single layer 2 ,

In intervals between the pimples 3 and within the pores 8th there is an electrolyte 9 for conducting ions. Through the pimples 3 Furthermore, a wettability of the outer single layer increases 2 by the electrolyte and a mechanical stability of the separator to external forces.

The nubs have a mean diameter d ₁ , a mean distance d ₂ and an average height d ₃ of 1 .mu.m. A mean pore size of pores 8th this single location 2 is about 100 nm, so that the quantities d ₁ , d ₂ and d _{3 are} each by a factor 10 are larger than the average pore size.

In 3 is a section of a cross-section of an electrochemical cell 10 shown here proposed type.

It includes a negative electrode 7 ' , a positive electrode 7 '' and a separator 1 here proposed type. The separator 1 consists of a separating layer 1 which comprises three individual layers: a left, the negative electrode 7 ' facing single layer 11 , a middle single layer 12 , and a right, the positive electrode 7 '' facing single layer 13 , These individual layers 11 . 12 . 13 are according to the basic module B1 described above 16 compiled. Thus, the two outer individual layers are based 11 and 13 each on a plastic without inorganic additives, while the middle single layer by an inorganic coating of the left single layer 11 given is. The inorganic coating 12 In this example, it includes an aluminum oxide weight fraction of 98%, as well as a 2% weight percentage added by additives having adhesive and bonding properties, to ensure safe lamination of the third single ply 13 with the coating 12 to achieve. In this example, the left single layer is 11 by polyethylene having a melting point of about 130 ° C and the right single layer by polypropylene, which ensures a mechanical integrity of the separator between 150 ° C and 190 ° C. Through the ceramic coating 12 is the integrity of the separator 1 secured even at higher temperatures. In this way, a particularly reliable shut-down Mechanimus is achieved (see above), in which above a temperature of about 130 ° C, the left single layer 11 melts and high impedance, while the separator through the middle and the right single layer 12 . 13 remains stable. By replacing the right single layer 13 by a polyethylene-based single layer the shut-down mechanism is amplified because then both outer layers melt simultaneously and become high impedance while the middle layer 12 takes over a supporting function by their ceramic content.

By replacing the left single layer 11 Due to a polypropylene-based single layer, this shut-down mechanism is omitted or shifted to higher temperatures. This is particularly advantageous in a series connection of several such electrochemical cells. In fact, by employing the shut-down mechanism in a single cell within such a series connection, a particularly large voltage drop can occur within this (high-resistance) cell, so that it can burn off. Therefore separators without shut-down mechanism are often more advantageous, especially for series connections.

Another advantage of the embodiment shown is a protection by the arrangement of the ceramic middle single layer 12 between the left and the right single position 11 and 12 before a chemical reaction of the inorganic components in the middle single layer 12 with one of the electrodes 7 ' and 7 '' , in particular before a reduction of contained in this single layer component on the negative electrode 7 ' or a corresponding oxidation at the positive electrode 7 '' , In addition, this arrangement provides protection of the central inorganic (ceramic) single layer 12 achieved before a mechanical abrasion, in particular during a processing process of the separator.

In 4 is a section of a cross-section of an electrochemical cell 10 shown here proposed type, which is designed in this example as a lithium-ion cell. It includes a negative electrode 7 ' , a positive electrode 7 '' and a separator 1 here proposed type. The separator 1 consists of a separating layer 1 which comprises two individual layers: a left, the negative electrode 7 ' facing single layer 11 and a right, the positive electrode 7 '' facing single layer 13 , These individual layers 11 and 13 are according to the basic module B1 described above 15 compiled. The negative electrode 7 ' facing single layer 11 is based solely on plastic while that of the positive electrode 7 '' facing single layer 13 has an inorganic portion.

The negative electrode 7 ' includes an active material of the above-mentioned material group C, namely lithium titanate, with which a particularly long life of the cell can be established. By lithium titanate are compared to graphite only relatively small lithium ion | Activities | _[BP4] on a surface of the negative electrode 7 ' allows. Therefore, in the separator described herein 1 in the negative electrode facing single layer 11 are completely dispensed with an inorganic portion and the single layer consist exclusively of the plastic polyethylene. The inorganic content within the positive electrode 7 '' facing single position 13 are by the first single layer 7 ' separated, so that in this way a reduction of inorganic parts within the right single layer 13 is suppressed.

The positive electrode 7 '' includes an active material of material group D, namely a Li-Co compound having a particularly high redox potential to the reaction Li → Li ⁺ of about 4.5 volts. The inorganic content is within that of the positive electrode 7 '' facing single position 13 90% and is given by silicon dioxide, which is particularly well suited for a positive electrode arrangement due to its electrochemical stability 7 '' suitable.

Due to the two-layer structure of the cell described here 10 can be the separator 1 made relatively thin, which can be realized a high energy density. At the same time, the ceramic content within the separator 1 achieved a high thermal and mechanical stability. The mechanical and electrochemical stability are provided by pimples 3 increased, which as in the case of 2 configured example, ie in particular have a height of about 1 micron.

In 5 is a section of a cross-section of an electrochemical cell 10 shown here proposed type, which is designed in this example as a lithium-ion cell. It includes a negative electrode 7 ' , a positive electrode 7 '' and a separator 1 here proposed type. The separator 1 consists of a separating layer 1 which comprises two individual layers: a left, the negative electrode 7 ' facing single layer 11 and a right, the positive electrode 7 '' facing single layer 13 , These individual layers both contain an inorganic component and thus form the basic component B3 described above 16 , The negative electrode 7 ' facing single layer 11 has an inorganic content of about 40%, which is given by spodumene (LiAlSi ₂ O ₆ ), that of the positive electrode 7 '' facing single layer 11 has an inorganic content of about 70%, which is given by a lithium phosphate such as Li _1.3 Al _0.3 Ti _1.7 (PO ₄ ) ₃ . Both are single layers 11 and 13 have been prepared in a casting process, wherein for the remaining mass fraction of PVDF-HFP, which acts as a binder, and acetone has been used as a solvent for the binder. In an alternative embodiment, both individual layers contain spodumene. The single layer with the higher inorganic Proportion, in this case that of the positive electrode 7 '' facing single layer 11 , has a higher thermal stability and performs a supporting function, especially at high temperatures.

The negative electrode 7 ' includes an active material from the above-mentioned material group A, namely graphite with a very small redox potential to the reaction Li → Li ⁺ of about 0.3 volts. The positive electrode 7 '' includes an active material of the above material group E, namely a Li-Ni compound having a redox potential to the reaction Li → Li ⁺ of about 4.0 volts.

In 6 is a section of a cross-section of an electrochemical cell 10 shown here proposed type, which is designed in this example as a lithium-ion cell. It includes a negative electrode 7 ' , a positive electrode 7 '' and a separator 1 here proposed type. The separator 1 consists of a separating layer 1 which comprises four individual layers: a left, the negative electrode 7 ' facing single layer 11 and a right, the positive electrode 7 '' facing single layer 13 , as well as two adjacent middle individual layers 12 . 12 ' , which in each case as ceramic coatings with an inorganic proportion of 98% of the left and the right single layer 11 . 13 are designed. These coatings 12 . 12 ' Both contain alumina. This includes the separator 1 a combination of a basic building block B3 16 with another basic module B3 16 ' ,

The negative electrode 7 ' includes an active material of the above-mentioned material group B, namely, tin and the positive electrode 7 '' an active material from the above-mentioned material group F, namely a Li-Mn-O compound redox potential to the reaction Li → Li ⁺ of about 4.5 volts.

For electrochemical stability of the separator is in the negative electrode 7 ' facing single position 11 an inorganic content of 60% and in the positive electrode 7 '' facing single layer 13 an inorganic content of 10% is set. In addition, on these two individual layers 11 and 13 each on one of the negative and positive electrode 7 ' . 7 '' facing outer surface (side) 17 . 17 ' a pattern of dimples having a mean height and an average spacing of 0.1 μm each is applied to increase the electrochemical stability of the separator 1 , A total thickness of the separator is, as in the preceding examples about 50 microns, so that in this example, the knobs are not shown.

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Cited patent literature

• EP 1942000 A1 [0007]

Claims (22)

Separator ( 1 ) for an electrochemical cell ( 10 ) with an electronically insulating separating layer ( 1 ), which have a multiplicity of pores ( 8th ) for receiving an electrolyte ( 9 ) and at least one layered single layer ( 2 . 11 . 12 . 12 ' . 13 ), characterized in that on at least one side ( 17 . 17 ' ) of the at least one single layer ( 2 . 11 . 12 . 12 ' . 13 ) a regular or random one of a large number of surveys ( 3 . 4 . 5 ) and / or depressions ( 3 ' . 4 ' ) existing pattern is applied. Separator ( 1 ) from Claim 1, characterized in that the elevations ( 3 . 4 . 5 ) and / or depressions ( 3 ' . 4 ' ) as pimples ( 3 ), Craters ( 3 ' ), Grooves ( 4 ), Ribs ( 4 ' ) and / or honeycomb structures ( 5 ) are configured. Separator ( 1 ) according to one of the preceding claims, characterized in that the pattern on the at least one individual layer ( 2 . 11 . 12 . 12 ' . 13 ) is applied by a forming process, in particular by rolling or impressions. Separator ( 1 ) according to one of the preceding claims, characterized in that the elevations and / or depressions are given by a surface roughness of a ceramic coating applied to the single layer. Separator ( 1 ) according to one of the preceding claims, characterized in that a mean distance (d ₂ ) between two adjacent elevations ( 3 . 4 . 5 ) or a mean distance (d ₂ ) between two adjacent recesses ( 3 ' . 4 ' ) is larger than a mean pore size by a factor X, and furthermore an average height (d ₃ ) of the elevations ( 3 . 4 . 5 ) or an average depth (d ₃ ) of the depressions ( 3 ' . 4 ' ) is greater by a factor Y than the mean pore size, wherein the factor X is in a range of 1 to 10,000 and the factor Y is in a range of 1 to 10,000. Separator ( 1 ) according to one of the preceding claims, characterized in that the elevations ( 3 . 4 . 5 ) have a height (d ₃ ) in a range between 0.1 μm and 10 μm and / or the depressions ( 3 ' . 4 ' ) have a depth (d ₃ ) in a range between 0.1 microns and 10 microns, wherein also a mean distance (d ₂ ) between the elevations ( 3 . 4 . 5 ) and / or depressions ( 3 ' . 4 ' ) is in a range between 0.1 microns and 10 microns. Separator ( 1 ) according to one of the preceding claims, characterized in that the pattern on an outer surface ( 17 . 17 ' ) of the separating layer ( 1 ) is applied. Separator ( 1 ) according to one of the preceding claims, characterized in that the separating layer ( 1 ) at least two individual layers ( 11 . 12 . 12 ' . 13 ), which lie flat against one another or are firmly connected to one another in a flat manner, in particular by lamination or coating. Separator ( 1 ) according to one of the preceding claims, characterized in that the separating layer ( 1 ) at least one single layer ( 2 . 11 . 12 . 12 ' . 13 ) containing an inorganic portion. Separator ( 1 ) according to one of the preceding claims, characterized in that an inorganic portion of the separating layer ( 1 ) is given by a ceramic, in particular by alumina, silica, spodumene, a phosphate, silicon carbide, silicon nitride, boron nitride, boron carbide, titanium diboride, zirconium diboride or by a mixing material consisting thereof, by lithium-conducting solid compounds, and / or glass fibers. Separator ( 1 ) according to one of the preceding claims, characterized in that the separating layer ( 1 ) at least one single layer ( 2 . 11 . 12 . 12 ' . 13 ) having a portion based on a plastic. Separator according to one of the preceding claims, characterized in that a portion of the separating layer ( 1 ) is given by polyolefin, in particular polyethylene or polypropylene, by polyvinylidene difluoride, hexafluoropropylene, Teflon, polycarbonates, polyethylene terephthalate, polyvinyl chloride, polyurethane and / or by a fleece or by a combination thereof. Separator ( 1 ) according to one of the preceding claims, characterized in that the separating layer ( 1 ) at least one or a combination of basic building blocks B1 ( 15 ), B2 ( 14 ) and B3 ( 16 . 16 ' ), wherein - basic building block B1 ( 15 ) from a first single layer ( 2 . 13 ) with an inorganic portion and a second single-layer based solely on plastic ( 2 . 11 ), - basic module B2 ( 14 ) from a first single layer ( 2 . 12 ) with an inorganic portion and a second and a third, each based solely on plastic individual layers ( 2 . 11 . 13 ), wherein the first single layer ( 2 . 12 ) between the second and third individual layers ( 2 . 11 . 13 ), and - basic module B3 ( 16 . 16 ' ) from a first and a second single layer ( 2 . 11 . 12 . 12 ' . 13 ) is constructed with different inorganic proportions. Electrochemical cell ( 10 ) with a negative and a positive electrode ( 7 ' . 7 '' ), characterized in that a separator ( 1 ) according to one of claims 1 to 13 together with an electrolyte ( 9 ) between the negative and the positive electrode ( 7 ' . 7 '' ), wherein the electrolyte ( 9 ) completely or partially from the pores ( 8th ) of the separating layer ( 1 ), a first outer surface ( 17 ) of the separating layer ( 1 ) with the negative electrode ( 7 ' ) in contact with one another and wherein a second outer surface ( 17 ' ) of the separating layer ( 1 ) with the positive electrode ( 7 ' ) is in contact with one another for producing an ion-conducting connection between the negative and the positive electrode ( 7 ' . 7 '' ). Electrochemical cell ( 10 ) of claim 14, characterized in that the pattern on the first outer surface ( 17 ) and / or on the second outer surface ( 17 ' ) of the separating layer ( 1 ) is arranged to improve a wettability of the release layer ( 1 ) with the electrolyte ( 9 ) and to reduce a contact area ( 6 ) between the release layer ( 1 ) and the electrodes ( 7 . 7 ' . 7 '' ) for increasing the electrochemical stability of the release layer ( 1 ). Electrochemical cell ( 10 ) according to one of claims 14 or 15, characterized in that an inorganic mass fraction of the separating layer ( 1 ) starting from the first outer layer ( 11 ) in a direction to the second outer layer ( 13 ) increases to improve electrochemical stability of the release layer ( 1 ). Electrochemical cell ( 10 ) according to one of claims 14 to 16, characterized in that a first outer layer ( 11 ) single layer ( 2 . 11 ) of the separating layer ( 1 ) has an inorganic mass fraction in a range between 10% and 98%. Electrochemical cell ( 10 ) according to one of claims 14 to 17, characterized in that a second outer layer ( 13 ) single layer ( 2 . 13 ) of the separating layer ( 1 ) has an inorganic mass fraction in a range between 10% and 98%. Electrochemical cell ( 10 ) according to one of claims 14 to 18, characterized in that the separating layer ( 1 ) one between a first outer layer ( 11 ) forming the first single layer ( 11 ) and one the second outer layer ( 13 ) forming second single layer ( 13 ) arranged third single layer ( 12 . 12 ' ) having an inorganic mass fraction in a range between 10% and 98%. Electrochemical cell ( 10 ) according to one of claims 14 to 19, characterized in that the electrochemical cell ( 10 ) a lithium-ion cell ( 10 ) is connected to a negative electrode ( 7 ' ) with an electrode material of one of the material groups A (graphite, soft carbon, hard carbon), B (silicon, tin) or C (lithium titanate) and / or a positive electrode ( 7 ' ) with an electrode material from one of the material groups D (Li-Co compounds), E (Li-Ni compounds, Li-Mn compounds, Li-Co-Ni-Mn compounds), F (Li-Fe-P) Compounds, Li-Mn-P compounds, Li-Co-P compounds). Electrochemical cell ( 10 ) according to claim 20, characterized in that an inorganic portion of a first outer layer ( 11 ) forming individual layer ( 11 ) of the separating layer ( 1 ) with a negative electrode ( 7 ' ) is between 40% and 98% with an electrode material of A, between 60% and 98% from B, or between 0% and 25% from C to improve the electrochemical stability of the separating layer (US Pat. 1 ). Electrochemical cell ( 10 ) according to one of claims 20 or 21, characterized in that an inorganic portion of a second outer layer ( 13 ) forming individual layer ( 2 . 13 ) at a positive electrode ( 7 '' ) with an electrode material of D between 40% and 98%, from E between 30% and 98%, or from F between 10% and 98%, to improve the electrochemical stability of the separating layer (US Pat. 1 ).

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