DE102013218499A1 - Separator of a lithium battery cell and lithium battery - Google Patents

Abstract

The invention relates to a separator (8) of a lithium battery cell (2) comprising at least one functional membrane (23), the functional membrane (23) having a voltage-dependent or temperature-dependent conduction capability of lithium ions (10), and a lithium ion flux the separator (8) is determined by the voltage-dependent or temperature-dependent conduction capability of lithium ions (10) of the functional membrane (23). It is provided that the change in state of the conduction capability of lithium ions (10) of the functional membrane (23) in a certain voltage range by a limit voltage of the lithium battery cell (2) and / or in a temperature range around a certain limit temperature of the lithium battery cell (2) reversible is. The invention also relates to a lithium battery cell (2), as well as a lithium battery with such a separator (8).

Description

State of the art

The invention relates to a separator of a lithium battery cell and a lithium battery cell and a lithium battery.

The cathode and the anode, d. H. the positive and negative electrodes of lithium battery cells are separated spatially and electrically by means of separators. At the same time, however, the separators for lithium ions are permeable. Thus, on the one hand, an internal short circuit between the electrodes of different polarity can be avoided and, on the other hand, an unhindered flow of ions within the cell take place, which allows the conversion of the stored chemical energy into electrical energy, the so-called electrochemical reaction.

In many applications, thin separators are used so that the internal resistance of the lithium battery cell is as low as possible and a high packing density can be achieved. As materials for separators are very fine-pored plastic films or nonwoven fabrics made of glass fibers. Ceramic films are also used because they have the advantage of being temperature resistant up to 450 ° C. In addition, since separators in lithium-ion batteries are said to be stable over many charge and discharge cycles and over several years, they are often fabricated from high quality materials. In this case, microporous carrier membranes made of plastic are used, which may be partially multilayered.

From the US 5,691,077 For example, a battery separator with three side-by-side membranes is known for use in lithium batteries, which has the ability to disrupt ion flow through the separator in response to rapid heat buildup in the cell. The first and the third microporous membrane consist of polypropylene and the second microporous membrane of polyethylene. The second membrane has a lower melting temperature than the first and third membranes.

From the WO 2007/120763 A2 are separators for electrochemical cells, eg. As lithium batteries, known, wherein the separators have a security layer that quickly shuts off the cell at a temperature limit. Here, thin, microporous polymer latex is used on a surface of a solgel or xerogel as a separator.

From the DE 102 19 423 A1 For example, a lithium cell with a separator is known which has an overcharge additive. As the cell becomes overloaded and the cell temperature becomes critical, the overcharge additive is degraded and the decomposition product slows the current flow in the cell within a short time.

Disclosure of the invention

An inventive separator of a lithium battery cell comprises at least one functional membrane, wherein the functional membrane has a voltage-dependent or temperature-dependent conduction capability of lithium ions, and a lithium ion flux through the separator is determined by the voltage-dependent or temperature-dependent conduction capability of lithium ion of the functional membrane. It is provided that the change in state of the conduction capability of lithium ions of the functional membrane in a certain voltage range by at least a certain threshold voltage of the lithium battery cell and / or in a certain temperature range is reversible by a certain limit temperature of the lithium battery cell.

Advantageous developments and improvements of the independent claim specified separator are possible by the measures listed in the dependent claims.

In one embodiment, the separator comprises a porous support membrane coated with the functional membrane. For example, the device could be realized as a diblock copolymer. For example, a diblock copolymer includes a first portion having a monomer of the porous support membrane and a second portion having a monomer of the functional membrane.

According to a further embodiment, the separator comprises at least two porous support membranes and at least one functional membrane, wherein at least one functional membrane is arranged between two porous support membranes. For example, the assembly could be realized as a triblock copolymer formed from a monomer of the porous support membrane in a first section, a functional membrane monomer in a second section, and a monomer of the porous support membrane in a third section.

According to further embodiments, the separator comprises a plurality of porous support membranes and a plurality of functional membranes, wherein the porous and the functional membranes are arranged alternately. Due to the fact that a large number of polymer strands exist within the separator and are disorderly entangled with one another, it is possible a corresponding functional protective layer can be constructed.

In one embodiment, the functional membrane has a temperature-dependent conduction capability of lithium ions. The particular temperature range in which the change in state of the conduction capability of lithium ion of the functional membrane is reversible preferably comprises a temperature range in which the battery is usually used and a range around a certain limit temperature, above which overheating of the cell is to be expected , The limit temperature is around 80 to 100 ° C. At least up to a defined value above the limit temperature, for example up to 2 ° C, 5 ° C or 10 ° C above the limit temperature, the change in state of the conductivity of lithium-ion is reversible, the value is material-dependent. Preferably, the determined temperature range includes a range of 10 ° C around a threshold temperature of 90 ° C.

The temperature-dependent conductivity of lithium ions below the limit temperature is greater than that above the limit temperature. Below the threshold temperature, the temperature-dependent conduction capability of lithium ions is preferably substantially constant. Even above the limit temperature, the temperature-dependent conduction capability of lithium ions is preferably substantially constant.

According to a preferred embodiment, the functional membrane with temperature-dependent conduction capability of lithium ions has a hydrogel or nanocomposites.

In another embodiment, the functional membrane has a voltage-dependent conduction capability of lithium ions. The particular voltage range in which the state change of the conduction capability of lithium ion of the functional membrane is reversible comprises at least an operative range which is a range of 2.5 to 4.5V. At least up to a defined upper limit above 4.5 V, for example up to 0.1 V, 0.5 V or 1 V above 4.5 V, the state change of the conduction capability of lithium ions is reversible. Analogously, at least up to a defined lower limit below 2.5 V, for example up to 0.1 V, 0.5 V or 1 V below 2.5 V, the change in state of the conductivity of lithium-ion reversible, the Value is material-dependent.

The determined voltage range preferably comprises a range of 500 mV around a limiting voltage of 4.5 V and / or a range of 500 mV about a limiting voltage of 2.5 V.

The voltage-dependent conduction capability of lithium ions within the operative area is preferably greater than outside the operative area. Preferably, the voltage-dependent conduction capability of lithium ions is essentially constant within the operative range. The voltage-dependent conduction capability of lithium ions below the operative range is also preferably constant. The voltage-dependent conduction capability of lithium ions above the operative range is also preferably constant.

The functional membrane preferably has a conductive polymer, in particular polypyrrole (PPy), nanocomposites or nanoporous nuclear track membranes.

According to the invention, a lithium battery cell is also provided with such a separator. The invention is preferably used in lithium-ion battery cells. However, it is not limited to lithium-ion battery cells, but can also be used in lithium-sulfur cells as well as in lithium-air cells.

According to the invention, a lithium battery with at least one such lithium battery cell is also made available, which is connectable to a drive system of a motor vehicle.

The terms "battery cell" and "battery" are used in the present description adapted to the usual language for accumulator or Akkumulatoreinheit. The battery preferably comprises one or more battery units, which may designate a battery cell, a battery module, a module string or a battery pack. The battery cells are preferably spatially combined and interconnected circuitry, for example, connected in series or parallel to modules. Each battery module are thus assigned a plurality of battery cells, which are connected in series and partially in addition in parallel in order to achieve the required power and energy data. The individual battery cells are preferably lithium battery cells with a voltage range of 2.5 to 4.2 volts. Several modules can form so-called Battery Direct Converters (BDCs), and several battery direct converters form a Battery Direct Inverter (BDI).

According to the invention, a motor vehicle is also provided with such a battery, wherein the battery is connected to a drive system of the motor vehicle. This is preferred Method applied to electrically powered vehicles, in which an interconnection of a plurality of battery cells to provide the necessary drive voltage.

Advantages of the invention

The integration of overheat protection within the lithium battery cell provides an effective preventive measure against excessive temperatures. The auto-triggering change in state of the lithium ion conductivity of the separator beyond a defined threshold temperature provides immediate protection that enhances the safety of lithium batteries. To avoid overheating the lithium battery cell, d. H. To avoid exceeding a critical temperature, while the lithium-ion flow is interrupted from a defined limit temperature. For this purpose, the functional membrane has a temperature-sensitive controllable permeability or conduction capability of lithium ions. When the defined limit temperature is exceeded, the functional membrane is structurally changed in such a way that it becomes impermeable to lithium ions. This physical or chemical process takes place in a very short time and brings the lithium-ion flow to a standstill, so that no overheating can take place.

The integration of overcharge protection within each lithium battery cell provides an effective preventive measure against excessive voltages. The automatic triggering function of the separator above a defined threshold voltage provides immediate protection that enhances the safety of lithium battery cells. As a result, both an overcharge of the cell, which is generally to be expected when exceeding a charging voltage of 4.2 V, be prevented, in which deposits metallic lithium at the anode. Likewise, a deep discharge protection can be achieved, with an allowable lower discharge voltage of lithium battery cells is about 2.5 V to avoid irreversible damage. To overload the cell, d. H. exceeding the maximum charging voltage to avoid the lithium-ion flow is interrupted from a defined threshold voltage. For this purpose, the functional membrane has an electrosensitive controllable conductance or permeability to lithium ions. The functional membrane is structurally changed so that it becomes impermeable to lithium ions and forms a separation property when the upper limit voltage or below the lower limit voltage is exceeded. This physical or chemical process takes place in a very short time and brings the lithium ion flow to a standstill, so that no overcharge or deep discharge can take place.

Brief description of the drawings

Embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

Show it

1 a lithium battery cell according to a first embodiment of the invention,

2 the lithium battery cell off 1 when operating under critical conditions,

3 a lithium battery cell according to a second embodiment of the invention,

4 the lithium battery cell off 3 when operating under critical conditions,

5 a lithium battery cell according to a third embodiment of the invention

6 the lithium battery cell off 5 when operating under critical conditions,

7a to 7c schematic constructions of separators according to various embodiments of the invention.

1 shows a schematic structure of a lithium battery cell 2 according to a first embodiment of the invention. The lithium battery cell 2 is in a housing 3 arranged and has a negative electrode 4 , a positive electrode 6 and one between the electrodes 4 . 6 arranged separator 8th on. The negative electrode 4 has a negative current collector 7 and a first active material 17 on at least one surface of the negative current collector 7 on. The positive electrode 6 has a positive current collector 5 and a second active material 15 on at least one surface of the positive current collector 5 on. The first active material 17 and the second active material 15 can each consist of a single component or of several components. The two electrodes 4 . 6 are in the example shown via an external wiring 20 with one the voltage between the electrodes 4 . 6 measuring voltage measuring device 28 electrically connected.

The negative electrode 4 has graphite in the example shown 18 as the first active material 17 and a negative current collector 7 made of copper. The negative electrode 4 may be formed from any material known for the production of lithium-ion anodes. Examples of anode storage materials include silicon (Si), germanium (Ge), lithium, a carbonaceous material such as graphite or amorphous carbons, or a metallic alloy of advantage. Hybrid electrodes with lithium alloy components are also common.

The positive electrode 6 indicates lithium cobalt dioxide (LiCoO ₂ ) as the second active material 15 and a positive current collector 5 made of aluminum. Shown are the cobalt atoms 14 , Lithium atoms 16 and the oxygen atoms 12 of lithium cobalt dioxide. The positive electrode 6 can be formed from a conventional material known for the production of lithium-ion cathodes. Suitable cathode storage materials are, for example, oxidic materials, in particular lithium cobalt dioxide (LiCoO ₂ ), lithium iron phosphate (LiFePO ₄ ), lithium manganese oxide spinel (LiMn ₂ O ₄ ) or nickel comprising mixed oxides. Also nickel / manganese / cobalt / aluminum mixed oxides, lithium metal phosphates or lithium manganese spinels are in use. Any mixtures thereof are possible and in use.

The electrode layer functioning as a cathode may be, for example, on a substrate or on the positive current collector 5 can be deposited directly, such as by a sputtering process, or else a composite of such materials with carriers, circuit mediators or binders can be used.

The current collectors 5 . 7 are expediently each formed from a highly electrically conductive material, such as a metal, an alloy or a highly conductive polymer. The current collectors 5 . 7 serve in particular to the electrical conductivity of the active materials 15 . 17 to improve and form electrical contacts from the layer system at a suitable location. The current collectors 5 . 7 be over the poles 24 . 26 to the connection for the external wiring 20 ,

Between the cathode 6 and the anode 4 is the separator 8th arranged, which is the cathode 6 and the anode 4 spatially separated from each other. The cathode 6 , the separator 8th and the anode 4 can in the case 3 , optionally with other, not shown separators stacked on one another, Z-folded or wound to achieve the required volumes and energy densities.

The separator 8th has a porous support membrane 22 on which, for example, a fine-pored plastic film, a nonwoven fabric made of glass fibers or films made of ceramic and a functional membrane 23 in the illustrated embodiment, as a one-sided coating of the porous support membrane 22 is present. The functional membrane 23 has a voltage-dependent or temperature-dependent conduction capability of lithium ions 10 on, so that the lithium ion flux 11 through the separator 8th from the voltage-dependent or temperature-dependent conduction capability of lithium ions 10 the functional membrane 23 is determined. The functional membrane 23 For this purpose, for example, a hydrogel, nanocomposites, includes a temperature-dependent conduction capability of lithium ions 10 to form a conductive polymer or nanoporous nuclear tracking membranes to provide a voltage-dependent conduction capability of lithium ions 10 train.

The operation of the secondary lithium battery cell 2 is due to one in consequence of the different electrochemical potentials of lithium in the two electrodes 4 . 6 resulting source voltage. At the end of the cell reaction, lithium ions are released 10 shifted from one electrode to the other electrode. When in 1 Charging process migrated positively charged lithium ions (Li ⁺ ions) 10 through the electrolyte from the positive electrode 6 between the levels of graphite 18 of the second active material 17 the negative electrode 4 while a charge current drives the electrons across the external circuitry 20 supplies. The lithium ion flux from the positive electrode 6 is with the reference numeral 11 Mistake. The lithium ions 10 form with the graphite 18 an intercalation compound (LixnC). When discharging (not shown), the lithium ions migrate 10 back to the first active material formed as lithium cobalt dioxide 15 and the electrons can pass through the external circuitry 20 to the positive electrode 4 flow. The lithium ion flux from the negative electrode 4 is with the reference numeral 13 provided and, for example, in 2 shown.

2 shows the lithium battery cell 2 under critical conditions. For example, critical conditions may be above a threshold temperature or outside a defined voltage range. Above the threshold temperature or outside a defined voltage range is the conduction capability of lithium ion of the functional membrane 23 so degraded that ideally no lithium ions 10 the separator 8th can happen. The functional membrane 23 and the porous support membrane 22 are arranged so that both the lithium-ion flux 11 from the cathode to the anode, as well as the lithium-ion flux 13 from the anode to the cathode through the porous support membrane 22 be prevented.

3 shows a lithium battery cell 2 according to a further embodiment of the invention. The lithium battery cell 2 is with respect to the anode 4 and the cathode 6 constructed analogously as the reference to 1 and 2 described embodiment, with the difference that the separator 8th consists of three layers. The functional membrane 23 is between two porous carrier membranes 22 arranged.

4 shows the lithium battery cell 2 according to the embodiment 3 when operating under critical conditions. The functional membrane 23 again has a reduced conductivity of lithium ions, so ideally no lithium ion flux 11 . 13 through the separator 8th can be done.

5 shows a further embodiment of the lithium battery cell 2 , which differ from the preceding embodiments also by the structure of the separator used 8th different. The separator 8th in this case comprises a multicomponent system which has a plurality of alternating polymer strands of porous support membranes and functional membranes.

As in 6 is shown in this embodiment also the lithium ion flux 11 . 13 through the separator 8th determined by the properties of the functional membranes.

7a schematically shows a two-layer structure of a separator 8th with a porous support membrane 22 the thickness D ₁ and a functional membrane 23 the thickness D ₂ , which are arranged side by side. The porous carrier membrane 22 is by membrane monomer building blocks 32 constructed and the functional membrane 23 by functional membrane monomer building blocks 34 , The membrane monomer building blocks 34 may be formed, in particular, as known molecules having a reactive double bond or with functional groups and / or ring-shaped structures (eg ethylene oxide or tetrahydrofuran) or as inorganic monomers (eg the orthosilicic acid H ₄ SiO ₄ ), which are prepared by chain polymerization, Polycondensation or polyaddition to polymers are formed.

7b schematically shows a three-layer structure of a separator 8th with a first porous support membrane 22 a thickness D ₁ , which by Membranmonomerbausteine 32 is constructed, a functional membrane 23 the thickness D ₂ , which by functional membrane monomer building blocks 34 is constructed, and a second porous support membrane 22 the thickness D ₃ , which by Membranmonomerbausteine 32 is constructed, with the membranes 22 . 23 are arranged side by side.

7c shows a further possible embodiment of a separator 8th with a plurality of juxtaposed porous membranes 22 and functional membranes 23 resulting from an alternating sequence of membrane monomer building blocks 32 and functional membrane monomer building blocks 34 is formed.

In the 7a and 7b shown thicknesses D ₁ , D ₂ and D _{3 of} the membranes 22 . 23 may be the same or different from each other.

The invention is not limited to the embodiments described herein and the aspects highlighted therein. Rather, within the scope given by the claims a variety of modifications are possible, which are within the scope of expert action.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 5691077 [0004]
• WO 2007/120763 A2 [0005]
• DE 10219423 A1 [0006]

Claims (11)

Separator ( 8th ) a lithium battery cell ( 2 ) comprising at least one functional membrane ( 23 ), the functional membrane ( 23 ) a voltage-dependent or temperature-dependent conduction capability of lithium ions ( 10 ), and a lithium ion flux ( 11 . 13 ) through the separator ( 8th ) of the voltage-dependent or temperature-dependent conduction capability of lithium ions ( 10 ) of the functional membrane ( 23 ), characterized in that the state change of the conduction capability of lithium ions ( 10 ) of the functional membrane ( 23 ) in a certain voltage range around at least a certain limit voltage of the lithium battery cell ( 2 ) and / or in a certain temperature range around a certain limit temperature of the lithium battery cell ( 2 ) is reversible. Separator ( 8th ) according to claim 1, characterized in that the separator ( 8th ) at least one porous support membrane ( 22 ) which interact with the functional membrane ( 23 ) or that the separator ( 8th ) at least two porous support membranes ( 22 ), wherein at least one functional membrane ( 23 ) between the two porous support membranes ( 22 ) or that the separator ( 8th ) several porous support membranes ( 22 ) and several functional membranes ( 23 ) and the porous support membranes ( 22 ) and the functional membranes ( 22 . 23 ) are arranged alternately. Separator ( 8th ) according to one of the preceding claims, characterized in that at least one functional membrane ( 23 ) a temperature-dependent conduction capability of lithium ions ( 10 ) and the determined temperature range includes a range of 10 ° C around a threshold temperature of 90 ° C. Separator ( 8th ) according to one of the preceding claims, characterized in that the temperature-dependent conduction capability of lithium ions ( 10 ) below the limit temperature is greater than above the limit temperature. Separator ( 8th ) according to one of the preceding claims, characterized in that at least one functional membrane ( 23 ) with temperature-dependent conduction capability of lithium ions ( 10 ) has a hydrogel or nanocomposites. Separator ( 8th ) according to one of the preceding claims, characterized in that at least one functional membrane ( 23 ) a voltage-dependent conduction capability of lithium ions ( 10 ) and the determined voltage range comprises a range of 500 mV around a cutoff voltage of 4.5V. Separator ( 8th ) according to one of the preceding claims, characterized in that at least one functional membrane ( 23 ) a voltage-dependent conduction capability of lithium ions ( 10 ) and the determined voltage range comprises a range of 500mV around a 2.5V cut-off voltage. Separator ( 8th ) according to one of the preceding claims, characterized in that the voltage-dependent conduction capability of lithium ions ( 10 ) is greater within an operating range between 2.5 V and 4.5 V than outside the range. Separator ( 8th ) according to one of the preceding claims, characterized in that at least one functional membrane ( 23 ) with voltage-dependent conduction capability of lithium ions ( 10 ) has a conductive polymer, in particular polypyrrole, or a nanoporous Kernspurmembran. Lithium battery cell ( 2 ) with a separator ( 8th ) according to one of claims 1 to 9. Lithium battery with at least one lithium battery cell ( 2 ) according to claim 10.

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