WO2015036297A1

WO2015036297A1 - Separator of a lithium battery cell and lithium battery

Info

Publication number: WO2015036297A1
Application number: PCT/EP2014/068696
Authority: WO
Inventors: Joachim Fetzer; Alexander Reitzle; Marc Heydemann; Ralf Angerbauer
Original assignee: Robert Bosch Gmbh
Priority date: 2013-09-16
Filing date: 2014-09-03
Publication date: 2015-03-19
Also published as: DE102013218499A1

Abstract

The invention relates to a separator (8) of a lithium battery cell (2), comprising at least one functional membrane (23), wherein the functional membrane (23) has a voltage-dependent or temperature-dependent capacity to allow lithium ions (10) to pass through, and a lithium ion flow through the separator (8) is defined by the voltage-dependent or temperature-dependent capacity of the functional membrane (23) to allow lithium ions (10) to pass through. In this case, provision is made for the change in state of the capacity of the functional membrane (23) to allow lithium ions (10) to pass through to be reversible within a defined voltage range about a limit voltage of the lithium battery cell (2) and/or within a temperature range about a defined limit temperature of the lithium battery cell (2). The invention also relates to a lithium battery cell (2) and to a lithium battery comprising such a separator (8).

Description

Description Separator of a Lithium Battery Cell and Lithium Battery Prior 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 ion flux can take place within the cell, 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. Moreover, since separators in lithium-ion batteries are said to be stable over many charging and discharging 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 US 5,691,077 a battery separator with three juxtaposed

Membranes for use in lithium batteries are known which have 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 WO 2007/120763 A2 separators for electrochemical cells, z. B.

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 DE 102 19 423 A1 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

A separator according to the invention of a lithium battery cell comprises at least one functional membrane, the functional membrane having a voltage-dependent or temperature-dependent conduction capability of lithium ions, and a lithium ion flux through the separator being determined by the voltage-dependent or temperature-dependent conduction capability of lithium ions 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 to at least a certain threshold voltage of the lithium battery cell and / or in a specific

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 has a plurality of porous

Carrier membranes and a plurality of functional membranes, wherein the porous and the functional membranes are arranged alternately. Because of that many

Polymer strands exist within the separator and thereby are disorderly entangled with each other, a corresponding functional protective layer can be constructed. In one embodiment, the functional membrane has a temperature dependent one

Transmittance of lithium ions on. 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 by a certain

Limit temperature above which an overheating of the cell is expected. The

Limit temperature is about 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 particular

Temperature range is a range of 10 ° C around a limit 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. Also above the limit temperature is the

Temperature-dependent conduction capability of lithium ions preferably substantially constant. According to a preferred embodiment, the functional membrane with temperature-dependent conductivity capability of lithium ions has a hydrogel or

Nanocomposites on. According to another embodiment, the functional membrane has a

voltage-dependent conduction capability of lithium ions. The certain one

Voltage range in which the state change of the conduction capability of lithium ion of the functional membrane is reversible, thereby comprises at least an operative range, which is a range of 2.5 to 4.5 V. 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.

Preferably, the determined voltage range comprises a range of 500mV around a cutoff voltage of 4.5V and / or a range of 500mV around a cutoff voltage of 2.5V. The voltage dependent conduction capability of lithium ions within the operational range is preferably greater than outside the operational 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 with

Lithium sulfur cells as well as lithium air cells are used. According to the invention, a lithium battery is also provided with at least one such lithium battery cell, which is provided with a drive system of a

Motor vehicle is connectable. 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 to parallel to the required performance and

Achieve 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 Converter (BDC), and several

Battery direct converter a battery direct inverter (BDI, Battery Direct Inverter).

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. Preferably, the method is used in 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. In order to avoid overheating of the lithium battery cell, ie to avoid exceeding a critical temperature, the lithium ion flow is interrupted at 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 is impermeable to lithium ions becomes. 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 overload of the cell, which generally when exceeding a

Charging voltage of 4.2 V is expected to be prevented, at 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. the

Exceeding the maximum charging voltage, to avoid the lithium-ion flow is interrupted from a defined limit voltage. For this purpose, the functional membrane has an electrosensitive controllable transmission capability or permeability to lithium ions. The functional membrane is structurally changed when the upper limit voltage is exceeded or when the lower limit voltage is exceeded

becomes impermeable to lithium ions and forms a separation property. 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 Exemplary embodiments of the invention are illustrated in the drawings and explained in more detail in the following description.

1 shows a lithium battery cell according to the invention according to a first

embodiment,

Fig. 2 shows the lithium battery cell of Fig. 1 in an operation below critical

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

Invention,

FIG. 4 shows the lithium battery cell of FIG. 3 operating under critical conditions. FIG

Conditions,

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

invention

FIG. 6 shows the lithium battery cell of FIG. 5 operating under critical conditions. FIG

Conditions,

7a to 7c are 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 arranged in a housing 3 and has a negative electrode 4, a positive electrode 6 and a separator 8 arranged between the electrodes 4, 6. 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. 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. The first active material 17 and the second active material 15 may each consist of a single component or of several components. In the illustrated example, the two electrodes 4, 6 are electrically connected via an external circuit 20 to a voltage measuring device 28 measuring the voltage between the electrodes 4, 6.

In the example shown, the negative electrode 4 has graphite 18 as first active material 17 and a negative current collector 7 made of copper. The negative electrode 4 may be formed of any material known for the production of lithium-ion anodes. As anode storage materials, silicon (Si), germanium (Ge), lithium, a carbonaceous material such as graphite or amorphous carbons, or a metallic alloy are advantageous. Hybrid electrodes with lithium alloy components are also common. The positive electrode 6 comprises lithium cobalt dioxide (LiCoO ₂ ) as the second active material 15 and a positive current collector 5 made of aluminum. Depicted are the cobalt atoms 14, lithium atoms 16 and the oxygen atoms 12 of the lithium cobalt dioxide. The positive electrode 6 may be formed of 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 acting as a cathode can be deposited directly on a substrate or on the positive current collector 5, for example by means of a

Sputtering, or it may be a composite of such materials with

Carrier substances, circuit mediators or binders are 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 are used in particular to improve the electrical conductivity of the active materials 15, 17 and to form electrical contacts from the layer system at a suitable location. The current collectors 5, 7 are connected via the poles 24, 26 to the connection for the external circuit 20. Between the cathode 6 and the anode 4, the separator 8 is arranged, which the

Cathode 6 and the anode 4 spatially separated from each other. The cathode 6, the separator 8 and the anode 4 can in the housing 3, optionally with other, not shown

Separators stacked on each other, Z-folded or wound to achieve the required volumes and energy densities.

The separator 8 has a porous support membrane 22, which is for example a fine-pored plastic film, a nonwoven fabric made of glass fibers or films made of ceramic and a functional membrane 23, which is present in the illustrated embodiment as a one-sided coating of the porous support membrane 22. The functional membrane 23 has a voltage-dependent or temperature-dependent Durchleitungsfähigkeit of lithium ions 10, so that the lithium-ion flux 1 1 through the separator 8 of the voltage-dependent or temperature-dependent

Transmittance of lithium ions 10 of the functional membrane 23 is determined. The functional membrane 23 comprises, for example, a hydrogel, nanocomposites for forming a temperature-dependent conduction capability of lithium ions 10, or a conductive polymer or nanoporous nuclear tracking membranes to form a voltage-dependent conduction capability of lithium ions 10.

The mode of operation of the secondary lithium battery cell 2 is based on a source voltage arising as a result of the different electrochemical potentials of the lithium in the two electrodes 4, 6. As the cell reaction progresses, lithium ions 10 are shifted from one electrode to the other electrode. In the charging process shown in FIG. 1, positively charged lithium ions (Li ⁺ ions) 10 migrate through the electrolyte from the positive electrode 6 between the planes of the graphite 18 of the second active material 17 of the negative electrode 4, while charging current transfers the electrons the external circuitry 20 provides. The lithium ion flux from the positive electrode 6 is provided with the reference numeral 11. The lithium ions 10 form an intercalation compound (LixnC) with the graphite 18. When discharging (not shown), the lithium ions 10 travel back into the first active material 15 formed as lithium cobalt dioxide, and the electrons can flow to the positive electrode 4 via the external wiring 20. The lithium ion flux from the negative electrode 4 is provided with the reference numeral 13 and shown for example in Figure 2.

Fig. 2 shows the lithium battery cell 2 under critical conditions. For example, critical conditions may be above a threshold temperature or outside a defined one

Voltage range be. Above the threshold temperature or outside a defined voltage range, the conduction capability of lithium ions of the functional membrane 23 is reduced such that ideally no lithium ions 10 can pass through the separator 8. The functional membrane 23 and the porous support membrane 22 are arranged so that both the lithium-ion flux 1 1 from the cathode to the anode, and the lithium-ion flow 13 from the anode to the cathode through the porous

Carrier membrane 22 can be prevented.

Fig. 3 shows a lithium battery cell 2 according to another embodiment of the invention. The lithium battery cell 2 is constructed analogously to the anode 4 and the cathode 6 as the embodiment described with reference to Figures 1 and 2, with the difference that the separator 8 consists of three layers. The functional membrane 23 is arranged between two porous support membranes 22. Fig. 4 shows the lithium battery cell 2 according to the embodiment of Fig. 3 when operating under critical conditions. The functional membrane 23 in turn has a reduced passage capability of lithium ions, so that ideally no lithium ion flow 11, 13 can take place through the separator 8. Fig. 5 shows another embodiment of the lithium battery cell 2, which differs from the previous embodiments also by the structure of the used

Separators 8 differentiates. In this case, the separator 8 comprises a multicomponent system which comprises a multiplicity of polymer strands of porous, arranged alternately

Having carrier membranes and functional membranes.

As shown in Fig. 6, in this embodiment as well, the lithium ion flux 1 1, 13 is determined by the separator 8 by the properties of the functional membranes.

Fig. 7a shows schematically a two-layer structure of a separator 8 with a porous support membrane 22 of thickness D-ι and a functional membrane 23 of thickness D ₂ , which are arranged side by side. The porous support membrane 22 is through

Membrane monomer building blocks 32 and the functional membrane 23 by functional membrane monomer building blocks 34. The membrane monomer building blocks 34 can be used in particular as known molecules having a reactive double bond or with functional groups and / or annular structures (eg

Tetrahydrofuran) or as inorganic monomers (for example, the orthosilicic acid H ₄ Si0 ₄ ), which are formed by chain polymerization, polycondensation or polyaddition to form polymers. Fig. 7b shows schematically a three-layered structure of a separator 8 with a first porous support membrane 22 of a thickness D-ι, which is constructed by Membraneonomerbausteine 32, a functional membrane 23 of thickness D ₂ , which is constructed by functional membrane monomer building blocks 34, and a second porous support membrane 22 of thickness D ₃ , which is constructed by membrane monomer building blocks 32, wherein the membranes 22, 23 are arranged side by side. FIG. 7 c shows a further possible embodiment of a separator 8 with a multiplicity of porous membranes 22 and functional membranes 23 arranged next to one another, which is formed by an alternating sequence of membrane monomer building blocks 32 and functional membrane monomer building blocks 34.

The thicknesses D ₁ , D ₂ and D _{3 of} the membranes 22, 23 shown in FIGS. 7 a and 7 b may be identical 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.

Claims

Claims 1. Separator (8) of a lithium battery cell (2), comprising at least one functional membrane (23), wherein the functional membrane (23) has a voltage-dependent or temperature-dependent conduction capability of lithium ions (10), and a lithium-ion flux (1 1, 13 ) is determined by the separator (8) from 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 by a certain limit temperature of the lithium battery cell (2) is reversible.

Second separator (8) according to claim 1, characterized in that the separator (8) has at least one porous support membrane (22) which is coated with the functional membrane (23), or that the separator (8) at least two porous support membranes (22), wherein at least one functional membrane (23) is arranged between the two porous support membranes (22), or that the separator (8) is more porous

Carrier membranes (22) and a plurality of functional membranes (23) and the porous support membranes (22) and the functional membranes (22, 23) are arranged alternately.

3. Separator (8) according to one of the preceding claims, characterized in that at least one functional membrane (23) has a temperature-dependent

Durchleitungsfähigkeit of lithium ions (10) and the certain

Temperature range includes a range of 10 ° C to a limit temperature of 90 ° C.

4. separator (8) according to any 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.

5. Separator (8) according to one of the preceding claims, characterized in that at least one functional membrane (23) with temperature-dependent

Durchleitungsfähigkeit of lithium ions (10) has a hydrogel or nanocomposites.

6. Separator (8) according to any one of the preceding claims, characterized in that at least one functional membrane (23) is a voltage-dependent

Transmittance of lithium ions (10) and the particular

Voltage range includes a range of 500 mV to a threshold voltage of 4.5V.

7. Separator (8) according to any one of the preceding claims, characterized in that at least one functional membrane (23) is a voltage-dependent

Transmittance of lithium ions (10) and the particular

Voltage range includes a range of 500 mV to a threshold voltage of 2.5V.

A separator (8) according to any one of the preceding claims, characterized in that the voltage-dependent conduction capability of lithium ions (10) is greater within an operational range between 2.5V and 4.5V than outside the range.

9. Separator (8) according to any one of the preceding claims, characterized in that at least one functional membrane (23) with voltage-dependent

Conduction capability of lithium ions (10) a conductive polymer, in particular

Polypyrrole, or has a nanoporous Kernspurmembran.

10. lithium battery cell (2) with a separator (8) according to any one of claims 1 to 9.

1 1. Lithium battery with at least one lithium battery cell (2) according to claim 10.