WO2019233505A1

WO2019233505A1 - Lithium accumulator provided with a safety system

Info

Publication number: WO2019233505A1
Application number: PCT/CZ2019/050028
Authority: WO
Inventors: Jaroslav Polívka
Original assignee: EXIMPO, akciová společnost
Priority date: 2018-06-07
Filing date: 2019-06-06
Publication date: 2019-12-12
Also published as: DE212019000298U1

Abstract

The invention relates to a lithium accumulator provided with a safety system comprising at least one container(2) with emergency liquid located within the housing(4) of the accumulator which will flood the electrode area with an emergency liquid if the emergency situation occurs. The emergency liquid is an inert vacuum oil. The safety system assures the safe operation of the accumulator by protecting the accumulator from flashing or exploding.

Description

Lithium accumulator provided with a safety system

Technical Field

The invention relates to a lithium accumulator provided with a safety system comprising at least one container with emergency liquid which will flood the electrode area with an emergency liquid if the emergency situation occurs. The emergency liquid is an inert vacuum oil. The safety system assures the safe operation of the accumulator by protecting the accumulator from flashing or exploding. Virtually any lithium accumulator known in the art can be equipped with the safety system disclosed in the present invention.

Background Art

Lithium accumulators belong to modem sources of electrical energy and they are especially suitable for mobile purposes and as "power reservoirs" of electrical energy obtained from, for example, alternative sources. The current and still unresolved issue of lithium accumulators is their safety. Lithium has the highest energy density and specific capacity compared to other metals, and thus the highest energy per volume. Lithium accumulators/batteries can therefore provide very high currents, which is often desirable (electromobiles), however, it is accompanied by a problem of overheating. In case of a short circuit, the accumulator can quickly overheat and explode. The materials of positive electrode are usually substances with a high proportion of chemically bound oxygen, and hence fire-promoting, while the materials of the negative electrodes are substances prone to self-inflammation in the air and in the humidity. Furthernore, the electrolyte is formed by a solution of lithium salt in an organic, and therefore a flammable liquid. The challenge for researchers in the field is, in addition to striving for maximum efficiency and capacity, above all a safety of operation.

Active accumulator protection typically resides in a usage of protective electronic circuits, which, in addition to voltage and current, also monitor the disproportionate rise in temperature and when it is exceeded they disconnect the accumulator circuit.

European patent EP 2 619 836 provided one possible solution for temperature control of a high capacity lithium accumulator. It disclosed an accumulator module suitable for a cooling system and includes a variant where a liquid electrolyte is used as a cooling medium. Czech Patent No. 306913 described a solution wherein a lithium accumulator consists of mutually detachable modules of negative and positive electrode which can be mechanically separated in the event of an emergency while the electrolyte is simultaneously removed from the negative electrode module and replaced by an emergency liquid in order to prevent undesired chemical reaction and eventual fire or explosion of the accumulator.

Czech Utility Model No. 30997 described a lithium accumulator with detachable modules of negative and positive electrodes and an expansion vessel containing an emergency liquid which floods the electrodes in the event of an accident.

The present invnetion relates in particular to the construction of a lithium accumulator with a safety system, which provides a high level of safety and explosion protection.

Description of the Invention

The present invention relates to a lithium accumulator equipped with a safety system comprising at least one container with emergency liquid. The safety system is located together with the electrodes (comprised in an electrode module) in an accumulator housing. The emergency liquid is an inert vacuum oil. The container comprising emergency liquid can be made for example from breakable material and can be completed with a detonator connected to a safety electronic module. If an emergency situation occures, as for example the accumulator temperature rises above a safe level or a short circuit occurs, the electronic safety module, which is a part of the safety system, initiates the detonator and breaks the container with the emergency liquid that floods the electrodes, displaces the electrolyte from the separators, and stops the ion flow.

In another embodiment of the invention the container comprising emergency liquid is made from thermoplastic material with low melting temperature. Melting temperature of the thermoplastic must be higher then the highest safe operation temperature of the accumulator and substantially lower than the temperature of inflammation of the electrolyte, e.g. 160 °C - 170 °C, which means melting temperature in the range 100 °C - 130 °C, preferably 105 °C - 110 °C. If dangerous increase in temperature during emergency situation occurs, the container will melt and the emergency liquid floods the electrodes. In such a case, there is no need for a detonator for breaking the container. In other embodiment of the invention, the container comprising emergency liquid is formed by a space between outher solid housing of the accumulator and the inner sleeve enclosing the electrode module. In such a case, the inner sleeve is made from thermoplastic material with low melting temperature, i.e. temperature in the range 100 °C - 130 °C. If dangerous increase in temperature during emergency situation occurs, the sleeve will melt and the emergency liquid immediately floods the electrodes from all directions.

The safety system assures the safe operation of the accumulator by protecting the accumulator against flashing or exploding, which can occur, inter alia, due to the decomposition of metallic lithium, or lithium crystals from lithium salts. This technical principle is applicable to both lithium accumulator cells and as well to an accumulator pack containing multiple cells.

Flooding of the electrodes with emergency liquid and consequently displacing the electrolyte from the separators and electrodes will prevent potential contact of lithium electrode (in any form and composition) with water and forming an explosive mixture of hydrogen and oxygen. Therfeore it would be possible to use water for extinguishing of fire of the accumulator according to the present invention. The safety system according to the present invention is usable in virtually any (in terms of material of electrodes) lithium cells or accumulators known in the art, for example for cells where one electrode is from lithium compounds and the other electrode contains graphite or other substances with the same function.

The emergency liquid container comprised within an accumulator is essentially of any shape that is adapted to be placed into the accumulator housing in the vicinity of the electrode module. In one embodiment, the container may be in the shape of a cylinder or elliptical cylinder, made of a rigid yet fragile material, for example glass, ceramic or a suitable plastic, more preferably glass. The container volume is any useful and practicable volume that can be determined by the skilled person. In some embodiments, the volume can be approximately 2 to 15 % of the accumulator cell volume, for example 5 to 12 % or preferably about 10 %, of the accumulator volume. In addition to the emergency liquid, the emergency liquid container may contain pressurized inert gas, preferably argon. The gas pressure will help to rapidly penetrate the emergency liquid into the spaces between the electrodes.

The function of the emergency liquid is to flood the electrodes when released from the container, to expel the electrolyte from the spaces between the electrodes, i.e. from the separators and the surface of the electrodes, and to stop the flow of ions. This will prevent the accumulator from flashing out or exploding.

Testing of various mineral oils and similar liquids has shown that the most advantageous emergency liquid is an inert vacuum oil (vacuum pump oil), especially the oil of the perfluoropolyether (PFPE) type. Such an oil has suitable properties in terms of emergency liquid requirements because it is a non-flammable and non-explosive liquid, completely devoid of oxidation ability, water immiscible and insoluble in most organic solvents, having low surface tension, and futhermore, biologically inert and environmentally friendly.

Suitable example of such oils is perfluoroalkylpolyether of the formula F-[CF(CF₃)-CF₂-0]_n- -CF2CF3 (n=20-30), available e.g. under the name KROTOX (DuPont) or oxidized polymerized l,l,2,3,3,3-hexafluoro-l-propene of the formula CF₃-0-[CF(CF3)-CF₂-0]_x- -(CF₂-0)_y (x=l0-50, y= 10-50), available e.g. under the name FOMBLIN (Solvay). Oxidized polymerized l,l,2,3,3,3-hexafluoro-l-propene (FOMBLIN) appears to be the most preferred.

The safety electronic module, as standard part of the safety system of lithium accumulator, enables electrical disconnection of the accumulator circuit, and comprises at least one electronic sensor, such as a temperature, current or shock/impact sensor, wherein at least one electronic sensor is connected to the detonator, preferably via the initiating chip. The safety electronic module preferably includes all three of the above sensors. The safety electronic module is therefore designed to monitor the current and temperature inside the cell, as well as possible shock/impact and to initiate the detonator and disconnect the accumulator circuit in the event of an emergency. If an emergency situation occurs, for example, the cell temperature rises above a safe level or a short circuit occurs, the safety electronic module activates the detonator that breaks the container with the emergency liquid. The standard safety electronics simultaneously disconnect the accumulator circuit.

As the detonator may be used standard detonator known to the persons skilled in the art, such as the detonator used in seatbelt pretensioners or airbags inflators. The detonator is located either directly inside the emergency liquid container or on its surface so that its explosion disintegrate the emergency liquid container.

In one preferred embodiment of the invention, the container for emergency liquid is made from thermoplastic material, for example semicrystallic thermoplastic, such as polyether. Preferrably low density polyether (LDPE) with melting temperature 105 °C - 110 °C is used. High density polyether (HDPE) with the melting temperature 110 °C - 130 °C can also be used. And also amorphous thermoplastics like polyvinylchlorid (PVC), polystyren (PS) or styren could be used. Also any mixture of the mentioned thermoplastics with corresponding melting temperature (about 110 °C) could be used.

The present invention further relates to an accumulator which, in addition to the above- mentioned safety system, comprises an electrode module comprising a negative electrode made of metal lithium and a positive electrode comprising vanadium oxide. Such accumulator provides high cell capacity and high specific energy together with enhanced safety.

In one embodiment, the housing of the accumulator according to the present invnetion is doubled; inside of the solid outer housing for providing mechanical protection, there is an inner sleeve, made fro example from an elastic material which allows to increase the volume. The housing is dimensioned to provide sufficient space for a possible increase in the volume of the electrode module and/or in some embodiments it can comprise additional expansion space. The expansion space can be filled by pressurized nitrogen that will help spreading the emergency liquid and also prevent the access of the air oxygen to the electrodes. The housing is provided with a positive and negative pole contact to which the current collectors of the respective electrodes are connected. For reasons of mechanical protection, the housing can still be layed out with additional resilient material.

In one preferred embodiment the container comprising emergency liquid is formed by the space between outher solid housing of the accumulator and the inner sleeve wrapping the electrode module. In such a case the inner sleeve is made from thermoplastic materials mentioned above like for example LDPE or HDPE.

The electrode module comprises negative and positive electrodes and a separator, whether in any configuration, preferably as a roll, bundle or column, preferably a Z-folded column. The electrodes can be made from standard materials used for Li or Li-ion cells known to those skilled in the art. However, the advantageous features of the present invnetion are best achieved when the negative electrode is made of metallic lithium (Li), preferably in the form of a film or foil, while the positive electrode contains vanadium oxides, preferably V₂O₅, and most preferably consists of a composite made of V₂O₅ and graphene. In a preferred embodiment the weights of Li and V₂O₅ used in the electrodes are in a ratio of about 1:10. One of the advantages of the accumulator cell with the above-mentioned electrodes is a significant increase in specific energy (the ratio of cell capacity and weight). Experiments have shown that the specific energy of the accumulator cell according to the present technical solution is up to 4 times higher in comparison with analogous cell with standard graphite and LiNMC electrodes.

In another embodiment, the electrode module is formed from an electrode sheet which is zig-zag folded into a Z-column. The electrode sheet is formed by at least one negative electrode sheet and at least one positive electrode sheet with the separator sheet inserted between them. Preferably, the negative electrode sheet is surrounded on both sides by the positive electrode sheet. The electrode sheet in one preferred embodiment contains one negative and two positive electrodes. The material of negative electrode as well as the material of positive electrode is pressed-in between two layers of the current collector made from a perforated metal sheet in form of e.g. metal mesh, expanded metal, perforated or porous metal foil. The inner separator sheet is pressed to the first, i.e. inner side of the positive electrode sheet adjacent to the negative electrode, and the outer separator is pressed to the other, i.e. outer side of the positive elctrode sheet. The separators may by saturaed by electrolyte during the manufacturing the electrode sheet.

The electrolyte for the accumulator according to the present technical solution is one of the common electrolytes of the type of organic solvent containing Li salts, which are known to the persons skilled in the art.

The material of the internal separator and the outer separator is preferably selected from the group consisting of a polyolefin porous film, a porous sheet of nonwoven glass or ceramic fibers based on Zr0₂, Al₂0₃, or corundum, wherein the outer separator is externally provided with a layer of thin Al film. The strength of this film is so low that after the detonator explosion, the pressure of the emergency liquid breaks through the film so that the Al film does not prevent the rapid penetration of the emergency liquid into the entire electrode module.

The current collector of the negative electrode is preferably made of copper (Cu), preferably in the form of expanded metal. The current collector of the negative electrode can be made also from lithium (Li), preferably in the form of expanded metal. The current collector of the positive electrode is preferably made of aluminum (Al), preferably in the form of expanded metal.

The method of manufacturing the lithium accumulator described above is not a subject of protection of the present invention, however, it will be briefly described as it will help to understand the design of the accumulator according to the present invention. The manufacture is in principle similar to the one described in EP 3 096 373. In the pressing and molding device, the active material of the negative electrode is pressed between the two moving parallel sheets of current collector of the negative electrode, the active material of the positive electrode is pressed between the two moving parallel sheets of the current collector of the positive electrode, wherein the inner separator is pressed onto the first side of the positive electrode sheet and the outer separator is pressed onto the other side while at the same time one positive electrode sheet is pressed to each side of the central sheet of the negative electrode, and the compressed electrode sheet is then folded into a Z-column. This manufacturing method is particularly suitable for the mass production of cylindrical accumulator cells using an electrode roll or prismatic accumulator where the Z-column is applied.

Description of the Figures

Fig. 1 shows a scheme of a rolled lithium accumulator where the electrode sheet is wound on a central container with emergency liquid and detonator and the entire coil is stored in a housing.

Fig. 2 demostrates a cross-sectional view of a compressed electrode sheet, preferably comprising a single negative electrode sheet enclosed on each side by a positive electrode sheet, wherein the individual layers of electrode materials, current collectors, and separators are visible. This diagram is only a demonstration of the qualitative composition of the electrode sheet, in the actual embodiment the thicknesses of the individual layers may not be identical.

Fig. 3 is a diagram of a device for manufacturing the electrode sheet.

Fig. 4 is a schematic representation of lithium accumulator wherein the electrode module comprises an electrode sheet folded into Z-column and wherein two containers with emergency liquid and a detonator are present in the housing of the accumulator, the containers being disposed on the free, liquid accessible sides of the column so that the emergency liquid can easily penetrate the electrodes after it is released from the containers.

Fig. 5 is a scheme of preferred embodiment of litium accumulator wherein a container filled with emergency liquid is formed by the interspace between outer solid housing of the accumulator and the inner sleeve wrapping the electrode module.

Examples of the Invention

Example 1

Figure 1 demonstrates one embodiment of a lithium accumulator comprising an electrode sheet l_ wound into a coil around a central container 2 made of glass comprising emergency liquid and detonator 3. The electrode sheet l_ is constituted by a sheet of negative electrode surrounded by a sheet of positive electrodes on both sides. The complete coil comprising the electrode sheet 1 and the emergency liquid container 2 is disposed in the housing 4, which is provided with a positive and a negative pole, and which further comprises a temperature, current and impact sensor connected to the detonator 3. The housing 4 comprises solid outer housing made of tough plastic and can also comprise inner housing made of flexible plastic or thermoplastics (not shown).

Figure 2 is a schematic cross-sectional view of the compressed electrode sheet l_ where the individual layers of material being visible (however, the thickness of the layers in the actual embodiment may not be identical). The material of negative electrode 5 is a film made of the metall lithium (Li) which is pressed between two negative electrode current collectors 6 made of copper (Cu) expanded metal. The material of positive electrode 8, the composite of V₂0₅and graphene, is pressed between two positive electrode current collectors 9 made of aluminum (Al) expanded metal. On the first, i.e. inner side of the positive electrode sheet, adjacent to the negative electrode, the inner separator 7 is pressed, and on the other side, i.e. the outer side, the external separator 1Ό provided with an aluminum foil (Al) is pressed. The separators 7, 1Ό are saturated with electrolyte which is carried out during the process of manufacturing of the electrode sheet.

The current collectors 6, 9 are connected to the respective pole contacts on the housing 4. The emergency liquid is an oxidized polymerized l,l,2,3,3,3-hexafluoro-l-propene of formula CF₃-0-[CF(CF₃)-CF-0]_x-(C₂-0)_y-CF₃ (x=l0-50, y=l0-50), available under the name FOMBLIN (Solvay).

In the case of an emergency, indicated by, for example, raising the temperature above a safe level, the temperature sensor activates the detonator 3 which breaks the container 2 with the emergency liquid that floods the electrodes of the electrode sheet l_ and displaces the electrolyte. The standard electronics simultaneously disconnect the electric circuit of the accumulator. This will prevent the accumulator from flashing or exploding.

Figure 3 is a diagram of an apparatus for manufacturing the lithium accumulator according to the present invnetion, one embodiment of which is shown in Figure 1. In the illustrated pressing and molding device, the active material of negative electrode 5 is pressed between two parallely moving sheets of negative electrode current collectors 6, the active material of the positive electrode 8 is pressed between two parallely moving sheets of positive electrode collectors 9, wherein the inner separator 7 being pressed onto the first side of the positive electrode sheet and the outer separator 1Ό is pressed onto the other side, while at the same time one positive electrode sheet is pressed to the central negative electrode sheet on each side thereof, and the compressed electrode sheet 1 is folded into the electrode collumn.

Example 2

In this embodiment the accumulator is nearly the same as in Example 1, however, central container 2 comprising the emergency liquid is made from LDPE with melting temperature 105 °C - l lO °C and does not contain any detonator 3. Under emergency situation characteized by increasing temperature above 110 °C, the container 2 will melt and the emergency liquid will flood the electrodes.

Example 3

A scheme of a preferred embodiment of the lithium accumulator comprising the electrode module comprising the electrode sheet 1 folded into Z-column is shown in Figure 4. The safety system comprising two emergency liquid containers 2 and detonators 3, is together with the electrode module housed in a solid housing 4 having a positive and negative pole contact and further comprising the inner flexible sleeve 11 made of resilient plastic and the expansion space 12. The expansion space can be filled with pressurized nitrogen gas which facilites spreading of the emergency liquid and lowers oxygen concentration in the surrounding of the electrodes under the emergency situation. The housing 4 is layed out from the inside by the resilient material 13. The safety system further comprises safety electronic module that is connected to the detonator 3 and includes a temperature, current and impact sensors.

The emergency liquid is an oxidized polymerized l,l,2,3,3,3-hexafluoro-l-propene of formula CF₃-0-[CF(CF₃)-CF-0]_x-(C₂-0)_y-CF₃ (x=l0-50, y=l0-50), available under the name FOMBLIN (Solvay).

In the case of an emergency, indicated by, for example, raising the temperature above a safe level, the temperature sensor activates the detonators 3 which break the containers 2 with the emergency liquid that floods the electrodes of the electrode sheet 1 and displaces the electrolyte into the inner sleeve 1T that may expand and/or into expansion spece 12. The standard electronics simultaneously disconnect the electric circuit of the accumulator. This will prevent the accumulator from flashing or exploding.

Example 4

In this embodiment, the accumulator is similar to the accumulator of Example 3 with a few differencies. The containers 2 for emergency liquid are made from LDPE with melting temperature 105 °C - 110 °C and no detonators 3 are present. Under emergency situation characteized by increasing temperature above 110 °C, the containers 2 will melt and the emergency liquid will flood the electrodes.

Example 5

In this embodiment, schematically demonstrated in Figure 5, the accumulator is similar to the accumulator of Example 3, however, there are no individual containers 2 and no detonators 3 like those shown in Figure 4. The electrode module is enclosed by the inner sleeve 1T made from LDPE with melting temperature l05 °C - H0 °C and the container 2 comprising emergency liquid is formed by the space between the outer solid housing 4 of the accumulator and the inner sleeve Ll. Under emergency situation characteized by increasing temperature above 110 °C, the sleeve l_l_ will melt and the emergency liquid will flood immediately the electrodes.

List of the reference numerals

1 ... electrode sheet

2 ... container comprising emergency liquid

3 ... detonator

4 ... outer solid housing

5 ... negative electrode

6 ... negative electrode current collector

1 ... inner separator

8 ... positive electrode

9 ... positive electrode current collector

10 ... outer separator

11 ... inner sleeve

12 ... expansion space

13 ... resilient material

Claims

1. A lithium accumulator comprising an electrode module comprising at least one negative electrode and at least one positive electrode, wherein the electrodes are separated by a separator saturated by an electrolyte, enclosed in a housing (4), characterized in that said accumulator comprises at least one container (2) located within the housing (4), the container (2) comprises an emergency liquid to be released in the event of an emergency situation and flooded electrodes, wherein the emergency liquid is an inert vacuum oil.

2. The lithium accumulator according to claim 1, characterized in that the inert vaccum oil is perfluoroalkylpolyether of formula F-[CF(CF₃)-CF₂-0]_n-CF₂CF₃ (n = 20-30).

3. The lithium accumulator according to claim 1, characterized in that the inert vaccum oil is oxidized polymerized l,l,2,3,3,3-hexafluoro-l-propene of formula CF₃-0-[CF(CF₃)- CF₂-0]_x-(CF₂-0)_y-CF₃ (x = 10-50, y = 10-50).

4. The lithium accumulator according to any one of claims 1 to 3, characterized in that the emergency liquid container (2) is made from glass, ceramic or plastic and comprises a detonator (3) for breaking the container (2).

5. The lithium accumulator according to any one of claims 1 to 3, characterized in that the container (2) for emergency liquid is made from thermoplastic material with melting temperature in the range of 100 °C - 130 °C.

6. The lithium accumulator according to claim 5, characterized in that the thermoplastic material is low density polyether, high density polyether, polyvinylchlorid, polystyren, styren or a mixture thereof.

7. The lithium accumulator according to any one of claims 1 to 4, characterized in that it comprises inside tho housing (4) the inner sleeve (11) enclosing the elecrode module, the inner sleeve (11) is made from elastic material or from thermoplastic material with melting temperature in the range of 100 °C - 130 °C.

8. The lithium accumulator according to claim 7, characterized in that the inner sleeve (11) is made from thermoplastic material selected from low density polyether, high density polyether, polyvinylchlorid, polystyren, styren or a mixture thereof.

9. The lithium accumulator cell according to claim 7 or 8, characterized in that the container (2) comprising the emergency liquid is formed by a space between the outer housing (4) and the inner sleeve (11).

10. The lithium accumulator cell according to any one of the previous claims, characterized in that the material of negative electrode (5) is metal Li and the material of positive electrode (8) is V₂O₅ or a mixture of V₂O₅ and graphene.

11. The lithium accumulator cell according to any one of the previous claims, characterized in that the electrode module comprises an electrode sheet (1) comprising negative electrode (5) sheet and two positive electrode (8) sheets which are compressed together, wherein the negative electrode (5) material is pressed between two negative electrode collectors (6), the positive electrode (8) material is pressed between two positive electrode current collectors (9), and an internal separator (7) is pressed onto the inner side of the positive electrode (8) sheet adjacent to the negative electrode (5), and an outer separator (10) is pressed onto the outer side of the positive electrode (8) sheet, wherein the separators (7, 10) are saturated by the electrolyte and the current collectors (6, 9) are connected to the respective poles on the cell housing (4), and wherein the electrode sheet (1) is Z-foled into a column.

12. The lithium accumulator according to any one of the previous claims, characterized in that the material of the inner separator (7) and the outer separator (10) is a polyolefin porous film or a porous layer of nonwoven glass or ceramic fibers, and the outer separator (10) comprises aluminium foil on one side.

13. The lithium accumulator according to claim 7 to 12, characterized in that between outer housing (4) and inner sleeve (11) is additional expansion space (12).