Patent Application
20110274949
Priority application DE 10 2009 005 498.7 is fully incorporated by reference into the present application.
The present invention relates to a galvanic cell for a battery. The invention is described in connection with lithium-ion batteries for supplying motor vehicle drives. It is pointed out that the invention can also find use independently of the chemistry, the design of the galvanic cell or independently of the nature of the supplied drive.
Batteries with a plurality of galvanic cells for supplying motor vehicle drives are known from the prior art. During the operation of such a battery, irreversible chemical reactions also occur in the galvanic cells. These irreversible reactions lead to a reduced charging capacity of the galvanic cells.
The problem underlying the invention is to obtain the charging capacity of the galvanic cells of a battery over a greater number of charging cycles. According to the invention, this is achieved by the subject-matters of the independent claims. Preferred developments of the invention are the subject-matter of the sub-claims.
A galvanic cell according to the invention with, in particular, a substantially prismatic or cylindrical shape comprises an electrode stack. In addition, the galvanic cell comprises at least one current conductor which is connected to the electrode stack. In addition, the galvanic cell comprises a sheathing that at least partially surrounds the electrode stack.
The at least one current conductor extends partially out of the sheathing. The sheathing comprises at least one first shaped part and one second shaped part. One shaped part has a higher thermal conductivity than the other shaped parts. The shaped parts are provided to at least partially surround the electrode stack.
In the present case, a galvanic cell is understood to mean a device which is also used for the delivery of electrical energy. The galvanic cell stores the energy in chemical form. Before delivery of an electric current, the chemical energy is converted into electrical energy. The galvanic cell is potentially also suitable for absorbing electrical energy, converting it into chemical energy and storing it. One then speaks of a rechargeable galvanic cell. The conversion of electrical into chemical energy or vice versa is bound up with losses and is accompanied by irreversible chemical reactions. The effect of the irreversible chemical reactions is that regions of the galvanic cell are no longer available for energy storage and energy conversion. The storage capacity or charging capacity of the galvanic cell thus diminishes with an increasing number of discharging and charging processes or charging cycles. The irreversible chemical reactions also increase with an increasing operating temperature of a galvanic cell. The shape of a galvanic cell can be selected depending on the available space at the place of use. The galvanic cell is preferably substantially cylindrical or prismatic.
In the present case, an electrode stack is understood to mean the arrangement of at least two electrodes and an electrolyte arranged between the latter. The electrolyte can be taken up in part by a separator. The separator then separates the electrodes. The electrode stack is also used for the storage of chemical energy and for its conversion into electrical energy. In the case of a rechargeable galvanic cell, the electrode stack is also capable of converting electrical energy into chemical energy. For example, the electrodes are constituted plate-shaped or film-like. The electrode stack can be coiled round and can have a substantially cylindrical shape. It is then more usual to speak of an electrode coil. In the following, the term electrode stack is also used for electrode coil. The electrode stack can comprise lithium or another alkali metal also in ionic form.
In the present case, a current conductor is understood to mean a device which also enables the flow of electrons from an electrode in the direction of an electrical consumer. The current conductor also acts in the opposite current direction. A current conductor is connected electrically to an electrode or an active electrode earth of the electrode stack and also to a power lead. The shape of a current conductor is adapted to the shape of the galvanic cell or the electrode stack. A current conductor is preferably constituted plate-shaped or film-like. Each electrode of the electrode stack preferably comprises its own current conductor or electrodes of like polarity are connected to a common current conductor.
In the present case, the sheathing is understood to mean a device which also hinders the exit of chemicals from the electrode stack into the surroundings. Furthermore, the sheathing can protect the chemical components of the electrode stack against undesired interaction with the surroundings. For example, the sheathing protects the electrode stack against the admission of water or water vapour from the surroundings. The sheathing can be constituted film-like. The sheathing should impair the passage of thermal energy as little as possible. In the present case, the sheathing comprises at least two shaped parts. The shaped parts preferably fit snugly at least partially with an electrode stack.
In the present case, a shaped part is understood to mean a solid body which is adapted to the shape of the electrode stack. Depending on the circumstances, a shaped part does not acquire its shape until the interaction with another shaped part or the electrode stack. In the case of a parallelepiped-shaped electrode stack, the shaped parts can be cut to shape so as to be substantially rectangular. Some dimensions of the shaped part are preferably selected larger than certain dimensions of the electrode stack. When two shaped parts are placed around the electrode stack, the shaped parts project partially beyond the electrode stack and partially form a projecting edge. An edge region of one shaped part preferably makes contact with an edge region of another shaped part, preferably in a two-dimensionally extending manner. One shaped part is constituted, for example, as a flat plate, whereas another shaped part fits snugly with the first shaped part around the electrode stack.
One shaped part for an electrode coil is constituted preferably cylindrical, the curvature of at least one shaped partshaped part of a cylindrical sheathing being adapted to the radius of an electrode coil.
One shaped partshaped part has a higher thermal conductivity than the other shaped partshaped parts and partially makes contact with the electrode stack in a heat-conducting manner. Depending on the temperature difference between the shaped partshaped part and the electrode stack, thermal energy is transferred from the electrode stack or into this electrode stack.
In the present case, surround is understood to mean that one shaped partshaped part can be brought into contact in sections with a second shaped partshaped part. The electrode stack thereby lies between the shaped partshaped parts concerned. The at least two shaped partshaped parts make two-dimensionally extending contact with one another in sections, preferably at least along a limiting edge or an edge region of a shaped partshaped part concerned.
In order to supply a motor vehicle drive, high electric currents are withdrawn from time to time from the battery and can lead to marked heating of the galvanic cells of a battery. With increasing temperature, irreversible chemical reactions also increase in a galvanic cell. According to the invention, the sheathing of the galvanic cell is constituted by a shaped partshaped part which is characterised by a distinctly higher thermal conductivity than the other parts of the sheathing. The thermal resistance can thus be reduced and the heat flow into the electrode stack or out of the electrode stack can be increased. A heat output in a galvanic cell with a smaller temperature difference can thus be carried away.
With the limitation of the operating temperature of a galvanic cell, irreversible chemical reactions are reduced, the charging capacities of the galvanic cells are retained over a large number of charging cycles and the underlying problem is solved.
Preferred embodiments of the invention are described below.
To advantage, at least two shaped partshaped parts of the sheathing are provided, to be connected to one another. The connection takes place, for example, in a friction-locked or preferably firmly bonded manner. Depending on the materials of the different shaped partshaped parts, the latter are connected to one another, for example, by gluing or a welding process. In particular, ultrasonic welding can be used to connect a metal shaped partshaped part with a thermoplastic shaped partshaped part. A preliminary treatment or activation of at least one of the surfaces of an involved shaped partshaped part may be useful here. A friction-locked or firmly bonded connection connects the shaped partshaped parts in such a way that a peripheral strip-shaped connection preferably seals the space between the shaped partshaped parts with respect to the surroundings. In order to improve the adhesion, inserted strips can also be used, for example a sealing strips. At least two shaped partshaped parts are preferably connected to one another, particularly in a firmly bonded manner, in a first connection region. This first connection region preferably runs along an edge region of an involved shaped partshaped part. The first connection region is constituted strip-shaped. It is not necessary for the first connection region to run around completely along the limiting edges of the shaped partshaped part. Before the connection of the shaped partshaped parts concerned, other insertions parts can be disposed in such a way that the latter are also connected with the shaped partshaped parts in a friction-locked or firmly bonded manner. In particular, the current conductors are inserted in such a way that the latter extend partially out of the sheathing. In the regions of the current conductors, the sheathing is thus also gas-tight with respect to the surroundings.
To advantage, at least one shaped partshaped part of the sheathing comprises a heat transfer region. This heat transfer region also serves to improve the heat transmission into the electrode stack or out of the latter. A first temperature-regulating medium preferably flows against the heat transfer region and/or the heat transfer region is in heat-conducting contact with a temperature-regulating element. A heat transfer region of a shaped partshaped part can also cover a predominant part of the surface of the shaped partshaped part. The heat transfer region can at the same time also be used to fix the galvanic cell to a temperature-regulating element, for example by screws, rivets, gluing or welding.
At least one shaped partshaped part of the sheathing is preferably constituted flexurally stiff. This shaped partshaped part can provide support for the electrode stack, protect the electrode stack against mechanical damage or be used for the mechanical connection of the galvanic cell with a receiving device. A flexurally stiff shaped partshaped part is preferably constituted as a metal plate or a sheet metal. The shaped partshaped part can be stiffened for example by crimping, upturned edge regions or ribs.
At least one shaped partshaped part of the sheathing is preferably constituted thin-walled. The wall thickness of a shaped partshaped part is preferably adapted to mechanical, electrical or thermal stressing. The wall thickness does not have to be uniform. A region of a thin-wall shaped partshaped part with a greater wall thickness can act as a heat sink or heat reservoir and thus contribute towards thermal energy being carried away from the electrode stack or transported into the latter. The thin-wall design of a shaped partshaped part also saves on weight and space. At least one shaped partshaped part is preferably constituted as a film, particularly preferably as a composite film. Metals or plastics can also be considered as materials for the composite film.
At least one shaped partshaped part of the sheathing preferably comprises a coating at least in sections. This coating is also used for adaptation to stresses to which the shaped partshaped part is subjected. For example, the coating is used for electrical insulation, for protecting the shaped partshaped part against the chemicals of the galvanic cell, for improving adhesion for an adhesive joint, for improving the thermal conductivity or for protection against damaging effects from the surroundings. A coating can produce a chemical activation of the surface of the shaped partshaped part. A coating is preferably made from a material which differs from the material of the shaped partshaped part. The at least one shaped partshaped part can also comprise a plurality of different coatings, which can also be disposed at different places on the shaped partshaped part. If a shaped partshaped part is in electrical contact with the electrode stack, a current conductor is preferably electrically insulated with respect to this shaped partshaped part.
To advantage, at least one shaped partshaped part of the sheathing comprises a cutout, in particular a shell. With this embodiment, the shaped partshaped part also acquires an increased planar moment of inertia or flexural strength. This cutout preferably at least partially accommodates the electrode stack. This also serves to protect the electrode stack. The wall thickness of a shaped partshaped part with a cutout is preferably adapted to the stress. A plurality of shaped partshaped parts of the sheathing can comprise cutouts, which jointly form a space for accommodating the electrode stack. One shaped partshaped part is preferably constituted as a deep-drawn or cold-extruded sheet metal. One shaped partshaped part is preferably constituted as a deep-drawn plastic sheet or a plastic film. A shaped partshaped part of the sheathing with a cutout additionally comprises at least a first connection region, which is provided for the connection with another shaped partshaped part.
In the case of a cylindrical galvanic cell or an electrode coil, at least one shaped partshaped part is preferably constituted shell-shaped. The curvature of the shell-shaped shaped partshaped part is adapted to the radius of the electrode coil.
To advantage, at least one shaped partshaped part comprises a second connection region. The second connection region is also used for fixing the galvanic cell, for example in a housing, in a frame or on a base plate. A second connection region is preferably constituted such that the connection of the shaped partshaped part concerned with another body takes place only in a predetermined manner.
For example, a second connection region has a geometrical shape which corresponds to a region of another body.
A connection between the shaped partshaped part and the other body only in a predetermined manner can preferably be achieved by means of an arrangement of shaped elements, for example holes and pegs. The arrangement of through-holes or threads can also permit a connection only in a predetermined manner. A second connection region is preferably spatially separated from a first connection region. At least one shaped partshaped part of the sheathing preferably comprises a plurality of separated second connection regions. The connection of the shaped partshaped part with another body takes place, for example, by means of rivets, screws, welding or gluing. A second connection region of a shaped partshaped part and a heat transfer region of said shaped partshaped part preferably coincide. In these regions, the shaped partshaped part is connected, for example, to a temperature-regulating element, a frame or to a base plate of the battery housing.
To advantage, at least two galvanic cells are grouped to form a battery. The at least two galvanic cells are preferably arranged parallel to one another. Prismatic or parallelepiped-shaped cells are preferably brought into contact with one another in a two-dimensionally extending manner and can form a substantially parallelepiped-shaped pack.
Cylindrical cells are preferably disposed in such a way that their longitudinal or symmetrical axes run parallel or coincide. The sheathing for the electrode coil is preferably constituted cylindrical, the curvature of at least one shaped partshaped part of a cylindrical sheathing being adapted to the radius of an electrode coil.
At least one temperature-regulating element is also assigned to the battery. The temperature-regulating element has a predetermined temperature, which may be variable over time. The temperature of the temperature-regulating element is preferably selected depending on the temperature of the electrode stack of a galvanic cell. A predetermined temperature gradient causes a heat flow into this electrode stack or out of this electrode stack. The temperature-regulating element exchanges thermal energy with the electrode stack via at least one shaped partshaped part or its heat transfer region, which is in contact with the temperature-regulating element. The existing galvanic cells can also be connected to the temperature-regulating element, in particular in a friction-locked or firmly bonded manner, via a second connection region.
To advantage, the temperature-regulating element comprises at least a first channel also for the adjustment of a preset temperature of the temperature-regulating element. This channel is preferably filled with a second temperature-regulating medium. A second temperature-regulating medium particularly preferably flows through this at least one channel. The flowing second temperature-regulating medium supplies thermal energy to the temperature-regulating element or removes thermal energy from the latter. The at least one temperature-regulating element is preferably in an active connection with a heat exchanger. The heat exchanger carries away thermal energy from this temperature-regulating element or supplies thermal energy to this temperature-regulating element, in particular by means of the second temperature-regulating medium. The heat exchanger and the temperature-regulating medium can also interact with the air-conditioning system of a motor vehicle. The heat exchanger can comprise an electric heating unit.
To advantage, a battery with at least two galvanic cells is operated in such a way that a first temperature-regulating medium flows against at least one shaped partshaped part of a galvanic cell. For example, ambient air or a coolant of the air-conditioning system of the motor vehicle is used as the first temperature-regulating medium. The first temperature-regulating medium can have a higher or lower temperature than the at least one shaped partshaped part, its heat transfer region, or than an electrode stack.
To advantage, a galvanic cell according to the invention is produced in such a way that at least two shaped partshaped parts of the sheathing are first placed together around an electrode stack. The current conductors of the galvanic cell can thereby be inserted. The two shaped partshaped parts are then connected to one another, especially in a firmly bonded manner, so that an, in particular, peripheral connection of at least two shaped parts is produced. A gas-tight sheathing around the electrode stack is thus preferably produced.
At least one shaped part is then transferred into a deformed state by bending, especially by upturning at least one edge region of the shaped part. The first connection region is preferably at least partially bent. A dimension of the at least one shaped part can thereby be reduced. To advantage, the upturned regions of the shaped part produce an additional mechanical protection of the electrode stack. To advantage, an upturned edge region increases the planar moment of inertia of the shaped part concerned.
Further advantages, features and possible applications of the present invention emerge from the following description in connection with the figures. In the figures:
At least one electrode of the galvanic cell, particularly preferably at least one cathode, comprises a compound with the formula LiMPO4, wherein M is at least one transition metal cation of the first row of the periodic table. The transition metal cation is preferably selected from the group comprising Mn, Fe, Ni and Ti or a combination of these elements. The compound preferably has an olivine structure, preferably a higher-order olivine.
In a further embodiment, at least one electrode of the galvanic cell, particularly preferably at least one cathode, preferably comprises a lithium manganate, preferably LiMn2O4 of the spinel type, a lithium cobaltate, preferably LiCoO2, or a lithium nickelate, preferably LiNiO2, or a mixture of two or three of these oxides, or a lithium mixed oxide which contains manganese, cobalt and nickel.
The negative and the positive electrode of a galvanic cell are preferably separated from one another by one or more separators. Such separator materials can for example also comprise porous inorganic materials, which are constituted such that a substance transport can take place through the separator normal to the separator layer, whereas a substance transport parallel to the separator layer is hindered or even prevented.
Particularly preferred are separator materials which comprise a porous inorganic material which is interspersed with particles or comprises such particles at least at its surface, which melt when a temperature threshold is reached or exceeded and which at least locally reduce the size of or close pores of the separator layer. Such particles can preferably be made from a material selected from a group of materials which comprises polymers or mixtures of polymers, waxes or mixtures of these materials.
An embodiment of the invention is particularly preferred wherein the separator layer is constituted in such a way that its pores are filled due to a capillary effect with the mobile component which participates in the chemical reaction as an educt, so that only a relatively small part of the total quantity of the mobile component present in the galvanic cell is located outside the pores of the separator layer. In this connection, the electrolyte present in the galvanic cell or one of its chemical components or a mixture of such components is a particularly preferred educt which, according to a particularly preferred example of embodiment of the invention, wets or saturates the whole porous separator layer as far as possible, but which is not to be found or to be found only in a negligible or relatively small quantity outside the separator layer. In the production of the galvanic cell, such an arrangement can be obtained by the fact that the porous separator is saturated with the electrolyte present in the galvanic cell or with another educt of a suitably selected chemical reaction, so that this educt is subsequently present for the most part only in the separator.
If, on account of a chemical reaction, only a local increase in pressure possibly occurs initially due to the formation of a gas bubble or due to local heating, this educt cannot continue to flow out of other regions into the reaction region. Insofar as and as long as it can still continue to flow, the availability of this educt at other points is correspondingly reduced. The reaction finally comes to a stop or at least remains limited to a preferably small region.
According to the invention, use is preferably made of a separator which is not electron-conducting or only poorly so, and which comprises an at least partially substance-permeable carrier. The carrier is preferably coated on at least one side with an inorganic material. As an at least partially substance-permeable carrier, use is preferably made of an organic material which is preferably constituted as a non-woven fabric. The organic material, which preferably comprises a polymer and particularly preferably a polyethylene terephthalate (PET), is coated with an inorganic, preferably ion-conducting material, which in addition is preferably ion-conducting in a temperature range from −40° C. to 200° C. The inorganic material preferably comprises at least one compound from the group of oxides, phosphates, sulphates, titanates, silicates, aluminosilicates with at least one of the elements Zr, Al, Li, particularly preferably zirconium oxide. The inorganic, ion-conducting material preferably comprises particles with a maximum diameter of less than 100 nm.
Such a separator is marketed, for example, under the brand name “Separion” by Evonik AG in Germany.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 005 498.7 | Jan 2009 | DE | national |
| 09 012 869.5 | Oct 2009 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP10/00256 | 1/18/2010 | WO | 00 | 7/19/2011 |
