DE102007023896A1 - Electrochemical energy storage and method for its operation - Google Patents

Abstract

The invention relates to an electrochemical energy store (1), at least one cell (3) having at least one cathode (7), an anode (5) and an electrolyte (17), which conducts current from the anode (5) to the cathode (7). allows. The electrochemical energy store (1) further comprises at least two storage containers (11) for receiving in each case an electrolyte or at least one storage container (11) for receiving at least one constituent of an electrolyte (17), the storage containers (11) receiving different electrolytes (17). or different components of the electrolyte are provided for different operating conditions. The invention further relates to a method for operating an electrochemical energy store (1), wherein, depending on the operating state, at least one constituent of the electrolyte (17) is removed from the cell (3), added or exchanged into the cell (3).

Description

State of the art

The The invention relates to an electrochemical energy store according to the preamble of claim 1. Furthermore, the invention relates to a method for the operation of an electrochemical energy store.

Around To achieve high energy densities, are currently lithium-ion batteries used. These have energy densities up to high energy batteries approximately 200 Ah / kg. As high-performance batteries energy densities up to 100 Ah / kg reached.

Of the Temperature range in which lithium-ion batteries are effective and working safely is limited. This is generally in the range between -10 ° C and 50 ° C. This Temperature range, however, is especially for applications in electrical and Hybrid vehicles are not enough. A vehicle must also be at low Temperatures, for example, after long periods in winter or at high temperatures, for example in the summer after long periods of use on heated asphalt, safe and reliable operation. Out For this reason, it is desired To provide accumulators that are safe in a temperature range of -30 ° C to + 80 ° C and reliable can be operated.

Disclosure of the invention

Advantages of the invention

One formed according to the invention electrochemical energy storage comprises at least one cell with at least one cathode, an anode and an electrolyte, which allows a flow of current from the anode to the cathode. The electrochemical energy store further comprises at least two pantries for receiving in each case an electrolyte or at least one storage container for containing a component of an electrolyte, wherein the storage chambers for holding different electrolytes or different basic components of the electrolyte for different operating states are provided.

There for the Temperature limit, within which an electrochemical energy storage be operated can, in essence, the electrolyte is responsible, in dependence from the formulation of the electrolyte of the electrochemical energy storage each operated in certain temperature ranges. As soon as the temperature outside the Limits for is the respective electrolyte, the performance of the electrochemical decreases Energy storage significantly and it can also be harmful Side reactions come, which increase the life of the electrochemical Shorten energy storage. By the inventive solution, in the at least two reservoir It is intended to accommodate each of an electrolyte easily possible, the electrolyte in dependence from the operating temperature of the electrochemical energy store use. So it is on the one hand possible if the reservoir each contain an electrolyte, first in the energy storage Pumped electrolyte contained in one of the storage tanks and subsequently the energy store with another electrolyte from a second reservoir to fill. If the reservoir contains only a part of the electrolyte, then this component becomes according to the temperature at which the electrochemical energy storage is operated, added or removed.

By the inventively designed electrochemical Energy storage leaves this always with the for the current temperature conditions optimal electrolyte mixture operate. So it is also possible, for example, the electrochemical Energy storage within the required by the automotive industry Temperature range from -30 ° C to + 80 ° C with the best possible Power to operate. harmful Side reactions, for example, when operating the energy storage outside the for the electrolyte temperatures may occur minimized. This will also the life of the electrochemical energy storage elevated. additionally Safety-critical situations, such as the so-called "Thermal Runaway "battery, which can lead to fires or explosions, for example, unlikely. That means, the battery is due to the temperature-matched electrolyte composition safer.

Around pump the electrolyte from the energy store into a storage container to be able to from a storage container to promote in the energy store, are the reservoirs each preferably over a pump connected to the cell.

In order that the electrolyte contained in the reservoir or the constituents of the electrolyte contained in the reservoir can not flow into the cells, if this is undesirable, the reservoirs are connected in a preferred embodiment via a distribution and closing device with the cells. The distribution and closing device comprises, for example, valves with which the storage containers can be closed with respect to the cell. Alternatively, it is also possible for the distribution and closing device to comprise, for example, selective membranes with which the storage containers can be closed relative to the cell. In particular, when the reservoir ent components of the electrolyte ent hold, the distribution and closing device preferably comprises selective membranes with which the reservoir can be closed. The membranes are selected so that they each pass only the component contained in the reservoir. In this way, it is also possible that the component can be recycled from the electrolyte back into the reservoir when the ambient conditions so require. Suitable membranes with which the reservoir can be closed are, for example, piezomembranes.

The Distribution and closing device over which the reservoir connected to the cell is preferably to a control system connected. By detecting the temperature can be determined with the help of Control system of the reservoir be released, the the for the appropriate ambient conditions suitable electrolyte or contains the component of the electrolyte to be supplied got to. That way, you can always get the right electrolyte or to realize the right composition in the cell. Corresponding can be over the Control system before feeding one for the ambient conditions match the electrolyte in the cell remove the electrolyte. Alternatively, it is also possible to not needed to be removed from the cell again.

Around a change of the electrolyte during the to allow ongoing operation of the electrochemical energy store, For example, when the electrochemical energy storage in a Motor vehicle is used while a ride with a big one Performance appraisal, as is the case for example uphill, or after a longer one Service life in winter, with a cryogenic electrolyte against a Mix for higher Temperatures must be replaced, adding, removing or replacing the at least one constituent of the electrolyte while of the operation in succession for individual cells. advantage this approach is that there is no significant performance penalty not for that pumped out the entire electrolyte for a short time and then by a new electrolyte is exchanged.

Of the Operating state of the electrochemical energy storage is preferably by the ambient temperature and the temperature in the cell of the determined electrochemical energy storage.

In a particularly preferred embodiment the electrochemical energy store is a lithium-ion accumulator.

Especially preferably as an electrolyte for the use at high temperatures, d. H. at temperatures in the range of 5 up to 80 ° C, is an electrolyte in which LiBOB (lithium bisoxalatoborate) in ethylene carbonate solved is and in addition a fire retardant, for example triethyl phosphate.

For use at low temperatures, ie at temperatures in the range of -40 to 10 ° C, the usually used as a solvent ethylene carbonate is the limiting factor. The ethylene carbonate is necessary in particular for the construction of the protective layer on the electrodes. However, if the protective layer is intact, the ethylene carbonate may be substituted for operation at low temperatures. A solvent that can be used at lower temperatures requires a lower melting and boiling point. Suitable solvents are, for example, methyl formate, diethyl carbonate, ethyl acetate, methylburyrate, ethyl butyrate and many esters, for example tetrahydrofuran and some of its derivatives. As a salt for the electrolyte is suitable at lower temperatures, for example, the currently commonly used LiPF. ₆ Another, possibly better suitable conducting salt is also LiBF ₄ .

Preferred as the electrolyte at low temperatures is, for example, LiPF ₆ or LiBF ₄ dissolved in methyl formate or diethyl carbonate. In addition, the electrolyte may also contain a small proportion of ethylene carbonate. The proportion of ethylene carbonate is preferably in the range from 0 to 30% by volume, in particular in the range from 0 to 10% by volume.

Brief description of the drawings

embodiments The invention is illustrated in the drawings and in the following Description closer explained.

It demonstrate:

1 a schematic representation of an energy storage device according to the invention in a first embodiment,

2 a schematic representation of an energy storage device according to the invention in a second embodiment.

Embodiments of the invention

In 1 schematically a inventively designed electrochemical energy storage is shown in a first embodiment.

An electrochemical energy storage 1 includes several cells 3 , Every cell 3 represents a galvanic unit in which electricity is generated by an electrochemical reaction. This includes each cell 3 at least one anode 5 as well as mindes at least one cathode 7 , The anode 5 and the cathode 7 are through a separator 9 separated from each other.

Furthermore, each cell contains 3 an electrolyte, which is not shown here. According to the invention, the electrolyte is liquid. In general, the electrolyte comprises a solvent having a high electrical constant to dissolve salts and as low a viscosity as possible to facilitate ion transport and at least one salt dissociated in the solvent.

If the electrochemical energy storage is a lithium-ion battery, so is the anode 5 for example, an anode common for lithium-ion batteries, as known to those skilled in the art. A suitable anode 5 contains, for example, a carbon-based intercalation compound, an alloy of lithium with tin and / or silicon, optionally also in a carbon matrix, metallic lithium or lithium titanate. The cathode is a common for lithium-ion batteries cathode, as is known in the art. Suitable materials for the cathode are, for example, lithium cobalt oxide, lithium nickel oxide, lithium cobalt nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium iron oxide, lithium manganese dioxide; Lithium manganese oxide and mixed oxides of lithium manganese oxide; Lithium iron phosphate, lithium manganese phosphate, lithium cobalt phosphate and lithium nickel phosphate. The preferred cathode material used is lithium cobalt oxide, lithium nickel oxide, lithium cobalt nickel oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, lithium manganese oxide, lithium iron phosphate and lithium manganese phosphate.

As a separator 9 Likewise suitable is any separator known to the person skilled in the art, as used in lithium-ion accumulators. The separator 9 is usually a semi-permeable membrane which is permeable to lithium ions.

When Material for the separator may be, for example, polypropylene, polyethylene, fluorinated hydrocarbons, ceramic-coated hydrocarbons, Fiberglass, materials based on cellulose or mixtures of aforementioned materials. Preferred materials for the separator are polyethylene and polypropylene.

According to the invention, the electrochemical energy store comprises 1 reservoir 11 for receiving in each case an electrolyte or components of an electrolyte. In the embodiment illustrated here, the electrochemical energy store comprises 1 three storage tanks 11 , If the reservoir 11 are provided to each receive an electrolyte, so according to the invention at least two reservoir 11 required, each of which can accommodate a different electrolyte. If the reservoir 11 It may be sufficient if only one storage container is provided for receiving only one or more constituents of the electrolyte 11 is provided.

The reservoir 11 are each connected to each cell via a connection containing at least one closure element 3 of the electrochemical energy store 1 connected. The closing elements are designed so that the connection to each cell 3 with the reservoir 11 can be closed or released separately, so that the cells 3 each independently filled or emptied. The closing elements and the connections from the storage containers 11 to the individual cells 3 are in the embodiment shown here in a distribution and closing device 13 ,

The reservoir 11 each contain different electrolytes, which under different operating conditions of the electrochemical energy storage 1 can be used. Usually, the electrolytes become dependent on the operating temperature of the electrochemical energy store 1 and the ambient temperature selected. So it is preferable if one of the reservoir 11 contains an electrolyte that can be used at low temperatures and another reservoir 11 contains an electrolyte that can be used at high temperatures.

Alternatively, it is also possible that the reservoir 11 contains a component of the electrolyte added to ensure safe operation of the electrochemical energy store 1 to allow at certain temperatures, said component rolyten the Elek stabilized in the predetermined temperature range. If the operating conditions take different values, for example, the temperature rises, it is possible to remove this component again from the electrolyte and into the reservoir 11 due. To make this possible, it is preferred if the distribution and closing device 13 includes a closure member comprising a selective membrane which is permeable to the ingredient to be added to or removed from the electrolyte and not to the remaining constituents of the electrolyte.

If the reservoir 11 each contain an electrolyte for different operating conditions, it is preferred if the distribution and closing device 13 further comprising a pump element with which the electrolyte from the cells 3 in an empty storage container 11 pumped out can be before another electrolyte in the cells 3 is supplied.

The limiting factor for the use of the electrolyte at high temperatures is the commonly used conductive salt LiPF ₆ . To the electrochemical energy storage 1 At high temperatures, it is therefore preferred that the conductive salt LiPF _{6 is} replaced by a salt, which also at high temperatures safe operation of the electrochemical energy storage 1 allowed. A suitable conductive salt is, for example, LiBOB (lithium bisoxalatoborate) or LiBF ₄ . However, it is preferred if only one salt is used to avoid mixed salts. In addition to the change of the conductive salt, it is also possible to exchange the solvent. Usually, the solvent used is ethylene carbonate. Since this has a high flash point, the use of ethylene carbonate at high temperatures is no risk. To the reliability of the electrochemical energy storage 1 When operating at high temperatures to increase it is also possible to use flame retardants, due to their sometimes very high boiling point or melting point at the temperatures at which electrochemical energy storage 1 Usually used, can not be used. Such flame retardants are, for example, hexamethoxycyclophosphazenes, alkyl phosphates, for example trimethyl phosphate, ethylene ethyl phosphate, methyl nonafluorobutyl ether. By using the flame retardants, the reliability of the electrochemical energy storage, especially when operating at higher temperatures, can be significantly improved. In addition, some of the flame retardants, for example, alkyl phosphates, for example, ethylene ethyl phosphate, improve a protective layer that forms on the electrodes. As a result, the aging stability of the electrochemical energy storage is also 1 improved.

Especially preferably as an electrolyte for use at high temperatures, d. H. at temperatures in the range of 50 to 90 ° C is an electrolyte in which LiBOB dissolved in ethylene carbonate is, and in addition a fire retardant, for example trimethyl phosphate.

For use at low temperatures, ie at temperatures in the range from -40 to 0 ° C, the solvent used as ethylene carbonate is the limiting factor. The ethylene carbonate is necessary in particular for the construction of the protective layer on the electrodes. However, if the protective layer is intact, the ethylene carbonate may be substituted for operation at low temperatures. A solvent that can be used at lower temperatures requires a low melting and boiling point. Suitable solvents are, for example, methyl formate, diethyl carbonate, ethyl acetate, methyl butyrate, ethyl butyrate and many esters, for example tetrahydrofuran and some of its derivatives. At low temperatures, for example, the generally used LiPF ₆ is suitable as a salt for the electrolyte. Another, possibly better suitable conducting salt is also LiBF ₄ .

Preferred as the electrolyte at low temperatures is, for example, LiPF ₆ or LiBF ₄ dissolved in methyl formate or diethyl carbonate. In addition, the electrolyte may also contain a small proportion of ethylene carbonate. The proportion of ethylene carbonate is preferably in the range from 0 to 30% by volume, in particular in the range from 0 to 10% by volume.

To control the replacement of the electrolyte or the supply or removal of components of the electrolyte is the distribution and closing device 13 preferably with a control unit 15 connected. The control unit 15 controls the opening or closing of the connections from the reservoir 11 into the individual cells 3 , For this purpose, in the control unit 15 For example, the ambient temperature and the operating temperature of the electrochemical energy storage 1 supervised. Depending on the ambient temperature and the operating temperature of the electrochemical energy storage 1 is selected with which electrolyte the cells 3 operate. If a wrong electrolyte is contained in the cells, it will first get out of the cells 3 in the reservoir 11 pumped out. Subsequently, the proper for the appropriate operating conditions electrolyte from a reservoir 11 into the cells 3 pumped.

If only components of the electrolyte in the reservoir 11 are contained, depending on the operating temperature, either components of the pre storage tank 11 into the cells 3 transported or out of the cell 3 in the reservoir 11 back.

To change the electrolyte in each cell 3 also during operation, it is preferred if the electrolyte from the cells 3 is exchanged one cell at a time. That is, first of all from a first cell 3 the electrolyte in a reservoir 11 is removed and another electrolyte from another reservoir 11 into the cell 3 is supplied. Once this process is completed, the electrolyte in a second cell is replaced in the same way. Of course it is also possible to remove the electrolyte from a cell 3 to remove while another electrolyte simultaneously into another cell 3 is fed. Furthermore, it is also possible to use the electrolyte in all cells 3 to exchange at the same time.

In 2 is an inventively designed electrochemical energy storage 1 shown in a second embodiment.

The in 2 illustrated electrochemical energy storage 1 is different from that of 1 in that the reservoir 11 are not arranged on one side, but on different sides of the electrochemical energy storage 1 , When an operation of the electrochemical energy storage 1 is provided with only two different electrolytes are two reservoirs 11 sufficient. It is necessary that each reservoir 11 has a volume which is sufficient to the entire electrolyte 17 from the electrochemical energy storage 1 take. It is either possible that every cell 3 of the electrochemical energy store 1 own storage container 11 for the electrolytes 17 or it is for multiple cells 3 common reservoir 11 intended. In particular, it is preferred if the entire electrochemical energy storage 1 only one storage tank for each electrolyte 11 that has all the cells 3 fed.

To the electrolyte 17 exchange, becomes the electrolyte 17 from the cells 3 first in an empty storage container 11 pumped. This is done via the distribution and closing device 13 with which the reservoir 11 towards the cells 3 is closable. In addition, in the distribution and closing device 13 be included a pump with which the electrolyte 17 from the cells 3 in the storage container 11 pumped out or from the storage containers 11 into the cells 3 can be pumped. Once the cell 3 is emptied, that is free of electrolyte, is from a full reservoir 11 another electrolyte via the distribution and closing device 13 into the cell 3 transported. Once the anode 5 and the cathode 7 with the electrolyte 17 in contact, a current flow is possible.

However, optimum operation is only possible if the anode 5 and the cathode 7 completely of electrolytes 17 are covered.

Claims (10)

Electrochemical energy store comprising at least one cell ( 3 ) with at least one cathode ( 7 ), an anode ( 5 ) and an electrolyte ( 17 ), which conducts current from the anode ( 5 ) to the cathode ( 7 ), characterized in that the electrochemical energy store 1 at least two storage containers ( 11 ) for receiving in each case an electrolyte ( 17 ) or at least one storage container ( 11 ) for receiving at least one constituent of an electrolyte, wherein the reservoirs ( 11 ) for receiving various electrolytes ( 17 ) or various components of the electrolyte are provided for different operating conditions. Electrochemical energy store according to claim 1, characterized in that the storage containers ( 11 ) each via a pump to the cell ( 3 ) are connected. Electrochemical energy store according to claim 1 or 2, characterized in that the reservoir ( 11 ) via a distribution and closing device ( 13 ) with the cells ( 3 ) are connected. Electrochemical energy store according to claim 3, characterized in that the distribution and closing device ( 13 ) Contains valves with which the cells ( 3 ) opposite the storage containers ( 11 ) are closable. Electrochemical energy store according to claim 3, characterized in that the distribution and closing device ( 13 ) contains selective membranes, with which the reservoirs ( 11 ) opposite the cell ( 3 ) are closable. Electrochemical energy store according to one of claims 1 to 5, characterized in that the electrochemical energy store ( 1 ), a control unit ( 15 ), which involves an exchange of the electrolyte ( 17 ) or of constituents of the electrolyte. Electrochemical energy store according to one of claims 1 to 6, characterized in that the electrochemical energy store ( 1 ) is a lithium-ion battery. Method for operating an electrochemical energy store ( 1 ) according to one of claims 1 to 7, wherein, depending on the operating state, at least one constituent of the electrolyte ( 17 ) from the cell ( 3 ) is removed into the cell ( 3 ) is added or exchanged. A method according to claim 8, characterized in that in an electrochemical energy store ( 1 ) with several cells ( 3 ) adding, removing or replacing the at least one constituent of the electrolyte ( 17 ) during operation, in each case for individual cells ( 3 ) is carried out. A method according to claim 8 or 9, characterized in that the operating condition by ambient temperature and temperature in the cell ( 3 ) of the electrochemical energy store ( 1 ) is determined.