DE102008004236A1 - Energy storage and electrical system with such energy storage - Google Patents

Abstract

The invention relates to an energy store (2), in particular a lithium-ion energy store, comprising a plurality of interconnected individual cells (1), each having a negative electrode (1.1) and a positive electrode (1.2) and an electrolyte (1.3) connecting them in an ionic manner. wherein the negative electrode (1.1) is formed of such an active material that its potential to lithium is greater than 1 V, and wherein the positive electrode (1.2) is formed of such an active material that its potential to lithium is less than 4.5V ,

Description

The The invention relates to an energy store, in particular a lithium-ion energy store, comprising several interconnected single cells, each one negative electrode and a positive electrode and one of these ionic having conductive connecting electrolytes. Furthermore The invention relates to a vehicle electrical system with such energy storage.

energy storage are often used as a back-up battery and / or on-board battery used in a vehicle, in particular in a hybrid vehicle, which usually consists of a combination of different types Drives, z. B. internal combustion engine and electric motor or fuel cell and energy storage exist. In this case, the energy storage for Starting an internal combustion engine and / or for the supply of electrical Be provided for consumers in the vehicle. Also, the energy can the energy storage for acceleration processes be used of the vehicle, the internal combustion engine at a favorable Torque curve of the electric motor effectively supported so that the internal combustion engine in a load-optimized speed range can be operated and the electric motor just at low Speeds provides the necessary torque.

Of the Electric motor is in particular as a starter / generator and / or electrical Drive executed. As a starter / generator, the electric motor usually replaces the existing starter and the alternator. In one execution as an electric drive, an additional torque, d. H. an acceleration torque, to propel the vehicle of be contributed to the electric motor. As a generator allows the electric motor recuperation of braking energy and on-board power supply.

in the Generally, the energy storage during driving recharged. The energy required for this comes from the implementation of the chemical energy of the fuel the internal combustion engine and the generator or via the fuel cell.

additionally can the energy storage by energy recovery during Brakes are recharged by the possibility is created to convert the braking energy into electrical energy (also called "regenerative braking") and not as heat loss to give to the environment.

For Such hybrid vehicle and use of energy storage for a hybrid vehicle and / or for on-board network support powerful storage with appropriate energy content, such as nickel metal hydride (NiMH) batteries, lithium ion batteries or double-layer capacitors required. To the appropriate To reach voltages include the batteries a plurality of single cells, e.g. B. 100 single cells, usually connected in series with each other.

From the prior art, for example from the DE 10 2004 053 479 A1 is a high-performance lithium-polymer battery is known, which consists of several interconnected single cells, which has titanate as a negative electrode material and iron phosphates as a positive electrode material.

Problematic compared to conventional NiMH batteries with a certain overcharge tolerance is that lithium-ion energy storage in case of overload damage take, in particular, catch fire or explode.

A such overload of individual cells is in a series connection despite limited total voltage always possible if individual cells due to manufacturing tolerances, different Impedances and / or capacities in their electrochemical States diverge more and more apart.

Around To avoid this, it is known the cells of a lithium-ion energy storage to balance at regular intervals.

While in electrostatic energy storage, such as so-called double-layer capacitors, which can store much less energy than lithium-ion batteries, due to fast relaxation times a symmetrization during operation is possible in electrochemical energy storage, such as the lithium-ion battery, the symmetrization For example, in phases of rest, ie in phases in which no energy is removed from the energy storage performed. As a result, the quiescent voltages of the individual cells of the electrochemical energy store are achieved with good accuracy, wherein the states of charge are matched by a suitable electronic circuit to each other. In this case, the cell is detected with the lowest voltage in the battery string, while the remaining cells as long as power, which is converted via a resistor in thermal power, is removed until all cells are adjusted to the state of charge of the aforementioned cell. Such an electronic circuit is very expensive. In addition, the symmetrization leads to the loss of stored energy, decrease in the state of charge, load the scarf tion by heat and a significant component cost and wear and corrosion on the contacts.

Of the Invention is therefore the object of an energy storage specify which largely maintenance-free, in particular symmetrierungsfrei and can be operated safely against overloading. In addition, a maintenance-free as possible Specify electrical system.

The Task is the energy storage by the in the claim 1 specified characteristics solved. Regarding the electrical system The object is achieved by the im Claim 11 specified features solved.

advantageous Further developments of the invention are the subject of the dependent claims.

Of the Energy storage according to the invention, in particular a lithium-ion energy storage comprises several interconnected Single cells, each having a negative electrode and a positive Electrode and an ionically conductive connecting these electrolytes have, wherein the negative electrode of such an active material is formed that their potential to lithium greater 1 V, and the positive electrode of such an active material is formed, that its a potential compared to lithium of less than 4.5V.

By Such a reduced voltage having structure the respective single cells are on the surfaces of the positive and negative electrode thick film formation and thus Side reactions largely avoided. Thus, hardly any heat loss occurs one and the charging power is fully implemented, thereby the single cells largely evenly or with small differences are loaded and a balancing hardly still or less often required.

Under Potential becomes in particular the chemical potential of the respective ones Electrode opposite metallic lithium of a reference electrode understood, which consists of the energy difference of the bonding electrons during charge carrier exchange between electrons of the electrodes and the reference electrode, wherein the energy difference is a voltage difference (= Difference of potential energy) corresponds to and from the implementation the chemical energy into electrical energy results.

In One possible embodiment is the positive one Electrode designed such that it at full Lithium extraction has a stable sublattice. With others Words: The structure of the positive electrode is unchanged with complete lithium extraction. In addition, the positive Electrode with high lithium extraction with complete lithium extraction become. A resulting easily detectable impedance signal is used in particular to monitor the charging process of the Energy storage.

Prefers the charging of the energy store becomes largely overload-proof on the basis of the impedance signal executed by the corresponding individual cell Impedance signal is monitored and on reaching or exceeding a predetermined maximum limit, which is a complete loaded single cell represents this then, for example circuit technology is bridged, so that the following single cells analog until complete Charging all the individual cells of the energy storage are charged can. This is an overload of individual Single cells and a complex balancing of the energy storage safely avoided. In addition, through such an effective and safe charging without heat loss and power losses both the lifetime and a required maintenance cycle of the Energy storage significantly extended.

Preferably, the positive electrode is formed at least from a nanoscale, electrochemical active material, in particular from a two-phase active material. In this case, the positive electrode can be formed, for example, at least from a metal oxide, in particular lithium-intercalated iron phosphates LiFePO ₄ or manganese oxides LiMn ₂ O ₄ .

In contrast, the negative electrode is preferably formed at least from a nanoscale, electrochemical active material, in particular from a two-phase active material. In this case, the negative electrode can be formed, for example, at least from a metal oxide, in particular from lithium-intercalated titanates Li ₄ Ti ₅ O ₁₂ .

The positive and negative electrodes are preferably particularly thin, especially designed with a thickness in the mm or microns range. As a result, the heat losses are significantly reduced. Furthermore is through the use of two-phase materials as active materials for the electrodes a largely uniform Charging and discharging kinetics achieved in the stoichiometric range.

In a preferred embodiment, the electrolyte is a high boiling electrolyte. A high-boiling electrolyte is understood in particular to mean such an electrolyte which, by means of an additional solvent, has a higher boiling point than conventional electrolytes. For example, the electrolyte may be composed of a polymer or polymer mixture, in particular polyisobutene, polybutadiene or fluoroelastamers, such as terpolyme ren, with Leitsalzlösung from a conductive salt, in particular boron-containing conductive salt, such as lithium tetrafluoroborate, Lithiumbisoxalatoborat, lithium hexafluorophosphate and / or lithium perchlorate, and a high-boiling solvent of cyclic carbonates, such as ethylene carbonate, in particular diethylene carbonate, ethylmethyl carbonate, propylene carbonate, fluoroethylene carbonate, gamma butyrolactone, methyl acetate and or ethyl acetate. Also, the electrolyte can be formed in largely liquid form only from a high-boiling solvent, such as the above-mentioned carbonates or other materials, dissolved conductive salt of one of said materials.

ever By default, the energy store can be composed as follows: Active material approx. 15% by weight to 30% by weight, electrolyte 10% by weight up to 30% by weight and residual components, such as discharge electrodes, separator, 40 wt .-% to 75 wt .-%.

Conveniently, the single cells are connected in series with each other. Also can serially interconnected single cells in combination with parallel interconnected individual cells form an energy store.

Prefers is the energy storage in a vehicle electrical system of a vehicle, in particular a hybrid vehicle used. In this case, the invention is suitable Energy storage with the single cells described above as redundant Energy source in a vehicle electrical system and / or as an energy source for supply of consumers, in particular transient loads or temporary High current consumers in the electrical system. In addition, the energy storage as Rekuperationsspeicher for example implementation of braking energy into electrical energy. Also has such a electrochemically structured energy storage a good low temperature property on. By monitoring the charge of the energy storage cell-precise on the basis of impedance signals, the energy storage high intrinsic safety against overcharging, fire and Explosion on. In addition, a symmetrization of the individual cells is not necessary, so that the life of the energy storage significantly is extended. Preferably, the energy storage is in the electrical system as primary lithium battery or as secondary Lithium battery separately or in combination with an electric machine and / or a vehicle electrical system battery in a vehicle with or without Combustion engine used.

embodiments The invention will be explained in more detail with reference to a drawing.

The single figure shows a galvanic single cell 1 an energy store 2 , in particular a lithium-ion energy storage. Appropriately, the energy storage 2 to obtain a corresponding voltage from a plurality of individual cells connected in series or in parallel 1 educated.

The single cell 1 has a negative electrode 1.1 and a positive electrode 1.2 and one between these these ionically conductive connecting electrolytes 1.3 on. The electrodes 1.1 . 1.2 and one of several single cells 1 formed energy storage 2 whose outer electrodes (not shown in detail) are via discharge electrodes 3 . 4 with an external circuit, z. B. an electrical system 5 of a vehicle connected to the supply of electrical consumers.

In the electrodes 1.1 . 1.2 chemical redox reactions take place. The thereby released electrons are through the electrical system 5 from the negative electrode 1.1 to the positive electrode 1.2 transported and can do electrical work. At the same time are formed in a designed as a lithium-ion storage energy storage 2 via a so-called internal circuit through the electrolyte 1.3 Ions, in particular lithium ions Li ⁺ from the negative electrode 1.1 to the positive electrode 1.2 transported. The advantage of such a lithium-ion energy storage 2 lies in the high energy density, which by a corresponding number of particular serially interconnected individual cells 1 a high cell voltage is possible.

Both for the achievement of electronic and ionic conductivity are the electrodes 1.1 . 1.2 made of a suitable material. For the longest possible service life and large maintenance cycles and as symmetrical as possible operation corresponding electrode materials are provided, wherein the negative electrode 1.1 is formed from such an active material that its potential to lithium is greater than 1V. The positive electrode 1.2 is formed of such an active material that its potential to lithium is less than 4.5V.

In particular, as positive electrodes 1.2 (= Cathode) nanoscale, electrochemical active materials, especially two-phase active materials used. For example, transition metal oxides such as lithium-intercalated iron phosphates LiFePO ₄ or manganese oxides LiMn ₂ O ₄ are used. It can be added to increase the conductivity, for example, Leit- or lampblack. In particular, such a material composition is chosen that upon complete lithium extraction, the sub-grid of the positive electrode 1.2 is still stable and thus no significant change in the lattice structure is given.

As a negative electrode 1.1 Also nanoscale, electrochemical active materials, especially two-phase active materials are used. For example, the negative electrode 1.1 at least one metal oxide, in particular lithium-intercalated titanates Li ₄ Ti ₅ O ₁₂ formed. Alternatively, other materials may be used which in particular have such an open structure or layer structure that the lithium ions Li ⁺ can easily intercalate.

In addition, the active materials of the electrodes 1.1 . 1.2 with at least one binder, for. B. be added polyvinylidene fluoride.

In detail, for example, the negative electrode 1.1 composed as follows:

85 to 93% by weight of Li ₄ Ti ₅ O ₁₂
about 5 wt .-% binder
3 to 5 wt .-% Leitruß

and the positive electrode 1.2 :

80 to 85% by weight of LiFePO ₄
7 to 10 wt .-% binder
5 to 7 wt .-% Leitruß.

As lead-off electrodes 3 . 4 In particular, metal foils are applied to the electrodes 1.1 . 1.2 applied.

For the formation of the electrolyte 1.3 as a high-boiling electrolyte, it conventionally comprises a microporous membrane formed of a polymer or a polymer mixture, which exists between the electrodes 1.1 . 1.2 is arranged as a separator. In the membrane is as a conventional electrolyte material, a Leitsalzlösung of a conducting salt, especially boron-containing conductive salt, such as lithium tetrafluoroborate or Lithiumbisoxalatoborat, and a high-boiling solvent of cyclic carbonates, such as ethylene carbonate, especially diethylene carbonate or ethyl methyl carbonate, propylene carbonate, fluorine-ethylene carbonate, methyl acetate, ethyl acetate and / or Gammbutyrolacton.

Compared with conventional electrolytes, the electrolyte according to the invention is 1.3 composed of materials with a higher boiling point. As a result, conventional electrochemical side reactions and resulting heat losses are avoided, so that the entire charging power in charge of the single cell 1 is implemented.

By simply monitoring an impedance signal of the respective single cell 1 will ensure that the energy store 2 When loading is loaded cell by cell completely, so that irregularities are largely avoided and a symmetrization of the individual cells 1 hardly or rarely required. In detail, a complete loading of each individual cell 1 identified by monitoring the impedance signal to reach or exceed a predetermined limit, whereupon this single cell 1 bridges and then the next single cell 1 is loaded. Such a charging process of the energy storage 2 safely prevents overcharging and thus a critical state of the energy storage 2 ,

1

single cell

1.1

negative electrode

1.2

positive electrode

2

energy storage

3

lead-out

4

lead-out

5

board network

Li ⁺

Lithium-ion

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 102004053479 A1 [0007]

Claims (13)

Energy storage ( 2 ), in particular lithium-ion energy storage, comprising a plurality of interconnected individual cells ( 1 ), each having a negative electrode ( 1.1 ) and a positive electrode ( 1.2 ) and an ionically conducting electrolyte ( 1.3 ), wherein the negative electrode ( 1.1 ) is formed from such an active material that its potential to lithium is greater than 1 V, and wherein the positive electrode ( 1.2 ) is formed from such an active material that its potential to lithium is less than 4.5V. Energy store according to claim 1, wherein the positive electrode ( 1.2 ) has a stable sublattice upon complete lithium extraction. Energy store according to claim 2, wherein the positive electrode ( 1.2 ) is formed at least from a nanoscale, electrochemical active material. Energy storage according to claim 3, wherein the positive electrode ( 1.2 ) is formed at least from a two-phase active material. Energy store according to claim 3 or 4, wherein the positive electrode ( 1.2 ) is formed at least from a metal oxide, in particular from lithium-intercalated iron phosphates LiFePO ₄ or manganese oxides LiMn ₂ O ₄ . Energy store according to one of claims 1 to 5, wherein the negative electrode ( 1.1 ) is formed at least from a nanoscale, electrochemical active material. Energy store according to claim 6, wherein the negative electrode ( 1.1 ) is formed at least from a two-phase active material. Energy store according to claim 6 or 7, wherein the negative electrode ( 1.1 ) is formed at least from a metal oxide, in particular from lithium-intercalated titanates Li ₄ Ti ₅ O ₁₂ . Energy store according to one of claims 1 to 8, wherein the electrolyte ( 1.3 ) is a high-boiling electrolyte. Energy store according to claim 9, wherein the electrolyte ( 1.3 ) of a polymer or polymer mixture, in particular polyolefins, polyisobutene, polybutadiene or fluoroelastamers, such as terpolymers, admixed with conducting salt solution of a conducting salt, in particular boron-containing conducting salt, such as lithium tetrafluoroborate or lithium bisoxalatoborate, and a high-boiling solvent of cyclic carbonates, such as ethylene carbonate, in particular diethylene carbonate or ethylmethyl carbonate , Propylene carbonate, fluoroethylene carbonate, gamma-butyrolactone, methyl acetate and / or ethyl acetate. Energy store according to claim 9, wherein the electrolyte ( 1.3 ) is formed from a conducting salt, in particular boron-containing conducting salt, such as lithium tetrafluoroborate or lithium bisoxalatoborate, and a high-boiling solvent of cyclic carbonates, such as ethylene carbonate, in particular diethylene carbonate or ethylmethyl carbonate, propylene carbonate, fluoroethylene carbonate, gamma-butyrolactone, methyl acetate and / or ethyl acetate. Energy store according to one of claims 1 to 11, wherein the individual cells ( 1 ) are connected in series and / or in parallel with each other. Electrical system ( 5 ) for a vehicle with an energy store ( 2 ) according to one of claims 1 to 12 as a primary lithium battery or as a secondary lithium battery separately or in combination with an electric machine and / or an on-board battery in a vehicle with or without an internal combustion engine.