WO2015014764A2

WO2015014764A2 - Electrochemical storage module and method for examining an electrochemical storage cell in a module

Info

Publication number: WO2015014764A2
Application number: PCT/EP2014/066103
Authority: WO
Inventors: Jochen Bernhard GERSCHLER; Joerg Christoph WILHELM
Original assignee: Robert Bosch Gmbh; Samsung Sdi Co., Ltd.
Priority date: 2013-07-30
Filing date: 2014-07-25
Publication date: 2015-02-05
Also published as: DE102013214821A1; WO2015014764A3

Abstract

The invention relates to a method for examining an electrochemical storage cell in a module having a plurality of electrochemical storage cells. The method comprises the step of equalizing a state of charge between a first storage cell and a second storage cell by means of a direct current. As a second step, the present method comprises superposing an alternating signal on the direct current. Finally, the reaction of the first storage cell to the alternating signal is examined. The invention further relates to an electrochemical storage module that is capable of performing the aforementioned method.

Description

Description title

Electrochemical storage module and method for examining an electrochemical storage cell in a module

State of the art

The present invention relates to a method for examining an electrochemical storage cell in a module of a plurality

electrochemical storage cells. In particular, the present invention relates

The invention relates to a method for checking the state of health (SOH) of a battery or a rechargeable battery, comprising electrochemical storage cells, during operation.

In electrically powered vehicles (EVs, PHEVs or HEVs) today lithium-ion batteries are preferably installed, while other cell technologies are used. For this purpose, single cells are connected in series and parallel to a pack in order to achieve a high energy content and high performance. In this case, battery cells of all common

Accumulator technologies are used. It can be battery cells of type Pb - lead acid battery, NiCd - nickel-cadmium battery, NiH ₂ - nickel-hydrogen accumulator, NiMH - nickel-metal hydride accumulator, Li-ion - lithium-ion battery, LiPo - lithium polymer Battery, LiFe - Lithium Metal Battery, LiMn - Lithium Manganese Battery, LiFeP0 ₄ - Lithium Iron Phosphate Battery, LiTi - Lithium Titanium Battery, RAM - Rechargeable Alkaline Manganese, Ni-Fe - Nickel Iron - Battery, Na / NiCI - Sodium Nickel Chloride High Temperature Battery SCiB - Super Charge Ion Battery, Silver Zinc Battery, Silicone Battery, Vanadium Redox Battery and / or Zinc Bromine Battery can be used. Preference is given to using batteries of the lithium-ion battery type. For monitoring, several controllers are integrated in these packs, eg the

Measure single-cell voltages and temperatures and switch off the pack via relays if defined limit values are exceeded. This serves the Preventing uncontrolled overheating of the pack. In the case of the individual controllers, a distinction is made between the cell controllers, which usually monitor a single cell or modules of some cells, and the main controller, which communicates with the cell controllers and the vehicle via various interfaces, as well as various other sensor signals and drives actuators. The cell controllers are usually distinguished by the fact that they are integrated with balancing algorithms, with which it is possible to compensate for the charge states of different cells in inequality. This happens principally by shifting charge from one cell to another (active balancing). For this purpose, in the main controller algorithms for

Battery condition determination provided, e.g. State of charge and

Performance prediction. In most cases parameterised battery models are used. Disadvantage of these models is that the stored parameters change with the aging of the battery and must therefore be adapted. Aging caused by external factors, e.g. Temperature, maximum

Flow and charge conditions is dependent, can be difficult to determine and predict. Often it depends heavily on the actual operating history of the cells, so extrapolations from accelerated aging tests often provide only a rough parameter estimate over life. One way to minimize the uncertainty of this estimate is to use intelligent measurement techniques. One such in-situ cell-level technique is electrochemical impedance spectroscopy (EIS). EIS can be used to investigate the behavior of electrochemical storage over defined frequency ranges. The study of behavior over a complete

In this case, the frequency range does not only depict one size (e.g., the internal resistance), but qualifies and quantifies a variety of cell-specific processes and quantities. Here, the cell inductance and the

To name cell internal resistance, but also variables that correlate to charge transfer, carrier diffusion and electrochemical double layer, and thus significantly characterize the electrochemical cell reaction. Impedance spectroscopy techniques are now used in research laboratories for the characterization of electrochemical storage cells. In addition to a description of the respective system and its parameters, EIS is also suitable as a method for parameter measurement of batteries. Furthermore, EIS has been proven in the characterization of cells in accelerated aging tests. In contrast to post-mortem analysis, surveying with EIS is non-destructive. About the mapping of specific parameter variations Approximately qualitative and quantitative estimates of cell aging can be made. The aforementioned methods are described, for example, in DE 10 2009 000 336 A1 and DE 10 2009 000 337 A1. The problem with the known method is that the known excitation of

electrochemical storage cells exclusively in the state, in other words before or after the operation of the vehicle, are applicable or the energy must be interrupted at least for a certain period of time to examine the electrochemical cells by EIS. Disclosure of the invention

According to the invention, a method for examining an electrochemical storage cell in a module with a plurality of electrochemical

Memory cells proposed. The method may, for example, be performed by a cell controller on an electrochemical storage cell or on a module of a plurality of electrochemical storage cells. In this case, the electrochemical storage cell can be based in particular on lithium-ion technology. In particular, the pack of electrochemical storage cells is a battery or an accumulator for an at least partially electrically driven vehicle. The method comprises the

Step of equalizing a state of charge between a first memory cell and a second memory cell by means of a direct current. In other words, a cell balancing process is carried out, by means of which electrochemical energy is redirected via a flow of current from one memory cell to another memory cell. Such a process is often performed by a cell controller of a module and, alternatively or additionally, by a main controller of the battery. In this case, the direct current is superimposed by an alternating signal according to the invention. The alternating signal is an alternating current which is impressed by the cell controller or alternatively by the main controller. Next includes the

The method according to the invention comprises examining the response of the memory cell to the alternating signal. This may be, for example, an impedance test in which the real part (Re) and the imaginary part (Im) of the impedance of the electrochemical storage cell are recorded at the frequency of the alternating signal and compared with reference values. The investigation of electrochemical storage cells by measuring the dynamic impedance is (as described above in connection with the prior art) as electrochemical impedance spectroscopy (EIS). According to the invention, it is possible such a method by a cell controller of a

electrochemical storage cell during the balancing operation of

electrochemical storage cell, in other words, during superimposed charge and / or discharge, perform. In this way, the

Power output / recording of the electrochemical storage cell continued while the electrochemical storage cell in terms of their

Aging condition or in terms of their state of charge is examined.

The dependent claims show preferred developments of the invention.

Preferably, the alternating signal is a sinusoidal signal. This is the determined

Impedance particularly exactly the frequency used and therefore attributable to a particular cell state.

More preferably, the fundamental frequency of the alternating signal is time-variable. In other words, signals can be used which are a first

Time have a first frequency spectrum, which differs from a second frequency spectrum at a second time. Predefined individual frequencies can be used one after the other and, alternatively or additionally, continuous frequency changes can be applied. From the synopsis of the reactions of the electrochemical memory when excited with different frequencies, extensive information on the processes and states within the memory can be obtained.

More preferably, the alternating signal discrete, predefined

characteristic frequencies, of which at least one is in the MHz range and another frequency in the kHz range. In this way, a very broad frequency range is used for the investigation of the electrochemical storage cell. In particular, the different frequencies can be generated with little effort by, for example, system-inherent frequencies (e.g., the frequency of a switching converter within the

electrochemical storage system) can be used for excitation.

For example, smoothing of an electrical quantity from the

Electrochemical cell removed energy for the duration of the

Examining be suspended, so no extra Stimulation hardware is required. This reduces the effort to

Implementation of the method according to the invention.

Preferably, the alternating signal has a current amplitude which is smaller than the amount of the direct current used for balancing. Thus, the

Stimulation hardware (if necessary) be designed less powerful and the current-carrying hardware must not be designed (much) robust in terms of performance. According to another aspect of the present invention is a

proposed electrochemical storage module with at least a first memory cell and a second memory cell. Next includes the

electrochemical storage module, a cell controller for balancing a state of charge between the first memory cell and the second

Memory cell. The cell controller is set up to compensate for this

Direct current. According to the invention, the aforementioned balancing process is superimposed by means of an alternating signal. It is (as in

In connection with the first-mentioned aspect of the invention, the cell controller uses to generate an alternating signal which is impressed on the direct current. According to the invention, the reaction of the first

Memory cell in a method, as described in detail above, examined. In other words, cell behavior becomes complex

Impedance determined from voltage response and stimulating alternating signal. There are the same advantages as in the method according to the invention.

Further preferably, the cell controller is additionally set up to determine a temperature and, alternatively or additionally, an electrical voltage across the first and / or the second memory cell. In this way, it is possible to select a particularly critical cell from the module of electrochemical storage cells, in which aging influences are likely to occur first or most strongly. In this way, the inventive method can be limited to individual electrochemical cells, which reduces the complexity in terms of the structure and the method steps.

More preferably, the cell controller is connected to a measuring tap over the first and alternatively or additionally over the second memory cell. The measuring tap can, for example, to determine a temperature and / or a serve electrical voltage and alternatively or additionally an electric current. In this way, the cell controller is also set up to determine an impedance of the first and / or the second memory cell. More preferably, the cell controller is set up, the alternating signal as a function of a

Switching frequency of an arranged between the memory module and an electric motor inverter. In this case, the power consumption of the inverter on the electrochemical storage cell, which is to be examined, back and the pulsed power extraction to produce the

Alternating signal can be used. For this example, a

Smoothing device temporarily be disabled, so that the inverter causes alternating signals of suitable amplitude.

Brief description of the drawings

Hereinafter, embodiments of the invention will be described in detail with reference to the accompanying drawings. In the drawings:

Figure 1 is a schematic overview of an embodiment of an electrochemical storage module according to the present invention;

Figure 2 is a schematic overview of an alternative

Embodiment of an electrochemical storage module according to the present invention;

FIG. 3 shows a detailed view of input and output variables of an electrochemical storage cell during cell balancing;

Figure 4 is a schematic detail view of an electrochemical

Memory cell with electrical input and output variables when carrying out a method according to the invention;

Figure 5 is an overview of relationships electrochemical

Layers of an electrochemical storage, electrical equivalent circuit diagrams and their influence on real and

Imaginary part of a cell impedance; Figure 6 diagrams for visualization of real and imaginary part of a

Cell impedance at different aging conditions and cell temperatures; and

FIG. 7 shows a flow chart, visualizing steps of a

Embodiment of a method according to the invention.

Embodiments of the invention

Figure 1 shows a schematic view of a first embodiment of an electrochemical storage 10 (e.g., a lithium-ion battery). The electrochemical storage 10 is divided into electrochemical storage modules 1 1, 12, 13, 14, which are arranged in a series circuit, although the present invention could in principle also be used with cells connected in parallel. In this case, the memory module 1 1 represents the first module of the series connection. The memory module 14 represents the n-th module of the series connection. A respective memory module 1 1, 12, 13, 14 has a cell controller 21 assigned to it and electrically connected to it. 22, 23, 24 on. Left and right of the electrochemical storage 10 are the

Negative terminal 101 and the positive terminal 102 are arranged. The first

electrochemical storage module 1 1 comprises electrochemical storage cells 1 1 1, 1 12, 1 13, 1 14. Here, the memory cell 1 1 1 represents the first cell of the series circuit. The memory cell 1 14 here represents the n-th cell of the series circuit all memory cells 1 1 1, 1 12, 1 13, 1 14 taps are connected to the first cell controller 21 for measuring a respective cell voltage. The second electrochemical storage module 12 and the third electrochemical storage module 13 and fourth electrochemical storage module 14 are constructed accordingly.

FIG. 2 shows an alternative embodiment of the arrangement shown in FIG. In contrast to this, however, the cell controllers 21, 22, 23, 24 have a measuring tap only on one of the cells connected in series. By way of example, measuring taps over the cells 1 12, 122, 132, 142 are shown here. In this way, the cost of construction and operation of the electrochemical memory 10 is reduced. In order to minimize the possible disadvantages of this reduced information collection, it was previously found that the selected positions for the Measuring taps are the electrochemical cells with the highest critical aging processes.

FIG. 3 shows a current diagram over time for the cell balancing using the example of the arrangement 10 discussed in FIG. 1. The current 3 is considered to be more constant

DC formed, through which a cell of the electrochemical storage module 1 1 can be loaded. To the right of the electrochemical storage module 1 1, another current-time diagram is shown, which represents a negative direct current 5. By means of the negative direct current 5, a further cell of the electrochemical storage module 1 1 is discharged. By DC 5 of the cell is deprived of energy and through

DC 3, this energy is supplied to another cell for compensation.

FIG. 4 shows the arrangement illustrated in FIG. 3 when the charging current 3 is superimposed with an alternating signal 4 according to the invention. The amplitude of the

Alternating signal 4 is smaller than the amount of the charging current. 3

FIG. 5 shows in its upper region a schematic crystal layer 51, in which five different layers 510, 51 1, 512, 513 and 514

are arranged side by side. The crystal layers 510, 51 1, 512, 513, 514 are additionally marked with Roman numerals I-V and with

corresponding branches lV of an equivalent circuit model. The equivalent circuit consists of a series connection of two poles, each having a capacitance C | -C _v and a respective ohmic resistance R | R _{v are} modeled (RC parallel link). Between the schematic

Crystal layer 51 and the equivalent circuit diagram is an impedance diagram to real and imaginary part of the impedance of the crystal arrangement shown. An arrow indicates the overall impedance curve in the direction of increasing frequency f. The sections marked with Roman numerals I to V visualize the influences of the individual crystal layers 510 to 514. Below the equivalent circuit diagram for the individual crystal layers 510, 51 1, 512, 513 514, a diagram for the correlation between the electrochemical process and its correspondence in the impedance spectrum is shown , Below the axis for the real part of Z (Re (Z)) is a possible impedance-based

Equivalent circuit model shown. In other words, those in the

Equivalent circuit diagram model shown (connected in series) two-pole L, Rser, RSE CSEI, R _c t C _d i, Z _w and C _in t the respective frequency ranges dominant (complex) impedances of the illustrated crystal arrangement. For high frequencies (f> 1 kHz) most Li-ion systems show inductive impedances. These ranges are attributed to the structure or geometry of the porous active mass and the current collector as well as the internal and external contacting of the cell. The intersection of the complex impedance with the real axis shows the purely real resistance of the cell. This is mainly composed of ohmic components of the electrolyte resistance, but also of the resistors of current conductors and electrical contacting. This is followed in the case shown here by two superimposed compressed semicircles in the high and medium frequency range. The high-frequency semicircle is mainly attributed to the effects of passivation films and SEI in the electrode-electrolyte interface. The equivalent of the medium frequency semicircle is commonly used in charge transfer processes and effects of the

Double layer capacitance seen in conjunction with the transition from ionic to electrical conduction on the electrode surface. Often, the medium-frequency semicircle is influenced by another, at least indicated, lower-frequency semicircle or inclined capacitive straight line sections. Such courses in the low-frequency range correlate to solid-state diffusion processes (Warburgdiffusion) of lithium ions in the porous electrode matrix. For very small frequencies, the impedance of Li-ion systems is often almost pure-capacitive. This is associated with capacitive effects due to ion (de) intercalation into and out of the electrodes. Figure 6 shows three recorded at different cell temperatures

Impedance shares, each representing different aging states of an electrochemical storage. Plotted is the imaginary part of the impedance (Im (Z) / mOhm) over the real part (Re (Z) / mOhm), while in each case a first graph 61 an initial state (after 0 weeks), a second graph 62 an aging state after 6 weeks, a third graph 63 a

Aging condition after 12 weeks, a fourth graph 64 an aging condition after 24 weeks, a fifth graph 65 an aging condition after 36 weeks and a sixth graph 66 visualizing an aging condition of 70 weeks. The partial figure a) was taken at a cell temperature of 35 ° C. The partial figure b) has been recorded at a cell temperature of 50 ° C. The subfigure c) has been recorded at a cell temperature of 65 ° C. A second graph 62 shows one compared to the first graph 61 higher degree of aging. The following graphs 63 to 66 show the progressive aging on the basis of increasing aging states. The temperatures shown increase from part a) to part c). The DOD ("depth of discharge"), ie a measure of the extracted

Charge amount ") is 50% each with open circuit

Real part in relation to the imaginary part with increasing age and with increasing cell temperature significantly. It should be noted that the axes of the subfigure c) have a different scale than the axes of the subfigures a) and b).

FIG. 7 shows a flowchart visualizing steps according to FIG

Embodiment of a method according to the invention. In a first step 100, a charge state between a first memory cell and a second memory cell is compensated by means of a direct current. Such a process is called "balancing" to improve the performance of a composed of electrochemical storage cells

Memory arrangement referred to. In step 200, the DC signal is superimposed by means of an AC signal. The alternating signal may for example be a sinusoidal signal, which has a time-variable frequency and is designed, for example, as a sine sweep. This step may be performed concurrently with step 100. In step 300, the response of the applied memory cell to the AC signal is examined. In this case, for example, the real part and the imaginary part of the cell impedance are compared with one another at different frequencies and compared with predefined, stored references within the evaluation system. Also, step 300 may be performed concurrently with steps 100 and 200. in the

In response to the result of the examination, for example, an operating mode and / or a balancing parameter can be adapted. Although the present invention has been explained by way of embodiments described in detail in conjunction with the attached drawing figures, modifications and combinations of the features disclosed therein remain within the skill of the artisan, while the scope of the present invention is defined by the appended claims.

Claims

claims

1 . Method for examining an electrochemical storage cell (1 1 1 - 1 14; 121-124; 131-134; 141-144) in a module (1 1; 12; 13; 14) having a multiplicity of electrochemical storage cells (1 1 1 -1 14, 121-124, 131-134, 141-144) comprising the steps of:

Balancing (100) a state of charge between a first memory cell (1 1 1) and a second memory cell (1 12) by means of a direct current (3, 5),

Overlaying (200) of the direct current (3, 5) by means of a

Alternating signal (4), and

Examining (300) the response of the first memory cell (1 1 1) to the alternating signal (4).

2. The method of claim 1, wherein the alternating signal (4) comprises a sinusoidal signal.

3. The method according to any one of the preceding claims, wherein the

Alternating signal (4) has a time-varying fundamental frequency.

The method of claim 3, wherein the alternating signal (4) comprises discrete predefined fundamental frequencies, at least one of which is below 100 mHz and one above 0.9 kHz.

5. The method according to any one of the preceding claims, wherein the

Alternating signal (4) has a current amplitude which is smaller than the amount of the direct current (3).

6. The method according to any one of the preceding claims, wherein the step of examining a determination of a cell impedance and / or a

Cell capacity and / or cell impedance.

7. Electrochemical storage module (1 1, 12, 13, 14) comprising at least one first memory cell (1 1 1) and a second

Memory cell (1 12),

a cell controller (21, 22, 23, 24) for compensating a charge state between the first memory cell (1 1 1) and the second memory cell (1 12) by means of a direct current (3, 5), wherein the cell controller (21, 22, 23 , 24) is arranged to superimpose a direct current (3) for compensating the state of charge by means of an alternating signal (4), and

to investigate the response of the first memory cell (1 1 1) in a method according to any one of the preceding claims to the alternating signal (4).

8. An electrochemical storage module according to claim 7 wherein the

Cell controller (21, 22, 23, 24) is further configured to determine a temperature and / or an electrical voltage across the first memory cell (1 1 1) and / or the second memory cell (1 12).

9. Electrochemical storage module according to claim 7 or 8, wherein the cell controller (21, 22, 23, 24) is connected to a Meßabgriff over the first and / or the second memory cell (1 12).

10. An electrochemical storage module according to claim 7 to 9, wherein the

Cell controller (21, 22, 23, 24) is further adapted to select the alternating signal (4) in response to a switching frequency of an arranged between the memory module (1 1, 12, 13, 14) and an electric motor inverter