WO2011071375A1

WO2011071375A1 - Method and device for testing an electric energy storage component

Info

Publication number: WO2011071375A1
Application number: PCT/NL2010/050820
Authority: WO
Inventors: Egbert Wouter Joghum Robers
Original assignee: Epyon BV
Current assignee: Epyon BV
Priority date: 2009-12-08
Filing date: 2010-12-03
Publication date: 2011-06-16
Anticipated expiration: 2012-06-08
Also published as: NL2003923C2

Abstract

The present invention relates to a method and device for testing an electric energy storage component, such as a battery or a (super) capacitor, comprising charging the component with a first amount of energy, discharging the storage component with a second amount of energy and monitoring the respective voltage increase and/or decrease over the component during subsequent repetition of charging and discharging. The number of repetitions it takes before the voltage increase and/or decrease over the component exceeds a predetermined threshold value may be counted and used to qualify an energy storage component.

Description

Method and device for testing an electric energy storage component

The present invention relates to a method and device for testing an electric energy storage component.

Testing electric energy storage devices can be done for various reasons. One goal may be to determine the actual state of charge of the component, to find out if a charging operation is finished, another may be to determine the amount of energy present in the component, to estimate for example the time a device provided with the component can be used.

Yet another purpose may be to estimate the lifetime of the component, that is, the number of times it can be charged and discharged before it reaches the end of its lifetime and needs to be replaced or repaired. Ability to estimate the lifetime of a component, is of importance when designing electric apparatus, especially electric vehicles. Purchasers need to be informed how often they can recharge their vehicle, and how often maintenance or replacement is to be foreseen. Furthermore, the choice between various components may be based on the outcome of comparison tests between several components.

Methods according to the state of the art however have not proven to adequately and reliably predict the behaviour or lifetime of a component, or they do not offer decent ways for comparing the results of tests of various components, making it difficult to select the best component for a specific application, or to estimate the state of a component that is already in use.

Methods according to the art are usually based on using a nominal capacity of the energy storage device, as specified by the manufacturer of this component. However these choices appear to be rather arbitrary, which influences the correctness of the results. The European patent application EP 0 711 016 for example suggests to charge a battery with a percentage of the designed nominal capacity. A common remedy for solving these differences is to precede testing with a number of capacity charges to measure the initial capacity, and use this value instead of the nominal capacity, but this approach has the disadvantage of requiring more testing. It is a goal of the present invention to provide a method and device for testing electric energy storage component that overcomes the above mentioned disadvantages, or at least to provide a useful alternative.

The invention thereto proposes a method for testing an electric energy storage component, such as a battery or a (super) capacitor, comprising (A) repeating the steps of (Al) charging the component with a fixed amount of energy during a fixed amount of time and subsequently discharging the component to a voltage threshold; or (A2) charging the component to a voltage threshold and discharging the component with a fixed amount of energy during a fixed amount of time, (B) measuring the voltage difference increase and/or decrease over the component during step Al or A2, (C) counting the number of repetitions of steps Al or A2 it takes (CI) before the voltage increase and/or decrease over the component exceeds a predetermined threshold value, or (C2) before the component breaks down or fails.

This number is an indication of the speed of deterioration and the number of charging cycles the component can withstand before it breaks down or becomes useless, and can be used to qualify components to facilitate comparison.

For a capacitor or a like component, the method according to the invention is based on the fact that the capacity (coulomb per volt) decreases during deterioration of the component. For batteries, other calculation methods or models may be used. As a result, the voltage increase for a (predetermined) amount of energy (or a predetermined amount of charge / coulomb) increases during deterioration. Instead of measuring an amount of time it takes to charge or discharge the component for a certain percentage as is used according to the art, according to the present invention, a value that is directly related to the deterioration is measured. This makes the outcome of the measurement more reliable and better reproducible.

A further advantage is that the method according to the invention does not distinct between nominal and initial capacity, because the nominal capacity is does not need to be used, since components are compared on weight, price or volume instead of percentages of a nominal value.

The amount of energy during charging and discharging may be different, so that the voltage over the component increases or decreases during the measurements, but preferably it is the same. However, the component may be predetermined with a bias voltage upfront, and it does not necessarily be charged up to its maximum value.

Furthermore, the waveform and length of a current when charging or discharging the component may be different, and vary in time.

In general, a (predetermined) amount of energy may be calculated by integrating voltage times current over time. The amount of charge can be calculated by integrating current over time, wherein charge and energy may be exchanged as indicators. In case the charge is used as an indicator, the voltage over the (normally relative small) internal resistance of the capacitor or battery is in fact neglected.

In order to quantify the behaviour of the component, the method according to the invention may further comprise the step (D) of performing steps A-C for at least two electric energy storage components of a same type, wherein the fixed amount of energ; instep Al or A2 is chosen different for each of the at least two electric energy storage components.

Afterwards, a representation of the number of repetition steps compared to an electric energy storage component parameter such as its volume, mass or price can be generated (E). Herein, interpolation, extrapolation or modelling of the counted numbers of repetition steps for generating the representation.

The invention may comprise (dis)charging the component with a predetermined current value. This results in a predetermined - for example linear - de/increase of the voltage over the component, which makes the measurements easy. As an alternative, or at the same time, (dis)charging the component during a predetermined time is an option, resulting in a predetermined time wherein the voltage (de)/increases. In order to make a more realistic and thus more valuable simulation, the method may comprise the step of pausing during a predetermined time between steps A and B. Charging and discharging will in most circumstances take place quicker than in a real life situation, since only limited time resources are available for the testing.

In an advantageous embodiment, the method according to the invention comprises composing a number of graphs of voltage increase and/or decrease over the component during subsequent repetition of steps Al and A2 for a variety of components. Since the components deteriorate by the testing process, and even may be destructed thereby, preferably, only a few cycles are performed on the actual component, and the results of these tests are matched with the graphs, for estimation of the behaviour of the component. The graphs may be composed for various values of lifetime, weight, price, mass of a plurality of components, number of cycles, or energy quantity in order to be able to compare a large variety of components.

The graphs may be partly made by interpolation of measurements, and can for example be repeated for various percentages of charging and discharging of the component, wherein different percentages belong to different tests. For example the component can be charged and discharged between 0 and 100%, or between 20 and 80%>. The latter has positive effect on the lifetime and the number of charging and discharging cycles it can withstand.

Afterwards, each of the components from the plurality of components may be qualified with a rating. For a component to be tested, steps Al and A2 may be performed only a few times, and the results can then be mapped with the graph for rating the component.

The ratings and tests can be performed for determining if a component is suitable for a specific purpose, such as use in an electric vehicle, and a testing device, configured to perform the method according to the invention can be used for that purpose. Such testing device may for example be a programmable current source. In a further embodiment, such a testing device may be incorporated in the component, so that self tests can be performed at predetermined instances, or on demand, by a user of the component. An electric device, such as an electric vehicle, may also comprise an electronic energy storage device, wherein the testing device is provided with indicator means, for indicating a status of the energy storage component or for warning purposes.

The invention will now be explained in more detail with reference to the figures.

Figure 1 shows a schematic detailed view of the charging and discharging steps Al, A2. Figure 2 shows a graph with graphs, composed by testing a number of components.

Figure 1 shows a schematic detailed view 1 of the charging and discharging steps Al, A2 during time t. During the steps A of charging the component with a first amount of energy the voltage V over the component increases, and during steps A2 of discharging the storage component with a second amount of energy the voltage V decreases. During step B of monitoring the respective voltage increase and/or decrease over the component during subsequent repetition of steps Al and A2, a graph V_c with maximum values of the voltage may be composed. Step C of the method according to the invention is also shown, counting the number of repetitions of steps Al and A2 it takes before the voltage increase and/or decrease over the component exceeds a

predetermined threshold value V_t during step Al and/or A2. The increasing voltage increase per predetermined amount of energy is a result of a declining capacity of the energy storage component.

Figure 2 shows a graph with a plurality of graphs thus obtained. The points are measurements here, wherein for multiple measurements with the same type of energy storage component, different amounts of energy are used, for example 80%, 70%, 60%> or 50% of the full capacity. Capacity is well defined for a capacitor, but for a battery the term is used to indicate the amount of energy that can be stored. In fact, this is an amount of charge. The horizontal axis shows the number of cycles, and it is possible to determine the number of cycles it takes before a threshold voltage is reached. This number can be used as a qualification number for a specific type of energy storage component, in order to be able to compare it with other energy storage components. Here it is also possible to compare for example batteries with capacitors.

The vertical axis shows a normalised volume of the battery, that is, the volume the battery should have if it would have to deliver 1 kWh. This way, the graph can be used with another starting point, for example if a battery with 200 cycles is required for a specific purpose, battery 5 will be the largest battery for the specific purpose (9 litre/kWh), and battery 1 will be the smallest with 5,3 litre/kWh. If desired, according to the invention, a like graph could be made with a mass or a price on the vertical axis.

Furthermore, curves of an energy-mass ratio compared to the lifetime, the energy- volume ratio compared to the lifetime of the energy-mass ratio compared to the lifetime could be made. Such representation could be implemented in a model, such as a computer model.

The invention may further be embodies as a battery charger, in particular for charging vehicle batteries, and thereto be adapted to interact with a motor management system of a vehicle, for using at least part of data acquired by the motor management system for testing an energy storage device of the vehicle. The charging device may be integrated in the vehicle, but it may also be integrated in a charging station for vehicle batteries.

Claims

1. Method for testing an electric energy storage component, such as a battery or a (super) capacitor, comprising:

A. repeating the steps of:

Al . charging the component with a fixed amount of energy during a fixed amount of time and subsequently discharging the component to a voltage threshold; or

A2. charging the component to a voltage threshold and discharging the component with a fixed amount of energy during a fixed amount of time;

B. measuring the voltage difference increase and/or decrease over the component during step Al or A2;

C. counting the number of repetitions of steps Al or A2 it takes:

CI . before the voltage increase and/or decrease over the component exceeds a predetermined threshold value, or

C2. before the component breaks down or fails.

2. Method according to claim 1, comprising:

D. Performing steps A-C for at least two electric energy storage components of a same type, wherein the fixed amount of energy instep Al or A2 is chosen different for each of the at least two electric energy storage components.

3. Method according to claim 1 or 2, comprising:

E. Generating a representation of the number of repetition steps compared to an electric energy storage component parameter such as its volume, mass or price.

4. Method according to claim 3, wherein step E comprises:

interpolation, extrapolation or modelling of the counted numbers of repetition steps for generating the representation.

5. Method according to claim 1 or 2, wherein step A or step B comprises:

- (dis)charging the component with a predetermined current or power value.

6. Method according to any of the preceding claims, wherein step Al or step A2 comprises:

- (dis)charging the component during a predetermined time.

7. Method according to any of the preceding claims, comprising:

- pausing during a predetermined time between steps Al and A2.

8. Method according to any of the preceding claims, comprising:

- composing a number of graphs of voltage increase and/or decrease over the component during subsequent repetition of steps Al and A2 for a variety of

components, and/or composing a number of graphs for various values of lifetime, number of cycles, energy quantity, weight, price, mass of a plurality of components.

9. Method according to claim 8, qualifying each of the components from the plurality of components with a rating.

10. Method according to claim 8 or 9, comprising:

- performing steps Al and A2 a few times for a component, and mapping the results with the graph for rating the component.

11. Testing device for an electric energy storage component, configured for performing the method according to claims 1-10.

12. Electric energy storage device, comprising a testing device according to claim 11.

13. Electric device, such as an electric vehicle, comprising an electronic energy storage device according to claim 14, wherein the testing device is provided with measuring means, for measuring a status of the energy storage device.

14. Battery charger, in particular for charging vehicle batteries, comprising a testing device according to claim 13.

15. Battery charger according to claim 14, adapted to interact with a motor or battery management system of a vehicle, for using at least part of data acquired by the motor management system for testing an energy storage device of the vehicle.