DE102019211913A1 - Method for determining an aging condition of a battery, control unit and vehicle - Google Patents

Abstract

The invention relates to a method for determining an aging state of a battery (105) in a vehicle, the aging state (SoH) of the battery (105) using a map which correlates the internal resistance (ΔR) and the aging state (SoH) (200, 210 ). The invention further relates to a control device (120) which is designed to carry out the method, and also to a vehicle comprising at least one such control device (120).

Description

The invention relates to a method for determining an aging condition of a battery in a vehicle, the aging condition SoH the battery by means of a map which shows the internal resistance and the state of aging SoH correlated, is derived. Furthermore, the invention relates to a control device which is designed to carry out the method, and also to a vehicle comprising at least one such control device.

In order to determine the residual value of a rechargeable battery, including the accumulator, and to ensure its safe operation of the battery, it is regularly necessary to determine its aging state, the so-called "State of Health" ( SoH ) to estimate as accurately as possible. Usually the SoH determined by a (partial) loading / unloading process. A high accuracy of the current sensor is necessary for the determination by means of the charging process. A large loading stroke is also necessary to achieve sufficient accuracy.

However, batteries age particularly quickly when they are in a high state of charge, which is why it is sometimes not necessary to fully charge batteries. Often there is also an upper charging limit, for example defined by a user, which, for example, provides sufficient range for use as a vehicle battery for daily journeys or enables daily use when used in consumer electronics, such as notebooks, cell phones or the like. It often happens that a battery is rarely, or never, charged with a large charging stroke, so that a valid determination of the state of aging is not possible.

DE 10 2011 077 448 A1 describes a method for estimating at least one state variable describing the state of an electrical energy store by comparing at least one first operating quantity determined by measurement of a plurality of operating quantities of the energy store with at least one corresponding comparison quantity.

EP 1 961 621 A1 describes a battery state judgment method by which a state of a lead-acid battery is to be judged by measuring voltages without measuring currents.

EP 2 846 395 A2 describes a battery pack having a battery coupled to a load and a charger and having at least one battery cell and a battery management unit for controlling the charging of the battery from the charger and the discharge of the battery to determine a health condition of the cell.

The object of the present invention is therefore to at least partially overcome the disadvantages of the methods from the prior art.

This object is achieved according to the invention by the method, control unit and vehicle described below. The features listed individually in the description and the patent claims can be combined with one another in a technologically meaningful manner and can be supplemented by explanatory facts from the description and / or details from the figures, further embodiment variants of the invention being shown.

• - Bestimmen einer Innenwiderstandsgröße;
• - Ableiten des Alterungszustandes der Batterie aus der Innenwiderstandsgröße;
• - Verfahren zur Bestimmung eines Alterungszustandes SoH einer Batterie in einem Fahrzeug umfassend die Schritte:
• - Bestimmen einer Lastspannung bei Fahrzeugbetrieb;
• - Relaxation der Lastspannung nach dem Fahrzeugbetrieb;
• - Bestimmen einer Leerlaufspannung OCV nach der Relaxation;
• - Bestimmen eines Innenwiderstands ΔR aus der Lastspannung und der Leerlaufspannung;
• - Ableiten des Alterungszustandes SoH der Batterie mittels eines Kennfeldes, welches den Innenwiderstand ΔR und den Alterungszustand SoH miteinander korreliert.

According to a first aspect, a method for determining an aging state of a battery is described, comprising the steps:

• - determining an internal resistance quantity;
• - Deriving the aging condition of the battery from the internal resistance value;
• - Procedure for determining an aging condition SoH a battery in a vehicle comprising the steps:
• - determining a load voltage during vehicle operation;
• - relaxation of the load voltage after vehicle operation;
• - Determine an open circuit voltage OCV after relaxation;
• - Determine an internal resistance ΔR from the load voltage and the open circuit voltage;
• - Deriving the state of aging SoH the battery by means of a map which shows the internal resistance ΔR and the state of aging SoH correlated with each other.

The internal resistance of the cell is determined on the basis of the overvoltage and the current during discharge, preferably using the following equation: $${\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="DE102019211913A1\_0009.png"\; state="\{\{state\}\}">R</figure-callout>}}_{0\%}=\frac{\Delta U}{\mathrm{\Delta }\mathrm{I.}}=\frac{U_{relaxed}-U_{endOfD\mathrm{C.}H}}{{\mathrm{I.}}_{D\mathrm{C.}H}}.$$

It says ΔU for the surge.

If in the context of the present invention of the state of aging SoH is talked about, preferably the state of aging SoH at OCV Conditions meant SoH _OCV . Preferably forms the SoH _OCV the mobile lithium concentration.

In connection with the present invention, there has now been a strong correlation between the internal resistance already mentioned and the state of aging SoH found. Measurements of calendar-aged cells showed that a general trend of decreasing internal resistance at the end of discharge with decreasing SoH consists. This knowledge enables a corresponding map, which shows the internal resistance ΔR and the state of aging SoH correlated, to be stored in the map memory of a control unit, also referred to as a control unit or control unit, of a vehicle and by means of this map from the internal resistance obtained ΔR the state of aging SoH to determine. Here you make the already mentioned clear dependence on internal resistance and SoH advantage.

Insofar as there is talk of a battery in connection with the present invention, more precisely an accumulator is meant. A battery in the sense of the present invention comprises at least one electrochemical cell that can be discharged and charged.

According to a particularly preferred embodiment, the battery is a lithium-ion accumulator. According to the present invention, the term lithium-ion battery is used as a generic term for batteries based on lithium compounds in the electrochemical cell. The reactive materials in both the negative and positive electrodes and the electrolyte can contain lithium ions.

The reactants in the electrochemical reactions in a lithium ion battery are the negative and the positive electrode and the electrolyte provides a conductive medium so that lithium ions can move between the electrodes. Electrical energy flows from or into the battery if electrons flow through an external circuit during discharge or charging.

Both electrodes allow lithium ions to move in and out of their structures. During the discharge, the (positive) lithium ions move from the negative electrode (anode - usually graphite) to the positive electrode (cathode - formation of a lithium compound) through the electrolyte, while the electrons flow in the same direction through the external circuit. The opposite happens when the cell charges: lithium ions and electrons move back into the negative electrode in a state of higher energy.

According to a preferred embodiment, a method is described in which the overvoltage is determined ΔU at a certain charge level SoC takes place, in particular at 50%, 30%, particularly preferably at 20%. The condition can include that the stated value of the battery state is either exceeded or undershot. Furthermore, the switchover can take place continuously over a range, in particular based on the battery states mentioned. For this purpose, interpolation, in particular linear interpolation, can be used to switch between the battery ages determined by means of the first method and the method according to the invention from one method to the other. In particular, the switchover begins as a condition when the above-mentioned charging states are exceeded or undershot and ends when a second charging state is reached, which differs from the first in particular by 30%, preferably 20%, particularly preferably 10%.

According to a preferred embodiment, a method is described in which the state of charge SoC Is 0% to 20%.

According to a preferred embodiment, a method is described in which the derivation of the aging state SoH the battery takes place by means of the map at the end of discharge.

In connection with the present invention, the end of discharge refers to the point in time during the discharge process at which the voltage, preferably the load voltage when discharging, falls below a certain limit value. In the most general case, it is the location of the current-voltage characteristic, at which the characteristic of the voltage, in particular the load voltage, at low charge states SoC begins to fall off more.

Furthermore, in particular, the end of discharge represents a limit value, which can be referred to as a “cut-off” value, and denotes the minimum voltage during the discharge process and thus the end of discharge. The "cut-off" prevents the cell from over-discharging. Usually the characteristic curve of the voltage, in particular the load voltage, drops at low charge states SoC sharply. In other words, the voltage characteristic curve for discharge depends on the state of charge SoC a falling "edge" at low charge states. The "cut-off" value is preferably selected within this falling "edge". A value of 2.5 volts can be mentioned as an example.

In connection with the present invention, there has now been a strong correlation between the internal resistance already mentioned and the state of aging SoH found. Measurements of calendar-aged cells have shown that a general trend of decreasing internal resistance with decreasing SoH consists. This clear correlation was found especially at the end of discharge. The corresponding resistance value at the end of discharge is also used in connection with the present invention ΔR _0% designated.

• - Bestimmen einer Leerlaufspannung OCV in Abhängigkeit vom Alterungszustand SoH der Batterie;
• - Bestimmen einer Lastspannung in Abhängigkeit vom Alterungszustand SoH der Batterie;
• - Ermitteln einer Überspannung ΔU als Differenz der Lastspannung und der Leerlaufspannung OCV;
• - Ermitteln des Innenwiderstandes ΔR auf Grundlage der Überspannung.

According to a further preferred embodiment, a method is described, the characteristic diagram being determined at least by the steps:

• - Determine an open circuit voltage OCV depending on the state of aging SoH the battery;
• - Determining a load voltage depending on the state of aging SoH the battery;
• - Determine an overvoltage ΔU as the difference between the load voltage and the open circuit voltage OCV ;
• - Determine the internal resistance ΔR based on the surge.

The internal resistance is determined based on the overvoltage and the current.

According to a further embodiment, a method is described, the characteristic map depending on the charge state SoC the battery is determined.

In order to obtain the most comprehensive information possible about the voltage characteristics, the map is made for different SoC of the battery. Overall, the accuracy of the characteristic diagram and thus also the accuracy of the determination of the aging condition of the battery can be improved in accordance with the method according to the invention.

According to a further embodiment, a method is described, the characteristic diagram being determined as a function of the temperature.

The map is determined at different temperatures in order to obtain the most comprehensive information possible about the voltage characteristics. Overall, the accuracy of the characteristic diagram and thus also the accuracy of the determination of the aging condition of the battery can be improved in accordance with the method according to the invention. The temperature is particularly noteworthy since the characteristic diagram shows the internal resistance of the cell, which is based on the overvoltages, which are temperature-dependent as kinetic parameters.

According to a further preferred embodiment, a method is described in which the full-cell open-circuit voltage OCV from the open circuit voltage OCV the anode and the open circuit voltage OCV the cathode is constructed.

According to a further preferred embodiment, a method is described in which the full-cell load voltage is constructed from the load voltage of the anode and the load voltage of the cathode.

According to one embodiment, the determination of the open circuit voltage takes place as follows: To ensure that the OCV If possible, voltage is measured under no load OCV by an external additional voltage measurement if the battery has been switched off for a long time, preferably at least 10 minutes.

According to a first embodiment, the open circuit voltage is particularly preferably measured after the battery has not been loaded for a long time. Here, the battery to be identified must ideally be “disconnected” from the system and there must be no current flow into or out of the cell. This increases the accuracy of the method.

In the case of a system with a low-voltage network, a preferred measurement method is described below: The voltage measurement is carried out via a low-voltage network in the vehicle. The high-voltage battery is not switched on for this purpose and was switched off for as long as possible, for example at least 10 minutes, before the measurement. The voltage measurement can take place for the battery, one or more modules or just one or more individual cells.

In the case of a system without a low-voltage network, a preferred measurement method is described below: Since the high-voltage battery must not be loaded, the system requires a separate measurement system with a self-sufficient energy supply for voltage measurement. The measuring system can be operated, for example, via buffer capacitors, which are recharged accordingly after the high-voltage system has been connected.

Is a measurement of the actual OCV not possible, a voltage can be used that was measured after the battery has been loaded with as little current as possible for as long as possible.

This first embodiment described here for measuring the open circuit voltage enables particularly high accuracy.

According to a further embodiment, the open circuit voltage is particularly preferably measured when the cell has preferably been loaded with a current of less than a defined limit current for at least 10 minutes. A limit current of less than is exemplary C50 indicate, i.e. a discharge of the battery with this current in more than 50 hours if this current would be constantly present

This further embodiment is less accurate than the first embodiment, but can be done quickly and efficiently.

According to a further preferred embodiment, a further improvement in the accuracy for the determination of the open circuit voltage is achieved by estimating the relaxed voltage by extrapolation of the voltage curve outside the pause time.

• - Messung und/oder Berechnung und/oder Bestimmung wenigstens einer Zustandsgröße einer Batterie
• - Berechnung und/oder Bestimmung einer weiteren Größe unter Berücksichtigung der wenigstens einen Zustandsgröße

In a more general aspect, the invention relates to a method comprising the steps:

• - Measurement and / or calculation and / or determination of at least one state variable of a battery
• - Calculation and / or determination of a further variable, taking into account the at least one state variable

In the context of the present invention, the state variable can be the difference in the internal resistance of the battery. The further size can be an aging state of the battery, in particular the state of health, SoH , the battery.

• - Bestimmung der Überspannungen bei Entladeschluss
• - Berechnung des Innenwiderstandes
• - Abgleich des Innenwiderstandes mit einem Kennfeld zur Bestimmung des SoH

In a preferred embodiment, the method comprises the steps:

• - Determination of overvoltages at the end of discharge
• - Calculation of the internal resistance
• - Comparison of the internal resistance with a map to determine the SoH

The last-mentioned steps preferably take place when driving and / or operating the vehicle.

• Das Kennfeld kann dabei auch für unterschiedliche Temperaturen und SoCs bestimmt werden. Das Modell kann auch um weitere Alterungsmechanismen ergänzt werden, wie einem Anstieg des Innenwiderstandes und/oder Verlust von Aktivmaterial.

In a preferred embodiment, the method comprises prepared measurements, which can also be part of the method, in particular method steps:

• The map can also be used for different temperatures and SoCs be determined. The model can also be supplemented by other aging mechanisms, such as an increase in internal resistance and / or loss of active material.

• Bestimmung eines Batteriealterungszustandes mittels eines ersten Verfahrens. Bei Eintreten einer von dem Batteriezustand abhängigen Bedingung, disktrete oder kontinuierliche Umschaltung auf das erfindungsgemäße Verfahren zur Bestimmung einer Batteriealterung. Dabei kann der Batteriezustand beispielsweise ein bestimmter Ladezustand SoC, insbesondere 50 %, bevorzugt 30 %, besonders bevorzugt 20 % sein. Die Bedingung kann dabei umfassen, dass der genannte Wert des Batteriezustands entweder über- oder unterschritten wird. Weiterhin kann die Umschaltung über einen Bereich, insbesondere ausgehend von den genannten Batteriezuständen, kontinuierlich stattfinden. Dazu kann durch Interpolation, insbesondere lineare Interpolation, zwischen den mittels des ersten und des erfindungsgemäßen Verfahrens bestimmten Batteriealterungen von dem einen Verfahren auf das andere Verfahren umgeschaltet werden. Insbesondere beginnt die Umschaltung bei Über- oder Unterschreiten der genannten Ladezustände als Bedingung und endet bei Erreichen eines zweiten Ladezustands, der von dem ersten insbesondere um 30 %, bevorzugt 20 %, besonders bevorzugt 10 % unterschiedlich ist.

The invention also relates to a method for determining battery aging, comprising at least the following method steps:

• Determining a battery aging condition using a first method. When a condition dependent on the battery condition occurs, discrete or continuous switchover to the method according to the invention for determining a battery aging. The battery status can be, for example, a specific charge status SoC , in particular 50%, preferably 30%, particularly preferably 20%. The condition can include that the stated value of the battery state is either exceeded or undershot. Furthermore, the switchover can take place continuously over a range, in particular based on the battery states mentioned. For this purpose, interpolation, in particular linear interpolation, can be used to switch between the battery ages determined by means of the first method and the method according to the invention from one method to the other. In particular, the switchover begins as a condition when the above-mentioned charging states are exceeded or undershot and ends when a second charging state is reached, which differs from the first in particular by 30%, preferably 20%, particularly preferably 10%.

According to a further embodiment, a control device is described which is designed to carry out the method according to the invention. In connection with the present invention, the terms control unit and control unit are used synonymously.

According to a further embodiment, a vehicle is described comprising at least one such control unit.

Further preferred embodiments of the invention result from the other features mentioned in the subclaims.

Unless otherwise stated in the individual case, the various embodiments of the invention mentioned in this application can advantageously be combined with one another.

• 1a ein Verfahren zur Bestimmung der Leerlaufspannung OCV gemäß einer Ausführungsform;
• 1b ein Verfahren zur Bestimmung der Lastspannung gemäß einer Ausführungsform;
• 2a ein Verfahren zur Bestimmung eines Kennfeldes, welches den Innenwiderstand ΔR und den Alterungszustand SoH miteinander korreliert;
• 2b ein Verfahren zur Bestimmung eines Kennfeldes, welches den Innenwiderstand ΔR und den Alterungszustand SoH miteinander korreliert in Abhängigkeit vom Ladungszustand SoC der Batterie;
• 3 ein Verfahren zur Bestimmung des Alterungszustandes der Batterie gemäß einer Ausführungsform der Erfindung;
• 4 ein System zur Bestimmung des Alterungszustandes der Batterie gemäß einer Ausführungsform der Erfindung;
• 5 ein System zur Bestimmung des Alterungszustandes der Batterie gemäß einer weiteren Ausführungsform der Erfindung;
• 6 eine Abhängigkeit des Innenwiderstandes ΔR vom Alterungszustand SoH der Zelle;
• 7a Kennlinien der Halbzellen und der Vollzelle sowohl als OCV als auch bei Entladung und
• 7b eine Veränderung der Kennlinien der Halbzellen als auch der Vollzelle sowohl als OCV als auch bei Entladung nach anodischer Lithium-Entnahme.

The invention is explained below in exemplary embodiments with reference to the accompanying drawings. Show it:

• 1a a method for determining the open circuit voltage OCV according to one embodiment;
• 1b a method for determining the load voltage according to an embodiment;
• 2a a method for determining a map, which the internal resistance ΔR and the state of aging SoH correlated with each other;
• 2 B a method for determining a map, which the internal resistance ΔR and the state of aging SoH correlates with each other depending on the state of charge SoC the battery;
• 3rd a method for determining the aging condition of the battery according to an embodiment of the invention;
• 4th a system for determining the aging condition of the battery according to an embodiment of the invention;
• 5 a system for determining the aging condition of the battery according to a further embodiment of the invention;
• 6 a dependence of the internal resistance ΔR from the state of aging SoH the cell;
• 7a Characteristic curves of the half cells and the full cell both as OCV as well as at discharge and
• 7b a change in the characteristics of the half cells and the full cell both as OCV as well as when discharging after anodic lithium removal.

• Das Verfahren gemäß der Erfindung erfordert, dass als vorbereitende Maßnahme ein Kennfeld bestimmt wird, welches den Innenwiderstand ΔR mit dem Alterungszustand SoH korreliert. Mittels des Kennfeldes kann, nach Inbetriebnahme des Fahrzeugs, der Alterungszustand der Batterie nach Bestimmung des Innenwiderstands ΔR ermittelt werden. Um das Kennfeld zu ermitteln, werden zunächst die Leerlaufspannung OCV und die Lastspannung 20b bestimmt. Das Bestimmen der Leerlaufspannung OCV ist in 1a gezeigt.

1a shows the determination of the open circuit voltage OCV According to an embodiment for determining a map which shows the internal resistance ΔR with the state of aging SoH correlated. 1b shows the determination of the load voltage according to an embodiment for determining a map, which the internal resistance ΔR with the state of aging SoH correlated. The preferred steps for this are described in detail below:

• The method according to the invention requires that, as a preparatory measure, a map is determined which shows the internal resistance ΔR with the state of aging SoH correlated. After starting the vehicle, the map can be used to determine the aging condition of the battery after determining the internal resistance ΔR be determined. In order to determine the map, first the open circuit voltage OCV and the load voltage 20b certainly. Determining the open circuit voltage OCV is in 1a shown.

The open circuit voltage OCV , more precisely the full cell open circuit voltage 20a , can from the open circuit voltage OCV the anode 10a and the open circuit voltage OCV the cathode 15a can be constructed according to the following equation Eq 1a: $$O\mathrm{C.}{V}_{Full}\left(SO{\mathrm{C.}}_{Ocv}\right)=O\mathrm{C.}{V}_{\mathrm{C.}atH}\left(SO{\mathrm{C.}}_{Ocv}\right)-O\mathrm{C.}{V}_{An}\left(SO{\mathrm{C.}}_{Ocv}\right).$$

As can be seen from equation Eq 1a, the open circuit voltage is dependent on the state of charge of the cell. Measurements of the open circuit voltage at different charge states are preferably carried out. In particular, the open circuit voltage is preferably determined for states of charge of 0 to 20% SoCocv. Furthermore, the measurement should preferably take place at different temperatures. In addition, the charging cycles can also be varied. As an alternative or in addition to the measurement of the half cells, a measurement of the open circuit voltage can also be carried out OCV the full cell. If the open-circuit voltage of the full cell is measured in addition to the measurement of the half-cells, this can be used to check the constructed voltage. For standardized cells, the open circuit voltage can OCV from the literature 5a be removed.

The determination of the load voltage is in 1b shown. The load voltage, more precisely the full cell load voltage 20b , can be determined from the load voltage of the anode 10b and the load voltage of the cathode 15b can be constructed according to the following equation Eq 1b: $$U_{D\mathrm{C.}H,Full}\left(SO{\mathrm{C.}}_{Ocv}\right)=U_{D\mathrm{C.}H,\mathrm{C.}atH}\left(SO{\mathrm{C.}}_{Ocv}\right)-U_{D\mathrm{C.}H,An}\left(SO{\mathrm{C.}}_{Ocv}\right).$$

As can be seen from the equation, the load voltage depends on the state of charge of the cell. Measurements of the load voltage at different charge states are preferably carried out. In particular, the load voltage is preferably determined for states of charge of 0 to 20% SoCocv.

Furthermore, the measurement should take place at different temperatures, since in particular the load voltage can vary depending on the temperature. In addition, the charging cycles can also be varied. As an alternative or in addition to the measurement of the half cells, the load voltage of the full cell can also be measured. If the measurement of the load voltage of the full cell takes place in addition to the measurement of the half cells, this can be used to check the constructed voltage. For standardized cells, the load voltage can be found in the literature 5b be removed.

• Das Kennfeld 31a bei Entladeschluss kann bestimmt werden, nach dem Bestimmen der Leerlaufspannung 20a und ein Bestimmen der Lastspannung 20b, wie dies in 1a und 1b beschrieben worden ist. Hieraus lässt sich nun eine Überspannung ΔU als Differenz der Lastspannung 20a und der Leerlaufspannung 20b ermitteln und damit der Innenwiderstand ΔR auf Grundlage der Überspannung ΔU und unter Berücksichtigung des Entladestroms. Der Innenwiderstand ist zunächst in Abhängigkeit des Alterungszustandes SoH bestimmt worden, 30a. Durch Invertieren erhält man ein Kennfeld 31a, welches den Alterungszustand SoH in Abhängigkeit vom Innenwiderstand ΔR darstellt. Dieses Kennfeld 31a wird im Kennfeldspeicher 35a des Fahrzeuges abgelegt und kann zur Bestimmung des Alterungszustandes SoC der Batterie 105 gemäß der Verfahren gemäß der Erfindung genutzt werden.

2a shows a method for determining a map at the end of discharge, which the internal resistance ΔR and the state of aging SoH correlated with each other. 2 B shows a method for determining a map, which the internal resistance ΔR and the state of aging SoH correlates with each other depending on the state of charge SoC the battery. The preferred steps for this are described in detail below:

• The map 31a at the end of discharge can be determined after determining the open circuit voltage 20a and determining the load voltage 20b how this in 1a and 1b has been described. An overvoltage can now be derived from this ΔU as the difference in load voltage 20a and the open circuit voltage 20b determine and thus the internal resistance ΔR based on the surge ΔU and taking into account the discharge current. The internal resistance is initially dependent on the Aging condition SoH been determined 30a . A map is obtained by inverting 31a which indicates the state of aging SoH depending on the internal resistance ΔR represents. This map 31a is in the map memory 35a of the vehicle and can be used to determine the state of aging SoC the battery 105 be used according to the method according to the invention.

While in 2a the map 31a has been generally determined, the map 31b also preferably depending on the state of charge SoC be determined. This is in 2 B shown. First, the open circuit voltage is determined 20a and determining the load voltage 20b how this in 1a and 1b has been described. An overvoltage can now be derived from this ΔU as the difference in load voltage 20a and the open circuit voltage 20b determine and thus the internal resistance ΔR based on the surge ΔU and the discharge current. For different charge states SoC there are sometimes different values. The internal resistance is initially dependent on the state of aging SoH and depending on the state of charge SoC been determined 30b . A map is obtained by inverting 31b which indicates the state of aging SoH depending on the internal resistance ΔR and state of charge SoC represents. This map 31b is in the map memory 35b of the vehicle and can be used to determine the state of aging SoC the battery 105 be used according to the method according to the invention.

3rd shows a method for determining the aging state of the battery according to an embodiment of the invention. While driving 40 the load voltage is measured, 42 . The battery voltage can relax outside the operation of the vehicle, 44 . In other words, a cell voltage arises which essentially corresponds to the equilibrium voltage of the cell. The relaxation time should preferably be at least 30 minutes. The measured voltage then essentially corresponds to the open circuit voltage OCV , 46 . The internal resistance can be determined from the open circuit voltage and the load voltage. For this purpose, the overvoltage is determined using the following equation 2a Eq 2a : $$\mathrm{\Delta }U=U_{relaxed}-U_{endOfD\mathrm{C.}H},$$

Based on the overvoltage and the current at discharge, the internal resistance of the cell is determined using the following equation 2b, Eq 2nd : $${\mathrm{<figure-callout\; id="0"\; label="R"\; filenames="DE102019211913A1\_0009.png"\; state="\{\{state\}\}">R</figure-callout>}}_{0\%}=\frac{\mathrm{\Delta }R}{\mathrm{\Delta }\mathrm{I.}}=\frac{U_{relaxed}-U_{endOfD\mathrm{C.}H}}{{\mathrm{I.}}_{D\mathrm{C.}H}}.$$

A map showing the internal resistance ΔR correlated with the state of aging, was (as before using 1 and 2nd described) and stored in the map memory of the vehicle, 47 . Using the map, the internal resistance obtained can be used ΔR the state of aging can be determined 48 .

4th shows a system for determining the aging condition of the battery 105 according to an embodiment of the invention. The system includes a charger 100 , by means of which the battery 105 can be loaded. The battery contains an electrochemical cell 110 . Measuring devices are also provided. In particular, by means of the voltage measuring device 111 the battery voltage can be measured. This enables the determination of the open circuit voltage and the load voltage. An ammeter 112 allowed to measure the existing currents. Furthermore, a Temperature measuring device 113 provided to control the temperature. The information provided by the measuring devices 111 , 112 , 113 recorded become a control unit 120 transmitted. The internal resistance of the electrochemical cell can be determined from the open circuit voltage and the load voltage and the current measured during discharge 110 be determined. The map, which shows the internal resistance ΔR and the state of aging SoH correlated, is then in the map memory of the control unit 120 filed. Using the map, the internal resistance obtained can be used ΔR the aging of the battery 105 be determined. This is shown to the driver on the screen 130 displayed.

5 shows a system for determining the aging condition of the battery 105 according to a further embodiment of the invention. The system includes a charger 100 , by means of which the battery 105 can be loaded. The battery contains several electrochemical cells 110a , 110b , 110c . Measuring devices are also provided in each of the cells. In particular, by means of the voltage measuring device 111 the battery voltage can be measured. This enables the determination of the open circuit voltage and the load voltage. An ammeter 112 allowed to measure the existing currents. There is also a temperature measuring device 113 provided to control the temperature. The information provided by the measuring devices 111 , 112 , 113 for each of the cells 110a , 110b and 110c recorded become a control unit 120 transmitted. The internal resistance of the electrochemical cells can be determined from the open circuit voltage and the load voltage and the current measured during discharge 110a , 110b and 110c be determined. The map, which shows the internal resistance ΔR and the state of aging SoH correlated, is in the map memory of the control unit 120 filed. Using the map, the internal resistance obtained can be used ΔR the state of aging SoH each of the cells 110a , 110b , 110c individually and therefore also the entire battery 105 be determined. This is shown to the driver on the screen 130 displayed.

6 shows the dependence of the internal resistance ΔR from the state of aging SoH the cell. They are calendar measurements 200 of cells that were stored at different charge states and a temperature of 23 ° C. There is also a model characteristic 210 shown. The model characteristic 210 and the calendar measurements are in good agreement. The figure shows the general trend of decreasing internal resistance at the end of discharge with decreasing SoH with a decreasing amount of mobile lithium in the cell. Is a corresponding map showing the internal resistance ΔR and the state of aging SoH correlated, stored in the map memory of a control unit of a vehicle, can be obtained from the internal resistance obtained using this map ΔR the state of aging SoH , according to the method of the invention. Here you make the clear dependence on internal resistance and SoH advantage.

7a now shows the characteristics of the half cells and the full cell both as OCV as well as when discharging. The battery is in new condition. The voltage characteristic OCV the cathode 220 and the voltage characteristic of the cathode when discharged 222 are shown. Furthermore, the voltage characteristic OCV the anode 230 shown. From the voltage characteristic OCV the anode 230 and the voltage characteristic OCV the cathode 220 the voltage characteristic OCV the full cell 240 to construct. It was found for the anodic voltage characteristic that the overvoltages can be neglected to a good approximation. Therefore, only the voltage characteristic is for the anode OCV shown, which is assumed in the course of the approximation used here that this essentially coincides with the voltage characteristic when discharging. From the voltage characteristic of the cathode when discharging 222 and the voltage characteristic OCV the anode 230 therefore the voltage characteristic of the full cell 242 construct on discharge. The voltage characteristic curves of the full cell are preferably also measured - for the purpose of checking the constructed characteristic curves. In the present case, a lower voltage limit of 2.5 V has been set. This voltage value marks the end of discharge here. The figure can be seen that while the voltage characteristic OCV the full cell 240 a state of charge SoC of almost 0%, the voltage characteristic of the full cell when discharged 242 a state of charge SoC which is higher. Overall, this is the usable capacity C _hours less than the capacity below OCV conditions Cocv . These charge capacities are shown in the figure by the horizontal arrows. Furthermore, the overvoltage ΔU plotted as the difference in voltage OCV the full cell and the voltage of the full cell when discharging at the end of discharge, i.e. at 2.5 V.

7b now shows the change in the characteristics of the half cells as well as the full cell both as OCV as well as when discharging after anodic lithium removal.

7b shows like in the case of 7a the voltage characteristics of the battery when new. The voltage characteristic OCV the full cell 240 or the voltage characteristic of the full cell when discharging 242 can be constructed as described above. It is now shown how a reduction in the mobile lithium concentration at the anode leads to a shift in the characteristic curves in the event of battery aging. The figure shows the voltage characteristic shifted to the right (more generally formulated: the anode shifted in the direction of lower cathode lithiation) OCV the anode 230` resulting from the removal of lithium, the shifted voltage characteristic OCV the full cell 240` and the shifted voltage characteristic of the full cell when discharged 242 ' . Even the shifted characteristics of the full cell 240 ' and 242 ' result from the voltages of the half cells as described. The surge ΔU after battery aging it is shown as the difference in the shifted voltage OCV the full cell and the voltage of the full cell when discharging at the end of discharge, i.e. here at 2.5 V. It is evident that the surge ΔU compared to that in 7a described case of the new, i.e. non-aged, cell is less. The lower overvoltage corresponds to a lower internal resistance ΔR , which can be determined from the overvoltage, taking into account the current strength. This correlation of internal resistance and mobile lithium concentration, reflecting the aging condition SoH has already been described 6 discussed.

Reference symbol list

SoH

State of aging

SoC

State of charge

OCV

Open circuit voltage

ΔR

Internal resistance

5a

OCV Full cell literature

5b

Load voltage full cell literature

10a

Open circuit voltage OCV anode

10b

Anode load voltage

15a

Open circuit voltage OCV cathode

15b

Load voltage cathode

20a

Open circuit voltage OCV constructed

20b

Constructed load voltage

Eq1a

Equation 1a

Eq1b

Equation 1b

Eq2

Equation 2

30a

Map R ( SoH )

30b

Map R ( SoH , SoC )

31a

inverted map SoH ( R )

31b

inverted map SoH ( R , SoC )

35a

Memory with map

35b

Memory with map

40

Drive

42

Measure load voltage

44

Relaxation

46

Open circuit voltage OCV measure the voltage

47

Map R ( SoC ) determine

48

SoH determine by comparison with map

100

charger

105

battery

110, 110a, 110b, 110c

electrochemical cell

111

Tension meter

112

Ammeter

113

Temperature measuring device

120

Control unit / control unit

130

screen

200

calendar characteristic ΔR against SoH

210

Model characteristic curve ΔR against SoH

220

Voltage characteristic OCV cathode

222

Voltage characteristic curve cathode during discharge

230

Voltage characteristic OCV anode

230`

shifted voltage characteristic OCV anode

240

Voltage characteristic OCV Full cell

240`

shifted voltage characteristic OCV Full cell

242

Full cell voltage characteristic during discharge

242`

shifted voltage characteristic during discharge

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102011077448 A1 [0004]
• EP 1961621 A1 [0005]
• EP 2846395 A2 [0006]

Claims (10)

Method for determining an aging state of a battery (105) in a vehicle, comprising the steps: - determining (42) a load voltage during vehicle operation (40); - Relaxation (44) of the battery (105) after vehicle operation; - determining (46) an open circuit voltage (OCV) after relaxation; - determining an internal resistance (ΔR) from the load voltage and the open circuit voltage (OCV); - Deriving (48) the aging condition (SoH) of the battery (105) by means of a map (31a, 31b) which correlates the internal resistance (ΔR) and the aging condition with one another. Procedure according to the previous one Claim 1 , where the state of charge (SoC) is at most 20%. Method according to one of the preceding claims, wherein the characteristic diagram (31a, 31b) is determined by the steps: - determining (48) a full cell open circuit voltage (OCV) as a function of the aging state (SoH) of the battery (105); - determining (48) a full cell load voltage as a function of the aging state (SoH) of the battery (105); - Determining an overvoltage (ΔU) as the difference between the load voltage and the open circuit voltage (OCV); - Determine the internal resistance (ΔR) based on the overvoltage. Procedure according to the previous one Claim 3 , wherein the map (31a, 31b) is determined as a function of the state of charge (SoC) of the battery (105). Method according to one of the two previous Claims 3 or 4th , wherein the full cell open circuit voltage (OCV) is constructed from the open circuit voltage (OCV) of the anode (10a) and the open circuit voltage (OCV) of the cathode (15a). Method according to one of the preceding Claims 3 to 5 , wherein the full-cell load voltage is constructed from the load voltage of the anode (10b) and the load voltage of the cathode (15b). Method according to one of the preceding claims, wherein the battery (105) is a lithium-ion accumulator. Method according to one of the preceding claims, wherein the determination (42) of the load voltage takes place at the end of discharge. Control device (120) which is designed to carry out the method according to one of the preceding claims. Vehicle, comprising at least one control unit (120) according to Claim 9 .

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