Determining a state of charge and / or a state of health of a battery cell
Patent Information
- Authority / Receiving Office
- EP · EP
- Patent Type
- Applications
- Current Assignee / Owner
- SIEMENS AG
- Filing Date
- 2024-10-01
- Publication Date
- 2026-06-17
AI Technical Summary
Current methods for determining the state of charge (SoC) and state of health (SoH) of batteries, particularly lithium-ion batteries, are complex, inaccurate, and often rely on time-dependent measurements that are prone to errors due to internal self-discharge and ancillary reactions.
A procedure that involves measuring the resting voltage and expansion of the battery cell to determine the loads on the electrodes, which are then used to calculate the SoC and SoH, utilizing functional connections and a system of equations to solve for the unknown loads.
This method provides a more accurate and robust determination of SoC and SoH during battery operation, without requiring complex models or time-consuming calculations, and is applicable to various battery types, including lithium-ion batteries.
Smart Images
Figure EP2024077535_17042025_PF_FP_ABST
Abstract
Description
[0001] 202318806 1 Description Determination of a state of charge and / or a state of health of a battery cell The invention relates to a method according to the preamble of patent claim 1, a battery management system according to the preamble of patent claim 13 and a battery cell or a battery according to the preamble of patent claim 14. Determining the state of charge (SOC) and the state of health (SOH) of batteries, in particular lithium-ion batteries, as accurately as possible is crucial for assessing the performance and possible uses of the batteries. A typical aging mechanism of batteries or battery cells is the loss of electrochemically available charge. The increase in this electrochemically inactive charge leads to the state of health or the aging state of the battery decreasing over time.The temporal progression of the SOH is typically complex and depends on the specific operation of the battery and on a multitude of external influences. Typically, the determination of the SOC and the SOH using measured variables accessible during battery operation is not directly possible. Therefore, complex and thus error-prone or inaccurate methods are used for this purpose, which are provided, for example, by a battery management system. Typically, the SOH and SOC are calculated using time-dependent measured variables, such as current waveforms, voltage waveforms, and possibly temperature waveforms. The charges exchanged between the battery electrodes can also be determined using the current waveforms measured over time. Furthermore, internal self-discharge and side reactions of a battery cannot be measured.In addition, there are errors due to measurement accuracy, which can accumulate over longer charge determination times. Therefore, the measured charge cannot be used to determine the actual charge change between the electrodes, which leads to errors in the determined SOC or SOH. Other known methods use measurements of the internal resistance and temperature, for example impedance spectroscopy methods, and compare the recorded measured values with aging models. However, it is also important to know the charge currently stored in the electrodes, as the exact assignment of the measured resistance value to the model depends on this. Furthermore, a variety of manufacturer-specific approximate and heuristic methods for determining the SOC or SOH are known.The present invention is based on the object of providing an improved method for determining the state of charge and / or state of health of a battery cell, in particular during operation of the battery cell. The object is achieved by a method having the features of independent patent claim 1, by a battery management system having the features of independent patent claim 13 and by a battery cell or a battery having the features of independent patent claim 14. Advantageous embodiments and developments of the invention are specified in the dependent patent claims. 202318806 3 The inventive method for determining a state of charge SOC and / or a state of health SOH of a battery cell with a nominal charge ^^ (nominal capacity), wherein the nominal charge ^^ is a charge ^^. ା a first electrode and a charge ^^ ିa second electrode of the battery cell and an inactive charge ^^ ^ the battery cell, is characterized by at least the following steps: - Providing a first functional relationship ^^^ ^^ ା , ^^ ି ^ for a rest voltage of the battery cell; - Providing a second functional relationship ^^^ ^^ ା , ^^ ି , ^^ ^ ^ for an expansion of the battery cell; - recording a measured value ^^ of the open-circuit voltage; - recording a measured value ^^ of the expansion; and - determining the state of charge SOC and / or the state of health SOH by solving the system of equations ^^ ൌ ^^^ ^^ ା , ^^ ି ^, ^^ ൌ ^^^ ^^ ା , ^^ ି , ^^ ^ ^ and ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^The method according to the invention and / or one or more functions, features and / or steps of the method according to the invention and / or one of its embodiments can be computer-aided. In particular, the system of equations can be solved numerically using a computing unit, for example a computer. In this case, an exact solution of the system of equations is not required; it is sufficient to come as close as possible to an exact solution, for example up to a specified error limit. The order of the steps of the method does not imply a chronological sequence of the aforementioned steps. For example, the recording of the measured values and / or the provision of the functional relationships can take place in parallel. Features, embodiments and / or exemplary embodiments relating to the state of charge can be directly and clearly transferred analogously to the state of health.202318806 4 In principle, all of the above-mentioned quantities and dependencies can be time-dependent. The expansion of the battery cell can be an absolute spatial expansion of the battery cell, for example in a spatial direction, a relative expansion with respect to an original or initial expansion of the battery cell (difference value from the original expansion), an expansion normalized to an original or initial expansion of the battery cell, and / or a relative change in the absolute spatial expansion of the battery cell with respect to an original or initial expansion of the battery cell (difference quotient). In particular, the expansion is a volume normalized to an original volume. A functional relationship can be understood as the mathematical possibility of inferring the value of one or more further quantities from a value of one or more quantities.A functional relationship can, for example, be presented in the form of a function, in particular a fit function, a table, and / or a graph / diagram. The first functional relationship describes or models the dependence of the resting voltage. the battery cell from the charges of the electrodes ^^ ା , ^^ ି The second functional relationship describes or models the dependence of the expansion of the battery cell ^^^ ^^ ା , ^^ ି , ^^ ^ ^ from the charges of the electrodes ^^ ା , ^^ ି as well as the existing inactive charge ^^ ^. The battery cell comprises the first and second electrodes, which can also be referred to as the positive electrode and the negative electrode, respectively. Essentially, each electrode is associated with a charge or a capacity. If the battery has the nominal charge ^^, then 202318806 5 includes the charges of the electrodes ^^ ା , ^^ ି as well as possible inactive charges ^^ ^ , for example, due to the age of the battery cell. The charge ^^ is the nominal specified capacity of the battery cell at the beginning of its service life and is therefore known in advance, for example, from a manufacturer's specification. A basic idea of the present invention is that the state of charge and / or the state of health can be determined when the charges ^^ ା , ^^ ି and if necessary ^^ ^are known. However, the charges mentioned are not directly measurable. According to the invention, however, it is provided to determine the charges using measurable quantities, in this case the open-circuit voltage and the expansion of the battery cell. A third functional relationship is charge conservation ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^ used. In other words, it is intended to establish a system of equations by means of which the charges can be determined based on measured variables. Once the charges have been determined or their values calculated, the state of charge and / or health of the battery cell can be determined. To determine the three charges, three relationships and three measured variables are therefore fundamentally required. According to the invention, the three relationships are represented by the relationships ^^ ൌ ^^^ ^^ ା , ^^ ି ^, ^^ ൌ ^^^ ^^ ା , ^^ ି , ^^^ ^ and ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^ The three measured variables are the open-circuit voltage ^^, the expansion ^^, and the previously known nominal charge ^^ of the battery cell, which could also be additionally determined by means of a measurement. By solving the aforementioned system of equations with the three unknowns ^^ ା , ^^ ି and ^^ ^The charges can thus be determined. The functional relationships are provided, i.e. they are known in advance. For example, these can be determined in advance by measurements in the form of characteristic curves. The characteristic curves can be determined for a specific type of battery cell in advance, for example by measurements and / or simulations of the respective electrodes, side reactions and cells. As a result, the characteristic curves during operation and for the method according to the invention are known. The present invention can therefore be used to determine the state of charge or the state of health of the battery cell by determining the unknown charges that are not directly accessible by measurement. Current measured values of the open-circuit voltage, the expansion and the previously known value of the nominal charge (capacity) of the battery cell are used for this purpose.This makes it possible, in particular, to determine the SOC and / or SOH during operation of the battery cell. In other words, the charges are determined by measuring ^^ and ^^ at the current operating time, whereby the current SOC and / or SOH can be determined. A further basic idea of the invention is that the measurable expansion of the battery cell is used as an additional required relationship. The expansion is particularly advantageous because it also depends on the inactive charge. Furthermore, the use of the expansion is particularly advantageous for lithium-ion cells with an increased energy density. This is the case because their negative electrodes typically comprise a proportion of silicon. Even in small quantities, silicon exhibits a large change in volume (expansion) depending on the absorbed charge.As a result, the expansion, in this case in the sense of a change in volume, can be measured with sufficient precision. The next generations of batteries or battery cells, for example based on solid-state electrolytes and / or metallic lithium and / or sodium, as well as those based on the intercalation of sodium ions, also exhibit comparatively large volume changes, which can be used as expansion within the meaning of the present invention. Previous lithium-ion cells typically use intercalation electrodes with low volume expansion. Nevertheless, in this case, the expansion of the graphite electrode during charging of the battery cell can also be measured.Furthermore, side reactions within the battery cell, which typically lead to an increase in inactive charges, can induce a volume change and thus influence the (current) expansion of the battery cell. An example of this is the continuous development of the solid electrolyte interface (SEI) layer. An implicit assumption of the method according to the invention is that the functional relationships or dependencies, for example in the form of characteristic curves, of the relevant materials of the battery cell are known and do not change significantly during aging. This also applies in principle to electrodes composed of multiple components / materials. For example, the negative electrode can comprise graphite and silicon.However, a loss of electrode material, for example due to particles losing electrical contact with the rest of the electrode, can change the relative proportions of positive to negative electrode, and / or the relative active components within an electrode, which would also mean a change in the assumed and provided voltage and / or expansion characteristics. The occurrence of other side reactions, which may not have been taken into account in the functional relationships, can also fundamentally falsify the determined values. However, compared to the cited prior art, the present invention provides a more robust method for determining 202318806 8 the SOC and / or the SOH. The method is based on physical quantities that can be measured at any time during battery cell operation. Furthermore, the method does not require complex models and / or calculations.In particular, no calculation of charge shifts by temporal integration of current curves (Coulomb counting) is required. A battery management system according to the invention for a battery cell is characterized in that it is designed to determine a state of charge and / or state of health of the battery cell using a method according to the invention and / or one of its embodiments. For this purpose, the battery management system can comprise a first measuring device for detecting the open-circuit voltage, a second measuring device for detecting the expansion, for example a dilatometer, and a computing unit for solving the system of equations and for determining the state of charge and / or the state of health. In this case, the functional relationships can be stored and thus provided by means of the computing unit.Similar, equivalent, and equivalent advantages and / or embodiments of the battery management system according to the invention result from the method according to the invention. A battery cell or battery according to the invention is characterized in that it comprises a battery management system according to the invention. Similar, equivalent, and equivalent advantages and / or embodiments of the battery cell or battery according to the invention result from the method according to the invention and from the battery management system according to the invention. 202318806 9 According to an advantageous embodiment of the invention, the charges ^^ are used to determine the state of charge SOC and / or the state of health SOH. ା , ^^ ି and / or ^^ ^ by solving the system of equations ^^ ൌ ^^^ ^^ ା , ^^ ି ^, ^^^ ^^ ା , ^^ ି , ^^ ^ ^ and ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^determined. This advantageously means that the charges are known. From the known charges, the state of charge or the state of health can be determined. In principle, the SOC and / or SOH can be used directly as variables, so that an explicit determination of the charges is not required for the method according to the invention, but is advantageous. In an advantageous development of the invention, the state of charge SOC is determined using SOC ൌ ^^ ି / ^ ^^ ା ^ ^^ ି^ is determined. This determines an advantageous state of charge of the battery cell. In particular, the stated state of charge refers to the state of charge of the negative electrode. According to the present invention, a state of charge of the battery cell is determined, i.e. there are several possible technically useful definitions of the state of charge. For example, the state of charge can refer to the negative electrode through SOC ൌ ^^ି / ^ ^^ା ^ ^^ି^ ≡SOCି or to the positive electrode through SOC ൌ ^^ା / ^ ^^ା ^ ^^ି^ ≡SOCା. It should be noted here that the state of charge of a battery cell, which is not related to a component, does not exhibit a fixed dependence on expansion over its service life. Thus, within the scope of the present invention, the state of charge of the battery cell is always understood to be the state of charge of a component of the battery cell, in particular one of the electrodes.Here, the state of charge of the battery cell is the standardized charge stored by the respective component, in particular the electrode. 202318806 10 Equivalent and also encompassed by the invention is the use of SOC. ା and SOC ି instead of ^^ ା respectively ^^ ି as variables of the system of equations to be solved. Further variables that are mathematically equivalent to the charges in this sense can be provided. According to an advantageous embodiment of the invention, a state of health SOH of the battery cell is determined by SOH ൌ ^ ^^ ା ^ ^^ ି^ / ^^ is determined, i.e., by means of the charges or charge quantities. Advantageously, the State of Health (SOH) of the battery cell is determined in this way. In particular, the SOH is determined without cyclical charging and discharging of the battery cell. As a result, the SOH, like the SOC, can advantageously be determined during operation of the battery cell. In an advantageous development of the invention, a rate of change of the state of health SOH is determined, and the aging or aging rate of the battery cell is determined using the rate of change. The temporal rate of change of the SOH can, for example, be achieved by determining the SOH several times over time. In other words, the method is carried out several times in succession. Through this repeated determination of the SOH and, if appropriate, analogously to the SOC, the possibly complex and temporally non-linear rate of change of the SOH can thus be determined.This advantageously makes it possible to predict the aging behavior of the battery. According to an advantageous embodiment of the invention, the first functional relationship is represented by ^^^ ^^. ା , ^^ ି ^ ൌ ^^ ା ^ ^^ ା ^ െ ^^ ^ ^^ ି ^ provided, where ^^ ା ^ ^^ ା ^ a voltage characteristic of the first electrode and ^^ ^ ^^ ି ^ is a voltage characteristic of the second electrode. 202318806 11 In other words, the first functional relationship is provided by two voltage characteristics. Here, the characteristic for the open-circuit voltage results from the potential difference between the two electrodes. The characteristics can be determined in advance and, for example, stored within the battery management system and thus provided. In an advantageous development of the invention, the second functional relationship is provided by ^^^ ^^ ା , ^^ି , ^^ ^ ^ ൌ ^^ ା ^ ^^ ା ^ ^ ^^ ି ^ ^^ ି ^ ^ ^^ ^ ^ ^^ ^ ^ provided, where ^^ ା ^ ^^ ା ^ an expansion characteristic of the first electrode, ^^ ି ^ ^^ ି ^ an expansion characteristic of the second electrode and ^^ ^ ^ ^^ ^ ^ an expansion characteristic with respect to the inactive charge ^^ ^ In other words, the (total) expansion of the battery cell is the sum of the expansion related to the respective charges. Thus, each charge is associated with a charge-specific expansion. The expansion characteristics ^^ ା ^ ^^ ା ^, ^^ ି ^ ^^ ି ^ and ^^ ^ ^ ^^ ^^ depend on the chemical and structural composition of the respective electrodes or materials / components. They are therefore fundamentally also dependent on the temperature of the battery cell, so that a temperature-dependent correction of the characteristic curves is additionally advantageous. The characteristic curves as well as their possible temperature dependence or temperature-dependent correction can in turn be determined in advance and, for example, stored within the battery management system and thus made available. According to an advantageous embodiment of the invention, a temperature of the battery cell is thus detected, with the respective characteristic curves taking into account the dependence on the detected temperature. This advantageously allows a temperature correction to be carried out so that the SOC and / or SOH can be determined more precisely, particularly during operation of the battery cell.Thus, the temperature is used as a further measured variable, for example in addition to the voltage, the current and the expansion. In an advantageous development of the invention, the characteristic curves are provided as a function of the respective material composition, in particular of the electrodes. As a result, the characteristic curves advantageously take into account the material-specific composition of the electrodes and thus of the battery cell. According to an advantageous embodiment of the invention, the characteristic curves are provided as a function of the type of battery cell. This advantageously further improves the determination of the SOC because the specific battery type is taken into account. In an advantageous development of the invention, the measured value ^^ of the expansion is recorded by means of a dilatometer, a force measurement, a pressure measurement and / or by means of strain gauges.Advantageously, the aforementioned measuring methods enable a particularly precise determination of the expansion. Furthermore, the aforementioned measuring methods are advantageously possible during operation of the battery cell. According to the aforementioned measuring methods, the expansion can thus be determined and thus recorded directly or indirectly. According to an advantageous embodiment of the invention, the state of charge SOC and / or the state of health SOH are determined during operation of the battery cell. This advantageously eliminates the need to interrupt the operation of the battery cell, as is the case, for example, with known methods. The present invention advantageously enables the SOC to be determined during operation by using measured values (open-circuit voltage and expansion) that are accessible and recordable during operation.Further advantages, features and details of the invention emerge from the exemplary embodiments described below and from the drawings. The following show schematically: Figure 1 shows a flow diagram of a method according to an embodiment of the invention; Figure 2 shows a first characteristic curve with regard to an expansion of a battery cell; and Figure 3 shows a second characteristic curve with regard to an expansion of a battery cell. Similar, equivalent or equivalent elements can be provided with the same reference numerals in one of the figures or in the figures. Figure 1 shows a flow diagram of a method for determining a state of charge SOC and / or a state of health SOH of a battery cell according to an embodiment of the invention. The battery cell has a nominal charge ^^.Typically, the nominal charge ^^ of the battery cell is stored by means of a positive and negative electrode, or by means of a first and second electrode of the battery cell, or is lost in an electrochemically inactive form, for example, due to aging. Thus, ^^ ൌ ^^. ା ^ ^^ ି ^ ^^ ^ , where ^^ ^ The electrochemically inactive charge. The nominal charge or nominal capacity is typically known or can be measured at the beginning of the battery cell's service life. The aging state of the battery cell can be determined using SOH ൌ ^^ ୫ୟ^ / ^^ can be determined, where ^^ ୫ୟ^is the maximum storable electrical charge of the battery cell at a current point in time, and ^^ is the nominally specified capacity at the beginning of the battery cell's service life. The battery cell's state of charge can be determined using SOC ൌ ^^ / ^^ ୫ୟ^ The maximum storable charge corresponds to the electrochemically active components, so that ^^ ୫ୟ^ ൌ ^^ ା ^ ^^ ି Furthermore, the currently stored charge corresponds to the charge of the negative electrode, so that ^^ ൌ ^^ ି Thus, the aging state can be determined using SOH ൌ ^ ^^ ା ^ ^^ ି ^ / ^^ and the state of charge using SOC ൌ ^^ ି / ^ ^^ ା ^ ^^ ି^ can be determined. In other words, the charge state and / or the aging state of the battery cell can be determined using the mentioned charges. However, the metrological detection of the mentioned charge during operation of the battery cell is not directly possible. However, the present method and the method described below enable a determination during operation. In a first step S1 of the method, a first functional relationship for the open-circuit voltage of the battery cell. The open-circuit voltage of a battery cell is a key measurement that generally allows conclusions to be drawn about the charge state. The open-circuit voltage can be determined, for example, from the potential difference between the two electrodes by ^^^ ^^ ା , ^^ ି ^ ൌ ^^ ା ^ ^^ ା ^ െ ^^ ^ ^^ ି^ can be determined. 202318806 15 dependencies of the electrode voltages can be determined by the respective voltage characteristics ^^ ା ^ ^^ ା ^, ^^ . ^ ^^ ି ^ be given. In a second step S2 of the method, a second functional relationship ^^^ ^^ ା , ^^ ି , ^^ ^^ for an expansion of the battery cell. A basic idea of the invention is that three independent physical measured variables are required to determine the three unknown charges that are necessary for determining the state of charge and / or the state of aging. It has been shown that the expansion of the battery cell is particularly advantageously related to the charges and can also be detected during operation of the battery cell. In other words, a physical variable additional to the rest voltage is used, which correlates with the stored charge. In battery types that are particularly advantageous for the method, the charge is stored using active and / or inactive materials. As a result, due to their composition, the electrodes typically expand when they absorb charge and contract when they release charge.This results in a change in volume (expansion) of the electrode, which is transferred to a change in volume of the battery cell and / or a change in pressure within the battery cell. Thus, the expansion in the form of a change in volume and / or pressure or a change in pressure is a measurable quantity that is used to determine the stored charge of the battery cell. For several battery types, particularly lithium-ion batteries, the expansion can be recorded using dilatometers and correlated with the charge stored in the battery. In other words, the instantaneous expansion of the battery cell during operation of the battery cell can be measured, for example, by using a dilatometer, strain gauges, and / or other principles at the cell level, module level, and / or system level. Furthermore, the expansion can also be recorded indirectly via pressure measurements and / or force measurements.The expansion can be measured using electrode-specific and / or material-specific expansion curves. In other words, ^^^ ^^. ା , ^^ ି , ^^ ^ ^ ൌ ^^ ା ^ ^^ ା ^ ^ ^^ ି ^ ^^ ି ^ ^ ^^ ^ ^ ^^ ^ ^, where an expansion characteristic of the first electrode (positive electrode), ^^ ି ^ ^^ ି ^ an expansion characteristic of the second electrode (negative electrode) and ^^ ^ ^ ^^ ^ ^ an expansion characteristic with respect to the inactive charge ^^ ^The provided dependency or functional relationships can take a temperature dependency into account. In this case, a temperature of the battery cell is also recorded as a further measured variable and the dependencies are corrected accordingly. In a third step S3 of the method, a measured value ^^ of the open-circuit voltage is recorded. This can be done, for example, using known methods, i.e. basically by measuring voltages and / or currents. In a fourth step S4 of the method, a measured value ^^ of the expansion is recorded. This can be done, for example, using a dilatometer, using strain gauges and / or other known methods at the cell level, module level and / or system level. Furthermore, the expansion can be recorded using a pressure measurement and / or force measurement.According to a fifth step S5 of the method, at least the state of charge SOC and / or the state of health SOH is determined by 202318806 17 solving the system of equations ^^ ൌ ^^^ ^^. ା , ^^ ି ^, ^^ ൌ ^^^ ^^ ା , ^^ ି , ^^ ^ ^ and ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^ The state of charge can be determined, for example, using the relationship SOC ൌ ^^ ି / ^ ^^ ା ^ ^^ ି ^ possible. The health status can be determined, for example, using SOH ൌ ^ ^^ ା ^ ^^ ି ^ / ^^ possible. The three charges or charge values or capacities can be determined based on the three independent equations ^^ ൌ ^^^ ^^ ା , ^^ ି ^, ^^ ൌ ^^^ ^^ ା , ^^ ି , ^^ ^ ^ and ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^can typically be determined unambiguously. This can be done computer-aided. For example, from the measurement of the expansion ^^ ൌ ^^^ ^^ ା , ^^ ି , ^^ ^ ^ ൌ ^^ ା ^ ^^ ା ^ ^ ^^ ି ^ ^^ ି ^ ^ ^^ ^ ^ ^^ ^ ^ the inactive charge ^^ ^ depending on the further charges ^^ ା and ^^ ି In other words, after measuring the expansion ^^ ^ ൌ ^^^ ^^ ା , ^^ ି | ^^^, where ^^ denotes the functional relationship. Since the nominal capacity ^^ is typically known, for example from manufacturer specifications, ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^ the negative charge can be determined as a function of the positive charge. In other words, ^^ ି ൌ ^^^ ^^ ା | ^^, ^^^, where ^^ ^^ again denotes the functional relationship. Using the measured value of the resting voltage ^^ and the provided relationship, the dependence of the negative charge on the positive charge can finally be eliminated, so that ^^ ି ൌ ^^^ ^^, ^^, ^^^ is, where ^^ ^^ again denotes the functional relationship. Thus, ^^ ି determined by the measured values ^^ and ^^ as well as the known nominal capacity ^^. By inserting the determined value of the negative charge into the further relationships, the other charges ^^ can be determined analogously. ା and ^^ ^The charge level and / or the aging level of the battery cell can then be determined using the determined charges. Figure 2 shows a first characteristic curve relating to the expansion of a battery cell. Here, an electrode 202318806 18 of the battery cell comprises silicon, and only the expansion of the silicon material is shown. The charge level of the battery cell or component / electrode is plotted on an abscissa 100 of the diagram. The expansion, in this case in the form of a volume normalized to an original volume, Vol / Vol ୧୬୧ୟ୪ (Expansion = Vol / Vol ୧୬୧ୟ୪), plotted. The expansion or expansion characteristic curve 2 was recorded when the battery cell was charging. The expansion or expansion characteristic curve 2' was recorded when the battery cell was discharging. A substantially linear dependency is evident for both expansion characteristic curves 2, 2'. This relationship can be approximated, likewise in the non-linear case, by a fitting function. As a result, the dependency of the expansion on the charge or, equivalently, on the state of charge of the respective battery component is determined. The dependency determined in advance in this way can be provided for the method according to the invention and / or one of its embodiments. Figure 3 shows - analogous to Figure 2 - a second characteristic curve relating to an expansion of a battery cell. Here, one electrode of the battery cell comprises graphite, and only the expansion of the graphite material is shown.The state of charge of the battery cell or component is plotted along the abscissa 100 of the diagram. The expansion, represented in the form of a volume normalized to an original volume, Vol / Vol, is plotted along the ordinate 101 of the diagram. ୧୬୧ୟ୪ (Expansion = Vol / Vol ୧୬୧ୟ୪), is plotted. The expansion characteristic 2 of graphite, in contrast to the expansion characteristic of silicon, shows a plateau 3 which corresponds to a phase transition 3 of the graphite (2L → 2). Outside of the plateau 3, the relationship between expansion and 202318806 19 capacity or charge is again essentially linear. This relationship can be approximated, likewise in the non-linear case, by a fitting function. This determines the dependence of the expansion on the charge or, equivalently, on the state of charge of the respective battery component. The dependence determined in advance in this way can be provided for the method according to the invention and / or one of its embodiments.Although the invention has been illustrated and described in detail by the preferred embodiments, the invention is not limited by the disclosed examples, and other variations may be derived therefrom by those skilled in the art without departing from the scope of the invention.
[0002] 202318806 20 List of reference symbols S1 first step S2 second step S3 third step S4 fourth step S5 fifth step 2 expansion characteristic (charging) 2' expansion characteristic (discharging) 3 phase transition 100 abscissa 101 ordinate
Claims
202318806 21 claims 1. Method for determining a state of charge SOC and / or a state of health SOH of a battery cell with a nominal charge ^^, wherein the nominal charge ^^ is a charge ^^ ା a first electrode and a charge ^^ ି a second electrode of the battery cell and an inactive charge ^^ ^ of the battery cell, characterized by the steps: providing a first functional relationship for a rest voltage of the battery cell; providing a second functional relationship ^^ ^ ^ for an expansion of the battery cell; Recording a measured value ^^ of the rest voltage; - (S4) Recording a measured value ^^ of the expansion; and - (S5) Determining the state of charge SOC and / or the state of health SOH by solving the system of equations ^^ ൌ ^^^ ^^ ା , ^^ ି ^, ^^ ൌ ^^^ ^^ ା , ^^ ି , ^^ ^^ and ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^ 2. Method according to claim 1, characterized in that for determining the state of charge SOC and / or the state of health SOH the charges ^^ ା , ^^ ି and / or ^^ ^ by solving the system of equations ^^ ൌ ^^^ ^^ ା , ^^ ି ^, ^^^ ^^ ା , ^^ ି , ^^ ^ ^ and ^^ ൌ ^^ ା ^ ^^ ି ^ ^^ ^ 3. Method according to claim 2, characterized in that the state of charge SOC is determined by means of SOC ൌ ^^ ି / ^ ^^ ା ^ ^^ ି ^ is determined.
4. Method according to claim 2 or 3, characterized in that a state of health SOH of the battery cell is determined by SOH ൌ ^ ^^ ା ^ ^^ ି^ / ^^ is determined.
5. The method according to claim 4, characterized in that a temporal rate of change of the state of health SOH is determined, and by means of the rate of change an aging rate of the battery cell is determined.
6. The method according to one of the preceding claims, characterized in that the first functional relationship 202318806 22 by ^^^ ^^ ା , ^^ ି ^ ൌ ^^ ା ^ ^^ ା ^ െ ^^ ^ ^^ ି ^ is provided, where ^^ ା ^ ^^ ା ^ a voltage characteristic of the first electrode and is a voltage characteristic of the second electrode.
7. Method according to one of the preceding claims, characterized in that the second functional relationship is represented by ^^^ ^^ ା , ^^ ି , ^^ ^ ^ ^ ^^ ^ ^ ^^ ^ ^ is provided, where ^^ ା ^ ^^ ା^ an expansion characteristic (2, 2') of the first electrode, ^^ ି ^ ^^ ି ^ an expansion characteristic (2, 2') of the second electrode and ^^ ^ ^ ^^ ^ ^ an expansion characteristic (2, 2') with respect to the inactive charge ^^ ^is.
8. Method according to claim 6 or 7, characterized in that a temperature of the battery cell is detected, and the respective characteristic curves take into account the dependence on the detected temperature.
9. Method according to one of claims 6 to 8, characterized in that the characteristic curves are provided as a function of the respective material composition, in particular of the electrodes.
10. Method according to one of claims 6 to 9, characterized in that the characteristic curves are provided as a function of the type of battery cell.
11. Method according to one of the preceding claims, characterized in that the measured value ^^ of the expansion is detected by means of a dilatometer, a force measurement, a pressure measurement and / or by means of strain gauges.
12. Method according to one of the preceding claims, kennzeichnet dadurch, dass die Ermittlung des Ladezustandes SOC und / oder des Gesundheitszustandes SOH während eines Be-13. Battery management system for a battery cell, characterized in that it is designed to provide a charging 202318806 23 state SOC and / or a state of health SOH of the battery cell according to a method according to one of the preceding claims.
14. Battery cell or battery, characterized in that it comprises a battery management system according to the invention according to Anspruch 13 umfasst.