Method for diagnosing an energy storage unit of an aerosol generating device; aerosol generating device; and computer program

Abstract

The present disclosure relates to a method for diagnosing an energy storage unit of an aerosol generating device, the method comprising: applying a periodically varying current to the energy storage unit; measuring a plurality of impedance values of the energy storage unit, wherein each impedance value is measured for one of a set of independently spaced-apart frequencies of the periodically varying current; and determining, based on the plurality of impedance values, whether or not the energy storage unit is suitable for further usage in the aerosol generating device.

Description

[0001] METHOD FOR DIAGNOSING AN ENERGY STORAGE UNIT OF AN AEROSOL GENERATING DEVICE ; AEROSOL GENERATING DEVICE ; AND COMPUTER PROGRAM

[0002] TECHNICAL FIELD

[0003] The present disclosure relates to a method for diagnosing an energy storage unit of an aerosol generating device , to an aerosol generating device , and to a computer program .

[0004] BACKGROUND

[0005] An aerosol generating device is a portable ( i . e . hand-held) device which heats an aerosol generating material , without burning or combusting it , to a temperature typically in the range of 150 ° C to 300 ° C in order to generate a vapor which typically then cools and condenses to form an aerosol for inhalation by a user of the aerosol generating device . Commonly available aerosol generating devices may use one of a plurality of di f ferent techniques for heating the aerosol generating material . All these techniques require some kind of internal energy source . The energy is typically provided as electric energy by providing the aerosol generating device with an energy storage unit such as a battery or a capacitor, which is typically charged by an external power supply .

[0006] For reliable operation, the energy storage unit needs to be regularly monitored . This may include diagnosing the energy storage unit based on performance indicators such as the state of charge ( SoC ) and state of health ( SoH) of the energy storage unit . The SoC is usually defined as a present value of the remaining ( electric ) charge capacity of the energy storage unit relative to a (present ) value of the maximum charge capacity of the energy storage unit . The SoH is usually defined as the present value of the maximum charge capacity ( of an aged storage unit ) relative to an original value of the maximum charge , i . e . when the energy storage unit was new ( e . g . at a time when a number of charging / di scharging cycles is zero or close to zero ) . As an alternative, the SoH may be defined as the present value of internal resistance of the energy storage unit relative to an original value of the internal resistance value of the energy storage . In general , units of both of the SoC and the SoH may be given as a percentage [ % ] . Other electrical parameters such as an internal resistance or capacitance of the energy storage unit may be used as performance indicators .

[0007] SUMMARY

[0008] Due to time required to perform the necessary measurements and analysis of the measurement data, diagnosing the energy storage unit of an aerosol generating device may require signi ficant computational resources and may lead to a downtime in which the aerosol generating device is not fully operational . There is thus a need to reduce the computational resources and time required for diagnosing an energy storage unit of an aerosol generating device , and more in general to improve the diagnosi s of an energy storage unit .

[0009] One embodiment relates to a method for diagnosing an energy storage unit of an aerosol generating device . The method comprises applying a periodically varying current to the energy storage unit . The method further comprises measuring a plurality of impedance values of the energy storage unit , wherein each impedance value is measured for one of a set of independently spaced-apart frequencies of the periodically varying current . The method further comprises determining, based on the plurality of impedance values , whether or not the energy storage unit is suitable for further usage in the aerosol generating device .

[0010] Another embodiment relates to an aerosol generating device comprising a control unit configured to perform the method according to an embodiment . Further preferred embodiments are defined in the dependent claims .

[0011] The method according to an embodiment is able to reduce the computational resources and time required for diagnosing an energy storage unit of an aerosol generating device .

[0012] Further embodiments of the invention are as follows :

[0013] Embodiment El . A method for diagnosing an energy storage unit of an aerosol generating device , the method comprising : applying a periodically varying current to the energy storage unit ; measuring a plurality of impedance values of the energy storage unit , wherein each impedance value is measured for one of a set of independently spaced-apart frequencies of the periodically varying current ; and determining, based on the plurality of impedance values , whether or not the energy storage unit is suitable for further usage in the aerosol generating device .

[0014] Embodiment E2 . The method according to claim El , wherein measuring each impedance value comprises controlling the periodically varying current to have a corresponding one of the set of independently spaced-apart frequencies .

[0015] Embodiment E3 . The method according to any one of embodiments El to E2 , wherein the plurality of impedance values comprises : a first impedance value of the energy storage unit measured for a first frequency o f the periodically varying current ; a second impedance value of the energy storage unit measured for a second frequency of the periodically varying current ; wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on whether or not one or more of the first impedance value and the second impedance value is greater than a corresponding threshold value ; and wherein a ratio of a second frequency divided by a first frequency is between 20 to 500 , 000 .

[0016] Embodiment E4 . The method according to embodiment E3 , wherein the first frequency is between 0 . 1 Hz to 50 Hz , and / or the second frequency is between 1 kHz to 50 kHz .

[0017] Embodiment E5 . The method according to any one of embodiments E3 to E4 , wherein each of the corresponding threshold values is based on one or more of a state of charge , SoC, of the energy storage unit and a temperature of the energy storage unit .

[0018] Embodiment E 6 . The method according to any one of embodiments El to E5 , wherein the plurality of impedance values comprises at least three impedance values , and wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on a reconstructed electrochemical impedance spectrum derived by fitting a mathematical function representing a curve in the complex plane to the at least three impedance values .

[0019] Embodiment E7 . The method according to embodiment E 6 , wherein a third frequency is between 50 Hz and 1 kHz .

[0020] Embodiment E8 . The method according to any one of embodiments E 6 to E7 , wherein the plurality of impedance values comprises at most five impedance values .

[0021] Embodiment E9 . The method according to any one of embodiments E 6 to E8 , wherein the mathematical function corresponds to a semi-circle in the complex plane .

[0022] Embodiment E10 . The method according to any one of embodiments E 6 to E9 , wherein the reconstructed electrochemical impedance spectrum indicates an electrolyte resistance , a charge trans fer resistance , and an interface capacitance , and wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on whether or not one or more of the electrolyte resistance , the charge trans fer resistance , and the interface capacitance is greater than a corresponding threshold value .

[0023] Embodiment El l . An aerosol generating device comprising : an energy storage unit ; an inverter unit configured to generate a periodically varying current applied to the energy storage unit ; and a control unit configured to measure a plurality of impedance values of the energy storage unit , wherein each impedance value is measured for one of a set of independently spaced-apart frequencies of the periodically varying current ; and determine , based on the plurality of impedance values , whether or not the energy storage unit is suitable for further usage in the aerosol generating device .

[0024] Embodiment E12 . An aerosol generating device according to embodiment El l , wherein the control unit is configured to measure each impedance value by controlling the periodically varying current to have a corresponding one of the set of independently spaced-apart frequencies .

[0025] Embodiment E13 . An aerosol generating device according to embodiment El l or E12 , wherein the plurality of impedance values comprises : a first impedance value of the energy storage unit measured for a first frequency o f the periodically varying current ; a second impedance value of the energy storage unit measured for a second frequency of the periodically varying current ; wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on whether or not one or more of the first impedance value and the second impedance value is greater than a corresponding threshold value ; and wherein a ratio of a second frequency divided by a first frequency is between 20 to 500 , 000 . Embodiment E14 . An aerosol generating device according to any of embodiments El l to E13 , wherein the first frequency is between 0 . 1 Hz to 50 Hz , and / or the second frequency is between 1 kHz to 50 kHz .

[0026] Embodiment E15 . An aerosol generating device according to any of embodiments El l to E14 , wherein each of the corresponding threshold values is based on one or more of a state of charge , SoC, of the energy storage unit and a temperature of the energy storage unit .

[0027] Embodiment El 6 . An aerosol generating device according to any of embodiments El l to E15 , wherein the plurality of impedance values comprises at least three impedance values , and wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on a reconstructed electrochemical impedance spectrum derived by fitting a mathematical function representing a curve in the complex plane to the at least three impedance values .

[0028] Embodiment E17 . An aerosol generating device according to embodiment E16 , wherein a third frequency is between 50 Hz and

[0029] 1 kHz .

[0030] Embodiment E18 . An aerosol generating device according to any of embodiments E16 to E17 , wherein the plurality of impedance values comprises at most five impedance values .

[0031] Embodiment E19 . An aerosol generating device according to any of embodiments E16 to E18 , wherein the mathematical function corresponds to a semi-circle in the complex plane . Embodiment E20 . An aerosol generating device according to any of embodiments E16 to E19 , wherein the reconstructed electrochemical impedance spectrum indicates an electrolyte resistance , a charge trans fer resistance , and an interface capacitance , and wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on whether or not one or more of the electrolyte resistance , the charge trans fer resistance , and the interface capacitance is greater than a corresponding threshold value .

[0032] Embodiment E21 . A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any of embodiments El to E10 .

[0033] BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Embodiments of the present disclosure , which are presented for better understanding the inventive concepts , but which are not to be seen as limiting the invention, will now be described with reference to the figures in which :

[0035] Fig . 1 shows a diagrammatic view of an aerosol generating device according to an embodiment ;

[0036] Fig . 2 shows a flowchart for a method for diagnosing an energy storage unit of an aerosol generating device according to an embodiment ; Fig . 3A shows an exemplary evolution of a low frequency resistance RLF with respect to the number of charging / cycles of the energy storage unit ;

[0037] Fig . 3B shows an exemplary evolution of a high frequency resistance RHF with respect to the number of charging / cycles of the energy storage unit ;

[0038] Fig . 4 shows a plurality of reconstructed electrochemical impedance spectra fitted to a plurality of measurement points for a plurality of energy storage units ;

[0039] Fig . 5 shows Nyquist plot illustrating an ideali zed electrochemical impedance spectrum comprising a semi-circle ;

[0040] Fig . 6 shows schematic representation of Li-ion mass trans fer phenomena which occur in Li-ion battery electrodes and their respective Nyquist plots ;

[0041] Fig . 7 shows an exemplary evolution of a charge trans fer resistance RCf with respect to the number of charging / cycles of the energy storage unit ;

[0042] Fig . 8 illustrates a block diagram of a computer adapted to perform a method according to an embodiment .

[0043] DETAILED DESCRIPTION

[0044] The present disclosure shall now be described in conj unction with speci fic embodiments . The speci fic embodiments serve to provide the skilled person with a better understanding but are not intended to in any way restrict the scope of the present disclosure , which is defined by the appended claims . In particular, the embodiments described independently throughout the description can be combined to form further embodiments to the extent that they are not mutually exclusive .

[0045] Generally, an aerosol generating device is an electrical device which heats an aerosol generating material to produce an aerosol for inhalation by a user of the aerosol generating device . The aerosol generating material is heated to a temperature typically in the range of 150 ° C to 300 ° C such that a vapor is generated without burning or combusting the aerosol generating material . Subsequently, as the vapor cools down and condenses , the aerosol is formed which is inhaled by the user . The aerosol generating device is typically provided in a portal ( i . e . hand-held) form factor and comprises an energy storage unit serving as internal energy source of the aerosol generating device . The energy storage unit provides electric power to the aerosol generating device . The energy storage unit may store energy as an electrochemical potential between electrodes . The electrochemical energy is converted into electric energy by means of a chemical reaction, whereby electrons are trans ferred between the electrodes via an electric circuit . The energy storage unit may be a rechargeable battery .

[0046] Fig . 1 shows a diagrammatic view of an aerosol generating device 10 according to an embodiment . The aerosol generating device 10 comprises an energy storage unit 11 . The energy storage unit 11 may be a rechargeable battery such as a lithium-ion battery . The rechargeable battery may comprise one or more battery cells . The aerosol generating device 10 further comprises an inverter unit 12 configured to generate a periodically varying current applied to and / or drawn from the energy storage unit 11 . The inverter unit 12 may receive an input current and / or voltage supplied from an external power supply; in this case , the inverter unit 12 converts the input current and / or voltage into a periodically varying current . The periodically varying current may vary with a certain frequency, and the inverter unit 12 may vary the frequency by adj usting internal switching operations . As an example , the input current and / or voltage may be received during a charging process of the energy storage unit 11 via the external power supply . The aerosol generating device 10 may comprise a charging port for electrically connecting to the external power supply and / or to an external computing device . The charging port is not limited to a physical connection with the external power supply, and a wireless connection may be additionally or alternatively employed . The charging port may further be able to receive and transmit data . As an example , the charging port may be a Universal Serial Bus (USB ) port . Alternatively, the inverter unit 12 may receive an input current and / or voltage supplied from a secondary internal energy source ( e . g . another battery or a capacitor ) . The aerosol generating device 10 further comprises a control unit 13 configured to measure a plurality of impedance values of the energy storage unit , wherein each impedance value is measured for one of a set of independently spaced-apart frequencies of the periodically varying current . Furthermore , the control unit 13 may be configured to determine , based on the plurality of impedance values , whether or not the energy storage unit 11 is suitable for further usage in the aerosol generating device 10 . Moreover, the control unit 13 may be configured to perform a method for diagnosing the energy storage unit 11 . Further details on the method will be explained later with reference to Fig . 2 .

[0047] Further details of the aerosol generating device 10 are described for the sake of explanation and can be sel f-evidently omitted . The aerosol generating device 10 may further comprise a heating compartment 14 arranged to receive an aerosol generating article 20 . The aerosol generating article 20 may be generally cylindrical and include aerosol generating material 21 . At the proximal end, the aerosol generating article 20 may comprise a mouthpiece 22 having an outlet through which a user may inhale ( i . e . suck in) an aerosol that is generated by heating the aerosol generating material 21 . The aerosol generating material 21 may comprise any type of solid, semi-solid and liquid material . The aerosol generating material 21 may comprise plant derived material such as tobacco .

[0048] The aerosol generating device 10 may further comprise one or more heating elements 15 arranged to heat the aerosol generating material 21 . As an example , the one or more heating elements 15 may be provided as an induction heater with an induction coil with windings surrounding the heating compartment 14 for generating an alternating electromagnetic field therein . The inverter unit 12 may further be configured receive a direct current from the energy storage unit 11 and to generate an alternating current applied to the one or more heating elements 15 . The present disclosure is however not limited to an inductive heater, as in fact the also other heaters would be suitable for putting into practice the present disclosure . In case the one or more heating elements 15 are provided as an induction heater, the aerosol generating article 20 may include one or more susceptors (not shown) that couple with the electromagnetic field and generate heat due to eddy currents and / or magnetic hysteresis, which heat is then transferred from the susceptor to the aerosol generating material 21. As an example, the heating compartment 14 itself may be used as the susceptor by forming it from a high permeability material (e.g., permalloy) . As another example, the susceptor may be embedded inside the aerosol generating material 21 of the aerosol generating article 20. A combination thereof may be also used.

[0049] Alternatively, the one or more heating elements 15 may be provided as a resistive heater. Other means of generating aerosol may be used, including those that are configured to generate aerosol without a heating element, e.g. by using an ultrasonic transducer to atomize a liquid aerosol-forming substrate .

[0050] The control unit 13 may further be configured to control other operations of the aerosol generating device 10 such as controlling an amount of current or voltage supplied to or from the energy storage unit 11, the inverter unit 12, and / or the one or more heating elements 15. The control unit 13 may further be optionally configured to communicate with an external computing device coupled thereto. The external computing device may be coupled by wire (e.g. via the charging port) or wirelessly (e.g. via Bluetooth, Wi-Fi, or the like) . The control unit 13 may further be configured to track a number of charging / discharging cycles of the energy storage unit 11. The aerosol generating device 10 may optionally comprise one or more temperature sensors arranged to measure a corresponding temperature of one or more components (e.g., the energy storage unit 11 or the susceptor) of the aerosol generating device 10. The aerosol generating device 10 may optionally comprise one or more current and / or voltage sensors arranged to measure a corresponding current and / or voltage applied to one or more components of the aerosol generating device 10. The aerosol generating device 10 may optionally comprise a communication unit configured to transmit and / or receive signals (e.g. via Bluetooth, Wi-Fi, or the like) .

[0051] The aerosol generating device 10 may optionally comprise a user interface unit configured to notify the user about a status of the aerosol generating device 10. The status may indicate whether or not the aerosol generating device 10 is suitable for further usage. The interface unit may be provided by a light emitting diode (LED) for generating a visual notification, a loudspeaker for generating an audible notification, or a vibrating motor for generating a haptic notification. Alternatively, a notification about the about a status may be transmitted via the communication unit to an external computing device.

[0052] Fig. 2 shows a flowchart for a method 1000 for diagnosing an energy storage unit of an aerosol generating device according to an embodiment. The method 1000 preferably comprises the steps SHOO to S1300.

[0053] Step SHOO comprises applying a periodically varying current to the energy storage unit. The periodically varying current may be an alternating current. Alternatively, the periodically varying current may be a pulsating direct current. In this manner, the energy storage unit 11 may be optionally charged while performing the diagnosis . As an example , the pulsating direct current may be generated by chopping constant direct current supplied from the external power supply or recti fying an alternating current . As another example , the pulsating direct current may be generated by adding an alternating current and a constant direct current , wherein the alternating current has an absolute value that is less than the constant direct current at each point in time . As yet another example , the pulsating direct current may be generated by taking the maximum of an alternating current and a constant direct current at each point in time .

[0054] Step S 1200 comprises measuring a plurality of impedance values of the energy storage unit , wherein each impedance value is measured for one of a set of independently spaced-apart frequencies of the periodically varying current . Such measurements at the spaced-apart frequencies may be performed by repeating each measurement in step S 1200 after changing the frequency by the inverter unit 12 . The control unit 13 may communicate with the inverter unit 12 to control a value of the frequency applied to or drawn from the energy storage unit 11 . The impedance values may be given in units of Ohm (Q) . In one example , the set of independently spaced-apart frequencies may be denoted as { fi , f2 , ■■■, fw } , where N is a positive integer . In this example , " independently spaced-apart" means that frequency di f ferences Afi = fi+1- fi (where i = 1 , 2 , ..., N- l ) between neighboring frequencies in the set form an irregular series of values . In other words , in this example , the frequency di f ferences Af±are unevenly spaced such that it is not possible to derive one frequency in the set solely based on knowledge about the remaining frequencies in the set . In yet other words , in this example , all frequencies in the set are determined independently from each other . In particular, the set of independently spaced-apart frequencies does not correspond to a frequency scan, i . e . a set of equidistantly spaced-apart frequencies . The set of independently spaced-apart frequencies may be determined in advance .

[0055] Step S 1300 comprises determining, based on the plurality of impedance values , whether or not the energy storage unit 11 is suitable for further usage in the aerosol generating device 10 . The energy storage unit 11 may be considered suitable for further usage when it is determined that one or more of the plurality of impedance values satisfy one or more predetermined conditions . Each of the predetermined conditions may indicate an acceptable deviation from a target value . Satis fying predetermined condition means that the determined impedance value is within the acceptable deviation . Here , an "acceptable deviation" may be a deviation at which the energy storage unit 11 remains safe to use and / or maintains a performance suf ficient to continue powering the aerosol generating device 10 . Outside the acceptable deviation, the energy storage 11 may be considered as degraded and / or likely to cause an issue ( e . g . , short-circuit ) .

[0056] By measuring impedance values for each of independently spacedapart frequencies of a periodically varying current applied to an energy storage unit , it becomes possible to reduce the computational resources and time required for diagnosing the energy storage unit 11 of an aerosol generating device . In particular, it may become possible to reliably determine whether or not the energy storage unit 11 is suitable for further usage in the aerosol generating device 10 using les s computational resources and time compared to common diagnosis approaches . Hence , an improved diagnosis can be achieved .

[0057] In common diagnosis approaches , by consecutively sweeping from high frequency to low frequency or vice versa, a greater variety of frequencies of the periodically varying current are applied to and / or drawn from the energy storage unit 11 , and more impedance values are determined . According to such common diagnosis approaches , multiple parameters representing characteristics of the energy storage unit 11 may be wel l measured . However, such heavy and complex calculations may overburden the aerosol generating device 10 . The purpose of the proposed diagnosis method is determining whether the energy storage unit 11 may be suitable for further usage or not , rather than precisely measuring each parameter . Accordingly, by employing independently spaced-apart frequencies , an optimi zed diagnosis approach for an aerosol generating device 10 may be reali zed .

[0058] Measuring each impedance value may comprise controlling the periodically varying current to have ( at least ) a corresponding one of the set of independently spaced-apart frequencies . In other words , the periodically varying current may be adj usted to have a frequency corresponding to ( at least ) one of the set of independently spaced-apart frequencies .

[0059] The plurality of impedance values may comprise a first impedance value of the energy storage unit 11 measured for a first frequency of the periodically varying current , and a second impedance value of the energy storage unit 11 measured for a second frequency of the periodically varying current , wherein a ratio of a second frequency divided by a first frequency is between 20 to 500 , 000 ( the first frequency is thus di f ferent from the second frequency) . Furthermore , determining whether or not the energy storage unit 11 is suitable for further usage in the aerosol generating device 10 may be based on whether or not one or more of the first impedance value and the second impedance value is greater than a corresponding threshold value . In general , each impedance value tends to increase with increasing degradation of an energy storage unit . Thus , the control unit 13 may determine that the energy storage unit 11 is not suitable for further usage i f one or more of the first impedance value and the second impedance value is greater than the corresponding threshold value . In other words , the second frequency may be greater by a factor of 20 to 500 , 000 than the first frequency . Otherwise , the energy storage unit 11 may be determined not to be suitable for further usage .

[0060] For a complex valued impedance value Z =R + iX, the comparison to the corresponding threshold value may be performed based on a real part Re ( Z ) = R ( sometimes also denoted as Z ' ) of the impedance value Z ( i . e . a resistance value R) .

[0061] The first frequency may be between 0 . 1 Hz to 50 Hz . Alternatively, or in addition thereto , the second frequency may be between 1 kHz to 50 kHz . As an example , the first frequency may be 10 Hz and the second frequency may be 1 kHz . In this case , the ratio of a second frequency divided by a first frequency is 100 .

[0062] Fig . 3A shows an exemplary evolution of a low frequency resistance RLF with respect to the number of charging / cycles of the energy storage unit . The low frequency resistance RLF may correspond in one example to the real part of the first impedance value measured for a first frequency of 10 Hz . Fig . 3B shows an exemplary evolution of a high frequency resistance RHF with respect to the number of charging / cycles of the energy storage unit . The high frequency resistance RHF may correspond in one example to the real part of the second impedance value measured for a second frequency of 1 kHz ( in which case the high frequency resistance RHF may also be referred to as the 1 kHz resistance RlkHz) • It is observed that a degradation o f the energy storage unit 11 may proceed in accordance with the number of charging / discharging cycles of the energy storage unit 11 . In other words , an increase of the low frequency resistance RLF and high frequency resistance RHF is observed with respect to the number of charging / cycles due to progress of degradation of the energy storage unit 11 . Hence , a degree of the degradation may be obtained by comparing the first and second impedance values with the corresponding threshold values . In the example of Figs . 3A and 3B, it may be determined that the energy storage unit 11 is not suitable for further usage in the aerosol generating device 10 because the low frequency resistance exceeds the corresponding threshold . In another example (not depicted) , it may be determined that the energy storage unit 11 is not suitable for further usage when the respective (high frequency) resistance exceeds a respective threshold . In another example (not depicted) , it may be determined that the energy storage unit 11 is not suitable for further usage when the low frequency resistance value exceeds a respective threshold and the high frequency resistance exceeds a respective threshold . Alternatively, the degree of the degradation may be defined di f ferently between of high and low frequency resi stance values RHF, RLF and corresponding threshold values . According to this alternative definition, degree of the degradation may behave as analogue value . In practice , other parameters of energy storage unit such as a state of charge ( SoC ) and a temperature may influence the measurements for the plurality of impedance values . The SoC may be defined as a present value of the remaining ( electric ) charge capacity of the energy storage unit 11 relative to a present value of the maximum charge capacity of the energy storage unit . The temperature may be an internal temperature of the energy storage cell .

[0063] Each of the corresponding threshold values may be based on one or more of a state of charge ( SoC ) of the energy storage unit 11 and a temperature of the energy storage unit . In other words , each of the corresponding threshold values may be shi fted based on the SoC and / or temperature of the energy storage unit . The shi fts for the corresponding threshold values may be predetermined ( e . g . under laboratory conditions ) . As an example , the shi fts may be retrieved from a database ( e . g . a lookup table ) . Additionally or alternatively, measured impedance or resistance values may be modi fied based on the SoC and / or temperature of the energy storage unit .

[0064] The plurality of impedance values may comprise at least three impedance values . Furthermore , determining whether or not the energy storage unit 11 is suitable for further usage in the aerosol generating device 10 may be based on a reconstructed electrochemical impedance spectrum derived by fitting a mathematical function representing a curve in the complex plane to the at least three impedance values . Electrochemical impedance spectroscopy (EIS ) is a technique involving measuring impedance values of electrochemical systems across di f ferent frequencies and is widely used in fields like energy storage system, biomedical systems , corrosion studies , and the like . Fig . 4 shows a plurality of reconstructed electrochemical impedance spectra ( cf . curves ) fitted to a plurality of measurement points ( cf . small dots on the respective curves ) for a plurality of energy storage units . It is observed that for a maj ority of the reconstructed electrochemical impedance spectra it is suf ficient to measure an impedance value for each of at least three frequencies of the periodically varying current ( i . e . three measurement points , cf . three large dots ) which are independently spaced-apart from each other . In other words , an electrochemical impedance spectrum for an energy storage unit can be reconstructed with certain accuracy from which the degree of the degradation of an energy storage unit can be determined, based on a fit to at least three impedance values corresponding to three independently spaced-apart frequencies of the periodically varying current applied to the energy storage unit . In this manner, the electrochemical impedance spectrum for the energy storage unit 11 can be reconstructed with certain accuracy while minimi zing requirements for the computational resources and time . The inventors have in fact recogni zed that by choosing at least two , preferably three independently spaced-apart frequency values , it is possible to obtain a diagnosis of the storage unit with a relatively low usage of computational resources and / or in a relatively short time .

[0065] The plurality of impedance values may comprise a third frequency which is between 50 Hz and 1 kHz . As an example , the first frequency may be 10 Hz , the second frequency may be 1 kHz , and the third frequency may be 100 Hz . In fact , the inventors have found that these values provide an advantageous accuracy in the diagnosis with a relatively low usage of computational resources and / or in a relatively short time . The plurality of impedance values may comprise at most five impedance values . Compared to a case in which the plurality of impedance values comprises only three impedance values , the electrochemical impedance spectrum for the energy storage unit 11 can be reconstructed with higher accuracy while maintaining low requirements for the computational resources and time . Thus , accuracy may be increased while still balancing the computational resources and / or the required time for the diagnosis .

[0066] The mathematical function may correspond to a semi-circle in the complex plane . Fig . 5 shows Nyquist plot illustrating an ideali zed electrochemical impedance spectrum comprising a semi-circle 102 ( cf . bold line ) . The semi-circle 102 is located in the first quadrant (positive real and imaginary value ) and contains a first zero crossing point 108 and a second zero crossing point 110 intersecting or terminating at the real axis . The semi-circle 102 may be determined based on a fit to the at least three impedance values (measurement points ) .

[0067] For the case where the energy storage unit 11 is provided as a Li-ion battery, Fig . 6 shows schematic representation of Li- ion mass trans fer phenomena which occur in Li-ion battery electrodes and their respective Nyquist plots . Fig . 6 is taken from Reference

[0001] and a detailed description thereof can be found in section 2 . 5 of Reference

[0001] . In particular, Fig . 6 demonstrates the relationship between frequency ranges and corresponding parts of the Nyquist plot .

[0068] The reconstructed electrochemical impedance spectrum may indicate an electrolyte resistance , a charge trans fer resistance , and an interface capacitance . Furthermore , determining whether or not the energy storage unit 11 is suitable for further usage in the aerosol generating device 10 may be based on whether or not one or more of the electrolyte resistance, the charge transfer resistance, and the interface capacitance is greater than a corresponding threshold value.

[0069] The electrolyte resistance may also be referred to as a solution resistance Rsoiwhich may be defined as the distance between the origin to a first zero-cross point 108, as shown in Fig. 5. For an energy storage unit provided as a battery, the solution resistance Rsoimay indicate a resistance value coming from solution (i.e., electrolyte) in the battery. The charge transfer resistance Rctmay be defined as the distance between the first zero crossing point 108 and a second zero crossing point 110. For an energy storage unit provided as a battery, the charge transfer resistance Rctmay indicate the resistance value associated with a speed of a reaction of charged ions (e.g. Li+) on an electrode proceeds. The interface capacitance C±f (also known as electric double layer capacitance Cdi) is defined by Equation 1, wherein the frequency f corresponds to a frequency associated with an impedance value Z of the highest point 112 of the semi-circle, and wherein |Z' ' | denotes a magnitude of the imaginary part Z' ’ of said impedance value Z.

[0070] 1

[0071] Cif~ 2nf- |Z"|

[0072] [Equation 1]

[0073] Fig. 7 shows an exemplary evolution of a charge transfer resistance RCf with respect to the number of charging / cycles of the energy storage unit. An increase of the charge transfer resistance RCf can be observed with respect to the number of charging / cycles. Here, a degree of the degradation may be obtained by comparing the charge trans fer resistance RCf with the corresponding threshold value . In the example of Fig . 6 , it may be determined that the energy storage unit 11 is not suitable for further usage in the aerosol generating device 10 because the charge trans fer resistance RCf exceeds the corresponding threshold . The skilled person appreciated that a determination based on the solution resistance Rsoiand / or the interface capacitance C±f may be performed in a corresponding manner . A description thereof is thus omitted .

[0074] Among parameters measured by EIS , the charge trans fer resistance Rctand the interface capacitance C±f especially well reflect on the degree of the degradation . As described above , a measurement of the charge trans fer resistance Rctrequires the first and second zero crossing points 108 , 110 , and a measurement of the interface capacitance C±f requires the highest point 112 . Accordingly, respective frequencies of the plurality of impedance values may preferably be set so that the first and second zero crossing points 108 , 110 and / or the highest point 112 can be found .

[0075] When only two impedance values are used as the plurality of impedance values , the first impedance value measured for the high frequency may correspond to the second zero crossing point 110 , and the second impedance value measured for the low frequency may correspond to the first zero crossing point 108 . It is known that the first zero crossing point 108 may be measured when a frequency between 1 kHz to 50 kHz is applied, and the second zero crossing point 110 may be measured when a frequency between 0 . 1 Hz to 50 Hz is applied . Accordingly, the low frequency may be between 0 . 1 Hz to 50 Hz , and the high frequency may be between 1 kHz to 50 kHz . Even i f a respective imaginary part of the first and second impedance values does not equal zero , a magnitude thereof will be close to zero . Thus , a respective real part of the first and second impedance values may be deemed as the second and first zero crossing points 110 , 108 . I f the respective imaginary part of the first and second impedance values is suf ficiently small , the charge trans fer resistance value Rctmay be precisely measured . Thus , the degree of degradation of the energy storage unit 11 may be determined based on the charge trans fer resistance value Rctas described with reference to Fig . 5 . Otherwise , the degree of degradation of the energy storage unit 11 may alternatively be determined based on the low and high frequency resistance values as described with reference to Fig . 3A and Fig . 3B .

[0076] When the third frequency is employed in addition to above- mentioned low and high frequencies , the third frequency may preferably be set so that a third impedance value measured by the third frequency may correspond to the highest point 112 . It is known that the highest point 112 may be measured when a frequency around 100 Hz is applied . Accordingly, the third frequency may be 100 Hz .

[0077] In this manner, the third impedance value is not only beneficial to directly measure the interface capacity C±f , but also to indirectly improve the accuracy of the charge trans fer resistance Rct. The third impedance value may correspond to the highest point 112 or may be close to the highest point 112 , such that a semi-circle may be fitted based on the three impedance values . This fitted semi-circle may be beneficial to find the first and second zero crossing points 108 , 110 , by cooperating with the first and second impedance values .

[0078] Note prior to first usage of the energy storage unit 11 ( i . e . when the number of charging / discharging cycles equals zero ) , resistances such as the low frequency RLF (cf. Fig. 3A) and the charge transfer resistance Rct(cf. Fig. 7) may exhibit relatively large initial values which may then quickly settle at relatively lower values. The determining whether or not the energy storage unit 11 is suitable for further usage may thus be adapted. As an example, the determining may be adapted to discard impedance values measured when the number of charging / discharging cycles equals zero. As another example, the determining may be adapted by increasing the corresponding threshold value to be equal or greater than an impedance value measured when the number of charging / discharging cycles equals zero .

[0079] In another embodiment, a computer program (product) is provided, wherein the compute program (product) comprises instructions which, when the program is executed by a computer, cause the computer to carry out any of the steps of the method (s) above described. A computer according to such embodiment is illustrated in Fig. 8. In particular, Fig. 8 illustrates a computer 300 comprising a processor 320, an interface (IF) 310, and a memory 330. The interface 310 is capable of receiving information from an external device (e.g., via a USB port) and / or supply of power. The memory 330 is capable of storing information in a temporary (volatile) manner and / or non-volatile information. For example, instructions may be stored in the memory. The processor is capable of executing the instructions. The computer may be realized in a localized entity or in distributed manner across multiple entities interacting with each other.

[0080] What has been disclosed above in relation to a method would correspondingly apply to an aerosol generating device and vice versa. While various embodiments of the present disclosure have been described above, it should be understood that they have been presented by way of example, and not limitation. It will be apparent to persons skilled in the relevant art(s) that various changes in form and detail can be made therein. Thus, the above-described example embodiments are not limiting .

[0081] REFERENCE SIGNS

[0082] 10 aerosol generating device

[0083] 11 energy storage unit

[0084] 12 inverter unit

[0085] 13 control unit

[0086] 14 heating compartment

[0087] 15 heating element

[0088] 20 aerosol generating article

[0089] 21 aerosol generating material

[0090] 22 mouthpiece

[0091] REFERENCE DOCUMENTS

[0092] [1] : Vyroubal, Petr, and Tomas Kazda. "Equivalent circuit model parameters extraction for lithium ion batteries using electrochemical impedance spectroscopy." Journal of Energy Storage 15 (2018) : 23-31.

Claims

CLAIMS1 . A method for diagnosing an energy storage unit of an aerosol generating device , the method comprising : applying a periodically varying current to the energy storage unit ; measuring a plurality of impedance values of the energy storage unit , wherein each impedance value is measured for one of a set of independently spaced-apart frequencies of the periodically varying current ; and determining, based on the plurality of impedance values , whether or not the energy storage unit is suitable for further usage in the aerosol generating device .2 . The method according to claim 1 , wherein measuring each impedance value comprises controlling the periodically varying current to have a corresponding one of the set of independently spaced-apart frequencies .3 . The method according to any one of claims 1 to 2 , wherein the plurality of impedance values comprises : a first impedance value of the energy storage unit measured for a first frequency o f the periodically varying current ; a second impedance value of the energy storage unit measured for a second frequency of the periodically varying current ; wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on whether or not one or more of the first impedance value and the second impedance value is greater than a corresponding threshold value ; andwherein a ratio of a second frequency divided by a first frequency is between 20 to 500 , 000 .4 . The method according to claim 3 , wherein the first frequency is between 0 . 1 Hz to 50 Hz , and / or the second frequency is between 1 kHz to 50 kHz .5 . The method according to any one of claims 3 to 4 , wherein each of the corresponding threshold values is based on one or more of a state of charge , SoC, of the energy storage unit and a temperature of the energy storage unit .6 . The method according to any one of claims 1 to 5 , wherein the plurality of impedance values comprises at least three impedance values , and wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on a reconstructed electrochemical impedance spectrum derived by fitting a mathematical function representing a curve in the complex plane to the at least three impedance values .7 . The method according to claim 6 , wherein a third frequency is between 50 Hz and 1 kHz .8 . The method according to any one of claims 6 to 7 , wherein the plurality of impedance values comprises at most five impedance values .9 . The method according to any one of claims 6 to 8 , wherein the mathematical function corresponds to a semi-circle in the complex plane .10 . The method according to any one of claims 6 to 9 , wherein the reconstructed electrochemical impedance spectrum indicates an electrolyte resistance , a charge trans fer resistance , and an interface capacitance , and wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on whether or not one or more of the electrolyte resistance , the charge trans fer resistance , and the interface capacitance is greater than a corresponding threshold value .11 . An aerosol generating device comprising : an energy storage unit ; an inverter unit configured to generate a periodically varying current applied to the energy storage unit ; and a control unit configured to measure a plurality of impedance values of the energy storage unit , wherein each impedance value is measured for one of a set of independently spaced-apart frequencies of the periodically varying current ; and determine , based on the plurality of impedance values , whether or not the energy storage unit is suitable for further usage in the aerosol generating device .12 . An aerosol generating device according to claim 11 , wherein the control unit is configured to measure each impedance value by controlling the periodically varying current to have a corresponding one of the set of independently spaced-apart frequencies .13 . An aerosol generating device according to claim 11 or 12 , wherein the plurality of impedance values comprises :a first impedance value of the energy storage unit measured for a first frequency o f the periodically varying current ; a second impedance value of the energy storage unit measured for a second frequency of the periodically varying current ; wherein determining whether or not the energy storage unit is suitable for further usage in the aerosol generating device is based on whether or not one or more of the first impedance value and the second impedance value is greater than a corresponding threshold value ; and wherein a ratio of a second frequency divided by a first frequency is between 20 to 500 , 000 .14 . An aerosol generating device according to any of claims 11 to 13 , wherein the first frequency is between 0 . 1 Hz to 50 Hz , and / or the second frequency is between 1 kHz to 50 kHz .15 . A computer program comprising instructions which, when the program is executed by a computer, cause the computer to carry out the method of any of claims 1 to 10 .

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