METHODS AND SYSTEM FOR IN OPERANDO BATTERY STATE MONITORING

Abstract

A method and system for in operando, in situ, and real-time monitoring the state of an electrochemical device, e.g. battery, is provided, which is by means of an optical fiber probe inside the electrochemical device. The method includes: shedding an input light into the optical fiber probe and detecting an output light transmitted therefrom; and determining state of health of the electrochemical device based on the output light. The determination step can be based on a change of the refractive index or of the cladding mode or the surface plasmon resonance, all derived from the output light, in the instant state compared to a prior state. The method can simultaneously detect other parameters including state of charge, temperature, pressure, strain, displacement, vibration, or gas release inside the electrochemical device. With a core mode for correction, the determination of these parameters can also realize a high accuracy.

Claims

1. A method for monitoring a state of an electrochemical device by means of an optical fiber probe arranged inside the electrochemical device, the method comprising the steps of: (1) shedding an input light into the optical fiber probe and detecting an output light transmitted from the optical fiber probe; and (2) determining a state of health (SoH) of the electrochemical device based on the output light.

2. The method of claim 1, wherein step (2) of determining a state of health (SoH) of the electrochemical device based on the output light comprises the sub-steps of: (i) obtaining a refractive index based on the output light; and (ii) determining the SoH of the electrochemical device based on a change of the refractive index relative to a prior state of the electrochemical device.

3. The method of claim 2, wherein sub-step (i) of obtaining a refractive index based on the output light comprises the sub-steps of: (a) obtaining one of a cladding mode or a surface plasmon resonance (SPR) from the output light; and (b) calculating the refractive index based on the one of the cladding mode or the SPR.

4. The method of claim 3, wherein in sub-step (a) of obtaining one of a cladding mode or a surface plasmon resonance (SPR) from the output light, a core mode is further obtained from the output light, wherein in sub-step (b), the refractive index is calculated further with correction of the core mode.

5. The method of any one of claims 2-4, wherein sub-step (ii) of determining the SoH of the electrochemical device based on a change of the refractive index relative to a prior state of the electrochemical device further comprises: determining that the electrochemical device is unhealthy if the refractive index is changed by at least 1% relative to the prior state of the electrochemical device.

6. The method of claim 1, wherein step (2) of determining a state of health (SoH) of the electrochemical device based on the output light comprises the sub-steps of: (i) obtaining one of a cladding mode or a surface plasmon resonance (SPR) from the output light; and (ii) determining the SoH of the electrochemical device based on a wavelength shift or an amplitude change of the one of the cladding mode or the SPR relative to a prior state of the electrochemical device.

7. The method of claim 6, wherein sub-step (ii) of determining the SoH of the electrochemical device based on a wavelength shift or an amplitude change of the one of the cladding mode or the SPR relative to a prior state of the electrochemical device comprises the sub-steps of: taking a derivative of the one of the cladding mode or the SPR with respect to one selected from a group consisting of time, voltage, current, resistance and capacity; and determining the SoH of the electrochemical device based on the derivative.

8. The method of claim 6, wherein, wherein sub-step (ii) of determining the SoH of the electrochemical device based on a wavelength shift or an amplitude change of the one of the cladding mode or the SPR relative to a prior state of the electrochemical device comprises: (a) determining that the electrochemical device is unhealthy if an amplitude or wavelength of the one of the cladding mode or the SPR is changed by at least 1% relative to the prior state of the electrochemical device.

9. The method of claim 8, wherein at least one portion of a detection surface of the optical fiber probe is in contact with an electrolyte of the electrochemical device, wherein the determining that the electrochemical device is unhealthy in sub-step (a) comprises: determining that the electrolyte is unhealthy.

10. The method of claim 1, wherein step (2) of determining a state of health (SoH) of the electrochemical device based on the output light comprises the sub-steps of: (i) obtaining one of a cladding mode or a surface plasmon resonance (SPR) from the output light; and (ii) determining the electrochemical device is unhealthy if at least one secondary peak is present in the one of the cladding mode or the SPR.

11. The method of claim 10, wherein the optical fiber probe is inside or in a proximity of an electrode of the electrochemical device, wherein the determining that the electrochemical device is unhealthy in sub-step (ii) comprises: determining that the electrode is unhealthy.

12. The method of any one of preceding claims, further comprising, after step (1) of shedding an input light into the optical fiber probe and detecting an output light transmitted from the optical fiber probe: determining a state of charge (SoC) of the electrochemical device based on the output light.

13. The method of claim 12, wherein the determining a state of charge (SoC) of the electrochemical device based on the output light comprises the sub-steps of: (i) obtaining one of a cladding mode or an SPR from the output light; and (ii) determining the SoC of the electrochemical device based on the one of the cladding mode or the SPR.

14. The method of claim 13, wherein sub-step (ii) of determining the SoC of the electrochemical device based on the one of the cladding mode or the SPR comprises: calculating a refractive index based on the one of the cladding mode or the SPR; and determining the SoC based the refractive index.

15. The method of claim 13, wherein sub-step (ii) of determining the SoC of the electrochemical device based on the one of the cladding mode or the SPR comprises: taking a derivative of the one of the cladding mode or the SPR with respect to one selected from a group consisting of time, voltage, current, resistance and capacity; and determining the SoC based the derivative.

16. The method of any one of claims 13-15, wherein in sub-step (i) of obtaining one of a cladding mode or an SPR from the output light, a core mode is further obtained from the output light, wherein in sub-step (ii) of determining the SoC of the electrochemical device based on the one of the cladding mode or the SPR, the SoC is determined with further correction of the core mode.

17. The method of any one of preceding claims, further comprising, after step (1) of shedding an input light into the optical fiber probe and detecting an output light transmitted from the optical fiber probe: determining at least one of a temperature, a pressure, a strain, a displacement, a vibration, or a gas inside the electrochemical device based on the output light.

18. The method of claim 17, wherein a gas is determined in the sub-step of determining at least one of a temperature, a pressure, a strain, a displacement, a vibration, or a gas inside the electrochemical device based on the output light, wherein the gas comprises at least one of O.sub.2, H.sub.2, CO, CO.sub.2, C.sub.2H.sub.4, CH.sub.4, or HF.

19. A system for monitoring a state of an electrochemical device, comprising: an optical fiber probe arranged inside the electrochemical device; a light source apparatus, optically coupled to a first end of, and configured to provide an input light into, the optical fiber probe; a signal detection and processing apparatus optically coupled to the optical fiber probe, wherein the signal detection and processing apparatus is configured: to receive an output light from the optical fiber probe; to obtains signals from the output light; and to process the signals such that step (2) in any one of the method according to claims 1-17 is implemented.

20. The system of claim 19, wherein the optical fiber probe is one selected from a group consisting of an optical fiber with a grating, an optical fiber with a cavity, a microfiber, a nanofiber, a tapered fiber, a side-polished fiber, a microstructure fiber and a photonic crystal fiber.

21. The system of claim 20, wherein the optical fiber probe is an optical fiber with a grating, wherein a type of the grating is one selected from a group consisting of fiber Bragg grating (FBG), tilted fiber Bragg grating (TFBG), long period fiber grating (LPG), chirped fiber gratings, and phase shift gratings.

22. The system of claim 21, wherein the type of the gratings is tilted fiber Bragg grating (TFBG).

23. The system of claim 22, wherein the optical fiber probe comprises a core and a cladding surrounding the core, wherein the core is provided with a tilted grating having an inclination angle less than 90° relative to a longitudinal axis of the core.

24. The system of claim 23, wherein the inclination angle of the tilted grating is in a range of approximately 2°-45°.

25. The system of claim 23 or claim 24, wherein the optical fiber probe further comprises an SPR layer coating an outer surface of the cladding, wherein the SPR layer has a composition active to surface plasmon resonance (SPR), wherein the composition comprises at least one of gold (Au), silver (Ag), platinum (Pt), copper (Cu) or aluminum (Al), a semiconductor material, a metal oxide material, a two-dimensional (2D) material, or an optical metamaterial.

26. The system of claim 25, wherein the optical fiber probe further comprises a protective film layer over an outer surface of the SPR layer, wherein the protective film layer comprises at least one of diamond, silicon, indium tin oxide (ITO), zinc peroxide (ZnO2), tin oxide (SnO2), indium oxide (In□O□), polyethylene (PE) or polypropylene (PP).

27. The system of claim 25 or claim 26, wherein the optical fiber probe further comprises a transition film layer sandwiched between the cladding and the SPR layer, configured to improve adhesion of the base film layer to the optical fiber, wherein the transition film layer comprises at least one of titanium (Ti), molybdenum (Mo), or chromium (Cr).

28. The system of any one of claims 19-27, wherein the optical fiber probe comprises a mirror arranged at a second end thereof, wherein the mirror has a reflective surface facing inside the optical fiber probe.

29. The system of any one of claims 19-28, wherein the optical fiber probe has a single-point configuration.

30. The system of any one of claims 19-28, wherein the optical fiber probe has a multi-point configuration having a plurality of points arranged in series or in parallel.

31. The system of any one of claims 19-30, wherein the optical fiber probe is arranged such that at least one portion thereof is in contact with an electrolyte of the electrochemical device.

32. The system of any one of claims 19-30, wherein the optical fiber probe is arranged such that at least one portion thereof is in proximity of an electrode of the electrochemical device.

33. The system of any one of claims 19-32, wherein the electrochemical device is a battery or a supercapacitor.

34. The system of claim 33, wherein the electrochemical device is a battery, selected from a group consisting of a lithium-ion battery, a lead-acid battery, a lithium iron phosphate battery, a fuel battery, a sodium-ion battery, a sodium-sulfur battery, a flow battery, a solid state battery, a hybrid solid-liquid state battery, a lithium metal battery, or a Z.sub.n—MnO.sub.2 battery.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] FIGS. 1A and 1B respectively illustrate a perspective view of two embodiments of an optical fiber probe that is utilized for monitoring the battery state;

[0051] FIG. 2 illustrates a block diagram of an electrochemical device state monitoring system;

[0052] FIGS. 3A and 3B illustrate the evolution of cladding mode amplitude of the output optical signals in response to the electrolyte concentration;

[0053] FIGS. 4A and 4B illustrate the evolution of wavelengths of the output optical signals in response to the electrolyte concentration;

[0054] FIGS. 5A and 5B illustrate the evolution of wavelengths of the output optical signals in response to the temperature;

[0055] FIG. 6 shows the evolution of spectra of the output optical signals in response to the SoH of the electrochemical device;

[0056] FIGS. 7A-7C show the capacity retention together with the measured changes in refractive index and turbidity of electrolyte as a function of cycle number;

[0057] FIGS. 8A-8C show one kind of relationship between the dendrite growth state of the electrode and output light during charging and discharging;

[0058] FIGS. 9A and 9B show another relationship between the dendrite growth state of the electrode and output light during charging and discharging;

[0059] FIG. 10A shows the correspondence between the electrochemical signal, optical signal and the change rate of optical signal of electrolyte-electrode interactions near the electrode surface; and

[0060] FIG. 10B shows the relationship curve between the optical signal d(dB)/dt and the potential during charging and discharging.

DETAILED DESCRIPTION OF THE INVENTION

[0061] In the following, exemplary embodiments are provided below, which are described in sufficient detail to enable those of ordinary skill in the art to embody and implement the methods and systems described above. It is to be understood that these embodiments can be provided in many varying forms and should not be construed as a limitation to the scope covered by the present disclosure.

[0062] In a first aspect, an optical fiber probe that is utilized in the above mentioned method for in operando, in situ, and in a real time manner monitoring a state of an electrochemical device is provided. The optical fiber probe is arranged inside the electrochemical device (e.g. battery). FIGS. 1A and 1B respectively illustrate a perspective view of two embodiments of the optical fiber probe.

[0063] As shown in FIG. 1A, this embodiment of the optical fiber probe 100 is substantially an optical fiber with tilted fiber Bragg grating (i.e. TFBG), and comprises a core 10 and a cladding 20 coating the core 10, which are arranged coaxially to together form an optical fiber. The core 10 of the optical fiber probe 100 is provided with a tilted grating 12, i.e. a grating having an internal tilt angle θ (defined as an angle of each plane of the grating relative to a plane that is substantially perpendicular to the axis of the core 10). The cladding 20 of the optical fiber probe 100 is in contact with one component S, such as the electrolyte or the electrode, etc., of the electrochemical device, so as to determine the various parameters of the electrochemical device including SoH, and optionally the SoC, the internal temperature, the internal pressure, the internal strain, the internal displacement, and/or the internal vibration. Upon an input light 1 entering from a first side surface (i.e. light-in end surface) A into the optical fiber probe 100 and transmitting along the core 10, the tilted grating 12 can reflect and/or refract the input light into the cladding 20 of the optical fiber probe 100 (the light such reflected or refracted is shown as 2 in FIG. 1A). The output light thus emitted out from a second side surface (i.e. light-out end surface) B may comprise a core mode 3 and cladding mode 2. The cladding mode 2 may contain information that can be used for the determination of the various parameters as mentioned above.

[0064] FIG. 1B illustrates another embodiment of the optical fiber probe 100, which is configurationally similar to the embodiment shown in FIG. 1A, but differs by additionally comprising an SPR layer 30 coating an outside of the cladding 20. The SPR layer 30 may have a thickness of approximately 20-70 nm and preferably of approximately 30-50 nm, and may comprise a composition that is active to surface plasmon resonance (SPR), and thus upon an input light 1 entering from the light-in end surface A into the optical fiber probe 100 and transmitting along the core 10, the output light may include, in addition to the core mode 3 and the cladding mode 2, a surface plasmon wave (i.e. SPR) 4. The SPR 4 may contain information that can be used for the determination of the various parameters of the electrochemical device as mentioned above. In either of the two embodiments mentioned above, the input light 1 can be generated by a light source apparatus that is optically connected to the light-in end surface A of the optical fiber probe, and the output light can be captured by a signal detection and processing apparatus that is optically connected to the light-out end surface B of the optical fiber probe, which may comprise an optical spectrometer. Optionally for each of the two embodiments of the optical fiber probe 100 shown in FIGS. 1A and 1B, a mirror with a reflecting surface facing the inside of the optical fiber probe 100 may be arranged at the second end surface B of the optical fiber probe 100, which can reflect the output light back to thereby emit out of the first end surface A (which is thereby both a light-in end surface and a light-out end surface) of the optical fiber probe 100.

[0065] In addition to the embodiment of the optical fiber probe illustrated in FIG. 1B, optionally, a protective film layer may be arranged over an outer surface of the SPR layer, and a transition film layer may be sandwiched between the cladding and the SPR layer. More details for the SPR layer, the protective film layer, and/or the transition layer can be found above and will be skipped herein.

[0066] It is noted that there can be a variety of embodiments for the optical fiber probe in addition to the two embodiments illustrated in FIGS. 1A and 1B. For example, the optical fiber probe can be fiber gratings, a micro-nano fiber, a micro-structure fiber, a fiber micro-cavity, and the like. The material of the optical fiber can be quartz, polymer, micro-structured optical fiber and so on. Fiber gratings include, but are not limited to, uniform gratings, chirped fiber gratings, phase-shifted gratings, tilted fiber Bragg gratings (TFBG), fiber Bragg gratings (FBG), long-period fiber gratings (LPG), and for gratings prepared on optical fibers based on different doped materials. For example, a Bragg grating prepared based on doped polymethyl methacrylate (PMMA) fiber. The optical fiber probe can also be a structural improvement of the above-mentioned various gratings, such as micro-nano fiber gratings. In addition, the number of optical fiber probes involved in the present application is not limited. For example, it may be one or more. For another example, part of them may be tilted fiber gratings, and part of them may be fiber Bragg gratings. When there are multiple optical fiber probes, the connection mode of each optical fiber probe is also not limited. For example, they may be connected in series or in parallel. For the sake of simple description, the present application takes one TFBG as an example for description of the fiber probe.

[0067] In a second aspect, a monitoring system comprising the above mentioned optical fiber probe that is utilized for the in operando, in situ, and real-time monitoring of a state of an electrochemical device is further provided. As shown in FIG. 2, the system 1000 comprises, in addition to the optical fiber probe 100, a light source apparatus 200, and a signal detection and processing apparatus 300. The light source apparatus 200 and the signal detection and processing apparatus 300 are respectively configured to be optically connected to the optical fiber probe 100 (via a light-in end surface and a light-out end surface, respectively, which are not shown in FIG. 2). The optical fiber probe 100 of the monitoring system 1000 is operably coupled with the electrochemical device 2000 by specifically being arranged there inside. Regarding the different types and configurations for the light source apparatus 200 and the signal detection and processing apparatus 300, details can reference to the description set forth above.

[0068] In the monitoring system 1000, the light source apparatus 200 works by providing an input light into the optical fiber probe 100, and the signal detection and processing apparatus 300 works by receiving an output light from the optical fiber probe, obtaining signals from the output light, and processing the signals such that the various parameters of the electrochemical device 2000, including SoH, and optionally the SoC, the internal temperature, the internal pressure, the internal strain, the internal displacement, vibration, and/or gas, can be derived therefrom.

[0069] The optical fiber probe 100 may work on two different working modes. In the transmission mode, the light source apparatus 200 and the signal detection and processing apparatus 300 are respectively arranged at two opposing ends of the optical fiber probe 100 (i.e. the light-in end surface and the light-out end surface are different). In the reflection mode, the light source apparatus 200 and the signal detection and processing apparatus 300 are respectively arranged at a same side of the optical fiber probe 100, i.e. both are connected to a same first end surface (i.e. the light-out end surface is substantially also the light-in end surface), and in this mode, a mirror is arranged at a second end surface opposing to the first end surface to reflect the output light back to the first end surface. Further in this reflection mode, the monitoring system 1000 may further include an optical fiber circulator (not shown), which can separate the input optical pathway and the output optical pathway.

[0070] The following are noted. The electrochemical device may be a battery, which comprises an electrolyte and at least two types of electrodes, that is, at least a positive electrode and a negative electrode. The optical fiber probe can be partially immersed in the electrochemical device, or fully immersed in the electrochemical device. The position of the optical fiber probe in the electrochemical device is not limited. For example, it can be in the electrolyte or adjacent to the electrode. The “adjacent” referred to in the present application may mean that the optical fiber probe is in close contact with the electrode, or may mean that the optical fiber probe and the electrode are slightly apart, which is not limited in the embodiment of the present application.

[0071] In a third aspect, a method that substantially utilizes the above monitoring system 1000 for the in operando, in situ, and real-time monitoring of a state of an electrochemical device 2000 is further provided.

[0072] The method comprises the steps of: (1) shedding an input light into the optical fiber probe and detecting an output light transmitted from the optical fiber probe; and (2) determining a state of health (SoH) of the electrochemical device based on the output light.

[0073] Optionally, according to different embodiments of the method, after step (1), other type of information such as a state of charge (SoC), an internal temperature/pressure/strain/displacement/vibration/gas may also be determined by analyzing the output light.

[0074] Depending on the different signal processing approaches, step (2) may be realized by converting the output light into the calculation of a refractive index, and the determination of the various parameters, or alternatively by directly analyzing the cladding mode or SPR in the output light. A change of the refractive index or a change of the cladding mode or SPR (e.g. an amplitude change or a wavelength shift) in the instant state of the electrochemical device relative to a prior state of the electrochemical device may be examined, with the detection of such a change more than a certain pre-set threshold (e.g. 1%, 2%, 5%, 10%, 20%, or 50%, etc.) being regarded as an unhealthy state for the electrochemical device, or more specifically for the electrolyte or electrode if the actual arrangement of the optical fiber probe inside the electrochemical device is known.

[0075] In the following, three different examples (Examples 1, 2 and 3) are provided below for more detailed description, yet it is noted that these examples are for illustration purpose only and shall not be interpreted to limit the scope of the present disclosure.

[0076] This application uses TFBG and a lithium-ion battery as an example for description, and the angle and length of the TFBG are not limited in the embodiment of this application. In the following description, the angle of the inclined fiber grating used is θ and the length is L. The lithium-ion battery used includes two electrodes, namely a positive electrode and a negative electrode. According to another embodiment, the refractive index of the electrolyte can be derived from the amplitude of the cladding modes or SPR for detecting the SoH of the electrochemical devices. Namely, the amplitude of the cladding mode changes with the refractive index, indicating the degradation of the electrolyte and thus the decay in SoH of electrochemical devices. In other words, when the electrochemical devices degrade, the possible deterioration in electrolyte will induce its refractive index change and finally lead to the amplitude change of the output optical signals. Preferably, the electrochemical devices are determined to be unhealthy if the refractive index, measured by the amplitude method, is changed by at least 1%.

[0077] Specially, FIG. 3A provides an example of the evolution of cladding mode amplitude of the output optical signals in response to the electrolyte concentration. As shown in FIG. 3A, the abscissa and the ordinate represent the spectral range and the power (amplitude) of the output light, respectively. As an example, spectra within 1510 to 1515 nm and −32 to −26 dBm are shown in FIG. 3A. The solid, dash, dot, and dot dash lines indicates the output spectra when the probe immersed in the electrolyte at concentrations of A, B, C, and D, respectively, where A<B<C<D. FIG. 3A shows the different spectra with varied electrolyte concentration, that is, the amplitude of the cladding mode decreases with the concentration of electrolyte. Among the three cladding modes shown in FIG. 3A, at least one mode should be selected for the analysis. FIG. 3B thus provides the correlation between the refractive index of the electrolyte and the amplitude of one cladding mode. Notably, the refractive index of the electrolyte can be derived from the concentration according to the references, which is not discussed here. The abscissa and the ordinate of FIG. 3B represent the refractive index range (from 1.33 to 1.38) and the peak-to-dip power (from 1 to 6 dBm) of the output light, respectively. Note that the other amplitude analysis methods are feasible and not limited to the peak-to-dip power, for example, the power of a single peak or the upper and lower envelopes. FIG. 3B shows that the refractive index increases from A to D with the decrease of the peak-to-dip power.

[0078] According to another embodiment, the refractive index of the electrolyte can be derived from the wavelength of the output light for detecting the SoH of the electrochemical devices. Namely, the wavelength either increases or decreases with the refractive index. Note that the shifting direction of the wavelength depends on the type of optical probe and will not be discussed in detail here. When the electrochemical device becomes unhealthy and the refractive index of electrolyte changes, the real-time monitored wavelength will drift. Preferably, the electrochemical devices are determined to be unhealthy if the refractive index, measured by the amplitude method, is changed by at least 1%.

[0079] Specially, FIG. 4A provides an example of the evolution of wavelengths of the output optical signals in response to the electrolyte concentration. As shown in FIG. 4A, the abscissa and the ordinate represent the spectral range (from 1545 to 1548 nm as an example) and the power (amplitude, from −50 to −20 dBm as an example) of the output light, respectively. The solid, dash, dot, and dot dash lines indicates the output spectra when the probe immersed in the electrolyte at concentrations of A, B, C, and D, respectively, where A<B<C<D. FIG. 4A shows the different spectra with varied electrolyte concentration, that is, the wavelength of the cladding mode increases with the concentration of electrolyte. Among the three cladding modes shown in FIG. 3A, at least one mode should be selected for the analysis. FIG. 4B thus provides the correlation between the refractive index of the electrolyte and the wavelength of one cladding mode. The abscissa and the ordinate of FIG. 4B represent the refractive index range (from 1.33 to 1.38) and the wavelength (from 1547.10 to 1547.45 nm) of the output light, respectively. FIG. 4B shows that the refractive index increases from A to D with the increase of the wavelength.

[0080] According to another embodiment, the temperature of the device can be derived from the wavelength of the output light. Namely, the wavelength changes with the temperature.

[0081] Specially, FIG. 5A provides an example of the evolution of wavelengths of the output optical signals in response to the temperature. As shown in FIG. 5A, the abscissa and the ordinate represent the spectral range (from 1538 to 1541 nm and from 1589.7 to 1590.5 nm for cladding and core modes, respectively, as an example) and the power (amplitude, from −35 to −23 dBm and from −22.8 to −22.4 nm for cladding and core modes, respectively, as an example) of the output light, respectively. The solid, dash, and dot lines indicates the output spectra when the probe at temperatures of A, B, and C, respectively, where A<B<C. FIG. 5A shows the different spectra with varied temperature, that is, the wavelength of the cladding and core modes increases with the concentration of electrolyte. Among the three cladding modes and one core mode shown in FIG. 5A, at least one mode should be selected for the analysis. FIG. 5B thus provides the correlation between the temperature and the wavelength of one cladding and one core modes. The abscissa and the ordinate of FIG. 5B represent the temperature range (from 5 to 65° C.) and the wavelength (from 1539 to 1540.5 nm and from 1589.5 to 1591 nm) of the output light, respectively. The computation of refractive index and temperature can be conducted according to the calibration curves as shown in FIG. 3B, FIG. 4B, and FIG. 5B.

[0082] The following are specific applications of the above methods in detecting SoH of the battery.

[0083] In Example 1, the turbidity of the electrolyte can be derived from the amplitude of the guided cladding modes for detecting the SoH of the electrochemical devices. Namely, the amplitude of the guided cladding mode decreases with the turbidity of electrolyte, indicating the degradation of the electrolyte and thus the decay in SoH of electrochemical devices. In other words, when the electrochemical devices degrade, the possible deterioration in electrolyte will induce the change in turbidity and finally lead to the amplitude change of the output light. Preferably, the electrochemical devices are determined to be unhealthy if the turbidity metric, namely, the amplitude of the guided cladding modes, is changed by at least 1%.

[0084] Specially, FIG. 6 provides an example of the evolution of spectra of the output optical signals in response to the SoH of the electrochemical device. As shown in FIG. 6, the abscissa and the ordinate represent the spectral range (from 1500 to 1600 nm) and the power (amplitude, from −41 to −18 dBm) of the output light, respectively. The black, gay, and light gray lines indicate the output spectra when the electrochemical device at SoH of A, B, and C, respectively, where A>B>C. FIG. 6 shows the different spectra with varied SoH, that is, the amplitude of the guided cladding mode decreases with the decrease of SoH of electrochemical devices.

[0085] According to another embodiment, FIGS. 7A-7C show the capacity retention together with the measured changes in refractive index and turbidity of electrolyte as a function of cycle number. As shown, the abscissa represents the cycle number (from 3 to 125), while the ordinates in the top (FIG. 7A), middle (FIG. 7B), and bottom (FIG. 7C) panels represent the capacity retention (from 90 to 102%), the refractive index change (from −10 to 220 MU), and the turbidity change (from 0.85 to 1.05). The black squares and light gray diamonds indicate the data when the electrochemical device adopting a bad and a good electrolyte, respectively. FIG. 6 shows that the capacity retention of the electrochemical device with a bad electrolyte decreases faster than the one with a good electrolyte, and the fast degraded electrochemical device also presents more changes in refractive index and turbidity. These results support that the monitoring of refractive index and turbidity can be used to monitor the SoH of electrochemical devices.

[0086] In Example 2, the lithium dendrites can be derived from the power of the cut-off mode for detecting the SoH of the electrochemical devices.

[0087] Specially, the electrochemical device includes two symmetrical Li metal electrodes in liquid electrolyte. Symmetrical cells were assembled by two identical lithium metal electrodes with a distance in the quartz electrolytic cell. And the electrolyte includes 4 mol L.sup.−1 Lithium Hexafluorophosphate in ethylene carbonate (EC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) (1:1:1, v/v/v, respectively) was prepared (denoted as 4 mol L.sup.−1 LiPF.sub.6 EC:EMC:DMC). An optical fiber probe tightly attached to one of the electrode for surface-localized and fast changing ionic concentrations near the electrode surface.

[0088] In a possible implementation manner, the growth of dendrites can be qualitatively analyzed by the wavelength of the output light or the power change of the cladding mode. More specifically, it can be judged whether there is dendrite growth by observing whether the wavelength or the power of the cladding mode has a large change or whether there is a secondary peak.

[0089] FIGS. 8A-8C show the relationship between the dendrite growth state of the electrode and output light during charging and discharging. As shown in FIG. 8, the abscissa represents the measurement time (from 0 to 20000 s), while the ordinates in the top, middle, and bottom panels represent power the voltage (from −0.25 V to 0.20 V), power (from −0.6 dBm to 1.2 dBm) and power (from 0 dBm to 2.4 dBm). FIG. 8A shows the relationship between the voltage signal and time. Among them, “a” represents the charging process and “b” represents the discharging process. It means that during the period from 0 s to 20000 s, the charging voltage remains the same, and the discharge voltage remains the same, and the frequency of charging and discharging is equal, so as to measure the optical signal of the electrochemical device. FIG. 8B shows a graph of the optical signal change of the electrochemical device without dendrite growth. FIG. 8C shows a graph of the optical signal change of the electrochemical device with dendrite growth. It can be seen from the figures that in the absence of dendrite growth, the wavelength or the power of the cladding mode hardly changes or changes slightly, and there is only one main peak “c”. However, when there is dendrite growth, there are two phenomena of wavelength and cladding mode power, one is the increase in amplitude, and the other is the double peak, namely the main peak “c” and the secondary peak “d”. Therefore, the presence or absence of dendrite growth can be qualitatively judged from the wavelength or the power of the cladding mode. Notably, the electrochemical devices are determined to be unhealthy if dendrite growth.

[0090] In another possible implementation manner, the growth of dendrites can be quantitatively analyzed by the change of wavelength or the power of the cladding mode.

[0091] FIGS. 9A and 9B show the electrical signal and optical signal during charging and discharging. The abscissa of FIG. 9A indicates the measurement time (from 0 s to 40000 s), and the ordinate represents the voltage (from −04V to 0.4V.) Among them, “a” represents the charging process and “b” represents the discharging process. It means that during the period from 0 s to 40000 s, the charging voltage remains the same, and the discharge voltage remains the same, and the frequency of charging and discharging is equal, so as to measure the optical signal of the electrochemical device. FIG. 9B shows the change of the wavelength or the power of the cladding mode with the growth of dendrites. The abscissa represents the measurement time (from 0 to 40000 s), and the ordinate represents the wavelength or the power of the cladding mode (only the power of the cladding mode is shown in the figure), and the range is from −42 dBm to −36 dBm. From the figure, it can be seen that the wavelength or the power of the cladding mode has a certain quantitative relationship with the growth of dendrites. For example, linear relationships, quadratic function relationship, etc. The embodiments of this application are not limited.

[0092] Therefore, the much stronger optical response together with a noticeably distinctive secondary peak detected in Li-dendrite-growth condition. It reveals that the remarkable increase in optical response is result of an low efficient or blocked Li-ion transport in the vicinity of the Li metal electrode (means a reduced Coulombic efficiency of battery) and the noticeably distinctive secondary peak is originated from the dynamic balancing between Li-ion depletion and Li dendrite growth (like a “periodic respiration” effect in dendrite growth and dissolution within each charging/discharging cycle), thereby providing a potentially useful early warning of the dendrite growth and decrease the risk for catastrophic battery failure.

[0093] In Example 3, the ion transport can be derived from the power changes of the cladding mode or an SPR for detecting the state of charge (SoC) of the electrochemical devices.

[0094] During the charging and discharging process of the electrochemical device, ion transport activity occurs on the electrode-electrolyte surface. The process of ion transport will cause changes in the cladding mode or an SPR, which in turn can infer the SoC of the electrochemical device.

[0095] A possible implementation is to calculate the change in the refractive index of the electrolyte based on the cladding mode or an SPR, and determine the SoC according to the change in the refractive index. Its implementation can refer to the related descriptions of FIG. 3A to FIG. 4B.

[0096] Another possible implementation is to take a derivative of one of the cladding mode or an SPR with respect to time, so that the SoC of the electrochemical device can be determined. Optionally, the derivative is not limited to the first-order derivative, and it may also be a second-order derivative, a third-order derivative, and the like. This embodiment of the application does not limit this.

[0097] Herein, the optical fiber probe is a tilted fiber grating coated with a metal film, and the fiber probe is implanted into an electrode and tightly connected to the electrode surface, where the electrode can be plated with a MnO.sub.2 film. The embodiments of this application are not limited.

[0098] The curves of galvanostatic charge/discharge (GCD) test, SPR power and differential of light power are exhibited in FIG. 10A. The differential of light power (Double-dotted line FIG. 10A) is obtained by taking the derivative of the SPR power level with respect to time, which represents the rate of change of the optical power. It shown that the changes of electrochemical curves are highly consistent with the optical results. And most importantly, it is found that it shows a stable and reproducible correlation with ion transfer rate. At the time corresponding to the two discharging platforms of 0.62 V (point a) and 0.18 V (point b), the SPR power decreases, while the differential of light power curve reaches the peak. This is because ions quickly transfer and intercalate cathode material during discharge, thus reducing the ion concentration at the electrode-electrolyte interface. And optical curves flatten out towards the end of the discharge. While starting charging (point c), the optical signal decreased sharply and a peak was observed in d(dBm)/dt curve. Since both the electrochemical signal and optical signal are functions of time, the change rate of the optical signal can be mapped to the voltage as a P′/V relationship curve. FIG. 10B presents the P′/V curves of the first third charging and discharging cycles of MO cathode, which is similar in shape to the CV curve. The 1st cycle is irreversible due to the change in crystal structure, which is common in MnO.sub.2 electrode materials. The curve gradually levels off after the 2.sup.nd cycle, indicating a reversible redox reaction with ion intercalation/deintercalation. Furthermore, it can also observe a charging plateau and two discharging plateaus.

[0099] Finally, it should be noted that the foregoing embodiments are merely intended for describing the technical solutions of the present disclosure. Although the present disclosure is described in detail with reference to the foregoing embodiments, persons of ordinary skill in the art should understand that they may still make modifications to the technical solutions described in the foregoing embodiments or make equivalent replacements to some or all technical features thereof, without departing from the scope of the technical solutions of the embodiments of the present disclosure.