Optical fiber SPR (Surface Plasmon Resonance) sensor, sensing system and method for detecting density of electrolyte of lead-acid battery

Abstract

The invention relates to an optical fiber SPR (Surface Plasmon Resonance) sensor, a sensing system and a method for monitoring the electrolyte density of a lead-acid battery, and belongs to the technical field of battery monitoring. The optical fiber SPR sensor comprises a silver plating layer, a gold plating layer, a plastic coating layer, a fiber core and a cladding layer, the silver plating layer is located on the cross section of one end of the fiber core and the cladding layer, and the axial distance between the silver plating layer and the gold plating layer is 1.5 cm; the axial length of the silver plating layer is 60 nm, the axial length of the gold plating layer is 1-1.5 cm, and the thickness of the gold plating layer is 50 nm. The gold plating layer serves as a sensing area and is used for being in contact with the external environment to excite SPR signals. The silver plating layer serves as a reflecting surface and is plated on the end face of the multimode optical fiber to form the optical fiber SPR sensor. According to the technical scheme, the electrolyte density change of the lead-acid battery can be monitored in real time, and the optical fiber sensor is high in sensitivity and good in stability and can be implanted into the lead-acid battery to be used for a long time.

Description

Technical Field

[0001] The invention belongs to the technical field of battery monitoring, and in particular relates to an optical fiber SPR sensor, a sensing system and a method for monitoring the electrolyte density of a lead-acid battery. Background Art

[0002] Among electrochemical storage batteries, lead-acid batteries are one of the most widely used types. They are present in many fields, in the automotive industry where they have been used since the beginning, as energy storage devices for solar panels, in various telecommunication applications, remote systems, submarines, etc. Most applications require a reliable measurement of the battery status in order to improve the performance of the equipment by planning the available operating time or detecting faults as quickly as possible. Battery failure can cause huge economic losses and, for more sensitive equipment, even human loss or injury.

[0003] State of charge (SOC) is one of the most important parameters for evaluating batteries. It provides key information that is useful for improving battery operation, performance, reliability and life. Knowing the state of charge can avoid overcharging, which can lead to a shortened operating life or even battery failure. The measurement of electrolyte density provides an accurate value of the battery SOC. The electrolyte is formed by sulfuric acid diluted in water, and the specific density depends on the state of charge and battery type. However, during battery operation or under conditions such as overcharging, the battery electrolyte density will be abnormal, which can easily lead to lead-acid battery failure or even explosion and fire. Therefore, real-time monitoring of lead-acid battery electrolyte density is crucial. Summary of the invention

[0004] The present invention aims at solving the problems in the prior art and provides an optical fiber sensing system for real-time and high-sensitivity detection of electrolyte density of lead-acid batteries.

[0005] The invention provides an optical fiber SPR sensor, comprising an optical fiber sensing region, a plastic coating layer, a fiber core and a cladding; the optical fiber sensing region comprises a silver plating layer and a gold plating layer, and the optical fiber sensing region is located at the head end of the fiber core and the cladding; the silver plating layer is located at a cross section at one end of the fiber core and the cladding, and the distance between the silver plating layer and the gold plating layer is 1.5 cm; the length of the gold plating layer is 1 to 1.5 cm; the length of the silver plating layer is 60 nm, and the thickness of the gold plating layer is 50 nm.

[0006] Furthermore, the core diameter is 590-610 μm, and the length is 9-10 cm; the cladding diameter is 625-635 μm.

[0007] The present invention further provides a method for preparing a fiber optic SPR sensor, comprising the following steps:

[0008] Step 1: Remove 2mm of the plastic coating from the leading and trailing ends of the multimode optical fiber along the axial direction, and grind the cross section of the optical fiber perpendicular to the direction of the multimode optical fiber. After grinding it flat, take it out and wash it;

[0009] Step 2: Place the head end of the multimode optical fiber in a magnetron sputtering coating apparatus and silver-coat the polished cross section;

[0010] Step 3: remove the plastic coating layer 1.5 cm away from the silver coating on the multimode optical fiber and wash it, wherein the plastic coating layer is removed by 1 to 1.5 cm; ultrasonically wash the multimode optical fiber, and after washing, use a magnetron sputtering coating instrument to gold-plate the cladding at the position where the plastic coating layer is removed.

[0011] Furthermore, in step 2, during the silver plating, the magnetron sputtering current is 25 mA, and the time is 900 s; in step 3, during the gold plating, the magnetron sputtering current is 22 mA, and the time is 200 s.

[0012] The present invention further provides an optical fiber SPR sensing system, comprising: an optical fiber SPR sensor; the tail end of the optical fiber SPR sensor is connected to a 1×2Y optical fiber through an SMA905 optical fiber adapter; the 1×2Y optical fiber is respectively connected to a broadband light source and an optical fiber spectrometer; and the optical fiber spectrometer is connected to a computer.

[0013] Furthermore, the wavelength of the optical fiber spectrometer is 400-1100 nm.

[0014] The present invention further provides an application of an optical fiber SPR sensing system, wherein the optical fiber SPR sensing system is applied to detecting the electrolyte density of a lead-acid battery.

[0015] The present invention further provides an application method of an optical fiber SPR sensing system, comprising the following steps:

[0016] Step S1: implanting the end of the optical fiber SPR sensor with the silver coating from the injection port of the lead-acid battery, and immersing the gold coating area of ​​the optical fiber SPR sensor in the electrolyte, and the lead-acid battery electrolyte is dilute sulfuric acid;

[0017] Step S2: Connect the lead-acid battery to the charger and discharger, and start the charger and discharger to perform a charge and discharge cycle on the lead-acid battery;

[0018] Step S3: Use a fiber optic spectrometer to record the spectrum and central wavelength data.

[0019] Furthermore, light emitted by a broadband light source enters through one end of a 1×2Y optical fiber, is reflected back to the optical spectrometer by the silver coating of the optical fiber SPR sensor, and surface plasma resonance occurs in the optical fiber sensing area; when the gold coating of the optical fiber SPR sensor comes into contact with the lead-acid battery electrolyte, the incident light is attenuated and reflected, thereby forming a specific reflection spectrum and obtaining the refractive index; based on the refractive index, the density of the lead-acid battery electrolyte is determined.

[0020] Furthermore, when the lead-acid battery is discharged, dilute sulfuric acid reacts with the active substances on the cathode and anode plates to generate a new compound, lead sulfate. The sulfuric acid component is released from the electrolyte through discharge. The longer the discharge, the lower the density of sulfuric acid, the lower the refractive index of the electrolyte, and the corresponding optical fiber reflection spectrum produces a blue shift; when the lead-acid battery is charged, the lead sulfate produced on the anode and cathode plates will be decomposed and reduced into sulfuric acid, lead and lead peroxide, the concentration of the electrolyte in the battery gradually increases, the refractive index of the electrolyte rises, and the corresponding optical fiber reflection spectrum produces a red shift.

[0021] Beneficial effects of the present invention:

[0022] 1. The optical fiber SPR sensor of the present invention can be implanted inside the battery without causing damage to the battery, and realizes accurate and efficient detection of the electrolyte density of the lead-acid battery, and has the characteristics of high sensitivity and rapid response. The traditional BMS can only rely on the monitoring of external parameters such as voltage, current and external temperature, which solves the problem that the BMS cannot monitor the state change of the battery well.

[0023] 2. When preparing the optical fiber SPR sensor of the present invention, there is no need to perform a fusion process like other optical fiber sensors. It only needs to grind its end face to smoothly connect to the optical path. This feature greatly reduces the requirements for experimental conditions, brings great convenience to experimental operations, and is conducive to more extensive application in various experimental scenarios.

[0024] 3. The fiber SPR sensor of the present invention has an excellent ability to detect tiny refractive index changes, and its sensitivity is often several times higher than that of traditional fiber optic sensors. This high sensitivity allows the sensor to exhibit extraordinary performance in the detection of gases, liquids and biological samples. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 is a schematic diagram of a fiber optic SPR sensor for detecting electrolyte density of a lead-acid battery;

[0026] Figure 2 is a schematic diagram of a fiber optic SPR sensing system for detecting electrolyte density of a lead-acid battery;

[0027] Figure 3 This is the stability test diagram of the optical fiber SPR sensor, where: Figure 3 a is the resonance spectrum shift and local magnification of the optical fiber SPR sensor. Figure 3 b is the optical fiber SPR sensor spectrum resonance center wavelength shift diagram;

[0028] Figure 4 It is the performance test of the optical fiber SPR sensor, among which, Figure 4 a is the SPR resonance spectrum curve of electrolytes with different densities; Figure 4 b is the shift of the resonance center wavelength as the electrolyte density changes;

[0029] Figure 5 It is a linear fit of the central wavelength of the SPR curve as the electrolyte density changes.

[0030] Description of Reference Numerals

[0031] In the figure: 1. Silver plating, 2. Gold plating, 3. Plastic coating, 4. Fiber core and cladding, 5. Fiber SPR sensor, 6. Charger and discharge motor, 7. Lead-acid battery, 8. Broadband light source, 9. 1×2Y type optical fiber, 10. Ocean Optics fiber optic spectrometer, 11. Computer, 12. SMA905 fiber optic adapter. DETAILED DESCRIPTION

[0032] The present invention is further described below in conjunction with the accompanying drawings.

[0033] The experimental methods used in the following examples are conventional methods unless otherwise specified. The materials, reagents, methods and instruments used are conventional materials, reagents, methods and instruments in the art unless otherwise specified, and can be obtained through commercial channels by those skilled in the art.

[0034] The present invention discloses an optical fiber SPR sensor, such as Figure 1 As shown, it includes an optical fiber sensing area, a plastic coating layer 3, a fiber core and a cladding; the optical fiber sensing area includes a silver plating layer 1 and a gold plating layer 2, and the optical fiber sensing area is located at the axial head end of the fiber core and the cladding; the silver plating layer 1 is located at the cross section at one end of the fiber core and the cladding, and the axial distance between the silver plating layer 1 and the gold plating layer 2 is 1.5 cm; the axial length of the silver plating layer 1 is 60 nm, and the axial length of the gold plating layer 2 is 1 to 1.5 cm; the thickness of the gold plating layer 2 is 50 nm.

[0035] The present invention further discloses a method for preparing an optical fiber SPR sensor. The optical fiber SPR sensor is prepared by using a multimode optical fiber, and comprises the following steps:

[0036] Step 1: First, the multimode optical fiber needs to be preprocessed. The core and cladding materials of the multimode optical fiber are both made of silica. Select a multimode optical fiber with a length of 9 to 10 cm, a core diameter of 600±10μm, and a cladding diameter of 630±5μm.

[0037] Step 2: Remove 2mm of plastic coating from the end face area of ​​one end of the multimode optical fiber along the axial direction, and then insert it into the grinding disc so that the end face is exposed about 1mm from the grinding disc; place it on sandpaper of different roughness and grind the end face of the optical fiber perpendicular to the axial direction of the optical fiber, and observe it under a microscope until the end face of the optical fiber is flush with the end face of the grinding disc, otherwise continue grinding; after grinding, take it out and rinse it with anhydrous ethanol, and do the same treatment on the other end of the multimode optical fiber.

[0038] Step 3: Select one end section of the multimode optical fiber as the silver-plated surface, and then place it in a magnetron sputtering coating instrument for silver plating. The silver plating current is selected to be 25mA, and the time is 900s. After the silver plating is completed, apply purple glue to the silver-plated area to prevent oxidation.

[0039] Step 4: The axial distance between the silver-plated end face and the nearest end of the gold-plated area is 1.5 cm, the axial distance between the silver-plated end face and the farthest end of the gold-plated area is 2.5 to 3 cm, and the axial length of the gold-plated area is 1 to 1.5 cm. Under an electron microscope, use a knife to remove the plastic coating of the gold-plated area and rinse it with anhydrous ethanol. Put the silver-plated multimode optical fiber into an ultrasonic cleaner to clean the grease on the surface of the optical fiber; place the cleaned multimode optical fiber in the fixture of the coating instrument, control the current to 22 mA, and magnetron sputter gold film in the sensing area where 1 to 1.5 cm of the plastic coating layer is removed to stimulate SPR. The gold plating time is 200 s and the coating thickness is 50 nm. The fine control and condition setting of the preparation process ensure the high quality and reliability of the sensor, and finally a reflective optical fiber SPR sensor is obtained.

[0040] The present invention further discloses an optical fiber sensing system for real-time, high-sensitivity detection of electrolyte density of a lead-acid battery, comprising an optical fiber SPR sensor, a charger and discharger 6, a lead-acid battery 7, a broadband light source 8, a 1×2Y optical fiber 9, a computer 11, an ocean optical fiber spectrometer 10, and an SMA905 optical fiber adapter 12; the broadband light source 8 and the ocean optical fiber spectrometer 10 have no specified models, and the ocean optical fiber spectrometer 10 has a wavelength band of 400nm to 1100nm.

[0041] 1×2Y optical fiber 9 is used to connect broadband light source 8, Ocean Optics optical fiber spectrometer 10 and optical fiber SPR sensor. SMA905 optical fiber adapter 12 is used to connect 1×2Y optical fiber 9 with optical fiber SPR sensor with SMA905 interface to ensure the accuracy of optical path coupling. Computer 11 is used to run spectrum acquisition software, complete the acquisition and recording of optical fiber SPR spectrum data, and perform preliminary analysis of spectrum information.

[0042] The present invention further discloses an application method of an optical fiber sensing system for real-time and high-sensitivity detection of lead-acid battery electrolyte density, comprising the following steps:

[0043] Step S1: implant the silver-plated layer 1 of the optical fiber SPR sensor into the lead-acid battery 7 from the injection port, and completely immerse the sensing area of ​​the gold-plated layer 2 of the optical fiber sensor in the electrolyte, wherein the main component of the electrolyte of the lead-acid battery 7 is dilute sulfuric acid; the other end of the optical fiber SPR sensor is connected to the 1×2Y optical fiber 9 through the SMA905 optical fiber adapter 12 to access the optical path;

[0044] Step S2: Connect the lead-acid battery 7 to the charger and discharger 6, and start the charger and discharger 6 to perform a charge and discharge cycle on the battery;

[0045] Step S3: The light emitted by the broadband light source 8 enters from one end of the 1×2Y optical fiber 9 and is reflected by the silver coating 1 of the optical fiber SPR sensor back to the ocean optical spectrometer 10; wherein, the surface plasma resonance phenomenon occurs in the optical fiber sensing area, and when the gold coating 2 in the optical fiber sensing area contacts the electrolyte of the lead-acid battery 7, the incident light is attenuated and reflected, thereby forming a specific reflection spectrum. According to the characteristics of the reflection spectrum, the refractive index of the electrolyte in contact with the surface of the optical fiber sensing area can be deduced, and then the density change can be deduced.

[0046] Step S4: During the charge and discharge process of the lead-acid battery 7, the lead-acid battery electrode undergoes a redox reaction, causing the electrolyte density to change. The electrolyte density has a corresponding relationship with the refractive index. When the charge of the lead-acid battery 7 changes, its electrolyte density changes significantly, resulting in a change in the electrolyte refractive index. The change in refractive index causes the spectrum of the optical fiber SPR sensor to change. Through computer data acquisition, the electrolyte density change of the lead-acid battery 7 can be monitored in real time, thereby evaluating the battery SOC; when the lead-acid battery 7 is charged, the lead sulfate produced on the anode plate and the cathode plate will be decomposed and reduced into sulfuric acid, lead and lead peroxide, so the concentration of the electrolyte in the battery gradually increases, that is, the electrolyte refractive index rises, and the corresponding optical fiber SPR spectrum will produce a red shift; when the lead-acid battery 7 is connected to an external circuit for discharge, the dilute sulfuric acid will react with the active substances on the cathode and anode plates to generate a new compound, lead sulfate. The sulfuric acid component is released from the electrolyte through discharge. The longer the discharge, the lower the sulfuric acid density, the lower the electrolyte refractive index, and the corresponding optical fiber SPR spectrum will produce a blue shift.

[0047] The optical fiber SPR sensing system of the present invention can be used to monitor the battery sulfidation phenomenon when detecting the electrolyte density of the lead-acid battery. When a battery sulfidation failure occurs, lead sulfate crystals will adhere to the pores of the reaction material. This phenomenon will hinder the infiltration of the electrolyte and the transmission of the current, causing these insoluble lead sulfate crystals to be unable to normally participate in the chemical reaction process of the battery. Compared with healthy batteries, the capacity of the lead-acid battery with plate sulfidation and the full-charge electrolyte density will be significantly reduced. In this case, the resonant wavelength of the optical fiber SPR sensor will be significantly smaller. This change in resonant wavelength provides an important basis for monitoring the battery sulfidation status using an optical fiber SPR sensor, which helps to promptly discover the sulfidation problem of the battery, thereby providing a valuable reference for the maintenance and management of the battery.

[0048] Example 1

[0049] Combination Figure 1 This embodiment is described. A fiber SPR sensor for detecting the electrolyte density of a lead-acid battery in this embodiment includes a silver coating 1, a gold coating 2, a plastic coating 3, a core and a cladding 4. The middle sensing area of ​​the core and the cladding 4 is covered with a gold coating 2, the ends of the core and the cladding 4 are covered with a silver coating 1, and the core and the cladding 4 are uniformly covered with a plastic coating 3 along the axial direction; in this embodiment, the sensing area for exciting SPR is a gold coating 2, with an axial length of 1 to 1.5 cm. When the gold coating 2 in the optical fiber sensing area contacts the electrolyte of the lead-acid battery 7, the incident light will be attenuated and reflected, and a surface plasma resonance phenomenon will occur in the optical fiber sensing area, thereby forming a specific reflection spectrum. According to the characteristics of the reflection spectrum, the refractive index of the electrolyte in contact with the surface of the optical fiber sensing area can be deduced, and then the change in the electrolyte density can be deduced. The sensor is small in size, has a high sensitivity to the refractive index, and has good gold stability. It can exist stably in a complex chemical environment, so it is suitable for battery detection.

[0050] Example 2

[0051] Combination Figure 2The present embodiment is described. The present embodiment is a fiber optic sensing system for detecting the electrolyte density of a lead-acid battery. A fiber optic SPR sensor for detecting the electrolyte density of a lead-acid battery is used. The fiber optic sensing system for detecting the electrolyte density of a lead-acid battery includes a fiber optic SPR sensor, a broadband light source 8, a 1×2Y optical fiber 9, an ocean optical fiber spectrometer 10, a computer 11, and an SMA905 optical fiber adapter 12 which are connected in sequence. The LabVIEW program in the computer 11 is used to realize real-time display and acquisition of SPR spectrum data and data such as resonance wavelength. The unsilver-plated end of the fiber optic SPR sensor is connected to the single-port end of the 1×2Y optical fiber 9 through the SMA905 optical fiber adapter 12. The gold-plated layer 2 sensing area of ​​the fiber optic SPR sensor is completely immersed in the electrolyte through the lead-acid battery 7 injection port. The charger and discharger 6 is connected to and controls the charging and discharging of the lead-acid battery 7.

[0052] Example 3

[0053] Combination Figure 3 The present embodiment is described, and the stability test of the optical fiber SPR sensor of the present embodiment is performed. The resonant wavelength of the optical fiber SPR sensor can remain stable in the electrolyte for a long time. This is because the stability of gold is higher than that of other metals, and it is not easy to react with other substances in different environments. Therefore, gold can be implanted in the lead-acid battery 7 for long-term monitoring.

[0054] Embodiment 4:

[0055] Combination Figure 4 and Figure 5 The present embodiment is described as a method for detecting the electrolyte density of a lead-acid battery. The optical fiber SPR sensor is small in size and can be easily implanted in the electrolyte of a lead-acid battery 7. It has high sensitivity and can detect small changes in the electrolyte density of the lead-acid battery 7 during charging and discharging. The sensitivity is 275.5nm / g / cm 3 ,like Figure 4 As shown; the optical fiber sensor has good linearity, such as Figure 5 shown.

[0056] Embodiment 5:

[0057] The lead-acid battery 7 of this embodiment will undergo redox reactions on the plates during charging and discharging. During the charging process of the lead-acid battery 7, the lead sulfate on the anode reacts with water to generate lead dioxide and lead, while releasing dilute sulfuric acid. The density of dilute sulfuric acid increases, so the refractive index increases, and the resonant wavelength of the SPR spectrum red-shifts. The lead sulfate on the cathode is reduced to lead and sulfate ions. During the discharge process, the lead on the cathode reacts with sulfate ions to generate lead sulfate, and the lead oxide on the anode reacts with water to generate lead sulfate and water. The density of dilute sulfuric acid decreases, so the refractive index decreases, and the resonant wavelength of the SPR spectrum blue-shifts.

[0058] Finally, it should be noted that the above preferred embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail through the above preferred embodiments, those skilled in the art should understand that various changes can be made in form and details without departing from the scope defined by the claims of the present invention.

Claims

1. An optical fiber SPR sensor, characterized in that: The invention comprises an optical fiber sensing region, a plastic coating layer (3), a fiber core and a cladding; the optical fiber sensing region comprises a silver plating layer (1) and a gold plating layer (2), and the optical fiber sensing region is located at the head end of the fiber core and the cladding; the silver plating layer (1) is located at the cross section of one end of the fiber core and the cladding, and the distance between the silver plating layer (1) and the gold plating layer (2) is 1.5 cm; the length of the silver plating layer (1) is 60 nm, the length of the gold plating layer (2) is 1 to 1.5 cm, and the thickness of the gold plating layer (2) is 50 nm.

2. The optical fiber SPR sensor according to claim 1, characterized in that: The core diameter is 590-610 μm, and the length is 9-10 cm; the cladding diameter is 625-635 μm.

3. A method for preparing a fiber SPR sensor as claimed in claim 1 or 2, characterized in that: The following steps are involved: Step 1: Remove 2mm of the plastic coating from the leading and trailing ends of the multimode optical fiber along the axial direction, and grind the cross section of the optical fiber perpendicular to the direction of the multimode optical fiber. After grinding it flat, take it out and wash it; Step 2: Place the head end of the multimode optical fiber in a magnetron sputtering coating apparatus and silver-coat the polished cross section; Step 3: remove the plastic coating layer (3) 1.5 cm away from the silver coating layer (1) on the multimode optical fiber and wash it, perform ultrasonic washing on the multimode optical fiber, and after washing, use a magnetron sputtering coating device to plate gold on the cladding at the position where the plastic coating layer (3) is removed.

4. The preparation of the optical fiber SPR sensor according to claim 3, characterized in that: In step 2, during the silver plating, the magnetron sputtering current is 25 mA and the time is 900 s; in step 3, during the gold plating, the magnetron sputtering current is 22 mA and the time is 200 s.

5. A fiber SPR sensing system, characterized in that: include: The optical fiber SPR sensor according to claim 1; the tail end of the optical fiber SPR sensor is connected to a 1×2Y optical fiber (9) via an SMA905 optical fiber adapter (12); the 1×2Y optical fiber (9) is respectively connected to a broadband light source (8) and an optical fiber spectrometer (10); and the optical fiber spectrometer (10) is connected to a computer (11).

6. The optical fiber SPR sensing system according to claim 5, characterized in that: The wavelength of the optical fiber spectrometer is 400-1100nm.

7. An application of the optical fiber SPR sensing system as claimed in claim 5, characterized in that: The optical fiber SPR sensing system is used to detect the electrolyte density of a lead-acid battery.

8. An application method of the optical fiber SPR sensing system according to claim 7, characterized in that: The following steps are involved: Step S1: implanting one end of the optical fiber SPR sensor with the silver coating (1) from the injection port of the lead-acid battery (7), and immersing the gold coating (2) area of ​​the optical fiber SPR sensor in the electrolyte, wherein the electrolyte of the lead-acid battery (7) is dilute sulfuric acid; Step S2: connecting the lead-acid battery (7) to the charger (6), and starting the charger (6) to perform a charge-discharge cycle on the lead-acid battery (7); Step S3: Use a fiber optic spectrometer to record the spectrum and central wavelength data.

9. The application method of the optical fiber SPR sensing system according to claim 8, characterized in that: Light emitted by a broadband light source (8) enters through one end of a 1×2Y optical fiber (9), is reflected back to an optical spectrometer (10) by a silver coating (1) of an optical fiber SPR sensor, and surface plasma resonance occurs in the optical fiber sensing region; when the gold coating (2) of the optical fiber SPR sensor contacts the electrolyte of a lead-acid battery (7), the incident light is attenuated and reflected, thereby forming a specific reflection spectrum and obtaining a refractive index; and the density of the lead-acid battery electrolyte is determined based on the refractive index.

10. The application method of the optical fiber SPR sensing system according to claim 8, characterized in that: When the lead-acid battery (7) is discharged, dilute sulfuric acid reacts with the active substances on the cathode and anode plates to generate a new compound, lead sulfate. The sulfuric acid component is released from the electrolyte during discharge. The longer the discharge, the lower the density of sulfuric acid, the lower the refractive index of the electrolyte, and the corresponding optical fiber reflection spectrum is blue-shifted. When the lead-acid battery (7) is charged, the lead sulfate generated on the anode and cathode plates will be decomposed and reduced into sulfuric acid, lead and lead peroxide, the concentration of the electrolyte in the battery gradually increases, the refractive index of the electrolyte rises, and the corresponding optical fiber reflection spectrum is red-shifted.

Images