EP4005052A1

EP4005052A1 - Methods and arrangements for identifying the charge state of lithium-ion batteries using optical means

Info

Publication number: EP4005052A1
Application number: EP20749842.9A
Authority: EP
Inventors: Valentin Roscher; Christian Modrzynski; Florian Rittweger; Karl-Ragmar Riemschneider
Original assignee: Hochschule Fuer Angewandte Wissenschaften Hamburg Haw Hamburg; Hochschule Fuer Angewandte Wss Hamburg Haw Hamburg; Hochschule fuer Angewandte Wissenschaften Hamburg
Current assignee: Hochschule Fuer Angewandte Wissenschaften Hamburg Haw Hamburg; Hochschule Fuer Angewandte Wss Hamburg Haw Hamburg; Hochschule fuer Angewandte Wissenschaften Hamburg
Priority date: 2019-07-30
Filing date: 2020-07-28
Publication date: 2022-06-01
Also published as: DE102019005317A1; WO2021032418A1

Abstract

The invention relates to methods and arrangements for metrologically monitoring the charge state of lithium-ion batteries. In particular, the charge state of charge-storing electrode materials can be optically detected. According to the invention, the large-area light guidance through the separator and the optical interaction in the region of the separator are used for this purpose. Light from light sources is coupled into the separator film and coupled out once it has passed through a planar region. The entire surface of this region is contacted by the electrode films. The guided-through luminous power is influenced by the interaction of the light with the active electrode materials. The transmission power is detected by a light sensor and is used to indicate the charge state.

Description

Method and arrangements for recognizing the state of charge of

Lithium-ion batteries with optical means

description

The invention relates to methods and arrangements for metrological observation of the state of charge of lithium-ion batteries. In particular, the state of charge of charge-storing electrode materials can be detected optically. According to the invention, the light guide through the separator is used for this purpose.

State of the art

A number of methods and systems for detecting the state of charge of batteries and battery cells are known; they fulfill partial functions of battery management systems. Electrical variables are often recorded and evaluated to detect the state of charge.

In simple systems, voltage values of the battery cells or of the entire battery are determined and compared with specified values or characteristics. These methods have the disadvantage that the measurable voltage values are at least partially dependent on the current and past operating conditions. For example, a no-load voltage is established as a relationship between the voltage values and the state of charge only after reaching a state of equilibrium without current flow. This is only practically given after a long period of time without charging or discharging. This relationship between voltage value and state of charge is specified as the open circuit voltage characteristic. It is in turn dependent on other influences and variables such as temperature and aging of the cell.

Other methods also use current measurements and integrate these values over the operating time in order to create a calculated charge balance. These current-integrating processes are often coulomb counting processes - according to the unit of electrical power Charge coulomb - called. They require accurate and stable current measurements. The current-integrating methods have - like most integrating methods - the metrological problem of integration errors. In applications with very different battery currents, current measurements with large measuring ranges are required. If the battery currents are very dynamic, a high measurement density over time is required, which increases the integration error. With the help of voltage measurements, the effect of the integration error is reduced. Therefore voltage measurements and current measurements are often combined. Using model calculations, they lead to estimates of the battery charge level, which, however, often have considerable errors. The battery temperature is often also taken into account as an important non-electrical variable because it has a significant cross-influence. The aging of the battery is also an important influencing factor. The endeavor to obtain accurate estimates via model calculation led to complex models with a number of parameters. The model parameters are partially determined adaptively or adjusted. This modeling can be improved by acquiring additional measured variables using new methods.

Solutions are also known which determine certain state parameters of the battery cells in a combination of electrical stimulation and measurements. This includes the method of electrochemical impedance spectroscopy, which analyzes the capacitive and ohmic component of the internal resistance at different frequencies. For this purpose, for example, an alternating current is passed through the cell and the voltage response is evaluated synchronously. An expanded presentation of this can be found in ’Characterization of high-power lithium-ion batteries by electrochemical impedance spectroscopy. I, II ’(Andre et al., Journal of Power Sources, 2011).

In the case of methods based on electrical measured variables - with and without targeted stimulation - it can be disadvantageous that the models cannot take into account all cross-influences and operating conditions.

Only a few methods record other parameters beyond the aforementioned parameters, such as the internal cell pressure or the electrolyte level. In doing so, direct measurement principles - independent of the electrical quantities - are sought.

It has long been known for the electrolyte of lead batteries that the gravimetric density changes with the state of charge. It is also known that the optical density and the associated refractive index are also influenced. An investigation method for this is based on taking electrolyte samples and measuring them with a Refractometer. Methods have also been proposed for evaluating the change in the refractive index with the aid of optical fibers immersed in the liquid electrolyte. The article 'Density measurement into lead-acid-batteries with multi-point optical fiber sensors' (J. Marcos-Acevedo et al., I2MTC 2009 - International Instrumentation and Measurement Technology Conference, IEEE 2009) presents a solution for this.

For modern lithium-ion batteries, fiber-optic monitoring of the electrolyte is not suitable for determining the state of charge. In the technology of lithium-ion batteries, the electrolyte has the function of conducting ions between the storing electrode materials.

The electrolyte is not chemically changed in the battery process and there are no changes comparable to those of the electrolyte in lead batteries. In this respect, the proposal in the aforementioned article cannot be implemented.

For laboratory testing - but not for practical battery use - testing options are known that involve dismantling the battery cell. These studies are known as post-mortem analysis. They also include the storage electrode material.

It is known from these investigations that visible color changes of the electrode surface can occur depending on the state of charge. For example, the color of graphite anodes varies, depending on the charge, between black-gray, blue and red, and even metallic-gold color impressions. The article 'Direct in situ measurements of Li transport in Li-ion battery negative electrodes' (Stephen Harris et al., Chemical Physics Letters, 2010) shows this effect and introduces the optical observation of graphite electrodes using a microscope.

Furthermore, it is known from current research that the charge-dependent optical effects can be intensified by certain additives. This is described in the article 'Method and Measurement Setup for Battery State Determination Using Optical Effects in the Electrode Material' (Valentin Roscher and Karl-Ragmar Riemschneider, IEEE Transactions on Instrumentation and Measurement, 2018). As described there, for example the addition of indium tin oxide as an electrochromic marker in lithium iron phosphate cathodes causes a significant change in the reflectivity when lithium ions are stored in or removed from this electrode material. This is visible as a darkening or lightening of the cathode. For this purpose, test cells with transparent windows were developed, which enable camera observations in the laboratory. These test cells and the use of cameras, however, are not suitable for ordinary battery applications. In addition, commercial cells with a multilayered cell structure cannot be observed through external windows.

In order to change the usual cell constructions far less, it has already been proposed to introduce prepared optical fibers into the electrodes or to bring them up to the electrodes. The article ’Optical characterization of commercial lithiated graphite battery electrodes and in situ fiber optic evanescent wave spectroscopy’ (Particia Nieva, Abdul Ghannoum et al., ACS Applied Materials and Interfaces, 2016) describes this in more detail. There it is explained that the light guided through the prepared optical fibers has a measurable interaction with the surrounding electrode material. Losses of light transmission through the fiber depending on the state of charge can be recorded with a light sensor. A metrologically usable correlation between these losses and the state of charge was demonstrated. The article Optical battery sensors for electric vehicles ’(Valentin Roscher and Karl-Ragmar Riemschneider, Automobil-Sensorik 2, Springer-Verlag, 2018) deals with optical effects on the

Lithium iron phosphate cathodes and appropriately mentions the possibility of inserting glass fiber optical waveguides in lithium ion batteries.

Although the charge state of the electrodes can be observed directly during operation through the optical fibers inserted, this application of the optical measurement principle still has considerable disadvantages.

They are due to the optical fibers required, which have not been used in industrial battery production up to now. In particular, the preparation of the fiber and its introduction into the electrode are technologically complex steps. Light-conducting glass fibers become very sensitive after the necessary removal of the outer protective layer and break even under low loads due to bending, shear or tensile stress. These mechanical loads can hardly be avoided in industrial manufacturing processes. The use of protective coverings for the fiber - as in the communication application - is not possible.

Another disadvantage is that the regular cell structure at the point where the fibers are introduced is disrupted to a certain extent. As a result, the behavior on the fiber and in the rest of the electrode surface can differ from one another.

An additional disadvantage when recording the state of charge of the battery Optical fibers mean that the number of fibers introduced should be rather small for reasons of expense.

Typically, only one fiber can be inserted per electrode. This means that only one measured value can be recorded along the fiber, which must represent the entire area of the electrode with a small sample. In the case of an inhomogeneous electrode, a local deviation at some distance from the fiber would not be observable. Such an inhomogeneity could, however, form a weak point in the cell, which should actually be detected.

Known prior art literature

The following is a compilation of patents that describe the state of the art. Building on this, the proposed invention takes up existing problems and goes beyond the known prior art. On the one hand, optical methods are mentioned, followed by other methods that also have the acquisition of additional measured variables as their object, but are not based on optical methods.

The patent US20170131357A1 (Patricia Nieva et. Al., 2015) deals with the determination of the condition of lithium-ion batteries via fiber optic light guides. The invention uses glass fiber optical waveguides, which have considerable disadvantages for industrial production. By using glass fibers, the document differs significantly from the proposed invention, the object of which is to offer a solution without glass fibers.

The patent specification US9553465B2 (Ajay Raghavan, PARC Inc., 2014) deals with battery management by means of glass fiber optical waveguides introduced into the cell. The invention uses glass fiber optical waveguides to detect gas evolution in the cell. This deviates significantly from the proposed invention both in the metrological task and in the use of the glass fiber.

The patent US20150280290A1 (Bhaskar Saha, PARC Inc., 2015) deals with the detection of the intercalation levels in lithium-ion batteries by means of glass fiber optical fibers. Here, too, additional glass fibers must be introduced, which are not used in the present invention.

The patent US5949219A (Jonathan Weiss, 1998) describes the detection of the State of charge by means of fiber optic light guides in lead and lithium batteries. In lithium batteries, the absorption of the electrode material is measured by introducing several glass fibers into the cell, one of which emits light, which is guided by the remaining fibers to a light sensor after interaction with the environment. For lead-acid batteries, a solution is given that contains a glass fiber woven into a glass mat. The mat is used to position and fix the light-conducting glass fiber and does not take part in the measurement process. In this case, a light-conducting glass fiber is also used and not, as suggested in our own solution, the entire flat separator.

The patent US6356478B1 (Jonathan Weiss, 2002) describes a fiber optic chemical sensor for lead batteries. This document relates to the detection of the electrolyte state and not the electrodes. In addition, fiber optics are used. The solutions according to this patent are suitable for lead batteries; they cannot be used in lithium-ion batteries. The patent EP3098879A1 (Stephan Leuthner, Calin Wurm, 2015) describes the detection of decomposition products of the cathode. The solution is only able to determine a complete or partial destruction of the cell, which is associated with an at least partial malfunction in the event of severe aging. So it's not about recording the state of charge in regular operation. The solution uses an optical sensor as an exemplary embodiment, which in turn detects the discoloration of an indicator material that reacts with undesired oxygen. Even if, in a further exemplary embodiment, a light-conducting separator is proposed for supplying light to the sensor, only the indicator material is observed. In detail, there is also the need for a separate indicator substance (e.g. indigo, leucomethylene blue or luminol), which reacts with the oxygen produced in the event of a fault. This patent specification is to be distinguished from the proposals of the own invention both in the task and in the technical implementation.

The patent EP2883260B1 (James Dvorsky, Steven Rissner, 2013) describes a way of reporting the occurrence of dendrites in lithium-ion batteries. This dendrite formation does not take place in normal battery operation, but is a symptom of severe damage to the battery cell. As in the previous publication, the task is to report a state of particular aging up to and including a malfunction. For this purpose, a measurement of the light permeability of the separator is proposed. In detail, this measurement differs in that no two-dimensional recording of effects takes place, but only the dendrites that occur point by point have a certain influence on the light transmission through the separator. This takes advantage of the fact that the separator is attached to the Make the dendrites damaged or destroyed.

This is not the case with our own solution. This is about normal battery operation in which the separator is not damaged. This document thus differs from the present invention in three aspects (i) First of all, the task is clearly different: the publication mentioned merely wants to report an atypical critical situation. The present invention, on the other hand, aims to continuously monitor the state of charge as a regular value measurement task of the battery management (ii) Furthermore, the mentioned publication relates to the detection of a punctual effect of individual dendrites that occur. The present invention aims to capture a two-dimensional effect of the entire electrode surface (iii) In addition, the solutions of the cited document are associated with irreversible changes there due to the penetration of the dendrites into the separator layers. This irreversible and unique mode of operation differs from the present invention in that there is a fully reversible mode of operation, in particular in that the separator is not damaged.

The patent DE102014218277A1 (Jean Fanous, Martin Tenzer, 2014) describes a separator that includes an electrically conductive layer with the aim of detecting dendrite growth. For this purpose, the electrically conductive layer of the separator is not in electrical contact with the electrodes in the normal operating state. When the dendrite grows, the normal separator layer is destroyed and a short circuit with the electrically conductive part is created, which can be detected by a separate electrical contact. In this document there is no optical recording of measured values, nor is there any recording of the state of charge.

The patent US20090104510A1 (Ricardo Fulop, 2008) describes battery status monitoring by means of a reference electrode introduced into the cell. Although measuring sensors are placed in the battery, no optical measurements are made.

The patent specification W02006077519A1 (Peter Notten, 2006) deals with pressure and deformation measurements in battery cells. No optical measurements are taken. The patent specification W02004047215A1 (Karl-Ragmar Riemschneider, 2003) describes a wireless battery management system. Although this solution uses electronics for cell monitoring, it only obtains its data from electrical measurements.

US5667538A (John C. Bailey, 1991) describes an optical representation the state of charge. The status is recorded exclusively via electrical measurements, only the status is displayed optically.

Problem and proposed solution of the invention

Based on the described state of the art, optical measuring principles are to be used to determine the state of charge for industrially manufactured cell structures. The aforementioned disadvantages are intended to be overcome.

The following objects therefore arise for the invention. It should be stable in the industrial production process of the cells and be able to be implemented with little effort. It should not require any significant deviation in the cell structure in the active area of the electrodes and should therefore result in almost no change in the battery process. It should record the optical effects on the electrodes over the largest possible area in order to determine the state of charge from them.

The aim of the invention is to achieve the stated objects in that the separator placed between the electrodes is used to guide light and optical fibers are dispensed with. The separator touches the respective electrode surfaces of the anode and the cathode on both sides. The optical interaction takes place over a large area. The layer structure of the cell and the active material used for ion storage remain unchanged. No optical fibers are required in the cell. The light must be coupled in at the separator. An enclosed light source such as a light emitting diode (LED) can be used for this purpose. The coupling can take place on the front side or over a large area. In the latter case, a prism can advantageously be used. The light can be decoupled in a comparable manner and detected with a light sensor.

The two-dimensional interaction here relates to an interaction at the interfaces between the separator and at least one of the electrode surfaces. In addition, the interaction depends on the local light output in the separator; the interaction is recorded via the area integral. With the technically possible measurement resolution, optical effects are covered on at least 10% of the entire separator-electrode interface. Typically, however, the detectable interaction area of the interfaces is greater than 50% up to over 90%. The area can therefore be described as large.

By detecting the from coupling into the separator to decoupling The extent of the interaction with the electrode material can be measured by the transmitted light.

Embodiments of the invention

For the proposed solution it can advantageously be used that many common separator materials are already transparent or translucent. This means that they have at least some light-guiding properties. This property is generally further improved by wetting with the electrolyte. By choosing a separator material with a suitable refractive index for the electrolyte, the breakout of light can be influenced. In this way, the loss of the coupled-in light can be adjusted in relation to the length of the transmission.

Separators are usually optimized in such a way that they guarantee reliable electrical separation of the electrodes, but also enable good ion conduction. A favorable ion passage is achieved through a high porosity or a woven and permeable structure. In particular through the numerous pores of the separator material, the introduced light emerges from the area of the separator by scattering, reflection and diffraction. This promotes the intensive and extensive interaction with the surrounding electrode surfaces. This is therefore desirable for the development of the effect used for measurement purposes.

On the other hand, the pore structure counteracts the light conduction between the light source and the light sensor. Over long distances, this can lead to undesirably high losses in light output. In an advantageous embodiment variant of the invention, the light conduction of the separator or the separator film can be partially improved. In this way, light-conducting line structures or narrow strips can be created in the separator. These show a reduced porosity for a narrow, line-like area. In this way, the light introduced from the source can be largely evenly distributed over the surface of the separator.

The light can also be directed from the surface to the sensor. For example, tree-like branches for the incoming and outgoing line structure or strips with reduced porosity are suitable. These can be arranged in such a way that only short distances between them are illuminated in the separator. Overall, the number of pores in the separator remains almost the same. To compensate for the lines with a reduced number of pores, the porosity in the remaining, much larger areas can be increased slightly. Another advantageous variant relates to the production of the aforementioned line structures. For many polymer films commonly used as separators, it is possible, by means of limited heat treatment, to produce light-guiding line structures by locally strongly limited melting. This can be done with heated stamp molds for the lines or with spatially narrowly limited laser light.

A number of other design variants are advantageous. The use of inexpensive multicolored light-emitting diodes (LED) as light sources should be mentioned. The light sensors can be implemented as photodiodes, photoresistors or phototransistors. Integrated designs of light sensors as part of a silicon chip in combination with other functional units are also advantageous for light detection.

The control of the light sources and the evaluation of the light sensors can advantageously be carried out with a mixed signal circuit in combination with a microcontroller.

Description of the drawings

Some embodiments of the invention are shown in the drawings and are described in more detail below. The drawings show:

1a and 1b: Schematic examples for use in different types of battery cells.

Fig. 2: An embodiment for a battery cell with a wound structure.

FIGS. 3a to 3d: Examples of the position of the light sources and light sensors. Fig. 4: An arrangement for the coupling and decoupling of the light.

Fig. 5: Another arrangement for the coupling and decoupling of the light.

6: An exemplary embodiment with separator areas of different porosity.

7: An embodiment with a fluorescent component on the separator.

Fig. 8: The use of several light sources with different wavelength ranges.

Fig. 9: The use of several light sensors for different wavelength ranges.

10 shows an exemplary embodiment of the method according to the invention. 11 shows an exemplary embodiment of the method according to the invention based on several wavelengths.

12 shows an exemplary embodiment of the method according to the invention based on a multiplex measurement.

Detailed description of exemplary embodiments

The drawings Fig. 1a and 1b serve to illustrate the basic proposed solution of the invention.

The drawing Fig. 1a shows schematically the use of the invention on a pouch cell or a prismatic cell. In a graphically simplified manner, only one folded layer is shown there. From the light source (s) 100, light 129 is introduced into the separator or the separator film 103 with a coupling element 102. This separator film is located between the positive electrode or electrode film 106 and the negative electrode or electrode film 108. After the light has traveled a distance in the separator, this light 130 is decoupled again with a decoupling element 110 and fed to at least one light sensor 111. An optical interaction with at least one of the electrodes 106 or 108 has taken place on this path. This interaction influences the light output that is coupled out. This variable power is detected by measurement at the light sensor 111 and is related to the charge state of the electrodes, which is to be determined.

The drawing Fig. 1b shows schematically the use of the solution according to the invention on a round cell in which the layers are wound. The components and reference symbols correspond to FIG. 1 a. Here, the light is coupled into the wound separator over a large area at one end. For this purpose, the coupling element follows the winding as a shape. The decoupling element is located on the other face. It is also designed in such a way that it is coupled out from the surface. For this purpose, a decoupling element is also provided which follows the shape of the winding.

The drawing FIG. 2 shows a further exemplary embodiment on a cell with wound layer layers. From the light source (s) 200, the light 229 is introduced into the separator film with a coupling element 202 at one winding end of the separator film 203. This separator foil is located in a multilayer winding between the positive electrode foil 206 and the negative electrode foil 208. The light follows the winding from the outside into the center of the winding. On this path there is an optical interaction with at least one of the electrode surfaces 206 or 208. The separator and the electrodes are more curved as the winding increases. This curvature increases the interaction. A rod-shaped coupling-out element 210 is located in the center. The remaining light is coupled out 230 here and supplied to at least one light sensor 211. In a variation of this exemplary embodiment, the position of the light sensor and light source can be exchanged. Then the light passes through the winding from the inside out. The interaction results in a comparable way.

The drawings, FIGS. 3a, 3b, 3c and 3d show different positions of light sources 300 and light sensors 311 in the structure of a cell with wound layers. The schematic representation looks at the end of the winding. The following components are shown in detail: light source 300, light 329 to be coupled in, separator or separator film 303, positive and negative electrodes or electrode films 306 or 308, all viewed from the front, coupled-out light 330 and light sensor 311.

The drawing Fig. 3a shows an arrangement in which the light is introduced from the outside of the winding and is detected in the center by measurement.

The drawing Fig. 3b shows an arrangement in which the light is introduced in the center of the winding and measured on the outside.

The drawing FIG. 3c shows an arrangement in which the light is introduced from the outside of the winding, is passed through the center and is again detected by measurement on the outside.

The drawing Fig. 3d shows an arrangement in which the light is introduced in the center of the winding, is directed to the outside of the winding, there is guided back to the center and is again detected by measurement in the center. The latter position can advantageously utilize the cylindrical cavity in a wound cell, which is caused by manufacturing technology. For example, coupling-in and coupling-out elements and light diffusers can also be placed there in the separator film for uniform and areal distribution of the light to be coupled in and out. The same applies to compact evaluation electronics.

The drawing Fig. 4 shows schematically an arrangement for the coupling and decoupling of light as an embodiment. The light 429 from the light source (s) 400 is supplied to a prism 402. There, according to the known laws of refraction of the prism, the beam angle is influenced in such a way that effective coupling into the planar separator 403 takes place. The light then propagates 412 in a directional manner in the surface of the separator. After passing through this surface and interacting with at least one of the adjacent electrodes 406 and 408, the light 430 becomes with a prism 410 decoupled. Here the beam angle is directed from the surface to the light sensor 411. This coupling and decoupling with prisms has the advantage that the losses between the light source and separator or separator and light sensor are low and comparatively large areas and angular ranges are permitted in the construction. This is advantageous over direct coupling into the flat end regions of the separator or the separator films. The prisms can also be designed according to the Fresnel principle. They can also be designed as a deformation of the separator or comprise several separator layers with a prism structure. Prisms can also be used separately exclusively for coupling or exclusively for decoupling. The housings of the light sources and sensors can be shaped so that they already have matching prism structures themselves.

The drawing FIG. 5 shows a further schematic arrangement for coupling in and coupling out the light. In particular, a multiple layer structure of separator 503, electrode foils made of positive active material 506 and negative active material 508 and current conductors for the positive electrode 507 and for the negative electrode 509 is shown. Here the light 529 from at least one light source 500 is fed to the coupling elements 502. These coupling elements 502 are formed from the separator material and widened so that they have a multiple of the separator thickness. In this way, almost the entire height of the layer structure or the entire end face of a wound layer structure can be used for coupling. After the light has passed through and interacted with at least one of the adjacent electrode surfaces 506 and 508, coupling out of the light can be supported in a comparable manner. For this purpose, the decoupling elements 510 also have an expansion. Almost the entire height of the layer structure can thus also be used for coupling out. The coupled-out light 530 is then detected by the light sensor 511. The same applies to the end faces of winding structures. Technologically advantageous, the deformation for the coupling-in and coupling-out elements 502 and 510 can take place thermally. Conical prisms or microlens structures can also be formed during the expansion. These can be placed in hole structures of the electrical combination and derivation from the current collector foils.

It should be noted that the coupling or decoupling according to the embodiment described in FIG. 4 is used on one side of the separator, while the coupling or decoupling according to the embodiment described in FIG. 5 is used on the other side of the separator.

The drawing Fig. 6 shows an embodiment with separator areas of different Porosity. The porosity describes the volume ratio of separator material and unfilled cavities. It can be determined approximately via density measurements (ratio of mass to volume). The porosity can be set, for example, by an open-line structure provided at least on one surface of the separator. A greater porosity is present when the ratio of open-line accessible volumes in the separator body, or volumes created by surface roughness on either the separator body or the electrode surfaces is greater in relation to the total volume of the separator body.

Separator materials typically have a high porosity in order to take up the electrolyte in the pores and thus ensure ion conductivity. A high number of pores leads to intensive light scattering and diffraction effects. On the one hand, these effects contribute to promoting interaction, on the other hand, they lead to strong light losses. These losses can limit the practical useful distance that light can travel. If this usable distance is exceeded, the light outputs remaining at the sensor are metrologically unfavorable and difficult to separate from the thermal noise.

It is therefore proposed to equip the separator with areas in which the number of pores is reduced, which is to be understood as lower porosity. In these low-loss areas, the light can cover greater distances.

In particular, a comb-like shape of these areas with low porosity is possible. The illustrated embodiment shows the light sources 600, from which light 629 is introduced into the areas of low porosity of the separator film 604 with the aid of a coupling element 602. In these areas, the light is distributed linearly in the separator surface with high porosity 605 in order to enter into optical interaction with at least one of the electrode surfaces over comparatively short stretches 612. From this area, the light passing through is picked up again in structures with low porosity 604 and passed on to a decoupling element 610.

From there, the coupled-out light 630 is detected in at least one light sensor 611. In many separator materials, in particular thermoplastic polymers, the areas with low porosity can be advantageously produced by local heating. In a typical embodiment, the low-loss areas are only to be designed as narrow line structures with a very small surface area, so that the desired porosity of the entire separator is not fundamentally lost. This thermal treatment can be done so briefly that the surface has a lower refractive index than that internal core material of the separator gets. This again reduces the transmission losses in the areas of low porosity.

The drawing FIG. 7 shows an embodiment with a fluorescent component on the separator. The light source 700 initially couples light 729 of a specific wavelength range into the separator film 703 via a prism 702. When passing through the separator, it interacts with the surrounding material of the positive electrode 706 and / or the negative electrode 708. After passing through the separator, the light from the separator is guided into a fluorescent material 714. Part of the transmitted light is absorbed there and preferably emerges in a different wavelength range. This light passes through the separator and exits at the decoupling prism 710. The forward and backward propagation of light is shown schematically 712 and 713. With the aid of a wavelength filter 715, the fluorescence response is separated from the light from the original light source 700. A light sensor 711 detects the transmitted light power of the decoupled light 730 after the interaction. With the aid of the different wavelength ranges of irradiation and emission, undesired saturation of the light sensor 711 is avoided, so that it can be placed spatially close to the light source 700.

The drawing FIG. 8 schematically shows an exemplary embodiment with several light sources with different wavelength ranges in order to reduce the cross-influences of other variables such as temperature and pressure on the determination of the state of charge by forming reference values and the comparative calculation that takes place therewith. At the same time, systematic measurement errors such as fluctuating power of the light source due to aging or an unstable power supply are to be compensated. The same applies to influences on the absolute sensitivity of the light sensor. The absolute light output can also be changed by long-term changes to all light-conducting components. It is therefore proposed to use several light sources 800 and 801. These sources have different spectral characteristics, with a clear maximum of the emitted light outputs Pin 1 and Pin2 at different wavelengths lambda. This characteristic is shown schematically in diagrams 817 and 818. The light sources are operated in time division multiplex with the aid of an electronic changeover switch 819 in such a way that they are switched on in certain phases of a cycle and switched off in other phases. The light 829 from the light sources is coupled into the separator 803. The light passes through the battery cell 831 and there interacts with the electrode surfaces. The decoupled light 830 is detected by at least one light sensor 811 with a spectrally wide detection band which includes the maxima of the characteristics of the light sources. The output value of the light sensor 811 is temporarily stored in storing elements 822 and 823. The selection 820 of the respective storing element is controlled synchronously 821 with the switch-on phase of one of the light sources. This means that the transmission powers Poutl and Pout2 of the respective light sources are recorded separately. This is particularly advantageous if the charge state of the electrodes causes a different spectral distribution of the light power passing through. This is shown schematically in diagrams 825 and 826. The dashed line symbolizes, for example, the charged state and the solid line the discharged state. With the aid of a comparative calculation 824 of the temporarily stored values of Pout1 and Pout2, in particular with the aid of division, a value X that is largely independent of the absolute light output can be determined. This output value X is shown schematically in diagram 827. The comparison calculation is parameterized in such a way that a clearest possible, e.g. B. linear relationship between the state of charge and the output value X results. In the drawing, FIG. 8, two light sources and one light sensor are shown for reasons of clarity; the analogous expansion to more than two light sources and the use and comparative signal evaluation of more than two light sensors are not intended to be restricted by this.

The drawing FIG. 9 shows an exemplary embodiment with a plurality of light sensors which are intended to detect different wavelength ranges. The light 929 emitted from the light source 900 is coupled into the separator 903 arranged between the electrodes within the battery cell 931. The interaction to be recorded takes place there. The light is decoupled from the separator 930 and fed to two wavelength filters 915 and 916, respectively. These filters can advantageously be formed from colored transparent material. The filters can be designed as a prism arrangement that assigns different spectral ranges to different radiation angles. Another possibility is to use different microgrids. Line or array structures with several light sensor elements can be used here. Output powers separated according to spectral ranges are determined in the downstream light sensors 911. These can optionally be integrated or added up 932 and 933 to reduce the effects of noise. The output values 934 and 935 are subjected to a comparison calculation 924 in order to obtain an output value 928 for indicating the state of charge, which is less dependent on the absolute transmission of the entire spectrum. The advantage here is that the cross influences have a strong effect on the absolute transmission and are essentially independent of the wavelength. The same applies to fluctuations in the power of the light sources and other aging effects. In the drawing Fig. 9 only one light source and two light sensors are shown, the analogous extension to more than one light source and the use and comparative Signal evaluation from more than two light sensors is not restricted by this. A combination of the methods according to drawing FIG. 8 and drawing FIG. 9 can be advantageous.

The drawing FIG. 10 shows a flow chart for determining the state of charge of the battery by means of light transmission through the separator. The following steps take place. First, the light is generated 1040 from a light source, followed by a coupling 1041 into the separator. In this, the light is passed through and interacts 1042 with at least one of the electrode surfaces. After the light has been decoupled 1043 from the separator, the metrological detection 1044 of the light output takes place. This is used to determine the state of charge 1045 of the battery cell.

The drawing FIG. 11 shows a further flowchart for determining the state of charge of the battery by means of light conduction through the separator. A comparison calculation of different light outputs is used. Light 1140 is generated with a light source that is advantageously broadband. The coupling 1141 into the separator then takes place. Here the light propagation and interaction 1142 of the light with at least one of the electrode surfaces takes place. This is followed by decoupling 1143 from the separator. Various wavelength filters 1146 are arranged downstream of this. One filter is advantageously used for each light sensor. The detection of the light outputs 1144 as a function of the wavelength is thus carried out. A comparison calculation 1147 of at least two light outputs for different wavelength ranges is then carried out and is used to determine the state of charge 1145. This comparison advantageously also offers the possibility of reducing cross-influences or specimen scatter of the measuring components, since the specific parameter is of a relative and no longer absolute character.

The drawing FIG. 12 shows a further flow chart for determining the state of charge of the battery by means of light conduction through the separator. Another advantageous variant of the comparative calculation of different light outputs is used. Light 1240 is generated with at least two light sources which have different spectral properties. They are each switched on separately for separate periods of time. The time periods are controlled by a synchronization unit 1248. The coupling 1241 into the separator then takes place. Here, the light propagates and the light interacts 1242 with at least one of the electrode surfaces. This is followed by decoupling 1243 from the separator. The detection of the light 1244 takes place with a light sensor. This is beneficial like that broadband sensitive, that all wavelength ranges of the light sources are sufficiently detected. For each of the time periods in which a light source is switched on, the output values of the light sensor are stored separately 1249. The timing is also controlled by the synchronization unit 1248 in accordance with the switching on of the light sources. A comparison calculation 1247 of at least two stored output values is then carried out and is used to determine the state of charge 1245.

List of reference symbols

100 light sources

102 coupling element

103 Separator foil 106 Positive electrode foil

108 Negative electrode foil

110 decoupling element

111 light sensor

129 light to be coupled in 130 coupled out light

200 light source

202 coupling element

203 separator foil

206 Positive electrode sheet 208 Negative electrode sheet

210 decoupling element

211 light sensor

229 Light to be coupled

230 decoupled light 300 light source

303 separator foil

306 Positive Electrode Sheets

308 Positive Electrode Sheets

311 Light sensor 329 Light to be coupled

330 Decoupled light

400 light sources

402 coupling element in the form of a prism

403 Separator Foil 406 Positive Electrode Foil

408 Negative electrode foil

410 decoupling element in the form of a prism

411 light sensor

412 Light propagation in the separator film, schematically 429 Light to be coupled

430 decoupled light

500 light sources

502 coupling elements formed from the separator material

503 separator foils 506 positive electrode foils

507 Current collectors of the positive electrode foils

508 Negative electrode foils

509 current collector of the negative electrode foils

510 outcoupling elements formed from the separator material 511 light sensor

529 Light to be coupled

530 Decoupled light

600 light sources

602 coupling elements 604 areas of the separator film with low porosity Areas of the separator film with high porosity

Decoupling elements

Light sensors

Light propagation in the separator film schematically light to be coupled in light coupled out light source

Coupling element in the form of a prism

Separator film

Positive electrode

Negative electrode

Decoupling element in the form of a prism. Light sensor

Light propagation in the separator film in advance, schematically

Diagram of light propagation in the separator film, retrograde

Fluorescent material

Wavelength filter

Light to be coupled

Decoupled light

Light source, different in spectrum from further light source 801 light source, different in spectrum from further light source 800 separator film light sensor

Schematic spectrum of the coupled light power of the light source 800 Schematic spectrum of the coupled light power of the light source 801 Electronic switch

Electronic changeover switch for selecting memory 822 or 823, synchronization of changeover switches 819 and 820

Memory for output value of light sensor 811 with irradiation by light source 800 Memory for output value of light sensor 811 with irradiation by light source 801 Comparative calculation of the stored spectral light outputs 825 and 826 Schematic spectrum of the decoupled light output for the light source 800 Schematic spectrum of the decoupled light output for the light source 801 Sketch of the result the comparison calculation 824 as an indication of the state of charge light to be coupled in

Decoupled light after the interaction in the battery cell 831

Battery cell

Light source

Separator film

Light sensor for light detection after wavelength filter 915 wavelength filter different from further filter 916 wavelength filter different from further filter 915 comparative calculation of output values 934 and 935 result of comparative calculation 924 to indicate the state of charge light to be coupled in

Decoupled light after interaction in the battery cell 931 battery cell

Processing the output power of the light sensor 911 Processing the output power of the light sensor 912 Output value of the processing 932 935 Initial value of processing 933

1040 Light generation by means of a light source

1041 Coupling of light into the separator of the battery cell

1042 Light transmission and interaction in the separator

1043 Light extraction from the separator of the battery cell

1044 light detection

1045 Determination of the state of charge

1140 Light generation by means of a light source

1141 Light coupling into the separator of the battery cell

1142 Light transmission and interaction in the separator

1143 Light extraction from the separator of the battery cell

1144 light detection

1145 Determination of the state of charge

1146 wavelength filter

1147 Comparative calculation from the recorded light outputs

1240 light generation with different light sources

1241 Coupling of light into the separator of the battery cell

1242 Light transmission and interaction in the separator

1243 Light extraction from the separator of the battery cell

1244 light detection

1245 Determination of the state of charge

1247 Comparison calculation from the stored light outputs

1248 synchronization unit

1249 Storage of the recorded light outputs

Claims

Expectations

1. A method for the metrological observation of a state of charge of lithium ion battery cells with an optical sensor system, the method comprising: generating light with a light source arrangement (1040),

Coupling the light into a separate battery cell (1041),

Passing the light through the separator,

Decoupling the light from the separator,

Detecting the coupled-out light as transmission power (1044), determining the state of charge of the battery cell on the basis of the output of the coupled-in light and the detected transmission power (1045) as a function of a two-dimensional interaction of the coupled-in light (1042) between at least one electrode surface adjacent to the separator with an active electrode material and a surface of the separator, the interaction being based on the charge state-dependent optical properties of the active electrode material of the two-dimensional contacting surface of the separator and the electrode surface and the interaction including the two-dimensional surfaces and a two-dimensional part of the surfaces.

2. The method according to Claiml, wherein the transmission power is recorded for different spectral ranges and, when determining the state of charge, the transmission power for different spectral ranges is evaluated comparatively, taking advantage of the fact that the spectral reflection properties of the electrode surfaces (106 or 108), in particular their Color and / or their brightness values are charge-dependent.

3. The method according to any one of the preceding claims, wherein at least one of the coupling (102) of the light (129) and the coupling (110) of the light (130) into or from the separator via a surface of the separator (103) by means Prisms takes place.

4. The method according to any one of the preceding claims, wherein at least one of the coupling (102) of the light (129) and the coupling (110) of the light (130) into or out of the separator (103) via a widened edge surface of the separator takes place, in particular via an edge surface of a separator thickened at its edges.

5. The method according to any one of the preceding claims, wherein when determining the state of charge at least two selected spectral components of the coupled-in or coupled-out light (129 or 130) are evaluated separately according to the wavelength (932, 933) and By means of comparative referencing of measured values (924) of these spectral components, cross-influences of other physical quantities and systematic measurement errors on the determination of the state of charge are reduced.

6. The method according to any one of the preceding claims, wherein the coupling of light is coupling of light from several light sources of a light source arrangement with different spectral components of the wavelengths (800, 801), alternately switching on for a period of time in the switching cycle, in particular in time division multiplex (819, 820, 821) The decoupled light is recorded alternately (819, 820, 821) by at least one light sensor (811) of a light sensor arrangement, recorded sensor values are stored separately (822, 823) and successively recorded sensor values are comparatively evaluated (824).

7. The method according to any one of the preceding claims, wherein an at an interface of separator surface (103) and electrode surface (106, 108) with the transmitted light (712, 713) interacting electrochromic material is used for the detection of the reflection properties, which variable optical properties as a function of the ion charge of a positive electrode of the battery cell.

8. Arrangement of an optical sensor system for metrological observation of the state of charge of lithium-ion battery cells, the arrangement comprising: a light source arrangement (100) for generating light, a separator (103) which is placed between electrodes (106, 108) of a battery cell and touching the electrode surfaces of the electrodes flatly at at least one interface, a coupling element (102) which is connected to the separator (103) for coupling light (129) from the light source arrangement into the separator (103), with at least one of the interfaces between the separator and the electrode surfaces there is an interaction with light (712, 713) coupled into the separator and transmitted through the separator with at least one of the electrode surfaces, the interaction depending on the state of charge, a decoupling element (110) which connects to the separator (103 ) is connected to a decoupling of the transmitted light (130) after the interaction from the separator (103) to carry out a light sensor arrangement (111) in order to detect the decoupled light (130) as transmission power; and an evaluation unit which is designed to process the transmission power to determine the state of charge.

9. Arrangement according to claim 8, wherein the separator (103) is designed as a separator film, in particular as a flexible separator film.

10. Arrangement according to one of claims 8 to 9, wherein at least one of the

Coupling element (102) and the decoupling element (110) is designed as an arrangement with at least one prism.

11. Arrangement according to one of claims 8 to 10, wherein at least one of the coupling element (102) and the decoupling element (110) as expanded

Edge surface of the separator, in particular is designed as an edge surface of a separator thickened at its edges.

12. Arrangement according to one of claims 8 to 11, wherein the light source arrangement has a plurality of differently colored light sources (800, 801), the arrangement further comprising: a first electronic switch (819), which is designed to use the differently colored light sources for a period of time in the switching cycle, in particular to switch on in time division multiplex, a second electronic switch (820), which is designed by the

Light sensor arrangement to supply recorded values to a separate storage, and a controller (821) which is designed to synchronize the first changeover switch (819) and the second changeover switch (820) in such a way that recorded values can be stored separately for each switched on light source (822, 823) , wherein the evaluation unit is designed to jointly evaluate the stored values after at least one switching cycle (824).

13. Arrangement according to one of claims 8 to 12, wherein the light source arrangement has at least one light source with several wavelength ranges, in particular a broadband light source (100), which is designed to emit light with several spectral components, the arrangement further comprising: a filter arrangement (915 , 916), which is designed to allow the light (130) coupled out of the separator (103) to pass through for limited wavelength ranges, in particular colors, the filter arrangement (915, 916) being followed by separate light sensors (111) of the light sensor arrangement, the evaluation unit is designed to computationally evaluate sensor output values of the separate light sensors together (932, 933, 924).

14. Arrangement according to one of claims 8 to 13, wherein the light source arrangement has at least one light source with several wavelength ranges, in particular a broadband light source (100) which is designed to emit light with several spectral ranges, wherein the arrangement further comprises: a prism arrangement (410 ), which is designed to separate the light (130) coupled out of the separator (103) for individual wavelength ranges, in particular colors, according to wavelength ranges, the prism arrangement (410) each having separate light sensors (111) of the light sensor arrangement in corresponding exit angles of the light of the various Wavelengths are arranged downstream, wherein the evaluation unit is designed to computationally evaluate sensor output values of the separate light sensors together (932, 933, 924).

15. Arrangement according to one of claims 8 to 14, wherein at least one of the

Components light sources (100) and light sensors (111) is arranged in a center of a winding structure of electrodes and separator (106, 108, 103).

16. Arrangement according to one of claims 8 to 15, at least one of the components light sources (100) and light sensors (111) in an outer region of a winding structure

Electrodes and separator (106, 108, 103) is arranged.

17. Arrangement according to one of claims 8 to 16, wherein an arrangement of electrodes and separator (106, 108, 103) has at least one bend in the layer structure of the battery cell (931) which is designed to additionally absorb light from the separator (103) to the adjacent electrode material and thus to strengthen an interaction with the electrode material (106 or 108).

18. Arrangement according to one of claims 8 to 17, wherein the separator (103) is coated at least on the positive electrode side (106) with an electrochromic material, the reflection properties of which depend on an ionic charge of the positive electrode (106).