EP4473607A1

EP4473607A1 - Electrochemical sensor based on printed circuits enabling detection of soluble cations in battery cell

Info

Publication number: EP4473607A1
Application number: EP22702485.8A
Authority: EP
Inventors: Robert Dominko; Tina PALJK; Maria Victoria BRACAMONTE; Tomas SYROVY
Original assignee: University of Pardubice; Kemijski Institut
Current assignee: University of Pardubice; Kemijski Institut
Priority date: 2022-02-01
Filing date: 2022-02-01
Publication date: 2024-12-11
Also published as: WO2023147844A1

Abstract

The present invention relates to lithium-ion, sodium ion and lithium metal battery cells and an interdigitated circuit on the separator provided to detect dissolved metal ions, in particular transition metal ions inside the battery electrolyte. Moreover, the invention relates to the set-up for the measurement and the methodology for monitoring the state of health of a lithium-ion or a lithium metal battery cell of this type based on the detection of the amount of dissolved divalent and trivalent cations by using electrochemical principles of measurement. The invention also relates to a battery system comprising a plurality of battery cells of this type.

Description

Electrochemical sensor based on printed circuits enabling detection of soluble cations in battery cell

DESCRIPTION

FIELD OF THE INVENTION

The present invention relates to lithium-ion, sodium ion and lithium metal battery cells and an interdigitated circuit on the separator provided to detect dissolved metal cations, in particular transition metal ions, inside the battery electrolyte. Moreover, the invention relates to the set-up for the measurement and the methodology for monitoring the state of health of a battery cell based on the detection of the amount of dissolved divalent and trivalent cations by using electrochemical principles of measurement. The invention also relates to a battery system comprising a plurality of battery cells of this type.

BACKGROUN D OF THE INVENTION

The reliable and safe operation of batteries is of increasing importance in today's world. Understanding and diagnosing degradation processes in the battery cell would allow avoiding more serious and dangerous consequences. Current battery cells are monitored by measurements of voltage and temperature on the cell body and their operation is controlled through the Battery Management System (BMS), which controls all cells in the battery pack or module. For the more precise control, we need to monitor parameters within the cell with a spatial resolution. This will improve battery cell quality, reliability, lifetime, and safety.

All cathode electrode materials used in Lithium-ion batteries based on transition metal compounds endure the dissolution of transition metal ions into the electrolyte solution. It is widely established that the dissolved ions can migrate through the electrolyte to the negative electrode and deteriorate the Solid Electrolyte Interphase (SEI) layer. This phenomenon leads to malignant SEI growth, which increases the battery interfacial resistance, encourages electrolyte consumption and evolution of gasses, and creates severe damages to both electrodes. As a result, the aging of the battery cell is much faster than it would be if we prevented the dissolution of the metal from the oxidized structure. For instance, dissolution of the metal from the structure corresponds only to 30% of capacity drop due to degradation of the cathode material; other 70% is lost due to other processes listed above. Among all, the consequences of manganese dissolution are the most detrimental for Li-ion batteries durability and that prevents higher acceptability of Mn-rich lithium-ion battery cells for commercial purposes. The phenomenon of metal dissolution, in particular transition metal dissolution (manganese, cobalt, nickel, iron, aluminum, titanium, zinc and vanadium) is crucial for the aging of the lithium-ion battery and the definition of State of Charge (SoC), State of Safety (SoS), and State of Health (SoH) of such systems. Monitoring this phenomenon is therefore extremely important for understanding the mechanism of aging itself and supervision the condition of the battery.

Electrochemical detection is an elegant solution to track changes in the electrolyte composition as a function of the SoS, and SoH of the battery. Dominko et al. (Dominko et al. Electrochem. Comm. 2011 , 13 (2), 117-120) proposed a modified Swagelok cell with two additional perpendicular electrodes placed between two separators. In this way, they managed to detect soluble polysulfides in the electrolyte during Li-S battery operation. Wang et al. (Wang et al. Electrochim. Acta, 2021 , 386, 138366) managed to study the manganese dissolution phenomena through a similar modified Swagelok cell. We can consider the set-ups used in the laboratory as electrochemical sensors able to detect various species, but without miniaturization, they cannot be transferred into real commercial battery cells.

SUMMARY OF TH E INVENTION

The present invention provides a solution for detecting and quantitatively measuring the quantity of dissolved divalent and trivalent cation in batteries, more specifically in Li-ion, Na-ion and Lithium metal batteries. The solution is based on sensory element based preferably on two electrode structure, where current electrode system could be based on parallel lines or interdigital structure. Active material of sensor is printed between current electrodes and its electrical properties are influenced by presence of divalent or trivalent ions. The crucial characteristics are that printed sensory element is electrochemically stable in a Li-ion, Na-ion and Lithium metal battery environment and the active compounds capable of chelating cations or otherwise interacting with the cations allow the detection of very low amounts of dissolved divalent or trivalent metal cations, in particular manganese, cobalt, nickel, iron, vanadium, aluminum, titanium, zinc or any other transition metal cation which are problematic metals dissolving from the oxide structure during battery charging and discharging. With a resistive parallel or interdigitated circuit printed on the separator, metal cations can be detected by using a composite prepared from an electron conductive material that can be for example carbon, polymer, electronically conductive ceramics or metal, and a sensing agent, e.g. a chelating compound, whose electrical properties (resistance or capacitance) change if cations are trapped in their structure. The structure of the sensory element does not interfere with the operation of the battery. Fabrication of sensory elements by printing technique allows to desire high reproducibility of sensory response. The usage of the printing technique and preparation of sensory element directly to the separator does not increase significantly the cost of production and the final weight of the cell. Proposed sensory element allows monitoring the degree of degradation of the battery trough detecting the changes of electrical properties between the current electrodes printed on the separator. By engineering sensing agents, in particular chelating compounds, it is possible to optimize the selectivity of the sensor. Due to selectivity, degradation products resulting from irreversible oxidation or reduction reactions (for instance degradation of electrolyte, dissolved degradation products from interphases, degradation products from current collectors, or degradation products from other inactive or active components) can be detected.

The features will be further described and exemplified in the detailed description of the invention below. BRIEF DESCRIPTION OF THE FIGURES

FIG.1 is a schematic illustration of the configuration of the printed resistive parallel electrode circuit.

FIG.2 is a schematic illustration of the used battery cell configuration.

FIG.3 A) illustrates a graph showing the impedance response of the resistive interdigitated circuit printed on the separator soaked with the industrial battery electrolyte LP40 (1 M LiPFe in EC:DEC 1 :1 v:v). B) illustrates a graph showing the impedance response of the resistive interdigitated circuit printed on the separator soaked with a 20mM LiAcAc salt solution in the industrial battery electrolyte LP40 (1 M LiPFe in EC:DEC 1 :1 v:v). C) illustrates a graph showing the impedance response of the resistive interdigitated circuit printed on the separator soaked with a 10mM Mn(AcAc)2 salt solution in the industrial battery electrolyte LP40 (1 M LiPFe in EC:DEC 1 :1 v:v).

FIG.4 A) illustrates a graph showing the changing impedance response of the resistive interdigitated circuit printed on the separator soaked with the industrial battery electrolyte LP40 (1 M LiPFe in EC:DEC 1 :1 v:v) through time. B) illustrates a graph showing the changing impedance response of the resistive interdigitated circuit printed on the separator soaked with a 10mM Mn(AcAc)2 salt solution in the industrial battery electrolyte LP40 (1 M LiPFe in EC: DEC 1 :1 v:v) through time.

FIG.5 A) illustrates a graph showing the charge/discharge potential profile of the lithium- metal battery cell (Li/separator soaked with electrolyte/ 1 DC separator soaked with electrolyte/separator soaked with electrolyte I LiMn2O4 electrode). The used electrolyte was LP40 (1 M LiPFe in EC:DEC 1 :1 v:v). B) illustrates the impedance response of the IDC separator before and after cycling.

DETAILED DESCRIPTION OF THE INVENTION

In agreement with the present invention, a battery cell comprising at least one sensor - two current electrode sensory element in parallel or interdigitated electrode (IDE) configuration - is embodied and arranged in the battery cell. On the sensing layer - that is located between the two electrodes of the sensory element - any metal cations (divalent or trivalent), in particular transition metal ions, are adsorbed or bounded or trapped and their inclusion causes a change in the sensing layer changing the resistance or impedance response. Moreover, the invention relates to a method for monitoring the state of health, state of safety, state of charge, or any other state that can be monitored by detection of soluble degradation products within a Li-ion, Na-ion or a Lithium metal battery cell. The invention also relates to a battery system comprising a plurality of battery cells of this type and is not limited to these specific embodiments.

Thus, the invention provides a battery (1) comprising an anode (2), an anode current collector, a cathode (5), a cathode current collector, a separator (3) and an electrolyte, wherein the battery further comprises a sensing device in contact with the electrolyte but without electrical contact to the anode and the cathode, wherein the sensing device comprises a sensing layer, and two electrodes arranged in parallel to each other on the sensing layer, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal cations, in particular transition metal cations.

The sensing layer of the inventive battery preferably comprises an electrically conductive material and a sensing agent capable to react or interact with the divalent or trivalent metal cation, in particular transition metal cation, optionally on an inert carrier.

The electrically conductive material preferably comprises high surface area carbon such as carbon nanotubes or graphene, n-type conductive polymer, conductive ceramics and/or nanostructured metal particles.

The sensing agent preferably comprises an ion exchanging resin (Dowex ® M 4195 - poly-BPA, poly-PEI), an ionic liquid (1-n-butyl-3-methylimidazolizum tetrafluoroborate BMIM.BF4,, an ion-imprinted polymer (Mn²⁺ imprinted PAN-MMA copolymer, Roushani et а. 2017), a chelating agent (crown ethers such as: poly(undecylenyl oxymethyl-18-crown- б, poly(vinylbenzo-18-crown-6, N34EDTA),, a complexing agent (1-(2-Pyridylazo)-2- naphthol, 4-(2-Pyridylazo)resorcinol) , a bioorganic molecule, ionophore and/or an engineered material with specific functional groups (as bis-picolyamine BPA, polyethyleneimine PEI, 18-crown-6, aza-15-crown-5, tetrasodium edetate Na4EDTA, 4- vinylpyridine 4VP, disodium iminodiacetate IDANa2, dilithium maleate MALi2, lithium acrylate LiAA or oxygen/nitrogen functionalities (Polyaniline PANI).

The divalent and/or trivalent cations are preferably selected from the group consisting of manganese, cobalt, nickel, iron, aluminum, titanium, zinc and vanadium cations and/or mixtures thereof.

It is further preferred, that the weight ratio of the electrically conductive material and the sensing agent is in a range of about 0.5% : 99.5% to 65% : 35%.

The inert carrier can be an additionally provided inert support surface. Alternatively, the sensing layer can be provided on an inert surface already present inside the battery. An inert camer/surface can be any carrier or surface inside the battery cell that is not reactive with the battery cell. For example, a separator, a battery cell housing, or any other material inside the cell can serve as the camer/surface.

According to further preferred embodiments, the first and second electrodes comprise an electrically conductive material selected from metal (e.g. silver, gold, platinum, aluminum, nickel, tin, copper), carbon (e.g. graphite, GNP, glassy carbon, CNT, graphene), conductive polymer (e.g. PEDOT, PANI, PPY), conductive ceramics (e.g. ITO, TiONx) and combinations thereof, in particular wherein the electrical conductivity is higher than 1 x 10’⁵ ScnT¹.

The battery according to the invention may comprise means for determining resistance or capacitance. The inventive battery may be a lithium-ion, sodium-ion or lithium metal battery.

Exemplary embodiments of the invention are described in detail here under with reference to the accompanying drawings. Figure 1 illustrates the proposed configuration of the resistive circuit between two parallel sensory electrodes. The circuit includes two symmetrical electrodes C, which can be made of any electronically conductive material or composite, for example, metal-based ink or carbon-based ink or conductive polymer-based ink or mixture of any of the three mentioned inks. Metal can be silver, gold, platinum, aluminum, nickel, tin or any other metal that is inert toward lithium in the potential range. Carbon and conductive polymer inks are prepared from materials with electronic conductivity higher than 1 xiQ-⁵ Scmr¹. The electrodes can be printed, coated, or deposited on the chosen surface from liquid. The electrodes must be inert and insoluble inside the battery electrolyte and the battery electromagnetic field in the whole potential range of battery operation. The parallel current electrodes can be of various shapes (e.g. square, circles, spirals...) and different dimensions (e.g. thickness, length of the electrode, the gap between electrodes, shapes ...).

Between the two symmetrical electrodes C is located the sensing layer D. This can be seen in the close-up B. The sensing layer D is used as an active layer of sensor element and is composed of an electrical conductive material - such as high surface area carbon, n type conductive polymer, nanostructured metal particles - and a sensing agent, e.g. a complexing agent. Any compounds that react or interact with metal ions to form a stable complex can be use, such as: ion exchanging resins, ionic liquids, ion-imprinted polymers, chelating agents, complexing agents, bioorganic molecules, engineered materials with specific functional groups or oxygen/nitrogen functionalities, etc. The choice of the sensing agent (e.g. the complexing agent) depends on two factors, first the detected metal ions, in particular transition metal ions, and second on the desired chemi resistive response. The interaction between the analyte and the sensing layer is achieved by simple electrostatic reactions or covalent bonding or chemical reaction. The sensing layer composition may be varied by several components. The weight ratio of the electrical conductive material and the sensing agent, e.g. the complexing agent, can range from 0.5% : 99.5% to 65% : 35%. The sensing layer can be formed by printing techniques (screen printing, gravure printing, pad printing, flexography printing, inkjet printing, microdispensing, off-set printing) or by coating techniques (dip coating, spin coating, drop casting, slot-die, spiral bar coating, knife over edge coating, doctor blading, spray coating or any similar coating technique). The concentration, solid and volume of the used liquid/ink, film’s thickness, and other parameters can vary according to the requirements to chemiresistive performance of the sensor element.

Figure 2 illustrates the full battery cell (1) of the present invention. The cell includes a lithium metal or graphite anode (2), attached to a negative current collector. Part 3 represents the battery separator soaked with electrolyte medium. The separator, in the context of the present invention, is a porous or lithium or sodium conductive membrane, which prevents contact between the electrodes and the resistive interdigitated circuit. In the present invention, the electrolyte medium preferably comprises a polar solvent with different amounts of lithium or sodium salt. The concentration of lithium or sodium salt may vary from 0.2 to 30.0 M. A positive electrode (5) is in the contact with the separator membrane (3), opposite from the negative lithium or graphite anode. The positive electrode is attached to the positive current collector. The positive current collector may be constituted from an electrically conductive material. The positive electrode may be comprised of any lithium intercalation compound, either as a single-phase material or mixed with carbon or other conducting additives. The sensing part - consisting in a modified current collector system (A) printed, coated, or deposited on a support, e.g. a separator sheet (4) - is located inside the battery cell and soaked with the battery electrolyte medium. The sensing element can be located anywhere inside the battery cell: on the housing or on the separator sheet, on the battery interface or out of it, as long as it is in contact with the battery electrolyte and the metal ions can be adsorbed or bounded at least in part on the sensing layer. It is important, that there is no electrical contact between the sensor and the main electrodes of the battery cell. The two symmetrical electrodes (C) of the circuit (A) located on the separator sheet (4) are connected with two current collectors. The current collector can be any conductive material inert and insoluble in the battery electrolyte, for example, nickel.

In presence of divalent or trivalent metal ions, in particular transition metal ions, inside the battery electrolyte, the sensing layer of the sensors is subject to a change. The dissolved metal ions are captured by the sensing agent, in particular the complexing agent, and cause a change in the resistance or capacitance of the sensing layer. This change can be determined by resistive or impedimetric measurements or any similar electrochemical method allowing measurements of resistivity and capacitance of the cell. By measuring these parameters, we can detect and determine the composition changes of the electrolyte inside the battery cell. This built-in sensor allows to determine the State of Health, State of Safety and State of Charge of the battery or any other state related to the dissolution of metals, in particular transition metals or any other degradation products into electrolyte, to predict and avoid unsafe reactions inside the battery and battery failing.

The invention further provides a method for detecting the quantity of divalent and/or trivalent cations dissolved in an electrolyte, the method comprising contacting a sensing device with the electrolyte, wherein the sensing device comprises a sensing layer, and two electrodes arranged in parallel to each other on the sensing layer, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal cations, in particular transition metal cations; and measuring resistance or capacitance of the sensing layer.

Additionally, the invention provides a method for monitoring the battery’s status according to invention, comprising detecting the quantity of divalent and/or trivalent cations dissolved in the electrolyte by the above method.

A further embodiment of the invention is the use of a sensing device for detecting the quantity of divalent and/or trivalent cations dissolved in an electrolyte, the sensing device comprising a sensing layer, and two electrodes arranged in parallel to each other on the sensing layer, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal cations, in particular transition metal cations.

Further, the invention relates to the use of a sensing device for monitoring the battery’s status, in particular a lithium-ion, sodium-ion or lithium metal battery, the sensing device comprising a sensing layer, and two electrodes arranged in parallel to each other on the sensing layer, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal cations, in particular transition metal cations.

Preferred features and materials of the methods and uses of the invention are the same as described in more detail above in the context of a battery.

EXAMPLES

Examples CONFIGURATION OF THE RESISTIVE INTERDIGITATED CIRCUIT - SENSOR

Figure 1 shows the used configuration of the resistive interdigitated circuit A. The circular part of the sensor has an external diameter of 12 mm (external electrode), and an internal diameter of 10 mm (internal electrode). The gap between the two symmetrical electrodes is 1 mm. The straight-line part of the electrodes is 2 cm in length. At the end of the two straight lines, there are two contact pads of 4mm*4mm area. This is needed to achieve better contact with the current leads that connects the sensor with terminals outside of the cell. The gap between the circular part of the two symmetrical electrodes is dedicated to the sensing material composite. This configuration is suitable for any type of cell that allows additional terminals on the housing of the cell, for instance pouch cell. The size and the shape of two electrodes forming the circular part of the sensor and the gap between two electrodes can be easily fitted to any laboratory or commercial or any other type of the cell by adjusting the size and radius of electrodes. The gap between electrodes is a function of selectivity of complexing agent and its electrochemical properties (change of resistance during complexation of degradation products).

Example?: SENSORY ELEMENT PRINTED ON GLASSY FIBER SEPARATOR

Sensory element was printed on glassy fiber based filtration membrane. As a printing technique, contactless microdispensing technique was used. As a first layer, the waterborne, silver particle based ink formulation was printed. The ink consisted from silver flakes with average diameter 8 m and polymeric binder combine water soluble polymer and water insoluble polymer in dispersion form. The weight ratio of silver flakes to polymeric binder system was 5.7:1. The silver layer was printed at printing speed 400 mm/min. Printed layers were dried and cured at 125 °C for 30 minutes. As a second layers the carbon based composite was used. The ink was based on glassy carbon material and water based polymeric system. The polymeric binder again combine water-soluble polymer and water insoluble polymer in dispersion form. The weight ratio of glassy carbon particles to polymeric binder system was 4.3:1. The glassy carbon layers was printed at printing speed 300 mm/min. Printed layers were dried and cured at 125 °C for 30 minutes. As last layer sensitive active layer was printed. The ink formulation was consisted from material mentioned in example 5. The ink formulation was based on sensitive material: PVDF in weight ratio 1 :1. The ink formulation was prepared from 6% wt. solution of PVDF in NMP. In given solution the active material was properly homogenized to obtain homogeneous slurry. Prepared ink was used for printing of active layer of sensory element by using microdispensing technique. The printing speed 200 mm/min was used. The layer was then dried at 70 °C for 1 hour.

Example 3: CHOICE AND SYNTHESIS OF THE ION IMPRINTED POLYMER (according to procedure published in Roushani et al. J. of Be. Chem. 2017, vol. 804, 1- 6)

We chose an ion-imprinted polymer as the chelating agent to specifically detect manganese divalent ions. We prepared the material Mn(ll)-I IP by thermal polymerization in two steps. First, we prepared an Mn-1-(2-Pyridylazo)-2-naphthol (Mn-PAN) complex by mixing 1 mmol (0.396g) MnCl2*4H2O and 2 mmol (0.996 g) of PAN ligand in 100 rnL ethanol as a porogenic solvent, and stirring the mixture for 1 h under reflux conditions. Secondly, we copolymerized the Mn(PAN)2 complex with 4.7 mmol of Methacrylic acid (MMA), as a monomer, 30 mmol of ethylene glycol dimethacrylate (EGDMA), as a crosslinker, and 0.4 mmol 2,2'-azobisisobutyronitrile (AIBN), as a chemical initiator. We maintained the reaction temperature with an oil bath at 60 °C for 24 h. The resulting orange polymer was washed with deionized water, dried, and ground. For leaching Mn(ll) ions, the obtained Mn(ll)-IIP (Manganese(ll)-ion imprinted polymer) particles were swashed several times with 6M hydrochloric acid. We washed the precipitated particles with deionized water until a neutral pH value was set. The final Mn(l l)-l IP leached powder changed its color to white. The white powder was dried at 60 °C until constant mass was obtained/during 2-24 h.

The choice of the sensing agent depends on the metal ions, in particular transition metal ions to be detected and the desired chemiresistive response. This can be an ion exchanging resin, ionic liquid, ion-imprinted polymers, chelating agents, complexing agents, and materials with nitrogen functionalities.

Example 4: SELECTION OF THE ELECTRIC CONDUCTIVE COMPOUND

As the electric conductive compound of the sensing layer composite, we chose C-grade multi walled carbon nanotubes (MWCNT). The used carbon nanotubes are stable in the battery electrolyte and battery environment and are enough conductive for our purposes. However, other materials such as high surface area carbon (SWCNT, graphene, GNP, activated carbon), conductive polymers, conductive ceramics and/or nanostructured metal particles can be used.

Example 5: PREPARATION OF THE SENSING LAYER

We dissolved 0.1 g of leached Mn(ll)-IIP in the polar solvent 1-methyl-2-pyrrolidone (NMP) and added 0.5 g of MWCNTs. The mixture was ultrasonicated for one hour until we achieved a homogeneous suspension. The Mn(ll)-IIP/MWCNT mixture was then filtered and dried at 50 °C. The resulting composite was then mixed into 15 g of a solution of polyvinylidene fluoride (PVDF) in NMP (1 :25 weight ratio). The resulting slurry was drop cast into the gap between the two printed electrodes, as shown in figure 1. The sensor was then dried at 80 °C from 6-24h.

The sensing layer is used to modify the circuit and is composed of an electric conductive material and a complex agent. The interaction between the two compounds of the sensing layer is achieved by simple electrostatic reactions or covalent bonding or chemical reaction. The sensing layer composition may vary. The weight ratio of the electron conductive material and the complex agent can range from 0.5% : 99.5% to 65% : 35%. The sensing layer can be formed by printing or coating techniques mentioned above. The concentration, solids and volume of the used solution, film’s thickness, and other parameters can vary according to the needed chemiresistive performance of the sensor.

Example 6: IMPEDANCE RESPONSE OF THE SENSOR - RESISTIVE INTERDIGITATED CIRCUIT

We evaluated the chemiresistive response of the sensor - resistive interdigitated circuit. The sensor on the glassy fiber separator sheet was soaked in the electrolyte solution and packed inside a pouch bag. The two symmetrical electrodes were connected with the outside of the pouch bag through two current collectors made from nickel foil. Impedance spectra of all sensors were measured at OCV with a potential amplitude of 14.1 mV between 1 Mhz and 1 mHz.

Figure 3 shows the measured impedance spectra of three sensors soaked in three different electrolyte solutions. Figure 3 A shows the impedance response of the sensor soaked in the battery electrolyte LP40 (1 M LiPFe in EC:DEC v:v 1 :1). Figure 3B shows the impedance response of the sensor soaked in a 20mM solution of Lithium acetyl acetonate (LiACAC) salt in battery electrolyte LP40 (1 M LiPFe in EC:DEC v:v 1 :1). Figure 3C shows the impedance response of the sensor soaked in a 10mM solution of Manganese (II) acetylacetonate (Mn(ACAC)2) salt in battery electrolyte LP40 (1 M LiPFe in EC: DEC v:v 1 :1). The impedance spectra visible in figure 3 A and B are quite similar, the spectra in figure 3 C, where divalent manganese ions are present, instead shows a bigger first semicircle.

Figure 4 shows the measured impedance spectra of two sensors soaked in two different electrolyte solutions. Impedance spectra were repeatedly measured every 30 minutes. Figure 4 A shows 100 measured impedance spectra of the sensor soaked in the battery electrolyte LP40 (1 M LiPFe in EC: DEC v:v 1 :1). The spectra are not changing through time and it remains stable. Figure 4B shows 500 measured impedance spectra of the sensor soaked in a 10mM solution of Manganese (II) acetylacetonate (Mn(AcAc)2) salt in battery electrolyte LP40 (1 M LiPFe in EC: DEC v:v 1 :1). Due to the presence of Mn²⁺ ions inside the battery electrolyte, the sensing layer of the sensors is subject to a change. In this case the change can be determined by the impedance measurement at room temperature.

In presence of divalent or trivalent metal ions, in particular transition metal ions inside the battery electrolyte, the sensing layer of the sensors is subject to a change. The dissolved metal ions are captured by the complex agent and cause a change in the resistance or capacitance of the sensing layer. This change can be determined by resistive or impedance measurements or any similar electrochemical method allowing measurements of resistivity and capacitance of the cell. By measuring this change, we can detect and determine the composition changes of the battery electrolyte inside the battery cell. The same configuration can be used for measurements at different temperature (from -20 - to 50°C).

Example 7 INTEGRATION OF THE SENSOR INSIDE THE BATTERY CELL

The modified resistive interdigitated circuit - sensor was integrated inside the battery cell. Figure 2 illustrates the battery cell with the installed sensor. Sensor (4) was located between two separators (5) in the middle of the battery cell. The sensor was located between two separators to prevent contact between the sensor and the main electrodes of the battery. The battery cell (1) was packed in a pouch bag with four current collectors. The sensor was connected with the outside of the pouch bag with two current collectors made from nickel foil. The battery cell was connected with two current collectors: copper foil for the negative electrode, aluminum foil for the positive electrode. The physical connection of the electrodes could be replacing by wireless connections, which facilitate the data acquisition.

Example 8: SENSING PERFORMANCE UNDER REAL BATTERY OPERATION

To evaluate the sensing performance under real battery operation, a cell as described in example 7 was assembled. We used a lithium metal negative electrode, the sensor positioned between two Celgard® separators, and a positive electrode with LiMn2O4 active material. We chose LiMri2O4 active material because we know it is very much affected by transition metal dissolution. Figure 5A shows the charge/discharge potential profile of the battery cell. The cell was charged and discharged between 3.5 and 4.35 V with the current load of C/375 times at room temperature. Figure 5 B shows the measured impedance spectra of the sensor inside the battery before and after cycling. The impedance spectra of the sensor were measured at OCV with a potential amplitude of 14.1 mV between 1 Mhz and 1 mHz. Figure 5B shows a significant change in the impedance spectra before and after the use of the battery, the change is the same as shown in figures 3 and 4 and explained in example 6.

Claims

CLAIMS A battery (1) comprising an anode (2), an anode current collector, a cathode (5), a cathode current collector, a separator (3) and an electrolyte, wherein the battery further comprises a sensing device in contact with the electrolyte but without electrical contact to the anode and the cathode, wherein the sensing device comprises a sensing layer, and two electrodes arranged in parallel to each other on the sensing layer, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal cations, in particular transition metal cations. The battery according to claim 1 , wherein the sensing layer comprises an electrically conductive material and a sensing agent capable to react or interact with the divalent or trivalent metal cation, in particular transition metal cation, optionally on an inert carrier. The battery according to claim 2, wherein the electrically conductive material comprises high surface area carbon such as carbon nanotubes or graphene, n- type conductive polymer, electron conductive ceramics, and/or nanostructured metal particles and/or wherein the sensing agent comprises an ion exchanging resin, an ionic liquid, an ion-imprinted polymer, a chelating agent, a complexing agent, a bioorganic molecule, and/or an engineered material with specific functional groups or oxygen/nitrogen functionalities. The battery according to any one of the preceding claims, wherein the divalent and/or trivalent cations are selected from the group consisting of manganese, cobalt, nickel, iron, aluminum, titanium, zinc and vanadium cations. The battery according to any one of claims 2-4, wherein the weight ratio of the electrically conductive material and the sensing agent is in a range of about 0.5% : 99.5% to 65% : 35%. The battery according to any one of the preceding claims, wherein the first and second electrodes comprise an electrically conductive material selected from metal, carbon, conductive polymer, conductive ceramics and combinations thereof, in particular wherein the electrical conductivity is higher than 1 x 10’⁵ ScnT¹. The battery according to any one of the preceding claims, further comprising means for determining resistance or capacitance. The battery according to any one of the preceding claims, wherein the battery is a lithium-ion, sodium-ion or lithium metal battery. A method for detecting the quantity of divalent and/or trivalent cations dissolved in an electrolyte, the method comprising contacting a sensing device with the electrolyte, wherein the sensing device comprises a sensing layer, and two electrodes arranged in parallel to each other on the sensing layer, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal ion, in particular transition metal cations; and measuring resistance or capacitance of the sensing layer. A method for monitoring the battery’s status of a battery according to any one of claims 1-8, comprising detecting the quantity of divalent and/or trivalent cations dissolved in the electrolyte by the method of claim 9. Use of a sensing device for detecting the quantity of divalent and/or trivalent cations dissolved in an electrolyte, the sensing device comprising a sensing layer, and two electrodes arranged in parallel to each other on the sensing layer, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal cations, in particular transition metal cations. Use of a sensing device for monitoring the battery’s status of a battery, in particular a lithium-ion, sodium-ion or lithium metal battery, the sensing device comprising a sensing layer, and two electrodes arranged in parallel to each other on the sensing layer, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal cations, in particular transition metal cations. A method for preparing a battery according to any one of claims 1-8, comprising arranging two electrodes in parallel to each other on a support. printing a sensing layer on the support, to provide a sensing device, wherein the resistance or capacitance of the sensing layer is subject to change in the presence of divalent and/or trivalent metal cations, in particular transition metal cations, and positioning the sensing device inside a battery cell in contact with an electrolyte. The method according to claim 13, wherein the electrodes are printed, coated or deposited on the support. A battery system comprising a plurality of batteries according to any one of claims 1-8.