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EP-4453589-B1 - METHOD FOR DEGRADATION DIAGNOSIS OF AN ELECTROCHEMICAL CELL

EP4453589B1EP 4453589 B1EP4453589 B1EP 4453589B1EP-4453589-B1

Inventors

  • LACEY, Matthew
  • KLETT HUDSON, Matilda

Dates

Publication Date
20260513
Application Date
20221215

Claims (15)

  1. A method for degradation diagnosis of an electrochemical cell (5), wherein the method is characterised by comprising the following steps: a) by usage of a reference electrode (20), determining (S101) a first open circuit potential (P1), relative to a preselected potential scale, for a positive electrode (8) extracted from the electrochemical cell (5) and determining (S102) a second open circuit potential (P2), relative to the preselected potential scale, for a negative electrode (6) extracted from the electrochemical cell (5); b) obtaining (S103) a first charge value (Q1) by comparing the determined first open circuit potential (P1) to a first reference curve (38) of open circuit potential, relative to the preselected potential scale, as a function of charge for the positive electrode (8); c) obtaining (S104) a second charge value (Q2) by comparing the determined second open circuit potential (P2) to a second reference curve (36) of open circuit potential, relative to the preselected potential scale, as a function of charge for the negative electrode (6); d) arranging (S105) the first reference curve (38) and the second reference curve (36) on a common charge scale so that the obtained first charge value (Q1) and the obtained second charge value (Q2) are equal for the first and second reference curves (38, 36) on said common charge scale; and e) thereafter, based on the first and second reference curves (38, 36), determining (S107) remaining capacity as the difference in charge (ΔQ) on said common charge scale between a first predefined potential limit and a second predefined potential limit.
  2. The method according to claim 1, wherein said first predefined potential limit corresponds to an upper cutoff potential value (E 1 ) of the first reference curve (38), and said second predefined potential limit corresponds to an upper cutoff potential value (E 2 ) of the second reference curve (36).
  3. The method according to claim 1, wherein the method further comprises, between step d) and step e), f) determining (S106) an estimated cell voltage curve (40) as the difference between the first reference curve (38) and second reference curve (36) arranged on the common charge scale; and wherein said first predefined potential limit corresponds to a first pre-identified voltage (V 1 ) of the electrochemical cell (5) at a first state of charge, and the second predefined potential limit corresponds to a second pre-identified voltage (V 2 ) of the electrochemical cell (5) at a second state of charge.
  4. The method according to any one of the preceding claims, wherein the first open circuit potential is determined at a first location on the positive electrode (8), and the second open circuit potential is determined at a second location on the negative electrode (6), said first and second locations corresponding to a common region of the positive electrode (8) and negative electrode (6) within the electrochemical cell (5) before extraction of the positive and negative electrodes (8, 6).
  5. The method according to any one of the preceding claims, wherein said first reference curve (38) is a first scaled reference curve which has been scaled relative to a reference curve for the positive electrode (8) of an undegraded electrochemical cell (5) to account for estimated or predetermined loss of active material in the electrochemical cell (5), and said second reference curve (36) is a second scaled reference curve which has been scaled relative to a reference curve for the negative electrode (6) of an undegraded electrochemical cell (5) to account for estimated or predetermined loss of active material in the electrochemical cell (5).
  6. The method according to any one of the preceding claims, wherein the positive and the negative electrodes (8, 6) have been extracted from the electrochemical cell (5) after the electrochemical cell (5) has been fully discharged.
  7. The method according to any one of the preceding claims, wherein said predetermined first and second reference curves (38, 36) each are determined through measurement of open circuit potential relative to the preselected potential scale as a function of charge of an electrode of an undegraded electrochemical cell (5) having the same configuration as the electrochemical cell (5) which is diagnosed, and optionally followed by scaling to account for an estimated or predetermined loss of active material.
  8. The method according to any one of the preceding claims, further comprising determining a distribution of remaining capacity throughout the electrochemical cell (5) by repeating steps a) to e) for a plurality of locations on the positive and negative electrodes (8, 6) corresponding to different regions within the electrochemical cell (5).
  9. The method according to any one of the preceding claims, wherein the first open cell potential and the second open cell potential are determined without assembling samples of the positive and negative electrodes (8, 6) to a test cell.
  10. The method according to any one of the preceding claims, wherein the reference electrode (20) comprises: a porous separator (23) configured to be wetted with an electrolyte and arranged so that a surface of the porous separator (23) forms a distal end (21) of the reference electrode (20), said distal end (21) intended to be in contact with a sample electrode when the reference electrode (20) is in use, one or more reference electrode materials (24), selected to provide a reference potential of the preselected potential scale, arranged at a distance from the distal end (21) and in direct contact with the porous separator (23), a proximal end (22) configured to be connected to a circuit connected to a sample electrode, and a contact (25) configured to provide electrical connection between the one or more reference electrode materials (24) and the proximal end (22).
  11. The method according to claim 10, wherein the surface of the porous separator (23) forming the distal end (21) has an area which is less than 5 %, or less than 0.5 %, of the area of one side of any one of the positive electrode (8) and the negative electrode (6).
  12. The method according to any one of the preceding claims, wherein the method is performed by a control device.
  13. The method according to any one of claims 1-11, wherein the reference electrode (20) is a manually operated reference electrode (20).
  14. The method according to any one of the preceding claims, wherein the electrochemical cell (5) is a lithium-ion cell.
  15. The method according to claim 14, wherein the preselected potential scale is a potential scale selected from the group consisting of Li/Li+ scale, LiFePO 4 /FePO 4 scale, Li 7 Ti 5 O 12 /Li 4 Ti 5 O 12 scale, and LiMn 2 O 4 /Li 2 Mn 2 O 4 scale.

Description

TECHNICAL FIELD The present disclosure relates in general to a method for degradation diagnosis of an electrochemical cell. BACKGROUND The effort to reduce emissions and improve fuel economy of heavy vehicles, such as trucks and buses, has led to the development of vehicles comprising propulsion systems that uses one or more electrical machines. These electrical machines may be powered by energy storage devices, such as energy storage devices comprising secondary lithium-ion batteries, that require charging at designated charging stations or zones. Examples of such vehicles include Hybrid Electric Vehicles (HEVs), Plug-in Hybrid Electric Vehicles (PHEVs), and Battery Electric Vehicles (BEVs). Energy storage devices for vehicles, such as secondary lithium-ion energy storage devices, are built up from a number of individual electrochemical cells. These electrochemical cells can store or release energy through electrochemical reactions. Each electrochemical cell comprises an anode, a cathode and an electrolyte between the anode and the cathode. The electrolyte is an electrically insulating, but ionically conducting electrolyte enabling ions to move through the electrochemical cell. The electrochemical cell further comprises a separator arranged between the anode and cathode. The separator is configured to contain the electrolyte and to prevent short circuit between the anode and the cathode. The service life of an energy storage device, used for powering the electrical machine(s) of the vehicle, is an essential factor when considering the total life cost of the vehicle. Thus, there is a continuous effort to increase the service life of such energy storage devices. The service life of an energy storage device is dependent of the configuration of the energy storage device as such, for example by the selection of constituent materials of the energy storage device (such as the electrolyte and/or the electroactive materials). The service life is also affected by how the energy storage device is operated. In other words, the service life of an energy storage device is affected by for example how it is charged and discharged. For example, a low charging rate may in general lead to a lower risk of aging of energy storage device. However, this in turn also leads to an increase of the duration of the charging procedure, which may lead to longer times the vehicle is out of service. Li-ion electrochemical cells degrade through a variety of parasitic chemical reactions which can take place at both the positive and negative electrodes in the cell. Understanding the degradation of the electrochemical cell may be very important, both for the purpose of development of alternative configurations of electrochemical cells for increasing the service life of energy storage devices as well as evaluating the possibly for adapting control methods for the operation of an energy storage device comprising the electrochemical cell to thereby achieve a longer service life. In practice, the extent of degradation can be distributed very differently throughout the electrode area within a cell. In an automotive Li-ion cell, there may typically be about 1 m2 of electrode area for each electrode wound in a package often less than 0.5 L in volume. Uneven, or heterogeneous, degradation drives increasingly rapid degradation, which results in increasingly rapid loss of capacity and/or power of the cell. One of the most significant consequences of degradation is known as loss of lithium inventory (LLI). LLI is the result of different rates of degradation at each electrode which create a mismatch in the availability of lithium ions in each electrode, degrading the accessible capacity of the complete cell. In recent years, a number of academic groups have developed methods for determining LLI and other degradation consequences such as loss of active material (LAM), through analysis of cell voltage. One example of a previously known method relies on extracting the electrodes from the electrochemical cell, taking a small sample of each of the electrodes and forming a miniature test cell comprising said samples. Said miniature test cell is thereafter subjected to cycling and the cycling performance is recorded. This method is however very time consuming, primarily due to the duration for cycling of the miniature test cell which typically takes at least several hours. It may also require specific measures to be taken, before assembly into the miniature test cell, due to the electrodes typically comprising two layers of the electrode active material separated by the current collector. Before assembling the miniature test cell, one of these layers has to be removed (without damaging the other layer) from the current collector in order to allow proper electrical connection to the current collector. This is also quite time consuming and therefore adds to the total duration for the diagnosis. Furthermore, if desiring to investigate heterogenous aging of the ele