Battery characterisation and monitoring system
A method for non-invasive characterisation of a cell for a battery is provided, the method comprising: measuring a magnetic field generated by the cell using a plurality of magnetic field sensors positioned adjacent to the cell, the measuring producing magnetic field sensor data, wherein the measuring is performed while the cell is in a passive state; determining current density profile data across the cell based on the magnetic field sensor data; and determining a condition of the cell using the current density profile data.
1 . A method for non-invasive characterisation of an electrical charge storage device, the method comprising the following steps (i) to (iii):
(i) using a plurality of optically pumped magnetometers positioned adjacent to the electrical charge storage device to directly measure a magnetic field generated by electrochemical self-discharge of the electrical charge storage device, the measuring producing magnetic field sensor data, wherein the measuring is performed while the electrical charge storage device is in a passive state;
(ii) determining current density profile data across the electrical charge storage device based on the magnetic field sensor data; and
(iii) determining a condition of the electrical charge storage device using the current density profile data.
2 . A method as claimed in claim 1 , wherein the electrical charge storage device is a cell for a battery.
3 . A method as claimed in claim 2 , wherein the method is performed during a pre-use conditioning stage of the cell during the fabrication of the battery.
4 . A method as claimed in claim 3 , wherein the pre-use conditioning stage takes place at a temperature above 25° C. and/or the pre-use conditioning stage is performed for a period of one week or more.
5 . A method as claimed in claim 3 , wherein the pre-use conditioning stage comprises an ageing process for the cell.
6 . A method as claimed in claim 3 , wherein the condition of the cell, as determined from the current density profile data, is used to determine whether to continue with conditioning the cell during the pre-use conditioning stage, to modify the conditioning, to stop the conditioning, and/or to reject the cell.
7 . A method as claimed in claim 2 , wherein the determining of a condition of the cell comprises one or more of:
assessing growth of a solid electrolyte interface within the cell;
detecting one or more defects within the cell; and
detecting inhomogeneities within parts of the cell introduced during manufacture.
8 . A method as claimed in claim 2 , wherein the method comprises repeating steps (i) to (iii) in order to monitor developments in the condition of the cell.
9 . A method as claimed in claim 8 wherein the monitoring of developments in condition of the cell is used to assess a rate of growth of a solid electrolyte interface within the cell.
10 . A method as claimed in claim 2 , wherein the steps (i) to (iii) are repeated at intervals;
wherein the intervals are a duration of at least three hours or more, optionally twelve hours or more;
wherein the intervals are a duration of no greater than 72 hours; and/or
wherein the intervals are a duration in a range of 12-36 hours.
11 . A method as claimed in claim 2 , wherein the magnetic field sensors measure only electrochemical self-discharge of the cell.
12 . A method as claimed in claim 2 , wherein the method is applied to a cell of a used battery, to identify soft short circuits within the cell or to determine the self-discharge C-rate of the cell.
13 . A method as claimed in claim 1 , wherein the electrical charge storage device is in a state of full charge or partial charge when the method is performed, and/or wherein the method is performed before an external electrical load has been placed across terminals of the electrical charge storage device.
14 . A method as claimed in claim 1 , wherein the method comprises generating a current density image of the electrical charge storage device based on the determined current density profile.
15 . A method as claimed in claim 1 , wherein the method further comprises transporting the electrical charge storage device into a magnetically shielded environment.
16 . A method as claimed in claim 15 , wherein the magnetically shielded environment incorporates a degaussing mechanism to temporarily remove residual magnetic field from ferromagnetic components of the electrical charge storage device.
17 . A method as claimed in claim 1 , wherein the magnetic field sensors are arranged in a sensor array which is moved relative to the electrical charge storage device, the magnetic field sensors collectively measuring a band of the magnetic field adjacent the electrical charge storage device, the band extending in a transverse direction to a direction of relative movement as the sensor array passes over a surface of the electrical charge storage device.
18 . A method as claimed in claim 1 , wherein the magnetic field sensors are positioned within a distance of less than 10 mm from a surface of the electrical charge storage device during measuring of the magnetic field.
19 . A method as claimed in claim 1 , wherein the method is applied to any of: a fuel cell; a super capacitor; an electrochemical device; and an electrostatic device.