Direct measurement of current distribution in lithium-ion cells by magnetic field imaging

Abstract

Inhomogeneous current distribution in lithium-ion cells is a major reason for degradation. A method to measure the locally resolved current distribution is to map the magnetic field caused by the current flowing in the cell. This paper presents an unshielded measurement setup using anisotropic magnetoresistive (AMR) sensors to map the magnetic field of a cell during operation. Moreover, it proposes an algorithm to calculate the two-dimensional current distribution from magnetic field data. The achieved accuracy of the current density is 227 mA cm −2 at a local resolution of 4 mm 2 . The mathematical problem is reduced to a single matrix multiplication and takes into account specific characteristics of the measurement setup. Simulated and measured data are used to evaluate the proposed algorithm. Two cells with different geometries, capacities and tab designs are tested and compared. The paper provides guidance for the interpretation of the measurement data and introduces a measure to calculate the validity and accuracy, which can also be used to trim the parameters for the inverse problem. Possible fields of applications include end of line tests or state of health investigations where non-destructive and in-situ measurements are needed. • Nondestructive, locally resolved current distribution measurement. • Setup to precisely measure the magnetic field above the cell. • Algorithm to reconstitute current distribution from magnetic field image. • Current distribution measured for cells with different geometries. • Enables inhomogeneity analysis and defect detection in cells.