The experimental verification of a Lithium-ion battery for automotive life requirements utilizes significant laboratory resources and calendar time.  If the amount of life testing required to validate a cell design for automotive applications can be reduced, new cell designs could be confidently implemented at lower cost and in shorter time.  High precision coulometry (HPC) has recently emerged as a promising candidate for shortening the time required for validating cell life.  Literature examples have demonstrated improved identification of the mechanisms causing capacity fade¹ and qualitative sorting of higher performing cells².

Academic groups have pioneered this approach but have been primarily limited to testing low currents that are used to probe the rates of side reactions in calendar life scenarios.  Our research focus has been the design, development and validation of a 200 A, high precision (<50 ppm current and <25 ppm voltage) battery tester in partnership with Arbin Instruments and Sandia National Laboratory, with the support of the US Department of Energy (DOE) Advanced Research Projects Agency- Energy (ARPA-E)³.  The capability to perform high precision measurements at currents up to 200 A means the additional degradation brought about by high-rate cycling can be evaluated in addition to calendar assessments.  Additionally, we aim to quantitatively assess performance degradation trends by linking presently measured values to future performance.

Validation testing is presented using 5 Ah prismatic cells to quantify the reduction in test time that is practically achievable using high precision measurements.  Continuous cycle aging using multiple current profiles and ambient temperatures is conducted with periodic reference performance tests.  The mathematical relations between capacity, resistance, coulombic efficiency, and electrode endpoint slippage are leveraged to define various life prediction methods.  The reference performance test measurements from both the high precision tester and standard commercial reference tester are entered as inputs into the life prediction models.  Improved measurement precision can result in reduced uncertainty bands when extrapolating life metric trends into the latter stages of cell life. Enhanced measurement precision can also enable the quantification of long term trends at earlier stages of testing.

References:

1. A.J. Smith, J.C. Burns, D. Xiong, and J.R. Dahn, J. Electrochem. Soc., 158 (10), A1136 – A1142 (2011).

2. J.C. Burns, A. Kassam, N.N. Sinha, L.E. Downie, L. Solnickova, B.M. Way, and J.R. Dahn, J. Electrochem. Soc., 160 (9), A1451 – A1456 (2013).

3. A. Masias, The Bridge – National Academy of Engineering. 45 (1), 13 – 20 (2015).