Topic 10 min read

HPC: The importance of ultra-precision cyclers

Latest updated: December 17, 2019

Estimating the lifetime of a Li-ion battery through traditional methods typically involves the use of long-term cycling. In order to accelerate cell degradation and reduce testing times, high cycling-rates at elevated temperatures are often used. However, such testing conditions are not always representative of the real-life of the battery. As opposed to standard cycling techniques, High Precision Coulometry (HPC) measurements can provide a reliable estimation of battery lifetime quickly (3-4 weeks) as well as being a great tool for evaluating, and comparing, the stability of different cells.

 

High Precision Coulometry: Principles

High precision coulometry was first developed by Dr. Jeff Dahn’s laboratory at Dalhousie University, Nova Scotia, in 2010.

HPC analysis is based on high accuracy Coulombic Efficiency (CE) measurements of the battery which is thus described:

CE = [Charge delivered during discharge]/[Charge stored during the previous charge]

To calculate the CE per cycle, the battery is charged (positive current) up until a definite cut-off voltage and then discharged down to a definite cut-off voltage, possibly followed by a constant voltage period, and repeated n times (cycles).

Once the CE is calculated per cycle, the batteries’ HPC curves can then be interpreted.

 

Long term cycling results (left) vs. Short term coulombic efficiency (right).

 

High Precision Coulometry requires high-end analytical equipment

In order to obtain accurate HPC measurements and predict a battery’s long-term behavior, a cycler must be able to detect small capacity loss measurements during the few first cycles. Several cycler characteristics must be therefore be taken into account:

– Current accuracy and stability: responsible for a constant charge and discharge of the battery during cycling

– Voltage measurement accuracy: responsible for repeatable cut-off voltage

– Time base: responsible for a precise and accurate definition of the charge and discharge periods and the charge calculation

 

BCS-800 Series: the levels of precision you need for HPC results you can trust

With five current ranges, a 18-bit resolution and a 2 ms time base, BCS-800 cyclers deliver ultra-high precision measurements and are precise and stable enough to deliver HPC predictions you can trust.

The BCS-800 instruments allow CE measurements with typical RMSE values of around 11 ppm (Application Note 53).

 

 

HPC high precision coulometry coulombic efficiency life time