Coulombic efficiency and dQ/dV from raw cycler files (Beta)

This page calculates Coulombic efficiency, capacity retention and dQ/dV straight from raw Neware (.nda, .ndax), BioLogic (.mpr, .mpt) or Arbin (.res) files. The method is described below, so you can cite or reproduce it.

How to get the analysis

1. Upload one or more raw cycler files (up to 20 cells).
2. Choose Cycle numbering: keep the instrument's own count, or start a cycle with every charge (cathodes and full cells) or with every discharge (anode half-cells).
3. Optional, under More options: up to four cycles to plot (e.g. 1, 2, 10, 50), the dQ/dV voltage step, and the reference cycle for capacity retention.
4. Read the preview charts, then download Name - cycles.csv, Name - dQdV.csv or the Excel workbook, whose Charts sheet plots capacity and Coulombic efficiency against cycle number.

How the cycle summary is calculated

• Capacity and energy per cycle are totals of the cycler's recorded charge and energy.
• Coulombic efficiency is discharge capacity ÷ charge capacity of the same cycle. When a test starts with a discharge, as anode half-cells usually do, it is charge ÷ discharge instead. Short pulses such as resistance checks don't count when deciding which came first.
• Energy efficiency is the same ratio for energy.
• Capacity retention is each cycle's discharge capacity (charge capacity for discharge-first tests) relative to a reference: by default the first cycle that delivers at least 10 % of the largest capacity, which skips a partial first cycle.
• Mean charge and discharge voltages are energy ÷ capacity, and their difference is the voltage hysteresis.

With an active mass, entered or found in the file, specific capacities and energies per gram are added.

How dQ/dV is computed

For each cycle and direction, capacity increments are summed in fixed voltage bins and divided by the bin width. The bin is twice the typical voltage step between points, kept between 1 and 10 mV, unless you set it. A Gaussian filter with a width of 1.5 bins smooths the curve, and the raw values stay in the CSV next to it. Points recorded at constant voltage are excluded, since dQ/dV grows without bound there, and half-cycles with fewer than 10 points are skipped.

Several cells at once

With several files, each cell keeps its own outputs, and one extra table lists every cycle of every file, so cells from different instruments can be compared directly.

Format details: Neware .ndax, BioLogic .mpr, Arbin .res.

More about what this tool reads and writes: Battery Cycler Data Converter.