CV: Coulombic Efficiency and Capacitance Calculation

This Workflow uses the output data from Cyclic Voltammetry (CV) Data Extraction and Preprocessing to calculate the charge quantities for forward and reverse scans in each cycle through numerical integration, thereby obtaining coulombic efficiency and electrode capacitance.

Prerequisites

First execute Cyclic Voltammetry (CV) Data Extraction and Preprocessing to complete CV data extraction and obtain Excel files containing the Scans_Split sheet. Note: Output data from Cyclic Voltammetry (CV) Data Extraction and Preprocessing is not currently supported.

Steps

Select input folder: Use the file picker to select the folder containing the Excel data files output by Cyclic Voltammetry (CV) Data Extraction and Preprocessing. This folder typically contains CV extraction results at different scan rates.
The system automatically completes calculations and generates result files and visualization charts.

Scientific Principles

Charge Calculation

By definition of electric current, the charge $Q$ is the integral of current $I$ over time $t$ . For discrete data, numerical integration is performed using the Trapezoidal Rule:

Q = \int_{t_1}^{t_2} I(t)\, \mathrm{d}t \approx \sum_{k=1}^{N-1} \frac{I(t_k) + I(t_{k+1})}{2} \cdot \Delta t

where the time step $\Delta t$ is derived from the sampling interval and scan rate:

\Delta t = \frac{\Delta E_{\text{sample}}}{\nu}

Here $\Delta E_{\text{sample}}$ is the sampling voltage interval (V) and $\nu$ is the scan rate (V/s).

Coulombic Efficiency

Coulombic Efficiency (CE) is defined as the ratio of charge from the reverse scan (reduction process) to the forward scan (oxidation process):

\eta_{\text{CE}} = \frac{Q_{\text{reverse}}}{Q_{\text{forward}}} \times 100\%

This metric reflects the degree of reversibility of the electrode process. For an ideal fully reversible process, coulombic efficiency should approach 100%.

Capacitance Calculation

For electrode materials with capacitive characteristics, capacitance $C$ is defined as the ratio of charge to the potential window $\Delta E$ :

C = \frac{Q}{\Delta E} = \frac{\int |I|\, \mathrm{d}t}{E_{\text{high}} - E_{\text{low}}}

where $E_{\text{high}}$ and $E_{\text{low}}$ are the upper and lower limits of the scan potential window, respectively.

Output Files

Upon completion, a Coulombic_Efficiency.xlsx file is generated containing the following two sheets:

Summary_Stats

Groups statistics of coulombic efficiency and capacitance (mean and standard deviation) by scan rate, used to evaluate the repeatability and stability of test data.

Detailed_Per_Cycle

Contains detailed calculation results for each cycle in each file:

Field	Meaning
Q_Forward / Q_Reverse	Forward/reverse scan charge (C)
CE (%)	Coulombic efficiency
Cap_Forward / Cap_Reverse	Forward/reverse scan capacitance (F)
Cap_Avg	Average capacitance (F)

Further Analysis

Based on the output of this Workflow, further pseudocapacitance analysis such as CV/Pseudocapacitance Analysis: b-Value Kinetic Analysis or CV/Cdl: Double-Layer Capacitance and Electrochemically Active Surface Area Analysis can be conducted.

Cyclic Voltammetry (CV) Data Extraction and Preprocessing CV: Plot Last Cycle