Two Fundamental Views: Time-Based and Cycle-Based
MIMS Client organises battery test data into two primary chart modes, each answering a different class of engineering question:
- Time-based view: Plots one or more measured channels — voltage, current, capacity, energy, temperature, auxiliary inputs — against elapsed time. Shows the full waveform of a test at whatever logging resolution was configured. Used for waveform inspection, anomaly investigation, step-transition verification, and thermal event correlation.
- Cycle-based view: Plots per-cycle or per-half-cycle summary metrics — charge capacity, discharge capacity, coulombic efficiency, energy efficiency, ESR — against cycle number. Used for trend analysis across the full program duration: capacity fade curves, efficiency decay, impedance growth.
Both modes operate on the same underlying data file. Switching between them changes the aggregation level, not the data itself. Most analysis workflows use both: time-based inspection to verify individual cycles, cycle-based trending to assess the program as a whole.
Configuring Charts in MIMS Client
MIMS Client provides a flexible chart configuration interface with the following controls:
- Y-axis channel selection: Up to two independent Y-axes can be configured, each with its own scale range and unit. Common pairings are voltage (left axis) and current (right axis), or capacity (left) and efficiency (right).
- X-axis selection: In time-based mode, the X-axis is elapsed test time. In cycle-based mode, it is cycle number (CycleP or CycleC). Voltage can also be used as the X-axis for plotting capacity versus voltage and for dQ/dV analysis.
- Data range: Charts can be scoped to a specific cycle range, step range, or time window. Narrowing the range to a single cycle shows fine waveform detail; the full range shows long-program trends.
- Multi-channel overlay: Multiple channels from the same data file can be plotted simultaneously. Multiple data files can also be overlaid for direct cell-to-cell comparison.
- Zoom and pan: Interactive zoom focuses on specific regions; pan moves through the dataset without changing the zoom level.
Differential Capacity (dQ/dV) Plots
Differential capacity — incremental charge per unit voltage — is one of the most diagnostic visualisations available from standard battery test data. It requires no additional instrumentation beyond the standard voltage and capacity record. In MIMS, dQ/dV is calculated from the existing data file and plotted with voltage on the X-axis.
What dQ/dV reveals:
- Peaks correspond to electrochemical phase transitions at specific voltages. Their position, height, and sharpness fingerprint the chemistry.
- Peak broadening over cycles indicates kinetic degradation — increased polarisation and resistance.
- Peak shift indicates thermodynamic changes — lithium inventory loss or active material degradation.
- Peak disappearance indicates loss of a specific electrochemical phase — often irreversible capacity loss or lithium plating.
Key MIMS dQ/dV settings: Min. dV controls smoothing (5 mV is a typical starting point for Li-ion); Aux. no. enables electrode-specific dQ/dV using a reference electrode on an auxiliary voltage input; Connection polarity must be set correctly for reference electrode configurations.
Plotting Auxiliary and Thermal Data
Auxiliary inputs — thermocouples, thermistors, auxiliary voltage channels, and pressure sensors — are logged alongside electrical data in the same data record and share the same time index. Any auxiliary channel can be overlaid directly on the same time-based chart as voltage, current, and capacity without manual alignment.
Common auxiliary visualisation patterns:
- Temperature vs. voltage or time: Shows the thermal signature of each charge and discharge half-cycle. Used to identify localised heating, self-discharge events, and thermal runaway precursors.
- Reference electrode voltage: Plotted on the second Y-axis alongside full-cell voltage, enabling anode and cathode potential tracking — critical for understanding where capacity is being lost.
- Pressure vs. cycle number: For solid-state and pouch cell programs, pressure trends over cycle number reveal gas evolution, electrode swelling, and electrolyte decomposition.
- Calculated voltage (Vref): MIMS can display a computed full-cell voltage derived from reference electrode inputs — useful for validating the reference electrode measurement against the directly measured terminal voltage.
Real-Time Visualisation During Test Execution
MIMS provides five screen types for monitoring active tests. Three display live data that updates as records are written:
- Schedule screen: Tabular view of all active channels — current step, mode, voltage, current, capacity, and status. Primary tool for multi-channel monitoring at a glance.
- Channel screen: Detailed view of a single channel — all electrical and auxiliary values, step progress, end condition thresholds, and loop counters.
- Chart screen: Live strip-chart of selected channels versus time for a single active channel. Monitoring only — does not affect the running test or stored data.
MIMS Client connects to MIMS Server to display this live data. The server continues running and logging data regardless of whether the Client is open — disconnecting the client for chart reconfiguration does not affect test execution.
Visualisation by Program Type
| Program Type | Primary Chart Types |
|---|---|
| Cell characterisation | Voltage vs. capacity; dQ/dV; reference electrode overlays |
| Cycle life / reliability | Capacity vs. cycle number; CE vs. cycle number; ESR vs. cycle number |
| HPPC / pulse power | Voltage vs. time (high resolution); ESR at step transitions |
| Thermal / safety | Temperature vs. time overlaid with voltage; dT/dt derivative traces |
| Grid storage efficiency | Round-trip Wh efficiency vs. cycle; partial SoC voltage excursion profiles |
Frequently Asked Questions
Can I overlay data from multiple cells on the same chart?
Yes. MIMS Client allows multiple data files to be loaded simultaneously and plotted on the same chart axes. This is the standard approach for comparing cells from a test matrix — overlaying discharge curves for ten cells at three different temperatures to visualise the spread in capacity and voltage profile.
Does the Chart screen affect what data is stored?
No. The Chart screen in MIMS is a read-only monitoring view — it displays data as it is written by MIMS Server but cannot alter the logging configuration or the stored data record. Logging is controlled entirely by the report types configured in the test procedure.
My dQ/dV curves look very noisy — what is the cause?
Noisy dQ/dV curves are almost always a logging resolution issue. The dQ/dV calculation requires sufficient data density in the voltage domain. If the test used time-based logging only, there may be too few data points per millivolt in flat plateau regions. Adding a voltage-triggered report type (1–5 mV threshold) to future test procedures improves dQ/dV quality substantially. For existing data, increasing the Min. dV setting in MIMS smooths the curve at the cost of resolving fine peak structure.