Systematic Characterization of Lithium-Ion Cells for Electric Mobility and Grid Storage: A Case Study on Samsung INR21700-50G
Abstract
1. Introduction
2. Equivalent Circuit Model and Thermal Dynamics
- is the state of charge of the cell;
- Q is the cell capacity in ampere-hours;
- and represent the voltages across the two RC pairs;
- is the applied current, with discharge current defined as negative;
- is the ohmic internal resistance of the cell;
- is the open-circuit voltage as a function of SOC.
- , , and denote the core, surface, and ambient air temperatures, respectively.
- and are the lumped thermal conduction resistances between core-surface and surface-air, respectively.
- and are the lumped thermal capacitance of the core and surface layers, respectively.
- is the instantaneous heat generation rate inside the cell.
3. Test Procedures
3.1. Test Setup
3.2. Test Preparation
3.3. Static Capacity Test
3.4. Hybrid Pulse Power Characterization (HPPC) Test
3.5. Test Cases
4. Results
4.1. Static Capacity Test Results
4.2. HPPC Test Results
4.2.1. Open-Circuit Voltage
4.2.2. Charge/Discharge Power Capability
- The internal resistance increases significantly as SOC drops below 30%, and this effect is even more pronounced at sub-zero temperatures. This can be attributed to reduced lithium-ion mobility within the electrolyte [28], slower electrochemical reaction kinetics [29], and increased resistance at the solid-electrolyte interface.
- The DCIR increases with pulse duration for both discharge and regeneration phases, following the trend: . The OCV is a nonlinear function of SOC, and longer discharge pulses result in a greater SOC reduction, lowering the OCV baseline. This leads to a larger terminal voltage drop , and consequently, higher DCIR values. It is worth noting that although the ohmic resistance may decrease slightly during longer pulses due to self-heating, the DCIR is computed from the terminal voltage difference and applied current, and therefore reflects both resistive and dynamic effects.
- Discharge resistance values are generally higher than regeneration (charge) resistance values. This behavior is attributed to intrinsic asymmetries in electrochemical kinetics and internal polarization. During discharge, lithium deintercalation from the anode is more kinetically constrained, particularly at low temperatures, resulting in greater activation and concentration polarization and, consequently, larger voltage drops under load. In contrast, during regeneration, the lithium intercalation process exhibits lower kinetic limitations, leading to comparatively lower observed resistance [30,31].
- The difference between charge and discharge resistance is prominent for longer pulses. The increase in resistance observed during the 180 s pulse at C is primarily attributed to the cumulative effects of sustained high current under low-temperature conditions. At sub-zero temperatures, both ionic conductivity and charge-transfer kinetics are significantly diminished, leading to the formation of a lithium-ion concentration gradient and elevated overpotential during prolonged discharge, thereby increasing the measured resistance [32].
- Discharge power capability consistently decreases with decreasing SOC. At lower SOC levels, the voltage headroom and the effective power output decrease, while the internal resistance increases, resulting in reduced discharge performance.
- Regeneration (charging) power capability increases as SOC decreases. This is attributed to the greater voltage margin between the cell’s open-circuit voltage and the upper voltage limit, particularly at low SOCs.
- Pulse duration significantly affects power capabilities. Shorter pulses (e.g., 2 s and 10 s) result in higher power capabilities due to minimized voltage drop and thermal buildup. In contrast, longer pulses (30 s and 180 s) show reduced power handling, especially under extreme SOC or temperature conditions. This stems directly from Equations (12) and (13) as the power capability is inversely related to the pulse resistance. Under low or high SOC and extreme temperatures, the internal resistance of the cell tends to increase, leading to a reduction in power capability under these conditions.
- Temperature is a dominant influencing factor. Across all pulse durations and SOC levels, both discharge and regeneration capabilities are notably higher at elevated temperatures ( and ). Sub-zero temperatures () lead to severe performance degradation—regeneration power capability, in particular, is significantly reduced due to increased polarization and impedance.
5. Parameter Extraction from HPPC Data
6. Conclusions
- Internal resistance increases sharply at low SOC and sub-zero temperatures due to hindered ion transport and electrochemical kinetics.
- Discharge resistance consistently exceeds regeneration resistance, reflecting the asymmetric nature of charge and discharge processes.
- Longer pulse durations cause higher resistances due to increased polarization and thermal effects.
- Discharge power capability decreases with SOC, while regeneration power capability conversely increases, influenced by voltage margin constraints.
- Elevated temperatures (to a specific limit) significantly enhance power capabilities, whereas cold conditions degrade performance by over two-thirds.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
Abbreviations
Symbol | Description | Symbol | Description |
State of charge (dimensionless, 0–1) | Discharge resistance () | ||
Q | Cell capacity (Ah) | Regeneration resistance () | |
Applied current (A) | DCIR at respective pulses () | ||
Terminal voltage (V) | DCIR at respective pulses () | ||
Open-circuit voltage (V) | Core temperature (°C or K) | ||
Voltage across first RC pair (V) | Surface temperature (°C or K) | ||
Voltage across second RC pair (V) | Ambient air temperature (°C or K) | ||
Ohmic resistance () | Average cell temperature (°C or K) | ||
Resistances of RC pairs () | Thermal capacitances (J/K) | ||
Capacitances of RC pairs (F) | Thermal resistances (K/W) | ||
RC time constants (s) | Voltage drop during discharge pulse (V) | ||
Sampling time (s) | Voltage rise during charge pulse (V) | ||
Heat generation rate (W) | Current during discharge pulse (A) | ||
C-rate | Normalized charge/discharge rate | Current during charge pulse (A) | |
Minimum voltage in a discharge pulse (V) | Maximum voltage in a charge pulse (V) | ||
Discharge pulse power capability (W) | Charge pulse power capability (W) | ||
BMS | Battery management system | LIB | Lithium ion batteries |
H/BEV | Hybrid/Battery electric vehicle | ECM | Equivalent circuit model |
ECU | Electronic control unit | EKF | Extended Kalman filter |
NCA | Nickel Cobalt Aluminum | HPPC | Hybrid Power Pulse Characterization |
CC-CV | Constant current - Constant voltage | DCIR | Direct current internal resistance |
Appendix A
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Parameter | Value |
---|---|
Nominal Voltage | 3.6 V |
Maximum Voltage | 4.2 V |
Nominal Capacity | 4.9 Ah |
Discharge Cut-off Voltage | 2.5 V |
Continuous Discharge Rating | 9.8 A |
Cell Weight | 69 g |
Cell Dimensions | Height: Max. 70.80 mm |
Diameter: Max. 21.25 mm |
Temp. (C) | 1C | 0.2C | ||||
---|---|---|---|---|---|---|
MAE (V) | RMSE (V) | MAPE (%) | MAE (V) | RMSE (V) | MAPE (%) | |
0.032 | 0.038 | 0.876 | 0.036 | 0.044 | 1.003 | |
0 | 0.015 | 0.018 | 0.398 | 0.020 | 0.024 | 0.527 |
10 | 0.011 | 0.015 | 0.306 | 0.015 | 0.019 | 0.412 |
20 | 0.016 | 0.020 | 0.436 | 0.018 | 0.023 | 0.508 |
30 | 0.008 | 0.010 | 0.215 | 0.011 | 0.013 | 0.284 |
45 | 0.007 | 0.009 | 0.198 | 0.009 | 0.011 | 0.242 |
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Paudel, S.; Zhang, J.; Ayalew, B.; Singh, R. Systematic Characterization of Lithium-Ion Cells for Electric Mobility and Grid Storage: A Case Study on Samsung INR21700-50G. Batteries 2025, 11, 313. https://doi.org/10.3390/batteries11080313
Paudel S, Zhang J, Ayalew B, Singh R. Systematic Characterization of Lithium-Ion Cells for Electric Mobility and Grid Storage: A Case Study on Samsung INR21700-50G. Batteries. 2025; 11(8):313. https://doi.org/10.3390/batteries11080313
Chicago/Turabian StylePaudel, Saroj, Jiangfeng Zhang, Beshah Ayalew, and Rajendra Singh. 2025. "Systematic Characterization of Lithium-Ion Cells for Electric Mobility and Grid Storage: A Case Study on Samsung INR21700-50G" Batteries 11, no. 8: 313. https://doi.org/10.3390/batteries11080313
APA StylePaudel, S., Zhang, J., Ayalew, B., & Singh, R. (2025). Systematic Characterization of Lithium-Ion Cells for Electric Mobility and Grid Storage: A Case Study on Samsung INR21700-50G. Batteries, 11(8), 313. https://doi.org/10.3390/batteries11080313