1. Introduction
The rapid evolution of renewable energy systems and electric vehicles has intensified the demand for high-performance energy storage battery. Large-capacity variants, particularly lithium iron phosphate (LiFePO₄) batteries, are increasingly favored due to their high energy density and cost-effectiveness. However, thermal management and capacity retention remain critical challenges. During charge-discharge cycles, energy storage battery generate significant heat due to electrochemical reactions, internal resistance, and polarization effects. This heat accumulation accelerates capacity fade, compromises safety, and shortens operational lifespan.
Existing studies predominantly focus on small-format cells, leaving a knowledge gap regarding the thermal dynamics and aging mechanisms of large-capacity energy storage battery. This study systematically investigates the heat generation behavior and capacity degradation of a 280 Ah LiFePO₄ battery under varying discharge rates and ambient temperatures. Experimental insights aim to guide the design of thermal management systems (TMS) and optimize battery longevity.
2. Experimental Methodology
2.1 Battery Specifications and Test Platform
The tested energy storage battery (GSP71173204F) features a nominal capacity of 280 Ah and a voltage range of 2.0–3.65 V. Key parameters are summarized in Table 1.
Table 1: Specifications of the 280 Ah Energy Storage Battery
| Parameter | Value |
|---|---|
| Nominal Capacity | 280 Ah |
| Weight | 5.34 kg |
| Dimensions | 173×71×204 mm³ |
| Charging Cut-off Voltage | 3.65 V |
| Discharging Cut-off Voltage | 2.0 V |
A CT-4002-5V200A battery tester and R-TD-00RF environmental chamber maintained precise control over temperature (±0.5°C) and current. Surface temperatures at eight monitoring points (T1–T8) were recorded using a TCP-XL data logger.
2.2 Testing Protocols
- Internal Resistance Measurement: Hybrid Pulse Power Characterization (HPPC) was employed. Discharge/charge pulses (10 s duration, 30 s interval) were applied at fixed states of charge (SOC). Ohm resistance (RDRD) and polarization resistance (RpolRpol) were calculated as:RD=ΔV1I,Rpol=ΔV2−ΔV1I,R=RD+RpolRD=IΔV1,Rpol=IΔV2−ΔV1,R=RD+Rpolwhere ΔV1ΔV1 and ΔV2ΔV2 denote instantaneous and steady-state voltage drops, respectively.
- Entropic Heat Coefficient: Measured via open-circuit voltage (OCV) at eight temperatures (-15°C to 40°C):dUdT=ΔUΔTdTdU=ΔTΔU
- Cycling Tests: Batteries underwent 100 charge-discharge cycles (1.0 C rate) at 25°C, 35°C, and 45°C. Capacity fade and impedance evolution were tracked.
3. Results and Discussion
3.1 Heat Generation Characteristics
3.1.1 Impact of Discharge Rate
The energy storage battery exhibited a strong correlation between discharge rate and temperature rise (Fig. 1). At 1.0 C, the maximum temperature increase reached 21.64°C, compared to 3.5°C at 0.25 C. Heat flux density surged from 200 W/m² (0.25 C) to 600 W/m² (1.0 C), driven by intensified Joule heating and polarization losses.
Table 2: Temperature Rise and Heat Flux at Different Discharge Rates
| Discharge Rate | Max. Temp. Rise (°C) | Peak Heat Flux (W/m²) |
|---|---|---|
| 0.25 C | 3.5 | 200 |
| 0.5 C | 12.7 | 350 |
| 1.0 C | 21.64 | 600 |
Spatial temperature heterogeneity was prominent, with the negative terminal (T1) showing 15% higher temperatures than the bottom region (T4). This asymmetry underscores the need for localized cooling strategies in large-capacity energy storage battery.
3.1.2 Influence of Ambient Temperature
At low temperatures (-15°C), heat generation spiked due to increased electrolyte viscosity and internal resistance. Conversely, elevated ambient temperatures (45°C) reduced Joule heating but accelerated parasitic side reactions.
Table 3: Thermal Behavior Under Varying Ambient Temperatures
| Ambient Temp. (°C) | Avg. Heat Flux (W/m²) | Dominant Heat Source |
|---|---|---|
| -15 | 720 | Polarization + Joule Heating |
| 25 | 600 | Joule Heating |
| 45 | 480 | SEI Growth + Electrolyte Decomposition |
3.2 Capacity Attenuation Mechanisms
3.2.1 Temperature-Dependent Aging
High-temperature cycling (45°C) accelerated capacity fade by 2.26× compared to 25°C. Post-100 cycles, capacity retention dropped to 96.36% at 25°C versus 92.89% at 45°C (Table 4).
Table 4: Capacity Retention After 100 Cycles
| Ambient Temp. (°C) | Capacity Retention (%) | Capacity Loss (Ah) |
|---|---|---|
| 25 | 96.36 | 4.09 |
| 35 | 94.55 | 6.96 |
| 45 | 92.89 | 10.31 |
Electrochemical impedance spectroscopy (EIS) revealed rising polarization resistance (RpolRpol) with cycling, attributed to solid electrolyte interphase (SEI) thickening and active lithium loss.
3.2.2 Degradation Pathways
- Low Temperatures: Lithium plating at the anode dominated capacity loss.
- High Temperatures: SEI growth, electrolyte decomposition, and cathode structural degradation synergistically degraded performance.
4. Thermal Management Recommendations
- Localized Cooling: Prioritize heat extraction near the negative terminal to mitigate temperature gradients.
- Dynamic Temperature Control: Maintain operational temperatures near 25°C to balance efficiency and longevity.
- Multi-Zone Monitoring: Deploy sensors at critical regions (T1, T3, T6) for real-time thermal feedback.
5. Conclusion
This study elucidates the intricate interplay between heat generation, temperature distribution, and capacity fade in large-capacity energy storage battery. Key findings include:
- Discharge rates >1.0 C induce hazardous temperature spikes (>20°C).
- Ambient temperatures >35°C accelerate capacity decay by 1.5× per 10°C rise.
- Spatial thermal heterogeneity necessitates advanced cooling architectures.
By integrating these insights, next-generation TMS can enhance the safety and durability of energy storage battery, enabling their sustainable deployment in grid-scale and automotive applications.