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IEC 62813:2015 Lithium Ion Capacitors โ Test Methods for Electrical Characteristics
💡 What is IEC 62813? This standard specifies test methods for electrical characteristics of lithium ion capacitors (LICs) used in electric and electronic equipment, providing a unified framework for evaluating capacitance, internal resistance, leakage current, and lifetime performance.
1. Scope and Technology Background
IEC 62813 applies to lithium ion capacitors, which are hybrid energy storage devices combining the high energy density of lithium-ion batteries with the high power density and long cycle life of electric double-layer capacitors (EDLCs, also known as supercapacitors). LICs use a lithium-doped negative electrode and an activated carbon positive electrode, achieving energy densities of 10-30 Wh/L — significantly higher than conventional supercapacitors — while maintaining power densities of 5-15 kW/L.
The standard covers test methods for rated capacitance, DC internal resistance (DCIR), AC impedance, leakage current, self-discharge, and cycle life. It is applicable to LICs with rated voltages typically in the range of 2.2 V to 3.8 V.
⚠ Important Distinction: LICs must not be tested using methods designed for standard supercapacitors or batteries. The lithium-doped negative electrode introduces different electrochemical behaviour, particularly regarding voltage limits and charge/discharge control. Testing at incorrect voltage levels can cause permanent damage to the device.
2. Key Test Methods
| Parameter | Test Method | Acceptance Criteria (Typical) |
|---|---|---|
| Capacitance C | Constant current charge/discharge at 0.1C rate | ±15% of rated value |
| DC internal resistance | Voltage drop method at 1C discharge | ≤ 5 mΩ per 100 F |
| AC impedance (1 kHz) | AC bridge or impedance analyser | ≤ 3 mΩ at 1 kHz |
| Leakage current | After 30 min hold at rated voltage | ≤ 0.03 CV (µA) |
| Self-discharge rate | Voltage decay over 72 h at 25°C | ≤ 15% voltage drop |
| Cycle life | Charge/discharge cycles at rated current | ≥ 100 000 cycles to 80% C |
✅ Engineering Insight: The DC internal resistance of LICs is highly temperature-dependent, typically increasing by 2-3x from 25°C to -20°C. This characteristic is critical for applications operating in cold environments such as automotive starting and wireless remote monitoring. Designers should characterise DCIR across the full operating temperature range specified in the standard (−40°C to +70°C).
3. Practical Applications and Design Considerations
LICs are increasingly used in a wide range of applications:
Energy harvesting systems: LICs serve as intermediate storage in solar-powered IoT sensors, where their high cycle life (100,000+ cycles) eliminates the need for battery replacement. Their ability to operate across a wide temperature range makes them ideal for outdoor installations.
Backup power: In RAID controllers, smart meters, and industrial PLCs, LICs provide reliable backup power during short mains interruptions, replacing conventional batteries with longer life and lower maintenance requirements.
Peak power buffering: For electric vehicles and hybrid systems, LICs buffer regenerative braking energy and provide peak power for acceleration, reducing stress on the main battery and extending overall system life.
🚨 Safety Warning: Overvoltage is the primary failure mode for LICs. Exceeding the rated voltage by more than 0.1 V can cause lithium metal plating on the negative electrode, leading to internal short circuits and potential thermal runaway. All charging circuits must implement redundant voltage limiting with accuracy better than ± 1% of the rated voltage.
Frequently Asked Questions
Q: What is the typical voltage range for LICs?
A: Standard LICs operate between 2.2 V (fully discharged) and 3.8 V (fully charged), though specific products may have different ranges. The standard provides test methods applicable to all common LIC voltage ratings.
Q: How do LICs compare to EDLC supercapacitors?
A: LICs offer approximately 3-4x higher energy density than EDLCs while maintaining similar power density. However, LICs have lower maximum voltage (3.8 V vs 2.7 V for EDLCs) and require more precise voltage management.
Q: What cycling conditions are specified for life testing?
A: The standard specifies cycling between rated voltage and half rated voltage at rated current, at 25°C ± 5°C. End of life is defined as 80% of initial capacitance or 200% of initial DCIR.
Q: Are there storage recommendations for LICs?
A: Yes, LICs should be stored at 30-50% state of charge in a cool, dry environment (15-25°C, < 50% RH). Long-term storage at full charge accelerates aging and increases internal resistance.
