In recent years, the demand for advanced energy storage systems has grown significantly, driven by applications in electric vehicles, portable electronics, and renewable energy integration. Conventional liquid lithium-ion batteries, while widely used, pose safety risks such as electrolyte leakage, combustion, and explosion under conditions like overcharge, over-discharge, or short circuits. In contrast, solid-state batteries offer superior safety due to their solid electrolyte structure, which minimizes these hazards. This study focuses on high specific energy solid-state batteries, which exhibit exceptional performance metrics, including higher weight-specific energy and improved tolerance to extreme temperatures compared to traditional liquid lithium-ion batteries. The absence of standardized test methods for evaluating the electrical performance parameters of these solid-state batteries has hindered their widespread adoption. Thus, this research aims to develop and validate comprehensive test procedures for key electrical parameters, ensuring reliable assessment for engineering applications.
The electrical performance of high specific energy solid-state batteries is characterized by parameters such as weight-specific energy, discharge capacity retention at high rates, cycle life, and performance under low and high temperatures. For instance, these solid-state batteries can achieve a weight-specific energy of up to 450 Wh/kg, surpassing that of long-cycle solid-state batteries (around 350 Wh/kg) and conventional liquid lithium-ion batteries (approximately 400 Wh/kg). Additionally, they maintain 70% of their room-temperature discharge capacity at -20°C and 80% at 80°C, whereas liquid lithium-ion batteries often experience severe side reactions or failure above 55°C. Given these distinctions, it is crucial to establish tailored test methods that accurately reflect the unique properties of solid-state batteries. This paper details experimental investigations on these parameters, utilizing typical high specific energy solid-state battery samples to derive standardized test approaches.
To begin, we analyzed the key electrical performance parameters of high specific energy solid-state batteries. The weight-specific energy is a critical metric, defined as the energy output per unit mass, which directly impacts the energy density of battery systems. For solid-state batteries, this parameter is influenced by the electrode materials and solid electrolyte composition. Similarly, the discharge capacity retention at 1C rate indicates the battery’s ability to deliver power under high-current conditions, which is essential for applications requiring rapid discharge. Cycle life evaluates the longevity of solid-state batteries, reflecting their capacity retention over repeated charge-discharge cycles. Furthermore, performance under extreme temperatures—low and high—assesses the robustness of solid-state batteries in diverse environments. These parameters are interlinked and must be evaluated through systematic experiments to ensure the reliability of solid-state battery technologies.
In our experimental setup, we selected representative high specific energy solid-state battery samples for testing. The equipment included an ET-1000L-C2 high-low temperature test chamber, a BTS-5V200A16CH battery tester, and a BT300 electronic balance. All instruments were calibrated to meet accuracy standards, with temperature measurements within ±0.5°C, dimensional and mass measurements within ±0.1%, and voltage and current measurements within ±0.5%. The tests were conducted under controlled environmental conditions, typically at 25°C ± 3°C, unless specified otherwise. Below, we present detailed methodologies and results for each electrical performance parameter, incorporating tables and formulas to summarize the findings.
Weight-Specific Energy Test
The weight-specific energy test measures the energy output relative to the battery’s mass, providing insights into the energy density of solid-state batteries. The test procedure involved charging the solid-state battery at a constant current of 0.1C to a voltage of 4.35 V at 25°C ± 3°C, followed by a 15-minute rest period. Subsequently, the battery was discharged at 0.1C to a cut-off voltage of 3.0 V. The discharge capacity (in Ah) and discharge energy (E in Wh) were recorded directly from the testing software. The weight-specific energy (E_w) was calculated using the formula:
$$E_w = \frac{E}{W}$$
where E is the discharge energy in Wh, and W is the battery weight in kg. The合格判据 required E_w ≥ 450 Wh/kg for high specific energy solid-state batteries. In our tests, the average discharge energy was 57.12 Wh, with a battery weight of 0.1259 kg, resulting in E_w = 453.6 Wh/kg, which meets the requirement. This demonstrates the high energy density achievable with solid-state battery technology.
| Parameter | Value |
|---|---|
| Discharge Capacity (Ah) | 14.6 |
| Discharge Energy (Wh) | 57.12 |
| Battery Weight (kg) | 0.1259 |
| Calculated E_w (Wh/kg) | 453.6 |
1C Discharge Capacity Retention Rate Test
This test evaluates the ability of solid-state batteries to maintain discharge capacity under high-current conditions, which is vital for applications demanding high power output. The solid-state battery was charged at 0.2C to 4.35 V at 25°C ± 3°C, rested for 15 minutes, and then discharged at 1C to 3.0 V. The discharge capacity at 1C was compared to the initial capacity measured at 0.2C discharge. The合格判据 specified that the 1C discharge capacity should be at least 80% of the 0.2C discharge capacity. Our results showed an initial 0.2C discharge capacity of 14.28 Ah and a 1C discharge capacity of 13.62 Ah, yielding a retention rate of 95.4%. This high retention rate underscores the superior performance of solid-state batteries under high-rate discharges, attributed to their stable solid electrolyte interface.
| Discharge Rate | Discharge Capacity (Ah) | Retention Rate (%) |
|---|---|---|
| 0.2C | 14.28 | 100 |
| 1C | 13.62 | 95.4 |
Cycle Life Test
Cycle life testing assesses the longevity of solid-state batteries by subjecting them to repeated charge-discharge cycles. The solid-state battery was charged at 0.2C to 4.35 V and discharged at 0.5C to 3.0 V for 200 cycles at 25°C ± 3°C. The capacity retention after 200 cycles was required to be ≥80% of the initial capacity. The initial discharge capacity was 14.5 Ah, and after 200 cycles, it decreased to 11.75 Ah, resulting in a retention rate of 81.03%. This indicates that solid-state batteries can endure extended cycling with minimal degradation, making them suitable for long-term applications. The gradual capacity fade in solid-state batteries is often due to interfacial reactions and mechanical stress, but our results highlight their robustness.
| Cycle Number | Discharge Capacity (Ah) | Capacity Retention (%) |
|---|---|---|
| 1 | 14.5 | 100 |
| 200 | 11.75 | 81.03 |
Low-Temperature Discharge Capacity Test
This test examines the performance of solid-state batteries in cold environments, which is critical for applications in aerospace or cold climates. The solid-state battery was charged at 0.2C to 4.35 V at 25°C ± 3°C, rested for 15 minutes, and then placed in a -20°C ± 2°C environment for 8 hours. After this, it was discharged at 0.2C to 3.0 V. The合格判据 required the low-temperature discharge capacity to be at least 70% of the room-temperature capacity. The room-temperature discharge capacity was 13.98 Ah, and the low-temperature capacity was 11.48 Ah, giving a retention rate of 82.12%. This demonstrates that solid-state batteries maintain reliable operation even under severe cold conditions, owing to their solid electrolyte’s reduced sensitivity to temperature variations compared to liquid electrolytes.
| Condition | Discharge Capacity (Ah) | Retention Rate (%) |
|---|---|---|
| Room Temperature (25°C) | 13.98 | 100 |
| Low Temperature (-20°C) | 11.48 | 82.12 |
High-Temperature Discharge Capacity Test
High-temperature testing evaluates the thermal stability of solid-state batteries, which is essential for safety in high-heat applications. The solid-state battery was charged at 0.2C to 4.35 V at 25°C ± 3°C, rested for 15 minutes, and then placed in an 80°C ± 2°C environment for 8 hours before being discharged at 0.2C to 3.0 V. The合格判据 required the high-temperature discharge capacity to be at least 80% of the room-temperature capacity. The room-temperature capacity was 13.98 Ah, and the high-temperature capacity was 14.5 Ah, resulting in a retention rate of 103.7%. This exceptional performance highlights the advantage of solid-state batteries in high-temperature scenarios, where liquid lithium-ion batteries might fail due to electrolyte decomposition or thermal runaway.
| Condition | Discharge Capacity (Ah) | Retention Rate (%) |
|---|---|---|
| Room Temperature (25°C) | 13.98 | 100 |
| High Temperature (80°C) | 14.5 | 103.7 |
Standardized Test Methods for Electrical Performance Parameters
Based on our experimental findings, we have developed standardized test methods for evaluating the electrical performance of high specific energy solid-state batteries. These methods provide a framework for consistent assessment across different solid-state battery designs and applications. The environmental conditions for all tests are specified as: temperature between 15°C and 35°C, relative humidity between 20% and 80%, and atmospheric pressure between 86 kPa and 106 kPa, unless otherwise stated. The general charging procedure involves discharging the solid-state battery at 0.2C to 3.0 V, resting for 30 minutes, and then charging at 0.2C to 4.35 V, followed by a 15-minute rest.
For weight-specific energy, the solid-state battery is charged as per the general method and then discharged at 0.1C to 3.0 V. The weight-specific energy is calculated using the formula $$E_w = \frac{E}{W}$$, and it must be ≥450 Wh/kg. For the 1C discharge capacity retention rate, the solid-state battery is discharged at 0.2C to establish the initial capacity, then charged and discharged at 1C; the retention rate should be ≥80%. Cycle life testing involves 200 cycles of charging at 0.2C and discharging at 0.5C, with a capacity retention ≥80% after the cycles. Low-temperature discharge capacity requires testing at -20°C after an 8-hour soak, with capacity retention ≥70% compared to room temperature. High-temperature discharge capacity involves testing at 80°C after an 8-hour soak, with capacity retention ≥80%.
These standardized methods ensure that solid-state batteries are evaluated under realistic conditions, accounting for their unique material properties and performance characteristics. The use of solid-state electrolytes in these batteries enhances safety and stability, which is reflected in the test outcomes. For instance, the formula for capacity retention rate can be expressed as:
$$R = \frac{C_{\text{test}}}{C_{\text{initial}}} \times 100\%$$
where R is the retention rate, C_test is the discharge capacity under test conditions, and C_initial is the initial discharge capacity at room temperature. This formula is applicable across various tests to quantify performance degradation.
Application of Test Methods
The developed test methods have been applied in the formulation of enterprise product specifications and testing reports for institutions involved in solid-state battery research and development. For example, they have been utilized in assessing solid-state battery samples for academic and industrial projects, ensuring that the batteries meet the required standards for high specific energy applications. This application has facilitated the comparison of different solid-state battery designs and accelerated the commercialization of solid-state battery technologies. By providing a reliable assessment framework, these methods support quality control and performance validation in the production and deployment of solid-state batteries.
Conclusion
In this study, we have conducted comprehensive experiments to develop test methods for key electrical performance parameters of high specific energy solid-state batteries. Through tests on weight-specific energy, 1C discharge capacity retention, cycle life, low-temperature discharge capacity, and high-temperature discharge capacity, we have demonstrated the superior characteristics of solid-state batteries compared to conventional liquid lithium-ion batteries. The results confirm that solid-state batteries achieve high energy density, excellent rate capability, long cycle life, and robust performance under extreme temperatures. The standardized test methods derived from this research fill a critical gap in the evaluation of solid-state battery technologies, enabling accurate assessment for engineering applications. As solid-state batteries continue to evolve, these methods will play a vital role in ensuring their reliability and safety, ultimately supporting the advancement of next-generation energy storage systems.
Overall, the integration of solid-state electrolytes in battery designs offers significant advantages, and our work provides a foundation for future standardization efforts. We recommend further research into additional parameters, such as internal resistance and thermal runaway behavior, to enhance the comprehensive evaluation of solid-state batteries. The continued development of solid-state battery technology promises to revolutionize energy storage, and standardized testing will be crucial for its successful implementation.