In recent years, the rapid expansion of the electric vehicle (EV) market has led to a significant increase in retired power batteries, posing both environmental and economic challenges. We focus on the safety inspection and maintenance standards for retired China EV battery systems during their secondary use, particularly in echelon utilization scenarios. As the demand for sustainable energy solutions grows, ensuring the safe handling of these batteries becomes critical. We analyze the entire lifecycle characteristics of EV power battery packs and establish a comprehensive framework for evaluation and repair. This article proposes a multi-level inspection index system covering electrical performance, structural safety, and thermal management, along with graded maintenance protocols. Through case studies and theoretical modeling, we validate the applicability of these standards and recommend a standardized framework that integrates detection technologies, repair processes, and personnel certification. The goal is to provide theoretical support and practical guidance for enhancing the safety of echelon utilization, thereby supporting the circular economy in the EV sector.
The lifecycle of an EV power battery exhibits distinct phases, beginning with its primary use in vehicles and transitioning to retirement when capacity degrades to approximately 80% of its initial value. At this stage, the China EV battery may no longer meet the high-power demands of automobiles but remains viable for less intensive applications like energy storage or backup power systems. Echelon utilization involves systematically repurposing these retired batteries into secondary markets, such as photovoltaic power station frequency regulation, data center backup power, and low-speed electric vehicles. This process typically includes disassembly, sorting, performance testing, and system reconfiguration. However, risks arise from inconsistencies in cell performance and structural integrity, such as internal micro-short circuits due to metallic dendrite growth or stress imbalances during module reassembly, which can trigger thermal runaway events. We emphasize that proper handling of retired EV power battery units is essential to mitigate these hazards and maximize resource efficiency.
To address these challenges, we have developed a safety inspection technology system that encompasses electrical performance, structural safety, and thermal management. Electrical performance testing serves as the core entry criterion for echelon utilization of China EV batteries. It involves a multi-dimensional evaluation, including capacity decay rate, internal resistance changes, and dynamic operating condition simulations. For instance, the capacity retention rate is calculated using the formula: $$ \text{Capacity Retention Rate} = \frac{C_{\text{actual}}}{C_{\text{nominal}}} \times 100\% $$ where $C_{\text{actual}}$ is the measured capacity and $C_{\text{nominal}}$ is the original rated capacity. Batteries with an actual capacity below 70% of the nominal value are typically excluded from reuse. Additionally, internal resistance measurements must be conducted in a controlled environment at 25°C to minimize temperature-induced polarization effects. Dynamic tests simulate real-world scenarios like rapid acceleration and regenerative braking, with up to 500 charge-discharge cycles to verify voltage platform stability.
| Parameter | Test Method | Threshold | Remarks |
|---|---|---|---|
| Capacity Decay Rate | Constant current charge-discharge curve analysis | ≤ 30% | Non-linear degradation trends monitored |
| Internal Resistance Change | Polarization characteristics at 25°C | Increase ≤ 20% | Excludes temperature fluctuations |
| Voltage Stability | Dynamic工况 simulation | Variation ≤ 5% | Based on 500 cycles |
Structural safety assessment requires a cross-verification approach to ensure the integrity of retired China EV battery packs. We employ laser 3D scanning and ultrasonic flaw detection to evaluate shell integrity, with areas showing a thickness reduction exceeding 8% undergoing structural reinforcement. Connector corrosion is assessed through salt spray acceleration tests and historical service data analysis, particularly for batteries from coastal regions, which undergo additional cyclic humidity and heat tests. For terminal inspection, micron-level industrial endoscopes are used to detect intergranular corrosion cracks deeper than 50 μm or dendrite penetration, with an image database established to support manual re-inspection. This multi-faceted method helps identify potential failure points in EV power battery modules before they are redeployed.
Thermal management inspection is critical throughout the battery’s lifecycle and involves advanced monitoring techniques. We utilize distributed optical fiber temperature measurement to achieve a resolution of 0.1% on battery surfaces, enabling gradient current limiting protection in areas with abnormal temperature rises. The thermal runaway预警 system integrates dual gas sensors for hydrogen and carbon monoxide, with concentration change rates and absolute value thresholds triggering alarms within 300 ms. Furthermore, battery management system (BMS) functionality is tested in extreme environments ranging from -20°C to 55°C, verifying the adaptive balancing module’s precision under a 15% cell voltage deviation and assessing millisecond-level shutdown responses to simulated short circuits. These measures ensure that retired China EV batteries maintain safety in secondary applications, reducing the risk of incidents.
Moving to maintenance operations, we advocate for a graded approach based on the extent of damage in EV power battery systems. At the cell level, repairs focus on筛选 and revitalization of individual batteries. For cells with capacity衰减 not exceeding 30% and no internal short circuits, constant voltage repair methods are applied to restore electrode active material distribution. The revitalization process can be modeled using the equation: $$ V_{\text{repair}} = V_{\text{nominal}} + \Delta V \cdot e^{-t/\tau} $$ where $V_{\text{repair}}$ is the repair voltage, $V_{\text{nominal}}$ is the standard voltage, $\Delta V$ is the overpotential, $t$ is time, and $\tau$ is the time constant. At the module level, reconstruction of battery connections is necessary; if the number of failed cells exceeds 15% of the total, the entire module must be replaced and re-matched for impedance. System-level maintenance involves overall架构 upkeep, including insulation performance checks of high-voltage wiring and contact resistance measurements of connectors. Relay components subjected to more than three high-current shocks are preventively replaced to avoid future failures.
| Maintenance Level | Key Actions | Quantitative Thresholds | Post-Repair Verification |
|---|---|---|---|
| Cell Level | 筛选 and constant voltage repair | Capacity衰减 ≤ 30% | Insulation resistance test |
| Module Level | Impedance matching and replacement | Failed cells ≤ 15% | 72-hour simulated operation |
| System Level | Insulation and connector checks | Relay shocks ≥ 3 | Third-party certification |
Professional maintenance facilities for EV power battery must incorporate multiple protective systems. The spatial layout should separate live operation areas from static observation zones, equipped with independent exhaust systems and gas concentration monitoring devices. Explosion-proof walls must have a fire resistance rating of at least 2 hours, and conductive floor coatings should maintain a resistance value between $10^4$ and $10^6$ ohms. Personnel are required to wear static-dissipating overalls, and tools must be equipped with equipotential bonding devices to ensure that potential differences remain below the 36 V safety threshold during operations. These precautions are essential for handling retired China EV battery safely and preventing accidents.
Decisions on replacing key components in EV power battery systems are based on量化 assessment indicators. For example, copper-aluminum composite连接 sheets must be replaced if the contact resistance increases by more than 50% of the initial value or visible oxidation layers appear. Insulation materials are replaced when the dielectric loss tangent exceeds 0.05 or the breakdown voltage drops by 40%. After replacement,显微 infrared spectroscopy检测 is used to assess the compatibility between new and old materials, preventing structural cracks due to differences in thermal expansion coefficients. This meticulous approach ensures the longevity and safety of repurposed China EV battery units.
Post-maintenance certification follows a three-tier verification mechanism. The initial inspection includes insulation resistance tests and airtightness checks to eliminate basic hazards. The re-inspection phase involves continuous operation under simulated conditions for 72 hours, recording voltage fluctuations and temperature distribution data. The final certification is conducted by third-party agencies, focusing on the completeness of maintenance records and the clearance of fault codes. For batteries intended for energy storage applications, an additional 2-hour rate discharge test is performed to ensure they meet the safety entry standards for echelon utilization. This comprehensive process validates the reliability of retired EV power battery after repair.
In a typical case analysis, a 20 MWh energy storage project in eastern China utilized retired EV power battery modules to build a peak-shaving system. Our team applied a multi-dimensional evaluation model to筛选 over 3,000 retired modules, selecting 900 units that met the criteria. Cell-level inspections revealed that 12% of the units had electrolyte leakage, which was repaired using vacuum filling technology. During system reconfiguration, laser welding optimized module connections, reducing inter-cluster internal resistance differences to within 3%. Monitoring data over six months of operation showed that the repaired battery groups, under daily charge-discharge cycles, exhibited a 40% lower capacity decay rate compared to unrepaired groups, demonstrating the effectiveness of our graded maintenance standards for China EV battery.
Another case involved a low-speed electric vehicle company in southern China that established a battery repair center, handling approximately 20,000 sets of retired batteries annually. Addressing common issues like terminal corrosion, maintenance personnel developed a composite process of chemical polishing and nickel plating, restoring contact resistance to over 95% of the factory standard. For insulation material replacement, new composite materials with matched dielectric constants were used, reducing partial discharge levels. After repair, the battery groups underwent a 3,000 km road test, maintaining energy efficiency above 80% of the initial value, with a 60% reduction in repair costs compared to new purchases. This case highlights the economic benefits of standardized maintenance for EV power battery in China.
Based on our analysis, we recommend building a standardized framework for retired China EV battery that includes a hierarchical structure of basic universal standards, technical method standards, and evaluation norms. Basic standards should define terminology and safety thresholds, while technical standards detail core process parameters for activities like cell revitalization and module reassembly. Evaluation norms should set differentiated acceptance indicators for various application scenarios. We propose updating these standards every 24 months to incorporate emerging technologies, such as fast-charging battery repair and solid-state battery inspection. This adaptive approach ensures that the standards remain relevant as EV power battery technology evolves.
A full-process regulatory mechanism is essential to bridge data gaps across the industry chain. We suggest establishing a coding and traceability management platform for retired batteries, enabling tracking from recovery to disposal. A combination of self-inspection by enterprises and government spot checks should be implemented, with blind sample comparisons for testing agencies and a blacklist system for maintenance quality. Additionally, a risk预警 mechanism should automatically trigger fuse protection when temperature differences or capacity deviations within battery clusters exceed critical values. This integrated system enhances the safety management of China EV battery throughout their lifecycle.
For personnel qualification, we advocate a tiered certification system.初级 technicians should master basic disassembly and insulation detection skills, while高级 engineers need expertise in fault diagnosis and system reconfiguration. Training courses should cover six modules, including electrochemistry principles and high-voltage protection, with assessments using virtual simulation platforms to test emergency response capabilities. A continuing education credit system should require technicians to complete 40 hours of annual training on new technologies, ensuring they keep pace with industry advancements in EV power battery handling.
In conclusion, the safe echelon utilization of retired China EV battery is pivotal for environmental sustainability and economic efficiency. Our proposed inspection and maintenance standards, supported by empirical data and case studies, provide a robust framework for mitigating risks. By implementing graded testing, repair protocols, and standardized regulations, stakeholders can enhance the safety and reliability of EV power battery in secondary applications. Future efforts should focus on continuous improvement of these standards, fostering innovation in battery technologies and promoting a circular economy in the electric vehicle industry.