The repurposing of batteries, particularly lithium-ion batteries from electric vehicles, for secondary applications such as stationary energy storage is gaining traction as a sustainable solution to extend battery life and reduce waste. However, the lack of uniform standards for assessing, grading, and deploying repurposed batteries poses significant challenges. Emerging standards aim to address these gaps by establishing clear protocols for state-of-health evaluation, performance classification, and safety validation to ensure reliability in second-life applications.

State-of-health (SoH) assessment is the cornerstone of battery repurposing. SoH indicates the remaining useful capacity of a battery relative to its original specifications and is typically expressed as a percentage. Standardizing SoH measurement requires consistent methodologies for capacity testing, internal resistance analysis, and cycle life estimation. Current efforts focus on defining test conditions, including charge-discharge rates, temperature controls, and resting periods between tests, to minimize variability in results. A critical challenge lies in accounting for diverse battery chemistries, aging mechanisms, and prior usage histories, which can lead to inconsistent degradation patterns. For example, a battery cycled extensively at high temperatures may exhibit different degradation characteristics compared to one stored at partial charge for extended periods. Standardized SoH protocols must accommodate these variations while providing reliable metrics for second-life suitability.

Performance grading systems are another key area of standardization. Repurposed batteries are often categorized into tiers based on their residual capacity, power capability, and expected cycle life in secondary applications. A typical grading framework may include:
- Grade A: Batteries with over 80% residual capacity and low internal resistance, suitable for high-demand applications like commercial energy storage.
- Grade B: Batteries with 60-80% residual capacity, appropriate for less demanding uses such as residential storage or backup power.
- Grade C: Batteries below 60% capacity, often relegated to low-power applications or recycled.

These classifications help match batteries to appropriate second-life uses, but inconsistencies in testing methods can lead to misgrading. Standardization efforts aim to harmonize grading criteria, ensuring that batteries with similar performance characteristics are grouped uniformly across the industry. Additionally, grading systems must consider not only capacity but also power retention, thermal behavior, and cycle stability under second-life conditions.

Safety requirements for repurposed batteries are paramount, as degraded batteries may exhibit increased vulnerability to thermal runaway or mechanical failure. Emerging standards emphasize rigorous safety testing, including:
- Electrical abuse tests: Overcharge, short-circuit, and forced discharge scenarios to evaluate failure modes.
- Mechanical tests: Crush, vibration, and impact resistance assessments to simulate real-world conditions.
- Thermal tests: Exposure to extreme temperatures and thermal propagation analysis to gauge stability.

Degraded batteries often have weakened separators, increased electrode brittleness, or electrolyte decomposition, which can elevate safety risks. Standards must account for these factors by mandating additional safeguards, such as enhanced battery management systems (BMS) with tailored algorithms for second-life operation. For instance, a repurposed battery may require more conservative voltage and temperature limits than a new one to mitigate failure risks.

Standardizing degraded battery performance presents several challenges. First, the lack of historical data on long-term degradation in second-life applications makes it difficult to predict performance accurately. Batteries may degrade differently in stationary storage than in electric vehicles due to varying charge-discharge profiles and environmental conditions. Second, the heterogeneity of battery designs, chemistries, and aging histories complicates the creation of universal standards. A battery from one manufacturer may age differently than another, even under similar usage conditions, due to differences in cell construction or materials. Third, economic factors influence standardization. Strict standards may increase testing costs, making repurposing less viable, while lenient standards risk compromising safety and performance.

Efforts by organizations such as the International Electrotechnical Commission (IEC) and the Institute of Electrical and Electronics Engineers (IEEE) are underway to develop comprehensive frameworks for repurposed batteries. These frameworks aim to balance technical rigor with practicality, ensuring that standards are both scientifically sound and economically feasible. Key focus areas include:
- Defining minimum SoH thresholds for second-life eligibility.
- Establishing standardized testing protocols for performance and safety.
- Creating certification processes to validate compliance.

The evolution of these standards will play a critical role in scaling the repurposed battery market, providing clarity for manufacturers, recyclers, and end-users. As the industry matures, continuous refinement of standards will be necessary to address emerging technologies, new degradation patterns, and evolving safety concerns. The goal is to create a robust ecosystem where repurposed batteries can deliver reliable, safe, and sustainable energy storage solutions.