n the world of product safety, it could be said that there are two basic approaches to risk mitigation, proactive and reactive, with proactive being the preferred choice. Most would agree with the adage that “an ounce of prevention is worth a pound of cure,” but in truth, this oversimplifies the reality in which product manufacturers operate. As with most things in life, things are rarely black and white but rather a continuous spectrum of shades of gray.
To this, there are many competing aspects in all commercial product ventures. Could you make a product that was fully reliable under all conditions? Perhaps, but the odds are that it would be a commercial failure as it would take an inordinate amount of time to produce and be prohibitively expensive.
In today’s market, the traditional characteristics of safety, time to market, quality, cost, reliability, manufacturability, testability, and usability (to name a few) still apply. But these have been further augmented by more modern concerns of environmental impact, sustainability, social responsibility, and others. We mention these not to offer any judgment but only to note that the expectation that a product will perform flawlessly over its lifecycle is a difficult proposition given the myriad of competing needs.
The battery industry is no different when it comes to satisfying market requirements. With batteries having become ubiquitous in our daily lives as the world has migrated to all things becoming portable, the challenge for providers of these products has increased. With the advent of high-energy, rechargeable lithium-ion chemistries, battery performance has dramatically increased, but so have the risks.
No longer are battery packs simple devices. In most modern electronic products, they are better characterized as complex components of an integrated system with one key difference – most other components of such systems rarely have the ability to spontaneously overheat and burn (i.e., go to “thermal runaway”) with little to no warning, potentially resulting in personal injury, product damage, and the associated legal and market liabilities.
To ensure that such efforts are yielding the desired result, testing of both the components and the battery pack assembly is key, covering the aspects of safety as well as long-term reliability and performance. This testing should be initiated early in the product development process so that, if issues are uncovered, there is the time and flexibility to adjust the design, followed by retesting to verify the efficacy of the changes and to ensure that other problems were not inadvertently introduced. As the development process progresses, production samples should be built and evaluated to understand if manufacturing variations can create unanticipated safety risks.
Common testing protocols involve a combination of electrical, mechanical, and thermal overstress. Some involve the application of faults to better assess the inherent safety robustness of the battery pack. Other tests attempt to evaluate the product for stresses that might be common to a specific industry or use case. At a minimum, battery packs will be tested to the transportation requirements found in UN 38.3. Testing to one of the 62133-2 series of standards (IEC, EN, UL) is also commonly performed and is required for regulatory approval in many global markets.
Testing to such standards is usually conducted by accredited third-party testing laboratories with the end result being the authorized application of the testing lab’s mark to the product. This approval facilitates regulatory acceptance by government authorities and may also be a prerequisite for commercial entities such as retailers and distributors to offer the product for sale. Some approvals also require periodic post-market inspection of production facilities to ensure the design is still being manufactured as originally qualified. Infrequently, a testing laboratory or regulatory agency may mandate retesting when significant changes to the relevant test standards are implemented.
What if the battery pack is simply a purchased component and the purchaser was not involved in the design process and may not even have any visibility into the production of the battery pack? Similarly, what if the purchaser is procuring an end device that has an embedded battery pack? These are both very common situations for retailers and distributors who typically have very limited internal engineering resources.
Certainly, buying such products from reputable sources and checking for the presence of the requisite safety marks is a good start, but is it sufficient? Modern supply chains are global. Therefore, discerning where a product was manufactured and by whom can be a challenge in itself. This means that regardless of the actual manufacturer’s liability, a retailer’s or distributor’s brand can be put in jeopardy by a single video posted on social media that quickly goes viral. How can product risk be mitigated in this situation?
The general answer is to work backward beginning with production samples. A product teardown of new product samples by a knowledgeable third party can aid in assessing what risks exist with purchased products where the detailed design knowledge is not available. Although every product is different, an evaluation of a product from a portable energy safety perspective might include such items as:
- Verification of any regulatory marks on the product. Was the testing actually done and is the regulatory status current?
- Evaluation of insulating methods including their integrity and consistency
- Evaluation of conductor sizing
- Review of manufacturing quality indicators that might equate to latent defects
- Review of the safety circuit or other protective devices for proper operation under abnormal conditions such as over-voltage, over-current, short-circuit, and under-voltage
- Review of the charging circuit design. Does it subject the battery or cell to improper conditions?
- Determination of the cell manufacturer and type. This also includes an assessment of whether the cell might be counterfeit
- Cell examination (radiographs and/or CT scans), teardown, and construction analysis
- Review of the mechanical design of the product in terms of its ability to protect the safety-critical components
- End-user instructions and safety warnings
Many times, the criteria are drawn from marketing assertions as shown on the products’ packaging. Examples might include the number of hours that the device will operate in a given mode before needing to be recharged and how long that recharge might take. The evaluation can also go much further, perhaps considering the relative drop performance from a given height or the number of charge-discharge cycles before a loss of function is detected.
As a general rule, safety concerns tend towards the absolute given the nature of such risks to people and property. Conversely, performance concerns lend themselves towards a more relative evaluation against other competing market options.
With the right facilities and expertise available, a determination must be made about how to force the cell or battery into thermal runaway. Overcharging and surface heating are two common methods, although the design of the product and the chemistry of the cells will guide what method is most appropriate. Other considerations for such testing involve what data is to be collected and how. Video evidence is considered by most clients to be the most useful. It should be further supported by appropriate logging of relevant temperatures and possibly other product parameters, as well as forensic documentation of the actual effects to the end-product.
Although the above is presented in a relatively clinical fashion, the danger of injury and property damage is very real. Depending on the energy level of the particular sample, an exploding cell can produce temperatures above 1200 °C (2192 °F) and deadly shrapnel particularly in the case of large-format cells with metal cans. Readers are strongly cautioned to not attempt such testing without the proper expertise and containment equipment.
These factors make clear the importance of using retrospective methods to gain insights into what happened, how it happened, and why it happened. These methods collectively fall under the heading of lithium battery failure analysis.
Failures in the field can happen at any point in the battery’s life cycle and can vary significantly in severity and frequency. Responses to such issues also vary accordingly, ranging from simply replacing a product under warranty to retrieval of the product for a full forensic evaluation. For minor issues, it may be determined that a product change is not warranted. Conversely, safety issues may mandate a full product recall and rework of the design. In the end, failure analysis actions provide after-the-fact knowledge for organizations from which to make decisions that will impact future risk.
- Reduction of personal bias: A third-party test lab has no vested interest in the outcome of the analysis, nor do they have intimate knowledge of the product or company’s history.
- Independent verification: A third-party lab can help to independently verify the findings of an internal team or a supplier.
- Resource utilization: As noted previously, field safety events are generally an infrequent occurrence. Having an internal team staffed with the proper expertise and equipment to respond to such a rare event is generally not possible or even desirable.
- Diligence: In the most severe of cases such as potential product recalls, it may be valuable for the company to have an independent party involved to minimize negative perceptions regarding objectivity.
- Focus: Having failure analysis conducted by an external party may permit the company’s internal teams to remain focused on the day-to-day operations of their mainline business.
- Process rigor: An external testing lab will have already developed the processes and methods for orderly evaluation and documentation of field failures, with specific expertise in evidence preservation.
- Breadth of experience: Because of their focus on failure analysis spread across multiple clients over time, a third-party testing lab will generally have a wider range of technical experience when it comes to what constitutes typical versus atypical findings.
In terms of the supplemental information, basic product information is the starting point. This might include specifications and similar documents to support the work along with any relevant details regarding product history. These will not be used to prematurely assume conclusions, but rather to supplement the physical evidence and help prioritize the investigatory efforts.
Information on the specific unit along with incident details are also very important to piecing together what happened. How was the unit configured? Was it operating in a particular mode? Did the unit demonstrate anything unusual prior to the event? It is best to provide all of the information that is available and let the failure analysis team draw their own conclusions regarding relevance. It is important to realize that as the investigation moves forward, the relevance of such information may change as more information is learned.
The actual failed units will need to be delivered to the laboratory. In this situation, more is better. It is possible that there may be multiple failure modes at play and having additional samples may help to isolate these. It is also important to preserve the evidence as much as possible by limiting unnecessary handling, examining, or actual tampering which might further damage the unit and lead to erroneous findings.
Proper packaging is a must. It is best if all components of the reported system can be provided, i.e., the failed cell or battery, the end-device if applicable, charging devices and cables, etc., as it is possible that the root cause of the failure may have been external to the cell or battery that failed. Samples should be marked or segregated so that it is clear which components go together. In addition to the failed systems, it is also good if a fully functional new system can be provided for purposes of comparison.
What should you expect from your third-party expert? Every investigation is unique, and your provider should work with you to generate a project scope that meets your needs, and they should limit their efforts to that scope. Considerations include specific concerns, communication frequency, deliverables, and budget.
Be aware that the actual work of failure analysis involves a mix of analytical tools such as fault tree analysis (FTA) combined with empirical methods such as x-ray imaging, CT scanning, optical microscopy, product dissection (battery pack and cell teardowns), quantitative measurement, circuit testing, and replication testing. Not every tool is appropriate for every situation. Your provider will provide guidance on these technical aspects. In the end, your provider should provide your team a clear, unbiased analysis report that details the investigation and its associated findings.
What should you not expect from your provider? First, don’t expect speculation. This is a “just the facts” activity. If the evidence doesn’t support it, your provider shouldn’t be offering it up. Second, keep in mind that not every investigation yields the root cause or even the true failure mode. Depending upon the condition of the evidence and nature of the incident, it simply may not be feasible to reach this level of understanding. Conversely, the efforts may seek to eliminate likely root causes thus narrowing the possibilities.
When problems do occur in the field, consider the engagement of a reputable third-party failure analysis organization that specializes in cells and batteries. Their team of experts can help to assess what happened, how it happened, and possibly even why the incident occurred. In turn, your organization can use this information to objectively determine appropriate responses, both immediate and longer-term, to mitigate risk to your customers, your product, and your brand.