Safety and reliability are the key concerns when determining the right power source for a medical device. Lithium-ion (Li-ion) batteries are often considered for their higher energy density, lighter weight, longer cycle life, superior capacity retention, and ability to withstand a broad range of ambient temperatures. However, with an increasing number of potentially dangerous incidents — including fires and explosions — from Li-ion batteries, quality assurance is more important than ever for error and risk prevention, particularly for medical devices that use these power sources. Having a holistic quality approach across the battery product lifecycle is essential for achieving safe, high-quality, and environmentally friendly products.
Quality and your safety are the main requirements of Li-ion battery packs. For the development and manufacture of Li-ion battery packs, many factors must be considered from a quality assurance perspective in order to ensure basic requirements.
Battery pack definition. Quality assurance should already be a part of the creation and definition of the requirements proposal for the Li-ion battery pack to be developed. Therefore, the markets, customer needs, and application requirements must be considered. All applicable standards and regulations must also be included in the proposal. In addition, it is important to consider future requirements, recognizing which standards and regulations might change or be added during the development.
Supplier/manufacturer’s qualifications. The qualification of suppliers and manufacturers runs parallel to the development process. The selection and qualification is driven by the standard requirements and the previously defined requirements document. At this stage, fundamental quality management standards, as described in ISO 9001, ISO 13485, TS 16949, and ISO 14001, must be adhered to by suppliers and manufacturers.
The correct choice of suppliers to battery manufacturers and OEMs is crucial. Good supplier management includes supplier selection, supplier qualification, supplier development, and supplier assessment. This starts with an appropriate supplier selection process. Once a supplier has been chosen, it is necessary to assess, develop, and improve this supplier over time according to the requirements (see Figure 1).
For components and assemblies that do not conform to a standard, the manufacturing processes must be viewed in more detail and, where required, these processes must be validated and/or the results must be verified. Outsourced processes are also included in this assessment. The flowchart in Figure 2 provides the steps to follow and questions to ask to help identify when processes need to be validated.
The statistical process control, which is the recording of process key figures and the actions for correction and improvement derived from this work, should be used as an aid for controlling the manufacturing process.
Product development is based on the requirements catalog and runs parallel to the supplier development process noted above. Based on the requirements catalog, the battery is developed and tested and then verified by an internal department or external independent body. The requirements catalog can include everything from essential operational requirements and related functional requirements to features and benefits of the device. This qualification approach will determine whether the battery has met the criteria according to the V-model, a verification and validation model that reviews the implementation process over time from project definition through test and integration.
The battery is subjected to different tests and testing standards (e.g., electrical safety, temperature, shock, and vibration tests) in various environmental conditions (humidity, temperature, pressure). Charging and discharging cycles are performed with various current flows. The battery is then checked in the overall application system, making sure it meets all requirements.
Temperature and the value of charging/discharging currents has shown to be a special stress factor for the lifecycle and charge cycles of Li-ion batteries. Each battery carries its own risk, which must be assessed. There is a risk on the battery-cell level, and there is also the risk that the Li-ion battery poses in the medical device application. The use of process failure modes, effects, and criticality analysis (P-FMECA) is a common method of risk assessment, risk analysis, and risk/error. This method can be used to determine the cell-level risks as well as those that may be encountered once integrated into the medical device.
The materials used for the batteries must also be qualified during development. The battery supplier or an independent test laboratory must provide proof that the materials meet the requirements. The requirements catalog and the FMECA determine what those requirements must be.
Furthermore, the material flow — the flow and stock of materials between processes through the system — is also subject to quality assurance. Material flow analysis software is an example of one tool that has proven suitable for this task, which starts with the qualification of the material by means of initial sample inspection reports within the framework of the battery development.
Manufacturing. In the battery manufacturing process, the incoming material is subjected to an incoming materials test. It may also have been inspected at the manufacturer when it was shipped. For an incoming materials test, random samples are taken according to the defined acceptance quality limit (AQL) and tested according to predetermined test specifications.
In battery manufacture, a relevant quality control (QC) inspection is performed after each production step. It is important to distinguish between 100 percent QC testing and random sample testing, which consists of in-process quality control steps (IPQC). For IPQC steps, random sample quantities are tested at regular predetermined intervals, defined by quantity or time, in order to monitor the production process.
All assembled battery packs should undergo a 100 percent materials outgoing control (OQC). This multistep testing method provides for different quality gates through which a Li-ion battery pack must pass, thus ensuring the manufacturing and product quality.
Traceability. Each individual battery cell has its own serial number, which, in combination with the serial number of the assembled printed circuit board (PCB) in the memory chip of the pack, can also be linked to an ID number on the outside of the pack. This linking of the different numbers creates a unique device identifier (UDI). Additionally, the date code must be printed on the battery pack label. This marking allows for the identification of the assembly groups used.
This battery pack information, including manufacturing information, is stored, together with the results of the outgoing testing, in a separate external secured database. The traceability of the individual cells, the assembled PCBA, and the relevant battery pack production data, is therefore ensured (see Figure 3).
Logistics. Before lithium-metal or Liion cells and battery packs can be transported, they must be tested according to the UN38.3 testing method for transport. When this test is passed, the battery packs are marked accordingly with the UN symbol (see Figure 4). For the transport of Li-ion batteries, the correct packaging, package size, and quantity must be observed. Only Li-ion packs marked with the UN symbol may be transported. Without this marking, a transport permit is required.
Quality Assurance in the Marketplace
After the batteries enter the market in finished medical devices, quality assurance measures continue. A complaint management system according to the requirements of ISO 13485 guides this process.
All complaints related to batteries from the market are analyzed. For this, the frequency of the individual error indication is analyzed. For each error indication, the error causes are determined via an 8D error report (a structured corrective action process), which initiates correctional or preventative and improvement measures. The errors most commonly identified during analysis are “Ichikawa” and “5W” error codes.
The actions for improvement follow the PDCA (plan, do, check, act) cycle, a systematic series of steps for the continual improvement of a product or process, also known as the Deming Cycle (see Figure 5).1 In addition, the error risk and its effect on persons and property must be assessed for each error. Finally, market observations help all manufacturers in recognizing and preventing errors before their own products or the battery packs in their devices display these errors.
Environmental considerations. With an increase in environmental awareness and the impact of batteries on the environment, a functioning environmental management system is becoming more important than ever. Batteries contain a variety of chemicals and are toxic to the humans, wildlife, and the environment. Manufacturers of Li-ion battery packs and their production processes are checked to determine whether they comply with the current quality management standards (e.g., ISO 14001) and regulations (e.g., RoHS, REACH). In addition, the issues of ecological balance and the carbon footprint must be taken into account in the manufacture of Li-ion batteries.
In the EU, entities that put batteries on the market are obliged to take them back and must inform consumers where and how they can dispose of batteries for recycling. Li-ion batteries must be marked with the WEEE (Waste of Electrical and Electronic Equipment) label (represented by a crossed-out garbage bin) as well as with the Li-ion recycling symbol.
Furthermore, each country has its own recycling and statutory environmental requirements, which must be met. For Europe, these are the Restriction of Hazardous Substances (RoHS) Directive 2002/95/EC, the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulation, and the Battery Directive (2006/66/EC). For China, the China RoHS directive applies. Figure 6 shows an example of a battery with various country approvals and recycling symbols.
U.S. manufacturers follow the EU’s RoHS Directive. Also in the United States, the Rechargeable Battery Recycling Corporation (RBRC), a nonprofit organization dedicated to rechargeable battery recycling, has launched the Call2Recycle program with more than 30,000 Call2Recycle drop-off locations throughout the United States and Canada (see Figure 7). More than 175 manufacturers and marketers of portable rechargeable batteries and products fund the Call2Recycle program to help prevent rechargeable batteries from entering the solid waste stream.
Social responsibility. The United States is considered the pioneer in social responsibility. In 2010, the United States set new requirements for the minerals used in products, based on the OECD “Due Diligence Guidance” within the meaning of social responsibility.2 The regulation was codified in the Dodd-Frank Wall Street Reform and Consumer Protection Act – Conflict Minerals. All companies that commit to this regulation declare that the minerals tantalum, tin, tungsten, and gold that are used in their products (components) do not originate from the countries Democratic Republic of the Congo, Angola, Burundi, Central African Republic, Republic of the Congo, Rwanda, South Sudan, Tanzania, Uganda, or Zambia. Many U.S. and globally active companies have committed to the Dodd-Frank Act.
Development, design, testing, producing, and delivering a high-quality Li-ion battery pack requires a commitment to and an embracement of quality assurance. By following the guidelines above, companies can move toward developing exceptional products that are also safe and environmentally friendly. Moreover, batteries that meet these stringent requirements are suitable for integration into medical devices from neurostimulators and other implantables to portable monitors and infusion pumps.
- Deming, W.E.: Out of the Crisis. Massachusetts Institute of Technology, Cambridge 1982, ISBN 0-911379-01-0, S. 88.
- OECD (2013), OECD Due Diligence Guidance for Responsible Supply Chains of Minerals from Conflict-Affected and High-Risk Areas: Second Edition, OECD Publishing. ISBN 978-92-64-18501-2 (print), ISBN 978-92-64-18505-0 (PDF)
This article was written by Ulrich Sonndag, director of corporate quality, QMR, for RRC Power Solutions GmbH, Homburg, Germany. For more information, Click Here .