Safety of lithium-ion battery

The number of rechargeable lithium-ion batteries used in cordless applications is well above one billion units per year and it is expected to grow in the mid-term. Despite the high safety standards used in the production of these batteries, several incidents have been reported, raising questions about the safety of this technology. The aim of this document is to describe the risks associated with this technology, and how they are managed in order to guarantee a safe use of lithium- ion batteries. The following conclusions are drawn from this study. 1.

The safety protection is a fundamental function integrated in a lithium-ion battery, minimizing the occurrence of the flammability hazard and its consequences by a combination of prevention, protection and mitigation systems: Prevention and protection includes electronic protections, mechanical design and electric design incorporating the necessary redundancies to ensure the reliability of the safety protection: current and voltage control, state of charge and temperature management… 0 Mitigation systems reduce the consequences of defaults or abuse, e. G. Maternal shorts, temperature elevation, excess current, mechanical damage, through the usage of safety vents, heat protection or evacuation systems, mechanical protections… 2. Product compliance with well established international or private standards ultimate that the safety protection is adapted to the intended use. In addition, lithium-ion batteries have to be qualified for transport according to a UN safety standard, requiring manufacturers to comply with Safety Test requirements and a Quality Management System. One of the safest energy storage systems.

Billions of electrical and electronic equipments powered by these batteries are used worldwide on a daily basis confirming that the safety of lithium-ion batteries is well managed. 4. The major hazard offered by lithium-ion battery technologies is the evolution of a fire, as a exult of the flammability of the substances used in the battery. A large majority of incidents reported recently found their origin in the following: 0 Non-respect of UN provisions and packaging requirements prior to the transport of lithium-ion batteries.

Cells assembly by non-professionals for innovative applications. Concentration of lithium-ion cells in non-controlled storage conditions or areas. The lithium-ion battery Industry and RECHARGE are working at various levels of International and National Institutions to improve and guarantee the safety of lithium-ion batteries during use and transport while this battery technology is undergoing a strong market development. 3 A lithium-ion battery is an electrochemical device optimized to store and release energy in the context of a specific application.

All energy storage systems, whatever the system used, have a risk of unexpected environmental conditions or defaults which could create an accidental or uncontrolled energy release. Specific environmental conditions are often used to test and characterize the stability of the energy storage system, defining the frontier between the acceptable conditions of use and the abusive conditions. In case of accidental abusive conditions or defaults reducing some potential hazard occurrence, mitigations measures can be taken to avoid hazardous consequences.

Using this information, products can be designed to control their safety with appropriate means both for the risk prevention and for the consequences mitigation while controlling any hazardous event during normal usage. Table 1 below is describing some examples for different energy storage systems and the type of hazard they can offer. It appears that lithium-ion batteries have different behavior compared to other battery technologies, requiring the use of suitable risk intro and potential hazard mitigation, specifically relative to the so-called “thermal run-away’ associated with a fire hazard.

The aim of this document is to describe what are the risks associated with this technology, and how they are managed in order to guarantee a safe use of lithium-ion batteries. Energy storage Potential hazard Hazard Prevention Potential hazard control Water storage (hydraulic systems, dams,.. ) Rupture, water flows Avoid corrosion and mechanical rupture Manage water streams Liquid fuels (gasoline, diesel, ethanol,… ) Fire, explosion Avoid sparks, flames Manage fire and fume emissions Lead acid and Alkaline

Rechargeable batteries Hydrogen gas release (mainly in overcharge), explosion, Acid and Alkali release Avoid battery electrical abuse (e. G. Voltage control and protection) Manage gas flow release, neutralize spillage of acid or alkali,… Lithium-ion batteries corrosive electrolyte release, fire Avoid heat or flames, and battery electrical abuse. Manage fire and fumes emissions, neutralize spillage of electrolyte. TABLE 1 . Examples of different energy storage systems and the associated potential hazard. 4 3.

Lithium-ion batteries: key features The lithium-ion battery technology is currently used in a large range of applications, doth on the consumer, professional and industrial markets. Portable-Rechargeable Electronic devices such as mobile phones, laptops and tablets Cordless Power Tools E-Mobility Electric-Bikes Plug-In Hybrid Vehicles Electric Vehicles Stationary Industrial Energy Power Stations Modular units for Grid Interface Supply of ancillary services to the electrical grid Others Aeronautics Military, Marine,…

While other types of batteries, including lead-acid and nickel-metal hydride (in the first generation of the Toyota Pries hybrid) will continue to retain considerable market share in the short term, thumb-ion batteries are expected to dominate the market by 2017. Compared with other relevant battery types, lithium-ion batteries have the highest energy density as shown in Figure 2. Significant further improvements to the technology are expected in the coming years due to increases in the cell performance or via the battery engineering and design.

FIGURE 2. Energy Density Range for various battery technologies. (source. DAIMLER 2011) In the future, there will be also high demand for these batteries in the energy storage sector. Indeed, lithium-ion is also a technology of choice for large renewable energy arms in which smoothing functions are required along with ancillary services to the network (frequency regulation, primary power regulation), as both these requirements place a high demand on the battery cycling ability. 3. 2. Chemistry and technology 3. 2. 1 . A wide range of battery chemistries.

All lithium-ion technologies are based on the same principle: Lithium is stored in the anode (or negative electrode) and transported during the discharge to the cathode (or positive electrode) via an organic electrolyte. This principle is illustrated in Figure 3. The most popular materials are graphite for the anode and a metal oxide for most of Cobalt or made of iron phosphate. All of these materials have good lithium insertion or intercalation properties, allowing the storage of a large amount of electrical energy under a chemical form.

Some of them are illustrated in Figure 4. A. And 4. B. FIGURE 4. A. Various type of cell formats: cylindrical and prismatic lithium-ion battery As illustrated in Figure AAA, hard case cylindrical or prismatic cells are produced: these cells are generally made of an aluminum can with laser-welded or crimped cover. They contain liquid electrolyte. Soft case or В« pouch cells В» are also produced as shown in Figure b. These cells are using a thin illuminated plastic bag, glued with efferent type of polymers for the tightness.

In general, they contain a gel or polymer electrolyte which Justifies the qualification of “lithium-ion polymer” battery. FIGURE 4. B. Various type of cell formats: The pouch cell of a lithium-ion Polymer battery 8 The cells are assembled to form battery packs and batteries, embedded in hard casing with electro-technical and electronic management systems (BUMS).