Page | 003 from an exothermic chemical reaction that can result in a chain reaction thermal runaway of adjacent cells.
Manufacturer’s defects such as imperfections and/or contaminants in the manufacturing process can also lead to thermal runaway. The reaction vaporizes the organic electrolyte and pressurizes the cell casing. If (or when) the case fails, the flammable and toxic gases within the cell are released. The severity of a runaway battery reaction relates to the buildup and release of pressure from inside of the cell. Cells with a means of releasing this pressure (i.e., pressure relief vents or soft cases) typically produce less severe reactions than cells that serve to contain the pressure and rupture due to high pressure (i.e., unvented cylindrical cells). As a result, the cell construction can be a major variable pertaining to the severity of a battery incident.
The resulting reaction can look anywhere from a rapid venting of thick smoke (i.e., smoke bomb/smoker), to a road flare, to a steady burn, to a fireball to an explosion. See Figure 3.
Smokers Flares Burners Fireballs Explosions
Figure 3. General Battery Reactions
The severity of the reaction is generally a function of a number of parameters including battery size, chemistry, construction and the battery state of charge (SOC). In almost every significant battery reaction, the same hazardous components are produced, flammable by-products (e.g., aerosols, vapors and liquids), toxic gases and flying debris (some burning), and in most instances, sustained burning of the electrolyte and casing material.
During a venting reaction (i.e., no ignition of the vented products), the products consist primarily of electrolyte constituents. For most batteries, the products typically consist of carbon dioxide (CO2), carbon monoxide (CO), hydrogen (H2) and hydrocarbons (CxHx). These gases are flammable and present fire and explosion risk.
For the burning scenario, the electrolyte burns efficiently producing primarily carbon dioxide (CO2) and water (H2O) as the by-products. For most batteries, the products typically consist of CO2 and water vapor. The burning reaction also tends to liberate the fluorine from the lithium salt (typically LiPF6) dissolved in the electrolyte. The fluorine typically reacts with hydrogen to form hydrogen fluoride (HF). HF production is also proportional to the electrical energy stored in the cell/battery and can result in dangerous concentrations. HF reacts with the water vapor produced during the reaction and/or with the mucus membranes in the human body (i.e., eyes, nose, throat, lungs) and becomes hydrofluoric acid.
BEST STORAGE AND USE PRACTICES Procurement
• Purchase batteries from a reputable manufacturer or supplier.
• Avoid batteries shipped without protective packaging (i.e., hard plastic or equal).
Page 3 of 6 | November 2021 | www.ehs.washington.edu | Lithium-Ion Battery Safety
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