Research press release


Nature Communications

Materials science: Look inside an overheating Li-ion battery


今回、Paul Shearingたちは、2種類の市販のリチウムイオン電池(セル1とセル2)を外部から加熱し、熱画像法と非侵襲的高速度イメージングを用いて、内部構造を観察した。セル1は、故障を起こしても元の外形を保ち、発熱反応は完了した。その結果、電池の通気孔から最初は高温ガス、次いで溶解物質が噴出した。セル1内部の銅材料は溶けてしまっており、内部温度が摂氏1,085度以上に達したことを示している。セル2の場合には、内圧が急上昇してキャップ全体が外れた。現実の状況下でこれが起これば、電池内に酸素が流れ込み、熱暴走が加速する可能性がある。


For the first time, the failure of a lithium ion (Li-ion) battery due to overheating has been recorded, reports a paper published in Nature Communications. Li-ion batteries are vulnerable to thermal runaway, which occurs when the rate of heat generation is greater than the rate of heat lost. Although battery failure is rare, prevention of thermal runaway presents one of the greatest challenges for the safe operation of lithium-ion batteries.

Paul Shearing and colleagues subjected two commercial Li-ion batteries (Cell 1 and Cell 2) to external heat and used thermal imaging and non-invasive high speed imaging techniques to observe the internal structure. Cell 1 remained intact during battery failure which allowed the heat-generating reactions to run to completion, resulting in hot gas and then molten material jetting out through the battery’s vent. Copper material inside Cell 1 melted, indicating internal temperatures of at least 1,085°C. The rapid pressure rise in Cell 2 caused the entire cap of the cell to detach, which in real-world situations, could increase thermal runaway by allowing oxygen into the cell.

The authors found that thermal and electrochemical reactions inside both cells produced gas pockets that deformed the spiral wound layers of the cells. Cell 2 showed severe internal distortion of its architecture, which the authors suggest compromised the safety of the cell. Unlike Cell 2, Cell 1 was designed with a central cylindrical support, which seemed to help maintain structural integrity. The authors hope that their observations of the response of cells to thermal runaway will lead to improvements in the design of Li-ion batteries and improve their safety features.

doi: 10.1038/ncomms7924

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