Overcharge and thermal destructive testing of lithium metal oxide and lithium metal phosphate batteries incorporating optical diagnostics

•Imaging, including schlieren, show external features of battery abuse failures.•Venting spray forms in two regions: radially outwards and axial to the cell.•Thermal loading/overcharge combination are more energetic than either alone.•Reconnection (via internal short) in combination abuse leads to secondary failure.•Weak shock waves were seen in tests of K2 26650 lithium iron phosphate cells.

Lithium batteries have a tendency to fail violently under adverse conditions leading to the rapid venting of gas. Overcharge, thermal heating, and a combination of the two conditions are applied here to investigate the gas venting process. A test chamber has been constructed with data recordings including chamber pressure and temperature, battery voltage, current, and surface temperature as functions of time throughout the charging and failure processes. High-speed imaging and schlieren flow visualization are used to visualize the gas venting process. A direct comparison between lithium iron phosphate based K2 26650 and lithium nickel manganese cobalt oxide LG 18650 cells is made through a test series of the three failure methods. Failure under thermal, overcharge, and thermal-overcharge conditions are generally similar in terms of the gas venting process, but are observed to have increasingly energetic failures. The thermal-overcharge abuse condition demonstrates an ability to reconnect via internal short circuit even after an initial electrical failure seen as the refusal to accept charge. This reconnection is associated with a secondary, more energetic failure which can produce weak shock pressure waves.