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Yang et al. Energy Mater 2024;4:400061 https://dx.doi.org/10.20517/energymater.2023.144 Page 7 of 23

an external heat source, thus constituting thermal abuse. In addition, overcharging triggers an oxidation
reaction of the cathode electrolyte, releasing gases such as O . Along with the release of heat, the
2
temperature of the battery rises rapidly, leading to a thermal runaway reaction, which mainly results from
the intense reaction between the cathode and the electrolyte at high temperatures. At the same time, long-
term overdischarge will inevitably cause the negative potential of the LMBs to continue to rise until it
reaches the decomposition potential of the SEI. This will lead to SEI rupture and generate more heat, further
accelerating the thermal runaway process and ultimately causing battery combustion or even explosion.
Consequently, evaluating the safety performance of the battery under abusive conditions is crucial for
ensuring its safe operation.

Mechanical abuse
(1) Crush tests

Extrusion deforms the battery structure, causing failures of internal components, such as diaphragm
rupture or rupture of positive and negative materials, which can lead to internal short-circuit.
Consequently, this internal short-circuit generates a substantial amount of Joule heat, ultimately causing the
decomposition of the internal materials of the single cell. According to the national standard GB 38031-
2020, the testing procedure involves placing the fully charged battery between the extrusion plates, which
-1
extrude the battery at a speed of not more than 2 mm s . When the battery voltage drops to 0 V, the
deformation amount reaches 15%, or the extrusion pressure reaches 100 kN and is maintained for 10 min.
Following the extrusion, the battery is observed for one hour, and if no explosion or fire occurs during this
period, it is identified as safe.

(2) Nail penetration tests

The cell penetration test is conducted to simulate the thermal runaway process of a battery by artificially
inducing an internal short-circuit . This is achieved by subjecting the battery to a constant current charge
[63]
of 1C until it reaches the final voltage. Subsequently, a high-temperature steel needle, 5-8 mm in diameter, is
driven through the battery at a speed of (25 ± 5) mm s in a direction perpendicular to the battery pole
-1
piece. The needle is then left in the battery for observation for 1 h. If the battery does not explode or catch
fire during this time, the test is considered successful.

Electrical abuse
LMBs may be overcharged or overdischarged when used in a battery pack because of the different capacities
of the varying cells in the pack and the difficulty of keeping the state-of-charge (SOC) of each cell the same.
Consequently, it is inevitable that the cells in the battery pack will be overcharged or overdischarged to a
certain extent .
[64]

(1) Overcharge test

During the charging process, it is crucial to ensure that the charging current and voltage are within the
recommended limits. Excessive current and voltage can result in overcharge, significantly affecting the
battery life and even leading to safety hazards. To avoid these risks, it is recommended that the battery is
initially charged at a constant current of 1 C to 1.1 times the termination voltage of the battery in
accordance with GB 38031-2020. If the battery does not exhibit signs of explosion or fire during this test, it
can be deemed safe. This testing approach is essential for ensuring the integrity and safety of the charging
process.