Batteries work by shifting electrons from one electrode to a different in a circuit by way of an digital system. In a lithium-ion cell, nonetheless, the electrolyte liquid separating these electrodes can evaporate when overheated, inflicting a brief circuit and subsequent chain of exothermic reactions. This makes these small energy vegetation liable to catching hearth and even exploding.
Overcharging and mechanical abuse can improve the chance of damaging the interior regular state, inflicting a pointy improve in inner temperature and undesirable thermal runaway the place a number of cells are chained collectively. At the moment, which means lithium-ion batteries have a comparatively restricted vary of acceptable temperatures and voltages for steady operation.
Earlier work on exterior battery security designs included choices for vents, sensors or thermal fuses. Nonetheless, the addition of exterior parts provides weight, opposite to the preparation of ultra-light and high-performance cells. Optimistic temperature coefficient supplies are additionally an awesome thought, however they’ve disadvantages corresponding to low conductivity and huge leakage present, thus compromising battery efficiency.
Different teams have explored the use and chance of lithium-metal batteries as a substitute of lithium-ion. fire retardant electrolytes can stop the formation of deposits that promote brief circuits. However one other method is with a current-limiting switcher that’s delicate to inner temperature adjustments with out further weight or efficiency limitations. With this in thoughts, a analysis crew in China got down to develop an inner security expertise that may brake a lithium-ion battery and rapidly shut it down if it will get too sizzling.
The authors used a thermally sensitive memory polymer typically coated with conductive copper spray to create a fabric that conducts electrons – its capacity to modify to “insulator mode” throughout overheating. This works based mostly on a microscopic sample programmed into the polymer, which solely happens when the battery reaches temperatures above 197°F; this 3D mannequin can then break up the copper layer and cease the electron circulation. After testing, the “on-off” response was extraordinarily quick, with a full disconnect time of lower than 10 seconds.
In consequence, this expertise has the potential to make lithium-ion batteries a lot safer with out having to compromise on efficiency. However how probably are lithium-ion battery fires? Regardless of the dangers, these are nonetheless uncommon occasions: trade consultants estimate this determine. Less than one fire per 10 million battery cells. Nonetheless, lithium-ion batteries are so extensively used that dependable security options are wanted to fully stop these occasions from occurring.
Learn the total article: Premature Braking of Overheated Lithium-Ion Batteries by Shape Memory Current Collectors
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