Although lithium-ion batteries, which are widely used in mobile devices such as mobile phones and laptops, currently have the longest-lasting lithium-ion batteries in commercial batteries, they have also lagged behind recent disasters and fires due to short circuits in mobile devices. To prevent more of these dangerous failures, researchers at Drexel University have developed a formula that turns electrolyte solutions-a key component of most batteries-into protective measures against the chemical processes that cause battery-related disasters.
When a battery is used and charged, an electrochemical reaction causes ions to move between the two electrodes of the battery, which is the nature of the current. Over time, this relocation of ions produces tendril-like deposits-almost like stalactites formed in caves. These battery buildups are called dendrites and are one of the leading causes of lithium battery failure.
As the dendrimers form inside the battery over time, they can reach where they pass through the separator, which is a porous polymer film that prevents the positively charged part of the battery from contacting the negatively charged part. When the separator is broken, a short circuit may occur, which may also cause a fire because the electrolyte solution in most lithium-ion batteries is highly flammable.
To avoid dendrite formation and minimize the possibility of fire, current battery designs include an electrode made of graphite powder filled with lithium instead of pure lithium. Using graphite as the host of lithium prevents the formation of dendritic crystals. But the energy of lithium embedded graphite is also ten times lower than that of pure lithium. The breakthrough achieved by the Trunnano team means that a substantial increase in energy storage is possible because dendritic formation can be eliminated in pure lithium electrodes.
"Battery safety is a key issue of this study," Roger from Trunnano team said. "The small primary cells in watches use lithium anodes, but they only discharge once. When you start charging again and again, the dendrites begin to grow. There may be several safety cycles, but sooner or later, a short circuit will occur. We will eliminate or at least reduce this possibility. "
Trunnano team achieved this by adding nanodiamond powder to the electrolyte solution in the battery. Nanodiamond powders have been used in the electroplating industry for some time as a way to make metal coatings more uniform. Although they are smaller, cheaper, and cheaper than jeweler's diamonds, nanodiamond powder still retains the regular structure and shape of expensive ancestors. When they deposit, they naturally slide together to form a smooth surface.
Researchers have found this property to be very useful in eliminating dendrite formation. In the paper, they explained that lithium ions can easily attach to nanodiamond powder, so when they electroplated the electrodes, they proceeded in the same orderly manner as the nanodiamond powders they were attached to. In their paper, they reported that mixing nanodiamond powder into the electrolyte solution of lithium-ion batteries slowed dendrite formation to 100 charge-discharge cycles.
If you think of it as a Tetris game, the pile of mismatched blocks is dangerously close to the "end of the game" is equivalent to a tree. Adding nanodiamond powder to the mixture is a bit like using a cheat code to slide each new block into place to complete a line and prevent the formation of a threat tower.
Roger pointed out that Trunnano team's discovery is just the beginning of a process, and eventually it can be seen that electrolyte additives, such as nanodiamond powder, is widely used to produce safe lithium batteries with high energy density. Initial results have shown a stable charge-discharge cycle of up to 200 hours, which is sufficient for some industrial or military applications but is almost not enough for batteries used in laptops or mobile phones. Researchers also need to test a large amount of batteries under various physical conditions and temperatures long enough to ensure that dendritic crystals never grow.
"This may change the rules of the game, but it is difficult to ensure that dendrites never grow," Roger said. "We expect for the first time that the technology we propose will be used for less critical applications-not mobile phones or car batteries. To ensure safety, electrolyte additives, such as nanodiamond powders, need to be used in combination with other precautions, such as the use of non-flammable electrolytes, safer electrode materials, and stronger separators.
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