While lithium-ion batteries have seen steady improvements, a lot of research has been done into new chemistry that provides an even greater leap in performance. Some of this work has focused on materials such as silicon or sulfur that can store much more lithium than existing electrode materials. But other options get rid of electrode materials entirely. These include lithium air batteries and lithium metal batteries.
I had all of these issues with stability, with the technology-based batteries having shorter lifespans compared to current lithium-ion batteries (although batteries with some silicon are already in use). But on Thursday, a company announced that its lithium-metal battery in development has reached a stability that rivals current lithium-ion batteries, retaining 80 percent of its initial capacity for nearly 700 charge/discharge cycles — and that’s been validated by a lab. external test.
go to metal
Existing Lithium ion batteries They contain polar materials capable of storing lithium ions, or atoms, in gaps and pockets in their structure. Instead, lithium-metal batteries form a layer of lithium at one of the electrodes, eliminating the storage material, saving weight and size. Compared to current lithium-ion batteries, this would store the same amount of charge in either a smaller or lighter battery.
However, to date lithium-metal batteries tend to have limited life spans. Part of the problem comes from the uneven formation of lithium deposits over the course of multiple charge/discharge cycles. This can lead to the formation of metal spines called dendrites that can damage other battery components and possibly create an electrical short. The second problem is that lithium metal is highly reactive and can undergo reactions with chemicals in the battery electrolyte.
The same reactions can lead to electrolyte degradation. But they can also coat the electrode with materials that make it difficult to form a uniform lithium coating, creating a self-reinforcing problem. “All that new surface will react with the electrolyte and form different kinds of materials at the interface,” Wang told Ars. “And then those materials tend to also be shaped in a non-uniform way, and maybe parts of it become insulating, and other parts are exposed, and then you get more and more asymmetry.”
How do you prevent this? Since its founding, Cuberg has focused on the electrolyte. The company uses an ionic liquid as the basis for the electrolyte. Wang described this as an ionic salt that dissolves at room temperature (although the ions are often organic chemicals, not elements). It has been tried previously but tends to be sticky, which interferes with the movement of lithium ions. To help avoid this, Cuberg mixes in additional chemicals (one of which is an organic chemical called ether) to reduce viscosity and improve stability.
While this combination may react with lithium metal, it is designed to cause fewer problems when it does. “The other key factor is how you can tailor the reaction so that when it interacts, you get this kind of protective, uniform surface,” Wang said.
whats the result? For one, the charge density is much higher. While many current lithium-ion batteries have an energy density of 270 Wh/kg, the bag cell based on Cuberg’s technology hit 380 Wh/kg, an increase of 40 percent. When an independent tester put the battery through a one-hour discharge cycle and two-hour charge, it found that the battery took more than 670 cycles for its capacity to drop to 80 percent of its original capacity. For comparison, many lithium-ion batteries target a life of 500 cycles.
Wang noted that this test used a constant charge rate throughout the cycle, while many batteries now use an improved charging routine that changes the rate based on how close the battery is to a full charge. Since creating an even layer of lithium metal is very sensitive to the amount of lithium charge carriers deposited on the electrode, it is possible that better performance can be achieved.
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