Nanostructure Makes Batteries Better on Very First Charge

A tri-layered nanostructure for Li-ion anodes protects lithium from ambient air during manfuacturing

2 min read
Graphite/PMMA/Li trilayer electrode
Graphite/PMMA/Li trilayer electrode before (left) and after (right) being soaked in battery electrolyte for 24 hours. Before soaking in electrolyte, the trilayer electrode is stable in air. After soaking, lithium reacts with graphite and the color turns golden.
Photos: Yuan Yang/Columbia Engineering

Various nanomaterials have been drafted into the quest to improve the charge capacity of anodes (negative electrodes) in lithium-ion batteries. Their role primarily has been to help silicon—which offers ten times the charge capacity of graphite—last more than just a few charge/discharge cycles. Everything from graphene to nanofibers have been enlisted into help silicon better survive the rigors of the expansion and then contraction that occurs when silicon anodes are charged and discharged.

Now scientists at Columbia University have developed a nanostructure for the silicon anode of Li-ion batteries that will help them overcome one of their most challenging moments: the very first charge/discharge cycle that occurs during manufacturing.

It is in the manufacturing process of Li-ion batteries where the batteries first lose their energy capacity. After a Li-ion battery is first produced, it is goes through its first charge/discharge cycle so that part of its liquid electrolyte is reduced to a solid and that coat the anode of the battery. This process irreversibly depletes the amount of energy a battery can store by 10 percent for regular anodes but as much as 20 to 30 percent for next-generation silicon-based anodes.

“Through our design, we've been able to gain back this loss, and we think our method has great potential to increase the operation time of batteries for portable electronics and electrical vehicles,” said Yuan Yang, an assistant professor at Columbia, in a press release.

In research described in the journal Nano Letters, Yang and colleagues fabricated a three-layer structure for the anode consisting of silicon, lithium, and a polymer coating called PMMA (Polymethyl methacrylate). PMMA remains stable even in ambient air, providing a longer lasting battery that is cheaper to manufacture.

The battery industry has traditionally dealt with the problem of energy loss during the first charge/discharge cycles by adding more lithium-rich materials to the electrode. However, this was problematic because these materials are not stable in ambient air. In order to create conditions in which lithium-rich materials would not react to the moisture in the air, industry would create perfectly dry environments, which increased manufacturing costs.

The new tri-layered electrode structure developed by the Columbia researchers uses the PMMA to ensure that the lithium is not exposed to ambient air or moisture. The polymer layer is covered with an active material that can be artificial graphite or silicon nanoparticles. The polymer layer then dissolves in the electrolyte of the battery, which then exposes the lithium to the electrode.

“This way we were able to avoid any contact with air between unstable lithium and a lithiated electrode,” Yang explained. “So the trilayer-structured electrode can be operated in ambient air. This could be an attractive advance towards mass production of lithiated battery electrodes.”

The measured effects of this tri-layered structure for the manufacturing process are pretty striking. In state-of-the-art graphite electrodes the loss of capacity went down from 8 percent to 0.3 percent. The impact is even more dramatic in silicon-based anodes where the loss of capacity went from 13 percent to minus 15 percent, meaning that the electrode had more lithium than it actually needed. This extra bit of lithium comes in handy later in the batteries life after many charge/discharge cycles.

In continued research, Yang and his Columbia colleagues are looking to make the polymer layer even thinner and in so doing take up less room in the battery. The researchers are also looking at ways that they can scale up the technique.

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3 Ways 3D Chip Tech Is Upending Computing

AMD, Graphcore, and Intel show why the industry’s leading edge is going vertical

8 min read
Vertical
A stack of 3 images.  One of a chip, another is a group of chips and a single grey chip.
Intel; Graphcore; AMD
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A crop of high-performance processors is showing that the new direction for continuing Moore’s Law is all about up. Each generation of processor needs to perform better than the last, and, at its most basic, that means integrating more logic onto the silicon. But there are two problems: One is that our ability to shrink transistors and the logic and memory blocks they make up is slowing down. The other is that chips have reached their size limits. Photolithography tools can pattern only an area of about 850 square millimeters, which is about the size of a top-of-the-line Nvidia GPU.

For a few years now, developers of systems-on-chips have begun to break up their ever-larger designs into smaller chiplets and link them together inside the same package to effectively increase the silicon area, among other advantages. In CPUs, these links have mostly been so-called 2.5D, where the chiplets are set beside each other and connected using short, dense interconnects. Momentum for this type of integration will likely only grow now that most of the major manufacturers have agreed on a 2.5D chiplet-to-chiplet communications standard.

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