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Understanding silicon failure opens path to higher-capacity button battery cr2032

In silicon-wire lithium-ion batteries, electrolytes strip away silicon, which blocks electron pathways and greatly reduces the rechargeability of these promising devices.

The new paper (Nature Nanotechnology, "Progressive growth of the solid–electrolyte interphase toward the Si anode interior causes capacity fading") identifies this process as opening new avenues for research that could ultimately harness silicon's vast potential to revolutionize high-capacity, long-lasting batteries for everything from cell phones to cars.

"With this new understanding, we propose to improve the performance of silicon nanowire lithium-ion batteries by developing a coating approach that isolates silicon from the electrolyte," said Jinkyung Yoo, a Los Alamos National Laboratory staff scientist and corresponding author of the paper. Yoo is a semiconductor nanomaterials grower at the Center for Integrated Technologies (CINT), a Department of Energy user facility at Los Alamos and Sandia national laboratories.

Photos of silicon nanowires grown on stainless steel disks (clockwise from upper left) are shown in side, top, and macro views. The disks are about the size of a quarter. New research from Nature Nanotech has uncovered processes that limit the use of silicon in lithium-ion batteries and identified research pathways to overcome these issues. Batteries with silicon anodes have 10 times the electrical storage capacity of batteries with typical graphite-based anodes. (Image: Los Alamos National Laboratory)

The research, conducted by collaborators from a range of national laboratories and universities, integrated sensitive elemental tomography with cryogenic scanning transmission electron microscopy, an advanced analytical algorithm, and revealed in 3D the relevant structural and chemical evolution of silicon and the interaction of solid electrolytes.

Yoo grows a "forest" of silicon nanowires on a stainless steel disk to serve as an anode for battery experiments. The CINT facility at Los Alamos has the unique ability to grow such silicon wires directly on anodes.

Silicon is considered by both industry and national laboratory researchers to be the most promising high-capacity negative electrode material for practical applications in next-generation lithium-ion batteries. Batteries consist of an anode that brings electrons in and a cathode that moves electrons out to produce an electric current.

Using graphite-based anodes, lithium-ion batteries enable cell phones and electric vehicles to have a range of more than 400 miles. Development of next-generation batteries using silicon anodes, known to have 10 times the storage capacity of graphite anodes, has been hampered by capacity fade after repeated charging.

After 100 charge/discharge cycles, batteries using silicon can only manage 60% of their original storage capacity, not good enough for everyday technology.

Until now, no one knew exactly why.

In early applications, when silicon spherical particles were exposed to an electrolyte and charged, they swelled 300% and destroyed the anode. In all types of batteries, the process of exposing the anode to the electrolyte creates a reaction that forms the SEI. The SEI is essential for battery stability, which is essential for electrochemical reactions in batteries and critically controls how well they work.

When the SEI separates from the anode, as it does from silicon, the electrical contact is broken and the battery's capacity drops.

We used to think nanowires would solve the problem of silicon swelling in electrolytes because a wire can be stretched, but it turns out we didn't understand what was going on, Yoo explained.

The new research found that the electrolyte seeps throughout the silicon, forming pockets of SEI that disrupt the electron pathways, Yoo said. This process disconnects isolated islands of silicon in the anode that do not contribute to the battery's capacity. The next research step, Yoo said, is to coat the silicon particles or nanowires to maintain the integrity of the silicon in the presence of the electrolyte.

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