{"451631":{"#nid":"451631","#data":{"type":"news","title":"Nano-mechanical Study Offers New Assessment of Silicon for Next-gen Batteries","body":[{"value":"\u003Cp\u003EA detailed nano-mechanical study of mechanical degradation processes in silicon structures containing varying levels of lithium ions offers good news for researchers attempting to develop reliable next-generation rechargeable batteries using silicon-based electrodes.\u003C\/p\u003E\u003Cp\u003EAnodes \u2013 the negative electrodes \u2013 based on silicon can theoretically store up to ten times more lithium ions than conventional graphite electrodes, making the material attractive for use in high-performance lithium-ion batteries. However, the brittleness of the material has discouraged efforts to use pure silicon in battery anodes, which must withstand dramatic volume changes during charge and discharge cycles.\u003C\/p\u003E\u003Cp\u003EUsing a combination of experimental and simulation techniques, researchers from the Georgia Institute of Technology and three other research organizations have reported surprisingly high damage tolerance in electrochemically-lithiated silicon materials. The work suggests that all-silicon anodes may be commercially viable if battery charge levels are kept high enough to maintain the material in its ductile state.\u003C\/p\u003E\u003Cp\u003ESupported by the National Science Foundation, the research was reported September 24 in the journal \u003Cem\u003ENature Communications\u003C\/em\u003E.\u003C\/p\u003E\u003Cp\u003E\u201cSilicon has a very high theoretical capacity, but because of the perceived mechanical issues, people have been frustrated about using it in next-generation batteries,\u201d said \u003Ca href=\u0022http:\/\/www.me.gatech.edu\/faculty\/xia\u0022\u003EShuman Xia\u003C\/a\u003E, an assistant professor in the \u003Ca href=\u0022http:\/\/www.me.gatech.edu\/\u0022\u003EGeorge W. Woodruff School of Mechanical Engineering\u003C\/a\u003E at Georgia Tech. \u201cBut our research shows that lithiated silicon is not as brittle as we may have thought. If we work carefully with the operational window and depth of discharge, our results suggest we can potentially design very durable silicon-based batteries.\u201d\u003C\/p\u003E\u003Cp\u003ELithium ion batteries are used today in a wide range of applications from hand-held mobile devices up to laptop computers and electric vehicles. A new generation of high-capacity batteries could facilitate expanded transportation applications and large-scale storage of electricity produced by renewable sources.\u003C\/p\u003E\u003Cp\u003EThe challenge is to get more lithium ions into the anodes and cathodes of the batteries. Today\u2019s lithium batteries use graphite anodes, but silicon has been identified as an alternative because it can store substantially more lithium ions per atom. However, storing those ions produces a volume change of up to 280 percent, causing stress that can crack anodes made from pure silicon, leading to significant performance degradation. One strategy is to use a composite of silicon particles and graphite, but that does not realize the full potential of silicon for boosting battery capacity.\u003C\/p\u003E\u003Cp\u003EIn an effort to understand what was happening with the materials, the research team used a series of systematic nano-mechanical tests, backed up by molecular dynamics simulations. To facilitate their study, they used silicon nanowires and electrochemical cells containing silicon films that were about 300 nanometers in thickness.\u003C\/p\u003E\u003Cp\u003EThe researchers studied the stress produced by lithiation of the silicon thin films, and used a nanoindenter \u2013 a tiny tip used to apply pressure on the film surface \u2013 to study crack propagation in these thin films, which contained varying amounts of lithium ions. Lithium-lean silicon cracked under the indentation stress, but the researchers were surprised to find that above a certain concentration of lithium, they could no longer crack the thin film samples.\u003C\/p\u003E\u003Cp\u003EUsing unique experimental equipment to assess the effects of mechanical bending on partially lithiated silcon nanotires, researchers led by Professor Scott Mao at the University of Pittsburgh studied the nanowire damage mechanisms in real-time using a transmission electron microscope (TEM). Their in-situ testing showed that the silicon cores of the nanowires remained brittle, while the outer portion of the wires became more ductile as they absorbed lithium.\u003C\/p\u003E\u003Cp\u003E\u201cOur nanoindentation and TEM experiments were very consistent,\u201d said Xia. \u201cBoth suggest that lithiated silicon material becomes very tolerant of damage as the lithium concentration goes above a certain level \u2013 a lithium-to-silicon molar ratio of about 1.5. Beyond this level, we can\u2019t even induce cracking with very large indentation loads.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Ca href=\u0022http:\/\/www.me.gatech.edu\/faculty\/t_zhu\u0022\u003ETing Zhu\u003C\/a\u003E, a professor in Woodruff School of Mechanical Engineering at Georgia Tech, conducted detailed molecular dynamics simulations to understand what was happening in the electrochemically-lithiated silicon. As more lithium entered the silicon structures, he found, the ductile lithium-lithium and lithium-silicon bonds overcame the brittleness of the silicon-silicon bonds, giving the resulting lithium-silicon alloy more desirable fracture strength.\u003C\/p\u003E\u003Cp\u003E\u201cIn our simulation of lithium-rich alloys, the lithium-lithium bonds dominate,\u201d Zhu said. \u201cThe formation of damage and propagation of cracking can be effectively suppressed due to the large fraction of lithium-lithium and lithium-silicon bonds. Our simulation revealed the underpinnings of the alloy\u2019s transition from a brittle state to a ductile state.\u201d\u003C\/p\u003E\u003Cp\u003EUsing the results of the studies, the researchers charted the changing mechanical properties of the silicon structures as a function of their lithium content. By suggesting a range of operating conditions under which the silicon remains ductile, Xia hopes the work will cause battery engineers to take a new look at all-silicon electrodes.\u003C\/p\u003E\u003Cp\u003E\u201cOur work has fundamental and immediate implications for the development of high-capacity lithium-based batteries, both from practical and fundamental points of view,\u201d he said. \u201cLithiated silicon can have a very high damage tolerance beyond a threshold value of lithium concentration. This tells us that silicon-based batteries could be made very durable if we carefully control the depth of discharge.\u201d\u003C\/p\u003E\u003Cp\u003EIn future work, Xia and Zhu hope to study the mechanical properties of germanium, another potential anode material for high-rate rechargeable lithium-ion batteries. They will also look at all-solid batteries, which would operate without a liquid electrolyte to shuttle ions between the two electrodes. \u201cWe hope to find a solid electrolyte with both high lithium ion conductivity and good mechanical strength for replacing the current liquid electrolytes that are highly flammable,\u201d Zhu said.\u003C\/p\u003E\u003Cp\u003E\u201cThe research framework we have developed here is of general applicability to a very wide range of electrode materials,\u201d Xia noted. \u201cWe believe this work will stimulate a lot of new directions in battery research.\u201d\u003C\/p\u003E\u003Cp\u003E\u003Cem\u003EThis research was supported by the National Science Foundation through grants CMMI-1300458, CMMI-1100205 and NSF-DMR-1410936. The content is solely the responsibility of the authors and does not necessarily represent the official views of the National Science Foundation.\u003C\/em\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003ECITATION\u003C\/strong\u003E: Xueju Wang, et al., \u201c\u003Cem\u003EHigh Damage Tolerance of Electrochemically Lithiated Silicon\u003C\/em\u003E,\u201d (Nature Communications, 2015). (\u003Ca href=\u0022http:\/\/dx.doi.org\/10.1038\/ncomms9417\u0022\u003Ehttp:\/\/dx.doi.org\/10.1038\/ncomms9417\u003C\/a\u003E).\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EResearch News\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EGeorgia Institute of Technology\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003E177 North Avenue\u003C\/strong\u003E\u003Cbr \/\u003E\u003Cstrong\u003EAtlanta, Georgia 30332-0181 USA\u003C\/strong\u003E\u003C\/p\u003E\u003Cp\u003E\u003Cstrong\u003EMedia Relations Contact\u003C\/strong\u003E: John Toon (404-894-6986) (\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E)\u003Cbr \/\u003E\u003Cstrong\u003EWriter\u003C\/strong\u003E: John Toon\u003C\/p\u003E","summary":null,"format":"limited_html"}],"field_subtitle":"","field_summary":[{"value":"\u003Cp\u003EA detailed nano-mechanical study of mechanical degradation processes in silicon structures containing varying levels of lithium ions offers good news for researchers attempting to develop reliable next-generation rechargeable batteries using silicon-based electrodes.\u0026nbsp;\u003C\/p\u003E","format":"limited_html"}],"field_summary_sentence":[{"value":"A new nano-mechanical study of silicon structures offers good news for battery researchers."}],"uid":"27303","created_gmt":"2015-09-24 11:01:31","changed_gmt":"2016-10-08 03:19:36","author":"John Toon","boilerplate_text":"","field_publication":"","field_article_url":"","dateline":{"date":"2015-09-24T00:00:00-04:00","iso_date":"2015-09-24T00:00:00-04:00","tz":"America\/New_York"},"extras":[],"hg_media":{"451571":{"id":"451571","type":"image","title":"Examining thin film silicon","body":null,"created":"1449256280","gmt_created":"2015-12-04 19:11:20","changed":"1475895194","gmt_changed":"2016-10-08 02:53:14","alt":"Examining thin film silicon","file":{"fid":"203343","name":"silicon-anode003.jpg","image_path":"\/sites\/default\/files\/images\/silicon-anode003_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/silicon-anode003_0.jpg","mime":"image\/jpeg","size":1692767,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/silicon-anode003_0.jpg?itok=IxqCKEYR"}},"451581":{"id":"451581","type":"image","title":"Testing lithiated silicon","body":null,"created":"1449256280","gmt_created":"2015-12-04 19:11:20","changed":"1475895194","gmt_changed":"2016-10-08 02:53:14","alt":"Testing lithiated silicon","file":{"fid":"203344","name":"silicon-anode007.jpg","image_path":"\/sites\/default\/files\/images\/silicon-anode007_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/silicon-anode007_0.jpg","mime":"image\/jpeg","size":1401521,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/silicon-anode007_0.jpg?itok=2MKmT7JJ"}},"451591":{"id":"451591","type":"image","title":"Nano-mechanical studies of silicon films","body":null,"created":"1449256280","gmt_created":"2015-12-04 19:11:20","changed":"1475895194","gmt_changed":"2016-10-08 02:53:14","alt":"Nano-mechanical studies of silicon films","file":{"fid":"203345","name":"silicon-anode006.jpg","image_path":"\/sites\/default\/files\/images\/silicon-anode006_0.jpg","image_full_path":"http:\/\/hg.gatech.edu\/\/sites\/default\/files\/images\/silicon-anode006_0.jpg","mime":"image\/jpeg","size":1505174,"path_740":"http:\/\/hg.gatech.edu\/sites\/default\/files\/styles\/740xx_scale\/public\/images\/silicon-anode006_0.jpg?itok=Z86P8CW7"}}},"media_ids":["451571","451581","451591"],"groups":[{"id":"1188","name":"Research Horizons"}],"categories":[{"id":"144","name":"Energy"},{"id":"145","name":"Engineering"},{"id":"149","name":"Nanotechnology and Nanoscience"},{"id":"135","name":"Research"}],"keywords":[{"id":"142581","name":"anode. Shuman Xia"},{"id":"7826","name":"Batteries"},{"id":"142541","name":"lithiated silicon"},{"id":"142571","name":"lithium"},{"id":"142531","name":"nano-mechanical"},{"id":"92451","name":"Ting Zhu"}],"core_research_areas":[{"id":"39451","name":"Electronics and Nanotechnology"},{"id":"39531","name":"Energy and Sustainable Infrastructure"},{"id":"39471","name":"Materials"}],"news_room_topics":[{"id":"71881","name":"Science and Technology"}],"event_categories":[],"invited_audience":[],"affiliations":[],"classification":[],"areas_of_expertise":[],"news_and_recent_appearances":[],"phone":[],"contact":[{"value":"\u003Cp\u003EJohn Toon\u003C\/p\u003E\u003Cp\u003EResearch News\u003C\/p\u003E\u003Cp\u003E\u003Ca href=\u0022mailto:jtoon@gatech.edu\u0022\u003Ejtoon@gatech.edu\u003C\/a\u003E\u003C\/p\u003E\u003Cp\u003E(404) 894-6986\u003C\/p\u003E","format":"limited_html"}],"email":["jtoon@gatech.edu"],"slides":[],"orientation":[],"userdata":""}}}