![\"Lithiation](\"http:\/\/cafe.foundation\/blog\/wp-content\/uploads\/2016\/08\/HZB-lithiation-528x360.jpg\")
Lithiation in HZB cell, with majority of lithium ions adsorbed in thin layer closest to electrolyte boundary layer. \u00a0Lithium ions migrate through the electrolyte (yell0w) into the layer crystalline silicon (c-SI). \u00a0During the charging cycle, a 20-nm layer (red) develops on the silicon electrode, adsorbing extreme quantities of lithium ions. \u00a0Illustration: HZB<\/p><\/div>\n
Scientists at the HZB, led by \u00a0by Prof. Matthias Ballauff have directly observed for the first time a lithium-silicon half-cell during its charging and discharge cycles<\/a>.\u00a0 Dr. Beatrix-Kamelia Seidlhofero carried out the experiments using the neutron source located at the Institute Laue-Langevin in Grenoble, France.\u00a0 She explains, \u201cWe were able to precisely track where the lithium ions adsorb in the silicon electrode using neutron reflectometry methods, and also how fast they were moving.\u201d<\/p>\n This precision allowed the team to see how lithium ions \u201cmigrate\u201d into thin films of silicon \u2013 often the center of experiments to increase the energy stored in lithium batteries.\u00a0 Researchers determined the energy storage capacity of lithium-ion batteries \u201cmight be increased by six times\u201d by using silicon instead of graphite in the anodes.<\/p>\n Substantiating the idea that \u201cless is more,\u201d Dr. Seidlhofero found that, \u201cLithium ions do not penetrate deeply into the silicon. During the charge cycle, a 20-nm anode layer develops containing an extremely high proportion of lithium. This means extremely thin layers of silicon would be sufficient to achieve the maximal load of lithium.\u201d<\/p>\n Since 20 nanometers equals only 0.0000000787 inches, the material layer is extremely thin, and the materials needed to react with it are exceedingly small.\u00a0 Dr. Seidlhofero found two different zones on the test electrodes, with the action taking place close to the surface.\u00a0 Near the boundary to the electrolytes, the 20-nm layer showed extremely high lithium content, with 25 lithium atoms lodged among 10 silicon atoms.\u00a0 A second, adjacent layer contained only one lithium atom for 10 silicon atoms.\u00a0 Both layers combined are less than 100 nm thick after the second charging cycle, according to researchers.<\/p>\n Materials such as graphite used in many batteries can only \u201cstably adsorb\u201d a small number of lithium ions during charging.\u00a0 Silicon can adsorb many more ions, but tends to crack under stress.\u00a0 This stressing and relaxation eventually causes electrodes to crumble and batteries to fail.\u00a0 Other researchers have tried a variety of fixes for this problem over the last several years.<\/p>\n Note lithiation occurs most strongly at interface of electrode and electrolyte. Illustration: HZB<\/p><\/div>\n In HZB\u2019s testing, after discharging the battery, the team found about one remaining lithium ion per silicon node in the electrode\u2019s silicon boundary layer exposed to electrolytes.\u00a0 The fact that most of the activity takes place at a surface level might prevent flexing and cracking at deeper levels, but that\u2019s just your editor\u2019s shallow surmise.<\/p>\n The HZB\u00a0 press release concludes, \u201cSeidlhofer calculates from this that the theoretical maximum capacity of these types of silicon-lithium batteries lies at about 2300 mAh\/g. This is more than six times the theoretical maximum attainable capacity for a lithium-ion battery constructed with graphite (372 mAh\/g).\u201d<\/p>\n The Institute adds a grace note that \u201cvery thin silicon films should be sufficient for adsorbing the maximum possible amount of lithium, which in turn would save on material and especially on energy consumed during manufacture \u2013 less is more!\u201d<\/p>\n Certainly a 6X battery, all that much lighter for the same level of energy, would be heaven-sent as far as aircraft are concerned.<\/p>\n HZB’s findings are published as,\u00a0\u00a0“Lithiation of Crystalline Silicon As Analyzed by Operando Neutron Reflectivity,” in ACS Nano<\/em>. <\/a>\u00a0Authors include\u00a0Beatrix-Kamelia Seidlhofer, Bujar Jerliu, Marcus Trapp, Erwin H\u00fcger, Sebastian Risse, Robert Cubitt, Harald Schmidt, Roland Steitz, and Matthias Ballauff.<\/strong><\/p>\n![\"Note](\"http:\/\/cafe.foundation\/blog\/wp-content\/uploads\/2016\/08\/HZB-lithiation-2.gif\")