(Invited) Side Reactions and Cycling Efficiency with Silicon Electrode Surfaces

Energy storage materials – lithium-based portable energy storage technologies are an area of research that was born in the late 1960s / early 1970s, went global in the 1990s with portable consumer electronics, and is now being adapted to a variety of markets including electrification of vehicles, space flight, and grid storage.  While showing promise, these new applications may have different requirements (e.g. power, cost, volume) than ones optimized for consumer markets.  To increase energy density, many researchers are exploring ways to incorporate silicon into a battery.  Elemental silicon has many properties that make it a top candidate to replace graphitic carbon in next generation lithium-ion batteries.  It has (1) very high gravimetric capacity (~3600 mAh/g), (2) high volumetric capacity (~7400 mAh/L), and (3) low insertion cell voltage.  It also has many problems that must be overcome including (1) high volume expansion on lithiation, (2) an unstable SEI layer, and (3) instability of the fully charged anode to the electrolyte.  Although significant effort has been focused on silicon-based electrodes, e.g. understanding the role of morphology, particle size, or local structure – our work has been concentrated on electrode level interactions.  Using the knowledge gained from the materials level studies we are addressing what happens when the silicon is made into an electrode and exposed to the contents of an electrochemical cell [1-3].  Previous work by the Edstrom group [4-5] has shown that the normal passivation layer of silicon, namely silica, is in fact electrochemically active on the first charging cycle.  On first lithiation it reacts to form Li4SiO4.  This phase does not directly participate in the electrochemistry after this point, but does interact chemically with its environment to effect cycle efficiency and SEI stability [6].  In this talk we will discuss how, upon formation, it interacts with its environment and track these changes by FTIR, 29Si NMR, 7Li NMR, and PXRD with eventual formation of Li6Si2O7 and Li2SiO3. [1] C. Joyce, L.Trahey, S.A. Bauer, F. Dogan, and J, T. Vaughey Journal of The Electrochemical Society, 159,A909-A914 (2012). [2] F. Dogan, C. Joyce, and J. T. Vaughey Journal of The Electrochemical Society, 160,  A312-A319 (2013). [3] F. R. Brushett, L.Trahey, X. Xiao, J. T. Vaughey ACS Appl. Mater. Interfaces , 6, 4524−4534 (2014). [4] B. Philippe, R. DedryveÌre, M. Gorgoi, H. Rensmo, D. Gonbeau, K. Edström   J. Am. Chem. Soc., 135, 9829−9842 (2013). [5] ] B. Philippe, R. DedryveÌre, M. Gorgoi, H. Rensmo, D. Gonbeau, K. Edström   Chem. Mater., 25,394−404 (2013). [6] A. A. Hubaud, Z. Z.  Yang , D. J. Schroeder, F. Dogan, L. Trahey, J. T. Vaughey  Journal of Power Sources 282, 639-644 (2015) Figure 1 <jats:p /

Organosilane Coatings for Ni-Rich High-Voltage Lithium Ion Batteries

One of the more promising cathode materials for high-energy high-voltage lithium ion batteries (LIBs) are Ni-rich layered cathode materials such as LiNixMnyCozO2 (where x + y + z = 1). Although these cathode materials are attractive from a high capacity standpoint, they commonly suffer from poor structural stability at highly delithiated (charged) states leading to poor electrochemical performance.1-3 While incorporation of additives into the electrolyte provides one way to improve cycling performance in LIBs, surface coatings are becoming a widely adopted method to improve the cycling performance of high-voltage cathode materials. More widely investigated coating materials include oxide coatings (Al2O3, TiO2, etc.)4 while comparatively fewer studies have investigated organic monomer or polymer coatings (PEDOT, polyimide, etc.).5 Additionally, the mechanism of the coating interaction with the material is intriguing due to its importance in creating a performance-enhancing coating. In this work, the surface of LiNi0.5Mn0.3Co0.2O2 cathode materials were coated with organosilane reagents to investigate their effect on cell electrochemical performance. The impact of the cathode pretreatment, the weight percentage of organosilane used and the functionality of the organosilane used will be presented. Characterization of the organosilane coating using SEM shows a slight morphological change in the cathode surface while EDX and FTIR confirm the presence of a Si-containing coating. Half cells (Li/ LiNi0.5Mn0.3Co0.2O2) using the organosilane coated cathodes operating in the voltage window of 3.0 - 4.4 V showed similar cycling behavior to that of non-coated material. In conclusion, a new type of organic coating was utilized on Ni-rich cathode materials and this research explores a new type of coating for high voltage cathodes. References 1)      Son, I. H.; Park, J. H.; Kwon, S.; Mun, J. and Choi, J. W. Chem. Mat. 2015, 27, 7370-7379. 2)      Bak, S.-M.; Hu, E.; Zhou, Y.; Yu, X.; Senanayake, S. D.; Cho, S.-J.; Kim, K.-B.; Chung, K. Y.; Yang, X.-Q. and Nam, K.-W. ACS Appl. Mater. Interfaces 2014, 6, 22594-22601. 3)      Lin, F.; Markus, I. M.; Doeff, M. M.; Xin, H. L. Sci. Rep., 2014, 4, 5694. 4)      Xu, S.; Jacobs, R. M.; Nguyen, H. M.; Hao, S.; Mahanthappa, M.; Wolverton, C.; Morgan, D. J. Mater. Chem. A, 2015, 3, 17248. 5)      Zhang, J.; Lu, Q.; Fang, J.; Wang, J.; Yang, J. and NuLi, Y. ACS Appl. Mater. Interfaces 2014, 6, 17965-17973.</jats:p

Excitable Dynamics and Yap-Dependent Mechanical Cues Drive the Segmentation Clock

The periodic segmentation of the vertebrate body axis into somites, and later vertebrae, relies on a genetic oscillator (the segmentation clock) driving the rhythmic activity of signaling pathways in the presomitic mesoderm (PSM). To understand whether oscillations are an intrinsic property of individual cells or represent a population-level phenomenon, we established culture conditions for stable oscillations at the cellular level. This system was used to demonstrate that oscillations are a collective property of PSM cells that can be actively triggered in vitro by a dynamical quorum sensing signal involving Yap and Notch signaling. Manipulation of Yap-dependent mechanical cues is sufficient to predictably switch isolated PSM cells from a quiescent to an oscillatory state in vitro, a behavior reminiscent of excitability in other systems. Together, our work argues that the segmentation clock behaves as an excitable system, introducing a broader paradigm to study such dynamics in vertebrate morphogenesis

Intracellular Oscillations and Waves

Dynamic processes in living cells are highly organized in space and time. Unraveling the underlying molecular mechanisms of spatiotemporal pattern formation remains one of the outstanding challenges at the interface between physics and biology. A fundamental recurrent pattern found in many different cell types is that of self-sustained oscillations. They are involved in a wide range of cellular functions, including second messenger signaling, gene expression, and cytoskeletal dynamics. Here, we review recent developments in the field of cellular oscillations and focus on cases where concepts from physics have been instrumental for understanding the underlying mechanisms. We consider biochemical and genetic oscillators as well as oscillations that arise from chemo-mechanical coupling. Finally, we highlight recent studies of intracellular waves that have increasingly moved into the focus of this research field

Organosilane Cathode Coatings for High-Voltage Lithium Ion Batteries

One of the more promising cathode materials for high-energy high-voltage lithium ion batteries (LIBs) are Ni-rich layered cathode materials such as LiNixMnyCozO2 (where x + y + z = 1). Although these cathode materials are attractive from a high capacity standpoint, they commonly suffer from poor structural stability at highly delithiated (charged) states leading to poor electrochemical performance.1-3 To help aid these issues, surface coatings are becoming a widely adopted method to improve the cycling performance of high-voltage cathode materials. More widely investigated coating materials include oxide coatings (Al2O3, TiO2, etc.)4 while comparatively fewer studies have investigated organic monomer or polymer coatings (PEDOT, polyimide, etc.).5 In this work, the surface of LiNi0.5Mn0.3Co0.2O2 cathode materials were coated with organosilane reagents to investigate their effect on cell electrochemical performance. The impact of the weight percentage of organosilane used and the functionality of the organosilane used will be presented. Characterization of the organosilane coating using XRD, XPS and FTIR confirm the presence of a Si-containing coating. Cycling performance for half cells (Li/ LiNi0.5Mn0.3Co0.2O2) using the organosilane coated cathodes will be shown. In conclusion, a new type of organic coating was utilized on Ni-rich cathode materials and this research explores a new type of coating for high voltage cathodes. 1)      Son, I. H.; Park, J. H.; Kwon, S.; Mun, J. and Choi, J. W. Chem. Mat. 2015, 27, 7370-7379. 2)      Bak, S.-M.; Hu, E.; Zhou, Y.; Yu, X.; Senanayake, S. D.; Cho, S.-J.; Kim, K.-B.; Chung, K. Y.; Yang, X.-Q. and Nam, K.-W. ACS Appl. Mater. Interfaces 2014, 6, 22594-22601. 3)      Lin, F.; Markus, I. M.; Doeff, M. M.; Xin, H. L. Sci. Rep., 2014, 4, 5694. 4)      Xu, S.; Jacobs, R. M.; Nguyen, H. M.; Hao, S.; Mahanthappa, M.; Wolverton, C.; Morgan, D. J. Mater. Chem. A, 2015, 3, 17248. 5)      Zhang, J.; Lu, Q.; Fang, J.; Wang, J.; Yang, J. and NuLi, Y. ACS Appl. Mater. Interfaces 2014, 6, 17965-17973. </jats:p

Interfacial Study of the Role of SiO2 on Si Anodes Using Electrochemical Quartz Crystal Microbalance

One of the challenges associated with silicon as an anode material for Li-ion batteries is the formation of an unstable solid-electrolyte interphase which, forms continuously while consuming lithium and other components; and consequently contributes to irreversible capacity. To elucidate some of the details of the formation and subsequent dissolution of species that form during lithiation of silicon anodes we have produced thin film silicon electrodes with and without an oxide layer and analyzed these during lithiation and delithiation using an electrochemical quartz microbalance with in- situ dissipation (EQCM-D). Measurements were conducted both in EC:EMC and EC:DEC:FEC based electrolytes. Mass loss during lithiation was observed in both solvents systems when an oxide layer was present on the electrode and this was found to be associated with Li2O dissolution using solution and solid state NMR.</jats:p

Plutonium complexation by phosphonate-functionalized mesoporous silica

MCM-41-type mesoporous silica functionalized with the CMPO-based 'Ac-Phos' silane has been reported in the literature (1) to show good capacity as an acftinide sorbent material, with potential applications in environmental sequestration, aqueous waste separation and/or vitrification, and chemical sensing of actinides in solution. The study explores the complexation of Pu(IV and VI) and other selected actinides and lanthanides by SBA-15 type mesoporous silica functionalized with Ac-Phos. The Pu binding kinetics and binding capacity were determined for both the Ac-Phos functionalized and unmodified SBA-15. They analyzed the binding geometry and redox behavior of Pu(VI) by X-ray absorption spectroscopy (XAS). They discuss the synthesis and characterization of the functionalized mesoporous material, batch sorption experiments, and the detailed analyses of the actinide complexes that are formed. Structural measurements are paired with high-level quantum mechanical modeling to elucidate the binding mechanisms