Solid State NMR and Pair Distribution Function Studies of Silicon Electrodes for Lithium-Ion Batteries

The universally used negative electrode material in a LIB is carbon, because of its moderate capacity (372 mAhg-1 for graphite), cyclability and high rate capability. However, new, low cost, safe electrode materials with higher capacities are still urgently required for both portable and transportation applications. Silicon anodes are particularly attractive alternatives to carbon with extremely high gravimetric energy densities (3572 mAhg-1). Compared to graphite, silicon has a massive volumetric capacity of 8322 mAhcm-3 (calculated based on the original volume of silicon) which is approximately ten times that graphite. At room temperature, upon electrochemical lithiation, silicon undergoes a crystalline to amorphous phase transition forming a lithiated amorphous silicide phase. Unfortunately, due to the amorphous nature of the lithiated silicides, it is not possible to monitor all the structural changes that occur during lithium insertion/removal with conventional methods such as diffraction. The short range order of the amorphous materials remains unknown, preventing attempts to optimize performance based on electrochemical-structure correlations. In this work, a combination of local structure probes, ex-situ 7Li nuclear magnetic resonance (NMR) studies and pair distribution function (PDF) analysis of X-ray data was applied to investigate the changes in short range order that occur during the initial charge and discharge cycles. The distinct electrochemical profiles observed subsequent to the 1st discharge have been shown to be associated with the formation of distinct amorphous lithiated silicide structures. A (de)lithiation model consisting of four different mechanisms, each being valid for regions of the charge or discharge process is proposed to explain the hysteresis and the steps in the electrochemical profile observed during lithiation and delithiation of Si. A spontaneous reaction of the fully lithiated lithium silicide with the electrolyte is directly observed in the in situ NMR experiments; this mechanism results in self-discharge, and potentially capacity loss. The rate of this self-discharge process is much slower when CMC (carboxymethylcellulose) is used as the binder. Previous work has shown that the electrochemical performance of nanoparticulate crystalline silicon is different from the bulk. The lithiation and delithiation mechanisms of nano-Si for lithium ion batteries are studied by using ex-situ solid state MAS NMR and PDF analysis. The main differences vs. bulk lithiation and delithiation are identified by characterizing the amorphous phases formed

Synthesis, structural and electrochemical properties of V4O9 cathode for lithium batteries

Single-phase three-dimensional vanadium oxide (V4O9) was synthesized by reduction of V2O5 using a gas stream of ammonia/argon (NH3/Ar). The as-synthesized oxide, prepared by this simple gas reduction method was subsequently electrochemically transformed into a disordered rock salt type-“Li3.7V4O9” phase while cycling over the voltage window 3.5 to 1.8 V versus Li. The Li-deficient phase delivers an initial reversible capacity of ∼260 mAhg−1 at an average voltage of 2.5 V vs. Li+/Li0. Further cycling to 50 cycles yields a steady 225 mAhg−1. Ex situ X-ray diffraction studies confirmed that (de) intercalation phenomena follows a solid-solution electrochemical reaction mechanism. As demonstrated, the reversibility and capacity utilization of this V4O9 is found to be superior to battery grade, micron-sized V2O5 cathodes in lithium cells

Consequences of Utilizing a Redox-Active Polymeric Binder in Li-ion Batteries

Development of new polymeric binders can help enable the use of silicon-rich anodes in Li-ion batteries, by providing stronger adhesion to the active material particles. The compositional features that improve interfacial interactions and mechanical properties can often impart electronic conductivity and redox activity to these polymers, which are generally seen as beneficial to cell performance. Alternatively, it is also possible that the addition of charge-transferring centers to the electrode can accelerate cell degradation. Here, we use an aromatic polyimide (~320 mAh/g of reversible capacity) to explore how a redox-active conductive polymer can affect cell performance. We demonstrate that the lithiated polymer is less stable than the traditional binders upon storage, leading to increased rates of calendar aging. Furthermore, we show that the adhesion properties of the polymer deteriorate upon repeated cycling, to an extent that is proportional to the degree of delithiation of the binder. More critically, we show that progressive degradation of the redox behavior of the polymer leads to the release of extra Li+ into the cell, which can give the false perception of good performance even under conditions of poor stability. Our work suggests that redox-active conductive binders can sometimes be detrimental to cell performance, and that works evaluating new polymers must include careful experimental validation under realistic conditions

Silicon Anodes with Improved Calendar Life Enabled By Multivalent Additives

Silicon is widely recognized as the most promising upgrade for graphite anodes due to its much higher capacity, natural abundance, and ability to be directly applied in the slurry-based, roll-to-roll production lines. However, in addition to the fast capacity decay, silicon anodes also suffer from inferior calendar life in practical applications due to the unstable solid-electrode interface (SEI). Until now, strategies to effectively improve the calendar life by tailored SEIs remain largely unclear, especially in high-Si content, zero-graphite anodes. Here, silicon anodes with superior calendar life are developed by adding small concentrations of multivalent salts into the baseline electrolyte. The Ca additive reacts with the F ions in the electrolyte, forming a layer of nanocrystalline CaF2 that is closely coated around the silicon particles. The CaF2-enabled new SEI is strong and dense, which effectively protects the silicon core from side reactions, leading to lower capacity decay after calendar aging at high voltage. More importantly, the Ca additive is effective universally for all available commercial silicon or SiO sources. This study provides a feasible and low-cost solution for developing silicon anodes with long calendar life, paving the way towards commercially viable silicon anodes

Level of education and the risk of lymphoma in the European prospective investigation into cancer and nutrition.

INTRODUCTION: Lymphomas belong to the few cancer sites with increasing incidence over past decades, and only a few risk factors have been established. We explored the association between education and the incidence of lymphoma in the prospective EPIC study. MATERIALS AND METHODS: Within 3,567,410 person-years of follow-up, 1,319 lymphoma cases [1,253 non-Hodgkin lymphomas (NHL) and 66 Hodgkin lymphomas (HL)] were identified. Cox proportional hazard regression was used to examine the association between highest educational level (primary school or less, technical/professional school, secondary school, university) and lymphoma risk. RESULTS: Overall, no consistent associations between educational level and lymphoma risk were observed; however, associations were found for sub-groups of the cohort. We observed a higher risk of B-NHL (HR = 1.31, 95% CI = 1.02–1.68; n = 583) in women with the highest education level (university) but not in men. Concerning sub-classes of B-NHL, a positive association between education and risk of B cell chronic lymphatic leukaemia (BCLL) was observed only in women. In both genders, the risk of diffuse large B cell lymphoma (DLBCL) was significantly lower for subjects with university degree (HR = 0.46, 95% CI = 0.27–0.79) versus lowest educational level. No association was found for HL. CONCLUSION: We could not confirm an overall consistent association of education and risk of HL or NHL in this large prospective study; although, education was positively related to the incidence of BCLL and B-NHL (in women) but inversely to incidence of DLBCL. Due to limited number of cases in sub-classes and the large number of comparisons, the possibility of chance findings can not be excluded

Utilization of 29Si MAS-NMR to Understand Solid State Diffusion in Energy Storage Materials

The properties of many solid-state materials arise from critical interfaces tied to the structure, morphology, and composition of the materials under study. For many materials, identifying components that may be invisible to diffraction techniques or other bulk sensitive techniques (i.e. inductively coupled plasma (ICP)), may cause important information to be overlooked. These can include grain boundary phases, nanoscale coatings, amorphous layers, or second phases that influence the materials environment. In this short review, the use of 29Si MAS NMR as a local probe to detect silicon-containing phases in complex energy storage systems is explored with a focus is on silicon-containing materials and silicon electrodes. Examples highlighting the utility of 29Si MAS NMR include 1) examining copper diffusion into silicon as a method to create 3 dimensional electrodes, 2) using Mg(II) electrolyte additives to create in-situ nanoscale silicide coatings to inhibit low voltage parasitic side reactions and extend calendar life, and 3) studying the lithiation reactions of passivated silicon on different time scales.</jats:p

Direct Observation of Magnesium Ion Intercalation into a Spinel-Structured λ-Manganese Oxide at the Multi Length Scale

The growing market of electric vehicles and grid storage requires the current battery technology to be further advanced. However, LIBs, the best energy storage system based on redox reactions, are intrinsically limited in their charge storage capacity by structural and/or electronic factors. Multivalent ion storage systems are attractive among the alternative systems because, while they closely resemble systems using Li-ion, they can store more charge per mol of intercalated species. In particular, Mg-ion batteries are of great interest to surpass the current performance barriers of Li-ion technology. There is only one proven working positive electrode material, Chevrel phase, for Mg ion battery at a relatively low working voltage window.1, 2 When searching for high voltage Mg-intercalation positive electrodes, most previous studies of the possible electrochemistry of oxide compounds Mg2+ electrolytes have provided little information on the reaction mechanisms leading to the electrochemical data.3  In this work, direct evidence of the reversible intercalation of Mg2+ into a spinel host was obtained. The structural changes observed after intercalation/deintercalation into the cubic spinel structure, λ-MnO2, and from tetragonal Mg x Mn3-x O4 nanoparticles will be discussed.  Experimental observations by XRD, XAS, STEM-EDX, PDF and NMR were used to provide a robust understanding of the electrochemical reactions (see representative STEM-EDX in Figure 1).  The results confirm that spinel oxides are a potential cathode material for Mg batteries. They point at needs in the understanding of the mechanisms involved in multivalent ion storage, as well as the most efficient ways to characterize these reactions.  ADDIN EN.REFLIST 1.            D. Aurbach, Z. Lu, A. Schechter, Y. Gofer, H. Gizbar, R. Turgeman, Y. Cohen, M. Moshkovich, and E. Levi, Nature, 407 (6805), 724-727 (2000). 2.            H. D. Yoo, I. Shterenberg, Y. Gofer, G. Gershinsky, N. Pour, and D. Aurbach, Energ Environ Sci, 6 (8), 2265-2279 (2013). 3.            C. Yuan, Y. Zhang, Y. Pan, X. Liu, G. Wang, and D. Cao, Electrochimica Acta, 116 (0), 404-412 (2014). Figure 1 <jats:p /

Synthesis and Characterization of Lithium-Ion Conducting Ceramics for Lithium Metal Batteries

Abstract not Available.</jats:p

High Energy X-ray Scattering Studies as a Tool to Understand the Structural Changes that Occur Opon Lithium Deintercalation of Li[NixLi1/3-2x/3Mn2/3-x/3]O2 (0{Less than or Equal to}x{Less than or Equal to}1/2)

Abstract not Available.</jats:p