In this study we embed phase pure natural cubic-FeS 2 (pyrite) in a stabilized polyacrylonitrile (PAN) matrix. The PAN matrix confi nes FeS 2 's electroactive species (Fe 0 and S n 2− ) for good reversibility and effi ciency. Additionally, the stabilized PAN matrix can accommodate the 160% volume expansion of FeS 2 upon full discharge because it is not fully carbonized. At room temperature, our PAN-FeS 2 electrode delivers a specifi c capacity of 470 mAh g −1 on its 50th discharge. Using high-resolution transmission electron microscopy (HRTEM) we confi rm that FeS 2 particles are embedded in the PAN matrix and that FeS 2 's mobile electroactive species are confi ned during cycling. We also observe the formation of orthorhombic-FeS 2 at full charge, which validates the results of our previous all-solid-state FeS 2 battery study.The energy density of conventional Li-ion batteries with LiMO 2 (M = transition metal) cathodes and graphitic anodes is approaching a practical upper limit after two decades of optimization. In order to improve the energy density of Li-ion batteries further, new cathodes must be developed with capacities that compare to those of advanced anodes such as Si. [ 1 ] The FeS 2 conversion chemistry is a promising candidate to replace the LiMO 2 intercalation chemistry because FeS 2 is inexpensive, energy dense, and environmentally benign. The four electron reduction of cubic-FeS 2 (pyrite) with lithium (FeS 2 + 4Li + + 4e −

This paper reports a Si‐Ti‐Ni ternary alloy developed for commercial application as an anode material for lithium ion batteries. Our alloy exhibits a stable capacity above 900 mAh g−1 after 50 cycles and a high coulombic efficiency of up to 99.7% during cycling. To enable a highly reversible nano‐Si anode, melt spinning is employed to embed nano‐Si particles in a Ti4Ni4Si7 matrix. The Ti4Ni4Si7 matrix fulfills two important purposes. First, it reduces the maximum stress evolved in the nano‐Si particles by applying a compressive stress to mechanically confine Si expansion during lithiation. And second, the Ti4Ni4Si7 matrix is a good mixed conductor that isolates nano‐Si from the liquid electrolyte, thus preventing parasitic reactions responsible for the formation of a solid electrolyte interphase. Given that a coulombic efficiency above 99.5% is rarely reported for Si based anode materials, this alloy's performance suggests a promising new approach to engineering Si anode materials.

In this paper we demonstrate an all-solid-state Li-ion battery with a specific energy of 225 mWh g−1 based upon the combined mass of both the composite anode and cathode. To realize this full cell, we pair an iron sulfide and sulfur composite cathode with a Si-based anode. The anode active material is a Si-Ti-Ni alloy with good ionic and electronic conductivity that attains a stable specific capacity of 400 mAh g−1 based upon the total mass of the composite anode. To our knowledge, this is the highest stable Si-based all-solid-state anode specific capacity reported to date. To utilize both a lithium free anode and cathode, we adopt a pre-lithiation technique involving stabilized lithium metal powder. This is the first time that this technique has been demonstrated in an all-solid-state battery.

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Pure tin (Sn) metal nano-powder is investigated as a high capacity negative electrode for rechargeable all-solid-state Li-ion batteries. Sn is used to form a fully dense network intertwining with solid electrolyte negating necessary conductive additive. Galvanostatic cycling of the Sn composite electrode delivers a reversible capacity 800 mAh g −1 of Sn with a constant coulombic efficiency over 99.2%. We report on the effect of pressure and rate upon the delithiation mechanics, drawing correlations between Sn volume increase factors and stress accumulation over the course of Sn-Li phase transformations. Due to the fabricated electrode microstructure, we are able to operate the cell at ambient pressure conditions -the next step toward commercialization of the solid-state battery. We believe that this initial work provides new opportunities to study the electrochemical expansion of Sn with the inclusion of rigid electrolyte particles. In 1997, Fuji announced a tin (Sn)-based amorphous composite oxide material for commercial Li-ion batteries.1 Ensuing anode deployments include the Sony developed Sn-based compound (Sn-Co-C) in 2005.2 Although these were the first commercial deployments of Sn-based anodes, Sn has been extensively studied for decades as a candidate in rechargeable Li-ion batteries because of its substantial lithium storage capabilities and quicker charging times.3 Despite the theoretical capacity of Sn being lower than the currently spotlighted silicon (Si) anode, Sn has exceptionally appealing features: high gravimetric and volumetric capacity (959 mAh g −1 and 2,476 mAh mL −1 for 4.25 Li-ions), 4 excellent electrical conductivity (9.17 × 10 6 S m −1 ), and room temperature Li-ion diffusivity (5.9 × 10 −7 cm 2 s −1 of Li 4.4 Sn). 5 The commercialized Sn-Co-C anode by Sony provides a significant capacity advantage over the currently utilized graphite anode material (372 mAh g −1 ). However, wide use of the Sn-Co-C anode has been limited due to the high cost and environmental concerns about cobalt. Iron and nickel have been introduced as replacements for cobalt forming amorphous Sn-Fe and Sn-Ni with similar electrochemical properties to the Sn-Co alloy.6-10 Despite the low cost and high capacity of the Sn-Fe and Sn-Ni anodes, poor cycling stability and coulombic efficiency (CE) hinder their practical use in Li-ion batteries. These drawbacks mainly result from the notorious volume change of Sn (∼255% when 4.25 Li-ion inserted), 4,11 leading to a loss of electric contact, pulverization, and cracking.12 Therefore, controlling the microstructure of the expandable active material during lithiation/delithiation processes is a key point to realize a high energy-dense Li-ion battery using Sn-based anode materials.Recently, Molina Piper et al. reported the effect of compressive stress on the electrochemical performance of a Si anode in an allsolid-state Li-ion cell, which similarly suffers from pulverization due to immense volume changes.13 By applying external compressive stress to the silicon/solid-state elec...