Many transition metal sulfides are electronically conductive, electrochemically active and reversible in reactions with lithium. However, the application of transition metal sulfides as sulfur cathode additives in lithium-sulfur (Li-S) batteries has not been fully explored. In this study, Pyrite (FeS 2 ) is studied as a capacity contributing conductive additive in sulfur cathode for Li-S batteries. Electrochemically discharging the S-FeS 2 composite electrodes to 1.0 V activates the FeS 2 component, contributing to the improved Li-S cell discharge energy density. However, direct activation of the FeS 2 component in a fresh S-FeS 2 cell results in a significant shuttling effect in the subsequent charging process, preventing further cell cycling. The slight FeS 2 solubility in electrolyte and its activation alone in S-FeS 2 cells are not the root causes of the severe shuttling effect. The observed severe shuttling effect is strongly correlated to the 1 st charging of the activated S-FeS 2 electrode that promotes iron dissolution in electrolyte and the deposition of electronically conductive FeS on the anode SEI. Pre-cycling of the S-FeS 2 cell prior to the FeS 2 activation or the use of LiNO 3 electrolyte additive help to prevent the severe shuttling effect and allow the cell to cycle between 2.6 V to 1.0 V with an extra capacity contribution from the FeS 2 components. However, a more effective method of anode pre-passivation is still needed to fully protect the lithium surface from FeS deposition and allow the S-FeS 2 electrode to maintain high energy density over extended cycles. A mechanism explaining the observed phenomena based on the experimental data is proposed and discussed.

The oxygen reduction reaction (ORR) at the carbon-conductive polymer-silver (C-cp-Ag) composite electrode in non-aqueous electrolyte with small amounts of added water is the subject of this study. The contributions of the various components of the composite electrode were assessed by employing four electrodes: (1) glassy carbon (C), (2) polypyrrole coated glassy carbon (C-cp), (3) silver disk (Ag), and (4) carbon-polypyrrole-silver composite (C-cp-Ag). Notably, with 5000 ppm of water in non-aqueous solution, the ORR reaction at Ag and C-cp-Ag shows an n = 4 reduction, while ORR at C and C-cp display an n = 1 reduction. The results show that the use of a multilayer C-cp-Ag composite electrode provides the opportunity to achieve the four electron reduction of one O 2 molecule, with a low precious metal (Ag) loading. In metal air batteries, the cathode consists of the electroactive cathode material, oxygen (O 2 ) and the remainder of the inert electrode consisting of the current collector and oxygen reduction reaction (ORR) catalyst. Metal air batteries fall into a special category as the electroactive cathode material, oxygen (O 2 ), is available in excess from outside the battery. While the cathode current collector, the ORR catalyst and the oxygen reduction products all add mass, 1,2 metal air batteries still provide the opportunity for high energy densities relative to sealed battery technologies. 3,4 Notably, the structures and chemistries of the inert electrode (air electrode) can be varied to address ORR kinetic issues. Typically, a composite air electrode consists of an electrical conductor mixed with an ORR catalyst, often strengthened with a binder 5,6 and a support such as a metal mesh. 7,8 A disadvantage of the conventional air electrode fabrication strategy is that catalyst particles positioned within the electrode interior often have limited access to oxygen.With an earlier article, we introduced a new composite electrode paradigm for metal air batteries, and reported the preparation, characterization, and electrochemical activity of a carbon current collector-conductive polymer-silver (cc-cp-Ag) composite electrode. Enhanced oxygen reduction activity for our composite electrode was observed relative to coated glassy carbon or silver disk electrodes, at a low silver loading of < 0.3 mg cm −2 . Specifically, the role of the current collector toward the electrochemical reduction of oxygen, the role of the conductive polymer in improving the structural integrity of the composite electrode, and a quantitative study of the silver loading effect on ORR activity were all investigated. A notable advantage of the electrodeposition based strategy we developed is the ability to easily generate silver coated three-dimensionally structured composites via use of three dimensional electrically conductive substrates. Three dimensional electrodes can increase the active surface area, enabling reduction of more oxygen per unit planar area. This approach was utilized to prepare three-dimensionally structured carboncondu...

The Lithium-Sulfur (Li-S) battery has been a subject of intensive research in recent years due to its potential to provide much higher energy density and lower cost than the current state-of-the-art lithium-ion battery technology.  However, both cell reaction active materials, sulfur and Li2S, are electronically non-conductive, which leads to the low electrode utilization and fast capacity fade during cell cycling.  Large amounts of non-active carbon host materials must be added to boost sulfur electrode electronic conductivity for high rate discharge, which lowers the sulfur electrode specific energy density. Transition metal sulfides have been utilized as cathode material with high energy density and have been demonstrated to be rechargeable in lithium batteries.  Many of these sulfides are electronic conductive with conductivity comparable to that of graphite and carbon black.  Since they are also electrochemically active and can be cycled within the voltage window of sulfur battery, transition metal sulfides could be used as capacity contributing conductive cathode additive for sulfur batteries. We have investigated Titanium Disulfide (TiS2), Pyrite (FeS2) and Cupric Sulfide (CuS) as capacity-contributing conductive cathode additives to the sulfur electrodes in Li-S battery.  Sulfur electrodes containing the metal sulfide additives showed improved power capability under high rate discharge.  While the cyclability of the hybrid electrodes vary widely depending on the type of conductive additive, different and unique electrochemical behaviors were observed for hybrid electrodes with TiS2, FeS2 and CuS respectively.  Improved coin cell cycling performance was observed with TiS2 as the cathode additive at 1C discharge rate.  The TiS2 distribution within the hybrid electrode showed significant impact on cell cycling capacity fade.  The mechanisms associated with the electrochemical performance of each chemical system are discussed.

Battery failure manifested as an increase in cell impedance as a result of cathode dissolution is discussed. Analogous oxide and phosphate based materials exhibit similar electrochemical performance yet the phosphate based materials display increased structural stability and resistance to solvation formation in non-aqueous electrolytes. Structural modifications could optimize existing battery systems and address one of the main causes of increased cell impedance observed over time.