In light of the impeding depletion of fossil fuels and necessity to lower carbon dioxide emissions, economically viable high-performance batteries are urgently needed for numerous applications ranging from electric cars to stationary large-scale electricity storage. Due to its low raw material cost, non-toxicity and potentially high charge-storage capacity pyrite (FeS2) is a highly promising material for such next-generation batteries. In this work we present the electrochemical performance of FeS2 nanocrystals (NCs) as lithium-ion and sodium-ion storage materials. First, we show that nanoscopic FeS2 is a promising lithium-ion cathode material, delivering a capacity of 715 mA h g(-1) and average energy density of 1237 Wh kg(-1) for 100 cycles, twice higher than for commonly used LiCoO2 cathodes. Then we demonstrate, for the first time, that FeS2 NCs can serve as highly reversible sodium-ion anode material with long cycling life. As sodium-ion anode material, FeS2 NCs provide capacities above 500 mA h g(-1) for 400 cycles at a current rate of 1000 mA g(-1). In all our tests and control experiments, the performance of chemically synthesized nanoscale FeS2 clearly surpasses bulk FeS2 as well as large number of other nanostructured metal sulfides.

With demands placed on batteries constantly increasing, new positive electrode materials with higher energy density, satisfactory power density, and long-term cycling capabilities, are desired.

A lithium- and manganese-rich layered transition metal oxide (LMR-NCM) cathode active material (CAM) is processed on a pilot production line and assembled with graphite anodes to ≈7 Ah multilayer pouch cells. Each production step is outlined in detail and compared to NCA/graphite reference cells. Using laboratory coin cell data for different CAM loadings and cathode porosities, a simple calculation tool to extrapolate and optimize the energy density of multilayer pouch cells is presented and validated. Scanning electron microscopy and mercury porosimetry measurements of the cathodes elucidate the effect of the CAM morphology on the calendering process and explain the difficulty of achieving commonly used cathode porosities with LMR-NCM cathodes. Since LMR-NCMs exhibit strong gassing during the first cycles, a modified formation procedure based on on-line electrochemical mass spectroscopy is developed that allows stable cycling of LMR-NCM in multilayer pouch cells. After formation and degassing, LMR-NCM/graphite pouch cells have a 30% higher CAM-specific capacity and a ≈5%–10% higher cell-level energy density at a rate of C/10 compared to NCA/graphite cells. Rate capability, long-term cycling, and thermal behavior of the pouch cells in comparison with laboratory coin cells are investigated in Part II of this work.