We report that a solid‐state battery architecture enables the reversible, four electron storage of fully utilized solvothermally synthesized cubic‐FeS2 (pyrite). With a sulfide based glass electrolyte we successfully confine electro‐active species and permit the safe use of a lithium metal anode. These FeS2/Li solid‐state cells deliver a theoretical specific capacity of 894 mAh g−1 at 60 °C. We find that nanoparticles of orthorhombic‐FeS2 (marcasite) are generated upon recharge at 30–60 °C which explains a coincident change in rate kinetics.

We are currently in the midst of a race to discover and develop new battery materials capable of providing high energy-density at low cost. By combining a high-performance Si electrode architecture with a room temperature ionic liquid electrolyte, here we demonstrate a highly energy-dense lithium-ion cell with an impressively long cycling life, maintaining over 75% capacity after 500 cycles. Such high performance is enabled by a stable half-cell coulombic efficiency of 99.97%, averaged over the first 200 cycles. Equally as significant, our detailed characterization elucidates the previously convoluted mechanisms of the solid-electrolyte interphase on Si electrodes. We provide a theoretical simulation to model the interface and microstructural-compositional analyses that confirm our theoretical predictions and allow us to visualize the precise location and constitution of various interfacial components. This work provides new science related to the interfacial stability of Si-based materials while granting positive exposure to ionic liquid electrochemistry.

The molecular-layer deposition of a flexible coating onto Si electrodes produces high-capacity Si nanocomposite anodes. Using a reaction cascade based on inorganic trimethylaluminum and organic glycerol precursors, conventional nano-Si electrodes undergo surface modifications, resulting in anodes that can be cycled over 100 times with capacities of nearly 900 mA h g(-1) and Coulombic efficiencies in excess of 99%.

By cyclizing commercially available polyacrylonitrile (PAN), we show that it is possible to conformally coat nanoparticles of Si with a conjugated polymer. We utilize cyclized-PAN both as a binder and conductive additive because of its good mechanical resiliency to accommodate silicon's (Si) large expansion as well as its good ionic and electronic conductivity. By the 150 th cycle, our nano-Si/cyclized-PAN composite anodes exhibit a specifi c charge capacity of nearly 1500 mAh g − 1 with a coulombic efficiency (CE) approaching 100%. Because Si is naturally abundant and has such a high achievable specifi c capacity, [ 1 , 2 ] the next generation of Lithium-ion batteries will inevitably incorporate an advanced Si based anode like that presented here. At room temperature, Si can accommodate 3.75 mole Li per mole of Si (Li 15 Si 4 ) for a theoretical capacity of 3579 mAh g − 1 . [ 3 , 4 ] Despite these advantages, progress towards a commercially viable Si anode has been impeded by Si's rapid capacity fade, poor ionic transport and low CE.Rapid capacity fade is a primary cause for the delay of Si's commercialization. At room temperature, a volume expansion of 300% occurs upon full lithiation to Li 15 Si 4 . [5][6][7] Such a massive volumetric change can result in cracking and pulverization of the Si particles, which then leads to the interruption of electronic transport pathways and the electrochemical isolation of pulverized particles. [ 2 ] To better accommodate the large stresses and strains generated upon lithiation, utilization of nanoparticles, nanowires, and 3D nano-porous structures have been studied. Nano-Si based structures have the added benefi t of reducing the average Li + diffusion length into Si for faster charge and discharge rates. [8][9][10] However, nano-Si structures often suffer from poor CE due to the continual formation of a solid electrolyte interphase (SEI) layer at the large nano-Si/electrolyte interface. Adding to the frustration, many of these clever nano-Si based engineering solutions are rarely appropriate for commercialization because they may require expensive synthesis techniques. [11][12][13][14][15] Yet, recent work has shown that Si-C nano-composites may be promising candidates for viable, inexpensive, stable and effi cient high capacity anodes. Si-C conventional composites are typically prepared by carbonizing precursors [16][17][18] or by mechanically mixing Si with carbon. [ 19 , 20 ] The result are composites of Si particles embedded in carbon matrices. Unfortunately, these carbon matrices cannot accommodate Si's large volumetric changes because of their tendency for brittle failure. Cracking of these carbon matrices during cycling interrupts electronic conduction pathways and exposes fresh Si to the electrolyte which results in further SEI formation. Several studies using electronically conductive polymer based matrices or coatings have demonstrated better results. [21][22][23][24][25] For example, G. Liu et al. developed a cathodically (n-type) doped polymer binder that mai...

Cycle stability of solid-state lithium batteries (SSLBs) using a LiCoO 2 cathode is improved by atomic layer deposition (ALD) on active material powder with Al 2 O 3 . SSLBs with LiCoO 2 /Li 3.15 Ge 0.15 P 0.85 S 4 /77.5Li 2 S-22.5P 2 S 5 /Li structure were constructed and tested by charge-discharge cycling at a current density of 45 μA cm −2 with a voltage window of 3.3 ∼ 4.3 V (vs. Li/Li + ). Capacity degradation during cycling is suppressed dramatically by employing Al 2 O 3 ALD-coated LiCoO 2 in the composite cathode. Whereas only 70% of capacity retention is achieved for uncoated LiCoO 2 after 25 cycles, 90% of capacity retention is observed for LiCoO 2 with ALD Al 2 O 3 layers. Electrochemical impedance spectroscopy (EIS) and transmission electron microscopy (TEM) studies show that the presence of ALD Al 2 O 3 layers on the surface of LiCoO 2 reduces interfacial resistance development between LiCoO 2 and solid state electrolyte (SSE) during cycling.