Daniela Molina Piper

Reversible High‐Capacity Si Nanocomposite Anodes for Lithium‐ion Batteries Enabled by Molecular Layer Deposition

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%.

Stable silicon-ionic liquid interface for next-generation lithium-ion batteries

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.

Ionic liquid enabled FeS2 for high-energy-density lithium-ion batteries.

High-energy-density FeS2 cathodes en-abled by a bis(trifluoromethanesulfonyl)imide (TFSI-) anion-based room temperature ionic liquid (RTIL) electrolyte are demonstrated. A TFSI-based ionic liquid (IL) significantly mitigates polysulfide dissolution, and therefore the parasitic redox shuttle mechanism, that plagues sulfur-based electrode chemistries. FeS2 stabilization with a TFSI(-) -based IL results in one of the highest energy density cathodes, 542 W h kg(-1) (normalized to cathode composite mass), reported to date.

In Situ Transmission Electron Microscopy Probing of Native Oxide and Artificial Layers on Silicon Nanoparticles for Lithium Ion Batteries

Surface modification of silicon nanoparticles via molecular layer deposition (MLD) has been recently proved to be an effective way for dramatically enhancing the cyclic performance in lithium ion batteries. However, the fundamental mechanism of how this thin layer of coating functions is not known, which is complicated by the inevitable presence of native oxide of several nanometers on the silicon nanoparticle. Using in situ TEM, we probed in detail the structural and chemical evolution of both uncoated and coated silicon particles upon cyclic lithiation/delithation. We discovered that upon initial lithiation, the native oxide layer converts to crystalline Li2O islands, which essentially increases the impedance on the particle, resulting in ineffective lithiation/delithiation and therefore low Coulombic efficiency. In contrast, the alucone MLD-coated particles show extremely fast, thorough, and highly reversible lithiation behaviors, which are clarified to be associated with the mechanical flexibility and fast Li(+)/e(-) conductivity of the alucone coating. Surprisingly, the alucone MLD coating process chemically changes the silicon surface, essentially removing the native oxide layer, and therefore mitigates side reactions and detrimental effects of the native oxide. This study provides a vivid picture of how the MLD coating works to enhance the Coulombic efficiency, preserves capacity, and clarifies the role of the native oxide on silicon nanoparticles during cyclic lithiation and delithiation. More broadly, this work also demonstrates that the effect of the subtle chemical modification of the surface during the coating process may be of equal importance to the coating layer itself.

Hierarchical Porous Framework of Si‐Based Electrodes for Minimal Volumetric Expansion

A tunable hierarchical porous framework is fabricated to house the volumetric changes outputted by Si. The nSi@cPAN/cPAN electrodes only expand by 14.3% at full initial lithiation and remain within 23% expansion from its uncycled state after 20 cycles with remarkable cycling stability and high coulombic efficiencies in excess of 99.5%.

Optimized Silicon Electrode Architecture, Interface, and Microgeometry for Next‐Generation Lithium‐Ion Batteries

Optimized performance of silicon-ionic- liquid lithium-ion batteries through the implementation of a new electrode-microgeometry. The incorporation of 1D silicon nanowires into the cyclized-polyacrylonitrile-based electrode-architecture allows for greatly improved active material utilization, higher rate capabilities, and reduced interfacial reactions.

Doped Si nanoparticles with conformal carbon coating and cyclized- polyacrylonitrile network as high-capacity and high-rate lithium-ion battery anodes

Doped Si nanoparticles (SiNPs) with conformal carbon coating and cyclized-polyacrylonitrile (PAN) network displayed capacities of 3500 and 3000 mAh g(-1) at C/20 and C/10, respectively. At 1 C, the electrode preserves a specific discharge capacity of ∼1500 mAh g(-1) for at least 60 cycles without decay. Al2O3 atomic layer deposition (ALD) helps improve the initial Coulombic efficiency (CE) to 85%. The dual coating of conformal carbon and cyclized-PAN help alleviate volume change and facilitate charge transfer. Ultra-thin Al2O3 ALD layers help form a stable solid electrolyte interphase interface.

In Situ Engineering of the Electrode–Electrolyte Interface for Stabilized Overlithiated Cathodes

The first-ever demonstration of stabilized Si/lithium-manganese-rich full cells, capable of retaining >90% energy over early cycling and >90% capacity over more than 750 cycles at the 1C rate (100% depth-of-discharge), is made through the utilization of a modified ionic-liquid electrolyte capable of forming a favorable cathode-electrolyte interface.