Electrophoretic Deposition as a Versatile Low-Cost Tool to Construct a Synthetic Polymeric Solid-Electrolyte Interphase on Silicon Anodes: A Model System Investigation.

The cycling of next-generation, high-capacity silicon (Si) anodes capable of 3579 mAh·g-1 is greatly hindered by the instability of the solid-electrolyte interphase (SEI). The large volume changes of Si during (de)lithiation cause continuous cracking of the SEI and its reconstruction, leading to loss of lithium inventory and extensive consumption of electrolyte. The SEI formed in situ during cell cycling is mostly composed of molecular fragments and oligomers, the structure of which is difficult to tailor. In contrast, ex situ formation of a synthetic SEI provides greater flexibility to deposit long-chain, polymeric, and elastomeric components potentially capable of maintaining integrity against the large ∼350% volume expansion of Si while also enabling electronic passivation of the surface for longer cycling and calendar life. Furthermore, polymers are amenable to structural modifications, and the desired elasticity can be targeted by selection of the SEI polymer feedstock. Herein, electrophoretic deposition (EPD) is used to apply chitosan as a synthetic SEI on model Si thin film electrodes. Comparison of synthetic SEIs obtained without (Si/Chit) and with CH3COOLi (Si/Chit+CH3COOLi) added during EPD is performed to demonstrate a facile route to tuning of the polymer SEI chemistry. Atomic force and scanning electron microscopy reveal that addition of CH3COOLi at EPD assists in conformal deposition of the synthetic SEI. During electrochemical cycling, the Chit+CH3COOLi coating nearly doubles the capacity retention versus the reference bare Si thin film. X-ray photoelectron and Fourier transform infrared spectroscopy reveal that CH3COOLi caps the -NH2 groups of chitosan through amidation during EPD, which suppresses the catalytic reduction of the electrolyte. The presented approach demonstrates and validates EPD as a low-capital route to achieving and chemistry-tuning synthetic SEIs on Si electrodes. More broadly, the method is a promising avenue toward controlled and tailored polymeric SEIs on various conversion-type electrodes with high particle volumetric expansion.

Impact of Synthesis Chelation on the Crystallography and Capacity of Li-Rich Li1.2Ni0.13Mn0.54Fe0.13O2 Cathode Particles.

The quest for removal of cobalt from battery materials has intensified in the face of intensifying demand for batteries. Cobalt-free lithium-rich Li1.2Ni0.13Mn0.54Fe0.13O2 (LNMFO) is synthesized under variation of chelating agent ratio and pH using the sol-gel method. Systematic search of the chelation and pH space found that the extractable capacity of the synthesized LNMFO is most clearly correlated to the ratio of chelating agent to transition metal oxide; a ratio of transition metal to citric acid of 2:1 achieves greater capacity at the expense of relative capacity retention. Charge-discharge cycling, dQ/dV analysis, XRD, and Raman at different charging potentials are used to quantify the different degrees of activation of the Li2MnO3 phase in the LNMFO powders synthesized under different chelation ratios. SEM and HRTEM analysis are employed to understand the effect of particle size and crystallography on the activation of Li2MnO3 phase in the composite particles. An unprecedented use of the marching cube algorithm to evaluate atomic scale tortuosity of crystallographic planes in HRTEM revealed that subtle undulations in the planes in addition to stacking faults correlate to the extracted capacity and stability of the various LNMFO synthesized.

Correction: Revealing instability and irreversibility in nonaqueous sodium-O2 battery chemistry.

Correction for 'Revealing instability and irreversibility in nonaqueous sodium-O2 battery chemistry' by Sayed Youssef Sayed et al., Chem. Commun., 2016, 52, 9691-9694.

Revealing instability and irreversibility in nonaqueous sodium-O2 battery chemistry.

Charging kinetics and reversibility of Na-O2 batteries can be influenced greatly by the particle size of NaO2 formed upon discharge, and exposure time (reactivity) of NaO2 to the electrolyte. Micrometer-sized NaO2 cubes formed at high discharge rates were charged at smaller overpotentials compared to nanometer-sized counterparts formed at low rates.

The influence of transition metal oxides on the kinetics of Li2O2 oxidation in Li-O2 batteries: high activity of chromium oxides.

Reducing the energy loss associated with Li2O2 electrochemical oxidation is paramount to the development of efficient rechargeable lithium-oxygen (Li-O2) batteries for practical use. The influence of a series of perovskites with different eg filling on the kinetics of Li2O2 oxidation was examined using Li2O2-prefilled electrodes. While LaCrO3 is inactive for oxygen evolution upon water oxidation in alkaline solution, it was found to provide the highest specific current towards Li2O2 oxidation among all the perovskites examined. Further exploration of Cr-based catalysts showed that Cr nanoparticles (Cr NP) with an average particle size of 40 nm, having oxidized surfaces, had comparable surface area activities to LaCrO3 but much greater mass activities. Unlike Pt/C and Ru/C that promote electrolyte oxidation in addition to Li2O2 oxidation, no evidence of enhanced electrolyte oxidation was found for Cr NP relative to Vulcan carbon. X-ray absorption spectroscopy at the O K and Cr L edge revealed a redox process of Cr(3+) ↔ Cr(6+) on the surface of Cr NP upon Li2O2 oxidation, which might be responsible for the enhanced oxidation kinetics of Li2O2 and the reduced charging voltages of Li-O2 batteries.