Search

Conventional cathodes for Li-ion batteries (LIBs) are reaching their theoretical capacity limits. One way to meet the growing demands for high-capacity LIBs is by developing so-called Li-rich cathode materials that greatly benefit from additional capacities from anionic moieties in the structure. Li-rich materials are intrinsically subject to higher degrees of (de)intercalation, leaving the particles more prone to fractures and thus rapid capacity fade. Alkali-rich LiNaFeS₂ reversibly cycles with capacities exceeding 300 mAh g⁻¹, but its capacity fades faster than an isostructural material Li₂FeS₂. Using synchrotron-based transmission X-ray microscopy (TXM), we demonstrate that the capacity fade of LiNaFeS₂ stems from particle fractures in the first charge cycle. We improve the cycling performance of LiNaFeS₂ by means of cryomilling, which enhances capacity retention at cycle 50 by 76%. Through crystallographic and morphological characterization techniques, we confirm that cryomilling not only decreases particle and crystallite size while increasing microstrain but also prevents particles from fracturing. Cryomilling is a powerful tool to engineer nanoscale battery materials, and TXM allows the direct observation of morphological changes of the particles, which can be leveraged to develop next-generation cathode materials for LIBs.

Despite ongoing efforts to identify high-performance electrolytes for solid-state Li-ion batteries, thousands of prospective Li-containing structures remain unexplored. Here, we employ a semi-supervised learning approach to expedite identification of ionic conductors. We screen 180 unique descriptor representations and use agglomerative clustering to cluster ~26,000 Li-containing structures. The clusters are then labeled with experimental ionic conductivity data to assess the fitness of the descriptors. By inspecting clusters containing the highest conductivity labels, we identify 212 promising structures that are further screened using bond valence site energy and nudged elastic band calculations. Li3BS3 is identified as a potential high-conductivity material and selected for experimental characterization. With sufficient defect engineering, we show that Li3BS3 is a superionic conductor with room temperature ionic conductivity greater than 1 mS cm-1. While the semi-supervised method shows promise for identification of superionic conductors, the results illustrate a continued need for descriptors that explicitly encode for defects.

Recent research in medicinal chemistry suggests a correlation between an increase in the fraction of sp³ carbons, those bonded to four other atoms, in drug candidates with their improved success rate in clinical trials. As such, the development of robust and selective methods for the construction of C(sp³)-C(sp³) bonds remains a critical problem in modern organic chemistry. Owing to the broad availability of alkyl halides, their direct cross coupling—commonly known as cross-electrophile-coupling (XEC)—provides a promising route toward this objective. Such transformations circumvent the preparation of carbon nucleophiles used in traditional cross-coupling reactions as well as stability and functional group tolerance issues that commonly associate with these reagents. However, achieving high selectivity in C(sp³)-C(sp³) XEC remains a largely unmet challenge. Here, we employ electrochemistry to achieve the differential activation of alkyl halides by exploiting their disparate electronic and steric properties. Specifically, the selective cathodic reduction of a more substituted alkyl halide gives rise to a carbanion, which undergoes preferential coupling with a less substituted alkyl halide via bimolecular nucleophilic substitution (S_N2) to forge a new C–C bond. This transition-metal-free protocol enables efficient XEC of a variety of functionalized and unactivated alkyl electrophiles and exhibits improved chemoselectivity versus existing methods.