Zehao Cui

Fluorinated ether electrolytes are promising for high-energy-density lithium metal batteries, yet their translation to larger-scale production requires systematic control of solvent impurities generated during synthesis and purification. Using 2-(2-(2,2-difluoroethoxy)ethoxy)–1,1,1-trifluoroethane (F5DEE) as a high-performance model solvent, we compare gram- and kilogram-scale batches to correlate impurity origin, purification, and electrochemistry. Although upscaled F5DEE shows >99% purity by standard techniques, ppm-level moisture and organic impurities reduce Li Coulombic efficiency and increase cell variability. We classify impurities by generation pathway into retained intermediates, starting-material-derived analogues, side-reaction products, and purification-introduced residues. Distillation, adsorption, and reactive purification implicate water, alkoxide-derived byproducts, and amines as key performance-limiting species. However, excessive purification generates secondary impurities that degrade performance, revealing a removal–generation trade-off. Thermal, electrochemical, operando microcalorimetry, and online mass spectrometry analyses reveal impurity-dependent current-collector corrosion, heat release, gas evolution, and full-cell degradation. This route-resolved, source-to-consequence workflow provides a transferable qualification framework for electrolyte solvent scale-up.

Multimodal synchrotron analysis uncovers how Co, Mn, and Al dopants mitigate degradation and reinforce structural integrity in LiNiO ₂ cathodes.

Understanding the fundamental properties of electrode-electrolyte interphases (EEIs) is essential for designing electrolytes that support stable operation under high charging rates. In this study, we benchmark our fast-charging electrolyte (FCE) against the commercial LP57 electrolyte to identify the EEI characteristics that enhance fast-charging performance. By utilizing the latest advances in time-of-flight secondary ion mass spectrometry (TOF-SIMS) and focused-ion beam (FIB) techniques, we reveal the complex chemical architecture of the cathode-electrolyte interphase (CEI). Our findings indicate that stable battery operation under fast-charging conditions requires reduced surface reactivity rather than stabilizing the bulk integrity of the cathode. While inorganic species are often cited as beneficial for EEI composition, their distribution within the EEI is equally critical. Additionally, dynamic interactions between the cathode material and conductive carbon significantly affect CEI formation and alter the passivation layer chemistry. A chemically homogeneous distribution of CEI components passivating preferentially the active material particles is desired for enhanced performance. Notably, the amount of electrolyte decomposition species in the solid-electrolyte interphase (SEI) far outweighs their distribution within the SEI in determining better electrochemical performance. An inorganic-rich SEI effectively protects graphite particles, suppresses the accumulation of metallic lithium, and prevents the formation of lithium dendrites. Overall, an enhanced fast-charging performance can be achieved by tuning the interphase chemistry and architecture on both the cathode and anode sides.

Silicon-based anodes offer high specific capacities to enhance the energy density of lithium-ion batteries, but are severely hindered by the immense volume expansion and subsequent breakage of the solid-electrolyte-interphase (SEI) during cycling. Herein, we utilize an effective strategy, known as direct-contact prelithiation, to mitigate the challenges associated with expansion and surface instability in SiO_x/graphite (SG) anodes. It involves introducing lithium into the anode via physical contact with lithium metal and electrolyte before cycling. Prelithiation of SG anodes with an advanced localized high-concentration electrolyte is shown to develop a mechanically robust artificial SEI that tolerates better the electrode volume expansion. The modified SG anode paired with the high-Ni cathode LiNi_0.90Mn_0.05Co_0.05O₂ delivers a high initial capacity of 191 mA h g^-1 with 80% capacity retention over 150 cycles, compared to 46% retention with a conventional electrolyte. The bolstered SEI layer with reduced surface reactivity is due to the reduced electrolyte consumption and regulated SEI formation during cycling. Furthermore, the advanced electrolyte and fortified SG anode help reduce cathode degradation, transition-metal dissolution, and loss of active lithium. This study highlights viable prelithiation strategies to stabilize Si-based anodes for high-energy-density batteries through electrolyte design.