Animesh Dutta

Well-developed single crystal (SC) LiMn ₂ O ₄ (LMO) particles with distinct exposed facets were synthesized to minimize parasitic reactions between the electrochemically active surface and the electrolyte. Laue diffraction was employed to identify, for the first time, (110)-faceted SC-LMO as distinct from its (111)-faceted counterpart. The (110)-faceted SC-LMO demonstrated superior electrochemical performance relative to (111)-faceted SC-LMO and commercial SC-LMO in half-cells at 55 °C. Scanning Transmission X-ray Microscopy (STXM) revealed a higher surface Mn ²⁺ concentration on (111)-faceted particles after 200 cycles, consistent with more extensive surface reconstruction. Segmented cycling further established that the performance advantage of (110)-faceted SC-LMO is localized to the lower voltage plateau, while the upper plateau remains largely insensitive to both lithium stoichiometry and facet orientation. In single-layer pouch (SLP) full cells at elevated temperature, (110)-faceted SC-LMO retained 80% capacity over 350 cycles, comparable to commercial SC-LMO, while exhibiting the lowest Mn deposition rate on the anode among all materials evaluated.

LiNi _0.7 Mn _0.3 O ₂ (NM73) cathode materials were synthesized with small amounts (0–0.5 mol. %) of tungsten (W) using the all-dry synthesis method. Calcination temperatures between 875 and 975 °C were tested. Pure layered phases were obtained but cycling performance deteriorated when 0.5 mol.% W was added. As more W is added, the particles become less like single crystals and more like polycrystalline agglomerates. By electron-backscattering diffraction, the average grain size of NM73 made with 0.5 mol.% W decreases to 300 nm. Li-ion diffusion studies reveal that even though smaller grain sizes allow for a shorter diffusion path, the addition of W increases ionic resistivity. Adding 0.2 mol.% W creates the desired single crystalline morphology and enables excellent cycling performance. For comparison, LiOH·H ₂ O and a W precursor were mixed with Ni _0.7 Mn _0.3 (OH) ₂ co-precipitated precursors and calcined. At 975 °C, the elemental homogeneity of the all-dry NM73 material matched that of the NM73 material made from the co-precipitated precursor. Characterization by transmission electron microscopy and energy-dispersive spectroscopy reveals that W concentrates in the grain boundaries of the co-precipitated material and on the surface of the single crystals of the all-dry made material.

This work presents an evaluation of 1,3,2-dioxathiolane 2,2-dioxide (DTD) as an electrolyte additive for sodium layered oxide/hard carbon pouch cells. Several DTD concentrations (1–4 wt.%) were examined at 55 °C with cycling, open-circuit storage, gas generation, and symmetric cell impedance experiments. Increasing the DTD concentration suppresses gas evolution but also shortens cycle life and accelerates impedance growth. X-ray Photoelectron Spectroscopy analysis of the cycled electrodes reveals that higher concentrations of DTD directly correlate with an increased deposition of sulfate species on both the positive and negative electrode surfaces. Post-mortem electrolyte characterization by gas chromatography–mass spectrometry and nuclear magnetic resonance shows that DTD suppresses the formation of alkyl dicarbonates during long-term cycling, consistent with its effective passivation of the hard carbon electrode. In addition, ethylene carbonate (EC) formation in the initially EC-free solvent scales with the DTD content, suggesting a H ₂ O-induced decomposition pathway of DTD that generates EC. The proposed reaction pathway was validated using the hydrolysis-resistant derivative 4,4′-bi-1,3,2-dioxathiolane 2,2,2′,2′-tetraoxide (bis-DTD). Electrolyte analysis of post-cycled electrolytes confirmed the absence of EC formation. However, suppressing this reaction did not translate to improved cell longevity as DTD-containing cells exhibited enhanced capacity retention and lower impedance growth compared to their bis-DTD counterparts.

This study presents post-mortem analyses of NMC/graphite pouch cells, which exhibit exceptional capacity retention after up to 8 years or 22,000 charge-discharge cycles. Various NMC/graphite cells with different positive electrode compositions and particle morphologies were examined under a variety of cycling conditions, temperatures, C-rates, and upper cut-off voltages. The findings demonstrate that even after extended periods of continuous cycling, the NMC positive electrodes can maintain the integrity of their crystal structure with minimal transition metal dissolution. Additionally, there is minimal degradation of the electrolyte, and the artificial graphite negative electrode materials only show negligible changes. Ultimately, lithium loss at the negative electrode is the only notable aging mode in these cells. Furthermore, with optimized electrolytes and high-quality artificial graphite (AG), this parasitic reaction occurs at a low rate. As a result, lithium-ion cells can achieve remarkably long lifetimes. For example, a single-crystal NMC532/AG cell studied in this research retained 80% of its capacity, positive electrode crystal structure, and morphology, with minimal changes to the electrolyte after 6.8 years of continuous charge-discharge cycling.

Medium-nickel layered oxide (NMC) materials are widely adopted by cell manufacturers, as they provide higher energy density without compromising safety at high voltage. However, challenges such as poor rate capability and limited lifetime at higher cutoff voltages still hinder their broader application. Our analysis of vendor materials revealed that, among the multiple additives used to enhance performance, cobalt is also employed as a surface coating element by some vendors. This study demonstrates a simple process to achieve a cobalt-rich surface on the NMC cathode via an all-dry synthesis method, verified by X-ray Photoelectron Spectroscopy (XPS). Our Co-coated NMC samples achieve performance close to that of top-tier vendor samples that incorporate multiple coating additives. Transmission electron microscopy (TEM) further confirms the incorporation of cobalt on the surface of single-crystal Li _1+x (Ni _0.6 Mn _0.4 ) _1-x O ₂ . This work highlights the importance of a cobalt-rich surface, showing that minimal cobalt addition can significantly improve electrochemical performance at high cutoff voltages without requiring numerous additives.

Sodium-ion batteries (SIBs) present a promising alternative to lithium-ion batteries for large-scale energy storage, owing to the abundance of sodium resources and lower cost. However, the commonly used anode material, hard carbon (HC), limits volumetric energy density due to its porous structure and low density. Red phosphorus (P), with its high theoretical volumetric capacity (∼6000 mAh cm ^–3 ), is a compelling alternative but suffers from severe volume expansion and poor electronic conductivity. In this study, we investigated the potential of composite electrodes by blending red P with commercial HC to harness the complementary advantages of both materials. To optimize red P electrodes, SWCNT conductive additives, a PAANa binder, and carbonate-based electrolytes with an FEC additive were initially employed. Following this, a systematic investigation was conducted into different blending methods, specifically mechanical blending and physical vapor deposition (PVD). PVD significantly improved the uniformity and cycling stability of P/HC blends. Blending 5 wt% P via PVD enhanced specific capacity from ∼300 mAh g ^–1 (pure HC) to ∼420 mAh g ^–1 , maintaining excellent cycling stability over 100 cycles. These findings provide valuable guidance for developing high-capacity, stable SIB anodes and lay the groundwork for further optimization of P/HC composites.