Jeffin James Abraham

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.

LiFePO ₄ (LFP) cells show lower gravimetric and volumetric energy density than other types of Li-ion cells. To improve this, a Si-containing anode is employed in LFP cells. However, LFP cells with Si–C composites in the anode show more rapid capacity loss than cells with only graphite in the anode. Lithium alkoxides produced a poorly passivated negative electrode surfaces in carbonate electrolytes travel to the positive electrode and cause Fe dissolution. This Fe moves to the negative and compromises the SEI leading to Li inventory loss and capacity fade. It is more difficult to passivate Si–C effectively in typical electrolytes due to its large volume changes. To solve this issue, we use an electrolyte, based on the solvents sulfolane and toluene, where alkoxide production is impossible and which eliminates Fe dissolution from LFP. LFP/Si–C cells with sulfolane:toluene electrolytes show excellent capacity retention, much better than cells with traditional carbonate electrolytes. Alkoxide-suppressing additives were also explored in this work, and 10% FEC in an EC-free electrolyte also showed promising results. This will open the way to employ a Si–C–containing anode in LFP cells to achieve higher gravimetric and volumetric energy density without sacrificing lifetime.

Incorporating silicon–carbon (Si–C) composite negative electrodes into Li[Ni _{(1− x − y )} Mn _{( x )} Co _{( y )} ]O ₂ (NMC) lithium-ion cells offers a viable route toward higher energy density. However, the impact of increasing Si–C content in the negative electrode on cell abuse tolerance remains insufficiently understood. Here, we systematically evaluate the thermal stability of single-crystal Li[Ni _0.65 Mn _0.30 Co _0.05 ]O ₂ (Ni65) pouch cells containing 0%, 20% and 50% Si–C in the negative electrode across upper cut-off voltages of 3.9–4.4 V using accelerating rate calorimetry. By maintaining constant cathode chemistry while independently varying Si–C fraction, operating voltage, and Si–C architecture, we isolate the relative contributions of cathode delithiation levels and anode composition to self-heating and thermal runaway. Self-heating was found to scale primarily with the degree of cathode delithiation rather than Si–C content, with increasing operating voltage consistently accelerating thermal reactivity. Accordingly, at a given operating voltage, graphite-only and Si–C-containing cells exhibited nearly identical self-heating profiles. In contrast, thermal runaway severity, as reflected by gas generation and quantified by the mass ejected from the pouch cells, scaled strongly with energy density, reaching a maximum in 4.4 V cells containing 50% Si–C. These findings demonstrate the pivotal role of Si–C content, along with operating voltage, in determining the severity of thermal runaway.

LiMn _0.8 Fe _0.2 PO ₄ (LMFP)/graphite Li-ion cells are an emerging low-cost, Ni and Co free alternative to the existing NMC battery technology. Although cells with this chemistry are promising, various issues impact the commercialization of this material. A major failure mechanism identified in these cells is the loss of lithium inventory due to solid-electrolyte interphase breakdown when Mn dissolves from the positive electrode at high temperature and deposits on the negative electrode. Herein, we propose the use of various blends of conducting salts to minimize this failure mode in LMFP/graphite cells and extend cycle life. Using LiFSI or LiTFSI as the primary salt in combination with 20 wt% of different co-salts such as LiDFOB, LiBOB, and LiPF ₆ resulted in reduced Mn dissolution and deposition on the negative electrode and improved cycle life, especially for blends containing LiDFOB. However, Mn dissolution could not be completely prevented, and salt consumption occurred during cycling, requiring further optimization before these electrolytes can be used in applications.

Energy-dense lithium-ion (Li-ion) batteries are increasingly in demand for a wide range of energy storage applications. The introduction of silicon (Si) as a negative electrode candidate offers a promising route to meeting the high energy density requirements of next-generation Li-ion batteries. However, suitable electrolytes must be identified that can ensure both long cycle life and cell safety. In this study, a localized high-concentration electrolyte (LHCE) was evaluated for three different Si-containing negative electrode types: Chemical SiC (ChemSiC), micron-sized Si (μSi), and Mechanical SiC (MechSiC). These designations are based on the synthesis method and particle characteristics. A more conventional electrolyte formulation (CTRL) was used as a benchmark comparator. The LHCE demonstrated significant improvements in electrochemical performance for the μSi and Mechanical SiC cells, with smaller improvement observed for Chemical SiC compared to the CTRL electrolyte. Importantly, across all electrode types, the LHCE markedly enhanced thermal stability, delaying thermal runaway relative to the CTRL electrolyte. This LHCE does offer both improved electrochemical performance and enhanced safety for Si-containing Li-ion cells. However, the LHCE has low ionic conductivity, which will limit rate capability. These issues could limit practical application of this LHCE.

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.

Anodic dissolution (often referred to as corrosion) of the positive electrode aluminum current collector can be a limiting factor for the performance, lifetime, and safety of lithium-ion cells. The superior performance of lithium bis(fluorosulfonyl)imide (LiFSI) salt, especially in high-temperature lithium-ion cells, motivates this study of the Al current collector corrosion in electrolytes with and without LiFSI. With pure lithium hexafluorophosphate (LiPF₆) and lithium tetrafluoroborate (LiBF₄) or LiFSI blends of these salts, only minor Al corrosion currents were found in cyclic voltammetry (CV), open-circuit voltage storage, cycling experiments, and ultra-high precision coulometry; however severe corrosion was found with pure LiFSI. Importantly, there is a discrepancy between the results of CV experiments and actual NMC532/graphite pouch cell cycling in terms of the magnitudes and onset voltages of Al corrosion. For the latter, severe anodic dissolution was only observed when using LiFSI above 4.2 V, but for the former severe corrosion currents were already observed at 3.8 V vs Li⁺/Li when using bare Al foil in CV experiments. This discrepancy is likely due to proton scavenging by H⁺/Li⁺ exchange and/or solvent-mediated hydrogenation of layered oxide positive electrode materials - two mechanisms that are absent in cells with bare Al electrodes.

NASICON-based sodium Fluorophosphate Na₃V₂(PO₄)₂F₃ (NVPF) cathode materials have been widely analyzed in sodium-ion batteries (SIB) owing to their high energy density and high working voltages. However, the low electronic conductivity of NVPF is a factor hindering their efficient use. To enhance the electronic conductivity of NVPF, a porous Na₃V₂(PO₄)₂F₃ with Ti₃C₂-based MXene nanostructures was synthesized using a facile sol-gel method. NVPF acts as a bipolar or symmetric battery material from the presence of two redox couples at a low voltage of 1.4V and another at a high voltage of 3.6~4.1V. The benefits of a symmetric cell are many, including ease of fabrication, low volume expansion leading to higher safety, reduced cost of production, and easy recycling costs. In this work, the MXene-incorporated NVPF are analyzed in a symmetric cell, and the effect of incorporation of various MXene wt. percentages on the structural, thermal, and electrochemical performance of Na₃V₂(PO₄)₂F₃ in a sodium symmetric cell was thoroughly investigated. Structural analysis of the materials developed indicates that the MXene addition has not altered the crystal structure of the NVPF. The modification improved the electrochemical performance of NVPF in the sodium symmetric cell as indicated by its high specific discharge capacity of 92mAhg^-1 at a high C rate of 1C for the MXene 5wt% incorporated composite structures. The GITT analysis confirmed the improved diffusion kinetics of the MXene-incorporated samples, as evident from the calculated Na⁺ diffusion coefficients. The D_Na+ calculated was found to be 9.57x10^-9 cm²s^-1 for the 5wt% MXene incorporated sample and 4.14x10^-9 cm²s^-1 for pristine sample.

Lithium Manganese Iron Phosphate, LiMn_xFe_1-xPO₄, (LMFP), is a promising positive electrode material for Lithium-ion batteries. Introduced by Pahdi et al. in 1997 [1], it is an alternative to the high-cost Nickel Manganese Cobalt (NMC) layered oxides and the low energy density Lithium Iron Phosphate (LFP) positive electrode materials. The LMFP material has a higher operating voltage than LFP, shows good cyclability, is low cost, and has a stable structure. However, the LMFP material suffers from poor rate capability due to its poor electronic conductivity and poor ionic diffusion. This hampers its use for high C-rate applications. Tailoring electrolytes to ensure better ionic diffusion at the solid/electrolyte interface is one solution to improve rate capability of these LMFP cells. Herein, we study the effect of different salts and mixed salts on LMFP/graphite Li-ion pouch cells and come up with a suitable electrolyte combination for LMFP cells. The salts used in this study are readily available salts and the mixed salts were made with a combination of these readily available salts at different ratios. The tests were conducted in a 70 °C temperature box to accelerate failure in these cells, as a method to screen these salts/mixed salts. Our observations show that mixed salts play a significant role in improving the lifetime of these cells, with the best cell reaching the end of life (EOL) after ~280 cycles at 70 °C. As LMFP is prone to manganese dissolution, the amount of manganese deposited on the negative electrode was quantified using X-ray Fluorescence spectroscopy (XRF). The cells using mixed salts display a lower amount of manganese deposited on the graphite compared to the individual salts. The use of readily available mixed salt electrolytes seems to improve cycle life, which is promising for the future commercialization of the LMFP positive electrode Li-ion cells. References: K. Padhi et al. 1997 J. Electrochem. Soc. 144 1188 Figure 1. a) Discharge capacity, b) normalized discharge capacity, and c) normalized voltage hysteresis of LMFP cells containing different salts/mixed salts, cycled at 70 °C. Figure 1

The increasing demand for clean energy storage and electric vehicles is highlighting the need to develop Li-ion battery materials with low cost and abundant elements.^{1 , 2} Positive electrode materials such as LiFePO₄ (LFP) are good candidates to replace layered oxide materials due to the high relative abundance of Fe compared to other transition metals, such as Ni and Co.¹ Unfortunately, LFP suffers from low energy density.² LiMn_xFe_1-xPO₄ (LMFP) has been proposed as an alternative to LFP. It shares the same crystal structure as LFP with a portion of Fe sites substituted with Mn. The Mn^2+/3+ redox takes place at higher potential, improving the energy density.² In this work, we set to decouple the contribution of the Fe and Mn to cell failure in order to better understand this class of olivine materials. LiMn_0.8Fe_0.2PO₄/artificial graphite (AG) cells were cycled over varying voltage ranges to determine the capacity fade behaviour of each plateau, Fe (2.5-3.6 V) and Mn (3.6-4.2 V), as well as the full voltage range of the cell. The worst capacity fade was seen for cells cycled over the full voltage range, while very little capacity fade was seen for the Fe plateau and no capacity fade was seen for the Mn plateau, due to the Li reservoir from the negative electrode. In order to determine the capacity fade mechanism, differential voltage analysis was utilized.³ dV/dQ analysis shows no mass loss over any of the voltage ranges, large Li inventory loss for the full voltage range and Mn voltage region, and small Li inventory loss for the Fe region. X-ray fluorescence spectroscopy was used to determine the degree of Mn deposition on the negative electrode. The degree of Mn deposition was found to be well-correlated with the amount of Li inventory loss, demonstrating that the primary failure mode of LMFP/AG cells is Mn-catalyzed Li inventory loss. In order to fix that problem, we synthesized advanced LiMn_xFe_1-xPO₄ with different values of x and optimized material properties. We also developed novel electrolytes that reduce Li inventory loss even at elevated temperature. Overall, our work shall enable long-lived LMFP/graphite cells for longer cost electric vehicles and stationary energy storage. (1) Nitta, N.; Wu, F.; Lee, J. T.; Yushin, G. Li-Ion Battery Materials: Present and Future. Materials Today 2015, 18 (5), 252–264. https://doi.org/10.1016/j.mattod.2014.10.040. (2) Ryu, H.-H.; Hohyun Sun, H.; Myung, S.-T.; S. Yoon, C.; Sun, Y.-K. Reducing Cobalt from Lithium-Ion Batteries for the Electric Vehicle Era. Energy & Environmental Science 2021, 14 (2), 844–852. https://doi.org/10.1039/D0EE03581E. (3) Dahn, H. M.; Smith, A. J.; Burns, J. C.; Stevens, D. A.; Dahn, J. R. User-Friendly Differential Voltage Analysis Freeware for the Analysis of Degradation Mechanisms in Li-Ion Batteries. J. Electrochem. Soc. 2012, 159 (9), A1405. https://doi.org/10.1149/2.013209jes.