Matthew D. L. Garayt

Numerous efforts have been made to utilize silicon-based negative electrodes in lithium-ion batteries (LiBs). The main challenge with Si-based anodes is their significant volume expansion and contraction during cycling, which degrades LiB performance . Silicon-carbon composites are known to address many of the challenges of large-volume expansion and can deliver high specific capacity alongside acceptable cycle life. In this study, various chemically synthesized Si–C composites with different porous hard carbon precursors were investigated to examine the evolution of the filling of the carbon precursor pores with Si during impregnation via chemical vapor deposition using SiH ₄ gas. These samples were later etched with a high-pH solution to remove the Si in several steps, returning the structure to that of the carbon precursor to backtrack the changes in the carbon precursor. The as-received carbon precursor and the etched samples were compared using small-angle X-ray scattering and X-ray diffraction. These techniques, combined with high-resolution transmission electron microscopy, compression testing of the samples, and electrochemical performance measurements, provide a broad view of the evolution of the carbon precursor structure during Si deposition and during the charge/discharge processes in the LiB negative electrode, providing insight into the structure-performance-properties correlation of CVD-based Si–C composites.

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.

A novel multi-channel Online Electrochemical Mass Spectrometer was built to quantify gases in up to six battery cells for the study of interfacial gas generating reactions in alkali-ion cells. It measures an integral signal of the total evolved/consumed gases by sampling each cell once per hour using an automated switching sequence of computer-controlled valves optimized to remove residual gases from the central gas line connecting the six cells without affecting the vacuum chamber containing the quadrupole mass analyzer. It is demonstrated that the new multi-OEMS system enables reproducible gassing studies on machine-made double-sided graphite electrodes since the evolved gas volume easily exceeds the electrode pore volume, so that sluggish gas diffusion around the solid current collector can be avoided. Multi-OEMS can be used for rapid electrolyte additive screening as demonstrated for common CO ₂ forming additives like VC and FEC, C ₂ H ₄ forming additives like DTD, and novel additives like EC-bisDTD, a polycyclic compound combining EC and DTD, that can suppress gas generation. The multi-sampling approach accelerates systematic gassing experiments and still resolves interfacial gas generating reactions at relevant timescales for alkali-ion cells.

Lead (Pb) is of interest as a sodium alloying compound to increase the volumetric energy density of sodium-ion batteries. However, Pb has not been shown to cycle reversibly with the carbonate-based electrolytes common in sodium- and lithium-ion batteries. Moreover, the 387% volume expansion of Pb when fully sodiated results in continual sodium inventory loss at the negative electrode, even when far stabler glyme-based electrolytes are used. A lead-carbon (Pb-C) composite material, analogous to silicon-carbon composites, may be able to overcome these electrolyte stability issues. In this work, several Pb-C composites are shown to incorporate up to 27% Pb by mass and are synthesized by mechanical mixing of Pb and cellulose acetates followed by pyrolysis and carbon coating using chemical vapour deposition. The best Pb-C sample can be cycled more than 100 times in carbonate electrolyte with only 14% lower specific capacity than with monoglyme electrolyte. This is far superior to pure Pb and Pb blended with hard carbon, but additional work is encouraged to improve their performance further.

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.

Worldwide efforts to develop sodium-ion batteries have accelerated in recent years. There are several companies that are developing sodium-ion batteries, including CATL, HiNa, LiFUN, Natron, Tiamat, Faradion, and UNIGRID. Commercial sodium-ion cells are available at this time, but their energy density may not be sufficient for practical application. Now it is necessary to create sodium-ion cells with a volumetric energy density greater than that of LFP/graphite cells. The volumetric capacity of typical sodium-ion battery negative electrodes like hard carbon is limited to less than 450 mAh/cm ³ . Alloy-based negative electrodes such as phosphorus (P), tin (Sn), and lead (Pb) more than double the volumetric capacity of hard carbon, all having a theoretical volumetric capacity above 1,000 mAh/cm ³ in the fully sodiated state. [1] These alloy materials have massive volume expansion, with P expanding by almost 300% and both Sn and Pb expanding to about 400% of their initial volumes when fully sodiated. We will show that Sn and Pb have excellent half-cell cycling performance despite this large volume change, including high Coulometric efficiency. [2, 3] Pb experiences 387% volume expansion upon full sodiation, which leads to significant changes in the electrode morphology. We will track the morphology of Pb and Pb-hard carbon blended electrodes using SEM imaging. As well, each Na-Pb phase will be examined to analyze their physical properties. These analyses will show that the Pb particles restructure into ~1 µm particles (see Figure 1), even after just a single cycle, and surprisingly do not pulverize the hard carbon in a blended electrode. Single-walled carbon nanotubes appear to be necessary to maintain active material electrical connection. [4] Furthermore, we will show how to improve the formulation of the Pb negative electrode and evaluate capacity retention in half- and full-cell configurations, while investigating the potential degradation mechanisms. The impact of oxide impurities on the cycling stability of Pb negative electrodes will be studied using a controlled heat treatment procedure. The irreversible formation of Na ₂ O, a side product of the sodiation reaction of Pb oxide, results in sodium inventory loss, decreased first cycle efficiency, and a detrimental impact on the cell’s long-term cyclability. [5] Additionally, the thermal stability of fully sodiated Pb in the presence of ether-based electrolyte will be investigated. The results suggest that Pb not only provides an energy density advantage, but is also marginally more stable at elevated temperatures compared to hard carbon under the same testing conditions. Overall, we aim to provide valuable insights into the cyclability, degradation mechanisms and thermal stability of Pb, offering useful guidance for its future commercialization and deployment in sodium-ion batteries. [6] References [1] V. Chevrier and G. Ceder J. Electrochem. Soc. 158 (2011). [2] T. R. Jow and L. W. Shacklette J. Electrochem. Soc. 136 1 (1989). [3] M. Garayt, ⁼ L. Zhang, ⁼ Y. Zhang, ⁼ M. Obialor ⁼ et al. J. Electrochem. Soc. 171 070523 (2024). [4] M. Garayt et al. J. Electrochem. Soc. 171 120521 (2024). [5] M. Obialor et al. submitted (2025). [6] M. Obialor et al. manuscript in preparation (2025). Figure 1. SEM images of an ion-mill cross-section of a pristine Pb electrode (a) and desodiated Pb electrode after 106 cycles (b). Figure 1

The ability of lithium- and sodium-ion cells to hold their charge at elevated temperature over extended periods of time is important for a number of applications, e.g., electric vehicles and stationary battery systems for storage of renewable energy deployed in hot climates. We found that LFP and NMC-based lithium-ion cells can experience rapid self-discharge when stored at elevated temperatures, if they do not contain effective electrolyte additives. Cells with LFP positive electrodes show significantly more self-discharge than NMC-based cells. [1-3] Surprisingly, it was found that the rapid self-discharge could be attributed to the in-situ generation of a redox shuttle in commercial LFP and NMC/graphite cells. [1-3] A redox shuttle is a molecule that can diffuse between the positive and negative electrode of a battery and transport electrons from one side to the other through a reversible redox reaction, accepting an electron from the negative electrode and donating it to the positive electrode. This results in lithium ions being transferred from the negative to the positive electrode without charge being drawn from the cell. To fix the self-discharge problem, the origin and formation mechanism of the redox shuttle need to be investigated. First, the reversible and irreversible self-discharge of LFP- and NMC-based cells was quantified with a designated storage protocol. Subsequently, the influence of different formation temperatures on self-discharge was studied. Surprisingly, the visual inspection of the electrolyte extracted from pouch cells after high temperature formation revealed strong discoloration. [1-2] The extracted electrolytes with intense red and brown color showed relatively large shuttling currents in a newly developed Al/Li coin cell setup. [4] Ultra-high precision coulometry was used to detect inefficiencies during cycling, e.g., charge endpoint capacity slippage. [4] Electrolyte additives that effectively passivate the negative electrode, e.g., vinylene carbonate, were effective at preventing the redox shuttle generation as indicated by the absence of electrolyte discoloration, shuttling currents, and charge endpoint capacity slippage. [4] All evidence pointed to a shuttle molecule created at the negative electrode during the formation cycle, i.e., before a passivating solid-electrolyte interface is in place. But what is the shuttle molecule? The identity and formation mechanism of the redox shuttle were investigated by targeted experiments that probe the chemical stability of inactive cell components. We dissected many commercial lithium-ion cells from renowned manufacturers to investigate the composition of the inactive components (see Figure 1). [5] Such inactive components are laminated foils used in pouch cells, gaskets of cylindrical cells, adhesive tapes on the electrodes, separators, and metallized polymer current collectors composed of a thin polymer layer with Al or Cu deposited on both sides. All these components need to be chemically stable, as they could otherwise participate in detrimental side reactions during battery operation. Using gas chromatography and nuclear magnetic resonance spectroscopy, we show that different polymers have vastly different chemical stability against lithium alkoxides that are generated at the unpassivated negative electrode. [5] In the presence of alkoxides some of the polymers decompose into reaction products that can act as redox shuttles. Finally, we will explain how to make Li and Na-ion cells with chemically stable polymer components and demonstrate that self-discharge is virtually eliminated in these cells. [5-7] Figure 1 . A selection of mobile phone batteries that were dissected to find out which inactive components are causing self-discharge. Keywords : Lithium-ion cells, Sodium-ion cells, Self-discharge, Inactive components, Redox shuttles References : [1] T. Boulanger, M. Metzger et al. J. Electrochem. Soc. 169 , 040518 (2022). [2] S. Buechele, M. Metzger et al. J. Electrochem. Soc. 170 , 010511 (2023). [3] S. Buechele, M. Metzger et al. J. Electrochem. Soc. 170 , 010518 (2023). [4] T. Boetticher, M. Metzger et al. J. Electrochem. Soc. 170 , 060507 (2023). [5] A. Adamson, M. Metzger et al. Nature Materials 22 1380–1386 (2023). [6] Z. Ye, ⁼ H. Hijazi, ⁼ M. Metzger et al. J. Electrochem. Soc. 171 110503 (2024). [7] A. Adamson, M. Metzger et al. J. Electrochem. Soc. 172 010527 (2025). Figure 1

Lead (Pb), along with other alloy materials has emerged as a promising negative electrode material for sodium-ion batteries (SIBs) due to its high volumetric capacity. However, the presence of oxide impurities in Pb negative electrodes has been found to negatively impact cell performance. This study investigates the impact of oxide content on the initial capacity and cycling stability of Na/Pb half cells. A controlled heat treatment procedure enabled the formation of varying oxide amounts with increased exposure time, confirmed by X-ray diffraction to be Pb oxide (PbO). When PbO reacts with Na upon first charge, Na₂O is irreversibly formed, which consumes active Na inventory, decreases the first cycle efficiency, and leads to capacity fade. Long term cycling of oxidized Pb electrodes suggests that there is a permissible level of oxides in Pb-based Na-ion cells without severe impact on performance; specifically, in this study, this threshold was found to be ∼0.13 moles of PbO per 1 mol of Pb. Understanding the impact of PbO on cell performance can guide material selection and design of these relatively inexpensive, high capacity Pb-based negative electrodes for SIBs.

Sodium- (Na) alloying compounds such as lead (Pb) are of increasing interest for use in Na-ion full cells to increase their volumetric energy density. Full cells with NaNi_1/3Fe_1/3Mn_1/3O₂ (NFM111) as the positive electrode and pure Pb or Pb blended with hard carbon have competitive volumetric energy densities with LiFePO₄/graphite cells but suffer from limited capacity retention. The cause of the capacity fade is investigated using differential voltage analysis, with the shift loss and active masses of both electrodes compared to a full cell with a pure hard carbon negative electrode as the cells progress through up to 210 cycles. Shift loss from Na inventory loss at the negative electrode is the main culprit for capacity loss, with NFM111 active mass loss a secondary factor. Perhaps surprisingly, the negative electrodes’ active mass loss is minor and mostly occurs during the initial cycles where there is morphological restructuring of the Pb-containing electrodes. Importantly, the capacity fade rate after 106 cycles for the Pb and Pb blended with hard carbon full cells is comparable to the hard carbon full cells and indicates that through tailoring electrolyte recipes, Pb-containing full cells could eventually achieve the excellent lifetimes of hard carbon-based full cells.

In many cases capacity loss in transition metal oxide/hard carbon sodium-ion batteries aligns with the degradation of the electrolyte and a continuously reforming solid-electrolyte interphase at the negative electrode. In this work we further adapted electrolyte analysis methodologies to investigate the degradation of the electrolyte within sodium-ion batteries, specifically, the extraction of electrolytes from overfilled pouch cells and its subsequent analysis using a variety of analytical tools. The greatest degradation of the electrolyte occurs when sodium hexafluorophosphate and dimethyl carbonate are used together in a cell packaged with polyethylene terephthalate tape. We demonstrate that this degradation can be mitigated by changing the salt from sodium hexafluorophosphate to sodium bis(fluorosulfonyl)imide. Further, through several pouch bag experiments, where electrolyte is stored without a jellyroll, we demonstrate that the main pathway of electrolyte degradation stems from the formation of sodium alkoxides. Moreover, we show that such reactions proceed more rapidly in a sodium-based electrolyte as opposed to a lithium-based electrolyte. Additionally, the effect of polyethylene terephthalate tape degradation is explored for sodium-ion batteries. Finally, cell lifetimes are systematically rationalized throughout the work by considering the results of the electrolyte analysis after formation and correlations between solvent degradation and cell performance are illustrated.