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1. Unveiling the Thermal Stability of Sodium Ion Pouch Cells Using Accelerating Rate Calorimetry

   https://doi.org/10.1149/1945-7111/ad5e00  

   Chak, Chanmonirath Michael; Jayakumar, Rishivandhiga; Shipitsyn, Vadim; Bass, Ean; McCloskey, Reece; Zuo, Wenhua; Le, Phung_M L; Xu, Jun; Ma, Lin (July 2024, Journal of The Electrochemical Society)

   The thermal stability of ∼420 mAh Na_0.97Ca_0.03[Mn_0.39Fe_0.31Ni_0.22Zn_0.08]O₂(NCMFNZO)/hard carbon (HC) pouch cells was investigated using accelerating rate calorimetry (ARC) at elevated temperatures. 1 m NaPF₆in propylene carbonate (PC):ethyl methyl carbonate (EMC) (1:1 by volume) was used as a control electrolyte. Adding 2 wt% fluoroethylene carbonate to the electrolyte improves the cell’s thermal stability by decreasing the self-heating rate (SHR) across the whole testing temperature range. The selected states-of-charge (SoC), including 70%, 84%, and 100%, exhibit minimal impact on the exothermic behavior, except for a slight decrease in SHR after ∼275 °C at 70% SoC. When compared to traditional lithium-ion batteries operating at 100% SoC, NCMFNZO/HC pouch cells demonstrate inferior thermal stability compared to LiFePO₄(LFP)/graphite pouch cells, displaying a higher SHR from 220 to 300 °C. LiNi_0.8Mn_0.1Co_0.1O₂/graphite + SiO_xpouch cells exhibit the worst safety performance, with an early onset temperature of ∼100 °C and the highest SHR across the entire temperature range. These results offer a direct comparison of the impact of SoC and electrolyte compositions on the thermal stability of SIBs at elevated temperatures, highlighting that there is still room for improvement in SIBs safety performance compared to LFP/graphite chemistry. 

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2. Thermal Stability Comparison of LiFePO ₄ /Graphite and LiMn _0.6 Fe _0.4 PO ₄ /Graphite Pouch Cells using Accelerating Rate Calorimetry

   https://doi.org/10.1149/1945-7111/ae08f2  

   Chak, Chanmonirath Michael; Shipitsyn, Vadim; Ma, Lin (September 2025, Journal of The Electrochemical Society)

   LiMn_0.6Fe_0.4PO₄has attracted attention as a promising, high-energy, and cost-effective alternative to LiFePO₄(LFP) for lithium-ion batteries. However, its thermal stability, especially at full cell level, remains less understood compared to LFP. This study compares the cycling performance and thermal stability of LiMn_0.6Fe_0.4PO₄/graphite and LFP/graphite pouch cells using a consistent electrolyte formulation: 1.2 m lithium bis(fluorosulfonyl)imide (LiFSI) in ethylene carbonate (EC):ethyl methyl carbonate (EMC):dimethyl carbonate (DMC) (25:5:70 by volume) with 2 wt% vinylene carbonate (VC). Thermal stability was evaluated with two ∼250 mAh pouch cells through accelerating rate calorimetry at elevated temperatures. After roughly 275 cycles at C/3 and 40 °C, the LFP/graphite cells retained 91% of their initial capacity, while LMFP/graphite cells retained 89%, indicating slightly better electrochemical stability for LFP cells. Exothermic reactions in LMFP cells initiated around 125 °C, compared to 140 °C for LFP, implying higher thermal vulnerability. Despite this, both cell types exhibited similar self-heating rates below 0.1 °C min⁻¹, demonstrating strong safety performance. Overall, although LMFP offers a higher voltage window, its thermal stability and cycling performance still slightly lag behind LFP. 

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3. Fluorinated ethylene carbonate as additive to glyme electrolytes for robust sodium solid electrolyte interface

   https://doi.org/10.1016/j.xcrp.2023.101356  

   Sarkar, Susmita; Lefler, Matthew J.; Vishnugopi, Bairav S.; Nuwayhid, R. Blake; Love, Corey T.; Carter, Rachel; Mukherjee, Partha P. (April 2023, Cell Reports Physical Science)

   The utilization of alkali metal anodes is hindered by an inherent instability in organic electrolytes. Sodium is of growing interest due to its high natural abundance, but the carbonate electrolytes popular in lithium systems cannot form a stable solid electrolyte interphase (SEI) with a sodium electrode. Using half-cell and symmetric-cell analysis, we identify specific glyme (chain ether) electrolytes that produce thin, predominantly inorganic SEI at the sodium metal interface, and we study the effect of ethylene carbonate and fluoroethylene carbonate (FEC) additives on the SEI formed in these systems via X-ray photoelectron spectroscopy. Through in situ optical microscopy, we observe the onset and growth of sodium dendrites in these electrolytes. We determine that the SEI formed by glyme alone may not support extensive or extreme cycling conditions, but the addition of FEC provides a more robust SEI to facilitate numerous consistent sodium plating and stripping cycles. 

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4. Low-Concentration Electrolyte Design for Wide-Temperature Operation in Sodium Metal Batteries

   https://doi.org/10.1149/1945-7111/ada372  

   Zhang, Qipeng; Wang, Xin; Li, Hao; Qiao, Rui (January 2025, Journal of The Electrochemical Society)

   Sodium metal batteries (SMBs) are cost-effective and environmentally sustainable alternative to lithium batteries. However, at present, limitations such as poor compatibility, low coulombic efficiency (CE), and high electrolyte cost hinder their widespread application. Herein, we propose a non-flammable, low-concentration electrolyte composed of 0.3 M NaPF₆in propylene carbonate (PC), fluoroethylene carbonate (FEC), and 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE). This low-concentration electrolyte not only reduces cost but also delivers rapid ion diffusion and superior wetting properties. While the Na||FePO₄system with this electrolyte demonstrates slightly reduced performance at room temperature compared to standard-concentration formulations (S-PFT), it excels at both high (55 °C) and low (−20 °C) temperatures, showcasing its balanced performance. At 0.5 C (charge)/1 C (discharge), capacity retention reaches 92.8% at room temperature and 98.5% at elevated temperature, with CE values surpassing 99% and 99.63%, respectively, and significant performance sustained at −20 °C at 0.2 C. This electrolyte development thus offers a well-rounded, economically viable path to high-performance SMBs for diverse environmental applications. 

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5. Unveiling the Impact of Solvent Fluorination on Ether‑Based Electrolytes in Sodium‑Ion Pouch Cells

   https://doi.org/10.1149/1945-7111/ae204f  

   Jayakumar, Rishivandhiga; Cousineau, Benjamin; Chevrier, Vincent L; Chak, Chanmonirath Michael; Shipitsyn, Vadim; Zheng, Allen; Zhu, Yuwei; Pastel, Glenn; Yu, Zhiao; Mu, Linqin; et al (November 2025, Journal of The Electrochemical Society)

   Sodium-ion batteries (SIBs) with Earth-abundant elements are promising for global electrification, but electrolyte stability impacts electrochemical performance and safety. This study compares non-fluorinated 1,2-diethoxyethane (DEE) and fluorinated 1,2-bis(2,2-difluoroethoxy)ethane (F4DEE) as electrolyte solvents in Na_0.97Ca_0.03[Mn_0.39Fe_0.31Ni_0.22Zn_0.08]O₂(NCMFNZO)/hard carbon (HC) pouch cells up to 4.0 V. Fluorination slightly reduces ionic conductivity and increases viscosity but significantly enhances electrochemical stability and safety. Cells with F4DEE exhibit lower impedance, reduced gas evolution, and less voltage decay during high-voltage storage at 40 °C. Long-term cycling shows ∼85% capacity retention after 500 cycles at 25 °C and ∼80% at 40 °C with less transition metal dissolution, outperforming DEE-based cells. Isothermal microcalorimetry reveals lower parasitic heat generation with F4DEE, while soft X-ray absorption spectroscopy confirms stabilized Ni and Mn oxidation states, indicating suppressed electrolyte oxidation. Accelerating rate calorimetry reveals improved thermal stability with F4DEE. These findings highlight fluorinated ether solvents as a promising approach to enhance SIB lifespan and safety, with ongoing challenges requiring further solvent and additive optimization. 

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