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LiMn0.6Fe0.4PO4has 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 LiMn0.6Fe0.4PO4/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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Communication — The Impact of Co-solvent Selection for Dimethyl-2,5-dioxahexane carboxylate in Sodium Ion Batteries
Traditional linear carbonates including dimethyl carbonate (DMC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) were investigated as co-solvents for the dimethyl-2,5-dioxahexane carboxylate (DMOHC)-based electrolyte in Na0.97Ca0.03[Mn0.39Fe0.31Ni0.22Zn0.08]O2(NCMFNZO)/hard carbon (HC) pouch cells. The EMC-containing cell displays excellent electrochemical performance, exhibiting only a 1.6 mAh irreversible capacity loss during 500 h of storage at 4 V and 40 °C, and maintaining over 80% capacity retention after 200 cycles up to 4 V at 40 °C. Severe gas evolution and Na plating issues are present in all the tested systems.
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- Award ID(s):
- 2301719
- PAR ID:
- 10598758
- Publisher / Repository:
- IOP Science
- Date Published:
- Journal Name:
- ECS Advances
- Volume:
- 3
- Issue:
- 2
- ISSN:
- 2754-2734
- Page Range / eLocation ID:
- 020504
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The thermal stability of ∼420 mAh Na0.97Ca0.03[Mn0.39Fe0.31Ni0.22Zn0.08]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. LiNi0.8Mn0.1Co0.1O2/graphite + SiOxpouch 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.more » « less
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The effects of fluoroethylene carbonate (FEC) electrolyte additive on charged sodium ion electrode/electrolyte reactivity at elevated temperatures were investigated using accelerating rate calorimetry (ARC). The beneficial effect of FEC on cell lifetime was demonstrated using Na0.97Ca0.03[Mn0.39Fe0.31Ni0.22Zn0.08]O2(NCMFNZO)/hard carbon (HC) pouch cells first prior to ARC measurements. Electrodes from these pouch cells were utilized as sample materials and 1.0 M NaPF6in propylene carbonate (PC):ethyl methyl carbonate (EMC) (1:1 by vol.) was chosen as control electrolyte. Adding 2 wt% and 5 wt% FEC to the electrolyte does not significantly affect the reactivity of de-sodiated NCMFNZO compared to the control electrolyte. However, the addition of FEC obviously changed the reactivity between sodiated HC and electrolytes, especially by showing a suppression on the exothermal behavior between 160 °C and 230 °C. These results give a head to head comparison of the reactivity of FEC additive containing electrolytes with charged sodium ion electrode materials at elevated temperatures and show that the use of FEC at additive levels should not compromise the cell safety when extending cell lifetime.more » « less
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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.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript
- Journal Article:
- https://doi.org/10.1149/2754-2734/ad4e48
