EDP Sciences logo
Submit your paper
Search
Menu
All issues Volume 29 / No 4 (August 2024) Wuhan Univ. J. Nat. Sci., 29 4 (2024) 297-300 Full HTML
Open Access
Issue
Wuhan Univ. J. Nat. Sci.
Volume 29, Number 4, August 2024
Page(s) 297 - 300
DOI https://doi.org/10.1051/wujns/2024294297
Published online 04 September 2024

© Wuhan University 2024

Licence Creative CommonsThis is an Open Access article distributed under the terms of the Creative Commons Attribution License (https://creativecommons.org/licenses/by/4.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

Carbonate-based electrolytes still retain their top preference in sodium-ion battery (SIB) as in lithium-ion battery (LIBs) owing to their cost-effectiveness and accessibility. However, extensive studies have consistently demonstrated a mismatch between the hard carbon (HC) anode and carbonate-based electrolytes[1,2]. Specifically, as for low-concentration carbonate-based electrolytes (LCEs), the composition of solid electrolyte interphase (SEI) primarily comprises organic species, such as sodium dicarbonates ((ROCO2Na)2), semicarbonates (ROCO2Na)[3,4]. These components can offer flexibility and favorable conductivity, whereas their poor mechanical property renders them susceptible to crushing during cycling. Moreover, the significant solubility of organic species results in continuous decomposition of electrolytes and the formation of new SEI film during cycling. These side reactions would lead to substantial gas evolution and a subpar cycling performance.

As well recognized, the robust and uniform SEI is the key to maintaining the compatibility of the electrode/electrolyte interface, while the properties of SEI depend on its composition. Inorganic species like NaF and NaNxOy (arising from the decomposition of anions) have been identified with low solubility in organic electrolytes, thereby enhancing the integrity and stability of the SEI layer[5,6]. Given the poor solubility of nitrates in esters, constructing an electrode/electrolyte interface rich in fluorine seems to be a reliable approach to stabilize the long cycle life of SIBs. Approaches such as developing high-concentration electrolytes (HCEs) or high molar ratio electrolytes (HMREs) have been demonstrated the effectiveness in forming an anion-derived fluorinated (F)-rich SEI. However, the high viscosity and low ionic conductivity of HCEs and HMREs trigger sluggish Na+ kinetics and significantly worsen rate/cycle performance. How to reconcile the swift ion transport kinetics observed in LCEs with the excellent interfacial properties in HCEs remains a significant challenge.

To address the above-mentioned issues, an in-depth understanding of the incompatibility between HC anode and LCEs becomes imperative. The electron-rich surface of the HC anode during discharge tends to push the anions to the outer Helmholtz layer due to the Coulomb repulsion, instead the linear solvent with weaker polarity remains in the inner Helmholtz plane (IHP) and decomposes as the root component, resulting in solvent-derived SEI film and poor cycle life[7].

Hence, Chen et al[8] proposed a novel strategy to reconstruct the IHP of the HC anode (as shown in Fig. 1(a)). Firstly, introducing solvent that could preferentially absorb on HC surface into the electrolyte system, subsequently, leveraging its strong interaction with anions to draw anions into IHP, optimizing the Helmholtz layer and consequently forming an anion-induced F-rich interface (Fig. 1(b)). Moreover, the solvent is also expected to own flame-retardant characteristics so as to enhance the battery safety. As a proof of concept, tris(2,2,2-trifluoroethyl) phosphate (TFEP) was selected from eleven typical flame-retardant solvents by density functional theory methods with two key factors PFBE (PF6- binding energy) and CAE (carbon absorption energy) (Fig. 2(a)-(c)). As expected, the introduction of TFEP effectively reconstructs the IHP (Fig. 2(d)-(f)) and promotes the formation of a robust and thin F-rich SEI film on the surface of the HC anode (Fig. 2(g)-(i)), which manifests greatly enhanced mechanical stability, reduced SEI solubility, and accelerated Na+ ion diffusion kinetics, as evidenced by galvanostatic intermittent titration technique (GITT), time-of-flight secondary ion mass spectrometry (TOF-SIMS), atomic force microscope (AFM) and electrochemical impendence spectrum (EIS).

thumbnail Fig. 1 Strategy for the reconstruction of Helmholtz plane[8]

thumbnail Fig. 2 (a-c) Solvent selection results, (d-f) The differences of Helmholtz plane and EDLC in different electrolytes, (g-i) The properties of F-rich electrode/electrolyte in PD and PTD[8]

In conclusion, Prof Chen's group[8] realizes the reconstruction of Helmholtz plane of HC and greatly optimizes the property of electrode/electrolyte and electrochemical compatibility with ester-based electrolytes (Angew Chem Int Ed, 2024, e202407717). It is believed this novel understanding of regulating interfacial properties will provide guidance for the design of compatible LCEs and promote the development of low-cost, long-life and high-safe sodium-ion batteries.

References

  1. Sun T, Feng X L, Sun Q Q, et al. Solvation effect on the improved sodium storage performance of N-Heteropentacenequinone for sodium-ion batteries[J]. Angew Chem Int Ed, 2021, 60(51): 26806-26812. [Google Scholar]
  2. Yan L, Zhang G F, Wang J, et al. Revisiting electrolyte kinetics differences in sodium ion battery: Are esters really inferior to ethers?[J]. Energy Environ Mater, 2023, 6(4): e12523. [CrossRef] [Google Scholar]
  3. Zhang Q K, Zhang X Q, Wan J, et al. Homogeneous and mechanically stable solid-electrolyte interphase enabled by trioxane-modulated electrolytes for lithium metal batteries[J]. Nat Energy, 2023, 8: 725-735. [NASA ADS] [CrossRef] [Google Scholar]
  4. Fondard J, Irisarri E, Courrèges C, et al. SEI composition on hard carbon in Na-ion batteries after long cycling: Influence of salts (NaPF6, NaTFSI) and additives (FEC, DMCF)[J]. Journal of the Electrochemical Society, 2020, 167(7): 070526. [NASA ADS] [CrossRef] [Google Scholar]
  5. Hou L P, Li Y, Li Z, et al. Electrolyte design for improving mechanical stability of solid electrolyte interphase in lithium-sulfur batteries[J]. Angew Chem Int Ed, 2023, 62(32): e202305466. [CrossRef] [PubMed] [Google Scholar]
  6. Wang C T, Sun Z Q, Liu L, et al. A rooted interphase on sodium via in situ pre-implantation of fluorine atoms for high-performance sodium metal batteries[J]. Energy Environ Sci, 2023, 16(7): 3098-3109. [CrossRef] [Google Scholar]
  7. Yan G C, Alves-Dalla-Corte D, Yin W, et al. Assessment of the electrochemical stability of carbonate-based electrolytes in Na-ion batteries[J]. Electrochem Soc, 2018, 165(7): A1222. [CrossRef] [Google Scholar]
  8. Chen L, Chen M, Meng Q F, et al. Reconstructing Helmholtz plane enables robust F-rich interface for long-life and high-safe sodium-ion batteries[J]. Angew Chem Int Ed, 2024: e202407717. [Google Scholar]

All Figures

thumbnail Fig. 1 Strategy for the reconstruction of Helmholtz plane[8]
In the text
thumbnail Fig. 2 (a-c) Solvent selection results, (d-f) The differences of Helmholtz plane and EDLC in different electrolytes, (g-i) The properties of F-rich electrode/electrolyte in PD and PTD[8]
In the text

Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.

Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.

Initial download of the metrics may take a while.