The roles of electrolyte chemistry in hard carbon anode for potassium-ion batteries
Graphical abstract
Introduction
Lithium-ion batteries (LIBs) have been utilized in many applications in our lives, such as electrical vehicles (EVs), hybrid electric vehicles (HEVs), and portable electronics, due to their high energy density and relatively low cost [1], [2]. Moreover, due to the growing energy demand for intermit renewable energy, it is essential to keep improving energy storage technologies and developing novel reliable battery systems with lower costs [3], [4], [5], [6], [7], [8], [9], [10]. Potassium-ion batteries (PIBs) have drawn much attention in academia due to several merits of K ions as the charge carrier [11], [12], [13], [14]. K ions have similar physicochemical properties as Li ions but higher abundance on earth than the latter [15]. Thus, PIBs are considered promising large-scale energy storage devices in a renewable energy system [16]. The electricity produced from clean energy such as wind power and solar power can be stored as chemical energy in PIBs in the charging process and then be effectively released to households via electrical grids. Also, considering the similar working principles and assembly techniques of PIBs and LIBs, it is cost-effective to build PIB production lines from current LIB factories for commercialization in the future. Compared with commercial LIBs, PIBs benefit from low cost, environmentally benign, decent energy density, and high power density [17]. The colossal cost reduction could be ascribed to the cheap cathode and aluminum current collector. Especially in most popular PIB cathodes, transitional metal elements are iron or manganese instead of cobalt [18]. Even though LIBs still eclipse the other secondary battery systems in energy density, PIBs have started fulfilling the requirements of stationary energy storage devices with decent energy density and high power density [19], [20]. Especially, the ‘solvation effect’ in electrolytes enables K ions to diffuse smoothly at high current rates [21]. Although K ions have larger ionic radii (1.38 Å) than Li ions (0.76 Å) and Na ions (1.02 Å), K ions have the smallest Stokes’ radii (3.6 Å) compared with Li ions (4.8 Å) and Na ions (4.6 Å) in propylene carbonate (PC) as a non-aqueous solvent [22]. Therefore, K ions diffuse with less kinetic resistance than Li ions and exhibit relatively low standard potentials in popular organic solvents – the redox potential of K+/K is 0.15 V lower than that of Li+/Li in the mixture of ethylene carbonate (EC) with diethyl carbonate (DEC) – which promise potential high power density of PIBs [23].
Hard carbon (HC), as the most popular carbonaceous anode in PIBs, can realize high specific capacity at a low cost. Depending on the facile fabrication process, the structure of hard carbon is adjustable to maximize the storage of different charge carriers. The surface-adsorption and bulk-insertion contributions can also be tailored for battery and supercapacitor applications. However, due to the co-intercalation of K--solvent chelation, HC anodes without surface modification often suffer from severe structural damage and capacity fading during cycling, which is the main obstacle towards commercialization. Electrolytes contribute to solid-electrolyte interphase (SEI) formation and K-ion diffusion by decomposition and solvation effect, respectively. A reliable and elastic SEI can effectively suppress the capacity degradation and prevent irreversible side reactions [24]. PIB electrolytes often contain K salts and organic solvents (with additives). Popular K salts are KPF6, KClO4, KBF4, KN(SO2F)2 (potassium bis(fluorosulfonyl)imide, KFSI) and KN(SO2CF3)2 (potassium bis(trifluoromethanesulfonyl)imide, KTFSI). Carbonate ester and ether solvents, such as ethylene carbonate (EC), diethyl carbonate (DEC), and dimethoxyethane (DME), are often divided into chains and rings from the carbon arrangement. In this work, we report the macroscopic electrochemical effect of electrolytes on HC anodes and investigate the microscopic degradation mechanisms of HC in different electrolytes, especially the synergic contribution of inorganic anions (e.g., FSI-) and organic solvents (e.g., EC and DEC) in SEI formation and K-ion solvation/desolvation via electrochemical tests and characterization techniques.
Section snippets
Materials and sample preparation
Lignin with a molecular weight of 9966 g mol−1 (Advanced BioCarbon 3D Ltd) was used as the carbon precursor. Lignin is the second most abundant biofiber in nature and is composed of three interconnected monomers: sinapyl alcohol (S), coniferyl alcohol (G), and minor p-coumaryl alcohol (H). Pyrolysis, a facile carbon fabrication method, was applied to produce lignin-derived hard carbon (LHC). In a tubular furnace, lignin was pyrolyzed at 700 °C for 2 h with a heating rate of 5 °C min−1 in
Material characterizations
The morphology and structure of LHC are presented in Fig. 1. LHC’s XRD pattern in Fig. 1a displays two broad peaks centered at 22.0° and 43.1°, which are assigned to the (0 0 2) and (0 1 0) planes of graphite (JCPDS PDF No. 08-0415), respectively. According to Bragg’s law (nλ = 2dsinθ) [25], The d-spacing of LHC is estimated as 4.04 Å, which could be beneficial for hosting large-sized K ions. The broad peaks indicate the disorder and deficiencies in the typical hard carbon structure. Raman spectrum
Conclusion
In summary, we investigated the electrolyte effect on HC anode in PIBs using four common electrolytes and explained the differences in electrochemical performance from aspects of SEI formation, K-ion storage behaviors, solvated K-ion mobility, and battery degradation mechanisms. KFSI EC/DEC contributed to sufficient K-ion solvation and high-KF SEI formation, which prevented SEI corrosion and thus greatly enhanced the cycling stability and rate capability of LHC anode. The use of KFSI EC/DEC
Author contributions
Z.W. and J.L. conceived the idea, designed the research plan, and wrote the paper. Z.W. performed the synthesis and electrochemical experiments, analyzed the electrochemical and characterization results, and prepared the scientific figures. J.L. oversighted the whole project for the research activity planning and execution. J.Z. offered help in electrochemistry analysis and guidance on potassium-ion battery studies. S.S. and K.G. performed the wettability measurements. All co-authors
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
This work was supported by Nature Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), BC Knowledge Development Fund (BCKDF), Materials and Manufacturing Research Institute (MMRI), and the University of British Columbia (UBC). The authors would like to thank Dr. Michael C.P. Wang in 4D Labs at Simon Fraser University for the help on XPS characterization. The authors are grateful for Dr. Carmen Andrei in Canadian Centre for Electron Microscopy at
References (48)
- et al.
Li-ion battery materials: present and future
Mater. Today
(2015) - et al.
Development status and future prospect of non-aqueous potassium ion batteries for large scale energy storage
Nano Energy
(2019) - et al.
Potassium intercalation into graphite to realize high-voltage/high-power potassium-ion batteries and potassium-ion capacitors
Electrochem. Commun.
(2015) - et al.
Graphite as a potassium ion battery anode in carbonate-based electrolyte and ether-based electrolyte
J. Power Sources
(2019) - et al.
Potato derived biomass porous carbon as anode for potassium ion batteries
Electrochim. Acta
(2019) - et al.
Advancement in technologies for the depolymerization of lignin
Fuel Process. Technol.
(2018) - et al.
Surface tension of diethyl carbonate, 1,2-dimethoxyethane and diethyl adipate
Fluid Phase Equilib.
(2010) - et al.
TiS2 as a high performance potassium ion battery cathode in ether-based electrolyte
Energy Storage Mater.
(2018) - et al.
“Inner” and “outer” active surface of RuO2 electrodes
Electrochim. Acta
(1990) - et al.
Commercialization of lithium battery technologies for electric vehicles
Adv. Energy Mater.
(2019)
From lithium-ion to sodium-ion batteries: advantages, challenges, and surprises
Angew. Chem. Int. Ed.
Towards K-ion and Na-ion batteries as “beyond Li-ion”
The Chemical Record
A Nonflammable fluorinated carbonate electrolyte for sodium-ion batteries
Acta Phys. -Chim. Sin.
Enabling superior electrochemical properties for highly efficient potassium storage by impregnating ultrafine Sb nanocrystals within nanochannel-containing carbon nanofibers
Angew. Chem. Int. Ed. Engl.
Uniform yolk−shell Fe7S8@C nanoboxes as a general host material for the efficient storage of alkali metal ions
J. Alloy. Compd.
A yolk-shell-structured FePO4 cathode for high-rate and long-cycling sodium-ion batteries
Angew. Chem. Int. Ed. Engl.
Carbon quantum dot micelles tailored hollow carbon anode for fast potassium and sodium storage
Nano Energy
Comprehensive understanding of sodium-ion capacitors: definition, mechanisms, configurations, materials, key technologies, and future developments
Adv. Energy Mater.
Emerging non-aqueous potassium-ion batteries: challenges and opportunities
Chem. Mater.
Cathode materials for potassium-ion batteries: Current status and perspective
Electrochem. Energy Rev.
Candied-Haws-like architecture consisting of FeS2@C core-shell particles for efficient potassium storage
ACS Mater. Lett.
Kilogram-scale synthesis and functionalization of carbon dots for superior electrochemical potassium storage
ACS Nano
Abundances of chemical elements in the Earth’s crust
Geochem. Int.
Potassium-ion battery cathodes: past, present, and prospects
J. Power Sources
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