Low-cost and highly safe solid-phase sodium ion battery with a Sn–C nanocomposite anode
Graphical abstract
Introduction
Rechargeable lithium-ion batteries (LIBs) are the most commonly used battery for portable electronic devices and e-mobility applications and have potential for next-generation large-scale charge storage because of their higher energy and power densities compared to other rechargeable batteries. However, there is concern that the global lithium supply is insufficient to satisfy the increasing demand for LIBs. Sodium ion batteries (SIBs) are being considered as an alternative to LIBs for large-scale electrical energy storage devices and are attracting increasing attention due to abundant sodium resources and low price of starting materials [1]. Sodium intercalation is very similar to that of lithium, and the voltage, stability, and diffusion properties of SIBs are becoming competitive with those of LIBs. In this respect, sodium ions are much more efficient than lithium ions. However, sodium ions have a much larger radius (0.102 nm) than lithium ions (0.076 nm), and are heavier, which slows the deintercalation of Na ions and limits the cycling and speed performance [2], [3], [4], [5], [6]. Moreover, as demand for new applications in large energy storage increases, the energy density, power density, and safety of the systems need to be improved.
A few sodium storage anode materials have demonstrated suitable discharge capacity and efficient cyclability [5]. It is known that graphite is an excellent lithium-ion storage anode, but it fails to intercalate sodium effectively, attributed to the graphene interlayer distance (0.334 nm) being much smaller than the size of the sodium ions [6], [7]. Si-based materials are expected to be a next-generation anode for LIBs but not SIBs because Si cannot incorporate sodium ions [4]. To date, various anode materials for sodium ion storage have been explored, mainly metals and alloys (e.g., Sn, Sb, Ge, SnS2, and Na3P) [8], [9], metal oxides/sulfides [10], carbonaceous materials, and their composites [11]. Among them, Sn is a promising anode material because of its high theoretical capacity (847 mA h g−1 with Na15Sn4, Na/Na+), low cost, low environmental impact, and sufficiently low operation potentials versus Na/Na+. However, the 520% volume expansion when Sn is converted Na15Sn4 greatly limits the achievable capacity [6]. During electrochemical reaction, this enormous volume change will result in the continuous trituration of electrode active materials and a rapid degradation of the cyclability [12], [13]. Sn/Na batteries have low energy efficiency due to continuous sodiation, which causes the generation of residual stress at the Sn anode [5], [14], [15]. Sn can be composited with carbon or metal elements such as hard carbon and cobalt [4], [5], [16]. Carbon and cobalt retain their structural integrity during continuous desodiation, while Sn can reversibly alloy with sodium, and is completely converted to Na15Sn4. The latter acts as an active material that can provide a theoretical capacity of 847 mA h g−1 [1], [5], [17], [18]. The properties of the carbon-coated Sn particles are controlled by heat treatment, and during this process, reasonable stress control is obtained by accurately controlling the heat treatment temperature to prevent high volume changes [6], [19], [20], [21], [22], [23], [24]. When Sn is combined with a conductive matrix such as carbon [25], the aggregation of Sn is reduced and the volume expansion is somewhat compensated to maintain the structural integrity of the electrode. In addition, the Sn–C composite anode stabilizes the structure and interface of the Sn nanoparticles to improve the cycling performance [26].
Among the various electrolytes for high-performance SIBs, the conducting ceramic-based solid-state electrolytes have excellent safety, non-volatility, high ion conductivity, durability, and resistance to temperature changes [7]. The solid electrolyte is useful for an electrode with a high operation potential over a wider electrochemical potential window than commercial organic liquid electrolytes [8]. However, ceramic solid electrolytes have low mechanical strength and high interfacial resistance with electrodes, which is a large barrier in the development of high-safety solid-state SIBs. To solve these problems, a conducting ceramic was composited with a polymer and a low concentration of liquid electrolyte, which improved the mechanical properties, reduced the interfacial resistance, and increased the ion conductivity [27], [28]. Na3Zr2Si2PO12 is a Na-conducting ceramic with a NASICON structure and has high ion conductivity (>10–4 S cm−1). The application of a Na3Zr2Si2PO12-based composite solid-phase electrolyte can improve the electrochemical properties of Sn–C SIBs by suppressing the volume expansion of Sn particles.
In this study, Na3Zr2Si2PO12 was prepared using a simple and inexpensive a solid-state method [12], [13] and Sn–C nanocomposite was prepared using a simple, one-pot synthesis method using tin (IV) acetate and sucrose. To prepare a hybrid solid-phase electrolyte, Na3Zr2Si2PO12 was mixed with a polymer solution. The Na3Zr2Si2PO12-based hybrid solid-phase electrolyte (HSE) showed high ionic conductivity, high thermal stability, and high electrochemical stability. The Sn–C nanocomposite-based anode had a very stable cycling performance and excellent high-rate capability for SIBs. Moreover, to the best of our knowledge, this is the first report of a Sn–C nanocomposite-based SIB using a sodium-conducting ceramic composite solid-phase electrolyte.
Section snippets
Preparation of the HSE
Na3Zr2Si2PO12 was prepared by a wet solid-state reaction. The starting materials were SiO2 (99%, 10 μm; Daejung), Na3PO4∙12H2O (99%; Sigma Aldrich), and ZrO2 (99%, 5 μm; Sigma Aldrich). To obtain stoichiometric Na3Zr2Si2PO12, 0.1 M Na3PO4∙12H2O, 0.2 M SiO2, and 0.2 M ZrO2 were mixed in distilled water for 1 h using a high-energy ball mill, and the mixture was dried at 80 °C for 24 h in a drying oven. Then, the material was calcined in a box furnace (Hantech Co. Ltd. South Korea) in two steps:
Results and discussion
The XRD pattern of the Sn–C nanocomposite obtained by a simple one-pot synthesis process is shown in Fig. 1a. Elemental analysis revealed a carbon content of 50.3 wt.% and tin content of 49.7 wt.%. The aim of the synthesis experiment was to achieve the Sn–C structure to provide a stable electron conductivity matrix that minimizes the volume changes and prevents stress from the volume change of the Sn particles. In the XRD data of the Sn–C, metallic Sn and C peaks were observed. The Sn–C
Conclusions
The Sn–C/HSE nanocomposite enabled a high reversible capacity of the Sn anode for SIB applications. The Sn–C nanocomposite has a unique structure in which Sn nanoparticles are embedded in an amorphous carbon host derived from sucrose. The HSE was nonflammable and had a high ionic conductivity. Moreover, the HSE is expected to suppress the growth of sodium dendrites as it showed a stable plating/stripping voltage. The carbon host serves as a structural buffer to prevent the volume expansion of
Conflict of 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.
CRediT authorship contribution statement
Hakgyoon Yu: Methodology, Investigation, Writing - review & editing. Kyu Seomoon: Methodology. Jeha Kim: Methodology, Project administration. Jae-Kwang Kim: Supervision, Writing - review & editing.
References (42)
- et al.
J. Alloys Compd.
(2020) - et al.
Mater. Lett.
(2018) - et al.
J. Power Sources
(2019) - et al.
Electrochim. Acta
(2016) - et al.
Energy Storage Mater.
(2019) - et al.
Electrochim. Acta
(2014) - et al.
Electrochim. Acta
(2015) - et al.
Adv. Funct. Mater.
(2015) - et al.
J. Power Sources
(2016) - et al.
Energy Convers. Manag.
(2018)