Key Takeaways & Executive Findings
- •• FeNi bimetallic doped carbon coating on NaTi2(PO4)3 significantly enhances electronic conductivity and Na+ migration, improving rate capability and cycling stability. • The NTP–C–FeNi composite delivers a high reversible capacity of 116.75 mAh·g−1 at 0.1 A·g−1, retaining 95.9% of initial capacity, and maintains 85.3% capacity retention after 500 cycles at 1.5 A·g−1. • The synergistic effect of FeNi doping and carbon coating widens Na+ transport pathways and accelerates insertion/extraction, addressing the intrinsic poor conductivity of NTP. • The findings demonstrate the potential of bimetallic doped carbon-modified NTP as a promising anode material for practical aqueous sodium-ion batteries.
Abstract
NaTi2(PO4)3 (NTP) is a material with a NASICON structure, a three-dimensional open type skeleton, and suitable negative voltage window, which is widely regarded as a magnetic anode material for aqueous sodium ion batteries (ASIBs). However, NTP’s intrinsically poor conductivity hampers their use in ASIBs. Herein, bimetallic doped carbon material was designed and combined with the sol–gel method to prepare NaTi2(PO4)3–C–FeNi (NTP–C–FeNi) composite materials. This bimetallic doped carbon composite NTP material not only has a large specific surface area, but also effectively improves conductivity and promotes rapid migration of Na+. Following the rate performance test, NTP–C–FeNi retained a reversible capacity of 116.75 mAh·g−1 at 0.1 A·g−1, representing 95.9% of the first cycle capacity. After 500 cycles at 1.5 A·g−1, the cycle fixity was 85.3%. The enhancement of electrochemical performance may owe to the widening of pathways and acceleration of Na+ insertion/extraction facilitated by FeNi–C doping, while the carbon coating effectively promotes electrode charge transfer. The results indicate that the bimetallic doped carbon composite NaTi2(PO4)3 holds potential for practical applications in novel aqueous sodium ion battery systems.
1. Introduction
Battery technology is considered a reliable means for efficiently storing both conventional and renewable energy. Although lithium-ion batteries (LIBs) continue to dominate the market, it is anticipated that multiple battery types will coexist in the future [1–4]. Aqueous batteries are increasingly gaining attention due to their low cost, high safety, and environmental friendliness [5–6]. However, the consumption of lithium resources may lead to supply shortages [7–8]. As a result, aqueous sodium ion batteries (ASIBs), which are characterized by widespread resource availability, low production cost, and reduced environmental impact, are expected to emerge as a promising alternative to LIBs [9–11].
As the core component of batteries, the development of stable and reliable electrode materials has become a top priority [12]. NaTi2(PO4)3 (NTP) is characterized by a three-dimensional structure, enabling the reversible insertion and extraction of sodium ions, facilitating the reversible transformation between NaTi2(PO4)3 and Na3Ti2(PO4)3 [13]. Additionally, aqueous electrolytes are demonstrated to exhibit better conductivity, lower viscosity, and superior sodium ion transfer kinetics compared to non-aqueous electrolytes, outperforming lithium-ion secondary batteries in these aspects [14]. Nevertheless, owing to the isolated TiO6 octahedra within the NTP structure, the material exhibits poor electronic conductivity and suboptimal electrochemical performance in its pure phase.
In view of this, pure-phase NTP has been successively modified by researchers to improve its electrochemical performance. The general modifications include coating [15–17], structure optimization [18–20], and doping [21–23]. The performance of NTP materials can be improved through coating, resulting in higher energy density and longer cycle life. As reported by Xu et al. [24], carbon-coated porous NTP nanorods have been shown to significantly improve long-cycle performance. Furthermore, the optimization of the nanostructure provides nanoscale channels for sodium ions, and the large contact area between the electrolyte and the electrode facilitates enhanced electrochemical performance [25]. Additionally, the small particle size of NTP shortens the diffusion paths of Na+ and enhances the insertion and extraction of Na+, thereby improving the electrochemical performance of the electrodes. Wu et al. [26] designed, for the first time, a micro-sized 3D graphene network embedded with nanoscale porous NASICON-type NTP particles, which retained 80% of its initial charge capacity after 1000 cycles at 10 C. Doping of NTP can be divided into body doping and carbon layer doping. Doping the Ti sites in NTP with metal cations [27–28] can enlarge the size of the cell while keeping the original crystal structure unaffected, thereby providing a larger sodium ion transport channel and a larger intercalation space. For instance, Difi et al. [29] reported Na1.5Fe0.5T...
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Junling Che, Jiaojiao Yu, Tong Xu, Junchao Ma, Kang Yu, Jian Qin, Wei Ren, Yanmin Jia, Xifei Li (2025). Sodium storage properties of Fe, Ni-bimetallic doped carbon-modified NaTi2(PO4)3. Int. Journal of Minerals, Metallurgy and Materials (矿物冶金与材料学报). https://doi.org/10.1007/s12613-025-3087-9
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Frequently Asked Questions
What is the main challenge of NaTi2(PO4)3 in aqueous sodium-ion batteries?
NaTi2(PO4)3 (NTP) suffers from intrinsically poor electronic conductivity due to isolated TiO6 octahedra, which hampers its electrochemical performance in aqueous sodium-ion batteries.
How does FeNi bimetallic doping improve the performance of NaTi2(PO4)3?
FeNi bimetallic doping, combined with carbon coating, widens Na+ transport pathways and accelerates Na+ insertion/extraction, while the carbon coating enhances charge transfer, collectively improving conductivity and electrochemical performance.
What are the key electrochemical results of the NTP–C–FeNi composite?
The NTP–C–FeNi composite retained a reversible capacity of 116.75 mAh·g−1 at 0.1 A·g−1 (95.9% of initial capacity) and maintained 85.3% capacity retention after 500 cycles at 1.5 A·g−1.
What method was used to prepare the NTP–C–FeNi composite?
The composite was prepared using a sol–gel method combined with bimetallic doped carbon material design.
What is the potential application of this material?
The bimetallic doped carbon composite NaTi2(PO4)3 shows potential for practical applications in novel aqueous sodium-ion battery systems.
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