Research Development on Sodium-Ion Batteries

Energy production and storage technologies have attracted a great deal of attention for day-to-day applications. In recent decades, advances in lithium-ion battery (LIB) technology have improved living conditions around the globe. LIBs are used in most mobile electronic devices as well as in zero-emission electronic vehicles. However, there are increasing concerns regarding load leveling of renewable energy sources and the smart grid as well as the sustainability of lithium sources due to their limited availability and consequent expected price increase. Therefore, whether LIBs alone can satisfy the rising demand for small- and/or mid-to-large-format energy storage applications remains unclear. To mitigate these issues, recent research has focused on alternative energy storage systems. Sodium-ion batteries (SIBs) are considered as the best candidate power sources because sodium is widely available and exhibits similar chemistry to that of LIBs; therefore, SIBs are promising next-generation alternatives. Recently, sodiated layer transition metal oxides, phosphates and organic compounds have been introduced as cathode materials for SIBs. Simultaneously, recent developments have been facilitated by the use of select carbonaceous materials, transition metal oxides (or sulfides), and intermetallic and organic compounds as anodes for SIBs. Apart from electrode materials, suitable electrolytes, additives, and binders are equally important for the development of practical SIBs. Despite developments in electrode materials and other components, there remain several challenges, including cell design and electrode balancing, in the application of sodium ion cells. In this article, we summarize and discuss current research on materials and propose future directions for SIBs. This will provide important insights into scientific and practical issues in the development of SIBs.

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Sodium-ion batteries: present and future

Room-temperature stationary sodium-ion batteries have attracted great attention particularly in large-scale electric energy storage applications for renewable energy and smart grid because of the huge abundant sodium resources and low cost. In this article, a variety of electrode materials including cathodes and anodes as well as electrolytes for room-temperature stationary sodium-ion batteries are briefly reviewed. We compare the difference in storage behavior between Na and Li in their analogous electrodes and summarize the sodium storage mechanisms in the available electrode materials. This review also includes some new results from our group and our thoughts on developing new materials. Some perspectives and directions on designing better materials for practical applications are pointed out based on knowledge from the literature and our experience. Through this extensive literature review, the search for suitable electrode and electrolyte materials for stationary sodium-ion batteries is still challenging. However, after intensive research efforts, we believe that low-cost, long-life and room-temperature sodium-ion batteries would be promising for applications in large-scale energy storage system in the near future.

Room-temperature stationary sodium-ion batteries for large-scale electric energy storage

Lithium (Li) metal has been considered as an important substitute for the graphite anode to further boost the energy density of Li-ion batteries. However, Li dendrite growth during Li plating/stripping causes safety concern and poor lifespan of Li metal batteries (LMB). Herein, fluoroethylene carbonate (FEC) additives are used to form a LiF-rich solid electrolyte interphase (SEI). The FEC-induced SEI layer is compact and stable, and thus beneficial to obtain a uniform morphology of Li deposits. This uniform and dendrite-free morphology renders a significantly improved Coulombic efficiency of 98% within 100 cycles in a Li | Cu half-cell. When the FEC-protected Li metal anode matches a high-loading LiNi0.5Co0.2Mn0.3O2 (NMC) cathode (12 mg cm−2), a high initial capacity of 154 mAh g−1 (1.9 mAh cm−2) at 180.0 mA g−1 is obtained. This LMB with conversion-type Li metal anode and intercalation-type NMC cathode affords an emerging energy storage system to probe the energy chemistry of Li metal protection and demonstrates the material engineering of batteries with very high energy density.

Fluoroethylene Carbonate Additives to Render Uniform Li Deposits in Lithium Metal Batteries

The room temperature Na-ion secondary battery has been under focus lately due to its feasibility to compete against the already well-established Li-ion secondary battery. Although there are many obstacles to overcome before the Na-ion battery becomes commercially available, recent research discoveries corroborate that some of the cathode materials for the Na-ion battery have indeed indisputable advantages over its Li-ion counterparts. In this publication, a comprehensive review of layered oxides (NaTMO2, TM = Ti, V, Cr, Mn, Fe, Co, Ni, and a mixture of 2 or 3 elements) as a viable Na-ion battery cathode is presented. Single TM systems are well characterized not only for their electrochemical performance but also for their structural transitions during the cycle. Binary TM systems are investigated in order to address issues regarding low reversible capacity, capacity retention, operating voltage, and structural stability. As a consequence, some materials already have reached an energy density of 520 mW h g−1, which is comparable to that of LiFePO4. Furthermore, some ternary TM systems retained more than 72% of their capacity along with over 99.7% Coulombic efficiency for 275 cycles. The goal of this review is to present the development of Na layered oxide materials in the past as well as the state of the art today in order to emphasize the compatibility and durability of layered oxides as powerful candidates for Na-ion battery cathode materials.

A comprehensive review of sodium layered oxides: powerful cathodes for Na-ion batteries

P2-type Na0.67Mn0.65Fe0.2Ni0.15O2 Cathode Material with High-capacity for Sodium-ion Battery

Stable Na+ ion storage cathodes with adequate reversible capacity are now greatly needed for enabling Na-ion battery technology for large scale and low cost electric storage applications. In light of the superior Li+ ion storage performance of layered oxides, pure P2-phase Na0.67[Mn0.65Ni0.15Co0.2]O2 microflakes are synthesized by a simple sol–gel method and tested as a Na+ ion storage cathode. These layered microflakes exhibit a considerably high reversible capacity of 141 mA h g−1 and a slow capacity decay to 125 mA h g−1 after 50 cycles, showing much better cyclability than previous NaMnO2 compounds. To further enhance the structural and cycling stability, we partially substituted Co3+ by Al3+ ions in the transition-metal layer to synthesize Na0.67[Mn0.65Ni0.15Co0.15Al0.05]O2. As expected, the Al-substituted material demonstrates a greatly improved cycling stability with a 95.4% capacity retention over 50 cycles, possibly serving as a high capacity and stable cathode for Na-ion battery applications.

Synthesis and electrochemical behaviors of layered Na0.67[Mn0.65Co0.2Ni0.15]O2 microflakes as a stable cathode material for sodium-ion batteries

A honeycomb layered Na3Ni2SbO6 is synthesized as a cathode for sodium-ion batteries. This new host material exhibits a high capacity of 117 mA h g(-1), a remarkable cyclability with 70% capacity retention over 500 cycles at a 2C rate, and a superior rate capability with >75% capacity delivered even at a very high rate of 30 C (6000 mA g(-1)). These results open a new perspective to develop high-capacity and high-rate Na-ion batteries for widespread electric-energy-storage applications.

A honeycomb-layered Na3Ni2SbO6: a high-rate and cycle-stable cathode for sodium-ion batteries.

Na-stabilized Li1.2−xNax[Co0.13Ni0.13Mn0.54]O2 is synthesized by introducing larger Na ions into the Li slabs of the layered material through a simple polymer-pyrolysis method. The structural and morphological characterization reveals that the Na doping leads to a more ordered structure with regular cubic morphology and enlarged Li layer spacing. Electrochemical experiments show that the Na-doped Li1.17Na0.03[Co0.13Ni0.13Mn0.54]O2 electrode can deliver larger reversible discharge capacity (307 mA h g−1), higher initial coulombic efficiency (87%), greatly improved rate capability (139 mA h g−1 at 8 C) and cycling stability (89% capacity retention after 100 cycles) in comparison with the undoped Li1.2[Co0.13Ni0.13Mn0.54]O2 electrode. The superior electrochemical performance of the Na-doped material is due to the enhancement of the structural stability and the enlargement of the Li slab space of the layered material, which facilitate the stabilization of the host lattice and allow rapid diffusion of Li ions in the bulk lattice.

Enhanced high-rate capability and cycling stability of Na-stabilized layered Li1.2[Co0.13Ni0.13Mn0.54]O2 cathode material

Sodium-ion batteries are now considered as a low-cost alternative to lithium-ion technologies for large-scale energy storage applications; however, their safety is still a matter of great concern for practical applications. In this paper, a safer sodium-ion battery is proposed by introducing a nonflammable phosphate electrolyte (trimethyl phosphate, TMP) coupled with NaNi0.35Mn0.35Fe0.3O2 cathode and Sb-based alloy anode. The physical and electrochemical compatibilities of the TMP electrolyte are investigated by igniting, ionic conductivity, cyclic voltammetry, and charge-discharge measurements. The results exhibit that the TMP electrolyte with FEC additive is completely nonflammable and has wide electrochemical window (0-4.5 V vs. Na/Na+), in which both the Sb-based anode and NaNi0.35Mn0.35Fe0.3O2 cathode show high reversible capacity and cycling stability, similarly as in carbonate electrolyte. Based on these results, a nonflammable sodium-ion battery is constructed by use of Sb anode, NaNi0.35Mn0.35Fe0.3O2 cathode, and TMP + 10 vol% FEC electrolyte, which works very well with considerable capacity and cyclability, demonstrating a promising prospect to build safer sodium-ion batteries for large-scale energy storage applications.

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Dingding Yuan

Papers

P2-type Na0.67Mn0.65Fe0.2Ni0.15O2 Cathode Material with High-capacity for Sodium-ion Battery

Synthesis and electrochemical behaviors of layered Na0.67[Mn0.65Co0.2Ni0.15]O2 microflakes as a stable cathode material for sodium-ion batteries

A honeycomb-layered Na3Ni2SbO6: a high-rate and cycle-stable cathode for sodium-ion batteries.

Enhanced high-rate capability and cycling stability of Na-stabilized layered Li1.2[Co0.13Ni0.13Mn0.54]O2 cathode material

A Safer Sodium-Ion Battery Based on Nonflammable Organic Phosphate Electrolyte.