Routes to High Energy Cathodes of Sodium‐Ion Batteries

Abstract

and environmental friendliness of the batteries. As a rare metal element, Li resources in the earth and their accessibility at low cost are a serious concern for upcoming larger-scale EES applications. Therefore, it is greatly needed to develop new batteries that are built up from environmentally benign and sustainable electrode materials. In the development of these new technologies, ambient sodium-ion batteries (SIBs) are revived and actively investigated as promising alternatives to LIBs for the next-generation energy storage devices due to the natural abundance of Na resources and the similar intercalation chemistry of Na + ions to their lithium counterpart. As a "rockingchair" type battery, the charge-discharge reactions of SIBs take place through a reversible Na + -intercalation mechanism, while Na ions move off from the cathode host, pass through the electrolyte and then insert into the anode host during charge, and vice versa during discharge. Meanwhile, electrons move from anode to cathode during charge or from cathode to anode during discharge through the external circuit, thus storing or delivering electric energy in a direct electrochemical manner.Studies on Na-intercalation chemistry can be dated back to the early 1980s, [ 2,3 ] almost in the same period as the development of Li-ion technology. Soon after the fi rst demonstration of lithium intercalation compounds for battery application, [4][5][6] the Na insertion behavior of Na x CoO 2 was also revealed as a cathode host. [ 7,8 ] Earlier pioneering works on earlier development of Na-ion technologies were given in a recent review. [ 9 ] Unfortunately, development of SIBs has almost halted in the past three decades since the successful commercialization of LIBs in the 1990s. A major reason for this embarrassment is the diffi culty to fi nd Na-host materials with comparable high capacities and suitable working potentials as their Li analogues. Because of larger atomic weight and less negative potential of Na than Li, Na-host materials have to suffer from a lower energy density than their Li counterparts. Furthermore, the larger ion radius of Na + (1.02 Å) than that of Li + (0.76 Å) make them kinetically frustrated during their insertion and transport in the host lattices, which further decreases the capacity utilization and rate performance of the materials.In recent years, great efforts have been made to achieve considerable success in understanding the Na + intercalation chemistry and in developing Na-host materials. It is now recognized that Na-host materials cannot simply be duplicated from their lithium analogues. For example, Okada and Sodium-ion batteries (SIBs) are now being actively developed as low cost and sustainable alternatives to lithium-ion batteries (LIBs) for large-scale electric energy storage applications. In recent years, various inorganic and organic Na compounds, mostly mimicked from their Li counterparts, have been synthesized and tested for SIBs, and some of them indeed demonstrate comparable specifi c capacity to the presentl...

Progress in High‐Voltage Cathode Materials for Rechargeable Sodium‐Ion Batteries

“…[27] The ordered Na 2 RuO 3 with in-plan honeycomb ordering exhibited a capacity of 180 mA h g −1 based on a 1.3-electron reaction, while disordered Na 2 RuO 3 delivered only 135 mA h g −1 with a 1.0-electron reaction. The additional capacity delivered by the ordered Na 2 RuO 3 could be attributed to the formation of an ordered intermediate O1-phase NaRuO 3 . A shortest OO distance of 2.580 Å stemmed from the distortion of RuO 6 octahedra in the ordered [Na 1/3 Ru 2/3 ]O 2 slabs raised the energy level of the antibonding σ* orbital of the OO bond to the Fermi level, thereby triggering the O-redox reaction.…”

“…[2] The boosting market requirement for rechargeable batteries raises concerns on the economic sustainability of LIBs because of the rare elemental abundance of Li on earth (20 ppm) and its uneven geographic distribution. [3] Thus, rechargeable batteries built up from costeffective and naturally abundant electrode materials will become an appealing choice for next generation EES systems. [4] Sodium has a rich natural abundance, a wide global distribution (available from seawater), and a suitable electrochemical high-voltage layered Na x MO 2 (0 < x ≤ 1, M represents transitional metal), Na-rich materials Na 2 M′O 3 (M′ = Ir, Ru, Sn, etc.…”

Layered Oxide Cathodes for Sodium‐Ion Batteries: Phase Transition, Air Stability, and Performance

“…As a result, sodiumbased electroactive materials are enjoying renewed interest especially for very low cost systems for grid storage. [11,12] Given that cathode materials are the key component that determines energy density and cost, tremendous efforts have been devoted to exploring suitable positive electrode materials with high reversible capacity, rapid Na ions insertion/extraction, and good cycling stability in the past few years. [13,14] A broad range of compounds, including layered oxides, polyanionic frameworks, hexacyanoferrates, and organics, have…”

Flexible Electrodes for Sodium‐Ion Batteries: Recent Progress and Perspectives

“…To address this problem, optimizing the chemical composition, tailoring the lattice structures, and regulating the morphologies of the host materials seem to be the most applicable strategies, and there have already been several excellent reviews. [11][12][13][14][15][16] As for technological innovation, the traditional fabrication processes mainly based on the slurrycasting method not only make SIBs typically rigid, thick, bulky, and heavy, but also reduce the overall volumetric/gravimetric energy density of the electrode. In the traditional slurry-casting method, the binders are insulating and electrochemically inactive, which can not only decrease the electrical conductivity, but also has a detrimental effect on the cycling stability resulting from some side effects between the electrolyte and inactive materials.…”

“…In view of the rapidly booming attention on flexible SIBs, it is necessary to highlight the recent progress and perspectives. To the best of our knowledge, there have already been several excellent reviews devoted to SIBs [11][12][13][14][15][16] or flexible energy-storage devices, [17][18][19][20][21] but so far, there has been no comprehensive review focusing on flexible electrodes for SIBs up to now. Thus, the topic considered here is timely.…”