A Superior Low‐Cost Cathode for a Na‐Ion Battery

Abstract

A global priority is the development of low-cost, efficient storage of off-peak electric power and of electrical energy generated by energy sources other than fossil fuels (e.g. wind, solar, nuclear).[1] The rechargeable battery offers efficient electrical energy storage (EES), but the Li-ion battery used in hand-held devices is too expensive for large-scale EES. Unlike Li, Na is readily available worldwide and therefore much less costly than Li. However, the existing Na/S [2] and Zebra (Na/NiCl 2 ) [3] batteries are operating on molten electrodes at 250 to 350 8C. Therefore, there is a huge incentive to develop a room-temperature rechargeable, low-cost Na-ion battery (SIB) of high energy density capable of discharge/ charge at a high rate.To date, room-temperature rechargeable batteries have used as cathode oxide hosts into/from which the working ion, H + or Li + , can be inserted/extracted reversibly over a limited solid-solution range. These two working ions are able to be mobile guests in a host having a close-packed oxide-ion array. However, Na + is too large to be sufficiently mobile in a host with close-packed oxide ions; it needs a host framework with a larger interstitial space. Although Na + is stable coordinated by 12 oxide ions in an oxoperovskite, for example, the Na x WO 3 bronze, too high an activation energy is required for Na + transfer between these sites across a shared face coordinated by four oxide ions. The O-2p orbitals that s bond to the Na impede its motion. Replacement of the O 2À ions by (C N) À ions weakens bonding to the Na; the activation energy for Na + transfer is, therefore, strongly reduced, which makes attractive exploration of hexacyanoperovskites as cathode hosts for a rechargeable SIB. We report a synthesis route for a sodium manganese hexacyanoferrate (NMHFC) containing low-cost cations, and we demonstrate that the NMHFC provides a promising highrate performance as the cathode of a SIB of high specific energy density and efficient EES.Prussian blue and its analogues were investigated as hosts for alkali ions several years ago, [4] but that work received little attention. Cui and co-workers have recently reported stable Na + cyclability into potassium copper hexacyanoferrate in an aqueous electrolyte, [5] but an aqueous electrolyte limits the stable voltage of a rechargeable battery to 1.5 V. Therefore, we have chosen to investigate the hexacyano-perovskites in a non-aqueous electrolyte. We have reported the activities versus Na + /Na 0 of KMFe(CN) 6 with M = Fe, Co, Ni, Mn, Zn; high-spin M = Mn II showed a reversible plateau at 3.82 and 3.56 V, [6] respectively, on charge and discharge. We report herein removal of the Na + ion for a SIB to obtain a 3.4 V cathode in a Na half-cell with rhombohedral Na 1.72 MnFe(CN) 6 (NMHFC-1) and compare the performance with that of a cubic Na 1.40 MnFe(CN) 6 (NMHFC-2).The molar Na:Fe:Mn ratios of the sodium manganese hexacyanoferrates were obtained by inductively coupled plasma (ICP) analysis. All the metal atoms were normalized to the Mn c...

Effect of Concentrated Electrolyte on Aqueous Sodium-ion Battery with Sodium Manganese Hexacyanoferrate Cathode

“…3(b), two plateaus derived from Fe 2+ /Fe 3+ redox and Mn 2+ / Mn 3+ redox were observed on the first and second charge, and the first charge/discharge capacities were 124/116 mAh g ¹1 , respectively. These profiles and capacities were consistent with the previous reports 26,27 in non-aqueous electrolyte and the theoretical capacity (120 mAh g ¹1 ) of NMHCF hydrate, respectively. The reversible capacity on the NTP anode side was higher in 17 m NaClO 4 aq.…”

“…26,27 Briefly, Na 4 Fe(CN) 6 · 10H 2 O (99%, Sigma-Aldrich) and excess NaCl (99.5%, Nacalai Tesque) were dissolved in a solution of distilled water and ethanol. An aqueous solution of MnCl 2 ·4H 2 O (99.0%, Wako Pure Chemical Industries Ltd.) was dropped into the solution and stirred vigorously for 2 h. The suspension was filtered and washed by a water/ethanol solution three times, and a light green precipitate product was obtained.…”

Boron Substituted Na3V2(P1−xBxO4)3 Cathode Materials with Enhanced Performance for Sodium‐Ion Batteries

“…However, electrochemical performances in terms of rate capability and cycling life associated with SIBs did not come up to those of the lithium counterparts for their practical application. As compared with lithium‐ion, ionic radius of sodium‐ion is much larger, which severely restricts the ion diffusion kinetics of Na + in host material, especially in cathode materials 3, 4, 5, 6. Therefore, how to efficiently improve the diffusion kinetics of Na + is a significant issue for development of high performance electrode materials for SIBs.…”

Facile Method To Synthesize Na-Enriched Na1+xFeFe(CN)6 Frameworks as Cathode with Superior Electrochemical Performance for Sodium-Ion Batteries

“…After 400 cycles, the capacity of PB-5 was still 97% of the initial capacity, while the capacity retention of PB-1 was 91%, which was also higher compared with other cathode materials for sodium-ion batteries. [4][5][6][7][8][9][10][11][12][13][14][15][16][17] This demonstrates that the reduction of the vacancies and coordinating water in the Na1+xFe[Fe(CN)6] framework results in structural stability of the PB compound, which gives rise to a higher capacity and greater cycling stability during the charge-discharge processes. The discharge-charge curves with cycles of the Na1+xFe[Fe(CN)6] cathode are plotted in Figure S6.…”

“…Hence, it is crucial to develop a non-toxic, low-cost, high-capacity, stable cathode material for SIBs to ensure large-scale and long-term applications. Up to now, transition metal (M) oxides (NaxMO2+y), [4][5][6][7][8] phosphates, 9-12 fluorides, 13 and hexacyanoferrates [14][15][16][17] have been reported as cathode materials for SIBs. Few materials, however, can have both high capacity (> 100 mAh g-1) and long cycle life simultaneously.…”