Will Sodium Layered Oxides Ever Be Competitive for Sodium Ion Battery Applications?

Abstract

The Na-ion battery technology is rapidly developing as a possible alternative to Li-ion for massive electrochemical energy storage applications because of sustainability and cost reasons. Two types of technologies based either on sodium layered oxides Na x MO 2 (x ≤ 1, M = transition metal ion(s)) or on polyanionic compounds such as Na 3 V 2 (PO 4 ) 2 F 3 as positive electrode and carbon as negative electrode are presently being pursued. Herein, we benchmark the performance of full Na-ion cells based on several sodium layered oxide materials against Na 3 V 2 (PO 4 ) 2 F 3 /hard carbon cells. Although several studies report more attractive capacities for sodium layered oxides vs. Na metal (∼200 mAh g −1 ) than for polyanionic phases (∼120 mAh g −1 ), we find that such advantages are not maintained when assembling practical full Na-ion cells; the opposite of what is found for Li-ion technology. The reasons for such a loss of supremacy of the layered oxides against polyanionic compounds are discussed in terms of materials structural stability and composition so as to identify fundamental challenges that impede their practical applications. Finally, a few perspectives are given to design better sodium layered oxide electrode materials that could outweigh the performance of today's stellar Na 3 V 2 (PO 4 ) 2 F 3 .

Reaching the Energy Density Limit of Layered O3‐NaNi0.5Mn0.5O2 Electrodes via Dual Cu and Ti Substitution

“…[12,19,20,22,25] It has been proved that the substitution of Mn 4+ (d3) in NaNi 0.5 Mn 0.5 O 2 by Ti 4+ (d0) increases the MO bond ionicity which in turn leads to higher charge localization on oxygen and thus a discrimination of Na sites. The studied O3 NaNi 0.5−y Cu y Mn 0.5−z Ti z O 2 (y = 0, 0.05, 0.1; z = 0.1, 0.2) phases with co-substitution of Cu 2+ and Ti 4+ were found to have an enhanced stability against structural phase changes at high potential, hence enabling to reversibly access ≈0.9 Na + (equivalent to ≈200 mAh g −1 ) in the extended voltage window (up to 4.5 V vs Na + /Na 0 ) with satisfactory cyclability.…”

“…[1][2][3][4][5][6][7] Most of the Na-ion systems demonstrated till now use hard carbon (HC) as common negative electrode and either sodium layered oxides (Na x TMO 2 , 0 < x ≤ 1, TM = transition metals) or polyanionic compounds (Na 3 V 2 (PO 4 ) 2 F 3 ) as positive electrodes. [12] Whatever the figures of merit we have checked, such as specific energy, cyclability as well as rate capability, the 3D Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) phase outperforms the layered phases, irrespective of its high molecular weight and modest capacity (128 mAh g −1 , equivalent to 2 Na + exchange). [12] Whatever the figures of merit we have checked, such as specific energy, cyclability as well as rate capability, the 3D Na 3 V 2 (PO 4 ) 2 F 3 (NVPF) phase outperforms the layered phases, irrespective of its high molecular weight and modest capacity (128 mAh g −1 , equivalent to 2 Na + exchange).…”

“…[12,[16][17][18][19][20][21][22][23] Among these findings, recent studies have shown that increasing the ionicity of the crystal lattice with Ti 4+ substitution, apart from increasing the redox potential, also helps in reducing number of phase transitions, hence enabling a better cyclability over a larger voltage window. They show greater rate capabilities than Li-ion via the least number of phase transitions so as to ensure long cycle life while being able to utilize their total capacity in Na-ion full cells.…”

The Cathode Choice for Commercialization of Sodium‐Ion Batteries: Layered Transition Metal Oxides versus Prussian Blue Analogs

“…The energies were calculated based on the cathode weight. Reproduced under the terms and conditions of the Creative Commons CC 67. Copyright 2018, The Authors.…”

High Capacity and High‐Rate NASICON‐Na3.75V1.25Mn0.75(PO4)3 Cathode for Na‐Ion Batteries via Modulating Electronic and Crystal Structures

“…Interestingly, the Na 3.75 V 1.25 Mn 0.75 (PO 4 ) 3 exhibits capacities as high as 100 and 95 mA h g −1 at 1C and 2C, respectively and even 86% of its initial capacity (i.e., 104 mA h g −1 ) can be obtained during a discharge time of ≈20 min (i.e., 5C rate). Such stellar rate performance is found to be better than layered oxides and could be compared to Na 3 V 2 (PO 4 ) 2 F 3 cathode …”