Layered Oxide Cathodes for Sodium-Ion Batteries: Storage Mechanism, Electrochemistry, and Techno-economics

Abstract

Conspectus Lithium-ion batteries (LIBs) are ubiquitous in all modern portable electronic devices such as mobile phones and laptops as well as for powering hybrid electric vehicles and other large-scale devices. Sodium-ion batteries (NIBs), which possess a similar cell configuration and working mechanism, have already been proven as ideal alternatives for large-scale energy storage systems. The advantages of NIBs are as follows. First, sodium resources are abundantly distributed in the earth’s crust. Second, high-performance NIB cathode materials can be fabricated by using solely inexpensive and noncritical transition metals such as manganese and iron, which further reduces the cost of the required raw materials. Recently, the unprecedented demand for lithium and other critical minerals has driven the cost of these primary raw materials (which are utilized in LIBs) to a historic high and thus triggered the commercialization of NIBs. Sodium layered transition metal oxides (Na x TMO2, TM = transition metal/s), such as Mn-based sodium layered oxides, represent an important family of cathode materials with the potential to reduce costs, increase energy density and cycling stability, and improve the safety of NIBs for large-scale energy storage. However, these layered oxides face several key challenges, including irreversible phase transformations during cycling, poor air stability, complex charge-compensation mechanisms, and relatively high cost of the full cell compared to LiFePO4-based LIBs. Our work has focused on the techno-economic analysis, the degradation mechanism of Na x TMO2 upon cycling and air exposure, and the development of effective strategies to improve their electrochemical performances and air stability. Correlating structure–performance relationships and establishing general design strategies of Na x TMO2 must be considered for the commercialization of NIBs. In this Account, we discuss the recent progress in the development of air-stable, electrochemically stable, and cost-effective Na x TMO2. The favorable redox-active cations for Na x TMO2 are emphasized in terms of abundance, cost, supply, and energy density. Different working mechanisms related to Na x TMO2 are summarized, including the electrochemical reversibility, the main structural transformations during the charge and discharge processes, and the charge-compensation mechanisms that accompany the (de)intercalation of Na+ ions, followed by discussions to improve the stability toward ambient air and upon cycling. Then the techno-economics are presented, with an emphasis on cathodes with different chemical compositions, cost breakdown of battery packs, and Na deficiency, factors that are critical to the large-scale implementation. Finally, this Account concludes with an overview of the remaining challenges and new opportunities concerning the practical applications of Na x TMO2, with an emphasis on the cost, large-scale fabrication capability, and electrochemical performance.

W‐Doping Induced Efficient Tunnel‐to‐Layered Structure Transformation of Na0.44Mn1‐xWxO2: Phase Evolution, Sodium‐Storage Properties, and Moisture Stability

“…It is widely reported that the instability of transition metal oxides toward moisture leads to the great deterioration of electrochemical performance, which hinders the practical application of transition metal oxides. [ 24,50,51 ] To investigate the effect of the hydration/dehydration process on the electrochemical properties of the NMO‐1W‐D, the half‐cells based on the NMO‐1W‐D were assembled and evaluated. Interestingly, the dehydration NMO‐1W‐D electrode shows similar CV curves to the pristine NMO‐1 W ( Figure 6 a).…”

“…[ 23 ] Nonetheless, the P2‐Na x MnO 2 compounds are still haunted by irreversible structural changes/phase transitions during cycling, insufficient electrochemical performances, and air/moisture instability. [ 24–26 ]…”

Effect of Different Metal Ions between Nanolayers of Manganese Oxide for Water Oxidation Reaction under Acidic Conditions

“…In addition, these Mn oxides could be applied in the synthesis of new composites, sodium-ion batteries, oxidation, removal of toxic ions, catalysts, supercapacitors, and sensors …”

“…Other strategies with these Mn oxides could be also promising to investigate WOR activity. 82−86 In addition, these Mn oxides could be applied in the synthesis of new composites, 87 sodium-ion batteries, 88 oxidation, 89 removal of toxic ions, 90 catalysts, 91 supercapacitors, 92 and sensors. 93…”

Electrochemical Performance of Spongy Snowballs of O3-NaFeO2@SnO: Cathodes for Sodium Ion Batteries

“…The research interest in sodium insertion materials has been totally renewed as a result of the current conditions, which include energy difficulties and an increase in demand for large-scale batteries. After 2010, material research explored new sodium insertion materials for battery applications [5][6][7][8][9][10][11][12][13][14]. Some layered transition metal oxides have received a lot of attention as cathode materials for sodium ion batteries because they are sodium intercalation host materials [15][16][17][18].…”