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

Abstract

sources into large-scale grids, inexpensive, efficient, and fast-responding electrical energy storage (EES) systems are essential to store the off-peak energy and releasing the stored energy during the onpeak period. Among various EES systems, rechargeable batteries represent one of the most competitive technologies because of their high conversion efficiency and environmental friendliness. [1][2][3][4] For stationary EES systems, batteries with low cost, high safety, high rate capability, and long cycle stability are highly desired.Lithium (Li)-ion batteries (LIBs) have achieved great success in the market of portable electronics and electric vehicles since their commercialization by Sony Company in 1991. However, the shortage of Li resources in nature gives rise to a concern about its sustainable development in grid scale. Compared with Li, sodium resource has rich natural abundance in the earth crust and a worldwide distribution, consequently leading to a low price of sodium-based raw materials (e.g., the cost of Na 2 CO 3 is about 25-30 times lower than that of Li 2 CO 3 ). Besides, sodium has a suitable redox potential (E 0 (Na + /Na) = −2.71 V versus standard hydrogen electrode (SHE), 0.3 V above that of Li + /Li) and similar physical and chemical properties with lithium. [5,6] Therefore, rechargeable sodium-ion batteries (SIBs), which have a similar "rockingchair" working principle of LIBs, are emerging as an appealing choice as alternatives for LIBs. Note that it is difficult for SIBs to bypass LIBs in terms of energy densities because of the much higher weight of Na and lower standard electrochemical potential. [7][8][9][10] Nevertheless, the use of low-cost materials, including inexpensive Na-based raw materials and Al current collectors for both cathodes and anodes in SIBs, could significantly reduce the cost. In this case, SIBs could be applied where cost-effectiveness rather than energy density is the most critical issue, e.g., in the field of large-scale EES. 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, haveThe increasing demand for replacing conventional fossil fuels with clean energy or economical and sustainable energy storage drives better battery research today. Sodium-ion batteries (SIBs) are considered as a promising alternative for grid-scale storage applications due to their similar "rockingchair" sodium storage mechanism to lithium-ion batteries, the natural abundance, and the low cost of Na resources. Searching for appropriate electrode materials with acceptable electrochemical perfor...

Recent Progress of Layered Transition Metal Oxide Cathodes for Sodium‐Ion Batteries

“…For example, P3‐type Na 0.6 Mn 0.65 Ni 0.25 Co 0.10 O 2 is obtained after calcining at 700 °C, while P2‐type structures are prepared at 800, 900, and 1000 °C . The phase transformation from P3 or O3 to P2 is impossible through electrochemical desodiation because a high temperature heat‐treatment is required to break the MO bonds to form P2 phase …”

Manganese‐Oxide‐Based Electrode Materials for Energy Storage Applications: How Close Are We to the Theoretical Capacitance?

“…MnO x ‐based materials are also being studied for other ion batteries. For example, Na x MnO 2 and derivatives have been investigated as cathode materials of Na ion batteries . The study of MnO x ‐based materials for Na ion batteries mainly focus on the phase transition and thermal stability.…”

Recent Progress in Rechargeable Sodium‐Ion Batteries: toward High‐Power Applications

“…Because the large prismatic sites are energetically stabilized by large Na + in the P2‐type phase, while TMO 2 slabs glide (move) to form octahedral sites after Na + extraction and also by Na + /Li + exchange, resulting in the formation of a new O2 phase with a unique AB AC AB oxygen stacking. More details regarding the structure evolutions of P2‐type layered oxides could be found in Figure …”