P2 ‐type Na _x TmO ₂ oxides as cathodes for non‐aqueous sodium‐ion batteries—Structural evolution and commercial prospects

Abstract

Summary First‐generation sodium‐ion batteries (SIBs) are commercially launched by Faradion Ltd., UK, and HiNa Battery Technology Company Ltd., China, utilizing the transition metal oxide‐based cathodes. Currently, the commercial Faradion cells deliver ~1000 cycles at an energy density of ~140 to 150 Wh kg−1, whereas HiNa SIB cells deliver ~120 Wh kg−1. P2‐type, O3‐type, and composite P‐O and P‐P type transition metal oxide cathodes have generated much interest in the last few years. P2‐type layered oxides are critical as cathodes in achieving higher energy and power density in SIB technology, along with better C‐rate capabilities. Compared to their O3‐type counterparts, P2‐type layered transition metal oxides encounter lower activation energy barriers, enabling improved rate kinetics. However, P2‐type cathodes often face poor cycle stability due to undesirable phase changes during charge‐discharge cycles and structural instability to air and moisture. This review evaluates all the P2‐type layered oxide compounds as SIB cathodes, highlighting the strategies followed to meet the challenges and offers aspects of their successful commercialization.

Facilitating Layered Oxide Cathodes Based on Orbital Hybridization for Sodium‐Ion Batteries: Marvelous Air Stability, Controllable High Voltage, and Anion Redox Chemistry

“…Many layered oxide cathode materials experience hysteresis, capacity decline, cycling instability, and even a variety of chemical and physical reactions when exposed to air, leading to decreas electrochemical activity. [87][88][89] For solving these issues, several methods have been proposed, including microstructure modulation and surface structure modification, which introduce strong orbital hybridization inside the atomic structure to promote TM─O bonding and thus improve the stability of the material. [90][91][92] These new insights into the degrading mechanisms during air exposure will aid in creating air stable sodium layered oxide cathodes.…”

The Role of Surface Coating in P’2‐Na0.67Mn0.67Ni0.33O2: Enhancing Capacity and Stability of Layered Cathodes for Sodium‐ion Batteries

“…To solve the problem of the low‐capacity retention at high voltage, two main approaches are proposed in literature: i) to dope the material with other electrochemically active or inactive metal cations, such as Fe or Mg, [21–25] thus increasing the covalency of the Tm−O bond and modifying the electronic structure thus suppressing the O 2 evolution but lowering in some cases the average potential; ii) to protect the surface of the particles with a coating layer, such as with Al 2 O 3 or other materials and mechanically stabilizing the materials [25–31] …”

“…[20] As a confirmation of this, Zhang et al recently demonstrated the release of O 2 from the layered structure and the formation of an insulating layer on the particles that affects the subsequent electrochemical process. [21] To solve the problem of the low-capacity retention at high voltage, two main approaches are proposed in literature: i) to dope the material with other electrochemically active or inactive metal cations, such as Fe or Mg, [21][22][23][24][25] thus increasing the covalency of the TmÀ O bond and modifying the electronic structure thus suppressing the O 2 evolution but lowering in some cases the average potential; ii) to protect the surface of the particles with a coating layer, such as with Al 2 O 3 or other materials and mechanically stabilizing the materials. [25][26][27][28][29][30][31] Herein, we present a new coating approach performed by a wet chemistry method using magnesium oxide as a coating agent.…”

“…[21] To solve the problem of the low-capacity retention at high voltage, two main approaches are proposed in literature: i) to dope the material with other electrochemically active or inactive metal cations, such as Fe or Mg, [21][22][23][24][25] thus increasing the covalency of the TmÀ O bond and modifying the electronic structure thus suppressing the O 2 evolution but lowering in some cases the average potential; ii) to protect the surface of the particles with a coating layer, such as with Al 2 O 3 or other materials and mechanically stabilizing the materials. [25][26][27][28][29][30][31] Herein, we present a new coating approach performed by a wet chemistry method using magnesium oxide as a coating agent. Two different NMNO samples with 5 % and 7 % MgO coating are here proposed and fully characterized; the uncoated NMNO material is also presented as a benchmark.…”

Production of V‐Doped P2‐type Na0.67Mn0.5Fe0.43Al0.07O2Cathodes and Investigation of Na‐Ion Full Cells Performance

“…which improve the stability of the electrodes in the battery cells. [18,21] In the past years, the partially occupied differenttype TM oxides in Na x TMO 2 such as Na x (Mn y Ni z Co t )O 2 (y þ z þ t = 1) exhibit better battery performance and Na 0.67 Mn 0.5 Fe 0.5 O 2 is one of the most popular cathodes for Na-ion cells. [22][23][24] To improve the battery performance of Na 0.67 Mn 0.5 Fe 0.5 O 2 cathodes, the modification studies focused on the Mn and Fe sites in the structure such as Co, Ni, Cr, V, etc.…”