Topologically protected oxygen redox in a layered manganese oxide cathode for sustainable batteries

Abstract

Manganese could be the element of choice for cathode materials used in large-scale energy storage systems owning to its abundance and low toxicity levels. However, both lithium and sodium ion batteries adopting this electrode chemistry suffer from rapid performance fading, suggesting a major technical barrier that must be overcome. Here we report a P3-type layered manganese oxide cathode Na 0.6 Li 0.2 Mn 0.8 O 2 (NLMO) that delivers a high capacity of 240 mAh g −1 with outstanding cycling stability in a lithium half-cell. Combined experimental and theoretical characterizations reveal a characteristic topological feature that enables the good electrochemical performance. Specifically, the -α-γ-layer stacking provides topological protection for lattice oxygen redox, whereas the reversibility is absent in P2-structured NLMO which takes a -α-β-configuration. The identified new order parameter opens an avenue towards the rational design of reversible Mn-rich cathode materials for sustainable batteries. / 32Sustainable energy applications in today's society, especially transportation and grid, require safe high-energy density lithium (Li) and sodium (Na) ion batteries with low-cost and/or abundant natural resources 1, 2 . Compared to cobalt (Co) and nickel (Ni) as the major component of commercial cathode materials, redox active manganese is the element of choice for cathode materials used in large-scale energy storage systems owning to its abundance and low toxicity levels 3 . In particular, Li/Na-rich Mn-based cathodes exhibit the excellent capacity and high potential (> 4 V vs. Li + /Li or Na + /Na), resulting from the extra lattice oxygen redox (LOR) [4][5][6][7] . However, the poor cycling stability of LOR-related processes, including voltage hysteresis and voltage fade, hampers its practical use because of the irreversible local structural transformation or the lattice oxygen loss [8][9][10] . The stability and/or reversibility of LOR is correlated significantly with the atomic structure or the local oxygen coordination environment, as elaborated by various theories, including the oxygen lone-pair states [11][12][13] , reductive coupling mechanism [14][15][16][17] , O−O dimer 18,19 , ligand-to-metal charge transfer (LMCT) 13 , and critical oxygen hole 20 theories, as well as a number of other theories [21][22][23][24][25][26] . Thus, exploring crystal structures compatible with reversible LOR in Mn-rich oxides is desirable to meet the demand for sustainable energy storage.At present, the correlation between the specific atomic structures with reversible LOR in the electrode materials has not been well established. Kang et al. 27 found that transition metal (TM) layer stacking can control the voltage decay of LOR process by comparing O2-and O3-type Li x (Li 0.2 Ni 0.2 Mn 0.6 )O 2 . Li-excess disordered (rock salt) TM oxides, such as

Critical intermediate β‐Li2NiO3 phase for structural degradation of Ni‐rich layered cathodes during thermal runaway

“…The degree of Ni/Li disorder is refined to 2.26% via the Rietveld‐refined XRD (Supporting Information: Table S1). The slight Ni Li antisites manifest as sporadic dark spots (yellow‐dotted circles) in the ABF STEM image (Figure 2E), suggesting the ordered Ni Li antisite ions along the [1$$\bar{1}$$0] direction, as in the ribbon‐ordered superstructure of the TM layer in Na 0.6 Li 0.2 Mn 0.8 O 2 5 . The ribbon‐ordered Ni Li antisites gradually increase with the temperature rising from 100°C to 600°C (Supporting Information: Figure S1).…”

Realizing High-Performance Cathodes with Cationic and Anionic Redox Reactions in High-Sodium-Content P2-Type Oxides for Sodium-Ion Batteries

“…). − For example, Chen’s group found that Mg- and Ti-codoped Na 2/3 [Ni 2/9 Mg 1/9 Mn 5/9 Ti 1/9 ]­O 2 could regulate the crystal structure and enhance the electrochemical properties by suppressing the phase transition . Especially, when weak bonds like Li–O, Mg–O, or Zn–O bonds are introduced in the Na-deficient oxides, the anionic redox reaction O 2– /O n – could be triggered at a high working potential of around 4.2 V, which opens a new path to improve the specific capacity of these oxides. − Na 2/3 [Mg 0.28 Mn 0.72 ]­O 2 is reported to have a high initial charge/discharge capacity of above 150 mAh g –1 due to the contribution of the O redox process, which is close to its theoretical capacity based on the Na content of the compound. Similar cases were encountered in Na 0.6 Li 0.2 Mn 0.8 O 2 and Na 2/3 Zn 0.28 Mn 0.72 O 2 .…”

Correlating Mg Displacement with Topologically Regulated Lattice Oxygen Redox in Na-Ion Layered Oxide Cathodes

“…Compared to a Li-ion system, Na-ion layered oxides with P-type stacking can not only disfavor out-of-plane transition-metal (TM) migration but also provide ample void space to mediate the covalent bonding rearrangements upon LOR by virtue of the size mismatch between TM ions and prismatic Na sites, making them a more appropriate model system to harness the LOR activity. − P-type Na-ion layered oxides mainly comprise P2 and P3, in which the oxygen columns demonstrate “ABBA” and “ABBCCA” arrangements along the [001] direction, respectively (as delineated in Figure ). Recently, Hu and co-workers proposed that the topological character of -α-γ- stacks in P3-Na 0.6 Li 0.2 Mn 0.8 O 2 can provide unexpected protection for reversible LOR, while the topological character of P2-Na 0.6 Li 0.2 Mn 0.8 O 2 evolves from -α-β- to -α-γ- stacks as cycling progresses, which jeopardizes the reversibility of LOR . In addition to the interlayer stacks, endeavors have also been dedicated to the design of intralayer atom configurations.…”

“…Recently, Hu and co-workers proposed that the topological character of -α-γ-stacks in P3-Na 0.6 Li 0.2 Mn 0.8 O 2 can provide unexpected protection for reversible LOR, while the topological character of P2-Na 0.6 Li 0.2 Mn 0.8 O 2 evolves from -α-β-to -α-γ-stacks as cycling progresses, which jeopardizes the reversibility of LOR. 30 In addition to the interlayer stacks, endeavors have also been dedicated to the design of intralayer atom configurations. For instance, Bruce et al first reported that the voltage hysteresis can be largely reduced in LORactive materials through a ribbon-ordered superstructure that precludes the in-plane migration of TM ions.…”