A Rational Biphasic Tailoring Strategy Enabling High‐Performance Layered Cathodes for Sodium‐Ion Batteries

Self Cite

Li-and Mn-rich layered oxides (LMLOs) are promising cathode materials for Li-ion batteries (LIBs) owing to their high discharge capacity of above 250 mA h g −1 . A high voltage plateau related to the oxidation of lattice oxygen appears upon the first charge, but it cannot be recovered during discharge, resulting in the so-called voltage decay. Disappearance of the honeycomb superstructure of the layered structure at a slow C-rate (e.g., 0.1 C) has been proposed to cause the first-cycle voltage decay. By comparing the structural evolution of Li[Li 0.2 Ni 0.2 Mn 0.6 ]O 2 (LLNMO) at various current densities, the operando synchrotron-based X-ray diffraction results show that the lattice strain in bulk LLNMO is continuously increased over cycling, resulting in the first-cycle voltage loss upon Li-ion insertion. Unlike the LLNMO, the accumulated average lattice strain of LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811) and LiNi 0.6 Co 0.2 Mn 0.2 O 2 (NCM622) from the open-circuit voltage to 4.8 V could be released on discharge. These findings help to gain a deep understanding of the voltage decay in LMLOs.

Section: Resultsmentioning

confidence: 99%

Accumulated Lattice Strain as an Intrinsic Trigger for the First-Cycle Voltage Decay in Li-Rich 3d Layered Oxides

Wang

Zhao

Chen

et al. 2023

Self Cite

“…In this work, we present the one-pot synthesis of x Cr 2 O 3 -coated Na(Cr 1–2 x Al 2 x )O 2 and its remarkable cyclability in additive-free electrolytes. While numerous studies have investigated bulk doping or surface coating in other types of layered materials, − this is the first report on simultaneous doping and coating in NaCrO 2 . Through spectroscopic and microscopic analyses, we demonstrate that the phase separation of Cr 2 O 3 /Al-doped NaCrO 2 is preferred over the formation of Al 2 O 3 /NaCrO 2 or Na-deficient Na 1–2 x Cr 1–2 x Al 2 x O 2 .…”

Section: Introductionmentioning

confidence: 95%

Unprecedented Cyclability and Moisture Durability of NaCrO₂ Sodium-Ion Battery Cathode via Simultaneous Al Doping and Cr₂O₃ Coating

Ikhe

Park

Mwemezi

et al. 2023

Although there are many cathode candidates for sodium-ion batteries (NIBs), NaCrO 2 remains one of the most attractive materials due to its reasonable level of capacity, nearly flat reversible voltages, and high thermal stability. However, the cyclic stability of NaCrO 2 needs to be further improved in order to compete with other state-of-the-art NIB cathodes. In this study, we show that Cr 2 O 3 -coated and Al-doped NaCrO 2 , which is synthesized through a simple one-pot synthesis, can achieve unprecedented cyclic stability. We confirm the preferential formation of a Cr 2 O 3 shell and a Na(Cr 1−2x Al 2x )O 2 core, rather than xAl 2 O 3 /NaCrO 2 or Na 1/1+2x (Cr 1/1+2x Al 2x/1+2x )O 2 , through spectroscopic and microscopic methods. The core/shell compounds exhibit superior electrochemical properties compared to either Cr 2 O 3 -coated NaCrO 2 without Al dopants or Al-doped NaCrO 2 without shells because of their synergistic contributions. As a result, Na(Cr 0.98 Al 0.02 )O 2 with a thin Cr 2 O 3 layer (5 nm) shows no capacity fading during 1000 charge/discharge cycles while maintaining the rate capability of pristine NaCrO 2 . In addition, the compound is inert against humid air and water. We also discuss the reasons for the excellent performance of Cr 2 O 3 -coated Na(Cr 1−2x Al 2x )O 2 .

“…To achieve this capacity, NaNM55 undergoes a series of phase transformations (O3 – O’3 – P3 – P’3 – P3”) that limit capacity retention, resulting in a poor cycle life of only ∼35 cycles before falling below 80% of its initial capacity . Biphasic tailoring of compositions and doping with metals, such as Fe, Ti, Al, and Mg, have been used to mitigate the extent of this mechanical degradation, although more fundamental solutions are available. − Drawing on lithium-ion research, “single-crystal” particles offer a new and compelling way to reduce particle cracking during cycling without altering the chemical composition of the material. , Single-crystal here is defined more loosely as a grouping of isolated primary particles that are greater than 1 μm in size. Size will vary, as will the degree of agglomeration, but the motivation remains the same: large, accessible primary particles.…”

Section: Introductionmentioning

confidence: 99%

Facile Synthesis of O3-Type NaNi_0.5Mn_0.5O₂ Single Crystals with Improved Performance in Sodium-Ion Batteries

Darga

Manthiram

2022

Sodium-ion batteries can be a practical alternative to lithium-ion batteries due to the relatively high abundance of sodium and the projected scarcity of lithium. Both of these factors are critical considerations for grid-scale energy storage, but the central challenge to implementing sodium layered oxides in sodium-ion batteries is their relatively poor cycle life. Single-crystal particles with micrometer size can mitigate several failure mechanisms related to sodium layered oxides and can improve performance when compared to the commonly used polycrystalline particles. This work demonstrates a novel two-step moltensalt synthesis method using sodium chloride and metal oxides to form "single crystals" of a mixed-phase, spinel/rock-salt intermediate that crystallizes as micron-sized truncated octahedra. The mixed-phase spinel/rock-salt material is effectively used as a precursor to form O3-type NaNi 0.5 Mn 0.5 O 2 with large primary particles and substantially improved cycle life. This synthesis route offers the added benefit of using simple metal oxides instead of hydroxide precursors, eliminating the need for coprecipitation. Particle morphology is found to be a critical factor in mitigating the structural damages incurred during phase transformations and maintaining the electrochemical performance.