Synthesis and Electrochemistry of O3-type NaFeO₂–NaCo_0.5Ni_0.5O₂ Solid Solutions for Na-Ion Positive Electrodes

Abstract

The synthesis, structure, and electrochemistry in Na cells of NaFe MO positive electrode materials with M = Ni, CoNi, and Co are reported. In particular, the properties of O3-NaFeO-NaCoNiO solid solutions having compositions NaFe (CoNi)O with 0 ≤ x ≤ 0.5 are explored. It is found that the substitution of Fe in NaNiCoO causes an increase in first cycle energy density from 320 to 440 mWh/g in a 1.5-4.0 V test. However, capacity retention is generally reduced when x is increased for all M = Ni, CoNi, and Co. In general, NaFe MO samples with M = Co had the highest capacity retention for all values of x. Ex situ X-ray diffraction and Mössbauer results of as-prepared and charged materials are directly compared for NaFe (CoNi)O and NaFe CoO ( x = 0.4, 0.5). Iron was found to be in the +3 oxidation state in the as-prepared materials. A significant fraction of Fe is oxidized to Fe in these samples when they are charged to 4.0 V.

Promises and Challenges of Next-Generation “Beyond Li-ion” Batteries for Electric Vehicles and Grid Decarbonization

“…No significant improvement was observed in the operating voltages of P2–Na 0.75 Co 0.78 Ni 0.22 O 2 and O3–NaCo 0.5 Ni 0.5 O 2 compared with those of Mn-based Na layered oxides, consistent with the idea put forward in ref that the voltage of the Na and K compounds is largely controlled by the strong alkali–alkali interaction. Because Na + and K + ions are considerably larger than Li + , the interlayer distance between oxide layers in Na and K compounds is larger than that in Li compounds.…”

“…Na layered oxides typically have average voltages between 2.5 and 3.5 V. The voltage range is even lower for K layered oxides: The average discharge voltages for P3− K 0.5 MnO 2 , 68 P3−K 0.45 Mn 0.5 Co 0.5 O 2 , 69 and O3−KCrO 2 70 are all approximately 2.5 V. Attempts to increase the operating voltage of layered oxides by using transition metal species such as Co 3+/4+ and Ni 3+/4+ have had little success. 71 No significant improvement was observed in the operating voltages of P2−Na 0.75 Co 0.78 Ni 0.22 O 2 72 and O3−Na-Co 0.5 Ni 0.5 O 2 73 compared with those of Mn-based Na layered oxides, 59 consistent with the idea put forward in ref 52 that the voltage of the Na and K compounds is largely controlled by the strong alkali−alkali interaction. Because Na + and K + ions are considerably larger than Li + , the interlayer distance between oxide layers in Na and K compounds is larger than that in Li compounds.…”

“…The shaded areas show that the voltage profiles have similar slopes for a particular alkali metal (Li, purple; Na, green; K, blue). Data adapted from LiCoO 2 , Li­(NiCoMn) 0.33 O 2 , P2–Na 0.67 Mn 0.67 Ni 0.33 O 2 , P2–Na 0.75 Co 0.78 Ni 0.22 O 2 , P2–Na 0.67 Mn 0.65 Fe 0.2 Ni 0.15 O 2 , P2–Na 0.67 CoO 2 , P2–Na 0.67 Mn 0.5 Fe 0.5 O 2 , O3–NaMn 0.5 Ni 0.5 O 2 , O3–NaCo 0.5 Ni 0.5 O 2 , O3–NaLi 0.05 [Mn 0.5 Fe 0.25 Ni 0.25 ] 0.95 O 2 , O3–NaMn 0.25 Co 0.25 Fe 0.25 Ni 0.25 O 2 , P3–K 0.5 MnO 2 , P2–K 0.6 CoO 2 , P3–K 0.45 Mn 0.5 Co 0.5 O 2 , O3–KCrO 2. …”

Co-Substitution Enhances the Rate Capability and Stabilizes the Cyclic Performance of O3-Type Cathode NaNi0.45–xMn0.25Ti0.3CoxO2 for Sodium-Ion Storage at High Voltage

“…The prepared NaNi 0.45−x Mn 0.25 Ti 0.3 Co x O 2 (denoted as NMTCo x , x = 0.05 and 0.1) processes expanded interlayer space owing to cosubstitution, which facilitates Na + diffusion kinetics. 21 Moreover, the high voltage durability of the material can be improved without sacrificing capacity by the substitution of the electrochemically active Co 3+ . This study not only reveals that improved cycling and rate performance under high voltage can be achieved by co-substitution but also helps to elucidate the design of high-voltage cathode materials for SIBs.…”

Rationally designed Water-Insertable Layered Oxides with Synergistic Effect of Transition-Metal Elements for High-Performance Oxygen Evolution Reaction

“…Only 5% iron could be introduced into the layer-structured oxide, and an impurity phase of iron oxide started to appear when we substituted 10% of Co by iron in Na x CoO 2 . Although higher iron solubility in Na x CoO 2 can be realized by using an oxidative and extremely air-sensitive Na 2 O 2 sodium source, its strong water absorption behavior and easy reaction with CO 2 in the surrounding atmosphere make the synthesis possible only in the glove box, which is problematic for mass production. , Many-layered oxide cathodes for sodium ion batteries are air-sensitive, and they can react with H 2 O because of the large sodium layer spacing caused by the large sodium ion radius. , This may also be a concern for application in OER.…”