Abstract:Atomic layer deposition (ALD) is a commonly used coating technique for lithium ion battery electrodes. Recently, it has been applied to sodium ion battery anode materials. ALD is known to improve the cycling performance, Coulombic efficiency of batteries, and maintain electrode integrity. Here, the electrochemical performance of uncoated P2-NaNiMnO electrodes is compared to that of ALD-coated AlO P2-NaNiMnO electrodes. Given that ALD coatings are in the early stage of development for NIB cathode materials, lit… Show more
“…The electrochemical impedance spectra (EIS) of the above three samples are compared in Figure S9 (Supporting Information). The CV curves and charge/discharge profiles featuring smoother peaks or plateaus than those of the bulk materials, [28,36,41,43,44,46] along with the well-maintained voltage plateau at ≈4.2 V during cycling, suggest that the hierarchical nanofibers could effectively alleviate the Na + /vacancy ordering and P2-O2 phase transition occurring for the pristine materials. In addition, the electrochemical performance of the P3-type Na 2/3 Ni 1/3 Mn 2/3 O 2 (annealed at 700 °C for 6 h) has also been evaluated ( Figure S10 in the Supporting Information), which shows a much lower specific capacity with inferior cycling stability relative to the P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofibers.…”
Section: Resultsmentioning
confidence: 94%
“…This is because the P2 phase material possesses facile Na-ion diffusion in the presence of multi-Na vacancies compared with the P3 phase. [28,35,36,38,39,41,42,[44][45][46]48,51,53] This originates from the delicately tailored fibrous nanostructure composed of nanograins with high reactivity and high porosity that would accelerate the electronic/ionic transportation. The CV curves and charge/discharge profiles featuring smoother peaks or plateaus than those of the bulk materials, [28,36,41,43,44,46] along with the well-maintained voltage plateau at ≈4.2 V during cycling, suggest that the hierarchical nanofibers could effectively alleviate the Na + /vacancy ordering and P2-O2 phase transition occurring for the pristine materials.…”
Section: Resultsmentioning
confidence: 99%
“…[36,37] Dahn's group first investigated the Na-intercalation/deintercalation of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 , [38] revealing that the rapid capacity decay caused by the undesirable P2-O2 phase transition (with a large volume change of ≈23%) when charged to above 4.2 V was the main challenge hindering the wide application of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 .…”
Section: Introductionmentioning
confidence: 99%
“…doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . [44] Recently, Chou's team tested the cycling performance of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 in the voltage range of 2.0-4.0 V; the electrode maintained 89 mA h g −1 at 0.1 C and exhibited a significantly enhanced capacity retention of 71.2% even after 1200 cycles at 10 C. [36] Though these are very encouraging results, it should be noted that metal doping and surface modification cannot preclude the phase transition intrinsically, and the cyclic stability is still limited; additionally, narrowing the electrochemical window would sacrifice a large amount of capacity. [44] Recently, Chou's team tested the cycling performance of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 in the voltage range of 2.0-4.0 V; the electrode maintained 89 mA h g −1 at 0.1 C and exhibited a significantly enhanced capacity retention of 71.2% even after 1200 cycles at 10 C. [36] Though these are very encouraging results, it should be noted that metal doping and surface modification cannot preclude the phase transition intrinsically, and the cyclic stability is still limited; additionally, narrowing the electrochemical window would sacrifice a large amount of capacity.…”
Layered transition metal oxides (TMOs) are appealing cathode candidates for sodium-ion batteries (SIBs) by virtue of their facile 2D Na + diffusion paths and high theoretical capacities but suffer from poor cycling stability. Herein, taking P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 as an example, it is demonstrated that the hierarchical engineering of porous nanofibers assembled by nanoparticles can effectively boost the reaction kinetics and stabilize the structure. The P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofibers exhibit exceptional rate capability (166.7 mA h g −1 at 0.1 C with 73.4 mA h g −1 at 20 C) and significantly improved cycle life (≈81% capacity retention after 500 cycles) as cathode materials for SIBs. The highly reversible structure evolution and Ni/Mn valence change during sodium insertion/ extraction are verified by in operando X-ray diffraction and ex situ X-ray photoelectron spectroscopy, respectively. The facilitated electrode process kinetics are demonstrated by an additional study using the electrochemical measurements and density functional theory computations. More impressively, the prototype Na-ion full battery built with a Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofibers cathode and hard carbon anode delivers a promising energy density of 212.5 Wh kg −1 . The concept of designing a fibrous framework composed of small nanograins offers a new and generally applicable strategy for enhancing the Na-storage performance of layered TMO cathode materials.
“…The electrochemical impedance spectra (EIS) of the above three samples are compared in Figure S9 (Supporting Information). The CV curves and charge/discharge profiles featuring smoother peaks or plateaus than those of the bulk materials, [28,36,41,43,44,46] along with the well-maintained voltage plateau at ≈4.2 V during cycling, suggest that the hierarchical nanofibers could effectively alleviate the Na + /vacancy ordering and P2-O2 phase transition occurring for the pristine materials. In addition, the electrochemical performance of the P3-type Na 2/3 Ni 1/3 Mn 2/3 O 2 (annealed at 700 °C for 6 h) has also been evaluated ( Figure S10 in the Supporting Information), which shows a much lower specific capacity with inferior cycling stability relative to the P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofibers.…”
Section: Resultsmentioning
confidence: 94%
“…This is because the P2 phase material possesses facile Na-ion diffusion in the presence of multi-Na vacancies compared with the P3 phase. [28,35,36,38,39,41,42,[44][45][46]48,51,53] This originates from the delicately tailored fibrous nanostructure composed of nanograins with high reactivity and high porosity that would accelerate the electronic/ionic transportation. The CV curves and charge/discharge profiles featuring smoother peaks or plateaus than those of the bulk materials, [28,36,41,43,44,46] along with the well-maintained voltage plateau at ≈4.2 V during cycling, suggest that the hierarchical nanofibers could effectively alleviate the Na + /vacancy ordering and P2-O2 phase transition occurring for the pristine materials.…”
Section: Resultsmentioning
confidence: 99%
“…[36,37] Dahn's group first investigated the Na-intercalation/deintercalation of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 , [38] revealing that the rapid capacity decay caused by the undesirable P2-O2 phase transition (with a large volume change of ≈23%) when charged to above 4.2 V was the main challenge hindering the wide application of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 .…”
Section: Introductionmentioning
confidence: 99%
“…doping to stabilize the crystal structure, [28,[41][42][43] surface coating to suppress the unfavorable side reactions, [44][45][46] and lowering the charge cut-off voltage to eliminate the phase transformation, [36,47,48] have been adopted for modifying P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 . [44] Recently, Chou's team tested the cycling performance of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 in the voltage range of 2.0-4.0 V; the electrode maintained 89 mA h g −1 at 0.1 C and exhibited a significantly enhanced capacity retention of 71.2% even after 1200 cycles at 10 C. [36] Though these are very encouraging results, it should be noted that metal doping and surface modification cannot preclude the phase transition intrinsically, and the cyclic stability is still limited; additionally, narrowing the electrochemical window would sacrifice a large amount of capacity. [44] Recently, Chou's team tested the cycling performance of P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 in the voltage range of 2.0-4.0 V; the electrode maintained 89 mA h g −1 at 0.1 C and exhibited a significantly enhanced capacity retention of 71.2% even after 1200 cycles at 10 C. [36] Though these are very encouraging results, it should be noted that metal doping and surface modification cannot preclude the phase transition intrinsically, and the cyclic stability is still limited; additionally, narrowing the electrochemical window would sacrifice a large amount of capacity.…”
Layered transition metal oxides (TMOs) are appealing cathode candidates for sodium-ion batteries (SIBs) by virtue of their facile 2D Na + diffusion paths and high theoretical capacities but suffer from poor cycling stability. Herein, taking P2-type Na 2/3 Ni 1/3 Mn 2/3 O 2 as an example, it is demonstrated that the hierarchical engineering of porous nanofibers assembled by nanoparticles can effectively boost the reaction kinetics and stabilize the structure. The P2-Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofibers exhibit exceptional rate capability (166.7 mA h g −1 at 0.1 C with 73.4 mA h g −1 at 20 C) and significantly improved cycle life (≈81% capacity retention after 500 cycles) as cathode materials for SIBs. The highly reversible structure evolution and Ni/Mn valence change during sodium insertion/ extraction are verified by in operando X-ray diffraction and ex situ X-ray photoelectron spectroscopy, respectively. The facilitated electrode process kinetics are demonstrated by an additional study using the electrochemical measurements and density functional theory computations. More impressively, the prototype Na-ion full battery built with a Na 2/3 Ni 1/3 Mn 2/3 O 2 nanofibers cathode and hard carbon anode delivers a promising energy density of 212.5 Wh kg −1 . The concept of designing a fibrous framework composed of small nanograins offers a new and generally applicable strategy for enhancing the Na-storage performance of layered TMO cathode materials.
“…e) Nyquist plots of uncoated P2‐NaNiMnO cycled electrodes (red) and Al 2 O 3 ‐coated cycled electrodes (blue) and uncoated (blue), cycle 100. f) Elemental atomic percentage of the uncoated and ALD‐coated cycled electrodes at first charge 4.1, 4.5 V, 5 cycles, and 100 cycles. Reproduced with permission . Copyright 2017, American Chemical Society.…”
Section: The Electrode Engineering Of Traditional Sib Materials Desigmentioning
Sodium‐ion batteries (SIBs) have emerged as one of the most promising and competitive energy storage systems due to abundant sodium resources and its environmentally friendly features. However, further improvements in the engineering of the SIB electrode/electrolyte interphase—which directly determines the Na‐ion transfer behavior, material structure stability, and sodiation/desodiation property—are highly recommended to meet the continuously increasing requirements for secondary power sources. Reasonably speaking, to promote SIBs, the advanced and controllable interphase/electrode engineering approach exhibits promise by rationally designing the bulk electrode and generating a well‐defined interphase. Atomic layer deposition (ALD) technology, with atomic‐scale deposition, superior uniformity, excellent conformality, and a self‐limiting nature, is thus expected to address the current challenges facing SIBs in terms of low energy density, limited cycling life, and structural instability, and to promote innovations such as multifunctional electrodes and nanostructured materials for advanced SIBs. This review summarizes and discusses the most recent advancements in the interphase engineering of SIBs by ALD via modifying traditional electrodes and designing advanced electrodes (such as 3D, organic, and protected sodium metal electrodes). Furthermore, based on the recent critical progress and current scientific understanding, future perspectives for the engineering of next‐generation SIB electrodes by ALD can be provided.
Layered and spinel transition metal oxides are one of the most technologically important cathode materials for alkali metal ion batteries because of their high energy/power density and excellent electrochemical reversibility. However, similar to many other cathode materials, unstable electrochemical performance on long‐term cycling impacts the cycle life of batteries. Some of the challenges are transition metal dissolution, electrolyte decomposition, surface reconstruction, and chemomechanical breakdown of cathode materials. Most of these degradation phenomena originate from the surface of cathode materials. Owing to different local chemical environments, the surface chemistry of a cathode is distinctively unique from that of the bulk. Even though the surface region of a battery particle only accounts for a small fraction of the entire particle and contributes marginally to the overall capacity, surface‐related chemical and structural transformations can be the major factors in governing the degradation pathway of a cathode material. Herein, we have mechanistically discussed the origin and propagation of these degradation phenomena and their implications in the cycle life of a battery. Moreover, the techniques that mitigate and prevent these degradation pathways are explained. A complete understanding of the instability issues can promote a rational design of stable cathode materials for alkali metal ion batteries.
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