Highly stable Na2/3 (Mn0.54 Ni0.13 Co0.13 )O2 cathode modified by atomic layer deposition for sodium-ion batteries

High-Voltage Na0.76Ni0.25-x/2Mgx/2Mn0.75O2-xFx Cathode Improved by One-Step In Situ MgF2 Doping with Superior Low-Temperature Performance and Extra-Stable Air Stability

P2-NaxMnO2 has garnered significant attention due to its favorable Na+ conductivity and structural stability for large-scale energy storage fields. However, achieving a balance between high energy density and extended cycling stability remains a challenge due to the Jahn-Teller distortion of Mn3+ and anionic activity above 4.1 V. Herein, we propose a one-step in situ MgF2 strategy to synthesize a P2-Na0.76Ni0.225Mg0.025Mn0.75O1.95F0.05 cathode with improved Na-storage performance and decent water/air stability. By partially substituting cost-effective Mg for Ni and incorporating extra F for O, the optimized material demonstrates both enhanced capacity and structure stability via promoting Ni2+/Ni4+ and oxygen redox activity. It delivers a high capacity of 132.9 mA h g-1 with an elevated working potential of ≈3.48 V and maintains ≈83.0% capacity retention after 150 cycles at 100 mA g-1 within 2-4.3 V, compared to the 114.9 mA h g-1 capacity and 3.32 V discharging potential of the undoped Na0.76Ni0.25Mn0.75O2. While increasing the charging voltage to 4.5 V, 133.1 mA h g-1 capacity and 3.55 V discharging potential (vs Na/Na+) were achieved with 72.8% capacity retention after 100 cycles, far beyond that of the pristine sample (123.7 mA h g-1, 3.45 V, and 43.8%@100 cycles). Moreover, exceptional low-temperature cycling stability is achieved, with 95.0% after 150 cycles. Finally, the Na-storage mechanism of samples employing various doping strategies was investigated using in situ EIS, in situ XRD, and ex situ XPS techniques.

Surface modification and functionalization of powder materials by atomic layer deposition: a review

Powder materials are a class of industrial materials with many important applications. In some circumstances, surface modification and functionalization of these materials are essential for achieving or enhancing their expected performances. However, effective and precise surface modification of powder materials remains a challenge due to a series of problems such as high surface area, diffusion limitation, and particle agglomeration. Atomic layer deposition (ALD) is a cutting-edge thin film coating technology traditionally used in the semiconductor industry. ALD enables layer by layer thin film growth by alternating saturated surface reactions between the gaseous precursors and the substrate. The self-limiting nature of ALD surface reaction offers angstrom level thickness control as well as exceptional film conformality on complex structures. With these advantages, ALD has become a powerful tool to effectively fabricate powder materials for applications in many areas other than microelectronics. This review focuses on the unique capability of ALD in surface engineering of powder materials, including recent advances in the design of ALD reactors for powder fabrication, and applications of ALD in areas such as stabilization of particles, catalysts, energetic materials, batteries, wave absorbing materials and medicine. We intend to show the versatility and efficacy of ALD in fabricating various kinds of powder materials, and help the readers gain insights into the principles, methods, and unique effects of powder fabrication by ALD.

Atomic/molecular layer deposition for energy storage and conversion

Energy storage and conversion systems, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting, have played vital roles in the reduction of fossil fuel usage, addressing environmental issues and the development of electric vehicles. The fabrication and surface/interface engineering of electrode materials with refined structures are indispensable for achieving optimal performances for the different energy-related devices. Atomic layer deposition (ALD) and molecular layer deposition (MLD) techniques, the gas-phase thin film deposition processes with self-limiting and saturated surface reactions, have emerged as powerful techniques for surface and interface engineering in energy-related devices due to their exceptional capability of precise thickness control, excellent uniformity and conformity, tunable composition and relatively low deposition temperature. In the past few decades, ALD and MLD have been intensively studied for energy storage and conversion applications with remarkable progress. In this review, we give a comprehensive summary of the development and achievements of ALD and MLD and their applications for energy storage and conversion, including batteries, supercapacitors, fuel cells, solar cells, and photoelectrochemical water splitting. Moreover, the fundamental understanding of the mechanisms involved in different devices will be deeply reviewed. Furthermore, the large-scale potential of ALD and MLD techniques is discussed and predicted. Finally, we will provide insightful perspectives on future directions for new material design by ALD and MLD and untapped opportunities in energy storage and conversion.

Rational design of layered oxide materials for sodium-ion batteries

Sodium-ion batteries have captured widespread attention for grid-scale energy storage owing to the natural abundance of sodium. The performance of such batteries is limited by available electrode materials, especially for sodium-ion layered oxides, motivating the exploration of high compositional diversity. How the composition determines the structural chemistry is decisive for the electrochemical performance but very challenging to predict, especially for complex compositions. We introduce the "cationic potential" that captures the key interactions of layered materials and makes it possible to predict the stacking structures. This is demonstrated through the rational design and preparation of layered electrode materials with improved performance. As the stacking structure determines the functional properties, this methodology offers a solution toward the design of alkali metal layered oxides.

Nanoengineered Organic Electrodes for Highly Durable and Ultrafast Cycling of Organic Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have become increasingly important as next-generation energy storage systems for application in large-scale energy storage. It is very crucial to develop an eco-friendly and green SIB technique with superior performance for sustainable future use. Replacing the conventional inorganic electrode materials with green and safe organic electrodes will be a promising approach. However, the poor electrochemical kinetics, unstable electrode-electrolyte interface, high solubility of the electrodes in the electrolyte, and large amount of conductive carbon present great challenges for organic SIBs. In this study, the issues of organic electrodes are addressed through atomic-level manipulation of these organic molecules using a series of ultrathin (Å-level) metal oxide coatings (Al₂ O₃ , ZnO, and TiO₂ ). Uniform and precise coatings on the perylene-3,4,9,10-tetracarboxylicacid dianhydride by gas-phase atomic layer deposition technique shows a stable interphase, enhanced electrochemical kinetics (71C, 10 A g^-1 ), and excellent stability (89%-500 cycles) compared to conventional organic electrode (70%-200 cycles). Further studies reveal that the chemical stability of the metal oxide coating layer plays a critical role in influencing the redox behavior, and improving kinetics of organic electrodes. This study opens a new avenue for developing high-energy organic SIBs with performance equivalent to inorganic counterparts.

Atomic layer deposition of Al2O3 on P2-Na0.5Mn0.5Co0.5O2 as interfacial layer for high power sodium-ion batteries

Surface modification is one of the impressive and widely used technique to improve the electrochemical performance of sodium-ion batteries by modifying the electrode-electrolyte interface. Herein, we used the atomic layer deposition (ALD) to modify the surface of P2-Na_0.5Mn_0.5Co_0.5O₂ by sub-monolayer Al₂O₃ coating on the prefabricated electrodes. Phase purity is confirmed using various structural and morphological studies. The pristine electrode delivered an initial discharge capacity of 154 mAh g^-1 at 0.5C, and inferior rate performance of 23 mAh g^-1 at 40C rate. On the other hand, the interfacial modified cathode with 5 cycles of ALD coating delivers a high capacity of 174 and 45 mAh g^-1 at 0.5C and 40C rate, respectively. The Co^2+/3+ redox couple is utilized for the faradaic process with high reversibility along with suppressed P2-O2 phase transition. The presence of the Al₂O₃ layer acts as an artificial cathode electrolyte interface by suppressing the electrolyte oxidation at higher cutoff potentials. This is clearly validated by the reduced charge transfer resistance of surface modified electrodes after cycling at various current rates. Even at an elevated temperature condition (50 °C), interfacial layer significantly improves the safety of the cell and ensures the stability of the cathode.

Recent Progress of Layered Transition Metal Oxide Cathodes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) are attracting increasing attention and considered to be a low-cost complement or an alternative to lithium-ion batteries (LIBs), especially for large-scale energy storage. Their application, however, is limited because of the lack of suitable host materials to reversibly intercalate Na⁺ ions. Layered transition metal oxides (Na_x MO₂ , M = Fe, Mn, Ni, Co, Cr, Ti, V, and their combinations) appear to be promising cathode candidates for SIBs due to their simple structure, ease of synthesis, high operating potential, and feasibility for commercial production. In the present work, the structural evolution, electrochemical performance, and recent progress of Na_x MO₂ as cathode materials for SIBs are reviewed and summarized. Moreover, the existing drawbacks are discussed and several strategies are proposed to help alleviate these issues. In addition, the exploration of full cells based on Na_x MO₂ cathodes and future perspectives are discussed to provide guidance for the future commercialization of such systems.

Capacity Degradation Mechanism and Cycling Stability Enhancement of AlF3-Coated Nanorod Gradient Na[Ni0.65Co0.08Mn0.27]O2 Cathode for Sodium-Ion Batteries

O3-type Na[Ni _xCo _yMn _z]O₂ materials are attractive cathodes for sodium-ion batteries because of their full cell fabrication practicality, high energy density, and relatively easy technology transfer arising from their similarity to Li[Ni _xCo _yMn _z]O₂ materials, yet their performance viability with Ni-rich composition ( x ≥ 0.6) is still doubtful. More importantly, their capacity degradation mechanism remains to be established. In this paper, we introduce an O3-type Ni-rich AlF₃-coated nanorod gradient Na[Ni_0.65Co_0.08Mn_0.27]O₂ cathode with enhanced electrochemical performance in both half-cells and full cells. AlF₃-coated nanorod gradient Na[Ni_0.65Co_0.08Mn_0.27]O₂ particles were synthesized through a combination of dry ball-mill coating and columnar composition gradient design and deliver a discharge capacity of 168 mAh g^-1 with 90% capacity retention in half cells (50 cycles) and 132 mAh g^-1 with 90% capacity retention in full cells (200 cycles) at 75 mA g^-1 (0.5C, 1.5-4.1 V). Through analysis of the cycled electrodes, the capacity-degradation mechanism was unraveled in O3-type Ni-rich Na[Ni _xCo _yMn _z]O₂ from a structural perspective with emphasis on high-resolution transmission electron microscopy, providing valuable information on improving O3-type Na[Ni _xCo _yMn _z]O₂ cathode performance.

Designing High-Performance Nanostructured P2-type Cathode Based on a Template-free Modified Pechini Method for Sodium-Ion Batteries

Layered oxides are promising cathode materials for sodium-ion batteries because of their high theoretical capacities. However, many of these layered materials experience severe capacity decay when operated at high voltage (>4.25 V), hindering their practical application. It is essential to design high-voltage layered cathodes with improved stability for high-energy-density operation. Herein, nano P2-Na_2/3(Mn_0.54Ni_0.13Co_0.13)O₂ (NCM) materials are synthesized using a modified Pechini method as a prospective high-voltage sodium storage component without any modification. The changes in the local ionic state around Ni, Mn, and Co ions with respect to the calcination temperature are recorded using X-ray absorption fine structure analysis. Among the electrodes, NCM fired at 850 °C (NCM-850) exhibits excellent electrochemical properties with an initial capacity and energy density of 148 mAh g^-1 and 555 Wh kg^-1, respectively, when cycled between 2 and 4.5 V at 160 mA g^-1 along with improved cyclic stability after 100 charge/discharge cycles. In addition, the NCM-850 electrode is capable of maintaining a 75 mAh g^-1 capacity even at a current density of 3200 mA g^-1. In contrast, the cell fabricated with NCM obtained at 800 °C shows continuous capacity fading because of the formation of an impurity phase during the synthesis process. The obtained capacity, rate performance, and energy density along with prolonged cyclic life for the cell fabricated with the NCM-850 electrodes are some of the best reported values for sodium-ion batteries as compared to those of other p2-type sodium intercalating materials.

Electrochemical properties of novel FeV2O4 as an anode for Na-ion batteries

Spinel based transition metal oxide – FeV₂O₄ is applied as a novel anode for sodium-ion battery. The electrochemical tests indicate that FeV₂O₄ is generally controlled by pseudo-capacitive process. Using cost-effective and eco-friendly aqueous based binders, Sodium-Carboxymethylcellulose/Styrene butadiene rubber, a highly stable capacity of ~97 mAh∙g⁻¹ is obtained after 200 cycles. This is attributed to the strong hydrogen bonding of carboxyl and hydroxyl groups indicating superior binding with the active material and current collector which is confirmed by the ex-situ cross-section images of the electrode. Meanwhile, only ~27 mAh∙g⁻¹ is provided by the electrode using poly(vinylidene difluoride) due to severe detachment of the electrode material from the Cu foil after 200 cycles. The obtained results provide an insight into the possible applications of FeV₂O₄ as an anode material and the use of water-based binders to obtain highly stable electrochemical tests for sodium-ion battery.

Recent Progress in Iron-Based Electrode Materials for Grid-Scale Sodium-Ion Batteries

Grid-scale energy storage batteries with electrode materials made from low-cost, earth-abundant elements are needed to meet the requirements of sustainable energy systems. Sodium-ion batteries (SIBs) with iron-based electrodes offer an attractive combination of low cost, plentiful structural diversity and high stability, making them ideal candidates for grid-scale energy storage systems. Although various iron-based cathode and anode materials have been synthesized and evaluated for sodium storage, further improvements are still required in terms of energy/power density and long cyclic stability for commercialization. In this Review, progress in iron-based electrode materials for SIBs, including oxides, polyanions, ferrocyanides, and sulfides, is briefly summarized. In addition, the reaction mechanisms, electrochemical performance enhancements, structure-composition-performance relationships, merits and drawbacks of iron-based electrode materials for SIBs are discussed. Such iron-based electrode materials will be competitive and attractive electrodes for next-generation energy storage devices.

Feasibility of Cathode Surface Coating Technology for High-Energy Lithium-ion and Beyond-Lithium-ion Batteries

Cathode material degradation during cycling is one of the key obstacles to upgrading lithium-ion and beyond-lithium-ion batteries for high-energy and varied-temperature applications. Herein, we highlight recent progress in material surface-coating as the foremost solution to resist the surface phase-transitions and cracking in cathode particles in mono-valent (Li, Na, K) and multi-valent (Mg, Ca, Al) ion batteries under high-voltage and varied-temperature conditions. Importantly, we shed light on the future of materials surface-coating technology with possible research directions. In this regard, we provide our viewpoint on a novel hybrid surface-coating strategy, which has been successfully evaluated in LiCoO₂ -based-Li-ion cells under adverse conditions with industrial specifications for customer-demanding applications. The proposed coating strategy includes a first surface-coating of the as-prepared cathode powders (by sol-gel) and then an ultra-thin ceramic-oxide coating on their electrodes (by atomic-layer deposition). What makes it appealing for industry applications is that such a coating strategy can effectively maintain the integrity of materials under electro-mechanical stress, at the cathode particle and electrode- levels. Furthermore, it leads to improved energy-density and voltage retention at 4.55 V and 45 °C with highly loaded electrodes (≈24 mg.cm^-2 ). Finally, the development of this coating technology for beyond-lithium-ion batteries could be a major research challenge, but one that is viable.

Efficient Method of Designing Stable Layered Cathode Material for Sodium Ion Batteries Using Aluminum Doping

Despite their high specific capacity, sodium layered oxides suffer from severe capacity fading when cycled at higher voltages. This key issue must be addressed in order to develop high-performance cathodes for sodium ion batteries (SIBs). Herein, we present a comprehensive study on the influence of Al doping of Mn sites on the structural and electrochemical properties of a P2-Na_0.5Mn_0.5-xAl_xCo_0.5O₂ (x = 0, 0.02, or 0.05) cathode for SIBs. Detailed structural, morphological, and electrochemical investigations were carried out using X-ray diffraction, cyclic voltammetry, and galvanostatic charge-discharge measurements, and some new insights are proposed. Rietveld refinement confirmed that Al doping caused TMO₆ octahedra (TM = transition metal) shrinkage, resulting in wider interlayer spacing. After optimizing the aluminum concentration, the cathode exhibited remarkable electrochemical performance, with better stability and improved rate performance. Electrochemical impedance spectroscopy (EIS) measurements were performed at various states of charge to probe the surface and bulk effects of Al doping. The material presented here exhibits exceptional stability over 100 cycles within a 1.5-4.3 V window and outperforms several other Mn-Co-based cathodes for SIBs. This study presents a facile method for designing structurally stable cathodes for SIBs.

Improvement of the Cathode Electrolyte Interphase on P2-Na2/3Ni1/3Mn2/3O2 by Atomic Layer Deposition

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-Na_2/3Ni_1/3Mn_2/3O₂ electrodes is compared to that of ALD-coated Al₂O₃ P2-Na_2/3Ni_1/3Mn_2/3O₂ electrodes. Given that ALD coatings are in the early stage of development for NIB cathode materials, little is known about how ALD coatings, in particular aluminum oxide (Al₂O₃), affect the electrode-electrolyte interface. Therefore, full characterizations of its effects are presented in this work. For the first time, X-ray photoelectron spectroscopy (XPS) is used to elucidate the cathode electrolyte interphase (CEI) on ALD-coated electrodes. It contains less carbonate species and more inorganic species, which allows for fast Na kinetics, resulting in significant increase in Coulombic efficiency and decrease in cathode impedance. The effectiveness of Al₂O₃ ALD coating is also surprisingly reflected in the enhanced mechanical stability of the particle which prevents particle exfoliation.

Design and synthesis of a stable-performance P2-type layered cathode material for sodium ion batteries

P2-type Na_0.6Ni_0.2Co_0.2Mn_0.5Ti_0.1O₂ powders are successfully synthesized by a solid state reaction. Ex situ XRD reveals the phase transition process occurs at 4.1 V.