Oxide Cathodes For Sodium-Ion Batteries Research Articles

Challenges and Strategies toward Practical Application of Layered Transition Metal Oxide Cathodes for Sodium-Ion Batteries

Challenges and Strategies toward Practical Application of Layered Transition Metal Oxide Cathodes for Sodium-Ion Batteries

Realization High-Voltage Stabilization of O3-Type Layered Oxide Cathodes for Sodium-Ion Batteries by Sn Simultaneously Dual Modification

The total global production of lithium-ion batteries (LIBs) used in electric vehicles and stationary energy storage devices has increased sharply to reach the targeted Net Zero by 2050. This leads to concerns about the future and long-term availability and cost of critical raw materials (cobalt, nickel, lithium and copper) employed in LIBs. Therefore, alternative new-generation batteries with comparable performance but using less critical raw materials are needed.Sodium-ion Batteries (NIBs) offer a wealth of possibilities for inexpensive and sustainable energy storage devices. To maximize their potential, new cathode materials with high energy densities and stable structures are required. Cobalt-free sodium transition metal oxides of O3 type are a predominant cathode for NIBs due to their appreciable specific capacity, reduction in the use of critical elements, and the potential to rival LiFePO4 in terms of energy density. However, rapid capacity fading caused by serious structural and interfacial degradation hamper this process.Herein, we provide a novel Sn-modified O3-type NaNi1/3Fe1/3Mn1/3O2 cathode with improved high-voltage stability by bulk Sn doping and surface coating simultaneously. The bulk substitution of Sn4+ stabilizes the crystal structure by alleviating the irreversible high voltage phase transition and lattice structure degradation. In the meantime, the spontaneously formed tin rich surface layer effectively inhibits surface parasitic reactions and improves interfacial stability during cycling. As a result, the Sn-modified NaNi1/3Fe1/3Mn1/3O2 cathode exhibited excellent cycling performance by an almost doubled capacity retention increase after 200 cycles within 2.0-4.1V. The influence of Sn modification on the crystal structure and electrochemical properties has been investigated for the first time, and the mechanism was studied through an extensive analysis by in situ XRD, HRTEM, FIB-SEM, XPS and Mössbauer spectroscopy.This work offers an industrially feasible strategy to simultaneously stabilize the bulk structure and interface for O3-type layered cathodes for SIBs and raises the possibility of similar effective strategies to be employed for other energy storage materials Figure 1

High Voltage Ga-Doped P2-Type Na2/3 Ni0.2 Mn0.8 O2 Cathode for Sodium-Ion Batteries.

Ni/Mn-based oxide cathode materials have drawn great attention due to their high discharge voltage and large capacity, but structural instability at high potential causes rapid capacity decay. How to moderate the capacity loss while maintaining the advantages of high discharge voltage remains challenging. Herein, the replacement of Mn ions by Ga ions is proposed in the P2-Na2/3 Ni0.2 Mn0.8 O2 cathode for improving their cycling performances without sacrificing the high discharge voltage. With the introduction of Ga ions, the relative movement between the transition metal ions is restricted and more Na ions are retained in the lattice at high voltage, leading to an enhanced redox activity of Ni ions, validated by ex situ synchrotron X-ray absorption spectrum and X-ray photoelectron spectroscopy. Additionally, the P2-O2 phase transition is replaced by a P2-OP4 phase transition with a smaller volume change, reducing the lattice strain in the c-axis direction, as detected by operando/ex situ X-ray diffraction. Consequently, the Na2/3 Ni0.21 Mn0.74 Ga0.05 O2 electrode exhibits a high discharge voltage close to that of the undoped materials, while increasing voltage retention from 79% to 93% after 50 cycles. This work offers a new avenue for designing high-energy density Ni/Mn-based oxide cathodes for sodium-ion batteries.

Construction of environmental-stable and high-rate layered oxide cathodes for sodium-ion batteries

Layered manganese oxides, as dynamic cathodes for high energy density sodium ion batteries (SIBs), still suffer from not only rapid capacity decay, but also irreversible phase transition, unsatisfactory rate performance and air instability. In this work, Li/Ni/Ti co-doping Na0.72Li0.16Ni0.12Ti0.1Mn0.62O2 (NLNTMO) cathode was successfully synthesized and it revealed that the structure design not only effectively inhibits Jahn-Teller distortion to improve cycling stability but also enhances its resistance to air and moisture degradation. Besides, density functional theory (DFT) calculations reveal that Ti can slightly adjust the energy level of isolated O 2p and Mn 3d orbitals. The in-situ X-ray diffraction (XRD) analysis reveals the inhibition of the repulsive phase transition from P2–OP4/O2 and the occurrence of a solid solution reaction instead. As a result, NLNTMO cathode presents a high specific capacity of 198.6 mAh g−1 at 0.2C, 70 mAh g−1 at 20C (4 A g−1) and a high capacity retention of 80 % in 2.0–4.4 V after 200 cycles at 1C.

Structural Evolution of Air-Exposed Layered Oxide Cathodes for Sodium-Ion Batteries: An Example of Ni-doped NaxMnO2.

Sodium-ion batteries have recently aroused the interest of industries as possible replacements for lithium-ion batteries in some areas. With their high theoretical capacities and competitive prices, P2-type layered oxides (NaxTMO2) are among the obvious choices in terms of cathode materials. On the other hand, many of these materials are unstable in air due to their reactivity toward water and carbon dioxide. Here, Na0.67Mn0.9Ni0.1O2 (NMNO), one of such materials, has been synthesized by a classic sol-gel method and then exposed to air for several weeks as a way to allow a simple and reproducible transition toward a Na-rich birnessite phase. The transition between the anhydrous P2 to the hydrated birnessite structure has been followed via periodic XRD analyses, as well as neutron diffraction ones. Extensive electrochemical characterizations of both pristine NMNO and the air-exposed one vs sodium in organic medium showed comparable performances, with capacities fading from 140 to 60 mAh g-1 in around 100 cycles. Structural evolution of the air-exposed NMNO has been investigated both with ex situ synchrotron XRD and Raman. Finally, DFT analyses showed similar charge compensation mechanisms between P2 and birnessite phases, providing a reason for the similarities between the electrochemical properties of both materials.

The effect of configurational entropy on acoustic emission of P2-type layered oxide cathodes for sodium-ion batteries

Sodium-ion batteries (SIBs) see intensive research and commercialization efforts, aiming to establish them as an alternative to lithium-ion batteries. Among the reported cathode material families for SIBs, Na-deficient P2-type layered oxides are promising candidates, benefiting from fast sodium diffusion and therefore high charge/discharge rates. However, upon sodium extraction at high potentials, a transition from the P2 to O2 phase occurs, with the corresponding change in cell volume resulting in particle fracture and capacity degradation. A possible solution to this is to increase configurational entropy by introducing more elements into the transition-metal layer (so-called high-entropy concept), leading to some kind of structural stabilization. In this work, the acoustic emission (AE) of a series of P2-type layered oxide cathodes with increasing configurational entropy [Na0.67(Mn0.55Ni0.21Co0.24)O2, Na0.67(Mn0.45Ni0.18Co0.24Ti0.1Mg0.03)O2 and Na0.67(Mn0.45Ni0.18Co0.18Ti0.1Mg0.03Al0.04Fe0.02)O2] is recorded during SIB operation and correlated to the materials properties, namely change in c lattice parameter and cracking behavior. A structure-property relationship between entropy, manifested in the extent of phase transition, and detected AE is derived, supported by the classification of signals by peak frequency. This classification in combination with microscopy imaging allows to distinguish between inter- and intragranular fracture. Relatively more intergranular and less intragranular crack formation is observed with increasing configurational entropy.

Layered oxide cathodes for sodium-ion batteries: microstructure design, local chemistry and structural unit

Layered oxide cathodes for sodium-ion batteries: microstructure design, local chemistry and structural unit

Tailored P2/O3 phase-dependent electrochemical behavior of Mn-based cathode for sodium-ion batteries

The development of mixed structures is increasingly becoming an efficient way to improve the performance of layered oxide cathodes for sodium-ion batteries. Herein, the Na0.8Mn0.6Ni0.3Cu0.1O2 (NMNC) cathodes with varying fractions of P2/O3-type phases are prepared by adjusting the calcination conditions. The Rietveld refinement of X-ray diffraction (XRD) data confirms the increase in O3 phase fraction from 7 % to 27 % with the increase in calcination temperature from 850 °C to 950 °C. The sample prepared at 850 °C (NMNC-850) exhibits the highest specific capacity (139 mAh g−1, 100 mAh g−1, and 80 mAh g−1 at 0.1C, 1C, and 4C, respectively) and best rate performance among all samples in addition to an excellent cyclability with capacity retention of ~85 % after 100 cycles in 1.5–4.2 V range. The increase in the O3 phase fraction leads to a drastic degradation of rate performance. The galvanostatic intermittent titration technique confirms a diffusion coefficient of 5.13 × 10−13–5.25 × 10−10 cm2 s−1 in biphasic NMNC-850 sample. Ex-situ XRD studies confirm a reversible P2/O3 → P2/P3 → P2/O3 transformation in NNMC-850 during cycling. The improved electrochemical performance is attributed to the presence of non-identical neighboring phases in suppressing the phase transformations during cycling.

Annealing in Argon Universally Upgrades the Na‐Storage Performance of Mn‐Based Layered Oxide Cathodes by Creating Bulk Oxygen Vacancies

AbstractManganese‐rich layered oxide cathodes of sodium‐ion batteries (SIBs) are extremely promising for large‐scale energy storage owing to their high capacities and cost effectiveness, while the Jahn–Teller (J–T) distortion and low operating potential of Mn redox largely hinder their practical applications. Herein, we reveal that annealing in argon rather than conventional air is a universal strategy to comprehensively upgrade the Na‐storage performance of Mn‐based oxide cathodes. Bulk oxygen vacancies are introduced via this method, leading to reduced Mn valence, lowered Mn 3d‐orbital energy level, and formation of the new‐concept Mn domains. As a result, the energy density of the model P2‐Na0.75Mg0.25Mn0.75O2cathode increases by ≈50 % benefiting from the improved specific capacity and operating potential of Mn redox. The Mn domains can disrupt the cooperative J–T distortion, greatly promoting the cycling stability. This exciting finding opens a new avenue towards high‐performance Mn‐based oxide cathodes for SIBs.

Layered Oxide Cathodes for Sodium-Ion Batteries: Storage Mechanism, Electrochemistry, and Techno-economics.

ConspectusLithium-ion batteries (LIBs) are ubiquitous in all modern portable electronic devices such as mobile phones and laptops as well as for powering hybrid electric vehicles and other large-scale devices. Sodium-ion batteries (NIBs), which possess a similar cell configuration and working mechanism, have already been proven as ideal alternatives for large-scale energy storage systems. The advantages of NIBs are as follows. First, sodium resources are abundantly distributed in the earth's crust. Second, high-performance NIB cathode materials can be fabricated by using solely inexpensive and noncritical transition metals such as manganese and iron, which further reduces the cost of the required raw materials. Recently, the unprecedented demand for lithium and other critical minerals has driven the cost of these primary raw materials (which are utilized in LIBs) to a historic high and thus triggered the commercialization of NIBs.Sodium layered transition metal oxides (NaxTMO2, TM = transition metal/s), such as Mn-based sodium layered oxides, represent an important family of cathode materials with the potential to reduce costs, increase energy density and cycling stability, and improve the safety of NIBs for large-scale energy storage. However, these layered oxides face several key challenges, including irreversible phase transformations during cycling, poor air stability, complex charge-compensation mechanisms, and relatively high cost of the full cell compared to LiFePO4-based LIBs. Our work has focused on the techno-economic analysis, the degradation mechanism of NaxTMO2 upon cycling and air exposure, and the development of effective strategies to improve their electrochemical performances and air stability. Correlating structure-performance relationships and establishing general design strategies of NaxTMO2 must be considered for the commercialization of NIBs.In this Account, we discuss the recent progress in the development of air-stable, electrochemically stable, and cost-effective NaxTMO2. The favorable redox-active cations for NaxTMO2 are emphasized in terms of abundance, cost, supply, and energy density. Different working mechanisms related to NaxTMO2 are summarized, including the electrochemical reversibility, the main structural transformations during the charge and discharge processes, and the charge-compensation mechanisms that accompany the (de)intercalation of Na+ ions, followed by discussions to improve the stability toward ambient air and upon cycling. Then the techno-economics are presented, with an emphasis on cathodes with different chemical compositions, cost breakdown of battery packs, and Na deficiency, factors that are critical to the large-scale implementation. Finally, this Account concludes with an overview of the remaining challenges and new opportunities concerning the practical applications of NaxTMO2, with an emphasis on the cost, large-scale fabrication capability, and electrochemical performance.

Entropy modulation strategy of P2-type layered transition metal oxide cathodes for sodium-ion batteries with a high performance

Configuration entropy is increased by doping with multiple cations, whereby the material defects and active sites are increased and phase transition is inhibited at high voltage. Meanwhile, the sodium-ion diffusion rate was improved with the co-doping strategy.

Engineering crystal-facet modulation to obtain stable Mn-based P2-layered oxide cathodes for sodium-ion batteries

The undesirable phase transformation of Mn-based P2-layered oxide cathodes is a tremendous challenge in commercializing Mn-based oxide cathodes for sodium-ion batteries. In this work, Na0.67MnO2 cathode with stable P2-type structure was successfully synthesized by modulating its coordination numbers to suppress the preferred orientation growth of (001) crystal plane, which was realized to maintain a stable P2-type structure in the whole state of charging and discharging. Specifically, designing Mn2+ six coordination sites to lower the high surface energy of (001) crystal plane is an effective way to reduce nucleation rates, which leads to the production of few grain boundaries and the suppression of layer-to-layer stacking in the crystal growth stage. Due to their fewer grain boundaries and skeleton structure with layer-to-layer stacking, the interlaminar stress and intragranular fatigue cracks can be alleviated in the long-life cycling performance of Na0.67MnO2 cathode. Na0.67MnO2 cathodes derived from the precursor of Mn2+ six coordination sites (C-Na0.67MnO2) have more exposed {010} crystal face and enlarged sodium-ion diffusion channels and structure integrity compared to Na0.67MnO2 cathode prepared by the precursor of Mn2+ four coordination sites (O-Na0.67MnO2). Therefore, C-Na0.67MnO2 cathode delivers an initial capacity of 106.8 mAh/g and has excellent capacity retention of 94.8 % after 150 cycles at 80 mAh/g. The rational design strategy endows Mn-based P2-layered oxide cathodes with stable sodium-ion diffusion channels and lamellar structure.

Na2/3Li1/9[Ni2/9Li1/9Mn2/3]O2: A High-Performance Solid-Solution Reaction Layered Oxide Cathode Material for Sodium-Ion Batteries

Designing high-performance layered cathodes, in particular the P2-type groups, is still challenging for sodium-ion batteries. Taking advantage of the well-known Li/Ni mixing in Ni-rich layered cathodes for Li-ion batteries, a layered Na2/3Li1/9[Ni2/9Li1/9Mn2/3]O2 cathode with a superior rate and long-cycle performance is developed through Li-ion incorporation. Neutron diffraction indicates that the introduced Li ions occupy the intrinsic Na+ vacancies in the Na layer and transition metal layer concurrently. A facile solid-solution reaction mechanism upon cycling is also revealed by in situ X-ray diffraction, and ex situ X-ray photoelectron spectroscopy results demonstrate that the Ni2+/Ni4+ pairs participate in the electrochemical reactions, while the Mn ions remain unchanged. This material delivers ∼91.6% of the theoretical capacity initially and 64 mAh g–1 reversible capacity even at 20 C (∼58.2% of the capacity at 0.1 C) with 74.5% capacity retention after 1500 long-term cycles in the voltage range of 2.0–4.2 V. This approach can optimize the material structure design, providing some insights into designing high-rate and long-cycle life oxide cathodes for sodium-ion batteries.

Insights into the improved cycle and rate performance by ex-situ F and in-situ Mg dual doping of layered oxide cathodes for sodium-ion batteries

P2 phase layered manganese-based transition metal (TM) oxides have been extensively studied as cathode materials in Sodium ion batteries (SIBs). Herein, ex-situ F-doping P2-type layered Na0.67Ni0.15Fe0.2Mn0.65F0.05O1.95 (NFMF-005) is synthesized firstly by coprecipitation to reduce the capacity fading caused by irreversible phase transition and Jahn-Teller effect. Because the bond energy of OO and TM-O are changed owing to O sites are occupied by F, leading to the decrease of the interatomic distance of TM and the increase of the interlayer spacing, NFMF-005 can provide wider ion transport channel and suppress structural deformation. To inhibit phase transition completely and mitigate the slide of TM layers, in-situ Mg-doping is secondly carried out by electrochemical method after F-doping of NFMF-005. The obtained Mg-doping P2-type NM-NFMF005 possesses outstanding electrochemical performance, delivering the specific capacity of 229 mAh g−1, the capacity retention of 87.7% after 50 cycles and discharge specific capacity of 100 mAh g−1 at 10 C. Mg-Mg dimers are used to explain its superior performance, which exhibit pillar effect not only to stretch the interlayer space, but also to enhance the mechanical strength and improve structure stability. All the results illustrate that the double-doping of F and Mg can play synergistic role to promote the performance of SIBs. This work is promising to further expand strategies and areas of materials doping. This new electrochemical doping method will also provide guidance for the rational design of SIBs layered cathode materials.

Revealing the anionic redox chemistry in O3-type layered oxide cathode for sodium-ion batteries

Anion redox chemistry plays a crucial role in Na-deficient or Na-rich oxide cathodes for sodium-ion batteries (SIBs). But the oxygen redox chemistry has been rarely reported in O3-type (Na-full) layered oxides for SIBs. Herein, we reveal the anion redox chemistry in O3-type NaMn1/3Fe1/3Ni1/3O2 (MFN) cathode material, and propose an integrated strategy combining ZrO2 coating and Zr4+ doping to tune the anionic redox chemistry and crystal structures which improves the activity, reversibility, and stability of O2−. Oxygen redox reactions with high reversibility and cyclic stability mainly occur between 4.0 V and 4.3 V. The structure of Na-O-TM is regulated by Zr4+ doping, and the electronic state of O-2p occupies a higher energy level by the regulation of Na-O-TM structure. The electrons can migrate from O2- more easily and O2−/O− contribute more capacity. Zr4+ doping optimizes the lattice structure, enlarges the Na layer, and decreases TMO2 layer, which reduces the diffusion resistance of Na+ and increases the structural stability. ZrO2 layer effectively mitigates the corrosion of the electrolyte and ensures the integrity of the structure, which inhibits the formation of Na2CO3 on the surface and decreases CO2 release. This study not only reveals the anion redox chemistry in O3-type layered oxide cathode material but also is available for insights into regulating the redox activity, reversibility, and stability of oxygen.

Sodium transition metal oxides: the preferred cathode choice for future sodium-ion batteries?

This work provides guidance on controlling anionic redox activity and finding novel high-capacity transition metal oxide cathodes for sodium-ion batteries.

A comprehensive understanding of the anionic redox chemistry in layered oxide cathodes for sodium-ion batteries

Sodium-ion batteries (SIBs) have demonstrated great application prospects in large-scale energy storage systems and low-speed electric vehicles due to the cost effectiveness and abundant resources. Layered transition-metal oxides are recognized as one of the most attractive sodium-ion storage cathode candidates by virtue of their high compositional diversity, environmental friendliness, ease of synthesis, and promising theoretical capacities. The practicability, however, is still limited by the fact that the energy densities of most Na-storage layered oxide cathodes solely using the conventional cationic redox are not comparable to those of the lithium-ion storage counterparts. Recently, the strategy of activating anionic redox (O2−/O n −) which is popular in Li-rich layered materials has been successfully applied in oxide cathodes of SIBs to promote the energy density to a new level. It is interesting to note that excess Na is not the prerequisite to induce anionic redox in sodium oxides, indicating a new mechanism underlying Na-ion materials. Herein, the latest advances on the anionic redox chemistry in layered oxide cathodes for SIBs, including the fundamental theories, triggering strategies, and applicable cathode materials, are comprehensively reviewed. Moreover, the challenges (mainly O2 release) facing anionic redox are discussed, and the possible remedies are outlined for future developments toward a highly reversible oxygen usage. We believe that this review can provide a valuable guidance for the exploration of high-energy layered oxide cathode materials of SIBs.

Synthesis Control of Layered Oxide Cathodes for Sodium-Ion Batteries: A Necessary Step Toward Practicality

Interest in sodium-ion battery cathode materials, particularly for grid-scale energy-storage applications, has considerably increased in the last few years, sparking a push toward industrially prac...

Recent advances and prospects of layered transition metal oxide cathodes for sodium-ion batteries

Due to the high safety, long service life and outstanding energy density, lithium ion batteries (LIBs) have been widely used in portable energy storage devices. However, the uneven distribution and increasingly high price of lithium resources have hindered the further use of LIBs, particularly for large-scale energy storage. Sodium-ion batteries (SIBs) that have the same working principle as LIBs have, emerged as some of the most promising candidate devices for use in large-scale energy storage applications and low-speed electric automobiles, due to the low cost and abundant reserves of sodium resources. As a key component of SIBs, the cathode materials have a remarkable effect on the electrochemical performance. Layered transition metal oxides have been considered to be some of the most promising cathodes for SIBs due to their flexibility, versatility, and excellent electrochemical performances. Although layered materials face several challenges such as irreversible phase transition, inferior capacity retention and poor air stability, recent experimental studies have proposed corresponding strategies to solve these problems. Herein, we will survey the latest progress in the development of high-energy SIBs cathodes focusing on high-voltage, high-capacity and composite-structure cathode materials.

Large-Scale Synthesis of the Stable Co-Free Layered Oxide Cathode by the Synergetic Contribution of Multielement Chemical Substitution for Practical Sodium-Ion Battery.

The O3-type layered oxide cathodes for sodium-ion batteries (SIBs) are considered as one of the most promising systems to fully meet the requirement for future practical application. However, fatal issues in several respects such as poor air stability, irreversible complex multiphase evolution, inferior cycling lifespan, and poor industrial feasibility are restricting their commercialization development. Here, a stable Co-free O3-type NaNi0.4Cu0.05Mg0.05Mn0.4Ti0.1O2 cathode material with large-scale production could solve these problems for practical SIBs. Owing to the synergetic contribution of the multielement chemical substitution strategy, this novel cathode not only shows excellent air stability and thermal stability as well as a simple phase-transition process but also delivers outstanding battery performance in half-cell and full-cell systems. Meanwhile, various advanced characterization techniques are utilized to accurately decipher the crystalline formation process, atomic arrangement, structural evolution, and inherent effect mechanisms. Surprisingly, apart from restraining the unfavorable multiphase transformation and enhancing air stability, the accurate multielement chemical substitution engineering also shows a pinning effect to alleviate the lattice strains for the high structural reversibility and enlarges the interlayer spacing reasonably to enhance Na+ diffusion, resulting in excellent comprehensive performance. Overall, this study explores the fundamental scientific understandings of multielement chemical substitution strategy and opens up a new field for increasing the practicality to commercialization.