Research on electrochemical Na intercalation in battery system has been reported since the early 1980s but Na-ion batteries are not commercialized so far though studies on Li-ion batteries have been ...reported since the late 1970s and the practical batteries have been extensively utilized for portable device applications in the world since 1991. Now, targeted application of research and development for rechargeable batteries has changed toward realization of the sustainable energy society. With the change in social situation and development of the battery technology, studies on Na-ion batteries have been attracted significant interests since 2010. Although research interests of the electrode materials for Na-ion batteries are evoked in many researchers, advantages, disadvantages, and issues are not fully discussed for realizing the commercialization of Na-ion batteries. In this article, practical issues and perspective are reviewed on the basis of mainly our experimental experiences, know-how, and results, and the future direction is proposed to overcome the issues and to challenge the advanced performance.
Li‐ion battery commercialized by Sony in 1991 has the highest energy‐density among practical rechargeable batteries and is widely used in electronic devices, electric vehicles, and stationary energy ...storage system in the world. Moreover, the battery market is rapidly growing in the world and further fast‐growing is expected. With expansion of the demand and applications, price of lithium and cobalt resources is increasing. We are, therefore, motivated to study Na‐ and K‐ion batteries for stationary energy storage system because of much abundant Na and K resources and the wide distribution in the world. In this account, we review developments of Na‐ and K‐ion batteries with mainly introducing our previous and present researches in comparison to that of Li‐ion battery.
Li‐ion battery commercialized by Sony in 1991 has the highest energy‐density among rechargeable batteries and is widely used in the world. With expansion of the applications and rapid growing of the battery market, price of lithium and cobalt resources is increasing. In this account, we review developments of Na‐ and K‐ion batteries, consisting of much abundant Na and K, with mainly introducing our previous and present researches in comparison to that of Li‐ion battery.
Sodium 3d transition metal oxides for Na‐ion batteries have attracted attention of battery researchers because of their new chemistries and abundant material resources in the earth. Some companies ...have also developed Na‐ion battery prototypes mainly consisting of a layered oxide as a positive electrode material and hard carbon as the negative one for practical use. In this article, progress of Na‐containing layered transition‐metal oxides is reviewed in terms of fundamental chemistry and technology aspects for future batteries as a post Li‐ion battery. To realize practical positive electrode materials is still challenging and the practical issues are discussed. In this context the authors propose strategies for designing layered transition‐metal oxide materials toward realization of practical Na‐ion batteries.
Sodium 3d transition metal oxides have attracted much attention for battery researchers because of their new chemistries and abundant material‐resources. In this article, the progress of layered sodium 3d transition‐metal oxides is reviewed in terms of fundamental chemistry and technology for future batteries and the practical issues and strategies for designing the materials are discussed towards realization of practical Na‐ion batteries.
To realize a reversible solid‐state MnIII/IV redox couple in layered oxides, co‐operative Jahn–Teller distortion (CJTD) of six‐coordinate MnIII (t2g3–eg1) is a key factor in terms of structural and ...physical properties. We develop a single‐phase synthesis route for two polymorphs, namely distorted and undistorted P2‐type Na2/3MnO2 having different Mn stoichiometry, and investigate how the structural and stoichiometric difference influences electrochemical reaction. The distorted Na2/3MnO2 delivers 216 mAh g−1 as a 3 V class positive electrode, reaching 590 Wh (kg oxide)−1 with excellent cycle stability in a non‐aqueous Na cell and demonstrates better electrochemical behavior compared to undistorted Na2/3MnO2. Furthermore, reversible phase transitions correlated with CJTD are found upon (de)sodiation for distorted Na2/3MnO2, providing a new insight into utilization of the MnIII/IV redox couple for positive electrodes of Na‐ion batteries.
Highly reversible Na intercalation based on the MnIII/IV redox couple is demonstrated for Jahn–Teller‐distorted P2‐Na2/3MnO2 and a non‐distorted form having Mn off‐stoichiometry. The distorted Na2/3MnO2 delivers a higher energy of 590 Wh kg−1, accompanied by reversible phase transitions during Na extraction correlated with Na/vacancy ordering, charge order on Mn, and cooperative distortion.
Rechargeable batteries are capable of storing electric energy on the basis of pairing electrochemical redox reactions to realize sustainable energy society in our future. Since lithium-ion batteries ...with the highest specific energy among all the practical batteries were commercialized in 1991, many studies on lithium insertion materials and their electrochemical characterization have been reported to achieve even higher energy density, longer cycle life, and safer lithium-ion battery technologies. It is quite fortunate that the author had an opportunity to contribute to the research and development of lithium battery materials since 1997. In particular, studies on the influence of dissolved metallic ions like Mn2+, Co2+, Ni2+, Na+, and K+ ions in electrolyte solution on graphite negative electrodes in lithium-ion batteries motivated the author to extend the research scope to electrochemical sodium insertion chemistry. Furthermore, the author’s research experiences as a postdoctoral fellow in Dr. Delmas’ group in FY 2003 and a remarkable oral presentation on alpha-NaFeO2 electrode properties given by Professor Okada’s group in 2004 provided motivations and opened up new avenue toward the successful demonstration of non-aqueous sodium-ion batteries later in the career. Since 2009, the author’s research group has successfully demonstrated 3-volt class charge and discharge of a sodium-ion battery of a NaNi1/2Mn1/2O2 // hard carbon cell and a brand-new potassium-ion battery of a K2MnFe(CN)6 // graphite cell. The systematic studies of three different alkali-metal insertion systems synergistically induce deeper understanding and faster development of new materials for the next-generation rechargeable batteries.
Large-scale high-energy batteries with electrode materials made from the Earth-abundant elements are needed to achieve sustainable energy development. On the basis of material abundance, rechargeable ...sodium batteries with iron- and manganese-based positive electrode materials are the ideal candidates for large-scale batteries. In this review, iron- and manganese-based electrode materials, oxides, phosphates, fluorides, etc, as positive electrodes for rechargeable sodium batteries are reviewed. Iron and manganese compounds with sodium ions provide high structural flexibility. Two layered polymorphs, O3- and P2-type layered structures, show different electrode performance in Na cells related to the different phase transition and sodium migration processes on sodium extraction/insertion. Similar to layered oxides, iron/manganese phosphates and pyrophosphates also provide the different framework structures, which are used as sodium insertion host materials. Electrode performance and reaction mechanisms of the iron- and manganese-based electrode materials in Na cells are described and the similarities and differences with lithium counterparts are also discussed. Together with these results, the possibility of the high-energy battery system with electrode materials made from only Earth-abundant elements is reviewed.
High‐entropy layered oxide materials containing various metals that exhibit smooth voltage curves and excellent electrochemical performances have attracted attention in the development of positive ...electrode materials for sodium‐ion batteries. However, a smooth voltage curve can be obtained by suppression of the Na+‐vacancy ordering, and therefore, transition metal slabs do not need to be more multi‐element than necessary. Here, the Na+‐vacancy ordering is found to be disturbed by dual substitution of TiIV for MnIV and ZnII for NiII in P2‐Na2/3Ni1/3Mn2/3O2. Dual‐substituted Na2/3Ni1/4Mn1/2Ti1/6Zn1/12O2 demonstrates almost non‐step voltage curves with a reversible capacity of 114 mAh g−1 and less structural changes with a high crystalline structure maintained during charging and discharging. Synchrotron X‐ray, neutron, and electron diffraction measurements reveal that dual‐substitution with TiIV and ZnII uniquely promotes in‐plane NiII–MnIV ordering, which is quite different from the disordered mixing in conventional multiple metal substitution.
Dual‐substitution by Ti and Zn for Mn and Ni, respectively, in P2 type Na2/3Ni1/3Mn2/3O2 maintains in‐plane Ni–Mn ordering but disrupts Na+‐vacancy ordering, resulting in long‐cycling‐life non‐aqueous Na cells with smooth charge–discharge voltage curves and little structural change from the P2‐type layered structure.
Hard carbons represent the anode of choice for sodium-ion batteries. Their structure, sodium storage mechanism and sustainability are reviewed, highlighting the challenges for the rational design of ...optimized anode materials through the deep understanding of the structure–function correlations.
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Hard carbons are extensively studied for application as anode materials in sodium-ion batteries, but only recently a great interest has been focused toward the understanding of the sodium storage mechanism and the comprehension of the structure–function correlation. Although several interesting mechanisms have been proposed, a general mechanism explaining the observed electrochemical processes is still missing, which is essentially originating from the remaining uncertainty on the complex hard carbons structure. The achievement of an in-depth understanding of the processes occurring upon sodiation, however, is of great importance for a rational design of optimized anode materials.
In this review, we aim at providing a comprehensive overview of the up-to-date known structural models of hard carbons and their correlation with the proposed models for the sodium-ion storage mechanisms. In this regard, a particular focus is set on the most powerful analytical tools to study the structure of hard carbons (upon de-/sodiation) and a critical discussion on how to interpret and perform such analysis. Targeting the eventual commercialization of hard carbon anodes for sodium-ion batteries – after having established a fundamental understanding – we close this review with a careful evaluation of potential strategies to ensure a high degree of sustainability, since this is undoubtedly a crucial parameter to take into account for the future large-scale production of hard carbons.
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