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.
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.
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.
Extremely high capacity hard carbon for Na‐ion battery, delivering 478 mAh g−1, is successfully synthesized by heating a freeze‐dried mixture of magnesium gluconate and glucose by a MgO‐template ...technique. Influences of synthetic conditions and nano‐structures on electrochemical Na storage properties in the hard carbon are systematically studied to maximize the reversible capacity. Nano‐sized MgO particles are formed in a carbon matrix prepared by pre‐treatment of the mixture at 600 °C. Through acid leaching of MgO and carbonization at 1500 °C, resultant hard carbon demonstrates an extraordinarily large reversible capacity of 478 mAh g−1 with a high Coulombic efficiency of 88 % at the first cycle.
Mg‐templated hard carbon as an extremely high capacity negative electrode material for Na‐ion batteries is successfully synthesized by heating a freeze‐dried mixture of magnesium gluconate and glucose. The hard carbon demonstrates an extraordinarily large reversible capacity of 478 mAh g−1 with a high Coulombic efficiency of 88 % at the first cycle. Owing to the low potential operation, estimated energy density of the full cell is very high.
Lithium‐ion batteries have the highest energy density among practical secondary batteries and are widely used for electronic devices, electric vehicles, and even stationary energy‐storage systems. ...Along with the expansion of demand and applications, the concern about resources of lithium and cobalt is growing. Therefore, secondary batteries composed of abundant elements are required to complement lithium‐ion batteries. In recent years, the development of potassium‐ion batteries has attracted much attention, especially for large‐scale energy storage. In order to realize potassium‐ion batteries, various compounds are proposed and investigated as positive electrode materials, including layered transition‐metal oxides, Prussian blue analogues, and polyanionic compounds. This article offers a review of polyanionic compounds which are typically composed of abundant elements and expected high operating potential. Furthermore, we deliver our new results to partially compensate for lack of studies and provide a future perspective.
In recent years, the development of K‐ion batteries based on abundant elements has attracted attention. This article offers a review of polyanionic compounds as cathode materials for K‐ion batteries. Furthermore, we deliver our new results to partially compensate for lack of studies and provide a future perspective.
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