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Layered lithium manganese oxides suffer from irreversible phase transitions induced by Mn migration and/or dissolution associated with the Jahn-Teller effect (JTE) of Mn 3+ , leading to inevitable capacity fading during cycling. The popular doping strategy of oxidizing Mn 3+ to Mn 4+ to relieve the JTE cannot completely eliminate the detrimental structural collapse from the cooperative JTE. Therefore, they are considered to be impractical for commercial use as cathode materials. Here, we demonstrate a layered lithium manganese oxide that can be charged and discharged without any serious structural collapse using metastable Li-birnessite with controlled structural disorder. Although Li-birnessite is thermodynamically unstable under ambient conditions, Li ion exchange into Na-birnessite followed by an optimal dehydration resulted in a disordered Li-birnessite. The control over crystal water in the interlayer provides intriguing short-range order therein, which can help to suppress parasitic Mn migration and dissolution, thereby ensuring a reversible electrochemical cycling. The Mn redox behavior and local structure change of the Li-birnessite were investigated by ex situ soft X-ray absorption spectroscopy (sXAS) and X-ray pair distribution function (PDF) analysis. The combined sXAS and PDF with electrochemical analyses disclosed that the reversible Mn redox and suppressed phase transitions in Dh Li-birnessite contribute to dramatically improving its electrochemical reversiblity during cycling. Our findings underscore the substantial effects of controlled static disorder on the structural stability and electrochemical reversibility of a layered lithium manganese oxide, Li-birnessite, which extends the practical capacity of layered oxides close to their theoretical limit.

The fact that ordered materials are rarely perfectly crystalline is widely acknowledged among materials scientists, but its impact is often overlooked or underestimated when studying how structure relates to properties. Various investigations demonstrate that intrinsic and extrinsic defects, and disorder generated by physicochemical reactions, are responsible for unexpectedly detrimental or beneficial functionalities. The task remains to modulate the disorder to produce desired properties in materials. As disorder is often correlated with local interactions, it is controllable. In this Review, we explore the structural disorder in cathode materials as a novel approach for improving their electrochemical performance. We revisit cathode materials for alkali-ion batteries and outline the origins and beneficial consequences of disorder. Focusing on layered, cubic rocksalt and other metal oxides, we discuss how disorder improves electrochemical properties of cathode materials and which interactions generate the disorder. We also present the potential pitfalls of disorder that must be considered. We conclude with perspectives for enhancing the electrochemical performance of cathode materials by using disorder., (© 2024. Springer Nature Limited.)

The design of temperature-adaptive Zn-air batteries (ZABs) with long life spans and high energy efficiencies is challenging owing to sluggish oxygen reduction reaction (ORR) kinetics and an unstable Zn/electrolyte interface. Herein, a quasi-solid-state ZAB is designed by combining atomically dispersed Fe-N-C catalysts containing pyridinic N vacancies (FeNC-V N ) with a polarized organo-hydrogel electrolyte. First-principles calculation predicts that adjacent V N sites effectively enhance the covalency of Fe-N x moieties and moderately weaken *OH binding energies, significantly boosting the ORR kinetics and stability. In situ Raman spectra reveal the dynamic evolution of *O 2 - and *OOH on the FeNC-V N cathode in the aqueous ZAB, proving that the 4e - associative mechanism is dominant. Moreover, the ethylene glycol-modulated organo-hydrogel electrolyte forms a zincophilic protective layer on the Zn anode surface and tailors the [Zn(H 2 O) 6 ] 2+ solvation sheath, effectively guiding epitaxial deposition of Zn 2+ on the Zn (002) plane and suppressing side reactions. The assembled quasi-solid-state ZAB demonstrates a long life span of over 1076 h at 2 mA cm -2 at -20 °C, outperforming most reported ZABs.

Li-rich cathodes are extensively investigated as their energy density is superior to Li stoichiometric cathode materials. In addition to the transition metal redox, this intriguing electrochemical performance originates from the redox reaction of the anionic sublattice. This new redox process, the so-called anionic redox or, more directly, oxygen redox in the case of oxides, almost doubles the energy density of Li-rich cathodes compared to conventional cathodes. Numerous theoretical and experimental investigations have thoroughly established the current understanding of the oxygen redox of Li-rich cathodes. However, different reports are occasionally contradictory, indicating that current knowledge remains incomplete. Moreover, several practical issues still hinder the real-world application of Li-rich cathodes. As these issues are related to phenomena resulting from the electronic to atomic evolution induced by unstable oxygen redox, a fundamental multiscale understanding is essential for solving the problem. In this review, the current mechanistic understanding of oxygen redox, the origin of the practical problems, and how current studies tackle the issues are summarized., (© 2023 Wiley-VCH GmbH.)

Lithium-oxygen batteries have the potential to become the most eminent solution for future energy storage with their theoretical energy density exceeding all existing batteries. However, the insulating and insoluble discharge product (lithium peroxide; Li 2 O 2 ) impairs practical application. Conventional catalyst designs based on the electronic structure and interfacial charge transfer descriptors have not been able to overcome these limitations due to Li 2 O 2 . Herein, we revisit the role of heterogeneous catalysts as substrates to regulate Li 2 O 2 growth and the formation of solid/solid reaction interfaces. We demonstrate that controlled solid/solid interfacial structure design is a critical performance parameter beyond the inherent electronic structure. In particular, the Cu 2 O substrate in this study induces a homogeneous deposition of Pd atoms, which leads to well-controlled growth of Li 2 O 2 resolving mass and charge transport limits (i.e., the bottleneck of oxygen reduction/evolution reactions), thus improving reversibility, capacity, and durability of the cells by dissipating electrochemical and mechanical stress. We thus verified the essential role of solid/solid interfaces to regulate the nucleation and growth process of Li 2 O 2 in lithium-oxygen batteries.

Sodium layered oxides generally suffer from deep-desodiation instability in P2 structure and sluggish kinetics in O3 structure. It will be great to design P2/O3 biphasic materials that bring the complementary merits of both structures. However, such exploration is hindered by the ambiguous mechanism of material formation. Herein, supported by theoretical simulations and various spectroscopies, we prove that P2/O3 biphasic structures essentially originate from the internal heterogeneity of cationic potential, which can be realized by constraining the temperature-driven ion diffusion during solid-state reactions. Consequently, P2/O3 biphasic Na 0.7 Ni 0.2 Cu 0.1 Fe 0.2 Mn 0.5 O 2- δ with well-designed quaternary composition is successfully obtained, exhibiting much-improved rate capabilities (62 mAh g -1 at 2.4 A g -1 ) and cycling stabilities (84% capacity retention after 500 cycles) than its single-phase analogues. Furthermore, synchrotron-based diffraction and X-ray absorption spectroscopy are employed to unravel the underlying sodium-storage mechanism of the P2/O3 biphasic structure. This work presents new insights toward the rational design of advanced layered cathodes for sodium-ion batteries., Competing Interests: Conflict of interest The authors declare that they have no conflict of interest., (Copyright © 2022. Published by Elsevier B.V.)

Activation of oxygen redox during the first cycle has been reported as the main trigger of voltage hysteresis during further cycles in high-energy-density Li-rich 3d-transition-metal layered oxides. However, it remains unclear whether hysteresis only occurs due to oxygen redox. Here, it is identified that the voltage hysteresis can highly correlate to cationic reduction during discharge in the Li-rich layered oxide, Li 1.2 Ni 0.4 Mn 0.4 O 2 . In this material, the potential region of discharge accompanied by hysteresis is apparently separated from that of discharge unrelated to hysteresis. The quantitative analysis of soft/hard X-ray absorption spectroscopies discloses that hysteresis is associated with an incomplete cationic reduction of Ni during discharge. The galvanostatic intermittent titration technique shows that the inevitable energy consumption caused by hysteresis corresponds to an overpotential of 0.3 V. The results unveil that hysteresis can also be affected by cationic redox in Li-rich layered cathodes, implying that oxygen redox cannot be the only reason for the evolution of voltage hysteresis. Therefore, appropriate control of both cationic and anionic redox of Li-rich layered oxides will allow them to reach their maximum energy density and efficiency., (© 2022 The Authors. Advanced Science published by Wiley-VCH GmbH.)

The Jahn-Teller effect (JTE) is one of the most important determinators of how much stress layered cathode materials undergo during charge and discharge; however, many reports have shown that traces of superstructure exist in pristine layered materials and irreversible phase transitions occur even after eliminating the JTE. A careful consideration of the energy of cationic distortion using a Taylor expansion indicated that second-order JTE (pseudo-JTE) is more widespread than the aforementioned JTE because of the various bonding states that occur between bonding and antibonding molecular orbitals in transition-metal octahedra. As a model case, a P2-type Mn-rich cathode (Na 3/4 MnO 2 ) was investigated in detail. MnO 6 octahedra are well known to undergo either elongation or contraction in a specific direction due to JTE. Here, the substitution of Li for Mn (Na 3/4 (Li 1/4 Mn 3/4 )O 2 ) helped to oxidize Mn 3+ to Mn 4+ suppressing JTE; however, the MnO 6 octahedra remained asymmetric with a clear trace of the superstructure. With various advanced analyses, we disclose the pseudo-JTE as a general reason for the asymmetric distortions of the MnO 6 octahedra. These distortions lead to the significant electrochemical degradation of Na 3/4 Li 1/4 Mn 3/4 O 2 . The suppression of the pseudo-JTE modulates phase transition behaviors during Na intercalation/deintercalation and thereby improves all of the electrochemical properties. The insight obtained by coupling a theoretical background for the pseudo-JTE with verified layered cathode material lattice changes implies that many previous approaches can be rationalized by regulating pseudo-JTE. This suggests that the pseudo-JTE should be thought more important than the well-known JTE for layered cathode materials.

A defect engineering of inorganic solids garners great deal of research activities because of its high efficacy to optimize diverse energy-related functionalities of nanostructured materials. In this study, a novel in situ defect engineering route to maximize electrocatalytic redox activity of inorganic nanosheet is developed by using holey nanostructured substrate with strong interfacial electronic coupling. Density functional theory calculations and in situ spectroscopic analyses confirm that efficient interfacial charge transfer takes place between holey TiN and Ni-Fe-layered double hydroxide (LDH), leading to the feedback formation of nitrogen vacancies and a maximization of cation redox activity. The holey TiN-LDH nanohybrid is found to exhibit a superior functionality as an oxygen electrocatalyst and electrode for Li-O 2 batteries compared to its non-holey homologues. The great impact of hybridization-driven vacancy introduction on the electrochemical performance originates from an efficient electrochemical activation of both Fe and Ni ions during electrocatalytic process, a reinforcement of interfacial electronic coupling, an increase in electrochemical active sites, and an improvement in electrocatalysis/charge-transfer kinetics., (© 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Sodium ion batteries (SIB) have received much research attention in the past decades as they are considered to be one alternative to the currently prevalent lithium ion batteries, and carbonaceous and organic compounds present two promising classes of SIB electrode materials advantaged by abundance of their constituent elements and reduced environmental footprints. To accelerate the development of these materials for SIB applications, future research directions must be guided by a thorough understanding of the charge storage mechanism. This review presents recent efforts in mechanism elucidation for these two classes of SIB electrode materials since, compared to their inorganic counterparts, they have unique challenges in material analysis. Topics covered will include characterization techniques and analytical frameworks for mechanism elucidation, emphasizing the advantages and limitations of individual experimental methodologies and providing a commentary on scientific rigor in result interpretation.

The increasing demand to efficiently store and utilize the electricity from renewable energy resources in a sustainable way has boosted the request for sodium-ion battery technology due to the high abundance of sodium sources worldwide. Na superionic conductor (NASICON) structured cathodes with a robust polyanionic framework have been intriguing because of their open 3D structure and superior thermal stability. The ever-increasing demand for higher energy densities with NASICON-structured cathodes motivates us to activate multielectron reactions, thus utilizing the third sodium ion toward higher voltage and larger capacity, both of which have been the bottlenecks for commercializing sodium-ion batteries. A doping strategy with Cr inspired by first-principles calculations enables the activation of multielectron redox reactions of the redox couples V 2+ /V 3+ , V 3+ /V 4+ , and V 4+ /V 5+ , resulting in remarkably improved energy density even in comparison to the layer structured oxides and Prussian blue analogues. This work also comprehensively clarifies the role of the Cr dopant during sodium storage and the valence electron transition process of both V and Cr. Our findings highlight the importance of a broadly applicable doping strategy for achieving multielectron reactions of NASICON-type cathodes with higher energy densities in sodium-ion batteries.

Metal phosphides as anode materials for alkali-metal ion batteries have captured considerable interest due to their high theoretical capacities and electronic conductivity. However, they suffer from huge volume expansion and element segregation during repetitive insertion/extraction of guest ions, leading to structure deterioration and rapid capacity decay. Herein, an amorphous Sn 0.5 Ge 0.5 P 3 was constructed through a two-phase intermediate strategy based on the elemental composition modulation from two crystalline counterparts and applied in alkali-metal ion batteries. Differing from crystalline P-based compounds, the amorphous structure of Sn 0.5 Ge 0.5 P 3 effectively reduces the volume variation from above 300% to 225% during cycling. The ordered distribution of cations and anions in the short-range ensures the uniform distribution of each element during cycles and thus contributes to durable cycling stability. Moreover, the long-range disordered structure of amorphous material shortens the ion transport distance, which facilitates diffusion kinetics. Benefiting from the aforementioned effects, the amorphous Sn 0.5 Ge 0.5 P 3 delivers a high Na storage capacity of 1132 mAh g -1 at 0.1 A g -1 over 100 cycles. Even at high current densities of 2 and 10 A g -1 , its capacities still reach 666 and 321 mAh g -1 , respectively. As an anode for Li storage, the Sn 0.5 Ge 0.5 P 3 similarly also exhibits better cycling stability and rate performance compared to its crystalline counterparts. Significantly, the two-phase transition strategy is generally applicable to achieving other amorphous metal phosphides such as GeP 2 . This work would be helpful for constructing high-performance amorphous anode materials for alkali-metal ion batteries.

Nitrogen-doped porous carbons containing atomically dispersed iron are prime candidates for substituting platinum-based catalysts for oxygen reduction reaction (ORR) in fuel cells. These carbon catalysts are classically synthesizedviacomplicated routes involving multiple heat-treatment steps to form the desired Fe-N x sites. We herein developed a highly active FeNC catalyst comprising of exclusive Fe-N x sites by a simplified solid-state synthesis protocol involving only a single heat-treatment. Imidazole is pyrolyzed in the presence of an inorganic salt-melt resulting in highly porous carbon sheets decorated with abundant Fe-N x centers, which yielded a high density of electrochemically accessible active sites (1.36 × 10 19 sites g -1 ) as determined by the in situ nitrite stripping technique. The optimized catalyst delivered a remarkable ORR activity with a half-wave potential (E 1/2 ) of 0.905 V RHE in alkaline electrolyte surpassing the benchmark Pt catalyst by 55 mV. In acidic electrolyte, an E 1/2 of 0.760 V RHE is achieved at a low loading level (0.29 mg cm -2 ). In PEMFC tests, a current density of 2.3 mA cm -2 is achieved at 0.90 V iR-free under H 2 -O 2 conditions, reflecting high kinetic activity of the optimized catalyst., Competing Interests: Declaration of Competing Interest There are no conflicts to declare., (Copyright © 2021 Elsevier Inc. All rights reserved.)

Layered transition-metal oxides have attracted intensive interest for cathode materials of sodium-ion batteries. However, they are hindered by the limited capacity and inferior phase transition due to the gliding of transition-metal layers upon Na + extraction and insertion in the cathode materials. Here, we report that the large-sized K + is riveted in the prismatic Na + sites of P2-Na 0.612 K 0.056 MnO 2 to enable more thermodynamically favorable Na + vacancies. The Mn-O bonds are reinforced to reduce phase transition during charge and discharge. 0.901 Na + per formula are reversibly extracted and inserted, in which only the two-phase transition of P2 ↔ P'2 occurs at low voltages. It exhibits the highest specific capacity of 240.5 mAh g -1 and energy density of 654 Wh kg -1 based on the redox of Mn 3+ /Mn 4+ , and a capacity retention of 98.2% after 100 cycles. This investigation will shed lights on the tuneable chemical environments of transition-metal oxides for advanced cathode materials and promote the development of sodium-ion batteries.

Two-dimensional (2D) mesoporous heterostructures combining ultrathin nanosheet morphology, periodic porous surface structures, and diverse hybrid compositions have become increasingly important for renewable energy storage and electronics. However, it remains a great challenge to develop a universal method to prepare 2D mesoporous heterostructures. Herein, we report a composite-micelle-directed interfacial assembly method to synthesize heterostructures of an ultrathin 2D material covered with mesoporous monolayers assembled on both sides. To demonstrate the concept, we first fabricated a new sandwichlike carbon@MXene@carbon mesoporous heterostructure through the self-assembly of exfoliated MXene nanosheets and block copolymer F127/melamine-formaldehyde resin composite micelles and subsequent thermal treatment. Finally, we demonstrate that the carbon@MXene@carbon mesoporous heterostructured nanosheets manifest remarkably enhanced electrochemical performance as a cathode material for lithium-sulfur batteries., (© 2020 Wiley-VCH GmbH.)

Transition-metal oxides are promising anode materials for sodium ion batteries (SIBs) and have attracted a great deal of attention because of their natural abundance and high theoretical capacities. However, they suffer from low conductivity and large volumetric/structural variation during sodiation/desodiation processes, leading to unsatisfactory cycling stability and poor rate capability. This study proposes a novel conversion reaction using CoSnO 3 (CSO) nanocubes uniformly wrapped in graphene nanosheets, which are fabricated using a wet-chemical strategy followed by low-temperature heat treatment. This optimized composite exhibits durable cyclability and high rate capability, which can be attributed to the strong interaction between reduced graphene oxide and CSO through its surface oxygen moieties. It develops a facile conversion reaction route, thereby leading to SnO 2 formation during charging. This interactive phenomenon further contributes to improving the reaction kinetics and restraining the volume expansion during cycling. This study may provide a facile approach for addressing irreversible conversion of high-capacity oxide materials toward advanced SIBs.

Redox reactions of oxygen have been considered critical in controlling the electrochemical properties of lithium-excessive layered-oxide electrodes. However, conventional electrode materials without overlithiation remain the most practical. Typically, cationic redox reactions are believed to dominate the electrochemical processes in conventional electrodes. Herein, we show unambiguous evidence of reversible anionic redox reactions in LiNi 1/3 Co 1/3 Mn 1/3 O 2 . The typical involvement of oxygen through hybridization with transition metals is discussed, as well as the intrinsic oxygen redox process at high potentials, which is 75 % reversible during initial cycling and 63 % retained after 10 cycles. Our results clarify the reaction mechanism at high potentials in conventional layered electrodes involving both cationic and anionic reactions and indicate the potential of utilizing reversible oxygen redox reactions in conventional layered oxides for high-capacity lithium-ion batteries., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

We present a unique composite assembly of rhombohedral Li 3 V 2 (PO 4 ) 3 and carbon nanofiber, which simultaneously facilitates Li-ion transport as well as electron transfer. For the synthesis of this composite, the inorganic precursors were confined in electron-spun nanofibers, and then, through controlled annealing, Na 3 V 2 (PO 4 ) 3 particulates were grown with controllable crystallite size and partially embedded into carbon nanofibers with precisely controlled diameter. The rhombohedral Li 3 V 2 (PO 4 ) 3 could be successfully obtained by ion exchange from Na to Li in the prepared Na 3 V 2 (PO 4 ) 3 . The final rhombohedral Li 3 V 2 (PO 4 ) 3 particles anchored onto the carbon nanofibers exhibited excellent electrochemical performance with fast kinetics for Li-ion batteries. Suprisingly it maintains 69 and 41 mAh/g even at 100 C as cathode and anode. Several advanced characterizations revealed that its ultrafast kinetics could be attributed to synergistic effect resulting from the distinctive microstructure of the composite and the structural superiority of highly symmetric rhombohedral Li 3 V 2 (PO 4 ) 3 over its monoclinic homologue for Li-ion transport.

Mesoporous metal sulfide hybrid (meso-MoS 2 /CoMo 2 S 4 ) materials via a soft-templating approach using diblock copolymer polystyrene- block -poly(acrylic acid) micelles are reported. The formation of the meso-MoS 2 /CoMo 2 S 4 heterostructures is based on the sophisticated coassembly of dithiooxamide and metal precursors ( i.e. , Co 2+ , PMo 12 ), which are subsequently annealed in nitrogen atmosphere to generate the mesoporous material. Decomposing the polymer leaves behind mesopores throughout the spherical MoS 2 /CoMo 2 S 4 hybrid particles, generating numerous electrochemical active sites in a network of pores that enable faster charge transfer and mass/gas diffusion that enhance the electrocatalytic performance of MoS 2 /CoMo 2 S 4 . Doping the spherical meso-MoS 2 /CoMo 2 S 4 heterostructures with iron improves the electronic properties of the hybrid meso-Fe-MoS 2 /CoMo 2 S 4 material and consequently results in its superior electrochemical activities for both hydrogen evolution reaction and oxygen evolution reaction.

The composite GeP 3 /C@rGO as a sodium ion battery anode material was fabricated by introducing a carbon matrix into GeP 3 through high-energy ball milling, followed by encapsulating the resultant composite with graphene via a solution-based ultrasonic method. To delineate the individual role of carbon matrix and graphene, material characterization and electrochemical analyses were performed for GeP 3 /C@rGO and three other samples: bare GeP 3 , GeP 3 with graphene coating (GeP 3 @rGO), and GeP 3 with carbon matrix (GeP 3 /C). GeP 3 /C@rGO exhibits the highest electric conductivity (5.89 × 10 -1 S cm -1 ) and the largest surface area (167.85 m 2 g -1 ) among the four samples. The as-prepared GeP 3 /C@rGO delivered a reversible high capacity of 1084 mA h g -1 at 50 mA g -1 , excellent rate capacity (435.4 mA h g -1 at a high rate of 5 A g -1 ), and long-term cycling stability (400 cycles with a reversible capacity of 823.3 mA h g -1 at 0.2 A g -1 ), all of which outperform the other three samples. The kinetics investigation reveals a "pseudocapacitive behavior" in GeP 3 /C and GeP 3 /C@rGO, where solely faradic reactions took place in bare GeP 3 and GeP 3 @rGO with a typical "battery behavior". Based on ex-situ X-ray photoelectron spectroscopy and ex-situ electrochemical impedance spectroscopy, the carbon matrix serves to activate and stabilize the interior of the composite, while the graphene protects and restrains the exterior surface. Benefiting from the synergistic combination of these two components, GeP 3 /C@rGO achieved extremely stable cycling stability as well as outstanding rate performance.

With the increase of device requirements, rechargeable lithium-ion batteries are facing tremendous challenges in large-scale applications due to the high price and gradual shortage of lithium sources. In contrast, multivalent ion batteries, such as aluminum, magnesium, and zinc, are promising candidates for the next-generation energy-storage systems because of their high volumetric energy density, safe operation, and abundant reserves. The strong intercalation between multivalent ions and the host materials, however, will cause lower ion-diffusion kinetics and a poor discharge capacity. One of the main challenges is to search for a suitable cathode material with a high capacity and good structural stability to overcome the abovementioned problems. Two-dimensional layered materials, with characteristic unique structural features, good conductivity, and high electrochemically active surface, have attracted attention from researchers during the past decade. In this review, the design approach and synthetic procedures for the preparation of two-dimensional materials as cathodes for multivalent ion batteries, including interlayer engineering, two-dimensional heterostructures, pore/hole engineering, and heteroatom doping, are summarized. Meanwhile, the relationship between the design configuration and optimized electrochemical performance is rationally and systematically presented. Additionally, perspectives for the sustainable synthesis of cathode materials are proposed for multivalent metal-ion chemistry., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The main drawback of organic electrode materials is their solubility in the electrolyte, leading to the shuttle effect. Using N,N'-dimethylphenazine (DMPZ) as a highly soluble cathode material, and its PF 6 - and triflimide salts as models for its first oxidation state, a poor correlation was found between solubility and battery operability. Extensive electrochemical experiments suggest that the shuttle effect is unlikely to be mediated by molecular diffusion as commonly understood, but rather by electron-hopping via the electron self-exchange reaction based on spectroscopic results. These findings led to two counter-strategies to prevent the hopping process: the pre-treatment of the anode to form a solid-electrolyte interface and using DMPZ salt rather than neutral DMPZ as the active material. These strategies improved coulombic efficiency and capacity retention, demonstrating that solubility of organic materials does not necessarily exclude their applications in batteries., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An efficient way to improve the electrocatalyst and Li-O 2 battery performances of metal oxide is developed by an exquisite synergistic control over structural disorder and surface bonding nature. The effects of amorphous nature and surface chemical environment on the functionalities of metal oxide are systematically investigated with well-crystalline and amorphous MnO 2 nanocrystals with/without surface anchoring of highly oxidized iodate clusters. The amorphous MnO 2 nanocrystal containing anchored iodate clusters shows much better performance as an oxygen evolution electrocatalyst and cathode catalyst for Li-O 2 batteries than both iodate-free amorphous and well-crystalline homologues, underscoring the remarkable advantage of simultaneous enhancement of structural disorder and surface electron density. In situ X-ray absorption spectroscopic analysis demonstrates the promoted formation of double (MnO) bond, a critical step of oxygen evolution reaction, upon amorphization caused by the poor orbital overlap inside highly disordered crystallites. The beneficial effects of iodate anchoring and amorphization on electrocatalyst functionality are attributable to the alteration of surface bonding character, stabilization of Jahn-Teller active Mn 3+ species, and enhanced charge transfer of interfaces. The present study underscores that fine-tuning of structural disorder and surface bonding nature provides an effective methodology to explore efficient metal oxide-based electrocatalysts., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The accelerating development of technologies requires a significant energy consumption, and consequently the demand for advanced energy storage devices is increasing at a high rate. In the last two decades, lithium-ion batteries have been the most robust technology, supplying high energy and power density. Improving cathode materials is one of the ways to satisfy the need for even better batteries. Therefore developing new types of positive electrode materials by increasing cell voltage and capacity with stability is the best way towards the next-generation Li rechargeable batteries. To achieve this goal, understanding the principles of the materials and recognizing the problems confronting the state-of-the-art cathode materials are essential prerequisites. This Review presents various high-energy cathode materials which can be used to build next-generation lithium-ion batteries. It includes nickel and lithium-rich layered oxide materials, high voltage spinel oxides, polyanion, cation disordered rock-salt oxides and conversion materials. Particular emphasis is given to the general reaction and degradation mechanisms during the operation as well as the main challenges and strategies to overcome the drawbacks of these materials., (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Carbon aerogels (CAs) with 3D interconnected networks hold promise for application in areas such as pollutant treatment, energy storage, and electrocatalysis. In spite of this, it remains challenging to synthesize high-performance CAs on a large scale in a simple and sustainable manner. We report an eco-friendly method for the scalable synthesis of ultralight and superporous CAs by using cheap and widely available agarose (AG) biomass as the carbon precursor. Zeolitic imidazolate framework-8 (ZIF-8) with high porosity is introduced into the AG aerogels to increase the specific surface area and enable heteroatom doping. After pyrolysis under inert atmosphere, the ZIF-8/AG-derived nitrogen-doped CAs show a highly interconnected porous mazelike structure with a low density of 24 mg cm -3 , a high specific surface area of 516 m 2  g -1 , and a large pore volume of 0.58 cm -3  g -1 . The resulting CAs exhibit significant potential for application in the adsorption of organic pollutants., (© 2020 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Transition metal sulfides (TMS), as promising electroactive materials for asymmetric supercapacitors, have been limited due to their relatively poor conductivity and cycle stability. Here ternary Ni 3 S 2 /MnS/CuS composites were assembled in situ on nickel foam (NF) using a hydrothermal method via electrostatic adsorption of Ni + , Mn 2+ and Cu 2+ ions on a reduced graphene (rGO) nanosheet template. The chemical structure was characterized by various analytic methods. Ni 3 S 2 /MnS/CuS has spherical morphology assembled from closely packed nanosheets, while Ni 3 S 2 /MnS/CuS@rGO has a three-dimensional porous spherical structure with much lower diameter because rGO nanosheets can play the role of a template to induce the growth of Ni 3 S 2 /MnS/CuS. At a current density of 1 A g -1 , the specific capacitance was obtained to be 1028 F g -1 for Ni 3 S 2 /MnS/CuS, 628.6 F g -1 for Ni 3 S 2 /MnS@rGO, and 2042 F g -1 for Ni 3 S 2 /MnS/CuS@rGO, respectively. Charge transfer resistance ( R ct ) of Ni 3 S 2 /MnS/CuS@rGO (0.001 Ω) was much lower than that of Ni 3 S 2 /MnS@rGO by 0.02 Ω, and lower than that of Ni 3 S 2 /MnS/CuS by 0.017 Ω. After 5000 cycles, the Ni 3 S 2 -MnS-CuS@RGO electrode maintains 78.3% of the initial capacity at 20 A g -1 . An asymmetric supercapacitor was subsequently assembled using Ni 3 S 2 /MnS/CuS@rGO as the positive electrode and rGO as the negative electrode. The specific capacitance of asymmetric batteries was maintained at 90.8% of the initial state after 5000 GCD., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Irreversible phase transformation of layered structure into spinel structure is considered detrimental for most of the layered structure cathode materials. Here we report that this presumably irreversible phase transformation can be rendered to be reversible in sodium birnessite (Na x MnO 2 ·yH 2 O) as a basic structural unit. This layered structure contains crystal water, which facilitates the formation of a metastable spinel-like phase and the unusual reversal back to layered structure. The mechanism of this phase reversibility was elucidated by combined soft and hard X-ray absorption spectroscopy with X-ray diffraction, corroborated by first-principle calculations and kinetics investigation. These results show that the reversibility, modulated by the crystal water content between the layered and spinel-like phases during the electrochemical reaction, could activate new cation sites, enhance ion diffusion kinetics and improve its structural stability. This work thus provides in-depth insights into the intercalating materials capable of reversible framework changes, thereby setting the precedent for alternative approaches to the development of cathode materials for next-generation rechargeable batteries.

The crystal structure of the gadolinium iron bismuthide Gd 6 FeBi 2 has been characterized by single-crystal X-ray diffraction data and analyzed in detail using first-principles calculations. The structure is isotypic with the Zr 6 CoAl 2 structure, which is a variant of the ZrNiAl structure and its binary prototype Fe 2 P (Pearson code hP9, Wyckoff sequence g f d a). As such, the structure is best viewed as an array of tricapped trigonal prisms of Gd atoms centered alternately by Fe and Bi. The magnetic-ordering temperature of this compound (ca 350 K) is much higher than that of other rare-earth metal-rich phases with the same or related structures. It is also higher than the ordering temperature of many other Gd-rich ternary phases, where the magnetic exchange is typically governed by Ruderman-Kittel-Kasuya-Yosida (RKKY) interactions. First-principles calculations reveal a larger than expected Gd magnetic moment, with the additional contribution arising from the Gd 5d electrons. The electronic structure analysis suggests strong Gd 5d-Fe 3d hybridization to be the cause of this effect, rather than weak interactions between Gd and Bi. These details are of importance for understanding the magnetic response and explaining the high ordering temperature in this material.

Palladium (Pd) plays an important role in numerous catalytic reactions, such as methanol and ethanol oxidation, oxygen reduction, hydrogenation, coupling reactions, and carbon monoxide oxidation. Creating Pd-based nanoarchitectures with increased active surface sites, higher density of low-coordinated atoms, and maximized surface coverage for the reactants is important. To address the limitations of pure Pd, various Pd-based nanoarchitectures, including alloys, intermetallics, and supported Pd nanomaterials, have been fabricated by combining Pd with other elements with similar or higher catalytic activity for many catalytic reactions. Herein, recent advances in the preparation of Pd-based nanoarchitectures through solution-phase chemical reduction and electrochemical deposition methods are summarized. Finally, the trend and future outlook in the development of Pd nanocatalysts toward practical catalytic applications are discussed., (© 2019 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Manganese based layered oxides have received increasing attention as cathode materials for sodium ion batteries due to their high theoretical capacities and good sodium ion conductivities. However, the Jahn-Teller distortion arising from the manganese (III) centers destabilizes the host structure and deteriorates the cycling life. Herein, we report that zinc-doped Na 0.833 [Li 0.25 Mn 0.75 ]O 2 can not only suppress the Jahn-Teller effect but also reduce the inherent phase separations. The reduction of manganese (III) amount in the zinc-doped sample, as predicted by first-principles calculations, has been confirmed by its high binding energies and the reduced octahedral structural variations. In the viewpoint of thermodynamics, the zinc-doped sample has lower formation energy, more stable ground states, and fewer spinodal decomposition regions than those of the undoped sample, all of which make it charge or discharge without any phase transition. Hence, the zinc-doped sample shows superior cycling performance, demonstrating that zinc doping is an effective strategy for developing high-performance layered cathode materials.

An effective chemical way to optimize the oxygen electrocatalyst and Li-O 2 electrode functionalities of metal oxide can be developed by the control of chemical bond nature with the surface anchoring of highly oxidized selenate (SeO 4 2- ) clusters. The bond competition between (Se 6+ -O) and (Mn-O) bonds is quite effective in stabilizing Jahn-Teller-active Mn 3+ state and in increasing oxygen electron density of α-MnO 2 nanowire (NW). The selenate-anchored α-MnO 2 NW shows excellent oxygen electrocatalytic activity and electrode performance for Li-O 2 batteries, which is due to the improved charge transfer kinetics and reversible formation/decomposition of Li 2 O 2 . The present study underscores that the surface anchoring of highly oxidized cluster can provide a facile, effective way of improving the oxygen electrocatalyst and electrochemical performances of nanostructured metal oxide in Li-O 2 cells., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Dual ion batteries based on Na + and PF 6 - received considerable attention due to their high operating voltage and the abundant Na resources. Here, cheap and easily obtained graphite that served as a cathode material for dual ion battery delivered a very high average discharge platform (4.52 V vs Na + /Na) by using sodium hexafluorophosphate in propylene carbonate as electrolyte. Moreover, the all-carbon dual ion batteries with graphite as cathode and hard carbon as anode exhibited an ultrahigh discharge voltage of 4.3 V, and a reversible capacity of 62 mAh·g -1 at 40 mA·g -1 . Phase changes have been investigated in detail through in situ X-ray diffraction and in situ Raman characterizations. The stable structure provides long life cycling performance, and the pseudocapacitance behavior also demonstrates its benefits to the rate capability. Thus, dual ion batteries based on sodium chemistry are very promising to find their applications in future.

Owing to the low-cost, safety, dendrite-free formation, and two-electron redox properties of magnesium (Mg), rechargeable Mg batteries are considered as promising next-generation secondary batteries with high specific capacity and energy density. However, the clumsy Mg 2+ with high polarity inclines to sluggish Mg insertion/deinsertion, leading to inadequate reversible capacity and rate performance. Herein, 2D VOPO 4 nanosheets with expanded interlayer spacing (1.42 nm) are prepared and applied in rechargeable magnesium batteries for the first time. The interlayer expansion provides enough diffusion space for fast kinetics of MgCl + ion flux with low polarization. Benefiting from the structural configuration, the Mg battery exhibits a remarkable reversible capacity of 310 mAh g -1 at 50 mA g -1 , excellent rate capability, and good cycling stability (192 mAh g -1 at 100 mA g -1 even after 500 cycles). In addition, density functional theory (DFT) computations are conducted to understand the electrode behavior with decreased MgCl + migration energy barrier compared with Mg 2+ . This approach, based on the regulation of interlayer distance to control cation insertion, represents a promising guideline for electrode material design on the development of advanced secondary multivalent-ion batteries., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The redox units of polyaniline (PAni) are used cooperatively, and in situ, to assemble ruthenium (Ru) nanoclusters in a hierarchically ordered carbon electrode. The oxidized quinonoid imine (QI) units in PAni bond Ru complex ions selectively, whereas reduced benzenoid amine (BA) units cannot. By electrochemically tuning the ratio of QI to BA, Ru complexes are spatially confined in the outer layer of hierarchical PAni frameworks. Carbonization of Ru-PAni hybrids induces nucleation on the outer surface of the carbon support, generating nearly monodisperse Ru nanoclusters. The optimized catalyst has a low loading of approximately 2 wt % Ru, but exhibits a mass activity for the hydrogen evolution reaction that is about 6.8 times better than commercial 20 wt % Pt/C catalyst., (© 2018 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Sub-50 nm iron-nitrogen-doped hollow carbon sphere-encapsulated iron carbide nanoparticles (Fe 3 C-Fe,N/C) are synthesized by using a triblock copolymer of poly(styrene- b -2-vinylpyridine- b -ethylene oxide) as a soft template. Their typical features, including a large surface area (879.5 m 2 g -1 ), small hollow size (≈16 nm), and nitrogen-doped mesoporous carbon shell, and encapsulated Fe 3 C nanoparticles generate a highly active oxygen reduction reaction (ORR) performance. Fe 3 C-Fe,N/C hollow spheres exhibit an ORR performance comparable to that of commercially available 20 wt% Pt/C in alkaline electrolyte, with a similar half-wave potential, an electron transfer number close to 4, and lower H 2 O 2 yield of less than 5%. It also shows noticeable ORR catalytic activity under acidic conditions, with a high half-wave potential of 0.714 V, which is only 59 mV lower than that of 20 wt% Pt/C. Moreover, Fe 3 C-Fe,N/C has remarkable long-term durability and tolerance to methanol poisoning, exceeding Pt/C regardless of the electrolyte.

This work reports the template-free fabrication of mesoporous Al 2 O 3 nanospheres with greatly enhanced textural characteristics through a newly developed post-synthesis "water-ethanol" treatment of aluminium glycerate nanospheres followed by high temperature calcination. The proposed "water-ethanol" treatment is highly advantageous as the resulting mesoporous Al 2 O 3 nanospheres exhibit 2-4 times higher surface area (up to 251 m 2 g -1 ), narrower pore size distribution, and significantly lower crystallization temperature than those obtained without any post-synthesis treatment. To demonstrate the generality of the proposed strategy, a nearly identical post-synthesis "water treatment" method is successfully used to prepare mesoporous monometallic (e.g., manganese oxide (MnO 2 )) and bimetallic oxide (e.g., CuCo 2 O 4 and MnCo 2 O 4 ) nanospheres assembled of nanosheets or nanoplates with highly enhanced textural characteristics from the corresponding monometallic and bimetallic glycerate nanospheres, respectively. When evaluated as molybdenum (Mo) adsorbents for potential use in molybdenum-99/technetium-99m ( 99 Mo/ 99m Tc) generators, the treated mesoporous Al 2 O 3 nanospheres display higher molybdenum adsorption performance than non-treated Al 2 O 3 nanospheres and commercial Al 2 O 3 , thereby suggesting the effectiveness of the proposed strategy for improving the functional performance of oxide materials. It is expected that the proposed method can be utilized to prepare other mesoporous metal oxides with enhanced textural characteristics and functional performance., (© 2018 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The development of next-generation energy-storage devices with high power, high energy density, and safety is critical for the success of large-scale energy-storage systems (ESSs), such as electric vehicles. Rechargeable sodium-oxygen (Na-O 2 ) batteries offer a new and promising opportunity for low-cost, high-energy-density, and relatively efficient electrochemical systems. Although the specific energy density of the Na-O 2 battery is lower than that of the lithium-oxygen (Li-O 2 ) battery, the abundance and low cost of sodium resources offer major advantages for its practical application in the near future. However, little has so far been reported regarding the cell chemistry, to explain the rate-limiting parameters and the corresponding low round-trip efficiency and cycle degradation. Consequently, an elucidation of the reaction mechanism is needed for both lithium-oxygen and sodium-oxygen cells. An in-depth understanding of the differences and similarities between Li-O 2 and Na-O 2 battery systems, in terms of thermodynamics and a structural viewpoint, will be meaningful to promote the development of advanced metal-oxygen batteries. State-of-the-art battery design principles for high-energy-density lithium-oxygen and sodium-oxygen batteries are thus reviewed in depth here. Major drawbacks, reaction mechanisms, and recent strategies to improve performance are also summarized., (© 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A synergistic approach for advanced cathode materials is proposed. Sodium manganese oxide with a layered-tunnel hybrid structure was designed, synthesized, and subsequently investigated. The layered-tunnel hybrid structure provides fast Na ion diffusivity and high structural stability thanks to the tunnel phase, enabling high rate capability and greatly improved cycling stability compared to that of the pure P2 layered phase while retaining the high specific capacity of the P2 layered phase. The hybrid structure provided a decent discharge capacity of 133.4 mAh g -1 even at 8 C, which exceeds the reported best rate capability for Mn-based cathodes. It also displayed an impressive cycling stability, maintaining 83.3 mAh g -1 after 700 cycles at 10 C. Theoretical calculation and the potentiostatic intermittent titration technique (PITT) demonstrated that this hybrid structure helps enhance Na ion diffusivity during charge and discharge, attaining, as a result, an unprecendented electrochemical performance.

Fast lithium ion and electron transport inside electrode materials are essential to realize its superb electrochemical performances for lithium rechargeable batteries. Herein, a distinctive structure of cathode material is proposed, which can simultaneously satisfy these requirements. Nanosized Li 3 V 2 (PO 4 ) 3 (LVP) particles can be successfully grown up on the carbon nanofiber via electrospinning method followed by a controlled heat-treatment. Herein, LVP particles are anchored onto the surface of carbon nanofiber, and with this growing process, the size of LVP particles as well as the thickness of carbon nanofiber can be regulated together. The morphological features of this composite structure enable not only direct contact between electrolytes and LVP particles that can enhance lithium ion diffusivity, but also fast electron transport through 1D carbon network along nanofibers simultaneously. Finally, it is demonstrated that this unique structure is an ideal one to realize high electron transport and ion diffusivity together, which are essential for enhancing the electrochemical performances of electrode materials.

Development of high performance electrode materials for energy storage is one of the most important issues for our future society. However, a lack of clear analytical views limits critical understanding of electrode materials. This review covers useful analytical work using X-ray diffraction, X-ray absorption spectroscopy, microscopy and neutron diffraction for ion storage systems. The in situ observation facilitates comprehending real-time ion storage behaviour while the ion storage system is operating, which help us to understand detailed physical and chemical properties. We will discuss how the tools have been used to reveal detailed reaction mechanisms and underlying properties of electrode materials.

High voltage (5-V class) spinel LiCr 0.2 Ni 0.4 Mn 1.4 O 4 is one of the most promising cathode materials to meet the energy requirements of lithium-ion batteries for electric vehicles and hybrid electric vehicles. For the mass production of this material (1 kg or higher), different synthesis routes will lead to different electrochemical performances, even with similar morphology and similar crystal structure obtained from laboratory X-ray diffraction, and the reason for this issue is still not clear. Herein, we have investigated the reasons for the different electrochemical performances resulting from three common synthesis routes (spray pyrolysis, coprecipitation, and sol-gel). Taking advantage of the high-resolution X-ray beam in synchrotron X-ray diffraction, we find that varying phase composition and the generated impurities, rather than the particle distribution, are likely to be the main reasons for the detected electrochemical variations. A higher amount of impurities will result in greater charge transfer resistance, inferior cycling stability, and more oxygen/lithium vacancies. Therefore, it is very important to obtain a deeper understanding with the help of higher-resolution X-rays and to provide better guidance for mass production of this cathode material for practical applications.

Considering that the high capacity, long-term cycle life, and high-rate capability of anode materials for sodium-ion batteries (SIBs) is a bottleneck currently, a series of Co-doped FeS2 solid solutions with different Co contents were prepared by a facile solvothermal method, and for the first time their Na-storage properties were investigated. The optimized Co0.5 Fe0.5 S2 (Fe0.5) has discharge capacities of 0.220 Ah g(-1) after 5000 cycles at 2 A g(-1) and 0.172 Ah g(-1) even at 20 A g(-1) with compatible ether-based electrolyte in a voltage window of 0.8-2.9 V. The Fe0.5 sample transforms to layered Nax Co0.5 Fe0.5 S2 by initial activation, and the layered structure is maintained during following cycles. The redox reactions of Nax Co0.5 Fe0.5 S2 are dominated by pseudocapacitive behavior, leading to fast Na(+) insertion/extraction and durable cycle life. A Na3 V2 (PO4 )3 /Fe0.5 full cell was assembled, delivering an initial capacity of 0.340 Ah g(-1) ., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Molybdenum disulfide is popular for rechargeable batteries, especially in Li-ion batteries, because of its layered structure and relatively high specific capacity. In this paper, we report MoS2-C nanocomposites that are synthesized by a hydrothermal process, and their use as anode material for Li-ion batteries. Ascorbic acid is used as the carbon source, and the carbon contents can be tuned from 2.5 wt % to 16.2 wt %. With increasing of carbon content, the morphology of MoS2-C nanocomposites changes from nanoflowers to nanospheres, and the particle size is decreased from 200 to 60 nm. This change is caused by the chemical complex interaction of ascorbic acid. The MoS2-C nanocomposite with 8.4 wt % C features a high capacity of 970 mAh g(-1) and sustains a capacity retention ratio of nearly 100% after 100 cycles. When the current increases to 1000 mA g(-1), the capacity still reaches 730 mAh g(-1). The above manifests that the carbon coating layer does not only accelerate the charge transfer kinetics to supply quick discharging and charging, but also hold the integrity of the electrode materials as evidenced by the long cycling stability. Therefore, MoS2-based nanocomposites could be used as commercial anode materials in Li-ion batteries.

Tin sulfide (SnS) 3D flowers containing hierarchical nanosheet subunits are synthesized using a simple polyol process. The Li ion cells incorporating SnS 3D flowers exhibit an excellent rate capability, as well as good cycling stability, compared to SnS bulks and Sn nanoparticles. These desirable properties can be attributed to their unique morphology having not only large surface reaction area but also enough space between individual 2D nanosheets, which alleviates the pulverization of SnS., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A hexagonally ordered mesoporous cobalt phosphate (CoPi) material is prepared by a facile one-pot soft-templating strategy using cetyltrimethylammonium bromide template. Because of its highly accessible surface area and crystalline framework with abundant active sites, the mesoporous CoPi shows a high catalytic activity for the oxygen evolution reaction compared to previously reported noble/transition-metal and nonmetal catalysts., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Graphite-nanoplate-coated Bi2 S3 composite (Bi2 S3 @C) has been prepared by a simple, scalable, and energy-efficient precipitation method combined with ball milling. The Bi2 S3 @C composite was used as the cathode material for sodium-sulfide batteries. It delivered an initial capacity of 550 mAh g(-1) and high stable specific energy in the range of 275-300 Wh kg(-1) at 0.1 C, with an enhanced capacity retention of 69 % over 100 cycles. The unique structure demonstrates superior cycling stability, with a capacity drop of 0.3 % per cycle over 100 cycles, compared with that of bare Bi2 S3 . The sodium storage mechanism of Bi2 S3 was investigated based on ex situ X-ray diffraction and scanning transmission electron microscopy., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Li4Ti5O12 is a promising anode material for rechargeable lithium batteries due to its well-known zero strain and superb kinetic properties. However, Li4Ti5O12 shows low energy density above 1 V vs Li(+)/Li. In order to improve the energy density of Li4Ti5O12, its low-voltage intercalation behavior beyond Li7Ti5O12 has been demonstrated. In this approach, the extended voltage window is accompanied by the decomposition of liquid electrolyte below 1 V, which would lead to an excessive formation of solid electrolyte interphase (SEI) films. We demonstrate an effective method to improve electrochemical performance of Li4Ti5O12 in a wide working voltage range by coating Li4Ti5O12 powder with p-type semiconductor NiOx. Ex situ XRD, XPS, and FTIR results show that the NiOx coating suppresses electrochemical reduction reactions of the organic SEI components to Li2CO3, thereby promoting reversibility of the charge/discharge process. The NiOx coating layer offers a stable SEI film for enhanced rate capability and cyclability.